Distillation is a fundamentally important process in both chemistry and industry. Distillation probably accounts for 90% of all separation processes in the chemical industry and is also a significant user of energy due to the necessary heating involved. The distillation exhibit allows visitors to see a very graphic example of a simple distillation using just two components, and the addition of iodine makes this visible.




   Description of the Experiment   

All that the visitor has to do is to press the illuminated button marked Start which will allow the distillation process to start.
The visitor sees the heating element in the boiler glow red and the mixture starts to boil.
The temperature meter will show the temperature of the boiler and the column top temperature will be low.

After a short period of time the column itself begins to bubble and the colour gradient develops from dark brown at the bottom to light brown at the top, which then becomes clear.
Distillate is collected continuously from the condenser and fed back to the boiler This distillation cycle can be repeated as necessary.

   Duration   

About 4 minutes for the distillation and a further 2 minutes for the exhibit to return to the resting state

   Conclusion   

As the process of distillation relies on the equilibria between liquid and vapour as the temperature decreases along the length of the distillation column, then it is important to show that this difference exists. Also a change of colour along the length of the column helps to visualise the continuous change of composition.

   Detailed Conclusion   

The fundamental principle that lies behind distillation is that the composition of a liquid mixture (ie two different liquids mixed together) is different from the composition of its vapour mixture, due to differences in volatility of the liquids in the mixture.

If you mix two liquids (one boils at 100C, the other at 50C) then the vapour above the liquid will have much more of the 50C substance than the 100C substance.

If you then remove the vapour and cool it, so that it condenses, then the new liquid mixture will have much more 50C substance than the 100C substance.

If you start again heating the new liquid condensed from the vapour (at a slightly lower temperature because it has more of the substance that boils at a lower temperature), then the vapour will again have even more 50C substance than the 100C substance, and so on.

If you do this enough times, then you can get all of the 50C substance separate from the 100C substance.

You can get this to happen without having to remove the vapour each time, and you then have continuous distillation, and there is a temperature gradient up the column from hot at the bottom to cool at the top.

This is what our exhibit shows.