Extraction of Essential Oils and Volatile Molecules

Abstract

Fundamental studies of the transfer processes in steam extraction (steam distillation) have identified a paradoxical situation in which gradients of temperature and essential oil vapor pressure are both directed towards the core, resulting in a flow in the opposite direction to that required for an extraction operation. Steam distillation is thus a front progression operation. In order to intensify essential oil (EO) extraction and improve the quality of both extract and residue, instant controlled pressure drop (DIC) treatment was defined and used as a direct extraction–texturing treatment. With DIC treatment, volatile molecules can be removed by autovaporization, followed by a total pressure gradient (Darcy-type law) which substantially reduces extraction time. Thus, the processing time of DIC-EO extraction is about 4 min compared to several hours (or even days) with hydro- or steam distillation. This is obviously linked to low heat energy consumption. The final essential oil that is extracted meets the various quality requirements in terms of the absence of thermal degradation. In addition, DIC treatment can also be used to expand the compact plant and to enhance its technological aptitude for a second operation such as drying, solvent extraction, and press extraction.