Pharmaceutical Engineering

1. EVAPORATION
Ms. Supriya R. Bhamare
Assistant Professor
Sir. Dr. M. S. Gosavi College of Pharmaceutical
Educational and Center, Nashik.

2. Unit processes in which heat
transfer will be needed
❖Evaporation : Heat is
supplied in order to convert a
liquid into a vapour, which
subsequently removed.
❖Distillation: Heat is
supplied to a liquid mixture
for converting the liquid in
the vapour so that the
individual vapour
components are condensed at
the another place.

3. ❖Sterilization : For the sterilization of
pharmaceuticals, autoclaves are used with steam as a
heating medium. Dry heat is used to sterilize glass
apparatus.

4. ❖Drying : Heat is
Supplied to the product to
be dried and small quantity
of moisture is removed
from that product till it
become dry.
❖Crystallization :
Saturated solution is heated
to bring about super
saturation, which promotes
the crystallization of drugs.

5. Definition
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⚫Evaporation is a type of phase transition; it
is the process by which molecules in a liquid
state (e.g water) spontaneously become
gaseous (e.g water vapor).
⚫The equipment used for evaporation is
known as Evaporator.

6. Purpose of evaporation:
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⚫To concentrate solution by removing the
vapor from a boiling liquid solution .
⚫In the majority of cases, evaporation refers
to the removal of water from an aqueous
solution.
⚫Example: concentration of aqueous
solutions of sugar, sodium chloride, sodium
hydroxide, glycerol, glue, milk, and orange
juice.
⚫In these cases the concentrated solution is
the desired product and the evaporated water
is normally discarded.

7. Evaporation and Distillation
7
Evaporation Distillation
In evaporation,
vaporization takes place
below the boiling point.
In the distillation method,
vaporization takes place at the
boiling point
Evaporation takes place
only from the surface of
the liquid
Distillation takes place
from the whole liquid
mass.
It takes place below boiling point
so there is no bubble formation in
evaporation.
At the boiling point of the
distillation process, the liquid
forms bubbles.
Evaporation is not
necessarily separation or
purifying technique.
Distillation is a
separation or purifying
technique
Evaporation is a slow process. Distillation happens rapidly.

8. Evaporation and Drying
8
⚫The term drying usually refers the removal of
relatively small amounts of water from solid or
nearly solid material, whereas Evaporation is
usually limited to the removal of relatively
large amounts of water from solutions.
⚫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.

9. Applications of evaporation
⚫Manufacturing of bulk drugs.
⚫Manufacturing of biological products.
⚫Manufacturing of food products.
⚫Manufacturing of demineralised water.
⚫Minimizethe chances of chemical
reactions.
⚫Prepare the product for next
operation like drying.
⚫Improve product storage life.
⚫Decrease the impact of microbial growth.
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10. Factors affecting rate of evaporation
⚫ Rate of evaporation α 1/ atmospheric pressure
⚫ M α SL (Va-Vp)
P
Where,
M= mass of vapor formed in
unit time (rate of evaporation)
SL = surface area of liquid exposed to the atmosphere
Va= maximum aqueous vapor pressure of air
Vp= pressure exerted due to liquid present in air
P= atmospheric pressure
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11. ⚫Temperature:
Higher the temperature greaterwill be
the evaporation.
⚫ Vapor pressure:
Lower the pressure ,greater will be the
evaporation.
⚫ Surface area:
Greater the surface area of the liquid,
greater will be the evaporation.
⚫ Time of evaporation:
Exposure time is longer, more will be the
evaporation

12. Equipments used for evaporation
1. Evaporators with heating medium in jacket:
Ex. Steam jacketed kettle
2. Evaporators with tube placed horizontally:
Ex. Horizontal tube evaporator
3. Evaporators with tube placed vertically
4. Climbing film evaporator
5. Forced Circulation evaporator
6. Multiple effect evaporator

14. Conduction is the process by which heat energy is
transmitted through collisions between
neighboring atoms or molecules.
Convection is the circular motion that happens
when warmer air or liquid — which has faster
moving molecules, making it less dense — rises,
while the cooler

21. Vertical tube evaporator (short tube evaporator)
It consist of vertical shell having it short tube bundle.
Principle:
Liquid is passed through the vertical
tubes and steam is supplied from outside
tubes.
Heat transfer takes place from condensing steam on
tubes and the liquids inside tube gets
heated.
The solvent evaporates, vapor escapes
from the top and concentrated liquid is
collected from bottom.
Solution tube evaporated is inside the tube and steam
flows outside the tubes.

22. Construction:
⮚ Consist of vertical cylindrical body/shell made up
of cast iron with dome shaped top and bottom
having short vertical tube bundles. (so called as
short tube evaporator).
⮚ Calandria are fitted at the bottom which consist
of number of vertical tubes with diameter 0.05-
0.075 meters & length of 1- 2 meters. (Calandria
heating element) also called as calandria type
evaporator
⮚ About 100 such tubes are fitted in the body
of 2.5 m or more diameters.
⮚ Inlets are provided for steam and feed. Outlets are
provided for vapor, concentrated products, non-
condensed.

23. Working:
⮚ Feed/thin liquor is introduced into tube side and steam
from outside in the steam space of calandria.
⮚ The feed introduced in such a way as to maintain the
liquid level slightly above the top of tubes.
⮚ The condensate is passed through corresponding outlet
and non condensed gases escape through the vent.
⮚ The liquid inside spouts up through the tubes heated by
steam and begins to boil. (The vertical tubes receives
the heat and conduct it to the liquid.) The vapor
escapes tough top outlet.
⮚ Vapour formed will rise through tubes come to liquid
surface from which they are disengaged into vapour
space removed from vapour outlet. Steam is supplied
until concentrated liquid is obtained collected from the
bottom outlet.

24. Advantages:
⮚ Relatively inexpensive; Increases the heating surface 10-15
times.
⮚ High heat transfer coefficient than steam jacketed kettle.
⮚ Vigorous circulation enhances rate of heat
transfer.
⮚ More units can be joined.
Disadvantages:
⮚ Larger floor space required.
⮚ Not suitable for viscous liquids
⮚ Liquid to be maintained above calandria.
⮚ Complicated- increased installation cost. Pressure has to
maintain.
⮚ Cleaning and maintenance is difficult.
Uses:
⮚ Manufacture of cascara extract, sugar, salt,
caustic soda etc

30. Falling film evaporator
Principle:
Feed enters from the top and flows down the walls of the tube.
The liquid get heated rapidly due to heat transfer from steam.
The liquid boils and becomes vapor, which forms small
bubbles.
They tend to fuse to form layers of bubbles, which flow down
the tubes.
Concentration takes place during downward journey. Vapor
and liquid are separated at the bottom.

31. Construction
It resembles climbing film evaporator, but it is
Inverted. Feed inlet is from the top of the steam
Compartment.
The outlet of the product is at bottom and is
connected to a cyclone separator.
Working:
Steam is supplied into the steam compartment.
Feed enters from the top of the tubes.
The feed flows down the walls of the tubes and
the liquid gets heat rapidly.
The feed absorbs heat, solvent begins to boil
and solvent gets evaporated.
Vapor and liquid are separated in the cyclone
separator. 2

32. ADVANTAGES
Suitable for high viscous liquids.
Liquid hold up time is less.
Liquid is not overheated.
Highly acidic and corrosive feeds can be
concentrated.
DISADVANTAGES
Not for suspensions, salting and scaling liquids.
Poor feed distribution in tubes.
Feed ratio is high.
USES
Separate volatile and non volatile liquids
Concentration of yeast extracts
Manufacture of gelatin
Extracts of tea and coffee

34. Forced circulation evaporator
Principle:
⮚ Liquid is circulated through the tubes at high pressure by
means of pump.
⮚ Hence boiling does not takes place as boiling point is
elevated (increased).
⮚ Forced circulation creates agitation.
⮚ When liquid leaves the tube and enters the vapor head,
pressure falls suddenly. (high pressure zone to low
pressure zone B.P. decrease will evaporation rate will
increase.
⮚ This leads to flashing of superheated liquor. Thus
evaporation is effected.
⮚ Pump generates pressure due to this energy on the feed.

36. ⮚ Construction:
The steam jacketed tubes are hold between two tube sheets
⮚ Heating unit consists of steam jacketed tubes.
⮚ Inside diameter is 0.1 m – 2.5 m. The part of tubes projects
into vapour head (flash chamber) which consist of a
deflector.
⮚ The vapour head connected to return pipe which runs
downwards and enters into the inlet of a pump.
Inlets are provided for steam and feed.
Outlets are provided for vapor, concentrated
products, non condensed gases and
condensate.
⮚ Pump is connected near the inlet.

37. ⮚ Working:
Steam is introduced in calendria (steam jacketed tube/heating
element).
⮚ Pump sends the liquid to the tubes with positive velocity.
As the liquids moves up through tubes/pipes, it gets heated. &
begins to boil.
⮚ The mixture of vapor and liquid moves upward with high velocity.
The mixture strikes deflector which throws liquid downward.
⮚ This shows effective separation of liquid & vapour.
⮚ Vapour enter in cyclone separator (based on densities) & leaves
equipment. (solid content or non evaporated material goes return to
the evaporator), this results in effective separation of liquid and
vapor.
The concentrated the product /liquid return o pump for further
evaporation.
⮚ Finally the product collected from outlet.

38. USE:
⮚ Useful for heat sensitive material/ Suitable for thermolabile
substance
⮚ Insulin and liver extract
⮚ Suitable for corrosive solution.
⮚ Crystallizing operations
ADVANTAGES:
⮚ High heat transfer coefficient due to rapid circulation.
⮚ Salting, scaling are not possible due to forced circulation.
⮚ Suitable for high viscous preparations
⮚ Due to rapid circulation suitable for heat suitable material.
DISADVANTAGES
⮚ Equipment is expensive
⮚ It has high residence time for liquid
⮚ More power supply is required