Phase behaviour for aqueous two-phase systems containing the ionic liquid 1-butylpyridinium tetrafluoroborate/1-butyl-4-methylpyridinium tetrafluoroborate and organic salts (sodium tartrate/ammonium citrate/trisodium citrate) at different temperatures

Highlights: • Phase behavior of [BPy]BF4 + Salt + H2O systems at different temperature was studied. • LLE of ATPS composed with [4-MBP][BF4] and different salts have been experimentally determined. • Good agreement has been obtained with several empirical expressions. • Salting-out ability can be related to Gibbs free energy of hydration of the constituent ions and EEV. • The effects of temperature and alkyl chain length of the ionic liquids have been discussed. -- Abstract: The binodal curves of 1-butylpyridinium tetrafluoroborate + sodium tartrate at T = (298.15, 308.15 and 328.15) K and 1-butyl-4-methylpyridinium tetrafluoroborate + sodium tartrate/ammonium citrate/trisodium citrate at T = 298.15 K were experimentally determined. Three empirical equations were used to correlate the binodal data. The tie-line data were successfully correlated using the Othmer–Tobias and Bancroft and two-parameter equations. Factors affecting the binodal curves, such as temperature and the nature of the ionic liquids, were also studied. The two-phase area expanded with a decrease in temperature, whereas the absolute value of the slope of the ties slightly decreased with an increase in temperature. With an increase in the alkyl chain length of the ionic liquids (ILs) in the investigated systems, the binodal curves shifted closer to the origin. Finally, the effective excluded volume (EEV) values obtained from the binodal model were determined, and the salting-out ability decreased in the following order: Na3C6H5O7 > Na2C4H4O6 > (NH4)3C6H5O7