Separation of toluene from n-heptane, 2,3-dimethylpentane, and cyclohexane using binary mixtures of [4empy][Tf2N] and [emim][DCA] ionic liquids as extraction solvents

Abstract

The use of ionic liquids (ILs) in the separation of aromatic hydrocarbons from alkanes could decrease the environmental impact of the aromatic extraction units, reducing the number of steps and simplifying the solvent recovery. Mixing ILs has been also revealed as a useful tool to tune the extractive and physical properties of IL-based solvents. In this work, the suitability of binary mixtures of 1-ethyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4empy][Tf2N]) and 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]) ILs as aromatic extraction solvent has been evaluated. For this purpose, we have studied the liquid–liquid extraction of toluene from a straight-chain alkane (n-heptane), a branched-chain alkane (2,3-dimethylpentane), and a cycloalkane (cyclohexane) at 313.2K, using {[4empy][Tf2N]+[emim][DCA]} mixed IL solvents. A physical characterization of the IL mixtures has also been performed by measuring their densities and dynamic viscosities as a function of temperature. Extractive and physical properties of the mixed IL solvents have been intermediate between the values of pure ILs. A {[4empy][Tf2N]+[emim][DCA]} mixture with a 0.3mole fraction of [4empy][Tf2N] has shown extractive properties better than those of sulfolane for the extraction of toluene from alkanes and adequate densities and viscosities. Finally, a log-linear mixing rule has successfully estimated the extractive properties of the mixed ILs, and the use of predictive models of densities and viscosities of binary IL mixtures has also been studied.