Density functional theory study on the absorption of CO_2 by the ionic liquid of 1-butyl-3-methylimidazolium acetate

摘要

The absorptions of CO_2 on the 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]) with different substituents are calculated systematically at GGA/PW91 level. Three hydrogen bonds are formed between [Ac]~- and cations of 1-n-[Bmim][Ac] ([NBmim]~+) and 1-tert-[Bmim][Ac] ([TBmim]~+). The interaction between CO_2 and the [NBmim][Ac] by a C-O bond is much weaker than that with the [TBmim][Ac] by forming a O…O…C…C four member-ring. The chemisorption of CO_2 on the ion pairs of [NBmim][Ac] is much weaker than that on the [TBmim][Ac], resulted from the absorption energies analysis. The frontier molecular orbitals shows the electronic density overlap between absorbed CO_2 and the [Ac]~- in CO_(2-)[NBmim][Ac] is much weaker than that in [TBmim][Ac]. Therefore, the chemisorption of CO_2 on the ion pair of [NBmim][Ac] is much weaker than that on the [TBmim][Ac]. The ionic liquids based [NBmim]~+ can be used repetitively, and the adsorbed CO_2 would be easier desorbed.