To investigate the effect of cyanide ions on the solubility of CO2 in ionic liquid, we measured the solubility of CO2 in three ionic liquids which contain three different numbers of cyanide anions, 1-butyl-3-methylimidazolium thiocyanate ([c4mim][SCN]), 1-butyl-3-methylimidazolium dicyanamide ([c4mim][N(CN)2]) and 1-butyl-3-methylimidazolium tricyanomethanide ([c4mim][C(CN)3]). The solubility of CO2 in ionic liquids was determined by measuring bubble-point pressure in high-pressure variable-volume view cell at temperatures from 303.15 to 373.15 K in 10 K intervals. The measured data were correlated with the Peng-Robinson equation of state (PR-EoS) using the van der Waals one fluid mixing rules. The critical properties and acentric factor of ionic liquids were estimated by using the modified Lydersen-Joback-Reid method. As a result, the calculated data were relatively well agreed with the experimental results and, as is commonly known, the solubility of CO2 was observed to increase with increasing pressure and with decreasing temperature. The results also show that the highest solubility was obtained by [c4mim][C(CN)3] among those three experimented ionic liquids while [c4mim][SCN] had the lowest. This implies that the CO2 solubility is affected by the number of cyanide anions contained in ionic liquid. From this result, it is concluded that the cyanide anion enhances the CO2 solubility in ionic liquid and that the ionic liquid which contains more cyanide anions has higher CO2 solubility.
