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

Liquid-liquid equilibria (LLE) for file 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 efficiency was influenced by the concentrations of the salts and their Homeister series: Na3PO4 > Na2CO3 > Na2SO4 > NaH2PO4 > NaCl. These data are exposed to be useful for the development and design of the extraction process using ILs based oil the ATPS. This proposed method also provided an effective route for the recovery of hydrophilic IL from aqueous solutions.