Thermal degradation and phase partitioning characteristics of non-metallic fractions in waste printed circuit boards

Thermochemical valorization of non-metallic fractions (NMFs) from waste printed circuit boards (WPCBs) is essential for circular economy objectives, yet remains hindered by the release of toxic brominated pollutants. This study systematically evaluates the pyrolysis of NMFs containing 14–16 wt% bromine, a concentration reflecting the high density of brominated flame retardants in the organic matrix. Kinetic analysis elucidates a two-stage decomposition mechanism governed by epoxy network C–O bond cleavage, occurring predominantly between 350 and 400 °C. Despite low gaseous yields (0.3–0.5 wt%), the gas phase poses significant environmental risks. Dynamic monitoring reveals a temperature-dependent shift in volatile organic compound (VOC) speciation: aromatic hydrocarbons dominate at 300–400 °C, whereas elevated temperatures trigger a surge in halogenated species. Bromine partitions overwhelmingly into the gas phase, with hydrogen bromide (HBr) emerging as the dominant inorganic species, accounting for over 86% of water-soluble exhaust ions. Experimental data identifies 500 °C as a critical temperature threshold. Exceeding this limit induces the formation of stable polycyclic aromatics and the concentrated release of corrosive HBr and brominated VOCs—direct precursors to hazardous PBDD/Fs. Consequently, 500 °C serves as a fundamental engineering design criterion. Operating below this limit maximizes the recovery of high-value phenolic chemical feedstocks while effectively mitigating toxicological risks. These findings provide a quantitative mechanistic basis for industrial emission standards and underscore the mandatory integration of off-gas debromination in large-scale WPCB recycling deployments.

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