Microwave Catalytic Co-Pyrolysis of Waste Printed Circuit Boards and Alkaline Metal Compounds for Br Conversion and Material Recovery

Microwave-assisted co-pyrolysis of waste printed circuit boards (WPCBs) with alkaline metal oxides was conducted to investigate the properties of pyrolysis products and the fixation of bromine. The yield of solid pyrolysis products decreased with increasing temperature, while the bromine content and percentage of inorganic bromine increased with the rise in temperature, reaching 93.34% and 94.27%, respectively, at 600°C. The addition of Ca(OH)2 facilitated the composite reaction of brominated epoxy resin, resulting in an increase in the relative percentage of phenol and other compounds. The bromine content in the pyrolysis residue was determined by oxygen bomb ion chromatography. The conversion and immobilization of organic bromine in the product were promoted by Ca(OH)2, which reacted with bromine radicals to form CaBr2, leading to a significant improvement in the immobilization efficiency of bromine in the solid pyrolysis product and a reduction in the content of bromine in the gas and liquid phases. The study proposed a mechanism of the conversion of organic bromine by Ca(OH)2. This study demonstrates the ability of Ca(OH)2 to immobilize organic bromine in the green recovery process of WPCB by pyrolysis.