Measurements and correlation of solid–liquid equilibria of the HI + I 2 + H 2O system

Abstract

The Sulfur–Iodine thermochemical cycle (SI) for water decomposition is a promising candidate for generating hydrogen (H 2) from nuclear energy. An important challenge to the SI process is decomposition of hydrogen iodide (HI) into H 2 and iodine (I 2). 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 I 2 is high, precipitation is a possible process. Determining the feasibility of this requires solid–liquid equilibrium. While binary solubilities are available for I 2 with HI and H 2O, 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 I 2 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.