Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

7 DISTILLATION TECHNOLOGY FOR ESSENTIAL OILS
a) As the plant material near the bottom of the still comes in
direct contact with the fi re from the furnace, it may char and
thus impart an objectionable odor to the essential oil.
b) The prolonged action of hot water can cause hydrolysis of
some constituents of the essential oil, such as esters.
c) Heat control is diffi cult, which may lead to variable rates of
distillation.
d) The process is slow and distillation times are much longer
than those of steam distillation.
7.3.2 Water and Steam Distillation
To eliminate some of the drawbacks of water distillation, some
modifi cations were made to the distillation units. A perforated grid was introduced
in the still, to support the plant material and to avoid its direct contact
with the hot furnace bottom. When the water level is kept below the grid, the
essential oil is distilled by the rising steam from the boiling water. This mode
of distillation is generally termed water and steam distillation.
The fi eld distillation unit (FDU), also known as a directly fi redtype
distillation unit, is designed according to the principle of water and
steam distillation. The FDU consists of a still or tank made of mild stainless
steel with a perforated grid and is fi tted directly to a brick furnace. A chimney
is connected to the furnace to minimize the pollution at the workplace and
also to induce proper fi ring and draft. The plant material is loaded on the
perforated grid of the tank and water is fi lled below it. The tank is connected
to the condenser through a vapor line. The water is boiled and the steam
vapors pass through the herb, vaporize the oil and get condensed, mostly in
a coil condenser by cooling water. The condensate (oil-vapor mixture) is then
separated in the oil separator.
These units are simple to fabricate and can be installed in the
farmer’s fi eld. Due to their simple construction, low cost and easy operation,
FDUs are extremely popular with essential oil producers in developing
countries. The furnace is always fueled by locally available fi rewood or straw.
This makes the unit suited for use in remote areas where the raw material
is available. This also helps in reducing transportation costs in the production
of essential oils. FDUs are currently fi nding application in distillation of
patchouli oil in Indonesia, aromatic grass and mint oil in India, citronella oil
in Taiwan and many more all over the world. A local FDU currently being used
by rural farmers in India for the distillation of mint oils is shown in Figure 2.
Such fi eld units generally can hold 100-2000 kg plant material. Total time
for distillation with these units is about 6-8 h.
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