High-pressure phase equilibria of systems with ionic liquids

In this work, the phase behavior of the binary systems of carbon dioxide (CO2) + 1-ethyl-3-methylimidazolium hexafluorophosphate ([emim][PF6]), CO2 + 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), and CO2 + 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF6]) have been studied experimentally. A synthetic method was used to measure vapor-liquid boundaries. Pressures up to 97 MPa have been applied. The effect of the different alkyl groups on the CO2 solubility in the various ionic liquids has been analysed. Also, it has been shown that the phase behavior of the systems CO2 + [emim][PF6] and CO2 + [bmim][PF6] are completely different in comparison with the phase behavior of the systems trifluoromethane (CHF3) + [emim][PF6] and CHF3 + [bmim][PF6], respectively.