关键词: 质子化离子液体, 多元胺, 二氧化硫, 吸收, 分子间氢键作用

Abstract:

A computational study was conducted to investigate the absorption of sulfur dioxide (SO₂) by protic ionic liquids (PILs) comprising the cations of N-hexylammonium ([HHexam]⁺), hexylethylenediaminium ([HHexen]⁺), hexyldiethylenetriaminium ([HHexdien]⁺), and the anion of TFSA[(CF₃SO₂)₂N^-]. The most stable configurations of PILs-nSO₂ (n=1,2,3,4,5,6) were determined by using density functional theory (DFT) at the M06-2X/6-311G(d,p) level. The results revealed that N—H…O type hydrogen bonding was formed between the polar N—H groups on the cations and the O atoms in SO₂. The analysis of vibrational frequency, second-order perturbation energy, and electron density revealed that the maximum hydrogen bonding was achieved when [HHexam][TFSA], [HHexen][TFSA] and [HHexdien][TFSA] combined with 3, 4, and 5 molecules of SO₂, respectively, with maximum hydrogen bond energies of 57, 67, and 85 kJ/mol. The absence of further hydrogen bonding networks with SO₂ suggests that SO₂ absorption has reached saturation. The data also indicate that the SO₂ absorption capacity increases with the number of amino groups in the PILs structure. COSMOtherm software calculations corroborate the findings, revealing an increasing trend for the SO₂ solubilities from 5.0 to 5.3 to 6.2 mol in 1 mol PILs above, respectively. That is, as the number of amino groups in the cationic structure increases, its ability to absorb SO₂ increases, which is basically consistent with the conclusions obtained from density functional theory calculations.

Key words: protic ionic liquids, polyamine, sulfur dioxide, absorption, intermolecular hydrogen bonding