CO2 solubility measurement in 1-hexyl-3-methylimidazolium ([HMIM]) cation based ionic liquids

• We measured solubility of CO2 in [HMIM][Tf2N], [HMIM][TfO], [HMIM][MeSO4], [HMIM][BF4], and [HMIM][PF6].
• Solubility of CO2 decreased commensurate to increases in temperature.
• In [HMIM] cation-based IL, CO2 solubility increases with increasing fluoro-alkyl group.
• The PR-EoS well correlates these CO2 + ionic liquid systems.
• The solubility of CO2 change depends much more on the anion combination than the cation combination.

In this study, we measured the solubility of carbon dioxide in five different ionic liquids: 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][Tf2N]), 1-hexyl-3-methylimidazolium trifluoromethanesulfonate ([HMIM][TfO]), 1-hexyl-3-methylimidazolium methylsulfate ([HMIM][MeSO4]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIM][BF4]) and 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM][PF6]). The temperatures during the experimental measurements ranged from 303.15 to 373.15 K in 10 K intervals. The solubility of carbon dioxide (CO2) was determined by measuring the bubble point pressure at a fixed temperature. Experimental data were correlated by using the PR-EoS and Modified-Joback–Reid method. The solubility for all the ionic liquids increased with higher pressure conditions and decreased with higher temperatures. The bubble point pressure increased linearly with increasing temperature at a fixed mole fraction of CO2. In addition, we investigated the anion exerting influence of the fluorine content on the solubility of carbon dioxide in 5 different ionic liquids in this study. As a result, the solubility of CO2 in [HMIM][Tf2N] was found to be the highest, while the solubility of CO2 in [HMIM][MeSO4] proved to be the lowest. Furthermore, we also compared the solubility of CO2 in [HMP]-cation based ionic liquids and examined the solubility data of CO2 with respect to [Cnmpy][Tf2N]-based ionic liquid systems. Also, we compared the [HMIM] cation-based ionic liquid systems and the [BMP] cation-based ionic liquid systems. As a result, we concluded that the solubility change depends much more on the anion combination than on the cation combination for the systems studied here.

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