Drying
Drying:
Drying generally refers to the removal of a liquid from a solid by evaporation.
So it is defined as the removal of a liquid from a solid material by the
application of heat and is accomplished by the transfer of a liquid from a
surface into an unsaturated vapor phase.
The
necessary heat of vaporization is provided by—
a.
Conduction from
a solid surface
b.
Convection from
a hot gas or
c.
Radiation from a
source.
In
general, drying of a solid means the removal of relatively small amount of
water or liquid from the solid material to reduce the content of residual fluid
to an acceptable low value.
Water
or other liquids can be removed mechanically from the solid by non-thermal
processes such as extraction, expression, desiccation, absorption, adsorption
etc. or thermally by vaporization. But mechanical methods are not generally
considered drying; only the thermal processes are called drying.
So,
drying is a process of removing of liquid or liquids from a mixture of
solid-liquid matrix by evaporation usually by the application of heat.
Freeze-drying— no heat is applied.
Purpose of drying: Drying
is necessary for the following purposes:
1. Drying
is most commonly used in pharmaceutical manufacturing as a unit process in the preparation of granules, which can be dispensed in bulk or converted into
tablets or capsules.
2. It is also used
in the processing of materials e.g. the preparation of dried Al (OH)3,
the spray drying of lactose and the preparation of powdered extracts.
3. It can be used
to reduce bulk and weight, thereby lowering the cost of transportation and
storage.
4.
It aids in the
preservation of animal and vegetable drugs by minimizing mold and bacterial
growth in moisture-laden materials.
5. Drying reduces
the chance of degradation by hydrolysis or oxidation; e.g., presence of
moisture causes instability of dried syrups.
Drying
Reviewed by M H Islam
on
5:21 PM
Rating:
Reviewed by M H Islam
on
5:21 PM
Rating:
