Liquid–liquid equilibria of ionic liquid N-butylpyridinium tetrafluoroborate and disodium hydrogen phosphate/sodium chloride/sodium sulfate/ammonium sulfate aqueous two-phase systems at T = 298.15 K: Experiment and correlation

• We study phase behavior of [BPy]BF4 + Salt + H2O systems at T = 298.15 K.
• Good agreement has been obtained with several empirical expressions.
• Salting-out ability is Na2HPO4 > Na2SO4 > (NH4)2SO4 > NaCl.
• Absolute value of tie-line slopes increases with the increasing charge on the salts.

Liquid–liquid equilibrium data for N-butylpyridinium tetrafluoroborate ([BPy]BF4) + Salt(disodium hydrogen phosphate, sodium chloride, sodium sulfate, and ammonium sulfate) + H2O systems have been determined experimentally at T = 298.15 K. The binodal curves are fitted to an empirical nonlinear expression developed by Merchuk, and the tie lines were described by the Othmer–Tobias, Bancroft, and two-parameter equations. Factors affecting the binodal curves such as salts are also studied. It was found that the salting-out behavior indicates that Na2HPO4 > Na2SO4 > (NH4)2SO4 > NaCl, which may be related to the Gibbs free energy of hydration of the ions (ΔGhyd). Furthermore, the tie-line was also discussed to evaluate the phase separation abilities of the investigated systems. These data are exposed to be useful for the development and design of the extraction process using ILs.