Perovskite dense membrane reactors for the partial oxidation of methane to synthesis gas

Perovskite dense membrane reactors have potential applications in methane partial oxidation to syngas ({dollar}rm CHsb4 + 1/2Osb2 to 2Hsb2 + CO{dollar}) using air as an economical oxygen source. A two-dimensional nonisothermal mathematical model was developed to simulate oxidation of methane to syngas in a tube-and-shell catalytic membrane reactor. The three-layer membrane consisted of an inert large-pore support, an O{dollar}sb2{dollar}-semipermeable dense perovskite layer and a porous catalytic layer. Comparisons were made to the conventional fixed-bed reactor, and to membrane reactors which were isothermal, adiabatic or wall-cooled. The simulation results implied that the temperature rise in exothermic partial oxidation reactions might be mitigated substantially by the use of a dense membrane reactor and that a high rate of O{dollar}sb2{dollar} permeation would be required.; Experiments for O{dollar}sb2{dollar} permeation rate measurement in a He/air gradient showed that O{dollar}sb2{dollar} permeation rates decreased with time, and eventually reached steady state. Steady-state oxygen permeation rates for {dollar}rm Lasb{lcub}1-x{rcub}Asbsp{lcub}x{rcub}{lcub}prime{rcub}Fesb{lcub}0.8{rcub}Cosb{lcub}0.2{rcub}Osb{lcub}3-delta{rcub}{dollar} perovskites were in the order {dollar}rm Asbsp{lcub}x{rcub}{lcub}prime{rcub}=Basb{lcub}o.8{rcub} > Basb{lcub}0.6{rcub} > Casb{lcub}0.6{rcub} > Srsb{lcub}0.6{rcub}{dollar}. Oxygen permeation rates could be increased by one order of magnitude by engineering the A-site cation substitution.; A {dollar}rm Lasb{lcub}0.2{rcub}Basb{lcub}0.8{rcub}Fesb{lcub}0.8{rcub}Cosb{lcub}0.2{rcub}Osb{lcub}3-delta{rcub}{dollar} disk-shaped membrane adopted for the reaction experiments showed a stable and high oxygen permeation rate (0.8 cm{dollar}sp3{dollar}(STP)/cm{dollar}sp2{dollar}/min) at 850{dollar}spcirc{dollar}C for 60 days under a diluted methane stream. The product in a blank run contained mainly CO{dollar}sb2{dollar}, H{dollar}sb2{dollar}O, CH{dollar}sb4{dollar} and O{dollar}sb2{dollar} which could be further reformed to CO and H{dollar}sb2{dollar} in a downstream catalytic bed. 95% CH{dollar}sb4{dollar} conversion and near 100% CO selectivity were obtained, at an adequate inlet methane concentration. Packing 5% Ni/Al{dollar}sb2{dollar}O{dollar}sb3{dollar} catalyst directly on the membrane reaction-side surface reduced the O{dollar}sb2{dollar} partial pressure, increasing the driving force for oxygen transport, and resulted in a five-fold increase in O{dollar}sb2{dollar} permeation. The results of characterization showed that membrane reaction-side surface was affected by the reducing atmosphere and gas species while barium enrichment was found on the air-side surface. The membrane interior was stabilized by the continuous oxygen transport from the air side.