Demonstration of Colloid Mill, Planetary Mixer, Fluidized Bed Dryer & Freeze Dryer.

1. EXPERIMENT NO. 2
Demonstration of Colloid Mill, Planetary
Mixer, Fluidized Bed Dryer & Freeze Dryer.
Pharmaceutical Engineering Practical
S. I MAKRANI
Assistant Professor
Department of Pharmaceutics
Ali Allana College of Pharmacy Akkalkuwa

2. [1]
Experiment No: 2
 Aim: Demonstration of Colloid Mill, Planetary Mixer, Fluidized Bed Dryer & Freeze Dryer.
 References:
1) Md. Rageeb Md. Usman, Prerna K. Mahajan, Dr. Mohammed Zuber Shaikh, Dr. Neelesh
Chaubey, Keerthy H. S. Practical Book of Pharmaceutical Engineering, first edition July 2018,
published by Nirali Prakashan, page no 81-91
2) C.V.S Subrahmanyam. J. Thimma Setty, Sarasija Suresh,V. Kusum Devi, Pharmaceutical
Engineering: Principles and practices Vallabh Prakashan, latest edition ,Page no 160, 220,397,401.
3)………………..
 Requirements:
Colloid Mill, Planetary Mixer, Fluidized Bed Dryer, Freeze Dryer.
Colloid Mill
Colloidal Mill is used to reduce the particle size of a solid present in different liquid forms or solid
forms of the pharmaceutical ingredients in pharmaceutical industry.Colloidal Mill reduces the size
of particles of solids that are suspended in a liquid, when a liquid suspended in another liquid,
meaning that they are immiscible, this machine is used alternatively to reduce the size of droplet.
 Principle:
 Colloidal mill works on the principle of rotor-stator.
 The size reduction is affected due to shearing, when the material is passed between the narrow
gap of milling surfaces of rotor and stator.
 A rotor turns at high speeds of 3000 – 20000rpm.
 The high levels of hydraulic shear applied to the process liquid disrupt structures in the fluid.
The rotor and stator surface covered with metal toothed coverings which cut and shear the solid.
Basic parts:
 It consists of an inlet hopper which is used to feed the material into the mill.
 It consists of a rotor and stator which are used to reduce the particles size by applying the
shearing force.
 It consists of an outlet which is used to discharge the reduced particles.
 Construction:
 A colloidal mill consist of a high speed rotor and a stator with a conical milling surfaces
between
 Which is an adjustable clearance ranging from 0.002 to 0.03 inches.
 The rotor speed is 3000 to 20000rpm. The material to be ground should be pre milled as finely
as possible to prevent damage to the colloidal mill.
 Rotors and the stator may be smooth surfaced or rough surface. With the rotor and the stator
there is a thin uniform film of material between them and it is subjected to the maximum
amount of shear.

3. [2]
 Rough surfaced mill add intense eddy current, turbulence and the impaction of the particles to
the shearing action.
Figure. Construction of Colloid Mill

4. [3]
 Working:
 The material is placed into the mill though the inlet hopper. It is then passed through the narrow
gap between the rotor and stator and thus reduced the fine particle size. A colloid mill is a
hydraulic shear producing device.
 The colloid mill works to reduce the size of the suspended droplets. The mill allows the solid
particles to become so small.
 The process of colloid milling is done through the addition of the heavier liquid into the
chamber of the mill that performs the shearing process.
 In other model the stator remains constant and the rotor will do the function of rotation. It
creates the amount of hydraulic shear needed to break down the materials.
 Uses:
Colloid mills are used in the following industries:
 Pharmaceutical
 Cosmetic
 Paint
 Soap
 Textile
 Paper
 Food
 Pharmaceutical Applications
 The main use of a colloid mill is the dispersion of solid particles within a liquid.
 It is frequently used to increase the stability of suspensions and emulsions.
 It is used for the formation of the efficient emulsification, homogenization, dispersion and
mixing during the course of cutting, milling and shocking with high frequency.
 It is used to reduce the particle size in suspension in a liquid or to reduce the droplet size of a
liquid suspended in another liquid.
 Particles size of as small as 3 microns can be obtained by the colloidal mill.
 Fibrous materials can be milled using rough surfaced rotor and stator.
 It is mainly used in pharmaceutical purpose for the preparations colloidal dispersions,
suspensions, emulsions and ointments.
 Colloidal mill is utilized in a number of industries including, food and beverage,
pharmaceuticals and chemicals.
 Colloidal mill is ideal for small, medium and large scale tablet batching systems.
 Colloidal mill can be sterilized. So it can be mainly used in the production of the sterile
products.

5. [4]
Planetary Mixer
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.
 Priciple:
Mechanism of mixing is shear. Shear is applied between moving blade and stationary wall. Mixing
arm moves around its own axis and around the central axis so that it reaches every spot of the
vessel. The plates in the blades are sloped so that powder makes an upward movement to achieve
tumbling action also.
 Construction:
Also called as change-can mixers
 Consists of mixing paddles fixed on the rotating arm.
 Arm rotates about its own axis and also travels in a circular path around the mixing vessel.
 Movement is alogous to that of planes.
 Various size and shapes of paddles available.
 The paddle is shaped to the size of the vessel.

6. [5]
Figure. Construction of Planetary Mixer

7. [6]
 Working:
 Material is loaded in the vessel
 Paddle is rotated at a slow speed .
 The small clearance between the mixing vessel and paddle provides a kneading and shearing
action which ensures mixing of the material.
 Intermittent scrapping also required to ensure perfectand uniform mixing.
 Uses:
 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.
 Application:
 Tablet Coatings
 Tablet Granulations
 Antacid Powder Blends
 Collagen Solutions
 Dental Composites
 Advantages:
 Ease of cleaning
 Ease of discharge
 Semi-continuous operation
 Capital cost
 Energy savings

8. [7]
Fluidized Bed Dryer
Fluidized bed dryer (also called fluid bed dryer) is a kind of equipment used extensively in the
pharmaceutical industries to reduce the moisture content of pharmaceutical powder and granules.
 Principle
The equipment works on a principle of fluidization of the feed materials. In fluidization process, hot
air is introduced at high pressure through a perforated bed of moist solid particulate. The wet solids
are lifted from the bottom and suspended in a stream of air (fluidized state). Heat transfer is
accomplished by direct contact between the wet solid and hot gases. The vaporized liquid is carried
away by the drying gasses. Sometimes to save energy, the exit gas is partially recycled.
Types of Fluidized-Bed Dryers
1. Conventional Fluidized Bed Dryers
Conventional fluidized bed dryers include;
 Batch fluidized bed dryers.
 Semi-continuous fluidized bed dryers.
 Well-mixed, continuous fluidized dryers.
 Plug flow fluidized bed dryer.
2. Modified Fluidized Bed Dryers
Various types of modified fluidized bed dryers have been developed and are applied in many
industrial processes to overcome some of the problems encountered while using conventional
fluidized bed dryers for a drying process.
They include but not limited to;
 Hybrid fluidized bed dryers
 Pulsating fluidized bed dryers
 Fluidized bed dryer with immersed heat exchange.
 Mechanically assisted fluidized bed dryer.
 Vibrated fluidized bed dryer.
 Agitated fluidized bed dryer/swirl fluidizers.
 Fluidized bed dryers of inert particles.
 Spouted bed dryer.
 Recirculating fluidized bed dryer.
 Jetting fluidized bed dryer.
 Superheated steam fluidized bed dryer.
 Fluidized bed freeze dryer.
 Heat pump fluidized dryers.

9. [8]
 Construction:
Two types of FBD are available, vertical and horizontal which are made up of stainless steel or
plastic. Vertical type is used for batch drying and horizontal is used for continuous drying. A
detachable vessel is placed at the bottom of dryer for loading and unloading of material. This vessel
has perforated mesh through which hot air with high pressure is passed. Bag filters are placed above
the vessel for collection of dried material.
Figure. Construction of Fluidized Bed Dryer

10. [9]
A typical fluidized bed dryer consists of the following components
a. Air preparatory unit.
b. Product container.
c. Exhaust filter.
d. Exhaust blower.
e. Control panel.
f. Air distribution plate.
g. Spray nozzle.
h. Solution deliver.
 Working:
The material to be dried is placed in detachable vessel at bottom of the dryer. The air is introduced
from below through the prefilter, which is heated by means of heaters installed therein.
Simultaneously fan is also allowed to work. As the velocity of air is increased, the bed begins to
expand and further increase causes turbulent motion of particles called fluidization. The
granules/particles remain suspended in air stream. Later on, a state of pressure is reached at which
frictional drag on the granules/particles is equal to the force of gravity. The particles rise in stream
of air due to high velocity of gas, this condition is called fluidised state.
 Advantages of fluidized bed dryer:
 Thermal efficiency is 2-8 times than tray drier
 It is available in different sizes having drying capacity in range of 5- 250 kg/hour.
 Free flowing granules/particles are made.
 It can also be used for mixing the material with high efficiency.
 It can be used for both batch and continuous drying.
 Loading and unloading of material is very easy due to detachable vessel
 Higher drying temperatures than tray and truck dryer.
 3. Lower capital and maintenance cost
 4. Reduced contact time for drying.
 5. Ease of control.
 Disadvantages
 Poor fluidization and low flexibility especially if the feed is too wet.
 Not the best choice of equipment when organic solvents need to be removed during drying.
 Non-uniform product quality for certain types of fluidized bed dryers.
 Entertainment of fine particles.
 High potential for attrition; and in some cases agglomeration of fine particles.

11. [10]
Freeze Dryer.
Freeze drying is also known as lyophiliztion. This is a techniques used for preservation of foods etc
 Principle
The process of Lyophillization or freezing drying include the conversion of the material directly
from the solid phase to the gaseous phase, without going through the liquid phase (sublimation)
Freeze -drying is carried out using the principle of sublimation drying technique , the material to be
dried is frozen rapidly at low temperature , and then under the appropriate vacuum , so that the
sublimation of frozen water molecules directly into a steam escape process. Frozen the product was
dried to obtain a lyophilisate called (lyophilizer), the process is called lyophilized (lyophilization)
Sublimation:
In a sublimation procedure, a solid change without going through the phase of liquid, directly into
vapour.
The freeze-drying procedure the sublimation process can be described in a simple way as –
Freeze: The item is solidified, it happens in a flask, tray, or in a vial.
Vacuum: The item is placed in a deeper vacuum which is below the water triple point.
Dry: Here, the heat energy is included to the item which causes the solid to sublime or purify.
 Construction:
The main components of freeze drying equipment are:
 Refrigeration System
 Vacuum System
 Control System
 Product Chamber or Manifold
 Condenser

12. [11]
 The refrigeration system cools the (ice) condenser located inside the freeze dryer. The
refrigeration system can also be employed to cool shelves in the product chamber for the
freezing of the product.
 The vacuum system consists of a separate vacuum pump connected to an airtight condenser and
attached product chamber.
 Control systems vary in complexity and usually include temperature and pressure sensing
ability. Advanced controllers will allow the programming of a complete “recipe” for freeze
drying and will include options to monitor how the freeze drying process is progressing.
Choosing a control system for the freeze dryer depends on the application and use (i.e. lab vs.
production).
 Product chambers are typically either a manifold with attached flasks, or, a larger chamber with
a system of shelves on which to place the product.
 The purpose of the condenser is to attract the vapors being sublimed off of the product. Because
the condenser is maintained at a lower energy level relative to the product ice, the vapors
condense and turn back into solid form (ice) in the condenser.
Figure. Schematic diagram of freeze dryer
 Working:
A freeze dryer works in three phases
 Freezing Phase
 Primary Drying (Sublimation) Phase
 Secondary Drying (Adsorption) Phase

13. [12]
Freezing Phase
 Freeze dryers use various methods to freeze the product. Freezing can be done in a freezer, a chilled
bath (shell freezer), or on a shelf in the freeze dryer. The freeze dryer cools the material below its
triple point to ensure that sublimation, rather than melting, will occur. This preserves the material’s
physical form.
Primary Drying (Sublimation) Phase
 A freeze dryer’s second phase is primary drying (sublimation), in which the pressure is lowered and
heat is added to the material in order for the water to sublimate. The freeze dryer’s vacuum speeds
sublimation. The freeze dryer’s cold condenser provides a surface for the water vapor to adhere and
solidify. The condenser also protects the vacuum pump from the water vapor. About 95% of the
water in the material is removed in this phase. Primary drying can be a slow process. Too much
heat can alter the structure of the material.
Secondary Drying (Adsorption) Phase
 A freeze dryer’s final phase is secondary drying (adsorption), during which the ionically-bound
water molecules are removed. By raising the temperature higher than in the primary drying phase,
the bonds are broken between the material and the water molecules. Freeze dried materials retain a
porous structure. After the freeze dryer completes its process, the vacuum can be broken with an
inert gas before the material is sealed. Most materials can be dried to 1-5% residual moisture.
 Applications of freeze drying
The process of freeze drying can be employed in following field
 Food industry
 Dairy industry
 Nutraceuticals
 Pharmaceuticals
 Research
 Pet food