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.”
The 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
1. Liquid extracts, soft extracts & dry extracts.
2. In the concentration of blood plasma & serum.
3. It is also used in the manufacture of drugs containing, antibiotics, enzymes, hormones & many
other substances.
4. Used in purification of vitamins.
5. Concentration of proteins, biological products.
6. Stripping of solvents from vegetable & plant or herbal extracts.
7. Removal of water & solvents from fermentation broths.
8. In sugar industry
9. In dehydrating milk, which is then used in many food products

12. Crystallization

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

14. Background:
oOne of the oldest unit operation of industrial separations.
oThe oldest crystallization techniques are applied in salt and sugar production (Myerson, 2001).
oCrystallization is especially used for high quality products, which have high purity grade.
oMany 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
The 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:
o solvent evaporation,
ocooling,
ochemical reaction and
o 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:
o crystals are formed when particles gather into clusters.
oThe clusters become stable nuclei after achieving the critical cluster size
oThere are two different nucleation formations –
oPrimary nucleation:
o1.homogenous
ois spontaneous and homogeneous in the absence of foreign particles.
o2.heterogenous:
oInduced by foreign particles –nucleation formation heterogeneous
oand lower supersaturation concentration compared to homogeneous primary nucleation shown in
graph.

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

19. Concentration and temperature
for formations of nucleation

20. 2.Crystal Growth:
oThe 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.
o Crystal growth rate is affected by various physical factors such as :
osurface tension of solution,
o pressure,
otemperature,
orelative crystal velocity in the solution,
oReynolds number and other factors

21. 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.

22. 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.

24. oChemical industry produces 70% of all solid materials by crystallization and precipitation.
oReason: low temperatures and energy consumptions.
oMain crystallization processes
1.Cooling crystallization: crystals are formed by cooling the solution.
2.Evaporative crystallization:
oSolvent is removed by evaporation.
oBut it requires a lot more energy than cooling crystallization.
oIn industrial scale the crystallization reactors may be either batch or continuous reactors e.g.
crystallizers.

25. Conclusion:
oCrystallization is an important downstream processing method in bioprocess technology and in all chemical
industry.
ocrystallization has an advantage compared to other solid liquid separation operations such as distillation since
crystallization is a rather energy efficient.
oIn addition the yielded product has very high purity level.
oEven 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.

26. Applications:
Crystallization is also an important technique:
o in the desalination of seawater,
othe freeze-concentration of fruit juices,
othe recovery of valuable materials such as metal salts from electroplating processes,
o the production of materials for the electronic industries and
oin biotechnological operations such as the processing of proteins.
The industrial applications of crystallization are not necessarily used for the production of pure
solids substances.
oBut 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.

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