Measurements and correlation of solid-liquid equilibria of the HI + I ₂ + 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.