Performance of tubular SrFe(Al)O3−δ–SrAl2O4 composite membranes in CO2- and CH4-containing atmospheres

The stability and oxygen permeability of dense tubular membranes, made of (SrFeO3−δ)0.7(SrAl2O4)0.3 (SFSA) composite by cold isostatic pressing, were assessed under air/CO2 and air/(CH4 + CO2) gradients at 973–1173 K. Mixed-conducting SFSA, comprising SrFe(Al)O3−δ perovskite-like and SrAl2O4-based phases, was selected as a model membrane material for the natural gas conversion reactors due to its attractive oxygen transport, catalytic and thermomechanical properties. As partial dissolution of SrAl2O4 in the perovskite-like component leads to strontium deficiency of the perovskite phase, the composite exhibits an improved stability with respect to interaction with CO2, although thermogravimetric analysis showed that carbon dioxide adsorption on SFSA is still significant. No degradation was revealed in the course of oxygen permeation tests during 200–300 h with subsequent scanning electron microscopy inspection. However, contrary to that observed for SFSA powders, methane conversion in the tubular SFSA membranes without surface modification results in predominant total combustion caused by the slow kinetics of the reforming reactions. Significantly higher conversion efficiency and synthesis gas yields were achieved passing the pre-reacted gas mixtures into an additional reactor with Pt/LaNiO3/Al2O3 catalyst bed at the tubular membrane outlet.