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

Abstract

A membrane reactor for the oxidative coupling of CH₄ has been constructed with an oxide ion–electron hole mixed conductor, BaCe_0.8Gd_0.2O_3–α. 10% CH₄ diluted with Ar and an O₂–Ar mixture at a given ratio were fed into opposite sides of the membrane at 1173 K. The formation rate of C₂–hydrocarbons (ethane and especially ethene) in the CH₄ compartment increased with P_o2 in the O₂–Ar compartment. This enhancement was due to electrochemical oxygen permeation, causing the conductor to short-circuit itself, resulting form the mixed conduction. For comparison, 10% CH₄ and a small amount of O₂ were co-fed into one side of the membrane. The membrane operation gave a C₂ selectivity two times that of the co-feed operation for all CH₄ conversions. From a catalytic study using BaCe_1–xGd_xO_{3 –α} powders as catalyst, it was found that increasing both the oxide-ion and electron-hole conductivities enhanced the formation of C₂ 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.