Liquid–liquid extraction of toluene from n-heptane by {[emim][TCM] + [emim][DCA]} binary ionic liquid mixtures

Ionic liquids (ILs) have been widely researched to replace organic solvents in the liquid–liquid extraction of aromatics from their mixtures with aliphatic hydrocarbons. However, the ILs studied so far have exhibited high dynamic viscosities and most of them have not shown better extractive properties than those of conventional solvents. Recently, the 1-ethyl-3-methylimidazolium tricyanomethanide ([emim][TCM]) and the 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]) ILs have been proposed as aromatic extraction solvents. Both ILs have shown high toluene distribution ratios and toluene/n-heptane selectivities, dynamic viscosities comparable to the sulfolane value, and adequate thermal stabilities. In this paper, we have mixed [emim][TCM] and [emim][DCA]} ILs to obtain an IL-based solvent with intermediate extractive and physical properties between the values of pure ILs. The liquid–liquid equilibrium (LLE) of the n-heptane + toluene + {[emim][TCM] + [emim][DCA]} pseudoternary system at 313.2 K and atmospheric pressure has been measured. LLE data have been validated using the Othmer–Tobias correlation and fitted to the NRTL model. Densities and viscosities of the mixed ILs have also been determined as a function of temperature, and the reliability of several predictive models of these physical properties has been studied. The {[emim][TCM] + [emim][DCA]} IL mixture with [emim][TCM] mole fraction of 0.8 has shown suitable physical properties and extractive properties higher than the sulfolane values. Therefore, this IL-based solvent could be considered as a potential substitute of conventional solvents used in the extraction of aromatics.