Improving Carbon Dioxide Solubility in Ionic Liquids

J. Phys. Chem. B 2007, 111, 9001-9009

9001

Improving Carbon Dioxide Solubility in Ionic Liquids
Mark J. Muldoon,† Sudhir N. V. K. Aki,‡ Jessica L. Anderson, JaNeille K. Dixon, and
Joan F. Brennecke*
Department of Chemical and Biomolecular Engineering, UniVersity of Notre Dame,
Notre Dame, Indiana 46556
ReceiVed: March 8, 2007; In Final Form: May 4, 2007

Previously we showed that CO2 could be used to extract organic molecules from ionic liquids without contamination of the ionic liquid. Consequently a number of other groups demonstrated that ionic liquid/CO2 biphasic systems could be used for homogeneously catalyzed reactions. Large differences in the solubility of various gases in ionic liquids present the possibility of using them for gas separations. More recently we and others have shown that the presence of CO2 increases the solubility of other gases that are poorly soluble in the ionic liquid phase. Therefore, a knowledge and understanding of the phase behavior of these ionic liquid/
CO2 systems is important. With the aim of finding ionic liquids that improve CO2 solubility and gaining more information to help us understand how to design CO2-philic ionic liquids, we present the low- and high-pressure measurements of CO2 solubility in a range of ionic liquids possessing structures likely to increase the solubility of CO2. We examined the CO2 solubility in a number of ionic liquids with systematic increases in fluorination. We also studied nonfluorinated ionic liquids that have structural features known to improve
CO2 solubility in other compounds such as polymers, for example, carbonyl groups and long alkyl chains with branching or ether linkages. Results show that ionic liquids containing increased fluoroalkyl chains on either the cation or anion do improve CO2 solubility when compared to less fluorinated ionic liquids previously studied. It was also found that it was possible to obtain similar, high levels of CO2 solubility in

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