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.
Authors: Xiu FR, Qi Y, Wang S, Nie W, Weng H, Chen M. ; Full Source: Journal of Hazardous Materials. 2017 Oct 18; 344:333-342. doi: 10.1016/j.jhazmat.2017.10.033. [Epub ahead of print]