Recent experiments showing reaction-driven propulsion at nanoscales have appeared as a possible mechanism for the transport of particles that may help us to not only understand chemo-mechanical transduction in biological systems, but also to create novel artificial motors that mimic living organisms and which can be harnessed to perform desired tasks. Reaction-driven propulsion consists of the generation of a localized potential gradient by an on-board surface chemical reaction. In this study, we propose and investigate a model for self-propulsion of a colloidal particle --- the osmotic motor --- immersed in a dispersion of ``bath\" particles. The non-equilibrium concentration of bath particles induced by a surface chemical reaction creates an osmotic pressure imbalance on the motor causing it to move. The departure of the bath particle concentration distribution from equilibrium is governed by the Damkohler number Da --- the ratio of the speed of reaction to that of diffusion --- which is employed to calculate the driving force on the motor, and from which the self-induced osmotic velocity is determined via application of Stokes drag law. To illustrate the significant physics in osmotic propulsion, a first-order surface reaction on a portion of the motor's surface is assumed, for the most part, in this work. The implications of these features for different bath particle concentrations and motor sizes are discussed. Furthermore, we investigate the role played by the distribution of reactions on the motor's surface. Different responses are expected depending on the amount of reactive surface in the limiting behaviors of the reaction speed. Lastly, we consider a motor with constant production of particles on a hemisphere as a model that resembles actin-based motility of biological cells and organelles.
\r\n\r\nThis research demonstrates that such an osmotic motor is possible and addresses such questions as: How fast can the motor move? How large of a force can it generate? What is the efficiency of such an osmotic motor? All motor behaviors discussed in this work are shown, after appropriate scaling, to be in good agreement with Brownian dynamics simulations.
\r\n", "doi": "10.7907/W8X1-FQ17", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:2457", "collection": "thesis", "collection_id": "2457", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06052005-221223", "primary_object_url": { "basename": "00Chapters123.pdf", "content": "final", "filesize": 8257006, "license": "other", "mime_type": "application/pdf", "url": "/2457/1/00Chapters123.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Computational Strategy in Catalyst Design", "author": [ { "family_name": "Nielsen", "given_name": "Robert J.", "orcid": "0000-0002-7962-0186", "clpid": "Nielsen-Robert-J" } ], "thesis_advisor": [ { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "thesis_committee": [ { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" }, { "family_name": "Stoltz", "given_name": "Brian M.", "clpid": "Stoltz-B-M" }, { "family_name": "Tirrell", "given_name": "David A.", "clpid": "Tirrell-D-A" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Peters", "given_name": "Jonas C.", "clpid": "Peters-J-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The strategy and efficacy of applying computational tools to the development of new catalytic cycles is discussed using the enantioselective palladium-catalyzed aerobic oxidation of secondary alcohols as a model case. The key interactions responsible for the unique reactivity of ((\u2013)-sparteine)PdX2 complexes (X = chloride, acetate) in kinetic resolutions of secondary alcohols are elucidated using density functional theory with the Poisson-Boltzmann polarizable continuum solvent model. Enantioselectivities in these reactions are found to follow directly from calculated energies of diastereomeric beta-hydride elimination transition states incorporating (R) and (S) substrates. This relationship reveals an important role of the anion, namely to communicate the steric interaction of the ligand on one side of the PdII square plane and the substrate on the other side. When no anion is included, no enantioselectivity is predicted. Locating these transition states in different solvents shows that higher dielectrics stabilize the charge separation between the anion and metal and draw the anion farther into solution. Thus the solvent influences the barrier height (rate) and selectivity of the oxidation.
\r\n\r\nBased on this understanding, computational assays for selectivity, reaction rate and stability are developed and used to screen possible mimics of the natural product (\u2013)-sparteine which could be synthesized in both antipodes. Derivatives of the bispidine and bispidinone structures are predicted to have high selectivity but poor stability on palladium. Experimental results verify that catalytically active (bispidine)PdX2 complexes do not form.
\r\n\r\nMechanisms by which palladium diacetate complexes of N-heterocyclic carbenes may oxidize alcohols (a reaction known to occur with no enantioselectivity) are examined computationally. The strong trans effect of the carbene distinguishes the behavior of these complexes from other palladium catalysts. No traditional beta-hydride elimination is predicted to be capable of generating the high deuterium kinetic isotope effect measured using this catalyst. Instead, the low-energy pathway consistent with previous experimental observations (KIE, activation parameters, kinetics) is a \"reductive\" beta-hydride elimination, in which the beta-hydrogen of the alcohol is transferred directly to a bound acetate ligand. Assuming that relative energies of transition states of this type will determine enantioselectivity, new, chiral carbene ligands are hypothesized and screened. Careful placement of stereocenters and steric bulk has led to ligands with high predicted enantioselectivity and stability.
\r\n\r\nRecurring factors in the induction of selectivity by asymmetric ligands are observed. Strengths and weaknesses of quantum chemistry as applied to catalytic cycles are discussed, along with the synergy of theory and experiment. Common pitfalls and areas in need of improvement are highlighted.
", "doi": "10.7907/60VH-AQ40", "publication_date": "2005", "thesis_type": "phd", "thesis_year": "2005" }, { "id": "thesis:4814", "collection": "thesis", "collection_id": "4814", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12062004-232639", "primary_object_url": { "basename": "thesis.pdf", "content": "final", "filesize": 3454192, "license": "other", "mime_type": "application/pdf", "url": "/4814/1/thesis.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Defect Chemistry and Proton Conductivity in Ba-based Perovskites", "author": [ { "family_name": "Wu", "given_name": "Jian", "clpid": "Wu-Jian" } ], "thesis_advisor": [ { "family_name": "Haile", "given_name": "Sossina M.", "clpid": "Haile-S-M" } ], "thesis_committee": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" }, { "family_name": "Haile", "given_name": "Sossina M.", "clpid": "Haile-S-M" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The site incorporation mechanism of M\u00b3\u207a dopants into A\u00b2\u207aB\u2074\u207aO\u2083 perovskites controls the overall defect chemistry and thus their transport properties. For charge balance reasons, incorporation onto the A\u00b2\u207a site would require the creation of negatively charged point defects, such as cation vacancies, whereas incorporation onto the B\u2074\u207a site is accompanied by the generation of positively charged defects, typically oxygen vacancies. Oxygen vacancy content, in turn, is relevant to proton conducting oxides in which protons are introduced via the dissolution of hydroxyl ions at vacant oxygen sites.
\r\n\r\nThis work proposes that, on the basis of X-ray powder diffraction studies, electron microscopy, chemical analysis, thermal gravimetric analysis, AC impedance spectroscopy, extended X-ray fine structure (EXAFS) and atomistic simulation, that nominally B-site doped barium cerate can exhibit dopant partitioning partially as a consequence of barium evaporation at elevated temperatures. Such partitioning and the presence of significant dopant concentrations on the A-site negatively impact proton conductivity. As a consequence of the greater ability of larger cations to exist on the Ba site, the H\u2082O adsorption and proton conductivities of large-cation doped barium cerates are lower than those of small-cation doped analogs.
\r\n\r\nA series of dopants, La, Nd, Sm, Gd and Yb are adopted in doped BaCeO\u2083 with the composition BaCe0.85M0.15O3-\u03b4. Yb doped BaCeO\u2083 yields the highest proton conductivity among all the doped samples. Compositional non-stoichiometry, which is closely tied to sample processing, is studied in a Bax0.85M0.15O3\u00b1\u03b4 series. It is indicated that low temperature synthesis is beneficial to reduce barium evaporation at elevated temperatures and in turn increase the proton conductivity. The chemical stability of BaCeO\u2083 is investigated and Zr is used to stabilize BaCeO\u2083 in CO\u2082-rich atmosphere effectively. This result helps to commercialize doped BaCeO\u2083 as the electrolyte material for SOFCs.
", "doi": "10.7907/VTCG-T978", "publication_date": "2005", "thesis_type": "phd", "thesis_year": "2005" }, { "id": "thesis:2352", "collection": "thesis", "collection_id": "2352", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06012004-152711", "primary_object_url": { "basename": "thesis.pdf", "content": "final", "filesize": 4357072, "license": "other", "mime_type": "application/pdf", "url": "/2352/1/thesis.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "High-Pressure Microdischarges as Microreactors for Materials Applications", "author": [ { "family_name": "Sankaran", "given_name": "Ramanathan Mohan", "orcid": "0000-0002-9399-4790", "clpid": "Sankaran-Ramanathan-Mohan" } ], "thesis_advisor": [ { "family_name": "Giapis", "given_name": "Konstantinos P.", "clpid": "Giapis-K-P" } ], "thesis_committee": [ { "family_name": "Giapis", "given_name": "Konstantinos P.", "clpid": "Giapis-K-P" }, { "family_name": "Collier", "given_name": "C. Patrick", "clpid": "Collier-C-P" }, { "family_name": "Goodwin", "given_name": "David G.", "clpid": "Goodwin-D-G" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This thesis describes a novel \"microplasma\" source that is suitable for microreactor applications. The high-pressure \"microplasma\" is a direct current microdischarge, formed between two metal electrodes: a cathode with a pin-hole (diameter~100 \u00b5m) and an anode of unspecified shape. Strong radial electric fields are produced in the microhollow cathode geometry, causing electrons to oscillate (Pendel effect). As a result of enhanced ionization processes, it is possible to produce a stable high-intensity discharge at pressures of 1 atmosphere or higher. We have utilized these microdischarges for several applications including pattern transfer, diamond deposition, excimer emission, and nanoparticle synthesis.
\r\n\r\nMaskless etching of structures for MEMS and microfluidic applications is achieved by forming microplasmas in complex patterns within a stencil mask in contact with the surface to be patterned. In one application, CF4/Ar microdischarges are formed inside planar copper-polyimide stencil masks that permit direct etching of silicon wafers. To deposit films, microdischarges are formed inside metal capillaries that accommodate flow. A plasma microjet is created and directed towards a heated substrate that enables deposition of polycrystalline diamond films over small spatial scales. Simultaneous operation of multiple micodischarges could form the basis of a combinatorial tool for rapid materials development.
\r\n\r\nMicrodischarges in capillary tubes can serve as sources of intense UV radiation. Excimer emission in argon (Ar2*) at 128 nm has been studied by vacuum UV spectroscopy. A method to increase the on-axis excimer radiation is demonstrated by adding discharges in a linear array. Building of emitting volume shows potential for intensifying excimer emission.
\r\n\r\nThe properties of microdischarges are especially conducive to applications as short-residence time reactors. For example, microdischarges are attractive for nanoparticle synthesis since the residence time of particle nucleation can be limited in the reactor to time scales on the order of milliseconds. This methodology has been used to produce silicon particles with mean sizes of 1-5 nm and narrow size distributions. The silicon nanoparticles exhibit blue photoluminescence at room temperature suggesting quantum confinement. The pristine nature of the nanoparticles enables fundamental studies of surface functionalization.
", "doi": "10.7907/DP21-7606", "publication_date": "2004", "thesis_type": "phd", "thesis_year": "2004" }, { "id": "thesis:2039", "collection": "thesis", "collection_id": "2039", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05252004-102344", "primary_object_url": { "basename": "aw_master.pdf", "content": "final", "filesize": 3377734, "license": "other", "mime_type": "application/pdf", "url": "/2039/1/aw_master.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. Synthesis, Characterization, and Base Catalysis of Organic-Functionalized Molecular Sieves. II. Selective Oxidation of Ethane via Heteropolyanion-Containing Solid Catalysts", "author": [ { "family_name": "Wight", "given_name": "Andrea Palmisano", "clpid": "Wight-Andrea-Palmisano" } ], "thesis_advisor": [ { "family_name": "Davis", "given_name": "Mark E.", "clpid": "Davis-M-E" } ], "thesis_committee": [ { "family_name": "Davis", "given_name": "Mark E.", "clpid": "Davis-M-E" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Labinger", "given_name": "Jay A.", "clpid": "Labinger-J-A" }, { "family_name": "Zones", "given_name": "Stacey I.", "clpid": "Zones-S-I" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis is composed of two separate and unrelated projects. The first project examines the preparation of functional groups that can serve as immobilized bases in molecular sieves. Many heterogeneous, base catalysts are not able to promote diverse reaction types that require strong bases as catalysts. Additionally, some of the stronger solid base catalysts are sensitive to carbon dioxide and moisture in air and therefore are not easily suitable for recycling. Organic-functionalized molecular sieves possess an organic moiety within the pore space of a molecular sieve by incorporation of an organosilane directly into the synthesis gel of the molecular sieve. Previous work reported by Davis and co-workers demonstrated the incorporation of an acid site in zeolite Beta (*BEA type) and its use in shape-selective acid catalysis.
\r\n\r\nHere, a phosphonium functionality is prepared from halogen-containing alkyl groups in *BEA to allow the incorporation of a strong base (OH-) within the molecular sieve for base catalysis. Characterization of the phosphonium-containing material prepared is accomplished. Shape-selective chemical reactions and ion-exchanges are presented, and the results of these experiments suggest that the functional groups are located within the molecular sieve pore space, although the exact structure of these moieties is not conclusively obtained.
\r\n\r\nThe second part of this thesis examines the use of niobium- and pyridine-exchanged heteropolyanions as catalyst precursors for the selective oxidation of light alkanes with dioxygen. The versatility of many oxidation catalysts is limited, thereby restricting potential usefulness. Alkenes, typically used as feedstock, are becoming costly as their demand for use in many other industrial processes increases. The use of light alkanes as reactants for selective oxidation would allow one to take advantage of an under-utilized and relatively inexpensive feedstock for selective oxidation.
\r\n\r\nNiobium- and pyridine-exchanged heteropolyanions (HPAs) have been shown to produce highly active and selective catalysts for the oxidation of propane and n-butane to acrylic acid and maleic acid, respectively, by Davis and co-workers. Specifically, molybdophosphoric acid and molybdovanadophosphoric acid were exchanged with niobium oxalate and pyridine to produce the exchanged HPAs (denoted NbPMo12pyr and NbPMo11Vpyr, respectively). Preliminary work in these studies indicates that the exchanged HPAs may also be effective for the oxidation of ethane to acetic acid. The application of this catalyst system to the selective oxidation of ethane to acetic acid and ethylene is explored here.
\r\n\r\nThe exchanged heteropolyanions give higher ethane conversion at elevated pressures (230 psig and 280oC) but better yields at atmospheric pressure and 380oC. Variations of steam flow rates or reaction temperatures are not observed to improve acetic acid space-time-yield (STY). Lower gas-hourly-space-velocity (GHSV) causes the ethylene and acetic acid to over-oxidize to COx. The maximum STY of acetic acid using NbPMo12pyr is 0.021 mmol/min/g catalyst at 380oC, 0 psig, and flows of 16: 8: 16: 20 mL/min of ethane: oxygen: helium: steam.
\r\n\r\nAt elevated pressure (230 psig) the addition of vanadium into the Keggin ion precursor is shown to decrease conversion (from 6.0% to 2.2%) but improve selectivity to ethylene (from 23.2% to 46.8%). The formation of acetic acid is not affected (0.002 mmol/min/g catalyst). At atmospheric pressure the addition of vanadium into the Keggin precursor does have a favorable affect on the acetic acid formation. NbPMo11Vpyr is shown to have a maximum acetic acid production of 0.062 mmol/min/g catalyst at 380oC, 0 psig, and flows of 16: 8: 16: 20 mL/min of ethane: oxygen: helium: steam.
\r\n\r\nThe addition of both Nb and pyridine to the HPA is crucial for active catalyst formation, for reactions both at atmospheric pressure and 230 psig. Substitution of other metals for Nb does not yield materials that give significant ethane conversion.
\r\n\r\nHigher ethane/oxygen ratios increase the selectivity to acetic acid over NbPMo12pyr at atmospheric pressure. The oxidation of ethylene over NbPMo12pyr is accomplished, and the results indicate that acetic acid is formed from ethylene during the oxidation of ethane. D2O is substituted as the source of steam, and the observation that acetic acid contains deuterium shows that the steam in the feed is involved in its formation.
\r\n\r\nThe data obtained from NbPMo11Vpyr suggest that this precursor can give a catalyst that is active and selective for producing ethylene and acetic acid from ethane and dioxygen. Further experimentation is necessary to optimize performance.
", "doi": "10.7907/DCKV-0007", "publication_date": "2004", "thesis_type": "phd", "thesis_year": "2004" }, { "id": "thesis:486", "collection": "thesis", "collection_id": "486", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02042003-160317", "primary_object_url": { "basename": "1-28-03_thesis.pdf", "content": "final", "filesize": 3461756, "license": "other", "mime_type": "application/pdf", "url": "/486/1/1-28-03_thesis.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Engineering Dioxygenases by Laboratory Evolution: A Comparison of Evolutionary Search Strategies", "author": [ { "family_name": "Joern", "given_name": "John Michael", "clpid": "Joern-John-Michael" } ], "thesis_advisor": [ { "family_name": "Arnold", "given_name": "Frances Hamilton", "orcid": "0000-0002-4027-364X", "clpid": "Arnold-F-H" } ], "thesis_committee": [ { "family_name": "Arnold", "given_name": "Frances Hamilton", "orcid": "0000-0002-4027-364X", "clpid": "Arnold-F-H" }, { "family_name": "Rees", "given_name": "Douglas C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Due to the unique and difficult chemistry they perform, the aromatic ring-hydroxylating dioxygenases are of interest as industrial catalysts. Unfortunately, an application-specific array of problems limits their utility. To address these problems through laboratory evolution, I developed methods for high-throughput screening of tens of thousands of dioxygenase variants. These methods rely on a phenol detection reagent (Gibbs reagent) and can be applied to liquid cultures or to growing bacterial colonies expressing variant enzymes.
\r\n\r\nRecombination of genes encoding homologous enzymes (\"family shuffling\") has emerged as a promising tool for evolutionary protein engineering. Using the dioxygenases as a model system, I have investigated the value of recombination as a search strategy for laboratory evolution. Chimeric dioxygenase libraries constructed by DNA shuffling are first evaluated for biases that limit sequence diversity using a probe hybridization approach in lieu of sequencing. This analysis shows that crossovers preferentially occur in regions with high sequence identity and that certain parent sequences can be preferred at particular gene positions.
\r\n\r\nHigh-throughput functional screening allowed characterization of substrate specificity for hundreds of dioxygenase chimeras. These data are coupled with sequence data to reveal sequence-function relationships and demonstrate the utility of recombination as a tool for functional genomics. One region of sequence is shown to be a primary determinant of substrate specificity for the enzymes studied. Furthermore, several sets of variant enzymes with similar functionality are shown to have sequence similarities.
\r\n\r\nRecombination and random mutagenesis are compared as search strategies for generating functionally-diverse dioxygenases. I screened similarly sized libraries of chimeric and mutant dioxygenases for variants with altered substrate specificity or activity toward n-hexylbenzene, which is not accepted by the parent enzymes. Both recombination and random mutagenesis gave rise to enzymes with altered substrate specificity, although such enzymes were more frequent in the chimeric libraries and more distinct specificities were found in the chimeric libraries. Only chimeras were active toward n-hexylbenzene. These results support the view that recombination is an effective search strategy for evolving substrate specificity, and may be more effective than random mutagenesis.
", "doi": "10.7907/61KV-P379", "publication_date": "2003", "thesis_type": "phd", "thesis_year": "2003" }, { "id": "thesis:2374", "collection": "thesis", "collection_id": "2374", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06022003-074653", "primary_object_url": { "basename": "Thesis08Jun03.pdf", "content": "final", "filesize": 4053288, "license": "other", "mime_type": "application/pdf", "url": "/2374/1/Thesis08Jun03.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Toward an Understanding of the Indirect Climatic Effect of Aerosols", "author": [ { "family_name": "Nenes", "given_name": "Athanasios", "orcid": "0000-0003-3873-9970", "clpid": "Nenes-Athanasios" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis is motivated by the need to improve our understanding of the aerosol indirect effect. The activation of aerosol into cloud droplets has been extensively studied, using a comprehensive numerical cloud droplet activation model. Using this model, the effect of water vapor mass transfer limitations on the cloud droplet activation process was first studied; it was found that mass transfer limitations are important for activation under polluted conditions. The potential effect of (currently unresolved) \"chemical effects\" on cloud droplet number (e.g., the presence soluble gases and surface active species) was also assessed. It was seen that small changes in aerosol and gas-phase composition can have a strong effect on cloud droplet number, and should be included in future estimates of the aerosol indirect effect.
\r\n\r\nA comprehensive aerosol activation parameterization was developed for use in a first-principle assessment of the aerosol indirect effect. This new parameterization introduces the concept of \"population splitting,\" in which the droplets are separated into two populations, each with its own growth characteristics. The effect of water vapor mass transfer limitations is explicitly introduced. The parameterization allows for treatment of chemical effects. The new parameterization shows excellent and robust agreement with a detailed numerical parcel model.
\r\n\r\nPreviously unidentified mechanisms of aerosol-cloud interactions were also explored. Aerosol, when it contains black carbon, can absorb light and heat the droplet enough to affect its activation behavior. This can affect cloud properties in numerous and counterintuitive ways; black carbon heating can dissipate clouds, but may also increase cloud lifetime (and lead to a climatic cooling) by decreasing the probability of drizzle formation.
\r\n\r\nFinally, the performance of instruments used for measuring the concentration of cloud condensation nuclei (CCN) was assessed. Each design exhibits different limitations and sources of uncertainty, but all show decreased ability to measure CCN of low critical supersaturation (<0.1%). The performance of the instrumentation can be very sensitive to the operating conditions. Therefore, an in-depth theoretical understanding of the instrumentation is necessary; otherwise, CCN measurements may be subject to considerable uncertainty.
", "doi": "10.7907/S02W-0573", "publication_date": "2003", "thesis_type": "phd", "thesis_year": "2003" }, { "id": "thesis:5495", "collection": "thesis", "collection_id": "5495", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01062010-084034470", "primary_object_url": { "basename": "Piccione_pm_2002.pdf", "content": "final", "filesize": 8240658, "license": "other", "mime_type": "application/pdf", "url": "/5495/1/Piccione_pm_2002.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Thermodynamics of Formation of Molecular Sieves", "author": [ { "family_name": "Piccione", "given_name": "Patrick Manuel", "clpid": "Piccione-Patrick-Manuel" } ], "thesis_advisor": [ { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" } ], "thesis_committee": [ { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Navrotsky", "given_name": "Alexandra", "orcid": "0000-0002-3260-0364", "clpid": "Navrotsky-Alexandra" }, { "family_name": "Zones", "given_name": "Stacey I.", "clpid": "Zones-S-I" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Molecular sieves, porous, crystalline frameworks with pore sizes of molecular dimensions, are of great industrial importance as detergents, catalysts and absorbants. Despite their technological importance, the syntheses of these materials are still not well understood and typically rely on extensive series of trials to produce new framework structures.
\r\n\r\nThermodynamic investigations are undertaken to better understand the energetic differences amongst molecular sieve frameworks and the mechanisms and interactions important in molecular sieve self-assembly. The enthalpies relative to quartz at 298.15 K are determined by high-temperature solution calorimetry for a collection of calcined pure-silica molecular sieves with diverse structural features. Si0_2 molecular sieves are shown to be only modestly (6.8-14.4 kJ/mol) metastable with respect to quartz. A strong linear correlation between enthalpy and molar volume is observed, implying that the overall packing quality determines the relative enthalpies of Si0_2 molecular sieves. Silanol (Si-O-H) defect sites lead to an additional destabilization of no more than 2.4 kJ/mol. The entropies of four pure-silica molecular sieves spanning the entire range of molar volumes available to Si0_2 frameworks are determined by the integration of heat capacity measurements from 5 to 400 K. The entropies of these structures are almost identical (3.2-4.2 J\u2219K^(-1)\u2219mol^(-1) above quartz), hence the empty pore volume and cages do not contribute appreciably to the vibrational density of states. The enthalpy and entropy data are combined to calculate the Gibbs free energies of transition from quartz to eight other silica polymorphs, including four molecular sieves as well as silica glass. At typical synthesis conditions, the available thermal energy is RT = 3.5 kJ/mol. The molecular sieve Gibbs free energies are only slightly larger than RT at 5.5-12.6 kJ/mol above quartz and lie in the same energetic region as the amorphous precursors used for molecular sieve preparation. There are therefore no significant thermodynamic barriers to transformations among silica polymorphs. Thus the role of SDA in molecular sieve syntheses is not the stabilization of otherwise very unstable phases.
\r\n\r\nInteraction enthalpies between inorganic frameworks and organic SDAs are measured by HF solution calorimetry for six molecular sieve/SDA pairs. The enthalpies are only moderately exothermic (-1.1 to -5.9 kJ/mol SiO_2), as expected if the predominant interactions are van der Waals contacts between the hydrophobic silica frameworks and the hydrocarbon portions of the SDAs. Interaction entropies can be estimated for three framework/SDA pairs, and, when used in combination with the interaction enthalpies, allow the calculation of the Gibbs free energies of interaction between these three inorganic/organic pairs. The latter values range from -2.0 to -5.4 kJ/mol SiO_2, smaller in magnitude than twice the available thermal energy at molecular sieve synthesis temperatures. This energy range is comparable to the range observed for the molecular sieve frameworks alone, showing that energetics of both the frameworks and of the molecular sieve/SDA interactions must be considered in order to adequately describe molecular sieve synthesis. The energetics of the synthesis of molecular sieves (considering all components present in the synthesis mixture) are examined here and also reveal small differences between various molecular sieve/SDA combinations. The energetic contribution of the effective dilution experienced by the SDA upon occlusion is similar in magnitude to the other energetic effects. The strong selectivity of organic SDAs experimentally observed in the face of the comparatively small energetic differences suggests that kinetic factors dominate in molecular sieve preparation.
", "doi": "10.7907/TQVE-FW28", "publication_date": "2002", "thesis_type": "phd", "thesis_year": "2002" }, { "id": "thesis:6109", "collection": "thesis", "collection_id": "6109", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10062010-111511765", "primary_object_url": { "basename": "Pantu_p_2001.pdf", "content": "final", "filesize": 32331729, "license": "other", "mime_type": "application/pdf", "url": "/6109/1/Pantu_p_2001.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Methane Conversion to Synthesis Gas over Platinum Supported on Rare Earth Oxides", "author": [ { "family_name": "Pantu", "given_name": "Piboon", "clpid": "Pantu-Piboon" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" }, { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The central theme of this research is to study methane conversion to synthesis gas focusing on the redox capabilities of cerium oxide. Reaction of methane with platinum or ruthenium supported on Ce_(1-x)Zr_xO_2 (x=0, 0.2, 0.5) in the absence of gaseous oxygen was studied in a packed-bed reactor at 550-700\u00b0C. The oxidation of methane utilized lattice oxygen of the support, which was subsequently restored by reacting with oxygen in a separate step. Thus, by using theredox property of cerium oxide, methane oxidation can be carried out by air without diluting the product with nitrogen. Addition of ZrO_2 into CeO_2 increased the reducibility of the oxide as well as the rate of methane oxidation but decreased the selectivity to CO and H_2. The rate of oxidation was initially very fast but slowed down as the oxide support became progressively reduced. On the other hand, the selectivity increased with the reduction of the support and sharply rose to over 90% as the support attained 10%,40%, and 65% degree of reduction for the oxide compositions x=0, 0.2, and 0.5, respectively.
\r\n\r\nPartial oxidation of methane to synthesis gas over 0.5wt% Pt/Al_2O_3 and 0.5wt% PtfCeO_2 catalysts was studied in a packed-bed reactor. At temperatures up to 650\u00b0C, the PtfCeO_2 catalyst gave higher conversion and higher selectivity but the activity and selectivity became comparable to those of Pt/Al_2O_3 above 700\u00b0C. The Pt/CeO_2 catalyst also maintained high conversion and high selectivity when the CH_4:O_2 feed ratio varied from 1.7 to 2.3 while the Pt/Al_2O_3 catalyst had considerably lower selectivity under methane-rich conditions. The effect of reducibility of support on the catalytic activity was discussed. A multiple microreactor system for parallel testing of heterogeneous catalysts was developed. The reactor system was composed of nine tubular microreactors housed in a single wider tube and used a multiposition valve to conduct the reaction products sequentially from each microreactor to a mass spectrometer for analysis. The catalyst samples were prepared in the form of thin films coated on quartz rods for convenience of preparation and loading samples in the reactors. The system was tested with the reaction of methane reforming with carbon dioxide over Pt/Ce_(1-x)Gd_xO_(2-0.5x) and Pt/Ce_(1-x)Sm_xO_(2-0.5x) at 650\u00b0C and 700\u00b0C. The measurements showed that Pt/CeO_2 had the highest activity and, generally, the activity increased with cerium oxide content. After exposure to the feed stream for 2-3 hours at 700\u00b0C, most catalysts suffered significant deactivation with the exception of the mixed oxides with 25-85% samarium oxide that maintained relatively stable activity.
", "doi": "10.7907/rksa-xc11", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:4492", "collection": "thesis", "collection_id": "4492", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11102005-135122", "primary_object_url": { "basename": "Luo_l_2001.pdf", "content": "final", "filesize": 12298676, "license": "other", "mime_type": "application/pdf", "url": "/4492/1/Luo_l_2001.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Partial Oxidation of Propane Over Vanadium-Containing Zeolite Catalysts", "author": [ { "family_name": "Luo", "given_name": "Lin", "clpid": "Luo-Lin" } ], "thesis_advisor": [ { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" } ], "thesis_committee": [ { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Labinger", "given_name": "Jay A.", "orcid": "0000-0002-1942-9232", "clpid": "Labinger-J-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Over the past few decades, significant efforts have been devoted to the development of new catalysts and processes for the partial oxidation of cheap and abundant light alkanes directly into oxygenates and olefins. One of the main challenges in the partial oxidation of light alkanes is that they are usually less reactive than the desired products, and further oxidation to total oxidation products, COx, is thermodynamically favored. With a few exceptions, e.g., partial oxidation of n-butane to malefic anhydride by V-P-O and a oxidation of propane to acrylonitrile by V-Al-Sb, catalysts investigated for the partial oxidation of light alkanes consist of complicated elemental compositions of metal oxides that have less than desirable catalytic behavior.
\r\n\r\nCompared to the traditional bulk metal oxides where the active sites selective for partial oxidation of hydrocarbons are usually lattice oxygens, small metal oxide clusters that do not have lattice energies are anticipated to offer oxygen with a lower energetic barrier. Thus, by using metal oxide clusters, the reaction temperature for oxidation of hydrocarbons may possibly be lowered and total oxidation reduced. Zeolites have been shown to be able to provide an excellent matrix for stabilizing metal oxide clusters. Here, a new approach is investigated for the partial oxidation of propane that combines the tunable advantages of zeolites with possibility of high reactivity of metal oxide clusters by using zeolite supported metal oxide clusters as catalysts.
\r\n\r\nVarious methods are employed to synthesize zeolite supported small metal oxide clusters, including ion-exchange-hydrolysis, liquid phase impregnation, vapor phase impregnation, and post-synthesis modification methods. Vanadium is used as the transition metal of interest and is combined with zeolite L, beta and SSZ-33. Vanadium oxide clusters are successfully incorporated inside zeolites and they have remarkably lower reduction temperatures than the bulk metal oxide. These zeolite based catalysts are studied for propane oxidation. The influence of the locations of the vanadium, the acidity of the zeolite matrix, the hydrophobicity of the zeolite framework and the addition of a second metal(Mo and Sb) are discussed. It is found that vanadium oxide cluster catalysts (VxOy/zeolite L, VxOy/zeolite beta, V-Sb/zeolite beta, V-Mo/zeolite beta) are not particularly selective for the partial oxidation of propane at the reaction conditions investigated (contact time 2 s, reaction temperature 350-450\u00b0C, feed gas molar ratio C3H8:O2:H2O:He=4:2:4:5), and most of the vanadium-containing zeolite beta catalysts are as active as V2O5 (as suggested by the turnover frequency).
\r\n\r\nA considerable amount of acetic acid is produced with vanadyl ion-exchanged zeolite beta (VO-H-beta), with a selectivity to acetic acid of 21.1% at propane conversion 1.62% (350\u00b0C). It appears that more valuable oxygenates, e.g., acrylic acid, may have been produced in the reaction and overoxidized to COx, since feeding acrylic acid into this VO-H-beta reaction system at 350\u00b0C results in complete oxidation of the acid to CO\u2093. Motivated by these data, the reaction pathways for propane and propylene oxidation are investigated on this catalyst. For comparison, reaction pathways are also studied with a \"Mitsubishi\" type catalyst, Mo1V0.3Te0.23Nb0.120x, one of the best catalysts for propane partial oxidation to acrylic acid. With VO-H-beta, propylene is the primary product of propane oxidation and acetic acid is a sequential oxidation product of the formed propylene possibly through an acetone intermediate. Mo1V0.3Te0.23Nb0.120x also gives propylene as the primary product of propane oxidation and the propylene thus formed further oxidizes to acrylic acid and acetone. Reactions of individual oxygenate compounds, e.g., propanal, acrolein, etc., suggest a need to further suppress the total oxidation and to improve allylic oxidation feature for the zeolite based catalysts.
", "doi": "10.7907/ce5g-3606", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:4490", "collection": "thesis", "collection_id": "4490", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11102005-103556", "primary_object_url": { "basename": "Lai_r_2001.pdf", "content": "final", "filesize": 4700896, "license": "other", "mime_type": "application/pdf", "url": "/4490/1/Lai_r_2001.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Synthesis and Characterization of ZSM-5 Zeolite Membranes", "author": [ { "family_name": "Lai", "given_name": "Re", "clpid": "Lai-Re" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "thesis_committee": [ { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Synthesis of ZSM-5 zeolite membranes supported on porous alumina substrates was conducted in autoclave reactors. The film morphologies and structures were characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Gas adsorption was used to estimate the crystalline fraction of the products. The gas permeation properties of the membranes were evaluated for H\u2082, CH\u2084, O\u2082, N\u2082, and n-butane and other gases singly or in mixtures.
\r\n\r\nZSM-5 film formation on alumina and other surfaces in certain clear, tetrapropylammonium(TPA\u207a)-containing synthesis solutions was found to be preceded by a gel layer. The presence of alumina and other substrates of a high Hamaker constant facilitated formation of the surface gel layer and accelerated zeolite crystallization. Aluminum added to the solution or leached from alumina substrates had dual effects, to induce surface gelation and to retard crystallization of that layer as well as crystallization in the bulk solution.
\r\n\r\nGrowth of ZSM-5 membranes was facilitated by using alumina tubes pre-coated with silicalite seeds. Accompanied with gradual growth of an external polycrystalline layer, siliceous deposits accumulated as deep as 100 \u00b5m inside the pores of the support, converting gradually from amorphous to crystalline. Pure gas permeation results are presented for membranes prepared in a solution of composition SiO\u2082: 0.15TPAB4: 0.7NaOH: 98H\u2082O using 0.4 and 2 \u00b5m seeds.
\r\n\r\nOrganic-free hydrogel reaction mixtures were further used to grow ZSM-5 membranes on seeded porous alumina substrates, eliminating the crack-prone calcination step for removing organic TPA\u207a templates from as-synthesized ZSM-5. The optimum composition SiO\u2082: 0.0125Al\u2082O\u2083: 0.2675Na\u2082O: 46H\u2082O was identified to produce membranes with permeation selectivities for H\u2082 over n-butane above 10\u2074 and for O\u2082 over N\u2082 9-10. The permeation was strongly activated with the activation energies increasing sharply with molecular size.
\r\n\r\nParallel synthesis of zeolite films was developed to expedite composition screening. The films prepared in an array reactor of multiple wells each containing 35 micro-liter synthesis solution displayed morphology similar to that produced by the conventional synthesis. The method was applied to explore the composition space of clear, organic-free synthesis solutions for ZSM-5 films growth: SiO\u2082: (700-300)Al\u2082O\u2083: (0.5-0.7)NaOH: 80H\u2082O.
", "doi": "10.7907/m5xs-mq20", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:4490", "collection": "thesis", "collection_id": "4490", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11102005-103556", "primary_object_url": { "basename": "Lai_r_2001.pdf", "content": "final", "filesize": 4700896, "license": "other", "mime_type": "application/pdf", "url": "/4490/1/Lai_r_2001.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Synthesis and Characterization of ZSM-5 Zeolite Membranes", "author": [ { "family_name": "Lai", "given_name": "Re", "clpid": "Lai-Re" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" } ], "thesis_committee": [ { "family_name": "Anson", "given_name": "Fred C.", "clpid": "Anson-F-C" }, { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Synthesis of ZSM-5 zeolite membranes supported on porous alumina substrates was conducted in autoclave reactors. The film morphologies and structures were characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Gas adsorption was used to estimate the crystalline fraction of the products. The gas permeation properties of the membranes were evaluated for H\u2082, CH\u2084, O\u2082, N\u2082, and n-butane and other gases singly or in mixtures.
\r\n\r\nZSM-5 film formation on alumina and other surfaces in certain clear, tetrapropylammonium(TPA\u207a)-containing synthesis solutions was found to be preceded by a gel layer. The presence of alumina and other substrates of a high Hamaker constant facilitated formation of the surface gel layer and accelerated zeolite crystallization. Aluminum added to the solution or leached from alumina substrates had dual effects, to induce surface gelation and to retard crystallization of that layer as well as crystallization in the bulk solution.
\r\n\r\nGrowth of ZSM-5 membranes was facilitated by using alumina tubes pre-coated with silicalite seeds. Accompanied with gradual growth of an external polycrystalline layer, siliceous deposits accumulated as deep as 100 \u00b5m inside the pores of the support, converting gradually from amorphous to crystalline. Pure gas permeation results are presented for membranes prepared in a solution of composition SiO\u2082: 0.15TPAB4: 0.7NaOH: 98H\u2082O using 0.4 and 2 \u00b5m seeds.
\r\n\r\nOrganic-free hydrogel reaction mixtures were further used to grow ZSM-5 membranes on seeded porous alumina substrates, eliminating the crack-prone calcination step for removing organic TPA\u207a templates from as-synthesized ZSM-5. The optimum composition SiO\u2082: 0.0125Al\u2082O\u2083: 0.2675Na\u2082O: 46H\u2082O was identified to produce membranes with permeation selectivities for H\u2082 over n-butane above 10\u2074 and for O\u2082 over N\u2082 9-10. The permeation was strongly activated with the activation energies increasing sharply with molecular size.
\r\n\r\nParallel synthesis of zeolite films was developed to expedite composition screening. The films prepared in an array reactor of multiple wells each containing 35 micro-liter synthesis solution displayed morphology similar to that produced by the conventional synthesis. The method was applied to explore the composition space of clear, organic-free synthesis solutions for ZSM-5 films growth: SiO\u2082: (700-300)Al\u2082O\u2083: (0.5-0.7)NaOH: 80H\u2082O.
", "doi": "10.7907/m5xs-mq20", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:1285", "collection": "thesis", "collection_id": "1285", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04072005-081230", "primary_object_url": { "basename": "Ostraat_ml_2001.pdf", "content": "final", "filesize": 11763159, "license": "other", "mime_type": "application/pdf", "url": "/1285/1/Ostraat_ml_2001.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Synthesis and Characterization of Aerosol Silicon Nanoparticle Nonvolatile Floating Gate Memory Devices", "author": [ { "family_name": "Ostraat", "given_name": "Michele Louisa", "orcid": "0000-0003-2678-6171", "clpid": "Ostraat-Michele-Louisa" } ], "thesis_advisor": [ { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" } ], "thesis_committee": [ { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Atwater", "given_name": "Harry Albert", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Silicon nanoparticle-based floating gate metal-oxide-semiconductor (MOS) field effect devices have potential for terabit cm-2 density nonvolatile memory applications. Aerosol synthesis of silicon nanoparticles is an important route toward the formation of discontinuous silicon nanoparticle floating gate structures that affords excellent control over particle size and size distribution, particle density, and oxide passivation. We have fabricated nanoparticle memory devices in a conventional MOS ultra-large scale integration (ULSI) process with channel lengths from 0.2 - 10 \u00b5m with a silicon nanoparticle floating gate fabricated by aerosol deposition.
\r\n\r\nSiO2 passivated silicon nanoparticles have been synthesized in an ultra clean two-stage aerosol reactor that is interfaced to a 200 mm wafer deposition chamber in a class 100 cleanroom. We synthesize silicon nanoparticles by thermal decomposition of silane gas at 950\u00b0C to produce single crystal, nonagglomerated nanoparticles. The second reactor stage passivated the silicon nanoparticles with a thin thermal oxide grown at 1050\u00b0C. Particles are thermophoretically deposited onto 200 mm silicon wafers with densities from 1013 particles cm-2 at the wafer center to 1011 particles cm-2 at the wafer edge in tens of minutes. We have fabricated floating gate memory devices in which the dielectric layer contains a discontinuous nanoparticle layer containing either (i) 2 -4 nm crystalline core diameter with 1 nm thermal oxide; or (ii) 6 - 15 nm crystalline core diameter with 2 nm thermal oxide. Cross-sectional transmission electron microscopy (TEM) verifies the presence of a silicon nanoparticle floating gate layer and planar TEM confirms nanoparticle morphology, size, and density.
\r\n\r\nAerosol floating gate devices exhibit normal transistor behavior and have promising nonvolatile device performance. Aerosol nanoparticle devices with 0.2 mm channel lengths exhibit threshold voltages < 5 V with large threshold voltage shifts (~ 2 V), submicrosecond program times and millisecond erase times. No degradation in program/erase threshold voltage swing was observed during 105 program and erase cycles, although some threshold voltage shift due to charge trapping was observed. Electrostatic modeling indicates when a discontinuous nanoparticle layer can be modeled as a continuous sheet charge embedded within oxide and when it should be modeled as individual nanoparticles in an array.
", "doi": "10.7907/FDGV-GS71", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:6129", "collection": "thesis", "collection_id": "6129", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10122010-083542958", "type": "thesis", "title": "Interaction of Hydrogen with Novel Carbon Materials", "author": [ { "family_name": "Ye", "given_name": "Yun", "clpid": "Ye-Yun" } ], "thesis_advisor": [ { "family_name": "Cass", "given_name": "Glen Rowan", "clpid": "Cass-G-R" }, { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Ahn", "given_name": "Channing C.", "clpid": "Ahn-C-C" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Bowman", "given_name": "Robert Clark, Jr.", "clpid": "Bowman-Robert-Clark-Jr" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The hydrogen storage properties of sonic carbon materials were studied. Graphite nanofibers (GNF) were synthesized by catalytic decomposion of ethylene and hydrogen. Catalyst supported carbon materials were prepared by impregnation process. Hydrogen desorption and adsorption properties of graphite nanofibers, single-walled carbon nanotubes (SWNT), fullerene materials and catalysts supported carbon materials were measured volumetrically using a Sievert's apparatus. The hydrogen desorption capacity of GNF was typically less than 0.2 wt.%. A phase transition between crystal SWNT and a new hydride phase was found at high pressures at 80K. The phase transition was of first order, and involved the separation of the individual tubes within a rope, exposing a high surface area for hydrogen adsorption. From the change in chemical potential of the hydrogen gas upon adsorption, we were able to calculate the cohesive van der Waals energy between the tubes as 5 mcV/C atom. This is much smaller than expected from previous theoretical work, and shows that defects in the crystal structure cause large suppressions of the cohesive energy. We were able to alter this cohesive energy by changing the state of the material. Over several cycles of isotherm measurements at 77 K, the hydrogen storage capacities of one of the fullerite samples increased from an initial value of 0.4 wt% for the first cycle to a capacity of 4.2 wt% for the fourth cycle. Correspondingly, the surface area increased from 0.9 m^2/gm to 11 m^2/gm and showed a phase transformation, characterized by X-ray powder diffraction. By adding Ni particles onto the sample, the hydrogen storage capacity of fullerite and activated carbon sample was increased. The adsorption of hydrogen on Ni particle can not account for the total increased capacity even by assuming complete coverage of hydrogen molecules on the Ni particle surface.", "doi": "10.7907/z8wn-gs34", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:6129", "collection": "thesis", "collection_id": "6129", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10122010-083542958", "type": "thesis", "title": "Interaction of Hydrogen with Novel Carbon Materials", "author": [ { "family_name": "Ye", "given_name": "Yun", "clpid": "Ye-Yun" } ], "thesis_advisor": [ { "family_name": "Cass", "given_name": "Glen Rowan", "clpid": "Cass-G-R" }, { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Ahn", "given_name": "Channing C.", "clpid": "Ahn-C-C" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Bowman", "given_name": "Robert Clark, Jr.", "clpid": "Bowman-Robert-Clark-Jr" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The hydrogen storage properties of sonic carbon materials were studied. Graphite nanofibers (GNF) were synthesized by catalytic decomposion of ethylene and hydrogen. Catalyst supported carbon materials were prepared by impregnation process. Hydrogen desorption and adsorption properties of graphite nanofibers, single-walled carbon nanotubes (SWNT), fullerene materials and catalysts supported carbon materials were measured volumetrically using a Sievert's apparatus. The hydrogen desorption capacity of GNF was typically less than 0.2 wt.%. A phase transition between crystal SWNT and a new hydride phase was found at high pressures at 80K. The phase transition was of first order, and involved the separation of the individual tubes within a rope, exposing a high surface area for hydrogen adsorption. From the change in chemical potential of the hydrogen gas upon adsorption, we were able to calculate the cohesive van der Waals energy between the tubes as 5 mcV/C atom. This is much smaller than expected from previous theoretical work, and shows that defects in the crystal structure cause large suppressions of the cohesive energy. We were able to alter this cohesive energy by changing the state of the material. Over several cycles of isotherm measurements at 77 K, the hydrogen storage capacities of one of the fullerite samples increased from an initial value of 0.4 wt% for the first cycle to a capacity of 4.2 wt% for the fourth cycle. Correspondingly, the surface area increased from 0.9 m^2/gm to 11 m^2/gm and showed a phase transformation, characterized by X-ray powder diffraction. By adding Ni particles onto the sample, the hydrogen storage capacity of fullerite and activated carbon sample was increased. The adsorption of hydrogen on Ni particle can not account for the total increased capacity even by assuming complete coverage of hydrogen molecules on the Ni particle surface.", "doi": "10.7907/z8wn-gs34", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:3274", "collection": "thesis", "collection_id": "3274", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08292008-110129", "primary_object_url": { "basename": "Zhou_w_2001.pdf", "content": "final", "filesize": 7877319, "license": "other", "mime_type": "application/pdf", "url": "/3274/1/Zhou_w_2001.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Dynamics and Shear Alignment Behavior of a Model Thermotropic Liquid Crystalline Polymer", "author": [ { "family_name": "Zhou", "given_name": "Weijun", "clpid": "Zhou-Weijun" } ], "thesis_advisor": [ { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" } ], "thesis_committee": [ { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Tirrell", "given_name": "David A.", "orcid": "0000-0003-3175-4596", "clpid": "Tirrell-D-A" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "orcid": "0000-0002-3361-6114", "clpid": "Wang-Zhen-Gang" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Although liquid crystalline polymers (LCPs) emerged as important engineering materials in the early 1970s, the current level of understanding still falls short of allowing deliberate manipulation of macroscopic orientation, leading to poor control of morphology and material properties. The flow behavior of rod-like LCP solutions (lyotropic) are fairly well understood, yet little progress has been made on LCP melts (thermotropic) because of the formidable experimental difficulties with commercial thermotropes. A simple extension of the knowledge obtained from rod-like LCP solutions to thermotropic LCPs is unlikely to hold due to the enhanced molecular flexibility and intimate molecular contact in LCP melts.
\r\n\r\nThe primary concern of this thesis is therefore the flow behavior of thermotropic LCPs, with an emphasis on how flow influences orientation and morphology and how this depends on molecular structure. For this purpose we synthesized a model thermotropic LCP selected for its chemical stability, wide nematic range and optical transparency. This main-chain LCP, designated as DHMS-7,9, has alternating mesogen and spacer structure with dihydroxy-[alpha]-methylstilbene as mesogen and two different lengths of alkyl spacers (-C\u2087H\u2081\u2084- and -C\u2089H\u2081\u2088-). A range of molecular weights were prepared to probe the effects of chain flexibility (ratio of chain length of persistence length). Synthesis was scaled up to provide adequate quantities for physical studies (rheology, rheo-conoscopy and rheo-WAXS).
\r\n\r\nThe director response of a monodomain during shear flow is followed by in situ optical conoscopy using a custom-made shear cell. We observe that the director rotates opposite to the vorticity in shear for DHMS-7,9 using planar monodomain samples, demonstrating conclusively that it is flow aligning throughout its nematic temperature range. Director rotation is solely a function of applied strain, independent of shear rate, showing that the Leslie-Ericksen theory is applicable to polymeric nematics for shear rates that are low relative to their molecular relaxation. Comparisons of the observed tumbling parameter of DHMS-7,9 with predictions from available molecular models lead us to infer that molecular flexibility produces shear alignment for this class of thermotropic LCPs. To identify the effect of chain flexibility on the dynamics of this LCP, the rotational viscosity and shear viscosity were measured as functions of molecular weight. Both viscosities showed weaker sensitivity to molecular weight above a characteristic molecular weight, suggesting a crossover to semiflexible character at high molecular weight.
\r\n\r\nRheology and shear orientation behavior of DHMS-7,9 are markedly different from that of nematic lyotropic LCPs. Synchrotron WAXS measurements in steady shear show that molecular orientation is relatively high and nearly independent of shear rate. In transient shear during flow inception, flow reversal, and step up/down shear rate, neither shear stress nor orientation parameter shows multiple oscillations. Thus, both steady and transient responses of DHMS-7,9 are characteristic of flow-aligning liquid crystals, in contrast to tumbling rod-like LCPs, which show complex shear rate dependence in steady shear and oscillatory response to these transient flows.
\r\n\r\nAn interesting feature of DHMS-7,9 is the existence of a mysterious liquid crystalline phase--Phase X. The flow behavior of Phase X is completely different from that of the nematic phase. A striking flip of the orientation from the flow direction to the vorticity direction occurs below a critical shear rate. This orientational flipping is reversible in response to step changes of temperature and/or shear rate. In addition, we found that oscillatory shear flow also induces a similar type of orientational flipping. Examination of the linear viscoelastic properties as a function of orientation in Phase X suggests rheological similarity to layered fluids.
", "doi": "10.7907/dv2d-w145", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:5123", "collection": "thesis", "collection_id": "5123", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12222006-125228", "primary_object_url": { "basename": "Griffin_RJ_2000.pdf", "content": "final", "filesize": 45759393, "license": "other", "mime_type": "application/pdf", "url": "/5123/1/Griffin_RJ_2000.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Experimental and computational studies of secondary organic aerosol formation", "author": [ { "family_name": "Griffin", "given_name": "Robert John", "clpid": "Griffin-R-J" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Dabdub", "given_name": "Donald", "clpid": "Dabdub-D" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Organic species are important constituents of tropospheric particulate matter in remote, rural, and urban areas. Such aerosol can be primary (emitted in the particle phase as solids or liquids) or secondary (formed in situ as condensable vapors) in nature. Secondary organic aerosol (SOA) is formed when products resulting from the gas-phase oxidation of a parent organic species partition to the particle phase. This partitioning can occur via condensation onto existing inorganic aerosol (heterogeneous-heteromolecular nucleation), absorption into an existing organic aerosol, dissolution to the aerosol aqueous phase, or homogeneous-heteromolecular nucleation.\n\nSOA yield is defined as the amount of SOA formed per the amount of a parent organic species that is oxidized. This yield depends functionally on stoichiometric and partitioning coefficients for each of the oxidation products formed and the total amount of organic aerosol mass available to act as absorptive media. Appropriate yield parameters are developed for a series of parent organics using smog chamber experiments. The effects of parent organic structure and the oxidizing species on SOA yield are also examined during the smog chamber experiments. Such yield parameters are used to model SOA formation from the oxidation of biogenic organic species on a global and annual scale. Yield parameters can also be used to define a new concept, the incremental aerosol reactivity for parent organic species, which is a convenient way of ranking parent organics in terms of their SOA-forming potentials.\n\nEfforts to improve the simulation of SOA formation in the California Institute of Technology three-dimensional air quality model are also described. The Caltech Atmospheric Chemistry Mechanism was designed to predict concentrations of the highly functionalized secondary organic oxidation products capable of leading to SOA. A module that treats formation of SOA thermodynamically is used to predict the distribution of these products between the gas- and aerosol-phases. The new mechanism and thermodynamic module will used to simulate a smog episode that occurred in 1993 in the South Coast Air Basin of California.", "doi": "10.7907/2F9Q-1772", "publication_date": "2000", "thesis_type": "phd", "thesis_year": "2000" }, { "id": "thesis:785", "collection": "thesis", "collection_id": "785", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02272008-083453", "primary_object_url": { "basename": "Yeung_ch_1999.pdf", "content": "final", "filesize": 7060334, "license": "other", "mime_type": "application/pdf", "url": "/785/1/Yeung_ch_1999.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Nonlinear control of rotating stall and surge with axisymmetric bleed and air injection on axial flow compressors", "author": [ { "family_name": "Yeung", "given_name": "Chung-hei (Simon)", "clpid": "Yeung-C-S" } ], "thesis_advisor": [ { "family_name": "Murray", "given_name": "Richard M.", "clpid": "Murray-R-M" } ], "thesis_committee": [ { "family_name": "Murray", "given_name": "Richard M.", "clpid": "Murray-R-M" }, { "family_name": "Culick", "given_name": "Fred E. C.", "clpid": "Culick-F-E-C" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Caughey", "given_name": "Thomas Kirk", "clpid": "Caughey-T-K" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The study of compressor instabilities in gas turbine engines has received much attention in recent ears. In particular, rotating stall and surge are major causes of problems ranging from component stress and lifespan reduction to engine explosion. In this thesis, modeling and control of rotating stall and surge using bleed valve and air injection is studied and validated on a low speed, single stage, axial compressor at Caltech.\n\nBleed valve control of stall is achieved only when the compressor characteristic is actuated, due to the fast growth rate of the stall cell compared to the rate limit of the valve. Furthermore, experimental results show that the actuator rate requirement for stall control is reduced by a factor of fourteen via compressor characteristic actuation. Analytical expressions based on low order models (2-3 states) and a high fidelity simulation (37 states) tool are developed to estimate the minimum rate requirement of a bleed valve for control of stall. A comparison of the tools to experiments show a good qualitative agreement, with increasing quantitative accuracy as the complexity of the underlying model increases.\n\nAir injection control of stall and surge is also investigated. Simultaneous control of stall and surge is achieved using axisymmetric air injection. Three cases with different injector back pressure are studied. Surge control via binary air injection is achieved in all three cases. Simultaneous stall and surge control is achieved for two of the cases, but is not achieved for the lowest authority case. This is consistent with previous results for control of stall with axisymmetric air injection without a plenum attached.\n\nNon\u2014axisymmetric air injection control of stall and surge is also studied. Three existing control algorithms found in literature are modeled and analyzed. A three\u2014state model is obtained for each algorithm. For two cases, conditions for linear stability and bifurcation criticality on control of rotating stall are derived and expressed in terms of implementation\u2014oriented variables such as number of injectors. For the third case, bifurcation criticality conditions are not obtained due to complexity, though linear stability property is derived. A theoretical comparison between the three algorithms is made, via the use of low\u2014order models, to investigate pros and cons of the algorithms in the context of operability.\n\nThe effects of static distortion on the compressor facility at Caltech is characterized experimentally. Results consistent with literature are obtained. Simulations via a high fidelity model (34 states) are also performed and show good qualitative as well as quantitative agreement to experiments. A non\u2014axisymmetric pulsed air injection controller for stall is shown to be robust to static distortion.", "doi": "10.7907/1wef-gp10", "publication_date": "1999", "thesis_type": "phd", "thesis_year": "1999" }, { "id": "thesis:4576", "collection": "thesis", "collection_id": "4576", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-152437", "primary_object_url": { "basename": "Jones_c_1999.pdf", "content": "final", "filesize": 8608188, "license": "other", "mime_type": "application/pdf", "url": "/4576/1/Jones_c_1999.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Organic-functionalized molecular sieves (OFMS'S): A new class of materials", "author": [ { "family_name": "Jones", "given_name": "Christopher W.", "clpid": "Jones-C-W" } ], "thesis_advisor": [ { "family_name": "Davis", "given_name": "Mark E.", "clpid": "Davis-M-E" } ], "thesis_committee": [ { "family_name": "Davis", "given_name": "Mark E.", "clpid": "Davis-M-E" }, { "family_name": "Tirrell", "given_name": "David A.", "clpid": "Tirrell-D-A" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Labinger", "given_name": "Jay A.", "clpid": "Labinger-J-A" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Throughout the last two decades, there has been a tremendous interest and growth in molecular sieve science. In particular, substantial attention has been paid to the development of new molecular sieves for catalytic applications, as molecular sieves have the unique ability to promote reactions in a shape-selective manner. To increase the variety of reactions that can be catalyzed by molecular sieves, recent efforts have focused on generating new types of active sites in molecular sieves by incorporating transition metals into the silicate framework or by supporting metal-based species within the micropores. Despite this, there are still many chemistries that can not be carried out over molecular sieve catalysts where significant benefit could be gained if the reaction were to be accomplished in a shape-selective manner. To address this problem, I have prepared a new class of molecular sieves that contain intracrystalline organic functionalities [denoted organic-functionalized molecular sieves (OFMS's)]. Previous attempts to synthesize silicate-based molecular sieves with organic functionalities within the micropores have focused on grafting organic groups onto preformed zeolites. However, this is not a viable route to the production of OFMS's that can function as shape-selective catalysts, as the organic groups preferentially functionalize the external crystal surface. Here, the problems with this approach are circumvented by preparing OFMS's by direct synthesis.\n\nAttempts to synthesize OFMS's directly both in the presence and absence of organic structure-directing agents (SDA's) are described. Pure-silica beta zeolites containing a variety of intracrystalline organic groups are synthesized using tetraethyl ammonium fluoride (TEAF) as the SDA. Porosity is generated by removing the occluded TEAF by solvent-extraction techniques. Following extraction, the exposed organic functionalities are further altered by chemical techniques, e.g., amines to imines, phenethyl groups to phenethylsulfonic acid groups. The ability to perform shape-selective acid catalysis (phenethylsulfonic acid) and shape-selective formation of imines from amines indicates that the organic moieties reside largely in the micropores of the molecular sieve. Several preparation variables have an impact on the nature of the resulting OFMS's, the most of important of which are the synthetic method, silicon source, and extraction method. The effects of these synthetic factors on the crystal size and morphology, porosity and hydrophobicity of the products are discussed.", "doi": "10.7907/6xz1-hh23", "publication_date": "1999", "thesis_type": "phd", "thesis_year": "1999" }, { "id": "thesis:323", "collection": "thesis", "collection_id": "323", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01242008-085938", "primary_object_url": { "basename": "Kusaka_i_1998.pdf", "content": "final", "filesize": 6819732, "license": "other", "mime_type": "application/pdf", "url": "/323/1/Kusaka_i_1998.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Molecular Theory of Vapor Phase Nucleation", "author": [ { "family_name": "Kusaka", "given_name": "Isamu", "clpid": "Kusaka-Isamu" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "orcid": "0000-0002-3361-6114", "clpid": "Wang-Zhen-Gang" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "orcid": "0000-0002-3361-6114", "clpid": "Wang-Zhen-Gang" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "An attempt has been made to establish the foundation of molecular level theory of vapor phase nucleation. We have focused on evaluating the reversible work of cluster formation and followed two major trends in this direction, namely, statistical mechanical density functional theory and molecular level simulation.\r\n\r\nWe applied density functional theory to heterogeneous nucleation onto an ion. Our prime interest is to predict a sign preference of nucleation rate, which has been experimentally observed yet remained inexplicable in the classical framework. The theory indicates that asymmetry in ion-molecule interaction is directly responsible for the sign preference. The predicted sign dependence decreases as the supersaturation is increased. Our results from density functional theory agree well with the existing experimental observations.\r\n\r\nMolecular simulation offers an alternative to molecular level approach. A long-standing issue of fundamental importance in cluster simulation is the precise definition of a cluster. Thus far, all attempts of defining a cluster had introduced ad hoc criteria to determine unambiguously whether a given molecule in the system belongs to vapor or to a cluster for any instantaneous configuration of molecules. From a careful examination of the context in which a cluster should be introduced into nucleation theory, we conclude that such a criterion is unnecessary. Then, we present a new approach to cluster simulation which is free of any arbitrariness involved in the definition of a cluster. Instead, it preferentially and automatically generates the physical clusters, defined as the density fluctuations that lead to nucleation, and determines their equilibrium distribution in a single simulation. The latter feature permits one to completely bypass the computationally demanding free energy evaluation that is necessary in a conventional simulation. The method is applied first to water using the SPC/E model. We then turn to H2SO4/H2O binary system to obtain a large section of the reversible work surface. The resulting surface is markedly different from that in classical theory and indicates that the rate limiting step of stable particle formation in this system is the binary collision of the sulfuric acid hydrates.\r\n", "doi": "10.7907/jwwk-0n13", "publication_date": "1998", "thesis_type": "phd", "thesis_year": "1998" }, { "id": "thesis:2684", "collection": "thesis", "collection_id": "2684", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06222005-110302", "primary_object_url": { "basename": "Yurkovetsky_Y_1998.pdf", "content": "final", "filesize": 11158780, "license": "other", "mime_type": "application/pdf", "url": "/2684/1/Yurkovetsky_Y_1998.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "I. Statistical mechanics of bubbly liquids. II. Behavior of sheared suspensions of non-Brownian particles", "author": [ { "family_name": "Yurkovetsky", "given_name": "Yevgeny", "clpid": "Yurkovetsky-Y" } ], "thesis_advisor": [ { "family_name": "Brady", "given_name": "John F.", "clpid": "Brady-J-F" } ], "thesis_committee": [ { "family_name": "Brady", "given_name": "John F.", "clpid": "Brady-J-F" }, { "family_name": "Brennen", "given_name": "Christopher E.", "clpid": "Brennen-C-E" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Kornfield", "given_name": "Julia A.", "clpid": "Kornfield-J-A" }, { "family_name": "Hunt", "given_name": "Melany L.", "clpid": "Hunt-M-L" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "clpid": "Wang-Zhen-Gang" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nI. Statistical mechanics of bubbly liquids. The dynamics of bubbles at high Reynolds numbers is studied from the viewpoint of statistical mechanics. Individual bubbles are treated as dipoles in potential flow. A virtual mass matrix of the system of bubbles is introduced, which depends on the instantaneous positions of the bubbles, and is used to calculate the energy of the bubbly flow as a quadratic form of the bubbles' velocities. The energy is shown to be the system's Hamiltonian and is used to construct a canonical ensemble partition function, which explicitly includes the total impulse of the suspension along with its energy. The Hamiltonian is decomposed into an effective potential due to the bubbles' collective motion and a kinetic term due to the random motion about the mean. An effective bubble temperature - a measure of the relative importance of the bubbles' relative to collective motion--is derived with the help of the impulse-dependent partition function. Two effective potentials are shown to operate: one, due to the mean motion of the bubbles, dominates at low bubble temperatures where it leads to their grouping in flat clusters normal to the direction of the collective motion, while the other, temperature invariant, is due to the bubbles' position-dependent virtual mass and results in their mutual repulsion. Numerical evidence is presented for the existence of the effective potentials, the condensed and dispersed phases and a phase transition.\r\n\r\nII. Behavior of sheared suspensions of non-Brownian particles. Suspensions of non-Brownian particles in simple shear flow of a Newtonian solvent in the range of particle phase concentration, [...], from 0.05 to 0.52, are studied numerically by Stokesian Dynamics. The simulations are a function of [...] and the dimensionless shear rate, [...], which measures the relative importance of the shear and short-ranged interparticle forces. The pair-distribution functions, shear viscosity, normal stress differences, suspension pressure, long-time self-diffusion coefficients, and mean square of the particle velocity fluctuations in the velocity-gradient and vorticity directions are computed, tabulated and plotted. In concentrated suspensions ([...] > 0.45), two distinct microstructural patterns are shown to exist at the highest and lowest shear rates. At [...] = 0.1 the particles form hexagonally packed strings in the flow direction. As [...] increases, the strings are gradually being replaced by non-compact clusters of particles kept together by strong lubrication forces while the particle pair-distribution displays a broken fore-aft symmetry. These changes in the microstructure are accompanied by increases in the shear viscosity, normal stress differences, suspension pressure, longtime self-diffusion coefficients, and fluctuational motion. Agreement is found between the simulation results and the theoretical predictions of Brady and Morris (1997).\r\n", "doi": "10.7907/NMJQ-2X32", "publication_date": "1998", "thesis_type": "phd", "thesis_year": "1998" }, { "id": "thesis:117", "collection": "thesis", "collection_id": "117", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-150302", "primary_object_url": { "basename": "Khodabandeh_s_1997.pdf", "content": "final", "filesize": 6345664, "license": "other", "mime_type": "application/pdf", "url": "/117/1/Khodabandeh_s_1997.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Synthesis of Alkaline-earth Zeolites", "author": [ { "family_name": "Khodabandeh", "given_name": "Shervin", "clpid": "Khodabandeh-Shervin" } ], "thesis_advisor": [ { "family_name": "Davis", "given_name": "Mark E.", "clpid": "Davis-M-E" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Davis", "given_name": "Mark E.", "clpid": "Davis-M-E" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Giapis", "given_name": "Konstantinos P.", "clpid": "Giapis-K-P" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Zeolite molecular sieves have found extensive applications in ion-exchange, separation and catalytic processes, particularly in the chemical and petroleum industries. Currently, the state-of-the-art in synthesis of high-silica zeolites involves the use of complex organic molecules to direct the formation of zeolitic materials with novel pore structures. While efforts towards preparation of new zeolites using organic molecules as structure-directing agents continues, synthesis of calcium and other alkaline-earth zeolites has not received much attention since the inception of the systematic investigation of zeolite synthesis some 35 years ago. Of the approximate 50 natural zeolites discovered to date, over 20% have eluded synthesis and another 10% have proven exceedingly difficult to synthesize at typical hydrothermal conditions. The overwhelming majority of these zeolites are calcium-dominant. The difficulty encountered in the synthesis of these alkaline-earth zeolites is in direct contrast to their natural occurrence as alteration products of volcanic glasses. Thus, the objective of this work is developing practical methodolgies for the synthesis of alkaline-earth zeolites.
\r\n\r\nHydrothermal transformation of perlite (a natural rhyolitic glass) to calcium zeolites is investigated as a first step towards developing synthesis procedures for the preparation of calcium and other alkaline-earth zeolites from pure starting reagents. In particular, synthetic analogues of the calcium zeolites gismondine, heulandite and epistilbite are obtained as alteration products of perlite glass reacting with calcium-containing solutions. The influence of the solution phase species and their concentrations, the pH and the temperature on the distribution of the zeolite products obtained are discussed. It is observed that the crystallization of heulandite from perlite is preceded by the transient formation of a gismondine-type zeolite most similar to the synthetic zeolite P1. This information is exploited to devise methodology for the preparation of zeolite P1 from pure starting reagents and its subsequent conversion to calcium and other alkaline-earth zeolites upon treatment with solutions containing alkaline-earth cations. Thus, a novel approach for the synthesis of alkaline-earth zeolites based on the hydrothermal conversion of zeolite P1 is developed. Details of the synthesis procedures are enumerated for the preparation of alkaline-earth zeolites CIT-3 (HEU), CIT-4 (BRE), epistilbite (EPI), harmotome (PHI), and yugawaralite (YUG). Transformation of zeolite P1 to alkaline-earth zeolites is governed by factors such as the Si/Al ratio of the starting P1 material, the composition of the solution phase and the presence or absence of seed crystals. The effects of these factors on the products obtained, i.e., phase selectivity, are discussed.
", "doi": "10.7907/35dq-qn66", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:17086", "collection": "thesis", "collection_id": "17086", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03212025-215725447", "type": "thesis", "title": "I. The Use of Spherosiloxanes as Molecular Building Blocks for Material and Thin Films. II. A Method of Using SC-Cut Quartz Oscillators for Chemical Sensing", "author": [ { "family_name": "Nagel", "given_name": "John Frederick", "clpid": "Nagel-John-Frederick" } ], "thesis_advisor": [ { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" } ], "thesis_committee": [ { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" }, { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Giapis", "given_name": "Konstantinos P.", "orcid": "0000-0002-7393-298X", "clpid": "Giapis-K-P" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The ability to prepare a priori ordered materials of a desired structure is a long\r\nstanding goal in materials research. Recently, there has been great interest in the use of\r\nwell-defined molecular precursors that can, in principle, be combined in a regular way\r\nwithout degradation to produce ordered materials. This process has been dubbed \"lego-chemistry.\"\r\nThis work examines the use of spherosiloxanes, a family of polyhedral silicate\r\ncage molecules, as molecular building blocks for the synthesis of bulk microporous\r\nmaterials and microporous thin films.
\r\n\r\nThe process for synthesizing and functionalizing the spherosiloxanes with a variety\r\nof reactive functional ligands is presented. The reactive molecules are characterized\r\nusing a suite of analytical and spectroscopic techniques. In order to achieve some degree\r\nof control over the condensation process, a binary reaction mechanism utilizing nonhydrolytic\r\nreaction conditions is proposed for the production of bulk materials. Experimental\r\nresults from the non-hydrolytic condensation of spherosiloxanes are presented.\r\nThe effects of adding various catalysts to the reaction mixture are described. A multinuclear\r\nsolution NMR study was performed on monomeric silicate analogues of the\r\nspherosiloxanes in order to elucidate the non-hydrolytic reaction pathways. It is found\r\nthat under the conditions of interest ligand exchange predominates over condensation.
\r\n\r\nA reaction scheme and growth mechanism for the production of a microporous\r\nthin film from spherosiloxane precursors is presented and discussed. It is speculated that\r\nsuch an ordered film could function as a framework for the production of a molecular electronic\r\ndevice. The first important steps in this scheme, namely the condensation behavior\r\nof spherosiloxanes on the Si (100) - (2x1) reconstructed surface, are explored through a\r\nvariety of surface characterization techniques. In particular, low temperature STM is used\r\nto record the nature of the species condensed on the surface. An image of a single isolated\r\n(CH3O)8Si8O12 is recorded and its position and orientation are discussed in the context of the reaction scheme. A HREELS/TPD study of the spherosiloxanes on the same surface is\r\nperformed and the results discussed.
\r\n\r\nA new technique for chemical sensing is proposed and is based on the recently\r\ndeveloped SC-cut quartz oscillator used in conjunction with the analytical technique\r\nknown as thermal programmed desorption (TPD). This technique is developed in order to\r\naddress the need to develop new sensing techniques that are sensitive, selective and cost\r\nefficient, for application to the rising threats of terrorism and pollution present today. The\r\ntechnique utilizes two vibrational modes of the crystal, one very sensitive and one relatively\r\ninsensitive to changes in temperature, that are monitored throughout the experiment.\r\nThe two mode sensing allows in principle for the simultaneous monitoring of the mass and\r\ntemperature of the sensor.
\r\n\r\nA system for evaluating the performance of this sensor is designed and built, and\r\nincludes an automated data acquisition and control system. The sensor is tested using a\r\nvariety of chemically selective coatings and analytes. The structure and morphology of\r\nthe coating used is shown to have a significant effect on the oscillation behavior of the\r\ncrystal used. TPD experiments are performed with the sensor in order to evaluate its characteristics.\r\nIn nearly all cases, it is impossible to discern any desorption signal during the\r\nTPD experiment. A dual mode analysis that is used to deconvolute the temperature and\r\nmass responses of the sensor fails to distinguish any desorption signals except from a very\r\nheavily loaded sample, i.e., water on a polyethyleneimine coated crystal where bulk\r\nabsorption occurs. A TPD experiment is performed on a hydrated, PEI coated crystal\r\nusing a Cahn microbalance, and a relationship between the mass loading and frequency\r\nchange is determined for this system. These values are used to calculate the frequency\r\nresponse for a typical coating where only surface adsorption occurs, and the result is\r\nbelow the minimum detection level of the system. Based on these data, it is determined\r\nthat the SC-cut sensor fails to show the sensitivity necessary for application as a practical\r\nsensor device.
", "doi": "10.7907/wkz6-jt81", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:17603", "collection": "thesis", "collection_id": "17603", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08072025-210544236", "primary_object_url": { "basename": "Baxter-Drayton_YV_1997.pdf", "content": "final", "filesize": 36191781, "license": "other", "mime_type": "application/pdf", "url": "/17603/1/Baxter-Drayton_YV_1997.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Dynamics of Flocculated Dispersions", "author": [ { "family_name": "Baxter-Drayton", "given_name": "Yvette Valencia", "clpid": "Baxter-Drayton-Yvette-Valencia" } ], "thesis_advisor": [ { "family_name": "Brady", "given_name": "John F.", "orcid": "0000-0001-5817-9128", "clpid": "Brady-J-F" } ], "thesis_committee": [ { "family_name": "Brady", "given_name": "John F.", "orcid": "0000-0001-5817-9128", "clpid": "Brady-J-F" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "orcid": "0000-0002-3361-6114", "clpid": "Wang-Zhen-Gang" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The rheological behavior of Brownian electrorheological (ER) fluids is studied\r\nas a model for flocculated colloidal dispersions. The ER fluid has the advantages\r\nthat the interparticle potential energy can be varied by simply changing the applied\r\nfield strength, and the microstructure consists of essentially linear chains of particles\r\naligned with the field direction. Studies of the quiescent suspension structure find a\r\ndispersed region, an equilibrium flocculated region, and a kinetically flocculated region\r\nfor low, moderate, and large attractive potential well depths, Umin/kT, respectively.\r\nUnder simple shear flow, the suspension has a high-shear-rate Newtonian viscosity\r\nand a shear thinning viscosity at lower shear rates. For moderate attractive potential\r\nwell depths the suspension has a low-shear viscosity that scales as exp(Umin/kT).\r\nFurthermore, the low-shear limiting behavior is seen at shear rates that scale as\r\nexp(-Umin/kT). The first normal stress difference is also presented. It was found\r\nthat due to the electric field the suspension structure is anisotropic with respect to\r\nthe compressional axis, and the first normal stress difference does not decay with the\r\nshear rate as it does for Brownian hard-spheres, but approaches a low-shear limiting\r\nvalue.
\r\n\r\nA theory is proposed that makes use of the time scale of diffusion for aggregated\r\nparticles out of their mutual potential well, \u03c4 ~ (a2/D)(kT/Umin)exp(Umin/kT),\r\nmuch in the spirit of the Eyring theory, to describe the rheology of the flocculated\r\ndispersion. Here a is the particle radius and D is the diffusivity of an isolated particle.\r\nWhen the shear rate is non-dimensionalized by \u03c4, the reduced viscosity data for all\r\nfield strengths collapse onto a single universal curve. Although we use a relatively\r\nsmall monolayer suspension, our simulation results compare well to the limited experimental\r\nand theoretical work on Brownian ER suspensions. The scaling relationship\r\nfor the low-shear viscosity has also been evidenced in other studies of flocculated\r\ndispersions.
\r\n\r\nThe model is tested for its general applicability by a study of the rheology of\r\na three-dimensional flocculated dispersion with an isotropic potential by molecular\r\ndynamics simulation and by analysis of experimental data obtained independently by\r\nBuscall, McGowan and Morton-Jones for a depletion flocculated dispersion. In both\r\ncases the suspension has a low-shear viscosity that scales exponentially with the pair\r\npotential well depth, and the low-shear limiting behavior was observed at a shear rate\r\nthat scales inverse exponentially with the pair potential well depth, Umin/kT. The\r\nreduced viscosity data collapse onto a single curve when plotted as a function of the\r\nshear rate non-dimensionalized by the escape time scale, and the model was found to\r\npredict the reduced curves.
\r\n\r\n", "doi": "10.7907/vqnw-np85", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:207", "collection": "thesis", "collection_id": "207", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01162008-153136", "primary_object_url": { "basename": "Kothare_mv_1997.pdf", "content": "final", "filesize": 10270567, "license": "other", "mime_type": "application/pdf", "url": "/207/1/Kothare_mv_1997.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Control of Systems Subject to Constraints", "author": [ { "family_name": "Kothare", "given_name": "Mayuresh V.", "clpid": "Kothare-Mayuresh-V" } ], "thesis_advisor": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" } ], "thesis_committee": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" }, { "family_name": "Doyle", "given_name": "John Comstock", "clpid": "Doyle-J-C" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Murray", "given_name": "Richard M.", "clpid": "Murray-R-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Every operating control system must deal with constraints. On the one hand, the range and rate of change of the input or manipulated variable is limited by the physical nature of the actuator (saturation limits). On the other hand, process state variables or outputs (pressures, temperatures, voltages) may not be allowed to exceed certain bounds arising from equipment limitation, safety considerations, or environmental regulations.
\r\n\r\nA rich theory exists for designing controllers - both linear (H2/H\u221e, LQG, LTR, pole-placement) and nonlinear (nonlinear H\u221e, control, feedback linearization, sliding mode control, gain scheduling). However, none of these popular and fashionable controller design techniques account for the presence of input or output constraints. Although occasionally these constraints may be neglected, in general, they lead to design and operating problems unless they are accounted for properly.
\r\n\r\nIn traditional control practice, overrides or mode selection schemes are used to deal with output constraints: they switch between a \"bank\" of controllers, each of which is designed to achieve a specific objective. In both cases (saturation limit and mode selection), a control input nonlinearity is introduced into the operating system.
\r\n\r\nDespite its significance, the study of the constrained control problem has received far less attention than the traditional unconstrained (linear and nonlinear) control theory. With few exceptions, most of the controller design techniques for constrained systems are by-and-large ad-hoc, with very little guarantees of stability, performance and robustness to plant model uncertainty.
\r\n\r\nThe objective of this thesis is to take a broad approach towards the constrained control problem. One part of the thesis is devoted to the development of a systematic and unifying theory for studying the so-called Anti-Windup Bumpless Transfer (AWBT) problem. The other part aims towards the development of a general novel approach for the synthesis of a robust model predictive control (MPC) algorithm.
\r\n", "doi": "10.7907/anhq-xj51", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:95", "collection": "thesis", "collection_id": "95", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01092008-135803", "primary_object_url": { "basename": "Fernandes_ne_1997.pdf", "content": "final", "filesize": 4649283, "license": "other", "mime_type": "application/pdf", "url": "/95/1/Fernandes_ne_1997.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Diffusion in mesoporous glass : simulations and experiments", "author": [ { "family_name": "Fernandes", "given_name": "Neil Edward", "clpid": "Fernandes-N-E" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Giapis", "given_name": "Konstantinos P.", "clpid": "Giapis-K-P" }, { "family_name": "Davis", "given_name": "Mark E.", "clpid": "Davis-M-E" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe diffusivities of simple gases in mesoporous glass were studied by experiment and simulation.\r\n\r\nPorous Vycor[...] glass was modified by deposition of silica on the internal pore surface using consecutive cycles of liquid phase silylation with silicon tetrachloride, and hydrolysis. Macroscopically uniform deposition was achieved by exploiting the self limiting nature of the reaction and the extent of deposition was monitored by the weight change of the samples. Weight increases as high as 24% were recorded and the average pore diameter was estimated to decrease from [...]. Permeation measurements were conducted in the Henry's law region at various levels of deposition for hydrogen, methane, isobutane and nitrogen, at temperatures between 60[degrees]C and 180[degrees]C. The measurements were compared to values calculated with a model using the effective medium approximation to treat network effects and Clausing's correction to account for conductances in pores of finite aspect ratio. The calculated values proved to be inaccurate for hydrogen, overestimating the permeance by a factor of two at high levels of deposition possibly because of non-ideal pore shapes accentuated by the deposition. For nitrogen and methane the agreement between calculations and measurements was better due to a fortuitous cancellation of deviations caused by the enhanced potential energy well within the pores and the non ideal pore shape. The intrapore potential energy effect was especially strong for isobutane and as a result the calculated flux was always less than the experimental.\r\n\r\nIn an effort to understand the importance of the intrapore potential and pore surface roughness on diffusion, molecular dynamics simulations of nitrogen and isobutane in a mesoporous glass pore, under free molecular flow conditions, were conducted for pores of diameter [...], and for temperatures between 200K and 800K. To study the effect of the intrapore potential, the gases were treated as simple Lennard-Jones atoms and the pore was simulated as a perfect cylinder exerting a 9-3 potential, but with its surface roughened by the superposition of spherical Lennard-Jones atoms representing silica tetrahedra. The molecular trajectories were calculated by the application of Nose-Hooverian mechanics and no momentum transfer was allowed between the pore walls and the gas molecules. Random walk behavior resulted from the resulting specular collisions. The effect of the intrapore potential was decoupled into two contributions. The effective diffusivity was respectively increased and decreased by a partitioning effect (or Henry's law adsorption) and a path curvature effect (the trapping of molecules near the surface). In pores of radius [...], both effects were present for temperatures as high as 500K, and were enhanced as the temperature decreased. For nitrogen, the combination of effects canceled over the temperature range of 500-200K and resulted in a temperature dependence similar to that of Knudsen diffusion. For isobutane, the partitioning effect overwhelmed the path curvature effect, resulting in significant surface flows at temperatures as high as 500K. At a temperature of 393K, as the pore radius was reduced from [...], the path curvature effect decreased and the partitioning effect increased. Although the intrapore potential becomes more negative as the pore size decreases, the magnitude of the potential energy barrier trapping molecules near the surface also decreases. The effect of surface roughness was studied through a hard sphere dynamics version of the above simulation. Diffusivities were obtained for various surface coverage of the silica tetrahedra. The specular reflection condition resulted in diffusivities at least twice that of the Knudsen value.", "doi": "10.7907/HPPB-TJ55", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:4493", "collection": "thesis", "collection_id": "4493", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11102005-141042", "primary_object_url": { "basename": "Yan_y_1997.pdf", "content": "final", "filesize": 17311051, "license": "other", "mime_type": "application/pdf", "url": "/4493/1/Yan_y_1997.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Preparation of zeolite ZSM-5 membranes", "author": [ { "family_name": "Yan", "given_name": "Yushan", "clpid": "Yan-Yushan" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Davis", "given_name": "Mark E.", "clpid": "Davis-M-E" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Davis", "given_name": "Mark E.", "clpid": "Davis-M-E" }, { "family_name": "Giapis", "given_name": "Konstantinos P.", "clpid": "Giapis-K-P" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "clpid": "Wang-Zhen-Gang" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nZeolite ZSM-5 membranes were prepared on porous [...] disks by in-situ crystallization using a clear solution of optimized composition [...]. During the synthesis, the disk was fixed horizontally at the air-liquid interface and a continuous polycrystalline zeolite film of about 10 \u00b5m thickness formed on the bottom surface of disk. Extensive experimentation was carried out to find the optimal composition. Pure gas permeation measurements of the most successful preparation yielded hydrogen:isobutane and n-butane:isobutane ratios of 151 and 18 at room temperature and 54 and 31 at 185\u00b0C, respectively.\r\n\r\nElectron probe microanalysis of the cross section of a membrane prepared on a bare alumina disk revealed a layer of crystalline or amorphous silica extending 80 \u00b5m inside the pores of the support. It is believed that this internal layer adds resistance to permeation and degrades selectivity. To limit the excessive penetration of siliceous species into the support pores, a diffusion barrier was introduced into the pores of the support prior to zeolite crystallization by impregnating the disk with a 1:1 molar mixture of furfuryl alcohol and tetraethylorthosilicate, polymerizing the mixture retained in the disk, and carbonizing the resulting polymer. Following carbonization, a partial carbon burnoff was carried out to generate a carbon-free region near the surface of the support. Membranes synthesized using barriers have n-butane flux and n-butane:isobutane selectivity 2.7 x [...] and 45 at 185\u00b0C which are, respectively, about 1.6 and 4 times as large as those of membranes prepared without the use of barriers.\r\n\r\nThe n-butane:isobutane selectivity of ZSM-5 membranes was substantially improved (e.g. 322 vs. 45 at 185\u00b0C) by a post-synthetic coking treatment which was accomplished by impregnating the membranes with liquid 1,3,5-triisopropylbenzene (TIPB) for 24 hours at room temperature and then calcining them in air at 500\u00b0C for 2 hours. Calcination at 500\u00b0C for up to 30 hours does not destroy the high n-butane:isobutane selectivity. Thermogravimetric analysis experiments suggest that microdefects in the zeolite membranes were selectively eliminated by the TIPB coking treatment while the intracrystalline pore space of the ZSM-5 was not affected.\r\n\r\nA model of surface-induced nucleation, crystal growth, and crystal adhesion was proposed for the aforementioned heterogeneous hydrothermal synthesis system. During the synthesis, aluminosilicates in the aged solution interact favorably with and travel toward the [...] surface, resulting in concentration and nucleation in the vicinity of the surface. Some of the nuclei become attached to the surface and grow into a zeolite film while others settle and produce loose zeolite crystals at the bottom of the autoclave. The nutrients for crystal growth is supplied by active gel particles and the synthesis solution. Surface -OH groups on the substrate appear important for crystal adhesion via condensation. As for zeolite membrane formation on a surface of certain area, the location and orientation of the surface as well as the amount of synthesis liquid accessible to the surface are critical for the quality of the zeolite membrane.\r\n", "doi": "10.7907/05FZ-JS07", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:4988", "collection": "thesis", "collection_id": "4988", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12132007-085351", "primary_object_url": { "basename": "Gupta_vk_1996.pdf", "content": "final", "filesize": 8373125, "license": "other", "mime_type": "application/pdf", "url": "/4988/1/Gupta_vk_1996.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Controlling molecular and microstructural alignment in anisotropic polymer systems", "author": [ { "family_name": "Gupta", "given_name": "Vinay Kumar", "clpid": "Gupta-V-K" } ], "thesis_advisor": [ { "family_name": "Kornfield", "given_name": "Julia A.", "clpid": "Kornfield-J-A" } ], "thesis_committee": [ { "family_name": "Kornfield", "given_name": "Julia A.", "clpid": "Kornfield-J-A" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Brady", "given_name": "John F.", "clpid": "Brady-J-F" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "clpid": "Wang-Zhen-Gang" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Molecular and microstructural orientation plays a key role in determining the useful mechanical, optical and electrical properties of a large class of polymeric materials. Realization of the technological promise of these materials requires rational control of the microstructure and understanding of the processing-structure-property relationships. Towards this end, we focus on the material properties and dynamical processes that affect molecular order of two complex polymeric systems (a) Ultra-thin Langmuir-Blodgett films of a hairy-rodlike polymer, and (b) Lamellar diblock copolymer melts of polystyrene and polyisoprene (PS-PI).\n\nWe accomplish our objective by improving and tying together existing analytic techniques into instruments extremely effective for measuring molecular orientation and order. For fundamental insights into the nature of alignment in ultra-thin (~ few nanometers thick) LB films, we integrate laser scanning microscopy (LSM) with polarization-modulation (PM) polarimetry. PM-LSM possesses high spatial resolution, sensitivity and speed, and allows us to image the anisotropy in films as thin as two molecular layers. To monitor the dynamics of flow alignment in diblock copolymers, in situ and in real time, we combine polarization-modulation polarimetry with rheometry. This rheo-optical technique enables us to monitor the evolution of microstructure by measuring the optical anisotropy, and correlate it with changes in macroscopic mechanical observables, such as stress and strain.\n\nUsing PM-LSM we have investigated the interplay of molecular weight, layer thickness and thermal annealing in controlling molecular order in rodlike polymer LB films. Upon investigating two different molecular weights of the polymer, we find lowering of molecular order in deposited films with increase in molecular weight. Furthermore, thermal annealing improves alignment only for films of shorter rodlike polymers (~ lower molecular weight). We believe that the underlying cause for these results is a difference in the structure of the deposited films for the longer polymer because of the relative changes in timescales for the macromolecular relaxation and the monolayer deformation during deposition. We also find that for both molecular weights, the substrate exerts an anchoring effect on the first two layers adjacent to it and suppresses improvement in alignment on annealing. This inability to improve alignment has important consequences for applications such as molecular electronics where monolayers or bilayers having a high degree of orientation are required.\n\nIn-situ measurement of flow birefringence during oscillatory shear alignment, clarifies the evolution of the lamellar orientation distribution for a diblock copolymer melt. Shearing results in \"parallel\" or \"perpendicular\" alignment i. e. layers normal to either the velocity gradient or the vorticity axis, respectively (Figure 1.1). Both states of alignment occur via an initial \"fast\" process followed by a \"slow\" one. The fast process is dominated by the depletion of the projection of the orientation distribution along either the perpendicular direction or the \"transverse\" direction (layers normal to the flow). This resulting biaxial distribution is then transformed into a well-aligned uniaxial one during the slow process. Surprisingly, at particular frequencies, the projection along the perpendicular direction can disappear faster than the projection along the transverse direction. In both the fast and the slow processes the time evolution of birefringence follows a highly non-linear scaling with strain; the scaling being different for the fast and slow processes. A systematic study of the effects of strain on shear alignment in block copolymers led to the discovery that strain affects not only the dynamics of alignment, but also the direction. This phenomenon expands the range of parameters that can be used to flip the direction of alignment. In relation to previous studies that examined the regimes of alignment only in terms of temperature and frequency, this phenomenon necessitates consideration of a third dimension - strain.", "doi": "10.7907/xb3f-3a10", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:109", "collection": "thesis", "collection_id": "109", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-085702", "primary_object_url": { "basename": "Morris_jf_1996.pdf", "content": "final", "filesize": 9844570, "license": "other", "mime_type": "application/pdf", "url": "/109/1/Morris_jf_1996.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Suspensions: microstructure, diffusion, and inhomogeneous flow", "author": [ { "family_name": "Morris", "given_name": "Jeffrey Franklin", "clpid": "Morris-J-F" } ], "thesis_advisor": [ { "family_name": "Brady", "given_name": "John F.", "clpid": "Brady-J-F" } ], "thesis_committee": [ { "family_name": "Brady", "given_name": "John F.", "clpid": "Brady-J-F" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Kornfield", "given_name": "Julia A.", "clpid": "Kornfield-J-A" }, { "family_name": "Marcus", "given_name": "Rudolph A.", "clpid": "Marcus-R-A" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "clpid": "Wang-Zhen-Gang" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA theory of self-diffusivity in sheared suspensions valid for any particle volume fraction [phi], Peclet number Pe, and lengthscale of disturbance in [phi] is developed. The theory is applied to the determination of the full tensor self-diffusivity in a weakly- sheared (Pe << 1) suspension of hydrodynamically-interacting hard spheres and a strongly-sheared (Pe >> 1) suspension of hard spheres without hydrodynamic interactions, both at [phi] << 1.\r\n\r\nThe influence of weak Brownian motion alone and in conjunction with a repulsive interparticle force of hard-sphere type upon the pair-distribution function, g(r) where r is the separation vector of a pair of particles, is analyzed for a suspension of spheres at Pe >> 1 and [phi] << 1. At large Pe, the radial fluxes of pair probability due to advection and Brownian diffusion balance in a thin [...] boundary layer at contact, with a the sphere radius. The boundary-layer analyses demonstrate that Brownian diffusion renders g finite at contact in the absence of interparticle forces, and that within the boundary layer there is generally a large excess of pair probability along the compressional axes. By calculation of the bulk normal stress differences in the case with repulsive forces, it is shown how this asymmetry of the microstructure yields non-Newtonian constitutive behavior in the limit Pe[superscript -1] = 0.\r\n\r\nHydrodynamic resistance functions relating the particle and bulk motions to the bulk isotropic stress are developed. Application of these functions is demonstrated by calculations of the shear-induced correction to the osmotic pressure and the particle contribution to the pressure in a sheared lattice.\r\n\r\nPressure-driven flow in a channel at vanishing Reynolds number of a suspension of particles denser than the suspending fluid has been dynamically simulated by Stokesian Dynamics over ranges of the particle fraction, channel width, and a buoyancy parameter characterizing the relative strength of the buoyancy to shearing forces. The predictions of the flow by the suspension-balance model are in good agreement with simulation results.\r\n", "doi": "10.7907/069F-Z696", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:15", "collection": "thesis", "collection_id": "15", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01032008-082416", "primary_object_url": { "basename": "Rubin_sf_1996.pdf", "content": "final", "filesize": 12348211, "license": "other", "mime_type": "application/pdf", "url": "/15/1/Rubin_sf_1996.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Viscoelasticity and dynamics of alignment in side-group liquid crystalline polymers", "author": [ { "family_name": "Rubin", "given_name": "Susan Felicia", "clpid": "Rubin-S-F" } ], "thesis_advisor": [ { "family_name": "Kornfield", "given_name": "Julia A.", "clpid": "Kornfield-J-A" } ], "thesis_committee": [ { "family_name": "Kornfield", "given_name": "Julia A.", "clpid": "Kornfield-J-A" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Hubbell", "given_name": "Jeffrey A.", "clpid": "Hubbell-J-A" }, { "family_name": "Brady", "given_name": "John F.", "clpid": "Brady-J-F" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "clpid": "Wang-Zhen-Gang" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nSide-group liquid-crystalline polymers (SG-LCPs) consist of a flexible polymeric backbone and rigid mesogens (molecules forming LC phases), attached laterally to the backbone via flexible spacers. Since the dynamics of the mesogen field and polymeric backbone are partially decoupled, uniformly-aligned SG-LCP materials show promise in a variety of applications such as non-linear optical materials, optical data storage media, and stress sensors, which require switching of the mesogen orientation. Recent work has shown that uniform alignment of SG-LCP materials can be accomplished using flow-fields. However, the mechanisms of alignment, which are essential for the development of effective and rational processing strategies for the SG-LCP materials, remain poorly understood. To address this need, we focus on the viscoelastic properties of nematic and smectic SG-LCPs and the dynamics of field-induced alignment of SG-LCPs.\r\n\r\nWe have investigated the dynamic mechanical response of SG-LCPs having methacrylate backbone, hexamethylene spacer, and phenyl benzoate mesogens as a function of molecular weight in the isotropic, nematic, and smectic phases [...], and have discovered a unique molecular-weight dependence of the sensitivity of the dynamic modulus to nematic order of the melt. Nematic order produced a profound change in the dynamics of the entangled SG-LPCs relative to the isotropic phase; however, this effect was absent in the unentangled SG-LCPs. In SGLCPs with smectic order, there was increase in the elastic character of the fluid with smectic ordering, but the incremental effect in a system that was entangled was relatively small. Oscillatory shear with large amplitude [...] induced macroscopic alignment in the nematic phase for all the SG-LCPs studied and could be used to alter the microstructure in the smectic liquid. Shearing the smectic phase produced a decrease in modulus, whereas shearing in the nematic phase followed by cooling into the smectic phase produced an increase in modulus.\r\n\r\nTo assess the effect of the coupling between the mesogen and the backbone on field- induced orientation of nematic SG-LCPs, we have compared magnetically aligned and flow-aligned nematic SG-LCPs. Magnetic forces act primarily on the mesogens, and the backbone conformation changes to accommodate the torques on its pendant mesogens. In contrast, oscillatory shear can couple to the relaxation modes of both the director field and backbone. We have discovered that while the flow-aligned material exhibits distinct low-frequency relaxation dynamics, the relaxation of magnetically- aligned monodomains is indistinguishable from that of polydomain nematic melts. This suggests that flow alignment and magnetic alignment produce qualitatively distinct changes in the fluid miscostructure. We have further compared the processes of shear- and magnetic-alignment by monitoring the evolution of director orientation in nematic SG-LCP melts, in-situ, through visible transmittance (related to the liquid-crystalline domain size) and visible birefringence (related to the molecular orientation).", "doi": "10.7907/bdjk-n270", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:4987", "collection": "thesis", "collection_id": "4987", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12132007-083330", "primary_object_url": { "basename": "Dabdub_d_1996.pdf", "content": "final", "filesize": 22329563, "license": "other", "mime_type": "application/pdf", "url": "/4987/1/Dabdub_d_1996.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Mathematical modeling of air pollution dynamics by parallel computation", "author": [ { "family_name": "Dabdub", "given_name": "Donald", "clpid": "Dabdub-D" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Van de Velde", "given_name": "Eric", "clpid": "van-de-Velde-E" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Keller", "given_name": "Herbert Bishop", "clpid": "Keller-H-B" }, { "family_name": "Chandy", "given_name": "K. Mani", "clpid": "Chandy-K-M" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The use of massively parallel computers provides an avenue to overcome the computational requirements in the study of atmospheric chemical dynamics. General considerations on parallel implementation of air quality models are outlined including domain decomposition strategies, algorithm evaluation and design, portability, modularity, and buffering techniques used in I/O operations. Results are given for the implementation of the CIT urban air pollution model on distributed memory multiple instruction / multiple data (MIMD) machines ranging from a cluster of workstations to a 512 node Intel Paragon.\r\n\r\nThe central challenge in developing a parallel air pollution model is the implementation of the chemistry and transport operators used in the solution of the atmospheric reaction-diffusion equation. The chemistry operator is generally the most computationally intensive step in atmospheric air quality models. A new method based on Richardson extrapolation to solve the chemical kinetics is presented. The transport operator is the most challenging to solve numerically. Because of its hyperbolic nature non-physical oscillations and/or negative concentrations appear near steep gradient regions of the solution. Six algorithms for solving the advection equation are compared to determine their suitability for use in parallel photochemical air quality models. Four algorithms for filtering the numerical noise produced when solving the advection equation are also compared.\r\n\r\nA speed-up factor of 94.9 has been measured when the I/O, transport, and chemistry portions of the model are performed in parallel. This work provides the computational infrastructure required to incorporate new physico-chemical phenomena in the next generation of urban- or regional-scale air quality models.\r\n\r\nFinally, the SARMAP model is used to model the San Joaquin Valley of California. SARMAP is the updated version of RADM. It can be considered a state-of-the- art regional air pollution model. Like the CIT model, SARMAP incorporates the following atmospheric phenomena: gas-phase chemistry, advection and diffusion. In addition, SARMAP incorporates aqueous-phase chemistry and transport through cumulus clouds. Sensitivity studies performed show a significant dependence of ozone model predictions on boundary conditions.", "doi": "10.7907/k1ap-np35", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:4972", "collection": "thesis", "collection_id": "4972", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12122007-111327", "primary_object_url": { "basename": "Dartt_cb_1996.pdf", "content": "final", "filesize": 6583349, "license": "other", "mime_type": "application/pdf", "url": "/4972/1/Dartt_cb_1996.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Synthesis and characterization of titanium-containing molecular sieves", "author": [ { "family_name": "Dartt", "given_name": "Christopher Bruce", "clpid": "Dartt-Christopher-Bruce" } ], "thesis_advisor": [ { "family_name": "Davis", "given_name": "Mark E.", "clpid": "Davis-M-E" } ], "thesis_committee": [ { "family_name": "Davis", "given_name": "Mark E.", "clpid": "Davis-M-E" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Zones", "given_name": "Stacey I.", "clpid": "Zones-S-I" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The use of zeolites and molecular sieves as catalysts for important organic reactions is reviewed. One emerging area of particular interest is the use of titanium-containing molecular sieves as partial oxidation catalysts and is chosen for further study.\r\n\r\nIn order to elucidate the relationships between the physicochemical properties of titanium-containing molecular sieves and their ability to act as partial oxidation catalysts, titanium-containing pure-silica ZSM-5 (TS-1) materials are synthesized using different methods. The activities of the titanium-containing catalysts for the oxidation of alkanes, alkenes, and phenol at temperatures below 100 [degrees]C using aqueous hydrogen peroxide H2O2 as the oxidant are reported. The relationships between the physicochemical and catalytic properties of these titanium silicates are discussed. The effects of added aluminum and sodium on the catalytic activity of TS-1 are described. The addition of sodium during the synthesis of TS-1 is detrimental to the catalytic activity while sodium incorporation into pre-formed TS-1 is not. The framework substitution of aluminum for silicon appears to decrease the amount of framework titanium.\r\n\r\nThe relationships between catalytic performance and physicochemical properties that are controlled through synthetic methods are further investigated using a series of titanium-containing molecular sieves. Titanium-containing pure-silica ZSM-5 (TS- 1), pure-silica ZSM-48 (Ti-ZSM-48) and zeolite beta (Ti-Al-beta) are synthesized and characterized by X-ray powder diffraction (XRD), elemental analysis, physical adsorption of N2, Fourier transform infrared (FT-IR), FT-Raman, and diffuse reflectance ultraviolet (DR-UV) spectroscopies. TS-1 is synthesized by five different methods. All materials are evaluated for their ability to oxidize 1-hexene and n-octane using aqueous H2O2 as the oxidant. The relationships between the physicochemical and catalytic properties of these titanium-containing zeolites are discussed. TS-1 samples synthesized at high pH are catalytically active and framework titanium is shown to be necessary for olefin epoxidation and alkane hydroxylation to occur. The existence of anatase in active TS-1 samples results in decreased hydrogen peroxide efficiencies in the epoxidation reaction. TS-1 produced at pH=7.4 and Ti-ZSM-48 each contain anatase and are not active. Ti-beta is found to contain framework titanium and be free of anatase. However, at the conditions used in this study these samples are not able to activate 1-hexene or n-octane.\r\n\r\nIn attempts to prepare large pore titanium-containing molecular sieves, postsynthetic incorporation of titanium in the borosilicate SSZ-33 and the direct synthesis of an aluminum-free titanium-containing zeolite Beta (Ti-Beta) are reported. These materials are characterized by XRD, FT-IR, FT-Raman, and DR-UV spectroscopies. The molecular sieves are shown to catalyze the epoxidation of various olefins using aqueous hydrogen peroxide as the oxidant. The physicochemical properties as found by the characterization methods are correlated to the catalytic data and the results compared to a high quality sample of TS-1. The modified SSZ-33 samples contain titanium primarily in the form of isolated tetrahedrally coordinated Ti atoms, although some extra-framework Ti is observed by Raman and DR-UV spectroscopies. Ti-Beta samples show no evidence of extra-framework titanium. For the epoxidation of cis-cyclooctene, the Ti-Beta catalysts give quantitative conversion to epoxide, and both the Ti-Beta and Ti-SSZ-33 catalysts are able to epoxidize substrates too large to be oxidized by TS-1.\r\n", "doi": "10.7907/0pnv-rt94", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:5069", "collection": "thesis", "collection_id": "5069", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12192007-112031", "type": "thesis", "title": "Model Predictive Control (MPC) for Constrained Nonlinear Systems", "author": [ { "family_name": "De Oliveira", "given_name": "Simone Loureiro", "clpid": "DeOliveira-Simone-Loureiro" } ], "thesis_advisor": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" } ], "thesis_committee": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Doyle", "given_name": "John Comstock", "clpid": "Doyle-J-C" }, { "family_name": "Murray", "given_name": "Richard M.", "clpid": "Murray-R-M" }, { "family_name": "Wiggins", "given_name": "Stephen R.", "clpid": "Wiggins-S-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis addresses the development of stabilizing model predictive control algorithms for nonlinear systems subject to input and state constraints and in the presence of parametric and/or structural uncertainty, disturbances and measurement noise.
\r\n\r\nOur basic model predictive control (MPC) scheme consists of a finite horizon MPC technique with the introduction of an additional state constraint which we have denoted contractive constraint. This is a Lyapunov-based approach in which a Lyapunov function chosen a priori is decreased, not continuously, but discretely; it is allowed to increase at other times (between prediction horizons). We will show \r\nin this work that the implementation of this additional constraint into the on-line optimization makes it possible to prove rather strong stability properties of the closed-loop system. In the nominal case and in the absence of disturbances, it is possible to show that the presence of the contractive constraint renders the closed-loop system exponentially stable. We will also examine how the stability properties weaken as structural and/or parametric model/plant mismatch, disturbances and measurement noise are considered.
\r\n\r\nAnother important aspect considered in this work is the computational efficiency and implement ability of the algorithms proposed. The MPC schemes previously proposed in the literature which are able to guarantee stability of the closed-loop system involve the solution of a nonlinear programming problem at each time step in order to find the optimal (or, at least, feasible) control sequence. Nonlinear programming is the general case in which both the objective and constraint functions may be non-linear, and is the most difficult of the smooth optimization problems.
\r\n\r\nDue to the difficulties inherent to solving nonlinear programming problems and since MPC requires the optimal (or feasible) solution to be computed on-line, it is important that an alternative implementation be found which guarantees that the problem can be solved in a finite number of steps. It is well-known that both linear and quadratic programming (QP) problems satisfy this requirement.
\r\n\r\nIf a standard quadratic objective function is used and the input/state constraints are linear in the decision variables, then the contractive constraint (which is originally a quadratic constraint) can be implemented in such a way that the optimization problem to be solved in the prediction step of the MPC algorithm is reduced to a QP. Having linear input/state constraints means that a linear approximation of the original nonlinear system has to be used in the prediction as well as in the computation of the contractive constraint. Thus, in order to make the algorithm more easily implementable we introduce the difficulty of having to handle the mismatch between the real nonlinear system and its linear approximation which is used for prediction. In other words, we now have a robust MPC control problem at hand. In this case, it is the contractive constraint which comes to the rescue and allows the MPC controller to stabilize the closed-loop system spite of the linear/nonlinear mismatch, for certain choices of the contractive parameter (the parameter which defines how much \"shrinkage\" of the states is required during one prediction horizon).
\r\n\r\nIn summary, this thesis is an application of contractive principles to model predictive control and it is dedicated to robust stability analysis, design and implementation of state and output feedback \"contractive\" MPC schemes.
\r\n", "doi": "10.7907/MXYW-TB71", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:2631", "collection": "thesis", "collection_id": "2631", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06172005-085103", "primary_object_url": { "basename": "Lobo_rf_1995.pdf", "content": "final", "filesize": 7848477, "license": "other", "mime_type": "application/pdf", "url": "/2631/1/Lobo_rf_1995.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The Synthesis and Characterization of Novel High-Silica Zeolites", "author": [ { "family_name": "Lobo", "given_name": "Raul Francisco", "clpid": "Lobo-Raul-Francisco" } ], "thesis_advisor": [ { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" } ], "thesis_committee": [ { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" }, { "family_name": "Myers", "given_name": "Andrew G.", "clpid": "Myers-A-G" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The synthesis and characterization of high-silica molecular sieves is reviewed using molecular recognition phenomena and structure-direction as the unifying themes. A comparative analysis between the synthesis conditions employed and the zeolite structures formed is carried out starting with the synthesis of clathradils or 0-dimensional zeolites, and extending to one-dimensional, multi-dimensional zeosils. The review finishes with the analysis of the combined effects of heteroatoms (Al, B and Zn) and organic structure-directing agents in zeolite product selectivity and thermodynamic stability.\r\n\r\nStructure-direction phenomena is further investigated using the synthesis and characterization of the pure-silica zeolite SSZ-24, prepared using the chiral molecule N(16)methylsparteinium hydroxide as the structure-directing agent. The material is characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), solid-state NMR spectroscopy, fourier transform IR spectroscopy (FTIR) and physical adsorption experiments. The B-substituted SSZ-24 prepared here is the first example where the isomorphous substitution of B for Si in the SSZ-24 framework is accomplished during synthesis using sodium borate as the source of B. The B can be easily substituted by Al. The Al-substituted SSZ-24 is an active catalyst for the cracking of alkanes and may be potentially useful in refinery and chemical processes.\r\n\r\nThe structure solutions and a detailed structural characterizations of the disordered zeolites SSZ-26 and SSZ-33 is presented. These two materials are the first synthetic zeolites with intersecting open 10- and 12-ring pore systems. SSZ-26 and SSZ-33 are expected to show a combination of reaction activity, selectivity and stability unique among known zeolites. SSZ-26 and SSZ-33 may be very useful for catalytic applications in the petrochemical and refining industries. The feasibility of synthesizing a zeolite whose pore structure has been designed a priori is demonstrated with the zeolite SSZ-26 and its structure-directing agent.\r\n\r\nThe synthesis of a new borosilicate, CIT-1, is described. The proposed structure of CIT-1 is confirmed by a Rietveld refinement of the synchrotron XRD pattern. CIT-1 is demonstrated to be an ordered polymorph of the SSZ-33 zeolites. The catalytic properties of CIT-1 are compared to the catalytic properties of known high-silica zeolites (ZSM-5 and zeolite beta) and CIT-1 is shown to be a very active catalyst for the cracking of n-butane. The synthesis of CIT-1 supports the idea that the chiral polymorph A of zeolite beta can be synthesized using the appropriate structure-directing agent.\r\n\r\nA combination of molecular modeling and 1H MAS NMR spectroscopy are used to characterize the interactions of structure-directing agents with the zeolite framework. The results indicate that to simulate correctly the energetic interaction and motional properties of structure-directing agents in zeolites, short-range and long-range forces, water molecules, silanol groups and defects need to be considered simultaneously.\r\n", "doi": "10.7907/01DX-QC48", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:4224", "collection": "thesis", "collection_id": "4224", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10232007-141113", "primary_object_url": { "basename": "Zheng_zq_1995.pdf", "content": "final", "filesize": 17648921, "license": "other", "mime_type": "application/pdf", "url": "/4224/1/Zheng_zq_1995.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Robust control of systems subject to constraints", "author": [ { "family_name": "Zheng", "given_name": "Zhi Qiang (Alex)", "clpid": "Zheng-Z-Q-A" } ], "thesis_advisor": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" } ], "thesis_committee": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" }, { "family_name": "Sideris", "given_name": "Athanasios", "clpid": "Sideris-A" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Doyle", "given_name": "John Comstock", "clpid": "Doyle-J-C" }, { "family_name": "Brady", "given_name": "John F.", "clpid": "Brady-J-F" }, { "family_name": "Murray", "given_name": "Richard M.", "clpid": "Murray-R-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Most practical control problems are dominated by constraints. Although a rich theory has been developed for the robust control of linear systems, very little is known about the robust control of linear systems with constraints. Over the years various model-based algorithms (given a generic term Model Predictive Control) have been used in industry to control complex multivariable systems with operating constraints. The design and tuning of these controllers is difficult for two reasons:\n\n1. Process models are always inaccurate which implies that the controllers must be robust.\n\n2. Even in the simplest case where process models are linear, the overall systems are nonlinear because of the constraints.\n\nDespite Model Predictive Control's considerable practical importance, there is very little theory to guide the design and tuning of these controllers for stability and robustness. It is the goal of this thesis to develop such a theory. Specifically, a general framework based on Model Predictive Control is developed to synthesize controllers for discrete-time linear systems subject to constraints with robust stability and performance guarantees.", "doi": "10.7907/q8vt-s855", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:3503", "collection": "thesis", "collection_id": "3503", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09122007-075846", "primary_object_url": { "basename": "Bekiaris_n_1995.pdf", "content": "final", "filesize": 10931760, "license": "other", "mime_type": "application/pdf", "url": "/3503/1/Bekiaris_n_1995.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Multiple steady states in distillation", "author": [ { "family_name": "Bekiaris", "given_name": "Nikolaos", "clpid": "Bekiaris-N" } ], "thesis_advisor": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" } ], "thesis_committee": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Brady", "given_name": "John F.", "clpid": "Brady-J-F" }, { "family_name": "Wiggins", "given_name": "Stephen R.", "clpid": "Wiggins-S-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nWe study multiple steady states in distillation. We first analyze the simplest case of ternary homogeneous azeotropic mixtures. We show that in the case of infinite reflux and an infinite number of trays ([...] case) one can construct bifurcation diagrams on physical grounds with the distillate flow as the bifurcation parameter. Multiple steady states exist when the distillate flow varies non-monotonically along the continuation path of the bifurcation diagram. We derive a necessary and sufficient condition for the existence of these multiple steady states based on the geometry of the distillation region boundaries. We also locate in the composition triangle the feed compositions that lead to these multiple steady states.\r\n\r\nWe further note that most of these results are independent of the thermodynamic model used. We show that the prediction of the existence of multiple steady states in the [...] case has relevant implications for columns operating at finite reflux and with a finite number of trays. Using numerically constructed bifurcation diagrams for specific examples, we show that these multiplicities tend to vanish for small columns and/or for low reflux flows. Nevertheless, the [...] multiplicities do exist for columns at realistic operating conditions. We comment on the effect of multiplicities on column design and operation for some specific examples. \r\n\r\nWe then extend the homogeneous mixture results to ternary heterogeneous mixtures. We study the [...] case in much more depth and detail by demonstrating how the [...] analysis can be applied to different column designs. More specifically, we show how the feasible distillate and bottom product paths can be located for tray or packed columns, with or without decanter and with different types of condenser and reboiler. We derive the fully detailed, necessary and sufficient condition for the existence of these multiple steady states based on the geometry of the product paths. Simulation results for finite columns show that the predictions carry over to the finite case.\r\n\r\nThe complete list of the [...] case predictions is presented. The implications of these multiplicities for column design, synthesis and simulation are demonstrated. More specifically, we show how the [...] predictions can be useful for the selection of the entrainer, the equipment and the separation scheme. We show that, in some cases, the column operation at an unstable steady state may have some advantages. The important issue of the effect of the thermodynamic phase equilibrium on the existence of multiplicities is discussed. Using the [...] analysis, we identify entire mixture classes for which multiplicities are inherent and robust. Mixtures with ambiguous VLE data are studied; we show that in some cases a slight VLE difference between models and/or experimental data may affect the existence of multiplicities while other, major VLE discrepancies do not. Finally, we identify the key issues and the pitfalls one should be cautious about when designing or computing the composition profile of an azeotropic distillation column with a commercial simulator.\r\n", "doi": "10.7907/S6MC-5V73", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:2631", "collection": "thesis", "collection_id": "2631", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06172005-085103", "primary_object_url": { "basename": "Lobo_rf_1995.pdf", "content": "final", "filesize": 7848477, "license": "other", "mime_type": "application/pdf", "url": "/2631/1/Lobo_rf_1995.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The Synthesis and Characterization of Novel High-Silica Zeolites", "author": [ { "family_name": "Lobo", "given_name": "Raul Francisco", "clpid": "Lobo-Raul-Francisco" } ], "thesis_advisor": [ { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" } ], "thesis_committee": [ { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" }, { "family_name": "Myers", "given_name": "Andrew G.", "clpid": "Myers-A-G" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The synthesis and characterization of high-silica molecular sieves is reviewed using molecular recognition phenomena and structure-direction as the unifying themes. A comparative analysis between the synthesis conditions employed and the zeolite structures formed is carried out starting with the synthesis of clathradils or 0-dimensional zeolites, and extending to one-dimensional, multi-dimensional zeosils. The review finishes with the analysis of the combined effects of heteroatoms (Al, B and Zn) and organic structure-directing agents in zeolite product selectivity and thermodynamic stability.\r\n\r\nStructure-direction phenomena is further investigated using the synthesis and characterization of the pure-silica zeolite SSZ-24, prepared using the chiral molecule N(16)methylsparteinium hydroxide as the structure-directing agent. The material is characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), solid-state NMR spectroscopy, fourier transform IR spectroscopy (FTIR) and physical adsorption experiments. The B-substituted SSZ-24 prepared here is the first example where the isomorphous substitution of B for Si in the SSZ-24 framework is accomplished during synthesis using sodium borate as the source of B. The B can be easily substituted by Al. The Al-substituted SSZ-24 is an active catalyst for the cracking of alkanes and may be potentially useful in refinery and chemical processes.\r\n\r\nThe structure solutions and a detailed structural characterizations of the disordered zeolites SSZ-26 and SSZ-33 is presented. These two materials are the first synthetic zeolites with intersecting open 10- and 12-ring pore systems. SSZ-26 and SSZ-33 are expected to show a combination of reaction activity, selectivity and stability unique among known zeolites. SSZ-26 and SSZ-33 may be very useful for catalytic applications in the petrochemical and refining industries. The feasibility of synthesizing a zeolite whose pore structure has been designed a priori is demonstrated with the zeolite SSZ-26 and its structure-directing agent.\r\n\r\nThe synthesis of a new borosilicate, CIT-1, is described. The proposed structure of CIT-1 is confirmed by a Rietveld refinement of the synchrotron XRD pattern. CIT-1 is demonstrated to be an ordered polymorph of the SSZ-33 zeolites. The catalytic properties of CIT-1 are compared to the catalytic properties of known high-silica zeolites (ZSM-5 and zeolite beta) and CIT-1 is shown to be a very active catalyst for the cracking of n-butane. The synthesis of CIT-1 supports the idea that the chiral polymorph A of zeolite beta can be synthesized using the appropriate structure-directing agent.\r\n\r\nA combination of molecular modeling and 1H MAS NMR spectroscopy are used to characterize the interactions of structure-directing agents with the zeolite framework. The results indicate that to simulate correctly the energetic interaction and motional properties of structure-directing agents in zeolites, short-range and long-range forces, water molecules, silanol groups and defects need to be considered simultaneously.\r\n", "doi": "10.7907/01DX-QC48", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:3199", "collection": "thesis", "collection_id": "3199", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08222007-105213", "primary_object_url": { "basename": "Braatz_rd_1993.pdf", "content": "final", "filesize": 7747644, "license": "other", "mime_type": "application/pdf", "url": "/3199/1/Braatz_rd_1993.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Robust Loopshaping for Process Control", "author": [ { "family_name": "Braatz", "given_name": "Richard Dean", "orcid": "0000-0003-4304-3484", "clpid": "Braatz-Richard-Dean" } ], "thesis_advisor": [ { "family_name": "Morari", "given_name": "Manfred", "orcid": "0000-0002-7696-5058", "clpid": "Morari-M" } ], "thesis_committee": [ { "family_name": "Morari", "given_name": "Manfred", "orcid": "0000-0002-7696-5058", "clpid": "Morari-M" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Doyle", "given_name": "John Comstock", "orcid": "0000-0002-1828-2486", "clpid": "Doyle-J-C" }, { "family_name": "Murray", "given_name": "Richard M.", "orcid": "0000-0002-5785-7481", "clpid": "Murray-R-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Strong trends in chemical engineering and plant operation have made the control of processes increasingly difficult and have driven the process industry's demand for improved control techniques. Improved control leads to savings in resources, smaller downtimes, improved safety, and reduced pollution.
\r\n\r\nThough the need for improved process control is clear, advanced control methodologies have had only limited acceptance and application in industrial practice. The reason for this gap between control theory and practice is that existing control methodologies do not adequately address all of the following control system requirements and problems associated with control design:\r\n
A framework is presented to address these control requirements/problems in a general, unified manner. The approach will be demonstrated on adhesive coating processes and distillation columns.
", "doi": "10.7907/vqmv-kw76", "publication_date": "1993", "thesis_type": "phd", "thesis_year": "1993" }, { "id": "thesis:3029", "collection": "thesis", "collection_id": "3029", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08062007-150332", "primary_object_url": { "basename": "Kim_yp_1992.pdf", "content": "final", "filesize": 8931579, "license": "other", "mime_type": "application/pdf", "url": "/3029/1/Kim_yp_1992.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Simulation of multicomponent aerosol dynamics", "author": [ { "family_name": "Kim", "given_name": "Yong Pyo", "clpid": "Kim-Y-P" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Okuyama", "given_name": "Kikuo", "clpid": "Okuyama-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Chemical composition and, therefore, several physical properties, such as refractive index or density, of an aerosol system may be distributed in one particle size. The effect of these particles of the same size but different properties, so-called mixed particles, on aerosol dynamics can be important. Several aspects of the number-property distribution; effect on aerosol dynamics and importance, definition, state of the art of the measurement technique, available data, and numerical schemes are discussed and further research directions are discussed.\r\n\r\nThe moving sectional method is extended to simulate multicomponent aerosol dynamics resulting from condensation/evaporation processes. This method uses a Lagrangian approach in which section boundaries and component masses in a section vary according to the characteristics of condensation/evaporation rates while conserving number concentration in a section throughout the simulation. Simulation of model problems for which new analytical solutions have been obtained shows excellent agreement with the analytical solutions. Limitations and applicability of the sectional method are discussed.\r\n\r\nA technique for direct numerical solution of the multicomponent aerosol general dynamic equation is developed and tested. The method obtains the aerosol size-composition distribution without the need to make any a priori assumptions about the nature of the distribution. Numerical solutions are compared with analytical solutions for model problems of pure condensation/evaporation, pure coagulation, and simultaneous condensation and coagulation. The advantages, applicability, and the limitations of the approach are discussed.\r\n\r\nAn analysis of the tandem differential mobility analyzer (TDMA) is proposed in which the conditioner between the two DMAs is simulated by the multicomponent aerosol general dynamic equation (GDE). The use of the TDMA to separate an externally mixed aerosol is illustrated by simulating the data of Liu et al. (1978).\r\n\r\nNumerical issues in grid-based photochemical air quality models are reviewed. Numerical schemes for advection and chemical kinetics in gas-phase and for dynamics in aerosol-phase are compared.\r\n\r\nFinally, a numerical code is developed based on direct numerical solution of the multicomponent aerosol general dynamic equation.", "doi": "10.7907/SE1X-K706", "publication_date": "1992", "thesis_type": "phd", "thesis_year": "1992" }, { "id": "thesis:3036", "collection": "thesis", "collection_id": "3036", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08072007-075230", "primary_object_url": { "basename": "Li_x_1992.pdf", "content": "final", "filesize": 6250035, "license": "other", "mime_type": "application/pdf", "url": "/3036/1/Li_x_1992.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Experimental Studies of Char Oxidation and Fume Formation from Pyrite", "author": [ { "family_name": "Li", "given_name": "Xiaoming", "clpid": "Li-Xiaoming" } ], "thesis_advisor": [ { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "clpid": "Hoffmann-M-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Pulverized coal combustion is nowadays the most commonly used technology for power generation from coal. The detailed understanding of the coal combustion process is of fundamental importance to the design of more economic and efficient combustion devices and to the control of gaseous and particulate pollutant emission. This thesis presents an experimental study of (a) thermally induced changes of char structure and their effect on its combustion reactivity and (b) the mechanism of ash formation under conditions pertinent to pulverized coal combustion.
\r\n\r\nPyrolyzed or partially oxidized coal char was generated in a drop-tube furnace from a Pittsburgh seam hvA bituminous coal (PSOC 1451). The char was characterized by elemental analysis and N2 adsorption for specific surface area and pore volume distribution to better understand the influence of oxygen and residence time on the char structure. The reactivities of chars produced under different oxygen contents and residence times were examined by oxidation in a thermogravimetric analyzer. The conversion of the combustible material at high temperature was measured using ash as a tracer.
\r\n\r\nThe pyrolysis and combustion of pyrite particles were studied with an electrodynamic balance and a drop-tube reactor. Two types of pyrite were examined, a natural pyrite (85% purity) and a synthetic pyrite (99.9% purity). Fume particles formed from individual pyrite particles were observed directly in electrodynamic balance experiments. The drop tube reactor experiments allow measurements of the fume particle concentration and size distribution. The nature of the fume was characterized using a Transmission Electron Microscope equipped with energy dispersive X-ray analysis. Physical mechanisms that might lead to the release of iron rich fragments were investigated.
", "doi": "10.7907/3kmh-j058", "publication_date": "1992", "thesis_type": "phd", "thesis_year": "1992" }, { "id": "thesis:2861", "collection": "thesis", "collection_id": "2861", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07122007-131336", "primary_object_url": { "basename": "Rogak_sn_1991.pdf", "content": "final", "filesize": 45204556, "license": "other", "mime_type": "application/pdf", "url": "/2861/1/Rogak_sn_1991.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Aerosol dynamics of agglomerates", "author": [ { "family_name": "Rogak", "given_name": "Steven Nicholas", "clpid": "Rogak-S-N" } ], "thesis_advisor": [ { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" } ], "thesis_committee": [ { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Fultz", "given_name": "Brent T.", "clpid": "Fultz-B-T" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" }, { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The mobility, charging, coagulation and mass-transfer properties of aerosol agglomerates were related to the particle and the background gas mean free path \u03bb. The mobility-equivalent diameter dm of a self-similar cluster of spheres in the continuum regime \u03bb<<dm was calculated to be proportional to the radius of gyration Rg of the cluster for fractal dimension Df>1.3. Slender-body behavior is approached for Df<1.3. In the free-molecule regime dm<<\u03bb, dm is nearly equal to the projected-area diameter dA. In the transition regime dm~\u03bb, dm depends on both dA and Rg. In general, there is a divergence of dA and Rg as the agglomerate size increases, but it is very gradual for typical aerosol agglomerates, for which dm~dA in the transition regime.
\r\n\r\nThe mass transfer of nanometer-sized 211Pb clusters to TiO2 agglomerates was investigated with an Epiphaniometer. The measured mass-transfer-equivalent diameters of the agglomerates were within 10% of dm. The lead cluster mean free path was nearly the same as \u03bb. For an analogous phenomenon, the bipolar diffusion charging of agglomerates, it was found that the charging-equivalent diameter of the agglomerates was ~10% larger than dm.
\r\n\r\nThese measurements were incorporated into a model describing the coagulation of agglomerates in the transition regime. Particles smaller than the primary particle diameter d1 were assumed to coalesce rapidly, while large particles were assumed to be solid with a fractal structure. In the transition regime, the agglomerate mean free paths are much smaller than dm even when dm<\t\u03bb. This leads to distinctly different dynamic behavior than predicted by previous models developed for the continuum or free-molecule regimes. The enhancement of coagulation over that of dense spheres is large for aerosols with median diameters slightly greater than d1 but smaller for aerosols consisting of much larger particles.
\r\n", "doi": "10.7907/PVDQ-PN74", "publication_date": "1991", "thesis_type": "phd", "thesis_year": "1991" }, { "id": "thesis:2853", "collection": "thesis", "collection_id": "2853", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07112007-084012", "primary_object_url": { "basename": "Doyle_fj_1991.pdf", "content": "final", "filesize": 31620386, "license": "other", "mime_type": "application/pdf", "url": "/2853/1/Doyle_fj_1991.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Robustness properties of nonlinear process control and implications for the design and control of a packed bed reactor", "author": [ { "family_name": "Doyle", "given_name": "Francis Joseph, III", "clpid": "Doyle-Francis-Joseph-III" } ], "thesis_advisor": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" } ], "thesis_committee": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" }, { "family_name": "Sideris", "given_name": "Athanasios", "clpid": "Sideris-A" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Burdick", "given_name": "Joel Wakeman", "clpid": "Burdick-J-W" }, { "family_name": "Doyle", "given_name": "John Comstock", "clpid": "Doyle-J-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The robustness properties of nonlinear process control are studied with particular emphasis on applications to the design and control of a catalytic fixed bed reactor.\r\n\r\nAnalysis tools are developed to determine the stability and performance of nonlinear dynamical systems. The results are based upon new extensions of the structured singular value to a class of nonlinear and time-varying systems. Conic sectors are utilized in approximating the static nonlinearities present and an algorithm is developed for optimal conic sector calculation.\r\n\r\nThe synthesis tools of differential geometry are studied with respect to their closed loop robust performance properties. New results in approximate linearization are contrasted with exact linearization and linear control. It is shown that the approximate linearization technique is superior with respect to disturbance handling, optimization of the resultant transformations, and range of applicability.\r\n\r\nNonlinear approaches for the control of a packed bed reactor are investigated. In particular, the differential geometric technique of input-output linearization is found to yield superior closed-loop performance over regions of open-loop parametric sensitivity. The synthesis of a linearizing controller for this nonlinear distributed parameter system involves a two-tier approach. In the first stage, a low order nonlinear model is developed for the reactor. This is accomplished by treating the active transport mechanisms in the bed as a nonlinear wave which propagates through the bed in response to changes in the operating conditions. The resultant lumped parameter model facilitates the design of the input-output linearizing controller in the second tier of this scheme. The implementational hurdles for this approach are identified and comparisons are drawn on the strengths of this approach over robust linear control for the reactor.\r\n\r\nPractical guidelines are developed for the design of packed bed reactors. The criteria result from requirements on the radial temperature profile, temperature sensitivity, and acceptable pressure drop. The stabilizing effects of feedback control for industrial fixed bed catalytic reactors are addressed. Simulations support the result that violation of the proposed criteria leads to unacceptable closed-loop performance.\r\n\r\nIn conclusion, general guidelines are constructed from a series of case studies on the proper selection of linear versus \"linearizing\" control. The relative performance is measured by the region of attraction, magnitude of manipulated variable action, and sensitivity to input disturbances. The work represents the first objective evaluation of the strengths and limitations of input-output linearization compared to linear control.", "doi": "10.7907/3n52-hk32", "publication_date": "1991", "thesis_type": "phd", "thesis_year": "1991" }, { "id": "thesis:1649", "collection": "thesis", "collection_id": "1649", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05062004-154106", "primary_object_url": { "basename": "Pandis_sn_1991.pdf", "content": "final", "filesize": 12221876, "license": "other", "mime_type": "application/pdf", "url": "/1649/1/Pandis_sn_1991.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Studies of physicochemical processes in atmospheric particles and acid deposition", "author": [ { "family_name": "Pandis", "given_name": "Spyros N.", "orcid": "0000-0001-8085-9795", "clpid": "Pandis-S-N" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Cass", "given_name": "Glen Rowan", "clpid": "Cass-G-R" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAtmospheric particles, or particulate matter, can be solid or liquid with diameters varying from around 0.002[micrometers] to roughly 100[micrometers]. Atmospheric aerosol sources can be classified as primary or secondary, with the primary aerosol being directly emitted from the corresponding sources and the secondary particles being formed in the atmosphere, for example, from gas-phase chemical reactions that produce condensable vapors. At the same time aerosol particles are ultimately connected with the formation of water droplets and equivalently with the formation of clouds and fogs in the atmosphere.\r\n\r\nThe first part of this thesis concerns the mathematical modeling of wet and dry acid deposition and of the relevant physicochemical processes. Acid deposition consists of the delivery of acidic substances, principally sulfuric and nitric acid, from the atmosphere to the earth's surface. Upon emission to the atmosphere, SO2 and NOx, are photochemically oxidized, yielding sulfuric and nitric acid vapors. Sulfuric acid is rapidly incorporated into aerosol particles, while nitric acid may be scavenged by particles or droplets or remain in the gas phase. Even in the absence of an aqueous phase (no clouds or fog), the acidic gases and dry particles can be transported to and deposited at ground level; this process is called dry deposition. When an aqueous phase is present (inside a cloud or a fog), gas-phase species like SO2, HNO3, NH3 and aerosol particles are scavenged by water droplets resulting in a solution that can be significantly acidic. Additional cloudwater or fogwater acidity beyond that attained purely from scavenging of gases and particles results from aqueous-phase chemistry, most notably oxidation of dissolved SO2 to sulfuric acid. These acidic droplets can reach the earth's surface either as precipitation or as impacted cloud and fogwater, in the processes termed wet deposition. If they are not rained or deposited out the aqueous droplets can evaporate leaving as residue new aerosol particles that may themselves undergo dry deposition to the earth's surface. The effects of acid deposition include soil and lake acidification, forest decline and deterioration of cultural monuments.\r\n\r\nMathematical models are a major tool in our effort to understand and ultimately control acid deposition. The development of such a mathematical model represents a major challenge as it requires the ability to describe the entire range of atmospheric physicochemical phenomena.\r\n\r\nAs a first step in the modeling, a comprehensive chemical mechanism for aqueous-phase atmospheric chemistry was developed and its detailed sensitivity analysis was performed. The main aqueous-phase reaction pathways for the system are the oxidation of S(IV) to S(VI) by H2O2, OH, HO2, O2 (catalysed by Fe3+ and Mn2+), O3, and [...]. The dominant pathway for HNO3(aq) acidity is scavenging of nitric acid from the gas phase. HCOOH is produced because of the reaction of HCHO(aq) with OH(aq). The gas-phase concentrations of SO2, H2O2, HO2, OH, O3, HCHO, NH3, HNO3, and HCl are of primary importance. Increase of the liquid water content of the cloud results in a decrease of the sulfate concentration, but an increase of the total sulfate amount in the aqueous-phase. On the basis of the sensitivity analysis, a condensed mechanism was derived.\r\n\r\nThe next step was the development of a model that actually predicts the amount of liquid water in the atmosphere solving the energy balance. This Lagrangian model combines for the first time a detailed description of gas and aqueous-phase atmospheric chemistry with a treatment of the dynamics of radiation fog, that is the fog that is created due to the radiative cooling of the earth's surface to the space during the night. The model was evaluated against a well documented radiation fog episode in Bakersfield in the San Joaquin Valley of California over the period January 4-5, 1985. This application showed that the model predictions for temperature profile, fog development, liquid water content, gas-phase concentrations of SO2, HNO3, and NH3, pH, aqueous-phase concentrations of [...], [...], and [...], and finally deposition rates of the above ions match well the observed values. The fog was found to lead to a drastic increase of deposition rates over those in its absence for the major ionic species, with most notable being the increase of sulfate deposition. Several important differences were found to exist between the characteristics of a radiation fog and a representative cloud environment. Radiation fogs typically develop under stable conditions (very low wind speed) resulting in weak mixing and significant vertical gaseous species concentration gradients. Because of the proximity of the fog to ground-level sources of pollutants like SO2 and NOx, the corresponding gas-phase concentrations can reach much higher levels that in a cloud. In such a case, pathways for aqueous-phase sulfate production that are of secondary importance in a cloud environment may become significant in a fog.\r\n\r\nThe next level of treatment beyond assuming that all the water droplets have the size and chemical composition is to explicitly model the size-composition distribution of droplets as a result of nucleation on aerosol particles. A third model was developed to study the distribution of acidity and solute concentration among the various droplet sizes in a fog or a cloud. The major finding of this study was that significant solute concentration differences can occur in aqueous droplets inside a fog or a cloud. For the fog simulated, during the period of dense fog, the solute concentration in droplets larger than 10[micrometers] diameter increased with size, in such a way that droplets of diameter 20[micrometers] attain a solute concentration that is a factor of 3.6 larger than that in the 10[micrometer] droplets. Chemical processes tend to decrease the total solute mass concentration differences among the various droplet sizes. Low cooling rates of the system also tend to decrease these concentration differences while high cooling rates have exactly the opposite effect. The mass/size distribution of the condensation nuclei influences quantitatively, but not qualitatively, the above concentration differences.\r\n\r\nThe effects of equilibration processes on wet and dry deposition were then investigated and furthermore the accuracy of the currently used modelling approaches of these phenomena was examined. Atmospheric equilibration processes between two phases with different deposition velocities have the potential to affect significantly the amount of total material deposited on the ground. The magnitude of the effects of the equilibration processes depends primarily on the ratio of the deposition velocities of the two phases, on the production/emission rate of the gas-phase species, and on the initial distribution of species between the two phases.\r\n\r\nAt this point all the tools were available for the detailed investigation of the cyclical relationship between the aerosol and aqueous droplets; a polluted atmosphere with high aerosol concentration assists the formation of the aqueous phase which itself appears to enhance smog production, visibility reduction and aerosol sulfate levels after its dissipation. A model including descriptions of aerosol and droplet microphysics, gas and aqueous-phase chemistry and deposition was used to study the transformation of aerosol to fog droplets and back to aerosol in an urban environment. Fogs in polluted environments have the potential to increase aerosol sulfate concentrations, but at the same time to cause reductions in the aerosol concentration of nitrate, chloride, ammonium and sodium as well as in the total aerosol mass concentration. The sulfate produced during fog episodes favors the aerosol particles that have access to most of the fog liquid water which are usually the large particles. Aerosol scavenging efficiencies of around 80% were calculated for urban fogs. Sampling and subsequent mixing of fog droplets of different sizes may result in measured concentrations that are not fully representative of the fogwater chemical composition and can introduce errors in the reported values of the ionic species deposition velocities. Differences in the major ionic species deposition velocities can be explained by their distribution over the aerosol size spectrum and can be correlated with the species average diameter.\r\n\r\nThe second part of this work was focused on the experimental study of the mechanisms of formation of secondary aerosol particles due to the atmospheric photooxidation of hydrocarbons. In this smog chamber the aerosol forming potential of natural hydrocarbons was investigated. Natural hydrocarbons like the monoterpenes C10H16 and isoprene C5H8 are emitted by various trees and plants in significant quantities. Isoprene and [Beta]-pinene, at concentration levels ranging from a few ppb to a few ppm were reacted photoehemically with NOx, in the Caltech outdoor smog chamber facility. Aerosol formation from the isoprene photooxidation was found to be negligible even under extreme ambient conditions due to the relatively high vapor pressure of its condensable products. Aerosol carbon yield from the [Beta]-pinene photooxidation is as high as 8% and depends strongly on the initial HC/NOx ratio. The average vapor pressure of the [Beta]-pinene aerosol is estimated to be 37 [plus or minus] 24 ppt at 31?c. Monoterpene photooxidation can be a significant source of secondary aerosol in rural environments and in urban areas with extended natural vegetation.", "doi": "10.7907/Z6AN-AJ83", "publication_date": "1991", "thesis_type": "phd", "thesis_year": "1991" }, { "id": "thesis:2686", "collection": "thesis", "collection_id": "2686", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06222005-162441", "primary_object_url": { "basename": "Huang_dd-t_1991.pdf", "content": "final", "filesize": 10584952, "license": "other", "mime_type": "application/pdf", "url": "/2686/1/Huang_dd-t_1991.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Aerosol coagulation and nucleation", "author": [ { "family_name": "Huang", "given_name": "David Da-Teh", "clpid": "Huang-D-D" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Brady", "given_name": "John F.", "clpid": "Brady-J-F" }, { "family_name": "Okuyama", "given_name": "Kikuo", "clpid": "Okuyama-K" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "For aerosol Brownian coagulation in the transition regime of Knudsen number in the presence of an interparticle potential, the Fokker-Planck equation is solved by using the Grad's 13-moment method. The mass and energy accommodation coefficients that are used to describe the results of collisional processes are appropriately defined and interfaced with the Fokker-Planck moment equations. Analytical and numerical solutions of the number and energy flux profiles for the potential-free, power-law potential, van der Waals potential, and Coulombic potential situations are obtained. The results are in good agreement with those predicted by the flux-matching method of Fuchs. The present fundamental approach, therefore, provides theoretical support of the coagulation coefficient expression obtained by the empirical flux-matching method.\n \nFor coagulation between ultrafine particles, we solved the BGK equation for large but finite Knudsen number situations by taking into account the van der Waals potential and/or the Coulombic/image potential. We present closed form best-fit equations for data calculated from the theory. The conditions where either Coulombic, image, or van der Waals forces predominate are determined.\n\nA new expression of the image potential between a charged particle and an uncharged particle is obtained. We calculate the coagulation rate between the particles and are able to determine the enhancement of coagulation rate due to the interparticle potential in all size regimes.\n\nAn aerosol coagulation process is applied to the formation of aerosol particles in the semiconductor thin film preparation. In the CVD reactor, we consider simultaneous aerosol coagulation, diffusion, and generation of aerosol monomers by chemical reaction. The mass and number concentration of monomers and particles are computed as functions of temperature, pressure, input vapor concentration, and position in the reactor. The thin film growth rate can be subsequently evaluated. It is found that under certain circumstances, aerosol particle generation may significantly suppress the film growth due to monomers.\n\nThe formulation of the homogeneous nucleation free energy change of aerosol clusters is reexamined. It is shown that the inclusion of the cluster translational and rotational motion in the cluster formation free energy change is appropriate. The classical and statistical thermodynamics are shown to be consistent.\n\nThe cell model of liquids of statistical mechanics is employed to reevaluate the free energy change of cluster formation in aerosol nucleation. We provide a new molecular level theory that is applicable in the larger cluster size range where liquid-like properties begin to emerge and a cluster surface is present. The microcluster surface tension can be appropriately defined. The cluster rotational contribution to the free energy change, though it must be accounted for, is shown to be insignificant for liquid-like clusters.\n", "doi": "10.7907/G2RC-S602", "publication_date": "1991", "thesis_type": "phd", "thesis_year": "1991" }, { "id": "thesis:938", "collection": "thesis", "collection_id": "938", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03122007-135158", "type": "thesis", "title": "Molecular Beam Investigations of Surface Chemical Reactions and Dynamics", "author": [ { "family_name": "Mullins", "given_name": "Charles Buddie", "orcid": "0000-0003-1030-4801", "clpid": "Mullins-Charles-Buddie" } ], "thesis_advisor": [ { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" } ], "thesis_committee": [ { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" }, { "family_name": "McKoy", "given_name": "Basil Vincent", "clpid": "McKoy-B-V" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "clpid": "Beauchamp-J-L" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Experimental results from molecular beam investigations of trapping and dissociative chemisorption phenomena for several gas-surface systems are presented. The dissociative chemisorption of oxygen on Ir(110)-(1x2) in the limit of zero coverage So was studied as a function of incident kinetic energy Ei, incident angle \u03b8i and surface temperature Ts. Results from this investigation indicate that two mechanisms account for the initial chemisorption. At low incident kinetic energy (less than 4 kcal/mol) chemisorption mediated by trapping is primarily responsible for the dissociative adsorption while at high energies a direct mechanism can account for the results. In both energy ranges the initial dissociative chemisorption probability is insensitive to incident angle.
\r\n\r\nThe trapping of molecular ethane as well as the dissociative chemisorption of ethane on the clean Ir(110)-(1x2) surface has also been investigated. The initial trapping probability \u03b6o is found to decrease with incident kinetic energy from a value of ~0.98 at 1 kcal/mol to ~0.1 at 16 kcal/mol. These data scale with Eicos0.5\u03b8i. The initial dissociative chemisorption of ethane on Ir(110)-(1x2) occurs via a trapping-mediated mechanism at low Ei and a direct mechanism at high kinetic energies. In the trapping-mediated regime So decreases rapidly with increasing Ts. These data quantitatively support a kinetic model consistent with a trapping-mediated chemisorption mechanism. The difference in the activation energies for desorption and chemisorption from the physically adsorbed, trapped state Ed-Ec is 2.2\u00b10.2 kcal/mol. Chemisorption at high kinetic energies, in the direct regime, is independent of surface temperature.
\r\n\r\nAdditionally, the trapping probability of Ar on Pt(111) has been measured as a function of incident kinetic energy, and angle for Ts = 80, 190 and 273 K. The trapping probability decreases with increasing Ei in a manner that depends on both \u03b8i and Ts. The angular scaling law governing the trapping is a function of Ts such that \u03b6o scales with Eicos1.5\u03b8i at 80 K, Eicos1.0\u03b8i at 190 K and Eicos0.5\u03b8i at 273 K. These results suggest that parallel momentum dissipation becomes increasingly more important to the trapping dynamics as the surface temperature is increased.
\r\n", "doi": "10.7907/64s4-0182", "publication_date": "1990", "thesis_type": "phd", "thesis_year": "1990" }, { "id": "thesis:468", "collection": "thesis", "collection_id": "468", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02022007-144010", "type": "thesis", "title": "Effects of Cell Entrapment in Ca-Alginate on the Metabolism of Yeast Saccharomyces cerevisiae", "author": [ { "family_name": "Galazzo", "given_name": "Jorge Luis", "clpid": "Galazzo-Jorge-Luis" } ], "thesis_advisor": [ { "family_name": "Fox", "given_name": "Geoffrey C.", "clpid": "Fox-G-C" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Arnold", "given_name": "Frances Hamilton", "orcid": "0000-0002-4027-364X", "clpid": "Arnold-F-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Lidstrom", "given_name": "Mary E.", "clpid": "Lidstrom-M-E" }, { "family_name": "Fox", "given_name": "Geoffrey C.", "clpid": "Fox-G-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Saccharomyces cerevisiae cells grown in suspension have been immobilized in calcium-alginate beads. Fermentation rates and intracellular composition have been determined under nongrowing conditions in these Ca-alginate entrapped cells and for identical cells in suspension. Glucose uptake and ethanol and glycerol production are approximately two times faster in immobilized cells than in suspended cells. Intermediate metabolite levels such as fructose-1,6-diphosphate, glucose-6-phosphate and 3-phosphoglycerate have been determined by phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy under glucose fermenting conditions. Results show a different sugar phosphate composition in immobilized cells. Also, at steady-state glucose fermentation, the intracellular pH of entrapped cells is lower as indicated by the chemical shift of the intracellular inorganic phosphorus resonance. Carbon-13 NMR shows an increase in polysaccharide production in immobilized cells.
\r\n\r\nS. cerevisiae cells grown within a Ca-alginate matrix have a specific growth rate 40% lower that the growth rate of similar cells cultivated in suspension. Alginate-grown cells have been used to compare glucose fermentation under nongrowing conditions in suspended and Ca-entrapped cells. Fermentation rate is higher in immobilized cells than in suspended cells. The observed differences in intracellular components between suspended and immobilized cells are qualitatively similar to the differences observed for cells grown in suspension. Ethanol production rate is 2.7 times faster in immobilized alginate-grown cells than in suspended suspension-grown cells.
\r\n\r\nThese results suggest that cell immobilization is affecting cell metabolism at different levels. Catabolic regulation is altered as indicated in the nongrowing condition experiments. Also, anabolic regulation is altered as suggested by the changes in growth rate observed in cells growing within the immobilization matrix. The combination of these experimental determinations with knowledge of the metabolic pathways involved in S. cerevisiae allows the development of a quantitative in vivo description of most key pathway enzymes involved in yeast glucose catabolism. The evaluation of flux-control coefficients for all these steps indicates that alginate entrapment of suspension-grown cells increases the glucose uptake rate and shifts the step most influencing ethanol production from glucose uptake to phosphofructokinase. In alginate-grown cells, glucose uptake is limiting ethanol production in both suspended and immobilized cells. There is a 5% decrease in the glucose uptake flux-control coefficient of immobilized cells due to an increment in the glucose uptake rate. This increment increases ethanol production by approximately 100%.
\r\n\r\nAn analysis of the anticipated effects of genetic manipulation to improve the ethanol production rate in yeast S. cerevisiae using the framework of the metabolic control theory indicates that in suspended suspension-grown cells the highest improvement is obtained by increasing the activity of glucose transport, whereas in immobilized suspension-grown cells the greatest enhancement is obtained by incrementing the maximum activity of phosphofructokinase. This indicates that the metabolic engineering strategy to be used in order to enhance any properties in the cell will depend not only on the specific microorganism, but also on the environmental conditions in which it is placed. In conditions where several steps share the flux control in a pathway, a substantial enhancement in pathway rate will be possible only if the activities of all those steps are increased simultaneously.
", "doi": "10.7907/gq59-ka36", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:520", "collection": "thesis", "collection_id": "520", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02062007-104756", "type": "thesis", "title": "Area, Cost and Resilience Targets for Heat Exchanger Networks", "author": [ { "family_name": "Colberg", "given_name": "Richard Dale", "clpid": "Colberg-Richard-Dale" } ], "thesis_advisor": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" } ], "thesis_committee": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis presents improved area and capital cost targets for synthesis of heat exchanger networks (HEN) for fixed operating conditions, and a new resilience target for synthesis of HENs for changing, uncertain operating conditions. In addition, methods are presented to predict, before synthesis, the trade-off between cost and resilience.
\r\n\r\nA pair of \"transshipment\" nonlinear programs (NLP) is formulated to calculate the area and capital cost targets for HEN synthesis with unequal heat transfer coefficients and different capital cost laws (for different materials of construction, pressure ratings, etc.) when there are constraints on the number of matches, forbidden matches, and required matches with specified areas (for revamp synthesis). With these NLPs, the trade-off between area and number of units can be evaluated before synthesis. In addition to the targets themselves, solution of the NLPs yields \"ideal\" temperature profiles (much like the composite curves) for a HEN achieving the targets, and a selection of stream matches and their heat loads which provide an excellent starting point for synthesis of HENs achieving (within a few percent) the area and capital cost targets.
\r\n\r\nFor changing or uncertain operating conditions, a Class 1 resilience target is presented which predicts, given the nominal operating conditions, the largest uncertainty range for which a \"practical\" HEN (with few more units and stream splits than that required for nominal conditions) can be synthesized. This resilience target also predicts whether trade-offs (in utilities, number of units, or size of uncertainty range) must be made to achieve resilience, and the operating condition and constraint most likely to limit resilience.
\r\n\r\nA nonlinear program is formulated to calculate the Class 1 HEN resilience target. Trade-offs with minimum approach temperature, utility consumption, and nominal network area are presented. The use of the Class 1 resilience target as a synthesis tool is discussed.
\r\n\r\nFinally, a simple procedure to predict the trade-off between cost and resilience is introduced so that a process engineer can design for an economically \"optimal\" amount of resilience.
", "doi": "10.7907/pndd-bc72", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:520", "collection": "thesis", "collection_id": "520", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02062007-104756", "type": "thesis", "title": "Area, Cost and Resilience Targets for Heat Exchanger Networks", "author": [ { "family_name": "Colberg", "given_name": "Richard Dale", "clpid": "Colberg-Richard-Dale" } ], "thesis_advisor": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" } ], "thesis_committee": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis presents improved area and capital cost targets for synthesis of heat exchanger networks (HEN) for fixed operating conditions, and a new resilience target for synthesis of HENs for changing, uncertain operating conditions. In addition, methods are presented to predict, before synthesis, the trade-off between cost and resilience.
\r\n\r\nA pair of \"transshipment\" nonlinear programs (NLP) is formulated to calculate the area and capital cost targets for HEN synthesis with unequal heat transfer coefficients and different capital cost laws (for different materials of construction, pressure ratings, etc.) when there are constraints on the number of matches, forbidden matches, and required matches with specified areas (for revamp synthesis). With these NLPs, the trade-off between area and number of units can be evaluated before synthesis. In addition to the targets themselves, solution of the NLPs yields \"ideal\" temperature profiles (much like the composite curves) for a HEN achieving the targets, and a selection of stream matches and their heat loads which provide an excellent starting point for synthesis of HENs achieving (within a few percent) the area and capital cost targets.
\r\n\r\nFor changing or uncertain operating conditions, a Class 1 resilience target is presented which predicts, given the nominal operating conditions, the largest uncertainty range for which a \"practical\" HEN (with few more units and stream splits than that required for nominal conditions) can be synthesized. This resilience target also predicts whether trade-offs (in utilities, number of units, or size of uncertainty range) must be made to achieve resilience, and the operating condition and constraint most likely to limit resilience.
\r\n\r\nA nonlinear program is formulated to calculate the Class 1 HEN resilience target. Trade-offs with minimum approach temperature, utility consumption, and nominal network area are presented. The use of the Class 1 resilience target as a synthesis tool is discussed.
\r\n\r\nFinally, a simple procedure to predict the trade-off between cost and resilience is introduced so that a process engineer can design for an economically \"optimal\" amount of resilience.
", "doi": "10.7907/pndd-bc72", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:699", "collection": "thesis", "collection_id": "699", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02212007-133209", "type": "thesis", "title": "Synthesis, Characterization, and Kinetics of Mixed Copper-Aluminum and Iron-Aluminum Oxides for High-Temperature Desulfurization", "author": [ { "family_name": "Patrick", "given_name": "Valerie", "clpid": "Patrick-Valerie" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Arnold", "given_name": "Frances Hamilton", "orcid": "0000-0002-4027-364X", "clpid": "Arnold-F-H" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Hot-gas desulfurization is an important step for optimizing the process economics of new schemes for power generation from coal. Mixed oxides such as CuO\u2022Al\u2082O\u2083 and Fe\u2082O\u2083\u2022Al\u2082O\u2083 are attractive as high-temperature, regenerable, desulfurization sorbents because they exhibit higher performance than CuO and Fe\u2082O\u2083.
\r\n\r\nMixed copper-aluminum and iron-aluminum oxides were prepared in porous form by the citrate process under various calcination conditions for subsequent reduction and sulfidation studies. The oxide samples were characterized by several techniques to determine chemical structure and texture. For the mixed copper-aluminum oxides, atomic absorption spectroscopy (AAS) provided the fractions of copper, soluble and insoluble, in hot nitric acid which closely corresponded to CuO and CuAl\u2082O\u2084, respectively; x-ray diffraction (XRD) provided complementary information about the content of the pure and compound oxides; and a combination of x-ray line broadening, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) provided an estimate of the size of crystallites or phase domains. For the mixed iron-aluminum oxides, XRD identified crystalline phases, SEM revealed the changing surface texture with iron composition, and BET surface area measurements indicated the content of free alumina.
\r\n\r\nTemperature-programmed reduction (TPR) of mixed oxides was more complex than TPR of the pure, reducible oxides. The compound oxide, CuAl\u2082O\u2084, and part of CuO closely associated with Al\u2082O\u2083 were reduced much more slowly than bulk CuO. Similarly, the compound oxide, FeAl\u2082O\u2084, a solid solution between Fe\u2083O\u2084 and FeAl\u2082O\u2084, and Fe\u2083O\u2084 in close association with alumina were reduced much more slowly than bulk Fe\u2083O\u2084. While oxides of +1 oxidation state, Cu[2]O and CuAlO[2], were identified as reduction intermediates for TPR of CuAl\u2082O\u2084, no oxides of +1 oxidation state were identified for reduction of iron-aluminum oxides.
\r\n\r\nMixed copper-aluminum oxides were studied more extensively than mixed iron-aluminum oxides. The interaction between CuO and Al\u2082O\u2083 seen in TPR studies was further examined by XRD, diffuse reflectance spectroscopy, and laser Raman spectroscopy. Pronounced sintering of CuAl\u2082O\u2084 was observed to commence at temperatures in excess of 700\u00b0C, and the dispersion of copper on reduction of CuAl\u2082O\u2084 was poorer than that obtained by reduction of mixed oxide, CuO and Al\u2082O\u2083.
\r\n\r\nIn studies using a thermogravimetric analyzer, sulfidation of reduced sorbents produced high-temperature digenite (Cu\u2089\u208a\u2093S\u2085) in the case of copper aluminum samples, and high-temperature pyrrhotite (Fe\u2081\u208b\u2093S) in the case of iron-aluminum samples as the major crystalline products. Both CuAl\u2082O\u2084 and FeAl\u2082O\u2084 were found to be resistant to sulfidation as compared to the pure oxides, CuO and Fe\u2082O\u2083, and to mixed oxides, CuO-Al\u2082O\u2083 and Fe\u2082O\u2083-Al\u2082O\u2083. Formation of copper sulfate during air regeneration of sulfided Cu-Al-O samples was increased in the presence of free alumina.
", "doi": "10.7907/2TRJ-1P91", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:7909", "collection": "thesis", "collection_id": "7909", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06282013-092232283", "type": "thesis", "title": "Oxidative Chemisorption of SO\u2082 on \u03b3-Al\u2082O\u2083 and Deposition of H\u2082-Permselective SiO\u2082 Films", "author": [ { "family_name": "Nam", "given_name": "Suk Woo", "orcid": "0000-0002-4884-8137", "clpid": "Nam-Suk-Woo" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The interaction of SO\u2082 with \u03b3-Al\u2082O\u2083 and the deposition of H\u2082 permselective SiO\u2082 films have been investigated. The adsorption and oxidative adsorption of SO\u2082 on \u03b3-Al\u2082O\u2083 have been examined at temperatures 500-700\u00b0C by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). At temperatures above 500\u00b0C most of SO\u2082 adsorbed on the strong sites on alumina. The adsorbed SO\u2082 species was characterized by an IR band at 1065 cm\u207b\u00b9. The equilibrium coverage and initial rate of adsorption decreased with temperature suggesting a two-step adsorption. When \u03b3-Al\u2082O\u2083 was contacted with a mixture of SO\u2082 and O\u2082, adsorption of SO\u2082 and oxidation of the adsorbed SO\u2082 to a surface sulfate characterized by broad IR bands at 1070 cm\u207b\u00b9, 1390 cm\u207b\u00b9 took place. The results of a series of TGA experiments under different atmospheres strongly suggest that surface SO\u2082 and surface sulfate involve the same active sites such that SO\u2082 adsorption is inhibited by already formed sulfate. The results also indicate a broad range of site strengths.
\r\n\r\nThe desorption of adsorbed SO\u2082 and the reductive desorption of oxidatively adsorbed SO\u2082 have been investigated by microreactor experiments and thermogravimetric analysis (TGA). Temperature programmed reduction (TPR) of adsorbed SO\u2082 showed that SO\u2082 was desorbed without significant reaction with H\u2082 when H\u2082 concentration was low while considerable reaction occurred when 100% H\u2082 was used. SO\u2082 adsorbed on the strong sites on alumina was reduced to sulfur and H\u2082S. The isothermal reduction experiments of oxidatively adsorbed SO\u2082 reveal that the rate of reduction is very slow below 550\u00b0C even with 100% H\u2082. The reduction product is mainly composed of SO\u2082. TPR experiments of oxidatively adsorbed SO\u2082 showed that H\u2082S arose from a sulfate strongly chemisorbed on the surface.
\r\n\r\nFilms of amorphous SiO\u2082 were deposited within the walls of porous Vycor tubes by SiH\u2084 oxidation in an opposing reactants geometry : SiH\u2084 was passed inside the tube while O\u2082 was passed outside the tube. The two reactants diffused opposite to each other and reacted within a narrow front inside the tube wall to form a thin SiO\u2082 film. Once the pores were plugged the reactants could not reach each other and the reaction stopped. At 450\u00b0C and 0.1 and 0.33 atm of SiH\u2084 and O\u2082, the reaction was complete within 15 minutes. The thickness of the SiO\u2082 film was estimated to be about 0.1 \u00b5m. Measurements of H\u2082 and N\u2082 permeation rates showed that the SiO\u2082 film was highly selective to H\u2082 permeation. The H\u2082:N\u2082 flux at 450\u00b0C varied between 2000-3000.
\r\n\r\nThin SiO\u2082 films were heat treated in different gas mixtures to determine their stability in functioning as high-temperature hydrogen-permselective membranes. The films were heat-treated at 450-700\u00b0C in dry N\u2082, dry O\u2082, N\u2082-H\u2082O, and O\u2082-H\u2082O mixtures. The permeation rates of H\u2082 and N\u2082 changed depending on the original conditions of film formation as well as on the heat treatment. Heating in dry N\u2082 slowly reduced the permeation rates of both H\u2082 and N\u2082. Heating in a N\u2082-H\u2082O atmosphere led to a steeper decline of H\u2082 permeability. But the permeation rate of N\u2082 increased or decreased according to whether the film deposition had been carried out in the absence or presence of H\u2082O vapor, respectively. Thermal treatment in O\u2082 caused rapid decline of the permeation rates of H\u2082 and N\u2082 in films that were deposited under dry conditions. The decline was moderate in films deposited under wet conditions.
", "doi": "10.7907/8c25-cf68", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:468", "collection": "thesis", "collection_id": "468", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02022007-144010", "type": "thesis", "title": "Effects of Cell Entrapment in Ca-Alginate on the Metabolism of Yeast Saccharomyces cerevisiae", "author": [ { "family_name": "Galazzo", "given_name": "Jorge Luis", "clpid": "Galazzo-Jorge-Luis" } ], "thesis_advisor": [ { "family_name": "Fox", "given_name": "Geoffrey C.", "clpid": "Fox-G-C" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Arnold", "given_name": "Frances Hamilton", "orcid": "0000-0002-4027-364X", "clpid": "Arnold-F-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Lidstrom", "given_name": "Mary E.", "clpid": "Lidstrom-M-E" }, { "family_name": "Fox", "given_name": "Geoffrey C.", "clpid": "Fox-G-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Saccharomyces cerevisiae cells grown in suspension have been immobilized in calcium-alginate beads. Fermentation rates and intracellular composition have been determined under nongrowing conditions in these Ca-alginate entrapped cells and for identical cells in suspension. Glucose uptake and ethanol and glycerol production are approximately two times faster in immobilized cells than in suspended cells. Intermediate metabolite levels such as fructose-1,6-diphosphate, glucose-6-phosphate and 3-phosphoglycerate have been determined by phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy under glucose fermenting conditions. Results show a different sugar phosphate composition in immobilized cells. Also, at steady-state glucose fermentation, the intracellular pH of entrapped cells is lower as indicated by the chemical shift of the intracellular inorganic phosphorus resonance. Carbon-13 NMR shows an increase in polysaccharide production in immobilized cells.
\r\n\r\nS. cerevisiae cells grown within a Ca-alginate matrix have a specific growth rate 40% lower that the growth rate of similar cells cultivated in suspension. Alginate-grown cells have been used to compare glucose fermentation under nongrowing conditions in suspended and Ca-entrapped cells. Fermentation rate is higher in immobilized cells than in suspended cells. The observed differences in intracellular components between suspended and immobilized cells are qualitatively similar to the differences observed for cells grown in suspension. Ethanol production rate is 2.7 times faster in immobilized alginate-grown cells than in suspended suspension-grown cells.
\r\n\r\nThese results suggest that cell immobilization is affecting cell metabolism at different levels. Catabolic regulation is altered as indicated in the nongrowing condition experiments. Also, anabolic regulation is altered as suggested by the changes in growth rate observed in cells growing within the immobilization matrix. The combination of these experimental determinations with knowledge of the metabolic pathways involved in S. cerevisiae allows the development of a quantitative in vivo description of most key pathway enzymes involved in yeast glucose catabolism. The evaluation of flux-control coefficients for all these steps indicates that alginate entrapment of suspension-grown cells increases the glucose uptake rate and shifts the step most influencing ethanol production from glucose uptake to phosphofructokinase. In alginate-grown cells, glucose uptake is limiting ethanol production in both suspended and immobilized cells. There is a 5% decrease in the glucose uptake flux-control coefficient of immobilized cells due to an increment in the glucose uptake rate. This increment increases ethanol production by approximately 100%.
\r\n\r\nAn analysis of the anticipated effects of genetic manipulation to improve the ethanol production rate in yeast S. cerevisiae using the framework of the metabolic control theory indicates that in suspended suspension-grown cells the highest improvement is obtained by increasing the activity of glucose transport, whereas in immobilized suspension-grown cells the greatest enhancement is obtained by incrementing the maximum activity of phosphofructokinase. This indicates that the metabolic engineering strategy to be used in order to enhance any properties in the cell will depend not only on the specific microorganism, but also on the environmental conditions in which it is placed. In conditions where several steps share the flux control in a pathway, a substantial enhancement in pathway rate will be possible only if the activities of all those steps are increased simultaneously.
", "doi": "10.7907/gq59-ka36", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:4557", "collection": "thesis", "collection_id": "4557", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11142007-092219", "type": "thesis", "title": "A Fundamental Study of Char Combustion: Changes in Particle Morphology during Oxidation", "author": [ { "family_name": "Northrop", "given_name": "Paul Scott", "clpid": "Northrop-Paul-Scott" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" }, { "family_name": "Zukoski", "given_name": "Edward E.", "clpid": "Zukoski-E-E" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis presents a study of the morphological changes that occur in selected coal chars during oxidation at low temperature (725K-875K) and at high temperature (1400K-1600K). Gas adsorption and mercury porosimetry were the primary means by which these changes were monitored. An attempt was made to relate the observed reactivity of the char in oxygen to the evolving porous structure of the char. Initial pore structure was varied by using three different raw coals: a lignite, a subbituminous and high volatile A bituminous coal. In the case of the bituminous coal, pore structure was varied further by using different pyrolysis temperatures. Of course, while there were differences in the physical structure of the chars, there were differences in the chemical structure as well. In order to account for this, the chemical nature of the chars was monitored, using elemental analysis and oxygen chemisorption.
\r\n\r\nThe results of this study indicate that, at low temperatures, the rate of oxidation of the subbituminous and bituminous chars is proportional to the BET surface area beyond 20% conversion. The lignite char did not show such simple behavior because of the presence of large amounts of ash. For the high-temperature case, reaction appeared to be confined to the exterior of the particle and to the interior of the macropores.
\r\n\r\nTime-temperature histories of individual lignite char particles were obtained with a two-color pyrometer. A simplified model of single- particle-char combustion was used in conjunction with statistical analysis to infer kinetic parameters from the experimental time-temperature traces.
", "doi": "10.7907/5R3H-DV43", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:4449", "collection": "thesis", "collection_id": "4449", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11072007-112829", "type": "thesis", "title": "Bubble Dynamics and Breakup in Straining Flows", "author": [ { "family_name": "Kang", "given_name": "In Seok", "clpid": "Kang-In-Seok" } ], "thesis_advisor": [ { "family_name": "Leal", "given_name": "L. Gary", "clpid": "Leal-L-G" } ], "thesis_committee": [ { "family_name": "Leal", "given_name": "L. Gary", "clpid": "Leal-L-G" }, { "family_name": "Wu", "given_name": "Theodore Yao-tsu", "clpid": "Wu-T-Y-T" }, { "family_name": "Saffman", "given_name": "Philip G.", "clpid": "Saffman-P-G" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The dynamics and breakup of a bubble in axisymmetric flow fields has been investigated using numerical and analytical techniques. In particular, the transient bubble deformation, oscillation, and overshoot effects are considered in conjunction with the existence of steady-state solutions.
\r\n\r\nTo explore the dynamics of a bubble with a high degree of deformation, a numerical technique suitable for solving axisymmetric, unsteady free boundary problems in fluid mechanics has been developed. The technique is based on a finite-difference solution of the equations of motion on a moving orthogonal curvilinear coordinate system, which is constructed numerically and adjusted to fit the boundary at any time. For example, the steady and unsteady deformations of a bubble in uniaxial and biaxial straining flows are examined for wide ranges of the Reynolds number and the Weber number. The computations reveal that a bubble in a uniaxial straining flow extends indefinitely if the Weber number is larger than a critical value (W > Wc). Furthermore, it is shown that a bubble may not achieve a stable steady state even at subcritical values of the Weber number if the initial state is sufficiently different from the steady state. Potential flow solutions for uniaxial straining flow show that an initially deformed bubble undergoes oscillatory motion if W < Wc, with a frequency of oscillation that decreases as the Weber number increases and equals zero at the critical Weber number.
\r\n\r\nIn contrast to the uniaxial straining flow problem, a bubble at a finite Reynolds number in a biaxial straining flow has a stable steady state even though the deformation is extremely large. However, it is found that a bubble in a biaxial straining flow in the potential flow limit has exactly the same steady-state shape as in a uniaxial straining flow and a critical Weber number for breakup exists. Comparison of the results for the cases of high Reynolds numbers with the potential flow results suggests that the potential flow solution does not provide a uniformly valid approximation to the real flow at a high Reynolds number in the biaxial straining flow.
\r\n\r\nAs a complementary analytical study to the numerical analysis, the method of domain perturbations is used to investigate the problem of a nearly spherical bubble in an inviscid, axisymmetric straining flow. The steady-state solutions suggest the existence of a limit point at a critical value of the Weber number. Furthermore, the asymptotic analysis for oscillation has provided a formula of oscillation frequency for the principal mode such as \u03c9\u00b2 = \u03c9\u00b2\u2080(1 - 0.31W), where \u03c9\u2080 is the oscillation frequency of a bubble in a quiescent fluid.
\r\n\r\nTo include the weak viscous effect on the oscillation, a general formula for viscous pressure correction for a spherical bubble in an arbitrary axisymmetric flow has been derived in terms of the vorticity distribution. This formula has been applied to obtain the drag coefficient CD = 48/R by directly integrating the normal stress over the surface for a spherical bubble in a uniform streaming flow at a high Reynolds number, which has so far been possible only via indirect macroscopic balances. The direct method also reveals that the drag coefficient up to O(R)\u207b\u00b9 depends only on the O(1) vorticity distribution right on the bubble surface, and is independent of the vorticity distribution inside the fluid.
\r\n\r\nFinally, a voidage bubble in a fluidized bed is considered in the low Reynolds number limit. The problem has been formulated as a generalized drop problem with one additional parameter. The analysis shows that the steady and unsteady deformations in the creeping flow limit are exactly the same as the conventional drop problem even though the flow fields are different. The effect of the additional parameter on deformation first appears when inertial effects are considered.
\r\n", "doi": "10.7907/y91q-ff03", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:4449", "collection": "thesis", "collection_id": "4449", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11072007-112829", "type": "thesis", "title": "Bubble Dynamics and Breakup in Straining Flows", "author": [ { "family_name": "Kang", "given_name": "In Seok", "clpid": "Kang-In-Seok" } ], "thesis_advisor": [ { "family_name": "Leal", "given_name": "L. Gary", "clpid": "Leal-L-G" } ], "thesis_committee": [ { "family_name": "Leal", "given_name": "L. Gary", "clpid": "Leal-L-G" }, { "family_name": "Wu", "given_name": "Theodore Yao-tsu", "clpid": "Wu-T-Y-T" }, { "family_name": "Saffman", "given_name": "Philip G.", "clpid": "Saffman-P-G" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The dynamics and breakup of a bubble in axisymmetric flow fields has been investigated using numerical and analytical techniques. In particular, the transient bubble deformation, oscillation, and overshoot effects are considered in conjunction with the existence of steady-state solutions.
\r\n\r\nTo explore the dynamics of a bubble with a high degree of deformation, a numerical technique suitable for solving axisymmetric, unsteady free boundary problems in fluid mechanics has been developed. The technique is based on a finite-difference solution of the equations of motion on a moving orthogonal curvilinear coordinate system, which is constructed numerically and adjusted to fit the boundary at any time. For example, the steady and unsteady deformations of a bubble in uniaxial and biaxial straining flows are examined for wide ranges of the Reynolds number and the Weber number. The computations reveal that a bubble in a uniaxial straining flow extends indefinitely if the Weber number is larger than a critical value (W > Wc). Furthermore, it is shown that a bubble may not achieve a stable steady state even at subcritical values of the Weber number if the initial state is sufficiently different from the steady state. Potential flow solutions for uniaxial straining flow show that an initially deformed bubble undergoes oscillatory motion if W < Wc, with a frequency of oscillation that decreases as the Weber number increases and equals zero at the critical Weber number.
\r\n\r\nIn contrast to the uniaxial straining flow problem, a bubble at a finite Reynolds number in a biaxial straining flow has a stable steady state even though the deformation is extremely large. However, it is found that a bubble in a biaxial straining flow in the potential flow limit has exactly the same steady-state shape as in a uniaxial straining flow and a critical Weber number for breakup exists. Comparison of the results for the cases of high Reynolds numbers with the potential flow results suggests that the potential flow solution does not provide a uniformly valid approximation to the real flow at a high Reynolds number in the biaxial straining flow.
\r\n\r\nAs a complementary analytical study to the numerical analysis, the method of domain perturbations is used to investigate the problem of a nearly spherical bubble in an inviscid, axisymmetric straining flow. The steady-state solutions suggest the existence of a limit point at a critical value of the Weber number. Furthermore, the asymptotic analysis for oscillation has provided a formula of oscillation frequency for the principal mode such as \u03c9\u00b2 = \u03c9\u00b2\u2080(1 - 0.31W), where \u03c9\u2080 is the oscillation frequency of a bubble in a quiescent fluid.
\r\n\r\nTo include the weak viscous effect on the oscillation, a general formula for viscous pressure correction for a spherical bubble in an arbitrary axisymmetric flow has been derived in terms of the vorticity distribution. This formula has been applied to obtain the drag coefficient CD = 48/R by directly integrating the normal stress over the surface for a spherical bubble in a uniform streaming flow at a high Reynolds number, which has so far been possible only via indirect macroscopic balances. The direct method also reveals that the drag coefficient up to O(R)\u207b\u00b9 depends only on the O(1) vorticity distribution right on the bubble surface, and is independent of the vorticity distribution inside the fluid.
\r\n\r\nFinally, a voidage bubble in a fluidized bed is considered in the low Reynolds number limit. The problem has been formulated as a generalized drop problem with one additional parameter. The analysis shows that the steady and unsteady deformations in the creeping flow limit are exactly the same as the conventional drop problem even though the flow fields are different. The effect of the additional parameter on deformation first appears when inertial effects are considered.
\r\n", "doi": "10.7907/y91q-ff03", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:4462", "collection": "thesis", "collection_id": "4462", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11082007-092627", "type": "thesis", "title": "Ethanol Production by Saccharomyces cerevisiae Immobilized in Calcium Alginate", "author": [ { "family_name": "Hannoun", "given_name": "Betty Jane Miller", "clpid": "Hannoun-Betty-Jane-Miller" } ], "thesis_advisor": [ { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" } ], "thesis_committee": [ { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "clpid": "Hoffmann-M-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Glucose and ethanol diffusion coefficients in calcium alginate were measured in a diffusion cell using the lag time method. The diffusion coefficients decreased as the alginate concentration increased. Glucose and ethanol concentrations had no effect on the diffusion coefficients. Also the presence of 20% dead yeast cells had no effect on the diffusion coefficients.
\r\n\r\nExperiments were conducted under anaerobic conditions to determine the intrinsic, specific rates of growth, glucose uptake, and ethanol production for Saccharomyces cerevisiae immobilized in calcium alginate. The simultaneous processes of diffusion and reaction were analyzed in an alginate membrane to determine the intrinsic, specific growth and reaction rates from glucose and ethanol concentration measurements made outside the alginate phase. Under anaerobic conditions, the specific growth rate of immobilized S. cerevisiae decreased by 20% compared to the growth rate for suspended cells. The specific glucose uptake rate and specific ethanol production rate increased by a factor of four (4) compared to suspended cells. The ethanol yield remained the same and the biomass yield decreased to one-fifth (1/5) the yield for suspended cells.
\r\n\r\nFurther experiments were conducted under aerobic conditions to investigate the effects of dissolved oxygen concentration on the specific rates of growth, glucose uptake, and ethanol production of immobilized S. cerevisiae. Oxygen appears to affect immobilized cells similarly to the way it affects suspended cells.
\r\n\r\nA mathematical model was developed to quantify the effects of oxygen, glucose, and ethanol on the intrinsic, specific rates of growth, glucose uptake, and ethanol production of immobilized cells. The model was tested using S. cerevisiae immobilized in calcium alginate beads in a well-mixed batch reactor. The mathematical model accurately predicts the bulk fluid glucose and ethanol concentrations.
\r\n\r\nThe mathematical model for intrinsic, specific rates of growth, glucose uptake, and ethanol production was used to simulate the behavior of a continuous plug flow reactor and a continuous stirred tank reactor for ethanol production by S. cerevisiae immobilized in calcium alginate beads. Unsteady-state reactor operation was considered. The effects of bead size, feed glucose concentration, residence time, and dissolved oxygen concentration on reactor performance were investigated.
\r\n\r\n\r\n", "doi": "10.7907/53yk-0e29", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:4483", "collection": "thesis", "collection_id": "4483", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11092007-141214", "type": "thesis", "title": "Reactor Input Manipulation for Developing Models for Catalytic Reactions", "author": [ { "family_name": "Shanks", "given_name": "Brent Howard", "clpid": "Shanks-Brent-Howard" } ], "thesis_advisor": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "A variety of phenomenological experimental methods are employed to construct and validate kinetic models for heterogeneous catalytic reaction systems. Both static input and stimulus-response experiments are performed with particular emphasis placed on the novel feedback-induced bifurcation method. These techniques are applied to CO oxidation on Rh/Al\u2082O\u2083 and Ag/Al\u2082O\u2083 to identify kinetic models that are able to reproduce transient as well as steady-state experimental data.
\r\n\r\nStatic input experiments for CO oxidation on supported Rh, reduced at 170\u00b0C, reveal oscillatory responses for some inlet conditions. Two adsorbed CO species, linear and dicarbonyl forms, are observed with the linearly adsorbed CO shown from step-response experiments to be more reactive than CO adsorbed in the dicarbonyl form. The oscillations seem to be driven by surface temperature fluctuations rather than by interconversion between the adsorbed CO species.
\r\n\r\nSteady-state and step-response experiments at 147\u00b0C are used to estimate and to bound parameters in two reaction models that were previously postulated for CO oxidation on supported Ag. Data from feedback-induced steady-state bifurcation experiments are reproduced well by both models but neither reaction model is able to reproduce closed-loop Hopf bifurcation data. Also, long-time-scale transients observed in some step-response experiments are not accurately simulated by either model. A new model is proposed for CO oxidation on Ag/Al\u2082O\u2083, which incorporates a slow reversible step that forms an adsorbed oxygen species that blocks reaction sites. This model is able to reproduce the long-time-scale dynamics and a variety of cycled feedstream experiments.
\r\n\r\nThe feedback-induced bifurcation method is also applied to the CO oxidation reaction on supported Rh. After reducing the Rh/Al\u2082O\u2083 catalyst at 500\u00b0C, only linearly adsorbed CO is observed. Measurements of the fractional coverage of CO and the gas-phase CO are used for feedback control. The closed-loop bifurcation data are used to discriminate between two reaction models for CO oxidation on supported Rh, which are determined from steady-state experiments. Higher order dynamics resulting from closed-loop operation are also observed. The usefulness of various types of experimental feedback-induced bifurcations, as applied to model development, is discussed.
\r\n\r\nFinally, the feedback-induced bifurcation method is used to generate basis oscillations that are subjected to forced periodic operation. This provides a process in which entrainment behavior can be systematically examined. Experimental and simulated entrainment responses are compared and are found to be in close agreement.
\r\n", "doi": "10.7907/pf3v-jt53", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:4426", "collection": "thesis", "collection_id": "4426", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11062007-103728", "type": "thesis", "title": "Studies on Hot Gas H\u2082S Removal Sorbents in Fixed-Bed Reactors at High Temperatures", "author": [ { "family_name": "Bagajewicz", "given_name": "Miguel Jorge", "clpid": "Bagajewicz-Miguel-Jorge" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Experimental and theoretical studies in the field of fuel gas desulfurization at high temperatures are presented. The performance of different oxides as sorbents for high temperature H2S removal is evaluated. A fixed-bed microreactor was used for this purpose. Basically, streams containing different H2S concentrations were passed through the reactor and the outlet H2S concentration was measured as a function of time. Comparisons between observed and theoretical maximum conversion values are used as a measure of sorbent H2S removal efficiencies.
\r\n\r\nMost of the work was devoted to study zinc oxide and vanadium oxide, but other sorbents were also investigated. ZnO was studied because of its high equilibrium constant for sulfidation. High surface alumina-supported ZnO and high surface bulk ZnO were tested. Alumina-supported ZnO proved to have a smaller desulfurization capacity than bulk ZnO. In the case of V2O5, chemisorption of H2S on reduced vanadium oxide, rather than bulk sulfide formation, was found to be the mechanism of sulfur removal. Adsorption-desorption measurements were carried out in this case to investigate the behavior of the sorbent.
\r\n\r\nThe regeneration step, which restores the oxide by means of oxidation of the spent sulfide, was also studied in detail. The rate of ZnS oxidation was measured using a thermogravimetric analyzer. For the range of temperatures 650-700\u00b0C, the rate of reaction was consistent with Langmuir kinetics. The activation energy and the free energy of oxygen chemisorption were determined. An undesirable side reaction during oxidative regeneration is sulfate formation. The kinetics of this reaction was also investigated by thermogravimetric measurements.
\r\n\r\nTheoretical studies dealing with reaction and diffusion processes in pellets and fixed-bed reactors were conducted, to a large extent motivated by the need to describe desulfurization processes. One chapter is devoted to a survey of exact and approximate solutions for an isothermal fixed-bed gas-solid reactor. Approximate analytical solutions to a class of models of reaction and diffusion inside sorbent pellets are presented next. The last chapter is devoted to a traveling wave solution describing reaction fronts inside non-isothermal fixed-bed reactors. This provides a good analytical approach for the prediction of conditions for the formation of zinc sulfate during the regeneration of ZnS.
\r\n", "doi": "10.7907/WZZJ-H326", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:4535", "collection": "thesis", "collection_id": "4535", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11132007-081003", "type": "thesis", "title": "On the Combustion of Bituminous Coal Chars", "author": [ { "family_name": "Sahu", "given_name": "Ranajit", "clpid": "Sahu-Ranajit" } ], "thesis_advisor": [ { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" } ], "thesis_committee": [ { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Sabersky", "given_name": "Rolf H.", "clpid": "Sabersky-R-H" }, { "family_name": "Zukoski", "given_name": "Edward E.", "clpid": "Zukoski-E-E" }, { "family_name": "Brennen", "given_name": "Christopher E.", "clpid": "Brennen-C-E" }, { "family_name": "Roshko", "given_name": "Anatol", "clpid": "Roshko-A" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The combustion of chars from pulverized bituminous coals was experimentally and theoretically investigated. The chars were made by pyrolyzing size-graded PSOC 1451 coal particles in nitrogen at temperatures of 1000-1600K. Sized char particles were then used for further experiments. Low temperature reactivities of such cenospheric chars were measured at 800K on a thermogravimetric analyzer. The effects of initial coal size, char size, pyrolysis temperature, and oxygen concentration were investigated. Single particle combustion experiments were done in both air and 50% oxygen ambients at wall temperatures of 1000-1500K in a drop tube laminar flow furnace. Particle temperatures were measured during the entire course of combustion. From the complete temperature-time histories of such burning particles, the apparent activation energy and pre-exponential factors were inferred, using numerical models and statistical modelling techniques. Questions of particle-particle variability were addressed. The ignition transients of single burning particles were studied and a model that predicted delay times observed experimentally was developed. Char samples were also partially oxidized at temperatures in the range 1200-1500K (particle temperatures) and physically characterized. Methods of characterization included optical and electron microscopy, gas adsorption methods for specific surface area and pore volume distributions, and mercury porosimetry for pore volume distribution measurements. The results of these characterizations were compared with those done on chars oxidized at 500\u00b0C.
\r\n\r\nThe combustion of single char particles was numerically modelled. A continuum model for asymptotic shrinking-core combustion was developed using apparent reaction rates and temperature-dependent properties. Simplified assumptions were made regarding the gas-phase combustion. Parametric sensitivity of this model yielded significant insight into the combustion process. A more general continuum model was then developed. This model treated the internal pore structure more realistically, as inferred from experiments. The steady state diffusion equation was solved inside the particle to determine its theoretical temperature-time history. Good agreement with experiments was found. The model was extended to include the effects of some nonlinear kinetic reaction rate expressions. A discrete model for a cenospheric particle was also developed. This model consists of spherical voids randomly placed in a spherical particle. It simulates the combustion by taking into account the connectivity of the internal pore structure. This connectivity influences the access of reactant to the interior of the particle and, therefore, the extent of internal reaction. The changes in the internal connectivity led to a percolation type behavior in most particles.
", "doi": "10.7907/zrnz-qc25", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:4582", "collection": "thesis", "collection_id": "4582", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11152007-091715", "type": "thesis", "title": "A Fundamental Study of Char Oxidation Kinetics Using Model Materials", "author": [ { "family_name": "Levendis", "given_name": "Yiannis Angelo", "clpid": "Levendis-Yiannis-Angelo" } ], "thesis_advisor": [ { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "clpid": "Hoffmann-M-R" }, { "family_name": "Sabersky", "given_name": "Rolf H.", "clpid": "Sabersky-R-H" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "A fundamental study concerning the reactivity of carbon to oxygen, under conditions pertinent to the combustion of pulverized fuel particles, was conducted. Model, man-made materials have been synthesized and produced to aid in understanding the events that occur during pyrolysis and oxidation of chars. The benefit of employing synthetic materials, along with natural fuels, was that they allowed control of the purity and composition of the chars, as well as enabled production of particles of specific physical properties relevant to modeling combustion processes.
\r\n\r\nMonodisperse, spherical, glassy carbon particles, of various sizes, were manufactured from spraying and thermally treating a carbon-yielding, highly crosslinked polymer. Various pore-forming agents were introduced and copolymerized, aiming to alter the pore structure, density and pore size distribution of the materials. Characterization of the chars, at various stages of pyrolysis and partial oxidation, employed widely varying techniques such as mercury intrusion, gas sorption, helium pycnometry, wide and small-angle scattering and nuclear magnetic resonance. Upon characterization, the influence of the physical factors on the combustion behavior was accounted for and the intrinsic reaction rates of the chars were correlated with their chemical nature. The mechanisms of pore coarsening, opening of pore restrictions and development of a large accessible pore surface area in the interior of the particles, in conjunction to the kinetics of structural ordering and graphitization, have been shown to influence critically the reactivity of chars. furthermore, experiments with calcium treated chars revealed that the catalytic effect of mineral matter on enhancing the combustion rate is very important.
", "doi": "10.7907/FQBH-BT69", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:4427", "collection": "thesis", "collection_id": "4427", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11062007-104408", "type": "thesis", "title": "Host-Plasmid Interactions and Regulation of Cloned Gene Expression in Recombinant Cells", "author": [ { "family_name": "Da Silva", "given_name": "Nancy Anderson", "clpid": "Da-Silva-Nancy-Anderson" } ], "thesis_advisor": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Campbell", "given_name": "Judith L.", "clpid": "Campbell-J-L" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Lidstrom", "given_name": "Mary E.", "clpid": "Lidstrom-M-E" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Host-plasmid interactions and the regulation of cloned gene expression have been studied in recombinant cells, primarily Saccharomyces cerevisiae. The plasmids employed contain the inducible yeast GAL1, GAL10, or hybrid GAL10-CYC1 promoter cloned upstream of the Escherichia coli lacZ gene (for \u03b2-galactosidase). The promoters are controlled by the galactose regulatory circuit, and the yeast strains contain a reg1 mutation which interferes with catabolite repression. Therefore, cloned lacZ gene expression could be induced by galactose addition to glucose-containing medium. Batch and continuous fermentations were performed to study the effects of cloned gene product synthesis on the host cell, and to determine the important factors influencing the kinetics of growth, induction, and cloned gene product formation.
\r\n\r\nThe inducer (galactose) level had a strong influence on cloned lacZ gene expression. In batch culture, the initial specific rate of \u03b2-galactosidase synthesis increased with galactose concentration. A galactose concentration of 0.4% (in 0.4% glucose medium) was sufficient for high levels of expression that were approximately proportional to plasmid number (to an average plasmid number of at least 10). The relative galactose level, or galactose/glucose ratio, was also important, and cloned gene expression increased as this ratio increased.
\r\n\r\nPlasmid stability and promoter strength were also important factors. \u03b2-galactosidase production from an ARS1 plasmid was an order of magnitude lower than for the same plasmid with the 2\u00b5 origin. The effects of promoter strength were studied in both batch and continuous fermentations. Although at the expense of a growth rate reduction of 16%, the rate of expression from the stronger GAL1 promoter in batch culture was 3-5 times higher than for the GAL10 or GAL10-CYC1 promoters. In continuous culture, steady-state, \u03b2-galactosidase specific activity with the GAL1 promoter was 2-4 times greater than that for the GAL10-CYC1 promoter. Despite lower plasmid stability (72% versus 86%) and lower biomass concentration (0.98 versus 1.2 g/L), productivity was approximately 3 times higher with the stronger GAL1 promoter system.
\r\n\r\nCarbon-limited continuous fermentations were utilized to study the effects of dilution rate and induction of cloned gene expression on the recombinant system. Selection for faster growing cells, and the concentrations of glucose and galactose, were important in determining chemostat dynamics. For the GAL10-CYC1 promoter system, biomass concentration and \u03b2-galactosidase specific activity increased with decreasing dilution rate. The biomass trend is apparently due to the growth efficiency obtained at the various dilution rates, and the utilization of the inducer as an additional carbon source. Plasmid stability dropped after induction of lacZ gene expression and decreased with decreasing dilution rate. Despite lower plasmid stability and flow rate, overall productivity (activity/L/hr) was substantially higher at low dilution rate.
\r\n\r\nA temperature-sensitive (ts) strain of S. cerevisiae was constructed and characterized. In this strain, cloned lacZ gene expression can be induced by either a temperature-shift (T-shift) from 30\u00b0C to 35\u00b0C or by galactose addition. In batch culture at 35\u00b0C, cloned gene expression induced by T-shift was comparable or better than that observed for galactose induction under the same conditions. Higher levels were observed, however, for galactose induction at the preferred temperature of 30\u00b0C. At either temperature, the best levels of \u03b2-galactosidase synthesis were obtained for the ts strain in galactose-containing medium.
\r\n\r\nTheoretical yield factors have been estimated for recombinant cells to investigate the effect of plasmid-directed synthesis on metabolic stoichiometry. The analysis is based upon detailed accounting of ATP utilization for nutrient uptake and biosynthesis. The microorganism considered was E. coli; however, the method can be extended to other organisms for which metabolic ATP requirements can be reasonably estimated.
", "doi": "10.7907/pze3-dp83", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:2592", "collection": "thesis", "collection_id": "2592", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06142006-135258", "type": "thesis", "title": "A Theoretical Study of Reaction and Diffusion in Microstructured Materials", "author": [ { "family_name": "Loewenberg", "given_name": "Michael", "clpid": "Loewenberg-Michael" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Brady", "given_name": "John F.", "clpid": "Brady-J-F" }, { "family_name": "Leal", "given_name": "L. Gary", "clpid": "Leal-L-G" }, { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "A fundamental study of heterogeneous reaction and diffusion in random, microstructured materials has been conducted. A detailed, ensemble averaging approach has been developed for the analysis of diffusion-controlled reactions. The method was used to determine the reactant flux into a bounded or semi-infinite medium containing a dilute suspension of reactive, spherical particles under steady-state or transient conditions. The influence of the boundary was given explicit, detailed consideration and the results were compared with a mean-field treatment. Physical motivation is provided by the process of ash vaporization during pulverized coal combustion. The analysis was subsequently extended to study the decay of an initially uniform distribution of reactant which allows comparison with other theoretical approaches. The result suggests that the present method reproduces the solution to this well-known problem by a seemingly simpler, more physical approach. The configurational averaging technique was employed in a study of heterogeneous reaction in a porous material under diffusion-controlled conditions. The porous solid is assumed to have a bimodal pore structure with a random, isotropic distribution of cylindrical macro-pores. The results are relevant to the pulverized combustion of char from softening coals. In the diffusion-controlled limit, the results coincide with a simpler, single pore model.
\r\n\r\nA simplified model of char combustion has been developed which treats pore diffusion and growth coupled to gas-phase heat and mass transport. An efficient model-based algorithm was developed for the determination of oxidation rates from combustion data. These models were applied in two studies involving well-defined laboratory combustion experiments.
\r\n", "doi": "10.7907/5tgx-2d57", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:1626", "collection": "thesis", "collection_id": "1626", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05052006-082025", "primary_object_url": { "basename": "Edelstein_s_1987.pdf", "content": "final", "filesize": 5571003, "license": "other", "mime_type": "application/pdf", "url": "/1626/1/Edelstein_s_1987.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Adsorption of Sulphur Dioxide and Reduction of Sulphate on Alumina and Alkali-Alumina at High Temperatures", "author": [ { "family_name": "Edelstein", "given_name": "Sergio", "clpid": "Edelstein-Sergio" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Several interrelated problems in connection with the treatment of sulfur dioxide at temperatures between 700 and 800\u00b0C were studied. The interaction of SO2 with Al2O3 was studied experimentally using B.E.T., thermogravimetry and temperature-programmed desorption. Adsorption takes place through a wide range of binding energies, with some SO2 adsorbing irreversibly at temperatures below 800\u00b0C. The amount adsorbed depends on the surface history and thermal treatment. An adsorption isotherm based on a bimodal energy distribution provides an adequate description of the equilibrium process.
\r\n\r\nThe chemical composition, sulfation and regeneration of an alkali-alumina sorbent for sulfur dioxide were studied using thermogravimetry, gas chromatography, and X-ray photoelectron spectroscopy. The active sorbent consists of a thin layer of sodium and lithium aluminates supported on alumina. The rate of sulfation is proportional to the SO2 concentration in the gas, up to [SO2] \u2248 5000 ppm. The activation energy of the sulfation is E = 21.6 kcal/mole. The sulfated sorbent was regenerated by reduction with CO at 700-800\u00b0C. Sulfur removal from the sorbent and distribution of gaseous products were measured at different alkali loadings, temperatures and CO concentrations. The reduction takes place in two consecutive stages through a complex reaction network in which the alumina support plays a decisive role, both as a reactant and as a catalyst. A simplified reaction network is used as a basis for a kinetic model that provides an adequate description of the reduction process at moderate sorbent loadings.
", "doi": "10.7907/4CFM-WQ54", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:829", "collection": "thesis", "collection_id": "829", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03012008-135126", "primary_object_url": { "basename": "Lee_t_1987.pdf", "content": "final", "filesize": 5834334, "license": "other", "mime_type": "application/pdf", "url": "/829/1/Lee_t_1987.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Estimation of Petroleum Reservoir Properties", "author": [ { "family_name": "Lee", "given_name": "Tai-yong", "clpid": "Lee-Tai-yong" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" }, { "family_name": "Chen", "given_name": "Wen H.", "clpid": "Chen-Wen-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Numerical algorithms are developed to estimate petroleum reservoir properties such as absolute permeability, porosity, and relative permeabilities based on the noisy pressure and flow data. Regularization and spline approximation of spatially varying parameters are employed to convert the ill-posed nature of the problem to a well-posed one. A stabilizing functional with gradient operator is used to measure the non-smoothness of the parameter estimates. The number of spline coefficients along each spatial direction is chosen to be as much as the number of meshes for the reservoir PDE's. New history matching algorithms are developed that determine the regularization parameter during the computation without requiring a priori information and improve the parameter estimates stepwise. A partial conjugate gradient method is employed for the estimation of a single set of parameters, and the steepest descent algorithm is used for the simultaneous estimation of absolute and relative permeabilities. A rough parametric sensitivity analysis is carried out for the simultaneous estimation to improve the convergence. Numerical tests are carried out to estimate the parameters in single- and two-phase reservoirs for the different choices of the stabilizing functionals, the regularization parameters, and the degrees of spline approximation; and the effects of the observation error, the observation time, and the configuration of the observation points are investigated. The results show that the new algorithms generate better parameter estimates over the various possible choices of the estimation conditions.
", "doi": "10.7907/gs7z-gy70", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:4425", "collection": "thesis", "collection_id": "4425", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11062007-092509", "type": "thesis", "title": "Response and Failure of Fluid-Filled Tanks under Base Excitation", "author": [ { "family_name": "Natsiavas", "given_name": "Sotirios", "clpid": "Natsiavas-Sotirios" } ], "thesis_advisor": [ { "family_name": "Babcock", "given_name": "Charles D.", "clpid": "Babcock-C-D" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" }, { "family_name": "Babcock", "given_name": "Charles D.", "clpid": "Babcock-C-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "An analytical model is developed that leads to better understanding of the response of fluid-filled tanks whose bottom may separate from and lift off the foundation, during base excitation. First, the hydrodynamic problem is solved in closed form, for the most general motion of the structure. This eliminates the fluid response unknowns and therefore only the structural degrees-of-freedom need to be considered. Then, application of Hamilton's Principle in the structural domain sets up the system equations of motion. During this procedure, the uplifting behavior is modeled by an appropriate rotational spring, placed between the foundation and the bottom of the tank. Equivalent springs are also used for modeling the ground/structure interaction. Moreover, shell flexibility and liquid sloshing effects are also incorporated and investigated.
\r\n\r\nUsing this model, results are obtained and compared with experimental data. This comparison reveals some interesting effects of the base uplift on the system response. Ground flexibility is found to reduce the effective beam-type stiffness of the structure, but this reduction is much smaller than the substantial stiffness reduction induced by the possibility of uplifting. For the cases examined, the stiffness reduction due to the base uplift changes dramatically the dynamics of the system, which in turn alters the developed hydrodynamic loads, through the fluid/structure coupling process. Also, the shell flexibility effects - which can be important for the anchored tank case - are found to be negligible for an unanchored tank. Knowledge of the structural response leads to direct calculation of the hydrodynamic loads and consequently to prediction of failure. Buckling phenomena observed experimentally at the top and the bottom of scale model tanks are studied and explained.
\r\n", "doi": "10.7907/CNWT-V417", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:885", "collection": "thesis", "collection_id": "885", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03052008-111804", "primary_object_url": { "basename": "Grader_gs_1987.pdf", "content": "final", "filesize": 7213605, "license": "other", "mime_type": "application/pdf", "url": "/885/1/Grader_gs_1987.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Fourier Transform Infrared Spectroscopy of a Single Aerosol Particle", "author": [ { "family_name": "Sageev Grader", "given_name": "Gideon", "clpid": "Sageev-Grader-Gideon" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Baldeschwieler", "given_name": "John D.", "clpid": "Baldeschwieler-J-D" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Throughout this thesis, the phenomenon of radiation-induced particle size change is studied both on a theoretical as well as experimental level. The thrust of this study is aimed at using the size changes due to heat absorption to develop a technique for obtaining the particle chemical composition.
\r\n\r\nThe experiments here involve charged particles, generated with an impulse jet, and trapped by the electric field of an electrodynamic balance. The particles under study are all aqueous solutions of non-volatile salts, where upon heating a partial evaporation of water occurs. The evaporation and subsequent condensation processes are modeled in both the continuum and the transition regimes. The models developed are tested and the agreement between theory and experimental results is demonstrated. The models are also used to extract the values of the water, thermal, and mass accommodation coefficients from the data. The results for the thermal accommodation show that its value is near unity, however the corresponding results for the mass accommodation are not conclusive.
\r\n\r\nA method is developed for obtaining the molecular composition of a single suspended microparticle by Fourier transform infrared spectroscopy. The particle is irradiated simultaneously by the infrared output from a Michelson interferometer and the visible light from a dye laser. The laser is tuned to an edge of an optical resonance of the particle while the IR beam is chopped. Through evaporation and condensation the chopped IR beam causes a size modulation of the droplet, which in turn induces a fluctuation in the laser light scattered from the particle. The scattered light is detected at 90\u00b0 with a photomultiplier, and the amplitude of the light fluctuation is measured with a lock-in amplifier. The lock-in signal is then inverted by a discrete fast Fourier transform routine (FFT), to yield the particle absorption spectrum. Spectra of (NH4)2SO4 droplets at different solute concentrations are presented.
\r\n", "doi": "10.7907/de8x-sp79", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:870", "collection": "thesis", "collection_id": "870", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03042008-094030", "primary_object_url": { "basename": "O'Connor_kc_1987.pdf", "content": "final", "filesize": 5577339, "license": "other", "mime_type": "application/pdf", "url": "/870/1/O'Connor_kc_1987.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The Effects of Immobilization on Structure and Substrate Activation of Glutamate Dehydrogenase", "author": [ { "family_name": "O'Connor", "given_name": "Kim Claire", "clpid": "O'Connor-Kim-Claire" } ], "thesis_advisor": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Arnold", "given_name": "Frances Hamilton", "orcid": "0000-0002-4027-364X", "clpid": "Arnold-F-H" }, { "family_name": "Chan", "given_name": "Sunney I.", "orcid": "0000-0002-5348-2723", "clpid": "Chan-S-I" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Structure and substrate activation of bovine liver glutamate dehydrogenase were investigated when the enzyme was in its native state or was covalently bound via primary amino groups to a solid Sepharose bead. In this research, the enzyme was covalently bound directly to CNBr-activated Sepharose 4B or indirectly, via a six-carbon spacer arm, to CH-activated Sepharose 4B. Electron spin resonance spectroscopy was employed to study structure. This study required spin labeling glutamate dehydrogenase with either 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl or 4((4-(chloromercurio)benzoyl)amino)-2,2,6,6-tetramethyl-1-piperidinyloxy. Substrate activation of the deamination of glutamate by NAD was visible in Lineweaver-Burk plots of inverse rate vs. inverse substrate concentration.
\r\n\r\nThe electron spin resonance spectrum of glutamate dehydrogenase spin labeled with 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl was a composite consisting primarily of two populations of spin labels with outer peak separations of 33 gauss (population A) and 69 gauss (population B). For the native enzyme in solution, population A accounted for 10% of the spectrum. This percentage increased to 21 when the active site was saturated with substrates during spin labeling and increased to 34 when the enzyme was immobilized to either CNBror CH-activated Sepharose. The roles of aspecific labeling and structural heterogeneity in these spectral changes were discussed. Modification of the native and immobilized enzyme with pyridoxal 5'-phosphate characterized the binding site(s) for the spin label. Deconvolution of experimental spectra into populations A and B divulged a subpopulation of labels with a mobility unlike those of the two principal components. Linear combinations of the deconvoluted line shapes for populations A and B successfully represented all spectra of glutamate dehydrogenase from this and previous investigations.
\r\n\r\nConformational change in glutamate dehydrogenase was investigated by spin labeling the enzyme at cysteine 319 with 4((4-(chloromercurio)benzoyl)-amino)-2,2,6,6-tetramethyl-1-piperidinyloxy. Electron spin resonance spectra of spin-labeled glutamate dehydrogenase showed that immobilization of the enzyme on CNBr-activated Sepharose 4B suppressed conformational change induced by GTP and NADPH and profoundly altered that induced by aketoglutarate. Moreover, the spectrum of the immobilized enzyme provides evidence for structural heterogeneity at cysteine 319.
\r\n\r\nCovalently binding glutamate dehydrogenase to CNBr- and CH-activated Sepharose 4B altered the substrate activation pattern of the biocatalyst. Specifically, the sharp discontinuity, which characterizes Lineweaver-Burk plots of free enzyme kinetics with NAD as the varied substrate, became elongated when the biocatalyst was attached to either support. The elongated transition region contains two inflection points and resembles substrate activation of several other allosteric oligomers. Under the same experimental conditions, glutamate induced varying degrees of abrupt activation in immobilized glutamate dehydrogenase and inhibited the enzyme in solution. The intensity of this activation is inversely proportional to the rate constant of the biocatalyst-Sepharose conugate. These modified activation patterns may be due in part to increased structural heterogeneity and altered conformational change. The above kinetic results are free of mass transport effects: the external effectiveness factor was unity, the observable Thiele modulus was less than 2.0 \u2022 10-4, and reaction- generated pH change was less than 0.01 for all data reported in this paper.
\r\n", "doi": "10.7907/qavk-kj50", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:870", "collection": "thesis", "collection_id": "870", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03042008-094030", "primary_object_url": { "basename": "O'Connor_kc_1987.pdf", "content": "final", "filesize": 5577339, "license": "other", "mime_type": "application/pdf", "url": "/870/1/O'Connor_kc_1987.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The Effects of Immobilization on Structure and Substrate Activation of Glutamate Dehydrogenase", "author": [ { "family_name": "O'Connor", "given_name": "Kim Claire", "clpid": "O'Connor-Kim-Claire" } ], "thesis_advisor": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Arnold", "given_name": "Frances Hamilton", "orcid": "0000-0002-4027-364X", "clpid": "Arnold-F-H" }, { "family_name": "Chan", "given_name": "Sunney I.", "orcid": "0000-0002-5348-2723", "clpid": "Chan-S-I" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Structure and substrate activation of bovine liver glutamate dehydrogenase were investigated when the enzyme was in its native state or was covalently bound via primary amino groups to a solid Sepharose bead. In this research, the enzyme was covalently bound directly to CNBr-activated Sepharose 4B or indirectly, via a six-carbon spacer arm, to CH-activated Sepharose 4B. Electron spin resonance spectroscopy was employed to study structure. This study required spin labeling glutamate dehydrogenase with either 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl or 4((4-(chloromercurio)benzoyl)amino)-2,2,6,6-tetramethyl-1-piperidinyloxy. Substrate activation of the deamination of glutamate by NAD was visible in Lineweaver-Burk plots of inverse rate vs. inverse substrate concentration.
\r\n\r\nThe electron spin resonance spectrum of glutamate dehydrogenase spin labeled with 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl was a composite consisting primarily of two populations of spin labels with outer peak separations of 33 gauss (population A) and 69 gauss (population B). For the native enzyme in solution, population A accounted for 10% of the spectrum. This percentage increased to 21 when the active site was saturated with substrates during spin labeling and increased to 34 when the enzyme was immobilized to either CNBror CH-activated Sepharose. The roles of aspecific labeling and structural heterogeneity in these spectral changes were discussed. Modification of the native and immobilized enzyme with pyridoxal 5'-phosphate characterized the binding site(s) for the spin label. Deconvolution of experimental spectra into populations A and B divulged a subpopulation of labels with a mobility unlike those of the two principal components. Linear combinations of the deconvoluted line shapes for populations A and B successfully represented all spectra of glutamate dehydrogenase from this and previous investigations.
\r\n\r\nConformational change in glutamate dehydrogenase was investigated by spin labeling the enzyme at cysteine 319 with 4((4-(chloromercurio)benzoyl)-amino)-2,2,6,6-tetramethyl-1-piperidinyloxy. Electron spin resonance spectra of spin-labeled glutamate dehydrogenase showed that immobilization of the enzyme on CNBr-activated Sepharose 4B suppressed conformational change induced by GTP and NADPH and profoundly altered that induced by aketoglutarate. Moreover, the spectrum of the immobilized enzyme provides evidence for structural heterogeneity at cysteine 319.
\r\n\r\nCovalently binding glutamate dehydrogenase to CNBr- and CH-activated Sepharose 4B altered the substrate activation pattern of the biocatalyst. Specifically, the sharp discontinuity, which characterizes Lineweaver-Burk plots of free enzyme kinetics with NAD as the varied substrate, became elongated when the biocatalyst was attached to either support. The elongated transition region contains two inflection points and resembles substrate activation of several other allosteric oligomers. Under the same experimental conditions, glutamate induced varying degrees of abrupt activation in immobilized glutamate dehydrogenase and inhibited the enzyme in solution. The intensity of this activation is inversely proportional to the rate constant of the biocatalyst-Sepharose conugate. These modified activation patterns may be due in part to increased structural heterogeneity and altered conformational change. The above kinetic results are free of mass transport effects: the external effectiveness factor was unity, the observable Thiele modulus was less than 2.0 \u2022 10-4, and reaction- generated pH change was less than 0.01 for all data reported in this paper.
\r\n", "doi": "10.7907/qavk-kj50", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:1049", "collection": "thesis", "collection_id": "1049", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03212008-092922", "primary_object_url": { "basename": "Mandler_ja_1987.pdf", "content": "final", "filesize": 22500905, "license": "other", "mime_type": "application/pdf", "url": "/1049/1/Mandler_ja_1987.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Robust Control System Design for a Fixed-Bed Catalytic Reactor", "author": [ { "family_name": "Mandler", "given_name": "Jorge Anibal", "clpid": "Mandler-Jorge-Anibal" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" }, { "family_name": "Doyle", "given_name": "John Comstock", "clpid": "Doyle-J-C" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The design of control systems in the face of model uncertainty is addressed. A methodology for the design of robust control schemes is outlined, which employs the Structured Singular Value as an analysis tool and Internal Model Control as the synthesis framework. This methodology is applied to the design of control systems for a fixed-bed, laboratory, catalytic methanation reactor. The design procedure allows a clear insight on the fundamental limits to closed-loop performance and provides controllers with explicit stability and performance guarantees for the case of plant-model mismatch.
\r\n\r\nThe overall controller design effort is initiated with a careful mathematical modeling of the system. The original nonlinear partial differential equations are converted through collocation techniques into a nonlinear ordinary-differential/algebraic equation system amenable to dynamic simulation. Interactive software is developed for the open- and closed-loop simulation of general nonlinear differential-algebraic systems, which provides an efficient means to simulate the reactor model. Linearization and control-relevant model reduction techniques are applied to arrive at models appropriate for the control studies.
\r\n\r\nBoth the single-input single-output and the multivariable case are addressed. Three different control configurations are investigated in the context of the single- pass operation of the reactor. In each case-study presented, the controller design procedure is divided into four steps: first, the definition of the control objectives, which not only leads to the selection of the appropriate control configuration but also determines the most adequate design techniques to employ; second, a nominal design step, in which the system-inherent limitations to the closed-loop performance are highlighted; third, a characterization of the uncertainty and the use of this information in the design of robust controllers; and, fourth, the evaluation of the designs through nonlinear simulations.
\r\n\r\nThe thesis describes the first application of structured singular value-based analysis techniques to a chemical reactor system and is in essence the first comprehensive study of the application of robust control to fixed-bed reactors. The power of the new mathematical theory for robust control system design is demonstrated. It is shown that the design of control systems for complex, distributed systems such as the methanation reactor can be addressed in a practical way, and low-order controllers be adequately obtained, which possess near-optimal characteristics when applied in a realistic environment of uncertainty and unavailability of measurements.
\r\n", "doi": "10.7907/czeb-7c12", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:2584", "collection": "thesis", "collection_id": "2584", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06142006-100902", "type": "thesis", "title": "Interactions of Ammonia with Platinum and Ruthenium Surfaces", "author": [ { "family_name": "Tsai", "given_name": "Wilman", "clpid": "Tsai-Wilman" } ], "thesis_advisor": [ { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" }, { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Specific reaction rates (cm-2-s-1) of the catalytic decomposition of ammonia, the isotopic exchange between ammonia and deuterium, and the inhibition of the decomposition of ammonia by hydrogen (with ammonia to hydrogen partial pressure ratios varying from 1:1 to 1:4) on a polycrystalline platinum wire have been measured in a continuous stirred tank microreactor at pressures between 5 x 10-7 and 0.6 Torr and temperatures between 400 and 1200 K. At relatively low temperatures and/or high pressures, nitrogen adatoms are the dominant surface species, and the recombinative desorption of nitrogen controls the rate of decomposition of ammonia. At relatively high temperatures and/or low pressures, the surface coverage of all species is low, and a competition between the desorption of molecular ammonia and the cleavage of an N-H bond of molecularly adsorbed ammonia controls the rate of reaction. The kinetics of decomposition of ammonia as well as the results for the NH3 + D2 exchange reaction are described quantitatively by a mechanistic model employing independently measured adsorption-desorption parameters of NH3 and H2, and desorption parameters of N2. The model was extended to incorporate the nitrogen coverage-dependence of the rate coefficient of hydrogen desorption to describe the inhibition of the decomposition by hydrogen. The hydrogenation of NH2(a) to produce molecularly adsorbed ammonia is predicted to be the dominant factor in the inhibition of the decomposition of ammonia.
\r\n\r\nThe kinetics of adsorption and desorption of deuterium have been studied on Pt(110)-(1x2) surfaces on which various fractional coverages of nitrogen adatoms were deposited via the decomposition of ammonia at 400 K. Nitrogen selectively blocks the high temperature \u03b22-state of deuterium prior to poisoning the low temperature \u03b21-state. No evidence of a 'long-range' electronic perturbation of the surface by the nitrogen adatoms was found. The adsorption kinetics of deuterium on both clean and nitrogen-precovered Pt(110)-(1x2) surfaces were Langmuirian. Nitrogen modifies the preexponential factor and the activation energy of desorption of deuterium on Pt(110)-(1x2) by essentially rescaling the effective coverage of the deuterium. The results are consistent with findings from previous studies of the inhibition of the decomposition of ammonia by hydrogen on polycrystalline platinum.
\r\n\r\nSteady-state specific reaction rates have also been measured for the catalytic decomposition of ammonia on a Ru(001) surface at pressures of 10-6 and 2 x 10-6 Torr and temperatures between approximately 500 and 1250 K. Qualitatively, the kinetics are similar to those observed for ammonia decomposition on the polycrystalline platinum surface. Based on thermal desorption measurements during the steady-state decomposition of ammonia at 2 x 10-6 Torr, nitrogen adatoms are the dominant surface species, and the recombinative desorption of nitrogen is the major (and probably the only) elementary reaction that produces molecular nitrogen. The mechanistic model developed previously describes accurately the pressure and temperature dependence of both the decomposition kinetics and the measured steady-state coverage of nitrogen adatoms.
\r\n\r\nThe isotopic exchange reaction between 15NH3 and deuter m at steady-state has been studied on Ru(001) for a partial pressure ratio of ammonia to deuterium of 4:1 with a total pressure of 2.5 x 10-6 Torr at temperatures between 380 and 720 K. All three exchange products were observed, and a dissociative exchange mechanism was found to describe quantitatively the experimental data. This mechanistic model is discussed in terms of a potential energy diagram that describes the catalytic decomposition (or synthesis) of ammonia on Ru(001). The energy levels of and the activation barriers separating the chemisorbed intermediates in the ammonia decomposition and synthesis reactions, namely, NH3, NH2+H, NH+2H, N+3H are determined, and the dissociative chemisorption of molecular nitrogen on Ru(001) is found to be activated with an activation energy estimated to be approximately 5 kcal-mol-1 in the limit of zero surface coverage of nitrogen adatoms. Direct comparsion between the estimated barrier for the dissociative adsorption of nitrogen on polycrystalline platinum and Ru(001) surfaces indicates clearly that ruthenium is a superior catalyst to platinum for the synthesis of ammonia.
", "doi": "10.7907/4Y3N-2321", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:1633", "collection": "thesis", "collection_id": "1633", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05052006-140832", "type": "thesis", "title": "A Methodology for the Synthesis of Robust Control Systems for Multivariable Sampled-Data Processes", "author": [ { "family_name": "Zafiriou", "given_name": "Evanghelos", "clpid": "Zafiriou-Evanghelos" } ], "thesis_advisor": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" } ], "thesis_committee": [ { "family_name": "Morari", "given_name": "Manfred", "clpid": "Morari-M" }, { "family_name": "Caughey", "given_name": "Thomas Kirk", "clpid": "Caughey-T-K" }, { "family_name": "Doyle", "given_name": "John Comstock", "clpid": "Doyle-J-C" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The problem of the synthesis of multivariable controllers which are robust with respect to model-plant mismatch is addressed. A two-step design procedure based on the Internal Model Control (IMC) structure is used. In the first step the IMC controller is designed assuming no modeling error, and in the second step the IMC filter is designed to preserve the closed-loop characteristics in spite of model-plant mismatch.
\r\n\r\nTwo alternatives are provided for the first step. One of them allows the designer to satisfy structural performance specifications, in terms of the structure of the closed-loop interactions, their magnitude and duration. The closed-loop transfer function matrix is directly designed. The method requires only standard linear algebra operations and includes the construction of the IMC or the feedback controller in state-space. The second approach involves the minimization of the appropriately weighted H2-norm of the sensitivity transfer function matrix, that relates the errors to the external inputs (setpoints or disturbances). A method is given for the meaningful selection of a full matrix weight so that the H2-error is minimized for a set of external input directions and their linear combinations. The procedure is extended to open-loop unstable systems. In both approaches, special care is taken to avoid intersample rippling.
\r\n\r\nThe design of the filter in the second step is formulated as an optimization problem over the filter parameters. The objective function is constructed by using the Structured Singular Value theory so that the maximum singular value of the sensitivity transfer function remains bounded in spite of modeling error. The selection of the frequency bound is based on the properties of the design that was obtained in the first step. Analytic gradient expressions have been developed for the objective function. The optimization problem is an unconstrained one, solved with standard gradient search techniques. An iterative method for the selection of the appropriate sampling time is proposed, which explicitly takes into account model uncertainty information and performance specifications.
\r\n", "doi": "10.7907/m08p-9102", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:1019", "collection": "thesis", "collection_id": "1019", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03192008-120209", "primary_object_url": { "basename": "Grosz_r_1987.pdf", "content": "final", "filesize": 12672225, "license": "other", "mime_type": "application/pdf", "url": "/1019/1/Grosz_r_1987.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Biochemical and Mathematical Modeling of Microaerobic Continuous Ethanol Production by Saccharomyces cerevisiae", "author": [ { "family_name": "Grosz", "given_name": "Ron", "clpid": "Grosz-Ron" } ], "thesis_advisor": [ { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" }, { "family_name": "Hoffman", "given_name": "Allan S.", "clpid": "Hoffman-A-S" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The effect of the aeration intensity in the vicinity of 1Oppb of dissolved oxygen upon the steady state, continuous ethanol production by Saccharomyces cerevisiae is explored. The specific ethanol productivity increased by 30 to 50% as the aeration rate was reduced, but decreased to the original level as the aeration was further reduced to the lowest rates. These metabolic changes occurred when the respiration rate contributed negligibly to ATP energy production, excluding the Pasteur mechanism, and when the residual glucose level saturated the glucose transporter, excluding glucose kinetics as the cause.
\r\n\r\nTo expose the mechanism of the metabolic changes, the intracellular concentrations of ethanol, glycerol, ATP, glucose 6-phosphate, pyruvate, and NADH, the activities of the hexokinase, alcohol dehydrogenase, fumarase, and isocitrate dehydrogenase, and the cell viability were assayed. Rate-limiting steps were identified by the accumulation of upstream and the depletion of downstream metabolites. The enzyme activity and cofactor measurements elucidated the causes of the rate limitation.
\r\n\r\nBased on the assays, the metabolic acceleration with decreasing aeration was the result of an increasing glucose transporter activity, and ATP was the most likely activator. The reversal at yet lower aerations resulted from the continued accumulation of ATP until the downstream glycolytic kinases were inhibited.
\r\n\r\nHigh concentrations of silicone polymer antifoam decreased the resistance to glycerol transport across the cell membrane, enhancing glycerol production at the expense of ethanol production. Such cultures attained lower ATP concentrations.
\r\n\r\nThe biomass concentration in the fermentor was occasionally found to undergo hysteresis, characterized by extinction and ignition as critical aeration rates were passed. Hysteresis and associated phenomena were prevented by the addition of yeast extract and the removal of the antifoam from the medium. The higher ATP concentration of the low antifoam culture and the biosynthetic intermediates of yeast extract must participate in this transition.
\r\n\r\nMathematical models account for all observed phenomena. Featured by the model are the ATP activation of the glucose transporter, ATP wastage by ATPases and such processes, and oxygen induction of ATP waste reactions. Singularity theory was invoked to account for the transition from the hysteresis to monotonic biomass versus aeration bifurcation diagrams.
", "doi": "10.7907/29dc-ay81", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:1016", "collection": "thesis", "collection_id": "1016", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03192008-095816", "primary_object_url": { "basename": "Rollins_dk_1986.pdf", "content": "final", "filesize": 3011396, "license": "other", "mime_type": "application/pdf", "url": "/1016/1/Rollins_dk_1986.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Diffusion with Varying Drag; the Runaway Problem", "author": [ { "family_name": "Rollins", "given_name": "David Kenneth", "clpid": "Rollins-David-Kenneth" } ], "thesis_advisor": [ { "family_name": "Corngold", "given_name": "Noel Robert", "clpid": "Corngold-N-R" } ], "thesis_committee": [ { "family_name": "Corngold", "given_name": "Noel Robert", "clpid": "Corngold-N-R" }, { "family_name": "Lorenz", "given_name": "Jens", "clpid": "Lorenz-Jens" }, { "family_name": "Meiron", "given_name": "Daniel I.", "orcid": "0000-0003-0397-3775", "clpid": "Meiron-D-I" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "We study the motion of electrons in an ionized plasma of electrons and ions in an external electric field. A probability distribution function describes the electron motion and is a solution of a Fokker-Planck equation. In zero field, the solution approaches an equilibrium Maxwellian. For arbitrarily small field, electrons overcome the diffusive effects and are freely accelerated by the field. This is the electron runaway phenomenon.
\r\n\r\nWe treat the electric field as a small perturbation. We consider various diffusion coefficients for the one-dimensional problem and determine the runaway current as a function of the field strength. Diffusion coefficients, non-zero on a finite interval are examined. Some non-trivial cases of these can be solved exactly in terms of known special functions. The more realistic case where the diffusion coefficient decays with velocity is then considered. To determine the runaway current, the equivalent Schr\u00f6dinger eigenvalue problem is analyzed. The smallest eigenvalue is shown to be equal to the runaway current. Using asymptotic matching a solution can be constructed which is then used to evaluate the runaway current. The runaway current is exponentially small as a function of field strength. This method is used to extract results from the three-dimensional problem.
", "doi": "10.7907/mwvx-6b36", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:1016", "collection": "thesis", "collection_id": "1016", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03192008-095816", "primary_object_url": { "basename": "Rollins_dk_1986.pdf", "content": "final", "filesize": 3011396, "license": "other", "mime_type": "application/pdf", "url": "/1016/1/Rollins_dk_1986.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Diffusion with Varying Drag; the Runaway Problem", "author": [ { "family_name": "Rollins", "given_name": "David Kenneth", "clpid": "Rollins-David-Kenneth" } ], "thesis_advisor": [ { "family_name": "Corngold", "given_name": "Noel Robert", "clpid": "Corngold-N-R" } ], "thesis_committee": [ { "family_name": "Corngold", "given_name": "Noel Robert", "clpid": "Corngold-N-R" }, { "family_name": "Lorenz", "given_name": "Jens", "clpid": "Lorenz-Jens" }, { "family_name": "Meiron", "given_name": "Daniel I.", "orcid": "0000-0003-0397-3775", "clpid": "Meiron-D-I" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "We study the motion of electrons in an ionized plasma of electrons and ions in an external electric field. A probability distribution function describes the electron motion and is a solution of a Fokker-Planck equation. In zero field, the solution approaches an equilibrium Maxwellian. For arbitrarily small field, electrons overcome the diffusive effects and are freely accelerated by the field. This is the electron runaway phenomenon.
\r\n\r\nWe treat the electric field as a small perturbation. We consider various diffusion coefficients for the one-dimensional problem and determine the runaway current as a function of the field strength. Diffusion coefficients, non-zero on a finite interval are examined. Some non-trivial cases of these can be solved exactly in terms of known special functions. The more realistic case where the diffusion coefficient decays with velocity is then considered. To determine the runaway current, the equivalent Schr\u00f6dinger eigenvalue problem is analyzed. The smallest eigenvalue is shown to be equal to the runaway current. Using asymptotic matching a solution can be constructed which is then used to evaluate the runaway current. The runaway current is exponentially small as a function of field strength. This method is used to extract results from the three-dimensional problem.
", "doi": "10.7907/mwvx-6b36", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:918", "collection": "thesis", "collection_id": "918", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03102008-104251", "primary_object_url": { "basename": "Seo_jh_1986.pdf", "content": "final", "filesize": 4192860, "license": "other", "mime_type": "application/pdf", "url": "/918/1/Seo_jh_1986.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Investigations of Plasmid-Host Cell Interactions in Recombinant Escherichia coli Populations", "author": [ { "family_name": "Seo", "given_name": "Jin-Ho", "orcid": "0000-0002-4206-6046", "clpid": "Seo-Jin-Ho" } ], "thesis_advisor": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Campbell", "given_name": "Judith L.", "orcid": "0000-0001-8291-5551", "clpid": "Campbell-J-L" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Plasmid-host cell interactions have been characterized experimentally for recombinant Escherichia coli populations. The plasmids used contain pMB1 replication origins and propagate in E. coli at different copy number levels ranging from 12 to 408. Host E. coli HB101 strains transformed with those plasmids were used throughout this research.
\r\n\r\nThe specific growth rate and amount of cloned-gene product (\u03b2-lactamase) were determined in batch cultivations as a function of plasmid copy number. Maximum specific growth rates in LB and M9 media were reduced monotonically for increasing plasmid content per cell. The maximum specific growth rate for a recombinant strain with copy number 408 was reduced by 25% relative to the plasmid-free strain. The ratio of \u03b2-lactamase specific activity to plasmid content, as a measure of the overall efficiency of plasmid-gene expression, declines by a factor of 7 as the copy number increases from 12 to 408. The relationship between copy number and cloned-gene product activity can be reasonably approximated by a parabolic equation, with approximately linear proportionality for copy numbers up to 60 but subsequently with reduction in the product/copy number ratio.
\r\n\r\nInvestigations of environmental effects on plasmid content and \u03b2-lactamase activity have also been done in batch and continuous bioreactors. Plasmid copy number decreased when specific growth rate was increased by varying medium composition in a batch fermentor, or when dilution rate (inverse of residence time) was increased by increasing medium flow rate in a continuous fermentor. The response of plasmid-gene product formation to growth conditions in these two different reactor types is interesting. Batch experiments showed that the specific activity of \u03b2-lactamase is a gradual decreasing function of specific growth rate, whereas product activity has a maximum with respect to dilution rate in chemostat growth. Comparative analysis of genetic and environmental effects implies that both plasmid content and growth conditions should be taken into account in determining the productivity of recombinant cell populations.
\r\n\r\nFurther insight into the host-vector interactions was obtained by exploring plasmid amplification behavior and cell-cycle characteristics in the recombinant strains. Chloramphenicol-derived amplification kinetics were measured using flow cytometry, which allows direct determination of the total cellular DNA content after staining with mithramycin, a DNA-specific fluorescent dye. Both rates of plasmid amplification and final contents of amplified plasmids were found to be proportional to the average initial plasmid copy number obtained at steady-state growth.
\r\n\r\nThe measurements of the cell-cycle parameters in E. coli cells were performed using experimentally determined single-cell DNA content frequency functions in connection with mathematical analysis of cell growth. Plasmid-containing cells exhibit C and D times that are approximately 14 and 24 percent, respectively, smaller than corresponding values in the plasmidfree host. Mean cell sizes and cell mass at the point of replication initiation decrease 38 and 18 percent, respectively, relative to plasmid-free cells. These results agree qualitatively with the previous findings with E. coli B/r carrying F plasmids of various sizes. Interestingly, the effects of plasmid presence on C, D, average cell size, and initiation mass were found to be approximately independent of plasmid copy number in these host-vector systems.
\r\n\r\nFinally, mathematical description of plasmid propagation in cells which reproduce by binary fission was presented using a segregated, population balance model. With the population balance equations, the probability of plasmid loss, distribution of cellular plasmid content, and specific rate of product synthesis were determined based on different single-cell models of plasmid replication, partition, and gene expression. Control modes of plasmid replication during cell growth markedly affect the distribution of plasmid content and accordingly the specific rate of gene product synthesis. The degree of selection required for stable maintenance of plasmidharboring populations was derived by analyses that focused on the transient growth of plasmid-containing and plasmid-free cells in partially selective medium.
", "doi": "10.7907/RGTN-X895", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:918", "collection": "thesis", "collection_id": "918", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03102008-104251", "primary_object_url": { "basename": "Seo_jh_1986.pdf", "content": "final", "filesize": 4192860, "license": "other", "mime_type": "application/pdf", "url": "/918/1/Seo_jh_1986.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Investigations of Plasmid-Host Cell Interactions in Recombinant Escherichia coli Populations", "author": [ { "family_name": "Seo", "given_name": "Jin-Ho", "orcid": "0000-0002-4206-6046", "clpid": "Seo-Jin-Ho" } ], "thesis_advisor": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Campbell", "given_name": "Judith L.", "orcid": "0000-0001-8291-5551", "clpid": "Campbell-J-L" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Plasmid-host cell interactions have been characterized experimentally for recombinant Escherichia coli populations. The plasmids used contain pMB1 replication origins and propagate in E. coli at different copy number levels ranging from 12 to 408. Host E. coli HB101 strains transformed with those plasmids were used throughout this research.
\r\n\r\nThe specific growth rate and amount of cloned-gene product (\u03b2-lactamase) were determined in batch cultivations as a function of plasmid copy number. Maximum specific growth rates in LB and M9 media were reduced monotonically for increasing plasmid content per cell. The maximum specific growth rate for a recombinant strain with copy number 408 was reduced by 25% relative to the plasmid-free strain. The ratio of \u03b2-lactamase specific activity to plasmid content, as a measure of the overall efficiency of plasmid-gene expression, declines by a factor of 7 as the copy number increases from 12 to 408. The relationship between copy number and cloned-gene product activity can be reasonably approximated by a parabolic equation, with approximately linear proportionality for copy numbers up to 60 but subsequently with reduction in the product/copy number ratio.
\r\n\r\nInvestigations of environmental effects on plasmid content and \u03b2-lactamase activity have also been done in batch and continuous bioreactors. Plasmid copy number decreased when specific growth rate was increased by varying medium composition in a batch fermentor, or when dilution rate (inverse of residence time) was increased by increasing medium flow rate in a continuous fermentor. The response of plasmid-gene product formation to growth conditions in these two different reactor types is interesting. Batch experiments showed that the specific activity of \u03b2-lactamase is a gradual decreasing function of specific growth rate, whereas product activity has a maximum with respect to dilution rate in chemostat growth. Comparative analysis of genetic and environmental effects implies that both plasmid content and growth conditions should be taken into account in determining the productivity of recombinant cell populations.
\r\n\r\nFurther insight into the host-vector interactions was obtained by exploring plasmid amplification behavior and cell-cycle characteristics in the recombinant strains. Chloramphenicol-derived amplification kinetics were measured using flow cytometry, which allows direct determination of the total cellular DNA content after staining with mithramycin, a DNA-specific fluorescent dye. Both rates of plasmid amplification and final contents of amplified plasmids were found to be proportional to the average initial plasmid copy number obtained at steady-state growth.
\r\n\r\nThe measurements of the cell-cycle parameters in E. coli cells were performed using experimentally determined single-cell DNA content frequency functions in connection with mathematical analysis of cell growth. Plasmid-containing cells exhibit C and D times that are approximately 14 and 24 percent, respectively, smaller than corresponding values in the plasmidfree host. Mean cell sizes and cell mass at the point of replication initiation decrease 38 and 18 percent, respectively, relative to plasmid-free cells. These results agree qualitatively with the previous findings with E. coli B/r carrying F plasmids of various sizes. Interestingly, the effects of plasmid presence on C, D, average cell size, and initiation mass were found to be approximately independent of plasmid copy number in these host-vector systems.
\r\n\r\nFinally, mathematical description of plasmid propagation in cells which reproduce by binary fission was presented using a segregated, population balance model. With the population balance equations, the probability of plasmid loss, distribution of cellular plasmid content, and specific rate of product synthesis were determined based on different single-cell models of plasmid replication, partition, and gene expression. Control modes of plasmid replication during cell growth markedly affect the distribution of plasmid content and accordingly the specific rate of gene product synthesis. The degree of selection required for stable maintenance of plasmidharboring populations was derived by analyses that focused on the transient growth of plasmid-containing and plasmid-free cells in partially selective medium.
", "doi": "10.7907/RGTN-X895", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:3074", "collection": "thesis", "collection_id": "3074", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08092006-145027", "primary_object_url": { "basename": "Chang_kkc_1985.pdf", "content": "final", "filesize": 3558675, "license": "other", "mime_type": "application/pdf", "url": "/3074/1/Chang_kkc_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Calcium-Ion Exchange of Coal for Retention of Sulfur During Combustion", "author": [ { "family_name": "Chang", "given_name": "Karl Kho-Chung", "clpid": "Chang-Karl-Kho-Chung" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" }, { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Cass", "given_name": "Glen Rowan", "clpid": "Cass-G-R" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The kinetics of calcium-ion exchange of coal and the combustion of calcium-exchanged coals in a laminar flow furnace were investigated. Particle diffusion was found to be the rate-determining step for the process of ion exchange. A diffusion model gave good agreement with observed rates of ion exchange. Diffusion of ions in PSOC 680, a bituminous coal, was observed to be much slower than in PSOC 623, a lignite.
\r\n\r\nRetention of sulfur during combustion of calcium-exchanged coals was observed to increase with increasing particle residence and oxygen concentration in the combustion gas. Chemical reaction was found to be the rate-determining step in the capture of SO2 by CaO in coal ash. The results of this study were interpreted in a proposed mechanism for the release and capture of SO2.
", "doi": "10.7907/X4W7-D106", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:1260", "collection": "thesis", "collection_id": "1260", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04032008-111952", "primary_object_url": { "basename": "Doran_pm_1985.pdf", "content": "final", "filesize": 13902945, "license": "other", "mime_type": "application/pdf", "url": "/1260/1/Doran_pm_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Effects of Immobilization on the Metabolism of Yeast", "author": [ { "family_name": "Doran", "given_name": "Pauline Mavis", "orcid": "0000-0002-8682-4929", "clpid": "Doran-Pauline-Mavis" } ], "thesis_advisor": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The composition and kinetic properties of Saccharomyces cerevisiae were found to be substantially different when the cells were immobilized on gelatin. Batch fermentation experiments conducted in a gradientless reaction system allowed comparison of immobilized cell and suspended cell performance.
\r\n\r\nIn complete nutrient medium, the specific rate of ethanol production by the immobilized cells was 40-50% greater than for the suspended yeast. The immobilized cell consumed glucose twice as fast as the suspended cells, but their specific growth rate was reduced by 45%. Yields of biomass from the immobilized cell population were lower at one-third the value for the suspended cells.
\r\n\r\nCellular composition was also affected by immobilization. Measurements of intracellular polysaccharide levels showed that the immobilized yeast stored larger quantities of reserve carbohydrates and contained more structural polysaccharide than suspended cells. Flow cytometry was used to obtain DNA, RNA and protein frequency functions for suspended and immobilized cell populations. These data showed that the immobilized cells have higher ploidy than cells in suspension. The level of stable, double-stranded RNA in immobilized cells was only one-quarter that measured for suspended cells. The observed changes in immobilized cell metabolism and composition may have arisen from disturbance to the yeast cell cycle by cell attachment, causing alterations in the normal patterns of yeast bud development, DNA replication and synthesis of cell wall components.
\r\n\r\nRecovery from hydroxyurea-induced DNA synthesis inhibition was indicated by measurements of growth rate, DNA content and light scatter properties. The immobilized cells quickly developed an effective means for overcoming hydroxyurea-induced inhibition of replication, and proceeded to synthesize large amounts of DNA while still in the presence of the inhibitor. Stable RNA levels for immobilized cells remained low at 25% of the measured quantity for hydroxyurea-treated suspended cells. Synthesis of protein and RNA was not adversely affected in either cell type. Suspended cell protein pools increased by a factor of 1.8 following inhibition, while the immobilized cells contained 2.6 times the level of protein before hydroxyurea treatment.
\r\n\r\nFermentation properties of immobilized and suspended cells were changed by hydroxyurea. The specific rate of ethanol production by immobilized cells increased by an average of 24%, while, for the suspended cells, specific productivity was up to three times higher. Glucose consumption rates for both cell types also increased under the influence of hydroxyurea. Suspended cell polysaccharide content was reduced by 65%, while the immobilized cells, in contrast, contained 30% more polysaccharide after hydroxyurea treatment.
\r\n\r\nBiotin starvation of immobilized yeast was effective in reducing synthesis of DNA. Biotin-deficient immobilized S. cerevisiae contained approximately the same quantity of DNA as starved suspended cells, while RNA and protein levels were reduced. Glycerol was synthesized at the expense of ethanol during fermentation by biotin-deficient immobilized and suspended cells.
\r\n\r\nThe character and occurrence of glycolytic oscillations were affected by immobilization. Endogenous metabolism by immobilized cells gave rise to relaxation oscillations in the absence of external substrate. Addition of glucose to starved immobilized yeast also generated relaxation-type behaviour, while suspended cells produced only sinusoidal waveforms. Interpretation of these immobilized cell dynamics is discussed in terms of the kinetics and regulatory properties of energy metabolism in yeast.
", "doi": "10.7907/5445-rc32", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:1330", "collection": "thesis", "collection_id": "1330", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04102008-092241", "primary_object_url": { "basename": "Davison_bh_1985.pdf", "content": "final", "filesize": 5807192, "license": "other", "mime_type": "application/pdf", "url": "/1330/1/Davison_bh_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Dynamics and Coexistence of Microbial Mixed Cultures", "author": [ { "family_name": "Davison", "given_name": "Brian Henry", "orcid": "0000-0002-7408-3609", "clpid": "Davison-Brian-Henry" } ], "thesis_advisor": [ { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" } ], "thesis_committee": [ { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Various methods of establishing a persistent mixed culture were examined in continuous culture. A well-defined system consisting of Esherichia coli and Saccharomyces cerevisiae was used. The primary interaction was competition for glucose, the rate limiting nutrient. When this was the only interaction no coexistence is possible in a well mixed fermentor at constant conditions (i.e., a chemostat).
\r\n\r\nThe two microorganisms while competing for glucose were maintained in a stable cycle of coexistence by alternating the growth advantage between the two organisms by oscillating the pH in a chemostat. Pure culture experiments found S. cerevisiae to be insensitve to pH between 5 and 4.3 with a maximum specific growth rate (Umax) of 0.4/hr; while Umax of E. coli decreased from 0.6/hr at pH 5 to 0.1/hr at pH 4.3. Steady state and crossinoculation chemostat runs at a dilution rate of 0.17/hr confirmed the expectation that the mixed culture system is unstable at constant pH with E. coli dominating at pH 5 and S. cerevisiae dominating at pH 4.3. Three pH oscillation experiments were performed at D=0.17/hr with 1 gm/1 glucose feed. The 16 hr/16 hr cycle was stable for six periods with a stable alternating cycle of E. coli and S. cerevisiae being quickly established. A 18 hr pH5./14 hr pH4.3 cycle was found to be stable with smaller yeast concentrations. A 6hr/6hr cycle was found unstable with yeast washout. Simulation results were compared with these runs and were used to predict the onset of instability. Oscillations of pH can force stable persistence of a competing mixed culture that is otherwise unstable. Thus time varying conditions are experimentally demonstrated to be one explanation for competitive coexistence.
\r\n\r\nA mixed culture of Saccharomyces cerevisiae and Esherichia coli was established in a stable coexistence steady state in a chemostat under constant operating conditions at higher feed concentrations. The species competed for glucose, the growth limiting resource, and produced acetate and ethanol. The acetic acid was shown to be very inhibitory to E. coli in pure culture at pH 5 while ethanol inhibition was only marginal. No significant inhibition of S. cerevisiae growth was observed by either acetate or ethanol. Pure culture paramenters were measured and used in the analysis. Linearized stabilty analysis for the case when both organisms produce the inhibitor showed that a transition through three stable outcomes was possible as the feed concentration is lowered. Experimental studies verified these predictions and successive transitions from a yeast growth steady state, to a coexistence steady state, and to a E. coli growth steady state were obtained by lowering the glucose concentration in the feed from 10 to 5 to 2.5 g/l. This dynamic behavior is distinctly different form other competition-inhibition combinations and demostrates for the first time that coexistence is possible due to substrate competition and product inhibition.
\r\n\r\nA bioreactor with simultaneous fermentation and cell recycle was investigated. The reactor consisted of a typical fermentor and an attached inclined side-arm that allowed enhanced sedimentation. Due to the enhanced sedimentation in the side-arm settler the cells precipitate quickly and flow back into the reactor. A virtually cell free broth can be withdrawn through the side-arm while maintaining both a high flowrate and a high cell density. Continuous fermentations with S. cerevisiae demonstrated these features and the possibility of high cell densities at flowrates that ordinarially would lead to washout. Ethanol productivities and yields were high. Increased resistance to contamination was feasible and tested using E. coli as the model contaminant.
\r\n\r\nThis new reactor with size-selective properties was found to allow a coexistent mixed culture of Esherichia coli and Saccharomyces cerevisiae. The larger yeast population was retained and recycled at high efficiencies, while the smaller yet faster growing bacteria were removed preferentially through the side-arm. Stability analysis indicated that the coexistence of this system could be stable only if the yeast removal rate as a function of biomass was concave up. This would occur if growth continued in the side-arm. Another experimental system was devised to measure this removal rate function. A negative removal rate (i.e., a net addition of yeast to the fermentor) was observed at low biomass indicating growth in the settler and explaining the stability of the coexistence steady state.
\r\n\r\nA mixed culture, that was unstable during pure competition under constant well-mixed conditions as expressed in the Competitive Exclusion Principle, was made to persist indefinitely by the use of time-varying conditions (such as pH oscillations), or the addition of other interactions (such as inhibition), or the design of spatially nonuniform reactors (such as the side-arm settler).
", "doi": "10.7907/EC5N-4Y46", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:1260", "collection": "thesis", "collection_id": "1260", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04032008-111952", "primary_object_url": { "basename": "Doran_pm_1985.pdf", "content": "final", "filesize": 13902945, "license": "other", "mime_type": "application/pdf", "url": "/1260/1/Doran_pm_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Effects of Immobilization on the Metabolism of Yeast", "author": [ { "family_name": "Doran", "given_name": "Pauline Mavis", "orcid": "0000-0002-8682-4929", "clpid": "Doran-Pauline-Mavis" } ], "thesis_advisor": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The composition and kinetic properties of Saccharomyces cerevisiae were found to be substantially different when the cells were immobilized on gelatin. Batch fermentation experiments conducted in a gradientless reaction system allowed comparison of immobilized cell and suspended cell performance.
\r\n\r\nIn complete nutrient medium, the specific rate of ethanol production by the immobilized cells was 40-50% greater than for the suspended yeast. The immobilized cell consumed glucose twice as fast as the suspended cells, but their specific growth rate was reduced by 45%. Yields of biomass from the immobilized cell population were lower at one-third the value for the suspended cells.
\r\n\r\nCellular composition was also affected by immobilization. Measurements of intracellular polysaccharide levels showed that the immobilized yeast stored larger quantities of reserve carbohydrates and contained more structural polysaccharide than suspended cells. Flow cytometry was used to obtain DNA, RNA and protein frequency functions for suspended and immobilized cell populations. These data showed that the immobilized cells have higher ploidy than cells in suspension. The level of stable, double-stranded RNA in immobilized cells was only one-quarter that measured for suspended cells. The observed changes in immobilized cell metabolism and composition may have arisen from disturbance to the yeast cell cycle by cell attachment, causing alterations in the normal patterns of yeast bud development, DNA replication and synthesis of cell wall components.
\r\n\r\nRecovery from hydroxyurea-induced DNA synthesis inhibition was indicated by measurements of growth rate, DNA content and light scatter properties. The immobilized cells quickly developed an effective means for overcoming hydroxyurea-induced inhibition of replication, and proceeded to synthesize large amounts of DNA while still in the presence of the inhibitor. Stable RNA levels for immobilized cells remained low at 25% of the measured quantity for hydroxyurea-treated suspended cells. Synthesis of protein and RNA was not adversely affected in either cell type. Suspended cell protein pools increased by a factor of 1.8 following inhibition, while the immobilized cells contained 2.6 times the level of protein before hydroxyurea treatment.
\r\n\r\nFermentation properties of immobilized and suspended cells were changed by hydroxyurea. The specific rate of ethanol production by immobilized cells increased by an average of 24%, while, for the suspended cells, specific productivity was up to three times higher. Glucose consumption rates for both cell types also increased under the influence of hydroxyurea. Suspended cell polysaccharide content was reduced by 65%, while the immobilized cells, in contrast, contained 30% more polysaccharide after hydroxyurea treatment.
\r\n\r\nBiotin starvation of immobilized yeast was effective in reducing synthesis of DNA. Biotin-deficient immobilized S. cerevisiae contained approximately the same quantity of DNA as starved suspended cells, while RNA and protein levels were reduced. Glycerol was synthesized at the expense of ethanol during fermentation by biotin-deficient immobilized and suspended cells.
\r\n\r\nThe character and occurrence of glycolytic oscillations were affected by immobilization. Endogenous metabolism by immobilized cells gave rise to relaxation oscillations in the absence of external substrate. Addition of glucose to starved immobilized yeast also generated relaxation-type behaviour, while suspended cells produced only sinusoidal waveforms. Interpretation of these immobilized cell dynamics is discussed in terms of the kinetics and regulatory properties of energy metabolism in yeast.
", "doi": "10.7907/5445-rc32", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:1328", "collection": "thesis", "collection_id": "1328", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04102008-081200", "primary_object_url": { "basename": "Kalema_ws_1985.pdf", "content": "final", "filesize": 7351203, "license": "other", "mime_type": "application/pdf", "url": "/1328/1/Kalema_ws_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "A Study of Coal Oxidation", "author": [ { "family_name": "Kalema", "given_name": "William Samson", "clpid": "Kalema-William-Samson" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Three coals were oxidized in a fluidized bed, using air at temperatures from 175\u00b0C to 280\u00b0C and total pressures from 126 kPa. to 274 kPa., for periods of up to 24 hours. An infra-red analyzer was used to measure concentrations of carbon oxide gases in the fluidizing stream. Both CO and CO2 rates declined with time and increased with total pressure. The CO2/CO ratio increased with oxidation temperature.
\r\n\r\nOxidation at 200\u00b0C for 12 hours caused about a 10% loss in coal heating value; with most of that loss occurring in the first two hours. The loss of heating value correlated well, according to Dulong's formula, with the decrease in carbon and hydrogen content. The total and carboxylic ion-exchange capacities of the coal increased significantly with oxidation. The enhanced cation exchange capacity could be used to introduce calcium or other cations, which could help reduce emissions of sulfur oxides during coal combustion by foaming sulfates in the ash.
\r\n\r\nFTIR spectra of coal samples were obtained using diffuse reflectance spectroscopy and peak overlap was reduced significantly using the fourier self-deconvolution technique, The spectra of oxidized coal samples showed the progressive reduction in the intensities of aromatic, methyl, and methylene C-H peaks and the appearance or enhancement of a number of carbonyl peaks.
\r\n\r\nCarbon-13 NMR spectra of solid coal samples were obtained using the cross-polarization technique together with magic-angle spinning, and carbon aromaticities were estimated which, when combined with analyses for carbon and ash content, allowed the calculation of overall consumption of aromatic and aliphatic carbon. Both aromatic carbon and aliphatic carbon were consumed, even at 175\u00b0C. This finding disproved a previous theory that aromatic rings were oxidized only above 225\u00b0C.
\r\n", "doi": "10.7907/kr3w-an09", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:1335", "collection": "thesis", "collection_id": "1335", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04102008-152250", "primary_object_url": { "basename": "Pichaichanarong_p_1985.pdf", "content": "final", "filesize": 6088838, "license": "other", "mime_type": "application/pdf", "url": "/1335/1/Pichaichanarong_p_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Reactions of Phenoxy Radicals Under Coal Liquefaction Conditions", "author": [ { "family_name": "Pichaichanarong", "given_name": "Puvin", "clpid": "Pichaichanarong-Puvin" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" }, { "family_name": "Allen", "given_name": "David Thomas", "orcid": "0000-0001-6646-8755", "clpid": "Allen-David-Thomas" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis presents the results of model compound studies that address the rate parameters for hydrogen abstraction involving phenoxy radicals, and the products, pathways, and kinetics of phenoxy radical recombination, under coal liquefaction conditions. Thermolysis of selected mixtures of model compounds containing functionalities found in coal-related materials were conducted in a batch reactor at temperatures between 250 and 450\u00b0C. The reaction products were analyzed by GC, HPLC, GCMS, and NMR, with emphasis on the identification of radical recombination products. Reactions were modeled by free radical mechanisms and rate parameters at liquefaction temperatures for hydrogen abstraction and recombination reactions involving phenoxy radicals were determined.
\r\n\r\nPhenoxy radicals were found to be more reactive than benzyl radicals, rapidly abstracting hydrogen atoms to form stable molecules. Hydrogen abstraction by a phenoxy radical from a phenol was faster than from a hydrocarbon. Application of the rate parameters determined for one model compound mixture to other systems of compounds indicated good match with experimental data.
\r\n\r\nAnalysis of the recombination products revealed that, when no good hydrogen donor solvents were available, phenoxy-phenoxy radical recombination products were more abundant than phenoxy-benzyl recombination products. Certain differences and similarities were observed between the behavior of single-ring aromatics and their condensed-ring counterparts. Whereas phenol was quite stable at 400\u00b0C, 1-naphthol was found to undergo considerable conversion. A mechanistic scheme for 1-naphthol decomposition was proposed which accounted for the major reaction products. Thermolysis of various model compound mixtures indicated similar patterns exhibited by single-ring and double-ring aromatics with respect to the pathways of oxygen-oxygen and oxygen-carbon free radical recombination.
\r\n\r\nBimolecular reverse disproportionation was demonstrated to be satisfactory in explaining naphthol conversion. Furthermore, dehydration accounted for furan formation and concerted reactions could possibly be involved in naphthalene formation. Thus, in addition to unimolecular dissociation reactions, several pathways exist for the thermal reactions of oxygen compounds.
\r\n\r\nThese model compound studies indicated that the results of a simple model compound mixture could give insight into the understanding of a more complex reaction network. This insight will ultimately provide the link between model compound results and the reactions of coal-related materials.
\r\n", "doi": "10.7907/6nqa-0445", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:1330", "collection": "thesis", "collection_id": "1330", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04102008-092241", "primary_object_url": { "basename": "Davison_bh_1985.pdf", "content": "final", "filesize": 5807192, "license": "other", "mime_type": "application/pdf", "url": "/1330/1/Davison_bh_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Dynamics and Coexistence of Microbial Mixed Cultures", "author": [ { "family_name": "Davison", "given_name": "Brian Henry", "orcid": "0000-0002-7408-3609", "clpid": "Davison-Brian-Henry" } ], "thesis_advisor": [ { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" } ], "thesis_committee": [ { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Various methods of establishing a persistent mixed culture were examined in continuous culture. A well-defined system consisting of Esherichia coli and Saccharomyces cerevisiae was used. The primary interaction was competition for glucose, the rate limiting nutrient. When this was the only interaction no coexistence is possible in a well mixed fermentor at constant conditions (i.e., a chemostat).
\r\n\r\nThe two microorganisms while competing for glucose were maintained in a stable cycle of coexistence by alternating the growth advantage between the two organisms by oscillating the pH in a chemostat. Pure culture experiments found S. cerevisiae to be insensitve to pH between 5 and 4.3 with a maximum specific growth rate (Umax) of 0.4/hr; while Umax of E. coli decreased from 0.6/hr at pH 5 to 0.1/hr at pH 4.3. Steady state and crossinoculation chemostat runs at a dilution rate of 0.17/hr confirmed the expectation that the mixed culture system is unstable at constant pH with E. coli dominating at pH 5 and S. cerevisiae dominating at pH 4.3. Three pH oscillation experiments were performed at D=0.17/hr with 1 gm/1 glucose feed. The 16 hr/16 hr cycle was stable for six periods with a stable alternating cycle of E. coli and S. cerevisiae being quickly established. A 18 hr pH5./14 hr pH4.3 cycle was found to be stable with smaller yeast concentrations. A 6hr/6hr cycle was found unstable with yeast washout. Simulation results were compared with these runs and were used to predict the onset of instability. Oscillations of pH can force stable persistence of a competing mixed culture that is otherwise unstable. Thus time varying conditions are experimentally demonstrated to be one explanation for competitive coexistence.
\r\n\r\nA mixed culture of Saccharomyces cerevisiae and Esherichia coli was established in a stable coexistence steady state in a chemostat under constant operating conditions at higher feed concentrations. The species competed for glucose, the growth limiting resource, and produced acetate and ethanol. The acetic acid was shown to be very inhibitory to E. coli in pure culture at pH 5 while ethanol inhibition was only marginal. No significant inhibition of S. cerevisiae growth was observed by either acetate or ethanol. Pure culture paramenters were measured and used in the analysis. Linearized stabilty analysis for the case when both organisms produce the inhibitor showed that a transition through three stable outcomes was possible as the feed concentration is lowered. Experimental studies verified these predictions and successive transitions from a yeast growth steady state, to a coexistence steady state, and to a E. coli growth steady state were obtained by lowering the glucose concentration in the feed from 10 to 5 to 2.5 g/l. This dynamic behavior is distinctly different form other competition-inhibition combinations and demostrates for the first time that coexistence is possible due to substrate competition and product inhibition.
\r\n\r\nA bioreactor with simultaneous fermentation and cell recycle was investigated. The reactor consisted of a typical fermentor and an attached inclined side-arm that allowed enhanced sedimentation. Due to the enhanced sedimentation in the side-arm settler the cells precipitate quickly and flow back into the reactor. A virtually cell free broth can be withdrawn through the side-arm while maintaining both a high flowrate and a high cell density. Continuous fermentations with S. cerevisiae demonstrated these features and the possibility of high cell densities at flowrates that ordinarially would lead to washout. Ethanol productivities and yields were high. Increased resistance to contamination was feasible and tested using E. coli as the model contaminant.
\r\n\r\nThis new reactor with size-selective properties was found to allow a coexistent mixed culture of Esherichia coli and Saccharomyces cerevisiae. The larger yeast population was retained and recycled at high efficiencies, while the smaller yet faster growing bacteria were removed preferentially through the side-arm. Stability analysis indicated that the coexistence of this system could be stable only if the yeast removal rate as a function of biomass was concave up. This would occur if growth continued in the side-arm. Another experimental system was devised to measure this removal rate function. A negative removal rate (i.e., a net addition of yeast to the fermentor) was observed at low biomass indicating growth in the settler and explaining the stability of the coexistence steady state.
\r\n\r\nA mixed culture, that was unstable during pure competition under constant well-mixed conditions as expressed in the Competitive Exclusion Principle, was made to persist indefinitely by the use of time-varying conditions (such as pH oscillations), or the addition of other interactions (such as inhibition), or the design of spatially nonuniform reactors (such as the side-arm settler).
", "doi": "10.7907/EC5N-4Y46", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:11331", "collection": "thesis", "collection_id": "11331", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01032019-104846124", "primary_object_url": { "basename": "Weston_TA_1985.pdf", "content": "final", "filesize": 35690789, "license": "other", "mime_type": "application/pdf", "url": "/11331/1/Weston_TA_1985.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "The Regeneration of High Temperature Sulfur Dioxide Sorbents: the CO Reduction of Supported Alkali Sulfates", "author": [ { "family_name": "Weston", "given_name": "Theresa Ann", "orcid": "0000-0002-9822-7355", "clpid": "Weston-Theresa-Ann" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Voecks", "given_name": "Gerald E.", "orcid": "0009-0008-9371-5756", "clpid": "Voecks-Gerald-E" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The chemical reactions involved in the regeneration step of a high temperature SO2 removal process have been investigated. In particular, the CO reduction of supported alkali sulfates has been studied. Thermogravimetric measurements have yielded the time-resolved composition of sorbent and gaseous products during reduction with 10% CO at 700 and 800\u00b0C. FTIR was used to identify reaction intermediates . A flow microreactor was used to compare gaseous product selectivity between SO2, COS and elemental sulfur of sorbents reduced with 1 and 10% CO at 700 and 800\u00b0C.
\r\n\r\nThe experimental results show regeneration; i.e., sulfur removal is greatly increased by the presence of lithium in the sorbent material. Reaction between the support and the alkali material greatly influences the degree of regeneration. Support materials are apparently active in the catalysis of the reduction of SO2 to elemental sulfur and the reaction between elemental sulfur and CO to form COS, and therefore, influences the product selectivity. A reaction scheme which qualitatively explains the experimental results is proposed.
\r\n", "doi": "10.7907/cen1-hb98", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:464", "collection": "thesis", "collection_id": "464", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02022007-105020", "primary_object_url": { "basename": "Senior_cl_1984.pdf", "content": "final", "filesize": 8233143, "license": "other", "mime_type": "application/pdf", "url": "/464/1/Senior_cl_1984.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Submicron Aerosol Formation During Combustion of Pulverized Coal", "author": [ { "family_name": "Senior", "given_name": "Constance Lynn", "orcid": "0000-0002-1454-4194", "clpid": "Senior-Constance-Lynn" } ], "thesis_advisor": [ { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" } ], "thesis_committee": [ { "family_name": "Cass", "given_name": "Glen Rowan", "clpid": "Cass-G-R" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Zukoski", "given_name": "Edward E.", "clpid": "Zukoski-E-E" }, { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "A detailed investigation is conducted into the fundamental processes responsible for the formation of submicron aerosol during combustion of pulverized coal. To this end, both theoretical and experimental tools are developed.
\r\n\r\nThe first part of the work consists of a numerical simulation of the vaporization of ash and formation of aerosol. The work combines a model of a single, burning coal particle with one of the formation of aerosol by nucleation and the growth of aerosol by coagulation. A quasi-steady approach is used to model combustion and aerosol formation and this is shown to be valid a posteriori. Calculations are performed for vaporization of refractory oxides during combustion. The effect of thermophoresis on the transport of aerosol around a burning coal particle is found to be small. For refractory species like silica, nucleation typically occurs within 4-5 particle radii from the surface of the coal particle. Thus, in this case, nucleation is controlled by the combustion process. The vaporization rate is found to be weakly dependent on the presence of aerosol in the gas.
\r\n\r\nThe second part of this work is the development of an experimental system in which to study the aerosol formation processes. A new material is produced that is similar to coal in many respects, but is chemically simpler and more well-characterized. This makes it possible for the first time to study the fundamental aerosol formation processes without interference from the complex chemistry of coal ash. Experiments in a laminar drop-tube furnace confirm that this material burns in a manner similar to coal and that combustion produces an aerosol from vaporization of ash.
", "doi": "10.7907/70GT-H495", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:464", "collection": "thesis", "collection_id": "464", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02022007-105020", "primary_object_url": { "basename": "Senior_cl_1984.pdf", "content": "final", "filesize": 8233143, "license": "other", "mime_type": "application/pdf", "url": "/464/1/Senior_cl_1984.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Submicron Aerosol Formation During Combustion of Pulverized Coal", "author": [ { "family_name": "Senior", "given_name": "Constance Lynn", "orcid": "0000-0002-1454-4194", "clpid": "Senior-Constance-Lynn" } ], "thesis_advisor": [ { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" } ], "thesis_committee": [ { "family_name": "Cass", "given_name": "Glen Rowan", "clpid": "Cass-G-R" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Zukoski", "given_name": "Edward E.", "clpid": "Zukoski-E-E" }, { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "A detailed investigation is conducted into the fundamental processes responsible for the formation of submicron aerosol during combustion of pulverized coal. To this end, both theoretical and experimental tools are developed.
\r\n\r\nThe first part of the work consists of a numerical simulation of the vaporization of ash and formation of aerosol. The work combines a model of a single, burning coal particle with one of the formation of aerosol by nucleation and the growth of aerosol by coagulation. A quasi-steady approach is used to model combustion and aerosol formation and this is shown to be valid a posteriori. Calculations are performed for vaporization of refractory oxides during combustion. The effect of thermophoresis on the transport of aerosol around a burning coal particle is found to be small. For refractory species like silica, nucleation typically occurs within 4-5 particle radii from the surface of the coal particle. Thus, in this case, nucleation is controlled by the combustion process. The vaporization rate is found to be weakly dependent on the presence of aerosol in the gas.
\r\n\r\nThe second part of this work is the development of an experimental system in which to study the aerosol formation processes. A new material is produced that is similar to coal in many respects, but is chemically simpler and more well-characterized. This makes it possible for the first time to study the fundamental aerosol formation processes without interference from the complex chemistry of coal ash. Experiments in a laminar drop-tube furnace confirm that this material burns in a manner similar to coal and that combustion produces an aerosol from vaporization of ash.
", "doi": "10.7907/70GT-H495", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:1814", "collection": "thesis", "collection_id": "1814", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05152003-160535", "type": "thesis", "title": "Control Model Development for Packed Bed Chemical Reactors", "author": [ { "family_name": "Khanna", "given_name": "Rohit", "clpid": "Khanna-Rohit" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Morari", "given_name": "Manfred", "orcid": "0000-0002-7696-5058", "clpid": "Morari-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Although control algorithms have been conceived for industrial chemical systems, their acceptance by industry has been slow due to a lack of direct experimental evidence of their effectiveness and to volumes of conflicting, or at least incompatible, recommendations on control structure design. This thesis provides the basis for a concerted theoretical and experimental program in multivariable process control structure design for packed bed chemical reactors by presenting an in-depth control analysis of a practical, multivariable, distributed parameter system-the heat conduction problem defined by the simple diffusion equation-using both frequency-domain and time-domain analyses and the formulation, numerical solution, and analysis of a detailed model for packed bed reactors, along with reduction to a low-order state-space representation suitable for on-line process control.
\r\n\r\nThe study of the heat conduction system allowed for consideration of various control design techniques and the relation between measurement structure and control system design. This study shows that the choice of measurements and their locations significantly affects the optimal control design and the usefulness of the different design techniques and the importance of an accurate process model and the necessity of model reduction to a low-order state-space representation for control structure design and implementation.
\r\n\r\nThe second portion of this study provides a detailed mathematical modeling analysis of packed bed catalytic reactors that significantly extends previous studies in the detail of the model and in the consideration of all aspects of the model development and reduction to a state-space control representation. The general view that modeling simplifications are desired since they lead to a reduction in numerical solution effort is contested, and it is shown that many simplifications are no longer necessary with today's advanced computational capabilities. A unified approach to dynamic reactor modeling is developed and its importance in the accurate description of dynamic and steady state reactor behavior, in the investigation of reactor start-up or the effects of process disturbances, and in the development of an accurate reduced state-space model for the design of control structures to stabilize the reactor under various disturbances or to provide optimal system recovery from input changes is shown.
\r\n", "doi": "10.7907/VK3Y-QN30", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:66", "collection": "thesis", "collection_id": "66", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01082007-153733", "primary_object_url": { "basename": "San_ky_1984.pdf", "content": "final", "filesize": 8952014, "license": "other", "mime_type": "application/pdf", "url": "/66/1/San_ky_1984.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Studies on the On-Line Identification and Optimal Control of Bioreactors", "author": [ { "family_name": "San", "given_name": "Ka-Yiu", "clpid": "San-Ka-Yiu" } ], "thesis_advisor": [ { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "An integrated approach is presented for the on-line estimation of the state of a biochemical reactor from presently attainable real-time measurements. Elemental and macroscopic balances are used for the determination of the total rate of growth and state-of-the-art estimation techniques are subsequently employed for the elimination of process and measurement noise and the estimation of the state variables and unknown culture parameters. The proposed approach is very flexible in that as new sensors become available they can be easily incorporated within the present framework to estimate new variables or improve the accuracy of the old ones. The method does not require any model for the growth kinetics and is very sucessful in accurately estimating the above variables in the presence of intense noise and under both steady state and transient conditions. Computer simulation as well as experimental results obtained from this study clearly demonstrate the superb performance of such estimation methodology. State estimates obtained by the proposed method can be used for the development of adaptive optimal control schemes as well as for basic studies of the characteristic properties of microbial cultures.
\r\n", "doi": "10.7907/b5p1-5c02", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:4569", "collection": "thesis", "collection_id": "4569", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-102832", "primary_object_url": { "basename": "Gray_mr_1984.pdf", "content": "final", "filesize": 15456370, "license": "other", "mime_type": "application/pdf", "url": "/4569/1/Gray_mr_1984.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Effects of Moisture and Ash Content on the Pyrolysis of a Wood Derived Material", "author": [ { "family_name": "Gray", "given_name": "Murray Ross", "orcid": "0000-0003-2431-7312", "clpid": "Gray-Murray-Ross" } ], "thesis_advisor": [ { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" } ], "thesis_committee": [ { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" }, { "family_name": "Qader", "given_name": "Shaik A.", "clpid": "Qader-Shaik-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Moisture and ash are always present in wood to some extent, but their affect on its chemical behavior is not fully known. The influence of moisture and ash on the thermal degradation of wood was investigated by pyrolyzing samples of ground wood waste in a batch fluid-bed reactor at between 320 and 470\u00b0C in helium at 101-104 kPa. The wood samples were heated at about 300\u00b0C/min. so that drying and pyrolysis were simultaneous, Woodex\u00ae pellets were used in this study because their density was suitable for fluid-bed tests.
\r\n\r\nIn ash-free samples moisture suppressed the formation of pyrolysis tar at temperatures above 390\u00baC and increased the yield of char, relative to dry samples. A model for the behavior of free radicals during pyrolysis is proposed which gives qualitative agreement with the observed effect of temperature. The ion-exchange capacity of wood was used to disperse calcium atoms in the polymer matrix, which increased the formation of aqueous product during pyrolysis at the expense of tar by enhancing dehydration and fragmentation reactions. The native mineral components in the wood waste gave effects equivalent to calcium.
\r\n\r\nThe effect of moisture on char yield was independent of the ash components, but the yield of tar from Woodex containing moisture and ash exhibited a minimum at 390\u00b0C. Below 390\u00b0C the water hydrated catalyst sites to reduce reactivity. A kinetic model for hydration gave qualitative agreement with the observed effects of temperature. Above 390\u00b0C the degradation of tar became independent of the availability of catalyst sites, and was suppressed by the effect of water on the concentration of tar within the particles, and on the equilibrium of dehydration reactions.
", "doi": "10.7907/ZEMV-CV64", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:126", "collection": "thesis", "collection_id": "126", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01112007-103406", "type": "thesis", "title": "Dynamic and Steady-State Bifurcation for Modeling Chemical Reaction Systems", "author": [ { "family_name": "Lyberatos", "given_name": "Gerasimos", "orcid": "0000-0003-1663-4035", "clpid": "Lyberatos-Gerasimos" } ], "thesis_advisor": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Cohen", "given_name": "Donald S.", "clpid": "Cohen-D-S" }, { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Chemical reaction systems often exhibit nonlinear dynamic phenomena such as multiple steady states and different types of nonlinear oscillations. Furthermore, nonlinear dynamic models are essential for control and input optimization of chemical reactors. Methods of bifurcation theory are used for analysis of the nonlinear behavior of chemical reaction systems and for chemical reactor model discrimination and identification. The latter objective is attained by forcing \"tame\" chemical systems to bifurcate and provide valuable information about the nonlinear system nature. Discrimination between rival kinetic models is demonstrated and a strategy for accurate parameter estimation is developed. The problem of steady-state bifurcation to multiple steady states in the event that the original model equations are not reducible to a single algebraic equation is attacked using the simple geometrical method of Newton Polyhedra. This method is particularly useful for analysis of feedback induced steady-state bifurcations. The theory of normal forms is used to illustrate that systems when close to bifurcation exhibit even locally their non-linear characteristics. The most common types of bifurcation phenomena are discussed and the minimum number of feedback (or system) parameters that must be varied to attain the various bifurcational structures is determined. Systems that are easily reducible to normal forms (simpler locally equivalent polynomial systems) are identified with distinctive advantages for the study of steady state and eigenvalue structure close to bifurcation. The analogy between some chemical systems and a particle's motion in a potential field is exploited to gain special insights into the chemical systems' dynamics. Chemical examples include nitrous oxide decomposition on NiO catalyst, consecutive-competitive reaction systems in a CSTR, parallel nonisothermal reactions of arbitrary order in a CSTR, reactions between adsorbed chemical species, coupled oscillating autocatalytic CSTRs and a class of feedback regulated enzymatic reaction systems.
\r\n", "doi": "10.7907/bspw-np07", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:85", "collection": "thesis", "collection_id": "85", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01092007-104956", "primary_object_url": { "basename": "Kravaris_c_1984.pdf", "content": "final", "filesize": 7270039, "license": "other", "mime_type": "application/pdf", "url": "/85/1/Kravaris_c_1984.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Identification of Spatially-Varying Parameters in Distributed Parameter Systems", "author": [ { "family_name": "Kravaris", "given_name": "Constantine (Costas)", "orcid": "0000-0003-0951-9493", "clpid": "Kravaris-Constantine-Costas" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" }, { "family_name": "Caughey", "given_name": "Thomas Kirk", "clpid": "Caughey-T-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Identification of spatially-varying parameters in distributed parameter systems given an observation of the state is as a rule an ill-posed problem in the sense of Hadamard. Even in case when the solution is unique, it does not depend continuously on the data. The identification problem that motivated this work arises in the description of petroleum reservoirs and subsurface aquifers; it consists of identifying the spatially-varying parameter \u03b1(x,y) in the diffusion equation ut = (\u03b1ux)x + (\u03b1uy)y + f given an observation of u at a discrete set of spatial locations.
\r\n\r\nThe question of uniqueness of \u03b1 (identifiability problem) is first investigated. The analysis is restricted to the one-dimensional version of the above equation i.e. to ut = (\u03b1ux)x + f and an observation of u at a single point. The identifiability problem is formulated as an inverse Sturm-Liouville problem for (\u03b1y')' + \u03bby = 0. It is proved that the eigenvalues and the normalizing constants determine the above Sturm-Liouville operator uniquely. Identifiability and non-identifiability results are obtained for three special cases.
\r\n\r\nThe problem of constructing stable approximate solutions to identification problems in distributed parameter systems is next investigated. The concept of regularization, widely used in solving linear Fredholm integral equations, is developed for the solution of such problems. A general regularization identification theory is presented and applied to the identification of parabolic systems. Two alternative numerical approaches for the minimization of the smoothing functional are investigated: (i) classical Banach space gradient methods and (ii) discretized minimization methods. The latter use finite-dimensional convergent approximations in Sobolev spaces and are based on an appropriate convergence theorem. The performance of the regularization identification method is evaluated by numerical experiments on the identification of spatially-varying diffusivity \u03b1 in the diffusion equation.
", "doi": "10.7907/m0kv-m285", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:66", "collection": "thesis", "collection_id": "66", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01082007-153733", "primary_object_url": { "basename": "San_ky_1984.pdf", "content": "final", "filesize": 8952014, "license": "other", "mime_type": "application/pdf", "url": "/66/1/San_ky_1984.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Studies on the On-Line Identification and Optimal Control of Bioreactors", "author": [ { "family_name": "San", "given_name": "Ka-Yiu", "clpid": "San-Ka-Yiu" } ], "thesis_advisor": [ { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "An integrated approach is presented for the on-line estimation of the state of a biochemical reactor from presently attainable real-time measurements. Elemental and macroscopic balances are used for the determination of the total rate of growth and state-of-the-art estimation techniques are subsequently employed for the elimination of process and measurement noise and the estimation of the state variables and unknown culture parameters. The proposed approach is very flexible in that as new sensors become available they can be easily incorporated within the present framework to estimate new variables or improve the accuracy of the old ones. The method does not require any model for the growth kinetics and is very sucessful in accurately estimating the above variables in the presence of intense noise and under both steady state and transient conditions. Computer simulation as well as experimental results obtained from this study clearly demonstrate the superb performance of such estimation methodology. State estimates obtained by the proposed method can be used for the development of adaptive optimal control schemes as well as for basic studies of the characteristic properties of microbial cultures.
\r\n", "doi": "10.7907/b5p1-5c02", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:3293", "collection": "thesis", "collection_id": "3293", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08312006-082647", "type": "thesis", "title": "Modeling the Reactions of Coal Liquids", "author": [ { "family_name": "Allen", "given_name": "David Thomas", "orcid": "0000-0001-6646-8755", "clpid": "Allen-David-Thomas" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" }, { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis begins the development of a new approach to the kinetic modeling of complex hydrocarbon mixtures. The approach is based on functional group reactions and its implementation involves three steps. The first step is to characterize complex hydrocarbon mixtures, such as coal-derived liquids, heavy oils and shale oils, in terms of their constituent functional groups. A methodology is defined for estimating functional group concentrations from elemental analysis and NMR data. Mass spectra, infared spectra, separation yields and other analytical data may also be incorporated into the concentration estimates. The methodology is demonstrated for a heavy oil and for a wide variety of coal liquids.
\r\n\r\nThe concentrations provide a starting point for kinetic modeling. The second step of the modeling procedure is to determine the rates and pathways of the reactions of the functional groups by investigating the reactions of pure compounds containing the same functionalities. The reactions of a number of these model compound systems were examined. The studies focused on the reactions of atomic hydrogen under conditions appropriate to coal liquefaction.
\r\n\r\nThe final step in the modeling is the development of a mathematical model which can predict changes in functional group concentrations given initial concentrations and reaction rates. This is outside the scope of this thesis, but general guidelines and valid simplifications are discussed.
\r\n", "doi": "10.7907/ph4t-rb90", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:3353", "collection": "thesis", "collection_id": "3353", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09062006-080949", "primary_object_url": { "basename": "Pesthy_aj_1983.pdf", "content": "final", "filesize": 9245975, "license": "other", "mime_type": "application/pdf", "url": "/3353/1/Pesthy_aj_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Aerosol Formation and Growth in Laminar Flow", "author": [ { "family_name": "Pesthy", "given_name": "Andrew John", "clpid": "Pesthy-Andrew-John" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Cass", "given_name": "Glen Rowan", "clpid": "Cass-G-R" }, { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "A detailed theoretical analysis of aerosol nucleation and growth in laminar flow, including the important aspects of mass and energy transfer and aerosol size distribution dynamics, is presented. Simulations of dibutyl phthalate aerosol formation and growth in a laminar flow cooled tube, in the presence and absence of seed particles, are carried out using the classical and Lothe-Pound theories of homogeneous nucleation. The competition between new particle formation and vapor growth onto seed particles is explored in detail. The mathematical model is compared to experimental measurements of aerosol volume distribution and dibutyl phthalate mass balance for a laminar flow cooled tube without seed particles. The model with Lothe-Pound theory shows fair agreement with the mass balance data, but over-predicts the total aerosol number concentration by four orders of magnitude.
", "doi": "10.7907/X6ZW-RA12", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:296", "collection": "thesis", "collection_id": "296", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01232007-132837", "type": "thesis", "title": "The Gasification of Carbonaceous Materials in Molten Sodium Phosphate", "author": [ { "family_name": "Siddoway", "given_name": "Mark Alan", "clpid": "Siddoway-Mark-Alan" } ], "thesis_advisor": [ { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" } ], "thesis_committee": [ { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Herbolzheimer", "given_name": "Eric", "clpid": "Herbolzheimer-E" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The gasification rates of petroleum coke, char, and residual oil were measured in molten sodium phosphate. Both oxygen and steam were used as oxidants, and a variety of reactor configurations were studied. Reactors consisted of fused ceramic parts sealed into a reactor configuration using castable refractory.
\r\n\r\nThe reaction rate of carbon particles in a bubbling molten phosphate slurry was found to depend upon the rate of particle-bubble contacting. Upon contact, direct conversion of carbon particles with the gas phase occurs due to the large carbon-molten sodium phosphate contact angle (136\u00b0). The potential flow solution for flow around a bubble where particles are assumed to follow the streamlines gave a consistent picture of bubble-particle contacting. The reactivity of the carbon in the bulk liquid was found to be negligible due to the low solubility of oxygen in the melt.
\r\n\r\nGas phase (no salt) results were generated to establish base cases and to examine treatment effects on the reactivity of green sponge and green needle cokes. The reactivities of both were favorably affected by toluene extraction and adversely affected by calcination to 1300 K. Extraction decreased the agglomerating nature of the sponge coke. Both extracts were largely aromatic with the needle coke extract being more so.
\r\n\r\nMolten sodium phosphate was found to catalyze the gasification of petroleum coke by steam and by oxygen. Such catalytic effects are limited due to the large carbon-salt contact angle and may be obscured in slurry reactors by the rate of particle-bubble contacting being slow. The steam reforming of residual oil revealed that the carbonized product in the molten salt phase closely resembled sponge petroleum coke (as produced by delayed coking).
\r\n\r\nCold model experiments employing water and polymeric beads revealed that dilute slurries of small, non-wetting particles decreased the rise velocity of single bubbles and increased the rate of bubble coalescence in swarms. Dilute slurries of wetting particles had no effect in either case.
\r\n", "doi": "10.7907/3t1x-qd32", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:4642", "collection": "thesis", "collection_id": "4642", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11232005-112642", "primary_object_url": { "basename": "Krallik_jg_1982.pdf", "content": "final", "filesize": 57928595, "license": "other", "mime_type": "application/pdf", "url": "/4642/1/Krallik_jg_1982.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "An Investigation of the Applied Chemistry of the Reactions of Coal and Nitrogen Dioxide with a Particular Emphasis on Oxidative Desulfurization", "author": [ { "family_name": "Kralik", "given_name": "James Gregory", "clpid": "Kralik-James-Gregory" } ], "thesis_advisor": [ { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" } ], "thesis_committee": [ { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Kalvinskas", "given_name": "John J.", "clpid": "Kalvinskas-John-J" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The physical and chemical changes in coal resulting from mild oxidation at ambient conditions with NO2 were studied. Various liquid phases were used as transport media for the NO2. Subsequent to the oxidation, the coal was subjected to a wash with aqueous Na2CO3 at ambient conditions. Particular attention was given to the desulfurization of the coal. A mathematical model of the reactions between NO2 and coal at temperatures less than 100\u00b0C and a pressure of 1 atm was developed from the experimental data. This model included the simultaneous diffusion and reaction of NO2 in the solid-coal matrix and considered pore diffusion not to be controlling. The elemental composition and the energy content, after processing were extensively examined. The effect of the NO2 treatment on the pore structure was established.
\r\n", "doi": "10.7907/r7z7-6s05", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:4642", "collection": "thesis", "collection_id": "4642", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11232005-112642", "primary_object_url": { "basename": "Krallik_jg_1982.pdf", "content": "final", "filesize": 57928595, "license": "other", "mime_type": "application/pdf", "url": "/4642/1/Krallik_jg_1982.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "An Investigation of the Applied Chemistry of the Reactions of Coal and Nitrogen Dioxide with a Particular Emphasis on Oxidative Desulfurization", "author": [ { "family_name": "Kralik", "given_name": "James Gregory", "clpid": "Kralik-James-Gregory" } ], "thesis_advisor": [ { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" } ], "thesis_committee": [ { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Kalvinskas", "given_name": "John J.", "clpid": "Kalvinskas-John-J" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The physical and chemical changes in coal resulting from mild oxidation at ambient conditions with NO2 were studied. Various liquid phases were used as transport media for the NO2. Subsequent to the oxidation, the coal was subjected to a wash with aqueous Na2CO3 at ambient conditions. Particular attention was given to the desulfurization of the coal. A mathematical model of the reactions between NO2 and coal at temperatures less than 100\u00b0C and a pressure of 1 atm was developed from the experimental data. This model included the simultaneous diffusion and reaction of NO2 in the solid-coal matrix and considered pore diffusion not to be controlling. The elemental composition and the energy content, after processing were extensively examined. The effect of the NO2 treatment on the pore structure was established.
\r\n", "doi": "10.7907/r7z7-6s05", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:3461", "collection": "thesis", "collection_id": "3461", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09112006-132454", "type": "thesis", "title": "An Investigation of the Interaction of Water and of Saturated Hydrocarbons with the (110) Surface of Iridium", "author": [ { "family_name": "Wittrig", "given_name": "Thomas Stephen", "clpid": "Wittrig-Thomas-Stephen" } ], "thesis_advisor": [ { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" } ], "thesis_committee": [ { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" }, { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" }, { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The interactions of the reconstructed Ir(110)-(1x2) surface with water and with saturated hydrocarbons have been studied in an ultrahigh vacuum environment. The techniques of thermal desorption mass spectrometry (TDMS), ultrahigh photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy, contact potential difference measurements and low-energy electron diffraction (LEED) were utilized.
\r\n\r\nChapter 2 describes a refinement in the technique for modelling the kinetics of desorption of adsorbed species by an Arrhenius construction. The functional dependence of the energy of desorption and the rate coefficient on the surface coverage are accounted for. An explicit example is provided.
\r\n\r\nThe interaction of water with the Ir(110)-(1x2) surface is discussed in Chapter 3. It is shown that at most, 6% of the adsorbed water dissociates upon adsorption at a temperature of 130 K. Water does dissociate to OH groups when adsorbed on an Ir(110)-(1x2) surface with preadsorbed oxygen. Water exhibits a constant probability of adsorption for all submonolayer coverages. There exist four distinct thermal desorption states of water on the clean Ir(110)-(1x2) surface. A qualitative model is put forth to rationalize the complex thermal desorption behavior.
\r\n\r\nThe remaining chapters describe investigations of the adsorption and reaction of saturated hydrocarbons on Ir(110)-(1x2). Chapter 4 presents the results of a study of the interaction of cyclopropane and Ir(110). Chapter 5 considers the coadsorption of hydrogen and cyclopropane on Ir(110). Finally, Chapter 6 presents the results of a study of the adsorption and reaction of ethane, propane, isobutane and neopentane on Ir(110). These saturated hydrocarbons dissociated on the surface at some temperature below 130 K. In each case, this dissociation reaction is poisoned by the presence of adsorbed hydrogen on the surface. This leads to the identification of an active site for hydrocarbon dissociation on the surface. As the surface is heated, the carbon remains adsorbed on the surface and the hydrogen desorbs as H2. For ethane, one thermal desorption peak of H2 is observed that corresponds to hydrogen adsorbed in \u03b22 hydrogen adsites on the metal surface. This thermal desorption peak is observed for the remaining hydrocarbons, as well as two other thermal desorption states associated with hydrogen that exists in partially dehydrogenated hydrocarbon fragments present on the surface. No hydrocarbon species other than the one initially adsorbed were observed to desorb from the surface under any of the conditions reported in this work.
", "doi": "10.7907/7J0D-GQ82", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:3461", "collection": "thesis", "collection_id": "3461", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09112006-132454", "type": "thesis", "title": "An Investigation of the Interaction of Water and of Saturated Hydrocarbons with the (110) Surface of Iridium", "author": [ { "family_name": "Wittrig", "given_name": "Thomas Stephen", "clpid": "Wittrig-Thomas-Stephen" } ], "thesis_advisor": [ { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" } ], "thesis_committee": [ { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" }, { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" }, { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The interactions of the reconstructed Ir(110)-(1x2) surface with water and with saturated hydrocarbons have been studied in an ultrahigh vacuum environment. The techniques of thermal desorption mass spectrometry (TDMS), ultrahigh photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy, contact potential difference measurements and low-energy electron diffraction (LEED) were utilized.
\r\n\r\nChapter 2 describes a refinement in the technique for modelling the kinetics of desorption of adsorbed species by an Arrhenius construction. The functional dependence of the energy of desorption and the rate coefficient on the surface coverage are accounted for. An explicit example is provided.
\r\n\r\nThe interaction of water with the Ir(110)-(1x2) surface is discussed in Chapter 3. It is shown that at most, 6% of the adsorbed water dissociates upon adsorption at a temperature of 130 K. Water does dissociate to OH groups when adsorbed on an Ir(110)-(1x2) surface with preadsorbed oxygen. Water exhibits a constant probability of adsorption for all submonolayer coverages. There exist four distinct thermal desorption states of water on the clean Ir(110)-(1x2) surface. A qualitative model is put forth to rationalize the complex thermal desorption behavior.
\r\n\r\nThe remaining chapters describe investigations of the adsorption and reaction of saturated hydrocarbons on Ir(110)-(1x2). Chapter 4 presents the results of a study of the interaction of cyclopropane and Ir(110). Chapter 5 considers the coadsorption of hydrogen and cyclopropane on Ir(110). Finally, Chapter 6 presents the results of a study of the adsorption and reaction of ethane, propane, isobutane and neopentane on Ir(110). These saturated hydrocarbons dissociated on the surface at some temperature below 130 K. In each case, this dissociation reaction is poisoned by the presence of adsorbed hydrogen on the surface. This leads to the identification of an active site for hydrocarbon dissociation on the surface. As the surface is heated, the carbon remains adsorbed on the surface and the hydrogen desorbs as H2. For ethane, one thermal desorption peak of H2 is observed that corresponds to hydrogen adsorbed in \u03b22 hydrogen adsites on the metal surface. This thermal desorption peak is observed for the remaining hydrocarbons, as well as two other thermal desorption states associated with hydrogen that exists in partially dehydrogenated hydrocarbon fragments present on the surface. No hydrocarbon species other than the one initially adsorbed were observed to desorb from the surface under any of the conditions reported in this work.
", "doi": "10.7907/7J0D-GQ82", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:296", "collection": "thesis", "collection_id": "296", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01232007-132837", "type": "thesis", "title": "The Gasification of Carbonaceous Materials in Molten Sodium Phosphate", "author": [ { "family_name": "Siddoway", "given_name": "Mark Alan", "clpid": "Siddoway-Mark-Alan" } ], "thesis_advisor": [ { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" } ], "thesis_committee": [ { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Herbolzheimer", "given_name": "Eric", "clpid": "Herbolzheimer-E" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The gasification rates of petroleum coke, char, and residual oil were measured in molten sodium phosphate. Both oxygen and steam were used as oxidants, and a variety of reactor configurations were studied. Reactors consisted of fused ceramic parts sealed into a reactor configuration using castable refractory.
\r\n\r\nThe reaction rate of carbon particles in a bubbling molten phosphate slurry was found to depend upon the rate of particle-bubble contacting. Upon contact, direct conversion of carbon particles with the gas phase occurs due to the large carbon-molten sodium phosphate contact angle (136\u00b0). The potential flow solution for flow around a bubble where particles are assumed to follow the streamlines gave a consistent picture of bubble-particle contacting. The reactivity of the carbon in the bulk liquid was found to be negligible due to the low solubility of oxygen in the melt.
\r\n\r\nGas phase (no salt) results were generated to establish base cases and to examine treatment effects on the reactivity of green sponge and green needle cokes. The reactivities of both were favorably affected by toluene extraction and adversely affected by calcination to 1300 K. Extraction decreased the agglomerating nature of the sponge coke. Both extracts were largely aromatic with the needle coke extract being more so.
\r\n\r\nMolten sodium phosphate was found to catalyze the gasification of petroleum coke by steam and by oxygen. Such catalytic effects are limited due to the large carbon-salt contact angle and may be obscured in slurry reactors by the rate of particle-bubble contacting being slow. The steam reforming of residual oil revealed that the carbonized product in the molten salt phase closely resembled sponge petroleum coke (as produced by delayed coking).
\r\n\r\nCold model experiments employing water and polymeric beads revealed that dilute slurries of small, non-wetting particles decreased the rise velocity of single bubbles and increased the rate of bubble coalescence in swarms. Dilute slurries of wetting particles had no effect in either case.
\r\n", "doi": "10.7907/3t1x-qd32", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:11117", "collection": "thesis", "collection_id": "11117", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07122018-151932188", "type": "thesis", "title": "Steam Reforming of Methane on a Ni Catalyst Suspended in Molten Sodium Phosphates", "author": [ { "family_name": "Kaffes", "given_name": "Nicholas Alexandrou", "clpid": "Kaffes-Nicholas-Alexandrou" } ], "thesis_advisor": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "A molten salt bath was used to carry out the methane steam reforming reaction in the 800-l000\u00b0C range. The rate of methane pyrolysis was also determined under the same conditions to compare it to the rate of steam reforming. The molten salt baths used included a eutectic mixture of sodium pyrophosphate and sodium metaphosphate, a eutectic mixture of potassium pyrophosphate and potassium metaphosphate, a mixture of Na2O, P2O5 and V2O5 and a mixture of Na2O, P2O5 and NiO. Additional experiments were conducted in empty reactors.
\r\n\r\nIt was found that the rate of pyrolysis was not affected by any of the salt systems.The rate of the steam reforming reaction was low, about 10% of the pyrolysis rate, for the empty reactors and for all the salt systems except the system Na2O-P2O5-NiO under reducing conditions. Under reducing conditions, the nickel of this system was reduced to' metallic Ni which catalyzed the CH4-H2O reaction.
\r\n\r\nX-ray diffraction, electron microscope and electron microprobe analysis studies confirmed the hypothesis that under oxidizing conditions nickel was dissolved in the melt and under reducing conditions solid nickel particles were formed which were suspended in the melt. These particles were exposed to the reactant gases on bubble surfaces.
\r\n\r\nThis novel catalytic steam reforming system is especially suitable for handling residual oils of high sulfur and heavy metal content. The sulfur is captured by the salt melt whereas the nickel catalyst is regenerated by repeated cycles of dissolution into and reduction from the melt.
", "doi": "10.7907/9t7k-ge62", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:11117", "collection": "thesis", "collection_id": "11117", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07122018-151932188", "type": "thesis", "title": "Steam Reforming of Methane on a Ni Catalyst Suspended in Molten Sodium Phosphates", "author": [ { "family_name": "Kaffes", "given_name": "Nicholas Alexandrou", "clpid": "Kaffes-Nicholas-Alexandrou" } ], "thesis_advisor": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "thesis_committee": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" }, { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "A molten salt bath was used to carry out the methane steam reforming reaction in the 800-l000\u00b0C range. The rate of methane pyrolysis was also determined under the same conditions to compare it to the rate of steam reforming. The molten salt baths used included a eutectic mixture of sodium pyrophosphate and sodium metaphosphate, a eutectic mixture of potassium pyrophosphate and potassium metaphosphate, a mixture of Na2O, P2O5 and V2O5 and a mixture of Na2O, P2O5 and NiO. Additional experiments were conducted in empty reactors.
\r\n\r\nIt was found that the rate of pyrolysis was not affected by any of the salt systems.The rate of the steam reforming reaction was low, about 10% of the pyrolysis rate, for the empty reactors and for all the salt systems except the system Na2O-P2O5-NiO under reducing conditions. Under reducing conditions, the nickel of this system was reduced to' metallic Ni which catalyzed the CH4-H2O reaction.
\r\n\r\nX-ray diffraction, electron microscope and electron microprobe analysis studies confirmed the hypothesis that under oxidizing conditions nickel was dissolved in the melt and under reducing conditions solid nickel particles were formed which were suspended in the melt. These particles were exposed to the reactant gases on bubble surfaces.
\r\n\r\nThis novel catalytic steam reforming system is especially suitable for handling residual oils of high sulfur and heavy metal content. The sulfur is captured by the salt melt whereas the nickel catalyst is regenerated by repeated cycles of dissolution into and reduction from the melt.
", "doi": "10.7907/9t7k-ge62", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:4994", "collection": "thesis", "collection_id": "4994", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12142006-084027", "type": "thesis", "title": "A Fundamental Study of NO Reduction with Hydrogen over Ir(110)", "author": [ { "family_name": "Ibbotson", "given_name": "Dale Edward", "clpid": "Ibbotson-Dale-Edward" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Stephanopoulos", "given_name": "Gregory N.", "clpid": "Stephanopoulos-G-N" }, { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The heterogeneously catalyzed reduction of NO with hydrogen over Ir(110), as well as the chemisorption of the individual reactants and some of the products, has been studied at low pressures (<10-5) torr). The experiments were performed with several surface sensitive probes-thermal desorption mass spectrometry (TDS), contact potential difference (CPD) measurements, LEED, X-ray and UV photoelectron spectroscopies and Auger electron spectroscopy.
\r\n\r\nChapter 2 describes the chemisorption of hydrogen on Ir(110). The Ir(110)-(1x2) reconstructed surface is stable in hydrogen at pressures from 10-9 to 10-5 torr and surface temperatures from 130 to 1000 K, the conditions investigated. Absolute coverage measurements indicate the saturation density at 130 K on Ir(110) is (2.2\u00b10.2)x1015 atoms cm-2. Thermal desorption measurements indicate hydrogen obeys second order desorption kinetics and exhibits two features, \u03b21 and \u03b22 states, with intensities 2:1, respectively, which exchange isotopically with one another. However, \u03b22 hydrogen obeys first order adsorption kinetics with an initial probability of adsorption So equal to unity, while \u03b21 hydrogen has an So equal to 7x10-3 and obeys second order kinetics. Rate parameters for hydrogen desorption from Ir(110) show a sympathetic increase up to at least half of saturation for the \u03b22 state where Ed and \u03bdd assume values of 23 kcal-mole-1 and 1.5x10-2cm2-s-1, respectively. For the \u03b21 state, Ed = 17-100 kcal-mole-1 from 0 equal to 0.4-0.7 and \u03bdd maintains an average value of 10-7 cm2-s-1. The CPD and UPS measurements are used to infer probable binding sites for the \u03b21 and \u03b22 states of hydrogen which are consistent with the absolute coverage determined from TDS.
\r\n\r\nChapter 3 discusses the interaction of hydrogen and CO on Ir(110). The co-adsorption of hydrogen and CO was undertaken to understand the effects of a model poison, CO, for hydrogen chemisorption. The adsorption of hydrogen on adsorbed CO, or vice versa, causes less hydrogen to occupy the \u03b22 state and shifts the occupancy to the \u03b21 state preferentially. An apparent increase in the probability of adsorption of hydrogen in the \u03b21 state occurs for small CO coverages. At high CO coverages, the Ir(110) surface is poisoned to hydrogen adsorption. Exposing CO to preadsorbed hydrogen causes the binding energy of hydrogen to decrease with increasing CO exposure. Eventually, hydrogen is displaced from the surface for sufficient CO exposures. The induced dipole of hydrogen is unaffected by CO compared to the clean surface, as measured by the CPD. The results indicate CO poisons \u03b22 sites for hydrogen by a simple site blocking mechanism and may exclude \u03b21 sites at high CO coverages by a hydrogen-CO repulsive interaction.
\r\n\r\nChapter 4 presents the results for the molecular chemisorption of N2 and the coadsorption of N2 with hydrogen on Ir(110) at low temperatures. Photoelectron spectroscopy shows molecular levels of N2 at 8.0 (5\u03c3 + 1\u03c0) and 11.8 (4\u03c3) eV in the valence band and at 399.2 eV with a satellite at 404.2 eV in the N(1s) region. The kinetics of adsorption and desorption of N2 show that both precursor kinetics and interadsorbate interactions are important for this chemisorption system. Adsorption occurs with So equal to unity up to saturation coverage (4.8X1014 cm-2) and thermal desorption gives rise to two peaks. The activation energy for desorption varies between 8.5 and 6.0 kcal-mole-1 at low and high coverages, respectively. Results of the co-adsorption of N2 and hydrogen indicate that adsorbed N2 resides in the missing row troughs on Ir(110) - (1x2). Furthermore, N2 is displaced by hydrogen, and the \u03b22 state of hydrogen blocks virtually all N2 adsorption.
\r\n\r\nChapter 5 considers the chemisorption of NO on Ir(110). Adsorption of NO on Ir(110) proceeds by presursor kinetics with So equal to unity independent of surface temperature. Saturation of Ir(110) is achieved in molecular form at 9.6x1014 cm-2 below 300 K. Approximately 35% of a saturated overlayer desorbs as NO in two peaks with equal intensities. The balance desorbs as N2 and O2 where N2 begins to desorb after the first peak of NO is nearly completed. Estimates were made of the activation energies for the various surface reactions that occur as the surface is heated. At low coverages of NO, N2 desorbs with E equal to 36 kcal-mole-1. The activation energy for the dissociation of NO is near 25 kcal-mole-1 for a saturated overlayer, but varies for smaller coverages of NO. Desorption of NO at saturation is associated with energies of 23 and 33 kcal-mole-1 for the two peaks. The first peak represents desorption of NO from an oxygen-free surface and the second peak represents, at least in part, the recombination of nitrogen and oxygen adatoms on a partially oxidized surface. Oxygen tends to stabilize NO to dissociation and desorption as N2, as reflected in TDS. Moreover, UPS and CPD results indicate NO is stabilized on oxygen overlayers compared to the clean Ir(110) surface.
\r\n\r\nChapter 6 discusses the reaction of NO and deuterium to form N2, ND3 and D2O over Ir(110). In addition, the competitive co-adsorption of NO and deuterium and the thermal desorption of the resulting overlayer were performed to gain further insight into the observed steady state rates of reaction, via TDS and CPD measurements. Small precoverages of deuterium do not affect the adsorption kinetics of NO on Ir(110) but do cause more N2 to desorb relative to NO at saturation on the clean surface. Deuterium will adsorb on a saturated overlayer of NO. However, deuterium is strongly blocked from adsorbing on an Ir(110) surface that has both NO and oxygen adsorbed, which is a condition that occurs for some steady state reaction conditions. Under steady state conditions, the reduction of NO shows a marked hysteresis as the surface temperature is cycled for a large enough value of R(PD2/PNO). A plateau in the reduction rate appears at some T that persists as T decreases until at lower values of T the rate falls irreversibly. For larger values of R, ND3 is produced between 470 - 630 K and competes strongly with N2 production. Otherwise, N2 and D2O are the only products of the reduction reaction. Tentative explanations of the empirical rate models derived from the steady state rate data are discussed in light of XPS, UPS and LEED results that are presented as well.
", "doi": "10.7907/xnsj-m676", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:3639", "collection": "thesis", "collection_id": "3639", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09192006-130811", "type": "thesis", "title": "Coal Desulfurization by Selective Chlorinolysis", "author": [ { "family_name": "Vasilakos", "given_name": "Nikolaos Petrou", "clpid": "Vasilakos-Nikolaos-Petrou" } ], "thesis_advisor": [ { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" } ], "thesis_committee": [ { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" }, { "family_name": "Kalvinskas", "given_name": "John J.", "clpid": "Kalvinskas-John-J" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The desulfurization of coal by selective oxidation under slurry-phase chlorination conditions was investigated. Chemical reaction was found to be the rate-controlling step in carbon-tetrachloride chorination at 25\u00b0C for coal particles less than 150 \u00b5 in diameter. For larger particle sizes, a transition from chemical to intraparticlemass-transfer control was observed. The nitrogen-surface area of the coal decreased significantly as a result of the chlorination reaction.
\r\n\r\nThe reaction mechanism and the desulfurization patterns of chlorinolysis were studied under model-reaction and coal-chlorination conditions. Possible complete desulfurization schemes were considered.
\r\n\r\nThe role of solvents both in increasing the efficiency of the coal treatment and in providing alternative paths for coal beneficiation processes was also examined. The results of this study were interpreted within the frame of the solubility-parameter theory, utilizing the new experimental technique of solubility-parameter spectroscopy.
", "doi": "10.7907/05PE-T991", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:3814", "collection": "thesis", "collection_id": "3814", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09282006-095624", "type": "thesis", "title": "The Nature of Fluorinated Oxide Catalysts: A Nuclear Magnetic Resonance Investigation", "author": [ { "family_name": "Schlup", "given_name": "John Robert", "clpid": "Schlup-John-Robert" } ], "thesis_advisor": [ { "family_name": "Chan", "given_name": "Sunney I.", "orcid": "0000-0002-5348-2723", "clpid": "Chan-S-I" }, { "family_name": "Vaughan", "given_name": "Robert W.", "clpid": "Vaughan-R-W" } ], "thesis_committee": [ { "family_name": "Chan", "given_name": "Sunney I.", "orcid": "0000-0002-5348-2723", "clpid": "Chan-S-I" }, { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Fluorination of oxide catalysts has been shown to drastically change the catalytic properties of these materials. The catalytic activity of these materials has been studied using a wide variety of reactions. Research on fluorinated oxides has focused upon improving product yields and product selectivity and upon obtaining a better understanding of the unmodified oxide catalyst as changes due to fluorination are observed. The purpose of this investigation has been to demonstarate the utility of pulsed nuclear magnetic resonance (NMR) spectroscopy as a direct spectroscopic probe of the local chemical environment of the hydroxyl groups and the fluorine atoms of these materials.
\r\n\r\nQuantitative analysis of the hydroxyl group and fluorine atom concentrations of these materials is difficult. Most techniques used previously require temperatures in excess of 1200 K and result in destruction of the sample. NMR has been shown to be an effective non-destructive quantitative tool. Precision of 5% has been demonstrated with samples containing as few as 5 x 1018 hydrogen or fluorine atoms.
\r\n\r\nThe chemical shift interaction has shown that the fluorine forms covalent bonds to the silicon and aluminum atoms of silica, alumina, and various aluminosilicates. If an aluminosilicate contains 11 wt% alumina, only SiF and SiOH species are observed. SiF, SiOH, AlF, and Al0H species are observed for aluminosilicates containing 48 wt% alumina. The SiF bond is identical for all fluorinated silicas and aluminosilicates calcined at 873 K. The Carr-Purcell-Meiboom-Gill data show that the hydroxyl groups are well isolated from one another for all samples. The same is true for the fluorine atoms.
\r\n\r\nThe decay constants of the hydrogen and fluorine 90\u00b0-\u03c4-180\u00b0and Carr-Purcell-Meiboom-Gill experiments differ by at least a factor of ten. Therefore, the nuclei are experiencing fluctuations in their local magnetic fields, probably as a result of anisotropic motion or diffusion. The behavior of the spectra observed at temperatures between 110 K and 290 K is very dependent upon the type of oxide, the degree of fluorination, and the calcining temperature.
", "doi": "10.7907/b77t-rz15", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:3814", "collection": "thesis", "collection_id": "3814", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09282006-095624", "type": "thesis", "title": "The Nature of Fluorinated Oxide Catalysts: A Nuclear Magnetic Resonance Investigation", "author": [ { "family_name": "Schlup", "given_name": "John Robert", "clpid": "Schlup-John-Robert" } ], "thesis_advisor": [ { "family_name": "Chan", "given_name": "Sunney I.", "orcid": "0000-0002-5348-2723", "clpid": "Chan-S-I" }, { "family_name": "Vaughan", "given_name": "Robert W.", "clpid": "Vaughan-R-W" } ], "thesis_committee": [ { "family_name": "Chan", "given_name": "Sunney I.", "orcid": "0000-0002-5348-2723", "clpid": "Chan-S-I" }, { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Fluorination of oxide catalysts has been shown to drastically change the catalytic properties of these materials. The catalytic activity of these materials has been studied using a wide variety of reactions. Research on fluorinated oxides has focused upon improving product yields and product selectivity and upon obtaining a better understanding of the unmodified oxide catalyst as changes due to fluorination are observed. The purpose of this investigation has been to demonstarate the utility of pulsed nuclear magnetic resonance (NMR) spectroscopy as a direct spectroscopic probe of the local chemical environment of the hydroxyl groups and the fluorine atoms of these materials.
\r\n\r\nQuantitative analysis of the hydroxyl group and fluorine atom concentrations of these materials is difficult. Most techniques used previously require temperatures in excess of 1200 K and result in destruction of the sample. NMR has been shown to be an effective non-destructive quantitative tool. Precision of 5% has been demonstrated with samples containing as few as 5 x 1018 hydrogen or fluorine atoms.
\r\n\r\nThe chemical shift interaction has shown that the fluorine forms covalent bonds to the silicon and aluminum atoms of silica, alumina, and various aluminosilicates. If an aluminosilicate contains 11 wt% alumina, only SiF and SiOH species are observed. SiF, SiOH, AlF, and Al0H species are observed for aluminosilicates containing 48 wt% alumina. The SiF bond is identical for all fluorinated silicas and aluminosilicates calcined at 873 K. The Carr-Purcell-Meiboom-Gill data show that the hydroxyl groups are well isolated from one another for all samples. The same is true for the fluorine atoms.
\r\n\r\nThe decay constants of the hydrogen and fluorine 90\u00b0-\u03c4-180\u00b0and Carr-Purcell-Meiboom-Gill experiments differ by at least a factor of ten. Therefore, the nuclei are experiencing fluctuations in their local magnetic fields, probably as a result of anisotropic motion or diffusion. The behavior of the spectra observed at temperatures between 110 K and 290 K is very dependent upon the type of oxide, the degree of fluorination, and the calcining temperature.
", "doi": "10.7907/b77t-rz15", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:4164", "collection": "thesis", "collection_id": "4164", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10182006-083816", "type": "thesis", "title": "Laboratory Studies of Submicron Particle Formation in Pulverized Coal Combustion", "author": [ { "family_name": "Taylor", "given_name": "Dean Dalton", "clpid": "Taylor-Dean-Dalton" } ], "thesis_advisor": [ { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" } ], "thesis_committee": [ { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Sabersky", "given_name": "Rolf H.", "clpid": "Sabersky-R-H" }, { "family_name": "Zukoski", "given_name": "Edward E.", "clpid": "Zukoski-E-E" }, { "family_name": "Cass", "given_name": "Glen Rowan", "clpid": "Cass-G-R" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "A laboratory furnace was constructed to study the mechanism of submicron particle formation in pulverized coal boilers. Simulation was achieved by matching characteristic kinetic times in laboratory and field units. This was done by matching volumetric heat extraction rates. Reynolds number and geometric scaling were not deemed essential for the simulation.
\r\n\r\nCombustion-generated submicron aerosols from the laboratory furnace were characterized by size and composition distribution measurements using an electrical mobility analyzer and a low-pressure impactor. Elemental analysis of size-classified mass samples was done by alpha particle-induced X-ray emission spectrum analysis.
\r\n\r\nThe influence of macroscopic combustion parameters on the characteristics of fine particle emissions was investigated. Total submicron particle volume concentration was found to depend on burner type and to increase with temperature for each burner type tested. The particle volume concentration was found to increase with exhaust NO concentration.
\r\n\r\nThe fine particle composition was found to differ from that of larger residual ash particles which generally reflected the composition of the bulk ash. It was also found that combustion conditions (overall fuel-air equivalence ratio and wall temperature) influenced the composition of the smallest ash particles.
\r\n\r\nSpecies enrichment data are generally supportive of the vaporization-condensation mechanism of submicron particle formation. Measured dependence of particle volume-mean diameter is consistent with theoretical predictions based on free-molecular Brownian coagulation of particles formed by nucleation of vaporized ash. Strong dependence of submicron particle volume concentration on char particle temperatures in the hot zone further suggests vaporization of ash to be the principal source of material from which fine particles are formed.
\r\n\r\nA semi-quantitative combustion model was formulated to calculate char particle temperature-time histories in the laboratory furnace. An Arrhenius vaporization rate expression was fitted to the laboratory measurements of total submicron particle volume concentration using the particle temperature histories calculated from the combustion model. Estimates of kinetic parameters were compared with those of other investigators. The model calculations suggest that the mass-specific rate of ash vaporization is strongly dependent on parent coal particle size. This is due to higher burning temperatures of smaller particles together with a high apparent activation energy for ash vaporization.
\r\n\r\nRecommendations for further work are given.
", "doi": "10.7907/as3w-nf63", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:4164", "collection": "thesis", "collection_id": "4164", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10182006-083816", "type": "thesis", "title": "Laboratory Studies of Submicron Particle Formation in Pulverized Coal Combustion", "author": [ { "family_name": "Taylor", "given_name": "Dean Dalton", "clpid": "Taylor-Dean-Dalton" } ], "thesis_advisor": [ { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" } ], "thesis_committee": [ { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Sabersky", "given_name": "Rolf H.", "clpid": "Sabersky-R-H" }, { "family_name": "Zukoski", "given_name": "Edward E.", "clpid": "Zukoski-E-E" }, { "family_name": "Cass", "given_name": "Glen Rowan", "clpid": "Cass-G-R" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "A laboratory furnace was constructed to study the mechanism of submicron particle formation in pulverized coal boilers. Simulation was achieved by matching characteristic kinetic times in laboratory and field units. This was done by matching volumetric heat extraction rates. Reynolds number and geometric scaling were not deemed essential for the simulation.
\r\n\r\nCombustion-generated submicron aerosols from the laboratory furnace were characterized by size and composition distribution measurements using an electrical mobility analyzer and a low-pressure impactor. Elemental analysis of size-classified mass samples was done by alpha particle-induced X-ray emission spectrum analysis.
\r\n\r\nThe influence of macroscopic combustion parameters on the characteristics of fine particle emissions was investigated. Total submicron particle volume concentration was found to depend on burner type and to increase with temperature for each burner type tested. The particle volume concentration was found to increase with exhaust NO concentration.
\r\n\r\nThe fine particle composition was found to differ from that of larger residual ash particles which generally reflected the composition of the bulk ash. It was also found that combustion conditions (overall fuel-air equivalence ratio and wall temperature) influenced the composition of the smallest ash particles.
\r\n\r\nSpecies enrichment data are generally supportive of the vaporization-condensation mechanism of submicron particle formation. Measured dependence of particle volume-mean diameter is consistent with theoretical predictions based on free-molecular Brownian coagulation of particles formed by nucleation of vaporized ash. Strong dependence of submicron particle volume concentration on char particle temperatures in the hot zone further suggests vaporization of ash to be the principal source of material from which fine particles are formed.
\r\n\r\nA semi-quantitative combustion model was formulated to calculate char particle temperature-time histories in the laboratory furnace. An Arrhenius vaporization rate expression was fitted to the laboratory measurements of total submicron particle volume concentration using the particle temperature histories calculated from the combustion model. Estimates of kinetic parameters were compared with those of other investigators. The model calculations suggest that the mass-specific rate of ash vaporization is strongly dependent on parent coal particle size. This is due to higher burning temperatures of smaller particles together with a high apparent activation energy for ash vaporization.
\r\n\r\nRecommendations for further work are given.
", "doi": "10.7907/as3w-nf63", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:3922", "collection": "thesis", "collection_id": "3922", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10042006-154422", "type": "thesis", "title": "Catalytic Activity and Deactivation Mechanisms of Supported NiO in CH\u2084 Oxidation", "author": [ { "family_name": "Phichitkul", "given_name": "Charunya", "clpid": "Phichitkul-Charunya" } ], "thesis_advisor": [ { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Weinberg", "given_name": "William Henry", "clpid": "Weinberg-W-H" }, { "family_name": "Voecks", "given_name": "Gerald E.", "clpid": "Voecks-Gerald-E" }, { "family_name": "Bailey", "given_name": "James E.", "clpid": "Bailey-J-E" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The partial oxidation of CH4 was studied using a commercial Ni/\u03b1-Al2O3 catalyst. The results show that two operating regimes can be maintained: a low-conversion regime where CO2 and H2O are formed and a high-conversion regime where CO, CO2, H2 and H2O are formed. The latter regime is established by \"catalytic light-off\" which among other conditions depends on temperature, feed composition and catalyst activity. Prior to light-off, the catalyst is in the NiO form. Following light-off, the catalyst is in NiO form near the inlet and metallic form further downstream. A series of NiO/\u03b1-Al2O3, and NiO/ZrO2 catalysts were prepared by impregnation and calcination in air between 750 and 1050\u00b0C. These catalysts were characterized by the BET method, O2 chemisorption, X-ray diffraction, electron microscopy and ESCA. Test analyses indicate that the supported NiO particles are made up of a large number of small crystallites which become more dispersed after reduction and reunite after oxidation. The activity of these catalysts for CH4 oxidation under pre-light-off conditions was found to decrease dramatically with increasing calcination temperature. However, the calcined catalysts can be reactivated by reduction in H2 prior to reaction. The change in activity is attributed mainly to the change in specific activity of NiO which is explained in terms of the change in excess oxygen content.
", "doi": "10.7907/kmv4-kb66", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:3932", "collection": "thesis", "collection_id": "3932", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10052006-105445", "type": "thesis", "title": "Kinetics and Mechanism of the Co-Oxidation of Aldehydes and Model Organic Sulfur Compounds in Studies Related to the Oxo-Desulfurization of Fuel Oil and Coal", "author": [ { "family_name": "Bone", "given_name": "Russell Leslie", "clpid": "Bone-Russell-Leslie" } ], "thesis_advisor": [ { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" }, { "family_name": "Kalvinskas", "given_name": "John J.", "clpid": "Kalvinskas-John-J" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Reaction rates and mechanisms in the oxidation of organic sulfur compounds by perbenzoic acid generated in situ from benzaldehyde autoxidation were investigated. Dibenzothiophene and diphenyl sulfide were utilized as model sulfur compounds typical of those present in residual oil and coal. The aromatic nature of a fuel medium was simulated by bromobenzene solvent. Reaction samples were quantitatively analyzed primarily by means of high-pressure liquid chromatography. Diffusion of oxygen, peracid decomposition, and direct oxidation of aldehyde by peracid were found to limit the formation of peracid. Activation energies for decomposition of the peracid and for direct oxidation of the aldehyde by peracid were obtained and used to explain the maximum in oxidation efficiency with respect to temperature observed for dibenzothiophene. Perbenzoic acid was found to be selective in oxidizing diphenyl sulfide and dibenzothiophene to the corresponding sulfoxides and sulfones. At 75\u00b0C, diphenyl sulfide was only oxidized approximately twice as rapidly as dibenzothiophene, in contrast with the higher rates reported by other investigators. Both sulfur compounds were found to inhibit the rate of benzaldehyde autoxidation.
", "doi": "10.7907/68ap-3w86", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:3639", "collection": "thesis", "collection_id": "3639", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09192006-130811", "type": "thesis", "title": "Coal Desulfurization by Selective Chlorinolysis", "author": [ { "family_name": "Vasilakos", "given_name": "Nikolaos Petrou", "clpid": "Vasilakos-Nikolaos-Petrou" } ], "thesis_advisor": [ { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" } ], "thesis_committee": [ { "family_name": "Corcoran", "given_name": "William Harrison", "clpid": "Corcoran-W-H" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" }, { "family_name": "Kalvinskas", "given_name": "John J.", "clpid": "Kalvinskas-John-J" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The desulfurization of coal by selective oxidation under slurry-phase chlorination conditions was investigated. Chemical reaction was found to be the rate-controlling step in carbon-tetrachloride chorination at 25\u00b0C for coal particles less than 150 \u00b5 in diameter. For larger particle sizes, a transition from chemical to intraparticlemass-transfer control was observed. The nitrogen-surface area of the coal decreased significantly as a result of the chlorination reaction.
\r\n\r\nThe reaction mechanism and the desulfurization patterns of chlorinolysis were studied under model-reaction and coal-chlorination conditions. Possible complete desulfurization schemes were considered.
\r\n\r\nThe role of solvents both in increasing the efficiency of the coal treatment and in providing alternative paths for coal beneficiation processes was also examined. The results of this study were interpreted within the frame of the solubility-parameter theory, utilizing the new experimental technique of solubility-parameter spectroscopy.
", "doi": "10.7907/05PE-T991", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:4235", "collection": "thesis", "collection_id": "4235", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10242006-104534", "primary_object_url": { "basename": "Hunt_jr_1980.pdf", "content": "final", "filesize": 5947269, "license": "other", "mime_type": "application/pdf", "url": "/4235/1/Hunt_jr_1980.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Coagulation in Continuous Particle Size Distributions: Theory and Experimental Verification", "author": [ { "family_name": "Hunt", "given_name": "James Robert", "clpid": "Hunt-James-Robert" } ], "thesis_advisor": [ { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" } ], "thesis_committee": [ { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" }, { "family_name": "List", "given_name": "E. John", "clpid": "List-E-J" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Saffman", "given_name": "Philip G.", "clpid": "Saffman-P-G" }, { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Friedlander", "given_name": "Sheldon K.", "clpid": "Friedlander-S-K" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Previous theories for particle coagulation are not readily applicable to the continuous particle size distributions encountered in natural waters. By extending concepts developed in the analysis of aerosol dynamics, predictions of continuous particle size distributions were obtained dimensionally for size intervals dominated by Brownian, shear, differential sedimentation coagulation and gravitational settling. A dynamic steady state size distribution was assumed to exist, maintained by a constant flux of particle volume through the distribution. Predictions have been successfully compared with the shapes of particle size distributions measured in oceanic waters.\r\n \r\nAn experimental program was designed to test the predictions with cleaned clay and silica minerals in artificial seawater. A series of batch experiments was conducted at fluid shear rates of 1/2 to 32 sec-1 in a rotating cylinder apparatus. During the experiments, total suspended volumes were determined from suspension optical absorbance, and particle size distributions were measured with a Coulter Counter-multichannel analyzer system. The volume flux through the distribution was estimated from the rate of suspended particle volume removal, which was second order in suspended volume and depended on the fluid shear rate.\r\n \r\nThe Brownian and shear coagulation predictions were verified for the kaolinite, illite, and montmorillonite clays. The three clays were significantly different in the regions of Brownian and shear coagulation dominance and in the volume removal rates at low fluid shear rates. At higher shear rates the volume removal rates declined because of aggregate breakup by fluid shear in the rotating cylinder apparatus. Differences in the clay coagulation and breakup characteristics were explained by variations in clay aggregate porosities. Experiments with silica did not agree with predictions because the silica particles were not destabilized in seawater. Predictions for differential sedimentation coagulation and gravitational settling could not be tested because of larger aggregate breakup by the Coulter Counter.\r\n\r\nThe theoretical predictions have direct application to particle coagulation in oceanic waters and possible application to more complex systems, such as estuarine waters and water and wastewater treatment operations.", "doi": "10.7907/dbbb-v854", "publication_date": "1980", "thesis_type": "phd", "thesis_year": "1980" }, { "id": "thesis:4235", "collection": "thesis", "collection_id": "4235", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10242006-104534", "primary_object_url": { "basename": "Hunt_jr_1980.pdf", "content": "final", "filesize": 5947269, "license": "other", "mime_type": "application/pdf", "url": "/4235/1/Hunt_jr_1980.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Coagulation in Continuous Particle Size Distributions: Theory and Experimental Verification", "author": [ { "family_name": "Hunt", "given_name": "James Robert", "clpid": "Hunt-James-Robert" } ], "thesis_advisor": [ { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" } ], "thesis_committee": [ { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" }, { "family_name": "List", "given_name": "E. John", "clpid": "List-E-J" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" }, { "family_name": "Saffman", "given_name": "Philip G.", "clpid": "Saffman-P-G" }, { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Friedlander", "given_name": "Sheldon K.", "clpid": "Friedlander-S-K" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Previous theories for particle coagulation are not readily applicable to the continuous particle size distributions encountered in natural waters. By extending concepts developed in the analysis of aerosol dynamics, predictions of continuous particle size distributions were obtained dimensionally for size intervals dominated by Brownian, shear, differential sedimentation coagulation and gravitational settling. A dynamic steady state size distribution was assumed to exist, maintained by a constant flux of particle volume through the distribution. Predictions have been successfully compared with the shapes of particle size distributions measured in oceanic waters.\r\n \r\nAn experimental program was designed to test the predictions with cleaned clay and silica minerals in artificial seawater. A series of batch experiments was conducted at fluid shear rates of 1/2 to 32 sec-1 in a rotating cylinder apparatus. During the experiments, total suspended volumes were determined from suspension optical absorbance, and particle size distributions were measured with a Coulter Counter-multichannel analyzer system. The volume flux through the distribution was estimated from the rate of suspended particle volume removal, which was second order in suspended volume and depended on the fluid shear rate.\r\n \r\nThe Brownian and shear coagulation predictions were verified for the kaolinite, illite, and montmorillonite clays. The three clays were significantly different in the regions of Brownian and shear coagulation dominance and in the volume removal rates at low fluid shear rates. At higher shear rates the volume removal rates declined because of aggregate breakup by fluid shear in the rotating cylinder apparatus. Differences in the clay coagulation and breakup characteristics were explained by variations in clay aggregate porosities. Experiments with silica did not agree with predictions because the silica particles were not destabilized in seawater. Predictions for differential sedimentation coagulation and gravitational settling could not be tested because of larger aggregate breakup by the Coulter Counter.\r\n\r\nThe theoretical predictions have direct application to particle coagulation in oceanic waters and possible application to more complex systems, such as estuarine waters and water and wastewater treatment operations.", "doi": "10.7907/dbbb-v854", "publication_date": "1980", "thesis_type": "phd", "thesis_year": "1980" } ]