High CO2-resistance Ag modified La0.8Ca0.2Fe0.94O3-δ hollow fiber membrane with a three-layer sandwich structure for oxygen separation

Abstract

Cobalt-free mixed ionic and electronic conducting (MIEC) oxygen permeation membrane is a kind of promising materials for advanced air separation technology. However, its low oxygen permeability limits its practical application. In this work, we successfully prepared a type of La0.8Ca0.2Fe0.94O3-δ-0.05Ag (LCF-Ag) hollow fiber membrane with “three-layer sandwich” structure by using a combined one-step sintering and phase conversion technology. Under the same experimental conditions, the oxygen permeation flux of the membrane structure was 1.79 times that of the traditional membrane structure, and the maximum oxygen flux was achieved at 2.15 mL min−1 cm−2. The model fitting proved that the membrane with new structure can effectively reduce the resistance of bulk diffusion. The stability test of oxygen permeation flux was carried out alternately in pure He and CO2 atmosphere. The membrane displays high stability during the long-term operation of 240 h. Despite the oxygen flux had decreased slightly when CO2 was used as sweep gas due to chemical adsorption of CO2 to occupy the active sites on the membrane surface. The oxygen flux could be fully recovered once sweep gas switching to He, which indicates that the perovskite structure was not been damaged due to its good chemical stability. These results prove the feasibility of the new membrane structure for oxygen separation with CO2 resistance, which may expand their applications to membrane reactors where the presence of CO2 is not avoidable.