Effect of SO2 on CO2 Absorption in Flue Gas by Ionic Liquid 1-Ethyl-3-methylimidazolium Acetate

Significant efforts are being made to develop several novel solvents or materials for postcombustion CO2 capture technology. Traditional amine solvents suffer from mass loses due to its volatility and poisoning by flue gas impurities. Ionic liquids (ILs) are considered to be promising alternatives for CO2 capture due to their unique features, such as negligible vapor pressure. Despite the extensive research on CO2 capture by ILs, few studies have investigated the effect of flue gas components on CO2 absorption performance. Because of the large differences between CO2 and SO2 in the absorption capacity and partial pressure in flue gas, it is essential to study the role of SO2 in CO2 capture using ILs. This work focused on studying the effect of SO2 with low concentration on postcombustion CO2 capture by 1-ethyl-3-methylimidazolium acetate [C(2)mim][OAc] and explaining the microscopic mechanism through quantum chemical calculation. Results showed that the CO2 absorption capacity was largely decreased by 25% in the presence of SO2. After 5 cycles of regeneration, the initial absorption capacity of CO2 in [C(2)mim][OAc] remarkably decreased by 48%. Thus, the ionic liquid lost its excellent reversibility and regeneration property for CO, capture under continuous exposure to SO2. The quantum chemical calculation indicated that CO2 could hardly compete with SO2 for the main active sites in [C(2)mim][OAc]. In addition, the net charge transfer amount from acetate anion to CO2 significantly decreased from -0.537 to -0.039 e in the presence of SO,, which explained the decreased absorption capacity of CO2 in [C(2)mim][OAc].