Anion-dependent extraction mechanisms of dibenzothiophene in ionic liquids: DFT insights into molecular interactions for enhanced desulfurization

Abstract

The removal of sulfur-containing compounds, such as dibenzothiophene DBT, from petroleum-derived fuels remains a critical challenge due to the limitations of conventional hydrodesulfurization methods. Ionic liquids have emerged as promising solvents for sustainable extraction, yet the molecular mechanisms governing their selectivity remain underexplored. This study investigates four imidazolium-based ILs ([C₄mim][C₈H₁₇SO₄], [C₄mim][OTf], [C₄mim][Cl], and [C₄mim][PF₆]) to unravel the role of anion chemistry in DBT extraction. Through DFT analyses, It was identify hydrogen bonding, π-π interactions, Van der Waals interactions and anion polarization as key enthalpic drivers. However, experimental extraction efficiencies ([C₄mim][C₈H₁₇SO₄] > [C₄mim][OTf] > [C₄mim][Cl] > [C₄mim][PF₆]) deviate from DFT-predicted interaction energies, which is attributed to the influence of entropic effects and dynamic phase-separation processes. Notably, [C₄mim][C₈H₁₇SO₄]’s superior performance stems from its balanced hydrophobicity, numerous Van der Waals interactions and synergistic hydrogen bonding. These findings underscore the necessity of integrating molecular-scale simulations with macroscopic phase-behavior analyses to advance IL design for fuel purification.