EVAPORATION

EVAPORATION

1. BinuJa S.S SECOND SEM

2. INTRODUCTION… Process in which a liquid changes to the gaseous state at the free surface, below the boiling point through the transfer of heat energy. Net loss of water from a liquid surface that results from a phase change from a liquid to a vapour .

3. Surface phenomenon Mass transfer takes place from surface. No boiling occurs.

4. Practical definition… Removal of solvent from the solution by boiling the liquor in suitable vessel and withdrawing the vapour , leaving a concentrated liquid residue in the vessel.

5. Relationship can be expesssed by S = surface urea of the liquid exposed, m p = atmospheric pressure. kPa b = maximum vapour pressure at the temperature of air,kPa b’ = pressure due to the vapour of the liquid, actually present in the air. kPa K = constant, m/s

6. FACTORS AFFECTING … Temperature Vapour pressure Surface area Moisture content of the feed Time of evaporation Film and deposits Density

7. 1. TEMPERATURE higher the temperature greater the value of b greater will be the evaporation.

8. VAPOUR PRESSURE Directly proportional Lower the p value, the greater the evaporation. Lower the external pressure, the lower the boiling point of the liquid greater will be the evaporation.

9. SURFACE AREA Greater the surface area of the liquid greater will be the evaporation.

10. MOISTURE CONTENT OF THE-FEED Some drug constituents undergo hydrolysis readily in presence of moister at high temperatures. To prevent decomposition, the materialis exposed to lower temperature initially, then exposed to higher temperature for final concentration. Prepration of dry extract of belladonna.

11. TIME OF EVAPORATION Time of exposure is longer, greater will be the evaporation. Provided the constituents are thermostable Film evaporators are used.

12. FILM AND DEPOSITS Vegetable extracts are concentrated in steam pan, film may be formed. Film reduce evaporating surface. Stirring is necessary.

13. Type of evaporators 1. Evaporaters with heating medium in jacket. Steam jacketed kettle (evaporating pan) 2. Vapour heated evaporaters with tubular heating surfaces.

14. Steam jacketed kettle (evaporating pan)

15. USES Suitable for concentrating aqueous and thermostable liquors, eg : Liquorice extract. ADVANTAGES Constructed both for small scale and large scale operations. Simple in construction and easy to operate, clean and maintain. Low cost and maintenance. Wide variety of materials can be used for construction such as copper, stainless steel and aluminium . Stirring of the contents and removal of the product is easy

16. DISADVANTAGES Heat economy is less, hence cost per material production is more. Not suitable for heat sensitive materials due to long time of exposure. The heating area decreases as the product gets more concentrated. Boling point of the water cannot be reduced, since reduced pressure cannot be created in open type evaporater .

17. Horizontal tube evaporator

18. USES Cascara extract ADVANTAGES Cost per square metre of heating surface is less.

19. VERTICAL TUBE EVAPORATOR

20. USES Manufacture of cascara extract, sugar, salt, caustic soda. ADVANTAGES Tubes increase the heating surface nearly 10 to 15 times when compared to steam jacketed kettle. Vigorous circulation enhances the rate of heat transfer. A number of units can be joined to obtain more efficient effect.

21. DISADVANTAGE Evaporator is complicated. Increased installation cost.

22. CLIMBING FILM EVAPORATOR/ RISING FILM EVAPORATOR

23. USES Concentration of insulin, liver extracts and vitamins. ADVANTAGES Large area for heat transfer is provided employing long and narrow tubes. Time of contact between the liquor and the heating surface is very short. Tubes are not submerged. Low hold up and small floor space.

24. DISADVANTAGES If feed rate is high, the liquor may be concentrated insuffciently . Expensive Large head space is required.

25. FALLING FILM EVAPORATOR

26. USES Concentration of yeast extract Manufacture of gelatin Extracts of tea and coffee

27. ADVANTAGES Suitable for high viscous liquids Liquid hold up is less and hold-up time is very small. Highly acidic and corrosive feeds can be concentratred .

28. DISADVANTAGES Not suitable for suspension.

29. FORCED CIRCULATION EVAPORATOR

30. USES Concentration of insulin and liver extracts. Thermolabile subtances . ADVANTAGES Heat transfer coefficient is high due to rapid liquid movement. Suitable for high viscous preparations

31. DISADVANTAGES Hold-up of liquid is high. Expensive.

32. REFERENCE Pharmaceutical engineering Unit operations-2, C.V.S. Subrahmanyam , page no: 238 https://www.britannica.com/science/evaporation. https://www.sciencedaily.com/terms/evaporation. https://www.merriamwebster.com/dictionary/evaporation.