Enhancement of catalytic reaction by pressure swing adsorption

Abstract

A theoretical study of an adsorptive reactor which combines multibed pressure swing adsorption and chemical reaction is presented; such a reactor is referred to as a pressure swing reactor, or PSR. Studies have concentrated on an asymptotic case in which there is the ideal propagation of concentration waves within the reactor beds; the method of characteristics was employed in the solution of the governing PSR equations. The studies assessed the effects of operating conditions, and cycle configurations, on the PSR performance. Calculations indicate enhanced reactant conversion when compared to conventional steady state plug flow operation. In particular, for some reversible reactions, substantial improvements over equilibrium yields have been calculated. For example, for the dissociation reaction 2A ⇔ B + C, and where B is the only adsorbing component, approximately two-fold improvements over the equilibrium yield of product B have been predicted. Such reaction enhancement can be attributed to the limitation of the backward reaction, which results from the separation of the product species B and C. In addition to the method of characteristics, a cells-in-series method for the asymptotic case has been developed, and found to yield calculations consistent with the method of characteristics solutions. In a third numerical approach, the spatial discretisation technique of orthogonal collocation on finite elements was applied to the governing PSR equations, and the resulting system of ordinary differential equations solved by a standard integration algorithm. In this case, many of the simplifying model assumptions were relaxed, allowing, for example, the simulation of a non-isothermal PSR with finite mass transfer rates. One practical significance of reaction enhancement by pressure swing adsorption is a lower temperature of operation than in a conventional reactor. This would lead to savings in the energy requirements of the reactor, and limit the rate and degree of catalyst deactivation due to coke deposition or sintering.