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[Chemical Knowledge]：Pure MDI production and manufacturing methods and processes.

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

1.

pure MDI manufacturing methods are mainly phosgenation and nitrification method. The phosgenation method is to react aniline with formaldehyde under light to produce diphenylmethanediamine (MDA), and then MDA reacts with phosgene to obtain pure MDI. The nitration method is to react aniline with nitric acid to generate diphenylmethane dinitro compound (MDN), and then reduce MDN to obtain pure MDI. Both methods have their own advantages and disadvantages, which will be introduced separately below.

2. phosgenation

1. raw material preparation

phosgenation needs raw materials including aniline, formaldehyde and phosgene. Wherein, the molar ratio of aniline and formaldehyde is generally 1:2, and the amount of phosgene needs to be adjusted according to the reaction conditions.

2. reaction process

aniline and formaldehyde are added into the reactor, and the reaction is carried out under the condition of light to generate MDA. MDA reacts with phosgene to give pure MDI. The reaction temperature and pH value need to be controlled during the reaction to ensure the smooth progress of the reaction.

3. Post-treatment

After the reaction is completed, the reaction solution needs to be post-treated, including distillation, crystallization, centrifugation and other steps, so as to obtain a pure MDI product with higher purity.

3. nitration method

1. raw material preparation

nitration method needs raw materials including aniline and nitric acid. The molar ratio is generally 1:3-4.

2. reaction process

aniline and nitric acid are added into the reactor, and the reaction is carried out at a certain temperature and pressure to generate MDN. Then, the MDN is subjected to a reduction reaction to obtain pure MDI. The reduction method may be hydrogen reduction, metal reduction, or the like.

3. Post-treatment

After the reaction is completed, the reaction solution needs to be post-treated, including neutralization, water washing, distillation and other steps, so as to obtain a pure MDI product with higher purity. Comparison and Selection of Manufacturing Methods for

4.

Both phosgenation and nitration are effective methods for manufacturing pure MDI, but the two methods are different in terms of raw materials, reaction conditions and equipment investment. The raw materials of the phosgenation method are easy to obtain, the reaction conditions are relatively mild, but the equipment investment is relatively large; the equipment investment of the nitrification method is relatively small, but the raw material nitric acid is corrosive, and the equipment requirements are higher. Therefore, when selecting the manufacturing method, it is necessary to consider comprehensively according to the specific situation.

5. conclusion

pure MDI manufacturing method mainly has two kinds of phosgenation method and nitrification method, the two methods have advantages and disadvantages. When choosing a manufacturing method, it is necessary to consider factors such as raw material sources, equipment investment, and environmental protection requirements. At the same time, the reaction conditions and post-treatment process need to be strictly controlled during the manufacturing process to ensure the quality and purity of the product.

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