Liquid–Liquid Equilibrium of Imidazolium Ionic Liquids + Phosphate + Water Aqueous Two-Phase Systems and Correlation

Binodal curves of the aqueous 1-butyl-3-methylimidazolium tetrafluoroborate([C4mim]BF4) + kosmotropic salt (Na3PO4,(NH4)3PO4) + water aqueous two-phase systems were determined experimentally at 288.15, 298.15, 308.15 and 318.15 K. Three empirical equations were used to correlate the binodal data. All three empirical equations reproduce the data with a high degree of precision. The effect of temperature on the binodal curves was studied. Corresponding to two different salts, the two-phase area decreases with increasing temperature. From the binodal model for these systems, the effective excluded volumes (EEV) were obtained. The binodal curves and EEV both indicate that the salting-out abilities are in the order: Na3PO4 > (NH4)3PO4. And, the reliability of the tie-line compositions was proved by the empirical correlation with the Othmer–Tobias and Bancroft equations. The results show that the salting-out strength is greater at lower temperatures. Additionally, a relatively simple two-parameter equation was used for the correlation of the tie-line data.