Abstract

This study demonstrates that in addition to association, polarity, and other interactions, phase equilibria of the ionic liquid (IL) systems are also influenced by the global phase diagram factors, namely, the differences between values of the pure compound critical points. As these differences increase, increasing thus the system asymmetry, the extent of phase splits also increases, and the molar solubilities correspondingly decrease. It is shown that the pressure dependence of the IL densities indicate the higher experimentally inaccessible T-c and P-c values, making their systems more asymmetric, which reduces the solvent capacities and vice versa. In addition to this, phase equilibria are also influenced by the critical constants of the solvents. Their higher T-c and P-c values typically increase the symmetry, and therefore, the solubilities. The CP-PC-SAFT equation of state rigorously obeys the T-c and P-c of solvents and accurately represents the densities of ILs under a wide range of conditions. Such features endow this model with a remarkable predictive potential even while neglecting the association and polar interactions. In most of the cases, CP-PC-SAFT with k(12) = 0 correctly estimates the differences between solubilities in the experimentally investigated systems comprising fluoro- and chloromethanes, ethanes, ethenes, propanes, and propenes with [C(2)mim][Ntf(2)], [C(4)mim][Ntf(2)], [C(6)mim][Ntf(2)], [C(8)mim][Ntf(2)], [C(4)mim][PF6], [C(4)mim][BF4], and [C(8)mim][BF4]. The quantitative accuracy of this model is usually reasonably good as well. Although SAFT-VR-Mie obeys the literature T-c values of solutes, it overestimates their P-c. In addition to this, it yields higher imaginary critical constants of the considered ILs than CP-PC-SAFT. These factors may explain its tendency to underestimate the solubility data with k(12) = 0. Nevertheless, in most of the cases, SAFT-VR-Mie correctly describes the solubility tendencies in the considered systems.