Regulation mechanisms of debromination and product distribution in pyrolysis of waste printed circuit boards by pre-swelling and alkali loading

• Swelling destroys resin structure and promotes alkali diffusion to enhance debromination. • Alkali impregnation enriches bromine in inorganic salts for directional removal. • The synergistic effect of KOH/NaOH achieves a bromine removal rate of 95 %. To efficiently suppress brominated organic compounds during the pyrolysis process of waste printed circuit boards under low-additive conditions and produce debrominated pyrolysis oil, this study employed a method combining swelling pretreatment with alkali impregnation and pyrolysis debromination. The thermal weight loss characteristics and debromination effects of the pyrolysis oil produced from circuit boards impregnated with KOH, NaOH, and KOH/NaOH mixtures were investigated sequentially. The results show that, after swelling treatment and alkali impregnation, the initial pyrolysis characteristic temperature decreased, and the temperature range of pyrolysis weight loss significantly widened. Under similar loading conditions, KOH impregnation alone achieved better debromination than NaOH impregnation alone, while the KOH/NaOH mixture demonstrated a noticeable synergistic enhancement, resulting in the best debromination effect. When the ratio of KOH to NaOH was 2:1 and the loading amount was just 6 % of the circuit board weight, no brominated organic compounds were detected in the pyrolysis oil. This study demonstrates that the proposed method of swelling treatment followed by alkali impregnation and pyrolysis can efficiently achieve debromination with a significant reduction in alkali additive usage.