Sulfur dioxide absorption from flue gas using 1-methylimidazolium lactate ionic liquid: Performance and mechanism

The control of sulfur dioxide (SO 2 ) emissions from natural gas purification processes has become an urgent environmental priority due to increasing regulatory pressures and public concerns over air pollution. In this study, a series of 1-methylimidazolium-based ionic liquids ([MIM]-ILs) were synthesized and structurally characterized, followed by systematic evaluation of their SO 2 absorption capacities under simulated flue gas conditions (2000 ppm SO 2 ). Among them, [MIM]Lac showed the relatively better absorption performance, reaching a saturated capacity of 1.986 mol SO 2 per mol IL at a low concentration of 2000 ppm SO 2 . The regeneration experimental results demonstrated that [MIM]Lac achieved an optimal SO 2 removal efficiency of 99.71 % at 85 °C, indicating excellent thermal responsiveness. Even after 10 consecutive absorption-desorption cycles, [MIM]Lac retained 92.52 % of its initial absorption capacity, highlighting its outstanding cyclic stability and thermal durability. The insights based on FT-IR and 1 H NMR analyses revealed that SO 2 absorption by [MIM]Lac primarily involved the reversible chemical interactions between SO 2 and the lactate anion, particularly at the S O and S−O sites. This study provides a practical strategy for designing efficient SO 2 absorbents and the development of ionic liquid-based desulfurization systems.