Principles of molecular distillation
Molecular distillation uses the difference in the average free path of molecules to separate materials. The material to be separated forms a uniform liquid film on a heating plate. After heating, the material molecules escape. A condensing plate is set parallel to the heating plate. The temperature of the condensing plate is lower than the heating plate, and the distance from the heating plate should be less than the light molecule.
The average free path of γ is greater than the average free path of heavy molecules. In this way, most of the light molecules can reach the condensation surface to form a liquid outflow, and the heavy molecules return to the heating surface, thereby achieving separation.
Advantages of molecular distillation:
1. For the separation of high boiling point, heat sensitive and easy oxide materials, molecular distillation provides a good separation method, because molecular distillation is operated at a temperature far below the boiling point of the material, and the residence time of the material is short.
2, can be very effective in removing liquid substances such as organic solvents, odor, etc., which is a very effective method for liquid dissolution after solvent extraction.
3. The target product can be selectively distilled off, other impurities can be removed, and more than two substances can be separated at the same time through multi-stage separation.
4. The fractional distillation process of molecular distillation is a physical process, so it can well protect the separated materials from pollution and damage.
5. The mechanical film scraping system is adopted, which is different from other film formation defects such as falling film evaporators. In the short-range evaporator, the film thickness of the material is uniform and the flow characteristics are excellent. Because the areas of the liquid surface and the heating surface are almost equal, Excellent mass and heat transfer efficiency.
6. With central condensation, the cross-sectional area of material flow is equal to the evaporation surface, so that there is only a slight pressure drop between the evaporator and the condenser, which means that the vacuum at the end of the vacuum system is almost close to the vacuum of the evaporator. Extremely low working pressures ensure extremely low distillation temperatures, so molecular distillation is currently a milder distillation method.
Composition of molecular distillation equipment
A complete set of molecular distillation equipment mainly includes a feed system, a molecular still, a heating system, a cooling system, a vacuum system and a control system. In order to ensure the degree of vacuum, a two-stage pump is generally used, and a liquid nitrogen cold trap is provided to protect the vacuum pump. The molecular still is the heart of the entire plant. The development of molecular distillation devices is mainly reflected in the structural improvement of molecular stills.
As a new type of high-efficiency clean separation technology, molecular distillation has many advantages which have been recognized by domestic and foreign researchers. With the continuous development of industrialization in the 21st century, it has been applied in many areas of the national economy.
Application of molecular distillation in plastics and petrochemicals
In the process of polymer synthesis from monomers, an excess of monomer material always remains. By using molecular distillation to separate and purify polysaccharide esters, the appearance and yield of the product are higher than those of ordinary distilled products. The free TDI in the polyurethane prepolymer was separated at a feed temperature of 100 ° C and a distillation temperature of 150 ° C to obtain a high-purity polyurethane prepolymer. Liquid crystal molecules in waste display panels are separated and purified by molecular distillation and adsorption methods, and the technical indexes of the recovered materials are similar to the original products. The molecular distillation theory was applied to the petroleum industry, and the true boiling point curve describing the residual pressure of the heavy oil at the bottom of the vacuum distillation kettle was extended, and higher accuracy was obtained.
Application of molecular distillation in cosmetics industry
Isolate and purify the white mirabilis monoanhydride from polyvinyl anhydride, and obtain the low chroma monoanhydride, which can be used in the cosmetics industry and is a well-loved moisturizing ingredient. At present, many chemical companies have expanded molecular distillation to purify baimanhua monoanhydride to mass production.
Application of molecular distillation in food industry
EPA and DHA are eicosapentaenoic acid and eicosahexaenoic acid, respectively, which are mainly derived from w-3 polyunsaturated fatty acids in deep-sea fish oil, which have an activating effect on brain functions. Extraction of EPA and DHA
Technology is also a hot spot of concern for many researchers. At present, in the process of preparing EPA and DHA, molecular acetate is used to remove the acetate mixed in the product. The industrialization of highly unsaturated fatty acids in fish oil can obtain more than 70% content. EPA and DHA products.
Application of molecular distillation in the field of medicine
Molecular distillation is used to separate and synthesize the important intermediate of antihistamine, ethyl acetophenacetate. Through the four-stage molecular distillation operation, the crystal separation technology is used to achieve the isomers.
Requirements for the relative content of the two components. Vitamin E was extracted from soybean oil using a falling film molecular distillation device. At the same time, glyceryl octanoate was mixed with low-purity vitamin E and separated by molecular distillation, which greatly purified the vitamin E content.