Highly efficient SO2 absorption/activation and subsequent utilization by polyethylene glycol-functionalized Lewis basic ionic liquids

Abstract

Up to now, flue-gas desulfurization (FGD) is one of the most effective techniques to control SO₂ 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, PEG₁₅₀MeDABCONTf₂ gave an extremely high SO₂ capacity (4.38 mol mol⁻¹ IL), even under 0.1 bar SO₂ partial pressure (1.01 mol mol⁻¹ IL), presumably owing to the strong SO₂-philic characterization of the PEG chain. Furthermore, the absorbed SO₂ could be easy to release by just bubbling N₂ at room temperature, greatly reducing energy requirement for SO₂ desorption. In addition, SO₂/CO₂ selectivity (110) of PEG₁₅₀MeDABCONTf₂ is two times larger than the non-functionalized imidazolium IL (45). On the other hand, through activation of SO₂ with the tertiary nitrogen in the cation, Lewis basic ILs such as PEG₁₅₀MeDABCOBr proved to be efficient catalysts for the conversion of SO₂ 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 SO₂ absorption and subsequent transformation.