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Wuxi Dingfeng pressure vessel Co., Ltd. specializes in manufacturing electric heating reactor and stainless steel reactor
China chemical equipment manufacturer
With the third class pressure vessel manufacturing license
Special equipment manufacturing license No.: ts2210836-2020
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  • seventeen billion three hundred and fifty-one million six hundred and eighty-eight thousand eight hundred and fifty-eight
Short range molecular distillation equipment

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Short range molecular distillation equipment

The pressure difference between the boiling film and the condensing surface is the driving force of the steam flow direction. For a small pressure drop, the steam will flow. The short distance between boiling surface and condensing surface is required to operate at 1mbar. The distiller based on this principle is called short range distiller. The short range distiller (molecular distillation) has a built-in condenser opposite the heating surface and reduces the operating pressure to 0.001 mbar.
Short range distillation is a process of thermal separation under the pressure of 1 ~ 0.001 mbar. It has a lower boiling temperature and is suitable for heat sensitive and high boiling point substances. The utility model is composed of a cylindrical cylinder with a heating jacket, a rotor and a built-in condenser; The fixed frame of the rotor is precisely equipped with a film scraper and an anti splash device. The built-in condenser is located in the center of the evaporator, and the rotor rotates between the cylindrical cylinder and the condenser.
The short range distiller consists of a vertical cylinder heated externally, a central condenser and a film scraper rotating between the still and the condenser.
The distillation process is: the material is added from the top of the evaporator, and it is continuously and evenly distributed on the heating surface through the feed liquid distributor on the rotor, and then the film scraper scrapes the material liquid into a thin, turbulent liquid film, and advances downward in a spiral shape. In this process, the light molecules escaping from the heating surface will condense on the built-in condenser after a short route and almost without collision, and flow down the condenser tube and discharge through the discharge pipe at the bottom of the evaporator; The residual liquid, i.e. heavy molecules, is collected in the circular channel under the heating zone, and then flows out through the side discharge pipe.
It is also suitable for molecular distillation. The molecular flow flows directly from the heating surface to the condenser surface. As shown in the figure, the molecular distillation process can be divided into four steps as follows:
1. Molecular diffusion from the main body of the liquid phase to the evaporation surface
In general, the diffusion velocity in liquid phase is the main factor controlling the molecular distillation speed, so the thickness of liquid layer should be reduced and the flow of liquid layer should be strengthened.
2. Free evaporation of molecules on the surface of liquid layer
The evaporation rate increases with the increase of temperature, but the separation factor sometimes decreases with the increase of temperature. Therefore, the economic and reasonable distillation temperature should be selected on the premise of the thermal stability of the processed material.
3. Molecules fly from evaporation surface to condensation surface
The vapor molecules may collide with each other or with the remaining air molecules between the two sides during the process of flying from the evaporation to the condensation surface. Because evaporation molecules are much heavier than air molecules and most of them have the same direction of motion, their own collision has little effect on the flight direction and evaporation velocity. The number of residual gas molecules is the main factor affecting the direction of flight and evaporation rate.
4. Molecules condense on the condensation surface
As long as there is enough temperature difference between the hot and cold sides (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 condenser form.
It can be concluded that the conditions of molecular distillation are as follows:
1. The partial pressure of the residual gas must be very low, so that the average free path length of the residual gas is a multiple of the distance between the surface of the distiller and the condenser.
2. Under saturated pressure, the average free path length of steam molecules must be the same order of magnitude as the distance between the evaporator and condenser surface.
Under this ideal condition, evaporation occurs from the residual gas molecules without any obstacles. All vapor molecules reach the condenser surface without encountering other molecules and returning to the liquid. The evaporation rate reaches the maximum at the temperature. The evaporation rate is proportional to the pressure, so the distillate volume of molecular distillation is relatively small.
In SY short path distillation, the distance between condenser and heating surface is about 20 ~ 50 mm, and the pressure of residual gas is 10-3 mbar, the average free path length of residual gas molecules is about 2 times longer. All the necessary conditions of molecular distillation can be satisfied by the short-range distiller.
Molecular distillation has the following characteristics:
1. Ordinary distillation is carried out at boiling point temperature. Molecular distillation can be carried out at any temperature. As long as there is a temperature difference between the hot and cold sides, the separation goal can be achieved.
2. Ordinary distillation is a reversible process of evaporation and condensation, and phase equilibrium can be formed between liquid phase and gas phase; In the process of molecular distillation, the molecules escaping from the evaporation surface directly fly to the condensation surface without collision with other molecules. Therefore, the molecular distillation process is irreversible.
3. There are bubbling and boiling phenomena in ordinary distillation; The process of molecular distillation is free evaporation on the surface of the liquid layer without bubbling.
4. The separation factors indicating the separation capacity of ordinary distillation are related to the ratio of vapor pressure of components, while those of molecular distillation are related to the ratio of vapor pressure and molecular weight of components, and can be calculated from relative evaporation rate.

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