Catalyst Screening for Oxidative Coupling of Methane Integrated in Membrane Reactors

Increased availability of methane from shale gas and stranded gas deposits in the recent years may facilitate the production of ethylene by means of potentially more competitive routes than the state-of-the-art steam cracking processes. One appealing route is the oxidative coupling of methane (OCM), which is considered in this work for the production of ethylene by means of the use of catalytic membrane reactors (CMR) based on Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) ceramic material. In a first approach, a screening of 15 formulations as catalysts for the ethylene-ethane production was conducted on CMR consisting of disk-shaped planar BSCF membranes. At 900 degrees C, the maximum C-2 selectivity was 70%, reached with Ba0.5Sr0.5FeO3-delta and La0.5Ce0.1Sr0.4Co0.8Fe0.2O3-delta catalysts. On the other hand, low CH4 conversions (X-CH4) resulted in C-2 yields below 3%. Operation at 1,000 degrees C significantly shifted X-CH4 for all the activated membranes due to the decrease in CH4/O-2 ratios, thus obtaining C-2 yields close to 9% and productivities of ca. 1.2ml.min(-1).cm(-2) with Ce0.9Gd0.1O2-delta and Ba0.5Sr0.5Co0.8Fe0.2O3-delta impregnated with Mn-Na2WO4 catalysts. The performance of OCM reaction was also studied in a tubular catalytic membrane reactor. Tubular configuration improved C-2 yield by minimizing CH4/O-2 ratios up to 1.7, obtaining a maximum of 15.6% at 900 degrees C with a BSCF capillary membrane activated with a packed bed of 2 wt% Mn/5 wt% Na2WO4 on SiO2 catalyst.