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([C 4 mim]BF 4 ) + kosmotropic salt (Na 3 PO 4 ,(NH 4 ) 3 PO 4 ) + 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: Na 3 PO 4 > (NH 4 ) 3 PO 4 . 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.