Liquid–Liquid Equilibria and Process Simulation of Thiophene and n-Paraffins with Imidazolium Based [NTf₂] Ionic Liquids

New liquid–liquid equilibrium (LLE) data are presented for ternary systems relevant to extractive desulfurization, comprising thiophene, long chain n alkanes (n dodecane, n tetradecane, and n hexadecane), and a homologous series of 1 alkyl 3 methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids, [Cₙmim][NTf₂]. Phase equilibria were measured at 313.15K and atmospheric pressure to systematically assess the coupled influence of ionic liquid cation alkyl chain length and paraffinic hydrocarbon chain length on phase behavior and sulfur partitioning. Extraction performance was quantified in terms of distribution coefficients and selectivity, revealing a pronounced and tunable affinity of thiophene for the ionic liquid rich phase. Distribution coefficients ranging from 1.88 to 2.92 and selectivity values between 49 and 177 were obtained, depending on cation structure, indicating clear structure–property relationships within the [Cₙmim][NTf₂] family. The complete LLE datasets were successfully correlated using the Non Random Two Liquid (NRTL) activity coefficient model, yielding thermodynamically consistent binary interaction parameters with low root mean square deviations. The resulting ternary phase diagrams provide quantitative insight into the non-ideal interactions governing the selective solvation of aromatic sulfur compounds in [NTf₂]⁻ based ionic liquids. Overall, this work establishes benchmark thermodynamic data and molecular level structure–property relationships linking ionic liquid structure to extraction behavior. Process simulations indicate that a three-stage extractor employing [C8mim][NTf₂] can achieve ultra-low sulfur fuel (sulfur <10 ppm) at solvent to feed ratios above 1.3, while maintaining moderate and industrially feasible regeneration energy requirements.