1. Falling film molecular still
For the early form, the structure is simple, but due to the thickness of the liquid film, the efficiency is poor, the world is rarely used. The device USES gravity to make the material on the evaporation surface fall into a liquid film. When the material is heated, the evaporator condenses on the opposite side of the condensing surface. Falling film device for the early form, simple structure, on the evaporation surface of the formation of a thick liquid film, poor efficiency, now countries rarely used.
2. Scraping membrane molecular distillation device
In China, scraping membrane molecular distillation equipment and process application were developed in the late 1980s. The liquid film formed by the device is thin and the separation efficiency is high, but the structure is more complex than that of falling film. It takes the method of gravity to make the material on the evaporation surface into a liquid film falling down, but in order to make the liquid film on the evaporation surface thin and evenly distributed, a rotary scraper made of hard carbon or Teflon is set in the distiller.
The scraper can not only make the lower liquid layer be stirred fully but also accelerate the renewal of the liquid layer on the evaporation surface, thus strengthening the heat transfer and mass transfer process of the material. Its advantage is: the liquid film thickness is small, and along with the evaporation surface flow; The distillation material has a short residence time at the operating temperature and a low risk of thermal decomposition. The distillation process can be carried out continuously with a large production capacity.
3. Scraper molecular distillation unit (Wiped-Film Molecular Still)
Scraper technology (Wiped Film Style) USES a Smith 45 ° diagonal chute type scraper, the chute would lead to the downward movement of wall material around the distiller, through controllable scraper rotation will be able to provide a high level of thin-film hybrid, make the material produces tiny active effective movement, thus to achieve the shortest and controllable material residence time, and controllable film thickness, thus to achieve the best heat conduction, the mass transport, and separation efficiency.
The key outstanding advantages of this process are short feed liquid retention time, sufficient cooling by virtue of high vacuum performance, optimal mixing efficiency, and optimal material and heat transfer. The result of this efficient thermal separation technique is minimal product degradation and maximum product quality.
4. Centrifugal molecular distillation unit
Centrifugal molecular distillation unit centrifugal force film, thin film, high evaporation efficiency. But the structure is complex, manufacturing and operation are difficult. The device sends the material to the center of the rotating disc at high speed and forms a thin film on the rotating surface. At the same time, it is heated and evaporated to condense with the opposite condensing surface. The device is an ideal molecular distillation device at present. However, compared with the other two devices, the high-speed rotary disk is required and high vacuum sealing technology is required.
Compared with conventional distillation, molecular distillation has the following characteristics:
1. Ordinary distillation is separated at boiling temperature, while molecular distillation can be separated at any temperature as long as there is a sufficient temperature difference between the hot and cold sides. Therefore, the operating temperature of the molecular distillation is much lower than the boiling point of the material.
2. Common distillation has bubbling and boiling phenomenon, while molecular distillation is the free evaporation on the surface of the liquid film, the operating pressure is very low, generally 0.1-1pa, the heating time is very short, generally only 10 seconds to dozens of seconds.
3. The evaporation and condensation of ordinary distillation are reversible processes, and the liquid and gas phases are in dynamic phase equilibrium. In the process of molecular distillation, the molecules escaping from the heating surface directly fly to the condensing surface, and theoretically there is no possibility of returning to the heating surface. Therefore, there is no material that is difficult to be separated in molecular distillation.
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