Phase equilibrium and kinetics of O ₂-oxidation of limonene in high pressure carbon dioxide

The effect of phase equilibrium on the kinetics of O ₂-oxidation of limonene was studied. Vapour-liquid equilibrium measurements of the system (CO ₂ + O ₂ + limonene) were performed at 328 K and 8, 10, 10.7 and 11 MPa. In an attempt to establish a relation between vapour-liquid equilibrium data and the kinetics of limonene oxidation, different reactions were performed at 328 K and at different CO ₂ total pressures of 9.3 MPa, 10 MPa and 10.3 MPa (with the reaction mixture being biphasic) and at 12.2 MPa (in a single supercritical phase). The volumetric concentration of O ₂ in the liquid phase increased as CO ₂ was added to the system, although this behaviour was only observed close to the critical region. Kinetics of oxidation reactions performed at biphasic conditions, suggests that is the volumetric concentration of O ₂ in the liquid phase that is controlling the reaction rates.