Extraction of resinoids from St. John's wort (Hypericumperforatum L): II. Modeling of extraction kinetics

Abstract

The extraction of resinoids from St. John's wort (Hypericum perforatum L) was studied in a series of two papers. While the first part dealt with the effects of the operating conditions on the yield of resinoids (total extract) and process optimization, the mathematical models of extraction kinetics were analyzed in the second one. The extraction was carried out using an aqueous solution of ethanol (70 and 95 % v/v) at the hydromodulus (plant material to solvent ratio, w/v) of 1:5 or 1:10. The plant material was disintegrated and divided into three fractions (particle mean size 0.23, 0.57 and 1.05 mm). The temperature was 25, 50 or about 80?C (boiling temperature). Three models were applied for modeling the extraction kinetics: a model based on the film theory, a model based on unsteady state diffusion through solid material and the empirical Ponomarev equation. Because of its physical basis, the relative simplicity and good fitting of the experimental data, the model based on the film theory could be proposed for mathematical modeling of solid-liquid etraction processes.