Manufacturing Method of Pure MDI (Diphenylmethane Diisocyanate)
Pure MDI is an important chemical raw material, widely used in polyurethane, rubber, coatings and other fields. In this article, we will introduce the manufacturing methods of pure MDI, including photogasification method, nitration method and carbodiimide method.
I. Photogasification
Photogasification is the main method to produce pure MDI, the process includes aniline reacting with formaldehyde to generate diphenylmethane diamine (MDA), and MDA reacting with phosgene to generate pure MDI.The specific steps are as follows:
1. Reaction between aniline and formaldehyde
Aniline and formaldehyde are added to the reactor according to a certain proportion, and under the action of acid catalyst, the reaction generates diphenylmethane diamine (MDA), and the reaction generates diphenylmethane diamine (MDA), and the reaction generates diphenylmethane diamine (MDA). Methylenediamine (MDA).
2. Reaction of MDA with phosgene
MDA and phosgene are added to the reactor in a certain ratio, and under the protection of inert gas, the reaction generates pure MDI. the temperature and pressure need to be controlled during the reaction to ensure that the reaction goes on smoothly.
3. Purification
After the reaction, the product needs to be purified to remove the impurities. Usually distillation is used for purification to obtain pure MDI products with higher purity.
II. Nitrification
Nitrification is an earlier method of manufacturing pure MDI, and its process includes the reaction of aniline and nitric acid to generate nitroaniline, the reaction of nitroaniline and formaldehyde to generate dinitrodiphenylmethane, and finally the reduction to get pure MDI.The specific steps are as follows:
1. Nitrification of aniline
Aniline and nitric acid are added into a reactor according to a certain proportion, and the reaction is carried out under the action of an acidic catalyst to generate Nitroaniline. Reaction of nitroaniline with formaldehyde
Nitroaniline and formaldehyde are added to the reactor in a certain proportion, and under the action of alkaline catalyst, the reaction generates dinitrodiphenylmethane.
3. Reduction
The dinitrodiphenylmethane is subjected to a reduction reaction to obtain a pure MDI product. The reduction method can be chemical reduction or catalytic hydrogenation.
3. Carbodiimide method
Carbodiimide method is a new type of pure MDI manufacturing method, the process includes the reaction of aniline and urea to generate carbodiimide, and the reaction of carbodiimide and aniline to generate pure MDI. The specific steps are as follows:
1. Reaction between aniline and urea
Aniline and urea are added to the reactor according to a certain ratio, and the reaction is carried out to produce carbodiimide at a high temperature and high pressure. imine.
2. Reaction of carbodiimide with aniline
Carbodiimide and aniline are added to the reactor in a certain ratio, and the reaction is carried out under the protection of an inert gas to produce pure MDI. the temperature and pressure need to be controlled during the reaction to ensure that the reaction proceeds smoothly.
3. Purification
After the reaction is completed, the product needs to be purified to remove impurities from it. The purification is usually carried out by distillation to obtain pure MDI products with higher purity.
The above describes three manufacturing methods of pure MDI, each of which has its advantages and disadvantages and scope of application. In the actual production, the appropriate manufacturing method should be selected according to the specific situation to ensure the quality and yield of the product. At the same time, safety operation regulations should be strictly observed during the production process to ensure that the production is safe and smooth.
