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[Chemical Knowledge]：Manufacturing method and process of TDI

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In the field of chemical raw materials, toluene diisocyanate (TDI) is an important organic compound, which is widely used in polyurethane foam, coatings, elastomers and adhesives. This paper will introduce the manufacturing methods of TDI in detail, including phosgenation, nitration and carbodiimide.

1. phosgenation

phosgenation is a commonly used TDI manufacturing method, which is mainly divided into two steps: first, toluene and phosgene react with a catalyst to form benzophenone urea; Then, benzophenone urea is cracked to form TDI under heating conditions. Specific steps are as follows:

1. toluene and phosgene are mixed and introduced into a reactor containing a catalyst (such as triethylamine), and a certain temperature and pressure are controlled to react to generate benzophenone urea.
2. Benzophenone urea is heated to a certain temperature to crack it to form TDI and by-product carbon dioxide.

the method is easy to obtain raw materials and mature technology, a large number of by-products and wastes will be produced in the production process, causing certain pollution to the environment.

2. nitration

nitration is a more traditional TDI manufacturing method, mainly through the reaction of toluene and nitric acid to generate dinitrotoluene, and then reduce it to TDI. The specific steps are as follows:

1. mixing toluene with nitric acid, adding sulfuric acid as a catalyst, controlling a certain temperature and time, and reacting to generate dinitrotoluene.
2. Dinitrotoluene is reduced to TDI by a reducing agent such as hydrogen.

the process is simple, a large amount of acidic waste water and waste gas will be produced in the production process, which will cause great pollution to the environment.

3. Carbodiimide method

Carbodiimide method is a relatively new TDI manufacturing method, mainly through the reaction of carbodiimide and toluene to produce TDI. The specific steps are as follows:

1. mixing carbodiimide with toluene, adding a catalyst, controlling a certain temperature and pressure, and reacting to generate TDI and by-product carbon dioxide.
2. TDI is separated from unreacted toluene and carbon dioxide by distillation and other methods to obtain pure TDI product.

this method has the advantages of easy availability of raw materials, mild reaction conditions and high product purity, the activity of the catalyst has a great influence on the reaction, and the reaction conditions need to be strictly controlled.

4. other methods

In addition to the above methods, there are some other manufacturing methods, such as electrolysis, gas phase method, etc. These methods have their own advantages and disadvantages, and are suitable for different production conditions and needs.

In short, TDI manufacturing methods are diverse, and different methods are suitable for different production conditions and needs. In the production process, it is necessary to select the appropriate manufacturing method according to the actual situation, and strictly control the reaction conditions to ensure the quality and output of the product. At the same time, strengthen the treatment and recycling of waste to reduce the impact on the environment.

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