In-situ debromination mechanism based on self-activation and catalysis of Ca(OH)2 during pyrolysis of waste printed circuit boards.

• HBr and organic bromide were simultaneously removed by Ca(OH) 2. • The Ca(OH) 2 can be activated by captured HBr and its thermal decomposition. • The coordination of bromide and calcium can stretch and weaken the C-Br bond. Completely and deeply removed bromide from waste printed circuit boards (WPCBs) is necessary due to their toxicity and carcinogenicity. To achieve this purpose, calcium hydroxide (Ca(OH) 2) as a debromination agent was added during pyrolysis process of WPCBs. The results showed that hydrogen bromide (HBr), 4-bromophenol, 2-bromophenol and 2,4-dibromophenol were the main bromide species in pyrolysis products. The Ca(OH) 2 plays a significant role for removing HBr and organic bromide, but not affects products yield. Optimal removal efficiency for 4-bromophenol, 2-bromophenol and 2,4-dibromophenol reached 87.5 %, 74.6 % and 54.5 %, respectively. And debromination efficiency was related to the steric hindrance caused by bromide atoms. The Ca(OH) 2 can be activated by captured HBr and its thermal decomposition. And the newly-generated calcium bromide and calcium oxide significantly facilitate debromination due to their high surface energy and reactivity. The debromination mechanism was clarified by experiments coupled with computational chemistry: the coordination of bromide and calcium to form [Ph-Br···Ca2+ or [Ph-Br···Ca atom. Then, electrons were delivered form bromide atom to Ca2+ or Ca atom , which resulted in the stretch and weaken the C-Br bond. Hence, the C-Br bond was more easily to break. This work can provide support for designing novel and efficient debromination agents applied for high-temperature system. [ABSTRACT FROM AUTHOR]