Membrane reactors heterogeneous

Catalytic A catalytic-membrane reactor is a combination heterogeneous catalyst and permselective membrane that promotes a reaction, allowing one component to permeate. Many of the reactions studied involve H9. Membranes are metal (Pd, Ag), nonporous metal oxides, and porous structures of ceran iic and glass. Falconer, Noble, and Speriy [in Noble and Stern (eds.), op. cit., pp. 669-709] review status and potential developments. 

Membrane reactors can offer an improvement in performance over conventional reactor configurations for many types of reactions. Heterogeneous catalytic reactions in membrane reactors [1] and the membranes used in them [2,3] have been reviewed recently. One well studied application in this area is to remove a product from the reaction zone of an equilibrium limited reaction to obtain an increase in conversion [4-10]. The present study involves heterogeneous... 

Retention of Heterogenized Chiral Chemical Catalysts in a Membrane Reactor... 

Related to the experimental studies performed in our laboratory, in this review packed-bed membrane reactors were discussed. It should be mentioned that there are significant investigational activities devoted to study catalytically active membranes where the catalyst is deposited in either the membrane pores or on the inner or outer surface of the tubes [11]. Another similarly interesting and promising principle is based on using the Contactor type of membrane reactors, where the reactants are fed from different sides and react within the membrane [79]. Significant efforts have been made to exploit this principle for heterogeneously catalyzed gas-liquid reactions (three-phase membrane reactors) [80, 81]. 

J. A. Dalmon, Catalysis in membrane reactors, in Handbook of heterogeneous catalysis, Eds. G. Ertl, H. Knozinger, J. Weitkamp, Wiley-VCH, Weinheim, Chapter 9.3, 1997. 

A novel application of a symmetric porous membrane as a catalyst carrier but not as a permselective barrier is to use the membrane itself as the reaction zone for precise control of the stoichiometric ratio [Sloot et al., 1990]. In this case, the reactants are fed to the different sides of the membrane which is impregnated with a catalyst for a heterogeneous reaction. The products diffuse out of the membrane to its both sides. If the reaction rate is faster than the diffusion rate of the reactant in the membrane, a small reaction zone or theoretically a reaction plane will exist in the membrane. An interesting and important consequence of this type of membrane reactor is that within the reaction zone the molar fluxes of the reactants arc always in stoichiometric ratio and the presence of one reactant in the opposing side of the membrane is avoided. The reaction zone can be maintained inside the membrane as long as the membrane is symmeuic and not ultrathin. Therefore, membrane reactors of this fashion are particularly suited for those processes which require strict stoichiometric feed rates of premixed reactants. A symmetric porous a-alumina membrane of 4.5 mm thick was successfully tested to demonstrate the concept [Sloot et al., 1990]. 

Based on the above considerations, the types of reactions that are amenable to inorganic membrane reactors in the first wave of industrial implementation will probably be as follows (1) The reactions are heterogeneous catalytic reactions, particularly dehydrogenation processes (2) The reaction temperature exceeds approximately 200°C (3) When the reactions call for high-purity reactant(s) or produces) and the volume demand is relatively small, dense membrane reactors (e.g., Pd-based) can be used. On the other hand, if high productivity is critical for the process involved, porous membrane reactors are necessary to make the process economically viable. 

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. ... 

Veldsink J.W., A Catalytically Active, Non-permselective Membrane Reactor for Kinetically Fast, Strongly Exothermic Heterogeneous Reactions. Ph.D. dissertation, Twentc University of Technology, Enschede, the Netherlands (1993). 

Dalmon JA. Catalytic membrane reactors. In Handbook of Heterogeneous Catalysis. In Ertl G, Knbzinger H, and Weitkamp J (eds.), VCH Pub. 1997 Chapter 9.3 1387-1398. 

The heterogenization of catalysts in membrane is particularly suitable for catalyst design at the atomic and molecular level. One of the main advantages of the membrane reactors, compared to traditional reactors, is the possibility to recycle easily the catalyst. Moreover, the selective transport properties of the membranes can be used to shift the equilibrium conversion (e.g., esterihcation reaction), to remove selectively products and by-products from the reaction mixture, to supply selectively the reagents (e.g., oxygen for partial oxidation reactions). 

Membrane reactors using biological catalysts can be used in enantioselective processes. Methodologies for the preparation of emulsions (sub-micron) of oil in water have been developed and such emulsions have been used for kinetic resolutions in heterogeneous reactions catalyzed by enantioselective enzyme (Figure 43.4). A catalytic reactor containing membrane immobilized lipase has been realized. In this reactor, the substrate has been fed as emulsion [18]. The distribution of the water organic interface at the level of the immobUized enzyme has remarkably improved the property of transport, kinetic, and selectivity of the immobilized biocatalyst. 

Even if not really new, the concept of a membrane reactor has not been applied so intensively in homogeneous catalysis as in heterogeneous catalysis [20]. Nevertheless, the application of this concept in this area seems to be an exciting new topic, which opens up enormous possibilities of research and development. 

Catalytic membrane reactors (CMRs) are an interesting example of integrated system in which molecular separation and chemical conversions are combined in one step [8]. The heterogenization of catalysts in membrane is particularly suitable for catalyst design at the atomic and molecular... 

Since the first edition some reviews (and lots of patents) about the application of membranes and membrane reactors have been filed and published (for example [24]). Mostly, special aspects were in the foreground of investigations (such as the interplay of micelles or microemulsions and membranes, interfacial phenomena, three phase emulsion/solid heterogenization, or the properties of metal-based membranes [25]). 

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