Effect of the alkyl side chain of the 1-alkylpiperidinium-based ionic liquids on desulfurization of fuels

• Extraction of thiophene and benzothiophene from heptane.
• The ternary (liquid + liquid) equilibria using alkyl-piperidinium-based ILs.
• High selectivity and solute distribution ratio for the extraction of sulphur compounds form alkanes.
• [PMPIP][NTf2] was proposed as entrainer for the separation process.

In this work the desulfurization ability of three alkyl-piperidinium-based ionic liquids (PIPILs) from heptane, which is used as a model of gasoline and diesel oils, has been developed. With this aim, ternary (liquid + liquid) phase equilibrium data (LLE) have been obtained for mixtures of {PIPIL (1) + thiophene (2) + heptane (3)} at T = 298.15 K and ambient pressure and for the best thiophene entrainer {[PMPIP][NTf2] (1) + benzothiophene (2) + heptane (3)} at T = 308.15 K and ambient pressure. Three PIPILs have been studied: 1-propyl-1-methylpiperidinium bis{(trifluoromethyl)sulfonyl}imide [PMPIP][NTf2], 1-butyl-1-methylpiperidinium bis{(trifluoromethyl)sulfonyl}imide [BMPIP][NTf2] and 1-hexyl-1-methylpiperidinium bis{(trifluoromethyl)sulfonyl}imide, [HMPIP][NTf2]. The suitability of PIPILs used as solvents for extractive desulfurization has been evaluated in terms of solute distribution ratio and selectivity. Immiscibility was observed in the binary liquid systems of (thiophene, or benzothiophene + heptane) with all PIPILs used. One of proposed PIPILs, [PMPIP][NTf2] shows high selectivities and high distribution ratios for extraction of sulfur compounds. The data obtained have been correlated with the non-random two liquid NRTL model. The experimental tie-lines and the phase composition in mole fraction in the ternary systems were calculated with an average root mean square deviation (RMSD) of 0.0037.

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