Contributions to supercritical extraction of vegetable substrates in Latin America

Abstract

This manuscript summarizes basic and applied research on phase equilibrium and mass transfer kinetics involved in high-pressure CO 2 extraction of solid substrates. Most examples relate to the extraction of lipids and essential oils from native Latin American plants. Extraction rates of vegetable matrices depend on the external mass transfer coefficient ( k f), effective solute diffusivity in the solid substrate ( D e), solute solubility in high-pressure CO 2, and solute binding to the solid matrix. The initial stages of the extraction process depend on an operational solubility that is close to the thermodynamic solubility ( c sat) in the case of lipid extraction from oil-containing plant material, but lower than c sat in the case of essential oils, due probably to stronger interactions between essential oils than lipids and the solid matrix. Experimental values of k f exhibited considerable scattering and were several orders of magnitude smaller than corresponding values from literature correlations for the dissolution of solids or evaporation of liquids from films with supercritical fluids (SCFs), due to underestimation of the contribution of internal (solid phase) mechanisms to the total resistance to mass transfer and other aspects. D e values were 10–10 3 or 10 2–10 5 times smaller than binary diffusion coefficients of lipids and essential oils, respectively, in high-pressure CO 2, suggesting very pronounced limitations to mass transfer within the solid matrices in both cases. The integration of this information for the modeling, simulation, and scaling-up of laboratory data is thoroughly discussed. Finally, an example of economic feasibility is given for the installation of a SCF extraction plant for the recovery of lipids from wheat germ.