Distillation is the process of converting liquid into its vapours by heating and reconverting it again into liquid by condensing the vapours. The product obtained from the condensation of vapours is known as distillate or condensate. Container which collects the distillate is known as receiver. It results in essentially complete separation (nearly pure components).   It can be applied for two immiscible or non-reacting solid and liquid or liquid and liquid

1. DISTILLATION
Ms. Sneha Anil Pachore
Dept. of Pharmaceutics
Asst. Professor
Indira College of Pharmacy, Pune

2. DISTILLATION
 It is an unit operation which involves separation of a vaporizable component
from a multi-component system and subsequent condensation of
vapors. OR
 Also defined as separation of the components of a liquid mixture by a process
involving vaporization and subsequent condensation. OR
 It is defined as the separation of the components of a liquid mixture by a
process involving vaporization and subsequent condensation at another
place. OR
 Distillation is the process of converting liquid into its vapours by heating and
reconverting it again into liquid by condensing the vapours.
 The product obtained from the condensation of vapours is known as distillate
or condensate.
 Container which collects the distillate is known as receiver.
 It results in essentially complete separation (nearly pure components).

3. The individual molecules within the liquid are continuously in motion
 A small Percentage of these molecules attain enough kinetic energy to
leave the liquid phase This exerts an opposing pressure on the atmosphere
above the solution known as the vapor pressure, P
 When enough energy, in the form of heat, is imparted to the solution the
vapor pressure becomes equal to the atmospheric pressure and the liquid
begins to boil
 The vapor obtained from a boiling liquid, once cooled, will re-condense to a
liquid known as the distillate The complete process is called a distillation

4.  Applications
• Separation of volatile oils
• Purification of organic solvents
• Manufacture of official preparations
• Refining of petroleum products
• Recovery of solvents
• Quality control methods
• Separation of drugs obtained from plant and animal sources
• Purification of drugs obtained from chemical process

7. CLASSIFICATION OF DISTILLATION METHOD
Simple distillation
Flash distillation
Fractional distillation
Distillation under reduced pressure
Steam distillation
Molecular distillation

8. SIMPLE DISTILLATION
 Simple distillation is process of converting a single
constituent from a liquid into its vapour ,transferring the
vapour to another place and condensing it again into liquid.
Principle :
 Liquid boils when its vapour pressure is equal to atmospheric
pressure.
 Simple distillation is conducted at its boiling point.
 The heat is supplied to the liquid so that it boils.
 The resulting vapour is transferred to different place and
condensed.
 If the liquid of interest is volatile and remaining components
are non-volatile then simple distillation is useful means of
purification and separation.

9. CONSTRUCTION:
It consist of distillation
flask with a side arm
slopping downward which
is connected to condenser.
The condensed vapours are
collected in the flask called
‘receiver’.
The whole apparatus is
made of glass.
The condenser is connected
to receiver flask using
adapter .

11. WORKING
The distillation flask is filled one half to two third of its volume
with liquid to be distilled.
Add small pieces of porcelain to avoid bumping.
A thermometer is inserted .
The contents are heated gradually .the liquid begins to boil
after some time.
The vapour begins to rise up and passes down the side arm
into condenser.
The vapour is condensed and collected into the receiver.

12. USE :
 Used to prepare distilled water and water for injection.
 Used to prepare aromatic water.
 Used to separate non-volatile solids from volatile liquids.

13. FLASH DISTILLATION
 Flash distillation is defined as process in which entire liquid
mixture is suddenly vaporized(flash) by passing the feed from
high pressure zone to low pressure zone.
 It is also known as equilibrium distillation.
Principle :
 When hot liquid mixture is allowed to enter from a high pressure
into low pressure ,the entire liquid mixture is suddenly vaporized.
 This process is known as flash vaporization.
 During this process chamber where vaporization occurs gets
cooled .
 The individual vapour phase molecules of high boiling fraction
get condensed, while low boiling fraction remains as vapour.

14. CONT..
 This process requires certain amount of time.
 Therefore ,the liquid and vapour are kept in intimate contact
until equilibrium is achieved.
 Then liquid fraction is collected separately and separated
vapour is further allowed to condense.

15. CONSTRUCTION
 It consist of pump which is connected to feed reservoir.
 Pump pumps the feed (liquid mixture which is to be
separated) under high pressure into pipe which passes
through the heating chamber.
 The heating chamber contains suitable heating mechanism.
 The other end of the pipe is directly introduced into the
vapour –liquid separator through reducing valve.
 The liquid outlet is provided at the bottom and vapour outlet
is provided at the top of the separator.

17. WORKING :
 The feed is pumped through a heater at a certain pressure.
 The liquid get heated, which enter the vapour –liquid
separator through pressure reducing valve.
 Due to drop in pressure ,the hot liquid flashes, which further
enhances the vaporisation process.
 The sudden vaporisation induces cooling.
 The individual vapour phase molecule of high boiling fraction
gets condensed, while low boiling fraction remains as vapour.
 The mixture is allowed for a sufficient time ,so that vapour and
liquid portions separate and achieve equilibrium.
 The vapour is separated through a pipe from above and liquid
is collected from bottom of the separator.

18. DISTILLATION UNDER REDUCED PRESSURE ( VACUUM
DISTILLATION)
 Distillation under reduced pressure may be defined as
distillation process in which the liquid is distilled at
temperature lower than its boiling point by the application of
vacuum.
 Vacuum pumps, suction pumps etc. Are used to reduce the
pressure on the liquid surface.
Principle :
 Liquid boils when vapour pressure is equal to atmospheric
pressure .
 If the external pressure is reduced by applying vacuum ,the
boiling point of liquid decreases.
 Therefore , the liquid boils at lower temperature.

19. CONSTUCTION
 It consist of double neck distillation flask known as claisen
flask .
 In one of the necks of the claisen flask ,a thermometer is
fitted.
 The second neck a capillary tube is fitted which prevents
bumping of the heating liquid.
 The claisen flask is connected to a receiver through a
condenser.
 Vacuum pump is attached through a adapter to the receiver.

21. WORKING
 The liquid to be distilled is filled one –half to two –third
volume of flask.
 Small pieces of porcelain are added to the liquid for
facilitating distillation and prevent bumping.
 The capillary tube and thermometer are kept in place in the
flask.
 The required vacuum is applied.
 The contents are heated gradually.
 The temperature rises and liquid gets vaporised rapidly due to
vacuum.
 The vapour passes through condenser.
 The condensate is collected in the receiver.

22. STEAM DISTILLATION
 Steam distillation is method of distillation carried with aid of
steam and is used for separation of high-boiling
substances from non-volatile impurities.
 High boiling liquids cannot be purified by simple distillation,
since constituents in the mixture tends to decompose at
higher temperature.
 In such cases ,steam distillation is employed.
 Steam distillation is used for the separation of immiscible
liquids.

23. PRINCIPLE
 A mixture of immiscible liquids begins to boils when the sum
of their vapour pressure is equal to the atmospheric pressure.
 In consider the mixture water and turpentine, mixture boils
below boiling point of pure water, though the turpentine boils
at much higher temperature than that of water.
 For example ,boiling point of turpentine is about 160ºc . But
when it is mixed with water and heated ,the mixture boils at
about 95.6º c.
 At this temperature ,the vapour pressure of water is 647mmhg
and that of turpentine is 113 mm Hg.
 The sum of vapour pressure is 760 mmHg which normal
atmospheric pressure.
 Thus, high boiling substances may be distilled at temperature
much below its boiling point.

24. CONSTRUCTION
 It consist of metallic ‘steam can’ fitted with cork having two
holes.
 Through one of the holes, a long tube is passed so as to reach
almost the bottom of 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.

25. CONT..
 When steam starts coming out from the safety tube , it
indicate that the steam can is almost empty.
 Through another hole, the bent tube is passed.
 The other end of bent tube is connected to the flask
containing non-aqueous liquid.
 This tube should reach almost bottom of the flask.
 Through other hole ,a delivery tube is inserted which connects
the flask and the condenser.
 The condenser connected to receiver flask using adapter.

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

28. FRACTIONAL DISTILLATION
 Fractional distillation is process in which vaporisation of
liquid mixture gives rise to mixture of constituents from
which desired one is separated in pure form.
 This method is also known as rectification, bcz a part of the
vapour is collected and returned as liquid.
 This method is used to separate miscible volatile liquids
,whose boiling points are close, by means of a fractionating
column.
 In fractional distillation the vapour must pass through
fractionating column in which partial condensation of vapour is
allowed to occur.
 The condensation takes place in the fractionating column ,so
that a part of the condensing vapour returns to the still.

29. PRINCIPLE :
 When a liquid mixture is distilled ,the partial condensation of
the vapour is allowed to occur in fractionating column.
 In the column ,ascending vapour from the still is allowed to
come in contact with the condensing vapour returning to the
still.
 By condensing the vapour and reheating the liquid repeatedly,
equilibrium between liquid and vapour is set up at each stage,
which ultimately results in the separation of a more
volatile component.

30. CONSTRUCTION
 A laboratory scale fractional distillation unit
consist of :
 A source of heat
 Distillation flask
 A fractionating column
 A thermometer
 A condenser
 A receiver.

32. WORKING
 The mixture to be distilled is fed to boiler and heated usually
by steam.
 The liquid mixture is put into a distillation flask along with a
few pieces of porcelain to avoid bumping.
 Then fractionating column is fitted over the mouth of flask.
 Heat the mixture .
 As mixture boils ,vapour rises up the column.
 The vapour condenses on the glass plateforms known as tray,
insides the fractionating column, and runs back down into the
liquid below.
 This is known as ‘refluxing’ the distillate.

33. CONT..
 Only the most volatile fraction of the vapours remains in
gaseous form all the way to the top of the column.
 This fraction passes into condenser ,which cools it down to a
liquid ,and this liquid is collected in the receiver.

34. THEORY
 According to principle of colligative properties ,when a
substance is dissolved in a liquid ,the vapour pressure of
solvent is lowered.
 When two miscible liquids are mixed ,each may be considered
as a solution of one in the other.
 The vapour pressure of each component is lowered.
 The pressure excreted by each one is known as partial
pressure.

35. GENERAL METHODS FOR FRACTIONAL DISTILLATION
 Consider , mixture of two miscible liquid A and B containing
20% of A and 80% B.
 Liquid A (more volatile component ) is having a lower boiling
point than B (less volatile component).
 These liquids do not produce constant boiling point mixture.
 The boiling point composition curve of this mixture shown in
fig.
 1) When boiling point of the mixture is reached ,the vapour
composition curves are drawn as shown by lowest pair of
curves. These curves indicates that vapour contains 60% of A.

37. CONT..
 2) when this vapour is condensed ,the resulting liquid is again
heated to boiling point, this vapour gives the composition
containing 90% of A.
 3)This vapour impinging on a cool surface and gets
condensed. This fraction is revaporised by heating to its
boiling point. This boiling point curve of this distillate
indicates 98% of A.
 4) This fraction of vapour impinges on cooling surface. This
gives fourth pair of curve. Now this vapour contains higher
(more than 98%)proportion of A.
 5)The vapour moves to condenser at the top of the column
and gets condensed.

38. CONT..
 Thus ,repetition of these processes yield pure A .
 Once a low boiling point fraction has passed over ,distillation
should be stopped.
 The liquid available in the still is pure B.
 It can be collected as such.

39. AZEOTROPIC SOLUTION
 Azeotropic solution ( constant boiling point) cannot be
completely separated by fractional distillation, because either
vapour or the liquid in the still has mixture of components.
 The principle of azeotropic distillation lies in addition of a new
substance to the mixture so as to increases relative volatility of
one of the two key components and thus making separation
relatively easy.
 Azeotropic distillation is a distillation method in which
azeotropic mixture is broken by the addition of third
substance, which form a new azeotrope with one of the
component.

40. ADVANTAGE
 It is easy to use.
 It is highly effective and efficient.
 Disadvantages
 It can be expensive.
 it can contribute to environmental pollution.
 It cannot be used to separate miscible liquids which forms
azeotropic mixture

41. MOLECULAR DISTILLATION
 Molecular distillation is defined as a distillation process in
which each molecule in the vapour phase travels mean free
path and gets condensed individually without intermolecular
collisions on application of vacuum.
 This is also called as evaporative distillation or short path
distillation.
 Mean free path is the distance travelled by the molecules in
straight line without any collision.

42. PRINCIPLE
 The substances to be distilled have very low vapour pressure .
 Example are viscous liquids ,oils ,greases, waxy materials and
high molecular weight substances.
 These boils at very high temperature . In order to decrease
boiling point of the liquid , high vacuum must be applied.
 At very low pressure ,the distance between evaporative surface
and the condenser is approximately equal to the mean free
path of the vapour molecules.
 Molecules leaving the surface of the liquid are more likely hit
the condenser surface than to collide with other molecule.

43. TWO TYPES OF MOLECULAR DISTILLATION
 Falling film or wiped film molecular still
 Centrifugal molecular still
 Falling film molecular still
 Principle :
 In this method, vapourisation occurs from liquid film flowing
down a heated surface under high vacuum.
 The vapour travels a short distance and strike the condenser
nearby.
 Each molecule is condensed individually.
 The distillate is subsequently collected.

44. CONSTRUCTION
 The wall of the vessel are provided with suitable means of
heating (jacket).
 Wipers are provided adjacent to the vessel wall.
 Wipers are connected to rotating head through rotor.
 The condenser are arranged very close to the wall .
 Vacuum pump is connected to large diameter pipe at the
centre of the vessel.
 Provisions are made for collecting distillate and the
undistilled liquid residue at the bottom.

46. WORKING
 The vessel is heated by suitable means.
 Vacuum is applied at the centre of the vessel and wipers are
allowed to rotate.
 The feed is entered through inlet of the vessel. As a liquid
flows down the walls,it is spread to form a film by wipers .
Wipers are moving at the rate of 3 meter per second.
 The surface is already heated which causes the liquid film to
evaporate immediately.
 The vapour (molecules) travels its mean free path and strikes
the condenser.
 The condensate is collected into a vessel.
 The residue is collected from bottom of the vessel .

47. CENTRIFUGAL MOLECULAR STILL
 Principle :
 Liquid feed is introduced into vessel,which rotate at
very high speed (centrifugal action).
 This centrifugal force spread the liquid feed as thin
film.
 Due to heating, vapourisation occurs from film of
liquid on the sides of the vessel.
 The molecules of vapour travel a short distance and
gets condensed on the adjacent condenser.
 Each molecule condensed individually.
 Distillate is subsequently collected.


48. CONSTRUCTION
 It consist of bucket shaped vessel having diameter of
about 1 t0 1.5 meter.
 It is rotated with high speed using a motor.
 Radiant heaters are provided externally to heat the
fluid in the bucket.
 Condenser are closely arranged to evaporating
surface.
 Vacuum pump is connected to entire vessel at the top.
 Provision are made for introducing the feed into
centre of the bucket , for receiving the product .

50. WORKING
 Vacuum is applied at the centre of the vessel.
 The bucket shaped vessel is allowed to rotate at high speed.
 The feed is introduced from the centre of the vessel.
 Due to centrifugal action of the rotating bucket ,liquid moves
outward over the surface of the vessel and forms a film.
 Since , radiant heaters heat the surface, the liquid evaporates
directly from the film.
 The vapour travels its mean free path and strikes the
condenser.
 The condensate is collected into another vessel.