Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
solute. In the medicinal plant industry, generally ball mills and fl uid mills are
employed for powdering, and the optimum particle size is established prior
to the large-scale extraction.
5.3.3 Choice of Solvent
The following factors should be considered when selecting a
solvent for commercial use:
• Solvent power (selectivity). Only the active, desired constituents
should be extracted from the plant material, which
means that a high selectivity is required.
• Boiling temperature. The boiling point of the solvent is as
low as possible in order to facilitate removal of the solvent
from the product.
• Reactivity. The solvent should not react chemically with the
extract, nor should it readily decompose.
• Viscosity. A low viscosity of the solvent leads to low pressure
drop and good heat and mass transfer.
• Safety. The solvent should be non-fl ammable and non-corrosive,
and should not present a toxic hazard; its disposal
should not imperil the environment.
• Cost. The solvent should be readily available at low cost.
• Vapor pressure. To prevent loss of solvent by evaporation, a
low vapor pressure at operating temperature is required.
• Recovery. The solvent has to be separated easily from the
extract to produce a solvent-free extract.
5.3.4 Conditions for Extraction
Too fi ne particle size may result in problems with packing of
solids for extraction, preventing free fl ow of solvent through the solid bed. In
such a case, extraction is more diffi cult, especially when fi nely divided solids
are treated in an un-agitated state. Dispersion of the particles in liquid
solvent by agitation facilitates contact of the solid with the solvent. Agitation,
while giving good extraction, may cause suspension of fine particles in
overfl owing solution.
5.4 Method of Solid-liquid Extraction
are:
The three principle types of fl ow used in leaching systems
1. Single-stage system
2. Multistage counter-current system
3. Multistage co-current system
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