NDI (diisocyanate) is an important raw material for the production of chemicals, and is widely used in the fields of polyurethane, coatings, and adhesives. The manufacturing methods of NDI will be introduced below.
I. Photogasification Method
The photogasification method is a commonly used method for manufacturing NDI. This method takes aniline as raw material, generates diphenylmethane diisocyanate (MDI) through photogasification reaction, and then obtains NDI through separation, purification, etc. The specific steps are as follows:
1. React aniline with phosgene to generate aniline hydrochloride.
2. Aniline hydrochloride reacts with excess phosgene at low temperature to form diphenylmethane diisocyanate (MDI) and hydrogen chloride gas.
3. MDI and unreacted raw materials are separated by distillation and other methods to obtain MDI of higher purity.
4. MDI is cracked at high temperature to obtain NDI and methane gas.
5. Higher purity NDI is obtained by condensation, separation, etc.
The production process of the photogasification method is more mature, and higher purity NDI products can be obtained. However, the method uses toxic and harmful raw materials such as phosgene, which causes some harm to the environment and human health. Nitrification method
Nitrification method is a relatively new NDI manufacturing method. This method takes aniline as raw material, generates dinitroaniline through nitration reaction, and then obtains NDI through reduction, cyclization, etc. The specific steps are as follows:
1. React aniline with mixed acid (nitric acid and sulfuric acid) to generate dinitroaniline.
2. Dinitroaniline undergoes a reduction reaction to produce diaminobenzenamine.
3. Diaminobenzenamine is cyclized at high temperature to obtain NDI.
4. NDI is purified by crystallization and filtration to obtain a product with high purity.
The production process of the nitrification method is relatively simple, the operation is safer, and no toxic and harmful raw materials are used, which is friendly to the environment. However, the purity of the product obtained by this method is low, and further purification is required.
Third, other methods
In addition to the photogasification method and nitrification method, there are some other NDI manufacturing methods, such as electrochemical method, gas phase plasma method and so on. These methods are still in the laboratory research stage and have not yet achieved industrialized production.
In summary, the manufacturing methods of NDI mainly include the photogasification method and the nitrification method. Among them, the production process of the photogasification method is more mature and can obtain products with higher purity, but it uses toxic and harmful raw materials, which causes certain harm to the environment and human health. Nitrification production process is relatively simple, safer operation, and does not use toxic and harmful raw materials, friendly to the environment, but the purity of the products obtained is lower, and further purification is required. In the future, with the continuous progress and application of technology, there may be more environmentally friendly, efficient and economical NDI manufacturing methods.
