Interplay between propylene and H₂S co-adsorption on the H₂ flux characteristics of Pd-alloy membranes employed in propane dehydrogenation (PDH) processes

The role of propylene and H₂S exposure on Pd-Ag membranes was investigated by hydrogen flux measurements of a magnetron sputtered Pd77Ag23 film and first-principles calculations of hydrogen, sulfur and propylene adsorption on the membrane surface. Upon exposure to 10% propylene, the H₂ flux was lowered to 12% of its initial value prior to exposure, which was associated with propylene adsorption and coke formation based on qualitative assessments of the flux degradation kinetics and calculated propylene and hydrogen surface coverages. In the presence of 50–75 ppb H₂S, the H₂ flux showed a slower gradual decrease upon propylene exposure. Although sulfur adsorption also inhibits H₂ flux, this slower decrease resulted in a higher absolute H₂ flux in the presence H₂S already after 1 h of propylene exposure. Adsorbed sulfur on the membrane surface was suggested to limit coke formation due to a lower calculated surface coverage of propylene as well as a possibly lower migration of propylene and other intermediates across the membrane surface necessary for coke formatio