Solubility of carbon dioxide in ionic liquids

In this study, Carbon dioxide,(CO₂) absorption capacity in the mixture of 1-Butyl-1-Methylpyrrolidinium bis (trifluoromethylsulfonyl) imide with methanol, aqueous mixture of 2-methylpiperidine and aqueous 1-Butyl-3-Methylpyridinium tetrafluoroborat, [B3MPYR][BF4] was measured at constant temperature of 313K and at pressure range from 300-700psi. The concentration used for 1-Butyl-1-Methylpyrrolidinium bis (trifluoromethylsulfonyl) imide and methanol mixtures were 80 wt% methanol (CH₃OH)+ 20 wt% ionic liquid (IL) and 50 wt% CH₃OH + 50 wt% IL with total volume of 100ml. For another two ILs of the same concentration but mixed with water instead of methanol. In this work, it was found that in all the ionic liquids used, increasing the pressure will increase the CO₂ loading which is consistent with the theory as well as the behavior of other type of ionic liquids that have been published. The effect of ionic liquids concentration on CO₂ loading shows different behaviour for the three ILs mixtures studied. Increasing the ILs concentration for 1-Butyl- 1-Methylpyyrolidinium bis (trifluoromethylsulfonyl) imide with methanol mixture increases the CO₂ loading, however it decreases at pressure above 700 psi. Aqueous 1-Butyl-3-Methylpyridinium tetrafluoroborat shows contradict behavior where increasing the ILs concentration decreased the CO₂ loading but at higher pressure, greater than 550 psi, increasing the concentration will increase the CO₂ loading. For the aqueous 2-methylpiperidine the CO₂ loading increased as the IL concentration increases. The bulkiness of IL molecules and the ability of ionic liquid to capture CO₂ itself will effect the solubility of CO₂ in ionic liquids. In comparison of CO₂ loading between the ionic liquids, anion density of the ILs will affect the CO₂ loading in the ILs. The results shown that CO₂ absorption capacity of the ILs trend as follow C₆H₁₂N- >BF¯⁴> Tf₂N-.