Phase equilibrium engineering of the extraction of oils from seeds using carbon dioxide + propane solvent mixtures

The use of propane + carbon dioxide mixtures can offer special properties regarding solvent power, selectivity and safety. In the present work, we studied the phase equilibrium engineering for the extraction of fixed oils from ground seeds. The selection of operating conditions is based on a ternary diagram that limits the region of complete miscibility and non-flammable mixtures. On the basis of the selected conditions, we carried out extraction experiments of soy oil, sunflower oil and hiprose oil from ground seeds. The extraction studies covered a range of propane + CO2 solvent mixtures, at conditions of complete and/or partial miscibility with the oil. We observed that the oil extraction rate decreases as the CO2 concentration in the solvent mixture increases, even in the region of complete solvent + oil miscibility. This behavior is explained on the basis of the effect of the thermodynamic properties of the oil + solvent solution on the mass transfer rate.