Kinetic study on the slow pyrolysis of nonmetal fraction of waste printed circuit boards (NMF-WPCBs)

Abstract

In this study, the pyrolysis behaviour of nonmetal fraction of waste printed circuit boards (NMF-WPCBs) was studied based on five model-free methods and distributed activation energy model (DAEM). The possible decomposition mechanism was further probed using the Criado method. Thermogravimetric analysis indicated that the NMF-WPCBs pyrolysis process could be divided into three stages with temperatures of 37–330°C, 330–380°C and 380–1000°C. The mass loss at different heating rate was determined as 26.85–29.98%, 13.47–24.21% and 20.43–23.36% for these stages, respectively. The activation energy (E_α) from various model-free methods first increased with degree of conversion (α) increasing from 0.05 to 0.275, and then decreased beyond this range. The coefficient (R) from the Flynn–Wall–Ozawa (FWO) method was higher, and the resulting E_α fell into the range of 214.947–565.660 kJ mol⁻¹. For the DAEM method, the average E_α value was determined as 337.044 kJ mol⁻¹, comparable with 329.664 kJ mol⁻¹ from the FWO method. The thermal decomposition kinetics of NMF-WPCBs could be better described by the second-order reaction.