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.