Distillation- theory of distillation, general equipment for distillation, steam distillation, azeotropic distillation

1. DISTILLATION
BY- AISHWARYA RAJPUT
M. PHARMA. (Pharmaceutical chemistry)
BANASTHALI VIDHYAPITH, Rajasthan
Submitted to- Dr. Bhawna Sati

2. DISTILLATION
1. Theory of distillation
2. General equipments for distillation
3. Azeotropic distillation
4. Steam distillation

3. DISTILLATION
 Distillation is a process of separating and purifying the
components in a liquid mixture.
 It is defined as the separation of components of a
liquid mixture by a process involving vaporization and
subsequent condensation at another place.
 The distillation process involves two steps; (a)
converting a liquid into vapour phase and (b)
transferring the vapour to another place and
recovering the liquid by condensation.
 The feed liquid is known as distilland and the
condensed liquid is known as distillate or condensate.

4.  If one component is volatile and others are non-volatile , it is
possible to separate volatile components from non-volatile
components by distillation. In such cases distillation is
considered as a separation or purification method.
 When heat is supplied to a mixture, a more volatile liquid
evaporates readily than the les volatile liquid.
As a result, the condensed liquid consists of a high
proportion of highly volatile liquid and less amount of less
volatile liquid. Therefore, it is said to be partial separation
method.

5. DISTILLATION ASSEMBLY

6. THEORY OF DISTILLATION
 The primary data required to understand any distillation problem
are vapour liquid equilibrium relationship.
 Distillation method depends on the relative volatilities of the
components present in the mixture.
 BINARY MIXTURE- when two liquids are mixed together they may
be miscible with each other in all proportions. Such miscible
liquids are known as binary mixtures of liquid. Example- water and
acetone, water and ethyl alcohol.
 IDEAL SOLUTIONS- it is defined as the one in which there is no
change in the properties of the components other than dilution,
when they are mixed to form a solution.
 Heat is neither evolved nor absorbed during the mixing. The final
volume of the solution represents the additive properties of
individual constituents. Example- methanol and water.

7. RAOULT’S LAW
 Raoult’s law expresses a quantitative relationship between the
concentration and vapour pressure.
 It states that the partial vapour pressure of each volatile
constituent is equal to the vapour pressure of the pure constituent
multiplied by its mole fraction in the solution at the given
temperature.
 Consider a mixture of miscible liquids A and B. in this mixture:-
Let partial vapour pressure exerted by A= 𝑃𝐴
Let partial vapour pressure exerted by B= 𝑃𝐵
Let vapour pressure exerted by the pure component of A= 𝑃° 𝐴
Let vapour pressure exerted by the pure component of B=𝑃° 𝐵
Let mole fraction concentration of liquid A= 𝑋𝐴
Let mole fraction concentration of liquid B= 𝑋 𝐵

8.  Raoult’s law may be mathematically expressed as:-
partial vapour pressure= vapour pressure of pure liquid
* mole fraction of the liquid
𝑃𝐴 = 𝑃° 𝐴 𝑋𝐴
𝑃𝐵 = 𝑃° 𝐵 𝑋 𝐵
 Ideal solution is defined as one that obeys Raoult’s law.
Example- benzene and toluene.

9. DALTON’S LAW
 Dalton’s law of partial vapour pressure states that the total
pressure exerted by a mixture of ideal gases may be
considered as sum of the partial vapour pressure exerted by
each gas, if alone were present and occupied the total
volume.
 Dalton’s law is mathematically expressed as;
Total vapour pressure= partial pressure of A + partial
pressure of B
P= 𝑃𝐴 + 𝑃𝐵
∴ P= 𝑃° 𝐴 𝑋𝐴 + 𝑃° 𝐵 𝑋 𝐵
 Their properties are additive, i.e; the total vapor pressure
of the mixture is the weighed average of the vapour
pressures of pure individual constituents.

10. • Application:- according to an ideal solution, the component
having relatively greater vapour pressure will be distilled
first. This principle is used in simple distillation.
IDEAL CURVE OF RAOULT’S LAW-

11. REAL SOLUTIONS
 Most systems show varying degree of deviation from
Raoult’s law, depending on the nature of liquids and the
temperature. These solutions are known as Real
solutions.
 Deviations are observed because solute-solute, solvent-
solute and solvent-solvent interactions are unequal.
Example- chloroform and acetone.
 Mutual interactions lead to either lowering or enhancing
the vapour pressure of the mixture with respect to ideal
behaviour.

12.  Positive deviation- in some liquid systems, the vapour
pressure is greater than the sum of the partial pressure of
the individual components. Such systems are said to
exhibit positive deviation from Raoult’s law. Example-
benzene and ethanol.
 Negative deviation- In some liquid systems, the vapour
pressure is lower than that of the sum of partial pressures
of the individual components. Such systems are said to
exhibit negative deviation from Raoult’s law. Example-
chloroform and acetone.

14. VOLATILITY
 The volatility of any substance in a solution may
be defined as the equilibrium partial pressure of
the substance in the vapour phase divided by
the mole fraction of the substance in the
solution.
 Volatility of the component A, νₐ= partial
vapour pressure of A/ mole fraction of A
νₐ=
𝑃 𝐴
𝑋 𝐴
 The volatility of the material in the pure state is
equal to the vapour pressure of the material.

15. RELATIVE VOLATILITY
 Consider a liquid mixture containing 2
components A and B. In such a case, the
volatility of one component is expressed in
terms of the second. Relative volatility may be
defined as-
 Relative volatility, α = volatility of component A
/ volatility of component B
α= νₐ/ν 𝑏
∴ α= 𝑷 𝑨 𝑿 𝑩/𝑷 𝑩 𝑿 𝑨

16. GENERAL EQUIPMENTS FOR
DISTILLATION
 The general equipment either for laboratory use
or for industrial scale, consists of three parts:-
1. STILL
2. CONDENSER
3. RECIEVER

17. STILL
 It is a vaporizing chamber and used to place the material to
be distilled.
 The size of the still should be such that only one-half to
two-thirds full of liquid is filled. If the still is too large,
superheating and sometimes decomposition of liquid may
occur.
 The still is heated by suitable means (example- steam) for the
vaporization of volatile constituents.
 A condenser is attached to the still using appropriate joints.
 On laboratory scale RBF made of glass are used so that the
progress of the distillation can be noticed. At the same time
the feed can be added as and when required.
 Stills are made of stainless steel, copper or suitable material
to provide efficient heat transfer. In these stills, an
observation window is provided.
 Some liquids have a tendency to bump or froth, which
promotes the carrying of liquid with vapour. To prevent this a
trap is inserted between distillation flask and condenser.

18. CONDENSER
 Condenser helps in condensing the vapour. It is a heat
exchanger. It is kept cold by circulating water through water
jacket.
 The condenser is connected to the receiver through a
suitable adapter. Adapter may be employed where the
receiver cannot be conveniently supported at the end of
the condenser.
 Condenser is placed in an upright or oblique position.

19. CONDENSER
 Different types of condensers are used, three classes are
described below:-
1. Single surface condenser- examples are, Liebig condenser,
spiral(glass worm) condenser.
2. Double surface condenser- the efficiency of the condenser
increases.
3. Multi tubular condenser- these are usually made of metal
and used for large scale work. Its used in preparation of
distilled water and water for injection.

21. RECEIVER
 It is used to collect the distillate. It may be simple flask or
modified flasks such as Florentine receivers.

22.  Florentine receivers are used for the separation of oil and
water. These are of two types:-
 Type 1- Florentine receiver for oils heavier than water.
These are used for separation of oils heavier than water.
 Type 2- Florentine receiver for oils lighter than water. These
are used for separation of oils lighter than water.

23. STEAM DISTILLATION
 Steam distillation is a method of distillation carried
with the aid of steam and is used for the separation
of high boiling substances from non-volatile
impurities.
 It is used for the separation of immiscible liquids.
 Advantages- Volatile oils can be separated at a
lower temperature in steam distillation, without any
decomposition and loss of aroma.
 Disadvantages- Steam distillation is not suitable
when immiscible liquid and water react with each
other.

24. STEAM DISTILLATION
APPARATUS USED FOR LABORATORY SCALE-
 It consists of a metallic ‘steam can’ fitted with a cork having two
holes. Through one of the holes, a long tube is passed so as to
reach almost the bottom of the steam generator.
 This tube acts as safety tube, so that in case the pressure inside
the steam generator becomes too much, water will be forced
out of it and the pressure will be relieved.
 Moreover, when steam starts coming out from the safety tube,
it indicates that the steam can be almost empty.
 Through another hole, a bent is passed the other end of the
bent tube is connected to the flask containing non-aqueous
liquid through a rubber bung. This tube should reach almost the
bottom of the flask.
 Through the other hole of the rubber bung, a delivery tube is
inserted which connects the flask and the condenser. The
condenser is connected to a receiver flask using an adaptor.
Provisions are made to heat the steam can and flask.

25. STEAM DISTILLATION
PROCEDURE-
 The non-aqueous liquid is placed in the flask. A small
quantity of water is added to it. Steam can is filled with
the water.
 The steam generator and the flask are heated
simultaneously, so that a uniform flow of steam passes
through the boiling mixture. The mixture gets heated.
 The steam carries the volatile oil and passes into the
condenser, which is cooled by cold water. The condensed
immiscible liquid is collected into the receiver.
 Distillation is continued until all the non-aqueous liquid
has been distilled.
 In the receiver, water and organic liquid form two
separate layers, which can be easily separated using a
separating flask.

26. STEAM DISTILLATION

27. STEAM DISTILLATION
(Industrial Scale)
EQUIPMENT USED ON INDUSTRIAL SCALE-
 It consists of jacketed still with a perforated plate
which forms a false bottom. Holes are provided
on the top and side for charging and discharging.
 Florentine receiver is placed between the still
and condensor. The condensor is cooled by
circulating cold water.

28. STEAM DISTILLATION
(Industrial Scale)
PROCEDURE-
 The material from which the volatile oil has to be extracted is placed
in the still above the perforated plate. Steam is admitted to the
jacket of the still.
 The water and material present on the still are heated to boiling.
Simultaneously steam is also injected below the materials through a
steam pipe from the jacket.
 The steam carries the volatile oil and gets condensed in the
condenser, which is cooled by cold water. The condensate is
collected into the florentine receiver.
 Most volatile oils are lighter than water and well separated from the
distillate as an upper layer and removed from the upper spout. The
water can run off from the spout on the left and returns to the still.

29. STEAM DISTILLATION
(Industrial Scale)

30. STEAM DISTILLATION
Applications-
1. It is used for separation of immiscible liquids. Example-
toluene and water.
2. Used for extracting most of the volatile oils such as
clove and eucalyptus.
3. Camphor is distilled by this method.
4. Aromatic waters are prepared by this method.
5. Useful in purification of liquid with high boiling point,
example- essential oil of almond.

31. AZEOTROPIC DISTILLATION
 Azeotropic solution is a mixture of liquids that has a
constant boiling point because the vapour has the same
composition as the liquid mixture. The boiling point of
azeotropic mixture may be higher or lower than that of
any of its components.
 The components of the solution cannot be separated by
simple distillation and therefore azeotropic distillation is
done.
 The principle of azeotropic distillation lies in the addition
of a new substance to the mixture so as to increase the
relative volatility of one of the two key components and
thus making separation relatively easy.

32. AZEOTROPIC DISTILLATION
 Azeotropic distillation is a distillation method in which
azeotropic mixture is broken by the addition of a third
substance, which forms a new azeotrope with one of the
components.
 The relative volatility of the liquid mixture can be changed by
adding a third substance. Example- benzene is added to the
azeotropic mixture of water and ethyl alcohol.
 Benzene breaks the mixture water-ethyl alcohol and forms a
new azeotrope between benzene and ethyl alcohol.
 The volatility of water is enhanced. On distillation water distills
at 65.85˚C leaving alcohol and benzene behind. The boiling
point of this binary mixture is 68.2 ˚C and benzene gets
distilled leaving pure alcohol behind. It can be distilled off
at 78.3 ˚C . The benzene can be recycled.

33. AAPLICATIONS OF
AZEOTROPIC DISTILLATION
 It is used in preparation of absolute alcohol.
Alcohol is available in different concentrations
like 70%, 90% in combination with water.
Absolute alcohol is 100% alcohol without any
parts of water.
 This distillation is also used in petroleum
refineries.

34. REFERENCE
 Subrahmanyam. C.V.S., Setty. J. Thimma;
“Pharmaceutical Engineering”; reprint 2008;
Vallabh Prakashan, Delhi; year 2002; page no.-
293-336.
 https://www.britannica.com/science/azeotrope
 https://coggle.it/diagram/WjUJlrbZhwABmN3c/t
/distillation