Catalytic co-pyrolysis of rice straw and polystyrene for selective production of monocyclic aromatic hydrocarbons

Catalytic co-pyrolysis facilitates the efficient valorization of biomass and plastic waste while significantly boosting the yield of aromatic compounds in the pyrolysis products. In this study, catalytic co-pyrolysis of rice straw (RS) and polystyrene (PS) at a 1:1 mass ratio (designated as RS-PS) was carried out at 700 ℃ and pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) was used for analysis. The catalysts HZSM-5, Co/HZSM-5 and Pr/HZSM-5 were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) for characterization. The characterization analysis indicated that the introduction of Co and Pr did not change the surface functional groups and crystal structure of HZSM-5. The consequence demonstrated that the three catalysts accelerated the generation of monocyclic aromatic hydrocarbons (MAH) and were resistant to the formation of oxygen-containing compounds, and the modification of Co and Pr also inhibited the formation of N-compounds. Compared with HZSM-5 and Co/HZSM-5, Pr/HZSM-5 had better catalytic effect on RS-PS, it had higher selectivity for MAH and inhibited oxygen-containing compounds more thoroughly. When the mass ratio of Pr/HZSM-5 to RS-PS was maintained at 2:1, the MAH yield was the highest (90.47 %), while the formation of polycyclic aromatic hydrocarbons (PAHs) remained comparatively low at 7.07 %. The introduction of Pr metal site, improved the acidity and catalytic performance of HZSM-5 molecular siolites, thereby promoting Diels-Alder reactions between furans and olefins, facilitating aromatization during pyrolysis, and ultimately increasing the MAH content. It also promoted the conversion of phenols, furans and other oxygenated compounds into aromatic hydrocarbons through decarbonylation, decarboxylation, and dehydroxylation reactions, while simultaneously strengthening the suppression of oxygenated compound formation. This study can provide a promising catalytic strategy for the efficient valorization of biomass and plastic waste resources. The introduction of Pr enhanced the Diels-Alder reaction between furans and olefins, promoted the aromatization reaction during the pyrolysis process, and increased the aromatic hydrocarbons content.