Centrifugation in Pharmaceutical Engineering

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Presented by
Patan Basha
B Pharm (Pharmacist)

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Centrifugation
Centrifugation is a process that involves the use of the
centrifugal force for the separation of mixtures
The equipment used
for centrifugation is
called a centrifuge,
and the vessel that
spins the samples is
called a rotor

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Principle of centrifugation

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If a particle (mass = m kg) spins in a centrifuge
(radius r, m) at a velocity (v, m s-1) then the centrifugal
force (F, N) acting on the particle equals m v2/r.
The same particle experiences gravitational force
(G, Newton) = m g (where g = acceleration due to gravity)
F = m v2/r
F= centrifugal force
Centrifugal force (F)

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Centrifugal effect (C)
The centrifugal effect (C) is the ratio of these
two forces, so C = F/G, i.e. C indicates how much
greater F is than G
Centrifugal effect, C=
Force acting in radial direction
Gravitational force

7. Consider a body of mass ‘m” kg rotating in a circular path of radius “r” at a velocity of “v”
Centrifugal force =f= mv2/r
Same body is experiencing gravitational force, it can be expressed as “G= mg ,
where g = acceleration due to gravity, and m= mass
Centrifugal effect (C) = F/G
= mv2 /mgr
(v = 2 π r n )
c = (2π r n)2/ g r
= 4 π2rn2/ g
(d= r/2)
= 2 π2 d n2/ g
(g = 9.807)
C = 2.013 d n2

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Centrifugal effect, C= 2.0
 n= speed of rotation( revolution per second of centrifuge)
 d= diameter of rotation
 So we can say……….
 Centrifugal effect is dire
proportional to diameter
 Centrifugal effect is dire
proportional to (speed o

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Classification of centrifuges
There are two main types of centrifuge used to achieve
separation on an industrial scale,
(1) Filtration centrifuge: Those using perforated
baskets, which perform a filtration-type operation
(work like a spin-dryer) and
(2) Sedimentation centrifuge : Those with a solid
walled vessel, where particles sediment towards the
wall under the influence of the centrifugal force

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Perforated-basket centrifuges
(centrifugal filters)
It consists of a stainless steel perforated basket
(typically 1-2 m in diameter) lined with a filter cloth.
The basket rotates at a speed which is typically <25 s-1,
higher speeds tending to stress the basket excessively.
The product enters centrally and is thrown outwards by
centrifugal force and held against the filter cloth.
The filtrate is forced through the cloth and removed via the
liquid outlet; the solid material is retained on the cloth.
The cake can be washed if required by spraying water into
the centrifuge

11. zFig. Perforated basket centrifuge

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They are used to separate crystalline materials from the
preparation liquor,
e.g. in the preparation of aspirin, and for removing
precipitated proteins from insulin.
It can also handle concentrated slurries which might block
other filters, and gives a product with a very low moisture
content (typically around 2% w/w), which saves energy
during drying.
This centrifuge is operated batch wise.

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Tubular-bowl centrifuges
(centrifugal sedimenters)
the liquid overflowing from the top
The product enters at the bottom and
centrifugal force causes solids to be
deposited on the wall as it passes up
the bowl,
around 100 mm in diameter and 1 m
long, which rotates at 300-1000 s-1.
These consist of a cylindrical 'bowl',

14. Fig: Tubular-bowl centrifuge

15. This type of centrifuge can also be used to separate immiscible
liquids.
Rate of sediment can be control by controlling the inlet rate.
The uses of centrifugal sedimenters include liquid/liquid
separation,
e.g. during antibiotic manufacture and purification of fish
oils, the removal of very small particles, the removal of
solids that are Compressible and which easily block the
filter medium,
The separation of blood plasma from whole blood (need C
=3000),
The separation of different particle size fractions, and
examining the stability of emulsions

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Within the bowl, a screw conveyor is placed which rotate in the
same direction as the bowl, but at a slightly slower speed.
It consist of a cylindrical or conical bowl mounted horizontally
and capable of rotating at 50-65 rpm.
Separation is based on difference in the densities of solid and
liquid, without a porous medium.
This is a sedimentation centrifuge.
Continuous centrifuge

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