Bis(trifluoromethylsulfonyl)imide, or dicyanamide-based ionic liquids in the liquid–liquid extraction of hex-1-ene from hexane and cyclohexene from cyclohexane

Abstract

In this work we studied the applicability of four imidazolium-based ionic liquids (ILs) with different allyl-, or benzyl-substituents and bis(trifluoromethylsulfonyl)imide, or dicyanamide anions in the separation of hex-1-ene/hexane and cyclohexene/cyclohexane compounds. Experimental values for liquid–liquid equilibrium (LLE) were obtained for various binary and ternary mixtures of {IL (1)+hex-1-ene (2)+hexane (3)} or {IL (1)+cyclohexene (2)+cyclohexane (3)} at T=298.15K and p=0.1MPa. The ILs studied were as follows: 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [AMIM][NTf2], 1-allyl-3-methylimidazolium dicyanamide, [AMIM][DCA], 1-benzyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [BzMIM][NTf2], 1-benzyl-3-methylimidazolium dicyanamide, [BzMIM][DCA]. These ILs were chosen after the analysis of the selectivities calculated from the limiting activity coefficients data. The results are useful for the design an industrial process of extraction. The dicyanamide-based ILs showed excellent results in terms of selectivity, but bis(trifluoromethylsulfonyl)imide-based ILs revealed twice better solute distribution ratio. The chromatography analysis revealed that the ILs used as an entrainers were not present in the hydrocarbon-rich layer, which is convenient for production process, because eliminates the step needed for the separation of the solvent. The [AMIM][DCA] showed suitable extractive properties to replace nowadays methods of separation for hex-1-ene/hexane and cyclohexene/cyclohexane compounds. All experimental data were correlated with the NRTL model. The experimental tie-lines were calculated in good agreement with each other.