Principle:
A mixture of immiscible liquid boils when atmospheric pressure equals to their sum of vapour pressures.
Construction:
Laboratory Scale Steam Distillation Unit:
The general assembly of laboratory scale vacuum distillation units is as shown in the above Fig..
It consists of a metallic can to generate steam.
This metallic can is fitted with a cork having two holes.
A safety tube is passed through one of the holes and a bent tube is passed through the other.
The safety tube should reach almost the bottom of the flask.
In case the pressure inside the steam generator becomes too much, water will be forced out of the safety tube and the pressure will be released.
When steam starts coming out from the safety tube; it indicates that the steam can is almost empty.
The other end of the bent tube is connected to the flask containing non-aqueous liquid (for example, turpentine) through a rubber bung.
This tube should reach almost the bottom of the flask.
The flask is connected to a condenser through a delivery tube as shown in the Fig..
The condenser is connected to a receiver flask using an adaptor.
The steam can and flask are heated by a suitable method.
Working:
The non-aqueous liquid or oil to be purified or extracted is placed in the flask.
A small quantity of water is added to it.
Fill the steam can with water.
The steam can and the flask are heated simultaneously.
The steam generated in the steam can pass to the flask through the bent tube.
A uniform flow of steam passes through the boiling mixture in the flask.
The mixture gets heated.
The steam carries the volatile oil and passes into the condenser.
Cool water passes through the condenser.
The condensed liquid is collected into the receiver as distillate.
The distillate is the mixture of immiscible liquids.
The immiscible liquids form separate layers which can be easily separated using a separating flask.
Uses:
Steam distillation is used to separate immiscible liquids. For example, toluene water.
Most of the volatile oils are extracted by this method. For example, extraction of clove, anise and eucalyptus oil.
It is used to purify liquid with high boiling point. For example, the essential oil of almonds.
It is used to prepare aromatic waters.
Camphor is distilled by this method.
Advantages:
Useful for thermolabile substances.
Disadvantages:
Not suitable when the liquids in the mixture are reactive.
Commonly Asked Questions.
Define distillation and write in detail about Steam Distillation.
With help of a well labelled diagram describe the principle and working of the apparatus used for Steam Distillation.