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

Abstract

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 773K 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 20ppm H2S in H2 at 689.5kPa feed pressure, the H2 permeance of the Pd–20Au–13Ag alloy membrane was less inhibited at 773K than 723 or 673K. Both membranes were tested in a sour WGS mixture containing 20ppm H2S. The Pd–23Au membrane had a 29% H2 flux inhibition at 773K and 1.1MPa 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 773K. After H2S testing, sulfides were not detected using XRD.