Measurement and prediction of phase behaviour for 1-alkyl-3-methylimidazolium tetrafluoroborate and carbon dioxide: Effect of alkyl chain length in imidazolium cation

The high-pressure phase behaviour of the binary system {1-ethyl-methylimidazolium tetrafluoroborate ([EMIM][BF4]) + CO2} was determined over the temperature range of (293.2 to 323.2) K at intervals of 5.0 K with the CO2 mole fraction ranging from 0.153 to 0.578 by using a high-pressure variable-volume view cell. Further, the (vapour + liquid) equilibrium of the binary system {1-hexyl-methylimidazolium tetrafluoroborate ([HMIM][BF4]) + CO2} was measured over the temperature range of (303.2 to 328.2) K with the CO2 mole fraction ranging from 0.314 to 0.593. The Peng–Robinson equation of state along with two-parameter mixing rules has been employed to correlate the experimental results. In case of the ([EMIM][BF4] + CO2) system, the (vapour + liquid + liquid) equilibrium and (vapour + liquid) equilibrium have been observed at a high CO2 mole fraction. The experimental values obtained in this study were compared with the available phase behaviour data of the binary system (1-alkyl-3-methylimidazolium tetrafluoroborate + CO2) in order to investigate the effect of the alkyl chain length in the imidazolium cation on the phase behaviour of such systems.