(61c) Simulation and Optimization of the Supply-Chain of Plastic Recycling with Environmental Considerations

Industrial economies have historically relied on linear manufacturing processes whereby raw materials are transformed into useful products and later discarded as waste [1]. However, this economic structure has a substantial impact on natural resource depletion, particularly in the case of plastics [2]. As a result, there is growing interest in transitioning towards a circular economic model that emphasizes the recycling of waste plastic [3]. While mechanical recycling has been the primary method for plastic recycling, chemical recycling has recently emerged as a promising alternative as it allows the breakdown of polymers into their constituent monomers, enabling the material to be fully reused without material degradation [2-4]. In contrast to conventional mechanical recycling, the complexity of chemical recycling processes has limited their implementation at the industrial scale. To successfully transition to a circular economy of plastics, it is crucial to assess their environmental impact and minimize their carbon footprint [5].

This work applies a process system optimization framework to analyze the transition towards a circular economy for plastics, while minimizing the associated environmental impacts. We map the supply chain of plastic waste recycling through the various waste management practices in the US [3, 5, 6] (e.g., landfilling, incineration, mechanical and chemical recycling). An equation-based formulation is adapted for this purpose, based on a realistic representation of the US recycling industry. The model is designed to minimize the cost and the environmental impacts, subject to constraints related to material balances and product quality requirements. While the presented case study focuses on the recycling of PET waste, the framework can be extended to include other types of plastic waste feedstocks. A broad range of chemical recycling process types that have recently received increasing attention in the literature, such as hydrolysis, solvolysis, methanolysis, and mechanocatalysis are incorporated. Sensitivity analyses are performed to examine the impact of different circularity indices and process maturities on the plastic supply chain. Through our formulation, the Pareto optimal solution is identified to assess the trade-offs between economically sound and environmentally friendly network configurations. In summary, this study showcases the development of a decision-making tool to assess the plastic recycling industry at the supply-chain level. We anticipate that the results of this work will offer valuable insights for policymakers, industry stakeholders, and researchers in the quest for more sustainable recycling processes that minimize the environmental impact of plastics.

Citations

[1] S. Avraamidou, S. G. Baratsas, Y. Tian, and E. N. Pistikopoulos, "Circular Economy - A challenge and an opportunity for Process Systems Engineering," Computers & Chemical Engineering, vol. 133, pp. 106629-106629, 2020, doi: https://doi.org/10.1016/j.compchemeng.2019.106629.

[2] A. W. Tricker et al., "Stages and Kinetics of Mechanochemical Depolymerization of Poly (ethylene terephthalate) with Sodium Hydroxide," ACS Sustainable Chemistry & Engineering, 2022.

[3] H. Li et al., "Expanding plastics recycling technologies: chemical aspects, technology status and challenges," Green Chemistry, 2022.

[4] Y. Jiang et al., "Economic and environmental analysis to evaluate the potential value of co-optima diesel bioblendstocks to petroleum refiners," Fuel, vol. 333, p. 126233, 2023/02/01/ 2023, doi: https://doi.org/10.1016/j.fuel.2022.126233.

[5] U. S. Chaudhari et al., "Systems analysis approach to polyethylene terephthalate and olefin plastics supply chains in the circular economy: A review of data sets and models," ACS Sustainable Chemistry & Engineering, vol. 9, no. 22, pp. 7403-7421, 2021.

[6] J. Ma et al., "Economic evaluation of infrastructures for thermochemical upcycling of post-consumer plastic waste," Green Chemistry, vol. 25, no. 3, pp. 1032-1044, 2023.