Novel Molten Oxide Membrane for Ultrahigh Purity Oxygen Separation from Air

We present a novel solid/liquid Co3O4–36 wt % Bi2O3 composite that can be used as molten oxide membrane, MOM (Belousov, V. V. Electrical and Mass Transport Processes in Molten Oxide Membranes. Ionics 22, 2016, 451−469), for ultrahigh purity oxygen separation from air. This membrane material consists of Co3O4 solid grains and intergranular liquid channels (mainly molten Bi2O3). The solid grains conduct electrons, and the intergranular liquid channels predominantly conduct oxygen ions. The liquid channels also provide the membrane material gas tightness and ductility. This last property allows us to deal successfully with the problem of thermal incompatibility. Oxygen and nitrogen permeation fluxes, oxygen ion transport number, and conductivity of the composite were measured by the gas flow, volumetric measurements of the faradaic efficiency, and four-probe dc techniques, accordingly. The membrane material showed the highest oxygen selectivity jO2/jN2 > 105 and sufficient oxygen permeability 2.5 × 10–8 mol cm–1 s–1 at 850 °C. In the range of membrane thicknesses 1.5–3.3 mm, the oxygen permeation rate was controlled by chemical diffusion. The ease of the MOM fabrication, combined with superior oxygen selectivity and competitive oxygen permeability, shows the promise of the membrane material for ultrahigh purity oxygen separation from air.