Highly Selective Absorption of Low-Concentration SO2 over CO2 in Flue Gas through Cation-Tunable Protic Ionic Liquids

A cation-tunable strategy was reported for highly selective absorption of low-concentration SO2 over CO2 in flue gas, where the cation had a significant effect on the selectivity. The absorption capacity and selectivity of low-concentration SO2 by various ionic liquids (ILs) were investigated; therein, protic IL [THEEDH][Tetz] showed the best selectivity of 80.6 (120.4) under the atmosphere of 2000 ppm of SO2 and 15% CO2. Nuclear magnetic resonance spectroscopic investigations and quantum chemical calculations indicated that the effect of the cation on the electronegativity of the anion was significant, leading to an obvious increase in selectivity. This cation-tunable IL offered a significant improvement in the selective absorption of SO2 compared to traditional ILs, indicating its potential in acid gas separation in industry.