Solubility of CO2 in ionic liquids containing cyanide anions: [c2mim][SCN], [c2mim][N(CN)2], [c2mim][C(CN)3]

• The aim of this study was to explore the effect of cyanide anions on CO2 solubility.
• Solubility of CO2 in ionic liquid was measured from 303.15 to 373.15 K in 10 intervals.
• Experimental data were well correlated with PR-EoS.
• Solubility of CO2 increases as pressure increases and temperature decreases.
• Increase in the number of cyanide anion enhances the CO2 solubility in ionic liquid.

The solubility of CO2 in three ionic liquids which contains three different number of cyanide anions, 1-ethyl-3-methylimidazolium thiocyanate ([c2mim][SCN]), 1-ethyl-3-methylimidazolium dicyanamide ([c2mim][N(CN)2]), 1-ethyl-3-methylimidazolium tricyanomethanide ([c2mim][C(CN)3]) was measured in order to investigate the effects of cyanide anions on the solubility of CO2. The solubility of CO2 was determined by measuring the bubble point pressure at the temperature ranges from 303.15 to 373.15 K in 10 K intervals. Also, the measured data were correlated with the PR-EoS (Peng-Robinson equation of state) incorporated with the conventional van der Waals one fluid mixing rule. The critical properties of ionic liquids were estimated using the modified Lydersen–Joback–Reid method. As a result, the calculated data were comparatively well commensurate with the experimental results and, as is commonly known, the solubility of CO2 was observed to increase with increasing pressure and with decreasing temperature. Moreover, the results also show that the highest solubility was obtained by [c2mim][C(CN)3] among those three experimented ionic liquids while [c2mim][SCN] has the lowest. It 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 anion has higher CO2 solubility.