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

Abstract

The hydrogen flux, selectivity and stability of ∼1.9–3.8 μm 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 (STP) or 132 kg H 2 m −2 h −1 was measured at 400 °C. This flux corresponds to a permeance of 1.5 × 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 H 2 r e t n − p H 2 p e r m 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 × 10 −9 mol m −1 s −1 Pa −0.5 and 3.2 × 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 °C while the nitrogen leakage flux increases very slowly at higher temperatures ( P feed = 10 bar).