Steps of supercritical fluid extraction of natural products and their characteristic times

Kinetics of supercritical fluid extraction (SFE) from plants is variable due to different micro-structure of plants and their parts, different properties of extracted substances and solvents, and different flow patterns in the extractor. Variety of published mathematical models for SFE of natural products corresponds to this diversification. This study presents simplified equations of extraction curves in terms of characteristic times of four single extraction steps: internal diffusion, external mass transfer, hypothetic equilibrium extraction without mass transfer resistance, and displacement of the solution from the extractor. Preliminary evaluation of experimental extraction curves using these equations facilitates the choice of proper detailed model for SFE and enables estimation of changes in the extraction kinetics with the changes in operation conditions and extraction geometry.