Mathematical simulation of catalytic dehydrogenation of ethylbenzene to styrene in a composite palladium membrane reactor

The catalytic dehydrogenation of ethylbenzene to styrene was studied in a tubular palladium membrane reactor using a commercial styrene catalyst. A mathematical model of the membrane reactor is presented which takes into account the different mass transport mechanisms prevailing in the various layers of the membrane, that is, multicomponent diffusion in the stagnant gas films on both faces of the membrane, combined effective multicomponent diffusion, effective Knudsen diffusion, and viscous flow in the macroporous support, Knudsen diffusion in the microporous intermediate layer, and Sieverts' law of hydrogen transport through the Pd-film. A kinetic model from the literature [1-3] was adjusted to match conversion and selectivity observed during experiments with a commercial catalyst in a laboratory fixed-bed reactor. Simulation calculations based on the resulting effective kinetics were carried out fur industrially relevant operating conditions and various process configurations, that is, use of inert sweep gas, evacuation of the permeate gas, and oxidation of the permeated hydrogen. The results demonstrate that with the present catalyst used under typical process conditions (T, P, WHSV S/O) removal of hydrogen through the membrane gives only a small increase of styrene yield. However, the model predicts that by increasing the reaction pressure in the membrane reactor the kinetic limitation can be overcome and ethylbenzene conversion can be increased to above 90% without markedly decreasing styrene selectivity.