Mixing and Homogenization

1. MIXING
&
HOMOGENIZATION

2. MIXING

3. • Mixing is the most widely used operation in which two or more than two
substances combine together.
Objectives:
• Simple physical mixing of materials to form a uniform mixture.
• To promote the chemical reaction to get uniform products.
• Dispersion of solid in liquid to form suspension or paste.
• Dispersion of two immiscible liquids to form an emulsion.
Mixing:
OR
• An operation in which two or more components (in a separate or roughly mixed
condition) are treated so that each particle lies as nearly as possible in contact
with a particle of each of the other ingredients.

4. TYPES OF MIXTURES
1. Positive Mixtures
Example: Solutions, Syrups
2. Negative Mixtures
Example: Suspensions, Emulsions
3. Neutral Mixtures
Example: Pastes, Ointments

5. Equipment Used for Mixing of Powders
1. Tumbler mixer
2. Double cone mixer
3. Agitated powder mixer
4. Air mixer
Equipment Used for Mixing of Liquids
1. Propeller mixer
2. Turbine mixer
3. Paddle mixer
Equipment Used for Mixing of Semi-solids
1. Triple roller mill
2. Agitator mixer
3. Planetary mixer

6. 1. Liquid Mixing
2. Powder / Solid Mixing
3. Semi-solid Mixing
TYPES OF MIXING

7. 1. Liquid Mixing
• Liquid mixing is done in two ways as shown in below
Liquid – Solid Mixing Liquid – Liquid Mixing
1. Mixing of liquid and soluble solid
• By simple stirring
• E.g. Syrup solution
2. Mixing of liquid and insoluble
solid
• A liquid suspension will be produced
which is an unstable product.
• Suspending agent should be added to
produce stable suspension.
1. Mixing of two miscible liquids
(Homogeneous mixture).
• By simple stirring
• E.g. Solution
2. Mixing of two immiscible liquids
(Heterogeneous mixture).
• Addition of emulsifying agent will
produce emulsion.
• Continues stirring is needed to
ensure the components do not
separate out.

8. Mechanism of Liquid Mixing
Mechanism Description
Bulk Transport • Movement of large portion of a material from one location
to another location in a give system. Rotating blades and
paddles are used.
Laminar Mixing • Mixing of two dissimilar liquids through laminar flow, i.e.,
applied shear stretches the interface between them. Suitable
for liquids which require moderate mixing.
Turbulent Mixing • Highly effective, mixing is due to turbulent flow which
results in random fluctuation of the fluid velocity at any
given point within the system. Fluid velocity at a given
point changes in 3 directions.
Molecular Mixing • Mixing at molecular level in which molecules diffuse due to
thermal motion.

9. PROPELLER MIXER
• It Consist of angle blades attached at the end of the
shaft, rotated by means of motor.
• Any number of blades may be used but three
blades design is most common.
• Propeller is quiet small as compare to size of the
vessel (Ratio of diameter between propeller and
container is 1:20) but its operational speed (usually
8000rpm) compensate for the size and produce
efficient mixing in case of low viscosity fluids.
Construction:

10. Working:
• The material to be mixed is taken in a vessel and
the propeller bearing shaft is inserted.
• The angle blades of the propeller cause circulation
of the liquid in both axial and radial direction
ensuring good bulk transport but low shearing
force.
• The propeller may be installed in a number of
ways.
• The centrally mounted vertical propeller is
however not considered good as it produces
vortex.
Vortex in Liquid

11. Advantages:
• Used when high mixing capacity is required.
• Effective for liquids which have maximum viscosity of 2.0pascals.sec or slurry
up to 10% solids of fine mesh size.
• Effective gas-liquid dispersion is possible at laboratory scale.
Disadvantages:
• Propellers are not normally effective with liquids of viscosity greater than
5pascal.second, such as glycerine, castor oil etc.,
• The centrally mounted vertical propeller produces vortex.
Examples - Multivitamin elixirs, Disinfectant solutions are prepared using
propellers

12. 2. Powder or Solid Mixing
• Powder mixing may be regarded as an operation in which two or more than two
solid substances in particulate form intermingled in mixer by continuous
movement of particles.
• It is an example of neutral mixture and is one the most common operation
employed during preparation of different formulation like powder, tablets,
capsules etc.

13. Mechanisms of Powder Mixing
Mechanism Description
Convective Mixing /
Macro mixing
• There is bulk movement of groups of particles from one
part of powder bed to another. It occurs by an inversion
of the powder bed by means of blades or paddles.
Shear Mixing • This type of mixing occurs when a layer of material
flows over another layer resulting in the layers moving
at different speeds and therefore mixing at the layer
interface.
Diffusion Mixing /
Micro mixing
• Diffusive mechanism occurs by random movement of
particle within a powder bed and causes them to change
their relative position in relation to one another.

14. Double Cone Mixer / Blender
Construction and Working:
• Double cone mixer is made of stainless steel and is available in different
capacity ranging from 5 Kg to 200 Kg or even more.
• The rate of rotation should be optimum which depends on the size and shape of
tumbler as well as nature of material to be mixed.
• The rate of rotation commonly ranges from 30-100 RPM.
• The material to be blended is loaded approximately 50 to 60% of the total
capacity of the blender.
• As the blender rotates the material undergoes tumbling motion and mixes the
material thoroughly.

15. • Agitate blade can also be fixed in order to produce shearing action.
• The double cone blender is an efficient design for mixing powders different
densities and is used mainly for small quantity of powders.
• Mixing occurs due to tumbling motion.
Double cone Mixer or Blender

16. Advantages:
• If fragile granules are to be blended, it is suitable because of minimum attrition.
• They handle large capacities.
• Easy to clean , load, and unload.
• This equipment requires minimum maintenance.
Disadvantages:
• It needs high headspace for installation.
• It is not suitable for fine particulate system or ingredients of large differences in
the particle size distribution, because not enough shear is applied.
• If powders are free flowing, serial dilution is required for the addition of low
dose active ingredients.

17. Agitated Powder Mixer / Ribbon Blender
Principle:
• Mechanism involved in the Agitated
Powder Mixer is “Shear Mixing”.
• Shear is transferred by moving blades.
• High shear rates are effective in breaking
lumps and aggregates.
• Convective mixing also occurs as the
powder bed is lifted and allowed to
cascade to the bottom of the container.
• An equilibrium state of mixing can be
achieved.

18. Construction and Working:
• Consists of horizontal cylindrical trough usually open at the top. It is fitted with
two helical blades, which are mounted on the same shaft through the long axis
of the trough.
• Blades have both right and left hand twists.
• Blades are connected to fixed speed drive.
• It can be loaded by top loading and emptying is done through bottom port.

19. Uses:
• Used for mixing of finely divided solids, wet solid mass, and plastic solids.
• Uniform size and density materials can be easily mixed.
• Used for solid – solid and liquid – solid mixing.
Advantages:
• High shear can be applied by using perforated baffles, which bring about a
rubbing and breakdown aggregates.
• Headroom requires less space.
Disadvantages:
• It is a poor mixer, because movement of particles is two dimensional.
• Shearing action is less than in planetary mixer.
• Dead spots are observed in the mixer, though they are minimum.
• It has fixed speed drive.

20. Mixing of Semi-Solid
• The mixing of semi-solids is done for preparing ointments, creams,
Pill masses and wet mass for making granules etc.
• The mixing action include combination of low speed shear, smearing,
wiping, folding, stretching and compressing.
• The forces required for efficient mixing are high and consumption of
power is also high. Hence the equipment must be constructed in such
a way that it can tolerate these forces.
• Some semisolids exhibit dilatant property i.e., viscosity increases with
increase in shear rates. Therefore, mixing must be done at lower

21. Triple roller mill
Principle:
• High shear , which causes crushing of aggregates, particles and also distributes
the drug uniformly throughout the semi solid base.

22. Construction:
• The mill consists of three rollers
which are made of a hard abrasion-
resistant material.
• These rollers are arranged in such a
way that they come very close to each
other. These rollers are rotated at
different rates of speed.
• The material coming between the
rollers is crushed depending on the
gap between them and the difference
in rates of movement of the two
surfaces.

23. Working:
• The material after passing through
hopper, comes between roller 1 and 2 and
is reduced in size in the process.
• The gap between roller 2 and 3 is usually
less than that between 1 and 2, further
crushes and smoothens the mixture which
adheres to roller 2.
• A scraper is arranged in such a way, that
it can remove the mixed material from the
roller no. 3 and does not allow the
material which has not passed between
both sets of the rollers to reach the
scraper.

24. Advantages:
• Three roll mills are ideally suited for processing the smallest and also very large
quantities.
• Excellent temperature control.
• Avoid contamination.
• Extremely uniform dispersion is obtained.
• Low material loss.
• Easy cleaning

25. Planetary mixer
Principle:
• 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:
• It consists of a stationary vessel which is made up of stainless steel and it can be
removed.
• The blade is mounted from the top of the bowl.
• The mixing shaft is driven planetary gear connected to an electric motor.

26. Working:
• The blade is moved slowly at the initial
stage for premixing of the material and
finally at increased speed for active
mixing.
• In this way high shear can be applied
for thorough mixing.
• The blade and the stationary vessel
provide a kneading action and shear.
• This is due to narrow clearance between
the blade and the wall of the vessel.

27. Uses:
• Break down agglomerates rapidly.
• Low speeds are used for dry blending and fast for wet granulation.
Advantages:
• Speed of rotation can be varied at will.
• More useful for wet granulation process.
Disadvantages:
• Mechanical heat is build-up within the powder mix.
• It requires high power.
• It has limited size and is useful for batch work only.

28. HOMOGENIZATION

29. Homogenization
• Homogenization is the process of converting non-uniform mixture to a colloidal
state or a uniform mixture. It is done by reducing particle size of mixtures or
uniform dispersion of the mixtures making the product homogenous.
OR
• Homogenization is the process of preparing fine emulsion from a coarse
emulsion by converting the large globules to small globules.
• Homogenisation is done in an apparatus called “Homogeniser”.
Principle:
• The homogenizers are based on the principle that the large globules in a coarse
emulsion are broken into smaller globules by passing them under pressure
through a narrow orifice.

30. Equipment's
• The most commonly used equipment's are as below mentioned
1. Hand homogeniser
2. Silverson mixer homogeniser
3. Colloidal mill

31. Hand Homogeniser
Principle:
• It based on the principle that the large globules in a coarse emulsion are broken
into small globules by passing them under pressure through narrow orifice.
Construction:
• It consist of a hopper, small orifice, handle and a heavy base.
• Hand Homogeniser consist of a small stainless steel vessel mounted on a stand.
• Bottom of the vessel has opening to fit nozzle.
• A freely moving piston is operation in the cylinder.

32. Working:
• The emulsion prepared in mortar and pestle is placed in the hopper of
emulsifier.
• The piston is operated. The liquid to be homogenized is passed through the
nozzle under pressure which causes atomization and hence homogenisation can
be done.

33. Silverson Mixer Homogeniser
Principle:
• It works on the principle of combination of mixing and homogenisation.
Construction:
• It consist of Emulsifying head.
• To which number of blades are attached.
• It is surrounded by a fine mesh sieve made up of stainless steel.
• The head is rotated by means of small motor which rotates the blades at very
high speed.

34. • The emulsifying head is immersed in the liquid to be emulsified.
• The liquid to be mixed are sucked through the fine mesh and oil is reduced into
fine globule in this process.
• The process of mixing occurs the high speed rotation of blades.
• The mixed materials is then pulled out with a great force and thus the process of
and homogenisation occurs Simultaneously.
Working:
Applications:
• The mixer is used to obtain fine emulsion an suspension and other biphasic
liquid preparation.

36. Colloidal Mill
Principle:
• It works on the principle of shearing.
• The size reduction is affected due to shearing.
Construction:
• Colloidal Mill consist of rotor and stator.
• The milling surfaces are conical and the gap between rotor and stator ranges
from 0.002 to 0.003 inches.
• The rotor revolves at speeds of about 3000 to 20000rpm.
• The material to be size reduced is pre milled.
• Feeding the material through a hopper into the mill.

37. Working:
• The material and suspension is placed into the hopper of the mill.
• The material is thrown outwards, due to the centrifugal action of rotor.
• Particle size reduction is effected when the material is passes between the
milling surfaces.
• The product obtained from mill has a very fine particle size.
Applications:
• Colloidal Mill are frequently used for the preparation of pharmaceutical
suspension and emulsions, with a particle size of less than a micron.

39. Thank you..!