Nonisothermal pyrolysis kinetics of waste printed circuit boards and product characterization using TG-MS

With characteristics of high resources, complex composition, and high toxicity, the treatment and disposal of waste printed circuit boards (WPCBs) have attracted widespread attention, and pyrolysis is regarded as a potential recovery method. In this study, the behaviors, kinetics, and mechanisms of WPCBs pyrolysis were systematically investigated. The pyrolysis process could be divided into three stages: evaporation stage, reaction stage, and stabilization stage. The mass losses of these stages at different heating rates were determined to be < 1%, 10.84-14.11%, and 6.37-8.82%, respectively. Four model-free methods (Friedman, Tang, Starink, and Bosewell) and the distributed activation energy method (DAEM) were used to reveal the pyrolysis kinetics of WPCBs. According to the model-free methods, the apparent activation energy (E-alpha) decreased with increasing conversion (alpha) in the range of 0.05-0.25, then increased in the alpha range of 0.30-0.75, and finally decreased. The Bosewell method possessed the highest fitting degree, and the E-alpha was calculated as 133.94-204.01 kJ/mol. The components in volatile products were detected using thermogravimetry-mass spectrometry (TG-MS), and the main components were identified as CO2, CH4, H2O, phenol, etc. Based on characteristics of these products, the pyrolysis mechanisms of brominated and non-brominated structures in brominated epoxy resins were expounded.