Recycling of printed circuit board e-wastes: a combined study of pyrolysis characteristics, kinetics and evolved gas analyses at various particle sizes

The current study aimed to determine the characteristics and kinetic parameters for the pyrolysis of printed circuit board (PCB) wastes including the analysis of evolved gases during the processes at different particle sizes. First, PCB wastes were examined using SEM–EDS, SEM-Mapping and FTIR to gain a better understanding of their structures. Then, non-isothermal TG-FTIR analyses of PCB wastes were conducted from ambient temperature to 800 °C under N₂ atmosphere. The thermal decomposition of PCB wastes occurred in four stages. The second stage was determined as the main pyrolysis stage. The average apparent activation energies (E_a) of main pyrolysis stage calculated using the isoconversional methods (Friedman, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and Starink) were in the ranges of 205–240, 144–158 and 147–161 kJ mol⁻¹ ranges for the studied particle sizes of PCB-2 (180 μm–1.18 mm), PCB-3 (90–180 μm) and PCB-4 (63–90 μm), respectively, which pointed out an effect of particle size on E_a value conversely to a previously reported literature study. Moreover, Coats-Redfern and Criado methods confirmed each other and revealed the reaction mechanism of main pyrolysis stage as F2-2.5. Based on the evolved gas analyses, the most common emission of PCB wastes was CO₂ associated with plastic, brominated compounds, polycarbonate, and epoxy resins decomposition.