(566d) Economic and Environmental Investigation of Mechanochemical Technologies for Upcycling of Plastic Waste

The transition to circular economies stands as one of the most prevalent challenges of our times [1, 2]. Chemical recycling methods have emerged as a promising alternative as they allow the breakdown of polymers into their constituent monomers, enabling the material to be fully recycled. However, in contrast to conventional mechanical recycling, the complexity of chemical recycling processes have limited their implementation at the industrial scale [3]. One promising chemical recycling technology is mechanochemical depolymerization because of the high conversion rates achieved under mild conditions [2]. Our previous study indicated that the process can be economically viable for PET recycling at the industrial scale with identified economic metrics comparable to those conventional and alternative technologies [4, 5]. Nonetheless, integrating new technologies into the existing waste management network presents significant challenges because of the multiple stakeholders involved, various processing facilities, alternative options, and products [6].

To address these questions for mechanochemical recycling, this work applies a process system engineering framework that integrates value-chain, technoeconomic and life-cycle analyses. An equation-based formulation is adapted for this purpose, based on a realistic representation of the US recycling industry. The mathematical model is designed to minimize the environmental burden and the associated costs of the value-chain network, subject to constraints related to material balances and product quality requirements. Traditional waste management routes (e.g., landfilling, incineration, mechanical recycling) are incorporated within the superstructure network. Rigorous data from technoeconomic and life cycle analysis for mechanochemical depolymerization are detailed and incorporated within the modeling framework. Sensitivity analyses are performed to assess the impact of different design variables (e.g., efficiencies, economic parameters) to multiple objectives. Centralized as opposed to the existing decentralized market configuration scenarios are also examined. Further, the pareto-optimal solution is identified to discuss the trade-offs between environmental- and cost-friendly solutions for mechanochemistry. Finally, the results are compared with recent studies on competing recycling technologies [7, 8] to holistically assess the benefits and impacts of deploying mechanochemistry at the large scale. In summary, this study presents a computational framework that can be utilized to evaluate the employability of mechanochemical depolymerization, compare alternative pathways, and enable the design of cost-effective closed-loop value chains for waste plastics.

Citations

[1] I. Vollmer et al., "Beyond Mechanical Recycling: Giving New Life to Plastic Waste," Angew Chem Int Ed Engl, vol. 59, no. 36, pp. 15402-15423, Sep 1 2020, doi: 10.1002/anie.201915651.

[2] A. W. Tricker et al., "Stages and kinetics of mechanochemical depolymerization of poly (ethylene terephthalate) with sodium hydroxide," ACS Sustainable Chemistry & Engineering, vol. 10, no. 34, pp. 11338-11347, 2022.

[3] 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.

[4] E. Anglou, Y. Chang, A. Ganesan, S. Nair, C. Sievers, and F. Boukouvala, "Discrete Element Simulation and Economics of Mechanochemical Grinding of Plastic Waste at an Industrial Scale," in Computer Aided Chemical Engineering, vol. 52: Elsevier, 2023, pp. 2405-2410.

[5] E. Anglou et al., "Process development and techno-economic analysis for mechanochemical recycling of poly (ethylene terephthalate)," Chemical Engineering Journal, p. 148278, 2023.

[6] J. Ma et al., "Economic Evaluation of Infrastructures for Thermochemical Upcycling of Post-Consumer Plastic Waste," 2022.

[7] T. Uekert et al., "Technical, economic, and environmental comparison of closed-loop recycling technologies for common plastics," ACS Sustainable Chemistry & Engineering, vol. 11, no. 3, pp. 965-978, 2023.

[8] Y. Luo, E. Selvam, D. G. Vlachos, and M. Ierapetritou, "Economic and Environmental Benefits of Modular Microwave-Assisted Polyethylene Terephthalate Depolymerization," ACS Sustainable Chemistry & Engineering, vol. 11, no. 10, pp. 4209-4218, 2023.