Pyrolysis treatment of nonmetal fraction of waste printed circuit boards: Focusing on the fate of bromine

Abstract

Advanced thermal treatment of electronic waste offers advantages of volume reduction and energy recovery. In this work, the pyrolysis behaviour of nonmetallic fractions of waste printed circuit boards was studied. The fate of a bromine and thermal decomposition pathway of nonmetallic fractions of waste printed circuit boards were further probed. The thermogravimetric analysis showed that the temperatures of maximum mass loss were located at 319°C and 361°C, with mass loss of 29.6% and 50.6%, respectively. The Fourier transform infrared Spectroscopy analysis revealed that the spectra at temperatures of 300°C–400°C were complicated with larger absorbance intensity. The nonmetallic fractions of waste printed circuit boards decomposed drastically and more evolved products were detected in the temperature range of 600°C–1000°C. The gas chromatography–mass spectrometry analysis indicated that various brominated derivates were generated in addition to small molecules, such as CH4, H2O and CO. The release intensity of CH4 and H2O increased with temperature increasing and reached maximum at 600°C–800°C and 400°C–600°C. More bromoethane (C2H5Br) was formed as compared with HBr and methyl bromide (CH3Br). The release intensity of bromopropane (C3H7Br) and bromoacetone (C3H5BrO) were comparable, although smaller than that of bromopropene (C3H5Br). More dibromophenol (C6H4Br2O) was released than that of bromophenol (C6H5BrO) in the thermal treatment. During the thermal process, part of the ether bonds first ruptured forming bisphenol A, propyl alcohol and tetrabromobisphenol A. Then, the tetrabromobisphenol A decomposed into C6H5BrO and HBr, which further reacted with small molecules forming brominated derivates. It implied debromination of raw nonmetallic fractions of waste printed circuit boards or pyrolysis products should be applied for its environmentally sound treating.

Chemical and Process Engineering

“…These vapours were condensable and were collected as oil. It can also be seen in DTG curve that mass loss starts after 300 • C and the same behaviour is also followed in experiments (Rajagopal et al, 2017;Xiong et al, 2020). This observation was confirmed for both catalytic and non-catalytic pyrolysis which indicates that PCB sample starts to degrade at this temperature.…”

“…DTG curves for catalytic and non-catalytic experiments are shown in Figure 2. As observed in DTG curves, degradation reaction started at temperature of around 240 • C with first maximum degradation peaks at 300 • C. Similar observations are also available in the literature (Alenezi and Al-Fadhli, 2018;Evangelopoulos et al, 2015;Gao et al, 2020;Hao et al, 2014;Kim et al, 2013;Rajagopal et al, 2017;Sun et al, 2012;Xiong et al, 2020). It can be seen from Fig.…”

“…As reported in previous work, during thermal degradation, epoxy resins in PCBs rupture into bisphenol A and tetrabromobisphenol A. The bispheol A's further undergoes degradation to form phenols, phenols derivatives and other small molecules (Rajagopal et al, 2017;Shin et al, 2019;Xiong et al, 2020). In the present oil samples phenolic and aromatic compounds were found to possess a major fraction of oil.…”

“…In the temperature range of 300 to 400 • C, epoxy resins rupture into bisphenol A and tetrabisphenol A. These bisphenols further degrade to form phenols and phenol derivatives and the non-condensable gases like methane and oxygen which was released during cracking reactions were found in the gas samples (Rajagopal et al, 2017;Shin et al, 2019;Xiong et al, 2020). Some other unidentified compounds were also present in gases in a very low quantity.…”

Investigation of the thermal conversion behavior and reaction kinetics of the pyrolysis of bio-based polyurethane: A reference study

“…The peaks located at a wavenumber of 675 cm − 1 and at wavenumbers of 2185 and 2356 cm − 1 were ascribed to the C=O stretching vibration in CO 2 [44]. The occurrence of CO 2 was due to the breaking of urethane bonds in the polyurethane molecules [45]. One minor peak at 1200 cm − 1 was also detected, which was ascribed to the C-O-C asymmetric stretching mode [46].…”