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Laboratory display of distillation: 1: A heating device 2: Still pot 3: Still head 4: Thermometer/Boiling point temperature 5: Condenser 6: Cooling water in 7: Cooling water out 8: Distillate/receiving flask 9: Vacuum/gas inlet 10: Still receiver 11: Heat control 12: Stirrer speed control 13: Stirrer/heat plate 14: Heating (Oil/sand) bath 15: Stirring means e.g.(shown), boiling chips or mechanical stirrer 16: Cooling bath. [ 1 ] Distillation is a method of separating mixtures based on differences in volatility of components in a boiling liquid mixture. Distillation is a unit operation , or a physical separation process, and not a chemical reaction . Commercially, distillation has a number of applications.
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 100°C, the other at 50°C) then the vapour above the liquid will have much more of the 50°C substance than the 100°C substance. If you then remove the vapour and cool it, so that it condenses, then the new liquid mixture will have much more 50°C substance than the 100°C 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 50°C substance than the 100°C substance, and so on. If you do this enough times, then you can get all of the 50°C substance separate from the 100°C substance.
Distillation is based on the fact that the vapour of a boiling mixture will be richer in the components that have lower boiling points. Therefore, when this vapour is cooled and condensed, the condensate will contain more volatile components. At the same time, the original mixture will contain more of the less volatile material.