Enhancing H ₂ S Absorption Performance of Iron-Based Ionic Liquids Using Low-Viscosity Weak Lewis Basic Solvents: Experiment and Mechanistic Analysis

To address the high viscosity and strong acidity of conventional iron-based ionic liquids, a series of mixed solutions were prepared by blending FeCl 3 /[Nbmm]Br with low-viscosity, basic organic solvents. Quantum chemical calculations, including interaction energy, energy decomposition, interaction region indicator, and Atoms-in-Molecules analyses, were employed to investigate the molecular interactions between H 2 S and 11 industrially relevant solvents. Based on viscosity and H 2 S affinity, seven candidate solvents were identified. Among them, sulfolane demonstrated the highest stability when combined with FeCl 3 /[Nbmm]Br, which can be attributed to its weak Lewis basicity arising from the rigid four-membered ring and the steric hindrance of the electron-rich sulfone oxygen atoms. Response surface methodology was applied to optimize the absorption conditions, resulting in an optimal anion-to-cation molar ratio of 0.8 mol·mol –1, a solvent-to-IL ratio of 0.2 mL·mL –1, and a temperature of 26 °C. Under these conditions, the H 2 S loading reached 0.0173 mol·kg –1 ─comparable to that of pure FeCl 3 /[Nbmm]Br─while the viscosity was markedly reduced from 2749.21 to 35.34 mPa·s. Quantum chemical calculations and experimental studies revealed that the inclusion of weakly Lewis basic sulfolane reduces Fe–Cl interactions and alleviates the electron deficiency at the iron center, thereby lowering the cation’s electrostatic potential and moderating acidity.