Volumetric Properties and Solubility Parameters of Cyclohexane + CO₂ Mixtures at High Pressures and Their Modeling with the Sanchez–Lacombe Equation of State

Densities of mixtures of cyclohexane and carbon dioxide containing 0 to 50 wt % CO₂ were determined using a variable-volume view cell at pressures ranging from 5 to 35 MPa and temperatures ranging from 313 to 393 K covering a density range from 0.55 to 0.83 g/cm³. The data were modeled with the Sanchez–Lacombe (S-L) equation of state (EOS). Modeling was conducted both by treating each mixture as a pseudopure compound and by using the S-L parameters for the pure components with a composition- and temperature-dependent interaction parameter. Various thermodynamic properties for the mixtures such as the isothermal compressibility, isobaric expansivity, internal pressure, excess volumes, and solubility parameters were then evaluated. Mixture excess volumes were also determined, and they were modeled with Redlich–Kister type equations. The mixture density data were also modeled using the S-L parameters for pure components and a composition- and temperature-dependent interaction parameter. Isothermal compressibilities ranged from 0.0008 MPa^–1 for pure cyclohexane at 313 K and 35 MPa to 0.013 MPa^–1 for the mixture containing 50 wt % CO₂ at 393 K and 20 MPa. Isobaric expansivities ranged from 0.0008 K^–1 for cyclohexane at 35 MPa and 313 K to 0.0035 K^–1 for the 50 wt % CO₂ mixture at 20 MPa and 393 K. Internal pressures ranged from 83.8 MPa for 50 wt % CO₂ mixture at 20 MPa and 393 K to 275.5 MPa for cyclohexane at 35 MPa and 313 K. Solubility parameters ranged from 16.6 MPa^0.5 for cyclohexane at 35 MPa and 313 K to 9.2 MPa^0.5 for 50 wt % CO₂ mixture at 20 MPa and 393 K. The mixtures showed a high degree of nonideality with excess volumes ranging from approximately −20 cm³ mol^–1 for 50 wt % CO₂ mixture at 20 MPa and 393 K to +2 cm³ mol^–1 also for the 50 wt % CO₂ mixture at 20 MPa, but at 313 K.