Fluid-Phase Equilibrium Experiments and Modeling for CO₂ + C₆ Binary Systems

The phase behavior of the carbon dioxide and n-hexane binary mixture was examined. The entire available literature was reviewed and analyzed. Despite the apparent abundance of experimental data, both vapor–liquid equilibrium (VLE) and critical data, there is a high degree of discrepancy between them. Therefore, the liquid–vapor critical line was determined up to 117.0 bar and 383.15 K, as well as VLE data at different constant temperatures (313.15 to 383.15 K) using a 60 cm3 stainless-steel cell with sapphire windows connected to a gas chromatograph via rapid online sample injectors─ROLSI valves for accurate composition detection. The new and literature data were successfully calculated with several models (General Equation of state─GEOS, Peng–Robinson─PR, and Soave–Redlich–Kwong─SRK), in association with classical van der Waals mixing rules, i.e., one- (1PCMR) and two-parameter conventional (2PCMR) combining rules, as well as the PPR78 model. We also studied the influence of the structure of organic compounds (n-alkane, cycloalkane, and branched alkane-position isomers) with the same number of carbon atoms on the phase behavior of their corresponding binary systems at high pressures.