Solubility of carbon dioxide in some imidazolium and pyridinium-based ionic liquids and correlation with NRTL model

In this study, the solubility of carbon dioxide gas in a series of 1-alkyl-4-methyl pyridinium and 1-alkyl-3-methylimidazolium-based ionic liquids with various anions, viz. thiocyanate ([SCN]−), chloride ([Cl]−) and bromide ([Br]−) was investigated using a quartz crystal microbalance at 298.15 K and pressures up to 0.4 MPa. CO2 solubility in the ionic liquids correlates well with the non-random two-liquid (NRTL) model. The results indicate that the cation alkyl chain length and the type of anion have the main effects on the solubility of carbon dioxide in ionic liquids. CO2 solubility in both 1-alkyl-4-methyl pyridinium and 1-alkyl-3-methylimidazolium-based ionic liquids increased with increasing alkyl chain length of the cation. Also, CO2 solubility was strongly dependent on the selection of the anion. CO2 solubility in both 1-alkyl-4-methyl pyridinium and 1-alkyl-3-methylimidazolium-based ionic liquids increased as follows: [SCN]− > [Cl]− > [Br]−.