This document discusses various drying methods used in pharmaceutical manufacturing. It defines drying as removing liquid from a material through heat transfer and evaporation. Several dryer types are described, including drum dryers, spray dryers, tray dryers, tunnel dryers, rotary dryers, fluidized bed dryers, vacuum dryers, and freeze dryers. Each method is explained along with its advantages and disadvantages. Freeze drying and vacuum drying allow heat-sensitive materials to be dried at low temperatures. Larger dryers like spray dryers and rotary dryers provide continuous high-volume drying.

1. Supervised by
Dr. Hamiduddin
Presented By
Dr. Mohammed Abdullah Tauheed Ahmed

2. Definition
Drying is defined as a process in which the liquid is removed
from a material by application of heat & is accomplished by the
transfer of liquid from a surface into an unsaturated vapor
phase.

3. NEED OF DRYING
 To make products stable.
 Preparation of powder and granules.
 Reducing the bulk and weight.
 Dried before extraction to facilitate grinding and to avoid
deterioration.
 Preparation of certain products like dried Aluminum hydroxide,
spray dried lactose & powder extracts.

4. Choice of Method of Drying
 Product is sensitive to heat or not.
 Nature of solvent to be removed.
 Process is to be carried out under aseptic condition.
 Quantity of products to be dried.
 Available source of heat.
 Cost involved.

5. Types of dryer
Dryer for dilute solutions, Dryers for damp solid
suspensions and slurries. materials.
Drum dryer Tray or shelf dryer
Spray Dryer Tunnel dryer
Rotary dryer
Fluidized bed drying
Vacuum dryer
Freeze dryer

6. Drum Dryer
 Liquid is kept in a feeding pan
in which the heated drum is
applied to the surface and
spreads to a film which dries
rapidly.
 The dried product is scrapped
from the surface of the drum
by means of Doctors Knife’ in
the form of flakes.
 The drying rate can be
controlled by adjusting
rotation speed and temperature
of drum.

7.  Advantages
 It is quick method because of its large surface area, material is
dried in few seconds.
 Instrument is compact which requires small space for operation.
 The equipment can be enclosed in vacuum chamber thereby
temperature of drying can be reduced.

8. Uses
 Milk products
 Starch powder
 Iron salts
 Suspensions of kaolin or zinc oxide

9. Disadvantage
 The only disadvantage of drum dryer is that operating
conditions are critical and it is necessary to introduce careful
control on
 Feed rate
 Temperature of drum,
 Thickness of film
 Speed of rotation of drum.

10. Spray dryer:
 Spray dryers are used only
to dry liquid materials.
 Liquid is spread in fine
droplets into moving
stream of hot air where
they are evaporated rapidly
before reaching the wall of
the drying chamber.

11. Working
• Material is to be dried is fed to the
atomizer.
• Disc below the atomizer is spins @
35000 rpm.
• Hot air is introduced from inlet
•Dried powder is separated in cyclone
separator.
•Separated material is collected in
chamber. D. Atomizer
A. Heated air inlet
E. Drying chamber
•Flow rate is controlled by valve H. F. Solid gas separator
G. Product collector
H. Air controlling valve

12. Phenomenon

13. Caution
• Inlet air temperature should be constant. Too high
temp can result in improper drying. Similarly
excessive feed rate will affect the drying.
• Temperature should not exceed 350 c.

14. Advantages
 Material is dried few seconds.
 Since the evaporation rate is very high droplets are not
subjected to a very high temp.
 Spray dryer can be designed for drying in sterile conditions.
 The dried powder will have uniform particle size and
shape.
 Labour costs are low.
 Volatile solvent can be recovered.

15. Disadvantages
 Very bulky equipment 15mX6m drying chamber only.
 Lot of wastage of heat since air must be still hot when it leaves
the dryer to avoid condensation.
 Both above factor make it costly.

16. Uses
 Useful for all solution or in suspension form.
 For drying of thermo labile materials e.g. antibiotics.
 Suitable for both soluble and insoluble substances e.g.
citric acid, gelatin, starch.
 It can produce spherical particles in the respiratory range
e.g. dry powder inhalers.
 Drying of Boric Acid, Methyl cellulose, sulphur milk, soap
and detergents.

17. Dryers for damp solid materials
Tray Dryer and Truck dryer

18. Working
 They are essentially hot air
ovens.
 The material is to be dried is
spread in thin layers in trays
The heating is done by
forced circulation of large
volume of heated air by
means of fans.

19. Truck dryer
 In truck dryers the trays are
loaded on truck (racks fitted with
wheels) which can be pushed and
taken out easily from drying
chamber. In Pharmaceutical
industry truck dryers are
preferred over tray dryers because
of convenience in loading and
unloading the dry chamber.

20. Advantage
 Drying by means of truck or tray dryers is a batch process
rather than continuous.
 Each batch can be dried separately and same drying
equipment can be used for drying the variety of materials.

21. Tunnel Dryer
 It is modified form of the tray dryer in which oven is
replaced by a tunnel. The material to be dried is
entered at one end & dried material is collected from
the other end of the tunnel

22. Working
 The trays containing the wet material are kept over truck or
loaded on one or multiple belt conveyers which have an
automatic speed control.
 In the multiple belt conveyer system the partially dried material
which has completed one circle moves automatically from first
belt on to the second belt running in opposite direction.

23. Rotary Dryer
 It is modified form of tunnel dryer which consists of a
horizontal tube, slightly inclined

24. Working
 Horizontal slightly inclined tube is heated.
 Tube rotates slowly at about 10 rev/min due to rotation of tube
material is turned over by tumbling effect and drying takes place
from individual particles and not from static bed.
 When recovery of solvent is needed vacuum dryer may be fitted to
tube. Small vacuum rotary dryer are used for aseptic works.

25. Advantage
 These type of dryers are used for continuous drying of powders
and granules on large scale and several tones of drugs can be
dried per hour.

26. Fluidized bed dryer

27. Working
 In this dryer gas is allowed to
flow upward through the bed of
solid particles to be dried at a
velocity greater than the settling
velocity of the particles, due to
which particles get partially
suspended in the gas stream. This
behave like liquid and solids are
said to be fluidized.

28. Advantages
 5 kg to 200 kg of materials can be dried in 20 to 40 minutes.
 Drying is taken place from individual particles and not from
whole bed.
 Labor costs are reduced.
 Due to short drying time the unit has a high output.

29. Disadvantages
 Due to turbulence large quantity of fines are produced (this defect
may be overcome by using suitable binder.).
 Too wet granules stick together on drying therefore too wet
granules should not be used.
 Many powders develop electrostatic charges during fluidization.
So efficient electrical earthing of drying chamber is necessary.

30. Vacuum Dryer

31. Working
 For drying the material is spread on trays which are
placed on steam heated shelves in the jacket of
vacuum oven.
 It provides large surface area for heat transfer by
conduction and is provided with door.
 The oven is connected through condenser and receiver to a
vacuum pump. The vacuum pump can be directly
connected to oven.

32. Advantages
 Thermo labile substances can be dried at a low temperature and
chances of oxidation are reduced.
 During the manufacture of dry extract, a porous and friable
product is obtained which is especially useful in tablet
manufacturing.
 By the use of condenser the solvent can be recovered from the
product.

33. Disadvantages
 Heat transfer may be low and non uniform.
 It is not be suitable option for large scale drying.
 Labor and running costs are high.
 After drying a grinding process is necessary to get powder
product.
 There is danger that the finally powder material may be drawn off
by vacuum pump, and filter that requires frequent cleaning have
to be provided.

34. Freeze Drying
 In this process the initial liquid solution or suspension is
frozen, the pressure above the frozen state is reduced and the
water removed by sublimation.

35. Working
 P retreatment
 Pre freezing for solidifying water
 Primary Drying (Sublimation Under Vacuum)
 Secondary Drying
 Packing

36. Uses
 It is used in production of dosage forms which are thermo
labile such as injection solution and suspension.
 Used for drying the following products.
 Blood Plasma
 Bacterial and Viral Culture.
 Antibiotics and plant extract.
 Steroids, vitamins and enzymes.

37. Advantages
 Thermo labile materials can be dried.
 Denaturation does not occur.
 Loss of volatile matter is less.
 Material can be dried in its final container such as single dose
and multiple dose vials.
 Sterility can be maintained.

38. Disadvantages
 Equipment and running costs are high.
 The period of drying is high. Time can not be shorten.
 If packaging is to be done immediately after drying is
completed because product becomes lyophilic in nature.

39. Unani Methods of Drying
 Saya me khushk karna
 Dhoop me khushk karna
 Tannoor garm kamre me rakhna
 Chune ki potli dawa ke zaroof me rakhna
 Tahmees