Evaporation & crystalization

Evaporation &; crystalization

1. Evaporation This is oldest method of concentration. “ The removal of liquid from a solution by boiling the solution in a suitable vessel and withdrawing the vapour , leaving a concentrated liquid residue .” T he rate of vaporization depends on the diffusion of vapour through the boundary layers above the liquid.

2. Steps in downstream processing

3. Evaporators: The equipment used to remove water from the food product is called evaporators Evaporators are used to separate materials based on difference in their boiling points An evaporator is used to evaporate a volatile solvent, usually water, from a solution. Its purpose is to concentrate non-volatile solutes such as organic compounds, inorganic salts, acids or bases. Typical solutes include phosphoric acid, caustic soda, sodium chloride, sodium sulphate , gelatine , syrups and urea.

4. BASIC PARTS OF EVAPORATORS Heat exchanger Vacuum Vapor separator Condenser

5. Types of Evaporator:   Evaporators are divided mainly into three groups. Types: 1 . Natural circulation evaporator i ) Evaporating pans ii ) Evaporating stills iii ) Short tube evaporator .   2) Forced circulation evaporator. 3 ) Film evaporator Types : i) Wiped Film evaporator ii)Long Tube Evaporator a ) Climbing film evaporator b) Falling film evaporator

6. Falling Film Evaporator Short residence time at high temperature Feed pre heated to b.p . Flows down tubes Hot vapour flows down also Vaporisation occurs Concentrate and vapours separated on exit from base Vapour condensate removed at base A: Product B: Vapor C: Concentrate D: Heating Steam E: Condensate 1: Head 2: Calandria 3: Calandria , Lower part 4: Mixing Channel 5: Vapor Separator http://www.niroinc.com/html/evaporator/falling_film_evaporators.html

7. Evaporating Pans “On a manufacturing scale, liquid extracts containing water are evaporated in open pans called evaporating pans.” Construction : • The evaporating pan consists of Hemispherical shallow made of Copper Stainless steel Alluminium Enameled iron

8. Evaporating Pans Steam jacket • The hemispherical shape gives the best surface volume ratio for heating and the largest area for the disengagement of vapour . Advantages 1 ) They are simple, easy and cheap to construct. 2 ) They are easy to use and clean. 3 ) Stirring of the evaporating liquids can be done easily. 

9. Single effect Evaporation Nearly always the material to be evaporated flows inside the tubes . The boiling liquid is subjected under moderate vacuum Reducing the boiling temp of the liquid increases the temperature difference b/w the steam and the boiling liquid and thus increases the heat transfer rate in the evaporator. When a single evaporator is used, the vapor from the boiling liquid is condensed and discarded. Simple but does not use steam effectively. Single effect Evaporation

10. Multiple effect Evaporation If the vapor from one evaporator is fed into the steam chest of a second evaporator and the vapor from the second is sent to the condenser, the operation becomes double effect. The heat in the original steam is reused in the second effect and the evaporation economy increased. Also useful one the feed temp is very low, preheating Multiple effect Evaporation

11. APPLICATION OF EVAPORATION Evaporation is one of the most important processes in the manufacture of pharmaceuticals. • It is used in the preparation of Liquid extracts, soft extracts & dry extracts. In the concentration of blood plasma & serum. It is also used in the manufacture of drugs containing, antibiotics, enzymes, hormones & many other substances. Used in purification of vitamins. Concentration of proteins , biological products. Stripping of solvents from vegetable & plant or herbal extracts. Removal of water & solvents from fermentation broths. In sugar industry In dehydrating milk, which is then used in many food products

12. Crystallization

13. Crystallization: Crystallization is a separation and purification method widely used for final purification of components. Crystallization is widely used in chemical industry due to rather low operation temperatures and energy consumptions.

14. Background: O ne of the oldest unit operation of industrial separations. The oldest crystallization techniques are applied in salt and sugar production (Myerson, 2001). Crystallization is especially used for high quality products, which have high purity grade. Many organic liquids are purified by crystallization rather than by distillation, because enthalpies of crystallization are usually lower than enthalpies of vaporization.

15. Mechanism and processes: Crystallization consists of two stages: formation of nuclei and growth of crystals T he solution should be first supersaturated thus the solution must contain more dissolved material than it would at under normal conditions . Several methods can be used to obtain supersaturation such as: solvent evaporation, cooling , chemical reaction and addition of a second solvent to reduce the solubility of the solute, solvent layering and sublimation along with other methods.

16. STEPS: 1.Formation of nucleation: crystals are formed when particles gather into clusters. The clusters become stable nuclei after achieving the critical cluster size There are two different nucleation formations – Primary nucleation: 1.homogenous is spontaneous and homogeneous in the absence of foreign particles . 2.heterogenous: Induced by foreign particles –nucleation formation heterogeneous and lower supersaturation concentration compared to homogeneous primary nucleation shown in graph.

17. Secondary nucleation: It appears when crystals already exist in the solution and caused by collision of crystals. This type of nucleation formation is typical mechanism in industrial crystallization because of low supersaturation concentration.

18. Concentration and temperature for formations of nucleation

19. 2.Crystal Growth: The next step of crystallization is crystal growth where nucleus size increases after the critical cluster size is achieved. Crystal growth increases its own dimension in thin layers . Crystal growth rate is affected by various physical factors such as : surface tension of solution , pressure, temperature , relative crystal velocity in the solution, Reynolds number and other factors

20. Case study from bioprocess technology Used for high quality products with high purity requirements. Used in organic acid production. Most common organic acid is citric acid used in several industries like pharma cuticle, food and beverage industries.

21. After fermentation the broth is filtered and precipitated with Ca(OH)2 at pH of 7.2 and temperature of 70-90 °C. Calcium citrate crystals are formed in the reaction. After filtration the calcium citrate is reacted with sulfuric acid to precipitate the calcium in the form of calcium sulfate. Anhydrous citric acid is released (when reaction occurs above 40 °C ). then clarified with active carbon and crystallized with evaporation. The resulted product is citric acid which has very high purity level due to crystallization therefore is suitable for foodstuffs or pharmaceuticals.

22. Chemical industry produces 70% of all solid materials by crystallization and precipitation. Reason: low temperatures and energy consumptions. Main crystallization processes 1.Cooling crystallization: crystals are formed by cooling the solution . 2.Evaporative crystallization: Solvent is removed by evaporation. But it requires a lot more energy than cooling crystallization. In industrial scale the crystallization reactors may be either batch or continuous reactors e.g. crystallizers.

23. Conclusion: Crystallization is an important downstream processing method in bioprocess technology and in all chemical industry. crystallization has an advantage compared to other solid liquid separation operations such as distillation since crystallization is a rather energy efficient. In addition the yielded product has very high purity level. Even though crystallization is an old and effective method, new modelling and controlling techniques can develop the operation to even more effective with higher purity and yield with smaller cost in the future.

24. Applications: Crystallization is also an important technique: in the desalination of seawater, the freeze-concentration of fruit juices, the recovery of valuable materials such as metal salts from electroplating processes , the production of materials for the electronic industries and in biotechnological operations such as the processing of proteins . The industrial applications of crystallization are not necessarily used for the production of pure solids substances. But on large scale used for purification of substances liquid at room temp E.g . low-temperature crystallization can be used as purification method for liquid hydrocarbon mixtures in petroleum industry.

25. Simple but energy-consuming, normally using steam as the heat source in a large scale.