Two-stage co-pyroysis behaviors and product distribution of Enteromorpha and marine waste polypropylene catalyzed by Cu/HZSM-5

A two-stage co-pyrolysis approach was developed for the efficient utilization of marine waste plastics and biomass, with a focus on the influence of biomass components. HZSM-5 was modified with Cu via wet impregnation and applied in the catalytic co-pyrolysis of Enteromorpha and polypropylene under varying catalyst-to-feedstock ratios. The Cu/HZSM-5 catalyst was characterized using X-ray diffraction (XRD), N2 adsorption, and scanning electron microscopy (SEM). The results showed that Cu modification preserved the HZSM-5 framework while increasing pore size, enhancing catalytic cracking efficiency. Thermogravimetric and kinetic analyses revealed that Cu/HZSM-5 lowered the pyrolysis temperature, reduced residues, improved synergy, and decreased activation energy without altering the reaction mechanism. The catalyst significantly reduced oxygenated compounds and enhanced the formation of aromatic hydrocarbons in the oil products, reaching a maximum aromatic content of 90.20 % at a 6:5 catalyst-to-feedstock ratio in the second stage. Under the same conditions, hydrogen production in the gas phase also peaked at 47.91 %. Increased catalyst dosage decreased carbon and hydrogen content in the char while raising oxygen and nitrogen levels, with a higher H/C ratio mitigating char aromatization and densification. A reaction mechanism for Enteromorpha and polypropylene over Cu/HZSM-5 was proposed. This study provides insights into the catalytic co-pyrolysis of marine waste plastics and biomass with complex compositions.