Essential oils from seeds: solubility of limonene in supercritical CO2 andhow it is affected by fatty oil

Fatty oil influence on the solubility of limonene in CO2 was investigated u nder pressures 8-12 MPa at 313.2 K, a temperature typically applied in supe rcritical fluid extraction of essential oils. Solubility in CO2 was measure d using the dynamic method both for limonene and for the mixture of limonen e and blackcurrant seed oil. In the whole range of pressures applied, the c oncentration of fatty oil in the vapour phase is negligible in comparison w ith the concentration of limonene. Limonene is distributed between the liqu id phase rich in fatty oil and the vapour phase rich in CO2, and its equili brium concentration in the latter decreases with the diminishing limonene-t o-oil ratio in the saturator. There is a steep increase of the limonene par tition coefficient with pressure between 8 and 10 MPa, near the critical pr essure of the binary mixture of limonene and CO2. The observed behaviour of the three-component system was confirmed and explained by thermodynamic mo delling. The thermodynamic model applied was the Soave-Redlich-Kwong cubic equation of state with either the one fluid linear van der Waals mixing rul e or with the MHV2 mixing rule. Appropriate conditions for an efficient sup ercritical fluid extraction of essential oils from seeds follow from the re sults obtained. Extraction pressure should be approx. 20% larger than the c ritical pressure of the essential oil + CO2 binary mixture and rather tight packing of the ground seed in the bed should be applied. (C) 2001 Elsevier Science B.V. All rights reserved.