(696e) The Effect of Au Content in Composite Pd/Au Membranes Prepared by Galvanic Displacement On Hydrogen Permeance and H2S Resistance

Pd/Au alloy membranes have received increasing attention recently for separating hydrogen from hydrogen production processes with fossil fuels (e.g. coal gasification) due to the twofold beneficial characteristics. Pd/Au alloy membranes with Au content up to 20wt% showed higher H₂ permeability than pure Pd membranes. In addition, Pd/Au alloy membranes exhibited relatively high sulfur resistance without bulk sulfidation of the Pd/Au layer and less hydrogen permeance decline compared to pure Pd and other Pd alloy membranes in the presence of H₂S. However, the relationship between Au content in composite Pd/Au alloy membranes and hydrogen permeance and sulfur resistance was rarely studied in the literatures. Therefore, the objective of the work was to investigate the effect of the Au content in the composite Pd/Au alloy membranes on hydrogen permeance and the performance in the presence of H₂S. Three composite Pd/Au membranes with different Au content were prepared on 0.1-μm media grade porous Inconel supports with the electroless plating of Pd until gas tight followed by the Au displacement plating. Prior to the Pd plating, the supports were oxidized (700°C/12h), graded with Al₂O₃, and deposited with Pd/Ag barrier layer for the formation of intermetallic-diffusion barrier layers as well as the modification of the pore size. Three membranes with different Au content were prepared by sequentially depositing different number of Au layers on the membranes (i.e. 1 to 3 Au layers). Between Au layers, a thin Pd layer (0.5 ? 0.8 μm) was deposited for the Au displacement plating. The gravimetric thicknesses of the membranes prepared were 17 - 19 μm with approximately 4 ? 12 wt% Au. After annealing at 500°C in hydrogen, the Pd/Au membranes were characterized in the temperature range of 300 - 450°C in pure hydrogen and helium followed by the sulfur poisoning and recovery tests in the presence of small concentrations H₂S (0.2 - 5ppm) in the temperature range of 400 - 500°C. The Pd/Au membrane of 4 wt% Au showed a hydrogen permeance of 26.8 m³/(m²*h*atm^0.5) at 450°C with an ideal selectivity (J_H2/J_He, Δp=1 atm) of 4500 after 200 hour testing in pure H₂ and an activation energy of 11.7 kJ/mol. Upon H₂S testing, ~ 62% permeance loss has been observed after a 2 ppm H₂S/H₂ exposure at 450°C. However, the permeance was able to be fully recovered in pure H₂ at 500°C after the poisoning. The hydrogen permeance as well as the performance in H₂S of other Pd/Au membranes with different Au content (i.e. 8wt% and 12wt%) will also be presented with the discussion on the effects of H₂S poisoning on Pd/Au membranes as a function of Au content.