Temperature dependent transition point of purity versus flux for gas separation in Fe/Co-silica membranes

•H2 preferentially permeate though the FeCo silica for all H2/Ar gas mixtures.•A gas purity temperature dependent “transition point” as a function of flux.•The highest and lowest gas transition points at 70% and 43% H2 purity.•The higher the transition point, the better quality the membrane is.

This work investigates the performance of iron cobalt oxide silica membranes for the separation of binary gas mixtures containing H2 and Ar up to 500 °C. A series of membranes were prepared by fixing the iron/cobalt molar ratio at 10/90, 25/75 and 50/50. H2 preferentially permeated though the membranes, and H2 purity in the permeate stream increased with temperature for all H2/Ar binary gas mixtures. The fluxes of H2 from binary gas mixtures complied, for the most part, with a temperature dependent transport mechanism, similar to that delivered by single gas permeation. However, it was notable to observe a “transition point” where H2 purity versus H2 flux clearly changed from temperature independent to temperature dependent. This gas separation transition point was also found to be a function of the quality of the membrane. Indeed the best performing membrane (Fe/Co = 10/90) also had the highest gas separation transition point at ∼70% H2 purity. This reduced to ∼60% for the medium quality membrane (Fe/Co = 25/75) and was at its lowest ∼43% for the lower quality membrane (Fe/Co = 50/50). The binary gas fractions therefore affect the H2 fluxes and H2 purity more significantly than that expected in single gas permeation. Therefore, the relationship between membrane quality and gas separation transition point is established for the first time in this work.

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