Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
temperature of the chamber and by varying the pressure of the pump. The
dry powder is mixed with suitable diluents or excipients and blended in a
double cone mixer to obtain a homogeneous powder that can be straightaway
used, for example, for fi lling in capsules or making tablets.
1.2.2.3 Solvent Extraction
The principle of solid-liquid extraction is that when a solid material
comes in contact with a solvent, the soluble components in the solid material
move to the solvent. Thus, solvent extraction of plant material results in the
mass transfer of soluble active principle (medicinal ingredient) to the solvent,
and this takes place in a concentration gradient. The rate of mass transfer decreases
as the concentration of active principle in the solvent increases, until
equilibrium is reached, i.e. the concentrations of active principle in the solid material
and the solvent are the same. Thereafter, there will no longer be a mass
transfer of the active principle from plant material to the solvent.
Since mass transfer of the active principle also depends on its
solubility in the solvent, heating the solvent can enhances the mass transfer.
Moreover, if the solvent in equilibrium with the plant material is replaced with
fresh solvent, the concentration gradient is changed. This gives rise to different
types of extractions: cold percolation, hot percolation and concentration.
1.2.2.3.1 Cold Percolation
The extraction of plant material is carried out in a percolator
which is a tall cylindrical vessel with a conical bottom and a built-in false
bottom with a fi lter cloth. The percolator is connected to a condenser and a
receiver for stripping solvent from the marc.
The powdered material is fed into the percolator along with a
suitable solvent (ethyl alcohol or another non-polar solvent). The material
is left in contact with the solvent until equilibrium of the active principle is
achieved. The solvent extract, known as miscella, is taken out from the bottom
discharge valve of the percolator. Fresh solvent is added into the percolator
and the miscella is drained out after acquiring equilibrium. Overall,
the plant material is washed four to fi ve times until it gets exhausted. All
washes from the percolator are pooled and concentrated.
The solvent in the marc is stripped out by passing steam from
the bottom of the percolator. The solvent and steam vapors rise and are condensed
in a tubular condenser. The condensate, which is a mixture of alcohol
and water, is collected in a receiver and then subjected to fractional distillation
to get 95% pure ethyl alcohol which is again used as a fresh solvent.
This type of percolation is not effi cient as it takes a long time
to reach equilibrium due to the slow mass transfer rate. The mass transfer
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