The product cyclohexene couldn't be purified by the
recrystallization method because cyclohexene is a liquid
at room temperature.
Recrystallization is a process where an impure solid material
compound is purified by using proper solvent. This process involves
the dissolution of impure material in an appropriate solvent
followed by boiling this solution to it's boiling temperatures and
which is later cooled to room temperature slowly and by using
cooling conditions (if necessary) to obtain the solid material.
Filtering this solid material will give the pure product.
The limitation of this recrystallization process is that the
compound should be a solid, hence cyclohexene (is a liquid at room
temperature) will not be purified by recrystallization and will be
purified by the distillation process.