Density of n‑Heptane + n‑Dodecane and Carbon Dioxide + n‑Heptane + n‑Dodecane Mixtures up to 70 MPa from (293.15 to 363.15) K

Density measurements of the n-heptane + n-dodecane binary mixture were performed with a vibrating tube densitometer in the temperature range of (293.15 to 363.15) K and pressure up to 70 MPa at six different n-heptane mole fractions: x 1 = 0, 0.1999, 0.3991, 0.5999, 0.7998, and 1. Densities of the CO2 + n-heptane + n-dodecane ternary mixtures were also measured at the same temperature and pressure ranges for two different isopleths: CO2 (0.4904) + n-heptane (0.2548) + n-dodecane (0.2548), and CO2 (0.7425) + n-heptane (0.1288) + n-dodecane (0.1288). The obtained experimental data were correlated by a polynomial model and by a Tait-based equation. Density values for pure n-heptane and n-dodecane were found to be in agreement with literature data within approximately 0.3%. The isothermal compressibility and thermal expansion values of these mixtures were obtained by differentiation from the models as a function of pressure and temperature. Analysis of these properties pointed out that the polynomial model provided more accurate results related to derived properties. The excess volume of the mixtures was also determined. In general, they are negative, but they become positive for binary mixtures in the heptane-rich region as well as at higher pressures for ternary mixtures.