(Liquid + liquid) equilibrium of (imidazolium ionic liquids + organic salts) aqueous two-phase systems at T = 298.15 K and the influence of salts and ionic liquids on the phase separation

Abstract

(Liquid + liquid) equilibrium for the {1-ethyl-3-methylimidazolium tetrafluoroborate ([C 2mim]BF 4)/1-propyl-3-methylimidazolium tetrafluoroborate ([C 3mim]BF 4) + organic salt + H 2O} aqueous two-phase systems (ATPSs) have been experimentally ascertained at T = 298.15 K. Three empirical equations were used to correlate the binodal data. On the basis of the empirical equation of the binodal curve with the highest accuracy and lever rule, the (liquid + liquid) equilibrium data were calculated by MATLAB. The reliability of the tie line compositions was proved by the empirical correlation equations given by the Othmer–Tobias and Bancroft equations. The effective excluded volume (EEV) values obtained from the binodal model for these systems were determined. The EEV and the binodal curves plotted in molality both indicate that the salting-out abilities of the four salts follow the order: Na 3C 6H 5O 7 > (NH 4) 3C 6H 5O 7 > Na 2C 4H 4O 4 ≈ Na 2C 4H 4O 6, while the phase-separation abilities of the investigated ILs are in the order of [C 3mim]BF 4 > [C 2mim]BF 4. In the systems investigated, the effect of salts on the phase-forming capability was also evaluated in the shape of the salting-out coefficient obtained from fitting the tie-line data to a Setschenow-type equation. The phase-forming ability increases with the increase of salting-out coefficient.