Clarification and Filtration
Clarification:-
It is defined as the removal of solids in very less
concentration and filtrate is the required product.
Filtration:-
• Filtration is defined as the removal of solid particles or
suspended matter from the liquid or gas by passing it through a porous medium
which retains the solid particles but allows the fluid to pass is known as
Filtration.
Or
• Filtration may be defined as the separation of
intracellular liquid from solid by the use of pressure on semi permeable
membrane.
• The pores medium used to retain the solids is known as
filter media. The solids which get collected on the filter is called filter
cake. The spear liquid passing through the filter is known as filterate.
Theory of filtration.
• The theory of integration give an idea about the factor
influence the rate of interaction through the filtering media rather than the
mechanism by which the particles in retained.
• The factor affecting the rate of filtration where is
studies by a scientist name darey and he expressed it in he from of an equation
which is known as “Darcy’s Low” The equation is
This is also known as Darcy’s Law where
V = Volume of filtrate
t = Time of filtrations
dV/dt= Rate of change of volume with time or flow rate with
time k = Constants for the filter medium and filter cake
A = Area of filter medium
ΔP = Pressure difference above the filter medium and below
the filter medium
µ = Viscosity of the filtrate
l = Thickness of the filter cake & filter medium.
The above equation makes it clear that the rate of
filtration depend not only on the nature of liquid undergoing filtration but
also on so many other factors.
Factor affecting the
rate of filtration:
1. Pressure: –
The rate of filtration is directly proportional to the pressure difference
between the filter medium and filter cake.
2. Viscosity: The
rate of filtration is inversely proportional to the viscosity of the liquid
undergoing Filtration.
3. Surface area of
filter medium: The rate of filtration is directly proportional to the
surface area of filter media.
4. Temperature liquid to filtered
5. Particle size
6. Pore size of filter media
7. Thickness of cake
8. Nature of solid material.
Filter Medium:-
The surface of medium used for filtration for the separation
the solid particles from a liquid or gas is known as filter medium.
Ideal properties of
filter media
• It should not
absorb amount of the ingredients of the product to be filtered.
• It should be
chemically inert.
• It should good
power to retain the solid particles.
• It should give
a free passage to the liquid.
Some Filter media
used in Laboratories:
1. Filter Paper:
It is used as filter medium For small scale filtration. They are available in
different size of pores like Coarse, fine.
2. Filter cloth:
cotton clothes & synthetic clothes are commonly used as filter medium for
largest scale filtrations. Synthetic clothes are preferred over cotton clothes
because synthetic cloth has less absorbing properties.
3. Glass Wool: It
is used for filtering corrosive chemicals such as strong alkalies, strong
oxidizing agent etc. Glass wool consists of fine fibers of glass. It is used to
remove the coarse particles from strong acids, strong alkalies, etc.
4. Asbestos: It
is also used for filtering the corrosive liquids.
5. Cotton Wool:
Cotton wool is commonly used as filter media for coarse particles.
Filter Aids:
Filter aids are substances which increase the rate of
filtration by reducing the resistance of the filtrate and added externally to
the process of filtration.
Ideal properties of
Filter Aids
1. It should be chemically inert.
2. It should be free from impurities.
3. It should be insoluble in the liquid to be filtered.
4. It should form a porous cake.
5. It should be readily recoverable from liquid.
Filter Press:
The plate and frame press is widely used for filtrations in
pharmaceutical industries.
Construction of
Filter Press:
• It consists of plates and frames. Plates have grooved
surface to support the filter cloth and a free passage to the filtrate. The
frames are open with an inlet for the liquid to be filtered.
• Filter cloth is fixed on each side of the plate.
• The plates and frames are placed alternatively and
filtered in an outer frame of the press. Each plate works as a filtration unit.
The outlet of each plate is attached to a common outlet pipe.
Working of Filter
Press:
The liquid to be filtered is allowed to enter the frame
under pressure. The filtrate Presses through filter medium on to the surface of
the plate. The filtrate is collected in the plates. The cake is deposited in
the frames. The process of filtration is continued until the frame is filled
with filter cake. Thickness of filter cake depends on the solid contents
present in the filtering liquid.
Advantage of Filter
Press:
1. It requires less space
2. Filter medium can be used repeatedly.
3. Operation & handling easy
4. Filter medium can be used repeatedly.
Disadvantage of
Filter Press:
1. It is a batch process.
2. It is suitable only for those products which contain
about 5% or less solids.
3. The filter press is quite costly and labour cost involved
in replacement of Filter cloth and washing.
Sintered filter:
It sintered glass filters. The filter medium is made up of
glass particles. The fusion is done by heating the glass particles to a
temperature at which different particles adhere together without melting.
Sintered glass filters are designed primarily for vacuum
filtration and are available in different pore sizes.
The porosity of the filter depends on the size of granules
used in its preparation
Example:
Grade No | Pore Size | Use |
1. | 90-150 | Coarse material |
3. | 15-40 | Filtrations of fine ppt. |
5. | Upto 2 microns | Bacterial filtration. |
Sintered glass filters should be washed with hot HCL or HNO3
and then rinsed thoroughly with water.
Filter candles:-
• Filter candle for ceramic fiber or sintered ceramics.
• They are made up of porcelain or Kieselguhr.
• Kieselguhr candle are more permeable than porcelain
candles.
• One side of the candle is closed and the other side has an
opening which is connected to vacuum pump for reducing the pressure under it
during the filtration process.
• The candle is placed in the solution to be filtered and
the vacuum is applied.
• The filtration takes place from outside to inner side from
where it is removed when candle is filled.
• The inter candle get blocked with continuous use the
candle is washed by passing water in the opposite direction from inner side to
outer side This candles are used for sterilisation of solution.
Meta filters:-
• America filter consists of grooved drainage rod on which a
metal ring made from stainless steel are packed.
• These rings have a thickness of 0.8 mm, 15mm inside
diameter and 22 mm outer diameter.
• These rings are packed on the rod. The opening between the
rings vary from 25 μm.
• The filtration is carried out by applying vacuum.
• The filter is placed in the slurry to be filtered and the
filtration takes place from outside to inner side.
• These filters may filtration takes place with a steam
jacket for the filtration of very viscous liquids such as Syrups or Oily
Substances.
Uses of Metafilters:
• It is used for filtration of coarse particles.
• It is used as a Strainer.
