On the high pressure performance of thin supported Pd-23%Ag membranes-Evidence of ultrahigh hydrogen flux after air treatment

The hydrogen flux, selectivity and stability of similar to 1.9-3.8 mu m thick supported palladium alloy (Pd-23%Ag) films are reported. Applying a hydrogen feed pressure of 26 bar, one of the highest hydrogen fluxes reported equal to 2477 mL min(-1) cm(-2) (SIP) or 132 kg H-2 M-2 h(-1) was measured at 400 degrees C. This flux corresponds to a permeance of 1.5 x 10(-2) mol m(-2) s(-1) Pa-0.5. The H-2/N-2 permselectivity at 25 bar transmembrane pressure difference was 2900. Allowing the value of n to float between 0.5 and 1, in order to obtain the best fit between the fluxes and (p(H2ret)(n), p(H2perm)(n)), gives a value for n equal to 0.631 after air pre-treatment and correction for the support resistance. The analysis of flux data suggests that diffusional transport through the membrane is rate-limiting. By forcing n equal to 0.5, permeability values as a function of the pressure have been obtained linking it qualitatively to solution and diffusion behaviour. At the limiting value of zero hydrogen partial pressure, hydrogen permeabilities of 9.1 x 10(-9) mol m(-1) s(-1) Pa-0.5 and 3.2 x 10(-8) mol m(-1) s(-1) Pa-(0.5) have been obtained before and after air treatment, respectively. During continuous operation over 85 days, the membrane showed a good stability up to 350 degrees C while the nitrogen leakage flux increases very slowly at higher temperatures (P-feed =10 bar). (C) 2010 Elsevier B.V. All rights reserved.