A simple thermo-physical model for vapor–liquid equilibrium of the reactive HIx (HI–H2O–I2–H2) system

Thermodynamic phase equilibrium of the reactive HIx system encountered in the sulfur-iodine (SI) cycle has been identified as a basic research need for the hydrogen economy. In this communication, a simple NRTL (nonrandom two-liquid)-based vapor–liquid equilibrium (VLE) model is devised for the HIx system considering the HI decomposition reaction in the gas phase only. We propose a new set of NRTL binary interaction parameters as well as a new expression for the HI decomposition chemical equilibrium constant as a function of temperature. This simple VLE model with the use of only one set of NRTL binary parameters is capable of reproducing the Larousse et al. (Int. J. Hydrogen Energy 34 (2009) 3258–3266) experimental data for a wide range of pressures (1–24 bar) and HI concentrations beyond the azeotrope.