1. Steam distillation
By:
Mrs. D. R. Mali
Asssitant Professor
Pharmaceutical Chemistry
GES’s Sir Dr. M. S. Gosavi College of Pharmaceutical Education
and Research, Nashik.
2. Distillation is the process of separating the
components or substances from a liquid mixture
by using selective boiling and condensation.
It may result : Complete separation (pure
components), or Partial separation (selected
components in high conc.)
In industrial chemistry, distillation is a unit
operation of practically universal importance.
A physical separation process, not a chemical
reaction.
3. Aspecial type of distillation
Temperature sensitive materials like
natural aromatic compounds.
It once was a popular laboratory method
for
purification of organic compounds.
Distillation at lower temperatures,
reducing the deterioration of the desired
products.
4. Steam distillation may be applied under
reduced pressure: if the substances to be
distilled are very sensitive to heat.
After distillation the vapours are condensed.
The immediate product is a two-phase
system of water and the organic distillate,
allowing separation of the components by
decantation, partitioning or other suitable
methods.
5. When a mixture of two practically immiscible
liquids is heated liquid exerts its own vapour
pressure as a function of temperature as if
the other constituent were not present.
The vapour pressure of the whole system
increases.
Boiling begins when the sum of the vapour
pressures of the two immiscible liquids just
exceeds the atmospheric pressure.
6. In this way, many organic compounds insoluble
in water can be purified at a temperature well
below the point at which decomposition occurs.
For example, the boiling point of bromobenzene
is 156 °C and the boiling point of water is 100 °C,
but a mixture of the two boils at 95 °C.
Thus, bromobenzene can be easily distilled at a
temperature 61 °C below its normal boiling
point.
8. • A round-bottomed flask (C)
• A glass inlet tube which reaches almost to the
bottom of the flask
• A steam generator (D)
• Water condenser (double surface type) (E)
• An additional a still-head (B)
• Receiver (F)
9. The flask is clamped at an angle.
To prevent the solution in C from being
splashed into the entrance of the outlet
tube.
An addition a still-head is used in place of
the outlet tube, since spray will be
trapped in the still-head, and returned as
a steady stream of liquid to the flask C.
10. A vigorous current of steam blown in from D.
The mixture in C is thus rapidly heated
The vapour of the organic compound mixed
with steam passes over and is condensed in
E.
If the flask C contains a large volume of
material or material which requires
prolonged distillation, it should be heated by
a Bunsen burner.
11. If the organic compound which is being
steam-distilled is freely soluble in water, an
aqueous solution will ultimately collect in the
receiver F.
The compound must then be isolated by
ether extraction, etc.
Alternatively, a water-insoluble compound, if
liquid, will form a separate layer in F, or if
solid, will probably crystallise in the aqueous
distillate.
12.
13. Applications
It is employed in the manufacture of essential
oils, for use in perfumes for example. In this
method, steam is passed through plant material
containing desired oils.
Eucalyptus oil and orange oil obtained in the
industrial scale.
It is used to separate intermediate or final
products during synthesis of complex organic
compounds.
Also widely used in petroleum refineries and
petrochemical plants.
