Distillation, distillation process for pharma students, simple distillation, fractional distillation, distillation under reduced pressure, steam distillation, destructive distillation, water for injection and sterile water

1. DISTILLATION

2. Distillation is the process of converting liquid into its vapours by
heating and recovering the vapours. It is a method of separating
substances which different in their vapour pressure.
Distillation is a process of separating the component substances from
a liquid mixture by selective vaporization and condensation.
The distillation process is carried out in an apparatus which consists
of:-
 Still, in which volatile material is boiled.
 Condenser, in which vapours are condensed.
 Receiver, in which distillate is collected.
Types of Distillation processes:
1) Simple distillation
2) Distillation under reduced pressure
3) Fractional distillation
4) Steam distillation
5) Destructive distillation

3. SIMPLE DISTILLATION: It is a process of converting a liquid into its
vapour in a distillation still, transferring the vapour to another place
and condensing it again into liquid.
Apparatus: -
It consists of a distillation flask with a side
arm sloping downward which is connected
to a condenser.
The condensed vapours are collected in a
flask called receiver.
The whole apparatus is made of glass.
The distillation flask should be of such a size that it contain half to
two-thirds of the liquid to be distilled.
The thermometer is fitted in the distillation flask to note down the
temperature, at which the vapours are distilled.
Bumping is avoided by adding small pieces of porcelain or porous pot
before distillation.
Its only applicable if difference of boiling points are very large like 25-
350C.

4. Applications:
 Used for preparation of distilled water and water for injection.
 Many volatile oils and aromatic waters are prepared by simple
distillation.
 Organic solvents are purified by distillation.
 Many official compounds are prepared by distillation e.g. spirit of
nitrous ether and aromatic spirit of ammonia.
 Concentration of liquid and to separate non volatile solid from
volatile liquid such as alcohol and ether.

5. DISTILLATION UNDER REDUCED PRESSURE:
Liquid boils when its vapour pressure is equal to the atmospheric
pressure.The boiling point of the liquid may be lowered to the desired
temperature by reducing the pressure on its surface.
Apparatus:
It consists of a double neck distillation
flask (Claisen flask).
In one neck thermometer is fitted and
in second neck a capillary tube is fixed.
The distillation flask is connected to a
condenser.
The condensed vapours are collected in a flask, called receiver.
Vaccum pump is attached to the receiver to attain the desired degree
of vacuum.
Application:
 Used for the concentration of extracts containing thermolabile substances
 Used for separating substances which undergo decomposition when heated
under normal atmospheric pressure.
 Used for obtaining a light porous mass on distillation of the liquid extract.

6. VACUUM STILL:
The vacuum stills are used for distilling substances under reduced
pressure on a large scale.
Apparatus: This is generally made of stainless steel or
any other metal which can withstand a high vacuum.
The still is connected to a condenser.
The vacuum is created by means of a vacuum pump.
The vacuum still is filled by attaching a pipe to a tap
in the lower part of the hood and the pump is started.
The other end of the pipe dips into the liquid to be
distilled so that it can be drawn into the still.
Two receivers are generally attached to the condenser in order to collect the
distillate without stopping distillation.
Application:
 Distillation of substances that have a high boiling point at atmospheric
pressure.
 Distillation of thermolabile substances then gets damaged by a high
temperature.
 Removal of the last traces of a volatile solvent.

7. FRACTIONAL DISTILLATION (DISTILLATIONOF MISCIBLE LIQUIDS):
When a substance is dissolved in liquid, the vapour pressure of the liquid is lowered.
When to miscible liquids are mixed together, each will act as solute for the other.
So, when a mixture of two such liquids is heated, the vapour pressure of each is
lowered.
The pressure exerted by each liquid in the mixture is known as partial pressure.
The liquid boils when sum of the partial pressure is equal to the atmospheric
pressure.
Apparatus:
Fractionating column is fitted between the distillation
flask and condenser. Fractionating column is used for
continuous separation of two miscible liquids.
The distillation flask is connected to a condenser.
The condensed vapours are collected in a flask called
receiver.The liquid with higher boiling point is condensed
first and vapour become richer with the liquid having lower boiling point which get
condensed later.
Application:
 Alcohol is purified from the mixture of alcohol and water obtained from
fermentation tank.
 Used for the separation of miscible liquids such as alcohol and water, acetone
and water, chloroform and benzene.

8. STEAM DISTILLATION (DISTILLATIONOF IMMISCIBLE LIQUIDS):
When two immiscible liquids are mixed together, the liquid boils when sum of partial
pressure is equal to the atmospheric pressure. So, when a mixture of two such liquids
are heated, the vapour pressure of each is lowered.The pressure exerted by each
liquid in the mixture is known as partial pressure.
Apparatus:
Consists of steam can fitted with a cork having two holes.
Through one hole steam is passed through bent tube into
the flask containing non aqueous liquid.
The another tube (safety tube) is long and kept almost
to the bottom of the steam can. It will remove the
excess pressure incase the pressure is too much.
The delivery tube carries vapours from the flask is connected
to condenser and then condenser is connected to receiver.
The distillate is then collected in florentine receiver where oil is completely
separated from water.
Application:
 Used for the preparation of volatile oils.
 Used to determine the percentage of volatile oil in the drug.
 Used for the distillation of volatile oil for its purification without any
decomposition.

9. WATER FOR INJECTION I.P. AND PURIFIED WATER I.P.:
The potable water is used for the preparation of purified water. It
contains:
1. Dissolved gases such as carbon dioxide and ammonia
2. Dissolved salts and solids
This can be avoided by taking following precautions:
a. By heating the feed water:This removes the dissolved gases.The
solubility of gases decreases as temperature is raised.
b. A constant level device is attached to the boiler to avoid excessive
concentration of salts.

10. It consists of boiler which is made of cast
iron. It is connected to the condenser tubes
through the baffles.
Baffles are provided over the top of the
condenser tubes to avoid water drops
getting mixed with the vapours.
The cooling water enters at the bottom of
the condenser and is heated by condensing
vapours.
The flow rate is adjusted in such a way that
water gets heated at 90-950C before it
enters the boiler.
The top of the condenser is open so that
gases from the water can escape into the
atmosphere.
A constant level device is fitted in such a
way that only the heated water free from
gases enters the boiler.

11. STERILE WATER: It is water for injection which is
sterilized ad suitably packed. It contains no
antimicrobial agent or other added substances. It
has pH between 4.5-7.5. It must comply with sterility
test. It should also comply with the requirements of
the test for carbon dioxide, chloride, sulphate,
nitrates and nitrites, ammonium, calcium and heavy
metals. It must comply with pyrogen test.
Sterile water for injection should be stored in single
dose containers not larger than of one liter in size.

12. Purified water I.P. Water for Injection I.P.
Water free from volatile and nonvolatile
impurities
Free from volatile and nonvolatile
impurities, microorganisms and
pyrogens
Prepared by distillation, ion exchange
and reverse osmosis process
Prepared by distillation of potable water,
purified and distilled water
Contains no added substances Contains no added substances
Liable to contaminate by microbes, not
been used for parenteral preparation
Need not to be sterile but it should
comply with pyrogen test
Stored in tightly closed containers Stored in tightly closed neutral glass
containers