Liquid–liquid equilibria and NRTL thermodynamic modeling of thiophene extraction from ternary n-paraffin mixtures (C12, C14, and C16) with methylimidazolium hexafluorophosphate ionic liquids

Reducing sulfur content in fuels is vital for minimizing sulfur oxide emissions and their environmental impacts. This study examines the liquid–liquid extraction of thiophene (C₄H₄S) from model diesel fuels using imidazolium-based ionic liquids as selective solvents. The systems investigated involved n -dodecane, n -tetradecane, or n -hexadecane with thiophene and one of three ionic liquids: 1-octyl-3-methylimidazolium hexafluorophosphate [C 8 mim][PF₆], 1-nonyl-3-methylimidazolium hexafluorophosphate [C 9 mim][PF₆], and 1-decyl-3-methylimidazolium hexafluorophosphate [C 10 mim][PF₆]. Liquid–liquid equilibrium (LLE) data were measured at 313.15 K and 101.3 kPa, with distribution ratios and selectivity values determined to evaluate desulfurization efficiency. The effect of alkyl chain length in both the hydrocarbon and the ionic liquid phases was systematically investigated. The Non-Random Two-Liquid (NRTL) model successfully correlated the experimental data, yielding low root-mean-square deviations and reliable binary interaction parameters. Ternary phase diagrams, constructed with experimental and calculated tie-lines, illustrate the extraction performance. The findings ( K =2.57–4.49, S =128–625) demonstrate that the investigated ionic liquids exhibit high efficiency in thiophene extraction, underscoring their suitability as promising candidates for fuel desulfurization applications.