Enhanced oxygen separation through robust freeze-cast bilayered dual-phase membranes

Abstract

Dual-phase oxygen-permeable asymmetric membranes with enhanced oxygen permeation were prepared by combining freeze-casting, screen-printing, and constraint-sintering techniques. The membranes were evaluated under oxyfuel operating conditions. The prepared membranes are composed of an original ice-templated La0.6Sr0.4Co0.2Fe0.8O3-delta support with hierarchically oriented porosity and a top fully densified bilayered coating comprising a 10 mm-thick La0.6Sr0.4Co0.2Fe0.8O3-delta layer and a top protective 8 mm-thick layer made of an optimized NiFe2O4/Ce0.8Tb0.2O2-delta composite synthesized by the one-pot Pechini method. Preliminary analysis confirmed the thermochemical compatibility of the three involved phases at high temperature without any additional phase detected. This membrane exhibited a promising oxygen permeation value of 4.8 mLmin(-1)cm(-2) at 1000 degrees C upon using Ar and air as the sweep and feed gases, respectively. Mimicking oxyfuel operating conditions by switching argon to pure CO2 as a sweep gas at 1000 degrees C and air as feed enabled an oxygen flux value of 5.6 mLmin(-1)cm(-2) to be reached. Finally, under the same conditions and increasing the oxygen partial pressure to 0.1 MPa in the feed, the oxygen permeation reached 12 mLmin(-1)cm(-2). The influence of CO2 content in the sweep gas was studied and its reversible and positive effect over oxygen permeation at temperatures equal to or above 950 degrees C was revealed. Finally, the membrane stability over a period of 150 h under CO2-rich sweep gas showed a low degradation rate of 2.4 x 10(-2) mLmin(-1)cm(-2) per day.