Enhanced production of phenol and debromination by co-pyrolysis of the non-metallic fraction of printed circuit boards and waste tires

Abstract

The thermal treatment of plastic solid wastes has been widely considered as an environmentally friendly process for converting the inherent polymeric units into fuel or chemicals. In the proposed study, the co-pyrolysis of printed circuit boards (PCB) and waste tires (WT) was performed using thermogravimetry (TG) and pyrolysis-gas chromatography/mass spectrometry. PCB and WT were blended in various ratios to investigate synergistic effects on the product characteristics and heteroatom migration. The TG results show that the PCB/WT blends shifted the PCB decomposition peak from 325 to 357 °C but accelerated the WT decomposition at the later stages. The pyrolysis products of PCB consisted of phenolic and brominated compounds, whereas olefins were the predominant products during WT pyrolysis. The addition of WT significantly improved the formation of small phenolics at the expense of bisphenol A, leading to a 40–51% and 24–92% increase in the production of phenol and p-isopropylphenol, respectively. Meanwhile, the production of major compounds from WT pyrolysis, including isoprene and D-limonene, was significantly reduced, indicating that the H-donor sources in WT could be favorable for further decomposing PCB, while improving the phenol production. Furthermore, the co-pyrolysis of PCB and WT resulted in a 26–47% and 50–59% decrease in tetrabromobisphenol A and benzothiazole production, respectively, indicating the excellent removal of toxic compounds. Characterization of the pyrolytic char indicated that co-pyrolysis was beneficial for transforming sulfur compounds into sulfates, whereas the addition of 75% WT was able to capture 12 times the amount of bromine in the char. The results suggest that the co-pyrolysis of PCB and WT can be a potential treatment to increase the production of phenol in oils with a low bromine content.