This document discusses different types of distillation processes including simple distillation and fractional distillation. Simple distillation involves a single vaporization and condensation cycle that produces an impure distillate. Fractional distillation uses a fractionating column containing packing materials between the distillation flask and head. This allows for multiple vaporization and condensation cycles, improving separation of components in the mixture. The document describes components of distillation columns like trays, packings, reboilers and condensers and how they facilitate fractional distillation.

1. Simple Distillation &
Fractional Distillation
(Dr.) Mirza Salman Baig
Assistant Professor (Pharmaceutics)
AIKTC, School of Pharmacy,New Panvel
Affiliated to University of Mumbai (INDIA)

2. "Distillation is defined as the
separation of the components of liquid
mixture, by a processes involving
vaporization and subsequent
condensation"

3. Two steps
1.Converting liquid into vapor phase
(evaporation)
2.Recovering liquid from vapor by
condensation at another place.

4. Ideal Solution
• When two liquids are mixed togther it
is known as binary mixture.
• Ideal Solution is binary mixture of
liquid components and there is no
change in properties of other
substance.
• Heat is nither evolved nor absorbed
during mixture formation.

5. Raoults Law
• Raoults law states that, "the partial
vapour pressure of each volatile
constituent is equal to vapour
pressure of pure constituents
multiplied by its mole fraction"
PA = P0
A XA

6. Contd...
Partial Vapour pressure of liquid=
Vapour pressure of pure liquid × Mole
fraction of the liquid
pA = p0
A XA
pB = p0
B XB
Example Mixture of Ethylene Chloride
and benzene.

7. Daltons Law
The total pressure exerted by mixture
of ideal gas may be conciderd as
sum of partial vapour prerssure of
each gas (if alone were present and
occupied same volume)
P= pA + pB
P= p0
A XA + p0
B XB

8. Application of Law
• Component having higher vapour
pressure (lighter component) will be
distilled first....
This principle is used in simple
distillation

9. Ideal Mixture
(obey Raoults Law)

10. Non Ideal Liquid mixture
(real liquid)

11. Deviation from Raoults Law
•Negative
– (Adhesive Interaction)
–Acetone /chloroform
•Positive
– (Repulsion in two components)
–Benzene /Ethyl Alcohol

12. Volatility
vA= Partial vap pressure of a (pA)/
Mole fraction of A (XA)in solution

13. Equilibrium curve
Plot of mole fraction
of a more volatile
componennt in
vapours against its
mole fraction in
liquid.

14. VARIOUS TYPES OF
DISTILLATION
Ø Simple Distillation
Ø Fractional Distillation
Ø Vacuum Distillation
Molecular Distillation
Ø Azeotropic and Extractive distillation
Ø Steam distillation

15. Simple Distillation

16. Simple Distillation
Ø Single Vaporization/Condensation cycle of a
mixture that produces a distillate which is
always impure
Ø Therefore, it is impossible to completely
separate the components in a mixture with
Simple Distillation
Ø Relatively pure substances can be obtained
from a mixture with Simple Distillation if the
boiling points of the components differ by a
large amount (>25oC)

17. Simple Distillation

18. Simple Distillation
• Distillation still is initially filled with a feed
mixture, which evaporates and leaves the still in
the vapor form.
• This vapor, which is richer in the more volatile
component, is collected in the condenser at the
top and accumulated in a receiver.
• In this operation, no liquid is refluxed back to the
still, and no plates or packing materials are
present (fractionating column absent) inside
the still.
• This simple distillation still is an example of a
batch operation, often referred to as Rayleigh
distillation.

19. Simple Distillation
– It is mostly use to separate volatile liquid
from non/ volatile liquids.
– Its difficult get pure substance only by
simple distillation.
– If a small increment of the initial distillate
is separated and redistilled and this
process is repeated many times,
effectively producing multiple sequential
Vaporization/ Condensation Cycles, an
increasingly pure solution can be attained.
– Solution (feed) is Distilland
– Vid

20. Evaporation vs Distillation
• Distillation is used when condencate
is required.
• Evaporation is used when
concentrated liquid resedue is
needed as product.

21. Applications
• Sepration of volatile oil
• Purification of organic solvent
• Refining of petroleum products
• Seperation of drug obtained from
plant and animal.
• Purification of drug from animal
source.

22. Fractional Distillation

23. Fractional Distillation
Ø Fractionating Column inserted between the
Distillation Flask and the Distillation Head.
Ø The Fractionating Column, containing a variety
of packing materials,
Ø With each cycle within the column, the
composition of the vapor is progressively
enriched in the lower boiling liquid.
Ø This process continues until most of the lower
boiling compound is removed from the original
mixture and condensed in the receiving flask
Ø Vid

24. Fractional Distillation
Fractionating column is
important part of this assembly
which is absent in simple
distillation

25. Fractional Distillation (Cont.)
Ø When the lower boiling liquid (more volatile
liquid) effectively removed from the original
mixture, the temperature of mixture rises
and a second fraction containing some of
both compounds is produced.
Ø As the temperature approaches the near
the higher boiling point compound, the
distillate condensing into next part of
fractionating column will contain heavy
component (higher boiling point compound).

26. Fractionating column types
• Plate column
– Sieve plate
– Bubble cap
– Valve Plate
• Packed column

27. Column Efficiency
Ø A common measure of the efficiency of
a Fractionation Column is given by its
number of Theoretical Plates
Ø One Theoretical Plate is equivalent to
one Simple Distillation cycle, i.e., one
Vaporization / Condensation Cycle.
Ø The smaller the boiling point
difference, the greater the number
of theoretical plates a fractionating
column must have to achieve separation
of mixtures

28. Plate Efficiency
Overall Plate Effic.
= Theoretical plate required/ Actual no. of plates
Murphee Plate Effic.
= Actual Change in vapour composition/ Change in
composition if perfect composition is achived

29. HETP
• Hieght of packed section required to
give the change in composition that
would provided by theoretical plate.
• HETP= Hieght of column/
No. of theoretical plate

30. Main Components of Distillation
Columns
• A vertical shell where the separation of
liquid components is carried out
• Column internals trays/plates and/or
packings which are used to enhance
component separations
• A reboiler to provide the necessary
vaporisation for the distillation process
• A condenser to cool and condense the
vapour leaving the top of the column
• A reflux drum to hold the condensed vapour
from the top of the column so that liquid
(reflux) can be recycled back to the column

31. Contd...
The vertical shell
houses the column
internals and together
with the condenser and
reboiler, constitute a
distillation column.

32. Basic Terminology
• The liquid mixture that is to be
processed is known as the feed and this
is introduced somewhere near the
middle of the column to a tray known as
the feed tray.
• The feed tray divides the column into a
top (enriching or rectification) section
and a bottom (stripping) section.
• The feed flows down the column where
it is collected at the bottom in the
reboiler.

33. Basic Operation
• Heat is supplied to the reboiler
to generate vapour.
• The source of heat input can
be steam.
• The vapour raised in the
reboiler is re-introduced into
the unit at the bottom of the
column.
• The liquid removed from the
reboiler is known as the
bottoms product.

34. Basic Operation (contd...)
The vapour moves up the
column, and as it exits the
top of the unit, it is cooled
by a condenser.
The condensed liquid is
stored in a holding vessel
known as the reflux drum.
Some of this liquid is
recycled back to the top of
the column and this is called
the reflux.
The condensed liquid that is
removed from the system is
known as the distillate or top
product.
Thus, there are internal flows
of vapour and liquid within the
column as well as external
flows of feeds and product
streams, into and out of the
column.

35. COLUMN INTERNALS
• Bubble cap
• Sieve plate
• Column packing

36. Bubble cap tray

37. Bubble cap trays
• A bubble cap tray has riser or
chimney fitted over each hole,
and a cap that covers the riser.
•The cap is mounted so that
there is a space between riser
and cap to allow the passage of
vapour.
•Vapour rises through the
chimney and is directed
downward by the cap, finally
discharging through slots in the
cap, and finally bubbling through
the liquid on the tray.

38. Liquid and Vapour Flows in a Tray Column
Each tray has 2 conduits, one on each side, called
‘downcomers’. Liquid falls through the
downcomers by gravity from one tray to the one
below it. The flow across each plate is shown in
the diagram on the right.

39. A weir on the tray ensures that there is
always some liquid (holdup) on the tray
and is designed such that the the holdup
is at a suitable height, e.g. such that the
bubble caps are covered by liquid.
Being lighter, vapour flows up the
column and is forced to pass through
the liquid, via the openings on each tray.
The area allowed for the passage of
vapour on each tray is called the active
tray area.

40. Sieve Plate (tray)
• Sieve trays are simply metal
plates with holes in them.
• Vapour passes straight
upward through the liquid on
the plate.
• The arrangement, number
and size of the holes are
design parameters.
• Because of their efficiency,
wide operating range, ease of
maintenance and cost factors,
sieve and valve trays have
replaced bubble cap trays in
many applications.

41. Sieve Plate (tray)

42. • As the hotter vapour passes through the liquid
on the tray above, it transfers heat to the
liquid.
• In doing so, some of the vapour condenses
adding to the liquid on the tray.
• The condensate, however, is richer in the less
volatile components than is in the vapour.
• Additionally, because of the heat input from
the vapour, the liquid on the tray boils,
generating more vapour.
• This vapour, which moves up to the next tray
in the column, is richer in the more volatile
components.
• This continuous contacting between vapour
and liquid occurs on each tray in the column
and brings about the separation between low
boiling point components and those with
higher boiling

43. Plate (Tray) Designs
• A tray essentially acts as a mini- column, each
accomplishing a fraction of the separation task.
• From this we can deduce that the more trays
there are, the better the degree of separation and
that overall separation efficiency will depend
significantly on the design of the tray.
• Trays are designed to maximise vapour- liquid
contact by considering the liquid distribution
and vapour distribution on the tray.
• This is because better vapour/ liquid contact
means better separation at each tray, translating
to better column performance.

44. Packed column (Packings)
Packings are passive devices that are designed to
increase the interfacial area for vapour/ liquid
contact. The following pictures show 3 different types
of packings material pieces ..
These strangely shaped pieces are supposed to impart
good vapour/ liquid contact when a particular type is
placed together in numbers, without causing excessive
pressure/ drop across a packed section.
This is important because a high pressure drop would
mean that more energy is required to drive the vapour
up the distillation column.

45. Packings versus Trays
• Packings provide extra inter/ facial area for
liquid/ vapour contact
• efficiency of separation is increased for the
same column height
• packed columns are shorter than trayed
columns
• Packed columns are called continuous/
contact columns while trayed columns are
called staged/ contact columns because of the
manner in which vapour and liquid are
contacted.