Application of critical water-alcohol composite medium to treat waste printed circuit boards: Oil phase products characteristic and debromination

Critical water system used for decomposition and debromination of waste printed circuit board (PCBs) has two disadvantages: low value-added oil phase products and halfway debromination at low temperature condition. In this study, critical water-alcohol composite medium was found to be a promising method to surmount these disadvantages. Critical water-ethanol (CWE) and critical water-methanol (CWM) were selected as the composite medium. The temperature of CWE and CWM had a significant effect on the oil phase composition. At low temperature CWE/CWM of 300 °C, 4-(1-methylethyl)-phenol with high concentration could be recovered. CWM of 400 °C was beneficial to the generation of ether compounds and high level of anisole could be obtained, while 450 °C was beneficial to the generation of high level of multi-alkyl substituted phenol derivatives or benzene derivatives such as p-xylene. Br-free oil phase products could be obtained when the temperature of CWE/CWM ≥300 °C. Different oil phase products with high level of chemicals or chemical intermediates could be obtained by controlling the reaction conditions of CWE/CWM. It is believed that the additional value of the oil phase products derived from waste PCBs can be greatly improved by this new process.