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[Chemical Knowledge]：PC manufacturing methods and processes.

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PC (polycarbonate) is a widely used engineering plastic, because of its excellent mechanical properties, thermal stability, optical transparency and weather resistance. In the field of chemical production raw materials, the manufacturing methods of PC are mainly interfacial polycondensation and melt ester exchange. This article will detail these two manufacturing methods.

1. interfacial polycondensation method

interfacial polycondensation method is the earliest method used in the industrial production of PC, but also one of the most widely used methods. In this method, bisphenol A and phosgene are used as raw materials, and an interfacial polycondensation reaction is carried out in an alkaline aqueous solution to produce polycarbonate.

1. Raw material preparation
Bisphenol A: Bisphenol A is the main raw material of PC and should have high purity.
Phosgene: Phosgene is another important raw material in the production of PC, usually in liquid form.
Alkaline Absorbent: An aqueous solution of sodium hydroxide or potassium hydroxide is generally used as an alkaline absorbent.

2. Reaction Process
In the interfacial polycondensation method, bisphenol A and phosgene are reacted in an aqueous alkaline solution to form polycarbonate. The pH value, temperature and reaction time should be strictly controlled during the reaction. At the same time, it is necessary to add a phase transfer catalyst to increase the reaction rate.

3. post-treatment
After the reaction, post-treatment is required, including precipitation, washing, drying and granulation, in order to obtain high-quality PC products.

2. Melt Transesterification

Melt Transesterification is a recently developed PC manufacturing method. In this method, bisphenol A and diphenyl carbonate are used as raw materials, and a transesterification reaction is carried out in a molten state to produce a polycarbonate.

1. raw material preparation
bisphenol A: the same interface polycondensation method, bisphenol A is the main raw material of the melt ester exchange method.
Diphenyl Carbonate: Diphenyl carbonate is another starting material in the melt transesterification process.
Catalyst: Alkali metal compounds are usually used as catalysts.

2. reaction process
bisphenol A and diphenyl carbonate were mixed according to a certain proportion, and the catalyst was added to carry out the melt transesterification reaction under high temperature and high pressure. The polycarbonate formed by the reaction was discharged from the bottom of the reactor.

3. Post-treatment Polycarbonate obtained
melt transesterification needs to be extruded and pelletized to obtain PC granules.

3. the two methods are

interfacial polycondensation and melt transesterification have their own advantages and disadvantages. The interfacial polycondensation process is mature and the product quality is stable, but the use of phosgene in the production process has a certain impact on the environment. The melt transesterification law avoids the use of phosgene and is more environmentally friendly, but the equipment investment is larger and the operation technology is higher.

4. development trend

With the improvement of environmental awareness and the continuous progress of technology, melt transesterification is more and more widely used in PC production. In the future, the manufacturing method of PC will pay more attention to environmental protection and high efficiency, and the melt ester exchange method is expected to become the mainstream production method. At the same time, with the continuous emergence of new materials and new technologies, PC production processes and equipment will continue to be updated to improve production efficiency and product quality.

In summary, the production method of PC mainly includes an interfacial polycondensation method and a melt transesterification method. These two methods have their own advantages and disadvantages, and the appropriate production method should be selected according to the actual situation. In the future, with the continuous advancement of technology and the improvement of environmental awareness, PC manufacturing methods will pay more attention to environmental protection and efficiency.

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