Liquid-Liquid Equilibrium Compositions for the Iodine-HI-Water System of the Sulfur-Iodine Cycle At Elevated Temperatures and Pressures

Liquid-liquid equilibrium (LLE) phase behavior was investigated for the ternary system iodine-hydroiodic acid-water (I₂-HI-H₂O) at the elevated temperatures and pressures of interest for the reactive distillation column of the Sulfur-Iodine Cycle.  A continuous-flow apparatus, with wetted parts fabricated from tantalum-tungsten alloys, was designed and constructed for the highly corrosive conditions of this work.  A central feature of the apparatus is the equilibrium view cell, which allows for the observation and discernment of vapor-liquid, liquid-liquid, and liquid-liquid-vapor equilibria for HIx systems. 

LLE compositions for all components present were measured for both the lighter, water-rich phase as well as for the heavier, iodine-rich phase at temperatures to 250 °C at pressures approximately 10 bar above the region of VLLE.  HI feed compositions from 2-25 wt % were investigated, with the latter compositions nearing the system's plait point.

Implications of the results for the desired separation of the components of interest will also be discussed.