A brief introduction to drying, its process and main dryers used in pharmaceutical industries.

1. Drying & Its
Process
By:- Siddharth Kumar Sahu

2. Content
• Definition
• Applications of Drying
• Introduction to Drying Process
• Calculation
• Classification of Drying
oTray Dryer
oVacuum Dryer
oFluidised Bed Dryer
oFreeze Dryer (Lyophilisation)

3. Definition
• “Drying is defined as the removal of liquid from solids by
vaporisation with the aid of heat”
or
“Drying is defined as the removal of all or most of the
liquid or Other liquid from a material by the application
of heat to cause thermal vaporization.”
• There are different ways and mechanism to remove liquids.
Drying is accomplished by thermal technique and thus involve
the application of heat.

4. Applications of Drying
• Used in manufacturing of granules.
• Used to reduce the bulk & weight of material.
• It helps in the preservation of crude drugs or plant from mould
growth.
• It helps in the size reduction process.
• Drying makes materials more convenient in packaging,
transporting, preserving, fabricating, and improves quality of
products.

5. Introduction to Drying Process
• It can be described by three process…..
1. Energy transfer from an external source to the water or
organic solvent.
• Direct or indirect heat transfer.
2. Phase transformation from water solvent- from a liquid
state to vapour state.
3. Generated vapours is transfer to away from API/material.

6. Calculation
• The rate of drying of sample can measured by following
equation….
• Drying Rate =
𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑖𝑛 𝑠𝑎𝑚𝑝𝑙𝑒 (𝑘𝑔)
𝑇𝑖𝑚𝑒 ℎ × 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝐷𝑟𝑦 𝑆𝑜𝑙𝑖𝑑 (𝑘𝑔)
• Loss on Drying =
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑖𝑛 𝑠𝑎𝑚𝑝𝑙𝑒 (𝑘𝑔)
𝑇𝑜𝑡𝑎𝑙 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑤𝑒𝑡 𝑠𝑎𝑚𝑝𝑙𝑒 (𝑘𝑔)
× 100
• The measurement of moisture content is expressed in
• % moisture content =
𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑖𝑛 𝑠𝑎𝑚𝑝𝑙𝑒
𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒
× 100

7. Classification of Drying
• Static Bed Dryer
I. Tray dryer
II. Freeze dryer
• Moving Bed Dryer
I. Drum dryer
• Fluidised Bed Dryer
• Vacuum Bed Dryer
• Pneumatic Bed Dryer
I. Spray dryer

8. Tray Dryer
• Principle- Tray type of dryer is operates by passing hot
air, over the surface of a wet solid . That spread over
trays arranged in racks, and due to forced convection
moisture is removed.
• Construction-
• It is a double walled cabinet with Single or Two
doors.
• The gap between two walls is filled with high density
fibre glass wool insulation material to avoid heat
transfer.
• Stainless steel trays are placed on the movable
trolleys.

9. Tray Dryer

10. Vacuum Dryer
• Vacuum Dryer:
In vacuum dryer, material is dried by the application of
vacuum. When vacuum is created the pressure that is
lower so that water boils at a lower temperature. Hence
water evaporates faster.
• It is a good example of conduction drier.
• The oven is connected through a condenser and liquid
receiver to a vacuum pump.
Advantages of vacuum oven:
• Drying takes place at a low temperature.
• There is little air present so, there is minimum risk of
oxidation.

12. Fluidised Bed Dryer
• The equipment works on A principle of fluidization of the feed
materials.
• In fluidization process, hot air or gas flow is introduced
through the bed of solid particulates. ... Hence the bed is said
to be fluidized and the particles are suspended in the fluid.
• It is suitable to dry uniformly the processed material with
comparatively high moisture content to low moisture content.
• The wet powder is dried in a fluidized bed by heat exchange
with a gas.

13. Fluidised Bed Dryer construction…
Fluidized Bed Dryer Consists of A.....
• Compressed Air System,
• Pre-filter,
• Heating Device,
• A Perforated Platform,
• A Thermostat And A Timer.

14. Fluidised Bed Dryer Diagram….

15. Freeze Dryer
(LYOPHILIZATION)
• It is also called as sublimation drying process, In that process water
is sublimed & removed from the product after it is frozen at the
reduced pressure.
• Theory:
• Material is frozen in a container connected to a high vacuum
system.
• Under these conditions, heat transferred is used as latent heat of
sublimation to the product by means of radiant heat.
• Than water vapours are removed by condensation.

16. Construction:
• Chamber for vacuum drying: having shelves for keeping the
material.
• Vacuum source: vacuum pump is connected to the chamber.
• A heat source: heat is provided by conduction or radiation or
both.
• A vapour removal system: the condenser consists of large
cooled surface by solid carbon dioxide mixed with acetone or
ethanol

17. Working:
• Pre-treatment : first solution is concentrated under normal
vacuum dryer before introducing in the chamber.
• Pre-freezing : ampoules, vials & bottles having aqs. solution
is packed & frozen in cold shelves at a temperature below -
500C.
• Primary drying : The material is spread. Than temperature &
pressure is set. Than heat is supplied.
• Vapours are removed from the chamber. 98-99% moisture
removes during this drying.

18. • Secondary drying : remaining moisture is removed
by vacuum drying at 50-60 *C. Secondary drying takes
about 10-20 hrs.
• Than products are packed in aseptic condition
immediately after drying.

19. References
• R. M. Mehta, A textbook of “Pharmaceutics-1”, Sixth
Edition Reprint 2018, Vallabh Prakashan, Page No. 208-
223.
• www.google.com
• www.slideshare.net
o Introduction To Drying Processes Mr. R. R. Patil