Solubility of CO and NO in an Imidazolium-Based Lipidic Ionic Liquid.

Imidazolium-based ionic liquids have been extensively studied for their ability to dissolve a wide variety of gases and for their potential to be used as separation agents in industrial processes. For many short chain 1-alkyl-3-methylimidazolium bistriflimde salts, CO and NO solublities are very similar. In this work, the solubility of CO and NO has been measured in the lipidic ionic liquid 1-methyl-3-(Z-octadec-9-enyl)imidazolium bistriflimide ([oleyl-mim][NTf]) at 298 K, 310 and 323 K up to ∼2 MPa. NO was found to have higher solubility than CO under the same conditions, similar to the behavior observed when olive oil, a natural lipid, was the liquid solvent. However, the solubility of each gas on a mole fraction basis is lower in the ionic liquid than in olive oil. Comparison of the gas solubilities on a mass fraction basis demonstrates that CO solubility is nearly identical in both liquids; NO solubility is higher than CO for both liquids, but more so in the olive oil. The difference is attributed to the high mass fraction of the olive oil that is lipid-like in character. The differential solubility of NO/CO in this ionic liquid, in contrast to that of shorter chain 1-alkyl-3-methylimidazolium bistriflimide salts, gives physical insight into the solvent properties of this class of ionic liquids and provides further support for their lipid-like character.