(15a) Designing a Sustainable Supply Chain for Polyolefins Waste Management: A Multi-Objective Optimization Approach

Oluwadare Badejo, Borja Hernández , Marianthi Ierapetritou^*

Department of Chemical and Biomolecular Engineering, University of Delaware, 150 Academy St, Newark, DE 19716, United States.

Plastics have had a huge impact on modern culture because they have their outstanding properties (e.g., flexibility or hardness at low density) with low production costs. It is predicted that by the year 2050, mankind will have produced more than 30 billion tons of plastics, up from the current annual rate of production of over 380 million tons^1,2. Out of all the plastics produced, a staggering 72% of them are disposed into landfills or mismanaged. This fraction does not generate any value to the plastic waste and it causes significant impacts on the environment³.

In order to response to this plastic waste crisis, significant efforts have focused on enhancing the efficiency and scalability of upcycling technologies in the last years.^4,5 The implementation of these technologies together with a growing amount of plastic waste to be treated, require the adequate design of a supply chain since it can suppose up to 50% of the recycling or upcycling of the plastic waste⁶. This study aims to address this challenge by proposing a sustainable supply chain model for plastic waste management that considers both economic and environmental objectives. Specifically, a three-echelon supply chain model is proposed, which includes plastic collection sites, facilities, and consumers. The study covers a broad geographic area that spans 319 counties across eight different states in the United States and examines the feasibility of seven different technologies that yield a total of six specific products. The consumers in the proposed model include refineries and cities located in close proximity to the waste management sites.

We develop a mixed integer linear programming model that optimizes the location of conversion technologies, the technology type, and the capacity of the conversion technology. Additionally, we consider transportation modes, including gasoline, electrical, and hydrogen trucks. For this study we explore the multi-objective solution space using the epsilon constraint method to identify the solutions that balance economic and environmental benefits.

Our results show that pyrolysis is the most profitable technology, while mechanical recycling and hydrocracking are preferred for achieving the best environmental outcomes. Furthermore, we find that the transportation mode selection varies across the Pareto frontier, and the choice of which Pareto solution to implement will depend on policies that balance economic and environmental considerations. Overall, our study provides insights into how supply chain design can contribute to sustainable plastic waste management.

Bibliography

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(4) Santander, P.; Cruz Sanchez, F. A.; Boudaoud, H.; Camargo, M. Closed Loop Supply Chain Network for Local and Distributed Plastic Recycling for 3D Printing: A MILP-Based Optimization Approach. Resources, Conservation and Recycling 2020, 154, 104531. https://doi.org/10.1016/j.resconrec.2019.104531.

(5) Bing, X.; Bloemhof-Ruwaard, J. M.; van der Vorst, J. G. A. J. Sustainable Reverse Logistics Network Design for Household Plastic Waste. Flex Serv Manuf J 2014, 26 (1), 119–142. https://doi.org/10.1007/s10696-012-9149-0.

(6) Hernández, B.; Kots, P.; Selvam, E.; Vlachos, D. G.; Ierapetritou, M. G. Techno-Economic and Life Cycle Analyses of Thermochemical Upcycling Technologies of Low-Density Polyethylene Waste. ACS Sustainable Chem & Engineering. 2023, Under review.