Thesis (MScIng)--University of Stellenbosch, 2005. / Bibliography. Also available via the Internet.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Hydrogen Permeation; Pd-Ag Membranes; Electroless Plating. Includes bibliographical references (p. 114-118).

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.

Orientador: Teresa Massako Kakuta Ravagnani / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-08T19:44:43Z (GMT). No. of bitstreams: 1 Araujo_PauloJardelPereira_M.pdf: 1672087 bytes, checksum: 39df6a7017efe009f53dbd9aecb301b1 (MD5) Previous issue date: 2007 / Resumo: Estireno é um importante monômero na fabricação de termoplásticos e borrachas sintéticas. Grande parte de sua produção é baseada na desidrogenação catalítica do etilbenzeno. O aumento da produtividade do estireno pode ser alcançado utilizando-se membranas permseletivas para remoção do hidrogênio, suprimindo as reações reversíveis e secundárias. Este trabalho apresenta a simulação do processo de desidrogenação em um reator tubular de leito fixo catalítico envolto em membrana composta permseletiva. A modelagem matemática desenvolvida considera os diferentes mecanismos de transporte de massa que prevalecem nas várias camadas da membrana e no leito fixo catalítico. A remoção do Hidrogênio do leito catalítico foi realizada estabelecendo-se um gradiente de potencial químico de hidrogênio através da membrana. Duas formas de remoção de hidrogênio foram estudadas: pela aplicação de uma diferença de pressão através da membrana e pelo arraste com gás inerte. Um programa computacional foi implementado para descrever os perfis de temperatura, pressão e concentração ao longo de todo o reator, bem como a conversão do etilbenzeno, seletividade e produtividade de estireno. Comparando os resultados obtidos no leito fixo convencional operando na condição industrial padrão com os obtidos na aplicação de diferença de pressão através da membrana, observou-se um acréscimo na conversão de etilbenzeno de 19,89 % na mesma seletividade do estireno, representando um aumento de 19,12 % na produtividade de estireno. Este mesmo aumento foi também alcançado com o uso de gás de arraste inerte. Por este motivo, este procedimento é a opção mais recomendada, por agregar custo menor ao processo. Através da simulação do sistema em diferentes condições do processo e configurações do reator e da membrana, obteve-se um acréscimo de 40,98 % na produtividade de estireno comparada a do processo com leito fixo convencional / Abstract: Styrene is an important monomer in the manufacture of thermoplastic and synthetic rubbers. Most of the production is based on the catalytic dehydrogenation of ethylbenzene. The increase of the styrene productivity can be reached using permselectives membranes for hydrogen removal, suppressing the reversible and secondary reactions. This work presents the simulation of dehydrogenation process in tubular fixed bed reactor wrapped with permselective composite membrane. The mathematical modeling was developed considering the different mechanisms of mass transport that prevail in several membrane layers and in catalytic fixed bed. The removal of the permeated hydrogen was carried out establishing a gradient of chemical hydrogen potential through the membrane. Two forms of hydrogen removal were studied: the application of transmembrane pressure drop and the employment of inert sweep gas. A computational program was implemented to describe the profiles of temperature, pressure and concentration throughout all reactor, as . well as the ethylbenzene conversion, styrene selectivity and productivity. Comparing the simulation results obtained for conventional fixed bed reactor carried on standard industrial operation condition with application transmembrane pressure drop form, it shows an increase of 19.89 % in ethylbenzene conversion in the same styrene selectivity for, meaning an increase of 19.12% in styrene productivity. The same addition was obtained when the inert sweep gas was employed. Therefore, this last proceeding has been recommended as the better option, due to its lower operation cost. Through the system simulation at various operation conditions, using different reactor and membrane configurations, an increase of 40.98 % in the styrene productivity was reached comparing to conventional fixed bed process / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestre em Engenharia Química