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

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 [P-66614][3-CHO-Indo], [P-66614][2-CHO-Pyro], [P-66614][4-CHO-PhCOO], and [P-66614][4-CHO-PhO], were designed and prepared through an acid-base neutralization reaction. The absorption of SO2 in simulated acid gas (SO2/N-2 = 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 C=O center dot center dot center dot S interaction and C-H center dot center dot center dot O hydrogen bonding. Furthermore, the SO2 absorption process by the ILs could be repeated several times without loss of absorption capability.