Emissions of brominated compounds and polycyclic aromatic hydrocarbons during pyrolysis of E-waste debrominated in subcritical water

Abstract

Degradation of brominated flame retardants present in printed circuit boards (PCBs) was tested using subcritical water in a high pressure reactor. Debromination experiments were carried out in a batch stirred reactor at three different temperatures (225 °C, 250 °C and 275 °C) keeping a solid to liquid (S/L) ratio of PCB:water = 1:5 during 180 min. Results indicated that debromination efficiency was increased with temperature (18.5–63.6% of bromine present in the original PCB was removed). Thermal decomposition of the debrominated materials was studied and compared with that of the original PCB. Thermogravimetric analyses were performed at three different heating rates (5, 10 and 20 K min−1), studying both the pyrolysis (inert atmosphere) and combustion (in air). Pyrolysis runs of the debrominated materials were also performed in a quartz horizontal laboratory furnace at 850 °C, in order to study the emission of pollutants. More than 99% of the bromine was emitted in the form of HBr and Br2. Emissions of polycyclic aromatic hydrocarbons (PAHs) and bromophenols (BrPhs) decreased with the increase in the treatment temperature; naphthalene (10,800–18,300 mg kg−1 original sample) and monobrominated phenols (12.8–16.9 mg kg−1 original sample) were the most abundant compounds.