What do you know about the conditions and advantages of molecular distillation?

Molecular distillation is a kind of liquid-liquid separation technology, which mainly depends on the difference of average free path between different compounds At the same time, because the molecular distillation separation process can be carried out under high vacuum, it can be carried out at a temperature far lower than the boiling point of the compound As long as there is enough temperature difference between the cold and hot sides of molecular distillation (generally 70-100 ℃), and the form of condensation 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 form of condenser The conditions of molecular distillation are as follows: 1 The partial pressure of residual gas is lower, so that the average free path length of residual gas is multiple of the distance between the surface of distiller and condenser 2 Under the saturated pressure, the average free path length of steam molecule should have the same order of magnitude as the distance between the surface of evaporator and condenser In this ideal condition, evaporation takes place from the residual gas molecules without obstacles Steam molecules reach the condenser surface in the process of not encountering other molecules and returning to the liquid The evaporation rate reaches the possible high value of Zui at the temperature The evaporation rate is directly proportional to the pressure, so the amount of distillate in molecular distillation is relatively small In SPE short-range distillation, when the distance between condenser and heating surface is about 20 ~ 50mm and the pressure of residual gas is 10-3mbar, the average free path length of residual gas molecule is about twice as long The short distance distiller can reach the molecular distillation condition Advantages of molecular distillation: according to the principle of molecular distillation separation, molecular distillation separation mainly depends on the difference of average free path between light molecules and heavy molecules Meanwhile, the light molecules to be separated are easy to be cooled and obtain light fraction Therefore, molecular distillation technology has the following basic characteristics: 1 The theoretical molecular distillation and separation process under ultra-low pressure occurs between 0.01pa and 0.1pA The ultra-low distillation pressure can increase the average free path of molecular movement of compounds, and then expand the difference between the average free path of compounds to achieve separation The traditional distillation technology is mostly kettle distillation The compounds to be separated are first gasified at the boiling point to become gas The gaseous compounds are extracted as a whole under the action of vacuum pump and can be condensed when they flow through the condenser The long distance between the condenser and the evaporation surface makes the distance full of gaseous compounds, so it is difficult to reduce the pressure at the evaporation surface For molecular distillation technology, because the condenser and the evaporation surface are arranged very closely, once the compounds to be separated evaporate, they will be condensed immediately, so the partial pressure of the gaseous compounds between the condenser and the evaporator surface is very low, and the compounds can be separated under ultra-low pressure 2 The conventional distillation technology of low temperature distillation far away from the boiling point of compounds mainly depends on the different boiling points of compounds Therefore, in order to achieve the separation, the compounds to be separated must be in a boiling state Therefore, the separation process of conventional distillation technology needs a higher temperature Molecular distillation separation technology relies on the difference of average free path of molecular movement of compounds The distillation process with high vacuum degree can not only reduce the full point of compounds, but also further increase the difference of average free path between compounds, so the distillation process can be carried out at low temperature 3 In the process of rapid and separated molecular distillation separation, the compounds to be separated flow in from the upper part of the separator main body and out from the lower part On the surface of the evaporator, the compound to be separated will form a liquid film with a thickness of about 2mm under the action of the film-forming part The distillation of the liquid film is conducive to the escape of the compound to be separated At the same time, in the process of molecular distillation separation, the close arrangement of the condensation surface and the evaporation surface enables the compounds to be quickly condensed once they escape, thus reducing the residence time of the thermally sensitive compounds to be separated at high temperature, which is conducive to maintaining the characteristics of the compounds In general, molecular distillation can not only reduce the residence time of the compounds to be separated on the heating surface, but also shorten the high temperature gas residence time between the escape and condensation of the volatile.