High-pressure phase behavior of systems with ionic liquids: Part V. the binary system carbon dioxide + 1-butyl-3-methylimidazolium tetrafluoroborate

The phase behavior of the binary system consisting of the supercritical fluid carbon dioxide (CO₂) and the ionic liquid l-butyl-3-methylinudazolium tetrafluoroborate ([bmim][BF₄]) was studied experimentally. A synthetic method was used to measure its phase behavior. Bubble-point pressures of the system CO₂ + [bmim][BF ₄] are reported for carbon dioxide concentrations ranging from (10. 22 to 60.17) mole % and within a temperature fange of (278.47 to 368.22) K. The CO₂ + [bmim][BF₄] binary system has a twophase liquid-vapor region extending up to very high pressures. Most likely, the type of fluid-phase behavior is type III according to the classification of Scott and Van Konynenburg. The experimental results obtained were compared with the available phase behavior data of the binary system CO₂ + l-hexyl-3methylimidazolium tetrafluoroborate ([hmim][BF₄]) to investigate the effect of the length of the alkyl group on the phase behavior of this type of system. A larger alkyl group leads to lower bubble-point pressures and, therefore, to higher solubilities of carbon dioxide in the imidazolium-based ionic liquid.