Hydrogen & Clean Fuels - Abstract
Palladium-Copper Alloy Membrane Performance Under Continuous H2S Exposure
Palladium-copper alloys continue to be of interest for hydrogen membrane applications because of their high catalytic activity for hydrogen dissociation, high hydrogen permeability, robustness, and degradation resistance in the presence of sulfur-containing compounds. This sulfur tolerance makes these alloys attractive for membrane applications where sulfur compounds are likely to be present, such as hydrogen production via coal or biomass gasification. In this study, the permeances of a series of palladium-copper alloys were determined using a continuously flowing 1000 ppm hydrogen sulfide in hydrogen gas stream. Palladium-copper alloys containing 80, 60 and 53 wt-% palladium as well as pure palladium were evaluated over the temperature range of 350 to 900°C. The membrane samples used in this continuous flow study consisted of 1000 µm thick metal foils that were supported on Hastelloy® porous substrates. Permeances determined under high-pressure, high-temperture continuous flow conditions were compared to those measured under pure hydrogen conditions and to previous results from low-pressure transient permeance measurements under 1000 ppm hydrogen sulfide in hydrogen. Permeance results were also correlated with the alloy crystal structure. The hydrogen sulfide test results indicate that the crystalline phase of a specific alloy (bcc vs. fcc) strongly influences both permeance and sulfur poisoning resistance, agreeing well with our previous transient permeance measurements. The alloys exhibited sulfur poisoning resistance at temperatures corresponding to their fcc crystalline phase, but there was a significant decrease in permeance when exposed to hydrogen sulfide under bcc phase stability conditions.