Separation of aromatics
Benzene forms azeotropic mixtures with many
C6 - C8 alkanes. This means that the mixture
reaches a constant boiling point with a fixed proportion of benzene
and the alkane in both the liquid and vapour. Benzene cannot therefore
be separated from these alkanes by simple fractional distillation
and various other techniques have to be employed.
These mostly involve using solvents that dissolve
the aromatic components (mostly benzene, methylbenzene and dimethylbenzene)
but not the alkanes. Very polar solvents are used for this technique,
for example alcohols.