Preparation And Properties Of Tb-doped BaCeO3 Perovskite Hollow Fiber Hydrogen Permeable Membranes

As one type of the inorganic dense membrane,the BaCeO3 perovskite ceramic hydrogen permeation membrane,which generally possess low H2 permeation flux as a result of inherent low protonic and/or electronic conductivity,achieves hydrogen permeation through the transmembrane conduction of proton and electron.However,doping with a trivalent rare earth cation may be an effective way to enhance the conductive performance of the membrane.On the other hand,the hollow fibres exhibit many advantages i.e.facile high-temperature sealing,thin effective membrane thickness,and greater membrane area per unit packing volume.Hence,it is beneficial to improve the hydrogen permeation flux of the membrane.In this paper,Tb-doped BaCeO3 perovskite hollow fibre ceramic membrane was studied.After investigating the effect of different ions doping on the electrical conductivity as well as chemical and thermal stability of BaCeO3 perovskite,the material with the highest electrical conductivity was fabricated into hollow fibre membrane and their properties were investigated.And the influence of elevating surface exchange kinetics through membrane surface modification on the performance promotion of the provskite oxides and membranes was explored systemly.Finally,the application of prepared hollow fibre membrane in methane dehydrogenation reaction was discussed.Firstly,BaCeo.95Tb0.05O3-??BCTb?perovskite oxides was synthesized through a combined sol-gel and combustion method,and BCTb hollow fibre membranes were fabricated by phase-inversion and sintering technology.The results showed that the hydrogen permeation flux through the BCTb hollow fibre membranes reached up to 0.57 mL cm-2·s-1 at 1000 ? when H2-He and N2 flow was 40 and 30 mL·min-1,respectively.In order to explore the electrical conductivity and stability of doped BCTb oxides,BaCe0.85Tb_0.05M_0.1O_3-??BCTM?perovskite oxides doped with M=Co,Fe,Y,Zr,Mn were synthesized.The structural and chemical stability and electrical conductivity of the BCTM perovskites were measured in different atmospheres by the powder X-ray diffraction?XRD?and four-probe techniques.The results shows that the perovskite phase of BCTM oxides can be preserved well in H2 and water vapour-containing atmospheres,while may be reacted with CO2 into carbonates due to the strong alkalinity of the BaCeO3 composites.Doping with Mn or Co ions into the BCTb perovskite favors improving the electrical conductivity.Hereafter,Co element was selected and doped into the BCTb perovskite proton conducting oxides to elevate the electrical conductivity and H2 flux,and BaCe0.85Tb0.05Co0.1O3-??BCTCo?hollow fibre membranes were fabricated.The influence of sintering temperature on the powder and membrane properties was investigated in terms of crystal phase,morphology,porosity,mechanical strength,electrical conductivity and hydrogen/oxygen permeation.The H2 flux through the BCTCo hollow fibre membranes reached up to 0.385 mL cm 2·min^-1.As the effective thickness of the perovskite hollow fibre membranes decreases,the relative limiting effect of the surface exchange kinetics on the hydrogen permeation will become significant.In order to promoting the urface exchange kinetics for obtaining higher permeation fluxes,in this experiment,surface modification was performed by H2SO4 etching and/or by different Pd/Ni-loading method on the hollow fibre surface.The results indicated that coating porous Pd layers on the membrane surface could promote remarkably the H₂ flux,i.e.from 0.046 to 0.272 mL·cm-2·min-1 at 900 ? for the original and Pd-coated membrane,respectively.The H2SO4 etching would deteriorate the H2 permeation by the contamination of sulphur-containing compounds.H2 permeation fluxes at 1000 ?can be improved from the original 0.164 mL·cm-2·min-1 to 0.269 and 0.42 mL·cm-2·min-1 for the Ni and Pd particles-loaded membranes with maximum improvement by 64%and 155%,respectively.Loading of the catalyst on both sides may enhance the hydrogen permeation most effectively.The permeation enhancement depends on both the catalyst loading amount and structure.Catalytic dehydrogenation coupling of methane?DCM?into C2 products?C₂H₆,C₂H₄?represents one of the most effective ways to convert natural gas to more useful products.In this work,BCTCo hollow fibre membrane reactor with catalysts loaded on the inner surface of the membrane was explored for the DCM reaction.The results shows that the usage of BCTCo membrane could elevate the C2 product selectivity,and the methane reacted can be almost converted totally into C2 product by the BCTCo membrane reactor at 900 ?.