Chemical recycling of compact discs (CDs) with high temperature high pressure water

The increasing accumulation of plastic-based electronic waste, such as compact discs (CDs), poses a major challenge to the environment due to their longevity and limited recyclability. This study investigates the hydrothermal degradation of end-of-life CDs – which are mainly composed of polycarbonate – under subcritical and supercritical water conditions as a sustainable approach for waste recycling. The hydrothermal treatments were carried out at temperatures ranging from 250 °C to 450 °C for reaction times of 5 to 60 min. The resulting product phases, i.e. water-soluble, diethyl ether (DEE)-soluble and solid gaseous, were quantified. The composition of the DEE-soluble phase was characterised by gas chromatography. The results showed a strong dependence of the product distribution on temperature and residence time. The yield of the DEE-soluble phase peaked at 450 °C after 5 min (96.9 ± 1.0 %) and decreased at longer reaction times due to secondary decomposition into gas phase products. The major organic compounds in the DEE phase included bisphenol A, phenol and 4-isopropylphenol, while the concentration of other phenol derivatives such as 4-ethylphenol, 4-methylphenol (p-cresol) and 4-isopropenylphenol was generally low and below 5 %. These results show that hydrothermal treatment effectively converts waste CDs into valuable liquid and gaseous products, thereby reducing the amount of solid waste. The process offers a promising strategy for the recovery of resources from waste CDs.