Liquid–liquid equilibria and NRTL modeling for thiophene extraction from nC12, nC14 and nC16 using bis(trifluoromethylsulfonyl)imide–based pyrrolidinium and pyridinium ionic liquids

ABSTRACT Liquid–liquid equilibrium (LLE) data were determined at 313.15 K and 101.3 kPa for ternary systems containing thiophene, n-dodecane, n-tetradecane, or n-hexadecane, and the ionic liquids [C 3 C 1 Pyr][NTf₂], [C 4 C 1 Pyr][NTf₂], and [C 6 Py][NTf₂]. The measurements were undertaken to evaluate the effects of alkane chain length and ionic liquid cation structure on phase behavior and thiophene partitioning. All systems exhibited well-defined phase separation with preferential transfer of thiophene to the ionic-liquid-rich phase. Distribution coefficients ranged from 1.85 to 2.86 and selectivity values from 58 to 222, depending on solvent and hydrocarbon chain length. An increase in n -alkane carbon number (nC 12 < nC 14 < nC 16 ) led to higher extraction performance. Among the solvents studied, [C 6 Py][NTf₂] showed comparatively higher distribution coefficients, in comparison with pyrrolidinium-based ionic liquids. The experimental tie-line data were correlated using the NRTL activity coefficient model, which provided satisfactory representation of the phase equilibria with low root-mean-square deviations. A preliminary multistage countercurrent extraction simulation using [C 6 Py][NTf₂] indicates that ultra-low thiophene mass concentrations (below10 ppm) are achievable at practical solvent-to-feed ratios. The reported data contribute to the thermodynamic description of thiophene partitioning in [NTf₂]-based ionic liquid systems and provide parameters suitable for process analysis and design.