Definition Mechanism of Filtration Types of Filtration Theories of Filtration Factors influencing filtration Classification of Filtration

1. FILTRATION
PRESENTED BY- MS.HEERA VINAYAK KAREMORE
ASSISTANT PROFESSOR
M.PHARM (PHARMACEUTICAL CHEMISTRY)
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2. Contents:
1. Definition
2. Mechanism of filtration
3. Types of filtration
4. Theories of filtration
5. Factors influencing filtration
6. Classification of filtration
Pressure filtration – 1) plate and frame filter press
2) Meta filter
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3. Definition
Filtration
It may be define as a process of
separation of solids from a fluid by
passing the same through a porous
medium that retains the solids but
allows the fluid to pass through.
Clarification
When solid are present in very low
concentration i.e. not exceeding 1.0%
w/v, the process of its separation from
liquid is called clarification.
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4. Terms used in Filtration
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5. Mechanism of Filtration
Straining Impingement Entanglement Attractive Forces
Similar to sieving
i.e. particles of
larger size can’t
pass through
smaller pore size of
filter medium.
Solids having the
momentum move
along the path of
streaming flow and
strike (impinge) the
filter medium. Thus
the solids are
retained on the filter
medium.
Particles become
entwined (entangled)
in the masses of
fibers (of cloths with
fine hairy surface or
porous felt) due to
smaller size of
particles than the
pore size. Thus
solids are retained
within fiber medium.
Solids are retained
on the filter
medium as a result
of attractive force
between particles
and filter medium,
as in case of
electrostatic
filtration.
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6. Types of Filtration
Surface/screen filtration
It is a screening action by which
pores or holes of medium prevent
the passage of solids
Mechanism involved: straining and
impingement
For this, plates with holes or woven
sieves are used
Efficacy is defined in terms of
mean or maximum pore size
Depth filtration
In this slurry penetrates to a point
where the diameter of solid
particles is greater than that of the
tortuous void or channel
Mechanism: Entanglement
The solids are retained with a
gradient density structure by
physical restriction or by
adsorption properties or medium
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7. Theories of Filtration
 The flow of liquid through a filter follows the basic rules that govern the
flow of any liquid through the medium offering resistance
 The rate of flow may be expressed as-
Rate= driving force/resistance
 The rate of filtration may be expressed as volume(liters) per unit time(dv/dt)
 Driving force=pressure upstream – pressure downstream
 Resistance is not constant
 It is increase with an increase in the deposition of solids on the filter medium
 Therefore filtration is not a steady state
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8.  The rate of flow will be greatest at the beginning of filtration process, since
the resistance is minimum
 After forming of filter cake, its surface acts as filter medium and solids
continuously deposit adding to thickness of the cake
Powder or granule bed visualized as a bundle of capillaries
Upstream pressure, P1
Surface area
Length (L)
Downstream
pressure, P2
Viscosity flow
rate: m3/unit time
Fig.: Filtration process parameters
Resistance to flow is related to several factors given in fig.
Resistance to movement=(pressure upstream – pressure downstream)/length of capillaries 8

9. Poiseullie’s Equation
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10. Darcy’s Equation
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11.  Permeability may be defined quantitatively as the flow rate of a liquid of unit
viscosity across a unit area of cake having unit thickness under a pressure gradient
of unity
 This equation is valid for liquids flowing through sand, glass beds and various
porous media
 This model is applied to filter beds or cakes and other types of depth filter
 This equation is further modified by including characteristics of K by Kozeny-
Carman
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12. Kozeny-Carman (K-C) Equation
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13. Factors influencing filtration
Properties of solid Temperature
Objectives
Properties of solids in
slurry
Properties of liquids
• Particle shape
• Particle size
• Particle charge
• Density
• Particle size
distribution
• Rigidity or
compressibility
of solids under
pressure
• Tendency of
particle to
flocculate or
adhere together
• Density
• Viscosity
• Corrosiveness
• Rate of
formation of
filter cake
especially in
early stages of
filtration
• Whether the
solids or
liquid or both
are to be
collected
• Temperature
of suspension
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15. Pressure Filtration
Pressure filters can apply a large pressure differential across the septum to give
economically rapid filtration with viscous liquids or fine solids.
Due to the formation of cakes of low permeability, many types of slurry require higher
pressure difference for effective filtration than can be applied by vacuum techniques.
Pressure filters are used for such operations.
However, high operational pressures, may prohibit continuous operation because of
the difficulty of discharging the cake while the filter is under pressure.
Example is plate and frame filter press, meta filter, etc.
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16. Principle:
According to Kozeny-Carman equation, rate of filtration is directly
proportional to the overall pressure drop across filter medium and filter
cake.
The most common method of obtaining a pressure difference is applying
pressure on the surface of the slurry i.e. pumping the slurry onto the filter.
However, in the early stages of filtration, pressure difference should be
less.
This is to prevent the pores of the filter medium from clogging or
plugging, which subsequently increases resistance to the flow.
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17. Advantages
1. Cakes are obtained with very low moisture content.
2. Cakes may be disposed and flattened in layers provided they are not thixotropic and
sufficiently stable to support a tractor.
3. Intensive soluble recovery or removal of contaminants from the cake may be
achieved.
4. Clean filtrates may be produced by recirculating the filtrate for 1-2 minutes or by
precoating if a clear filtrate is required right from the start.
5. Solutions may be polished to a high degree of clarity.
6. The filter bodies and internals may be constructed from a wide variety of alloys
including synthetic materials for filter presses.
7. Pressure Filters are available in a wide level of automation from labor intensive
operator controlled up to fully automatic machines.
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18. Disadvantages
1. Cloth washing is difficult and if the solids are sticky a 3 mm precoat
from diatomite or perlite is required. - This adds another step prior to
filtration and if not done carefully and a too thin precoat is formed it
may leave areas with exposed cloth which will blind rapidly.
Conversely, if a too thick precoat is formed since the operator seeks
to be on the safe side, such a precoat consumes effective cake
volume.
2. The operator can hardly see the forming cake and is unable to carry
out an inspection while the filter is in operation.
3. The internals are difficult to clean and this may be a problem with
food grade applications.
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19. 1. Plate and Frame Filter Press
A filter press contains a set of plates designed to provide a series of chambers or
compartments in which solids may collect. The plates are covered with a filter medium
such as canvas. Slurry is admitted to each compartment under pressure; liquor passes
through the canvas and out a discharge pipe, leaving a wet cake of solids behind.
Construction
• Consist of plates and frames assembled alternately with a filter cloth over each side
of the plates
• The plates have channels cut in them so that clear filtrate liquid can drain down
along each plate
• The feed slurry is pumped into the press and flows through the duct into each of the
open frames so that slurry fills the frames
• The filtrate flows through the filter cloth and the solids build up as a cake on the
frame side of the cloth
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20. • The filtrate flows between the filter cloth and the face of the plate though the channels of the
outlet
• The filtration proceeds until the frames are completely filled with solids
Fig. Filter press. Assembly of plates and frame 20

21. Working :
 The slurry enters the frame
from the feed channel
The filtrate passes through the
filter medium on to the surface of
the plate while the solids form a
filter cake in the frame.
The filtrate then drained down
the surface of the plate , between
the projections on the surface and
escapes from the outlet.
Filtration is continued until the
frame is filled with filter cake,
when the process is stopped , the
frame emptied, and the cycle re-
started.
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22. Advantages &disadvantages
Advantages:
1. Construction is very simple and a wide variety of materials can be used.
2. It provides a large filtering area in a relatively small floor space.
3. It is versatile, the capacity being variable according to the thickness of the frames
and the number used.
4. The construction permits the use of considerable pressure difference.
5. Efficient washing of the cake is possible.
6. Operation and maintenance is straightforward , because there no moving parts,
filter cloths are easily renewable and, because all joints are external, any leaks are
visible and do not contaminate the filtrate.
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23. Disadvantages:
1. It is a batch filter, so it is a time consuming.
2. The filter press is an expensive filter, the emptying time, the labor
involved, and the wear and tear on the cloths resulting in high costs.
3. Operation is critical, as the frames should be full, otherwise washing is
inefficient and the cake is difficult to remove.
4. The filter press is used only for slurries containing less about 5 %
solids
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Principal-
• Mechanism is surface filtration
• In this , metal rings contain semicircular projection,
which are arranged as a nest to form channel on the
edges.
• This channel offers resistance (strainer) to the flow
of solids (course particals).
• The clear liquid is collected into receiver from the
top.
Meta filter

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Construction-
• Meta filter consist of a series of metal rings.
• These are threaded so that a channel is formed on the edges.
• It contains agrooved drainage column on which a series of metal rings
are packed.
• These rings are usually made up of stainless steel and have dimensions of
about 15.0mm internal diameter and 22.0mm external diameter.
• Each metal ring has a number of semicircular projection (0.8 mm in
thickness) on the side of surface.
• The projections are arranged as a next to form channel on the edges.
• These rings are tightened on the drainage column with a nut.
• Meta filter are know as edge filter.

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Uses-
• Perticularly useful for preparation of perticulate free solutions for
parenteral and opthalmic uses.
Working-

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Advantages-
• The rotary filter is automatic and is continues in operations , so that the
labour cost are very low.
• The filter has large capacity,so it is suitable for the filtration of highly
concentrated solutions.
• Variation of the speed of rotation enable the cake thickness to be
controlled.
• Pre coat of filter aid couled used to accelerate the filtration rate.
• Filter has large surface area.

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