Phase equilibrium for ternary liquid systems of water + di-(2-ethylhexyl)phosphoric acid + organic diluents: Thermodynamic study

• Ternary systems (water + extractant + diluents) were studied at 303.2–333.2 K, 0.1 MPa.
• Solubility of all ternary liquid systems exhibited type-II behavior.
• Tie-lines showed a change of extractant composition when temperatures increased.
• Solubility of modified Apelblat model correlated well with measured data (<4% RAD).
• ΔHd, ΔSd, ΔGd were obtained by van’t Hoff model to describe dissolution of water in diluents.

The influences of temperature on equilibrium solubility for the ternary liquid systems of water + di-(2-ethylhexyl)phosphoric acid + organic diluents were investigated by cloud point titration at T = 303.2–333.2 K and atmospheric pressure. Various organic diluents having different dielectric constants of kerosene (n/a), n-heptane (1.9), chlorobenzene (5.6) and 1-octanol (10.3) were designated to observe the polar influence on the solubility. All ternary systems exhibited the type II behavior, and their solubility increased with the polarity and studied temperatures. The tie-line data for each ternary liquid system were also studied and correlated by the Bachman plots. Moreover, the experimental solubility of water in the organic phases were predicted using the modified Apelblat equation, and the results were validated by the relative average deviation (RAD) as shown in a range of 0.01–4.09%. The dissolution thermodynamics of water in the organic phases were studied using the van’t Hoff model in order to determine its enthalpy (ΔHd), entropy (ΔSd) and Gibbs energy (ΔGd). The results indicated that the dissolution of water in the organic phases was endothermic and a non-spontaneous process and driven by entropy.

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