Membrane reactors offer the advantage over conventional fixed-bed reactors of combining chemical reaction and separation in a single unit. They can substantially improve the performance of reactions by selective removal of one of the reaction products or by controlled addition of a reactant. In the former case, conversion enhancement beyond the thermodynamic limit can be achieved for equilibrium-limited reactions, while in the latter, product selectivity can be improved by influencing the concentration and residence time of components giving rise to undesired reactions. Several articles which review experimental and theoretical studies of catalytic membrane reactors are available in the literature (Hsieh, 1991; Tsotsis et al., 1993; Saracco and Speccia, 1994; Zaman and Chakma, 1994).

Membrane Reactors with Nonuniform Catalyst Distribution

In this section we discuss theoretical studies addressing nonuniform distribution of catalyst in membrane reactors, in order to gain insight into the effect of catalyst location on this new reactor type, before addressing optimization issues in the following sections. Yeung et al. (1994) investigated the influence of the location of a Dirac-delta catalyst in pellets contained in an inert membrane reactor with catalyst on the feed side (IMRCF), a catalytic membrane reactor (CMR), and a conventional fixed-bed reactor (FBR). For the IMRCF and the FBR, the active catalyst is distributed in pellets placed inside the membrane or the reactor tube respectively, while for the CMR the active catalyst is distributed within the membrane itself as shown in Figure 5.1.