Basic concept of distillation and equipment's used in distillation

2. Learning Objectives
By Studying this topic learners will able to understand
Basic perceptions behind distillation process those
are integral part of the process.
various distillation equipment's and unique use of
each equipment.

3. DEFINITION
Distillation is defined as a method of separation of the
component substances from a liquid mixture by selective
vaporization and subsequent condensation.
Distillation method involves process which is carried out
in two steps as follows:
a) Vaporization: Conversion of liquid into vapor
phase
b) Condensation: Recovering liquid by condensation
of vapors

4. Statement:
The partial vapor pressure of each component of an
ideal mixture of liquids is equal to the vapor
pressure of the pure component multiplied by its
mole fraction in the mixture.
Basic Principles of Distillation-RAOULT'S LAW

5. Consider a mixture of miscible liquids A and B in this
mixture:
Let the partial vapor pressure exerted by A= PA k Pa
Let the partial vapor pressure exerted by B= PB k Pa
Let the vapor pressure exerted by the pure component, A=
PoA kPa.
Let the vapor pressure exerted by the pure component, B=
PoB kPa.
Let the mole fraction concentration of liquid, A=XA
Let the mole fraction concentration of liquid, B=XB
PA= PoA XA, PB= PoB XB
Basic Principles of Distillation-RAOULT'S LAW

6. Basic Principles of Distillation-RAOULT'S LAW
Raoult's law may be mathematically expressed as:
Partial vapor pressure of liquid = Vapor pressure of pure
liquid mole fraction of the liquid
PA= Po A XA
PB= Po B XB
Ideal solution obeys Raoult's law. These solutions are
known as perfect solutions. E.g. benzene and toluene.
P=PA+PB

7. Statement:
Total pressure exerted by a mixture of ideal gases may
be considered as sum of the partial vapor pressure
exerted by each gas, if alone present and occupied the
total volume.
Basic Principles of Distillation-DALTON'S LAW

8. It is expressed as:
Total pressure=Partial pressure of A + Partial pressure of B
P =PA + PB
By substituting Raoult's law equation:
P= Po A XA + Po B XB
Their properties are additive i.e., the total vapor pressure
of the mixture is the weighted average of the vapor
pressure of the pure individual constituent.
Basic Principles of Distillation-DALTON'S LAW

9. The partial pressure of the component varies linearly
from zero to full vapor pressure as the mole fraction
varies from zero to one.
The total pressure exerted by the system at a particular
composition is equal to the sum of the partial pressure
of its components.
Basic Principles of Distillation-DALTON'S LAW

10. SIMPLE DISTILLATION-PRINCIPLE
Liquid boils when its vapor pressure is equal to
atmospheric pressure.
Simple distillation is conducted at its boiling point.
Higher the relative volatility better is separation
Liquid is heated to form vapor an these vapor are
collected in different flask in the form of liquid.

11. SIMPLE DISTILLATION-CONSTRUCTION
It consists of distillation flask containing liquid
mixture taken for separation or purification of liquid
component and is also known as still pot.
On laboratory scale, round bottom flask made up of
glass is used so that the progress of distillation can
be viewed.
These round bottom flasks are having side arm
sloping downward and to which condenser can be
fitted.

12. Thermometer is inserted into the cork and fixed into
the flask.
Condenser is connected to receiver flask attached via
adaptor. Water is circulated through jacket of the
condenser.
SIMPLE DISTILLATION-CONSTRUCTION

13. SIMPLE DISTILLATION

14. SIMPLE DISTILLATION-WORKING
The liquid to be distilled is filled into the flask one
half to two third of its volume.
Bumping is avoided by adding small pieces of
porcelain before distillation.
The contents are heated gradually and liquid begin
to boil.
Vapor are formed, rise up and passes down to side
arm into condenser.
The temperature rises rapidly and reaches to
constant value.

15. SIMPLE DISTILLATION-WORKING
The temperature of distillate is noted; this is boiling
point of distillate.
The vapors are condensed and collected into
receiver.
Flame is adjusted such that one or two drops per
second collected in receiver.
Process continues until small volume of liquid
remains in the flask.

16. SIMPLE DISTILLATION-ADVANTAGES
It uses the difference in boiling points as a means of
separating different substances.
Energy consumption is less as compared to other
methods such as fractional distillation simple for
construction and operation as well as cost of
equipment is less.
Relatively fast and straight forward.

17. 1. Liquids with close boiling points cannot be
separated.
2. Simple distillation is not useful for separation
heat sensitive materials, as these materials may
undergo decomposition or chemical reaction.
SIMPLE DISTILLATION-DISADVANTAGES

18. SIMPLE DISTILLATION-APPLICATIONS
1. Preparation of distilled water, purified water
and water for injection.
2. Preparation of volatile and aromatic waters.
3. Purification of organic solvents.
4. Preparation of compounds such as spirit of
nitrous ether, aromatic spirit of ammonia etc.
5. Separation of non-volatile solids from volatile
liquids.
6. Preparation of wine and spirit.

19. FLASH DISTILLATION-PRINCIPLE
When a hot feed containing mixture of liquids is
allowed to enter from high pressure zone to low
pressure zone, the entire liquid mixture is suddenly
vaporized. This process is known as flash
vaporization.
During this process low boiling point liquid
undergoes vaporization and high boiling point liquid
condensed out.

20. This process requires certain amount of time. Hence
the liquid and vapor is kept in intimate contact until
equilibrium is achieved.
Thus separation of liquid mixture takes place.
FLASH DISTILLATION-PRINCIPLE

21. FLASH DISTILLATION

22. Equipment set up consists of a pump connected to
feed reservoir containing liquid mixture taken for
distillation process.
Heating chamber is heated by the steam and feed is
forwarded to pressure reduction valve.
Liquid-vapor separator is provided with vapor outlet
at the top and liquid outlet at the bottom of
separator.
Vapors from vapor outlet are then condensed.
FLASH DISTILLATION-CONSTRUCTION

23. In method of flash distillation, liquid mixture taken
for distillation is pumped to heating chamber at
certain pressure.
Generally steam is used as the heating media.
Liquid mixture is get heated by the steam.
Hot mixture is passed through the pressure reducing
valve, where low boiling point liquid is vaporized.
FLASH DISTILLATION-WORKING

24. The separation of the liquid vapor is carried out in
the vapor-liquid separation chamber.
Due to the reduction in pressure hot mixture flashes,
so the rate of vaporization is further increases.
Vaporized component escapes out from the liquid,
and removed from the top. Condensed liquid is
collected from the bottom.
FLASH DISTILLATION-WORKING

25. 1. It can be used as continuous distillation
process.
2. Flash distillation can be used for separating
multi-components liquid mixture systems of narrow
boiling range in combination with Fractional
distillation, especially in petroleum industry for
refining of crude oil.
FLASH DISTILLATION-ADVANTAGES

26. 1. It is not effective for separation of liquids with
comparable volatility.
2. It is not suitable for two component system.
3. It is not effective method of distillation where
pure component is needed as distillate.
FLASH DISTILLATION-DISADVANTAGES

27. 1. Flash distillation method is effectively used for
separating liquid components which are boils at
widely different boiling points.
2. Method of flash distillation is widely used in
petroleum industry for refining of crude oil.
FLASH DISTILLATION-APPLICATIONS

28. FRACTIONAL DISTILLATION- PRINCIPLE
This is a process in which vaporization of liquid
mixture gives rise to a mixture of constituents from
which the desired one is separated in pure form.
This method is used to separate miscible volatile
liquids whose boiling points are close by means of
fractionating column.
This is a mass transfer process involving counter
current diffusion of components at each equilibrium
stage.
When a liquid mixture is distilled , the partial
condensation of the vapor is allowed to occur in a
fractionating column.

29. In the column ascending vapor from the still is
allowed to come in contact with condensing
vapors from the still is allowed to come in
contact with the condensing vapors returning to
still.
This results in enrichment of the vapor with
more volatile components by condensing the
vapors and reheating the liquid.
FRACTIONAL DISTILLATION- PRINCIPLE

30. The fractionating column is inserted between still
and condenser.
Provision is made for supply of heat at the bottom of
the column
At the top of column a condenser is provided
The column has large area for providing sufficient
flow conditions. The broken lines across the column
represents contact devices.
FRACTIONAL DISTILLATION- CONSTRUCTION

31. FRACTIONAL DISTILLATION

32. The mixture to be distilled is fed to the boiler and
heated by steam.
Consider a mixture of two miscible liquids A and B
contains 20% A and 80% B.
Liquid A is having a lower boiling point than B (it
trickles down).
When this vapor is condensed, the resulting liquid is
again heated to boiling point , this vapor gives the
composition containing 90% of A
FRACTIONAL DISTILLATION- WORKING

33. This vapor impinges on a cool surface and gets
condensed. This fraction is re-vaporized by heating
to its boiling point.
The vapor moves to a condenser at the top of the
column and gets condensed.
FRACTIONAL DISTILLATION- WORKING

34. FRACTIONAL DISTILLATION- WORKING

35. Separation of a liquid mixture of components with less
difference in their boiling points cannot be effectively
separated by simple distillation method; repeated
distillations must be carried out. Such a mixture can be
effectively separated by using method of fractional
distillation in the single distillation process.
In fractional distillation, distillation columns can be
stacked for maximum efficiency.
Fractional distillation method is easy to use method
and is required only change from distillation head to
fractionating column.
FRACTIONAL DISTILLATION- AVANTAGES

36. Fractional columns used in fractional distillation are
an expensive one and also has risk of damage due to
high heat conditions.
Due to high temperature and high pressure
conditions, there is always a possibility of explosion
associated with fractional distillation.
Fractional distillation is a continuous process of
distillation, thus it cannot be used for distillation
involving separation of liquid mixture in small
quantity.
FRACTIONAL DISTILLATION- DISAVANTAGES

37. Due to the huge size of equipment it is not easy to
clean and sterilization of the equipment.
Fractional distillation cannot be used for separation
of temperature sensitive materials
FRACTIONAL DISTILLATION- DISAVANTAGES

38. Separation of miscible liquids such as acetone and
water, chloroform and benzene.
Separation of volatile liquids.
Separation of mixtures and purification of solvents,
chemicals and other naturally occurring material.
Fractional distillation is widely used in oil refineries,
where it is used in separating constituents of oil into
its basic components.
FRACTIONAL DISTILLATION- APPLICATIONS

39. In this process the liquid is distilled at temperatures
lower than its boiling point by the application of
vacuum.
The liquid boils when the vapor pressure is equal to
atmospheric pressure.
If external pressure is reduced by application of
vacuum, the boiling point of liquid decreases and the
liquid boils at a lower temperature.
Distillation Under Reduced Pressure- PRINCIPLE

40. E.g. water boils at 100C at an atmospheric pressure
of 760 mm Hg.
At 40C the vapor pressure of water is
approximately 70 mm Hg. Hence the external
pressure is reduced to 70 mm Hg water boils at 40C
Distillation Under Reduced Pressure- PRINCIPLE

41. Set up of equipment consists of a double neck
distillation flask which is known as Claisen flask.
One neck of Claisen flask is for placing thermometer
and another one for placing a fine capillary tube
which is dipped in boiling liquid to prevent bumping.
A stream of air can be passed to boiling liquid
through this capillary tube.
Distillation Under Reduced Pressure-
CONSTRUCTION

42. Generally, the water bath or oil bath is the source of
heating.
Remaining arrangement of assembly is same as that
in simple distillation only difference is of adaptor or
receiving bent which is having a provision for
connecting the assembly to the vacuum pump.
Distillation Under Reduced Pressure-
CONSTRUCTION

43. Distillation Under Reduced Pressure

44. Liquid mixture to be distilled is taken in the
distillation flask called a Claisen flask in an amount
about 2/3 of the volume of the flask.
To this boiling chip are added to reduce the bumping
of liquid to be distilled. Capillary tube is inserted to
dip it in liquid through one neck of the Claisen flask,
and the thermometer is placed at another neck of
Claisen flask.
Distillation Under Reduced Pressure- WORKING

45. Vacuum is applied and the flask is heated gradually.
The liquid starts vaporizing, vapors get condensed in
the condenser and this condensate is then collected
in the receiver.
It is found more convenient to distill liquid mixture
to be distilled in small volume, in comparison with
the excessively large volume of liquid mixture to be
distilled.
Distillation Under Reduced Pressure- WORKING

46. Advantages:
Extraction and purification of temperature sensitive
components can be done at lower temperatures
under reduced pressure.
Disadvantages:
In distillation under reduced pressure, unrelenting
foaming occurs. The stream of air can be passed on
to break the rising foam. The method is not suitable
for the preparation of semi-solid or solid extracts.
Distillation Under Reduced Pressure-
ADVANTAGES and DISAVANTAGES

47. Preventing degradation of active constituents: At high
temperature components of liquid mixture may
undergo decomposition. For example, at higher
temperature, a) processes like malt extract or
separation of pancreatin may lead to inactivation of
enzymes; b) separation and purification of vitamins like
thiamine and ascorbic acid may lead to oxidation of
these enzymes. Hence, extraction and purification of
these components should be done at lower
temperatures under reduced pressure.
Distillation Under Reduced Pressure-
APPLICATIONS

48. In the preparation of Cascara sagrada tablets,
initially the liquid is concentrated under partially
reduced pressure until residue has the consistency
of treacle. The pressure is then suddenly reduced,
leading to swelling up of semi-solid due to the
sudden evolution of water vapor, producing light
porous mass which can be passed through the sieve
to form a granular powder.
Distillation Under Reduced Pressure-
APPLICATIONS

49. Steam distillation is a special type of distillation
carried out with the help of steam.
Steam distillation is used for the separation of high-
boiling substances from non-volatile impurities,
where simple distillation cannot be useful, since the
constituents of such liquid mixtures tend to
decompose at higher temperature.
STEAM DISTILLATION

50. The substances taken from separation must be
immiscible with water and are generally organic
substances.
The ultimate product of distillation is two phase
system of water and the organic distillate.
STEAM DISTILLATION

51. A mixture of immiscible liquid boils when the sum of
their vapor pressure is equal to atmospheric
pressure.
For a system of mixture of high-boiling substance
with non-volatile impurities and water, it is found
that system starts boiling at a temperature below the
boiling point of water, though the high-boiling
substance boils at much higher temperature than
that of water.
STEAM DISTILLATION- PRINCIPLE

52. This process, thus allows distillation at lower
temperature which reduces decomposition of the
desired product.
E.g. boiling point of turpentine is about 160°C. But
when it is mixed with water and heated it boils at
about 95.6°C.
At this temperature the vapor pressure of water is
647 mm Hg and for turpentine is 113 mm Hg so the
total vapor pressure of the system is 760 mm Hg.
Which is normal atmospheric pressure.
STEAM DISTILLATION- PRINCIPLE

53. Set up consists of a steam can having two opening
one for safety tube and another one for tube
connected to distillation flask containing liquid
mixture for distillation reaching almost up to bottom
of distillation flask.
There is a provision to heat the steam can and
distillation flask. Remaining set up of equipment is
same as that of simple distillation.
STEAM DISTILLATION- CONSTRCTION

54. STEAM DISTILLATION

55. In distillation flask liquid mixture taken for distillation
is added, and to it a small amount of water is added.
Steam can is filled with water and heated for generation
of steam. A safety tube of steam can is useful; when
pressure in steam can raise, then it can be reduced by
forcing water out of the steam can.
Steam can and distillation flask is heated
simultaneously, so that uniform flow of steam passes
through the boiling mixture.
STEAM DISTILLATION- WORKING

56. Steam carries immiscible oil to the condenser.
The condensed immiscible oil along with water is
collected into the receiver. Distillation is continued
until all the immiscible oil has been extracted.
Water and immiscible oil form two separate layers
which can be separated with the help of separating
flask.
STEAM DISTILLATION- WORKING

57. It is a suitable method for separation of volatile oils
without any decomposition and loss of aroma.
It is a suitable method for distillation of substance
have low volatility, provided that its molecular
weight is substantially higher than water.
STEAM DISTILLATION- AVANTAGES

58. This method is not suitable when immiscible liquid
reacts with water.
Steam distillation is not a suitable method for liquids
miscible with water.
STEAM DISTILLATION- DISAVANTAGES

59. Separation of high-boiling substances from non-
volatile impurities.
Extraction of volatile natural oils such as clove,
eucalyptus.
Purification of high-boiling essential oils.
Preparation of aromatic waters, and perfumes.
Distillation of Camphor.
Petroleum refineries and petrochemical plants.
STEAM DISTILLATION- APPLICATION

60. Molecular distillation is a process of distillation with
application of vacuum in which each molecule in
vapor phase gets condensed discretely without
intermolecular interactions or collisions.
Molecular distillation is also called evaporative
distillation or short path distillation.
Method of molecular distillation is used for the
substances to be distilled have very low vapor
pressures.
MOLECULAR DISTILLATION- PRINCIPLE

61. High molecular weight substances, waxy substances,
viscous liquids, oils, greases, etc. boils at very high
temperature. In order to decrease boiling points of such
substances high vacuum must be applied.
Vapor pressure above the liquid surface is much lower
than that of the saturated vapors in equilibrium with
liquid. At very low pressure the distance between the
evaporating surface and the condenser is
approximately equal to mean free path of the vapor
molecules.
MOLECULAR DISTILLATION- PRINCIPLE

62. Thus, molecules leaving the surface of liquid are
more likely hit the condenser surface than to collide
with other molecules. In short, there will be no re-
condensation taking place at the surface of liquid.
At this very low pressure, the distance between the
evaporating surface and the condenser is
approximately equal to the mean free path of the
vapor molecule.
MOLECULAR DISTILLATION- PRINCIPLE

63. In this method, vaporization occurs from a film of
liquid flowing down a heating surface under high
vacuum.
Vapors then travels a short distance to strike the
condenser, where each molecule is discretely
condensed.
Falling Film Molecular Still or Wiped Film
Molecular Still- PRINCIPLE

64. It consists vessel wall acting as evaporating surface.
Heating jacket is provided along the walls of the
vessel. Wipers are just adjacent to the vessel wall
and are connected to a rotor. Justly close to
evaporating surface there is arrangement of the
condenser. The vacuum pump is connected through
tubing provided at the central part of the vessel.
Condensate is collected into the vessel and can be
taken out through product outlet and residue can be
taken out from bottom of vessel.
Falling Film Molecular Still or Wiped Film
Molecular Still- CONSTRUCTION

65. Falling Film Molecular Still or Wiped Film
Molecular Still

66. The vessel wall is heated by heating jacket. And
vacuum is applied by vacuum pump connected
through tubing provided at the central part of the
vessel.
The rotor is started so that wiper just adjacent to the
vessel wall rotates.
As liquid to be distilled flows down the vessel wall,
wiper spread it to form a film.
Falling Film Molecular Still or Wiped Film
Molecular Still- WORKING

67. Since the surface is already heated the liquid from
liquid film evaporates directly. Evaporating
molecules travels its mean free path and strikes the
surface of condenser nearby, where they discretely
condensed.
Condensate is collected into the vessel and can be
taken out through product outlet and the residue is
taken out from bottom of the vessel.
Falling Film Molecular Still or Wiped Film
Molecular Still- WORKING

68. In this method, vaporization occurs from a film of
liquid formed from very high speed centrifugal
action of rotating vessel.
Wall of vessel which is acting as evaporating surface,
under high vacuum vapors are formed from film of
liquid.
Vapors then travels a short distance to strike the
condenser, where each molecule is discretely
condensed.
Centrifugal Molecular Still- PRINCIPLE

69. It consists vessel which can be rotated at very high
speed.
The liquid to be distilled is fed into the center of the
vessel.
The vessel wall is acting as evaporating surface.
Radiant heaters are provided to heat the vessel wall.
Centrifugal Molecular Still- CONSTRUCTION

70. The condenser is arranged close to evaporating
surface. A vacuum pump is connected to entire
vessel at the top of the vessel.
Condensate is collected from the edges of condenser
into another vessel. Residue can be taken out from
bottom of the vessel and can be circulated through
feed inlet for further distillation.
Centrifugal Molecular Still- CONSTRUCTION

71. Centrifugal Molecular Still

72. It consists the vessel which is rotated at very high
speed.
The liquid to be distilled is fed into the center of the
vessel.
Due very high speed centrifugal action of rotating
vessel, the liquid form a film on the walls of the vessel.
The vessel wall is acting as evaporating surface and
which is provided with radiant heaters for heating the
vessel wall.
Since the surface is already heated the liquid from
liquid film evaporates directly.
Centrifugal Molecular Still- WORKING

73. Evaporating molecules travels its mean free path and
strikes the surface of condenser nearby, where they
discretely condensed.
The vacuum pump is connected to entire vessel at the
top of the vessel.
Condensate is collected from the edges of condenser
into another vessel.
Residue can be taken out from bottom of the vessel and
can be circulated through the feed inlet for further
distillation.
Centrifugal Molecular Still- WORKING

74. Material exposed to the distillation temperature only
for the few seconds a benefit for heat sensitive
materials.
Molecular distillation is a useful method for
preparation of components of high molecular weight.
This process does not involve any risk of contamination
with solvents and molecular change.
High rate of distillation can be obtained by increasing
distillation temperature.
MOLECULAR DISTILLATION- AVANTAGES

75. Construction and operation of molecular distillation are
complicated.
It is difficult for an individual molecule to travel any
distance without a collision. These collisions may be
between molecules of same evaporating substance, or
between molecules of evaporating substance and those
of any other gas present in the system.
Temperature of condenser surface must be controlled
in such a way that condensate can flow freely down the
condenser surface without forming a thick film.
MOLECULAR DISTILLATION- DISAVANTAGES

76. VALUE ADDITION