What is molecular distillation?

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In simple terms, distillation is defined as a method of purifying a liquid by boiling it and condensing its fumes. In other words, that is, a liquid that, when sufficiently heated and cooked, captures the distillation process and evaporates the resulting hot fumes, and collects the condensed vapors.

Molecular distillation is carried out under high vacuum conditions, where the mean free path of vapor molecules is greater than the distance between the evaporation surface and the condensation surface. Thus, we can separate the liquid mixture by utilizing the evaporation rate of each component in the raw material liquid.

What Is Molecular Distillation?

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The lower the pressure, the greater the mean free path of gas molecules at a certain temperature. When the pressure in the evaporation zone is very low (10 -2 to 10 -4 mmHg) and the condensation surface is close to the evaporation surface, the vertical distance between them is Smaller than the mean free path of gas molecules, vapor molecules vaporized from the evaporation surface can directly reach the condensation surface and condense without colliding with other molecules.

The working principle of molecular distillation

Molecular distillation is a special liquid-liquid separation technology. Unlike traditional distillation, which relies on the principle of different boiling points, it achieves separation based on the difference in the mean free path of molecular motion of different substances.


When the liquid mixture flows along the bottom plate and is heated, light and heavy molecules overflow from the liquid surface and enter the gas phase. Due to the different free paths of light and heavy molecules, the molecules of different substances move different distances after leaving the liquid surface. If a condensing plate can be installed correctly, the light molecules will be condensed and discharged when they reach the condensing plate. In contrast, the heavy molecules cannot reach the condensing plate and be released along the liquid mixture, thus achieving the purpose of material separation. The pressure difference between the boiling film and the condensing surface is the driving force for steam flow, and even a small pressure drop can cause steam to escape. Working at 1 bar requires a very short distance between the boiling and condensing sides. A still made according to this principle is called a short path still. Short path stills (molecular distillation) have a built-in condenser opposite the heating surface and bring the working pressure down to 0.001bar

Short-path distillation is a thermal separation technology process that operates at a pressure of 1~0.001bar and has a lower boiling point, ideal for heat-sensitive and high-boiling substances. The basic elements are a cylindrical drum with a heating jacket, rotor, and built-in condenser; a wiper and anti-splash device are precisely mounted on the fixed frame of the rotor. The built-in condenser is located in the center of the evaporator, and the rotor rotates between the cylinder and the condenser.

A short path still consists of an externally heated vertical cylinder and an intermediate condenser with a wiper that rotates between the still and the condenser.

The distillation process is: the material is added from the top of the evaporator, and the material and liquid distributor on the rotor is continuously and evenly distributed on the heating surface, and then the film scraper scrapes the material liquid into a thin turbulent liquid film, and spirally downward. Advance. During this process, the photo molecules overflowing from the heated surface are condensed into liquid on the built-in condenser after a short route and almost no collision, flow down the condenser tube, and are discharged through the discharge tube at the bottom of the evaporator; The residual liquid, the heavy molecules, is collected in the circular channel under the heating zone and flows out through the side discharge pipe.


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