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[Chemical Knowledge]：Production process and preparation method of toluene diisocyanate (TDI)

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Toluene diisocyanate, referred to as TDI, is an important chemical raw material, widely used in the production of polyurethane products. In this paper, the production process and its process flow of TDI will be introduced in combination with the production process and preparation method.

1. TDI production process

TDI production process is mainly divided into two kinds, namely: liquid phase oxygen method and gas phase method.

1. Liquid phase oxygen method

liquid phase oxygen method is mainly aniline and toluene diisocyanate after reaction, in a certain catalyst under the formation of TDI. The key steps are as follows:

A. Pre-distillation: aniline is heated and distilled to remove impurities to obtain high-purity aniline;

B. Synthesis reaction: aniline and tolylene diisocyanate are added into a reaction kettle, catalyst is added, and the reaction is carried out at a certain temperature and pressure.

C. Separation and purification: TDI is separated from the reaction product through the steps of adding water, concentrating and extracting, and after purification treatment, to obtain high purity TDI.

2. gas phase method

gas phase method is to convert aniline and toluene diisocyanate into TDI through nitrogen or hydrogen flowing catalyst bed at a certain temperature. The key steps are as follows:

A. mixing reaction: mixing aniline and tolylene diisocyanate, turning it into gaseous state by heating, and spraying it into the catalyst bed from the top;

B. synthesis reaction: in the catalyst bed, aniline and tolylene diisocyanate react with the catalyst to generate TDI;

C. separation and purification: the reaction product is quenched by quenching agent and then enters the cooling water, then, the TDI is separated from the TDI by adding water, concentrating, extracting and other steps, and purified to obtain high-purity TDI. The preparation method of

2. TDI
The preparation method of
TDI is mainly liquid phase method and gas phase method, and the preparation method of the two methods will be introduced respectively below.

1. liquid phase method

liquid phase method is the reaction of aniline and toluene diisocyanate by heating, by adding an appropriate amount of catalyst to promote the reaction, the generation of TDI. The specific implementation methods are as follows:

A. Select appropriate solvents: Disperse aniline and toluene diisocyanate in different solvents respectively, and mix the two solvents;

B. Add catalyst: Add appropriate amount of catalyst, such as sulfuric acid, to the solution, and continue stirring;

C. Heating reaction: under heating conditions, the mixed solution is reacted. After the reaction is completed, cooling and filtering to obtain a crude product;

D. Separation and purification: the crude product is washed, extracted, distilled and other processes to obtain high-purity TDI.