D Pharmacy First Year

1. Clarification &
Filteration
Mr. G.A.Shete

2.  Filtration :
 It is process of removal of solids or suspended matter in a liquid or gas by
passing through a porous medium in which solids are retained.
 Clarification :
 It is process of removal of solid in very less concentration from liquid,
concentration of solid is less than1%
 Theory of Filtration:
 The factors affecting rate of filtration were studies by a scientist named Darcy
& he expressed it in the form of equation, which is known as Darcy's law.
 The equation is: V=KA∆P
 ƞl

3. Sr no Filtration Clarification
1 It is process of removal of solids or
suspended matter in a liquid or gas by
passing through a porous medium in
which solids are retained
It is process of removal of solid in very
less concentration from liquid,
concentration of solid is less than1%
2 Can be achieved by using different
filter medias
Can be achieved by doing filtration or
centrifugation
3 Filter leaf, candle, press etc can be
used
Meta filter is used in clarification of
syrups and elixirs

4.  Factors which affect the rate of filtration are:
 1. Pressure: The rate of filtration of liquid is directly proportional to the pressure
difference between the filter medium and filter cake. Thus, the rate of filtration can be
increased by applying pressure on the liquid being filtered or by decreasing the
pressure beneath the filter.
 2. Viscosity: The rate of filtration is inversely proportional to the viscosity of the liquid
undergoing filtration. Liquids which are very viscous get filtered slowly. Reduction of
viscosity of a liquid by raising the temperature is frequently done in order to accelerate
filtration.
 3. Surface area of filter media: The rate of filtration is directly proportional to the
surface area of filter media. Filter press works on this principle.
 4. Temperature of liquid to be filtered: Viscosity is reduced by a rise in temperature
and filtration of viscous oils, syrups, etc. is often accelerated by filtering them while
they are still hot.

5.  5. Particle size: The rate of filtration is directly proportional to the particle
size of the solid to be removed. It is easier to filter a liquid having coarse
particles than that having finely divided particles.
 6. Pore size of filter media: The rate of filtration is directly proportional to
the pore size of filter media.
 7. Thickness of cake: The rate of filtration is inversely proportional to the
thickness of the filter cake formed during filtration. As the filtration process
proceeds, thickness of cake increases which decreases the rate of filtration.

6.  Filter Media:
 The surface upon which solids are retained in the process of filtration is
known as Filter media/medium.
 List of different filter media:
i) Filter paper
ii) Cotton wool
iii)Glass wool
iv) Asbestos
v) Fine muslin
vi) Filter cloth
vii) Membrane filters
viii) Sintered glass filters.

7.  Filter Aids:
 These are substances which reduces the resistance of the filtrate to flow. These
are added to the preparation in concentration from 0.1 to 0.5 % before
filtration.
 Ideal qualities of filter aid:
 It should remain suspended in the liquid.
 It should be free from impurities.
 It should be inert.
 It should have a particle size distribution suitable for retention of solid.
 It should have structure that permits formation of porous cake.
 Examples : Diatomite, Perlite, Asbestos, Cellulose, Activated Charcoal,
talc & Kaolin

8.  Filter Press:
 It consists of alternative plate and frame mounted on two parallel support bars. The
pressure can be applied through screw thread so that the plate and frame are rigidly
fixed between two end plates. The frame is open and is used as an inlet for material
to be filtered. Plates has grooved surface which give support to the filter cloth. The
plate and frame are made of non-corrosive material. Filter cloth is placed at each side
of the plate. Each plates acts as single filtration unit and outlet is connected to
common outlet for plate.
 Working:
 The slurry is pumped in under positive pressure up to 20 bar and fill each frame. The
filtrate passes through the cloths on opposite sides of the frame and runs down
between the studs on the plate surface. There is an outlet cock in the bottom right
hand corner of the frame allowing the filtrate to discharge in to channel. The solid in
the slurry build up to form cake in each frame which will eventually meet in the
center of the frame.

9. When the process is stopped, the frame is emptied and cycle is restarted. Thickness
of cake can be varied by using frame of different thickness.

10.  Advantages :
 The filtering media can be used repeatedly.
 Operation & maintenance is simple.
 It requires less space.
 It provides a large surface area for filtration.
 Efficient washing of cake is possible.
 Disadvantages :
 It is not a continuous process.
 It is used where the proportion of solid in the liquid to be filtered is about 5% or
less.
 The process becomes costlier because a lot of labour is required for washing &
replacement of the filter cloth.
 Leakage between the plates may take place through faulty assembly.

11.  Meta Filter:
 Construction:
 It consists of grooved, drainage rod on which a number of metallic ring are
packed. The rings are usually of stainless steel and have 0.8 mm outer
thickness, 15 mm inside diameter & 22 mm outer diameter. The rings have a
number of semicircular projections on one surface and when they are packed on
the rod, the opening between the rings about 0.2 mm.
 Working:
 The entire assembly is placed inside a pressure vessel, containing the liquid to
be filtered. When vacuum is applied liquid will flow from outside to inside. In
this form a Metafilter can only be used as strainer for coarse particle, but for
separation of fine particle a bed of suitable material kieselguhr is used. In this
way pack of ring act as a base on which the fine filtration medium is supported

12. Fig: Meta Filter
Uses:
It is mostly used for clarification of syrups, elixirs & parenteral solutions.

13.  Filter Leaf:
 It consists of metal frame enclosing a wire screen or a grooved plate. The
screen is covered by filter cloth which is fitted in frame, to grip the cloth.
The frame may be square, rectangle or circular in shape & outlet is
connected to vacuum.
 Working of Filter leaf:
 The filter leaf is placed in a vessel containing slurry. When vacuum is
applied, the liquid flows inside the filter through filter cloth, leaving behind
the cake on the surface of cloth. The cake can be washed by immersing in a
vessel containing water or reverse flow of air

14. Fig: Filter Leaf

15.  Filter Candle
 Construction:
 These are cylindrical candles with an opening, The opening is connected to
vacuum pump for reducing pressure under it, during filtration process. The
candles are made up of porcelain or Kieselguhr.
 Working :-
 The candle is placed in the solution be filtered. When vacuum is applied, the
liquid will pass through the thick wall of the candle & gets collected inside the
candle from where it is removed. It gets blocked by continuous use. This can be
cleaned by scratching the external surface with a nail brush & passing water
through it in the reverse direction.
 Use:
 These candles are used for sterilization of solutions.

16. Fig: Filter Candle
Disadvantage:
It has tendency to absorb materials from aqueous solutions, therefore, it is not
used commonly.

17. Thank You