Excess molar enthalpies for mixtures of supercritical carbon dioxide and limonene

Excess molar enthalpies ( H m E ) for mixtures of supercritical CO2 and limonene were measured at 308.15, 313.15 and 323.15 K and 7.64 and 10.00 MPa using an isothermal high-pressure flow calorimeter. The effects of pressure and temperature on the excess molar enthalpy of [CO2(x) + limonene(1 − x)] are large. Mixtures at 308.15 K and 10.00 MPa show slightly endothermic mixing in the limonene-rich region and moderately exothermic mixing for x > 0.5. Mixtures at the other conditions of temperature and pressure studied show exothermic mixing, excess molar enthalpies exhibit a minimum in the CO2-rich region. The lowest H m E values (≈−4500 J mol−1) are observed for mixtures at 313.15 K and 7.64 MPa. On the other hand, H m E at 7.64 MPa and 308.15, 313.15 and 323.15 K varies linearly with CO2 mole fraction in the two-phase region where a gaseous and a liquid mixture of fixed composition, for a given condition of temperature and pressure, are in equilibrium. These data are examined together with phase equilibria and critical parameters previously reported for CO2 + limonene. Excess molar enthalpies are simultaneously correlated using the Peng–Robinson equation of state and the classical mixing rule with one binary interaction parameter.