Experiments, correlations and COSMO-RS predictions for the extraction of benzothiophene from n-hexane using imidazolium-based ionic liquids

The extraction of benzothiophene from n-hexane was studied using 1-ethyl-3-methylimidazolium ethyl sulphate ([EMIM][EtSO4]) and 1-ethyl-3-methylimidazolium acetate ([EMIM][CH3COO]) at 308.15 K to analyze the performance of ionic liquids in the extractive desulphurization of aromatic sulphur compounds from petroleum fuels. A comparative study was done from the perspective of selectivity and distribution coefficient of the sulphur compounds. From the ternary LLE (liquid–liquid extraction) experiments, it was found that while the selectivity was higher for the ethyl sulphate-based ionic liquids, the distribution coefficient was higher for acetate-based ionic liquids. Selectivities as high as 245 and 203 were obtained for [EMIM][EtSO4] and [EMIM][CH3COO] with negligible loss of hydrocarbon. The experimental results were correlated using the NRTL and UNIQUAC models. The root mean square deviation (RMSD) values of 0.48% and 0.83% were obtained for [EMIM][EtSO4] and [EMIM][CH3COO] respectively, when using the NRTL model, and the corresponding RMSD values when using the UNIQUAC model were 0.693% and 1.053%. The quantum chemical based COnductor like Screening MOdel for Real Solvent (COSMO-RS) model was then used to predict the performance of single as well as mixed ionic liquids. RMSDs of 4.36% and 7.87% were achieved for [EMIM][EtSO4] and [EMIM][CH3COO] based system, which are satisfactory considering that the method is a priori.