MDI (diphenylmethane diisocyanate) is an important raw material for the production of chemicals, which is widely used in the fields of polyurethane, elastomers and coatings. In this article, we will introduce the manufacturing methods of MDI, including the phosgene method, non-phosgene method and biological method.
I. Photogas method
Photogas method is the most commonly used method in the production of MDI at present, and its process route includes the reaction of aniline and formaldehyde to generate diphenylmethane diamine (MDA), and the reaction of MDA and phosgene to generate MDI.The specific steps are as follows:
1. Reaction of aniline and formaldehyde
Aniline and formaldehyde are added to the reactor according to a certain molar ratio, and the temperature and time of the reaction are controlled to generate MDA.The reaction is exothermic, and it is required to produce MDA in the following manner. reaction is an exothermic reaction and the reaction temperature needs to be controlled to avoid the generation of by-products. The reaction of MDA with phosgene
MDA and phosgene are added to the reactor at a certain molar ratio, and the temperature and time of the reaction are controlled to produce MDI, which is a gas-phase reaction, and the pressure and temperature of the reactor need to be controlled in order to maintain the stability of the reaction.
Photogas method has a mature production process and stable product quality, but the use of toxic and harmful substances such as phosgene in the production process poses certain hazards to the environment and human health.
Two, non-photogas method
Non-photogas method is a kind of MDI manufacturing method that does not use phosgene as raw material, mainly including urea method, dimethyl carbonate method and so on. Among them, the urea method is one of the more mature methods in the current non-photogas method. The specific steps are as follows:
1. Reaction of aniline and urea
Aniline and urea are added to the reactor according to a certain molar ratio, and the temperature and time of the reaction are controlled to generate diphenylmethane diisocyanate (MDI) and water as a by-product.
2. MDI separation and purification
The reaction products are separated and purified to obtain MDI products with high purity.
Non-photogas method production process is more environmentally friendly, but product quality and yield is relatively low, need to further improve the technical level and equipment performance.
Third, 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 realized industrialized production. The specific steps are as follows:
1. Microbial fermentation
Using specific microbial strains, aniline and glucose, etc. as raw materials for fermentation, to generate MDA.
2. Conversion of MDA to MDI
Through a certain chemical reaction, MDA is converted into MDI.
Biological method has a great potential, but it needs to further solve the microbial strains' cultivation, the optimization of the fermentation conditions, the products' separation and purification and other technical difficulties. purification and other technical difficulties.
In conclusion, the manufacturing methods of MDI include phosgene, non-phosgene and biological methods. Different methods have different advantages, disadvantages and scope of application, and need to be selected and optimized according to the actual situation. Meanwhile, with the increasing awareness of environmental protection and the continuous progress of technology, the development of more environmentally friendly, efficient and economical MDI manufacturing methods has become the future development trend.
