Effect of the cation and anion of the ionic liquid on desulfurization of model fuels

Abstract

Ionic liquids (ILs) are known as a new solvents with high extraction capacity for aromatic sulfur and aromatic compounds from gasoline and diesel in comparison to the conventional solvents. In this work the desulfurization ability of 21 ionic liquids in the extraction of sulfur organic compounds from hydrocarbons, which were used as a model of gasoline and diesel oils by solvent extraction, has been developed. With this aim, ternary liquid–liquid phase equilibrium data (LLE) has been obtained for mixtures of {IL+model fuel (thiophene, benzothiophene, dibenzothiophene, toluene, tetralin)+heptane} at T=298.15K and ambient pressure. The ILs studied: pyridinium-, pyrrolidinium-, morpholinium-, imidazolium-, piperidinium-, phosphonium-, and ammonium-based with different anions as dicyanoamide, [DCA], tetracyanoborate, [TCB], tricyanomethanide, [TCM], bis{(trifluoromethyl)sulfonyl}imide, [NTf2], trifluorotris(perfluoroethyl)-phosphate, [FAP], trifluoroacetate, [TFA], and trifluoromethanesulfonate, [CF3SO3]. The suitability of ILs used as solvents for extractive desulfurization has been evaluated in terms of solute distribution coefficient and selectivity. Few of proposed ILs, as 1-butyl-4-methylpyridinium dicyanamide, [bmPY][DCA], 1-butyl-1-methylpyrrolidinium dicyanamide, [bmPYR][[DCA], and N-butyl-N-methylmorpholinium tricyanomethanide, [bmMOR][TCM] show high selectivities (>200) and high distribution coefficients (>1.2) for extraction of sulfur compounds. The experimental results obtained in this work are evaluated in view of the results reported in literature [1,2]. It is shown that the ionic liquids investigated in this work are able to extract sulfur in preference to toluene and tetralin. Moreover, the distribution coefficients for [bmPYR][TCM], [bmIM][TCM] and [bmPYR][TCB] ILs are the best for the extraction of thiophene, the [bmPY][DCA], [bmPYR][TCB], [bmPYR][TCM] and [bmIM][TCM] ILs have the best distribution coefficients for benzothiophene; the [bmPY][DCA], [bmPYR][TCM] and [P6,6,6,14][TCM] ILs have the best distribution coefficients for dibenzothiophene.