SO2 absorption in highly efficient chemical solvent AChBr + Gly compared with physical solvent ChBr + Gly

Abstract

Deep eutectic solvents (DESs) have been identified as optimal gas absorbents. A tertiary amine-containing task-specific DES AChBr+Gly and a conventional DES ChBr+Gly have been designed, prepared and used to capture SO2. It is found that absorption capacity of 3.74 and 2.97 mol of SO2 per mole of DES can be obtained by AChBr+Gly and ChBr+Gly, respectively, at 293.2 K and 1 bar. When SO2 partial pressure was decreased to 0.01 bar, the capacity decreased to 0.93 and 0.13 mol SO2 of per mole of AChBr+Gly and ChBr+Gly, respectively. Mechanism and thermodynamic studies show that absorption by former absorbent includes physisorption, quasi-chemisorption (a strong physisorption) and chemisorption, while absorption by later absorbent only includes physisorption and quasi-chemisorption. Two equations were first proposed for the description of SO2 absorption. In these equations, the physisorption capacity is correlated with Henry's law, and the quasi-chemisorption and chemisorption are correlated with the quasi-chemical equilibrium constant of halogen···SO2 interaction and the chemical equilibrium constant of tertiary amine···SO2 interaction, respectively. In addition, the corresponding enthalpy change, entropy change, and Gibbs energy change have been calculated and discussed.