Upcycling of Mixed Polyethylene Terephthalate/Polypropylene Plastic Waste Into High-Value Aromatics Through Catalytic...

Catalytic copyrolysis of mixed plastic waste presents an attractive route for sustainable chemical recovery from difficult-to-recycle polymers. In this study, we investigated the aromatic product distribution from thermal and catalytic copyrolysis of polyethylene terephthalate (PET) and polypropylene (PP) using Py-GC-MS/FID. The synergistic interaction between PET and PP was minimal under noncatalytic copyrolysis. In contrast, HY and HZSM-5 zeolites significantly upgraded the pyrolysis vapors by enhancing aromatic formation during copyrolysis. Specifically, HZSM-5 exhibited a high selectivity toward benzenes and napthalenes, whereas HY favored the formation of value-added oxygen-containing aromatics such as benzaldehyde. Further, the intrinsic interaction was elucidated for the catalytic copyrolysis. The formation of alkylbenzenes and simple polycyclic aromatic hydrocarbons during catalytic copyrolysis over both catalysts showed a positive synergistic effect, which was ascribed to alkylation reaction and hydrocarbon pool mechanism. In the presence of HY, aromatization during PP cracking generated substantial hydrogen, which stabilized PET-derived aromatic radicals and reduced catalyst coking, and thereby increased the detectable volatiles. This resulted in a positive synergistic effect on all aromatics, with benzaldehyde showing a particularly notable increase. This work deepens the understanding of the catalytic copyrolysis mechanism and supports its potential in upcycling mixed plastic waste into high-value aromatics.