Low-Pressure Solubility of Carbon Dioxide in Room-Temperature Ionic Liquids Measured with a Quartz Crystal Microbalance

Ruth E. Baltus, Benjamin H. Culbertson, Sheng Dai, Huimin Luo, David W. DePaoli

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Abstract

The solubility of carbon dioxide in a series of imidazolium-based room-temperature ionic liquids has been determined using a quartz crystal microbalance. Henry's constants were obtained for CO2 in nine different ionic liquids: 1-methyl-3-propylimidazolium bis[trifluoromethylsulfonyl]amide (C3mimTf2N), 1-n-butyl-3-methylimidazolium bis[trifluoromethylsulfonyl]amide (C 4mimTf2N), C6mimTf2N with polyethylenimine, 1-n-hexyl-3-methylimidazolium bis[trifluoromethylsulfonyl]amide (C6mimTf2N), 1-methyl-3-n-octylimidazolium bis [trifluoromethylsulfonyl] amide (C 3mimTf2N), 1-methyl-3-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)-imidazolium bis[trifluoromethylsulfonyl]amide (C3F13mimTf 2N), 1,4-dibutyl-3-phenylimidazolium bis[trifluoromethylsulfonyl]amide, 1-butyl-3-phenylimidazolium bis[trifluoromethylsulfonyl]amide, and 1-methyl-3-propylimidazolium hexafluorophosphate (C3mimPF6). All results were obtained at 25 °C with CO2 pressures at or less than 1 bar. A comparison of results helps in understanding the role of chemical structure on the separation capabilities of these materials. Notable among the results is a significantly greater measured CO2 solubility in the ionic liquid having the fluorine-substituted cation as compared to the corresponding ionic liquid with a nonfluorinated cation. CO2 solubility was found to be lower in the ionic liquid containing PF6- than for the corresponding liquid with Tf2N- anion. Addition of an imine polymer to the ionic liquid did not significantly change CO2 solubility characteristics. The presence of water had a minor effect on CO 2 solubility for C3mimTf2N for environments with a relative humidity of 40% or less. Henry's constant for CO2 in C3mimPF6 obtained in this study is in good agreement with previously reported Henry's constant values for CO2 in C 4mimPF6 that were obtained by other means. This study not only provides some important thermodynamic property information for these unique materials but also illustrates the utility of using a quartz crystal microbalance to obtain this information.

Original languageEnglish
Pages (from-to)721-727
Number of pages7
JournalJournal of Physical Chemistry B
Volume108
Issue number2
DOIs
StatePublished - Jan 15 2004

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