Supercritical Fractional Extraction of Fennel Seed Oil and Essential Oil:  Experiments and Mathematical Modeling

Abstract

Supercritical CO 2 extraction of fennel seeds has been performed in two steps; the first step was performed at 90 bar and 50 °C to obtain the selective extraction of essential oil. The second one was performed at 200 bar and 40 °C and allowed the extraction of vegetable oil. The experiments were performed using the fractional separation of the extracts using three different CO 2 flow rates (0.5, 1.0, and 1.5 kg/h). On the basis of the extraction results and of the analysis of scanning electron microscopy (SEM) images of the vegetable matter, mathematical models of the two extraction processes have been proposed. The extraction of fennel vegetable oil has been modeled using a model based on differential mass balances and on the concept of broken and intact cells as evidenced by SEM. Only one adjustable parameter has been used: the internal mass-transfer coefficient k t . A fairly good fitting of the experimental data was obtained by setting k t = 8 × 10 -8 m/s. The fennel essential oil extraction process was modeled as desorption from the vegetable matter plus a small mass-transfer resistance. The same internal mass-transfer coefficient value used for vegetable oil extraction allowed a fairly good fitting of the essential oil extraction data.