Oxygen Permeability Of Perovskite Tungsten-doped SrCoO₃ And (La_0.8Ca_0.2)_1.01FeO₃ Hollow Fiber Membranes

Air separation using mixed conducting perovskite hollow fiber membranes has many advantages,such as high separation efficiency,low energy consumption and simple operation compared to the conventional distillation methods.The disadvantage of perovskite material is its insufficient mechanical strength and low chemical stability in CO₂-containing atmosphere.For commercial applications,the oxygen flux is also required to be further improved.In this paper,the tungsten doped SrCoO₃ has been investigated.Doping helps to enhance the oxygen permeability and to improve the mechanical strength and chemical stability in CO₂-containing atmosphere.A series of SrCoxW1-xO₃-δ（0≤x≤0.25 SCW）powders were synthesized using sol-gel method.The hollow fiber membranes were prepared using a combined phase-inversion and sintering technology.The effects of tungsten（W）doping concentration,sweep flow rate,operational temperature and CO₂ concentration inside the sweep gas on the material structure,oxygen permeability and stability were carefully investigated.It was found that 10%W doping maximizes the performance of the resultant SrCoxW1-xO₃-δ（SCW0.1）hollow fiber membranes.The resultant hollow fiber membrane has the three-point bending strength of 93.89 MPa after calcination at 1250 °C for 4 hours.The oxygen flux can reach 4.0 mL·min^-1.cm^-2 operated under the He sweep gas flow rate of 180 mL-min^-1 at 900 ℃.The oxygen permeation flux of SCW0.1 hollow fiber abruptly decreased to zero in CO₂ atmosphere.However,it could be restored to 100%when the sweep gas was shifted to helium after 30 hours,indicating good short-time restoring ability.The oxygen permeability of Ag-modified SCW0.1 hollow fiber was increased to 0.7 mL·min^-1.cm^-2 at 950 0C.Doped Ba ions at A-site,the oxygen permeation flux of BSCW hollow fiber membrane was up to 4.75 mLmin^-1 cm^-2 under the He sweeping gas flow rate of 180 mL·min^-1 at 900 ℃ and the three-point bending strength of the resultant hollow fiber membrane can be enhanced to 177.00 MPa.The performance of(La_0.8Ca_0.2)1.01FeO₃-δ（LCF）hollow fiber membranes was also synthesized and investigated.The three-point bending strength can reach up to 320MPa,higher than any other perovskite hollow fibers.The oxygen permeability of LCF hollow fiber membranes can be significantly improved by acid surface treatment,increasing from 0.46 to 0.83 mL·min^-1·cm^-2operated at 950 ℃.The oxygen flux of BSCF-modified LCF hollow fiber was increased by 0.12 mL·min^-1·cm^-2 at 900 ℃.Despite low oxygen permeability,LCF hollow fiber membranes exhibit excellent stability,stably operated for 200 hour in CO₂ atmosphere.