Distillation is a thermodynamic separation process, which utilizes the different boiling points of the components in the mixed liquid or liquid-solid system to evaporate the low boiling point components, and then condenses to separate the unit operation process of the entire component, which is two kinds of evaporation and condensation A union of unit operations. The advantage is that there is no need to use other solvents other than the system components, thus ensuring that no new impurities will be introduced.