Theoretical Study on CO<sub>2</sub>/SO<sub>2</sub> Absorption Using <i>N</i>- Alkylethylenediaminium Protic Ionic Liquid

Abstract

The protic ionic liquids (PILs) comprising with N-2-ethylhexylethylenediaminium cation (HEtHex+) and bis (trifluoromethanesulfonate) imide anion (TFSA-) forming [HEtHex][TFSA] which has two amines in the polar group and available to absorbs acid gases such as CO2 and SO2. In order to study the CO2/SO2 absorption mechanism of [HEtHex][TFSA], the stable configurations of [HEtHex][TFSA]-nCO2 (n=1, 2, 3, 4) and [HEtHex][TFSA]-nSO2 (n=1, 2, 4, 6) are investigated using the density functional theory at the M06-2X/6-311G (d, p) level, then the interaction energy, molecular vibration frequency, second-order perturbation energy, electron density and Laplace value are calculated and analysed for the most stable configurations. The results show that N–H...O type weak or medium hydrogen bonding are mainly formed between [HEtHex][TFSA] and CO2/SO2 molecules. The hydrogen bonding interaction is stronger for [HEtHex][TFSA]-nSO2 comparing with [HEtHex][TFSA]-nCO2 and increases with increasing the number of CO2/SO2 molecules.