1. “Evaporation is the process of removal of solvent from the solution by boiling the liquid n a suitable
vessel & withdrawing the vapour, leaving a concentrated product.”
OR
“Evaporation is the process of a substance in a liquid state changing to a gaseous state due to an
increase in temperature/pressure.”
OR
“Evaporation means simply vaporization from the surface of a liquid. Vaporization of a liquid below its
boiling point is called as “evaporation”.
OR
“Evaporation is a process in which large quantities of liquid are vaporized to get a concentrated product
by applying heat.”
OR
“Evaporation is the process of vaporizing large quantity of volatile liquid to get concentrated product.”
Equipment used for evaporation are known as “evaporator”. It is a surface phenomenon thus no boiling
occurs. Either solution suspension can be subjected to evaporation but the only condition is that the
liquid must be volatile & solute must be non-volatile.
Deference between evaporation & other heat process
EVAPORATION OTHER HEAT PROCESS
The residue is concentrated liquid. Drying: The residue is solid.
Evaporating liquid is only one component is most
of the case.
Distillation: Evaporating liquid is a combination of
tow or more component.
No attempted is made to separate the mixture of
vapour.
Distillation: It is compulsory to separate each
component.
The purpose of evaporation is to get a
concentrated liquid only but not to get crystals.
Crystallization: The purpose of concentrating the
solution is to get the crystals.
EVAPORATION
2. Applications of Evaporation
1) It also used in the manufacture of bulk drugs containing, antibiotics, enzymes & hormones &
many of other substances.
2) It used in the manufacture of liquid extract, solid extract, herbal extract & dry extract etc.
3) Used in the purification of vitamins.
4) Concentration of biological product.
5) Concentration of penicillin & related products.
6) In demineralization of water.
7) Concentration of blood plasma & serum.
8) It is also used in formulation of biological products like enzymes, antibiotics & vitamins etc.
Miscellaneous: water containing minerals is subjected to evaporation t get demonetize water after
concentration. The water obtain by this process is used for human & other special purposes.
Objectives of Evaporation
01). Primary objective is reducing the volume of the product by some significant amount without loss of
nutrient components.
02). To make transport & storage easier as evaporation decreases the weight & volume of the product.
03). To remove large amount of liquid form product before dehydration process.
04). To improve stability of the product.
3. There are seven factors, the relationship may be expressed as;
M = KS/P (b-b’)
Where M= Mass of vapour form/unit time
S= surface area of liquid exposed
P= Atmospheric pressure.
b= Maximum vapour pressure at temperature of air.
b’= Pressure due to vapour of liquid actually present in the air.
K= Constant.
Temperature: At a given temperature some molecule posses higher kinetic energy then average
while other have lower than average kinetic energy. Fast moving molecule escape from the surface of
liquid into vapour, while slow moving molecule remain behind.
When temperature of liquid is released more molecule acquire sufficient kinetic energy & scape
from the surface to the vapour state.
This situation is below the boiling point of liquid. At boiling point the vapors are formed
throughout the liquid as well as from the surface.
Higher the temperature greater the value of b & have greater will higher.
Vapour pressure:
The rate of evaporation is directly proposonal to vapour pressure at the liquid. The lower value of P,
then greater will be the evaporation.
Lower the external pressure, however the boiling point of liquid & greater will be rate of evaporation.
Surface area: Greater surface area (s) greater will be the rate of evaporation of the liquid
there for evaporation is carried out in evaporator having larger surface area.
FACTORS EFFECTING THE RATE OF EVAPORATION
4. Moisture contain of the feed: Some drug undergoes hydrolysis rapidly in present of
moisture in high temperature to present decomposition the material is exposed to lower
temperature initially them expose to higher temperature cause final concentration.
Type of product required =
Type of product required some time decide the apparatus for evaporation open pan produce dry
concentration till evaporation heeled liquid concentration spray dryer produce dry product with good
solubility.
Time of evaporation: It the time exposer is larger, greater will be the evaporator
provided the constituents re thermo state. Exposer of drug to relatively high temperature for
short time periods may be less distractive them lower temperature for larger periods of time.
Film and deposit – When vasitable extract are concentration in steam pen. A film may
from on the surface are precipitate matter deposit on the heating surface film reduce the
evaporation surface precipitate motor hinder the transfer the heat to about this problem proper
steering to done.
ECONOMIC FACTORS
Economic of libber fuel fluid space and material are primary concentration the recovery of solvent and
utilization of best heat are also important.
5. STEAM JACKETED KETTLE (EVAPORATOR PAN)
Principle
Steam is supply to a jacketed kettle (evaporating pan) in which aqueous extracts is pace, steam give out
heat to the kettle. This is transfer to the aqueous extracts by conduction & convocation. The
temperature graze & solvent molecules transfer in to vapour take place. Starring & hence the process of
vaporization.
Construction
It is a hemispherical structure consisting of an inner pan called kettle and
outer pan called jacket. The two pans are joined to enclose a space through which steam is passed.
For smaller quantities, kettle is made up of a single sheet of metal for larger capacities, several sheets
are welded. Though several metals are used as a material of construction of the kettle. Copper is an
excellent material for the kettle, because of its good conductivity. If acidic material is evaporated, some
quantity of copper would dissolve. For such preparations, tinned copper is used. Iron is used for the
construction of the jacket, because it has minimum conductivity. To prevent rusting of the jacket, the
iron is either tinned or enameled on inner surface.
At the top of the jacket inlet for steam is provided. Condensate leaves the jacket through the outlet
provided at the bottom. Kettle is provided with one outlet for product discharging at its bottom.
6. The liquid to be evaporated is poured in to kettle. Steam is provided from
the steam inlet of jacket. This steam increases the temperature of liquid.
The condensed steam is removed from outlet at the bottom of jacket. The continuous stirring is
essential. To remove vapour and to prevents condensation of liquid liters & also to accelerate the rate of
evaporation fans are fitted. A kettle of capacity up to about 90 liter may be made to filt. The
concentrated product is collected from the outlet of kettle at the bottom.
USES
❑ It is suitable for concentrating aqueous liquid.
❑ It is suitable for concentrating thermo stable liquors such as liquorices extracts.
Advantages
Its cost of installation & maintenance is low.
It is constructed both for small scale & large-scale batch operations.
It is simple in construction & easy to operates, clean & maintain.
Stirring of the contents & removal of the product is easy.
It used for construction such as copper, stainless & aluminum.
WORKING
7. Principle
In horizontal tube evaporator steam is passed through the horizontal tube which are
immersed in the pool of the liquid outside the tube to be evaporated heat transfer takes place through
the tube & the liquid outside the tubes get heated. The solvent evaporate & scape from the top, the
concentrated liquid is collected from the bottom.
Construction
It consists of large cylindrical body made up of cast iron or steel, the average side ranges from 1.8 to 2.4-
meter, diameter & 2.4 to 3.6 meter in Hight.
The lower part consists of steam compartment with on inlate for steam at one & vent for non-condense
gas at another elte.
It has 6-8 stainless steel horizontal tubes in the steam compartment. An inlet for feed is provided at one
& outlet for vapour is placed at the top.
HORIZONTAL TUBE EVAPORATOR
8. Working
Feed is introduced into evaporator until tubes are immersed. Steam is introduced into the steam
compartment. Tubes receives heat from steam & conduct it to liquid. Steam condensate passes through
corresponding outlet. Feed receives heat & solvent gets evaporated. Vapour escapes through the outlet
placed on the top. This process is continued until a thick liquid id formed which is collected from the
outlet at bottom.
Uses
It is used for non-viscous solutions that do not deposit crystals on evaporation.
Advantages
❑ It provides more heating surface for evaporation.
❑ It requires less space for evaporation.
❑ It is cheap.
❑ The cost per square meter of heating surface is less in horizontal tube
evaporator.
Disadvantages
Liquid circulation is poor in this evaporator.
Not suitable for viscous liquids.
9. CLIMBING FILM EVAPORATOR
Principle
In climbing film evaporator, tubes a heated externally by steam. The pre-heated
feed enters from the bottom & flow up through the heated tube, the liquid gets heated rapidly due to
enhanced overall coefficient of preheated feed. The liquid near the wall because vapour & forms small
bubbles these fused with each other to form large bubbles which travels up in the tube. The liquid film is
between up from the top of the tube & strike the deflector.
This through the liquid concentrate down into the lower part where it is withdrawn.
Construction
It consists of steam jacketed tube. A deflector is placed at the top. The evaporator carries steam inlet,
bend outlet & condensate outlet. The feed inlet is from the bottom of the steam compartment.
10. Working
The preheated feed is introduced from the bottom of the evaporator. Steam
entered into the space outside the tube through the inlet, heat is transferred to the liquor through the
wall of the tube the liquid become vapour & forms small bubbles.
As more vapour is form the slug of liquid is below up in the tube facilating the liquid to spread as a film
over the wall.
This film of liquid continuous to vaporize rapidly, finally the mixture of liquid concentrate & vapour eject
from the top of the tube.
Uses
It is used for thermolabile substance such as insulin & vitamins.
Clear liquids, foaming liquid & corrosive solutions in large quantities can be operated.
Advantages
Long & narrow tubes provide large surface area.
It required low hold up & small floor space. It is suitable for foam forming liquid.
Disadvantages
It is expensive.
Difficult to clean & maintain.
Not use for very viscous liquids.
Construction is quite complicated.
11. FORCED CIRCULATION EVAPORATOR
PRINCIPLE
In forced circulation evaporator liquid is circulated through takes at high
pressure means of pump, hence boiling does not take place because boiling point is elevated forced
circulation of liquid also creeds some form of agitation when the liquid leaves the takes & enters the
vapour head, pressure falls suddenly. This leads to the flashing of super-heated liquor. Thus, evaporation
is affected.
CONSTRUCTION
The steam jacketed takes are held between two rube sheets. The tube measures osmotic pressure
meter inside diameter & 2.5m long.
WORKING
Steam is introduced into calandria. Pump sends the liquid to the tubes
with a positive velocity. As the liquid moves up through the tubes, it gets heated & beings to boil. As a
result, the vapour & liquid mixture rashes out of the tubes at high velocity. This mixture strikes the
deflector. The vapour enters the cyclone separator & leaves the equipment. This concentrated liquid
returns to pump for further evaporation. Finally, the concentrated product is collected.
12. USES
❑ It is used for thermolabile substance.
❑ It is used for to obtain concentration insulin & liver extracts.
❑ It is used for crystallizing operations.
ADVANTAGES
▪ The heat transfer coefficients are high due to rapid liquid movements.
▪ This evaporator is used for thermolabile substance because of rapid
evaporation.
• It is used for high viscous preparation because pumping mechanism is used.
DISADVANTAGES
The equipment is expensive because power is required for circulating the liquids.
Holding time of liquids is high.
