Measurements and correlation of solid–liquid equilibria of the HI + I2 + H2O system

The Sulfur–Iodine thermochemical cycle (SI) for water decomposition is a promising candidate for generating hydrogen (H2) from nuclear energy. An important challenge to the SI process is decomposition of hydrogen iodide (HI) into H2 and iodine (I2). KIER (Korea Institute of Energy Research) is developing a membrane-based electrolysis cell for this decomposition. The conversion is enhanced if excess iodine is removed before the electrolysis. Since the melting temperature of I2 is high, precipitation is a possible process. Determining the feasibility of this requires solid–liquid equilibrium. While binary solubilities are available for I2 with HI and H2O, very few ternary data have been reported. In this study, solid–liquid equilibrium data for the ternary (so-called HIx) mixtures were obtained at temperatures from 303 to 359 K at ambient pressure with the concentrations of HI and I2 iodine via titration. The data have been correlated by the phase and reaction equilibrium model developed at the University of Virginia (UVa model) with a small modification that does not change the model’s successful description of VLE and VLLE for reactive distillation.