Pharmaceutics I
Unit 8th

1. Introduction

2. Factors affecting rate of filtration

3. Filter media

4. Filter aids

5. Filtration equipments

6. Unani description

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.

Introduction (cont.)

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.

 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.

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.

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.

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.

“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.

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.

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.

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

Asbestos:

• Also used for filtering
the corrosive liquid.

• They impart alkalinity
to the filtrate.

• Alkaloids may get
absorbed.

• May contaminate the
filtrate.

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.

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.

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.

“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

Materials Chemical Advantages Disadvantages

composition

Diatomaceous earth Silica Wide size range Slightly soluble in

acid and alkalies

Perlite Silica Wide size range More soluble

+Aluminosilicate

Asbestose Aluminosilicate Very good retaintion More soluble

on coarse screen

Cellulose Cellulose Chemically inert Expensive

Carbon Carbon Non reactive with Expensive

strong alkalies

DIATOMACEOUS EARTH PERLITE

ASBESTOSE CELLULOSE CARBON

recoating: It requires suspending the filter aid in
a liquid and circulating the feed until the filter aid is
uniformly deposited on the filter septum.

Quantity required:

• 5-15 pounds / 1002 feet of filter area.

• Or filter cake thickness=1/16 to 1/8 inch

ody Mix:

• Direct addition of filter aid to the filter feed.

• Ratio of filter aid=0.1 to 0.5 % of total liquid.

• OR 1 kg filter cake : 1-2kg of filter aid.

Selection of method and equipment required
for filtration of a liquid depends on nature
of the material and quantity to be filtered as
well as the object of the operation.

FILTER FUNNEL:
• Funnels are conical shaped

devices

• Made up of Glass,
Aluminum, Polythene,
Stainless steel OR any
other suitable material.

• Neutral Glass made funnel
are most commonly used.

• White filter paper of
suitable pore size is folded
in such a way that it fits in
the funnel.

BUCHNER FUNNEL:
• Made up of porcelain.

• It has a perforated plate.

• Used for filtration under reduced
pressure.

HOT WATER
FUNNEL:

• These are doubled wall funnels
made up of metals.

• Viscous substances such as liquid
paraffin, Glycerin, Castor oil and
fatty substances like wool fat, bees
wax, ointments and cream etc are
filtered easily from this filter.

• Boiling water or steam is
circulated in jacketed funnel.

SEITZ FILTER:
• Consists of two parts.

• Lower part fitted with a perforated plate over
which compressed asbestos pad is placed.

• Upper part has a value through which
pressure can be applied.

• Both parts joined together by winged nuts.

 Advantages:

• No risk of contaminating the filtrate.

• Apparatus is very simple to use.

• For viscous solution they are more suitable.

 Disadvantages:

• Asbestos may shed loose fibers.

• Pad may absorbs sufficient amount of
medicament.

FILTER PRESS:
• It consists of hollow frames and solid plates.

• Plates have grooved surface to support the filter cloth.

• Each plate has an outlet for filtrate.

• Frames are opened with an inlet for the liquid to be
filtered.

Advantages:

• Construction is very simple.

• Used for coarse to fine filtration.

• Operation and maintenance is easy.

• Filter cloth can be easily replaced.

Disadvantages:

• Not economical for filtration of small quantities

• Leakage between the plates may take place

• Suitable when the slurry contain less than 5%
solids.

ROTARY FILTERS:
• They are used when the proportion of solid content in slurry is 15 to

30%.

• It consists of perforated matter drum wrapped with filter cloth.

• Drum is partially immersed in the tank containing the materials to
be filtered.

• Drum rotates at the slow speed and creates vacuum due to which
filtrate enters into the drum.

• Filter cake deposits on outer surface of the filter media.

• Cake is removed by scrapping with a knife.

Advantages:
• Labour costs are very low.

• Area of filtration is very high.

• Thickness of the filtration cake is controlled by
altering with the speed of rotation of drum.

Disadvantages:
• Very expensive.

• Can’t be used for slurries containing low
percentage of solids.

FILTER LEAF:
• It consists of frame in which drainage screen is

enclosed.

• Whole unit is covered with a filter media.

• Outlet is connected to the vacuum pump.

• Frames may be shaped in round square or rectangular.

Advantages:
• Liquid can be filtered form any vessel.

• Filter cake can be removed simply by washing or
blowing air.

• It is very economical.

Disadvantage:
• It is not effective when solid content in the liquid is

more than 5%.

VACUUM FILTRATION:

• Vacuum filtration is used primarily to collect a

desired solid.

• Vacuum filtration uses a Buchner funnel and a side-
arm flask.

• Vacuum filtration is faster than gravity filtration,
because the solvent or solution and air is forced
through the filter paper by the application of reduced
pressure.

To perform a vacuum
filtration:

• Clamp the flask securely to a
ring stand.

• Add a Buchner funnel with a
rubber funnel adaptor.

• Obtain a piece of filter paper
in the funnel that is small
enough to remain flat but
large enough to cover all of
the holes in the filter. If
necessary, you can cut a
larger piece of filter paper
down to size.

• Place the paper in the
funnel.

• Connect the side arm flask
to a vacuum source.
Always use thick-walled
tubes.

• Wet the paper with a small
amount of the solvent to
be used in the filtration.
This causes the paper to
adhere to the plate and
keeps materials from
passing under the paper
during filtration.

• Turn on the vacuum
source.

• Pour the mixture to be
filtered onto the filter
paper. The vacuum
should rapidly pull the
liquid through the
funnel.

• Rinse the cake with a
small amount of cold
fresh solvent to help
remove impurities that
were dissolved in the
filtrate.

• Carefully disconnect
the rubber tube.

• Remove the filter
paper and the
collected solid that is
on it.

In Unani System of Medicine these
terminologies are used for filtration:

• TARWEEQ:

done by the help of a utensil named as “RADOOQA” .

• TASFIYA

• TARSHEEH

• JARRE ALQI

These filter media are used for filtration:
• SAFI (cloth): made up of sooti, reshmeen,

malmal etc.

• MASAMDAR JAZIB KAGHAZ (filter paper)

• COTTON WOOL