Presentation on Azeotropic and Extractive Distillation. Introduction about distillation, azeotropic and extractive distillation and the difference between them.

1. Pharmaceutical Operations
Presentation
On
Azeotropic and Extractive
Distillation
Amity University, NOIDA
Amity Institute of Pharmacy
BY : UNNATI GARG

2. DISTILLATION
Distillation is the process of separating the components or substances from a
liquid mixture by selective boiling and condensation.

3. AZEOTROPIC DISTILLATION
In the distillation of mixture of liquids, the liquid can be heated to convert
them to gaseous state. Since they have different boiling points, they
condense back at different rate and can easily separate.
Some of the mixtures exhibit the same concentration in the vapor phase and
the liquid phase. They are called as azeotropes. Azeotropes cannot be
separated by simple distillation method as in contrast to ideal solutions with
one component typically more volatile than the other, if the mixture forms
an azeotrope than vapor and liquid concentrations will be same that
prevents the separation through simple approach.

4. Azeotropic Behaviour
Azeotropes are also known as constant boiling point mixtures.
There are two types of azeotropes: minimum boiling azeotrope and maximum boiling
azeotrope.
A) Minimum Boiling Azeotrope
• A solution that shows greater positive deviation from Raoult's law forms a minimum
boiling or positive azeotrope at a specific composition.
• The boiling point of this azeotrope is lower than the boiling points of its constituents.
• The interaction between the solvent-solvent and solute-solute molecules are weaker
than solvent-solute molecules which results in their low boiling point.

5. • Enthalpy of the mixture of its constituents is positive.
• Volume of the solution is higher than the sum of the invididual volumes of the constituents
because of low solute-solvent molecular interaction.
• For example, an ethanol-water mixture (obtained by fermentation of sugars) on fractional
distillation yields a solution containing approximately 95% by volume of ethanol. Once this
composition has been achieved, the liquid and vapour have the same composition, and no
further separation occurs.

6. B) Maximum Boiling Azeotrope
• A solution that shows large negative deviation
from Raoult's law forms a maximum boiling or
negative azeotrope at a specific composition. Nitric
acid and water is an example of this class of
azeotrope.
• The boiling point of this azeotrope is higher than the
boiling points of its constituents
• The interaction between the solvent-solvent and
solute-solute molecules are stronger than solvent-
solute molecules which results in their high boiling
point
• Volume of the solution is higher than the sum of the
invididual volumes of the constituents because of high
solute-solvent molecular interaction.

7. MECHANISM OF AZEOTROPIC DISTILLATION
• Azeotropic mixture cannot be separated by normal distillation method. Therefore
addition of a foreign substance which is called as entrainer decreases the boiling point
of azeotropic solution and separates the components of mixture at different boiling
points.
• Example of azeotropic distillation is separation of ethanol with water from its aqueous
solution. The boiling point of water is 100 °C and boiling point of ethanol is 78.3°C.
• By addition of benzene to the azeotropic mixture as entrainer, ethanol can be
separated out from the solution.

8. • Benzene breaks the mixture of water and ethanol and forms a new azeotrope between
benzene and ethanol
• The volatility of water (more polar liquid) is enhanced.
• On distillation, water distills at 65.85 ̊C leaving alcohol and benzene behind.
• The boiling point of this binary mixture is 68.2 ̊C and benzene gets distilled leaving pure
alcohol behind. It can be distilled off at 78.3 ̊C.
• The benzene can be recycled.
• Thus using fractional distillation method, absolute alcohol can be prepared.

9. TYPES OF AZEOTROPIC DISTILLATION
1. Heterogeneous Azeotropic Distillation
2. Homogeneous Azeotropic Distillation

10. 1. Heterogeneous Azeotropic Distillation
The heterogeneous azeotrope contains the vapor phase with two liquid
phases. Some common examples of heterogeneous azeotropic mixtures are
benzene with water, butanol with water and dichloromethane with water. In
the heterogeneous azeotropic distillation, the liquid phase of the mixture is
immiscible.

11. 2. Homogeneous Azeotropic Distillation
In the homogenous azeotrope the constituents of the mixture are
completely miscible with each other. In homogeneous azeotropic distillation
method, entrainer may or not form additional azeotropes after addition. This
distillation process is carried out in a sequence of columns.
The azeotropic mixture of A and B forms azeotropic mixture
with minimum boiling point. Here both the components must
belong to the same distillation region. Now fresh feed is mixed
with entrainer and distilled over. The A component is taken as
bottom product in 1st column whereas B is taken as top
product in 2nd column. Entrainer (E) is recovered as bottom
product in 2nd column 2 and recycled to 1st column.

12. APPLICATIONS
It is used for :
• Mainly separation of ethanol and water using benzene as an entrainer. This
process is known as dehydration of ethanol.
• Separation of isobutanol and water.
• Separation of benzene and cyclohexane.

13. ADVANTAGES
• It is a very energy efficient process and requires less energy as compared to
other processes.
• The equipments are easy to use and durable.
• The process is simple and risk factors are very less.

14. EXTRACTIVE DISTILLATION
•It 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.
•The method is used for mixtures having a low value of relative volatility,
nearing unity. Such mixtures cannot be separated by simple distillation,
because the volatility of the two components in the mixture is nearly the
same, causing them to evaporate at nearly the same temperature at a similar
rate, making normal distillation impractical.

15. Process flow diagram showing an extractive distillation apparatus. In this case the
mixture components A and B are separated in the first column through the solvent E
(recovered in the second column)

16. MECHANISM OF EXTRACTIVE DISTILLATION
•The method of extractive distillation uses a separation solvent, which is generally non-
volatile, has a high boiling point and is miscible with the mixture, but doesn't form an
azeotropic mixture.
•The solvent interacts differently with the components of the mixture thereby causing
their relative volatilities to change. This enables the new three-part mixture to be
separated by normal distillation.
•The original component with the greatest volatility separates out as the top product.
•The bottom product consists of a mixture of the solvent and the other component,
which can again be separated easily because the solvent does not form an azeotrope
with it. The bottom product can be separated by any of the methods available.

17. SOLVENT SELECTION
•It is important to select a suitable separation solvent for this type of
distillation.
•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 to be cited here is the separation of an azeotropic mixture
of benzene and cyclohexane, where aniline is one suitable solvent.

18. APPLICATIONS
It is widely used for :
• Separation of butadiene from a mixture of butane, butene and small
quantities of other unsaturated hydrocarbons. Here low polarity solvents like
furfural, etc. are used.
• Separation of benzene from the mixture of benzene-cyclohexane during the
production of cyclohexane from benzene via hydrogenation. Here propylene
glycol is used as an entrainer.

19. Azeotropic vs Extractive Distillation
Azeotropic Distillation Extractive Distillation
• Addition of new substance to the liquid mixture in
order to increase relative volatility of one of two
components and make separation easier
• 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.
• In this, the addition of an entrainer forms a separate
phase which is a sub-set of azeotropic distillation
methods
• In this, the solvent interacts differently with the
components of the mixture thereby causing their
relative volatilities to change
• It is known as azeotropic distillation because the
entrainer forms an azeotrope with one of the mixture
component.
• It is known as extractive distillation because the
function of the extraneous material is superficially
similar to that of solvent extraction.

20. Azeotropic Distillation Extractive Distillation
• Used when the mixture components have close boiling
point.
• Used when mixture components have very close boiling
point.
• Entrainer appears at the top of the column. • Entrainer appears at the bottom of the column.
• Example : Dehydration of Ethanol using cyclohexane or
benzene as an entrainer
• Example : Separation of butadiene from butane, butene or
other unsaturated hydrocarbons.

21. REFERENCES
•http://chemistry.tutorvista.com/inorganic-chemistry/azeotropic-distillation.html
•https://www.slideshare.net/RajdeepMal/non-conventional-distillation-process
•https://en.wikipedia.org/wiki/Extractivedistillation
•Pharmaceutical Engineering, K Sambamurthy, New Age International Limited Publishers,
Chapter-6, Distillation, Pg. 149-150
•Pharmaceutical Engineering: Unit Operations II, CVS Subramanayam, Edition 2015, Volume 2,
Ch-7, Distillation, Pg 220-221