PdAu and PdAuAg composite membranes for hydrogen separation from synthetic water-gas shift streams containing hydrogen sulfide

Electroless deposition was used to fabricate Pd-23Au and Pd-20Au-13Ag (wt%) membranes on Pall AccuSep® ZROD supports. The weight gain compositions of each film were corroborated with XRF analysis, EDS and XRD after testing. The membranes were annealed in a H2 atmosphere at temperatures of 773 K and higher. The Pd-20Au-13Ag alloy membrane had higher single-gas H2 permeability than a pure Pd membrane on a comparable support. In a mixture of 20 ppm H2S in H2 at 689.5 kPa feed pressure, the H2 permeance of the Pd-20Au-13Ag alloy membrane was less inhibited at 773 K than 723 or 673 K. Both membranes were tested in a sour WGS mixture containing 20 ppm H2S. The Pd-23Au membrane had a 29% H2 flux inhibition at 773 K and 1.1 MPa feed pressure, which is one of the best reported for a composite PdAu alloy membrane in a feed gas containing H2S. Although the H2 permeance of the Pd-20Au-13Ag alloy membrane was reduced more than the Pd-23Au membrane, it had a higher absolute H2 permeance in the sour WGS mixture. Once the H2S was removed from the WGS feed gas, the H2 permeance recovered at least 97% of its original value before H2S exposure to both membranes at 673 and 773 K. After H2S testing, sulfides were not detected using XRD.