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

Abstract

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 SO 2 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 SO 2 /g of DES (4.43 mol/mol) at 3000 ppm and 30 °C, which is the best performing DES for capturing SO 2 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 SO 2 . In particular, the enthalpy change (Δ r H m ), entropy change (Δ r S m ), and Gibbs free energy change (Δ r G m ) 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, 1 H 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 SO 2 . Further, a UNIQUAC method by Aspen Plus V12 is set up for the SO 2 absorption process with 6000 m 3 /h flue gas, indicating that the EG− Im−MTPB (1:2:1) DES can completely absorb SO 2 in the flue gas when the consumption of DES is 26.8 m 3 /h.