The effect of H2S on the performance of Pd and Pd/Au composite membrane

The performance of the Pd and the Pd/Au alloy (8 wt% Au) composite membrane prepared by the electroless and galvanic displacement deposition in a 54.8 ppm H2S/H2 mixture was investigated. Upon testing, the Pd membrane showed the permeance decline in two stages resulted from the surface site blocking and bulk sulfidation. The Pd membrane also failed to separate H2 from other gases after the H2S exposure due to the deterioration of the structure caused by the possible formation of bulk Pd4S. On the other hand, the Pd/Au alloy membrane exhibited resistance to bulk sulfidation and the permeance decline during the H2S exposure was mainly caused by the surface site blocking by the dissociative adsorption of H2S, which was essentially reversible as evidenced by the near full restoration of the H2 permeance in pure H2 at 500 °C. No significant change in He leak after the H2S tests substantiated that there was no significant structural changes of the Pd/Au alloy membrane due to the bulk sulfide formation. Higher temperatures resulted in less permeance loss during poisoning and more permeance restoration during recovery, which was due to the exothermic nature of the dissociative adsorption of H2S on metals.

Research highlights▶ Formation of bulk Pd4S caused irreversible permeance loss of the Pd membrane. ▶ Pd/Au membrane exhibited resistance to bulk sulfidation. ▶ Permeance loss of the Pd/Au membrane in H2S by site blocking was reversible. ▶ Site blocking was caused by H2S adsorption on the Pd/Au surface. ▶ Higher temperatures caused less permeance loss but with more fraction of permeance recoverable.