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Thesis--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references (leaves 80-83).

M.S.

Palladium membranes have been identified as the membranes of choice in hydrogen separation and purification processes due to their infinite selectivity to hydrogen when defect free. Despite their potentials in hydrogen processes, palladium membranes pose challenges in terms of cost and embritllement which occurs when palladium comes in contact with hydrogen at temperatures below 573 K. The challenges posed by palladium membranes have encouraged research into nonpalladium based membranes such as Silica and Alumina. This thesis investigates hydrogen permeation and separation in palladium membranes and also the use of nonpalladium membranes, Silica and Alumina membranes in hydrogen permeation. In this study, hydrogen permeation behavior was investigated for 3 types of membranes, Palladium, Silica and Alumina. Thin palladium films were deposited onto a 30 nm porous ceramic alumina support using both conventional and modified electroless plating methods. The hydrogen separation and purification behavior of the membranes were investigated including the effect of annealing at higher temperatures. Gas permeation through Silica and Alumina membranes was investigated for 5 single gases including hydrogen. The Silica and Alumina membranes were fabricated using the dip coating method and their hydrogen permeation behavior of investigated at different coatings. A thin Palladium (Pd1) membrane with a thickness of 2 μm was prepared over porous ceramic alumina support using the electroless plating method and a maximum hydrogen flux of 80.4 cm3 cm-2 min-1 was observed at 873 K and 0.4 bar after annealing the membrane. The hydrogen flux increased to 94.5 cm3 cm-2 min-1 at same temperature and pressure for the Palladium membrane (Pd2) prepared using the modified electroless plating method. The hydrogen flux increased to 98.1 cm3 cm2 min-1 for the palladium/silver (Pd/Ag) membrane prepared using the codeposition electroless plating method and the PdAg membrane avoided the hydrogen embrittlement at low temperature. Hydrogen purity for the membrane was also investigated for a reformate gas mixture and a maximum hydrogen purity of 99.93% was observed at 873 K and 0.4 bar. The hydrogen purity was observed to increase as a result of the addition of sulphur which surpresses the inhibition effect of the carbon monoxide in the reformate gas mixture. The presence of CO and CO2 was observed to lead to an increase of the exponential factor n above 0.5 as a result of the inhibiting effect of these compounds on hydrogen permeation. The value of the exponential factor n depicting the rate limiting step to hydrogen permeation in the palladium and palladium-alloy membranes was also investigated. Deviations from Sievert’s law were observed from the Palladium membranes inverstigated in this work. In single gas hydrogen permeation investigation for the Pd1 membrane prepared using the conventional electroless plating method, the value of the exponential factor n = 0.5 in accordance with Sievert’s law. However, for the mixed gas hydrogen separation investigation n=0.62 at 573 K which decreased to 0.55 when the membrane was annealed at 873 K. For the Pd2 membrane prepared using the modified elctroless plating method, n=1 at 573 K but the value decreased to 0.76 for the mixed gas hydrogen separation investigation at same temperature which depicts a deviation from Sievert’s law. In all the investigations carried out for the Pd3 palladium alloy membrane prepared using the co-deposition Pd/Ag electroless plating method at same conditions with the Pd1 and Pd2 membranes, n=0.5 in accordance with Sievert’s law. For the Nonpalladium based Silica and ceramic Alumina membranes, investigations were carried out for hydrogen permeation and 5 other single gases; He, CO2, CH4, N2 and Ar. For the Silica membranes, a maximum hydrogen permeance of 3.12-7 x 10 mol m-2 s-1 Pa-1 at 573 K and 0.4 bar was observed which increased to 4.05 x 10-7 mol m-2 s-1 Pa-1 at 573 K and 0.4 when the membrane was modified with Boehmite sol prior to deposition of the Silica layer. The permeance for hydrogen and the 5 single gases was investigated for the alumina membrane at 5 successive coatings. It was observed that the commercial alumina membrane displayed a maximum hydrogen permeance of 9.72 x 10-7 mol m-2 s-1 Pa-1 at 573 K and 0.4 bar which increased to 9.85 x 10-7 mol m-2 s-1 Pa-1 at same temperature and pressure when the membrane was modified with Boehmite sol.

Synthetic fuels produced using the Fischer-Tropsch technology will play an important role in the future of the transportation sector. The Fischer-Tropsch synthesis (FTS) allows converting synthesis gas (CO + H2) into fuels of outstanding quality. The synthesis gas can be obtained from different carbon sources: natural gas, coal and biomass. In order to maximize the yield of middle distillates, the process is carried out in two main steps: the FT-synthesis that produces long-chain hydrocarbons (waxes) and a hydrocracking step, to selectively convert the waxes into fuels. Diesel produced by this process is characterized by excellent combustion properties and reduced harmful tailpipe emissions compared to conventional diesel. Due to the growing interest in synthetic fuel production, from the industry and the academia, and to the peculiar characteristics of the Fischer-Tropsch products, research in hydrocracking has received renewed attention. Catalysts for the hydrocracking of long-chain paraffins have been the subject of the present work, which is the summary of four scientific publications. Noble metals supported on acid carriers have been compared, especially for what regards the mechanisms through which hydrocracking proceeds. The catalysts were synthesized and characterized by various techniques, including N2 physisorption, H2 chemisorption, TEM, pyridine adsorption FTIR, ammonia TPD, etc. It was shown that catalytic activity is mainly dependent on the acid support used; that selectivity is strongly dependent on conversion, high conversion favoring highly branched cracking products. Two main reaction routes were observed: bifunctional hydrocracking and hydrogenolytic cracking. Platinum-containing catalysts showed high selectivity towards the latter, while palladium/silica-alumina behaved as pure bifunctional catalysts. Catalyst deactivation was investigated and initial sintering of metal particles was observed. Coking was also a cause of deactivation. Formation of coke deposits was highly dependent on the metal loading of the catalysts. Metal loading also influenced catalyst selectivity, especially in the case of platinum/silica-alumina catalysts. Monofunctional hydrogenolysis on the platinum particles, superimposed to the bifunctional mechanism was observed. This route increased selectivity towards linear hydrocarbons and methane, with increasing amounts of platinum. The specific rate of hydrogenolysis was constant for different loadings of platinum on the same acid silica-alumina support. Using a different, less acid, support negatively affected the hydrogenolytic activity of the platinum catalytic sites. It was concluded that metal-support interactions might play an important role in the catalytic properties of platinum surfaces. This work has contributed to increasing the knowledge about hydrocracking of long-chain alkanes and pointed out some features that might have practical interest in the application of this technology to synthetic-fuel production. / Syntetiska drivmedel tillverkade genom Fischer-Tropsch teknologin kommer i framtiden att ha en betydande roll för transportsektorn. Fischer-Tropsch syntesen (FTS) möjliggör omvandling av syntesgas (CO + H2) till högkvalitativa bränslen. Syntesgasen kan erhållas från olika kolkällor: naturgas, kol och biomassa. För att maximera utbytet av medeldestillat, utförs processen i två huvudsteg: FT-syntes som producerar långa kolväten (vaxer) och ett hydrokrackning steg, för att selektivt omvandla vaxerna till bränslen. Diesel som produceras med denna process kännetecknas av utmärkta förbränningsegenskaper och ger upphov till minskade utsläpp av skadliga ämnen jämfört med vanlig diesel. På grund av det växande intresset för syntetiska bränslen, både från industrin och den akademiska världen, och av de speciella egenskaperna hos Fischer-Tropsch-produkter, har forskningen i vätekrackning fått förnyad uppmärksamhet. Ämnet för detta arbete, som är en sammanfattning av fyra vetenskapliga publikationer, är katalysatorer för hydrokrackning av långkedjiga paraffiner. Ädelmetaller uppburna på sura bärare har jämförts, särskilt vad gäller vätekrackningsmekanismer. Katalysatorerna preparerades och karaktäriserades med hjälp av olika tekniker, bland andra N2 fysisorption, H2 kemisorption, TEM, pyridin adsorption FTIR, ammoniak TPD, etc. Det visade sig att den katalytiska aktiviteten är främst beroende av surheten hos bärarmaterialet, att selektivitet är starkt beroende av omsättningen, där hög omsättning gynnar flergrenade krackningsprodukter. Två huvudsakliga reaktionsvägar observerades: bifunktionell vätekrackning och hydrogenolytisk crackning. Platinakatalysatorer visade hög selektivitet mot det senare, medan katalysatorer med palladium på kiseloxid-aluminiumoxid uppträdde som rena bifunktionella katalysatorer. Katalysatordeaktivering undersöktes och sintring av metallpartiklar observerades. Koksning var också en orsak till deaktivering. Koksbildning var starkt beroende av metallhalten i katalysatorerna. Metallhalten påverkade också selektivitet, särskilt för platina-kiseloxid-aluminiumoxidkatalysatorer. Monofunktionellt hydrogenolys på platinapartiklarna, observerades utöver den bifunktionella mekanismen. Med denna reaktionsväg ökade selektivitet mot linjära kolväten och metan, med ökande platinahalter på katalysator. Den specifika reaktionshastigheten för hydrogenolys var konstant för olika platinahalter på en sur kiseloxid-aluminiumoxidbärare. Den hydrogenolytiska aktiviteten hos platina katalytiska säten påverkas negativt när en mindre sur bärare användes. Slutsatsen var att interaktioner mellan metallen och bäraren kan spela en viktig roll för de katalytiska egenskaperna hos platina ytor. Detta arbete har bidragit till att öka kunskapen om vätekrackning av långkedjiga alkaner och påpekade vissa funktioner som kan ha praktiskt intresse vid tillämpningen av denna teknik för produktionen av syntetiska bränslen. / <p>QC 20131007</p>

Thesis (Ph. D.)--University of Florida, 1986. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 156-161).

As legislações ambientais estão cada vez mais severas em relação à quantidade de compostos sulfurados eliminada na atmosfera pela queima de combustíveis fósseis. Os processos de adsorção têm se destacado como uma alternativa promissora na remoção de sulfurados presentes em combustíveis. Nos estudos de adsorção, ensaios de cinética e isoterma usando banhos agitados são frequentemente utilizados na avaliação do desempenho dos adsorventes na remoção desejada. Apesar de úteis, tais ensaios apresentam algumas limitações quando os sistemas analisados envolvem elevadas relações entre a concentração inicial de soluto e massa de adsorvente. Alternativamente, este trabalho apresenta uma estratégia envolvendo a técnica da adsorção utilizando a calorimetria para o estudo de cinética e isoterma térmica de quinolina em uma sílica-alumina comercial a partir de soluções em n-hexadecano. Diferentemente das outras técnicas citadas, a adsorção por calorimetria possibilitou, em um único ensaio e com menos amostra, a obtenção da cinética térmica de adsorção, e de um ponto da isoterma térmica de adsorção. Adicionalmente, foi proposta uma modelagem dos fenômenos de transferência de calor e massa envolvidos durante o ensaio, visando simular a curva calorimétrica. Valores de coeficiente de difusão efetivo da quinolina na sílica-alumina em diferentes condições de concentração inicial de quinolina em n-hexadecano, a uma mesma temperatura, foram obtidos a partir do ajuste do modelo da curva calorimétrica aos dados experimentais / Environmental laws are becoming more stringent in relation to the amount of sulfur compounds eliminated into the atmosphere through the burning of fossil fuels. Adsorption processes have distinguished themselves as a promising alternative. On adsorption studies, kinetics and isotherm tests using agitated baths are often used to evaluate the performance of the adsorbents at the desired removal level. Despite the fact that they are useful, these tests have some limitations. Under analysis, these systems involve high ratios between the initial solute concentration and the mass of the adsorbent. Alternatively, this research presents a strategy involving the technique of adsorption calorimetry to the study of kinetics and isotherm adsorption of quinoline in a commercial silica-alumina from solutions of n-hexadecane. Opposed to other techniques mentioned, adsorption calorimetry by use of a single test can use a smaller quantity of the sample allowing for the collection of the adsorption kinetics and a point on the adsorption isotherm. In addition, a modeling of the phenomena of heat transfer and mass involved during a test was proposed, aiming to create a calorimetric curve simulation. Effective diffusion coefficient values of the quinoline in silica-alumina in different conditions of initial concentration of quinoline in n-hexadecane, at the same temperature, were obtained from the adjustment from the model to calorimetric curve to the experimental data

As legislações ambientais estão cada vez mais severas em relação à quantidade de compostos sulfurados eliminada na atmosfera pela queima de combustíveis fósseis. Os processos de adsorção têm se destacado como uma alternativa promissora na remoção de sulfurados presentes em combustíveis. Nos estudos de adsorção, ensaios de cinética e isoterma usando banhos agitados são frequentemente utilizados na avaliação do desempenho dos adsorventes na remoção desejada. Apesar de úteis, tais ensaios apresentam algumas limitações quando os sistemas analisados envolvem elevadas relações entre a concentração inicial de soluto e massa de adsorvente. Alternativamente, este trabalho apresenta uma estratégia envolvendo a técnica da adsorção utilizando a calorimetria para o estudo de cinética e isoterma térmica de quinolina em uma sílica-alumina comercial a partir de soluções em n-hexadecano. Diferentemente das outras técnicas citadas, a adsorção por calorimetria possibilitou, em um único ensaio e com menos amostra, a obtenção da cinética térmica de adsorção, e de um ponto da isoterma térmica de adsorção. Adicionalmente, foi proposta uma modelagem dos fenômenos de transferência de calor e massa envolvidos durante o ensaio, visando simular a curva calorimétrica. Valores de coeficiente de difusão efetivo da quinolina na sílica-alumina em diferentes condições de concentração inicial de quinolina em n-hexadecano, a uma mesma temperatura, foram obtidos a partir do ajuste do modelo da curva calorimétrica aos dados experimentais / Environmental laws are becoming more stringent in relation to the amount of sulfur compounds eliminated into the atmosphere through the burning of fossil fuels. Adsorption processes have distinguished themselves as a promising alternative. On adsorption studies, kinetics and isotherm tests using agitated baths are often used to evaluate the performance of the adsorbents at the desired removal level. Despite the fact that they are useful, these tests have some limitations. Under analysis, these systems involve high ratios between the initial solute concentration and the mass of the adsorbent. Alternatively, this research presents a strategy involving the technique of adsorption calorimetry to the study of kinetics and isotherm adsorption of quinoline in a commercial silica-alumina from solutions of n-hexadecane. Opposed to other techniques mentioned, adsorption calorimetry by use of a single test can use a smaller quantity of the sample allowing for the collection of the adsorption kinetics and a point on the adsorption isotherm. In addition, a modeling of the phenomena of heat transfer and mass involved during a test was proposed, aiming to create a calorimetric curve simulation. Effective diffusion coefficient values of the quinoline in silica-alumina in different conditions of initial concentration of quinoline in n-hexadecane, at the same temperature, were obtained from the adjustment from the model to calorimetric curve to the experimental data

[pt] Catalisadores de ferro suportados em sílica alumina e em sílica mesoporosa, além de nano partículas de ferro não suportadas, foram estudados. A preparação dos catalisadores suportados ocorreu pelo método de impregnação do ponto úmido incipiente com soluções aquosas de cloreto de ferro, para obter 2 por cento ou 5 por cento de metal, sendo um desses preparado pelo método da ureia, onde uma quantidade apropriada de uma solução aquosa de FeCl3·6H2O (99 por cento -Merck) foi misturada com ureia. As amostras foram caracterizadas por medidas de fisissorção de N2, difração de Raios-X (DRX), redução com temperatura programada (RTP) e microscopia eletrônica de transmissão (TEM). A quantidade de metal foi determinada usando espectroscopia de absorção atômica (EAA). Os suportes de sílica alumina e de sílica mesoporosa foram caracterizados ainda por análise termogravimétrica (ATG/DTG). As propriedades texturais mostraram que após a introdução do metal nos suportes, a área específica, o volume de poros e o diâmetro de poro decresceram conforme o teor metálico foi aumentado. As análises de DRX com refinamento de Rietveld detectaram a formação das fases de FeO, Fe3O4, Fe0, para todas as amostras suportadas. Os perfis de redução (RTP) para as amostras de ferro suportadas mostraram, principalmente, duas regiões de redução, a primeira atribuída a redução de Fe2O3 para FeO e a segunda a redução de FeO para Fe0. / [en] Iron catalysts supported on silica alumina and mesoporous material, beside non supported iron nanoparticles, were studied. The preparation of supported catalysts occurred by incipient wetness impregnation method with aqueous solutions of iron chloride to give 2 percent or 5 percent of metal. One iron catalyst supported on silica alumina was prepared by the method of urea, in which an appropriate amount of an aqueous solution of FeCl3·6H2O (99 percent - Merck) was mixed with urea for impregnation. The samples were characterized by measurements of N2 physisorption, X-ray diffraction (XRD), temperature programmed reduction with (TPR), transmission electron microscopy (TEM). The amount of metal embedded in each sample was determined using atomic absorption spectroscopy (AAS). The silica alumina and mesoporous silica supports were also characterized by thermogravimetric analysis (DTA/TGA). The textural properties showed that after introduction of the metal into the supports, the specific area, pore volume and pore diameter decreased as the metal content was increased. XRD analysis with Rietveld refinement showed the formation of phases the following phases FeO, Fe3O4, Fe0, for all supported samples. Reduction profiles (TPR) for the supported iron samples showed mainly two reduction regions, assigned for Fe2O3 to FeO and for FeO to Fe0, respectively.