(630b) A Cradle-to-Gate Life Cycle Assessment of Mechanochemical Recycling of Poly(ethylene Terephthalate) Waste

The increased accumulation of plastic waste in landfills and the natural environment poses significant environmental and human health challenges [1, 2]. In response, chemical recycling technologies are being investigated as promising recycling solutions. However, in contrast to conventional mechanical recycling, the complexity of chemical recycling processes have limited their wider implementation [3]. Mechanochemistry, a solvent-free process that utilizes mechanical energy to drive chemical reactions, has emerged as a promising chemical recycling technology [4, 5]. Our previous study indicated that this process can be economically viable for recycling poly(ethylene) terephthalate (PET) at industrial scale with profitability metrics comparable to those of conventional and alternative technologies [6].

In this study, we present a comprehensive life cycle assessment (LCA) of mechanochemical recycling of PET waste, starting with mixed plastic as feedstock and resulting in recycled PET resins. We quantify the contributions of individual processing steps and compare the overall environmental impacts of recycled PET to those of virgin PET production and alternative recycling methodologies. Our results indicate that mechanochemical recycling outperforms virgin PET production in all impact categories, with primary environmental burdens attributed to utilities and specific raw materials used in the process. Sensitivity analyses were also conducted, varying key process design parameters, energy sources and by-product treatment methods, revealing that the mechanochemical route exhibits lower environmental impacts across most indicators, even when considering worst-case scenarios. Overall, this study provides a detailed environmental evaluation of the mechanochemical recycling route, further informing the development of circular pathways for plastics.

References

1. Vollmer, I., et al., Beyond Mechanical Recycling: Giving New Life to Plastic Waste. Angew Chem Int Ed Engl, 2020. 59(36): p. 15402-15423.
2. Geyer, R., J.R. Jambeck, and K.L. Law, Production, use, and fate of all plastics ever made. Science Advances, 2017. 3(7): p. 25-29.
3. Chaudhari, U.S., 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, 2021. 9(22): p. 7403-7421.
4. Tricker, A.W., et al., Stages and kinetics of mechanochemical depolymerization of poly (ethylene terephthalate) with sodium hydroxide. ACS Sustainable Chemistry & Engineering, 2022. 10(34): p. 11338-11347.
5. Štrukil, V., Highly Efficient Solid‐State Hydrolysis of Waste Polyethylene Terephthalate by Mechanochemical Milling and Vapor‐Assisted Aging. ChemSusChem, 2021. 14(1): p. 330-338.
6. Anglou, E., et al., Process development and techno-economic analysis for mechanochemical recycling of poly (ethylene terephthalate). Chemical Engineering Journal, 2023: p. 148278.