Mixed conducting ceramic hollow-fiber membranes for air separation

Mixed conducting ceramic hollow-fiber membranes, which possess an asymmetric structure, were prepared by a combined phase inversion and sintering technique where precursors of the hollow fibers were first spun using a polymer solution containing suspended LSCF powders and were then sintered at elevated temperature. By controlling the weight ratio of the LSCF powder to the polymer binder, sintering temperature, and time, the LSCF hollow fibers with gastight properties have been prepared and evaluated using an apparatus developed during the course of this study. Using the gastight LSCF hollow fibers, a membrane module was assembled for air separation. The performances of the module for air separation have been studied under various operating modes and at different temperatures and feed flow rates both experimentally and theoretically. The results reveal that the surface exchange reaction at the downstream side is much more important than that at the upstream side, especially for lower operating temperatures. The porous inner surface of the prepared LSCF hollow-fiber membranes substantially favors the oxygen permeation when air is fed in the shell side of the membrane module. At high operating temperatures, oxygen permeation can be enhanced by the countercurrent flow operation. Vacuum operation favors the oxygen permeation kinetically in the LSCF hollow-fiber membrane modules. (c) 2005 American Institute of Chemical Engineers.