Editing Distillation (section)

===Fractional distillation===
{{Main|Fractional distillation}}
For many cases, the boiling points of the components in the mixture will be sufficiently close that [[Raoult's law]] must be taken into consideration. Therefore, fractional distillation must be used to separate the components by repeated vaporization-condensation cycles within a packed fractionating column. This separation, by successive distillations, is also referred to as rectification.<ref name=Perry/>

As the solution to be purified is heated, its vapors rise to the [[fractionating column]]. As it rises, it cools, condensing on the condenser walls and the surfaces of the packing material. Here, the condensate continues to be heated by the rising hot vapors; it vaporizes once more. However, the composition of the fresh vapors is determined once again by Raoult's law. Each vaporization-condensation cycle (called a ''[[theoretical plate]]'') will yield a purer solution of the more volatile component.<ref>[https://web.archive.org/web/20070903202418/http://wulfenite.fandm.edu/labtech/fractdistill.htm Fractional Distillation]. fandm.edu</ref> In reality, each cycle at a given temperature does not occur at exactly the same position in the fractionating column; ''theoretical plate'' is thus a concept rather than an accurate description.

More theoretical plates lead to better separations. A [[spinning band distillation]] system uses a spinning band of [[Polytetrafluoroethylene|PTFE]] or metal to force the rising vapors into close contact with the descending condensate, increasing the number of theoretical plates.<ref>[http://www.brinstrument.com/fractional-distillation/spinning_band_distillation.html Spinning Band Distillation] {{webarchive|url=https://web.archive.org/web/20060825161209/http://www.brinstrument.com/fractional-distillation/spinning_band_distillation.html |date=25 August 2006 }}. B/R Instrument Corporation (accessed 8 September 2006)</ref>