Computer-Assisted Design of Imidazolate-Based Ionic Liquids for Improving Sulfur Dioxide Capture, Carbon Dioxide...

A new strategy involving the computer-assisted design of substituted imidazolate-based ionic liquids (ILs) through tuning the absorption enthalpy as well as the basicity of the ILs to improve SO₂ capture, CO₂ capture, and SO₂ /CO₂ selectivity was explored. The best substituted imidazolate-based ILs as absorbents for different applications were first predicted. During absorption, high SO₂ capacities up to ≈5.3 and 2.4 molSO2  mol_IL^-1 could be achieved by ILs with the methylimidazolate anions under 1.0 and 0.1 bar (1 bar=0.1 MPa), respectively, through tuning multiple N⋅⋅⋅S interactions between SO₂ and the N atoms in the imidazolate anion with different substituents. In addition, CO₂ capture by the imidazolate-based ILs could also be easily tuned through changing the substituents of the ILs, and 4-bromoimidazolate IL showed a high CO₂ capacity but a low absorption enthalpy. Furthermore, a high selectivity for SO₂ /CO₂ could be reached by IL with 4,5-dicyanoimidazolate anion owing to its high SO₂ capacity but low CO₂ capacity. The results put forward in this work are in good agreement with the predictions. Quantum-chemical calculations and FTIR and NMR spectroscopy analysis methods were used to discuss the SO₂ and CO₂ absorption mechanisms.