High-pressure phase behavior of binary mixtures containing methylpyrrolidinium derivative ionic liquids and carbon dioxide

In this work, we measured the solubility of carbon dioxide in four different ionic liquids: N-propyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C3mpy][Tf2N]), N-pentyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C5mpy][Tf2N]), N-heptyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C7mpy][Tf2N]) and N-nonyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imde ([C9mpy][Tf2N]). The temperatures for the experimental measurements ranged from 303.15 to 373.15 K in 10 K intervals. The solubility of carbon dioxide (CO2) was determined by measuring the bubble point pressure at a fixed temperature. The experimental data was correlated by using the PR-EoS and Modified-Joback–Reid method. The solubility increased with increasing pressure and decreased with increasing temperature for all the ionic liquids. The bubble point pressure increased linearly with increasing temperature at a fixed mole fraction of CO2. We also studied the effect of cation alkyl chain length on the CO2 solubility. As the cation alkyl chain length became longer, the solubility of CO2 increased in ionic liquid. Additionally, we compared the solubility of CO2 in [BMP] cation-based ionic liquids systems with that in [Cnmpy][Tf2N]-based ionic liquids systems. As a result, we have concluded that the solubility change depends much more on the anion combination than on the cation alkyl chain length.

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► Solubility of CO2 in [C3mpy][Tf2N], [C5mpy][Tf2N], [C7mpy][Tf2N] and [C9mpy][Tf2N] at 303.15–373.15 K.
► Solubility of CO2 decreased commensurate to increases in temperature.
► In [Tf2N] anion-based IL, CO2 solubility increases with increasing alkyl group chain length.
► The PR-EoS well correlates these CO2 + ionic liquid systems.
► The solubility of CO2 change depends much more on the anion combination than the cation alkyl chain length.