Preparation And Oxygen Permeation Flux Of Tubular Oxygen Permeable Membranes

Mixed ionic-electronic conducting(MIEC)membranes are a kind of dense inorganic membranes that possess both oxygen ion conductivity and electronic conductivity,showing100% selectivity to oxygen at high temperature.For a practical industrial application,in addition to high oxygen permeation flux,MIEC membranes should possess good stability and high mechanical strength.Traditional disk-type membranes are difficult to be industrialized due to the difficulties in high-temperature sealing and poor mechanical strength.However,tubular membranes show many advantages,such as high volume/area ratio,easy to seal and assemble,thus have boarder application prospects.In this work,the plastic extrusion method was used to prepare capillary membranes and asymmetric tubular membranes,and the relationship between membrane preparation method and membrane performances was discussed.The related research contents are as follows:(1)Hollow fiber membranes prepared by traditional phase inversion method have the finger-like pores in the cross section and sulfate impurities in the membrane bulk,thus show low mechanical strength and degradation in oxygen permeability.In this work,the plastic extrusion method was used to prepare single-and dual-phase capillary membranes(with an outer diameter of 2.6-2.8 mm)to achieve fully dense cross-section and keep the pure phase.Experiment results show that the compressive force and 3-point bending fracture force of capillary membranes are much higher than those of hollow fiber membranes,showing excellent mechanical strength.The result of oxygen permeability test shows that the temperature,air pressure and oxygen partial pressure of feed side have a great influence on oxygen permeation fluxes,and have different effects on different capillary membranes.Oxygen permeation fluxes of both capillary membranes are higher than hollow fibers.This study shows that the plastic extrusion method is superior than the phase inversion method,indicated by capillary membranes has higher oxygen permeation flux and better mechanical strength than hollow fiber membranes.(2)In order to further improve oxygen permeation flux and decrease the sintering temperature of dual-phase membranes,a small amount of Cu was doped into the membrane material to reduce the sintering temperature by 200-300 ? C.Cu-doping has no significant effect on oxygen permeation flux.An asymmetrical tubular membrane supported by a porous support layer with outer diameter of about 5.35 mm was prepared by plastic extrusion,while a65-?m-thick dense layer was successfully prepared on the support by a dip-coating method.We found the oxygen permeation flux of this asymmetric tubular membrane is lower than that of 0.5-mm-thick disk-type membrane.In the presence of a surface oxygen exchange catalyst,a comparison of oxygen permeation flux under ambient and high air pressure of feed side was conducted,and different operation modes of sweep side were tried.Combined with microstructure characterization,we deduce that the oxygen permeation flux of the asymmetric tubular membrane is limited by pore structure of porous support layer and the distribution of catalyst in the porous support layer.