distillation methods .

1. POWERPOINT PRESENTATION
ON
DISTILLATION
SUBMITTED TO: DR. DHANDEEP SINGH
SUBMITTED BY: MANSI PANWAR
M.PHARMACY (Pharmaceutical chemistry)
PUP PATIALA

2. DISTILLATION
• Distillation is defined as the separation of components of a liquid mixture by a process
involving vaporization and subsequent condensation at another place .
• The feed liquid is known as Distilland.
• The condensed liquid is know as distillate or condensate .
• Distillation is called as partial separation method .
• Difference between three processes: evaporation ,drying and distillation
• Evaporation : it is used when concentrated liquid residue is required .the temp.is
maintained below its boiling point.
• Drying : it is used when dried solid residue is required as a product .
• Distillation: this operation is used when condensed vapour is required as a product .

3. • The separation operation called distillation utilizes vapor and liquid phases at
essentially the same temperature and pressure for the coexisting zones.
• It can be divided into two types:
1. Continuous type
2. Batch type
1. Continous type:
• Various kinds of devices such as random or structured packings and plates or trays are
used to bring the two phases into inti-mate contact.
• Trays are stacked one above the other and enclosed in a cylindrical shell to form a
column. Packings are also generally contained in a cylindrical shell between hold-down
and support plates.

4. Procedure : Feed entered into the column
Due to difference in gravities between vapour and liquid,
liquid runs into the column cascading from tray to tray
while vapour move upwards while contacting tray to tray
Liquid at bottom reboiled by a boiler and move upwards
while the remaining liquid withdrawn from bottom
Vapours get condensed by a condenser and can be
collected separately in a different flask
The lighter components resides in the vapour phase and
the heavy components resides in the liquid phase . Means
distillation occurs on the basis of relative volatility of
components .

5. • Batch type distillation operation:
• Batch distillation, which is the process of separating a specific quantity of a liquid mixture into
products, is used extensively in The laboratory and in small production units that may have to serve for
many mixture
• A batch distillation can be done in a single distillation column. When distillation of one batch is
completed, the column can be used for a completely different component mixture quickly and
efficiently. And also, this process can be completely automated.
• The simplest form of batch still consists of a heated vessel (pot or boiler), a condenser,
and one or more receiving tanks.
• No trays or packing are provided .

6. • Feed is charged into the vessel and brought to boiling. Vapors are condensed and collected
in a receiver. No reflux is returned.
• The rate of vaporization is sometimes controlled to prevent“bumping” the charge and to
avoid overloading the condenser, but other controls are minimal. This process is often
referred to as Rayleigh distillation.
• However, the batch distillation is highly subjected to contamination. That is because, when
the column is used for a separate batch after the completion of one distillation, trace
amount of the previous batch can be remaining in the system and thus, the following batch
can get contaminated (if the following batch is identical to the previous batch, this is not
something to be concerned).
• BASIC DIFFERENCE IN CONTINUOUS AND BATCH DISTILLATION
OPERATIONS IS In batch distillation some amount of mixture is taken for a distillation.
During the process no further liquid mixture added. Only distillate is taken out.
• In continuous distillation the mixture is added during the process and the same time
distillate is also collected.

7. • Some Important concepts :
When two liquids are mixed together ,they may be missile with each other in all proportions.
Such miscible liquids are known as binary mixtures of liquid .ex: ethyl alcohol and water .
Ideal solutions : these are 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 .
Ideal solution theory provides a model system to which real or non- Ideal solutions can be compared .
Raoults law: This 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 .
pA = P°A × XA
Where , pA = partial vapour pressure of component
p⁰A = vapour pressure of its pure constituent
XA = mole fraction
( ideal solutions follow RAOULTS LAW)
Daltons law : It states that total vapour pressure exerted by a mixture of ideal gases may be considered as the
sum of the partial vapour pressure exerted by each gas ,if alone were present and occupied the total volume .
P= pA +pB
P= P°A X A + p°B X B

8. • Application: according to an ideal solution ,the component having relatively greater
vapour pressure will distilled first .this principle is used in simple distillation.
• Most systems show a varying degree of deviation
From Raoults law ,depending on the nature of the
Liquids and the temperature .these solutions are
Known as real solutions .
• Deviations arise due to solute –solute,solute-solvent
And solvent –solvent interactions are unequal.
• Positive deviation : in some liquids vapour pressure is grater than sum of the
partial pressure of the individual components .such systems are known to exhibit
positive deviation from Raoults law. Ex: benzene and ethanol
• Negative deviation: in some liquid systems ,the vapour pressure is lower than
that of the sum of the partial pressures of the individual components .such
systems are said to exhibit negative deviation from Raoults law . Ex : chloroform
and acetone
• Application : complete separation of components cannot be achieved if large positive
or negative deviations from Raoults law aren’t observed .such solutions form so called
azeotropic mixtures.

9. Components of distillation
Assembly:
1. Still ( vaporizing chamber)
2. Condenser ( for condensing vapour )
3. Receiver ( for collecting the condensate)
Distillation
Flash
distillation
Simple
Distillation
Fractional
distillation
Distillation
under
reduced
pressure
Azeotropic
distillation
Steam
distillation
Molecular
distillation
Destructive
distillation

10. • Simple distillation:
It is a process of converting a single constituent from a liquid or mixture . Into its vapour ,
transferring the vapour to another place and recovering the liquid by condensing the vapour
,usually by allowing it to come in contact with a cold surface .
This process is called as differential distillation.,as it is bases on the differences in volatilities and vapour
pressures of the components in the mixture .
Principle : liquid boils when it’s vapour pressure is equal to atmospheric pressure. Simple distillation
is conducted at boiling point .
The higher the volatility higher will be the separation.

11. • Applications:
• It is used for the preparation of distilled water and water for injection.
• Volatile and aromatic waters are prepared
• Organic solvents are purified .
• A few official compounds are prepared by distillation. Ex.spirit of nitrous ether
and aromatic spirit of ammonia .

12. • FLASH DISTILLATION: IT Is DEFINED AS A PROCESS IN WHICH ENTIRE LIQUID MIXTURE IS
SUDDENLY VAPOURISED ( FLASH) BY PASSING THE FEED FROM A HIGH PRESSURE ZONE .
• IT IS ALSO KNOWN AS EQUILLIBRIUM DISTILLATION .( separation is attempted when the liquid and
vapour phases are In equillibrium.
• This process is continuous and does not involve rectification.
• PRINCIPLE :
• WHEN A HOT LIQUID MIXTURE IS ALLOWED TO ENTER FROM A HIGH PRESSURE ZONE
INTO A LOW PRESSURE ZONE , THE ENTIRE LIQUID MIXTURE IS SUDDENLY VAPOURIZED
.THE PROCESS IS TERMED AS FLASH VAPOURIZATION .
• CHAMBER COOLED AND HIGH BOILING FRACTION GET CONDENSE AND LOW BOILING
FRACTION REMAIN VAPOUR . THERE IS INTIMATE CONTACT BETWEEN THE LIQUID AND
VAPOUR PHASE UNTILL EUILLIBRIUM IS ACHIEVED .
• THE LIQUID FFRACTION ARE COLLECTED SEPARATLY.
• THE VAPOUR IS SEPARATED FROM THE LIQUID AND FURTHER ALLOWED TO CONDENSE.

13. Application:
1. It is used for separating components ,which boil at widely different temperature.
Widely used in petroleum industry for refining crude oil .

14. • Fractional distillation:
• It 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 process is also known as rectification , because a part of vapour is condensed and
returned in liquid .this method is used to separate missible volatile liquids, whose
boiling points are close ,by means of fractionating column.
• Difference between simple distillation and fractional distillation :
• In simple distillation vapour is directly passed through the condenser but in fractional
type it must pass through a fractionation column in which partial condensation of
vapour is allowed to occur .
• In simple distillation, condensate is collected directly to receiver, while in fractional
distillation ,condensation takes place in the fractionation column ,so that part of the
condensing vapour returns to the still .
• Principle :Fractional distillation is a mass transfer process involving counter
current diffusion of the components at each equillibrium stage . In this partial
condensation of the vapour is allowed to occur in a fractionation column . In the
column ,ascending vapour from the still is allowed to come in contact with the
condensing vapour returning to the still .this results in enrichment of the vapour
with more volatile component .

15. Boiling point curves
• A boiling point composition curve of a two-component mixture has
temperature on the y-axis and mole percent of one of the components on the
x-axis.
• The lowest curve on a boiling point composition diagram is called the liquid
composition line. This line tells you the mole percent of the compounds
when they are in the liquid phase at a given temperature.
• The highest curve is called the vapor composition line. This line tells you
the mole percent of the compounds when they are in the vapor phase at a
given temperature.
• Realize the liquid and vapor compositions are different at different
temperatures because some compounds are converted into gases easier than
others; they have lower boiling points. The vapor will always be enriched in
the lower boiling compound.

16. • The boiling point composition curve of a mixture of cyclohexane and toluene is shown
below.
• To use a boiling point composition curve, you first need to determine the mole percent
of one of your compounds in the two-component mixture.
• In the example above, you would determine the mole percent cyclohexane in your
mixture. Mole percent is calculated by taking the moles of one substance divided by
the total moles in the solution (the moles of both substances) x 100%. This number
tells you where to start on the x-axis of the boiling point composition

17. • When a substance begins to boil, the temperature remains constant; the liquid is turning into a gas. To visualize
this on the boiling point composition curve, you trace a horizontal line across from the liquid composition curve
to the vapor composition curve. If you trace down from where your horizontal line intersects the vapor
composition line, you can determine the mole percent of the compound in the vapor phase at that temperature.
• Once again using the cyclohexane/toluene example, if you start with a 50 mole percent solution of cyclohexane in
toluene, you can see from the boiling point composition curve that the liquid will boil at around 91 oC and the
composition of the vapor will be approximately 80% cyclohexane. The picture below represents one theoretical
plate – one vaporization-condensation cycle.
BUBBLE POINT CURVE :
• It is the temperature at which liquid start to boil .
DEW POINT CURVE :
• It is the temperature at which saturated vapour
start to condense .

18. • IN fractional distillation ,a column is inserted between the still and the condenser .
• A provision is made for the supply of heat (usually a steam coil)at the bottom of the
column .
• At the top of the column condenser is provided ,the column have large area for
providing sufficient flow conditions.
• The broken lines across the column represent the contacting devices.

19. WORKING:
• The mixture to be distilled is fed into the still and heated usually by steam.
the sequence of events occurring in the fractionating column can be
illustrated below :
• Suppose a mixture of A(20%) and B(80%).Where A is more volatile than B .
• when the boiling point of the mixture is reached ,the vapour composition
curve are drawn as shown by lowest pair of curves.these curves indicates
that the vapour contains 60% of A.
When this liquid is condensed ,the resulting liquid is again heated to boiling
point .this vapour gives the composition containing 90% of A(second pair of
the curves from the bottom).

20. These vapours goes condensed .this fraction is re -vapourised by
heating to its B.P. this B.P. curve of this distillate indicates 98% of
A( third pair of curves from the bottom ).
This fraction of vapour also get condensed and gives fourth pair
of of curves .this vapour contains higher (more than 98%)
proportion of A, i.e. vapour of pure component .
The vapour moves to condenser at the top of the column and
get condensed .
LIQUID B WILL BE REMAINED IN THE STILL AND CAN BE
COLLECTED AND CAN BE PURIFIED FURTHER BY SIMPLE
DISTILLSTION ASSEMBLY .

21. COLUMN EFFICIENCY
• A common measure of the efficiency of a fractionation column is given by no. of theoretical plates
• A theoretical plate is a hypothetical zone or stage in which two phases , such as liquid and the
vapour phase of substance ,establish an equilibrium with each other. .
• One theoretical plate is equal to one simple distillation cycle , i.e. one vapourization /condensation
cycle .
• The smaller the boiling point difference , greater the no. of theaoretical plates a fractionating
column must have to achieve separation of mixtures .
• Plate efficiency:
• theoretical plate required /actual no. of plates
• HETP (height equivalent to a theoretical plates) :
• height of packed section required that will give the sample separation as an equillibrium stage .
• HETP = ht. of the column /no. of theoretical plates

22. • other factors determining (EFFICIENCY OF FRACTIONATING COLUMN ):
i. Length of fractionating column: a state of dynamic equilibrium is required
for separation .A maximum degree of separation of the components is
obtained along the length of the column .
ii. Reflux ratio: it is the quotient of the amount of liquid returning through the
column to the amount to amount collected into the receiver during the
same interval of time .
iii. Heat input: heat input to the still should be controlled .if it is too little ,the
packaging is insufficiently wetted. if its too high ,velocity may be too great
for equilibrium to be attained .the size of the flame should be adjusted so
that liquid passes over at a rate of one drop for every two or three seconds.
iv. Column temperature : for a column operating at a temp. above 60 degree.
Heat loss should be prevented by insulation .

23. AZEOTROPIC AND EXTRACTIVE DISTILLATION
• Azeotropic solutions or constant boiling solutions cannot be completely
separated by fractional distillation because either the liquid or vapour will
contain the mixture of components .
• Some liquids cannot be separated into there pure components because the
volatilities of two nearly equal . Such mixtures are known as Azeotrope .
• AZEOTROPIC SOLUTION is a solution which distills unchanged at a constant
temperature . EX. 89.43 mol % mixture of ethanol and water at atmospheric
pressure .
• These solutions deviate from Raoultes law to a large extent .
These can be of two types : 1. minimum boiling azeotrope
2. maximum boiling azeotrope

24. MINIMUM BOILING AZEOTROPES :
• The azeotropic mixture has a lower boiling point than
that of component with least boiling point .At
minimum boiling temperature ,the liquid composition
remains constant and is equal to the vapour composition
(arising from such a liquid mixture ).
• The diagram on the right shows a positive azeoptrope of hypothetical constituents Xand Y.
• The bottom trace illustrates the boiling temperature of various compositions.below the
bottom trace only the liquid phase is in equilibrium.
• Above the top trace illustrates the vapour composition above the liquid at a given
temperature, above the top trace only the liquid is in equilibrium .
• Between the two traces liquid and vapour phase exist simultaneously in equillibrium: for
example heating a 25% X: 75% Y mixture to temperature AB would generate a vapour of
composition B over liquid of composition A.

25. • The azeotrope in the diagram is which where the two curves touch.
• The horizontal and vertical steps show the path of repeated distillations.
• Point A is the boiling point of non azeotropic mixture.the vapour that separates at that
temperature is composition B.
• The shapes of curves requires that the vapour at B be richer in constituent X than the liquid
at point A.
• The vapour is physically separated from the vapour liquid equillibrium system and is
cooled to point C where it condense .the resulting liquid (point C) is richer in X than it was
at point A.
• If the collected liquid is boiled again it progresses to point D and so on .
• The stepwise progression shows that how repeated distillation can never produce a distillate
that is richer in constituent X than the azeotrope.

26. EXAMPLES:

27. MAXIMUM BOILING AZEOTROPE :
• Each azeotrope have its boiling point .
the boiling point of azeotrope is more than any of
its constituents is called as maximum boiling
azeotrope.
• Diagram on the right shows the negative azeotrope
of components x and y.
• Again the bottom trace illustrates the boiling temperature at various
compositions,and again the below the bottom trace the mixture must be
entirely liquid phase.
• The top trace again illustrates the condensation temp. of various
compositions and again above the top trace mixture must be entirely vapour .

28. • The point A shown here is the boiling point with a composition chosen very near to the
azeotrope.
• The vapour is collected at the same temperature at point B. the vapour is cooled ,condensed
and collected at point C.
• This is the example of negative azeotrope so ,the distillate is farther from the azeotrope
than the original liquid mixture at point A was .
• So the distillate is poorer in constituent X and richer in constituent Y than the original
mixture.
• Because this process has removed a greater fraction of Y from the liquid than it had
originally ,residue must be poorer in Y and richer in X after distillation than before .
• If the point A had been chosen to the right of the azeotrope rather than to the left , the
distillate at point C would be farther to the right than A, which is to say that the distillate
would be richer in X and in Y than the original ,mixture .
• So in this case too, the distillate moves away from the azeotrope and the residue moves
towards it .
• This is the characteristic of negative azeotrope.

29. EXAMPLE:

30. Method of azeotropic distillation :
• In this method , azeotropic mixture is broken by the addition of third substance ,
which forms a new azeotrope with one of the components .
• The relative volatility of liquid mixture can be changed by adding a third substance.
For ex. Benzene is added to azeotropic mixture of ethyl alcohol and water .
• Benzene breaks the mixture and forms a new azeotrope between benzene and ethyl
alcohol .
• The volatility of the water is enhanced.
• On distillation water distills at 65.85⁰ C leaving alcohol and benzene behind .
The boiling point of this binary mixture is 68.2⁰C and benzene get distilled leaving
pure alcohol behind . It can be distilled off at 78.3⁰C.
The benzene can be recycled .and absolute alcohol can be prepared using fractional
distillation .
When glycerine is added to above mixture ,vapour pressure of water is lowered
.practically pure ethanol is prepared from fractional distillation .

31. • On the other hand in extractive distillation , the third substance added to azeotropic
mixture is relatively non volatile liquid compared to the components to be
sepaprated. The third component is withdrawn from the base of the fractionating
column .ex. Separation of toluene from paraffin hydrocarbons of approximately
same molecular weights .
• APPLICATIONS :
• ABSOLUTE ALCOHOL CAN BE PREPARED .
• PETROLEUM REFINERY AND DISTILLARIES USE THIS TYPE OF
DISTILLATION .

32. DISTILLATION UNDER REDUCED PRESSURE
• In this type of distillation process the
liquid is distilled at a temperature
lower than its boiling point under the
application of vaccum .
• Vaccum pumps ,suction pumps are
used to reduce the pressure on the
liquid surface .
• PRINCIPLE : liquid boils when
vapour pressure is equal to the
atmospheric pressure i.e. pressure on
its surface . If external pressure is
reduced by applying vaccum , the
boiling point of the liquid is decreases
.
• Liquid to be distilled filled in flask .small porcelain chips are added
to avoid bumping )
• The thermometer and cappilarry are placed in the flask .
• Required vaccum is applied.
• The contents are heated gradually .
• The temp. rises and liquid get vapourised
• The vapour pass through condenser
• And the condensate is collected in the receiver .
• The temp. is noted that should be less than its boiling point of the
liquid .

33. • APPLICATIONS :
• Peventing degradation of active costitutents at higher temperature . There
extraction can be done by distillation under reduced pressure .ex. Enzymes ,
vitamins etc.
• CHANGING PHYSICAL FORM :In the preparation of cascara sargada
tablets(laxative) ,the granular extract form dense and compact residue on drying at
atmospheric pressure . So to avoid that the liquid extract is concentrated at
reduces pressure which is helpful in forming light porous mass at the end .which
can be pass through the sieve to form granular powder .

34. STEAM DISTILLATION
• Steam distillation is a method of distillation carried out with the aid of steam and is used for separation
of high boiling substances from non volatile impurities .
• Higher boiling substances cannot be purified by simple distillation ,since the constituents in the mixture
tend to decompose at higher temperature .
• Steam distillation is used for the separation of immiscible liquid.
• PRINCIPLE : when a mixture of two practically immiscible liquids is heated while being
agitated to expose the surface of each liquid to the vapour phase ,each constituent
independently exert its own vapour pressure as a function of temperature as if the other
constituent were not present .
• Consequently ,the vapour pressure of whole system increases .boiling begins when the sum of
the vapour pressure of the two immiscible liquids just exceeds the atmospheric pressure .
• In this way , many organic compounds insoluble in water can be purified at a temperature
well below the point at which decomposition occurs .
• For ex. The boiling point of bromobenzene is 156⁰C and the boiling point of water is 100 ⁰C,
but a mixture of two boils at 95⁰C . Thus , bromobenzene can be easily distilled at a
temperature 61⁰C below its normal boiling point .

35. APPARATUS:
• The nonaqeuous liquid place in the flask .stam
can is filled with water .
• The steam generator and the flask heated
simultaneously .
• The mixture gets heated .
• The steam carries the volatile liquid 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 saparating flask .
• For volatile substances , which are miscible with
water , distillation with steam would involve the
same principle of fractional distillation .

36. APPLICATIONS :
• Steam distillation is used for the separation of immiscible liquids . Ex. Toluene
and water .
• This method is used for the extraction of volatile oils such as clove ,eucalyptus .
• It is useful in purification of liquid with high boiling point , for example
essential oil of almond .
• Camphor is distilled by this method .
• Aromatic waters can be prepared by this method .

37. MOLECULAR DISTILLATION
MOLECULAR DISTILLATION is defined as a distillation process in which
molecule in the vapour phase travels means free path and gets condensed individually
without intermolecular collisions on application of vaccum .
• This distillation is based on simple distillation and also termed as evaporative
distillation or short path distillation .
• Principle : the substance to be distilled have very low vapour pressure .
• Ex. Viscous liquids ,oils ,grease ,waxy material .
• They boil at very high temperature so in order to decrease the boiling point of
liquids high vaccum is applied .

38. Theory:
• The mean free path of a molecule is defined as the average distance through
which a molecule can move without coming into collision with another .
• The characteristic of substance influence the method of distillation :
• Liquids having low viscosity and density posses long mean path . Distillation is
simple .
• Substance having high pressure posses low mean free path .
• The mean free path can be increased by decreasing the viscosity which can be
obtained by high temperature and low pressure .thus , the non-volatile
substance become volatile and distillation is possible .

39. Instruments:
• FALLING FILM MOLECULAR STILL / WIPPED FILM MOLECULAR STILL
PRINCIPLE :
• In this method vapourization occurs from a film of liquid
flowing down a heated surface under high vaccum . The vapour travels a short
distance and strikes the condenser nearby .Each molecule is condensed
individually . distillate is subsequently collected .
WORKING : feed is entered through inlet of the vessel
liquid flows down film is formed with the help of wipers (moving at a rate of 3 m/s)
(The velocity of the film is 1.5 m/s)
Liquid film evaporates and vapour molecules travel its mean path and strike the condenser
The condensate is collected into the vessel . The residue is collected from the bottom of vessel and can be recirculated
through the feed port for further distillation . ( CAPACITY IS ABOUT 1000 lt /hr)

40. CENTRIFUGAL MOLECULAR STILL
• PRINCIPLE: In this method liquid feed is introduced into the vessel , which is rotating at a very high speed
(centrifugal action). On account of heating vapourization occurs from a film of liquid on the sides of the vessel . The
vapour molecules travels a short distance and gets condensed on the adjacent condenser . Each molecule is
condensed individually . The distillate is subsequently collected .
• WORKING : VACCUM IS APPLIED AT THE CENTRE OF THE VESSEL
THE INSTRUMENT ROTATES AT HIGH SPEED
THE FEED IS INTRODUCED FROM THE CENTRE AND DUE TO ROTATION
OF INSTRUMENT IT FORMS A FILM
DUE TO HEATING IT EVAPORATES DIRECTLY FROM THE FILM
THE VAPOUR MOLECULES TRAVELS ITS MEAN FREE PATH AND STRIKES THE CONDENSER .
THE CONDENSATE IS COLLECTED INTO ANOTHER VESSEL AND THE RESIDUE IS COLLECTED
FROM THE BOTTOM AND CAN BE RECIRCULATED FOR FURTHER DISTILLATION .

41. APPLICATIONS :
• MOLECULAR DISTILLATION IS USED FOR THE PURIFICATION AND SEPARATION OF
CHEMICALS OF LOW VAPOUR PRESSURE .
1. PURIFICATION OF CHEMICALS SUCH AS TRICRESYL PHOSPHATE , DIBUTYL
PTHALATE AND DIMETHYL PTHALATE .
2. IT IS USED IN THE SEPARATION OF FIXED OILS .
3. VITAMIN A IS SEPARATED FROM FISH LIVER OILAND OTHER VEGETABLE OILS
.
4. FREE FATTY ACIDS ARE DISTILLED AT 100 ⁰C . STEROIDS CAN BE OBTAINED
BETWEEN 100 ⁰ - 200 ⁰ C .
5. PROTEINS AND GUMS WILL BE REMAINED AS NON VOLATILE RESIDUES .