Comparative analyses of the diffusion coefficients from thyme for different extraction processes

Abstract

This work was aimed at analyzing the kinetics and mass transfer phenomena for different extraction processes from thyme (Thymus vulgaris L.) leaves. Different extraction processes with ethanol were studied, i.e., Soxhlet extraction and ultrasound-assisted batch extraction on the laboratory scale, as well as pilot plant batch extraction with mixing. The extraction processes with ethanol were compared to the process of supercritical carbon dioxide extraction performed at 10 MPa and 40 °C. The experimental data were analyzed by a mathematical model derived from the Fick's second law to determine and compare the diffusion coefficients in the periods of constant and decreasing extraction rates. In the fast extraction period, the values of the diffusion coefficients were one to three orders of magnitude higher compared to those determined for the period of slow extraction. The highest diffusion coefficient was recorded for the fast extraction period of supercritical fluid extraction. In the cases of the extraction processes with ethanol, ultrasound, stirring and increasing extraction temperature enhanced the mass transfer rate in the washing phase. On the other hand, ultrasound contributed the most to the increase of mass transfer rate in the period of slow extraction.