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The principle and detailed steps of the molecular distillation process

Date:2018/5/31Read:1087

The principle of the molecular distillation process
    Under certain vacuum conditions, the mean free path of the vapor molecules of the material at this time is greater than the distance between the evaporation surface and the condensing surface, so that the liquid mixture can be separated by utilizing the difference in evaporation rates of the components in the liquid.The liquid mixture flows along the heating plate and is heated. The light and heavy molecules will escape the liquid surface and enter the gas phase. Because the light and heavy molecules have different free paths, the molecules of different substances move away from the liquid surface and move different distances. If a condensing plate can be properly set, the light molecules reach the condensing plate to be condensed and discharged, while the heavy molecules cannot reach the condensing plate to discharge along the mixed solution. This is to achieve the purpose of material separation.
Detailed steps of the molecular distillation process
1. Diffusion of molecules from the liquid phase to the evaporation surface: In general, the diffusion rate in the liquid phase is the main factor controlling the rate of molecular distillation. Therefore, the thickness of the liquid layer and the flow of the liquid layer should be minimized.
2. Free evaporation of molecules on the surface of the liquid layer: Evaporation rate rises with increasing temperature, but the separation factor sometimes decreases with increasing temperature. Therefore, the thermal stability of the processed material should be premised , Choose economically reasonable distillation temperature.
3. The molecules fly from the evaporation surface to the condensing surface: During the process where the vapor molecules fly from the evaporation surface toward the condensing surface, they may collide with each other and may collide with air molecules that remain between the two surfaces. Since the evaporated molecules are much heavier than the air molecules, and most of them have the same direction of motion, their own collisions have little effect on the direction of flight and evaporation speed. The residual gas molecules are in a chaotic state of thermal movement between the two sides. Therefore, the number of residual gas molecules is the main factor that influences the direction of flight and the evaporation rate.
4. Condensation of molecules on the condensing surface: As long as a sufficient temperature difference between the hot and cold sides is ensured and the form of the condensing surface is reasonable and smooth, it is considered that the condensation step can be completed in an instant, so it is very important to choose a reasonable condenser form.

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