Tubular lanthanum cobaltite perovskite type membrane for oxygen permeation

摘要

Tubular La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ perovskite membranes were prepared by isostatic pressing. The oxygen permeation fluxes were measured at various downstream oxygen partial pressures and temperatures. The oxygen permeation flux through the tubular membrane is about 0.2l cm~3/cm~2 min(STP) at ll73 K, when the oxygen partial pressure on the feed (Po_2) and permeate sides (Po_2) are 0.2l and 1 x l0~3 atm, respectively. The oxygen permeation flux increases sharply around l073 K due to an orderdisorder transition of the oxygen vacancies. Oxygen permeation flux decreases with increasing downstream oxygen partial pressure. The change in oxygen permeation flux from unsteady state to steady state is analyzed using the oxygen vacancy concentration transfer model. Oxygen fluxes increase with increasing helium flow rate but are insensitive to the air flow rate, which is in agreement with the oxygen permeation flux equation. The oxygen flux decreased slightly after long-term operation over ll0h. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis indicates that SrSO_4, CoSO_4, SrO, Co_2O_3, and La_2O_3 are formed on the surfaces of the tubular membrane due to interaction with trace SO_2 in the air and helium, and segregation of surface elements.