STABILITY OF LA0.6SR0.4CO0.2FE0.8O3-DELTA PEROVSKITE MEMBRANES IN REDUCING AND NONREDUCING ENVIRONMENTS

The chemical stability of perovskite La0.6Sr0.4Co0.2Fe0.8O3-delta (LSC F-6428) has been investigated in connection with its potential use as a catalytic membrane for the oxidative coupling of methane (OCM). Once a steady-state oxygen-defect gradient is established (15-20 h), these membranes are found to be very stable under air/nitrogen gradients at temperatures up to 960 degrees C and they respond instantaneously to temperature changes with an apparent activation energy of 159 kJ/mol. However, serious near-surface etching occurs when one side of the memb rane is exposed to 100% CH4 at 850 degrees C and atmospheric pressure, which resulted in dramatic increases in oxygen flux (a factor of 5). While this also caused an increase in the OCM reaction rate, the selec tivity of C2+ hydrocarbons fell from 40 to 10%. It is also shown that stable operation under OCM conditions is possible if CH4 pressures are reduced to 0.1 atm but at; a cost of C2+ production rate.