Factors controlling the performance of catalytic dehydrogenation of ethylbenzene in palladium composite membrane reactors

Ethylbenzene dehydrogenation to styrene in a palladium composite membrane reactor was investigated. The reaction kinetics have been studied in a gradientless recycle reactor to develop a suitable kinetic model, which was subsequently used for the simulation of a hypothetical industrial-scale packed-bed membrane reactor. For this simulation, the measured hydrogen permeability of palladium composite membranes, prepared by different methods on asymmetric porous ceramic and porous sinter metal supports, was used. The results demonstrate that the performance of the membrane reactor is controlled both by the membrane permeability and by the reaction kinetics, i.e. 4-27 % savings of the ethylbenzene feed at equal styrene output are predicted for industrially relevant operating conditions. Besides savings of raw materials, a second advantage of the membrane reactor is seen in a reduced ethylbenzene load of the ethylbenzene/styrene fractionation column, thanks to the increased conversion. Moreover, a simplified heat management seems to be possible by utilizing the combustion of the permeated hydrogen to supply the heat required for the dehydrogenation. Concerning membrane permeability, the simulation demonstrates a noticeable contribution of the support to the overall hydrogen transport resistance when going for a tube size suitable for an industrial-scale reactor. Hence, care has to be taken not only of the permeability of the hydrogen permselective layer, but also of the thickness, porosity, and mean pore size of the support. All in all, the simulation results show that a packed-bed multitubular membrane reactor in fact offers the potential for substantially increasing the styrene yield in ethylbenzene dehydrogenation. What is needed are both high hydrogen permeability and high catalyst efficiency. However, a large-scale application obviously means a very big challenge not only in respect of the manufacture of highly permeable and resistive membranes but also in terms of maximizing catalyst efficiency and developing a suitable reactor design. (C) 1999 Elsevier Science Ltd. All rights reserved.