Hydrogen transport through a selection of thin Pd-alloy membranes: Membrane stability, H2S inhibition, and flux recovery in hydrogen and simulated WGS mixtures

Resistance to H2S is important for the use of Pd membranes in fossil-fuel power stations with integrated carbon capture. In the current article we present the H2S inhibition and subsequent H2 flux recovery of thin (∼2 μm) pure Pd, Pd77Ag23, Pd85Au15 and Pd70Cu30 membranes. Upon H2S exposure in H2/N2 feed mixtures, all the investigated thin Pd-alloy membranes exhibited a sharp decrease of the H2 flux depending of the H2S concentration. At 2 ppm, the H2 flux reduces to a value equal to around 20–40% compared to the H2 flux obtained in the absence of H2S; at 20 and 100 ppm H2S in the feed the H2 flux only equals 10–20% of its original value. The pure Pd membrane shows an instant failure during the exposure to 100 ppm H2S. After removal of 2 ppm H2S from the feed stream the H2 flux through the Pd, Pd85Au15 and Pd70Cu30 membranes recovers within 2 h. After the exposure to 20 ppm H2S only the H2 flux through the pure Pd, Pd85Au15 and Pd70Cu30 membranes recovers to the same extent. As opposite to these three alloys, the H2 flux through the Pd77Ag23 alloy is recovering much more slowly. When exposed to a simulated sour WGS mixture, the Pd85Au15 membrane experiences a loss of H2 flux down to 10–15% of the value obtained applying 62% H2 in N2 as feed. The extent of H2S poisoning is thus of the same magnitude in WGS mixtures and H2/N2 mixtures. No sign of unselective transport is observed for this membrane after 100 h of operation in a sour WGS mixture. Post-process characterisation show signs of surface roughening combined with grain growth, whilst multiple small pits are found primarily in the grain boundaries of the membrane feed surface after the long-term operation. This study demonstrates that thin Pd–Au and Pd–Cu membranes survive sour atmospheres, but at a cost of a significant loss of H2 flux.

In the current article we present the H2S inhibition and subsequent H2 flux recovery for pure Pd, Pd77Ag23, Pd85Au15 and Pd70Cu30 membranes. Upon H2S exposure in H2/N2 feed mixtures all the investigated Pd-alloy membranes exhibited a sharp decrease in H2 flux. At 2 ppm, the H2 flux dropped to a value equal to around 20–40% compared to the H2 flux obtained in the absence of H2S. The flux dropped a much larger extent at 20 and 100 ppm where the flux was reduced to 10–20% of its original value. The pure Pd membrane shows an instant failure during the exposure to 100 ppm H2S. After the removal of 2 ppm H2S from the feed stream the H2 flux through the Pd, Pd85Au15 and Pd70Cu30 membranes rapidly recovered within 2 h. After the exposure to 20 ppm H2S solely the H2 flux through the Pd85Au15 and Pd70Cu30 membranes recovered to such an extent that the original H2 flux was approached within a practical time-scale. For the Pd85Au15 membrane the H2 flux obtained in the sour WGS mixture equals around 10–15% of the value obtained applying 62% H2 in N2 as feed indicating that the extent of H2S poisoning in WGS mixture is similar to the poisoning in H2/N2 mixtures. No sign of unselective transport is observed for this membrane after 100 h of operation in sour WGS mixture. Post-process characterisation show sign of surface roughening combined with some grain growth, whilst multiple small-sized pits are found primarily in the grain boundaries of the membrane feed surface after the long-term operation.Figure optionsDownload high-quality image (123 K)Download as PowerPoint slideHighlights
► H2S inhibition and subsequent H2 flux recovery for pure Pd, Pd77Ag23, Pd85Au15 and Pd70Cu30 membranes are presented.
► Pd-alloy membranes prepared by magnetron sputtering have been found stable in sour feed gas mixtures.
► At 20 ppm H2S an effective H2 permeability equal to 8.3 × 10−10 mol m−1 s−1 Pa−0.5 has been obtained for the Pd85Au15 membrane.
► Flux penalty due to H2S is significant in absolute terms.