Preparation Of Ag-doped LCF Hollow Fiber Membrane Reactor And Its Application In Synthesis Of Synthetic Gas From Methane

As the energy transition has list in in the national plan,methane partial oxidation（POM）to syngas has gradually increased the great interests.However,how to provide high purity oxygen for partial oxidation of methane to syngas is still a challenge.Perovskite ceramic oxygen permeable hollow fiber membrane reactor has attracted extensive attention because of its low energy consumption,high separation efficiency and especially the advantages of coupling the reactor with separation.In this paper,the pure perovite oxide(La_0.2Ca_0.8)_1.01 Fe_0.95O_3-δ（LCF）and(La_0.2Ca_0.8)_1.01 Fe_0.95O_3-δ+0.05Ag（LCFA）composite powders were firstly synthesized by citric acid complex method.The properties of the LCFA powders calcined at 900℃and1250℃,respectively,after 3h were characterized by transmission electron microscope（TEM）and the results showed that Ag is uniform distribution in(La_0.2Ca_0.8)_1.01 Fe_0.95O_3-δgrain boundary and no reunion phenomenon at different temperatures.The properties of LCF and LCFA powders which were calcined at 900℃,were analyzed by X-ray diffraction（XRD）.The results show that LCF is a pure perovskite structure and LCFA is a composite powder of LCF and Ag.Dense oxygen permeable hollow fiber membranes of LCF and LCFA were prepared via phase inversion-sintering technology.The diluted silver paste was coated on the outer surface of LCF hollow fiber membrane to obtain(La_0.2Ca_0.8)_1.01Fe_0.95O_3-δ+△Ag（LCF+Ag）hollow fiber.The microstructure of LCFA hollow fiber membrane before and after the POM reaction was further characterized by scanning electron microscopy（SEM）.The structure of denes surface and porous cross section still stay in the hollow fiber.Oxygen permeability testing show that the oxygen permeation flux of LCF,LCFA and LCF+Ag hollow fiber 0.28,0.73,0.30mL·min^-1·cm^-2,respectively,when the temperature was set at 900℃with the air flow rate of 100 mL·min^-1 and purge gas He of 90 mL·min^-1.Compared with LCF,the oxygen permeation fluxes of LCFA and LCF+Ag were increased by 160%and7%,respectively.At the same temperature,the fluxes of LCFA hollow fiber membrane were 0.65,0.54 and 0.52 mL·min^-1·cm^-2,respectively,under 100%He,50%CO₂+50%He and 100%CO₂,indicating that the oxygen permeability slightly decreased with the increase of CO₂ concentration.Ni/LaNiO₃/γ-Al₂O₃ catalyst for partial oxidation of methane was prepared from nickel metal powder,γ-Al₂O₃ and home-made LaNiO₃ powder.The catalyst was coated on the inner surface of the LCFA hollow fiber membrane via injecting method.The oxygen permeable hollow fiber membrane of LCFA after POM reaction still remained stable and compact.At 925℃,when the air flow rate is set at 100 mL·min^-1and methane flow rate is set at 45 mL·min^-1,the methane conversion rate is up to94.3%,and the selectivity of CO is up to 97.4%.These reflect that the LCFA hollow fiber is a promising membrane reactor for partial oxidation performance of methane.