3. Introduction to Drying Process
• Drying can be described by three processes
operating simultaneously:
1. Energy transfer from an external source to the water or
organic solvent
Direct or Indirect Heat Transfer
2. Phase transformation of water/solvent from a liquid-like
state to a vapour state
Mass Transfer (solid characteristics)
3. Transfer vapour generated away from the API and out of
the drying equipment
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4. • Drying APIs is an important operation for the
production of consistent, stable, free-flowing materials
for formulation, packaging, storage and transport
• Particle attrition or agglomeration can result in major
differences in particle size distribution (PSD),
compressibility and flow characteristics
• Equipment selection
• Drying specifications
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CONTINUED.............
5. Conductive Drying of Wet Solids
• Mechanism of heat transfer:
• 1- Conduction:
• The transfer of heat from one part of a body to another, without
appreciable displacement of the particle is referred as conduction. This
mode of heat transfer is called molecular heat transfer, because it
involves the transfer of kinetic energy from one molecule to the one
adjacent to it, e.g. conduction of heat along the length of a metal rod
when one end is heated.
• 2- Convection:
• The transfer of heat from one point to another in a body of fluid, such as
a liquid or a gas, by a mixing process, is referred to as convection heat
transfer .In most cases convection involves the transfer of heat from a solid
surface to the bulk of the fluid, the change in heat induce a change in the
density of the liquid e.g. the conventional currents observed when water
is heated in a glass beaker.
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6. Continued….
• 3- Radiation:
• The transfer of heat by radiant energy in the form of electromagnetic
waves, which travel in straight lines at the speed of light, is referred to as
radiation heat transfer. As a body is heated, it emits radiant energy, e.g. sun
and infrared heat lamps. When this radiation strikes another body, portions
may be reflected
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7. Dryers in the Pharma Industry
Dryers can be classified according to:
Heat transferring methods
Direct: Fluidised, Tray, Spray, Rotary
Dryers, etc..
Indirect: Cone, Tumble, Pan Dryers, etc…
Continuous/ Batch processing
Continuous: large quantities/small residence
time
Batch: small quantities/ long residence time
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8. TRAY DRYERS
• A batch tray dryer consists of a stack of trays or
several stacks of trays placed in a large insulated
chamber in which hot air is circulated with
appropriately designed fans and guide vanes.
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10. ROTARY DRYERS
• The cascading rotary dryer is a continuously
operated direct contact dryer consisting of a
slowly revolving cylindrical shell that is
typically inclined to the horizontal a few degrees
to aid the transportation of the wet feedstock
which is introduced into the drum at the upper
end and the dried product withdrawn at the
lower end.
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12. For drying of granular solids or slurries, vacuum dryers of
various mechanical designs are available commercially.
They are more expensive than atmospheric pressure dryers
but are suited for heat-sensitive materials or when solvent
recovery is required
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VACCUM DRYERS
15. PRINCIPLE
• In the fluidized bed dryer, hot air or gas is passed
at high pressure through a perforated bottom of
the container containing granules to be dried.
• The granules are suspended in the stream of air
and are lifted from the bottom. This condition is
called fluidized state.
• The hot air is surrounded every granules to
completely dry them. Thus materials or granules
are uniformly dried.
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16. CONSTRUCTION
• Two types of fluidized bed dryers are available in the
pharmaceutical industry. There are vertical fluidized bed dryers
and horizontal fluidized bed dryers.
• The construction of the vertical fluidized bed dryer is made up of
the stain less steel or plastic. A detachable bowl is placed at the
bottom of the dryer, which is used for charging and discharging of
the materials.
• The bowl has a perforated bottom with a wire mesh support for
placing the materials to be dried. A fan is mounted in the upper
part for circulating hot air. Fresh air inlet, prefilter and heat
exchanger are connected serially to heat the air to the required
temperatures.
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17. Continued…..
• The temperature of the hot air and exit air are
monitered. Bag filters are placed above the drying
bowl for the recovery of the fines. The air flow is
adjusted by means of recircutilaon control and
fabric bags are provided to prevent the passage of
the fine particles. This type of the fluidised bed
dryer is a batch type dryer and the drying chamber
is removed from the unit for the charging and
dumping.
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18. WORKING
• The wet granules to be dried are placed in a detachable bowl. The
bowl is pushed in to the dryer. Fresh air is allowed to pass
through a prefilter, which subsequently gets heated by passing
through a heat exchanger.
• The hot air flows through the bottom of the bowl. Simultaneously
fan is allowed to rotate. The air velocity is gradually increased.
When the velocity of the air is greater than the settling velocity of
granules, the granules remains partially suspended in the gas
stream.
• After some times a point of pressure is reached at which the
frictional drag on the particles is equal to the force of the gravity.
The granules rise in the container because of high velocity gas 1.5
to 7.5 m per min and later fall back in a random boiling motion.
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19. Continued…..
• This condition is said to be fluidised state. The gas surrounds every
granules to completely dry them. The air leaves the dryer by passing
through the bag filters. The entrained particles remain adhered to the
inside the surface of the bags. Periogically the bags are shaken to
remove the entrained particles.
• Intense mixing between the granules and hot gas is provided
uniform conditions of the temperature, composition and particle size
distribution. Drying is achieved at constant rate and falling period is
very short. Any attempt to increase the air velocity may result in
entrainment.
• The residence time for the drying is about the 40 min. the materials
is left for the some times in the dryer for reaching ambient
temperature. The bowl is taken out for the discharging. The end
product is free flowing.
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20. PHARMACEUTICAL
APPLICATIONS
• It is used for the popularly drying of the
granules in the production of the tablets.
• It is used for the three operation such as
mixing, granulation and drying.
• It is modified for coating of granules.
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21. ADVANTAGES
• 1) It takes less time to complete drying that is 20 to 40
mins. Compared to 24 hours of tray dryer.
• 2) Handling time is also short. It is 15 times faster than
the tray dryer.
• 3) It is available in different sizes with the drying
capacity ranging from 5 to 200 kg per hour.
• 4) The drying containers are mobile, making handling
simple and reducing labour costs.
• 5) The thermal efficiency is 2 to 6 times greater than
the tray dryer.
• 6) It is also used for the mixing the ingredients and its
maixing efficiency is also high.
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22. DISADVANTAGES
• 1) Many organic powders develops electrostatic
charges during drying. To avoid this efficient
electrical earthing of the dryer is essential.
• 2) The turbelence of the fluidsed state of granules
may causes attrition of some materials resulting in
the production of fines.
• 3) But using a suitable binding agents this
problem can be solved. Fine particles may
become entrained and must be collected by bag
filters.
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23. FREEZE DRYER
• Highly heat-sensitive solids, such as some certain
biotechnological materials, pharmaceuticals and
foods with high flavor content, may be freeze dried
at a cost that is at least one order-of-magnitude
higher than that of spray drying – itself not an
inexpensive drying operation. Here, drying occurs
below the triple point of the liquid by sublimation
of the frozen moisture into vapour, which is then
removed from the drying chamber by mechanical
vacuum pumps or steam jet ejectors. Generally,
freeze drying yields the highest quality product of
any dehydration techniques
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25. Microwave and Radio Frequency Drying
• Unlike conduction, convection or radiation, dielectric
heating heats a material containing a polar compound
volumetrically, i.e., thermal energy supplied at the
surface does not have to be conducted into the interior,
as limited by Fourier's law of heat conduction. This
type of heating provides the following advantages:
• · Enhanced diffusion of heat and mass
• · Development of internal pressure gradients which
enhance drying rates
• · Increased drying rates without increasing surface
temperatures
• · Better product quality
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28. Definition
Mixing may be defined as a unit operation in which
two or more components, in an unmixed or partially
mixed state, are treated so that each unit (particle,
molecule etc.) of the components lies as nearly as
possible in contact with a unit of each of the other
components.
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29. Importance of mixing
1. To make simple physical mixture
In the production of tablets, capsules, sachets and
dry powders two or more powders or granules are
mixed.
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30. Physical change
Mixing may aim at producing a change that
is physical, for example the solution of a
soluble substance. In case of dissolving a
solid in a solvent mixing will take place by
diffusion but the process will be slow. In
this case agitation makes the process rapid.
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31. Dispersion
In case of emulsions and creams two immiscible
liquids are mixed where one liquid is dispersed into
other.
In suspension and pastes solid particles are
dispersed in a liquid by mixing.
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32. Objective of mixing
To ensure uniformity
To initiate or to enhance the physical or chemical
reactions e.g. diffusion, dissolution etc.
To make the following products:
Tablets
Suspensions
Emulsions
Pastes
Creams
Ointments
Solutions
Syrups
Tablet coatings
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33. Types of mixtures and energy
requirements
There are 3 types of mixtures:
Positive mixtures:
• Formed from materials such as, gases or miscible
liquids.
• The materials mix spontaneously and irreversibly
by diffusion
• No input of energy if time of mixing is unlimited,
although time will be shorten if energy is
supplied.
• Generally, these materials do not show any
problems during mixing.
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34. Continued…..
Negative mixtures:
materials have the tendency to separate out from each other.
Energy needs to be supplied to keep components adequately
dispersed.
Some separate faster, while for others, the separation is slower.
For example,
a) In a suspension, there is the dispersion of solid in the solution (fast
separation)
b) Emulsions, creams and viscous suspension have a slow separation.
c) Are more difficult to be formed and require high degree of mixing
efficiency.
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35. Continued…..
Neutral mixtures:
• Are static in behaviour
• Neither mixing nor de-mixing occurs, unless
acted upon by an external system of forces.
• Examples are:
a) Mixed powders
b) Pastes
c) Ointments.
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36. Mixing of semi-solids
• If the solid is not too coarse, the liquid is not too
viscous and the percentage of solids is not too
great, solids can be suspended in liquids by the
use of a propellers or a flat-bladed turbine in a
cylindrical container.
• Apparatus used:
• Planetary mixers and sigma blade mixers used as
agitator mixers
• Triple roller mills used as shear mixers-size reduction
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37. Planetary Mixers
• Planetary mixers are one of the most widely
used mixers in the pharmaceutical industry.
In the pharmaceutical industry, the planetary
mixer is often used for basic operations of
mixing, blending, and low-shear granulation.
This machine is also used in other industries
like cosmetics and personal care products, food,
glass, cements, ceramics, metal industry etc.
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39. Construction
• The Planetary Mixer have two blades which rotate
on their own axes, while they orbit the mix vessel
on a common axis.
• The blades continuously advance along the
periphery of the vessel, removing material from
the vessel wall and transporting it to the interior.
• These mixers are ideal for mixing and kneading
viscous pastes or putty-like materials.
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40. Uses of Planetary Mixers
• Planetary mixers are ideal for mixing of
pharmaceutical creams, ointments, ceramics,
color and pigments, resins, ink, cosmetic creams,
herbal creams etc.
• Planetary mixers are also ideal for mixing and
kneading viscous pastes under atmospheric or
vacuum conditions.
• Used in the mixing of viscous, heat sensitive and
cohesive pastes, dough and moist etc.
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42. SIGMA BLADE MIXER
It is an example of agitator mixers.
Its shape resemble the Greek letter sigma.
It uses 2 mixer blades.
Sigma blade mixer is a common form used to
handle semi-solids of plastic consistency.
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43. Continued…
The two blades rotate towards each other and
operate in a mixing vessel which has a double
trough shape, each blade fitting into a trough.
The two blades rotate at different speeds, one
usually about twice the speed of the other,
resulting in a lateral pulling of the material
and divisions into two troughs, while the
blade shape and difference in speed causes
end-to-end movement
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45. Uses of Sigma Blade Mixer
• It is used for wet granulation process in the
manufacture of tablets, in the production of
ointments and pill masses.
• This mixer is well suited to high viscosity
materials like grease, putty, toffee and bubble-
gum.
• With its strong construction and high power, the
sigma blade mixer can handle the heaviest plastic
materials and products like tablet granules, and
ointments that are mixed readily.
• It is used for solid-solid & liquid-solid mixing.
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