High-value products from the catalytic hydrolysis of polycarbonate waste

Abstract

The purpose of this study was to investigate the effect of additives on the recycling of waste polycarbonate (PC) by hydrolysis in a steam atmosphere. PC containing a variety of additives was obtained from waste electrical and electronic equipment (WEEE) and was hydrolyzed at 300 and 500 °C in a semibatch reactor in the presence of MgO and CaO. Valuable phenolic products were obtained at high yield, with a product distribution that was strongly dependent on temperature. Bisphenol A (BPA) was the major product formed from the hydrolysis of waste PC at 300 °C and was obtained in a maximum yield of 91%, and degradation products of BPA such as phenol and 4-isopropenyl phenol were obtained at 500 °C. The presence of polystyrene and triphenyl phosphate in waste PC reduced the rate of the reaction by preventing steam from interacting with the surface of PC. Although pure PC was completely hydrolyzed within 15 min, hydrolysis of waste PC took 30–60 min. However, the hydrolysis of PC in a steam atmosphere is an appropriate method for materials that cannot be treated by solvolysis. Phosphorus-containing fire retardants and inert polymers inhibit the hydrolysis of polycarbonate (PC), resulting in an increased reaction time. However, even in the presence of these materials, high yields of bisphenol-A and other phenols can be obtained from waste PC dependent on temperature. At 500 °C, polystyrene is also pyrolyzed.