Volumetric and phase behaviour of mixtures of tetracyanoborate-based ionic liquids with high pressure carbon dioxide

• High solubility of CO2 in tetracyanoborate-based ionic liquids.
• Higher than usual CO2-induced volume expansion of tetracyanoborate-based ionic liquids.
• Strikingly visible liquid volume expansions in sapphire tube apparatus.

The high-pressure solubility of carbon dioxide in ionic liquids based on tetracyanoborate anion, 1-ethyl-3-methylimidazolium tetracyanoborate ([emim][B(CN)4]) and 1-hexyl-3-methylimidazolium tetracyanoborate ([hmim][B(CN)4]), was determined experimentally at the temperature of 313.15 K and pressures up to 19 MPa. Additionally, measurements of volume expansion of a liquid phase, based on a change in total or molar volume of a liquid upon carbon dioxide addition, are reported. The obtained results show that CO2 has a high solubility in tetracyanoborate-based ionic liquids, comparable, or even slightly higher, to the CO2 solubility in fluorinated CO2-philic ionic liquids. Approximately 60% CO2-induced volume expansion of the liquid was observed at the highest pressures, an unprecedented result for ionic liquid+ CO2 systems.

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