EQUIPMENTS USED IN DISPERSE

SYSTEM

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 equipmentsA. MixersB. High speed dispersersC. Rotor stator mixersD. Planetary & KneadersE. Combination mixersF. In- line mixersG. Non- mechanical disperse processingH. Fine suspension and size reduction equipment

A - 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 mounted portable 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

B - 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 20,000 cps.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

C- 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 stator2. Rotating stator3. Axial flow rotor/stator mixers

RADIAL FLOW WITH STATOR ROTATING

STATORAXIAL FLOW ROTOR/STATOR MIXER

D – Planetary & Kneaders High shear

shaft/shaft and shaft/vessel

Designed for ultra high viscous materials (1,000,000 cps to 10,000,000 cps)

Expensives machines

Not designed for low viscosity (need tp get “hard phase” for good dispersion)

Planetary system

1 path 5-6 path after 1’ (60 path)

E - 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

Butterfly plus disperser It is combination of

high speed disperser with 3 blades @ 120°

It works well on high viscosity suspensions (not flowing materials)

Improved axial mixing Easier cleaning

compared to Planetary

Butterfly

Planetary plus disperser It is combination of

high speed disperser with planetary

It works well on extremely high viscosity suspensions

Expensive equipment (3 times anchor+disperer type)

Difficult to clean Complex maintenance

Planetary mixer

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

F – In Line Mixers

1.Rotor/stator mixer disperser emulsifier 2.Colloidal mill3.Piston homogenizer4.Ultrasonic vibrating homogenizer5.Micro fluidizer6.Low pressure cyclone emulsifier7.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

G - 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

H - Fine suspensions and size reduction equipment

Types:1. Triple roll mill2. Ball mill3. Agitated bead mill

Triple roll mill:• Disperse small tightly bound agglomerates

and hard discrete particlesParticles are subjected to

High shearMechanical 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

LimitationsTypically 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.