Experimental and Modeling Study of the Phase Behavior of (Heptane plus Carbon Dioxide plus Water) Mixtures

We report experimental measurements of three-phase equilibria in the system (heptane + carbon dioxide + water) obtained with a quasi-static analytical apparatus with compositional analysis by means of gas chromatography. The apparatus was calibrated by an absolute area method and the whole measurement system was validated by means of comparison with the published literature data of the system (heptane + carbon dioxide). The compositions of the three phases coexisting in equilibrium were measured along five isotherms at temperatures from (323.15 to 413.15) K with pressures ranging from approximately 2 MPa to the upper critical end point pressure at which the two nonaqueous phases became critical. The experimental results have been compared with the predictions of the statistical associating fluid theory for potentials of variable range. The unlike binary interaction parameters used here are consistent with a previous study for a ternary mixture of a different n-alkane, while the alkane water binary interaction parameter is found to be transferable and the alkane carbon dioxide binary interaction parameter is predicted using a modified Hudson-McCoubrey combining rule. Generally, good agreement between experiment and theory was found.