Perovskite-type ceramic membrane: Synthesis, oxygen permeation and membrane reactor performance for oxidative coupling of methane

La(1-x)Sr(x)Co(1-y)Fe(y)O(3-δ) perovskite-type oxides are typical of mixed-conducting ceramic membrane materials with very high oxygen semipermeability. In this study, several different synthesis methods were compared for the preparation of La_0.8Sr_0.2Co_0.6Fe_0.4O(3-δ) (LSCF) powders. The coprecipitation method was found most suitable for preparation of the LSCF powder in terms of processibility into dense ceramic membranes. The oxygen permeation flux through 1.85mm LSCF membrane exposed to O₂/N₂ mixture and helium is about 1x10^-7mol/cm²s at 950°C. The oxygen permeation flux increases sharply around 825°C due to an order-disorder transition of the oxygen vacancies in the membrane. Oxidative coupling of methane (OCM) was performed in the LSCF membrane reactor with one membrane surface exposed to O₂/N₂ mixture stream and other to CH₄/He mixture stream. At temperatures higher than 850°C, high C₂ selectivity (70-90%) and yield (10-18%) were achieved with a feed ratio (He/CH₄) of 40-90. The C₂ selectivity dropped dramatically to less than 40% as the He/CH₄ ratio decreased to 20. The surface catalytic properties for OCM of LSCF membranes strongly depend on the oxygen activity of the membrane surface exposed to methane stream. Copyright (C) 1998 Elsevier Science B.V.