Improving SO2 capture by basic ionic liquids in an acid gas mixture (10% vol SO2) through tethering a formyl group to the anions

Abstract

Low partial pressure SO₂ gas can be efficiently absorbed by ionic liquids (ILs), especially by basic ILs, through strong chemical interaction. However, it is still a challenge to achieve a high absorption capacity under these SO₂ conditions. In this work, a new class of formyl-containing aprotic task-specific ILs, including [P₆₆₆₁₄][3-CHO-Indo], [P₆₆₆₁₄][2-CHO-Pyro], [P₆₆₆₁₄][4-CHO-PhCOO], and [P₆₆₆₁₄][4-CHO-PhO], were designed and prepared through an acid–base neutralization reaction. The absorption of SO₂ in simulated acid gas (SO₂/N₂ = 10/90 vol) by these functional ILs was investigated. Compared with the formyl-free ILs, up to 100% increased capacity could be achieved by introducing a formyl group into the basic anions. In addition, the interactions between formyl-containing task-specific ILs and SO₂ were investigated through a combination of multiple techniques, including FT-IR, NMR, and quantum chemical calculations. It was found that the remarkable enhancement of SO₂ absorption capacity under low partial pressure was due to the CO⋯S interaction and C–H⋯O hydrogen bonding. Furthermore, the SO₂ absorption process by the ILs could be repeated several times without loss of absorption capability.