Rich Ether-Based Protic Ionic Liquids with Low Viscosity for Selective Absorption of SO2 through Multisite Interaction

Four low-viscosity protic ionic liquids (PILs) with the tertiary amine and rich ether skeletons are designed for selective absorption of SO2. To evaluate the selective absorption of SO2 by these PILs, the solubilities of SO2, CO2, and H2S are measured in the temperature range of 303.2–333.2 K and pressures up to 120 kPa by a volumetric method, respectively. The absorption of SO2 by [TMEA][MOAc] at 303.2 K and 101.3 kPa was found to be 10.424 mol·kg–1 (4.310 mol·mol–1), and the ideal selectivity of SO2/CO2 was 86.83. In addition, the solubility data are fitted using a reaction equilibrium thermodynamic model to obtain thermodynamics parameters including Gibbs free energy change (ΔrGm), enthalpy change (ΔrHm, ΔphyHm, ΔchemHm), and entropy change (ΔrSm). The mechanism of SO2 absorption by [TMEA][MOAc] is also investigated by FTIR and NMR analyses. Mechanistic and thermodynamic studies suggest that the high SO2 absorption is attributed to the O–SO2 multisite physical interaction. These ether-rich PILs are considered as a promising absorber because of their high SO2 solubility, good cycling performance, and low viscosity before and after absorption.