Phase behavior of an aqueous two-phase ionic liquid containing (N-butylpyridiniumtetrafluoroborate + sulfate salts + water) at different temperatures

Liquid-liquid equilibrium (LLE) data for N-butylpyridiniumtetrafluoroborate ([BPy]BF4) + sulfate salt + H2O systems have been determined experimentally at T = (298.15, 308.15, and 318.15) K. The binodal curves agree with an empirical nonlinear expression developed by Merchuk, while the tie-line data are described by the Othmer-Tobias, Bancroft, two-parameter, and Setschenow-type equations. Factors, such as salts, that affect the binodal curves are also studied. The effective excluded volume (EEV) values obtained from the bimodal models for the two systems were determined, and the salting-out capabilities of different salts follow the order of Na2SO4 > (NH4)2SO4, which may be related to the Gibbs free energy of hydration of the ions (△Ghyd). Furthermore, the tie line is also discussed to evaluate the phase separation capabilities of the investigated systems. These reported data provide a significant contribution to the further study of extraction processes using ionic liquids (ILs).