Membrane reactor for oxidative coupling of CH4 with an oxide ion-electron hole mixed conductor

A membrane reactor for the oxidative coupling of CH4 has been constructed with an oxide ion-electron hole mixed conductor, BaCe0.8Gd0.2O3-alpha. 10% CH4 diluted with Ar and an O-2-Ar mixture at a given ratio were fed into opposite sides of the membrane at 1173 K. The formation rate of C-2-hydrocarbons (ethane and especially ethene) in the CH4 compartment increased with P-O2 in the O-2-Ar compartment. This enhancement was due to electrochemical oxygen permeation, causing the conductor to short-circuit itself, resulting from the mixed conduction. For comparison, 10% CH4 and a small amount of O-2 were co-fed into one side of the membrane. The membrane operation gave a C-2 selectivity two times that of the co-feed operation for all CH4 conversions. From a catalytic study using BaCe1-xGdxO3-alpha powders as catalyst, it was found that increasing both the oxide-ion and electron-hole conductivities enhanced the formation of C-2 hydrocarbons, but reduced that of CO2. On the basis of these results, a mechanism for the oxidative coupling of CH4 of the mixed-conductor membrane was proposed.