Abstract
A commercial cylindrical 40A alumina membrane as both separator and reactor in a single unit operation has been studied experimentally and theoretically to enhance the equilibrium controlled catalytic reaction conversion. The alumina membranes, with or without catalyst modifications, were characterized by measuring the transport rates for ethylbenzene/hydrogen/helium gaseous system at high temperatures. Knudsen diffusion through the narrow membrane pores appeared to control the overall separation. The membrane with catalytic treatment yield effective diffusivities two orders of magnitude lower than the untreated one. EB and H$\sb2$ diffuse independently of one another in both modified and unmodified membranes. The permselective properties of metal impregnated alumina membranes were investigated as a function of pressure at 20$\sp\circ$C for pure helium, nitrogen and carbon dioxide, respectively. An increase in the amount of impregnated oxide decreased the permeability of the membrane due to the partial blocking of the membrane pores but increased the separation factor. The microporous alumina membranes were modified with active catalytic components to investigate the conversion of ethylbenzene to styrene. The most effective configuration utilized a 40A pore diameter, tubular alumina membrane coated on the fine membrane side with solutions of the active metal components and packed with granules of a commercial EB dehydrogenation catalyst. Chemical performance studies were compared with non-porous reactors running under parallel conditions. A wide range of parameter studies demonstrated that the conversion to ST could be strongly enhanced to 64-92% as compared to 35-64% obtained from non-membrane reactors. A second key finding was that the ST selectivity in the membrane reactor experiments could be increased to 93% at 92% conversion as compared to the selectivity of 70% at 64% conversion in parallel experiments in non-porous tubes. A mathematical model was derived. Numerical solution was obtained to predict and interpret the behavior of membrane reactor/separator. The theoretically calculated results agreed well with the chemical performance studies.