Pyrolysis of electronic waste and their mixtures: Kinetic and pyrolysate composition studies

Abstract

Electronic waste (e-waste) constitutes an important component of solid waste, and recovering valuable chemicals and resources from it holds a high priority in solid waste management. The various chemical functionalities present in the organic fraction of e-waste can be converted to valuable chemicals and fuel molecules by pyrolysis process. In this study, non-isothermal pyrolysis of waste printed circuit board (PCB), waste keyboard keys (KB), and their equal composition mixture is conducted in a thermogravimetric analyzer at different heating rates. The kinetic analysis was carried out using isoconversional method of Vyazovkin and the multi-Gaussian distributed activation energy model (DAEM). The average apparent activation energies of pyrolysis of PCB, PCB: KB, and KB, determined using the Vyazovkin method, were 188.4, 167.6, and 169 kJ mol−1, respectively. The apparent activation energy determined using the DAEM varied in a wide range owing to the decomposition of multiple pseudo-components. Analytical pyrolysis coupled with gas chromatograph/mass spectrometer (Py-GC/MS) was used to identify the pyrolysates from PCB, KB, and their mixtures at 500 °C. The major pyrolysate functional groups from PCB were phenolic derivatives (36%), oxygenates (26%), and phenyl phosphates (14.4%), while KB pyrolysis yielded aromatics (52%) containing styrene as the major compound. Pyrolysis of mixtures resulted in a net increase in the selectivity to aromatics with a concomitant decrease in oxygenates suggesting dehydration and decarboxylation to be the major reactions. A significant amount of nitriles was produced from the pyrolysis of mixtures owing to the decomposition of acrylonitrile-butadiene-styrene plastic that constitutes KB.