Equipments used in dispersed systems
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Transcript of Equipments used in dispersed systems
EQUIPMENTS USED IN DISPERSE SYSTEM
Presented by:
L.Pavani
Roll No:256212886018
M.Pharm 1st yr
Pharmaceutics
Guided by:
Dr.S.B.Bhanja
M.Pharm,Ph.D
Definition:
Dispersion system is defined as a
heterogenous two phase system in which
internal (dispersed,discontinous ) phase is
distributed or dispersed within the continuous
(external) phase or vehicle.
The internal and external phase may be
solids, liquids and also gases.
Eg.suspensions,emulsions,aerosols
Dispersion equipments
A. Mixers
B. High speed dispersers
C. Rotor stator mixers
D. Combination mixers
E. In- line mixers
F. Non- mechanical disperse processing
G. Fine suspension and size reduction
equipment
Mixers
Propeller mixers
Turbine mixers
Anchor mixers
Scraped surface agitators
Counter rotation
Propeller mixers
The most often used mixing implement is marine propeller mixer.
These machines use rounded,pitched,three blade design that produces mostly axial flow
They provide good flow and blending capabilities in small batches of low to medium viscosities
Propellers mixers can be installed on vertical centerline or through the side wall of process vessel
They can be operated at around 300-400rpm
These are used mostly for liquid-liquid blending applications in some easily producible suspensions.
PROPELLER MIXERS
Marine Propeller mixerClamp mountedportable mixer
Turbine mixers
The most versatile of all mixers in the entire span of
mixing equipments are the axial and radial flow turbines
Turbines mixers can be made to handle huge
batches,evenupto 5,00,00gal & suitable for
emulsification process.
Radial Flow turbine Axial flow turbine
Anchor mixer
It is low speed and low capability
The anchor agitator is a slow (50rpm) device whose sole function is to rotate the contents of a batch in a radial direction without providing any significant shear
They are typically designed to be able to withstand a maximum viscosity beyond which they might actually blend or break.
Scrapped surface agitators A flexible or movable
blades are attached to
the anchor for the
purpose of actually
scrapping the side
walls,they are known as
scraped surface
agitators
These are definitely
required in emulsification
equipment where heat
transfers are necessary
Counterrotation agitator
It consists of anchor agitator and counterrotating set of cross bars provides excellent blending
These works well on materials with viscosities from 5000-25,000cps
By installing a stationary baffle,some mixing capabilities are improved
High speed Dispersers
It is also called as saw blade disperser
This machine consists of a variable speed shaft connected to an impeller with a serrated edge
The tip speed is set around 4000 ft/min
The diameter of impeller should be 1/3 of diameter of vessel
The impeller should be located one impeller diameter off the bottom of vessel
It can deagglomerating particles when the viscosities between 10,000 to 20,000cps.
Application:It is used for pigment dispersion,dye stuffs,
carbon dispersion and paints
High speed disperser
Limitations:
Air incorporation is
another problem so it
is best used for
suspensions and not
for emulsions
Rotor/stator mixers This mixing machine uses an impeller that is
installed at a close tolerance to a stationary housing,which baffles and restrict the flow caused by the rotation of the impeller in the liquid.
Particles caught between rotor & stator are crushed and separated by mechanical action of the impeller.
They are three types:
1. Radial flow with stator
2. Rotating stator
3. Axial flow rotor/stator mixers
RADIAL FLOW WITH
STATOR ROTATING
STATOR
AXIAL FLOW ROTOR/STATOR
MIXER
COMBINATION MIXERS
Better control of temperature and pressures
Eliminates line loses caused by pumping from tank to tank
Saves floor space
Simplifies the process, save labor costs
Types : Anchor plus rotor/stator
Anchor plus disperser
Counter rotating with coaxial rotor/stator
Achor plus rotor/stator
It is combination of simple anchor
agitator with a rotor/stator mixer
It provides a high shear rates for
dispersion and emulsification
It is beneficial if there is
requirement to pull down powders
from the top
Limitation:
It is difficult to design the anchor
such that it allows the placement
of the high shear mixer close to
the bottom of the vessel.
Anchor plus disperser
It is combination of
high speed
disperser with an
anchor agitator
It works well on
medium to high
viscosity
suspensions
Counterrotating with coaxial
rotor/stator This design is known as triple action mixer,combines the
high viscosity mixing capabilities of counterrotating axial
flow cross bars with a standard anchor type scraped
surface agitator and also with a high speed rotor/stator
mixer
It is capable of generating fine dispersions and fine
droplets of the internal phase for stable emulsions
It can operated at viscosity of 50,000cps
They are always jacketed for heating and cooling
because it is necessary in case of preparation of creams
and ointments
Counterrotating with coaxial
rotor/stator
Advantages:
Handles wide range of
viscosities from water thin
to as high as 1million cps
Disperse and emulsifies
very efficiently
Provides shortest mixing
time
Disadvantages:
Difficult to clean due to
complicated design
IN LINE MIXERS
1.Rotor/stator mixer disperser emulsifier
2.Colloidal mill
3.Piston homogenizer
4.Ultrasonic vibrating homogenizer
5.Micro fluidizer
6.Low pressure cyclone emulsifier
7.Homogenizer/Extruders
8.Static mixer
Rotor stator mixer emulsifier
disperser
These mixers acting as submerged pumps design can be made that places the rotor/stator in a pump housing and allows for product to be pumped through itself.
The product inside the rotor/stator mixing pump,the droplets and particles subjected to a wide variety of high shear rates.
It is designed with fine tolerance rotor/stator gaps that promotes high shear rates and high amount of shear per pass through.
Stage 1
Stage 2
Stage 3
Colloid mill It is used to disperse the solids into liquids and
to emulsify liquid-liquid systems.
These generally used as polishing machines for emulsions or suspensions because they produce fine particle or droplet size product to enhance a products stability.
The rotor/stator gap is generally set between 0.030 & 0.001 inch.
They are operated at speed of 3600 rpm
The rotor diameter is 10-30cm provides flow rates in the area of 4000-6000L/hr depending upon the viscosity.
Colloidal mill
Advantages :
Shear rates high than in rotor/stator machines
Colloidal mill produces emulsions and suspensions with particle size distribution smaller than the particle sizes obtainable using fixed gap rotor/stator mixers.
Limitations :
Flow rates lower than in rotor/stator machines
Not used for abrasive products
Piston homogenizers
It is the most powerfull device for producing
emulsions and suspensions
It uses high power positive displacement piston
type pump to produce pressure of 3000-10,000
psig and then force the premixed product
through a specially designed restricting wall
where a extremely high shear forces are exerted
Here turbulence and high shear are the major
parameters in size reduction
Piston homogenizers It having continuous
Capabilities of 2500L/hr at
15hp to 50,000L/hr at
150hp
Limitations:
They cannot handle the
product feed above 200cps
High maintanence cost and
down time
Lack product homogenity
and batch to batch
variability
Ultrasonic vibrating
homogenizer
Has similarity with high pressure
homogenizer effective device for dispersing
and emulsifying
It uses a positive displacement pump to force
the premixed liquid through an elliptical
opening at a speed of 100m/sec
This high speed flow impinges on to the edge
of blade shaped obstacle called a vibrating
knife.
Ultrasonic vibrating
homogenizer
Capacities and
pressures of systems
range from laboratory
units, producing 4-
10L/min at 1200-1700
psig requiring 2-5hp,to
full scale productions
units with capacities of
upto 450L/min at
350psig requiring 60hp.
Continuous dual feed system configuration using
ultrasonic homogenizer
microfluidizer
This device uses a high pressure positive displacement pump operating at a pressure of 500-20,000psig which accelerate the process flow upto 500m/min through the interaction chamber
The interaction chamber consists of small channels known as micro channels having diameter narrow as 50μm and cause the flow of product to occur as very thin sheets.
The configuration of micro channels within the interaction chamber ressembles Y-shaped flow streams in which the process stream divides into these micro channels,creating two separate micro streams
The micro streams are then brought together in
an impingement area through which all of the
product must flow
At the impingement area the collision of the two
high speed flow streams in a very tight spot
creates various droplet size reduction and
different mixing mechanisms such a
cavitation,implosion,shears and turbulence
The micro fluidizer technology satisfy the
requirements for producing finest emulsions
known as micro emulsions
Flow path through the microfluidizer
Low pressure cyclone emulsifier
It is used for formation of emulsions and suspensions
the shear arises from the difference in the velocity of the fluid,as the fluid travels in a spiral towards the center
They operates in the 200psig and capacities of 7.5-225L/min.
The recommended viscosity limit is 1-2000cps.
They are capable of producing emulsions in the
2-10μm range.
Working :
Product enters through
tangential entry port
Product is forced to
circulate in concentric
layers towards the
center and ends of the
chamber
Shear arises from the
difference in the
velocity of fluid,as the
fluid travels in a spiral
towards the center Cross section of flow path
through the interaction
chamber
Homogenizer/Extruder
It is a high pressure homogenizer with an
adjustable valve having production capacities
from 8mL/hr to 12000mL/hr
A positive displacement pump produces
pressure up to 30,000psig.
The apparatus capable of producing fine
emulsions and liposomal dispersions
Static mixers
A true low shear and low energy requirement
device for emulsifying immiscible liquid
mixture is the static mixture.
It is also called as pipe line mixture,this
device is actually a series of specially
designed baffles in a cylindrical pipe.
These simple devices are extensively used for the preparation of unstable emulsions for liquid-liquid extraction purposes
Size distributions obtainable range from 100-1000μm
Nonchemical disperse
processing
Critical fluids liposome process:
Near critical or super critical fluid solvents with or
without polar co-solvents for the formation of
uniform and stable liposomes having high
encapsulation efficiences.
Super critical fluids can be uniquely used to
encapsulate very hydrophobic molecules
Super critical fluids are gases such as carbon
dioxide & propane
When these fluids compressed at conditions
above their critical temperature and
pressure,these substances become fluids
and ability to dissolve other materials.
The gaseous characteristics increases mass
transfer rates,thereby significantly reducing
processing time.
Small added amounts of visible polar co-
solvents such as alcohol can be used to
adjust polarity and to maximize the selectivity
and capacity of the solvents
Fine suspensions and size
reduction equipment
Types:
1. Triple roll mill
2. Ball mill
3. Agitated bead mill
Triple roll mill:
• Disperse small tightly bound agglomerates
and hard discrete particles
Particles are subjected to
High shear
Mechanical crushing
Smearing
BALL MILL
It is used for size reduction fine solid discrete
particles or for deagglomeration of very tightly
bound agglomerates.
The machine consists of cylindrical drum into
which a charge of heavy spherical balls
usually metal or ceramic is loaded along with
the components of the dispersion.
Ball mill
Limitations
Typically time consuming process,milling time are
often measured in days.
Agitated bead mills
A Modernized improvement of the ball mill is the
agitated bead mill
The bead mill uses a charge of inert small balls to 2-
8mm diameter
Media mill- if beads are ceramic
Shot mill- if beads are steel
Sand mill- if grains of sand are used
The Design consist of a cylinder which can be either
vertical or horizontal,that has a high speed
agitator,which is capable of fluidizing the charge of
beads,causing them to collide at very high speed.
The premix is pumped through the
housing.There is a high probability that each
particle must be repeatedly subjected to the high
stresses that result when the beads collide with
each other or the high speed impeller
Agitated bead mill is used in pigment dispersion
industry due to its fine solids grinding and
dispersing capabilities.It is not often used in
pharmaceutical industry except when particle
size requirements falls below 10μm.
Reference
Pharmaceutical dosage forms,disperse
systems volume 3 by
Lackman,Lieberman,Marcel Dekker,NY.pg
no:291-362
Pharmaceutical engineering(principles &
practices) by C.V.S.
Subrahmanyam.pg.no:155,161,229.