Thermodynamic representation of ionic liquids phase equilibrium with the Wilson-NRF model

Ionic liquids (ILs) with their limitless combinations of cations and anions can offer an optimal solvent for a specific purpose especially separation processes such as liquid-liquid extraction (LLE). The present work inquired phase behavior of 32-types ILs with various cations (including imidazolium, pyridinium, piperidinium, morpholinium, pyrrolidinium and phosphonium-based) and various anions (including Cl, FeCl4, BF4, B(CN)4, PF6, NTf2, FAP and alkylsulfates) in LLE systems. Calculation of LLE for 38 binary (220 Tie-Line) and 52 ternary (545 Tie-Line) systems were carried out using Wilson-Non-Random-Factor (Wilson-NRF) model. All the data were in the temperature range of 298.15-408.15 K. Therefore, in order to obtain an temperature-independent interaction parameters, the adjustable parameter assumed to be as a function of T as: λij = aij + bij/T. All the interaction parameters either for binary or ternary systems were directly regressed from the experimental data using an optimization program based on two objective functions. All the results were expressed by root mean square deviation (rmsd) between the calculated and experimental compositions (the solubility data from the literature). The applied model had very good satisfactory results for ternary and binary systems with rmsd values of 8.78 and 4.08 respectively. Besides, the effect of cation-type, anion-type and the other organic compound on the model behavior was illustrated. Finally, the results represented that Wilson-NRF model could be satisfying model for evaluation of thermodynamic behavior of various LLE containing ILs.