posted on 2023-11-30, 18:35authored byZhenyu Chen, Lu Zhan, Zhenming Xu
Bromine removal is significant in the recycling of waste
printed
circuit boards (WPCBs). This study found that the critical factors
limiting the debromination efficiency of conventional pyrolysis are
the formation of coke impeding mass transfer and conversion of bromine
into less volatile species, such as coking-Br and copper bromide.
According to frontier molecular orbital analysis and thermodynamic
equilibrium analysis, C–O bonds of resin are sites prone to
electrophilic reactions and copper bromide in residue may undergo
hydrolysis; therefore, introducing H2O during pyrolysis
was a feasible method for thorough debromination. Through pyrolysis
in a water vapor atmosphere, the diffusion limitation of debromination
was overcome, and resin was converted into light components; thereby,
rapid and deep removal of bromine was achieved. The result indicated
that 99.7% of bromine was removed, and the residue could be used as
a clean secondary resource. According to life-cycle assessment, pyrolysis
of WPCBs in water vapor could be expected to reduce 77 Kt of CO2 emission and increase financial benefits by 60 million dollars,
annually.