Polythermal Study of Component Solubility and Phase Equilibria in the Ternary Water–Dipropylamine–Diisopropylamine System for Extraction Applications

Phase equilibria, mutual solubility of components, and critical phenomena were studied using the visual polythermal method in mixtures of the ternary water–dipropylamine–diisopropylamine system over the temperature range of –5 to 90°C. Polytherms of phase states were constructed for fourteen sections of the composition triangle, revealing phase separation into two liquid phases. At temperatures below 0°C, some mixtures formed saturated solutions with a solid ice phase. The temperature dependence of the compositions corresponding to critical solubility points was determined using the liquid-phase volume ratio method. Component solubility was measured at twelve temperatures, and isothermal phase diagrams were constructed at –5.0, –4.7, –3.0, –2.0, –1.9, 0.0, 10.0, 15.0, 25.0, 27.3, 30.0, and 90.0°C. The topological transformation of the phase diagram with temperature changes is typical for ternary liquid systems containing a binary liquid system with strong intermolecular interactions, which, in this case, is the dipropylamine–diisopropylamine system. At 27.3–90.0°C, a delamination field extends from the water–dipropylamine side of the composition triangle to the water–diisopropylamine side, while below 27.3°C, the two-liquid-phase region shifts toward the water–dipropylamine boundary. Delamination field becomes metastable in the range of –4.7 to ‒1.9°C. As the temperature decreases, mutual solubility increases, and the two-liquid-phase region shrinks. A dipropylamine–diisopropylamine mixture shows potential for water extraction, extractive salt crystallization, seawater desalination, and the treatment of hypersaline solutions.