Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
7.4 Hydrodiffusion
This system was fi rst described in 1983. Unlike traditional
steam distillation, hydrodiffusion works on the diffusion principle of allowing
steam to enter the top of the plant charge and diffuse through the charge
by gravity. The process uses the principle of osmotic pressure to diffuse oil
from the oil glands. The system is connected to a steam source, and low
pressure steam is passed into the plant material from a boiler. The condenser,
which is directly under the basket within the still, is of the tube type. The
oil and water are collected below the condenser in a typical oil separator.
Hydrodiffusion is an effi cient process that is easy to use, especially regarding
the processes of loading and unloading the plant material. The yield of
oil is higher and the process is advantageous because of the reduced steam
consumption, shorter distillation time and absence of hydrolysis, as the raw
material does not come in contact with boiling water. However, because of
the downward fl ow of steam and condensate, co-extraction of other nonvolatile
compounds (such as lipids, chlorophyll and fatty acids) and polar
components makes the process complicated. Although it may seem that
hydrodiffusion is a better alternative to conventional distillation processes,
the fact remains that commercial ventures based on hydrodiffusion have not
been able to take off successfully.
7.5 Parameters Affecting Yield and Quality
of Essential Oils
The yield and quality of essential oil from steam distillation is
affected by the various process parameters. It is advisable to keep them in
mind while designing such systems. Some of the important parameters are
being listed below.
7.5.1 Mode of Distillation
The technique for distillation should be chosen considering the
boiling point of the essential oil and the nature of the herb, as the heat
content and temperature of steam can alter the distillation characteristics.
For high boiling oils such as woody oils (e.g. sandalwood, cedar wood) and
roots (e.g. Cyperus), the oil should be extracted using boiler-operated steam
distillation. Since the heat content and temperature of steam depend upon
its pressure, a change in steam pressure can alter the distillation characteristics.
High-boiling constituents of essential oils normally require highpressure
steam to distill over. For oil of rose and other fl orals, the material
is generally immersed in water, i.e. hydrodistillation, as fl owers tend to aggregate
and form lumps which cannot be distilled using water and steam
distillation or direct steam distillation.
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