Essential Oils Conventional Recovery Methods

According to ISO and AFNOR standards, essential oils are defined as products obtained from raw plant material which must be isolated by physical means only. The physical methods used are distillation (steam, steam-water and water), expression (also known as cold pressing for citrus peel oils), or dry distillation of natural materials. After distillation, the essential oil is physically separated from the aqueous phase (Fig. 22.1) [20-22]. 

Historically three types of distillation have been used water distillation, water-steam distillation, and steam distillation. Water distillation is sometimes referred to as indirect steam distillation. In this method, plant material is soaked in water 

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One of the first methods using microwave-assisted extraction of essential oil was presented in 1989 by Craveiro [44]. The essential oil of Lippia sidoides was extracted using microwave energy and compressed air only. Inspired by classical steam distillation, the CAMD technique used compressed air instead of vapor to extract the volatile oil. Typically, plant material is placed in a reactor inside the microwave cavity and heated. At the same time, a compressor, located outside the cavity, forces compressed air into the reactor. Volatile oil and vapor are then driven to the recovery flask outside the cavity. In 5 min CAMD provides an essential oil which is qualitatively and quantitatively identical with that produced by the conventional hydrodistillation method. 

Extraction recovery can be limited by one step or several steps. Microwaves cause more damage and destroy the essential oil cells in leaves or seeds more rapidly and effectively than conventional extraction methods, thus the desorption step, which can often be the limiting factor, is of minor importance in SEME. Solubility is rarely the limiting factor in solvent extraction if the solvent is well chosen. In the distillation of essential oils the solvent is always water, however, and aroma compounds can be totally different in structure and chemical characteristics, especially in their solubility. 

The recovery of oil from reservoir involves the flow of fluid through pores under a given temperature and pressure. However, it is known that high pressure alone sometimes does not help in the flow of oil (oil recovery) due to various chemicophysical forces. In these reservoirs, there are various specific surface forces (besides other forces), which are important for the oil recovery. In order to recover the vast amounts of residual oil in reservoirs, over the past decade enhanced oil recovery (EOR) methods are being applied. The conventional oil reservoirs during the past decades are now being subjected to EOR and with very positive results. The application of surface and colloid chemistry principles has been applied in EOR. In very simple terms, one can further describe the essential surface forces involved in EOR ... 

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