Dicarboxylic acid salts as task-specific ionic liquids for reversible absorption of SO2 with a low enthalpy change

Abstract

Six acid salt ionic liquids (ASILs), triethylbutylammonium dicarboxylates, have been synthesized to act as green materials for SO₂ capture. The experimental results reveal that the ASILs can trap SO₂ reversibly and chemically with a large capacity of 0.112 up to 0.232 (mass ratio) at 15.5 kPa and of 0.374 to 0.456 (mass ratio) at 100 kPa and 40 °C. Two of these ASILs are interestingly found to have a low viscosity that enables the fast mass transfer of SO₂. A reaction mechanism is proposed to explain the chemical absorption based on FTIR spectra and structural calculations using the density functional theory. Thermodynamic analysis indicates the enthalpy of the reaction of SO₂ with the ASILs is low (−29.9 and −42.2 kJ mol⁻¹ for [N₂₂₂₄][dimaleate] and [N₂₂₂₄][dimalonate], respectively). Additionally, the ASILs have a high thermal stability, which favors their potential application in flue gas desulfurization.