CO2 absorption features of 1-ethyl-3-methylimidazolium ionic liquids with 2, 4-pentanedionate and its fluorine derivatives. (May 2019)

• Record Type: Journal Article
• Authors: Umecky, Tatsuya; Abe, Mitsutoshi; Takamuku, Toshiyuki; Makino, Takashi; Kanakubo, Mitsuhiro
• Is Part Of: Journal of CO₂ utilization. Volume 31(2019)
• Page Start: 75
• Page End: 84
• Publication Date: 2019-05
• Subjects: Ionic liquid -- CO2 -- Chemisorption -- NMR -- Cation-CO2 zwitterion formation; Carbon dioxide -- Periodicals; Carbon dioxide -- Environmental aspects -- Periodicals; Carbon dioxide mitigation -- Periodicals; Carbon dioxide; Carbon dioxide -- Environmental aspects; Carbon dioxide mitigation; Periodicals; 628.53205
• DOI: 10.1016/j.jcou.2019.02.020
• Languages: English
• ISSNs: 2212-9820

Abstract

Graphical abstract: Highlights: [C2 mim][acac] chemically absorbed CO2 as well as [C2 mim][AcO] at atmospheric pressure. [C2 mim][tfacac], and [C2 mim][hfacac] absorbed only a negligible amount of CO2 under the same conditions. The stronger cation-anion interaction allows to draw the hydrogen atom at the 2-position of [C2mim]+ cation. Abstract: Basic 2, 4-pentanedionate anion is one of candidates for task-specific ionic liquids as CO2 chemical absorbents. However, there have been few reports on not only CO2 absorption but also physicochemical properties of 2, 4-pentanedionate ionic liquids. In this study, we prepared 1-ethyl-3-methylimidazolium ionic liquids with 2, 4-pentanedionate and its fluorine derivatives, i.e., 1-ethyl-3-methylimidazolium 2, 4-pentanedionate ([C2 mim][acac]), 1-ethyl-3-methylimidazolium 1, 1, 1-trifluoro-2, 4-pentanedionate ([C2 mim][tfacac]), and 1-ethyl-3-methylimidazolium 1, 1, 1, 5, 5, 5-hexafluoro-2, 4-pentanedionate ([C2 mim][hfacac]). A comparison of 1 H NMR spectra among the above and three conventional ionic liquids, 1-ethyl-3-methylimidazolium acetate ([C2 mim][AcO]), 1-ethyl-3-methylimidazolium 2, 2, 2-trifluoroacetate ([C2 mim][TFA]), and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2 mim][Tf2 N]), showed that the hydrogen atom at the 2-position of [C2 mim] + cation (H2c ) interacts with the anions, and the strength of the interaction increases in the order of [Tf2 N] – < [TFA] – ≈ [tfacac] – ≈ [hfacac] – < [acac] – < [AcO] – . [C2 mim][acac] chemically absorbed CO2 as well as [C2 mim][AcO] at atmospheric pressure, although the CO2 solubility of the former was lower than the latter. On the other hand, [C2 mim][Tf2 N], [C2 mim][TFA], [C2 mim][tfacac], and [C2 mim][hfacac] absorbed only a negligible amount of CO2 under the same conditions. The smaller chemisorption of [C2 mim][acac] is attributable to the weaker interactions of the H2c atom with the oxygen atoms of [acac] – . The stronger interaction between the cation and anion in the ionic liquids allows to draw the H2c atom at the initial stage of CO2 chemisorption.