Comparative study on several mixed conducting oxygen permeable membrane reactors

Three mixed conducting oxygen permeable membranes, i.e. SrCo0.5FeO3.25 (SC5FO), La0.15Sr0.85Ga0.3Fe0.7O3-delta (LSGFO) and Ba0.5Sr0.5 Co0.8Fe0.2O3-delta (BSCFO) were synthesized by wet chemical methods. A comparative study about their phase structures, phase and thermo-chemical stabilities, oxygen permeability and membrane reactor performance for partial oxidation of methane to syngas, was made. After annealing in an Ar atmosphere at elevated temperatures, the pure cubic perovskite structure was survived for LSGFO and BSCFO, but not for SC5FO. After H-2-TPR experiment, the original phase structures of BSCidiiFO and SC5FO were totally destroyed, but the basic perovskite structure of LSGFO was survived. Multi H2-TPR and re-oxidation results of BSCFO oxide demonstrated that it had excellent phase reversibilities. The oxygen permeabilities of SC5FO and LSCFO were very low, while a permeation flux as high as 1.1 mL/cm(2.)min was obtained for a BSCFO membrane at 850degreesC, which demonstrates its promising application for oxygen separation. Leaking problem was encountered for a SC5FO membrane reactor during POM reaction, while LSGFO and BSCFO membrane reactors were stably operated in the POM reaction. At 950degreesC, under POM reaction conditions, the oxygen permeation flux of LSGFO slowly increased with time, at last (about 300h was needed), a flux about 4 [STP]mL/cm(2.)min was obtained, which was 10 to 40 times higher than that under an air/He oxygen partial pressure gradient. The oxygen permeation flux of the BSCFO membrane can reach its steady state (850degreesC, 10.45 [STP]mL/cm(2.)min) much quicker (about 21h). The BSCFO and LSGFO reactors were stably operated for a long time without failure. The high POM operation stability of LSGFO is due to its high thermo-chemical stability. However, for BSCFO membrane reactor, it is due to its high oxygen permeability and excellent phase reversibility