Selective extraction of thiophene from n-alkanes using methylimidazolium [NTf2] ionic liquids: Experimental LLE and NRTL modeling

The removal of sulfur containing compounds, particularly aromatic species like thiophene from transportation fuels remains a major challenge despite the current industrial desulfurization methods. This study addresses this limitation via ionic liquid-based extraction process. Liquid–liquid equilibrium (LLE) data were measured at 313.15 K and atmospheric pressure for nine ternary systems consisting of thiophene with three representative n -alkanes fuels ( n -dodecane, n -tetradecane, and n -hexadecane), and three methylimidazolium-based ionic liquids containing [NTf 2 ] anion: [C 6 mim][NTf₂], [C 7 mim][NTf₂], and [bzmim][NTf₂].The extraction performance of the ionic liquids was evaluated using distribution coefficients and solvent selectivity. Results demonstrated exceptional performance with all systems achieving pronounced phase separation with negligible mutual solubility between the paraffinic and ionic-liquid-rich phases. The distribution coefficients were ranging from 2.09 to 3.64. Notably, [bzmim][NTf 2 ] emerged as the superior solvent delivering highest distribution coefficient and selectivity due to the enhanced π − π interactions between the benzyl group and the thiophene ring. Solvent selectivity increased with increasing alkane chain length in the order n -hexadecane > n -tetradecane > n -dodecane, indicating stronger steric exclusion of larger alkanes and stronger aromatic interactions with thiophene. The experimental LLE data were successfully correlated using the Non-Random Two-Liquid (NRTL) model, yielding a satisfactory representation of phase behavior with an average RMSD of 0.2048. These results demonstrate the suitability of methylimidazolium-based [NTf₂] ionic liquids as an effective, selective extractive solvents for the desulfurization of paraffinic fuel streams.