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

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Toluene diisocyanate (TDI) is an important chemical raw material, mainly used in the manufacture of polyurethane foams, elastomers and polyurethane coatings. This article will introduce the production process and preparation method of TDI.

1. TDI production process

TDI production process can be divided into two steps: first, through the oxidation reaction of toluene and air in the presence of a catalyst, the preparation of toluene diphenol, and then the reaction of toluene diphenol with isocyanate, TDI.

1. toluene oxidation preparation of toluene

toluene oxidation reaction is toluene as raw material, air or oxygen as oxidant, under the action of a catalyst oxidation reaction. The selectivity of toluene oxidation reaction is high, and the preparation of cresol is one of the main raw materials of TDI. The reaction process of

toluene oxidation reaction is as follows:

2CH3-C6H5 O2 --> 2 CH3C6H4OH

The catalyst for toluene oxidation reaction generally uses cobalt, manganese and other metal catalysts or ionic liquid catalysts. In addition, the reaction temperature, oxygen concentration and other process parameters can be reasonably controlled to improve the reaction efficiency and yield.

2. Preparation of TDI
by Reaction of Toluene with Isocyanate
The reaction of Toluene with Isocyanate is the core step in the preparation of TDI. The reaction is carried out in an inert solvent, and the reaction temperature is generally around 60°C. The chemical equation for the reaction of

toluene with isocyanate is as follows:

2CH3C6H4OH 2NCO-> (CH3C6H4NCO)2O H2O

The reaction will generate the precursor of TDI toluene diisocyanate (TODI), which is then decomposed under heating to generate TDI. The preparation process of

TDI is as follows:

1) Toluene and air are sent into a reaction kettle and catalyst is added;
2) oxygen is transported to the reaction kettle to start toluene oxidation reaction to prepare cresol;
3) Put cresol and isocyanate into inert solvent, heat to about 60 ℃, and stir continuously;
4) After TODI is generated, continue to heat and decompose, get TDI. There are three methods for preparing

2. TDI

TDI: acid gas phase method, hydrogen reduction method and liquid phase method. Among them, the acid gas phase method is the most commonly used method.

1. Acid gas phase method

The acid gas phase method is to oxidize toluene and air of TDI raw materials under the action of silver catalyst or silver dioxide catalyst to prepare toluene diphenol, and then react toluene diphenol and isocyanate in methanol and ethanol solvent to obtain TDI. The method produces TDI with high purity and high yield.