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: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:244", "collection": "thesis", "collection_id": "244", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01202002-221541", "primary_object_url": { "basename": "Winblade_nd_2001.pdf", "content": "final", "filesize": 9533440, "license": "other", "mime_type": "application/pdf", "url": "/244/1/Winblade_nd_2001.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Blocking Adhesion to Cell and Tissue Surfaces via Steric Stabilization with Graft Copolymers Containing Poly(Ethylene Glycol) and Phenylboronic Acid", "author": [ { "family_name": "Winblade", "given_name": "Natalie Dawn", "orcid": "0000-0003-1293-345X", "clpid": "Winblade-Natalie-Dawn" } ], "thesis_advisor": [ { "family_name": "Hubbell", "given_name": "Jeffrey A.", "orcid": "0000-0003-0276-5456", "clpid": "Hubbell-J-A" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Hubbell", "given_name": "Jeffrey A.", "orcid": "0000-0003-0276-5456", "clpid": "Hubbell-J-A" }, { "family_name": "Hoffman", "given_name": "Allan S.", "clpid": "Hoffman-A-S" }, { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" }, { "family_name": "Bjorkman", "given_name": "Pamela J.", "orcid": "0000-0002-2277-3990", "clpid": "Bjorkman-P-J" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Graft copolymers were designed to coat biological surfaces and thereby block subsequent adhesion and recognition events with other proteins, cells, and tissues. Inspired by polymeric steric stabilization of colloidal dispersions, the copolymers contain a backbone with affinity for biological surfaces and grafted side-chains that are resistant to adhesion of biological elements. Phenylboronic acid (PBA) moieties in the polymer backbone provided for binding, by forming reversible covalent complexes with cis-diols in oligosaccharides that are ubiquitous on cell surfaces and secreted macromolecules. The PBA moieties were conjugated to a poly-L-lysine (PLL) backbone via a secondary amine linker. Grafted poly(ethylene glycol) (PEG) side-chains provided for resistance of adhesion of proteins and cells. It was hypothesized that these PLL-g-(PEG;PBA) copolymers would spontaneously assemble on biological (e.g., cell or tissue) surfaces, where the PBA-containing backbone would bind to the surfaces and thereby anchor a dense PEG brush on the surface.
\r\n\r\nPLL-g-(PEG;PBA) copolymers were synthesized with varying degrees of PEG and PBA grafting. The pKa of the PBA groups was found to be circa 6, allowing for stronger binding at physiological pH than most PBA groups, which have pKas circa 8.8. The PLL-g-(PEG;PBA) copolymers were found to bind specifically to a mannan resin, where the PEG grafting ratio sterically controlled the binding. The copolymers coated red blood cells and blocked their agglutination by lectins and by blood group antibodies. The copolymers were also found to coat tissue culture polystyrene, adsorbed serum proteins, and extracellular matrix and to prevent the adhesion, spreading, and/or migration of rabbit lens epithelial cells on those surfaces. The copolymers displayed evidence of toxicity in vitro but no toxicity was seen when administered in vivo in models of posterior capsule opacification or peritoneal adhesion formation. PLL-g-(PEG;PBA) was found to interfere with the worsening of peritoneal adhesions following adhesiolysis. The efficacy of the copolymers was a function of the degree of PEG and PBA grafting, and PLL-g-(PEG;PBA) copolymers were found to be more effective than electrostatically-binding PLL-g-PEG copolymers. PLL-g-(PEG;PBA) copolymers have many possible clinical applications where blocking protein or cell interactions with cell, tissue, or biomaterial surfaces via a simple aqueous lavage is desired.
", "doi": "10.7907/B47A-E319", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:3115", "collection": "thesis", "collection_id": "3115", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08132007-143014", "primary_object_url": { "basename": "Pratt_a_2001.pdf", "content": "final", "filesize": 9666316, "license": "other", "mime_type": "application/pdf", "url": "/3115/1/Pratt_a_2001.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Cell-Responsive Synthetic Biomaterials Formed in situ", "author": [ { "family_name": "Pratt", "given_name": "Alison Beth", "clpid": "Pratt-Alison-Beth" } ], "thesis_advisor": [ { "family_name": "Hubbell", "given_name": "Jeffrey A.", "orcid": "0000-0003-0276-5456", "clpid": "Hubbell-J-A" }, { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "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": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" }, { "family_name": "Hubbell", "given_name": "Jeffrey A.", "orcid": "0000-0003-0276-5456", "clpid": "Hubbell-J-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Two-way communication between cells and their extracellular matrices plays an important role in establishing and maintaining cell and tissue morphology. Synthetic materials for tissue engineering have so far not been able to mimic these interactions. This work describes a new class of synthetic biomaterials that display the essential characteristics of naturally occurring matrices. The materials can be formed in contact with cells and tissues to create covalently cross-linked hydrogels which are effectively nonporous on the length scale of a cell process. The otherwise nonadhesive gels can be rendered specifically cell-adhesive by incorporation of ligands for cell surface adhesion molecules, such as integrins. The materials are degradable by plasmin, a proteolytic enzyme used by cells during proliferation and migration in natural matrices. Furthermore, the materials can be designed to sequester heparin-binding growth factors.
\r\n\r\nThe materials consist primarily of poly(ethylene glycol) which is cross-linked in situ by selective conjugate addition reactions of its termini, activated with conjugate acceptors such as vinylsulfones, with peptides containing three or more cysteine residues in the form of reduced thiols. The cross-linking peptides are designed such that they are hydrolyzed by plasmin. A simple cell migration assay was developed to evaluate the material design parameters. Human fibroblasts were observed to migrate out of microliter fibrin clots into the synthetic materials in a manner dependent on the type of material and the culture conditions. Inhibiting fibrinolysis with a plasmin-insensitive substrate or with a plasmin inhibitor, [epsilon]-amino-n-caproic acid, inhibited migration. Adding growth factors, FGF-2 or PDGF-BB, that upregulate plasminogen activation increased the rate of cell migration. Decreasing the amount of RGD within the materials decreased the rate and extent of cell migration in a concentration-dependent manner. Replacing the RGD peptide with an RDG peptide decreased the amount of outgrowth.
\r\n\r\nIn a critical size calvarial defect in the rat, the synthetic materials were formed in the presence of an osteoinductive protein, rhBMP-2, and supported de novo bone formation. Materials containing a heparin-based growth factor delivery system promoted significantly more bone than materials without the delivery system. After three weeks, 94% of the defect area was covered with new bone, and the opacity of the new bone was 84% of that of neighboring, uninjured bone.
", "doi": "10.7907/HFEF-7F61", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "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: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:4486", "collection": "thesis", "collection_id": "4486", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11102005-083452", "primary_object_url": { "basename": "Tsapatsis_m_1994.pdf", "content": "final", "filesize": 7120010, "license": "other", "mime_type": "application/pdf", "url": "/4486/1/Tsapatsis_m_1994.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Composite inorganic membranes for gas separations : chemical vapor deposition of hydrogen permselective oxide membranes and preparation of supported zeolite NaA films", "author": [ { "family_name": "Tsapatsis", "given_name": "Michael", "clpid": "Tsapatsis-M" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nHydrogen-perselective membranes were synthesized by chemical vapor deposition of SiO2, TiO2, Al2O3, and B2O3 layers within the pores of Vycor tubes. The deposition involved reaction of SiCl4, etc., with water at 100-800 [degrees]C depending on the chloride and the reaction geometry. The reactants were passed either through the bore of the support tube (one sided geometry) or separately through the bore and the outside surface of the support tube (opposing reactants geometry). Permselective SiO2 and B2O3 layers could be formed in either the one-sided or the two-sided (opposing reactants) geometry, while deposition of TiO2 and Al2O3 layers was achieved only in the two-sided geometry. The permeances at 450 [degrees]C were 0.3 and 0.1 [...]-min-atm for SiO2 membranes produced in the one-sided geometry and two-sided geometries respectively. The H2:N2 permeance ratios were 500-5000. The TiO2 and Al2O3 membranes had somewhat lower permeance and H2:N2 ratios. Annealing at high temperatures causes densification of the deposited material as evidenced by increased activation energy for H2 permeation and correspondingly reduced permeance. The presence of H2O vapor accelerates the densification process. The densified membranes had a H2 permeance as high as 0.1 [...](STP)/min-atm-[...] at 500 [degrees]C and a H2/N2 permeance ratio above 500.\n\nSilica, titania and alumina layers deposited in an opposing reactants geometry were characterized by scanning electron microscopy (SEM) and electron microprobe analysis (EPMA). The layers are asymmetric, having a long tail towards the side of the chloride flow and a sharp boundary at the other side. The deposit thickness is several tenths of microns while the totally plugged region is of order of one micron. Silica deposit layers prepared in the one-sided geometry were examined by transmission electron microscopy (TEM), SEM, and EPMA. When the deposit was confined inside the pores of the Vycor substrate, the membranes were mechanically stable, but when it extended substantially outside of the porous matrix, the stresses induced by thermal cycling led to crack formation and propagation. Electron microscopy revealed that the SiO2 deposit density is maximum in a region about 0.5 \u00b5m thick adjacent to the bore surface and gradually declines to zero within a depth of about 10 \u00b5m from the surface. The thin region of maximum deposit density is responsible for permselectivity, for it essentially blocks the permeation of nitrogen and larger molecules while allowing substantial permeation of hydrogen. This region contains about 10% by volume trapped voids and as a result has relatively high permeability as suggested by percolation theory.\n\nA mathematical model is developed for SiO2 deposition in porous Vycor using SiCl4 hydrolysis. The model describes reaction, diffusion and evolution of the pore structure due to accumulation of the solid product. The deposition reaction is described by transient heterogeneous kinetics in terms of the concentrations of silanol and chloride groups in the product layer as well as the concentrations of the gaseous reactants. Pore structure evolution was modeled by incorporating results of percolation theory in a continuum model. The model is capable of generating deposit profiles in good agreement with the experiment. It is shown that for typical deposition conditions the pseudosteady state approximation for surface species could lead to erroneous predictions. Pore connectivity interruption at a nonzero void fraction leads to thinner deposits and shorter deposition times for pore plugging compared to the corresponding ones for an infinitely connected medium.\n\nThe growth of zeolite NaA films on various inorganic substrates from a clear solution with composition 10 Na2O - 0.2 Al2O3 - 1SiO2 - 200 H2O was followed by XRD, SEM and TEM. Deposition geometries and conditions are identified for the development of uniform polycrystalline thin (<5\u00b5m) films consisting of intergrown crystals of zeolite NaA on porous and nonporous Al2O3 disks. The films exhibit high crystallinity good adhesion to the substrate and thermal stability. The deposition technique demonstrates potential for developing molecular sieve membranes.", "doi": "10.7907/RZP1-G920", "publication_date": "1994", "thesis_type": "phd", "thesis_year": "1994" }, { "id": "thesis:4748", "collection": "thesis", "collection_id": "4748", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12032007-142610", "primary_object_url": { "basename": "Kim_s_1994.pdf", "content": "final", "filesize": 10397686, "license": "other", "mime_type": "application/pdf", "url": "/4748/1/Kim_s_1994.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Chemical vapor deposition of permselective oxide membranes for hydrogen separation", "author": [ { "family_name": "Kim", "given_name": "Soojin", "clpid": "Kim-S" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nMembranes have recently emerged as energy-efficient means of gas separation. Oxide membranes that are effective for hydrogen separation at elevated temperatures (400-800\u00b0C) were developed. The membranes have high [...] selectivities along with permeances that are comparable to those of conventional polymeric membranes operating at ambient temperature.\n\nHydrogen-permselective membranes were synthesized by chemical vapor deposition of [...], [...], [...], and [...] layers within the pores of Vycor tubes. The deposition was carried out by continuous flow of [...], etc., and water in either the one-sided or the two-sided (opposing-reactants) geometry at 100-800\u00b0C. Permselective [...] layers could be formed in both geometries, while deposition of [...] and [...] layers was achieved only in the two-sided geometry. The permeation coefficients at 450\u00b0C were 0.3 and 0.1 [...] for [...] membranes produced in the one-sided geometry and two-sided geometries, respectively. The [...] permeation ratios were 500-5000. The [...] and [...] membranes had somewhat lower permeation coefficients and [...] ratios.\n\nThe [...] membranes prepared in the opposing-reactants geometry were characterized by scanning electron microscopy, electron microprobe analysis, and transmission electron microscopy. Examining tube cross section containing [...] deposit revealed that the membrane consisted of a thin region (approximately 1 [...] thick) of totally plugged pores and a broad region (100 [...]) of partially filled pores. The spatial density distribution of [...] in the tube cross section showed an asymmetric profile located close to the side of chloride flow indicating heterogeneous mechanism of the deposition reaction. The [...] permeance of the membranes decreased by 50-75%, and the selectivity diminished upon prolonged hydrothermal treatment.\n\nA mechanism of the deposition process is suggested involving heterogeneous reactions of gaseous chloride and surface hydroxyl groups and of water vapor with surface chloride groups on the growing deposit layer. The mechanism and kinetics of [...] deposition were investigated by thermogravimetric analysis. The reactions were decoupled by alternating reactions of [...] and [...] with the surface of Vycor glass. The results are interpreted by postulating two types of silanol groups Si-OH on the Vycor surface, paired and isolated. Reaction of [...] with paired silanols proceeds by competing steps which control the total extent of silylation. Upon reaction with [...], all surface Si-Cl groups are hydrolyzed regenerating Si-OH. Simultaneous silanol-silanol and silanol-surface chloride condensations eliminate [...] or HCl to form new Si-O-Si bridges with final product silica. A kinetic model incorporating the silylation, hydrolysis and condensation steps describes well the TGA data.\n\nThe reaction of the chlorosilanes with surface hydroxyls occurs very rapidly at temperatures above [...] and causes significant axial concentration gradients in the one-sided deposition, resulting in nonuniform deposit layer along the length of the tube. A new technique that eliminated the axial concentration gradients was used to deposit thin [...] layers on the surface of porous Vycor glass. Alternating vapor phase reaction with SiC14 and H2O was used to prepare membranes having [...] permeance of 0.3-0.4 [...] and [...] selectivity of 500-1000 at [...] 600\u00b0C. The [...] dosage at each silylation cycle, the concentration of initial surface -OH groups, and the reaction temperature influence significantly the deposit layer thickness. The membranes were stable to long hydrothermal treatments with the [...] permeance decreasing by about 20% and the selectivity increasing to more than 2000. The membrane properties after hydrothermal treatment are superior to those of membranes prepared by one-sided (steady flow) deposition due to thinner and more uniform deposit layers. A simple model incorporating diffusion and surface reaction was used to study the effect of various parameters on the formation of the deposit layer.", "doi": "10.7907/cme7-m131", "publication_date": "1994", "thesis_type": "phd", "thesis_year": "1994" }, { "id": "thesis:2972", "collection": "thesis", "collection_id": "2972", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07232007-152302", "primary_object_url": { "basename": "Choi_mk_1992.pdf", "content": "final", "filesize": 3426529, "license": "other", "mime_type": "application/pdf", "url": "/2972/1/Choi_mk_1992.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Particle Shape Effects on Gas-Solid Reactions", "author": [ { "family_name": "Choi", "given_name": "Moon Kyu", "clpid": "Choi-Moon-Kyu" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "A theoretical study of the reaction of nonspherical particles is carried out in the shrinking core regime to determine the effect of particle shape on total reaction rate, particle temperature, and to characterize the evolution of shape with consumption of particle. This problem involves the solution of the external diffusion and heat conduction equations with the reaction entering as a boundary condition over the particle surface. Firstly, the problem is treated isothermally by a domain perturbation technique to give analytical results for a slightly nonspherical particle and by the boundary integral technique for spheroids of arbitrary aspect ratio. Secondly, the nonisothermal problem is solved to give the pseudosteady and dynamic behaviors of nonspherical particles taking char combustion as an example. For the dynamic problem the diffusion and heat conduction in the gas phase are assumed to be at pseudosteady state with respect to the evolving particle temperature and particle size and shape. Lastly, the effect of surface roughness on the gas-solid reaction is similarly examined by representing the particle surface as a series in Legendre polynomials superimposed on an underlying spherical surface.
\r\n\r\nFor nonspherical particles of equal volume but varying shape reacting under isothermal or nonisothermal conditions, the total reaction rate increases with the aspect ratio and is approximately equal to that of the sphere of equal surface area, and the local reaction rate increases with the distance from the particle center. The pseudosteady particle temperature under nonisothermal conditions is essentially the same for various spheroidal particles of equal volume. The particle temperature approaches quickly and remains close to its pseudosteady trajectory with conversion. During reaction a particle becomes more and more nonspherical. As for the effect of roughness, from the method of domain perturbation the nth mode decreases if the Damkohler number Q > Qcr = n+1/n-2, and vice versa. For highly irregular particles, too, this criterion applies overall, but they do not have sharp critical values of Q showing mixed behavior in a certain range around Qcr.
", "doi": "10.7907/kg6r-ft80", "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:2911", "collection": "thesis", "collection_id": "2911", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07172007-090918", "primary_object_url": { "basename": "Wong_ba_1991.pdf", "content": "final", "filesize": 7858021, "license": "other", "mime_type": "application/pdf", "url": "/2911/1/Wong_ba_1991.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The oxidation of individually levitated char particles", "author": [ { "family_name": "Wong", "given_name": "Brian Alan", "clpid": "Wong-B-A" } ], "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": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "An electrodynamic balance was constructed for use as a single particle thermogravimetric analyzer. The electrodynamic balance uses a vertical DC field to levitate an electrically charged particle. An AC voltage is applied to a ring electrode surrounding the particle between the DC electrodes. This AC field provides a restoring force if the particle is displaced from the center of the balance. A carbon dioxide laser was used to heat the particle. The temperature of the particle was measured by a dual-wavelength optical pyrometer. Two materials were the subject of oxidation studies, a porous synthetic carbon, Spherocarb and char made from PSOC 1451 bituminous coal. Two studies were performed, an ignition study, and a low temperature oxidation study. In the ignition study, a suspended particle was heated by a series of 500 millisecond pulses from the laser, at increasing oxygen concentrations. The particle temperature trace shows the ignition delay as predicted by Semenov's thermal explosion theory. A simple isothermal sphere model was applied with literature values for the physical parameters. A reasonably good match of the data to the model was found. In the low temperature experiments char particles were heated in air to a temperature of about 600\u00b0C. Some of the particles did not react at constant diameter, as expected. In particular, Spherocarb shrank or densified, as noted by others. The char particles formed from a narrow size cut of PSOC 1451 bituminous coal devolatilized at 1200K also shrank in size as it reacted. However the char formed at 1600K did not shrink, but oxidized at constant diameter. The densification phenomenon, then, is dependent on the devolatilization process and charring temperature. Simple char oxidation models will not accurately predict the size changes of these shrinking chars.\n", "doi": "10.7907/tm62-ax11", "publication_date": "1991", "thesis_type": "phd", "thesis_year": "1991" }, { "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: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: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: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: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: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: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: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: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: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: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: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: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: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: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: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: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:4012", "collection": "thesis", "collection_id": "4012", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10102006-104201", "primary_object_url": { "basename": "Watson_at_1980.pdf", "content": "final", "filesize": 6511003, "license": "other", "mime_type": "application/pdf", "url": "/4012/1/Watson_at_1980.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Estimation of Two-Phase Petroleum Reservoir Properties", "author": [ { "family_name": "Watson", "given_name": "Albert Theodore", "clpid": "Watson-Albert-Theodore" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The estimation of petroleum reservoir properties on the basis of production rate and pressure observations at the wells is an essential component in the prediction of reservoir behavior. The reservoir properties to be estimated appear as parameters in the partial differential equations describing the flow of fluids in the reservoir. The estimation of these properties is referred to variously as the inverse or identification problem or as history matching. In this dissertation, new results have been obtained pertaining to the estimation of petroleum reservoir properties.\r\n\r\nMost of the prior analysis of the reservoir parameter estimation problem has been confined to reservoirs containing a single fluid phase, e.g., oil. We consider here reservoirs that contain two fluid phases, e.g., oil and water. The parameters to be estimated in such a case are the porosity and permeability, which depend on spatial location, and the saturation-dependent relative permeabilities. In this work we treat two basic problems in reservoir parameter estimation: (1) establishing the ability to estimate the desired parameters (so-called identifiability), and (2) developing and testing a new algorithm, based on optimal control theory, to carry out the estimation.\r\n \r\nIn regard to problem (1), we have extended the classic analytical (Buckley-Leverett) solution for incompressible flow to heterogeneous reservoirs. Analysis for an incompressible water flooding situation shows that the spatially varying properties at locations behind the saturation front have an effect on the pressure solution. The spatially varying properties can be uniquely determined based on data taken up to the time of water breakthrough. Only an integral value of the porosity can be determined from the water-oil ratio data alone; however, the spatially varying porosity may be determined when the initial saturation varies with location. The values of the relative permeabilities which are identifiable, and the information about the relative permeabilities obtained for other intervals of saturation, is established. Analytical expressions are derived for the sensitivity of the pressure and water-oil ratio observations to parameters appearing in functional forms of the relative permeabilities. When the relative permeabilities are represented as exponential functions, the coefficients and exponents can be uniquely determined.\r\n\r\nFor problem (2), an algorithm is developed for the estimation of porosity, permeability and the relative permeabilities for two-phase, compressible reservoirs. This work represents the first study for which relative permeabilities have been estimated based on a model generally used to represent fluid flow in petroleum reservoirs. An objective function, composed of the weighted sum of squares of the deviations between the observed and calculated values of pressure and water-oil ratio, is minimized by a first-order gradient method based on optimal control theory. The algorithm is tested for one and two-dimensional hypothetical water floods. The algorithm performed well for problems in which the porosity, permeability and relative permeability exponents were simultaneously estimated. The increase from one to two spatial variables does not appear to change the properties of the estimation problem. Small observation errors are shown not to significantly affect the convergence of the estimates.", "doi": "10.7907/004X-2856", "publication_date": "1980", "thesis_type": "phd", "thesis_year": "1980" }, { "id": "thesis:4942", "collection": "thesis", "collection_id": "4942", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12112006-085017", "primary_object_url": { "basename": "Jain_r_1980.pdf", "content": "final", "filesize": 11459168, "license": "other", "mime_type": "application/pdf", "url": "/4942/1/Jain_r_1980.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Mathematical Modeling and Experimental Studies of Thermal Reactions of Coal", "author": [ { "family_name": "Jain", "given_name": "Ravi", "clpid": "Jain-Ravi" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This dissertation discusses theoretical and experimental research on coal pyrolysis.\r\n\r\nIn the theoretical part, a mathematical model based on coal's chemical structure and its reactions is developed for computer simulation of pyrolysis. Firstly, the important organic functional groups of carbon, hydrogen and oxygen in medium and high rank coals are organized into a conceptual model for coal's chemical structure. Using the principles of thermochemistry of free radicals as guidelines, the important categories of chemical reactions in coal pyrolysis are postulated. A set of 41 series-parallel reactions represents the chemical change. It is concluded that there is no a priori distinction between volatiles and non-volatiles in a coal. They are both formed from the same chemical structure, and are basically an inevitable consequence of each other's formation.\r\n\r\nFor the purpose of mathematical modeling, coal is considered to be a population of randomly distributed functional groups on a matrix. A scheme based on statistical transformations is devised to compute concentrations of reacting configurations before and during pyrolysis. The rates of reactions are expressed in terms of these concentrations. Differential equations governing the rate of change of state variables with pyrolysis time are formulated and numerically integrated on the computer. Pyrolysis results are predicted in terms of the state variables.\r\n\r\nThe dependence of the yield and composition of volatiles on (a) transport parameters like particle size and pressure, and (b) kinetic parameters like time, temperature and time-temperature history, is investigated experimentally. Gaseous products are analyzed using chromatography, while tar is characterized by GPC, NMR and elemental analysis.\r\n\r\nBasic research on coal helps in developing a general \"theory\" about its structure and chemical behavior. It enhances our ability to meet process, economic and environmental goals in coal's industrial utilization.", "doi": "10.7907/HAV6-QD05", "publication_date": "1980", "thesis_type": "phd", "thesis_year": "1980" }, { "id": "thesis:4367", "collection": "thesis", "collection_id": "4367", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11022004-090942", "primary_object_url": { "basename": "Yortsos_yc_1979.pdf", "content": "final", "filesize": 11827700, "license": "other", "mime_type": "application/pdf", "url": "/4367/1/Yortsos_yc_1979.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Analytical Modelling of Oil Recovery by Steam Injection", "author": [ { "family_name": "Yortsos", "given_name": "Yanis Christos", "clpid": "Yortsos-Yanis-Christos" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This dissertation is concerned with the mathematical modelling of oil recovery by steam injection using analytical techniques.\r\n\r\nAn integral method for generating approximate solutions to the one and two- (three-) dimensional steam injection processes is presented. Due to the qualitatively different character of the problem the one- and two- (three-) dimensional cases are examined separately.\r\n\r\nThe applicability of the method for the determination of the rate of growth of the steam zone volume in one-dimensional systems is considered. An extensive study of the heat transfer in the surroundings and the hot liquid zone is carried out to complement the one-dimensional implementation of the technique. The resulting class of moving boundary problems and their methods of solution are discussed in detail. The results obtained are then combined with the integral technique to derive upper and lower bounds, asymptotic solutions and approximate solutions to the rate of growth of the steam zone. The important physical parameters are identified and their significance in the design of the process is outlined. In particular, the very important effect of heat transport in the surroundings and the hot liquid zone is fully accounted.\r\n\r\nFor two- (three-) dimensional systems, a more detailed version of the integral method is developed to account for the effect of gravity segregation in the determination of the steam front shape. A non-linear partial differential equation that describes the evolution of the steam front shape in gravity dominated systems is derived. The significance of the various physical parameters in the performance of a three-dimensional steam injection process is discussed by providing a solution to the equation derived, in the limit of predominantly viscous flows.\r\n\r\nA critical evaluation of the existing analytical models is presented and the regions of their validity established. The potential of the techniques developed, particularly in the heat transfer area, to treat a class of in-situ thermal methods is also clearly indicated.", "doi": "10.7907/T5A4-1W70", "publication_date": "1979", "thesis_type": "phd", "thesis_year": "1979" }, { "id": "thesis:17828", "collection": "thesis", "collection_id": "17828", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01202026-211950178", "primary_object_url": { "basename": "Cheong_PHK_1977.pdf", "content": "final", "filesize": 1934884, "license": "other", "mime_type": "application/pdf", "url": "/17828/1/Cheong_PHK_1977.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "A Modeling Study of Coal Pyrolysis", "author": [ { "family_name": "Cheong", "given_name": "Paul How-Kei", "clpid": "Cheong-Paul-How-Kei" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "A model of coal pyrolysis is developed with the elements of (i) structure, (ii) chemical reactions, and (iii) transport.
\r\n\r\n(i) The chemical structure of coal is modeled as aromatic clusters bearing aliphatic side chains, bridges, and phenolic functional groups, consistent with various spectroscopic data and known chemical behavior.
\r\n\r\n(ii) A detailed scheme of thermal free radical reactions leading to the formation of tar, gases and deactivated char is postulated. State variables are defined as concentrations of the participating functional groups to describe the stoichiometry and rates of these reactions.
\r\n\r\n(iii) Macropores and transitional pores partition the coal particle into smaller subunits in which transport of tarry and gaseous products is by means of activated diffusion. The transport model postulates an active surface region of the subunits and a process of renewal of that region. A counting procedure is devised to predict the amount of aromatic fragments that escape from the subunits.
\r\n\r\nThe physicochemical processes are translated into a system of ordinary differential equations in the state variables, parametrized by the initial conditions and appropriate rate parameters. Numerical simulation is performed for two case studies where the necessary parameters are deduced from available pyrolysis and structural data and from additional assumptions.
\r\n\r\nThe model is applicable within the range of primary pyrolysis ((650\u00b0c) and predicts the ultimate weight loss as well as the distribution of products as a function of temperature and coal type. A supplementary model is also formulated for the reaction and transport of volatile materials in the macropores. This model takes into account the effects of the external pressure and the particle size on the evolution of products.
", "doi": "10.7907/0am7-4v78", "publication_date": "1977", "thesis_type": "phd", "thesis_year": "1977" }, { "id": "thesis:4774", "collection": "thesis", "collection_id": "4774", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12042006-081055", "primary_object_url": { "basename": "Shah_pc_1977.pdf", "content": "final", "filesize": 10893741, "license": "other", "mime_type": "application/pdf", "url": "/4774/1/Shah_pc_1977.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Estimation of Properties in Petroleum Reservoirs", "author": [ { "family_name": "Shah", "given_name": "Piyush Chimanlal", "clpid": "Shah-Piyush-Chimanlal" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" }, { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "The determination of parameters in a dynamical system, on the basis of noisy observations of its state is variously known as parameter estimation, identification or the inverse problem. In this work, the determination of porous rock property distribution in a petroleum reservoir using the production rate records and observed pressures (the history matching problem) is considered.\r\n\r\nThe history matching problem is inherently underdetermined because of the large number of unknown parameters relative to the available data. The number of unknowns can be reduced by representing the distributions by a small number of parameters (parameterization). The commonly used zonation approach involves a parameterization, but introduces a considerable modeling error. In chapter 1, Bayesian estimation theory is extended to history matching as an alternative to zonation; it is sought to alleviate the underdeterminacy through specification of a priori statistical information about the unknown parameters. Application of Bayesian estimation and zonation to the problem of porosity and permeability estimation in a one-dimensional single-phase reservoir indicates that the former yields superior estimates; this holds true even when the prior statistics involve large errors. The application of the conjugate gradient and the Gauss-Newton (or Marquardt's) algorithms for history matching is investigated, and the numerical effort for zonation and Bayesian estimation in one- and two-dimensional reservoirs is estimated in detail.\r\n\r\nIn chapter 2, analytic expressions are derived for the sensitivities of an observed oil pressure to small, arbitrary changes in the porosity and permeability distributions in a one-dimensional reservoir. The results indicate that highly oscillatory components of either have very small influence on the pressure and thus cannot be determined by history matching. Further, the dependence of all the observed pressures on the unknown parameters is linearized, for small deviation, about two reference property distributions. The linear relation is analyzed to yield quantitative information concerning the statistical properties of the problem. Iterative corrections in the history matching algorithms are identified with various pseudo-inverses of the linear relation, thus explaining the properties of the resulting estimates. The nature of the linear relation is found to be not strongly dependent on the reference property distributions used for linearization; thus such analysis can be performed prior to estimation. It is discussed how the linearized analysis can be used to determine the determinacy of any given parameterization.\r\n\r\nThe information derived from the linearized analysis and that in the a priori statistics is synthesized in chapter 3 to predict covariances for the zonation and Bayesian estimates. Since the results of the linearized analysis depend only weakly on the reference distribution, the predicted covariances are valid for a class of reservoirs having \"true\" property distributions with identical prior statistics. A good agreement is found when the predicted variances are compared with actual mean square estimate errors in simulations with four distributions with given prior statistics. The sensitivity of the estimates and their covariance to changes and errors in the specification of the prior statistics are investigated in considerable detail. The determination of zonation with smallest trace of estimate covariance for a given problem is considered. The design of Marquardt's algorithm to yield the smallest expected total estimate error for a given zonation is discussed.", "doi": "10.7907/7DC3-EX92", "publication_date": "1977", "thesis_type": "phd", "thesis_year": "1977" }, { "id": "thesis:18546", "collection": "thesis", "collection_id": "18546", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05082026-170122915", "primary_object_url": { "basename": "Vatcha_SR_1976.pdf", "content": "final", "filesize": 111439062, "license": "other", "mime_type": "application/pdf", "url": "/18546/1/Vatcha_SR_1976.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Analysis and Design of Methanation Processes in the Production of Substitute Natural Gas from Coal", "author": [ { "family_name": "Vatcha", "given_name": "Sorab Rustom", "clpid": "Vatcha-Sorab-Rustom" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Methanation, the final major step common to all processes for the\r\nconversion of coal to substitute natural gas, upgrades the sulfur-free\r\nsynthesis gas to comply with the pipeline quality standards:
\r\n\r\n< 0.1 % CO,> 900 BTU/SCF (35.5 MJ/Nm3)
\r\n\r\nA reactor system featuring good temperature control and effective\r\nheat recovery is essential for effecting the strongly exothermic reaction\r\n(CO + 3H2 \u2192 CH4 + H2O) to a high overall conversion. The\r\ndifferent reactor arrangements of the leading processes (currently at\r\nthe pilot plant stage of development) are critically assessed and\r\ncompared: multistage adiabatic packed beds, fluidized bed, Raney nickel\r\ncoated tubes with circulating coolant, and a 3-phase slurry.
\r\n\r\nComputations of reaction equilibria and energy balances are performed\r\nto delineate operating conditions and maximum yields for both\r\nisothermal and adiabatic methanators in the range of total pressures\r\nfrom 50 to 90 atm. The effects of dry recycle and the concurrent shift\r\nreaction on the equilibrium composition and properties of the product\r\nstream from an isothermal methanator are shown. Graphs are provided for\r\npredicting the extent of formation of undesirable nickel carbonyl or\r\ncarbon (as graphite) at equilibrium.
\r\n\r\nOn the basis of a comprehensive literature survey, the intrinsic\r\nkinetics and selectivity are analyzed relative to catalyst properties.\r\nA thermodynamically consistent rate expression is formulated and\r\nemployed in methanator design. It is based on a published rate expression\r\napplicable to a commercial nickel-kieselguhr catalyst, Harshaw\r\nNi-0104T. Transport effects, catalyst deactivation, and their\r\ninfluence on reactor operation are examined. Intrapellet gradients of\r\nconcentration are usually significant while intrapellet temperature\r\ngradients are moderate.
\r\n\r\nA modular process simulator is developed and applied to the design\r\nof a commercial scale methanation system. A two-stage cylindrical\r\nradial flow packed reactor with feed split and cold recycle is selected\r\nfor the simulation studies. It is shown to be superior to the other\r\nconfigurations in many respects, notably by a low pressure drop.\r\nCooler-condensers of the vertical downflow type are designed by a\r\nrigorous finite element algorithm whose accuracy has been validated by\r\ncomparison with experimental results reported in the literature.
\r\n\r\nNearly all the published economic estimates have tended to understate\r\ncosts and there is a need for a uniform, standardized accounting\r\nprocedure. The sensitivities of the (free-market) product gas price to\r\n6 process and economic factors are estimated; it is most sensitive to\r\nthe cost of coal and least sensitive to the debt fraction.
\r\n\r\nSome key problems and promising directions for future research and\r\ndevelopment are identified. The development of more sulfur-tolerant,\r\nlong-lasting catalysts and reliable kinetic data under conditions of\r\nindustrial methanator operation deserve a high priority.
", "doi": "10.7907/n760-pt75", "publication_date": "1976", "thesis_type": "phd", "thesis_year": "1976" }, { "id": "thesis:10597", "collection": "thesis", "collection_id": "10597", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12072017-144658705", "type": "thesis", "title": "Characterization of Acid-Base Catalysts and its Application to Catalyst Poisoning", "author": [ { "family_name": "Bakshi", "given_name": "Kiran Ravindra", "clpid": "Bakshi-Kiran-Ravinda" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "orcid": "0000-0003-1468-6835", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Several commercial aluminas, silica-aluminas and clays are investigated \r\nfrom a standpoint of catalyst characterization and the influence of partial \r\ndeactivation on their activities for dehydration of primary alcohols. The \r\nstates of the various catalysts are characterized by calorimetric titr\u00adations \r\nwith n-butylamine and trichloroacetic acid and the resulting heat of \r\nadsorption curves are utilized to obtain acidity and basicity distributions \r\nfor each catalyst state. A division of these distributions into groups of \r\nsuitable acidic and basic site pairs leads to the development of a correla\u00adtion \r\nbetween the acid-base distributions and the catalyst activities. The postulates \r\nof the correlation are in agreement with the reaction mechanism previously \r\nproposed in the literature.
\r\n\r\nSeveral of these catalysts are subjected to poisoning by ammonia and \r\norganic bases of different strengths. Subsequent evaluation of the acid-base \r\ndistributions of the deactivated catalysts show subtle changes in the basicity \r\ndistributions depending upon the strength of the poison. The cor\u00adrelation \r\ndeveloped earlier is used to predict the activities and selectivities of \r\nthe deactivated catalysts. The good agreement between the predictions and \r\nthe experimental results substantiate the usefulness of the correlation.\r\nSubtle changes in selectivity caused by poisoning have been explained \r\nby the corresponding changes in the acid-base distributions, thus proving \r\nthe importance of such characterization.
\r\n\r\nKinetics of methanol and ethanol dehydration over some of these catalysts \r\nhave been studied to ascertain effects of changes in the catalyst state.\r\nThe rate expression
\r\n\r\nr = kKAcA1/2/(1 + KAcA1/2 + KWcW)
\r\n\r\ndescribes the experimental data for all the catalysts in their fresh as \r\nwell as poisoned states. Significant variations in k, KA and KW are \r\nob\u00adserved depending upon the catalyst states. Comparison of kinetics on fresh and \r\npoisoned catalyst states shows that poisoning increases the KA and KW \r\nfor ether formation in contrast to a decrease in these constants for olefin\r\nformation. These variations are attributed to interactions among poison\r\nmolecules and acid-base site pairs, thereby lending support to the reaction \r\nmechanism. Certain implications of nonseparable kinetics are investigated\r\nto show significant changes in total conversion and product distribution upon \r\nreversal of flow direction through a graded reactor.
\r\n", "doi": "10.7907/VEWJ-1D21", "publication_date": "1975", "thesis_type": "phd", "thesis_year": "1975" }, { "id": "thesis:9676", "collection": "thesis", "collection_id": "9676", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04182016-100200035", "primary_object_url": { "basename": "Hsu_gc_1972.pdf", "content": "final", "filesize": 61658664, "license": "other", "mime_type": "application/pdf", "url": "/9676/1/Hsu_gc_1972.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Estimation of Catalyst Activity Profiles and Deactivation Parameters from Reactor Operating Data with Applications to Naphtha Reforming", "author": [ { "family_name": "Hsu", "given_name": "George Chi", "clpid": "Hsu-George-Chi" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Techniques are developed for estimating activity profiles in fixed bed reactors and catalyst deactivation parameters from operating reactor data. These techniques are applicable, in general, to most industrial catalytic processes. The catalytic reforming of naphthas is taken as a broad example to illustrate the estimation schemes and to signify the physical meaning of the kinetic parameters of the estimation equations. The work is described in two parts. Part I deals with the modeling of kinetic rate expressions and the derivation of the working equations for estimation. Part II concentrates on developing various estimation techniques.
\r\n\r\nPart I: The reactions used to describe naphtha reforming are dehydrogenation and dehydroisomerization of cycloparaffins; isomerization, dehydrocyclization and hydrocracking of paraffins; and the catalyst deactivation reactions, namely coking on alumina sites and sintering of platinum crystallites. The rate expressions for the above reactions are formulated, and the effects of transport limitations on the overall reaction rates are discussed in the appendices. Moreover, various types of interaction between the metallic and acidic active centers of reforming catalysts are discussed as characterizing the different types of reforming reactions.
\r\n\r\nPart II: In catalytic reactor operation, the activity distribution along the reactor determines the kinetics of the main reaction and is needed for predicting the effect of changes in the feed state and the operating conditions on the reactor output. In the case of a monofunctional catalyst and of bifunctional catalysts in limiting conditions, the cumulative activity is sufficient for predicting steady\r\nreactor output. The estimation of this cumulative activity can be carried out easily from measurements at the reactor exit. For a general bifunctional catalytic system, the detailed activity distribution is needed for describing the reactor operation, and some approximation must be made to obtain practicable estimation schemes. This is accomplished by parametrization techniques using measurements at a few\r\npoints along the reactor. Such parametrization techniques are illustrated numerically with a simplified model of naphtha reforming.
\r\n\r\nTo determine long term catalyst utilization and regeneration policies, it is necessary to estimate catalyst deactivation parameters from the the current operating data. For a first order deactivation model with a monofunctional catalyst or with a bifunctional catalyst in special limiting circumstances, analytical techniques are presented to transform the partial differential equations to ordinary differential equations which admit more feasible estimation schemes. Numerical examples include the catalytic oxidation of butene to butadiene and a simplified model of naphtha reforming. For a general bifunctional system or in the case of a monofunctional catalyst subject to general power law deactivation, the estimation can only be accomplished approximately. The basic feature of an appropriate estimation scheme involves approximating the activity profile by certain polynomials and then estimating the deactivation parameters from the integrated form of the deactivation equation by regression techniques. Different bifunctional systems must be treated by different estimation algorithms, which are illustrated by several cases of naphtha reforming with different feed or catalyst composition.
\r\n\r\n", "doi": "10.7907/9RNN-8952", "publication_date": "1972", "thesis_type": "phd", "thesis_year": "1972" }, { "id": "thesis:10935", "collection": "thesis", "collection_id": "10935", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05252018-085149423", "primary_object_url": { "basename": "Hwang_MK_1971.pdf", "content": "final", "filesize": 44044310, "license": "other", "mime_type": "application/pdf", "url": "/10935/1/Hwang_MK_1971.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Estimation and Control of Stochastic Chemical Systems", "author": [ { "family_name": "Hwang", "given_name": "Myung Kyu", "clpid": "Hwang-Myung-Kyu" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Chapter II
\r\n\r\nThe control of nonlinear lumped-parameter systems is \r\nconsidered with unknown random inputs and measurement noise. \r\nA scheme is developed whereby a nonlinear filter is included \r\nin the control loop to improve system performance. Pure \r\ntime delays in the control loop are also examined. A computational \r\nexample is presented for the proportional control on temperature \r\nof a CSTR subject to random disturbances, applying a nonlinear least \r\nsquare filter.
\r\n\r\nChapter III
\r\n\r\nLeast square filtering and interpolation algorithms are derived \r\nfor states and parameters in nonlinear distributed systems with unknown \r\nadditive volume, boundary and observation noises, and with volume and \r\nboundary dynamical inputs governed by stochastic ordinary differential \r\nequations. Observations are assumed to be made continuously in time at \r\ncontinuous or discrete spatial locations. Two methods are presented\r\nfor derivation of the filter. One is the limiting procedure of the \r\nfinite dimensional description of partial differential equation systems \r\nalong the spatial axis, applying known filter equations in ordinary \r\ndifferential equation systems. The other is to define a least square \r\nestimation criterion and convert the estimation problem into an optimal \r\ncontrol problem, using extended invariant imbedding technique in\r\npartial differential equations. As an example, the derived filter is \r\nused to estimate the state and parameter in a nonlinear hyperbolic system \r\ndescribing a tubular plug flow chemical reactor. Also a heat\r\nconduction problem is studied with the filtering and interpolation \r\nalgorithms.
\r\n\r\nChapter IV
\r\n\r\nNew necessary and sufficient conditions are presented for the \r\nobservability of systems described by nonlinear ordinary differential \r\nequations with nonlinear observations. The conditions are based on \r\nextension of the necessary and sufficient conditions for observability \r\nof time-varying linear systems to the linearized trajectory of the \r\nnonlinear system. The result is that the local observability of \r\nany initial condition can be readily determined, and the observability \r\nof the entire initial domain can be computed. The observability of \r\ncon\u00adstant parameters appearing in the differential equations is also \r\nconsidered.
", "doi": "10.7907/BG3X-F787", "publication_date": "1971", "thesis_type": "phd", "thesis_year": "1971" }, { "id": "thesis:9081", "collection": "thesis", "collection_id": "9081", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08062015-144055650", "primary_object_url": { "basename": "Lindgren_rg_1970.pdf", "content": "final", "filesize": 67412174, "license": "other", "mime_type": "application/pdf", "url": "/9081/1/Lindgren_rg_1970.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Theory of the Positive Column of a Gas Discharge", "author": [ { "family_name": "Lindgren", "given_name": "Robert Gary", "clpid": "Lindgren-Robert-Gary" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "An attempt is made to provide a theoretical explanation of the effect of the positive column on the voltage-current characteristic of a glow or an arc discharge. Such theories have been developed before, and all are based on balancing the production and loss of charged particles and accounting for the energy supplied to the plasma by the applied electric field. Differences among the theories arise from the approximations and omissions made in selecting processes that affect the particle and energy balances. This work is primarily concerned with the deviation from the ambipolar description of the positive column caused by space charge, electron-ion volume recombination, and temperature inhomogeneities.
\r\n\r\nThe presentation is divided into three parts, the first of which involved the derivation of the final macroscopic equations from kinetic theory. The final equations are obtained by taking the first three moments of the Boltzmann equation for each of the three species in the plasma. Although the method used and the equations obtained are not novel, the derivation is carried out in detail in order to appraise the validity of numerous approximations and to justify the use of data from other sources. The equations are applied to a molecular hydrogen discharge contained between parallel walls. The applied electric field is parallel to the walls, and the dependent variables\u2014electron and ion flux to the walls, electron and ion densities, transverse electric field, and gas temperature\u2014vary only in the direction perpendicular to the walls. The mathematical description is given by a sixth-order nonlinear two-point boundary value problem which contains the applied field as a parameter. The amount of neutral gas and its temperature at the walls are held fixed, and the relation between the applied field and the electron density at the center of the discharge is obtained in the process of solving the problem. This relation corresponds to that between current and voltage and is used to interpret the effect of space charge, recombination, and temperature inhomogeneities on the voltage-current characteristic of the discharge.
\r\n\r\nThe complete solution of the equations is impractical both numerically and analytically, and in Part II the gas temperature is assumed uniform so as to focus on the combined effects of space charge and recombination. The terms representing these effects are treated as perturbations to equations that would otherwise describe the ambipolar situation. However, the term representing space charge is not negligible in a thin boundary layer or sheath near the walls, and consequently the perturbation problem is singular. Separate solutions must be obtained in the sheath and in the main region of the discharge, and the relation between the electron density and the applied field is not determined until these solutions are matched.
\r\n\r\nIn Part III the electron and ion densities are assumed equal, and the complicated space-charge calculation is thereby replaced by the ambipolar description. Recombination and temperature inhomogeneities are both important at high values of the electron density. However, the formulation of the problem permits a comparison of the relative effects, and temperature inhomogeneities are shown to be important at lower values of the electron density than recombination. The equations are solved by a direct numerical integration and by treating the term representing temperature inhomogeneities as a perturbation.
\r\n\r\nThe conclusions reached in the study are primarily concerned with the association of the relation between electron density and axial field with the voltage-current characteristic. It is known that the effect of space charge can account for the subnormal glow discharge and that the normal glow corresponds to a close approach to an ambipolar situation. The effect of temperature inhomogeneities helps explain the decreasing characteristic of the arc, and the effect of recombination is not expected to appear except at very high electron densities.
\r\n", "doi": "10.7907/B4W0-ST96", "publication_date": "1970", "thesis_type": "phd", "thesis_year": "1970" }, { "id": "thesis:3956", "collection": "thesis", "collection_id": "3956", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10072002-143841", "primary_object_url": { "basename": "Chu_f_1969.pdf", "content": "final", "filesize": 6156545, "license": "other", "mime_type": "application/pdf", "url": "/3956/1/Chu_f_1969.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Investigations on Some Diffusion Problems in Rarefied Gases", "author": [ { "family_name": "Chu", "given_name": "Frank I-Chien", "clpid": "Chu-Frank-I-Chien" } ], "thesis_advisor": [ { "family_name": "Gavalas", "given_name": "George R.", "clpid": "Gavalas-G-R" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This is a theoretical study of diffusion problems in transitional rarefied gases with surface dissociation and recombination reactions. The method of composite solution, which is a simplified version of the exact composite expansion theory with similarity to the mean free path method, has proved to be very successful.\r\n\r\nBoth the methods of Lester Lees and of composite solution have been used to solve the problem of simultaneous heat and mass transfer of a partially dissociated diatomic gas of transitional rarefaction from a hot fine wire to a surrounding cylinder. We have employed a sticking probability to describe the dissociation reaction of the diatomic gas at the wire but have used continuum type boundary conditions at the outer cylinder. We have also assumed a small total temperature variation and a small mole fraction of the dissociated atoms. The results obtained by both methods are identical and agree very well with the existing formulas in many limiting cases.\r\n\r\nOwing to its simplicity, the method of composite solution was applied to the problem of a subsonic viscous flow past a sphere for small Mach number but arbitrary Knudsen number. This problem was considered both as a prerequisite for the investigation of mass transfer from a sphere to a stream of gas mixtures and as a means to acquire familiarity with the matching procedures. The result for the drag force agrees with the known formulas in both the free molecular flow limit and the continuum limit. The agreement with experimental data in the transitional flow regimes is less satisfactory.\r\n\r\nThe method of composite solution was then applied to the problem of mass transfer from a sphere to a partially dissociated diatomic gas. Surface recombination reaction was assumed to take place at the sphere while the flow conditions were the same as those in the previous problem. Small mole fraction of the dissociated atoms was also assumed, with the implication of a uniform temperature field. The concentration and flux of the dissociated atoms were found in terms of the sticking probability of the recombination reaction.\r\n\r\nThe problem of simultaneous diffusion and reaction of dissociated atoms in the interior of a sphere is also very interesting and practically important. We have studied the special case of a very fast reaction where the concentration of atoms at the surface of the sphere is given. A new method of solving this unsteady state diffusion problem with moving boundary was proposed and has proved to be more advantageous than the existing ones.\r\n\r\nFinally, the sticking probabilities employed in the previous problems were obtained for various mechanisms of dissociation and recombination reactions. These sticking probabilities turn out to be constant over a wide range of Knudsen number and vanish in the continuum limit.", "doi": "10.7907/SAKW-WA48", "publication_date": "1969", "thesis_type": "phd", "thesis_year": "1969" } ]