Measurement of CO<inf>2</inf> solubility in cyanide anion based ionic liquids; [c<inf>4</inf>mim][SCN], [c<inf>4</inf>mim][N(CN)<inf>2</inf>], [c<inf>4</inf>mim][C(CN)<inf>3</inf>]

To investigate the effect of cyanide ions on the solubility of CO<inf>2</inf> in ionic liquid, we measured the solubility of CO<inf>2</inf> in three ionic liquids which contain three different numbers of cyanide anions, 1-butyl-3-methylimidazolium thiocyanate ([c<inf>4</inf>mim][SCN]), 1-butyl-3-methylimidazolium dicyanamide ([c<inf>4</inf>mim][N(CN)<inf>2</inf>]) and 1-butyl-3-methylimidazolium tricyanomethanide ([c<inf>4</inf>mim][C(CN)<inf>3</inf>]). The solubility of CO<inf>2</inf> 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 CO<inf>2</inf> was observed to increase with increasing pressure and with decreasing temperature. The results also show that the highest solubility was obtained by [c<inf>4</inf>mim][C(CN)<inf>3</inf>] among those three experimented ionic liquids while [c<inf>4</inf>mim][SCN] had the lowest. This implies that the CO<inf>2</inf> 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 CO<inf>2</inf> solubility in ionic liquid and that the ionic liquid which contains more cyanide anions has higher CO<inf>2</inf> solubility.