Energy recovery from waste printed circuit boards using microwave pyrolysis: product characteristics, reaction kinetics, and benefits

Energy recovery from waste printed circuit boards (PCBs) was carried out by using microwave pyrolysis. According to thermogravimetric analysis, the maximum weight loss rate of waste PCBs occurred at 323 degrees C. When waste PCBs was heated under microwave irradiation at 300 W, the temperature can be reached within 10 min. Compared with conventional pyrolysis, microwave pyrolysis can provide higher weight loss of waste PCBs by 3-5 wt%. Microwave pyrolysis is helpful for the delamination of waste PCBs. Almost 71% of the gaseous product can be directly used as a fuel or converted into other forms of energy. Microwave pyrolysis can produce more HBr than conventional pyrolysis by approximately 17%. The main components of liquid product were phenols and phenyls. The overall energy recovery from waste PCBs using microwave pyrolysis can be 62%. According to kinetic analysis, it would need 20 min of processing time to decompose the combustible fraction of waste PCBs at 300 W. The maximum processing capacity of the microwave pyrolysis system for waste PCBs can be 1.36 kg, with the energy production of 2710 kJ. Furthermore, the pyrolyzed PCBs can be further processed to recycle valuable metals. Therefore, microwave pyrolysis of waste PCBs can be a complete and effective circular economy system to create high energy and economic benefits.