Excess molar enthalpies for mixtures of supercritical carbon dioxide and 1,8-cineole

Excess molar enthalpies (HE m) for mixtures of supercritical CO2 and 1,8-cineole were measured at 308.15, 313.15 and 323.15 K and 7.64 MPa and at 308.15 and 323.15 K 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) + 1,8-cineole (1 − x)] are large. Mixtures at 308.15 K and 10.00 MPa show slightly endothermic mixing in the 1,8-cineole-rich region and moderately exothermic mixing for x > 0.2. Excess molar enthalpies become very exothermic at the other conditions of temperature and pressure studied. The lowest HE m values (≈−4900 J mol−1) are observed for CO2-rich mixtures at 313.15 K and 7.64 MPa. These data are examined together with phase equilibria and critical parameters previously reported for [CO2 + 1,8-cineole]. The large negative values of HE m are related to the carbon dioxide change of state from that of a low-density fluid to that of a liquid-mixture component in CO2-rich mixtures.