Thermal depolymerization of polyethylene terephthalate waste and its use in coal-blending coking

This work proposed a strategy to improve the caking index of polyethylene terephthalate (PET) waste, in which low-temperature pyrolysis treatment (LTPT) was used to depolymerize PET waste. The mechanism of G modification was revealed combining thermogravimetric (TG) analysis, Fourier transform infrared spectroscopy, pyrolysis-gas chromatography with mass spectrometric detection, and solid-state ¹³C nuclear magnetic resonance spectroscopy. Furthermore, crucible coking experiments were also conducted using industrial coal mixture and treated PET with the optimum G (PET300) or raw PET to evaluate the applicability of PET waste in coal-blending coking. According to characterization results of coke reactivity (CR), coke strength after reaction (CSR) indices, TG-related curves, pore volumes, and Raman spectra of the resultant cokes, LTPT could greatly increase the G of PET, and the optimum temperature was 300 °C. Specifically, compared with the coke obtained from the blend with PET, the CR of the coke produced from the blend with PET300 decreased by 4.9%, whereas the CSR of the increased by 7.4%, suggesting that LTPT could increase the proportion of PET used for coal-blending coking. The improvement in G is attributed to the changes in C‒O/C=O ratio, aliphatic H and aromaticity caused by LTPT.