Aromatic enriched oil production via microwave-assisted catalytic co-pyrolysis of baked semen abutilon seeds and waste expanded polystyrene

Abstract

Co-pyrolysis of biomass and plastic waste presents a promising strategy for waste valorization and fuel upgrading. This study explored microwave-assisted co-pyrolysis of expanded polystyrene (EPS) and Semen Abutilon seeds (SAS) using metal oxides (Al₂O₃, CaO), inorganic salts (Na₂CO₃, Fe(NO₃)₃·9H₂O), and zeolite (ZSM-5) as catalysts. The effects of catalyst type, microwave power (460–860 W), and pyrolysis temperature (400–600 °C) on oil yield and composition were evaluated. Using an EPS:SAS blend ratio of 2:1, optimal conditions were identified as 660 W and 500 °C, with CaO emerging as the most effective catalyst, achieving a maximum oil yield (70.53 wt%), thermal efficiency (47.33 %), and recovery efficiency (98.83 %). Compared to non-catalytic pyrolysis (52.02 wt%), CaO and Al₂O₃ increased oil yield by 35.56 % and 25.94 %, respectively, showing positive synergistic effects of 10.13 % and 2.79 %. The use of Fe(NO₃)₃·9H₂O resulted in oil with a high-calorific value (42.53 MJ/kg), while ZSM-5 reduced water content (from 12.60 to 3.37 wt%). Although SAS-derived oil was rich in oxygenated hydrocarbons (74.92 area%), catalytic co-pyrolysis promoted deoxygenation and aromatization reactions, yielding oil high in aromatic hydrocarbons (87.54–91.77 area%). These results confirm SAS and EPS as synergistic feedstocks capable of producing high-quality oils through microwave-assisted co-pyrolysis.