Sulfur tolerant PdAu and PdAuPt alloy hydrogen separation membranes

Palladium (Pd) based alloy membranes of PdAu and PdAuPt were fabricated using magnetron sputtering. Membranes ranging in thickness from 9 to 33 μm were tested under pure gas and mixed gas conditions including U.S. Department of Energy (DOE) specified simulated synthesis gas mixtures containing H2, H2O, CO and CO2, and up to 75 ppmv H2S. In pure hydrogen gas, the PdAu alloy exhibited higher permeabilities than pure Pd in agreement with published values for cold rolled and electrodeposited membranes of similar compositions. The addition of Pt in concentrations ranging from 4.3 to 12.9 mass% lowered the permeability in pure hydrogen gas to slightly below pure Pd. For thicker (25–33 μm) PdAuPt membranes pretreated in air (versus nitrogen) at 400 °C before exposure to hydrogen, an increase in permeability of 10–20% was observed, which is lower than that reported in the literature suggesting that some surface properties of thinner foils may boost permeability. A thick (33 μm) Pd–10Au–10Pt foil evaluated under the DOE conditions, showed good recovery in flux after exposure to syngas containing sulfur. The flux dropped from 0.212 to 0.167 mol m−2 s−1 when 20 ppmv of H2S was added to the gas mixture. When the H2S was removed from the gas mixture the flux returned to its original value of 0.212 mol m−2 s−1. However, in the presence of H2S the permeate purity somewhat degraded over time. The hydrogen permeability, as observed for other membranes, was depressed both by water-gas shift mixtures (with or without H2S) but it appears that either high quantities of Au or the presence of Pt, or both, are inhibiting sulfide formation, thereby improving both permeability and stability under mixture gas conditions with H2S.

► PdAu alloy exhibited permeabilities higher than pure Pd and the addition of Pt lowered the permeability in pure gas to slightly below pure Pd. ► A thick (33 μm) PdAuPt foil evaluated under the DOE conditions, showed good recovery in flux after exposure to sulfur. ► The addition of Pt to the PdAu alloy improves both permeability and stability in syngas mixtures containing H2S.