Coupling of Steam and CaO Derived from Oyster Shells in the Pyrolysis of Waste Poly(ethylene terephthalate) for the Selective Production of Aromatic Hydrocarbons

In light of escalating environmental concerns, the development of innovative and effective recycling techniques for poly(ethylene terephthalate) (PET) waste is crucial for sustainable waste management. In this study, an active CaO was prepared from oyster shells (AOSC) and utilized in the selective conversion of PET into aromatic hydrocarbons (benzene and biphenyl) by coupling steam-assisted prepyrolysis and CaO-catalyzed pyrolysis. The physicochemical properties of AOSC and commercial CaO were characterized. The influences of the catalyst preparation methods, catalytic pyrolysis temperatures (550–750 °C), and AOSC/PET ratios (2–10) on the formation of benzene and biphenyl were systematically investigated using a lab-scale pyrolysis apparatus. The results unveiled that AOSC possessed high specific surface area, large pore volume, and abundant basic sites, which were 2.78, 8.7, and 1.62 times higher than those of commercial CaO, respectively. At the steam-assisted prepyrolysis temperature of 300 °C, catalytic pyrolysis temperature of 650 °C, and AOSC/PET ratio of 6, the yields of benzene and biphenyl could reach 27.34 and 2.97 wt %, significantly higher than those obtained from noncatalytic PET pyrolysis (5.67 and 1.22 wt %). In addition, the spent catalysts were also characterized, demonstrating that AOSC exhibited good anticoke performance with a lower coke amount of 10.37 mg/g compared to that of commercial CaO (20.24 mg/g) after pyrolysis. This study not only lays the foundation for sustainable management of waste PET but also demonstrates the potential of utilizing waste seashells to produce valuable resources, thereby promoting a circular economy and mitigating environmental pollution.