Four production processes of polycarbonate

Polycarbonate (PC) resin production process is divided into solution phosgene method, ester exchange melting polycondensation method, interface polycondensation phosgene method and non-phosgene exchange melting polycondensation method.

Solution phosgene method

Solution phosgene method is an interfacial condensation polymerization of phosgene and bisphenol A in alkaline aqueous solution and dichloromethane (or dichloroethane) solvent.The polycarbonate product was prepared by washing, precipitation, drying, extrusion and granulation.This process is economical, and there are environmental problems, it has been completely eliminated.

Ester exchange melting polycondensation

Ester exchange melting polycondensation is called ester exchange method for short, also known as bulk polymerization.It is an indirect phosgene process.Diphenyl carbonate (DPC) was produced by phosgene reaction using phenol as raw material.Then in the presence of A small amount of lithium halide or lithium hydroxide and other catalysts and additives, the ester exchange reaction with bisphenol A at high temperature and high vacuum was carried out to generate low polymer.The polycarbonate product was further prepared by condensation polymerization.The process is short, solvent-free, completely closed, pollution-free, and the production cost is slightly lower than that of the phosgene method.But the optical performance of the product is poor.Catalyst is easy to pollute.The by-product phenol is difficult to remove, and the product has low molecular weight and limited application range.Combined with the restrictions of stirring and heat transfer, it is difficult to achieve large tonnage industrial production.

Iii. Interface condensation phosgene method

Interfacial polycondensation phosgene method can reaction at room temperature, the aggregation device is simple, and can obtain high molecular weight resin, but the highly toxic phosgene will cause serious environmental pollution and safety problems, the reaction of residual sodium chloride and methylene chloride resin coloring and thermal degradation, removing impurities and salt needs advanced separation technology and equipment.In addition, a large number of solvents need to be recovered during the reaction, which complicates the process and increases the cost.

Iv. Non-phosgene ester exchange melting polycondensation method

Non phosgene ester exchange under high temperature and high vacuum melting polycondensation method, higher requirements on equipment, to exclude reaction of generated in the process of low molecular material, reactor structure has some special requirements, especially after the polycondensation reactor, material melt viscosity is very high, often influence further reaction, so it is difficult to produce resin of high molecular weight, in order to avoid occur under high temperature and high vacuum side effects caused by product branched, coloring, crosslinking, so require high purity raw materials, especially the quality of bisphenol A (bpa) must be strictly controlled, but ester exchange method need not poisonous phosgene, post-processing can be avoided, the reaction without solvent, without recovery system,The whole process is relatively simple.