Catalytic properties of oxygen semipermeable perovskite-type ceramic membrane materials for oxidative coupling of methane

The catalytic properties for the oxidative coupling of methane (OCM) of La0.8Sr0.2CoO3 (LSC) and SrCo0.8Fe0.2O3 (SCF) in solid solution were studied and compared with those of 5 wt% Li/MgO, using a steady/unsteady state packed-bed reactor and a transient microbalance. The results of the steady-state cofeed experiments show that LSC possesses OCM catalytic properties similar to those of Li/MgO in terms of C-2 yield and selectivity at temperatures of around 800 degrees C, The former gives a larger C-2 space time yield than the latter, SCF exhibits poor OCM catalytic properties at 700-850 degrees C. To further examine the suitability of LSC as a membrane material for use in a dense membrane reactor for OCM, the instant OCM selectivity and activity and oxygen consumption rate for LSC and 5% Li/MgO on exposure to pure methane in cyclic feed mode were measured respectively at 850 degrees C and 800 degrees C, For both materials, the unsteady-state cyclic feed operation gives smaller initial OCM activity and larger initial C-2 selectivity than the cofeed steady state operation. Li/MgO quickly loses its OCM activity and selectivity in the unsteady state operation due to rapid consumption of the active sites, Up to 5 min of methane run time, LSC maintains appreciable OCM activity with poorer C-2 selectivity as compared to the steady state cofeed operation. The surface of LSC membrane at low oxygen partial pressure may become nonselective for OCM in membrane reactor applications. (C) 1996 Academic Press, Inc.