Superefficient Absorption of Low-Concentration SO2 in Flue Gas Using New Ternary Imidazole-Based Deep Eutectic Solvents: Mechanism, Thermodynamics, and Process Analysis

New ternary deep eutectic solvents (DESs), including imidazole (Im), ethylene glycol (EG), and methyltriphenyl phosphonium bromide (MTPB), were synthesized at different molar ratios to absorb SO2 in flue gas. Excitingly, the EG–Im–MTPB (1:2:1) DES has achieved the unexpected achievement of its absorption capacity being greatly improved to 0.65 g of SO2/g of DES (4.43 mol/mol) at 3000 ppm and 30 °C, which is the best performing DES for capturing SO2 under the same conditions ever reported. The aftereffects of thermodynamic investigation demonstrate that there is a solid compound communication between EG–Im–MTPB (1:2:1) DES and SO2. In particular, the enthalpy change (ΔrHm), entropy change (ΔrSm), and Gibbs free energy change (ΔrGm) were plainly determined as −50.45 kJ/mol, −114.57 J mol–1 K–1, and −16.20 kJ/mol, separately. The Fourier transform infrared, 1H nuclear magnetic resonance, and quantum chemistry calculation results confirm that multiple active sites, including the N atom of Im and the Br atom of MTPB, are the main factors by which DES effectively absorbs SO2. Further, a UNIQUAC method by Aspen Plus V12 is set up for the SO2 absorption process with 6000 m3/h flue gas, indicating that the EG–Im–MTPB (1:2:1) DES can completely absorb SO2 in the flue gas when the consumption of DES is 26.8 m3/h.