Pervaporation of water from aqueous HI using Nafion®-117 membranes for the sulfur-iodine thermochemical water splitting process

Nafion®-117 membranes have been successfully used to remove water from aqueous hydriodic acid (HI) by pervaporation. HI feeds were concentrated from approximately 1.7 to 5 M, and permeate concentrations ranged from 10 ^-3 to 10^-4 M, regardless of the feed HI concentration. Temperatures examined were 22, 50, 70, and 100°C. Using 180 μm thick films, fluxes at 22°C were 0.43 kg/m² h, and increased with increasing system temperature to a maximum of 1.5 kg/m² h at 100°C. Durability studies over a period of 3 months operation revealed little membrane degradation and, in all cases, the membranes retained their bulk physical properties in that they remained flexible and plastic. More intensive thermomechanical testing revealed changes in the membrane morphology upon pervaporation of the HI feed at 100°C, however, these changes were not reflected in the observed water transport behavior.