Filteration

FILTRATION
by
Suchita Gokhale
Assistant professor
Ideal college of pharmacy AND RESEARCH, Kalyan

• Filtration is a physical, biological or chemical operation that
separates solid matter and fluid from a mixture with a filter medium that
has a complex structure through which only the fluid can pass.
• Filtrate is the medium that passes through filter medium
Suchita Gokhale , Assistant professor IDEAL COLLEGE OF PHARMACY AND RESEARCH, Kalyan

Basic mechanism of filtration removal of solids from the suspension
or slurry using porous medium…..resulting in filtrate
The size of the largest particles that can successfully pass through a
filter is called the effective pore size of that filter.

• Difference exists between filtration and adsorption. In adsorption, the
physical nature of the particles is responsible for the separation, while
in filtration the use of a membrane is involved.
Filtration differs from adsorption, where it is not the physical size of
particles that causes separation but the effects of surface charge.
Some adsorption devices containing activated charcoal and ion
exchange resin are commercially called filters, although filtration is not
their principal function.
PARTICLES ARE
ADSORBED ON
THE SURFACE
LIQUID GETS
STRAINED
FROM THE
POROUS
PARTICLES

APPLICATIONS
• Filtration is used to separate particles and fluid in a
suspension, where the fluid can be a liquid, a gas or a
supercritical fluid. Depending on the application, either
one or both of the components may be isolated.
• Filtration, as a physical operation is very important in
chemistry for the separation of materials of different
chemical composition.
• Production of sterile products examples:1. HEPA filters
and laminar air flow 2. Membrane filters
• Production of liquid orals : This very important to get
clear oral liquids examples : elixirs, aromatic waters
• Bacteria proof filters are used for thermolabile products
or substances where heat sterilization is not possible
examples: 0.5% ophthalmic solution

FACTORS AFFECTING FILTERATION
• 1.PRESSURE: The rate of filtration is directly
proportional to the pressure difference between filter
medium and filter cake thus rate of filtration can be
increased by applying pressure on the liquid being
filtered of by decreasing pressure beneath the filter
• 2. VISCOSITY: The rate of filtration is inversely
proportional to viscosity of liquid undergoing filtration.
Liquid viscous in consistency get filtered slowly than
liquids with low viscosity
• 3. SURFACE AREA AND FILTER MEDIUM: The rate
of filtration is directly proportional to the surface area
of filter media. using fluted funnel increases the
effective surface area of filter paper for filtration.
• 4.TEMPERATURE of liquid to be filtered: Temperature
play important role in rate of filtration, Viscosity is
reduced by a rise in temperature and filtration of
viscous oils, syrups
• 5. PARTICLE SIZE :The rate of filtration is
directly proportional to the particle size of the
solid to be removed, it is easier to remove smaller
or coarse particle size liquids because the filtering
medium has small particle size
• 6.PORE SIZE OF FILTER MEDIUM:The rate of
filtration is directly proportional to pore size of the
filter media.The liquid having coarse particles
requires a coarse filtering media to remove them
so the rate of filtration is increased when a coarse
filter medium is used for filtration.
• 7. THICKNESS OF CAKE :The rate of filtration
is inversely proportional to the thickness of the
filter cake formed during the process of filtration,
the solid particles start depositing on the filter
medium thus increasing the thickness of the cake
and decreases the rate of filtration.

FILTER MEDIA AND FILTER AID
•Filter media: The filter
medium acts as a
mechanical support for the
filter cake and it is
responsible for the
collection of solids.
•Minimum cake thickness
of discharge for different
types of filter are
Filter type Minimum design thickness
Belt 3.0-5.0
Roll discharge 1.0
Standard scraper 6.5
Coil 3.0-5.0
String discharge 6.5
Horizontal belt 3.0-5.0
Horizontal table 19.0

MATERIAL USED AS FILTER MEDIA
• Woven materials such as Belts or cloths:
woven material is made of wool, cotton, silk
& synthetic fibers etc. are used. Synthetic
fibers have greater chemical resistance than
wool or cotton. The choice of fibers also
depends on the physical state & chemical
constitution of the slurry. It includes mainly
of two types.
1.Monofilament woven cloth: The yarns of a
monofilament fabric are not only impermeable
but also fairly smooth and cylindrical.
2.Multifilament woven cloth: The chief
difficulty encountered when dealing with
multifilament media is the highly complex
geometry of the fibres and yarns that make
up the cloth. Even in a fabric of apparently
simple weave and construction, such as a
plain-weave, continuous filament cloth.
• Perforated sheet metal: stainless steel
plates have pores which act as channels
as in case of Meta filter.
• Bed of granular solid built up on a
supporting medium: examples of
granular solids are gravel, sand,
asbestos, paper, pulp & kieselguhr.
• Prefabricated porous solid unit:
sintered glass, sintered metal,
earthenware and porous plastics are
material used for fabrication.
• Membrane filter media: it includes
surface & depth type of cartridges.

MATERIAL USED AS FILTER MEDIA

Criteriafor choice of filter medium:
There are three criteria for choice of
filter medium.
• 1. Size of particle retained by the
medium.
• 2. The permeability of the clean
medium.
• 3. The solid holding capacity of the
medium and the resistance to fluid
flow of the used medium.

How Filters Work: Filtration Mechanisms
• There are four basic filtration mechanisms:
SEDIMENTATION : The mechanism of sedimentation is due to force of gravity and the
associate settling velocity of the particle, which causes it to cross the streamlines and
reach the collector.
• INTERCEPTION : Interception of particles is common for large particles. If a large
enough particle follows the streamline, that lies very close to the media surface it will hit
the media grain and be captured.
• BROWNIAN DIFFUSION : Diffusion towards media granules occurs for very small
particles, such as viruses. Particles move randomly about within the fluid, due to
thermal gradients. This mechanism is only important for particles with diameters < 1
micron.
• INERTIA : Attachment by inertia occurs when larger particles move fast enough to
travel off their streamlines and bump into media grains.

BASIC MECHANISM FOR FILTERATION INSTRUMENT

CLASSIFICATION OF
FILTERATION

FILTERS
PRESSURE FILTERS
PLATE FRAME
FILTER
META FILTER
VACCUM FILTERS FILTER LEAF
CENTRIFUGAL
FILTERS
CENTRIFUGES
CLASSIFICATION OF FILTERATION INSTRUMENTS

FILTERS
CONTINUOUS
FILTRATION
DISCHARGED AND
FILTRATE SEPARATED
DISCONTINUOUS
FILTRATION
FILTER IS REMOVED
AND SOLID COLLECTED
CLASSIFICATION BASED ON FILTERATION OPERATION

PLATE AND FRAME FILTER
Principle:
1. Based on Surface filtration ,which
performs Filtration & Separation
during its Press operation.
2. A filter press consists of a series of
chambers containing square or
rectangular filter plates supported in
a frame. Once the filter chambers
are loaded with slurry, the plates are
forced together with hydraulic rams
that generate pressures typically in
the region of 100 pounds per square
inch (70,000kg per m2).
3. Each plate is covered by a material or
membrane that acts as the initial filter
when the press is in operation. As the
solid filter cake builds up, the cake adds
to the removal of fine particles. The
solution coming through the filter, called
the filtrate, will be very pure. If it is not
wanted the filtrate can be drained away
for safe disposal.
4.At the end of the compression, the solid
filter cake can be removed. The whole
process is often computer controlled to
make it automatic or semi-automatic.

1.The filter press is made of two
types of units, plate and frames
usually ,made of aluminium alloy.
2. Sometimes these are lacquered
for protection against corrosive
material and suitable for steam
sterilisation.
3.Frame contains a open space
inside where in the slurry reservoir is
maintained for filtration and an inlet
to receive the slurry

•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.
•The plate has studded or
grooved surface to support the
filter cloth and an outlet. It is
indicated by one dot in
description

PLATE AND FRAME FILTER

As filtration proceeds, the resistance of the cake increases and filtration rate
decreases.
At a certain point process is stopped and press is emptied and cycle is restarted
Two filter cakes are formed, which will be collected at the centre.
The filtrate drains between the projection of the surface of the plate and escape from
the outlet.
Slurry enter the frame and feed channel which will pass through the filter medium
on the surface of the plate.
The solid or filter cake is formed Cake thickness is half of the frame thickness because
on each side of frame continuously filtration process takes place.

WASHING
OPERATION
To wash filter cake
the outlets of
washing plates are
closed
Water is pumped in the washing
channel.Water enter to inlets
on the surface of washing
plates.
Water passes through the filter cloth and
enters frame which contains the cake ,
pumped water will wash the cake pass
through filter cloth and enter down the
surface .
Finally washed water escape through outlet
of that plate

• ADVANTAGES
• The filtering media can be used
repeatedly
• Operation and maintenance is
simple
• It provides a large surface area for
filtration
• Efficient washing of cake is possible
• DISADVANTAGES
• It is not a continuous process
• It is used where the proportion
of solid in the liquid to be
filtered is about 5%or less
• process becomes costly, lots of
labour is required for washing
and replacement of filter cloth
• leakage between the plates
may takes place through faulty
assembly

FILTER LEAF
It is the simplest form of filter. It consists of a frame enclosing a drainage screen
or a grooved plate.
Filter cloth is used as the filtering medium, whole unit being covered with filter
cloth.The frame used may be of any shape i.e. square, rectangular or circular.

WORKING :The filter leaf is placed in the vessel containing
the liquid to be filtered.
Vacuum is applied and the pressure inside the leaf is
decreased.
Due to the difference in external pressure and pressure
inside the leaf, the liquid moves inside the filter through
filter cloth.The filtrate is collected in the receiver and
cake gets collected outside the cloth.
Uses: This method has advantages that method can be
filtered and cake can be washed immersing it in vessel
containing water.The cake can be removed by flowing air
in opposite direction .

ROTARY DRUM FILTER
The most common type of continuous vacuum filter is the rotary drum filter in which liquor is
sucked through a moving septum to deposit a cake of solids.The cake is moved out of the filtering
zone, washed, sucked dry and dislodged from the septum.
CONSTRUCTION: It is consisting on a sheet metal drum.The diameter of drum ranges from 1 to 10
feet.This drum is carried on moving system. A vacuum system is also attached so that during
filtration whole drum work under vacuum, the surface of the drum is divided in to different section
by stripes.
1. Cake formation zone
2. Washing zone
3. Drying zone
4. Cake removal zone
These steps are parallel to the axis of drum and welded to the shell. Filter medium is held by metal
strips on drum and covered by filter cloth.
In each section there are many pipes which open inside the cover plates.The side cover plate,
there is also stationary valve plate for filtrate receiver. Suchita Gokhale , Assistant professor IDEAL COLLEGE OF PHARMACY AND RESEARCH, Kalyan

WORKING: Before filtration rotary drum filter is dip in tank of filter aid for
precoating purpose commonly is precoated up to 3 “ to 5”By diatomaceous earth
OR purified wood cellulose. After that drum is rotated in slurry tank at a speed of 1
to 2 rpm i.e1/3 rd. of drum is dip in slurry tank.
A layer of solid builds in the form of cake
on the surface of panel(filter cloth) in
cake formation zone and filtrate pass
through pipes and goes to vacuum
receiver collected in tank.
As the panel leave the cake formation
zone it enters to washing zone and in
which water is sprayed on cake to extract
all filtrate from cake and it sent to wash
vacuum receiver.

Membrane Filtration
• Microfiltration (bacteria – portable water, 0.5 – 5 microns). Pore
size specified.
• Ultrafiltration (macromolecules, molecular mass 1000 – 106, 0.5
– 10-3 microns). Cut-off mol. wt. specified.
• Nanofiltration (low molecular weight, non-volatile organics from
water e.g. sugars). Cut off mol. wt. specified.
• Reverse osmosis (salts)

Membrane types
• Dense
• High porosity
• Narrow pore size distribution

Ultrafiltration(UF)
Uses a finely porous membrane to separate water and
microsolutes from macromolecules and colloids.
Membrane pore diameter 0.001 – 0.1 μm.
Nominal ‘cut off’ molecular weight rating assigned to
membrane.
Membrane performance affected by:
• Concentration polarisation
• Membrane fouling
• Membrane cleaning
• Operating pressure

Spiral wound UF module

UF
Membrane materials (Loeb- Sourirajan
process)
• Polyacrylonitrile (PAN)
• PVC/PAN copolymers
• Polysulphone
• PVDF (polyvinylidene difluoride)
• PES (polyethersulfone)
• Cellulose acetate (CA)
• Plate and frame
Modules
• Tubular
• Spiral wound
• Capillary hollow fibre

Microfiltration (MF)
Porous membrane; particle diameter 0.1 – 10 μm
Microfiltration lies between UF and conventional filtration.
In-line or crossflow operation.
Screen filters/depth filters (see Baker fig. 7.3, p 279)
Challenge tests developed for pore diameter and pore size.

MF
Membrane materials
• Cellulose acetate/cellulose nitrate
• PAN – PVC
• PVDF
• PS

Reverse osmosis
Miscible solutions of different concentration
separated by a membrane that is permeable to
solvent but impermeable to solute. Diffusion of
solvent occurs from less concentrated to a
more concentrated solution where solvent
activity is lower (osmosis).
Osmotic pressure is pressure required to equalise
solvent activities.
If P > osmotic pressure is applied to more
concentrated solution, solvent will diffuse from
concentrated solution to dilute solution
through membrane (reverse osmosis).

The permeate is nearly pure water at ~
1atm. and very high pressure is
applied to the feed solution to make
the activity of the water slightly
greater than that in the permeate.
This provides an activity gradient
across the membrane even though
the concentration of water in the
product is higher than that in the feed.
Reverse osmosis
Permeate is pure water at 1 atm. and
room temperature and feed
solution is at high Pressure.
No phase change.
Polymeric membranes used e.g.
cellulose acetate
20 – 50 atm. operating pressure.
Concentration polarisation at
membrane surface.

Membrane materials
• Asymmetric cellulose acetate
• Polyamides
• Sulphonated polysulphones
• Substituted PVA
• Interfacial composite membranes
• Composite membranes
• Nanofiltration membranes (lower
pressure, lower rejection; used for
lower feed solution
concentrations)
Ref. Baker p203

Filteration

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Filteration

Similar to Filteration (20)

Recently uploaded

Recently uploaded (20)

Filteration