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[Chemical Knowledge]：Production method and process of polyisocyanate

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The manufacturing method
of polyisocyanate
1. Introduction

polyisocyanate (Polyisocyanate, referred to as PI) is a kind of important chemical production raw materials, widely used in polyurethane, elastomers, coatings, adhesives and other fields. With the continuous development of science and technology, the manufacturing method of polyisocyanate has been continuously improved and optimized. In this paper, the manufacturing methods of polyisocyanate are introduced in detail, including phosgenation, nitration and carbodiimide.

2. phosgenation

phosgenation is a commonly used method for the manufacture of polyisocyanates, mainly by reacting phosgene with amine compounds to form isocyanates. Specifically, the phosgenation method is an addition reaction of an amine compound and phosgene under the action of a catalyst to generate the corresponding isocyanate. Commonly used catalysts include organic base catalysts such as triethylamine and pyridine. The advantages of

phosgenation method are that high purity isocyanate products can be prepared, the reaction conditions are relatively mild, and the operation is simple. However, a large amount of by-products and waste will be produced during the use of this method, which will pollute the environment, so effective environmental protection measures need to be taken.

3. Nitration

Nitration is a method for preparing polyisocyanate by nitration reaction. Specifically, the nitration method is a nitration reaction of amine compounds and nitric acid under acidic conditions to generate corresponding nitro compounds. The nitro compound is then reduced to the amino compound under the action of a reducing agent and finally reacted with phosgene to form the corresponding isocyanate.

nitration process has the advantage of producing high purity isocyanate products with relatively little waste. However, the reaction conditions and the ratio of raw materials need to be strictly controlled during the operation of the method to ensure the selectivity and yield of the reaction.

4. carbodiimide method

carbodiimide method is a new method of manufacturing polyisocyanate, mainly through the carbodiimide and amine compounds to generate the corresponding isocyanate. Specifically, the carbodiimide method is an addition reaction of carbodiimide with an amine compound under the action of a catalyst to produce the corresponding isocyanate. Commonly used catalysts include triphenylphosphine, triethylamine and the like. The advantages of

carbodiimide method are mild reaction conditions, simple operation, high yield, and can reduce environmental pollution. However, this method requires the use of a relatively expensive carbodiimide as a raw material, and is therefore costly.

5. Conclusion There are many methods for the manufacture of

polyisocyanates, including phosgenation, nitration and carbodiimide. Different methods have their own advantages and disadvantages, and the appropriate manufacturing method should be selected according to the specific product requirements and process conditions. At the same time, in order to ensure product quality and environmental protection requirements, it is necessary to strictly control the reaction conditions and raw material ratio, optimize the production process, and improve the yield and selectivity.

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