Excess molar enthalpies for mixtures of supercritical carbon dioxide and limonene

Abstract

Excess molar enthalpies (HmE) for mixtures of supercritical CO2 and limonene were measured at 308.15, 313.15 and 323.15K and 7.64 and 10.00MPa 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 308.15K and 10.00MPa 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 HmE values (≈−4500Jmol−1) are observed for mixtures at 313.15K and 7.64MPa. On the other hand, HmE at 7.64MPa and 308.15, 313.15 and 323.15K 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.