Investigating the SO2 absorption behavior of pyrimidine-based deep eutectic solvents via a dual-site thermodynamic model

Abstract

Deep eutectic solvents (DESs), composed of hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs), are widely used in flue gas desulfurization due to their excellent SO₂ absorption properties. In this work, 14 DESs with pyrimidine derivatives and their isomers (including 2-aminopyrimidine (AmPyr), 2-chloropyrimidine, 2-bromopyrimidine, 4-amino-2-hydroxypyrimidine, 2,4-dihydroxypyrimidine, 4,6-diaminopyrimidene, 2-aminopyrazine, and 3-aminopyridazine, respectively) as HBDs and 1-ethyl-3-methylimidazolium chloride (C₂mimCl) and 1-ethyl-3-methylimidazolium bromide as HBAs have been successfully prepared and used for SO₂ absorption. Among them, C₂mimCl-7 + AmPyr exhibited the highest SO₂ absorption (19.032 mol kg⁻¹, at 298.15 K and 1.0 bar), rapid gas–liquid equilibrium within 40 s, and an exceptional ideal selectivity of 528.7 for SO₂/CO₂. After 30 cycles of absorption–desorption, the SO₂ absorption capacity remained as high as 18.265 mol kg⁻¹. A dual-site reaction equilibrium thermodynamic model (DS-RETM) was established for absorption behavior analysis. Using C₂mimCl-7 + AmPyr as a case study, Henry's constant, equilibrium constants, and other thermodynamic parameters were determined. DS-RETM fitting further enabled visualization of the potential absorption behavior of each DES component, facilitating comparison of HBA and HBD effects on SO₂ absorption. This study offers new insights into the development of high-performance flue gas desulfurization absorbents and introduces a novel model for thermodynamic analysis of SO₂ absorption in DESs.

Keywords: Deep eutectic solvents; SO₂ absorption; Pyrimidine; Thermodynamic; Selectivity.