A Polythermal Study of Two-phase and Three-phase States and Salting-in–Salting-out Effects in the Ternary System Potassium Iodide–Water–Triethylamine

Phase equilibria and critical phenomena in the ternary system potassium iodide–water–triethylamine, where the liquid subsystem is characterized by LCST = 18.3°C, were studied by the visual-polythermal method in a range of 0.0–60.0°C. Two- and three-liquid phase states, monotectics, and saturated solutions are realized in these component mixtures. The temperature of formation of the critical tie line of the monotectic state (1.9°C) was determined. The isotherms of phase states plotted for fifteen temperatures have revealed the topological transformation of the phase diagram of the studied system. Small concentrations of potassium iodide have a salting-in effect on heterogeneous mixtures of water and triethylamine, causing their homogenization. Further introduction of potassium iodide into these solutions and an increase in temperature led to phase separation. In the phase diagram, there is a field of three liquid phases inside the two-phase state field in the range of 10.1–18.4°C. Possibly, the appearance and disappearance of the third liquid phase is caused by the salting-in–salting-out effect of potassium iodide upon triethylamine hydrates. It was found that potassium iodide effectively salted-out triethylamine from its aqueous solutions above 20.0°C and the studied system can be used as an extraction one.

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