Effects of Particle Size and Heating Rate on Evolution of Products from Pyrolysis of Phenolic Circuit Boards

Pyrolysis is an attractive means of recovering resources from waste integrated printed circuit boards (PCBs) because organic materials they contain are converted into gas, tar, and char that can be recycled and valuable metals are left for further processing. In this study, we examined the effects of particle size (0.15 and 3.0mm) and heating rate (5 degrees C/min, 25 degrees C/min, 100 degrees C/min, 300 degrees C/min, 600 degrees C/min) on products evolved during rapid pyrolysis of phenolic PCBs. A PCB was pyrolyzed at 675 degrees C under a nitrogen atmosphere in an experimental laboratory-scale fixed-bed reactor and decomposed at 700 degrees C in a thermogravimetric analyzer. Data obtained suggest that rapid heating and large particles were associated with increased local overheating and pressure, which promoted the cracking of volatile compounds into lower molecular weight compounds and increased yield of volatile gases. Furthermore, microexplosions may have occurred within the pyrolyzing PCB, which cracked the surface of the char, released volatile gases, and increased the char's porosity.