Highly stable La0.6Sr0.4Co0.2Fe0.8O3−δ hollow fibre membrane for air separation swept by steam or steam mixture
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Perovskite oxide ceramic membranes have the potentials for industrial oxygen production, particularly to replace the conventional expensive air separation units, which is of significance to improve the viability of the clean energy technologies like IGCC and Oxyfuel projects. In most of these applications, the steam presence is unavoidable thus requiring these membranes to be stable in the steam-containing atmosphere under high temperatures. In this work, La0.6Sr0.4Co0.2Fe0.8O3-a (LSCF) perovskite hollow fibre membrane was prepared and tested for O2 separation in the presence of steam in the sweep gas. Three membranes were successfully tested at temperature of 900°C using the sweep containing 3%, 4-12% and 100% steam (balanced by helium) for 370, 200 and 500h, respectively. In the long run, the steam can etch the membrane surface, as evidenced by the leaching of iron and the formation of strontium carbonate. This etching process however is too slow to cause substantial damage on the membrane performance. Using pure steam sweep, the LSCF membrane was operated at 900°C for nearly 500h without any sign of O2 flux decay, compared favourably with Ba0.5Sr0.5Co0.8Fe0.2O3-a (BSCF) hollow fibre membranes, which only lasted for 90h. In contrast to the severe poisoning effects of other acid gases like SO2 or NOx on the O2 permeation through similar LSCF membrane, the detrimental effect of steam is negligible. In fact, the presence of minor steam less than 12% in the sweep is kinetically favourable for the surface oxygen exchange reactions, leading to the improvement of the O2 flux.
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