Membrane performance on electro-electrodialysis of HI–I2–H2O mixture for IS process

Research and development of a water-splitting hydrogen-production method, called the iodine–sulfur (IS) process, has been conducted as one of the heat applications of high temperature gas-cooled reactor. Among the unit operations in this IS process, we have investigated electro-electrodialysis (EED) using an ion-exchange membrane to increase a hydrogen iodide (HI) concentration in an HI–I2–H2O mixture. With the aim of maximizing EED performance, new membrane materials were prepared by the radiation-induced graft polymerization and were examined in terms of their proton permeability through the membrane, i.e., transport number, t+ and conductivity, σ at different I2 concentrations in the HI–I2–H2O mixture. t+ increased and σ decreased with an increase in the feed I2 molality. The EED model derived by the Nernst–Planck theory suggested that this trend could be explained exclusively by the variation of the diffusion coefficient of I−.