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_α) decreased with increasing conversion (α) in the range of 0.05–0.25, then increased in the α range of 0.30–0.75, and finally decreased. The Bosewell method possessed the highest fitting degree, and the E_α 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, CH_4, H₂O, phenol, etc. Based on characteristics of these products, the pyrolysis mechanisms of brominated and non-brominated structures in brominated epoxy resins were expounded.