Drying and Pharmaceutical Dryer

 

DRYING

·      Drying involves removal of water or another
solvent by evaporation from a solid, semisolid or liquid by application of heat and finally a liquid free solid product is obtained.

·        
Drying is accomplished by thermal techniques but nonthermal drying processes such as
squeezing wetted sponge, adsorption by desiccant (desiccation) and extraction are also used.

·      In bio products like food, grains, and
pharmaceuticals like vaccines, the
solvent
to be removed is almost invariably water.

Difference between Drying
and
Evaporation

Drying

Evaporation

Done to get a stable dry product.

Final product is
either concentrated

Suspension
or wet slurry.

Removal
of less amount of moisture.

Removal
of large amount of liquid.

Drying occurs below boiling point.

Evaporation
occurs
more at boiling point.

Emphasize on solid product.

Emphasize on reducing the volume.

 

·        
The main objectives of drying include to preserve foods and increase their shelf life by reducing
the water content and water activity; avoid the need for use of refrigeration systems
for transport and storage (expensive);
reduce space requirements
for storage and transport.

·        
In pharmaceutical technology, drying is
carried out for one or more of the fallowing reasons:

1.
To avoid or eliminate moisture which may
lead to corrosion and decrease the
product or drug stability.

2.      
To improve or keep the good properties of a material like
granules, e.g. Flowability,
compressibility.

APPLICATIONS OF DRYING

·        
Preparation of bulk drugs: In the preparation of bulk drugs, drying is the final stage of processing. A few examples are dried aluminum hydroxide, spray dried lactose and powdered extracts.

·        
Preservation of drug products: Drying is necessary in order to avoid deterioration. For examples protection of blood products, skin, tissues and crude drugs from microbial growth.

·        
Improved characteristics: Drying produces materials of spherical shape, uniform size, free flowing
and enhanced solubility.

·        
Improved
handling:

To reduce the cost
of transportation of large volume materials.

·        
To make the materials easy or more stable for handling. Drying reduces moisture
content.

·        
Drying
as final step:
Drying is the final step in evaporation, filtration, and
crystallizati
on

Mechanism
of drying

• Involves both heat and mass transfer

• Rate of evaporation is related to rate of heat transfer as

             dW/d=q/ƛ

• The rate equation for mass transfer

            dW/d=KA (Hs-H
g )

Moisture
content

• Bound moisture and free moisture

• % moisture content=  
weight of water in samplex100/ weight of dry sample

• If exactly 5 g of moist sample is brought to a constant dry
weight of 4g, calculate loss on drying and moisture content

• Percent MC is more realistic value in determination of dryer
load capacity

• Equilibrium moisture content depends on

– Temperature and humidity of air

– Properties of the material

Rate of
drying & Time of drying

Classification
and types of dryers

·        
Static Bed
Dryers (Ex. Tray Dryers, Freeze Dryer)

·        
Moving Bed Dryer (Ex. Drum Dryer)

·        
Fluidised Bed Dryer

·        
Vacuum Dryer

·        
Pneumatic Dryer (Ex. Spray Dryer)

TRAY DRYER

Principle

·        
The basic working principle of this incredible machine is the continuous circulation
of hot air.

·  
In the tray dryer,
moisture is removed from the solids that are placed in the tray by
a forced convectional heating.

·        
The moist air is removed is partially but in a simultaneous
fashion.




















1 thought on “Drying and Pharmaceutical Dryer”

Leave a Comment