Highly efficient SO ₂ absorption/activation and subsequent utilization by polyethylene glycol-functionalized Lewis basic ionic liquids

Up to now, flue-gas desulfurization (FGD) is one of the most effective techniques to control SO ₂ emission from the combustion of fossil fuels. The conventional technology for FGD poses serious inherent drawbacks such as formation of byproducts and volatilization of solvents. In this work, polyethylene glycol (PEG)-functionalized Lewis basic ionic liquids (ILs) derived from DABCO were proved to be highly efficient absorbents for FGD due to its specific features such as high thermal stability, negligible vapor pressure, high loading capacity. Notably, PEG ₁₅₀MeDABCONTf ₂ gave an extremely high SO ₂ capacity (4.38 mol mol ^-1 IL), even under 0.1 bar SO ₂ partial pressure (1.01 mol mol ^-1 IL), presumably owing to the strong SO ₂-philic characterization of the PEG chain. Furthermore, the absorbed SO ₂ could be easy to release by just bubbling N ₂ at room temperature, greatly reducing energy requirement for SO ₂ desorption. In addition, SO ₂/CO ₂ selectivity (110) of PEG ₁₅₀MeDABCONTf ₂ is two times larger than the non-functionalized imidazolium IL (45). On the other hand, through activation of SO ₂ with the tertiary nitrogen in the cation, Lewis basic ILs such as PEG ₁₅₀MeDABCOBr proved to be efficient catalysts for the conversion of SO ₂ to some value-added chemicals such as cyclic sulfites without utilization of any organic solvent or additive. Thus, this protocol would pave the way for the development of technological innovation towards efficient and low energy demanded practical process for SO ₂ absorption and subsequent transformation.