Applications of Porous Membrane Reactors

Assabumrungrat, S., Rienchalanusarn, T, Praserthdam, P. and Goto, S. (2002) Theoretical study of the application of porous membrane reactor to oxidative dehydrogenation of w-butane. Chemical Engineering Journal, 85,69-79. 

Coronas J., Menendez M. and Santamaria J., Methane oxidative coupling using porous ceramic membrane reactors. Part II. Reaction studies, Chem. Engng. Sci. 49 2015 (1994). Coronas J., Menendez M. and Santamaria J., Development of ceramic membrane reactors with non-uniform permeation pattern. Application to methane oxidative coupling, Chem. Eng. Sci. 49 4749 (1994). 

Milne, D., Glasser, D., HUdebrandt, D., Hausherger, B., 2004. Application of the attainable region concept to the oxidative dehydrogenation of 1-butane in inert porous membrane reactors. Ind. Eng. Chem. Res. 43, 7208. 

When a PMR equipped with a photocatalytic membrane with photoactive skin layer was appfied for gas phase reactions, an improvement in the efficiency of decomposition, compared to a conventional photocatalytic reactor with T1O2 film immobilized on a non-porous support, was observed (Tsuru et al., 2003). In the case of the photocatalytic reaction conducted in the PMR, all reactants permeate through the pores of the 1102 active layer, which results in more effective contact between the reactants and the photoactive I1O2 surface. Application of a membrane allows control of the residence time of the reactants, thus improving the reaction rate. Moreover, the transport of organic compounds to the IIO2 surface is enhanced by forced convection in addition to transport by diffusion, and a larger surface area could be utilized for the photocatalytic reaction when conducted in the PMR. 

This chapter reviews the possibilities that the application of a membrane in a catalytic reactor can improve the selectivity of a catalytic oxidation process to achieve a more compact system or to otherwise increase competitiveness. Classification differentiates between those reactors using dense membranes and those using porous membranes. Dense membranes provide high selectivity towards oxygen or hydrogen and the selective separation of one of these compounds under the reaction conditions is the key element in membrane reactors using such membranes. Porous membranes may have many different operation strategies and the contribution to the reaction can be based on a variety of approaches reactant distribution, controlled contact of reactants or improved flow. Difficulties for the application of membrane reactors in industrial operation are also discussed. 

A carbon membrane reactor constitutes one of the most promising applications of carbon membranes. The performance of a carbon membrane for gas separation and for the dehydrogenation of cyclohexane to benzene was examined by Itoh and Ha-raya [29], They concluded that the performance of their caibon membrane reactor for dehydrogenation was fairly good compared with that of a normal reactor, i.e. functioning at equilibrium [29], On the other hand, Lapkin [30] used a macro-porous phenolic resin carbon membrane as a contactor for the hydration of propene in a catalytic reactor. He found that the use of this porous contactor-type reactor for his high-pressure catalytic reaction is practical. 

From these two generic configurations, different variations can be found in the literature. In case (a) the membrane can be dense or porous, active or inactive. In case (b) the membrane can be dense or porous. Moreover, some applications (see Sections A9.3.3.2 and A9.3.3.3) do not require permselective membranes. A complete nomenclature of the different membrane reactors has been proposed by Tsotsis et al. [6],... 

Much of the impetus for the awakened interest and utilization of inorganic membranes recently came hom a history of about forty or fifty years of some large scale successes of porous ceramic membranes for gaseous diffusion to enrich uranium in the military weapons and nuclear power reactor applications. In the gaseous diffusion literature, the porous membranes are referred to as the porous barriers. For nuclear power generation, uranium enrichment can account for approximately 10% of the operating costs (Charpin and Rigny, 1989]. 

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]. 

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