Novel sulfone-based deep eutectic solvents for efficient selective absorption separation of SO2 from CO2: Experimental study and molecular insights

Novel sulfolane-based DESs with exceptionally low viscosity were developed. • The potential formation of DESs was disclosed via molecular dynamics simulations. • High SO₂ absorption capacity and satisfied SO₂/CO₂ selectivity was achieved. • Cooperative absorption mechanism revealed by DFT and molecular dynamics simulations. • Excellent reversibility over four consecutive absorption-desorption cycles. To address the limitations of conventional flue gas desulfurization technologies and the challenges of high viscosity and poor selectivity in many deep eutectic solvents (DESs), this work develops a series of novel low-viscosity sulfolane-based DESs for selective SO₂ capture. Four DESs were prepared by combining sulfolane (Sul) with four hydrogen bond donors (HBDs): imidazole (Im), caprolactam (CPL), 3-aminopyrazole (3-AP), and 4-methylimidazole (4-MI) at a 1:1 molar ratio. These DESs exhibit exceptionally low viscosities (below 20 mPa·s at 313.2 K) and fast gas–liquid mass transfer. Among them, Sul-Im demonstrates outstanding performance, achieving a high SO₂ absorption capacity of 9.38 mol/kg at 313.2 K and 1.0 atm, excellent SO₂/CO₂ selectivity of 24.5, and rapid absorption equilibrium within 400 s. Spectroscopic characterizations together with density functional theory calculations and molecular dynamics simulations reveal a cooperative absorption mechanism: the N site of imidazole acts as the dominant Lewis basic site for strong interaction with SO₂, while the O sites of sulfolane provide a polar solvation environment that further stabilizes SO₂ through Lewis acid–base and dipole–dipole interactions. Moreover, Sul-Im exhibits excellent reversibility over four consecutive absorption–desorption cycles with no significant capacity loss. These sulfolane-based DESs offer a compelling combination of low viscosity, high SO₂ capacity, fast kinetics, and good regenerability, positioning them as promising and sustainable solvents for selective SO₂ removal from CO₂-containing flue gas. Download: Download high-res image (155KB) Download: Download full-size image This work develops a series of novel sulfone-based deep eutectic solvents for the highly selective capture of SO 2 from CO 2 through experimental study and molecular simulation insights.