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1 Particle-size reduction & separation .pdf
- 1. By: Chernet T.(B.Pharm., M.Sc. in Pharmaceutics) Bahir Dar University, CMHS, Department of Pharmacy 1 Unit operations in Pharmaceutical Technology Love Each Other
- 2. Outline 2 INTRODUCTION Pharmaceuticaltechnology Industrial pharmacy Unit operations Size reduction Size separation Mixing Drying Filtration and clarification
- 3. Pharmaceutical technology 3 PharmaceuticalTechnology is an applied science for the development, manufacture and testing of dosage forms It is application of scientific knowledge or technology to pharmacy and the pharmaceutical industry It covers Pre-formulation, formulation, manufacturing and packaging Equipment and instruments used for production, QC , QA & cGMP Unit operations in manufacturing of drugs The role of genetic engineering in the dev’t of pharmaceutical products Biopharmaceuticals
- 4. Pharmaceutical technology 4 Industrialpharmacy is one discipline in the pharmaceutical technology concerned with: The theoretical and practical aspects of pertinent unit operations Milling, mixing, drying, filtration, centrifugation, crystallization Formulation, manufacturing and packaging of d/nt dosage forms Equipment and instruments used for Production, quality control, overall quality assurance and cGMP
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- 6. Objectives 6 At theend of this sub-topic, the student will be able to: Define size reduction Discuss the pharmaceutical applications of particle size reduction Describe the mechanisms of particle size reduction The equipments commonly used for particle size reduction Define size separation Knows the pharmaceutical application of size separation Understand the different techniques of size separation
- 7. Pharmaceutical processing 7 Drugsare not used “as they are” They need to be processed I. Isolation of the active drug II. Conversion of the drug into medicine
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- 9. Breakdown of process 9 The number of individual processes in pharmaceutical factory is great and the process seems complicated Each one can be broken down into a series of steps, called operations. Pharmaceutical manufacturing processes can be divided into a number of process called unit operations
- 10. Unit operations 10 Unitoperations in pharmaceutical technology refers to The individual operations/processes that make up the whole process of drug manufacturing. A process may have many unit operations to obtain the desired product. The common unit operations or processes involved are: Size reduction Size separation Mixing Drying Filtration Centrifugation Crystallization
- 11. Particle Size Reduction 11 Materials are rarely found in the required size range. It is often necessary either to decrease or to increase the particle size. In simple term: So, size reduction means decreasing the size of an object or material
- 12. Size reduction 12 Definition: Itis a unit operation in which materials are reduced to a finer/coarser particles before they are formulated into a suitable dosage form. The operation is carried out to obtain the desired size with the help of d/nt equipment's. It is also referred as o Comminution, grinding, milling, pulverization or crushing
- 13. Particle Size Reduction... 13 Objectivesof Size Reduction Increase surface area Increase the area of contact b/n the solids and the dissolving fluid This will help in rapid dissolution Facilitate Absorption & Bioavailability An increased dissolution rate, increased bioavailability and Increase therapeutic efficiency. The extraction of crude drugs is facilitated with an increase in surface area b/c solvent can easily penetrate into the tissues resulting in quick extraction of their active constituents
- 14. Particle Size Reduction... 14 Improve mixing efficiency The mixing of several solid ingredients is easier and more uniform if the ingredients are reduced to narrow size range. Content uniformity Improve the quality of certain dosage forms The physical appearance of ointments, pastes and creams can be improved by reducing its particle size. Smooth texture and elegant appearance All the ophthalmic preparations must be free from gritty particles to avoid irritation of the eye
- 15. Particle Size Reduction... 15 Facilitate drying rate Drying of wet masses can be facilitated by milling. Milling → ↑surface area → ↑Drying. Reduce the distance the moisture must travel within the particle to reach the surface of the solid Improve Stability Size reduction with subsequent drying increases stability of moisture sensitive materials Emulsion – Reduced Size of oil droplets results in reduction in rate of creaming Suspension – Reduced Size of particles results in a decrease in rate of sedimentation
- 16. 16 Disadvantages: A possiblechange in polymorphic form of the active ingredient Possible degradation of the drug as a result of heat buildup during milling. Adsorption of unwanted moisture due to the increased surface area. May cause problems in the flowability A decrease in particle size may create static charge problems causing agglomeration, decreasing surface area.
- 17. Particle Size Reduction... 17 Mechanismsof size reduction Cutting (Slicing) Compression Impact Attrition Size reduction methods If you are given a chalk, an incense, a stone and ordered to reduce their size, how can you do that?
- 18. 18 Method Mechanism EquipmentsUse Cutting Here the material is cut into pieces by means of a sharp blade or blades. Cutter mill fibrous crude drugs Compression (pressure) The material is crushed by application of pressure. Particles disintegrate by two rigid forces. Compressi on mill Soft materials Impact The material is more or less stationary and is hit by an object moving at high speed A moving particle strikes a stationary surface. Hammer mill Almost all drugs Attrition The material is subjected to pressure as in compression, but the surfaces are moving relative to each other, breakdown of materials result from rubbing action of two surfaces Roller mills Soft and fibrous materials Attrition and impact Combined impact and attrition methods Ball, Fluid energy, Pin mills
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- 20. Methods and equipments 20 All milling equipments consist of three basic parts: 1. Feeding part (feed chute): to deliver the material 2. Milling chamber: where size reduction takes place 3. Receiver: to discharge size reduced product Some are also fitted with dust collector Sieves/screens for classifying the particles by size
- 21. Cutter mill 21 Consistsof a series of knives attached to rotor which act against a series of stationary knives attached to the mill covering. Feed enters through the top hopper. The rotor rotates and both stationary and rotating knives cut the material into pieces. The lower part consists of a screen, so that material is retained in the mill until sufficient degree of size reduction has been achieved.
- 22. Cutter mill 22 Advantages Easy to clean, operate and maintenance cost is less Less wear and tear Good for coarse grinding. Wide range of materials (soft-fibrous-tough). Roots ,peels or barks prior to extraction Sieve being detachable – different sizes can be used as per need. Disadvantages Not suitable for fine grinding. Very hard material cannot be grinded. Sticky materials cannot be used.
- 23. Hammer mill Principle:Impact Upper part – Feed hopper. Lower part – Screen of desired size, through which materials can escape, when sufficiently size reduced. Screen is replaceable as per size required. It essentially contains rotating central shaft to which hammers are attached. The hammers swing out to a radial position when the shaft is rotated.
- 24. Hammer mill... 24 Advantages It is rapid in action, and is capable of grinding many different types of materials (Versatility) The product size can be controlled by variation of rotor speed hammer type and size and shape of mesh. Disadvantages High speed of operation generates heat that may affect thermo-labile materials or drugs containing gum, fat, resin or other sticky material Not useful for abrasive material
- 25. Fluid energy mill 25 Workingprinciple: material is reduced in size by attrition and impact A fluid usually air, is injected at very high pressure. The feed stock is suspended within a high velocity stream of air. The high kinetic energy of the air causes the particles to impact-with each other with sufficient momentum for fracture to occur.
- 26. Fluid energy mill... 26 The high velocity of the air gives rise to zones of turbulence. Turbulence ensures that the level of particle-particle collisions is high enough to produce substantial size reduction by impact and some attrition. There is an internal classifier, by which finer & lighter particles are discharged and heavier particles are retained until reduction to small size. The finer particles are dragged by air suck leaving the mill, while larger, heavy particles are carried downward to the grinding chamber
- 27. Fluid energy mill... 27 Advantages The particle size of the product is smaller than that produced by any other method of size reduction. Gases at the nozzles lead to cooling, counteracting the usual frictional heat that can affect heat-sensitive (thermo-labile) materials. Since the size reduction is by inter-particulate attrition there is little or no abrasion of the mill and no contamination of the product. Disadvantage High cost, High energy consumption Limited production capacity , premilling is required
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- 29. Particle-size separation 29 Sizereduction results in particles of somewhat varying sizes. To control the particle size distribution, the size-reduced material must be sifted to get fractions of narrow size ranges. Particle size separation: is a unit operation that involves the separation of mixture of various size of particles into two or more portions with the help of d/nt techniques
- 30. Size Separation 30 Standardsfor powders for pharmaceutical purposes are laid down principally in the Indian Pharmacopoeia. it states that the degree of coarseness or fineness of a powder is differentiated by the size of the mesh of the sieve through which it passes. The IP specifies five grades of powder and the number of the sieve through which all the particles must pass. Grade of powder Sieve through w/h all particles must pass Coarse 10 Moderately coarse 22 Moderately fine 44 Fine 85 Very Fine 120
- 31. Particle-size separation 31 Methodsof particle size separtaion. I. Size separation by sieving Agitation Brush the sieve II. Size separation by fluid classification Sedimentation methods Elutriation methods
- 32. Size separation bysieving 32 Size separation of powder is done by passing the powdered material through a set of sieves. Sieves are arranged in descending order i.e. sieve of larger size is at the top and the smallest one at the bottom.The bottom sieve is attached to the receiving pan. The number of the sieve indicates the number of meshes included in a length of 25.4 mm (1inch) in each direction parallel to the wires A No. 5 sieve has 5 meshes per inch in each direction
- 33. Size separation bysieving 33 Agitation methods Size separation is achieved by electrically or mechanically induced oscillation or vibration of the sieve meshes Oscillation:The sieve is mounted on a frame that oscillates back and forth. It is a simple method but the material may roll on the surface of the sieve Vibration : The sieve is vibrated at high speed by means of an electric device. The rapid vibration helps small enough particles to pass through it. less likely to clog due to rapid vibration
- 34. Size separation bysieving 34 Size separation by vibration
- 35. size separation bysieving 35 Brushing methods A brush is used to move particles on the surface of the sieve and to keep the meshes clear and prevents openings blockage. Sieving is the most widely used method for particle size analysis • In-expensive , simple , rapid, and Llittle variation between operators
- 36. size separation byfluid classification 36 A methods of particle size separation based on sedimentation or on elutriation Sedimentation methods Utilizes the differences in settling velocities of particles with different size and density
- 37. Continued….. 37 The divisionof particles into size fractions depends on the time of sedimentation. Size fractions can be collected after predetermined times. Disadvantages of this method It does not give a clean split of particle sizes Because some small particles will be near the bottom of the tank at the beginning of the process and so will be removed with the coarse particles.
- 38. Continued……. 38 Elutriation methods oElutriation is a process for separating particles based on their size and density, using a stream of gas flowing in a direction opposite to the direction of sedimentation. o If the upward velocity of the fluid is less than the settling velocity of the particle, sedimentation occurs and the particle moves downwards against the flow of fluid.
- 39. Particle-size separation 39 Conversely,if the settling velocity of the particle is less than the upward fluid velocity, the particle moves upwards with the fluid flow. Therefore, in the case of elutriation, particles are divided into different size fractions depending on the velocity of the fluid.
- 40. Particle-size separation 40 Separationof powders into several size fractions can be effected by using a number of elutriators connected in series. The suspension is fed into the bottom of the narrowest column, overflowing from the top into the bottom of the next widest column and so on. As the column diameter increases; the fluid velocity decreases and therefore particles of decreasing size will be separated.
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