Palladium–gold membranes in mixed gas streams with hydrogen sulfide: Effect of alloy content and fabrication technique

Abstract

Self-supported Pd–Au membranes were produced by magnetron sputtering and cold working with compositions between 7 and 20 wt% Au. Permeation tests were performed in synthetic water-gas shift reaction mixtures with up to 50 ppm H 2S. Membranes with higher gold content showed less flux inhibition by either carbon or sulfur containing species, regardless of fabrication technique or thickness. A 20 wt% Au alloy had the same permeability in pure hydrogen as it did in a sulfur-free WGS mixture, and only lost 40% of its permeability in a 20 ppm H 2S mixture. However, membranes produced by sputtering experienced irreversible loss of hydrogen selectivity when exposed to mixtures containing sulfur, caused by a significant decrease in membrane thickness. No equivalent decrease in thickness or selectivity was observed for cold-worked membranes. This metal loss is explained by a corrosive mechanism in which palladium sulfides flake off the feed surface and are entrained. Although sulfidation also occurs in cold-worked membranes only sputtered membranes display this corrosion, due to a different microstructure in which grains are oriented perpendicular to the surface.