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 ∼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 H2 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 H2/N2 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 (pH2retn−pH2permn), 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 (Pfeed = 10 bar).

Research highlights▶ We report for the first time the effect of air exposure on the materials separation properties, i.e. hydrogen permeation and stability of these thin membranes on tubular porous stainless steel supports up to a partial pressure difference of hydrogen of 25 bar. ▶ Applying a hydrogen feed pressure of 26 bar, one of the highest H2 fluxes reported equal to 2477 mL min−1 cm−2 (STP) was measured at 400 °C, which corresponds to a permeance of 1.5 × 10−2 mol m−2 s−1 Pa−0.5. ▶ At this pressure, the H2/N2 permselectivity at 25 bar transmembrane pressure difference was 2900. ▶ Stability over a period of 85 days is reported.