Phase Behavior for the Aqueous Two-Phase Systems Containing the Ionic Liquid 1-Butyl-3-methylimidazolium Tetrafluoroborate and Kosmotropic Salts

Abstract

Liquid−liquid equilibria (LLE) for the aqueous 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) + kosmotropic salt (Na3PO4, Na2CO3, Na2SO4, NaH2PO4, NaCl) systems have been determined experimentally at T= 298.15 K and in part at T = (313.15 to 333.15) K. The binodal curves are fitted to an empirical nonlinear expression developed by Merchuk, and the tie lines were described by the Othmer−Tobias and Bancroft equations. Factors affecting the binodal curves such as salts and temperature are also studied. It was found that the salting-out ability of different salts may also be related to the Gibbs energy of hydration of the ions, and the order of salting-out ability of the anions follows the Hofmerister series for the strength of the kosmotropic salts. It was also demonstrated that the two-phase area was expanded with a decrease in temperature. [Bmim]BF4 could be recovered from aqueous solution using the aqueous two-phase system (ATPS), and the recovery efficiency could reach 98.77 %. The recovery ef...