Selective recovery of aliphatics from aromatics in the presence of the {[4empy][Tf2N] + [emim][DCA]} ionic liquid mixture

• (Vapor + liquid) equilibria for aliphatic + aromatic + {[4empy][Tf2N] + [emim][DCA]} were determined.
• Aliphatic relative volatilities from all aromatics were highly increased by the ionic liquid mixture.
• Low temperatures and the highest content of [emim][DCA] maximized the aliphatic relative volatilities from aromatics.
• The flipping phenomenon was shown in favor to the alkane in the {n-heptane + benzene} and {n-octane + toluene} systems.

Lately, the use of binary mixtures of ionic liquids (ILs) has been revealed as an interesting election in order to find alternative solvents in the liquid–liquid extraction of aromatics from aliphatics. Specifically, the {[4empy][Tf2N] + [emim][DCA]} mixture has exhibited both aromatic selectivity and distribution ratios higher than sulfolane in the BTEX separation from several gasolines and naphthas. Moreover, its density and viscosity are comparable with those showed by sulfolane, and its thermal stability is also quite high. However, the absence of (vapor + liquid) equilibria (VLE) studies concerning aliphatics/aromatics mixtures in ILs has not led to propose a recovery section to selectively separate aliphatics, aromatics, and the IL-based solvent. For that reason, the aim of this work is to study the VLE of several {aliphatic + aromatic} systems in the presence of {[4empy][Tf2N] + [emim][DCA]} mixture over the whole composition range of the IL mixture and also at several temperatures. The results showed high aliphatic relative volatility from all aromatics, fact that would facilitate the selective separation of aliphatics, BTEX, and ILs. On the other hand, the Yalkowsky–Roseman log-linear model was successfully apply to predict the phase behavior of {aliphatic + aromatic + [4empy][Tf2N] + [emim][DCA]} systems.

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