Manufacturing method of polyisocyanate
I. Introduction
Polyisocyanate (PI for short) is an important class of raw materials for the production of chemicals, which is widely used in the fields of polyurethane, elastomers, coatings, adhesives and so on. With the continuous development of science and technology, the manufacturing method of polyisocyanate has been continuously improved and optimized. This article will introduce the manufacturing methods of polyisocyanate in detail, including the photogasification method, nitration method and carbodiimide method.
II. Photogasification method
Photogasification method is a commonly used method to manufacture polyisocyanates, mainly through the reaction of phosgene and amine compounds to generate isocyanates. Specifically, the photogasification method is to generate the corresponding isocyanate by addition reaction between amine compounds and phosgene under the action of catalyst. Commonly used catalysts include triethylamine, pyridine and other organic base catalysts. The advantages of the
photogasification method are that high purity isocyanate products can be prepared, the reaction conditions are relatively mild, and the operation is simple. However, the use of this method will produce a large number of by-products and waste, causing pollution to the environment, so effective environmental protection measures need to be taken.
III. Nitrification method
Nitrification method is a method of preparing polyisocyanate through nitrification reaction. Specifically, the nitrification method is to nitrify amine compounds with nitric acid under acidic conditions to generate the corresponding nitro compounds. Then, the nitro compounds are reduced to amino compounds under the action of a reducing agent, and finally reacted with phosgene to generate the corresponding isocyanate. The advantage of the
nitrification method is that high purity isocyanate products can be prepared, and at the same time, relatively little waste is generated. However, the operation of this method requires strict control of the reaction conditions and raw material ratios to ensure the selectivity and yield of the reaction.
Four, carbodiimide method
Carbodiimide method is a new method of manufacturing polyisocyanate, mainly through the carbodiimide and amine compounds reaction to generate the corresponding isocyanate. Specifically, the Carbodiimide Method is to generate the corresponding isocyanate by the addition reaction between carbodiimide and amine compounds under the action of catalyst. Commonly used catalysts include triphenylphosphine and triethylamine. The advantages of the
Carbodiimide method are mild reaction conditions, easy operation, high yield, and reduced environmental pollution. However, the method requires the use of more expensive carbodiimide as the raw material, so the cost is higher.
V.Conclusion
There are various methods for the manufacture of polyisocyanates, including the photogasification method, the nitration method and the carbodiimide method. Different methods have their own advantages and disadvantages, and a suitable manufacturing method should be selected according to the specific product requirements and process conditions. At the same time, in order to ensure the quality of the product and environmental requirements, it is necessary to strictly control the reaction conditions and raw material ratios, optimize the production process, and improve the yield and selectivity.
