(732b) Effect of Exposure to Water Gas Shift Gases Containing Sulfur On the Performance of Palladium Alloy Membranes

Hydrogen derived from fossil fuel and biomass resources has to be separated and purified for it to be used in fuel cells and turbines. Metal membranes must be able to efficiently purify hydrogen at the relatively high temperatures and pressures typical of catalytically steam reformed gasified coal and biomass. Membranes must also be able to withstand long-term operation in the presence of common constituents of water-gas shift (WGS) gases including CO and H₂S. Using electroless plating techniques, pinhole-free Pd?Au membranes less than 10 μm thick were deposited onto AccuSep® (Pall Corp.) porous stainless steel supports coated with a yttria-stabilized zirconia metallic interdiffusion barrier. Pd?Au membranes containing up to 23 wt.% Au were prepared with a range of thicknesses (1.7-9.8 microns). The supported thin film Pd?Au membranes were tested at 400°C in different concentrations of simulated WGS gases containing H₂, H₂O, CO, CO₂, and 20 ppm H₂S in tests lasting for up to 120 hours. For example, a 3.6-micron thick Pd-5.5wt.%Au membrane had a hydrogen flux of 1.36 mol m² s^-1 in a mixture of 50% H₂, 30% CO₂, 19% H₂O and 1% CO at a transmembrane pressure differential of 11.4 bar. The hydrogen purity was 99.993%. Pd?Au alloys displayed stable hydrogen flux during exposure to WGS gases without sulfur. Greater resistance to sulfur was observed with increasing Au content and the membranes recovered a majority of their original H₂ flux after testing in WGS mixtures containing 20 ppm H₂S. However, exposure to H₂S eventually resulted in a decrease in hydrogen selectivity of the composite membranes. The performance of the Pd?Au composite membranes will be compared to results using self-supported Pd?Au alloy foils.