Catalysis pyrolysis debromination from waste printed circuit boards: Catalysts selection, parameter effects, products, and mechanisms

As a typical e-waste, waste printed circuit boards (WPCBs), are the most valuable and hazardous components containing all the basic and precious metals as well as toxic substances such as heavy metals, brominated epoxy resins (BERs) and brominated flame retardants (BFRs). Due to their high toxicity and carcinogenicity, effective treatment of BERs and BFRs is the key to achieve the environmental-friendly recycling of WPCBs. Recently, catalysis pyrolysis has proven an efficient and promising approach to removing and recovering bromides from WPCBs. The selection of catalysts and pyrolysis parameters mutually affect the debromination of WPCBs including products and mechanisms. However, there are few studies that focus on analyzing and summarizing the above aspects. Herein, this review first introduces types of catalysts (metals, oxides, hydroxides, molecular sieve, etc.) and figures out that metals are regarded as the most suitable catalysts for WPCBs debromination due to their high efficiency and easy to recycle. Then, the interactive effects of catalyst types and pyrolysis parameters on the debromination efficiency are analyzed, and it was found that temperature ranging from 500 to 600 °C, rapid heating rates, small-size samples and in-situ metals were more suitable for debromination. Moreover, a new idea of in-situ catalysis pyrolysis using self-compositions in WPCBs is highlighted, which point out that the defects of catalysts during the reaction process could promote debromination performance. This review summarizes the key knowledge about catalysis pyrolysis debromination from WPCBs, which will devote to the recycle WPCBs more efficiently and environmental-friendly.