This document discusses various distillation techniques used to separate liquid mixtures. It begins by defining distillation as a process that separates substances based on differences in their vapor pressures. It then describes several distillation methods including simple distillation, fractional distillation, steam distillation, and molecular distillation. For each method, it provides details on the operating principles, typical equipment setup, and common applications. The document serves to introduce various distillation unit operations and their uses in separating chemical substances.

1. DISTILLATION
B. PHARM SECOND YEAR
BY -SHALINI K. DHAWALE
ASSISTANT PROFESSOR
D. K. PATIL INSTITUTE OF PHARMACY, LOHA, NANDED

2. DISTILLATION
 Distillation is an unit operation which in liquid components or
substances are separated from a liquid mixture by selective
boiling and condensation at different places.
 It is a process of converting liquid into its vapours by heating
and reconverting it again into liquid by condensing the vapours.
 It is a method of separating substances which differ in their
vapour pressures.
 The feed liquid is called as distill and the condensed liquid is
known as distillate or condensate.
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3. Applications Of Distillation
 Used in chemical industries, pharmaceutical and food industries
and environmental technologies and in petroleum refineries.
 Used in food industries for concentrating essential oils and
flavours.
 It can be used in purification of solvents.
 It is used to purify the product which are obtained by extraction,
and to recover expensive solvents used during extraction
process.
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4. Different Methods Of Distillation
 Simple Distillation
 Flash Distillation
 Fractional Distillation
 Distillation Under Reduced Pressure
 Steam Distillation
 Molecular Distillation
 Destructive Distillation.
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5. Simple Distillation
 Simple distillation is a process of converting a single constituents from a
liquid into its vapours, transferring the vapours to another place and
recovering the liquid by condensing the vapours.
 This process is known as differential distillation, as distillation is based
on the differences in volatilities and vapour pressures of components in
the mixture.
 Principle: liquid boils when its vapour pressure is equals to atmospheric
pressure, when liquid mixture is boiled it forms the vapours of volatile
components. This vapours is condensed in another part of distillation
apparatus.
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6. Construction and working
 It consist of distillation flask with side arm sloping downwards. Condenser is
fitted into side arm by means of a cork.
 The condenser is usually water condenser, that is jacketed for circulation of
water and it is connected to the receiver flask using adapter.
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7. Construction and working
 Fill the distillation flask. The flask should be filled less than two third so that
when boiling starts the liquid should not enter into the condenser, which can
affect purity of the distillate.
 Heat the distillation flask slowly until the liquid begins to boil, vapours will
begin to rise through the neck of the distillation flask.
 As the vapours pass through the condenser they will condense and drip into the
collection receiver.
 Many organic compounds are flammable and if vapours pass through the
condenser without condensing they may ignite as the come in contact with the
heat source.
 Remove all heating source from distillation flask before all of liquid is
vapourized.
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8. Applications
 Used for preparation of distilled water and water for injection,
 Many volatile oils and aromatic water are prepared by simple
distillation.
 Used in purification of organic solvents.
 Concentration of liquid and to separate nonvolatile solid from
volatile liquid.
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9. Flash Distillation
 Flash distillation is a process in which entire liquid mixture is suddenly
vapourised(flash) by passing a feed from high pressure zone to a low
pressure zone,
 Principle: when a hot liq. Mixture is allowed to enter from high pressure
zone to low pressure zone the entire mixture suddenly vaporizes. During
this process the chamber gets cooled because of sudden drop in boiling
point.
 Because of this cooling the less volatile component condenses and
converted into liquid where as more volatile component still remains in
vapour phase.
 The liquid fraction is collected separately. The vapour are further
condensed and collected.
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10. Construction and working
 It consist of pump which is connected to a feed reservoir. Pump helps in
pumping the feed into heating chamber which consist of suitable heating
mechanism.
 The other end of pipe is directly introduced in vapour liquid separator through
a pressure reducing valve.
 The vapour outlet is provided at top and liquid outlet at bottom of separator.
 The feed is pumped through a heater at a certain pressure. The liquid gets
heated and enters the vapour liquid separator through pressure reducing valve.
 Due to drop in pressure the liquid flashes, which further enhances
vapourization process and there is flash boiling of liquid mixture.
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11. Construction and working
 The mixture is allowed to remain for sufficient time so that the vapour and
liquid portions separate and achieve equilibrium.
 It is used in continuous mode by providing the continuous feeding.
 Uses: it is used for separating components which boil at widely different temp.
 It is used for obtaining multi-component systems of narrow boiling range.
 It can be used in continuous mode.
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12. Fractional distillation
 Fractional distillation is a process in which vaporisation of liquid mixture give
rise to a mixture of constituents from which the desired one is separated.
 This method is used to separate miscible volatile liquid whose boiling points
are close.
 Principle: Fraction distillation is a mass transfer process involving counter
current diffusion of the component at each equilibrium stage.
 When a liquid mixture is distilled the partial condensation of vapour occurs at
the fractionating column. In column the ascending vapour from the still is
allowed to come in contact with the condensing vapour returning to the still
 This results in enrichment of vapour with more volatile component which
results in separation of more volatile component,
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13. Construction and working of fractional distillation
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 The mixture is put into the distillation flask along with few anti – bumping
granules and the fractionating column is fitted into the top. The fractional
distillation column is set up with the heat source at the bottom on the still pot
 As the distance from the still pot increases a temperature gradient is formed in
the column. It is coolest at top and hottest at bottom.

14. Fractional distillation
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WORKING
 The mixture is taken in distillation flask and heated
 Vapours formed consist of more volatile component with less volatile
components. Vapours starts travelling in fractionating column,
 Condensation of vapours of less volatile liquid will start before than
those of more volatile liquid
 The process of distillation and condensation is repeated. The vapours
of more volatile components will reach at the top from there they are
taken into condenser and finally the substance is transferred to
container. The remaining liquid in distillation flask get enriched in
components with higher boiling points.

15. Uses
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 To separate crude oils into its various components such as gasoline, kerosene,
diesel, paraffin oil and liberating oils.
 Used for purification of water.
 It is used for separating acetone and water,
Disadvantage
Fractional distillation can’t be used for miscible liquids.

16. Distillation under reduced pressure
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 Vacuum distillation is also called as distillation under reduced pressure,
Used for purifying and separating thermally unstable liquid compounds.
Principle: The boiling point of liquid is lowered to the desired temperature by
reducing the pressure on its surface. As a result of this a liquid can be boiled
and distilled without any decomposition at temperature much below its normal
boiling point.

17. Construction And Working
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 It is carried out in a specially designed double neck distillation flask known as claisen
flask.
 The main neck of which is fitted with a long capillary tube and side neck being fitted
with thermometer
 The side tube is connected to a condenser carrying a receiver at the other end , the
receiver is attached to a vacuum pump to reduce the pressure.
 Heating of claisen flask is not started until the desired vacuum has been attained.
Advantages :
 The compounds decompose on heating to their boiling point can be purified using this
method
 It is more fuel economical as it makes liquid boil at temprature below the normal
boiling point

18. Steam distillation
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 Principle:
 When a mixture of two immiscible liquids is heated and agited, then the
mixture boils when the sum of vapour pressure equals to the atmospheric
pressure.

19. Construction and working
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 Steam distillation consist of metallic steam can fitted with a cork having two holes,
through one of the hole a long tube is passed so as to reach almost the bottom of
steam generator.
 This tube is act as safety tube, in case pressure inside steam generator becomes
much water will be forced out of it and pressure will be reduced.
 Through another hole, a bent tube is passed which is connected to flask containing
non aqueous liquid this tube almost reach bottom of flask.
 The delivery tube is inserted to connect flask and condenser, the conductor is
connected to receiver flask using an adaptor, provision are made to heat the steam
can and flask.
 The non aqueous liquid is placed in flask, a small quantity of water is added to it,
steam can is filled with water.

20. Construction and working
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 Steam generator and flask are heated simultaneously so that uniform flow of steam
passes through boiling mixture.
 The mixture gets heated, steam carries 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 non aqueous liquid has been distilled.
 Advantages
 used for separation of immiscible liquids, this method is used for extracting most of
the volatile oils such as clove, anise, eucalyptus.
 Useful in purification of liquid with high boiling point,
 Volatile oils are separated at lower temperature in steam distillation without
decomposition and loss of aroma.

21. Molecular Distillation
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 Molecular distillation is defined as a process in which each molecule in vapour
phase travels the mean free path and gets condensed individually without
intermolecular collision on application of vacuum.
 Principle:
 Mean free path is average distance travelled by molecule in a straight line
without any collision.
 The distillant molecules should get chance to reach evaporating surface and
therfore the layer of distillant should be thin to overcome the pressure of the
layers above to come to the surface .
 Therefore the distillant maintained in a thin layer, vapour is evolved from the
surface only and therfore is called as evaporative distillation.

22. Applications of molecular distillation
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 Purification of chemicals such as tricresyl phosphate, dibutyl phthalate and
dimethyl phthalate.
 Vit. A is separated from fish liver oil.
 Free fatty acid are distilled at 100°C.
 Used in refining of fixed oils

23. THANK YOU…
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