12.2 Distillation

LEARNING GOALS

After   Chapter 12.2,   you will    be  able    to:

Differentiate   between the separatory  capabilities    of  simple, vacuum, and fractional

distillation

Recall  the conditions  in  which   distillation    is  a   helpful separatory  technique

Select  the best    distillation    technique   for a   given   solute  mixture

Extraction requires two solvents that are immiscible in order to separate the product. But what
happens when the product itself is a liquid that is soluble in the solvent? This is where distillation
comes in handy. Distillation takes advantage of differences in boiling point to separate two liquids
by evaporation and condensation. The liquid with the lower boiling point will vaporize first, and the
vapors will rise up the distillation column to condense in a water-cooled condenser. This
condensate then drips down into a vessel. The end product is called the distillate. The heating
temperature is kept low so that the liquid with the higher boiling point will not be able to boil and
therefore will remain liquid in the initial container. This is the process that is used to make liquor at
a distillery. Because ethanol boils at a lower temperature than water, we can use distillation to
make beverages with high ethanol contents.

SIMPLE DISTILLATION

Simple distillation, as the name indicates, is the least complex version of distillation. It proceeds
precisely as described above. This technique should only be used to separate liquids that boil below
150°C and have at least a 25°C difference in boiling points. These restrictions prevent the
temperature from becoming so high that the compounds degrade and provide a large enough
difference in boiling points that the second compound won’t accidentally boil off into the distillate.