Separation of sulfur compounds from alkanes with 1-alkylcyanopyridinium-based ionic liquids

•Extraction of sulfur-compounds from alkanes.•The ternary (liquid + liquid) equilibria using alkyl-cyanopyridinium-based ILs was measured.•High selectivity and solute distribution ratio for the extraction of thiophene and benzotiophene was found.•[BCN4PY][TCM] was proposed as entrainer for the separation process.

In this work, we studied the applicability of new 1-alkyl-cyanopyridinium-based ionic liquids (ILs) in the extraction of aromatic-sulfur compounds from aliphatic mixtures. The synthesis of new 1-alkyl-cyanopyridinium-based ionic liquids is presented. Experimental data for (liquid + liquid) equilibrium (LLE) were obtained for various binary and ternary mixtures of {IL (1) + thiophene, or benzothiophene (2) + heptane (3)} at T = 308.15 K and ambient pressure. Three ILs have been studied: 1-butyl-3-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide [BCN3Py][NTf2], 1-butyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide [BCN4Py][NTf2] and 1-hexyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [HCN4Py][NTf2]. One of the IL showed excellent results in terms of sulfur compounds selectivity and solute distribution ratio compared to what is currently used in industry. Chromatography analysis showed that the IL used as an entrainer was not present in the alkane layer. This eliminates the step needed for the separation of the solvent. A comparative study of the separation effectiveness of [BCN4Py][NTf2] in this work in comparison with other reported ILs was performed for choosing the best solvent for the intended separation. Density and viscosity of [BCN4Py][NTf2] were measured over a range of temperature from (278.15 to 358.15) K. The non-random two liquid NRTL model was used successfully to correlate the experimental tie-lines and to calculate the phase composition error in mole fraction in the ternary systems.

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