Pharmaceutical engineering (SEM-3) UNIT 4-2

UNIT 4-2
Ms. Payal Pilaji
Assistant Professor

 Centrifugation is a process which involves the use of the centrifugal force
for the sedimentation of heterogeneous mixtures with a centrifuge, used in
industry and in laboratory settings.
 This process is used to separate two immiscible liquids.
 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.
 Centrifuge is a device for separating particles from a solution according to
there size, shape, density, viscosity of the medium1.

Theory of centrifugation
 The centrifuge works on sedimentation. Spinning sample at a high speed.
 The component of a mixture is subjected to centrifugal force.
 Dense particle migrate away from axis of rotation and lighter ones towards it.
 Relative Centrifugal Force (RCF)
 RCF is the ratio of the centrifugal acceleration at a specified radius and the speed to the standard acceleration of
gravity.
 Relative Centrifugal force is defined as f=Mω2 r
Where,
 F= intensity of centrifugal force M= mass of particle ω= angular velocity of rotation
 R= distance of migrating particles from central axis of rotation.
 The RCF value for any centrifuge may be calculated from the following equation:
 RCF = 1.18 × r × (rpm) 2 ×10-5

CLASSIFICATION OF CENTRIFUGES
Sedimentation centrifuge
 It is a centrifuge that produces sedimentation of solids based on the
difference in the densities of two or more phases of the mixture
Filtration centrifuge
 It is a centrifuge in which solids pass through the porous medium based
on the difference in the densities of the solid and liquid phases

Principle:
Perforated basket (bowl) centrifuge is a filtration
centrifuge.
 The separation is through a perforated wall based
on the difference in the densities of solid and liquid
phases. The bowl contains a perforated side-wall.
 During centrifugation, the liquid phase passes
through the perforated wall, while solid phase is
retained in the bowl.
The solid is removed after cutting the sediment by
a blade after stopping the centrifuge.
PERFORATED BASKET CENTRIFUGE

Construction:
It consists of a basket, made of steel (sometimes covered with
vulcanite or lead) or copper or monel or any other suitable metal.
The basket may have a diameter of 0.90 metres and a capacity of
0.085 metre cube.
The basket is suspended on vertical shaft and is driven by a motor
using suitable power systems such as belt pulleys, water turbines and
electric motors.
Surrounding the basket, a casing stationary is provided which
collects the filtrate and discharges it at the outlet.

Working:
The material is kept in the basket when the basket is stationary.
Power is applied to rotate the basket and maximum speed must be attained quickly.
The basket runs at 1000 revolutions per minute.
During centrifugation, the liquid passes through the perforated wall, while the solid
phase retains in the basket. The liquid leaves the basket and is collected at the outlet.
The cake is then spun to dry as much as possible.
After a definite period of time, the power is turned off. By applying a brake th
centrifuge is stopped.
The basket is brought to rest.
The solid cake is cut using a blade and then unloaded manually.

NON-PERFORATED BASKET CENTRIFUGE Principle:
This is a sedimentation centrifuge.
The separation is based on the difference in the densities of solid
and liquid phases without a porous barrier.
The bowl contains a non-perforated side-wall.
During centrifugation, solid phase is retained on the sides of the
basket, while the
liquid remains at the top, which is removed by a skimming tube.

Construction:
It consists of a basket, which may be made of steel or any other suitable metal.
The basket is suspended on vertical shaft and is driven by a motor using a suitable power
system.
Working:
The suspension is fed continuously into the basket.
During centrifugation, solid phase is retained on the sides of the basket, while liquid remains
on the top.
The liquid is removed over a weir or through a skimming tube.
When a suitable depth of solids has been deposited on the walls of the basket, the operation is
stooped.
The solids are then scraped off by hand or using a scraper blade.

SUPERCENTRIFUGE
Supercentrifuge is a continuous centrifuge used for separating two
immiscible liquid phases.
Principle:
It is a sedimentation centrifuge.
The separation is based on the difference in the densities between two
immiscible liquids.
Centrifugation is done in the bowl of small centrifuge.
During centrifugation, the heavier liquid is thrown against the wall, while
the lighter liquid remains as an inner layer.
The two layers are simultaneously separated using modified weirs.

Construction:
 It consists of a long hollow cylindrical bowl of
small diameter.
 It is suspended from a flexible spindle at the top
and guided at the bottom by loose-fit bushing.
 Two liquid outlets are provided at different
heights at the top of the bowl, for simultaneous
recovery of the separated liquids using modified
weirs

Working:
 The centrifuge is allowed to rotate on its longitudinal axis at a high frequency usually about 2000
revolutions per minute with the help of drive-assembly.
 The feed is introduced from the bottom of the centrifuge using a pressure system.
 During centrifugation, two liquid phases separate based on the difference in their densities.
 The heavier liquid is thrown against the wall, while the lighter liquid forms an inner layer. Both
liquids rise to the top of the vertical bowl.
 The liquid-liquid interface (the so-called neutral zone) is maintained by an hydraulic balance.
 These two layers are simultaneously separately removed from different heights through modified
weirs.
 Thus the supercentrifuge can work for continuous separation of immiscible liquid phases.
Uses
 It is used for separating liquid phases of emulsions in food and pharmaceuticals

Pharmaceutical engineering (SEM-3) UNIT 4-2

More Related Content

What's hot

Similar to Pharmaceutical engineering (SEM-3) UNIT 4-2

More from payalpilaji

Recently uploaded

Pharmaceutical engineering (SEM-3) UNIT 4-2