Phase behavior of the ternary 1-hexyl-3-methylimidazolium tetrafluoroborate + carbon dioxide + methanol system

The phase behavior of the ternary system consisting of the ionic liquid (IL) 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim+][BF4−]) + carbon dioxide (CO2) + methanol is studied experimentally using the Cailletet apparatus. Experimental data for all phase transitions within a temperature range of 254.64–348.17 K, a pressure range of 2.102–13.189 MPa and a CO2 fraction range of 40.20–69.98 mol% are collected, while the ratio [hmim+][BF4−]:methanol is kept constant at 1:19. Only at CO2 concentrations between 66.47 and 68.04% the usual ‘two-phase’–‘three-phase’–‘two-phase’–‘one-phase’ transition upon CO2 pressure increase is found. At lower and higher CO2 fractions, the number of phase transitions observed is lower. All observed phase transitions do not involve criticality.