fluidised bed dryer

1. DISPERSION EQUIPMENT AND TECHNIQUES N.VARSHAPRIYA 170113886004

2. DISPERSE SYSTEMS The term “disperse system” refers to a system in which one substance(the dispersed phase) is distributed in discrete units , through out a second substance(the continuous phase or vehicle). Each phase can exist in solid, liquid or gaseous state. It is composed of: dispersed phase : substance that is distributed dispersion medium : vehicle

3. FACTORS INFLUENCING SELECTION PROCESS Suspensions: Viscosity Density Particle shape , size and distribution Emulsions: Surface tension Chemical activity of liquid phases Surfactants stabilizers

4. MIXING/DISPERSION EQUIPMENT Mixers High Speed Dispersers Rotor/Stator Mixers Combination Mixers Inline Mixers Non Mechanical Disperse Processing Fine suspension and size reduction equipment

5. Mixers: Propeller mixers Turbine mixers Anchor mixers Scraped-Surface agitators Counter rotation

6. HIGH SPEED DISPERSERS It is known as saw-blade disperser Consist of variable speed shaft connected to impeller with a serrated edge Rotate at high speed in order to produce shear and pumping Tip speed of disperser should be set around4000ft/min Diameter of impeller should be around 1/3 of diameter of dispersion vessel Impeller should be located one impeller diameter off the bottom vessel

7. Limitations: It is ineffective if viscosity is low. Suitable for suspensions not emulsions. Air incorporation is another problem. Tip speed of both laboratory and full size production units should be kept constant. Applications: This is used to disperse pigments in to liquids. Designed specifically to disperse powders.

8. ROTOR/STATOR MIXERS Important machine used for dispersing and emulsifying. It uses an impeller that is installed at close tolerance to stationary housing , which baffles and restricts the flow caused by the rotation of the impeller in liquid. Gap between rotor and stator is usually around ½-2mm(500-2000um). Particles as small as 50um or liquid droplets as small as 1um are not likely to be directly stressed by rotor and stator. They produce fine dispersions and emulsions. All rotor/stator design variations are made to provide a combination of flow and high shear rates.

9. RADIAL FLOW WITH STATOR Uses a radial flow impeller to pump outward from the stator to the sides of tank , to optimize shear versus flow. It is capable of positive mechanical grinding. Since the gap between rotor and stator ranges from 0.015-0.060 inch(380-1500um) auxiliary marine type impeller is added to provide some axial-flow pumping along with the radial Flow high shear mixing. A wide variety of mixing head configurations are available : 1. a stator with round holes 2. a stator with vertical slot 3. Fine screen stator

10. The Wetting Head (A) with large round holes works best for general purpose mixing . It generates vigorous flow and rapidly reduces the size of large particles. The Slotted Head (B) provides the most popular Combination of high shear and efficient flow rate . it is ideal for emulsions and medium Viscosity materials. The Fine Hole Head (C) provides the highest Shear possible at the expense of a slower flow rate. it is most suitable for low viscosity Emulsion and fine dispersions.

11. Different types of rotors

12. ROTATING STATOR In this design the impeller and the stator both rotate on the drive shaft. Several different configurations are offered: turbon cone type impeller. rotating stator mixing head. Turbon cone type impeller : uses conical impeller with vanes connecting cone to shaft. It will pump from smaller open end of the cone through larger opening. In another impeller rotates at high speeds of 1800-3600rpm while the stator only rotates at 10%of this speed.

13. The stators are designed with outside vanes , which are forced by the liquid to rotate the stator at a slower rate . This vanes are credited as providing additional pumping for blending. Advantages: T hey achieve the levels of shear rate and pumping capability without the support structure. They are simpler and easier to clean. Less maintenance . Limitations: Mechanical instability due to high speed of operation. Long-shafted machines are difficult and expensive.

14. AXIAL-FLOW ROTOR MIXERS By installing an Axial-Flow Impeller in a stationary Housing , a combination of the high shear rate ability with the efficient pumping ability of axial flow impellers can be obtained. It is known as eppenbach Mixer. For low viscosity materials flow rate is high so a baffle plate is necessary to deflect the flow so that product doesn’t leave the vessel i.e., mixers can pump in an upward direction. Baffle plate can be used to optimize certain performance traits of the mixers . Plate can be set directly at the surface which give most active mixing .

15. Baffle plate can be lowered if lesser level of turbulence is desired and prevent splashing. The amount of flow required and the amount of flow produced by a given size mixer depends on the viscosity and the design of specific mixer. Manufacturer should select equipment based on their viscosity and pumping capability Ratio of Allowable tank diameter to rotor diameter Maximum Viscosity (centipoise) 1:4 30,000 -70,000 1:6 20,000 - 30,000 1:8 10,000 - 20,000 1:10 5,000 - 10,000 1:15 2,000 - 5,000 1:20 < 2,000

16. Advantage: Handles high viscosity materials and larger batches with less horse power and capital cost. Disadvantage: Produces less turbulence and shear on their own then radial flow impeller. Application: It is capable of producing emulsions and suspensions Shear rates are generated in the gap between high speed rotor and the stator.

17. Combination Mixers The viscosities during processing of a emulsion and suspension change from water – thin to thick creams and paste Designing one simple agitator mixers to handle both high and low viscosities at different shear rates required usually impossible. Some of the mixers and dispersers can be installed in the same process vessel to give multi viscosity and multi shear rate capability in one controllable batch. Advantages: Better control of temperature and pressure . Eliminates line losses caused by pumping from tank to tank Saves floor space.

18. Anchor Plus Rotor Anchor supplies the slow moving of the viscous product from the heat transfer surfaces while rotor provides high shear rates for dispersion and emulsification. Advantages: Simplicity and low capital cost . Beneficial to Pull down powders from the top. Obtain adequate mixing under laminar flow c onditions in high viscosity applications. Disadvantages: Physically difficult to design anchor. Brace is usually required to strengthen the anchor and there placement is problem.

19. Anchor Plus Disperser Ability to work with high viscosity liquids especially for handling suspensions. The Wide diameter of the disperser blade also contributes to the problem of locating the blade close to the bottom of the batch. As long as air incorporation is not a problem, the combination anchor with high speed disperser works well on medium to high viscosity suspensions. This combination is less costly than more complicated designs using co-axial shafting. The Anchor gives the formulator the ability to work with high viscosity liquids.

20. Counter Rotating with Co-axial Rotor It is also known as triple action mixer . It combines the high viscosity mixing capabilities of counter rotating axial flow cross bars with a standard anchor type scrapped surface agitator and also with a high speed rotor mixer. It is capable of generating fine dispersions and fine droplets of the internal phase for stable emulsions There are always jacketed for heating and cooling. Disadvantages: Complicated design Difficulty of cleaning due to extra mixing capability

21. References: Pharmaceutical dosage form – disperse system vol-2 , second edition edited by Herbert A.lieberman, Martin M.Rieger and Gilbert S.Banker. Remington, the science and Practice of pharmacy 21 st edition, vol-1. The theory and Practice of industrial pharmacy, Leon Lachman, Herbert A.lieberman 2009 edition. Websites: www.mixers.com www.walkerep.com www.feldmeier.com

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