PEROVSKITE-TYPE OXIDE MEMBRANES FOR THE OXIDATIVE COUPLING OF METHANE

A series of ion-conducting perovskites of the form [La(1-x)A(x)] [Co0. 2Fe0.8]O3-delta (x = 0.4, 0.6 for A = Sr; x = 0.8 for A = Ba) were inv estigated for their use as a catalytic membrane for the oxidative coup ling of methane (OCM). A-site cations consisting of La0.4Sr0.6 and La0 .2Ba0.8 produce materials with the highest oxygen fluxes and result ac hieved with a powdered catalyst in a packed-bed reactor configuration. Selectivities in these materials appear to be limited by high oxygen ion recombination rates that compete for oxygen with the desired coupl ing reaction(s). The results also indicate that oxygen fluxes are not limited by diffusion, but by surface exchange rates at the oxygen-lean side of the membrane. The study on stability of these materials showe d that all three perovskites could be reduced in a pure methane or eth ane stream at 1,023 K but they were totally stable under reaction cond itions where oxygen is present.