1. Filtration is used to separate solids from liquids using a porous medium, and is affected by factors like thickness of the filter medium, viscosity of the fluid, pressure difference, and area. 2. Darcy's equation quantifies the factors that affect filtration rate. Methods to increase rate include increasing pressure/area or decreasing thickness/viscosity. 3. Filter aids like diatomaceous earth are added to improve flow rate and decrease cake thickness. They are commonly used in pharmaceutical, chemical and food industries. 4. Key filtration methods are gravity, vacuum, centrifugal and pressure filtration. Filter presses use pressure and plates to filter large volumes.

1. FILTRATION
Presented By Rafiul Basher Rabby
Student of North South University

2. Properties of the slurry
that affects Filtration
1
2
3 4
5
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• These five factors
will affect the choice
of filtration method
as well as the rate of
filtration.

3. Factors affecting Rate of Filtration
Thickness of
the Filter
medium (L, m)
Viscosity of the
Fluid (μ, Pa s)
Pressure
difference (∆P,
Pa)
Area (A, m2)
The chosen filtration process must remove the contaminants from the product
• At an acceptably fast rate
• Economically
Aulton’s Pharmaceutics

4. Darcy’s Equation
• All the factors that affect the rate of filtration is compiled into one equation by Henry Darcy (1830)
• The equation represents rate of flow through the capillaries of the filter medium and the filter
cake.
𝑑𝑉
𝑑𝑡
=
𝐾𝐴∆𝑃
𝜇𝑙
• V =Volume of filtrate
• t =Time of filtration
• A = Area of filter medium
• ∆𝑃 = Pressure drop across filter medium and
filter cake
• 𝜇 =Viscosity of the filtrate
• l = thickness of the cake
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K is a constant representing the
resistance of the filter medium and filter
cake

5. Methods used to increase the Rate of
Filtration
•Increase the area available for
filtration
Increase the pressure difference across
the filter cake
Decrease the viscosity of the filtrate
Decrease the thickness of the filter
cake
Increase the permeability of the cake
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6. Mechanisms of Filtration
•Straining Impingement Entanglement
Attractive
forces
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7. Filter Aids:
Filtration is the separation of solids from liquids by forcing the liquid to flow through a porous medium and
depositing the solids on the medium. A filter aid (finely divided material added to the liquid to be filtered) helps
control flow and solids removal. an agent consisting of solid particles (as of diatomite) that improves filtering
efficiency (as by increasing the permeability of the filter cake) and that is either added to the suspension to be
filtered or placed on the filter as a layer through which the liquid must pass.
Filter aids may be used in either or both two ways:
“Filter Aids” is a group of inert materials that can be used in filtration pretreatment. There are two objectives
related to the addition of filter aids. One is to form a layer of second medium which protects the basic medium of
the system. This is commonly referred to as “precoat”. The second objective of filter aids is to improve the flow
rate by decreasing cake compressibility and increasing cake permeability. This type of usage is termed as “admix”
or “body feed”. Filtration without filter aid, with precoat, and with precoat and body feed is shown in Fig.

8. The common filter aids are diatomaceous earth (DE), perlite, cellulose and others. Diatomaceous earth (DE) is the
skeleton of ancient diatoms (Fig. 2a). They are mined from ancient seabed, processed, and classified to make
different grade of filter aids. DE is the most commonly used filter aid today. However, the crystalline type DE is a
suspicious carcinogen and inhalation needs to be avoided during handling.

9.  Here are different grades of commercial DE. A finer grade may be employed to increase the clarity of filtrate. The
smaller the filter aid particle size, the smaller the process particles can be removed. However, the filtration rate is
lower. There is always a balance between initial filtrate clarity and filtration rate. The particle size capture by
various filter aids may also vary because of liquid viscosity, surface charge, etc.

10.  Perlite is another important mineral filter aid. It is a particular variety o
naturally occurring glassy volcanic rock, characterized by onion like, splintery
breakage planes. After crushing and heating, this rock will expand in an explosive
fashion to about ten times its original volume.
 Diatomaceous earth and perlite are silica based minerals.
There are several other special materials used as filter aids,
including asbestos, cellulose, agricultural fibers, saw dust, rice hull ash,
paper fibers etc.

11. Body feed:
Addition of filter aid to the liquid to be filtered is referred to as bodyfeed.The type and grade as well
as quantity to be added is vitally important to obtain the highest filtration flowrate consistent with the clarification
required. Filter aid dosage varies with the solids content and other variables specific to each application. In
general, a dosage of ½ of the percent solids by weight is close. Bodyfeed can be added directly to the tank of
liquid to be filtered, or dosed from a slurry tank into the filter inlet.
 Ideal Propertise of Filter Aids :
 Chemically inert
 Insoluble in liquids
 Free from impurities
 Low specific gravity
 Form a porous cake
 Free from moisture
 Suitable particle size with irregular shape

12. How to use filter Aid?
In general, CELITE, diatomite (diatomaceous earth) has a more intricate particle shape and thus
provides a more tortuous path for suspended particles to be trapped. HARBORLITE (expanded amorphous
aluminum silicate) will usually handle similar filtration tasks but cannot always achieve the same removal
efficiency. Fibra Cel, cellulose fiber is generally used in high temperature, highly alkaline environments where
filter aid solubility would be a problem.
Clarification of Filters:
The term is applied when solid do not exceed 1.0% nad filtrate is the priacy product.
Purpose:
To remove the undesirable solids that interfere with the transparency of such natural products.
Example: Honey or fruit juice extraction

13. Classification of Filtration (machinery)
There are Four types of Filtration based on their external force namely-
Gravity Filtration
Vacuum Filtration
Centrifuge
filtration
Pressure Filtration
Filtration

14.  GravityFiltration:
Gravity filtration is the method of choice to remove solid impurities from an organic liquid. The impurity can be a
drying agent or an undesired side product or leftover reactant. It can be used to collect solid product.
A filtration procedure called "hot gravity filtration" is used to separate insoluble impurities from a
hot solution. Hot filtrations require fluted filter paper and careful attention to the procedure to keep the apparatus
warm but covered so that solvent does not evaporate.
To perform a standard gravity filtration, first select the size of filter paper that, when folded, will be a
few millimeters below the rim of your stemmed funnel. Fold the paper into a cone by first folding it in half, and
then in half again, as shown.

15. Next, support the glass funnel in a ring or place it in the neck of an Erlenmeyer flask. Wet the filter paper
with a few milliliters of the solvent to be used in the following procedure. Wetting the paper holds it in place
against the glass funnel. Pour the mixture to be filtered through the funnel, in portions if necessary.

16.  VacuumFiltration:
Vacuum filtration is used primarily to collect a desired solid, for instance, the collection of crystals in a
recrystallization procedure. Vacuum filtration uses a Buchner funnel and a side-arm flask. Vacuum filtration is
faster than gravity filtration. Do not use vacuum filtration to filter a solid from a liquid if it is the liquid that you
want, and if the liquid is low boiling.
 To perform a vacuum filtration, clamp the flask securely to a ring stand.
 Add a Buchner funnel with a rubber funnel adaptor.

17.  Connect the side arm flask to a vacuum source.
Always use thick-walled tubing , since tubing
Will collapse under reduced pressure.
 Wet the paper with a small amount of the solvent to be used in the
filtration. Make sure the paper is secure on the filter, that air is
being drawn through the paper, all of your apparatus is securely clamped.
 Pour the mixture to be filtered onto the filter paper. The vacuum
should rapidly pull the liquid through the funnel. If this happens,
start over and carefully pour portions of the solution onto the
very center of the paper.

18.  Carefully disconnect the rubber tubing.
 Remove the filter paper and the collected solid that is on it.
 Usually you will need to set the product on a watch glass
and let it air dry for a while.

19. Centrifuge filters:
Centrifugal filters are used in laboratory settings to manipulate peptides, proteins, oligonucleotides, DNA, and RNA
samples. The devices successfully clean up labeling and PCR reactions, isolate specific sections, buffer exchange,
clarify samples, and remove particulates. The centrifugal filters will meet concentration, purification, separation and
desalting procedure requirements.
Pressure Filtration:
Pressure type filter holders can be used for ultra cleaning or sterilizing liquids and gases. Advantege holders have
been designed to maximize flow rates and to minimize holder resistance and can be used in either batch or continuous
filtration procedures.
 Pressure filters may be grouped as shown in the tree to the right.
The sizes for standard equipment are as follows:-
 Filterpress up to 1000 m2 and 20 m3 cake.
 Horizontal Plate Filter up to 60 m2 and 4 m3 cake capacity

20.  Vertical Leaf Filter up to 100 m2 and 7 m3 cake capacity in vertical pressure vessels and up to 300 m2 and 20
m3 cake capacity in horizontal vessels.
 Nutsche Filter up to 16 m2 and 8 m3 cake capacity.
 Automatic Filter up to 120 m2.
 Candle Filter up to 120 m2.
 Pneumatic Filter up to 90 m2

21. Filter leaf and filter press (plate and frame press)
Principle:
 The mechanism is surface filtration.
 The slurry enters the frame by pressure and flows through the filter medium.
 The filtrate is collected on the plates and sent to the outlets.
 A number of frames and plates are used so that the surface area increases and consequently large
volumes of slurry can be processed simultaneously with or without washing.

22. How they work
The working operation of the filter frame and plate process can be described in two steps namely-
1. Filtration operation
2.Washing operation
Filtration operation:
Slurry enters the frame from the feed channel and passes through the filter medium on the surface of
the plate.
The solid forms a filter cake and remain in the frame.
The thickness of the cake is half of the frame thickness because on each side of frame filtration
occurs.
The filtrate drains between the projection of the surface of the plate and escape from the outlet.
As filtrate ion proceeds the resistance of the cake increases and filtration rate decrease.
At a certain point process is stopped and press is emptied and cycle is restarted.

23. Washing operation:
The procedures for the washing the press are as shown in the following steps
■ Filtration proceeds in the ordinary way until the frames are filled with cake.
■ To wash the filter cake the outlets of the washing plates are closed.
■ Wash water is pumped into the washing channel. The water enters through the inlets
on to the surface of the washing plates.
■ Finally washed water escapes through the outlets of that plate.

24. Application…
Pharmaceutical industry :
Enzymes, amino acids, antibiotics, pharmaceutical intermediates, bulk drugs, medicine, blood products,
antibiotics calcium phytate, Chinese inositol, growth derived sand, organic phosphorus, glucoamylase.
Chemical industry:
Dyes, pesticides, silicic acid, glycerin, white carbon, busy, sodium carbonate, additives, basic chemicals,
chemical filler, pigment, white alumina, manganese, caustic soda, soda ash, alkali salts mud, saponin,
graphite.
Food industry :
Wine filter press, yeast, fruit juice filter press, edible oil, vegetable oil, soy sauce, sugar mills, rice wine,
white wine, fruit juices, soft drinks, beer, yeast, citric acid, vegetable protein, plant density sweetener,
glucose.
Environmental Engineering :
Chemical waste water, wastewater filter press, mining wastewater filter press, domestic wastewater, waste
water, waste steel, waste removal, leather waste water, ports silt, mud, salt mud wastewater.
Clay industry :
Kaolin, bentonite, activated clay, clay, electronic ceramics clay.

25. ADVANTAGES…
 Construction of the filter press is simple and variety of materials can be used.
 It is provided a large filtering area in the relatively small floor space.
 The sturdy construction permits the use of the considerable pressure difference.
 Efficient washing of the cake is possible.
 It produces dry cake in the form of slab.

26. DISADVANTAGES…
 It is a batch filter so there is a good deal of down time which is non productive.
 The filter press is an expensive filter.
 Operation is critical as the frames should be full other wise the washing is inefficient and the cake is
difficult to remove.
 The filter press is used for the slurries containing less than 5% solids.