A question about short path distillation (molecular distillation)
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This post was last written by b_j_Edited by y on 2009-12-3 17:13 "Due to the different effective diameters of molecules of different masses, the average free path of light molecules is generally larger, while that of heavy molecules is smaller. If a condensation surface is set up where the surface away from the liquid is less than the mean free path of light molecules and greater than the mean free path of heavy molecules, the light molecules will be condensed when they reach the condensation surface, causing the light molecules to continuously escape. ； If the heavy molecules cannot reach the condensation surface, they will collide and return to the solution. They will soon reach a dynamic equilibrium with the heavy molecules in the liquid phase and no longer appear to escape from the liquid phase. Through this method, light molecules and heavy molecules can be separated. ” The question is as follows: 1. If I want to use molecular distillation to separate A and B, the molecular weight A>B, but the boiling point A
Based on the poster's description of molecular distillation, I think molecules with small molecular weights are easily evaporated. Since it is molecular distillation, it is different from ordinary distillation. Ordinary distillation can separate based on boiling point, but in molecular distillation, as long as you determine the appropriate condensation surface, heavy molecules cannot be separated even if the boiling point is low. This is purely a personal understanding, please forgive me.
Materials with low molecular weight also have relatively low boiling points, so in molecular distillation they will still reach the condensation surface before materials with large molecular weight. The main feature of molecular distillation is that in a near-limit vacuum state, the boiling point of the material* * The boiling point is lower than normal pressure, so it is very suitable for materials with high boiling point and heat sensitivity. But its separation efficiency is very low.
What if it is wiped film molecular distillation? How efficient is the separation?
If it is still boiling point A under this vacuum
According to the formula of molecular free path, it is related to pressure, temperature, molecular weight, flow rate, rotation speed, etc. Small molecular free path, high boiling point
The basis for judgment is the molecular free path, neither the boiling point nor the molecular weight. However, when the molecular free path is unknown, it can be inferred from the boiling point. A light molecule refers to a molecule with a small free path. Generally, the molecular free path is small and the boiling point is high.