Excess molar enthalpies for mixtures of supercritical CO 2 and linalool

Abstract

Excess molar enthalpies ( H m E ) for mixtures of supercritical CO 2 and linalool were measured at conditions of temperature and pressure typical of supercritical extraction processes: 313.15 and 323.15 K and 7.64, 10.00 and 12.00 MPa. The measurements were carried out using an isothermal high-pressure flow calorimeter. The effects of pressure and temperature on the excess molar enthalpy are large. Mixtures formed by low-density carbon dioxide and linalool show very exothermic mixing and excess molar enthalpies exhibit a minimum in the CO 2-rich region. The lowest H m E values (≈−4000 J mol −1) are observed for mixtures at 313.15 K and 7.64 MPa. Mixtures formed by high-density carbon dioxide and linalool show considerably endothermic mixing (≈400–600 J mol −1) in the linalool-rich region and moderately exothermic mixing for the other compositions. On the other hand, H m E at 7.64 MPa and 313.15 and 323.15 K varies linearly with CO 2 mole fraction in the two-phase region where a gaseous mixture and a liquid mixture of fixed composition, for a given condition of temperature and pressure, are in equilibrium. Results are analyzed in terms of phase equilibria, pure carbon dioxide density and CO 2–terpene molecular interactions. Excess molar enthalpies are simultaneously correlated using the Soave–Redlich–Kwong and Peng–Robinson equations of state and the classical mixing rule. The significance of these large variations of H m E with temperature and pressure in the design of supercritical fluid deterpenation processes is discussed.