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The manufacturing method of pure MDI (Diphenylmethane diisocyanate) is an important organic compound in the field of chemical raw materials, widely used in polyurethane, elastomers, coatings, adhesives, and other fields. This article will introduce the manufacturing method of pure MDI

1、 Overview: There are two main manufacturing methods for pure MDI: phosgenation and nitrification. The phosgene method involves reacting aniline with formaldehyde under light to produce diphenylmethane diamine (MDA), which is then reacted with phosgene to obtain pure MDI. The nitration rule is to react aniline with nitric acid to produce diphenylmethane dinitro compound (MDN), which is then reduced to obtain pure MDI. Both methods have their advantages and disadvantages, which will be introduced separately below

2、 Phosgene gasification method 

1 The raw materials required for the phosgene method include aniline, formaldehyde, and phosgene. Among them, the molar ratio of aniline to formaldehyde is generally 1:2, and the amount of phosgene needs to be adjusted according to the reaction situation

2. The reaction process involves adding aniline and formaldehyde to the reactor and reacting under light conditions to generate MDA. MDA reacts with phosgene to obtain pure MDI. During the reaction process, it is necessary to control the reaction temperature and pH value to ensure the smooth progress of the reaction

3. After the reaction is completed, it is necessary to perform post-treatment on the reaction solution, including distillation, crystallization, centrifugation, etc., to obtain a pure MDI product with high purity

3、 Nitrification method 

1 The raw materials required for the nitration method include aniline and nitric acid. The molar ratio is generally 1:3-4

2. The reaction process involves adding aniline and nitric acid to the reactor and reacting at a certain temperature and pressure to generate MDN. Then, the MDN is subjected to a reduction reaction to obtain pure MDI. Reduction methods can include hydrogen reduction, metal reduction, and other methods

3. After the reaction is completed, it is necessary to perform post-treatment on the reaction solution, including neutralization, water washing, distillation, etc., to obtain a pure MDI product with high purity

4、 Comparison and Selection of Manufacturing Methods: Phosgene Gasification and Nitrification are both effective methods for manufacturing pure MDI, but the two methods differ in terms of raw materials, reaction conditions, equipment investment, and so on. The raw materials for the phosgenation method are readily available and the reaction conditions are relatively mild, but the equipment investment is relatively high; The investment in nitration equipment is relatively small, but the raw material nitric acid is corrosive and requires high equipment requirements. Therefore, when choosing a manufacturing method, it is necessary to consider the specific situation comprehensively

5、 Conclusion: There are two main manufacturing methods for pure MDI: phosgenation and nitrification, each with its own advantages and disadvantages. When choosing a manufacturing method, it is necessary to comprehensively consider factors such as raw material sources, equipment investment, and environmental protection requirements. Meanwhile, strict control of reaction conditions and post-treatment processes is required during the manufacturing process to ensure product quality and purity.