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

摘要

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.