Polycarbonate Production from BPA, Phenol and Phosgene

The process under analysis comprises four major sections: (1) DPC synthesis; (2) DPC purification; (3) Polymerization; (4) Polycarbonate finishing.

Diphenyl carbonate synthesis. Initially, phenol is reacted with phosgene to produce diphenyl carbonate (DPC). The phosgenation reaction is carried out in three fixed bed reactors filled with gamma-alumina connected in series. The product from phosgenation mainly containing phenol and diphenyl carbonate is directed to the DPC purification. The waste gas coming from the phosgenation, mostly containing HCl and inert gases, is fed to a HCl recovery unit, where hydrochloric acid with a concentration of 32 wt% is obtained as by-product.

DPC purification. The effluent from the DPC synthesis is fed to a set of distillation columns for the purification of diphenyl carbonate and recovery of unconverted phenol, which is recycled to the DPC synthesis.

Polymerization. Purified diphenyl carbonate, bisphenol A and sodium dihydrogen phosphite are mixed and heated to form a melt, which is subsequently fed to a oligomerization step, where low molecular weight oligomers are generated. The oligomers are directed to more severe conditions, then polymerization is completed in two CSTR operating in series. Polymerization is interrupted by addition of n-butyl tosylate, which deactivates the catalyst. Phenol and other by-products are continuously removed and sent to a distillation column, where phenol is withdrawn from overhead and recycled to the DPC synthesis.

Polycarbonate finishing. The polymer melt is filtered, and a mix of additives is added. The mixture is homogenized and pelletized. Finally, the Polycarbonate pellets are conveyed to homogenization system and fed to the packing system.