Dryers and Freeze Drying.

Dryers and their classification with description of Freeze Dryers

1. INDUSTRIAL PHARMACY


ASSIGNMENT#1

DRYERS




SUBMITTED BY
HAFSA AZAM (D18E32)

SUBMITTED TO
DR. ATIF RAZA

DEPARTMENT OF PHARMACY

2. DRYERS
DRYING:
The removal of liquid from a material by the application of heat and is
accomplished by the transfer of a liquid from the surface into an unsaturated vapor phase is
known as drying.
 Drying and evaporation are distinguishable merely by the relative quantities of liquid
removed from the solid.
CLASSIFFICATION:
Drying can be done by:
 Thermal method (by the application of heat)
 Non-thermal methods
The non-thermal methods include Expression of a solid to remove liquid.
The extraction of liquid from a solid by use of solvent.
Adsorption of water from a solvent by the use of desiccants.
PURPOSE:
Drying is most commonly used in pharmaceutical manufacturing as a unit process in the
preparation of granules, which can be dispensed in bulk or converted into tablets or
capsules.
In the processing of materials e.g: the preparation of dried aluminium hydroxide.
Can also be used to reduce the bulk of weight, thereby lowering the cost of transportation
and storage.
Aids in preservation of animal and vegetable drugs by minimizing mold and bacterial growth
in moisture-laden material.
INTRUMENT USED FOR DRYING:
The instrument used for the purpose of drying is dryer.
CLASSIFICATION:
Dryers maybe classified in several different ways depending on the criteria used. Two useful
classifications are based on:
 the method of heat transfer
 the method of solid handling.

3. CLASSIFICATION BASED ON METHOD OF HEAT TRANSFER
Dryers are classified on the basis of method of heat transfer i.e; conduction, convection,
radiation. This type of classification is important in demonstrating gross differences in dryer
design, operation and energy requirements.

CLASSIFICATION BASED ON METHOD OF SOLID HANDLING
When dryers are classified according to this type of method the major criterion is the
presence or absence of agitation of material to be dried. A dryer that produces excessive
agitation is contraindicated when the dried material is friable and subject to attrition. On
the other hand, if the dried product is intended to be pulverized then the drying time can be
reduced and the process is made more efficient by the use of a dryer that produces intense
agitation during drying cycle.
The dryers on the basis of method of solid handling are classified into:
 Dryers in which material is not agitated:
o Static bed dryers
 Batch type (tray and truck, vacuum shelf, freeze)
 Continuous type (tunnel, conveyor, drum)
 Dryers in which material is agitated:
o Moving bed dryers
 Batch type (vacuum tumble, pan)
 Continuous type (rotary, turbo-tray, vibrating conveyor, tower and
cascade, screw conveyor)
o Fluidized bed dryers
 Batch type(vertical)
 Continuous type (horizontal vibrating conveyor)
o Pneumatic dryers
 Continuous type (spray, flash)
CLASSIFICATION TREE OF DRYERS BASED ON METHOD OF SOLID
HANDLING

4. FREEZE DRYERS:
Many products of pharmaceutical interest lose their viability in liquid state and readily
deteriorate if dried in air at normal atmospheric pressure. These materials maybe heat-
sensitive or may react readily with oxygen, so that in order to be stabilized they must be
dehydrated to a solid state.
The material to be dried is first frozen and then subjected under a high vacuum to heat
(supplied by conduction or radiation or both) so that frozen liquid sublimes leaving only the
solid, dried components of original liquid.
dryers
material not
agitated
static bed
dryers
batchtype
tray and
truck
vacuum
shelf
freeze
continuous
type
tunnel
conveyor
drum
material
agitated
moving bed
dryers
batch
type
vacuum
tumble
pan
continuous
type
rotary
turbo-tray
vibrating
conveyor
tower and
cascade
screw
conveyor
fluidized
bed dryers
batch
type
vertical
continuous
type
horizontal
vibrating
conveyor
pneumatic
dryers
continuous
type
spray
flash

5. MATERIALS DRIED BY FREEZE DRYING:
The materials dried by freeze drying include;
 Blood serum
 Plasma antibiotics
 Hormones
 Bacterial cultures
 Vaccines
 Many food stuffs etc.
Freeze drying is also known as lyophilization, gelsiccation or drying by sublimation.
PRINCIPLE:
Freeze drying depends on the phenomenon of sublimation, whereby water
passes directly from a solid state (ice) to the vapor state without passing through liquid
state.

Schematic pressure-temperature diagram for water showing the conditions of various
phases
From the graph it is clear that, sublimation can take place at the temperature and pressure
below the triple point, 4.579mm Hg and 0.0099◦C.
The pressure and temperature at which the frozen liquid vaporizes without converting to
liquid state is known as eutectic point.
REQUIREMENTS OF FREEZE DRYING:
1. The vapor pressure of water on the surface of the material being dried must be
higher than the partial pressure of enveloping atmosphere i.e; there must be a
positive vapor pressure driving force.

6. 2. The latent heat of vaporization must be introduced to the drying solid at such a rate
as to maintain desirable temperature levels at both surface and interior.
3. Provision must be made for the removal of evaporated moisture.
CONSTRUCTION:
Freeze dryers are composed of four basic components:
a. A chamber for vacuum drying
b. A vacuum source
c. A heat source
d. A vapor-removal system
The chamber for vacuum drying is generally designed for batch operations.
Special inlet and outlet mechanisms have been designed in some chambers to achieve
continuous drying operation.
Vacuum is achieved by pumps, steam ejectors or a combination of two.






Basic components of a typical freeze-dryer

7. WORKING:
Heat is provided by conduction or radiation or both.
Three different methods for removal of water vapors are employed:
Condensers
Desiccants
Pumps
The water vapor is removed from drying chamber and condensed in the form of a thin layer
of ice on a heat-transfer surface in the condenser.
The ice is removed intermittently by melting it with a heated fluid that is circulated through
the condenser, or in case of continuous operation by scraper blades.
In general, scraper blades and desiccants are used for large volume biologicals (serum,
penicillin) and usually not used for preparing pharmaceutical dosage forms.
STAGES OF FREEZE DRYING:
1. Pre-freezing (this avoids foaming)
2. Vacuum (reduce pressure sufficiently)
3. Primary drying (can remove unbound water)
4. Secondary drying (used to remove bound water or traces of water left after primary
drying)
FREEZE DRYING OF FIBRINOGEN:
There are seven shelves and the area of each shelf 1200 mm × 900 mm. The shelf
temperature can be adjusted in the range of − 50—70 °C. The temperature of
condenser is − 70 °C. The ultimate vacuum pressure is less than
2.6 Pa. Thermocouples are placed inside the vials on the tray during the freeze
drying process.

8. The process of freeze drying is divided into three steps. Firstly, the shelf is cooled to
− 5 °C rapidly and hold at − 5 °C for 20 minutes. Then the shelf is cooled to − 50 °C
quickly. When the temperature of the samples is cooled to − 45 °C and held for one
hour, the primary drying begins. The chamber is vacuumed to the pressure of
20 Pa and the shelf temperature is increased to − 10 °C. When the primary drying
ends after 65 hours, the secondary drying begins. Finally, increase the shelf
temperature to 5 °C, holding for 5 hours and increase the shelf temperature to
35 °C, holding for four hours. Then the whole freeze drying process ends.

ADVANTAGES:
1. Pharmaceutical companies use freeze drying to increase the shelf life of the product
such as vaccines and other injectable. By removing the water from material and then
sealing it in a vial, material can be easily stored, shipped and reconstituted when
needed.
2. Freeze-drying is used to preserve food and make it very light weight. The
process has been popularized in the forms of freeze- dried ice cream; an
example of astronaut food.
3. Minimum damage to the heat labile material.
4. Creation of porous friable structures.
5. Speed and completeness of rehydration.
6. The ability to sterile filter liquids just before dispensing.
7. The substance may be stored at room temperature without refrigeration and
be protected against spoilage for many years.
DISADVANTAGES :
1. High capital cost of equipment
2. High energy cost
3. Lengthy process time (typically 4-10 hrs. per drying cycle)
4. Possible damage to products due to change in pH and tonicity.



BIBLIOGRAPHY
 THE THEORY AND PRACTICE OF INDUSTRIAL PHARMACY BY LACHMAN/LIBERMAN’S
 https://www.biotechnologynotes.com/food-biotechnology/food-
technology/industrial-freeze-drying-process-applications-advantages-disadvantages-
food-
technology/14221#:~:text=Pharmaceutical%20companies%20often%20use%20freez
e,its%20original%20form%20for%20injection.

9.  https://www.biotechnologynotes.com/food-biotechnology/food-
technology/industrial-freeze-drying-process-applications-advantages-disadvantages-
food-
technology/14221#:~:text=Pharmaceutical%20companies%20often%20use%20freez
e,its%20original%20form%20for%20injection.