Brief Analysis Of The Process Of Molecular Distillation To Achieve Material Separation

During molecular distillation, the bulk mixture flows along with the heating plate and is heated, and light and heavy molecules will escape from the liquid surface and enter the gas phase because the free paths of light and heavy molecules are different. Therefore, the movement distance of molecules of different substances after escaping from the liquid surface is different. If a condensing plate can be set properly, light molecules reach the condensing plate and are condensed and discharged, while heavy molecules cannot reach the condensing plate and are discharged along with the mixed liquid. This can achieve the purpose of material separation.

Molecular distillation can be divided into the following four processes:
1. Molecules diffuse from the main body of the liquid phase to the evaporation surface. Generally, the diffusion rate in the liquid phase is the main factor that controls the rate of molecular distillation.
2. Free evaporation of molecules on the surface of the liquid layer. The evaporation rate increases with increasing temperature, but the separation factor sometimes decreases with increasing temperature. Therefore, the economical and reasonable distillation temperature should be selected on the premise of the thermal stability of the processed material.
3. The molecules flying from the evaporation surface to the condensation surface may cause each other to collide with each other, or may collide with air molecules remaining between the two surfaces. Since evaporating molecules are much heavier than air molecules, and most of them have the same direction of motion, their collisions have little effect on the direction of flying and the rate of evaporation.
4. The molecules condense on the condensation surface, as long as there is a temperature difference between the cold and hot sides, and the form of the condensation surface is reasonable and smooth, it is considered that the condensation step can be completed, so it is also important for molecular distillation to choose a reasonable condenser form.

Since the materials entering the molecular distillation equipment are generally pre-processed materials, various impurities generated by the pre-treatment must remain in them. Among all the impurities, the corrosivity of hydrofluoric acid is relatively strong; although it is non-combustible, it will react with most metals to generate hydrogen gas and cause an explosion. In this case, it is necessary to use a complete set of molecular distillation equipment specially used for processing hydrofluoric acid-containing materials.

It is because of the special environment of high temperature and vacuum of molecular distillation equipment, plastic materials that do not react with HF cannot be used, and the metal materials of general manufacturing equipment such as 304 and 316 stainless steel all react with HF. Although platinum, gold, and silver do not react with hydrofluoric acid, they are too expensive to be used in the industry.

In view of the special environment of high temperature and vacuum, the molecular distillation and thin-film equipment are protected by spraying polytetrafluoroethylene compound, which not only ensures the strength of the equipment but also ensures the corrosion resistance of the equipment. The unique spraying process and structural design can Ensure that the coating does not come off in a vacuum and high-temperature environment.

For parts that are not easy to spray, non-metallic components are used locally for different functional requirements. For example, the heat exchange tube component is made of silicon carbide, which is stable and reliable in HF, and the heat transfer coefficient is 5 times that of stainless steel; and the structure is compact, safe, and durable.

For different HF-containing materials, while carrying out conventional process design, it will provide a one-to-one design for anti-corrosion according to the characteristics of different materials, to ensure the safe use of molecular distillation equipment and the smooth realization of the distillation effect.

Brief Analysis Of The Process Of Molecular Distillation To Achieve Material Separation