Pharmaceutical Engineering: Size separation

objectives, applications, mechanism of size separation, the official standard of powders, sieves, sieve shaker, cyclone separator, air separator, bag filter, elutriation tank

1. SIZE SEPARATION
Parag Jain
Assistant Professor
Chhattrapati Shivaji Institute
of Pharmacy
Durg, Chhattisgarh
Presented by

2. Size separation:
• Size separation is a unit operation that involves the
separation of a mixture of various sizes of particles
into two or more portions by means of screening
surfaces.
• It is also known as sieving, shifting, classifying or
screening.
• This is based on the size, shape, and density of the
particles

3. Importance:
• To formulate a uniform dosage form
• To prepare granules of required size
• As a quality control tool for analysis
• To test the efficiency of a size reduction equipment
or process
• To separate undesirable particles
• To optimize the process condition (screening feed
rate)

4. Sieve
• It is simplest and sieving is the most frequently used
• It is made up of wood or metal fitted with a wire cloth which is
made up of copper alloys, stainless steel, silk, nylon or terylene
, having a specific diameter of the wire.
• Each sieve is given a definite number which indicate a
number of the meshes present in a length of 2.54 cm or
one inch.
• Sieve numbers: 4,6,10, 22, 44, 60, 85, 120

5. Sieves commonly used in pharmaceutical processing includes:
•Woven wire sieves
•Bolting cloth sieves
•Closely spaced bars
•Punched plates

6. PERFORATED PLATE SIEVES
■Sieves may also be made by drilling holes in metal plate,
so that this type will have circular apertures as against
the square apertures of the wire mesh sieve.
■In general, these sieves are used in the larger sizes and
can be made with greater accuracy than
wire-mesh sieves, as
susceptible to distortion
well as being less
in use. This type is
commonly used also as screens in impact mills.

7. Usually, the holes are spaced with their centers
arranged at the apices of equilateral triangles, so that
all the apertures are equidistant
A
Perforated plate sieve.

8. ■Similar standards are laid down with the appropriate
equivalent specifications for plate thickness and
nominal width of the bridge (dimension A in the
Figure) which control the strength of the sieve in the same
way as wire diameter in wire mesh sieves.

9. Materials Used for Sieves
1)The wire should be of
uniform, circular
cross-section.
2)The material should have suitable strength
to avoid distortion
3)Be resistant to corrosion by any substances
that may be sifted.

10. METALS
❑ Iron wire
Advantage
cheap,
Disadvantage
•
Rusting
•
Iron contamination of products

11. METALS
❑Coated Iron (coating with galvanizing or tinning).
Advantage
•
Increases the protection against corrosion
•
Increases the strength
Disadvantage
Coating after manufacture lead to some
variation in the mesh size.

12. METALS
❑Copper
Advantage
Avoiding the risk of iron contamination
Disadvantage
As a soft metal, meshes can be distorted
easily.

13. METALS
□ Copper Alloys (brass and phosphor-bronze)
possessing good
Advantages
•
Resemble copper in
resistance to corrosion
•
Their strength is greater so that less risk
of the meshes distortion.

14. METALS
□Stainless Steel
Advantages
•
Good resistance to corrosion
for pharmaceutical
•
Adequate strength
•
The most suitable
purposes.
Disadvantages
Expensive

15. NON-METALS
□Used when all risk
of metallic contamination be avoided.
□Used for sieves with fine meshes, since
non-metal fibers are stronger than a metal
wire of similar thickness.

16. NON-METALS
□ Materials of natural origin (hair
and silk), are used but synthetic
fibers (nylon and terylene)
are more suitable
Advantages of synthetic fibers
•
Have more strength and resistance to
corrosion.
•
can be extruded in all
a wide variety
diameters, so
of sieves to beenabling
made.

17. Standards for Powders
•Standards for powders for pharmaceutical purposes
are laid down principally in the Indian
Pharmacopoeia which states, that
the degree of coarseness or fineness of a
powder is differentiated and expressed by the
size of the mesh of the sieve through which the
powder is able to pass.

18. Grading of powders
Coarse powder : 10/44
Moderately coarse powder : 22/60
Moderately fine powder : 44/85
Fine powder : 85
Very fine powder : 120

19. Sieving Methods
❖Sieves should be used and stored with care, since a sieve
is of little value if the meshes become damaged or
distorted.
of the
should
use of
never
sieves for
be forced
❖With the exception
granulation, material
through a sieve.
❖ Particles, if small enough, will pass through a
sieve easily if it is shaken, tapped, or brushed.

20. Sieving
• Separation of coarse particles from fine particles by using
set of sieves.
Sieving Methods:
• Agitation
• Brushing
• Centrifugation

22. Agitation method
• Oscillation
• Vibration
• Gyration

23. Oscillation method
• Moves back and forth
• Material roll on the surface of the sieve

24. Vibration method
• Sieve move with High speed
• Rapid vibration imparted to the particles on the sieve
• Particles are less likely to “blind” the mesh

25. Gyration method
• Rotatary movement small amplitude.
• Considerable intensity.
• Spinning motion to the particles.
• Particles suitably oriented to pass through the sieve.

26. Mechanical Sieve Shaker
Fig: 29.1

27. Sieve details
• Set of 12 sieves
• Arranged in ascending order
• From 6 to 200 No
• Large size sieve at the top
• Small size at the bottom
• Receiver at the bottom of the small size sieve

28. Sieving procedure
• Powder kept in top sieve
• Shake the sieve
• Sieve gyrates and vibrates
• Weight of powder on each sieve
• Find the percentage of residue in each sieve
• Percentage = Residue in each sieve X 100
Total wt of powder

29. Advantages
• Size analysis data under controlled condition
• Inexpensive
• Simple & Rapid process
• Little variation between operation

30. Disadvantages
•Over loading sieve result error
• Insufficient time leads to wrong results
• Electrostatic attractions leads to aggregation
• Humidity, Hygroscopic powders leads to aggregation
• Pale like or long fibrous will not pass

31. I. MECHANICAL SIEVING METHODS
Principle:
Based on methods as:
Agitation
Brush the sieve
Use centrifugal force

32. 1. Agitation Methods
Sieves may be agitated in a number of different ways:
▪Oscillation (move back and forth)
The sieve is mounted in a frame
that oscillating.
Advantages
Simple method
Disadvantages
The material may roll on the surface of the sieve,
and fibrous materials tend to “ball”.

33. ▪Vibration
The mesh is vibrated at high speed, often by an
electrical device.
Advantages
The rapid vibration is imparted to
the particles on the sieve and the
particles are less likely to “blind” the
mesh.

34. 2. Brushing Methods
■A brush can be used to move the particles on the surface of
the sieve and to keep the meshes clear.
■A single brush across the diameter of an ordinary circular
sieve, rotating about the mid-point, is effective;
■In large-scale production a horizontal cylindrical sieve is
employed, with a spiral brush rotating on the longitudinal
axis of the sieve.

35. 3. Centrifugal Methods
■Use a vertical cylindrical sieve with a high speed
rotor inside the cylinder, so that particles are
thrown outwards by centrifugal force.
of air created by the movement
■The current
helps sieving.
■Especially is useful with very fine powders.

36. ■Industrial methods of particle size separation
based on sedimentation or on elutriation.
■Wet sieving is more efficient than the dry process,
because particles are suspended
passing easily through the sieve
readily and
with less
blinding of the meshes.
II.WET SIEVING METHODS
(FLUID CLASSIFICATION)

37. A suspension of the solids in a fluid, most commonly water, is
placed in a tank and allowed to stand for a suitable time.
The upper layer is then removed, giving a single separation, or
the suspension may be collected as a number of fractions by
arranging for the pump inlet to remain just below the surface.
The suspension pumped out will then contain
successively coarser particles.
SEDIMENTATION METHODS
1. Sedimentation Tank

38. Advantages
Simple process
Disadvantages
•
A batch process only
•
It does not give a clean split of particle sizes because some
small particles will be near the bottom of the tank at the
beginning of the process and so will be removed with the
coarse particles.

39. Cyclone Separator
Principle:
•It is used to separate solid from fluids
• It depends not only on the particle size, but also on density of
particles
• It is also possible to allow fine particles to be carried by the fluid
Working:
• Feed is introduced tangentially at very high velocity of air
• Rotatory movement takes place within the vessel
• Centrifugal force through the solids to the walls
• As the speed of air diminishes the particles fall to the conical
base

40. Fig: 31.2 Cyclone separator

41. Uses
• used to separate the solids from gases
• used to separate the solids from liquids
• used to separate the heavy or coarse fraction from
fine dust

42. Air Separator
Principle:
• Centrifugal force is used to separate solids
• The air environment is obtained by means of rotating
disc and blades
•To improve separation the stationary blades are used

43. Uses
• its often attached to ball mill / hammer mill

44. Bag Filter
Principle:
• In a bag filter, size separation of fines.
• The fines is achieved in two steps.
• In the first step, the milled powder is passed through a bag
filter(cloth) by applying suction on the opposite side of feed
entry.
• In the next step, pressure applied in order to shake the bags
so that powder adhering to the bag falls off, which is collected
from the conical balance

46. Construction
• It consist of a number of bags made of cotton or wool fabric.
• A hopper is arranged at the bottom of the filter to receive the
feed.
• At the top of the metal container, a provision is made for the
exhaust.
• Adjacent to this, a bell crank level arrangement is made to
bring the filters to normal atmospheric conditions

47. Working
•The working of bag filter consist of two steps
• In the first step, the feed is separated from air by passing it
through the cloth bags
• In the subsequent step, the bags are shaken to collect the
fines that are adhere to the bags.
Uses:
• Its used along with the cyclone separator.
• It is connected to the discharge end of the fluidized energy
mill

48. ELUTRIATION METHODS
■Elutriation depends on the movement
of a fluid against the direction of
sedimentation of the particles.
■For the gravitational system, the
apparatus consists simply of a
vertical column with
near the bottom
an inlet
for the
suspension, an outlet at the base
for coarse particles, and an overflow
near the top for fluid and fine
particles.
Fluid and fine
particles
Suspension
Coarse
particles

49. One column will give a single
separation into two fractions, but it
must be remembered that this will
not give a clean cut, since there is a
velocity gradient across the tube,
resulting in the separation of
particles of different sizes according
to the distance from the wall.
Elutriation
Fluid and fine
particles
Suspension
Coarse
particles

50. ■If more than one fraction is required, a number of tubes of
increasing area of cross-section can be connected in series. With
the same overall flow-rate, the velocity will decrease in
succeeding tubes as the area of cross-section increases, giving a
number of fractions.
Multi-stage elutriator
(1) to (4) are fractions of
decreasing particle size

51. ■Advantages
A.The process is continuous.
B.The separation is quicker than with sedimentation
be dilute; which may
■Disadvantages
The suspension has to
sometimes be undesirable.

52. APPLICATIONS OF SEDIMENTATION
AND ELUTRIATION
Both methods are used for similar purposes,
usually following a size reduction process, with the
object of separating oversize particles, which may
be returned for further grinding, used for other
purposes, or discarded according to the
circumstances.

53. Website: www.probecell.com Email: [email protected]
Ph: 7415211131
Office: Smriti Nagar, Bhilai, Chhattisgarh - 490020
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