Design Directions for Composite Catalytic Hollow Fibre Membranes for Condensation Reactions

Abstract

Pervaporation membrane reactors are ideal candidates to enhance conversion in reversible reactions generating water as a by-product. The equilibrium displacement can be enhanced by catalytic membranes due to the close integration of reaction and separation. In this paper, the viability of composite catalytic hollow fibre pervaporation membranes for condensation reactions is examined. The esterification reaction between acetic acid and butanol has been taken as a model reaction, for which a parametric model study was carried out to provide a fundamental understanding of the composite catalytic membrane reactor behaviour. With increasing catalytic layer thickness, the conversion becomes no longer limited by the amount of catalyst present in the reactor but by diffusion in the catalytic layer. External mass transfer was never found to be rate-limiting. An optimum catalytic layer thickness was found to be around 100 μm under the prevailing conditions, which is within practically reachable dimensions. At this optimum catalytic layer thickness, the performance of a catalytic membrane reactor exceeds the performance of an inert membrane reactor due to the close integration of reaction and separation. This shows the potential added value of such a membrane system compared with more usual reactor designs. The exact value of this optimum is a function of the reaction kinetics and the membrane permeability.