The document discusses various filtration methods and terms used in filtration. It describes different types of filtration processes like clarification, ultrafiltration, and cake filtration. It also discusses factors affecting filtration rate and various filter media used including filter paper, woven materials, membranes, and sintered glass. Different types of filters are also summarized like gravity filters, vacuum filters, pressure filters, and centrifugal filters. Rotary vacuum filters and pressure filters are described in more detail.

1. Rokon
Student ,
Department of Pharmacy, WUB

2.  Filtration: The separation of solid
from a fluid by means of a porous
medium that retains the solid but allows
the fluid to pass.
 Clarification: This term is applied
when solid do not exceed 1.0% and
filtrate is the primary product.

3.  Ultra-Filtration: Separation of
intermicellar liquid from solid by
the use of pressure on a semi
permeable membrane.
 Cake Filtration: If
recovery of solid is desired, the
process is called cake filtration.

4.  Feed or Slurry: The suspension of solid
and liquid to be filtered is known as the
slurry or feed.
 Filter Medium: The porous medium
used to retain the solids is described as
the filter medium.
 Filter Cake: The accumulation of solids
on the filter is referred to as the filter
cake.
 Filtrate: The clear liquid passing through
the filter is the filtrate.

5.  The flow of solid is resisted by the
filter medium while the liquid is allow
to pass.
 As the filtration proceeds the
retention of the solid on the filter
media goes on increasing which acts
as a secondary and some times more
efficient filtering media.

7. 1. Area of filter surface.
2. Particle size of cake solids.
3. Pore size of filter media.
4. The resistant of the filter cake and
filter media.
5. Viscosity of liquid to be filter.
6. Temperature.
7. Pressure difference across the filter.

8. Where:
V= Volume of filtrate
T= Time
A= Filter area
P= Total pressure drop through cake and filter
media.
µ= Filtrate viscosity
α= Average specific Cake resistant
W= Weight of dry cake solids.
R=Resistant of filter medium and filter.

9. “The surface upon which solids are deposited in a
filter is called the Filter medium”.
PROPERTIES OF IDEAL FILTER MEDIA:
1. Chemically inert.
2. High retention power.
3. Sufficient mechanical strength.
4. Absorbs negligible amount of material.
5. Resistant to the corrosive action of liquid.
Selection of filter media depends on followings:
1. Size of particle to be filtered.
2. Amount of liquid to be filtered.
3. Nature of product to be filtered.
4. Purpose of filter.

10.  Filter paper:
Filter paper is a common filter
medium since it offers controlled
porosity, limited absorption
characteristic, and low cost
 It has different grades and
qualities different pore size such
as coarse medium and fine.
Disadvantages:
 They shed very fine particle to
the filtrate.
 Absorb small quantity of liquid.

11.  Woven Material:
Cotton silk wool nylon & glass etc.
 Nylon cloth:
 Superior to the cotton cloth.
 Not affected by molds, fungus and bacteria.
 Has negligible absorption properties.
 It is extremely strong as compared to cotton cloth.
 Woven wire cloth:
 Made from stainless steel.
 Easily cleaned.
 Long lasting.
 Resistant to the chemicals.

12.  Cotton Wool:
Commonly used.
Small tough of cotton
wool placed in the
neck of funnel.
 Glass wool:
Use for filtering highly
corrosive chemicals.
May contaminate the
filtrate with glass
fibers

13.  Asbestos:
Also used for filtering
the corrosive liquid.
They impart
alkalinity to the
filtrate.
Alkaloids may get
absorbed.
May contaminate the
filtrate.

14.  Membrane Filter:
 These are very
common among the
ultra filtration methods.
 Made up of cellulose,
Polyvinylchloride,
Nylon and other
cellulose derivatives.
 They rare very fine
having a very vide
range of pore size from
8µ down to 0.22µ.

15. Pore size (in µ) Particles removed
0.2 All bacteria
0.45 All coliform group bacteria
0.8 All air born particles
1.2 All Non living particles considered dangerous in I.V. Fluid.
5 All Significant cell from body fluid
 Advantages:
 Bacteria are removed by sieving
 Absorption of medicament is negligible
 In every new operation, a new disc is used
 Filtration is quite rapid
 Don’t liberate particles to the filtrate.
 Disadvantages:
 Fine pores may get clogged easily
 Soluble in certain organic solutions e.g. ketones and
esters
 Very brittle when dry.

16.  Craft Paper:
 Mainly used in plate and frame filters.
 They offer controlled porosity
 Limited absorption.
 Quite cheap.
 Sintered Glass:
 Consist of Pyrex glass powder.
 Used for filtering parenteral preparations.
 Useful for filtering the corrosive liquid and oxidizing
agent.
 Don’t shed particles.
 Don’t absorbs any liquid.
 Can be easily washed.

17. “The substances which when added to the liquid to
be filtered, reduce the resistance of the filter cake
and increase the filtration”.
 Properties of Filter Aids:
 Chemically inert
 Low specific gravity
 Insoluble in liquids
 Form a porous cake
 Free from impurities
 Suitable particle size with irregular shape
 Able to remain suspended in liquids
 Free from moisture

18. Materials Chemical
composition
Advantages Disadvantages
Diatomaceous earth Silica Wide size range Slightly soluble in
acid and alkalies
Perlite Silica
+Aluminosilicate
Wide size range More soluble
Asbestose Aluminosilicate Very good retaintion
on coarse screen
More soluble
Cellulose Cellulose Chemically inert Expensive
Carbon Carbon Non reactive with
strong alkalies
Expensive

19. Four groups may be listed:
1. Gravity filters
2. Vacuum filters
3. Pressure filters
4. Centrifugal filters

20.  Employing thick
granular beds
 widely used in water
filtration e.g. Sand
Filter

21. Vacuum filters operate practically at
higher pressure differentials than
gravity filters.
1. Leaf filter
2. Rotary vacuum filter

22.  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 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.

23. 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.
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.

24.  In large –scale operation, continuous operation is
sometimes desirable and it may be necessary to filter
slurries containing a high proportion of solids.
 The rotary filter is continuous in operation and has a
system for removing the cake that is formed , so, it is
suitable for use with concentrated slurries.
 It is a metal cylinder mounted horizontally, the curved
surface being a perforated plate, supporting a filter
cloth. Internally, it is divided into several sectors and
a separate connection is made between each sector
and a special rotary valve.

25. 25

26.  The drum is immersed to the required depth in the
slurry, which is agitated to prevent settling of the
solids, and vacuum is applied to those sectors of the
drum which is submerged.
 A cake of the desired thickness is produced by
adjusting the speed of rotation of the drum. Each
sector is immersed in turn in the slurry and the cake is
then washed and partially dried by means of a current
of air. Finally, pressure is applied under the cloth to
aid the removal of the cake. Removal of the washed
and partially dried cake is affected by means of a
doctor knife.

27. Dr. O. Alkarim

28.  Summary of the process:
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.

29. 1. The rotary filter is automatic and is continuous in
operation, so that the labor 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.

30. 1. The rotary filter is a complex piece of equipment , with
many moving parts and is very expensive.
2. In addition to the filter itself, some accessories are connected
,e.g. a vacuum pump, vacuum receivers , slurry pumps and
agitators are required.
3. The cake tends to crack due to the air drawn through by the
vacuum system, so that washing and drying are not efficient.
4. Being a vacuum filter, the pressure difference is limited to 1
bar and hot filtrates may boil.
5. It is suitable only for straight- forward slurries

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

32.  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 are the sweet-land filter, plate and frame
filter press.

33. This press is made up of two units, known
respectively as plates and frames, with a filter
medium, usually filter cloth, between the two.
The frame is open, with an inlet for the slurry,
while the plate has grooved surface to support
the filter cloth, and with an outlet for the
filtrate

34. Dr. O. Alkarim

35. 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.

36.  Channels for the slurry inlet and the filtrate outlet can be
arranged by fitting eyes to the plates and frames. This has the
advantages that the filtrate from each plate can be seen and, in
the event of a broken cloth, the faulty plate can be isolated and
the filtration continued with one plate less.
 The thickness of the cake can be varied by using frames of
different thickness and, in general, there will be an optimum
thickness of filter cake for any slurry, depending on the solids
content of the slurry and the resistance of the filter cake.
 As filtration proceeds, the resistance of the cake increases and
the filtration rate will decrease. At a certain point it will be
preferable in terms of the overall output of the process, to stop
and empty the press rather than to continue filtration at a very
low flow rate.
 Plates and frames may be made in various metals to provide
resistance to corrosion or prevent metallic contamination of
the product. Non-metals e.g. plastics is lighter, also varieties of
wood are satisfactory materials of construction.
 Plates and frames may be of considerable size, of about 1m
square

37. 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.

38. 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 labor costs , it is most suitable for
expensive materials .e.g. the removal of precipitated
proteins from insulin liquors.

39. These are basic tools for micro-filtration,
useful in the preparation of sterile
solutions. These filters are made by
casting of various esters of cellulose, or
from nylon, Teflon, polyvinyl chloride.
The filter is a thin membrane with millions
of pores per square centimeter of filter
surface.

40. Dr. O. Alkarim

41. Principle:
 It is a thin porous membrane in which pre filter and membrane filter are
combined in a single unit.
 The filtration action is mainly sieve like and particles are retained on
the surface.
Construction:
 It has cylindrical configuration made with disposable or changeable
filter media.
 Made up of either plastic or metal.
 Consist of two membrane filters (sieve like) made of polypropylene:
pre filter and actual filter for filtration.
 A protective layer surrounds them.
 The cartridge are housed in a holder and a number of cartridges can
be placed in a same housing.
 The housing is closed with the lid.
 Housing has provisions for slurry inlet and outlets.

42. 42

43. Working:
Uses:
 Particularly useful for preparation of particulate free solutions for
parenterals and ophthalmic uses.
 This filter holder will process 1000 – 15000 litres of sterile solution
per hour.
43
Slurry is
pumped
into
cartridge
holder
It passes
through
cartridge
filter unit
by
straining
The clear
liquid
passes
through
the
centre
Moves
up to
collect
through
outlet

44. Advantages:
 Autoclaving can be done for sterile operations due to stainless
steel construction.
 Cartridge with self cleaning devices are advantageous.
 Rapid disassembling as well as reusing of filter medium is
possible.
 Cartridge are not brittle, when they are dry.
 Used as in-line continuous filtration, which reduces handling of
solutions. It minimize chances of contaminations.
Disadvantages:
 A number of manufactures provide the components, which are
generally not interchangeable between suppliers.
 Cost of disposable elements offsets the labour saving in terms of
assembly and cleaning of cartridge clarifiers.
44

45. Principle:
 Depth filtration
 Mechanism is impingement and entanglement of solids on account
of low pressure differential.
 The slurry enters the sand bed and the clear liquid is collected from
the bottom outlet.
45

46.  It is a closed system and consists of cylindrical tank with
a bottom containing a number of brass strainers.
 These are mounted on false bottom or connected to a
modified embedded in concrete.
 The strainers have narrow slots sawed in them.
 Above this 6-12 m depth sand layer is placed, which acts
as a filter medium.
 Baffles are arranged at the point of feed inlet, in order to
prevent the disturbance of sand by direct stream.
 Provisions is made at the bottom for collecting the filtrate.
46

47. The feed is introduced
from the top at
pressure through the
baffles.
The feed is passed
smoothly at a uniform
rate onto the sand
medium
Filtration is achieved
by straining
mechanism through
sand medium
Then, the feed is
passed through the
strainer, so that further
filtration takes place
and particles are
retained
The precipitate is
discarded
The filtrate is collected
fro bottom
47

48.  When the precipitate clogs the sand (indicated by
reduced filtration rate), back washing permits the
regeneration of the filter bed.
 During this operation, water moves up through the sand
bed and moves out from the inlet.
Uses:
 Used for filtration of boiler feed or water for similar
purposes.
 Mainly used when solids are little and large volume of
feed is to be handled.
 They are applicable only to the separation of precipitates
that can be removed from the sand.
48

49.  Feed containing precipitates that are gelatinous
or form a coat on sand can’t be filtered through
the sand, because back washing does not permit
regeneration.
 Feed containing finely divided solids can’t be
separate by this.
 Can’t remove bacteria. In such cases,
coagulants such as ferrous sulphate, are added
to feed before filtration.
49

50. Thank You