Insight into pyrolysis behavior of waste printed circuit boards using in-situ Py-TOF-MS combined with Py-GC/MS: Primary volatiles evolution and catalytic effect of coated copper

The real-time detection of primary volatiles is essential for properly understanding the pyrolysis behaviors of waste printed circuit boards (WPCBs) and the catalytic effect of coated copper. In this study, in-situ pyrolysis time-of-flight mass spectrometry was used in conjunction with pyrolysis-gas chromatography/mass spectrometry to detect primary volatiles and identify the main compositions of pyrolysis oil. The results revealed that the presence of Cu has an obvious inhibitory effect on WPCBs pyrolysis, resulting in a decrease in formed phenolic and etheric compounds such as phenol (11.75 % in Cu-coated WPCBs vs 17.02 % in non-Cu WPCBs), p-isopropenylphenol (4.25 % vs 6.56 %) in the initial pyrolysis stage. Nevertheless, Cu can trigger the C-Br bond to fracture in brominated epoxy resin, and subsequently released •Br radicals are captured by active Cu to form coordination compound Cu…Br, thereby lowering the production of bromides such as CH₃Br (reduced by 0.44 %), 2-bromo-p-cymene (reduced by 0.84 %), and 2,6-dibromo-phenol (reduced by 0.49 %). As temperature increases, Cu promotes the degradation of WPCBs residues, especially the curing agent in it, and the released free radicals subsequently react to form macromolecular compounds like 1,1'-[1,2-ethanediylbis(oxy)] bis-benzene and 1-amino-8-naphthol-3,6-disulfonic acid. Additionally, debromination occurred at high temperatures as a result of the Cu-induced Ulmann cross-coupling reaction. The obtained results can provide the theoretical foundation for sustainable WPCBs conversion and debromination.