Systems Analysis Approach to PET and Olefin Plastics Supply Chains in the Circular Economy

Plastic waste has become a global crisis on our planet. Most of the plastic waste generated in the U.S. was landfilled (~76%) and only a small fraction was recycled (~9%) in 2018 ¹. Of this total plastic waste generated, polyethylene terephthalate (PET) and polyolefins such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) represent a significant portion (~80%) of valuable plastic waste stream. The current plastic linear take-make-dispose system in the U.S. represents not just environmental threat but also an economic loss of ≈ $10 billion/year of embodied value ending up in landfills ². Therefore, a systems approach is needed to tackle this plastic waste crisis and move towards circular economy. However, the environmental, economic, and social impacts of implementing a circular economy in plastic waste supply chains are still lacking, and trade-offs among these impacts at the systems level are still unknown.

To address this research gap, our study presents a novel framework called a ‘systems analysis framework for PET and olefin plastics in a circular economy’ ³. This framework identifies different processes involved in a plastic waste supply chain and quantifies the environmental, economic and social impacts of plastic waste in a circular economy. The presented framework can address many different research questions such as, but are not limited to:

• How would the optimized material flow of plastics look like in a future circular economy with minimum environmental impacts, when compared with the linear economy?
• What combinations of recycling technologies are needed to achieve a system with minimum energy consumption and environmental impacts?
• What are the environmental and economic trade-offs of implementing a circular economy at systems level, when compared with linear economy?
• What unit operations within the various chemical recycling technologies for PET and olefin plastics consume the most energy and emit most pollution?
• How would process level changes (e.g. process intensification, energy integration) affect the economic and environmental performance of the chemical recycling processes?

The first research objective of this study was to identify the availability and quality of datasets, process models, and knowledge gaps associated with plastic waste supply chain processes. The second research objective of this study was to showcase an application of the presented framework by conducting a preliminary systems analysis of PET bottles in a circular economy to address some of the research questions highlighted above. For this research purpose, we developed a simple model that utilized a linear programming optimization method to minimize environmental impacts of implementing a circular economy in a PET bottle supply chain. This model enables system-level understanding of the causes of greenhouse gas (GHG) emissions and interaction among the system processes. The key result from our optimization model indicated that a combination of both mechanical and chemical recycling technologies is needed to achieve a system with least GHG emissions, specifically reductions of 24% when compared with the linear economy ⁴.

References

1. USEPA. National Overview: Facts and Figures on Materials, Wastes and Recycling. 2019. Available at: https://www.epa.gov/sites/production/files/2020-11/documents/2018_tables_and_figures_fnl_508.pdf (Last accessed: March 29, 2020).

2. Sherwin, G. Closed Loop Partners- The Circular Shift: Four Key Drivers of Circularity in North America. 2020. Available at: https://www.closedlooppartners.com/closed-loop-partners-launches-report-on-unprecedented-shifts-in-the-circular-economy-in-north-america/ (Last accessed: March 29, 2020).

3. Shonnard, D. R.; Tipaldo, E.; Thompson, V.; Pearce, J. M.; Caneba, G. T.; Handler, R., Systems analysis for PET and olefin polymers in a circular economy. Procedia CIRP 2019, 80, 602-606, DOI 10.1016/j.procir.2019.01.072.

4. Chaudhari, U.; Lin Y.; Thompson V.; Hander R.; Joshua J.M.; Caneba G.; Muhuri P.; Watkins D.; Shonnard, D., Systems analysis approach to PET and olefin plastics supply chains in the circular economy: A review of Datasets and Models. ACS Sustainable Chemistry and Engineering (Awaiting final decision), 2021.