Performance of a mixed-conducting ceramic membrane reactor with high oxygen permeability for methane conversion

A mixed-conducting perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCFO) ceramic membrane reactor with high oxygen permeability was applied for the activation of methane. The membrane reactor has intrinsic catalytic activities for methane conversion to ethane and ethylene. C-2 selectivity up to 40-70% was achieved, albeit that conversion rate were low, typically 0.5-3.5% at 800-900 degreesC with a 50% helium diluted methane inlet stream at a flow rate of 34 ml/min. Large amount of unreacted molecular oxygen was detected in the eluted gas and the oxygen permeation flux improved only slightly compared with that under non-reactive air/He experiments. The partial oxidation of methane to syngas in a BSCFO membrane reactor was also performed by packing LiLaNiO/gamma -Al2O3 with 10% Ni loading as the catalyst. At the initial stage, oxygen permeation flux, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation flux to reach its steady state. 98.5% CH4 conversion, 93.0% CO selectivity and 10.45 ml/cm(2) min oxygen permeation flux were achieved under steady state at 850 degreesC. Methane conversion and oxygen permeation flux increased with increasing temperature, No fracture of the membrane reactor was observed during syngas production. However, H-2-TPR investigation demonstrated that the BSCFO was unstable under reducing atmosphere, yet the material was found to have excellent phase reversibility. A membrane reactor made from BSCFO was successfully operated for the POM reaction at 875 degreesC for more than 500h without failure, with a stable oxygen permeation flux of about 11.5 ml/cm(2) min. (C) 2001 Elsevier Science B.V. All rights reserved.

Mechanistic studies of methane partial oxidation to syngas over LiNiLaOx/Al2O3 catalyst

Temperature-programmed reduction (TPR) characterization of the LiNiLaOx/Al2O3 catalyst before or after partial oxidation of methane (POM) reaction and a series of O-2, CH4 and CH4/O-2 pulse reaction experiments over the catalyst under different pretreatments were performed. It was found that CH4 dissociatively adsorbs on active center nickel producing H-2 and surface carbon, C(a). The surface carbon reacts with surface lattice oxygen or surface adsorbed oxygen to produce CO. Because the activation barrier for the reaction C(a)+ O(a) =CO(a) is the highest among all the elementary reactions, the rate-determining step of the POM may be the reaction C(a) + O(a) =CO(a).