Effect of flow configuration on the behavior of a membrane reactor operating without sweep gas

A simulation study of a multitubular membrane reactor for the water gas shift reaction is presented. No sweep gas is considered. Two alternative flow configurations between the retentate and permeate streams are compared: cocurrent and countercurrent. The influence of the flow scheme on the ignition temperatures, CO conversions and axial temperature profiles is analyzed. Simple algebraic equations are derived to predict the temperature rise along the reactor length. The cocurrent scheme enables the attenuation of the thermal effects in the membrane reactor, by minimizing the temperature rise in the catalyst bed. Conversely, the temperature rise corresponding to the countercurrent scheme is considerably higher than that of the cocurrent configuration. Both thermal increases exceed the temperature rise of a conventional adiabatic fixed-bed reactor. Under countercurrent flow, the membrane reactor could exhibit steady-state multiplicity because of the heat feedback introduced by the permeate stream.