Model-based approach for specifying requirements on membranes to be applicable in membrane reactors of the extractor type

Membrane reactors, which integrate reaction and selective transport, have been proposed for dosing reactants into a reactor (’distributors’) and for selectively removing specific products from a reactor (’extractors’). Although there are a few successful applications the attractive concept appears to be still not sufficiently exploited. One of the reasons is the fact that membrane candidates are typically developed and characterized without taking explicitly into account the requirements of the specific reactions of interest.

We present an isothermal dimensionless steady state plug flow model for a tubular membrane reactor of the extractor type. The short-cut model is formulated to support evaluating the kinetic compatibility between the main reaction and the removal of the target component over the reactor wall. Incorporation of the relevant reactions, the convection processes on both feed and sweep sides and component specific withdrawal rates allows specifying properties of membranes required to exploit the potential of the concept. The key parameters of the short-cut model are two characteristic Damköhler numbers and the reaction and transport selectivities. These numbers and the model allow efficiently evaluating the impact of different possible operating conditions and geometric properties of the reactor and the membrane.

After presenting in the first part simulation results for various model reactions, the short-cut model is applied to the homogeneously catalyzed hydroformylation of 1-butene to n-pentanal accompanied by the undesired consecutive aldol condensation. The conceptual approach is applied to evaluate the potential of two commercially available polymeric membrane candidates, which differ in permeability and selectivity. The analysis based on experimentally determined reaction and transport rates rapidly predicts that both membranes do not offer potential for application in a single tubular membrane reactor. To outperform conventional operation, in particular the selectivity of these membranes must be improved.