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

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MDI (diphenylmethane diisocyanate) is an important raw material for chemical production, which is widely used in polyurethane, elastomers, coatings and other fields. This article will introduce the manufacturing methods of MDI, including phosgene method, non-phosgene method and biological method.

1. Phosgene

Phosgene method is the most commonly used method in MDI production at present, and its process route includes the reaction of aniline and formaldehyde to produce diphenylmethanediamine (MDA), and the reaction of MDA and phosgene to produce MDI. The specific steps are as follows:

1. aniline and formaldehyde reaction

aniline and formaldehyde are added into the reactor according to a certain molar ratio, and the reaction temperature and time are controlled to generate MDA. The reaction is an exothermic reaction and it is necessary to control the reaction temperature to avoid the formation of by-products.

2. MDA and phosgene reaction

MDA and phosgene are added into the reactor according to a certain molar ratio, and the reaction temperature and time are controlled to generate MDI. The reaction is a gas phase reaction, and it is necessary to control the pressure and temperature of the reactor to maintain the stability of the reaction.
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phosgene method has mature production technology and stable product quality, the use of phosgene and other toxic and harmful substances in the production process has caused certain harm to the environment and human health.

2. Non-phosgene method

The non-phosgene method is a method for manufacturing MDI without using phosgene as a raw material, and mainly includes a urea method, a dimethyl carbonate method, and the like. Among them, the urea method is one of the more mature methods in the non-phosgene method. The specific steps are as follows:

1. Reaction of aniline with urea

Aniline and urea are added into a reactor according to a certain molar ratio, and the reaction temperature and time are controlled to generate diphenylmethane diisocyanate (MDI) and by-product water.

2. MDI separation and purification

The reaction product is separated and purified to obtain a higher purity MDI product.

non-phosgene production process is more environmentally friendly, but the product quality and yield are relatively low, and it is necessary to further improve the technical level and equipment performance.

3. biological method

biological method is a method of producing MDI through microbial fermentation, which has the advantages of environmental protection and sustainability. At present, the biological method is still in the research stage and has not yet achieved industrial production. The specific steps are as follows:

1. Microbial fermentation

uses specific microbial strains to ferment aniline and glucose as raw materials to generate MDA.

2. MDA into MDI

through a certain chemical reaction, the MDA into MDI.

biological method has great potential, but it needs to further solve the technical problems such as the cultivation of microbial strains, the optimization of fermentation conditions, and the separation and purification of products.

In summary, the manufacturing methods of MDI include phosgene method, non-phosgene method and biological method, etc. Different methods have different advantages and disadvantages and scope of application, and need to be selected and optimized according to the actual situation. At the same time, with the continuous improvement of environmental awareness and technological progress, the development of more environmentally friendly, efficient and economical MDI manufacturing methods has become the future development trend.

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