Toward Building Circularity in Sustainable Plastic Waste Conversion

The escalating levels of plastic waste have created an urgent need for sustainable recycling methods aligned with the circular economy (CE) goals. Leveraging process systems engineering (PSE) models, which facilitate sustainability-driven problem-solving, this work proposes a comprehensive mathematical framework optimizing diverse recycling technologies─pyrolysis, gasification, mechanical recycling, and incineration─balancing economic feasibility and CE contributions. Recognizing the versatility of chemical recycling derivatives, this model explores their applications in methanol and ammonia synthesis, hydrogen production, and more, emphasizing plastic waste’s potential to yield energy and valuable products through open- and closed-loop pathways. A novel CE metric was introduced to assess recycling pathways across critical indicators. An illustrative case study of 20 scenarios highlights pyrolysis refinery technology as promising sustainable fuel and olefin production, tripling profitability, and improving circularity by over 25%. Combining methanol synthesis and pyrolysis refinery maximizes circularity to 44% enhancement. The flexible weight allocation for the individual circularity metrics during optimization highlights the emphasis on tailored solutions aligned with system-specific needs. Comparative analyses between plastic waste and conventional feedstocks unveil a cost-effective landscape that is dependent on the product. Capacity-level sensitivity analysis consistently demonstrates the superior performance of optimal solutions compared with the base case regarding circularity and profitability.