Liquid–liquid equilibrium tie-line compositions at elevated temperatures and pressures for the I2–H2O and HI–I2–H2O systems of the Sulfur–Iodine Cycle

Liquid–liquid equilibrium (LLE) tie-line compositions were measured for the binary system iodine–water and the ternary system hydrogen iodide–iodine–water (HI–I2–H2O) at 199.1 and 252.2 °C, at pressures of 60 bar, conditions of interest for the reactive distillation column of the Sulfur–Iodine Cycle. To keep the HI decomposition reaction negligible, a continuous-flow apparatus was used to minimize residence times at the elevated temperatures. Sixteen equilibrium tie lines were measured, using overall feed compositions ranging from 0.0 to 3.3 mol % HI, and the plait-point composition for 199.1 °C was estimated. Sample compositions for the lighter, water-rich phase and the heavier, I2-rich phase were both determined via titration of HI and I2, with water being obtained by difference. The phase behavior indicates that the selectivity of HI for the aqueous phase can be large, ranging from 10 to 100+ for tie lines removed from the critical region.