Pervaporation of water from aqueous hydriodic acid and iodine mixtures using Nafion^® membranes

The sulfur-iodine (S-I) process for generation of hydrogen has been proposed as a thermochemical cycle for study due to its predicted high efficiencies. Improvements in the cycle that will yield the greatest gain in both operating and capital costs involve chemical separations. To date, membrane processes have been largely unexplored. In this work, a materials compatibility study into the application of Nafion-117^® and Nafion-112^® as membranes for the pervaporation of water from aqueous mixtures of hydriodic acid (HI) and HI/iodine at 134 °C was conducted. Significant water permeability was measured with respect to feed water concentration, and high separation factors were calculated. Most surprisingly, HI and HI/iodine feeds acted very differently in that HI-iodine complexes formed result in higher fluxes and separation factors than what was observed for HI alone.