Density Functional Theory Study on the Absorption of CO2 by the Ionic Liquid of 1-butyl-3-methylimidazolium Acetate

The absorptions of CO2on the 1-butyl-3-methylimidazolium acetate ([Bmi [Ac]) with different substituents are calculated systematically at GGA/PW91 level. Three hydrogen bonds are formed between [A and cations of 1-n-[Bmi [A ([NBmi+) and 1-tert-[Bmi [A ([TBmi+). The interaction between CO2and the [NBmi [A by a C-O bond is much weaker than that with the [TBmi [A by forming a O...O...C...C four member-ring. The chemisorption of CO2on the ion pairs of [NBmi [A is much weaker than that on the [TBmi [A, resulted from the absorption energies analysis. The frontier molecular orbitals shows the electronic density overlap between absorbed CO2and the [A in CO2-[NBmi [A is much weaker than that in [TBmi [A. Therefore, the chemisorption of CO2on the ion pair of [NBmi [A is much weaker than that on the [TBmi [A. The ionic liquids based [NBmi+can be used repetitively, and the adsorbed CO2would be easier desorbed.