Kinetics and thermodynamics during pyrolysis of scrap printed circuit board by TGA

Scrap printed circuit board (SPCB) is a typical organic waste, which could be utilized as a resource by pyrolysis technology. The pyrolysis characteristics of SPCB were studied by thermogravimetric analysis (TGA) to reveal the reaction kinetics and thermodynamics during the pyrolysis process. Under N₂ atmosphere, the effects of different heating rates, e.g. 5 ℃/min, 10 ℃/min and 15 ℃/min, on the thermal decomposition behavior of SPCB were investigated in detail. The results observed showed that the pyrolysis process was mainly occurred in the temperature range of about 250 ℃ to 400 ℃. With the increase of heating rates, the thermogravimetry (TG) curves of SPCB was gradually deviated to the high temperature direction. For the derivative thermogravimetry (DTG) curves, there was an obvious mass loss peak, and the corresponding peak temperature kept increasing, indicating that there was a significant thermal hysteresis phenomenon. The Flynn-Wall-Ozawa (FWO) model, Kissinger-Akahira-Sunose (KAS) model and Friedman (FM) model were used to analyze the thermogravimetric data. The average apparent activation energies (E_a) were 168.46 kJ/mol, 167.31 kJ/mol and 234.84 kJ/mol, respectively, which increased with the increase of conversion rate. The thermodynamic parameters were calculated using FWO model. Under the same heating rate, the Gibbs free energy change (ΔG) was gradually decreased with the increase of conversion rate, while the corresponding enthalpy change (ΔH) and entropy change (ΔS) were all increased. Meanwhile, at the same conversion, both of ΔH and ΔS decreased slightly with the increase of heating rate, while ΔG was increased gradually.