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

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 H2S. 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 H2S 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.