Membrane Reactor/Separator: A Design for Bimolecular Reactant Addition

Abstract

A membrane reactor (MBR) is used to investigate the effect of selective reactant addition on series-parallel reaction networks, such as the oxidative dehydrogenation of ethane to ethylene. Ethylene is favored in an oxygen-lean environment, while excess oxygen favors the formation of combustion products. Control of the reactant ratio (ethane to oxygen) is crucial to both the overall selectivity and the hydrocarbon conversion. Traditional reactor designs co-feed the bimolecular reactants at the top of the reactor at some preset feed ratio. The MBR uses a tube (porous alumina membrane) and shell configuration. One reactant is fed at the top of a catalyst bed packed within the membrane core. The other reactant permeates into the tube along the length of the reactor via an imposed pressure drop. The reactant ratio is large at the top of the MBR, which leads to high selectivities; as the oxygen is consumed, it is replenished via downstream permeation to improve the ethane conversion. The MBR and a plug flow reactor (PFR) are evaluated at 600 [ddot]C, with identical space velocities, and using a magnesium oxide catalyst doped with samarium oxide. At low to moderate reactant feed ratios, the ethylene yield in the MBR exceeds the PFR by a factor of three, under some conditions. At higher feed ratios, the performance of the PFR nears or exceeds the performance of the MBR.