Sammendrag
In the current article we present the long-term performance of 10 μm-thick Pd77Ag23 membranes under the exposure to varying concentrations of H2S ranging from 5 ppb to 20 ppm at temperatures of 350 and 450 °C. Membranes are exposed to H2S during 265 hours followed by either a H2 flux recovery study, or rapid quenching allowing for post-process characterisation. The results show that the magnitude of the H2 flux inhibition is largely influenced by the H2S level. Up to 30% reduction in H2 flux is seen during long-term exposure to 2 ppm of H2S at 450 °C, a level below the thermodynamic level for sulphide formation. After H2S removal, close to full H2 flux recoveries are seen. At H2S levels above 5 ppm, the level where Pd4S formation is thermodynamically expected on pure Pd at 450 °C, the H2 flux is largely inhibited, and sulphide formation is confirmed by XRD and XPS analysis of long-term exposed membrane films. In addition, we have experimentally evaluated the H2 permeation and recovery under exposure to upset (10 minute) H2S concentrations between 2 and 20 ppm H2S at 450 °C. Short exposures (10-min) to H2S result as well in a large inhibition of the H2 flux: e.g. a 10-min exposure to 20 ppm H2S inhibits the H2 flux by more than 80%. Despite the large inhibition full H2 flux recoveries are obtained, even for membrane films exposed to H2S concentrations above the thermodynamic limit for sulphide formation (5–20 ppm).