Experimental and modeling studies on Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) tubular membranes for air separation

Mixed-conducting ceramic membranes for air separation were studied experimentally and theoretically. Dense tubular Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) membranes were successfully prepared by the plastic extrusion method. Oxygen permeation through the membranes was measured at different oxygen partial pressures in the feed stream (0.1925 x 10(5) to 1.01325 x 10(5) Pa (0.19-1.0 atm)) and different temperatures, between 700degreesC and 900degreesC. The effects of air flow rate and sweeping helium flow rate on the oxygen permeation were also investigated. A mathematic model has been developed to simulate the process of air separation in the BSCF membrane permeator for four cases, each under co-current or cross-flow patterns with purge or vacuum operation. The calculated results from the cross-flow pattern with purge operation are in good agreement with experimental data. Moreover, parametric study under co-current flow with vacuum operation reveals that the air flow rate should be sufficiently high to fully utilize the separation capacity of the membrane. Higher vacuum levels and smaller inner diameter of the membrane tubes are essential to achieve higher separation efficiencies. The theoretical solutions also indicate that there is an optimal shell side pressure and optimal tube length, under which the oxygen productivity reaches its maximum with a fixed air flow rate. (C) 2004 Elsevier B.V. All rights reserved.