Combined reaction and separation in pressure swing processes

Abstract

Theoretical studies of a novel reactor which combines pressure swing adsorption (PSA) and chemical reaction are presented; such a reactor is referred to as a pressure swing reactor, or PSR. The design is based on a conventional two-bed PSA process, in which many of the usual cycle configurations for operation are possible, e.g. simple and purge cycles. Each bed contains a mixture of an active catalyst for reaction, and a selective adsorbent for the adsorption of one or more of the reaction species. Theoretical calculations predict that such a process may lead to greater conversions than conventional steady flow reactors, and thus allow a lower temperature of operation for a desired conversion. Furthermore, for equilibrium reactions of the general form aA ⇌ bB + cC, and especially when an adsorbent can be chosen such that the adsorption equilibrium constants are in the sequence HB > [HA, HC], possible improvements over equilibrium conversions are indicated. In this work, theoretical investigations have concentrated on three types of reversible reaction schemes; isomerisation, dissociation/disproportionation, and dehydrogenation; potential advantages of a PSR have been illustrated for these. As a test case, experimental investigations have concentrated on the dehydrogenation reaction of methylcyclohexane to toluene, for which a Pt Al2O3 catalyst was found to have suitable activity at temperatures as low as 450 K. Pulse chromatography experiments have been carried out to scan the high temperature (400 K to 700 K) adsorption properties of methylcyclohexane, toluene and hydrogen on some commercial adsorbents; clay-based adsorbents were found to be particularly suitable for this case, yielding the desired sequence of adsorption strengths. © 1995.