Mixed-conducting (electronic and ionic conducting) dense ceramics are used in many applications, including fuel cells, gas separation membranes, batteries, sensors, and electrocatalysis. This paper describes mixed-conducting ceramic membranes that are being developed to selectively remove oxygen and hydrogen from gas streams in a nongalvanic mode of operation (i.e., with no electrodes or external power supply). Ceramic membranes made of Sr-Fe-Co oxide (SFC), which exhibits high combined electronic and oxygen ionic conductivities, can be used for high-purity oxygen separation and/or partial oxidation of methane to synthesis gas (syngas, a mixture of CO and H_2). The electronic and ionic conductivities of SFC were found to be comparable in magnitude. Steady-state oxygen permeability of SFC has been measured as a function of oxygen-partial-pressure gradient and temperature. For a approxapprox3-mm-thick membrane, the oxygen permeability was approxapprox2.5 scccentre dotcm~(-2)centre dotmin~(-1) at 900 deg C. Oxygen permeation increases as membrane thickness decreases. Tubular SFC membranes have been fabricated and operated at 900 deg C for approxapprox1000 h in converting methane into syngas. The oxygen permeated through the membrane reacted with methane in the presence of a catalyst and produced syngas.
展开▼
