STEAM DISTILLATION

STEAM DISTILLATION

Steam Distillation is a method of distilling a compound at a temperature below its normal boiling point.
The underlined principle being that when a mixture of compound is distilled, it boils at a temperature at which the sum of their vapor pressures is equal to atmospheric pressure.
Usually the process is used to distill an organic liquid or low melting solid that is immiscible with water.

It is particularly used when a volatile product has to be separated from a mixture which is mainly in -volatile
Steam can be supplied from the steam generator or a pipe laboratory supply, or water can be added to the distillation flask.
Either way, it’s important that the distillation flask is heated so that water doesn’t accumulate in it.

In the simple water addition method, a two necked flask containing mixture and a few anti-bumping granules is fitted with the dropping funnel containing water and a splash head.
All forms of steam distillation require an efficient double-surfaced condenser since large amount of steam have to be condensed.
The flow of water need to be faster than usual, so the tubing must be securely attached.

A large receiver should be used. Usually a conical flask and spare receiver should be at hand as the volume of distillate is often very large.
Ensure that the distillation flask is no more than half full at the start of the distillation and heat the crude compound water mixture to boiling before adding additional water.
When an immiscible substance is being steam distilled, the distillate may be cloudy and low melting solid will separate out as the distillate cools.
From time to time, add more water to keep the distillation flask half full.

When a low melting solid is being steam distilled, it may begin to collect in the condenser and could block it if allowed to continue.
In such cases, periodically clear the condenser by turning off the water supply and detach the tubing from the tap to allow the condenser to empty.

As the condenser heats up, the solid will melt and flow into the receiver.
Once the condenser is cleared, reconnect the tubing and turn on the water supply again.
The steam distillation should be continued until the cooled distillate shows no further traces of the immiscible organic compound.
Solid is recovered from the distillate by simple filtration and then dried to remove any remaining water
Immiscible liquids are separated from the water in a separating funnel then dried over a drying agent.

When steam is supplied from a generator or a pipe laboratory supply, the dropping funnel is replaced by steam inlet pipe.
Before the flask is charged, adjust it so it is long enough to reach the bottom of the distillation flask.
The distillation procedure is otherwise the same as in the water addition method.
When the distillation is finished, dismantle the apparatus while it is still warm.
This will prevent residues in the flask from hardening on its surface and so make cleaning easier.