Hydrogen permeation in a palladium membrane tube: Impacts of outlet and vacuum degree

Palladium (Pd) membranes are a crucial device for separating hydrogen and are usually operated at normal pressure on the permeate side with a single outlet. Instead of these common operating conditions, the difference between using a double outlet and a single outlet is studied. Four different vacuum degrees (15-60 kPa) are applied on the permeate side, and the results are compared with the non-vacuum operations. Situations under the vacuum and the effects of temperatures (300-400 degrees C) on H-2 permeation are discussed. Finally, the influences of different feed gas mixtures (H-2/N-2, H-2/CO2, and H-2/CO) on the Pd membrane performance are investigated. The results show that there is no difference in H-2 permeation impact the single outlet and the double outlet on the permeate side. When a vacuum is imposed on the permeate side, the H2 permeation rate and H-2 recovery are efficiently intensified, that is, when the pressure difference is 9 atm, they increase from 73.21 to 84.51% and from 0.0035378 to 0.0040808 mol.s(-1), respectively. Moreover, the H2 recovery can be improved to up to 68.44% under a vacuum degree of 60 kPa. At a given Reynolds number, an increase in temperature increases the H-2 permeation rate but lowers its recovery, stemming from more H-2 in the feed gas. This study also investigates the feed gas of H-2/N-2 under a vacuum to provide a useful insight into H-2 production and separation from ammonia, and the results are compared with two different feed gases of H-2/CO2 and H-2/CO mixtures. The results suggest that the impurities (i.e., N-2, CO2, and CO) have a negative influence on the Pd membrane, which causes the H2 permeation rate to decrease, and the effect of N-2 is the least significant compared to the other two. (c) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.