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  2. CONTENTS  Definition of drying  Importance of drying  Difference between drying and evaporation  Equipments  References 2
  3. DRYING  Drying is defined as removal of the liquid from a material by application of heat & is accomplished by transfer of a liquid from the surface into an unsaturated vapor phase .  Drying is the final removal of water from material (usually by heat)  Drying is commonly the last stage in a manufacture process  Non-thermal drying 1- As Squeezing wetted sponge 2- Adsorption by desiccant (desiccation) 3- Extraction. 3
  4. Difference between drying and evaporation Sl. No. Drying Evaporation 1. In drying processes, the main operation usually carried out on solid materials, e.g. powders, or products In evaporation processes, the main operation usually carried out on liquid materials, e.g. solution, or products 2. Drying in most of the cases means the removal of relatively small amounts of water from solids Evaporation include the removal of large amounts of water from solutions. 3. In most cases, drying involves the removal of water at temperatures below its boiling point Whereas evaporation means the removal of water by boiling a solution. 4. In drying , water is usually removed by circulating air over the material in order to carry away the water vapour While in evaporation , water is removed from the material as pure water vapour mixed with other gases. 4
  5. Preservation of drug products Preparation of bulk drugs Improved handling Improved characteristics Applications…. 5
  6. Preservation of drug products…. 6 • Drying is necessary in order to avoid deterioration. A few examples are… • --blood products, tissues… undergo microbial growth • --effervescent tablets, synthetic & semi synthetic drugs undergo…. chemical decomposition.
  7. Preparation of Bulk Drugs…. 7 • Drying is the final stage of processing . Eg: • *dried aluminium hydroxide • *spray dried lactose • *powdered extracts (in fig..chamomile powder), e.t.c
  8. Improved characteristics… Drying produces materials of spherical shape, uniform size, free flowing & enhanced solubility. Some specific areas of imp are…  1. Granules are dried to improve the fluidity & compression characteristics. These are essential for production of tablets and capsules.  2. Viscous & sticky materials are not free flowing. Drying modifies these characteristics 8
  9. IMPROVED HANDLING….  Removal of moisture makes the material light in weight and reduces bulk.  Thus cost of transportation will be less & storage will be efficient.  If moisture is present, size reduction of drugs is difficult.  Drying reduces the moisture content. 9
  10. Theories of Drying….  Drying involves both heat transfer as well as mass transfer 10
  11. It is the amount of water (moisture) held by the material that exerts an equilibrium vapour pressure equal to that of pure water at the same pressure. Bound water (moisture) It is the minimum water(moisture) held by the material that exerts an equilibrium vapour pressure less than the pure water at the same temperature. 11
  12. Hygroscopic materials Water in: -fine cpillaries -Cell and fibre walls -Physical interaction Bound water Vapour pressure of wet solids is less than the v.p of pure water Non-Hygroscopic materials Water in void spaces UnBound water Vapour pressure of wet solids is equal to v.p of pure water 12
  13. Equipments 1. Drum dryer (Film drying) 2. Spray dryer 3. Freeze Dryer 4. Tray drier 5. Fluidized Bed Dryer 6. Vacuum Dryer 13
  14. Drum Dryer (Film Drying) 14
  15. Drum Dryer (Film Drying)  It consists of a drum of about 0.75-1.5 m in diameter and 2-4 m in length, heated internally, usually by steam and rotated on its longitudinal axis.  Working: The liquid is applied to the surface and spread to a film, this may be done in various ways, but the simplest method is that shown in the diagram, where the drum dips into a feed pan. Drying rate is controlled by using a suitable speed of rotation and the drum temperature. The product is scraped from the surface of the drum by means of a doctor knife. 15
  16. Uses It is used for drying solution, slurries, suspensions etc and also the dry products like this • Milk products • Starch products • Ferrous salts • Suspension of zinc oxide & kaolin • Yeast • Pigments • Antibiotics 16
  17. Adantages  Drying time is less, only in few seconds.  Drum dryer occupies less space  Product are obtained is completely dried and it’s final form  Rate of heat & mass transfer is high Disadvantages • Maintenance cost is higher • Skilled operators are essential to control feed rate • Not suitable for solution of salts with less solubility 17
  18. Spray Dryer 18
  19. Spray Dryer Working : Drying of the material in spray dryer involves 3 steps (1) Atomization of the liquid (2) Drying of the liquid droplets (3) Recovery of the dried product  The spray dryer provides a large surface area for heat and mass transfer by atomizing the liquid to small droplets.  These are sprayed into a stream of hot air, so that each droplet dries to a solid particle.  The drying chamber resembles the cyclone ensuring good circulation of air, to facilitate heat and mass transfer, and that dried particles are separated by the centrifugal action.  Spray dryer can be operated efficiently at various feed rates. 19
  20. Uses  Product obtained are better than other dryer  Product quantity to be dried is large 20 It is continuous process & dried completely 3 to 30 sec. Labor cost is low Product of uniform & controllable size is obtained Products shows excellent solubility Suitable for drying of sterile products Disadvantages It is bulky and expensive Huge equipment not always easy to operate Thermal efficiency is low Advantages
  21. Tray dryer 21
  22. Tray dryer  Air flows in direction of the arrows over each shelf in turn.  The wet material is spread on shallow trays resting on the shelves.  Electrical elements or steam-heated pipes are positioned as shown, so that the air is periodically reheated after it has cooled by passage over the wet material on one shelf before it passes on the next. 22
  23. Uses Following substances can be dried  Sticky material  Plastic substances  Granular mass  precipitates 23
  24. Advantages  Handling of the material can be done without looses  Tray dryer is operated batch-wise (a) Each batch of material are separate entity (b) Equipment is readily adjusted for use in drying a wide variety of material Disadvantages  It require more labour to load and unload 24
  25. Fluidized Bed Dryer 25
  26. Fluidized Bed Dryer  ‘Fluidized’ means something that behaves like liquid. In the fluidized bed dryer, the mixture of solids and gas behave like a liquid and solid are called fluidized.  It provides good contact between hot air and particles to obtain efficient drying.  The hot air is passed through a mesh, which supports the conical vessel with a porous base.  This vessel is filled with powder to be dried. 26
  27. Uses: It Is Popularly Used For The Drying of Granules in the Production of Tablets. Advantages :  Require less time for drying i.e., 20 to 40 min.  It is available in different sizes with the drying capacity 5 to 200 kg  Labour cost are low  Also used for mixing the ingredients  Hot spot are not observed in the dryer  Higher drying temp. can be used 27
  28. Disadantages  Some powder are organic which develop electrostatic charges to avoid this, efficient electrical earthing of the dryer is essential. 28
  29. Vacuum Dryer 29 Steam or Water Jacket Condenser Connection to Vaccum Pump Condensate Receiver
  30. Vacuum Dryer  This equipment is a good example of conduction drier. The vacuum oven consists of a jacketed vessel to withstand vacuum within the oven.  There are supports for the shelves giving a larger area for conduction heat transfer. The oven can be closed by a door.  The oven is connected through a condenser and liquid receiver to a vacuum pump.  Operating pressure can be as low as 0.03-0.03 bar, at which pressures water boils at 25-35 0C. 30
  31. Advantages  It provides large surface area for heat transfer  Handling of the material, trays and equipment is easy  It is easy for switching over to the next material  Hot water of desired temp. can be supplied Disadvantages: It has a limited capacity It is more expensive than tray dryer 31
  32. Freeze Dryer 32
  33. Freeze Dryer  Freeze drying is a process used to dry extremely heat- sensitive materials. It allows the drying , without excessive damage, of proteins, blood products and even microorganisms, which retain a small but significant viability.  In this process the initial liquid solution or suspension is frozen, the pressure above the frozen state is reduced and the water removed by sublimation.  Thus a liquid-to-vapour transition takes place, but here three states of matter involved: liquid to solid, then solid to vapour. 33
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