Study on low-temperature pyrolysis of large-size printed circuit boards

• An energy-saving pyrolysis process of printed circuit board (PCB) was experimented.
• The metals fate from PCB pyrolysis products was the focus.
• Endothermic heat of PCB pyrolysis reaction was calculated.
• Lower pyrolysis temperature and large-size PCB improve recycling economic benefits.

An energy-saving pyrolysis process of FR4-type printed circuit board (PCB) was designed with lower pyrolysis temperature (500 °C) and large-size PCB sample (16–20 cm2). The pyrolysis experiment of the PCB was carried out based on the process. The properties of pyrolytic gas and tar were compared to the pyrolysis results of previous process with high temperature (800 °C) and small-size PCB (1.5–2 cm2 or powder). Endothermic heat of PCB pyrolysis reaction was calculated based on the experiment data collected. The results showed that: (1) PCB pyrolysis produced 10.17 wt% of gas, 18.23 wt% of tar and 71.60 wt% of solid particle. Similar to previous studies, CO, CO2, 2-methyl propene was the main components in pyrolysis gas and the pyrolysis tar consisted of phenol and alkyl aromatics. However, the content of propylene, bromomethane, and bromine were significantly different in the pyrolysis gas of this study. (2) Metals and fiberglass were easier to be separated compared to the case of regular pyrolysis with 800 °C pyrolysis final temperature and small-size sample. Copper sheets and fiberglass which adhere to a plenty of carbon were collected manually; a little amount of gold and nickel stayed in the residue. (3) Endothermic heat of PCB pyrolysis reaction is about 19.692 MJ/kg. The calorific capacity is about 2.386 MJ for pyrolytic gas and 4.502 MJ for tar from each kilogram PCB pyrolysis. The overall calorific capacity of pyrolytic gas and tar accounts for 35% of required pyrolysis heat.