Separation behavior of hydrogen isotopes via water pervaporation using proton conductive membranes†

In this study, we investigated pervaporative hydrogen isotope separation behaviors in proton-conductive membranes. Perfluorosulfonic acid (Nafion) and polybenzimidazole membranes exhibited similar hydrogen isotope separation factors, with varying water permeation fluxes based on membrane type and thickness. Increasing temperature improved water permeation flux, while the H/D separation factor remained unaffected. The highest H/D separation factor (1.086) was achieved with a single layer of Nafion at reduced vacuum, surpassing the ¹⁶O/¹⁸O separation factor (1.015). The observed H/D separation behavior is attributed to the mobility difference between hydrons (H⁺ and D⁺) rather than bulk water diffusion (H₃O⁺ and H₂DO⁺). Experiments with heavy metal-exchanged Nafion membranes suggested a negligible contribution of direct H/D ion exchange of sulfonic acid to the overall H/D separation factor. Additionally, water pervaporation through two membranes increased the H/D separation factor.