Two-stage catalytic pyrolysis and debromination of printed circuit boards: Effect of zero-valent Fe and Ni metals

Abstract

The non-metallic fraction of waste printed circuit boards (PCBs) has received extensive attention for material recycling, due to the potential risk of brominated flame retardants and heavy metals in PCBs. Here, the catalytic pyrolysis of PCBs was performed at 400–600 °C in a two-stage fixed bed reactor. Low-cost Fe and Ni metals were investigated for their catalytic effect on the product yields and bromine removal from the pyrolysis products. In the absence of additives, the maximum oil yield of 50.1 wt% was obtained at 500 °C from the PCBs pyrolysis. The addition of Ni particles decreased the oil yield to 29.1 wt%, and increased the gas yield to 9.6 wt% at 600 °C. The Fe/Ni mixture had a synergistic effect on the product yields, which depended on different pyrolysis temperatures. The composition of the oils from the PCBs pyrolysis was dominated by phenol derivatives. The presence of Fe or Ni particles promoted the formation of phenol and other aromatic compounds, such as benzene and toluene. Moreover, the transformation of bromine species was exhaustively investigated. The higher temperature promoted the conversion of brominated compounds into HBr. Fe particles exhibited excellent debromination performance, which not only reduced the formation of organobromine compounds, but also captured some of the evolved bromine.