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Objectives

Objectives. Definition of mixing Objectives of Mixing Types of Mixtures Mechanisms of Mixing. Mixing: Most Commonly used operation in daily life. Used in food, Plastic, Glass, Paint, Paper, fertilizer Industries. In Pharmaceutical Industry :

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Objectives

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  1. Objectives • Definition of mixing • Objectives of Mixing • Types of Mixtures • Mechanisms of Mixing PH 101.32

  2. Mixing: Most Commonly used operation in daily life. Used in food, Plastic, Glass, Paint, Paper, fertilizer Industries. In Pharmaceutical Industry : Liquids, Viscous Liquids, Semi – solids & Solids require Mixing. PH 101.32

  3. Introduction In Pharmaceutical Industry generally Mixing is Carried out to obtain. A true solution : • When two miscible liquids are mixed together An emulsion: • when two immiscible liquids are mixed in presence of emulsifying agent . A solution: • when Solid is dissolved in a Vehicle. PH 101.32

  4. A Suspension: • when an insoluble solid is mixed with a vehicle in presence of a suspending agent. An ointment : • When a solid or liquid is mixed with a semisolid base A powder: • When two or more solid substances are mixed together PH 101.32

  5. Definition Mixing is a process in which two or more than two components are mixed in such a way that each particle of any one ingredient lies as nearly as possible to the adjacent particle of other ingredient. PH 101.32

  6. Objectives of Mixing • To ensue uniformity of composition between mixed ingredients • To enhance the Physical or chemical reactions PH 101.32

  7. Type of Mixtures • Positive Mixtures • Negative Mixtures • Neutral Mixtures PH 101.32

  8. Positive Mixtures • Mixed by diffusion Process • No energy required • Do not create any problem Eg :- Two gases or two miscible liquids. PH 101.32

  9. Negative Mixtures • Difficult to prepare. • Required a higher degree of Mixing & external force • Tendency to separate out unless they are continuously stirred. Eg: Suspensions & Emulsions. PH 101.32

  10. Neutral Mixtures • Static in their behaviour • No tendency to mix spontaneously • Do not separate out easily. Eg:- Pastes, Ointments , Mixed powder etc. PH 101.32

  11. Mechanisms of Mixing • Convective Mixing • Shear Mixing • Diffusive Mixing PH 101.32

  12. Convective Mixing: Transfer of groups of adjacent particles from one place to another within the mixture. Shear Mixing: Shear forces created within the mass of the material by using agitator arm Diffusive Mixing: When materials tilted, gravitational forces cause the upper layers to slip & diffusion of individual particles take place PH 101.32

  13. Objectives • Liquid mixing • Sub groups of liquid mixing • Stages of liquid mixing • Equipment of Liquid mixers: • Shaker mixers • Propeller mixers PH 101.33

  14. Sub Groups of Liquid Mixing Mixing of liquids in liquids • Mixing of two miscible liquids Eg: solutions • Mixing of two immiscible liquids Eg: emulsions PH 101.33

  15. Mixing of Liquids and Solids • Liquids and soluble solids eg : solutions • Liquids and insoluble solids eg : suspensions PH 101.33

  16. Mixing of Liquids and Liquids Stages of mixing: • Localized mixing: Shear is applied to the particles of the fluid • General movement: Takes all the particles of the bulk through the shearing zone to produce uniform product PH 101.33

  17. Small scale preparation of emulsion • Suitable apparatus: mortar & pestle • Shear forces produced • General movement also produced • Two stages of preparation of emulsions: • Primary emulsion • Secondary emulsion PH 101.33

  18. Mixing of liquids & soluble solids • These are homogeneous mixtures eg: solutions PH 101.33

  19. Mixing of Liquids & Insoluble Solids • These are heterogeneous mixtures eg: suspensions • Suitable apparatus for small scale preparation: • Mortar & pestle PH 101.33

  20. Mixing of Liquids • Liquid- liquid mixing is considered as a simple operation compared to solid – liquid mixing. • It involves the formation of homogeneous system. • Liquid mixing involves the application of shear. • Agitation and mixing are not synonymous. • Agitation: It refers to the induced motion of a material in a specified way, usually in circular pattern inside a container. • Mixing: It refers to the random distribution into or through one another of two or more separate phases PH 101.32

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  26. Equipment for Liquid Mixing • Shaker mixers • Propeller mixers • Turbine mixers • Paddle mixers PH 101.33

  27. Shaker mixers Limited use in industries: The container itself moves to mix the liquid. • Reasons: Variable mixing efficiency Changes in viscosity Constructional characters like use of baffles • Oscillatory movement : for small scale work • Rotary movement : for large scale work PH 101.33

  28. Propeller mixers Mostly widely used in industries: • For liquids of low viscosity • Not suitable for viscous liquids like glycerin, castor oil etc., • Size of propeller small as compared to container PH 101.33

  29. Propeller mixers • Propeller rotates at a very high speed up to 8000 rpm • Undesirable vortex formation & entrapment of air are resulted due to high speed of propeller • Can be avoided by number of ways shown in the diagram PH 101.33

  30. Propeller mixers Fig: 33.1 PH 101.33

  31. Propeller mixers Fig: 33.2 PH 101.33

  32. Propeller mixers Fig: 33.3 PH 101.33

  33. Objective • Turbine Mixers • Paddle Mixers • Homogenization • Homogenizers PH 101.34

  34. Turbine Mixers • Consist of Circular disc impeller • Rotate at lower speed than propeller • Produce greater shear force than propeller • Used for liquid of high viscosity • Special application in preparation of emulsions PH 101.34

  35. Fig : 34.1 PH 101.34

  36. Paddle Mixers • Paddles used as impellers • Rotate at low speed of 100 r.p.m • Paddles consist of blades attached to vertical shaft • Blades have large surface area • Effectively mix viscous liquids & semisolids PH 101.34

  37. Paddle Mixers Fig: 34.2 PH 101.34

  38. Homogenization Definition:- Process of conversion of coarse emulsion into colloidal state of uniform composition. PH 101.34

  39. Various types of Homogenizers • Hand Homogenizer (Emulsifier) • Knaewood Mixer • Silver son– Mixer – Emulsifier • Colloid Mill PH 101.34

  40. Emulsifier • Most commonly used hand homogenizer • Reduction in the globular size increasers with the speed of pumping PH 101.34

  41. Fig: 34.3 PH 101.34

  42. Knewood Mixer • Effective mixing machine • Effective mixing action because both beaters & axis rotate producing Planetary action • Due to planetary action mixing of whole of the liquid is affected Different types of beaters available PH 101.34

  43. Fig: 34.4 PH 101.34

  44. Colloid Mill • Works on the principle of shearing • Consists of rotor & stator • Gap between rotor stator can be adjusted from 0.005 to 0.075 cm • Rotor rotates at a speed of 3000 to 20,000 r.p.m. PH 101.34

  45. Colloid Mill • Material already reduced to fine particles is fed through hopper • Material thrown outward in the mill by centrifugal action. • Material passes through narrow gap between rotor & stator • The size of the material is reduced • Fine particles collected from outlet. PH 101.34

  46. Fig: 34.5 PH 101.34

  47. Colloid mill Fig: 34.6 PH 101.34

  48. Advantages • Useful for preparing pharmaceutical suspensions, emulsions, lotions, ointments & creams. • Capable of producing particles in micron size. • Size reduction is always carried out in presence of a liquid. PH 101.34

  49. Silverson Mixer – Emulsifier • Consists of emulsifying head which consists of number of blades & covered with fine mesh sieve. • Blades rotate at a very high speed to produce shearing action PH 101.35

  50. Silverson Mixer – Emulsifier • The emulsifying head is rotated by means of motor & immersed in the liquids to be emulsified • The liquids to be mixed are sucked through fine mesh & subjected to vigorous mixing by high speed rotation of blades. PH 101.35

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