Polycarbonate

Polycarbonates are a group of thermoplastic polymers containing carbonate groups in their chemical structures. A balance of useful features, including temperature resistance, impact resistance and optical properties, positions polycarbonates between commodity plastics and engineering plastics. They are easily worked, molded, and thermoformed. Because of these properties, polycarbonates find many applications. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. Although many other diols have been tested in place of bis-phenol A, it remains from far the most common polycarbonate.

Manufacturing from allyl chloride

Allyl chloride is prepared by temperature chlorination of propylene. Epichlorohydrin is manufactured from allyl chloride in two steps, beginning with the addition of hypochlorous acid, which affords a mixture of two alcohols. In the second step, this mixture is treated with base to give the epoxide.

Phosgene manufacturing process

The main polycarbonate is produced by the reaction of bisphenol A and phosgene. The first step of the synthesis involves treatment of bisphenol A with sodium hydroxide, which deprotonates the hydroxyl groups of the bisphenol A. The diphenoxide reacts with phosgene to give a chloroformate, which subsequently is attacked by another phenoxide. About one million tons of polycarbonate is produced in this way annually.

Transesterification manufacturing process

An alternative route to polycarbonates entails transesterification from bisphenol A and diphenyl carbonate. The diphenyl carbonate is derived in part from carbon monoxide, this route being “greener” than the phosgene method but consumes more energy. It produces a “chlorine free” polycarbonate.

GAB Neumann’s process equipment

The phosgene manufacturing process involves the absorption and further processing of large amounts of hydrochloric acid therefore the need for corrosion resistant process equipment. GAB Neumann supplies annular groove graphite heat exchangers, graphite coolers, graphite heaters, graphite block heat exchangers and other corrosion resistant process equipment such as graphite absorbers or graphite columns to the polycarbonate producing companies using the phosgene route. GAB Neumann also supplies silicon carbide heat exchangers for the recovery and concentration of spent nitric and sulfuric acid mixtures.

Associated products:

Impervious graphite annular groove heavy-duty condensers

Impervious graphite annular groove partial condensers

Impervious graphite block heat exchangers

Impervious graphite columns

Hydrochloric acid recovery units