Extraction of Essential Oils and Cuticular Waxes with Compressed CO2: Effect of Extraction Pressure and Temperature

The extraction of essential oils from an aromatic herb using compressed CO 2 as the solvent was studied. Oregano ( Origanum virens L.) bracts were used as the herbaceous matrix. The effect of the extraction pressure and temperature on the extraction of essential oils and other co-extracted components (cuticular waxes) by compressed CO 2 was investigated. Pressure and temperature were varied from 50 to 300 bar and 300 to 320 K, respectively, covering within these ranges gas, liquid, and supercritical carbon dioxide. Moderate conditions, with solvent densities between 0.3 and 0.5 kg·m -3, were found to be sufficient for efficient extraction of essential oils. The use of more severe conditions (high pressures and temperature), despite slight advantages for the rate and yields of essential oils extraction, led to significant co-extraction of waxes and, consequently, to extracts with lower essential oil content. For CO 2 densities below 0.25 kg·m -3, selective extraction of individual essential oils was observed. At these low-density conditions, the lighter and more volatile hydrocarbons were preferentially extracted.