Supercritical fractional extraction of fennel seed oil and essential oil: Experiments and mathematical modeling

Supercritical CO2 extraction of fennel seeds has been performed in two step s; the first step was performed at 90 bar and 50 degrees C to obtain the se lective extraction of essential oil. The second one was performed at 200 ba r and 40 degrees C and allowed the extraction of vegetable oil. The experim ents were performed using the fractional separation of the extracts using t hree different CO2 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 (SE M) images of the vegetable matter, mathematical models of the two extractio n processes have been proposed. The extraction of fennel vegetable oil has been modeled using a model based on differential mass balances and on the c oncept of broken and intact cells as evidenced by SEM. Only one adjustable parameter has been used: the internal mass-transfer coefficient kt. A fairl y good fitting of the experimental data was obtained by setting k(t) = 8 x 10(-8) m/s. The fennel essential oil extraction process was modeled as deso rption from the vegetable matter plus a small mass-transfer resistance. The same internal mass-transfer coefficient value used for vegetable oil extra ction allowed a fairly good fitting of the essential oil extraction data.