The technique used for purification of steam volatile water...

Steam distillation technique is applied to separate substances which are steam volatile and are immiscible with water. It is often used to purify liquids that decompose at boiling point.

The main advantage of steam distillation over conventional distillation is that the steam distillation procedure is carried out at lower temperatures and components can be separated from a mixture below their decomposition point.
The given compound is steam volatile, insoluble in water and decomposes at its boiling point. So, steam distillation techniques will be used for purification.