Molecular distillation is a special liquid-liquid separation technique. It differs from traditional distillation by the principle of separation of boiling points, but by the difference in the mean free path of molecular motion of different substances.
When the liquid mixture flows along the heating plate and is heated, the light and heavy molecules will escape from the liquid surface and enter the gas phase. Since the free paths of the light and heavy molecules are different, the molecules of different substances move away from the liquid surface and have different moving distances. If a condensing plate can be properly set, the light molecules reach the condensing plate and are condensed and discharged, and the heavy molecules can not reach the condensing plate and discharge along the mixed liquid to achieve the purpose of material separation.
The pressure difference between the boiling membrane and the condensing surface of the molecular distillation apparatus is the driving force of the flow direction of the steam, which causes a flow of steam for a small pressure drop. Operation at 1 mbar requires a short distance between the boiling and condensing surfaces. A distiller based on this principle is called a short path distiller. The short path distiller (molecular distillation) has a built-in condenser on the opposite side of the heating surface and reduces the operating pressure to 0.001 mbar.