Thermodynamic properties of some aqueous ionic liquid solutions using ion-SAFT-VR EOS

The statistical association fluid theory (SAFT) approach for attractive potentials of variable range combined with interionic interactions, to describe some aqueous solutions of imidazolium ionic liquids (ILs) with different anion structures. The anions analyzed encompass [SCN]^-, [DCA]^–, [BF4]^-, [NTF₂]^- and [PF₆]^- which show the effect of systematically change of the substituents on the anion. The proposed equation of state is a combination of a square-well variable range and a mean spherical approximation (MSA) corresponding to the restrictive primitive model to describe the long-range interactions of ILs. Water is characterized as a bipolar associating liquid combining the four-site model and a square-well potential with a constant dielectric continuum. The accurate predictions of volumetric properties for pure ILs and $p\rho T$ of water as well as the thermodynamic properties of binary aqueous IL solutions are significant evidence of the capability and excellent performance of the ion-SAFT-VR model. Parameters of the new version of the model have been reported and the model tested for an impressively large number of data sets. For binary mixtures of ILs and water, binary interaction coefficients were obtained by fitting experimental data at constant pressure and phase concentrations. The results show the satisfactory predictability of the ion-SAFT-VR EOS in modeling the thermodynamic properties of bulk systems, which indicates the reliability of the employed EOS. Due to the excellent results obtained for pure IL densities and the satisfactory results observed for aqueous solution of ILs, we can confidently conclude that the approach provides an overall commendable description of most IL systems.