What is MD molecular (short-range) distiller

Source：m.itangmei.cn Release date： 2025-02-25

MD molecular (short-range) distiller is a device for liquid-liquid separation under high vacuum conditions. The following is a detailed introduction about it:
1. Working principle
Utilizing the difference in mean free path of molecular motion: molecules of different substances have different mean free paths of motion under high vacuum. At a certain temperature, the lower the pressure, the larger the average free path of gas molecules. When the pressure in the evaporation space is very low and the condensation surface is close to the evaporation surface with a vertical distance less than the average free path of gas molecules, the vapor molecules vaporized from the evaporation surface can directly reach the condensation surface without colliding with other molecules and condense. The liquid mixture flows along the heating plate and is heated. Light and heavy molecules escape from the liquid surface and enter the gas phase. Due to the different free paths of light and heavy molecules, if the condensation plate is properly set, light molecules can reach the condensation plate and be condensed and discharged, while heavy molecules cannot reach the condensation plate and are discharged along the mixed liquid, thus achieving material separation.
Driven by pressure difference: The pressure difference between the boiling film and the condensation surface is the driving force for steam flow, and even a small pressure drop can cause steam flow, enabling molecular distillation to continue.
2. Structural composition
Cylindrical cylinder with heating jacket: used to hold materials and heat them, allowing them to evaporate at a specific temperature.
Rotor: It rotates between the cylindrical body and the condenser, and its fixed frame is correctly equipped with a scraper and anti splash device. The rotor drives the scraper to rotate, evenly distributing the material on the heating surface and scraping it into a very thin liquid film to increase the evaporation area and efficiency.
Built in condenser: located at the center of the evaporator, used to condense light molecules escaping from the evaporation surface. After reaching the condensation surface, light molecules are cooled and condensed into liquid, which flows down the condenser tubes and is discharged through the discharge tube located at the bottom of the evaporator.
3. Main types
Falling film molecular distiller: using gravity to make the material on the evaporation surface turn into a liquid film and fall down. The structure is simple, but the liquid film is thick and the efficiency is poor, which is rarely adopted by countries today.
Scrap film molecular distiller: A rotating scraper is installed in the distiller to fully stir the downstream liquid layer, accelerate liquid layer renewal, and enhance heat and mass transfer. The liquid film is thin, the separation efficiency is high, the risk of thermal decomposition of the distilled material is low, and it can be continuously produced with high production capacity. However, the liquid distribution device is difficult to improve, and there is rolling phenomenon when the liquid flows.
Centrifugal molecular distiller: using centrifugal force to form a thin film, high evaporation efficiency, shorter material heating time, larger processing capacity, but complex structure, difficult vacuum sealing, and high manufacturing cost.
4. Characteristics
Low distillation temperature: Operating at a temperature far below the boiling point of the material, separation can be achieved as long as there is a temperature difference, which can avoid the thermal decomposition of the separated substance.
High distillation vacuum degree: A high vacuum degree can be obtained internally, usually operated under very low pressure, and the material is not easily oxidized or damaged.
Thin distilled liquid film and high heat transfer efficiency: The action of a scraper or centrifugal force causes the material to form an extremely thin liquid film, increasing the heat transfer area and improving heat transfer efficiency.
The heating time of the material is short: the distance between the heated liquid surface and the condensation surface is less than the average free path of light molecules, and the light molecules escaping from the liquid surface reach the condensation surface almost without collision. The residence time at distillation temperature is generally a few seconds to tens of seconds, reducing the chance of material thermal decomposition.
High degree of separation: capable of separating substances that are difficult to separate by conventional distillation, with higher relative volatility and higher distillation efficiency than conventional distillation.
No boiling and bubbling phenomenon: It is a free evaporation on the surface of the liquid layer, carried out under low pressure, with no dissolved air in the liquid. During the distillation process, the entire liquid will not boil and there will be no bubbling phenomenon.
5. Application Fields
In the field of petrochemicals：it is used for vacuum distillation of crude oil, refining of lubricating oil, etc. It can separate high boiling point components at lower temperatures, avoiding problems such as thermal cracking and coking at high temperatures.
In the food industry：it can be used for the extraction and refining of natural flavors, vitamins, oils, etc., effectively retaining thermosensitive ingredients and nutrients in food and improving product quality.
In the field of medicine: used for the separation of drug intermediates, extraction of natural drugs, etc., it can avoid the decomposition and deterioration of drugs at high temperatures, and improve the purity and quality of drugs.
In the field of chemical engineering：it can be used for purifying cosmetic raw materials, devolatilization of polymer materials, etc. It can remove impurities and low molecular substances, improve product performance and quality.

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