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

Abstract

Excess molar enthalpies ( H m E ) for mixtures of supercritical CO 2 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 [CO 2 ( 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 H m E values (≈−4900 J mol −1) are observed for CO 2-rich mixtures at 313.15 K and 7.64 MPa. These data are examined together with phase equilibria and critical parameters previously reported for [CO 2 + 1,8-cineole]. The large negative values of H m E are related to the carbon dioxide change of state from that of a low-density fluid to that of a liquid-mixture component in CO 2-rich mixtures.