Oxygen Permeation And Catalytic Reaction Of La_0.7Sr_0.3FeO_3-δ

Lao.7Sr0.3FeO3-δ (LSF) and Lao.6Sro.4Coo.2Ni0.8O3-δ (LSCN) perovskite powders were both prepared through a sol-gel method using ethylene glycol and citric acid (CA) as complexing agents simultaneously. The microstructure, the crystalline phase and the size distribution of the prepared powders were investigated by SEM, XRD, and laser grain analyzer measurements, respectively. The catalytic reaction performance of the LSCN powders used for catalytic reforming of methane were also studied. The experimental results indicate that the LSF powders were single crystal perovskite. There were no loss of metal ions in preparation process. The average diameter of LSCN powders were3.26μm. LSCN catalyst have been shown good catalytic performances in the temperature range of650-1000℃.LSF hollow fibre membranes were prepared by the phase inversion and sintering technique. Differernt sintering temperatures were investigated in order to analyze how they affected the propoties of the LSF hollow fibers, for example, micro-structure, crystalling phase, porosity, mechanical strength and oxygen permeation. At the same time, oxygen permeation of different sweep gases were also studied. With the sintering temperature improved, the micropores of LSF inner and outer surfaces decreased slowly, and the crystal grain increased with clear crystal boundaries. The mechnical strength of the LSF hollow fiber membranes developed with the sintering temperature. When the temperature was high enough, the mechnical strength tended to steady. In other words, when the sintering temperature was1400℃, the mechnical strength of the membrane can reach134MPa. The porosity and oxygen permeation reduced when the sintering temperature was increased.The effect of oxygen permeation flux was different on LSF hollow fibre membranes with different sweep gas. The oxygen permeation flux was improved under methane or hydrogen sweeping condition and decreased under CO2sweeping condition. But the LSF membrane still exhibited appreciable oxygen flux even under the pure CO2sweeping condition. At950℃, the oxygen flux under pure methane and pure helium reached3.54mL·cm-2·min-1and1.42mL·cm-2·min-1, respectively, reduced to0.92mL·cm-2·min-1when using pure CO2 as the sweep gas. The membranes showed good stability under pure CO2and pure helium, but become worse under pure methane, and the microscopic structure of LSF hollow fibre membranes was changed.Dense ceramic hollow fibre membranes were employed to fabricate hollow fibre membrane reactors for methane reforming to syngas. The methane conversion, carbon monoxide and hydrogen selective obviously improved with the reaction temperature improved and the catalyst filled. With reaction time and the methane concentration increased, the methane conversion rate increased, but carbon monoxide and hydrogen selective gradually reduced. When LSCN was packed inside the reactor as the catalysts, the methane conversion, the CO selectivity and oxygen permeation flux were obviously improved significantly. The methane conversion was92%at900℃, and the CO selectivity and oxygen permeation flux were36%and6.06mL·cm-2·min-1, respectively.