High-Pressure Phase Equilibria of the Pseudoternary Mixture Sunflower Oil plus Ethanol plus Carbon Dioxide

Carbon dioxide can act as an expanding medium to carry out enzymatic reactions. Particularly, by dissolving CO2 in mixtures comprising lipid-type substances and simultaneously increasing the pressure, the miscibility among reactants is enhanced, viscosity of the reaction mixture decreases, and diffusion of reactants and products is improved. Knowledge about the phase equilibrium behavior of the reactive mixture + CO2 allows an adequate selection of conditions to achieve the homogeneous phase during reaction. In this work, phase equilibria data of the pseudoternary system sunflower oil + ethanol + CO2 at two different conditions (313 K and 13 MPa; 333 K and 20 MPa) were investigated to provide an understanding of the phase behavior of vegetable oil ethanolysis reactions in CO2-expanded media. Measurements were carried out by the analytical static method, using a variable-volume view cell equipped with a cold end light and a magnetic stirrer. Experimental tie-lines were determined for both types of equilibria observed: liquid + liquid and liquid + supercritical phase equilibria. Additionally, the experimental compositions obtained were correlated using a group contribution thermodynamic model.