Low-Carbon Thermochemical Upcycling of Plastic Waste with Steel Slag at Elevated Temperatures

Plastic waste (PW) poses a severe global environmental threat, with thermochemical upcycling offering a promising solution. However, conventional pyrolysis faces challenges in terms of energy intensity and catalyst dependency. This study proposes a synergistic approach using high-temperature steel slag (SS) as both a heat carrier and a catalyst for low-carbon PW upcycling. We investigate the co-pyrolysis of four major plastics─HDPE, PP, PS, and PET─with SS and its primary oxides (CaO, MgO, SiO2, Al2O3, Fe2O3, TiO2) via TG-FTIR-GC/MS. Results demonstrate that SS significantly alters product selectivity: PS pyrolysis yields >90% aromatic hydrocarbons (mainly styrene), PET decomposition shifts from acids to acetaldehyde/CO2, while HDPE/PP primarily generate alkenes/alkanes. Kinetic analysis (Freeman-Carroll method) confirms reduced activation energies (e.g., 208 kJ·mol–1 for PET/SS vs 318 kJ·mol–1 for pure PET). Crucially, waste heat from SS (1173–1673 K) exceeds pyrolysis energy demands by 41–73 MWh/t-SS, enabling net energy recovery. This work validates SS as a sustainable dual-functional material for scalable PW valorization.