Measurement of CO₂ Solubility in Ionic Liquids: [BMP][Tf₂N] and [BMP][MeSO₄] by Measuring Bubble-Point Pressure

Abstract

This paper presents the bubble-point pressure data of CO 2 in ionic liquids 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][Tf 2 N]) and 1-butyl-1-methylpyrrolidinium methylsulfate ([BMP][MeSO 4 ]). In our research, the high-pressure phase behavior of carbon dioxide in [BMP][Tf 2 N] and [BMP][MeSO 4 ] were observed at pressure up to about 100 MPa in a temperature range from (303.15 to 373.15) K in 10 K intervals by using a high-pressure variable-volume view cell. To investigate the effect of different anion on the solubility of CO 2 in the [BMP] cation based ionic liquids, we compared three [BMP] cation based systems; [BMP][Tf 2 N] +, [BMP][TfO] +, and [BMP][MeSO 4 ] + CO 2 . In all systems, at lower mole fraction of CO 2 (below 0.3), the solubility is approximately the same, however above 0.3 mol fraction, the ration between pressure and CO 2 mol fraction decreases sharply. Although these experiments have used the same cation, it would appear that the ratio decreases more sharply as the alkyl group chain length of the anion decreases. It can also be observed that when the alkyl group chain lengths are similar, the system containing fluoroalkyl group chain shows higher solubility. However at this stage a thorough analysis of these effects cannot be made. Additionally, the solubility of CO 2 decreases linearly with rising temperatures at a fixed mole fraction of CO 2 . The experimental data for the CO 2 + ionic liquid system were correlated using the Peng−Robinson equation of state.