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

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.