Product characteristics and potential energy recovery for microwave assisted pyrolysis of waste printed circuit boards in a continuously operated auger pyrolyser

Abstract

The efficient disposal and recycling of nonmetal materials from waste printed circuit boards (WPCBs) can be a significant challenge due to their toxicity and complexity. In this paper, the characteristics and energy recovery of products from WPCBs pyrolysis at different temperatures were investigated using a two-mode auger pyrolyzer operated continuously under microwave irradiation. The results indicated that the organic matter in WPCBs was almost completely recovered (88.03%) and the maximum condensate yield (22.66 wt%) was obtained at 550 °C, with lower brominated compounds (1.83%) and higher phenols recovery (80.4%). Pyrolysis oil with low moisture content (0.5–2%) could be directly separated in-situ from condensates. Pyrolysis residue (PR) was further separated into valuable glass fiber and powder char with a certain degree graphitization by ball-milling. Bromine and sulfur mostly remained in powder char. The highest yields of CO (11.61 wt%) and H2 (1.50 wt%) were obtained at 750 °C. Energy balance analysis showed that 90.25% of energy was recovered at 550 °C, providing an energy efficiency as high as 72.00%. Bromine mainly remained in PR in the form of inorganic bromine (44.35–56.00 wt%), and was transferred to gas phases (HBr and CH3Br) with temperature increasing.