Vacuum distillation is a distillation technique performed under reduced pressure that allows compounds to boil and be separated at temperatures below their normal boiling points. This technique is useful for separating compounds with high boiling points over 200°C that may decompose if boiled at their normal temperature, or compounds that are otherwise difficult to distill. Under reduced pressure, the boiling point of compounds is lowered, facilitating separation based on differences in boiling points.

1. Vacuum Distillation

2. Vacuum Distillation:
Principle:
 Vacuum distillation is a special method of separating
compounds at pressure lower than the standard
atmospheric pressure.
 Under this condition, the compounds boil below their
normal boiling temperature.
 Hence, vacuum distillation is best suited for
separation of compounds with higher boiling points
(more than 200°C), which tend to decompose at their
boiling temperature.

3.  Vacuum distillation is a method of distillation
performed under reduced pressure.
 As with distillation, this technique separates compounds
based on differences in boiling points.
 This technique is used when the boiling point of the
desired compound is difficult to achieve or will cause the
compound to decompose.
 For examples The boiling point of ethanol is 79°C
and under vacuum (28 inHg) it drops to around
34°C.

5. Construction and working:
 The crude liquid is heated in distillation flask fitted with
a water condenser, receiver and vacuum pump.
 As the pressure is reduced, the liquid begins to boil at a
much lower temperature than its normal boiling point.
The vapor is condensed by water condenser and the pure
liquid collects in the receiver.

6.  Vacuum distillation can be conducted without heating
the mixture, as is usually followed in other distillation
types.
 For the separation of some aromatic compounds,
vacuum distillation is used along with steam distillation.
 When vacuum distillation is combined with fractional
distillation method, components of a mixture get
separated very easily.

7. Applications:
This method is used for the purification of high
boiling liquids and liquids which decompose at or
below their boiling points.