Liquid–liquid equilibrium phase behavior of iminazolium-based ionic liquid aqueous two-phase systems composed of 1-alkyl-3-methyl imidazolium tetrafluoroborate and different electrolytes ZnSO4, MgSO4 and Li2SO4 at 298.15 K: Experimental and correlation

Ionic liquid-based aqueous two-phase systems offer an attractive alternative to volatile organic solvents in liquid–liquid extraction. In this work, the phase diagrams of the 1-alkyl-3-methyl imidazolium tetrafluoroborate ([C2mim]BF4/[C4mim]BF4) + ZnSO4/MgSO4/Li2SO4 + H2O ATPSs were determined at 298.15 K. Three empirical equations were used to correlate the binodal data and the optimum equation was selected. 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 three salts follow the order: ZnSO4 > MgSO4 > Li2SO4, while the phase-separation abilities of the investigated ILs are in the order of [C4mim]BF4 > [C2mim]BF4. Finally, the liquid–liquid equilibrium data were successfully correlated by the Othmer-Tobias and Bancroft equations, meanwhile the slope of tie line increased with an increase in cation alkyl chain length.

► We discuss the liquid–liquid equilibrium of imidazolium ILs + sulfate salts ATPSs.
► The optimum equation was selected to correlate the binodal data.
► We correlate the tie-lines using some appropriate equations.
► The salting-out ability is ZnSO4 > MgSO4 > Li2SO4.
► The phase-separation abilities are in the order of [C4mim]BF4 > [C2mim]BF4.