Highly efficient SO2 capture by phenyl-containing azole-based ionic liquids through multiple-site interactions

Abstract

Ionic liquids are suitable for the absorption of acid gases such as SO₂ because of their unique properties. In this work, a new method was developed for the highly efficient capture of SO₂ by introducing a phenyl group into the azole-based ionic liquids. It was found that these phenyl-containing azole-based ionic liquids reacted with SO₂ through multiple-site interactions between the anion and SO₂, resulting in an extremely high SO₂ capacity of up to ∼5.7 mole per mole ionic liquid. Spectroscopic investigations and quantum calculations show that the dramatic enhancement in the SO₂ capacity originated from the enhanced π⋯S interaction between the phenyl group on the anion and SO₂. Furthermore, the captured SO₂ was easy to release by heating or bubbling N₂ through the ionic liquid. This efficient and reversible process using these phenyl-containing azole-based ionic liquids with an enhanced π⋯S interaction provides an excellent alternative to current SO₂ capture technologies.