Azeotropic Distillation Extractive distillation Vacuum distillation Steam distillation Molecular Distillation

1. Distillation
(part 2)
(Dr.) Mirza Salman Baig
Assistant Professor (Pharmaceutics)
AIKTC, School of Pharmacy,New Panvel
Affiliated to University of Mumbai (INDIA)

2. Distillation Types
• Azeotropic Distillation
• Extractive distillation
• Vacuum distillation
• Steam distillation
• Molecular Distillation

3. Azeotropic Distillation

4. Azeotropic Distillation
• Principle:- Addition of new
substance to the liquid mixture in
order to increase relative volitility
of one of two components and make
seperation easier.
• Ex- Benzene is added to mixture of
water and EtOH

5. Azeotropic Distillation
Ø This occurs because, when an azeotrope is
boiled, the resulting vapor has the same
ratio of constituents as the original mixture.
Ø Because their composition is unchanged by
distillation, azeotropes are also called
constant boiling mixtures.
Ø Positive azeotrope is 95.63% ethanol and
4.37% water (by weight).
Ø Ethanol boils at 78.4°C, water boils at 100°C,
but the azeotrope boils at 78.2°C.
Ø Negative azeotrope is hydrochloric acid at a
concentration of 20.2% and 79.8% water (by
weight). Hydrogen chloride boils at −84°C
and water at 100°C, but the azeotrope boils
at 110°C.

6. Azeotropic distillation
Ø Azeotropic distillation usually refers to the
specific technique of adding another
component to generate a new, lower-boiling
azeotrope that is heterogeneous (e.g.
producing two, immiscible liquid phases),
such as the example below with the addition
of benzene to water and ethanol.
Ø This practice of adding an entrainer which
forms a separate phase is a specific sub-set
of (industrial) azeotropic distillation methods,
or combination thereof.

7. Contd...
• Example - distillation of ethanol/water, using
normal distillation techniques, ethanol can
only be purified to approximately 96% .
• Some uses require a higher percentage of
alcohol, eg. when used as a gasoline
additive.
• Material separation agent- The addition of a
Material Separation Agent, such as benzene.
• Molecular sieves- For the distillation of
ethanol for gasoline addition, the most
common means of breaking the azeotrope is
the use of molecular sieves.

8. Extractive distillation

9. Extractive distillation
• Extractive distillation is defined as
distillation in the presence of a
miscible, high boiling, relatively non-
volatile component, the solvent, that
forms no azeotrope with the other
components in the mixture.
• When third substance added to
azeotropic mixture is non volatile.
• Ex- Glycerien addion reduce
vapour pressure of water.

10. Extractive Distillation
(Contd...)
Ø The method of extractive distillation uses a
separation solvent, which is generally
nonvolatile, has a high boiling point and is
miscible with the mixture, but doesn't form an
azeotropic mixture.
Ø The solvent interacts differently with the
components of the mixture thereby causing
their relative volatilities to change.

11. Extractive Distillation
(Contd...)
• The solvent must alter the relative
volatility by a wide enough margin for a
successful result. The quantity, cost and
availability of the solvent should be
considered.
• The solvent should be easily separable
from the bottom product, and should not
react chemically with the components or
the mixture, or cause corrosion in the
equipment.
• A classic example is of aniline as suitable
solvent.

12. Distillation under reduced pressure
(Vacuum distillation)

13. Distillation under reduced pressure
(vacuum distillation)
• Liquid distillation at lower pressure than
normal boiling point by applying vacuum.
• Mass of vapour formed =
Vapour pressure of evaporating liquid /
External pressure
• Application-
– Preventing degradation of active components
– Changing physical form (to produce light porous
mass of Cascara sagrada extract.

14. Vacuum Distillation
Ø Vacuum distillation is a method of
distillation whereby the pressure above
the liquid mixture to be distilled is reduced
to less than its vapor pressure (usually
less than atmospheric pressure) causing
evaporation of the most volatile liquid(s)
(those with the lowest boiling points).
Ø This distillation method works on the
principle that boiling occurs when the
vapor pressure of a liquid exceeds the
ambient (sorrounding) pressure.

15. Vacuum distillation (Contd...)
• Vacuum distillation is used with or without
heating the solution.
• Temperature sensitive materials (such as
beta carotene) require vacuum distillation
to remove solvents from the mixture
without damaging the product.
• Vacuum distillation is sometimes referred
to as low temperature distillation.
• This type of distillation is in use in the oil
industry.

16. Advantages of Vacuum Distillation
Ø Industrial-scale vacuum distillation has
several advantages.
• One tool to reduce the number of stages
needed is to utilize vacuum distillation.
Vacuum distillation columns typically used in
oil refineries have diameters ranging up to
about 14 meters (46 feet), heights ranging up
to about 50 meters (164 feet), and feed rates
ranging up to about 25,400 cubic meters per
day (160,000 barrels per day).
• Vacuum distillation increases the relative
volatility of the key components in many
applications. Lower pressures increase
relative volatilities in most systems.

17. Advantages of Vacuum Distillation
• A second advantage of vacuum distillation is
the reduced temperature requirement at lower
pressures. For many systems, the products
degrade at high temperatures.
• Vacuum distillation can improve a separation
by:
• Prevention of product degradation or polymer
formation because of reduced pressure
leading to lower tower bottoms temperatures.
• Increasing capacity, yield, and purity.
• Another advantage of vacuum distillation is
the reduced capital cost, at the expense of
slightly more operating cost. Utilizing vacuum
distillation can reduce the height and diameter,
and thus the capital cost of a distillation
column.

18. Distillation under reduced
pressure (Vacuum distillation)

19. Distillation under reduced
pressure (industrial scale)

20. Steam distillation

21. Steam distillation
• Principle - Mixture of immiscible
liquids bigin to boil when the sum of
there vapour pressure is equal to
atmospheric pressure.
• Application Separation of high boiling
point liquid from non volatile impurity.
• Ex- to separate toulene / water.

22. Steam Distillation still (industrial scale)

23. Molecular Distillation

24. Molecular Distillation
Ø A special application of the simple
distillation is molecular distillation,
known also as evaporative distillation or
short path distillation.
Ø Theory of molecular distillation:-
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.
Ø For material that are regarded as non
volatile under ordinary conditions of
temperature and pressure are generally
removed by increasing the mean free path.

25. Mean free path
• Average distance through a molecule can move
without collision with other molecules.

26. Molecular Distillation
• It is the distillation processes where
each molecule in vapour phase
travels mean free path and get
condense on condenser surface
without intercollision.
• Distance between evaporating
surface and condensor surface is
approx. equal to mean free path.
• Short path distillation

27. Molecular Distillation (cont.)
Characteristics of the molecular
distillation process:-
• Very high vacuum
• Evaporating surface must be close to
the condensing surface
• The liquid area is large to avoid
boiling and evolution of the vapors is
from surface only.

28. Molecular Distillation (cont.)
Applications of molecular distillation:-
Ø Purification of oils
Ø Separation of vitamins

29. Wiped film molecular still
• Evaporative
distill insted
of boiling
• High vacuum
• short path

30. Centrifugal molecular still
• Feed introduced
in center
• Rotation of bucket
form the film
which is heated
by radiation.
• Vapouts condense
at condensor
surface.