Inorganic membranes and membrane reactors
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FEATURED REVIEW
Inorganic Membranes and Membrane Reactors SunZlrak Hwang ~
Department of Chemical Engineering~ University of Cincinnati, Cincinnati, Oil 45221-0 f 71
Abstract-The inorganic membrane reactor is a combined unit operation of chemical reactions and mclnbmne separations. By having a membrane reactor\ the downstream separation load can be reduced. Also, the yields can be increased and conversion can be improved tbr equilibrium limited reactions, However, many of the industrial chemical reactions take place at high temperature that the conventional polymeric membranes cannot withstand. A great deal of research has been done recently to develop ion-conducting ceramic membranes. Ma W of these have been successthlly employed to term membrane reactors ibr many industrially relevant chemical reactions, such as hydrogenation, dehydrogenation, oxidatkm, coupled reactions, and decompositkm reactions. An overview is given t~r the area of inorganic membrane preparations and membrane reactors. Many cxalnples of petrochemical interests arc presented, including hydrocarbon conversions and fuet cell applications.
Key words: Inorganic Membranes. Inorganic Membr'aale Reactkms. Ceramic MemN'anes. Palladium Membranes, Fuel Cells
sure drop) * Resistance to microbial attacks 9 High flux (throughput) , Easy cleaning (steam or backflushes) , Long life 9 Easy modification to add catalytic activity
INTRODUCTION
"['he interest in inorganic membranes goes beyond the scientific curiosity, The long history of hydrogen purification with palladium foils, helium separation with fused quartz, and oxygen separation with silver represents the successful industrial applications of inorganic membranes, t lowever, since the gas permeability through these metals is much lower than that through polymeric membranes, attention has lamely been focused on polymer membranes for practical applications. The progress of inoganic memtxanes had been relatively dormant until the development of thin composite metal membranes and ion-conducting ceramic membranes, These membranes, unlike the polymeric membranes, offer virtually complete separation. Since the inorganic membranes can withstand high tcanpemtures and hostile environments, their applications to membrane reactors for many industrial processes attracted considerable attention. The concept of a membrane reactor was tirst successfully proven in bioreactor applications with polymeric membranes and appropriate enzymes as catalysts. In this review paper, the recent development of inorganic membranes and their use in membrane reactor applications will be discussed with relevant references. For further details, readers are referred to other recent review papers in the field [Armor, 1998: Saracco et aI,, 1994, 1999; Saracco and Specchia, I994; Drioli, 2001: Boddeker et at.0 2001; Stmkides, 2000; Zaman and Chakma, 1994],
While there arc so many advantages for inorganic membranes, some disadvantages are very critical and serious enough to hamper the pro~,ess of industrial application of ino+anic memb
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