Miscellaneous Process
By: Dr. Tahseen Ismail
Spray Drying
Spray drying is one of the methods of desiccation by which
solutions or slurries are dried.
 The apparatus used for this purpose is known as spray drier.
These driers consist of a hot air chamber into which liquid to
be dried is fed from the top and hot air is supplied from the
base.
 The spraying of the liquid is done either by pressure jets. By
the high current of hot air the liquid is sprayed
in the form of a mist, the droplets of which are readily
evaporated and the dried particles fall to the bottom of the
chamber from where they are collected.
 The exhausted air leaves the chamber through the air outlet.
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Different types of spray driers are available with
various modifications. In some forms of spray
driers the liquid to be dried and hot air enters
from the top of the chamber and in others from
the bottom. Still in other types liquid is fed from
the top and hot air from the bottom
Applications
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1. These driers are very useful because the drying is
very rapid as large surface of liquid is exposed to hot air
and temperature required for drying is also low.
Therefore heat sensitive products can be dried
conveniently.
2. Spray drying is used for drying blood plasma, milk
and enzyme preparations such as pancreatin and
pepsin.
3. Spray driers can be designed for drying under sterile
conditions.
4. Solid and liquid particles can be encapsulated by
employing spray drying.
Levigation
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The process of levigations is also known as wet
grinding. In this method the particle size of a
substance is reduced to fine state of subdivision
by triturating the substance with a few drops of
liquids to which it is insoluble, in a glass mortar
with the pestle or on a slab with spatula .The
most commonly used levigating agents includes
are oils, water, alcohols and glycerin.
Uses of levigation
Can be use to incorporate solid substances into:
 dermatological preparations
ophthalmic ointments.
suspensions
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Pulverization by Intervention
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This is a process by which the solid substances are
reduced to a fine powder by mean of triturating the
solid using suitable solvent which can bee easily
removed by the end of process.
Camphor is triturated with few drop of alcohols, ether
or chloroform it can be powdered easily. The solvent
added evaporate quickly leaving behind fine subdivided particles of camphor.
Similarly iodine crystals may be powdered with the
help of small quantiy of ether.
Elutriation:
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Definition: “Elutriation is the process in which the particles
of the fluid move in a direction opposite to that of the
sedimentation. (Downward movement)”
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Explanation: In gravitational sedimentation the particles will
move vertically downward while the fluid travels vertically
upward.
If the velocity of the fluid is less then the setting velocity of
the particles, then the particles will move downward against
the stream of fluid. If the setting velocity of particles is less
then the velocity fluid, the particles will move upward.
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In other words small size particles will move upward
while the large size particles will move downward.
So Elutriation is the process of separation of fine
particles from course particles. The particles size can
also be measured by this process.
Apparatus used for Elutriation
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The apparatus used for Elutriation process is
called as Elutriator.
They are of two types:
Gravitational Elutriation
Centrifugal Elutriation
Gravitational Elutriation
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1- Gravitational Elutriation:
In gravitational Elutriation the fluid particles move
downward due to sedimentation (force of gravity)
while the lighter particles remain upward.
Centrifugal Elutriation:
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Centrifugal Elutriation causes the fluid stream to
rotate under high centrifugal force to suspend the
particles. These particles which are too large to rotate
with direction of flow of fluid, separates out on the
wall of the elutriator. However the fine particles move
easily with the stream of fluid.
Uses of Elutriation
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Heavy and light Kaolin can be separated by this
process, because the particles of heavy Kaolin move
downward and those of the light Kaolin move
upward.
DECANTATION
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Decantation is a process for the separation of mixtures.
Method:
Method consists of allowing the slurry to stand in a suitable
vessel until the solids either settle down at the bottom. Now
carefully pouring a solution from a container in order to leave
the precipitate (sediment) in the bottom of the original container.
Usually a small amount of solution must be left in the container,
and care must be taken to prevent a small amount of precipitate
from flowing with the solution out of the container. It is
generally used to separate a liquid from an insoluble solid (e.g. in
red wine, where the wine is decanted from the potassium bi
tartrate crystals).
Separation of liquid from any other
immiscible liquid can also be done by
decantation .For example,
 the oil and water extracted from olives
may be decanted to obtain the olive oil.
 A mixture of kerosene and water can also
be separated through decantation
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CENTRIFUGATION
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Centrifugation is a process that involves the use of the
centrifugal force for the separation of mixtures, used in industry
and in laboratory settings.
More-dense components of the mixture migrate away from the
axis of the centrifuge, while less-dense components of the
mixture migrate towards the axis.
The effective gravitational force on a test tube may be increased
so as to more rapidly and completely cause the precipitate
("pellet") to gather on the bottom of the tube. The remaining
solution is properly called the "supernate" or "supernatant
liquid".
The supernatant liquid is then either quickly decanted from the
tube without disturbing the precipitate, or withdrawn with a
Pasteur pipette.
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The rate of centrifugation is specified by the
acceleration applied to the sample, typically measured in
revolutions per minute (RPM).
The particles' settling velocity in centrifugation is a
function of their
size and shape,
centrifugal acceleration,
the volume fraction of solids present,
the density difference between the particle and the
liquid,
viscosity.
VAPORIZATION
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Vaporization of an element or compound is a phase transition from the
liquid or solid phase to gas phase.
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There are three types of vaporization:
evaporation,
boiling and
sublimation.
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Evaporation is a phase transition from the liquid phase to gas phase that
occurs at temperatures below the boiling temperature at a given pressure.
Note: evaporation usually occurs on the surface.
Boiling is a phase transition from the liquid phase to gas phase that occurs at
or above the temperature the boiling temperature.
Note: boiling occurs below the surface.