The document discusses various drying techniques used in the pharmaceutical industry including tray drying, fluidized bed drying, vacuum drying, and freeze drying. Tray drying uses heated air circulation to dry materials on shelves. Fluidized bed drying uses heated air to fluidize and dry particles. Vacuum drying occurs below atmospheric pressure allowing drying at lower temperatures. Freeze drying works by freezing materials and then sublimating ice under vacuum to dry heat-sensitive substances. Each method has advantages and disadvantages for different material types and applications.

1. Mr. G.A.Shete

2.  Drying:
 The final removal of liquid from solids by vaporization with
the aid of heat.
 The equipment used for drying is called a Dryer.
 Theory of Drying:
It involves both Heat & Mass transfer.
Two steps are involved i.e.
Heat must be supplied to provide latent heat of
vaporization.
The liberated vapour must be removed by moving an air
stream.
dw/dØ = q / λ

3. dw/dØ =the rate of evaporation pounds of water per hour
q= overall rate of heat transfer
λ= latent heat of vapourisation of water (BTU per hour)
 Applications of Drying:
 In the pharmaceutical industry it is used as a unit process in the
manufacture of granules which can be dispensed in bulk or
converted into tablets or capsules
 Drying can also be used to reduce the bulk & weight of the
material, thereby lowering the cost of transportation & storage.
 It helps in the preservation of crude drugs of plant from mould
growth , which occurs due to presence of moisture.
 It helps in the size reduction of crude drugs. The presence of
moisture in the crude drug does not allow it to get powdered
easily.

4.  Drying is also used in the processing of materials i.e. the
preparation of dried aluminum hydroxide, the spray drying of
lactose & in the preparation of solid extracts.
 Factor affecting the rate of drying:
 Surface area of material: increase in surface area leads to
increase in rate of drying.
 Rate of heat transfer by increasing airflow, temperature
gradient.
 Moisture content of the material: time taken for drying will be
more if the moisture content is more.
 Time and temperature: High temperature with less time drying
will takes place without degrading the material.
 Difference in humidity (Hs-Hg) between surface layer and
atmospheric: if difference is more rate of drying will be fast

5.  FLUIDISED BED DRYER
 Working of FBD
 Two types of FBD are used in pharmaceutical industry. There
are:
 1. Vertical FBD
 2. Horizontal FBD
 The fluidizing air stream is induced by a fan which is mounted
in the upper part of dryer.
 The air is heated to the required temperature in air heaters and
passed through the wet material contained in a drying chamber
fitted with a wire mesh support at bottom. The air flow rate is
adjusted by means of recirculation control and fabric filter bags
are provided to prevent the passage of fine particles. This type
of FBD is a batch type dryer and the

6.  drying chamber is removed from the unit for charging ad
dumping. The FBD available in different capacities
ranging from 5 kg to 200 kg with an average drying time
of about 20-40 min.
Fig: Fluidised Bed Dryer

7.  Use:
Used in granulation process for tablet preparation
It is used in coating.
Used for drying of filter cake.
 Advantages:
It give high drying rate.
Suitable for thermolabile material.
Drying takes place of individual particles.
Temperature can be controlled.
Prevent the risk of migration of soluble material.
It can mostly used for drying of granules.
 Disadvantages:
Turbulence produces cause attrition of particles.
Movement can generate electrical charges.

8.  TRAY DRYER
 The simplest form of dryer , the source of heat ( electric heater
or steam coil) is at floor level & relies on natural convection.
Therefore no efficient heat transfer. Modern dryer consists of
well insulated cabinet wit strategically placed fans and heating
coils.
 The air circulates through the dryer at 200- 2000 feet / mins. In
small ovens , there may be provision for a single passage of
heated air , while in large units, the thermal efficiency is
improved by recirculation of air which is reheated after its
passage over each shelf.
 The forced air circulation increases heat transfer & reduces
local vapour concentration.

9.  Application of tray dryer.
 1) For drying of crude drugs
 2)For chemicals
 3)For powders
 4)For Granules used in tablet manufacturing

10.  VACUUM DRYER
 This equipment is a good example of conduction drier.
The vacuum oven consists of a jacketed vessel to
withstand vacuum within the oven.
 There are supports for the shelves giving a larger area for
conduction heat transfer. The oven can be closed by a
door.
 The oven is connected through a condenser and liquid
receiver to a vacuum pump. Operating pressure can be as
low as 0.03-0.06 bar. At this pressure water boils at 25-
35C. In the Pharma industry an oven of the size of about
1.5 m cubes having 20 shelves is commonly used.

11. Fig: Vaccum Dryer

12.  Advantages:
It is useful for drying of heat sensitive materials
because drying take place at a low temperature.
A porous & soft dry extract is produced when a liquid
extract is dried in a vaccum dryer.
The valuable solvent can be recovered from the
extract.
 Disadvantages:
The labour & running costs are rather high.
The vaccum dryer is of limited capacity.
Heat transfer coefficients are low.

13.  FREEZE DRYER or 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. Vapour pressure of material is reduced
below the vapour pressure at which it is dried i.e. below
the triple point.
Under these conditions, heat transferred is used as latent
heat of sublimation to the product by means of radiant heat.
Ice sublimes to vapours. Water vapours are removed by
condensation.

14.  Construction:
 Components of Freeze dryer:
 A chamber for vacuum drying
 A vacuum source
 A heat source
 A vapour removal system
 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.

15.  Working:
 Pre-treatment : first solution is concentrated under normal
vacuum dryer before introducing in the chamber. This reduces
drying time by 8-10 times.
 Pre-freezing : Ampoules, vials & bottles having aqueous
solution is packed & frozen in cold shelves at a temperature
below -50C.
 Primary drying :
 The material is spread. Temperature & pressure are kept below
the triple point of water. Heat is supplied. Ice sublimes into
vapours. Vapours are removed from the chamber. 98-99%
moisture removes during primary drying.
 Secondary drying :
 Remaining moisture is removed by vacuum drying at 50-
60C. Secondary drying takes about 10-20 hrs.

16. Fig: Freeze Dryer
Packing :
Biological products are dried packed in aseptic condition
immediately after drying.
Use:
Thermolabile substances, microbiological cultures, biological
products.

17.  Advantages:
 The product obtained is light and porous having excellent
solubility.
 The chances of hydrolysis are minimized as drying takes
place at a very low temperature.
 Drying takes place under vacuum; hence oxidation is
minimized as there is no contact with air.
 The heat-sensitive materials can be dried.
 The loss of volatile material is minimum.
 The freeze-dried material can be stored at room
temperature if it is properly sealed in an inert atmosphere.
 The sterility of the product can be maintained.

18.  Disadvantages:
 The process is very expensive because a complicated plant
is used.
 The product obtained is very hygroscopic, so packaging
requires special precautions.
 The period of drying is quite long.(usually not less than 10
hours)