1. Objectives The importance of drying in pharmacy
The differences between drying and evaporation
Definition of drying
Purpose of drying
The names of different dryers used in pharmacy PH

2. Why do we dry the clothes?
Why do we dry the green leaves or crude drugs?
Why do we dry the washed vessels?
Why do we dry the tablet granules?
Why do we dry the bottles, glass apparatus after cleaning? PH

3. Importance of drying Drying is done to carry out size reduction
Drying is done to avoid deterioration on storage
Drying is done to dry the tablet granules to reduce the moisture
Drying reduces the bulk and weight hence, less transportation charges
Drying is done for certain preparations
Ex: spray dried lactose PH

4. Definition
It is defined as a process in which the liquid is removed from a material by the use of heat PH

5. Differences Drying Removal of less amount of moisture
Drying occurs below boiling
point
Done to get a stable dry
product
Emphasize on solid product
Evaporation
Removal of large amount of
liquid
Evaporation occurs more at
boiling point
Generally done for
concentration
Emphasize on reducing the
volume PH

6. Choice of method and equipment
Used in drying are depends on:
Physical characteristics of the product
Thermolabile or not
Nature of solvent used
Quantity of the product
Source of heat applied
Economic factors PH

7. Types of dryers Dryers for dilute solutions, suspensions and slurries
a) Drum dryer
b) Spray dryer
Dryers for damp solid materials
a) Tray or shelf dryer
b) Tunnel dryer
c) Rotary dryer
d) Fluidized bed dryers (FBD)
e) Vacuum dryer
f) Freeze dryer PH

8. Tray dryer Also known as cabinet or compartment dryer
These are essentially hot air ovens
Material spread in trays in thin layer
In large scale, heating is done by forced circulation
Fig: 58.1 PH

9. Material is over heated It is long duration process
It is for batch process
Material is over heated
It is long duration process
Loading and unloading, labour costs are more
Fig: 58.2 PH

10. Truck dryer Trays are loaded on trucks (racks fitted with wheels)
Loaded trucks are pushed and taken
out of the drying chamber
Convenient in loading and unloading of the material
Fig: 58.3 PH

11. Vacuum dryer Also known as vacuum oven Consists of jacketed vessel
Has to withstand vacuum in the
oven and steam present in the jacket
Oven and dryer can be loaded with air tight seal
Connected to a vacuum pump through a condenser and receiver
At a vaccum of 0.03 to 0.06 bar water boils at 350 C
Fig: 58.4 PH

12. Advantages Very suitable for heat sensitive products
Porous and friable product is obtained
Valuable solvents can be recovered
Fig: 58.5 PH

13. Disadvantages Heat transfer may be low and non uniform
Limited capacity
Labour and running costs are high
Finely divided powder may be drawn into the vacuum pump
Fig: 58.6 PH

14. Objectives Construction and working of fluidized bed dryer
Advantages and disadvantages of fluidized bed dryer PH

15. Fluidized bed dryer (FBD)
Gas is allowed to flow upward through
a bed of material
Velocity should be greater than the
settling velocity of the particles
Particles are lifted in the gas stream
Fig: 59.1 PH

16. The mixture of solid and gas is fluidized
Each solid particle is surrounded by drying gas
Drying takes place at a shorter period
Fig: 59.2 PH

17. Types of Fluidized bed dryers
Vertical type fluidized bed dryer
Used for batch process
Horizontal type fluidized bed dryer
Used for continuous drying PH

18. Fig: 59.3 PH

19. Fig: 59.4 PH

20. Vertical type Fluidized Bed Dryer
Material to be dried is placed in Stainless Steel chamber having perforated bottom
Drying chamber fitted with wheel facilitates for loading and unloading
Filtered hot air passes through the bed with the help of induction fan PH

21. If the velocity of the air increases, the bed begins to expand
Further increase in velocity causes rapid expansion
Particles show a turbulent motion and “ fluidized ”
Fig: 59.5 PH

22. Moist air is carried away quickly
Efficient heat exchange takes place between individual particles and hot air
Moist air is carried away quickly
5kg to 200kg can be dried in about minutes
Fig: 59.6 PH

23. Advantages
These dryers are efficient and 15 times faster than conventional Tray dryers
Drying takes place from the individual particle and not from the whole bed
Heating time is short for thermolabile product PH

24. Advantages Free flowing product is obtained
Due to short time, unit has high output
Drying temperature is uniform PH

25. Disadvantages
Due to turbulent action more fines are produced but, can be avoided by using suitable binders
For too wet granules not suitable, as they stick together
May develop electrostatic charges and can be avoided by earthing the unit PH

26. Objectives The principle of freeze drying The working of freeze dryer
Advantages and disadvantages of freeze dryer PH

27. Freeze Drying It is also known as sublimation drying
It is also known as lyophillization as the
dried product has great affinity for water
( lyophillic = water loving) PH

28. Principle
First the material to be dried is frozen in suitable container
By connecting to a vacuum system, the vapor pressure is greatly reduced
The temperature and pressure reduced to the values below the triple point
Mild heat is supplied and the frozen ice sublimes directly to vapor state PH

29. Components of Freeze dryer
Chamber for chilling the sample
A vacuum source
A heat source
A vapor removal system
Fig: 60.1 PH

30. Process It is carried out for batch process
The product is frozen first by putting on a shelf circulating refrigerants
After freezing, vacuum is applied to the chamber PH

31. Fig: 60.2 PH

32. Process is continued till a dry, spongy solid is obtained
Mild heat is supplied to the product by electric coils or by circulating hot water
Process is continued till a dry, spongy solid is obtained PH

33. Products to be freeze dried are sterilized and aseptically distributed into final containers
Container kept open during the process and sealed immediately after drying process
Fig: 60.3 PH

34. Advantages The product is light, porous with good solubility
No chances of hydrolysis because, drying is at low temperature
No chances of oxidation because of no contact with air
Freeze dried products are more stable than vacuum dried product PH

35. Disadvantages Very expensive Time taking process
Dried product is very hygroscopic and requires special packing precautions PH

36. Uses Mostly suitable for highly thermolabile products
Used for drying biological products such as blood plasma, vaccines, enzymes, microbiological cultures, hormones and antibiotics PH