Filtration is the process of separating solids from liquids by passing them through a porous medium that retains the solids but allows the liquid to pass through. There are several types of filtration equipment that operate using different mechanisms and forces like pressure, vacuum, and centrifugal force. The plate and frame filter press is a common pressure filter that operates in batches. It consists of filter plates and frames arranged alternately to form channels for slurry inlet and filtrate outlet. The slurry is filtered from the frames forming a filter cake that can also be washed during the process.

1. FILTRATION
Presented by-
Mrs. Ritu Kamboj
Assistant Professor
M Pharma (Pharmaceutices)

2. DEFINITION
Filtration:- It may be defined 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 solids are present in very low concentration, i.e.,
not exceeding 1.0% w/v, the process of its separation from liquids is
called clarification

3. Basics terms used in filtration
Feed
Filter medium
Filtrate
Slurry FILTER
MEDIUM
FILTRATE
SLURRY
FILTER
CAKE
Suspension to be filtered
Porous medium
used to retain the
solids
Accumulation
of retained solids
on filter
Clear liquid
passes through the
filter medium

4. PROCESS OF FILTTRATION
The filter medium
pore are smaller
than the particle size
to be filtered
Filter medium is
placed on a mesh
(support)
slurry is passed
over the filter
medium
Due to changes
pressure difference
across the filter then
fluid passes through
the filter medium
Gravitational
force shows on
the liquid
columns
Solids are
trapped on the
surface of filter
medium

5. Applications of filtration
 production of sterile products
 production of bulk drugs
Production of liquid of oral formulations
 Effluent and waste water treatment

6. Mechanisms of filtration
The mechanisms of filtration is based upon the particles which are retained
on filter paper during filtration . These mechanisms are:-
Impingement
Entanglement
Attractive
forces
Straining
 Similar to sieving,
Larger particles cannot passes through small pore size of
filter.
Solids having the momentum move along the path of
streamline flow and strike(impinge) the filter medium. So that
solids retain on the filter
Particles become entangled in the mass of fibers due to smaller
size of particles than pore size. thus the solids are retained on
filter medium
Due to attractive forces between particles and filter medium.
solids are retained on filter medium

7. TYPES OF FILTRATION
Surface filtration Depth filtration
Particles
Screen
Screen filter with diect
passage of the carrier
molecules.
 straining and impingement
are responsible for surface
filtration .
Depth filtration : slurry penetrates
to apoint where the diameter of
solids particles is greater than that
of the tortuous void space
Entanglement are responsible for
depth filtration

8. FACTOR AFFECTING RATE OF FILTRATION
1. Area of filter surface
2. Properties of solids and liquids
3. Proportion of solids in slurry
4. Particle size of cake solids
5. Pore size of filter media
6. The resistant of the filter cake and filter medium
7. Viscosity of liquid to be filter
8. Temperature
9. Pressure difference across the filter
10. Gravitational force
11. Centrifugal force

9. 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 (litres) per
unit time (dv/dt).
Driving force = pressure upstream – pressure downstream
Resistance is not constant.
It increases with an increase in the deposition of solids on the
filter medium.
Therefore filtration is not a steady state.

10. 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
Downstream
pressure, P2
upstream
pressure, P1
L
Surface area
Velocity Flow rate:m3/unit time
Figure: Filtration process parameters

11. THEORIES OF FILTRATION
BASED UPON THE THREE EQUIATIONS
THESE ARE:-
1. POISEULLE’S EQUATION
2. DARCY’S EQUATION
1. KOZENY CARMEN EQUATION

12. Poiseuille’s Equation
Poiseuille considered that filtration is similar to the streamline
flow of liquid under pressure through capillaries.
Poiseuille's Equation is-
Where, V = rate of flow, m3/s (l/s)
ΔP= Pressure difference across the filter, Pa
r = radius of capillary in the filter bed, m
L = thickness of filter cake (capillary length), m
𝝶 = viscosity of filtrate, Pa.s
Note:-If the cake is composed of bulky mass of particles and
the liquid flows through the interstice, then flow of liquids
through these may be expressed by this equation.

13. DARCY’s EQUATION
Poiseuille's law assumes that the capillaries found in the filter
are highly irregular and non-uniform.
The factors influencing the rate of filtration has been incorporated
into an equation by Darcy, which is:
Where, K = permeability coefficient of cake, m2
A = surface area of porous bed (filter medium)
K depends on characteristics of cake, such as porosity, specific
surface area and compressibility.

14. Kozeny-Carman equation
Kozeny-Carman equation is widely used for filtration.
Where,
𝝴 = porosity of cake (bed)
S = specific surface area of particles comprising the cake m2 / m3
K = Kozeny constant (usually taken as 5)
Other terms are same as previous equations
Limitations:
 It does not consider the fact that depth of granular bed is lesser
than the actual path traversed by the fluid.
The actual path is not same through out the bed, but it is
sinuous or tortuous.

15. Classification of filtration equipments
 based on the external force :
Filters
Pressure filters
Vacuum
filters
Centrifugal filter
Filter press Filter leaf CentrifugeMetafilter

16. Classification of filtration equipments
 based on the operation of filtration :
Filters
Continuous
filtration
Discontinuous
filtration
Discharge and filtrate are
separated steadily
Separation is uninterrupted
Discharge of filtered solids is
intermittent
 filtrate removed continuous
 operation stop
Collect solids

17. Classification of filtration equipments
 based on the nature of filtration :
Filters
Cake filters
Clarifying
filters
Cross-flow filter
Remove large
amount of solids
Remove small
amount of solids
Feed of suspension
flows under pressure
at a fairly high
velocity across the
filter medium.

18. Pressure Filters:
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 whilst the filter is under pressure.
Examples :-
1. sweetland filter
2. plate and frame filter press

20. Plate and Frame Press

21. Plate and Frame filter press

22. PLATE AND FRAME FILTER PRESS
Principle
 Based upon surface filtration
 the slurry enters the frame by pressure and flows through the filter medium.
The filtrate is collected on plates and sent to outlet
 surface area increased with the help of plate and frames then large volume of
slurry can be proceed
The Filter press is made of two types of units, plate and
frames.
Usually made of aluminium alloy.
Sometimes, these are also lacquered for protection against
corrosive chemicals and made suitable for steam
sterilization.
Frame
It contains a open space inside wherein the slurry reservoir
is
maintained for filtration and an inlet to receive the slurry.
It is indicated by two dots in description.
Slurry inlet
Handle to rest
on rod

23. Frames of different thickness are available.
It is selected based on the thickness of cake formed during
filtration.
Optimum thickness of frame should be chosen.
Plate
The plate has a studded or grooved surface to support the filter
cloth and an outlet.
It is indicated by one dot in description.
Through channels
Filtrate outlet

24. Plate supports the filter medium, receiving the filtrate and
outlet.
The filter medium usually cloth is interposed between plate
and frame.
Plate, filter medium, frame, filter medium and plate are
arranged in sequence and clamed to a supporting structure.
It is normally described by dots as 1.2.1.2.1 so on.
A number of plates and frames are employed so that the
filtration area is as large as necessary.
Number of filtration units are operated in parallel.
Channels for slurry inlet and filtrate outlet can be arranged
by fitting eyes to the plates and frames, these join together to
form
a channel.
In some types only one inlet channel is formed, while each
plate is having individual outlets controlled by valves.

25. Working of filter press
Working can be divided into two steps-
1. Filtration operation
2. Washing operation
Filtration operation
Frame- showed by 2 dots
Plate – showed by 1 dot
PRINCIPLE OF FILTRATION OPERATION

26. FILTRATION OPERATION

27. Washing operation:-
1. When washing of cake is also required modified plate and
frame filter is used.
2. For this purpose an additional channel is included called as
washing plate and are identified by 3 dots.
3. In the half of the washing plate, there is a connection from
wash water cannel to the surface of plate.
4. The sequence of arrangement of plates and frames can be
represented by dots as 1.2.3.2.1.2.3.2.1 so on (between 1
and 1, 2.3.2 must be arranged

28. PROCEDURE FOR WASHING THE FILTER PRESS
Filtration proceeds in the ordinary way until the frames are filled with cake
To wash the filter cake, the outlets of washing plates are closed.
Wash water is pumped in the washing channel.
The water enters through the inlets on the surface of washing plate.
Finally washed water escapes through the outlet of that plate.
Water passes through the filter cloth and enters frame which contains the
cake.
Then water washes the cake, passes through the filter cloth and enters the
plate down the surface.
Step-1
Step-2
Step-3
Step-4
Step-5

30. Important key points.
wash is efficient only if the frames are full with filter cake
If the solid do not fill the frame completely, the wash water causes the cake
to break (on the washing plate side of the frame), then washing will be less
effective.
Hence it is essential to allow the frames become completely filled with
washing cake.
This helps not only in emptying the frames but also helps in washing the
cake correctly.
Uses:
1.Sterile filtrate can by obtain by using asbestos and cellulose filter sheet
(for this, whole filter press and filter medium have been sterilized
previously).
2.Filtration of viscous liquid can also be done by incorporating
heating/cooling coils in the press.

31. 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.
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
labour 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 for
slurries containing less about 5 %
solids
5- In view of the high labour costs ,
it is most suitable for expensive
materials.e.g.the removal of
precipitated proteins from insulin
liquors.

32. B- Vacuum filters
 Vacuum filters operate practically at higher pressure differentials than
gravity filters.
 Rotary vacuum filter and the leaf filter are most extensively used.
The leaf filter:
 The leaf filter is consisting of a frame enclosing a drainage screen or
grooved plate , the whole unite being covered with filter cloth.
 The outlet for the filtrate connects to the inside of the frame, the general
arrangement is shown in the Fig. which represents a vertical section through
the leaf. The frame may be circular, square or rectangular shapes.
The operation: The leaf filter is immersed in the slurry
and a receiver and a vacuum system connected to
the filtrate outlet.
Advantages:
1- The slurry can be filtered from any vessel.
2-The cake can be washed simply by immersing
the filter in a vessel of Water.
3-Removal of the cake is facilitated by the use of reverse
air flow.
.Fig. Filter leaf

33. Filter leaf

34. Vacuum Filter
4- The filter can be modified by employing a suitable number of
unites.
5- The leaf filter is most satisfactory if the solids content of the
slurry is not
too high, 5 % being a suitable maximum.
6- Labor costs for operating the filter are comparatively
moderate.
An alternative method is to enclose the filter leaf in a
special vessel into which the slurry is pumped under
pressure. A number of leaves are connected to a common
outlet, to provide a large area for filtration e.g. Sweetland
filter.

35. Sweetland filter (variant of filter leaf)
An alternative method is to enclose the filter leaf in a
special
vessel into which the slurry is pumped under pressure.
A number of leaves are connected to a common outlet, to
provide a large area for filtration.

36. Metafilter
Principle:
Mechanism is surface filtration.
 In this, metal rings contain semicircular projections, which are arranged as a
nest to form channels on the edges.
This channel offers resistance (strainer) to the flow of solids (coarse particles).
The clear liquid is collected into receiver from the top.
Construction:
Metafilter consists of a series of metal rings.
These are threaded so that a channel is formed on the edges.
It contains a grooved 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 15.0
mm internal diameter and 22.0 mm external diameter.
Each metal ring has a number of semicircular projections (0.8mm in thickness) on one
side of surface.
The projections are arranged as a nest to form channels on the edges.
These rings are tightened on the drainage column with a nut.
Metafilters are also known as edge filters.

37. Working:
Step-1 Filters are placed in a vessel
Step -2 Slurry is pumped under pressure or occasionally by
applying reduced pressure to the outlet side
Step-3 Slurry passes through the channels formed on the edges
between the rings
Step-4 The clear liquid rises up and collected from the outlet into
receiver

38. Uses
1 Metafilters can be used for-
2 Clarification of syrups
3 Filtration of injection solutions
4 Clarification of insulin liquors
5 Filtration of viscous liquids can be achieved by applying
pressure.
Working continue …………..
For separation of fine particles, a bed of suitable materials such
kieselguhr is first built up.
The pack of rings serves essentially as a base on which the true
filter medium is supported.

39. Rotary drum filter
Principle:
Slurry filtered through sieve like mechanism on the rotation
drum surface, under the condition of vacuum.
In addition compression, drying (using hot air), and removing the
filter cake (using knife) are possible.
Construction:
1.It consist of a metal cylinder mounted horizontally.
2.The drum may be up to 3 meters in diameter and 3.5 meters in
length and gives surface area of 20 meter square.
3.The curved surface being a perforated plate, supporting a filter
cloth.
4. Internally, it is divided into several sectors and a separate
connection is made between each sector and a special rotary
valve.

40. Rotary drum filter

41. Working
The drum is dipped into the slurry and vacuum applied to the
outlet, which is connected to the filtrate receiver.
When the cake has formed, the cake drained or partially dried
by vacuum.
The drum is sprayed with water to wash the cake.
 Retaining the vacuum connection drains the cake and produces
partial dryness then, removed by a doctor knife.
When the solids of the slurry are too much that the filter cloth
becomes blocked with the particles, a pre-coat filter may be
used.
 A pre-coat of filter aid is deposited on the drum prior to the
filtration process.

42. Uses
The rotary filter for continuous operation on large quantities
of slurry.
Suitable for slurry contains considerable amounts of solids in
the range 15- 30%.
Examples of pharmaceutical application include:-
1.The collection of calcium carbonate, magnesium carbonate,
and starch.
2.The separation of the mycelium from the fermentation liquor
in the manufacture of antibiotics.

43. Disadvantages
1) The rotary filter is a complex piece of equipment , with many
2) moving parts and is very expensive,.
3) In addition to the filter itself, some accessories are connecte,e.g., a vacuum
pump, vacuum receivers , slurry pumps and agitators are required .
4) The cake tends to crack due to the air drawn through by the vacuum system,
so that washing and drying are not efficient.
5) Being a vacuum filter, the pressure difference is limited to 1 bar and hot
filtrates may boil.
6) It is suitable only for straight- forward slurries
Advantages
1) The rotary filter is automatic and is continuous in operation, so that the
labour costs are very low
2) The filter has a large capacity , so it is suitable for the filtration of highly
concentrated solutions.
3) Variation of the speed of rotation enables the cake thickness to be
controlled.
4) Pre-coat of filter aid could used to accelerate the filtration rate.
5) Filter has large surface area.

44. A centrifuge consists of a basket in which mixture of solid and liquid , or mixture
of two liquids is rotated at high speed so that it is separated into its constituents by
the action of centrifugal force.
Types of baskets:
A- Imperforated, in which the liquid is removed through a skimming tube ,
while the solid particles, sediment to the wall.
In pharmacy, the centrifuge is commonly used for drying crystals and for
separating emulsions into their constituent liquids.
B- Perforated basket, in which the liquid passes out through the holes.
1-The perforated basket centrifuge:
 A vessel about 1m. in diameter and its outer wall is perforated. It is mounted on a
vertical shaft by means it can be rotated at a high speed. An outer casing with an
outlet collects the liquid thrown out from the basket.
 The drive motor may be below the centrifuge and it is called under-driven,
 Other form is over-driven,.
D- Centrifugal Filters

45. Advantages of a centrifuge:
1- It is very compact, occupying very little floor space,
2- It is capable of handling slurries with high proportions
of solids .
3- The final product has generally, a very low moisture
content if compared to a filter cake of a similar
material.
Disadvantages:
1- Batch process
2- It involves a considerable labour cost, making the
process expensive.
Advantages & Disadvantages:

46. Perforated basket centrifuge

47. 2-THE PUSHER-TYPE CENTRIFUGE
This type of centrifuge is used for the separation of
suspensions, and is fitted with a perforated basket.
The operation:
I. The feed is introduced through a centrally located conical
funnel, and the cake is formed in the space between the
flange and the vertical base of the basket.
II. A reciprocating pusher disc moves the formed cake along
the surface of the basket freeing the surface for further cake
deposition.
III.The pusher makes one stroke forward and backward, until
a further layer of solids is built up when a second stroke
follows, and so on. The filtrate passes through the holes of
the basket and is collected by suitable piping.
IV.In a second stage, a washing spray is admitted by a
perforated head.
V. In a third stage, drainage, and partial drying of the cake
takes place after which the dry solid may be automatically
collected

49. Advantages:
1- Continuously operated apparatus.
2-Thus reducing the coast of operation
Disadvantages: The pusher piston mechanism adds to the initial
costs of the centrifuge.
3- The Tubular centrifuge ( Supercentrifuge)
Principle of operation : High centrifugal effects can be obtained
by using a centrifuge of small diameter rotated at a high
speed.
Uses:
1- It can separate solids of small particle size from liquids.
2- It can be used to separate immiscible liquids from one another
e.g. the two components of emulsion.
3- It can be used for filtration of very diluted suspensions i.e.
solutions containing very low concentration of solids.

50. Advantages:
 1- Due to the very high centrifugal speed ( 15.000- 60,000),
 It can be used for clarification of much diluted solutions due
to the accelerated gravitational force.
 On separation of two immiscible liquids , the centrifugal force
will form two layers, with the heavier liquid adjacent the wall.

51. Equipment selection:
Ideally the equipment chosen should allow a fast filtration rate to
minimize production costs, be cheap to by and run, be easily cleaned
and resistant to corrosion, and be capable of filtering large volumes of
products.
There are a number of product – related factors that should be considered
when selecting a filter for a particulate process.
These include:
1- The chemical nature of the product. Interactions with the filter medium
may lead to leaching of the filter components, degradation or swelling
of the filter medium or adsorption of components of the filtered product
on the filter. All of these may influence the efficiency of the filtration
process or the quality of the filtered product.
2- The volume to be filtered and the filtration rate required
3- The operating pressure needed. This is governing the
The disc- Bowl Centrifuge

52. 4- The amount of material to be removed. Prefilters
(decantation) may be required or filter where the cake
can be continuously removed.
5- The degree of filtration required. This affect the
chosen pore size of membrane filters or the filter
grade to be used.
6- If sterility is required , then the equipment should itself
be capable of being sterilized, and must ensure that
contamination does not occur after the product has
passed the filter.
7- The product viscosity and filtration temperature. A
high product viscosity may require elevated pressure
to be used.

53. Application of solid/liquid filtration
Improvement of the appearance of solutions, mouth washes,
etc..
Removal of potential irritants, e.g. from eye drop preparations
or solutions applied to mucous membranes.
Recovery of desired solid material from suspension or slurry
,e.g. to obtain drug after crystallization process.
Certain operations, such as the extraction of vegetable drugs
with a solvent, may yield a turbid product with a small quantity
fine suspended colloidal matter; this can be removed by filtration.
Detection of microorganisms present in liquids, This can be
achieved by analyzing a suitable filter on which the bacteria are
retained .This method can also be used to assess the efficiency of
preservatives.