Drying
Drying is defined as removal of small amounts of water or
other liquid from a material by the application of heat.
Applications:
Preparation of bulk drugs
Preservation of drug products
Improved characteristics
Improved handling
Spray Drying
Principle:
The fluid to be
dried is atomized into fine droplets,which are thrown radially into a moving
stream of hot gas.
The temperature of
the droplets is immediately increased and fine droplets get dried and result in
spherical particles.
Spray Drying process
Concentration of feed
Atomization
Droplet air contact
Droplet drying
seperation
Advantages
·
Continous process
·
Uniform size particles
·
Suitable for drying sterile products
·
Soluton or suspension can be dried in one step.
·
Sutiable for both thermolabile and thermostable
materials.
Disadvantages
·
Equipment is bulky and expensive
·
Thermal efficiency is low as much heat is lost
in the discharged gases.
·
Rapid drug release rates often exhibiting a
burst effect
Uses
·
Used if
the quantity of material to be dried is large
·
If the
product is thermolabile
Examples : Vaccines , Vitamins, Plasma, Serum,
Chloramphenicol , Dextran
Spray Congealing
o
This
process is alternative to spray drying for the encapsulation of solid particles
o
The transition of a melt from a soft or fluid
state to a rigid or solid state by cooling is called congealing.
o
Spray cooling (alternatively spray congealing)
is defined as a process by which a melt is formed into particles of spherical
shape by spraying the melt into a cooling chamber through which ambient or
cooled, low temperature air is passing.
o
Rotary (wheel) atomizers and nozzles are used to
spray the melt.
o
It is a most convenient method of transforming
melted feedstocks into free-flowing
particulates
of controlled particle size.
Principle :
·
Particles are suspended in a molten coating
material and resultant slurry is pumped into spray dryer in which cold air is
circulated.
·
Slurry droplets congeal on coming into contact
with air and are collected.
·
Coating agents employed are waxes
·
Higher amount of coating agents than that in
spray drying are required.
Uses
·
Taste masking
·
Sustained release formulations
Submitted :Miss.Rubiya Yasmeen.
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