Membrane reactor applications

Characterization of a Zeoiite Membrane for Catalytic Membrane Reactor Application... 

Giomo, L. and Drioli, E. (2000) Biocatalytic membrane reactors applications and perspectives. Trends in Biotechnology, 18, 339-349. 

Carbon molecular sieve membranes Resistant to contaminants Intermediate hydrogen flux and selectivity Intermediate hydrogen flux and selectivity High water permeability Pilot-scale testing in low temperature WGS membrane reactor application Need demonstration of long-term stability and durability in practical applications... 

Hong, M., R.D. Noble, and J.L. Falconer, Highly selective H2 Separation Zeolite Membranes for Coal Gasification Membrane Reactor Applications, Annual Technical Progress Report, U.S. DOE Contract DE-FG26-02NT41536, December 2005. 

V-Ti-Ni alloys and Fe- /Co-Based metallic glasses have been evaluated with respect to hydrogen permeability for potential use in hydrogen purification membrane reactor application. Microstructural characterization of the V-Ti-Ni alloy using SEM has shown similar microstructural features to a previously evaluated Nb-Ti-Ni alloy namely, the occurrence of a primary phase surrounded by interdendritic eutectic. 

Kikuchi E. Membrane reactor application to hydrogen production. Catal Today 2000 56 97-101. 

Kurungot, S., Yamaguchi, T., Nakao, S.-L, Rh/y-AljOj catalytic layer integrated with sol-gel synthesized microporous silica membrane for combact membrane reactor applications, Catal. Lett. 2003, 86, 273-278. 

Drioli, E. and Giorno, L. (1999) Biocatalytic Membrane Reactors Application in Biotechnology and the Pharmaceutical Industry, Taylor Francis Publisher, Padstow, UK. 

Figure 17.1 Field of biochemical membrane reactors application.

The latter two modes circumscribe the role of ceramic membranes in membrane reactors. In the case of membrane reactor applications, the ceramic membranes must be crack-free. In addition, it is desirable for the membrane to exhibit good permselectivity characteristics. 

Ilias and Govind(lO) have reviewed the development of high temperature membranes lor membrane reactor application. Hsieh(4) has summarized the technology in the area of important inorganic membranes, the thermal and mechanical stabilities of these membranes, selective permeabilities, catalyst impregnation, membrane/reaction considerations, reactor configuration, and reaction coupling. 

Membranes prepared by the majority of the established methods have limitations in their pore sizes. To make membranes with finer pore diameters suitable for more demanding separation and membrane reactor applications, a widely practiced technique is to modify the pores or the surface of an existing membrane structure which has already been made. This encompasses a variety of techniques. Some of them are based on gas or vapor phase reactions. Others modifications occur in liquid phase. Some progress having pore diameters in the molecular sieving range has been made. 

The inorganic membrane reactor technology is in a state characterized by very few in practice but many of promise. Since the potential payoff of this technology is enormous, it deserves a close-up look. This and the following three chapters are, therefore, devoted to the review and summary of the various aspects of inorganic membrane reactors applications, material, catalytic and engineering issues. 

Typically liquid-phase reactions do not require high temperatures, and as such organic membranes may be suitable for the membrane reactor applications. Justification of using inorganic membranes for these applications comes from such factors as better chemical stability and beuer control and containment of the catalysts. 

Membrane surface contamination. Although not as hydrogen selective as Pd and its alloys, other metals such as niobium and vanadium in dense form also have moderate to high hydrogen permselectivity and potentially can be considered as membrane materials. Inevitably the membrane surface is contaminated with non-metal impurities prior to or during separation or membrane reactor applications. 

When using commercial inorganic membranes for separation or membrane reactor applications at relatively high temperatures, say, greater than 400°C or so, care should be taken to assess their thermal or hydrothermal stability under the application conditions. This is particularly relevant for small pore membranes because they are often made at a temperature not far from 400 C. Even if such an exposure does not yield any phase changes, there may be particle coarsening (and consequently pore growth) involved. 

The combination of high temperature and chemical exposure poses a very challenging material problem that is quite common in high-temperature membrane reactor applications. The consequence of structural degradation as a result of such a combination not only affects the permeability and permselectivity but also leads to physical integrity or mechanical properties. These issues apply to both metal and ceramic membranes. 

Non-oxide ceramic materials such as silicon carbide has been used commercially as a membrane support material and studied as a potential membrane material. Silicon nitride has also the potential of being a ceramic membrane material. In fact, both materials have been used in other high-temperature structural ceramic applications. Oxidation resistance of these non-oxide ceramics as membrane materials for membrane reactor applications is obviously very important. The oxidation rate is related to the reactive surface area thus oxidation of porous non-oxide ceramics depends on their open porosity. The generally accepted oxidation mechanism of porous silicon nitride materials consists of two... 

Despite the aforementioned efforts, membrane flux decline due to fouling continues to be a major operational issue. Attempts have been made to modify inorganic membranes, mostly their surfaces, to render them less prone to foulant adsorption. One of the frequently encountered fouling problems in biotechnology and food applications is protein adsorption. In membrane reactor applications which are largely associated with hydrocarbons, carbonaceous deposits pose as one of the operational problems. 

Critical to both gas separation and membrane reactor applications, fluid leakage and any potential re-mixing of the separated species have to be avoided. The problems could arise if pin-holes or structural defects exist or if the ends of the membrane elements or the connections between the membrane elements and assembly housings or pipings are not properly sealed. 

Finally, the current status of the inorganic membrane technology is summarized for an overall perspective. The future is speculated based on that perspective to provide a framework for future developments in the synthesis, fabrication and assembly of inorganic membranes and their uses for traditional liquid-phase separation, high-temperature gas separation and membrane reactor applications. 

Coupling two operations like membrane separation and a catalytic reaction or adsorption in a given process of synthesis, purification, or decontamination of effluents is intrinsically interesting from a general technical-economical point of view. Ceramic membranes are ideal solid-fluid contactors, which can be efficiently used to couple separation and heterogeneous catalysis for membrane reactor applications. ... 

A major drawback of surface diffusion for high-temperature membrane reactor application lies in the fact that adsorptive bonds l>etween molecules and surfaces become less and less strong as long as temperature increases, thus lowering the separation factors achievable. 

Rios GM, Belleville MP, Paolucci D, and Sanchez J. Progress in enzymatic membrane reactors. J. Membr. Sci. 2004 242 189-196. Giomo L and Drioli E. Biocatalytic membrane reactors applications and perspectives. Tibtech 2000 18 339-349. 

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