Enhanced debromination by Fe particles during the catalytic pyrolysis of non-metallic fractions of printed circuit boards over ZSM-5 and Ni/SiO₂-Al₂O₃ catalyst

A two-stage fixed-bed reactor was used to investigate the catalytic pyrolysis of non-metallic fractions of printed circuit boards (PCBs) over ZSM-5 and Ni/SiO₂-Al₂O₃ (Ni/SA) catalysts. The addition of Fe particles to the catalyst was evaluated for bromine removal from the pyrolysis products. Results showed that the oil yield was significantly reduced from 50.1 wt% to 41.2 wt% by ZSM-5 catalyst and 36.0 wt% by Ni/SA catalyst, respectively, with corresponding increases of aqueous and gas products. The addition of Fe particles to ZSM-5 catalyst slightly altered the product yields, whereas the mixture of Fe and Ni/SA catalyst largely reduced the oil yield to 25.6 wt%, along with the highest gas yield of 20.3 wt%. The results suggested that the mixture of Fe-Ni/SA catalyst accelerated the cracking of vapor products derived from PCBs rather than the Fe-ZSM-5 mixture. Moreover, ZSM-5 catalyst favored the formation of single ring aromatics in the oils, such as benzene and toluene. The presence of Fe particles increased the concentration of phenol in the oils. The ZSM-5 and Ni/SA catalyst demonstrated great debromination performance for the conversion of organobromine compounds into HBr, reducing the bromine content in oils from 8.74 wt% to 5.96 wt% and 5.46 wt%, respectively. Furthermore, the addition of Fe particles reduced both the organobromine compounds and evolved HBr, which resulted in less than 3.8% of Br being transferred in the oil whereas more than 50% of bromine was fixed in Fe particles.