2025 Spring Meeting and 21st Global Congress on Process Safety

(177a) Systematic Frameworks for Assessing Circular Supply Chain Networks: Applications to the Polyethylene Terephthalate (PET) Supply Chain

Authors

Ana I. Torres - Presenter, Facultad De Ingeniería Udelar
The appeal of a circular economy (CE) is rooted in the possibility of achieving lower environmental impact at minimal expense. However, several challenges prevent practical applications of a circular economy. Our work applies optimization and system dynamics (SD)-based modeling approaches for informed decision-making regarding CE strategies.

In the first part of the talk, we pose and solve a multi-objective problem to analyze the feasibility of a circular PET network over the conventional linear counterpart. Here, we build a holistic process flowsheet (superstructure) of current and potential processes encompassing the PET supply chain, from raw material extraction to processes handling end-of-life (EOL) products. This consideration includes conventional fossil-based processes, biomass-based processes, current and emerging recycling technologies, and existing EOL treatment pathways (landfilling and waste-to-energy). Recycling technologies include mechanical recycling, pyrolysis, hydrolysis, methanolysis, and glycolysis. We formulate a multi-objective optimization problem to find the pathways that minimize the annualized network cost (CapEx and OpEx), greenhouse gas (GHG) emissions, and net virgin material consumption. From this assessment, we determine that a circular PET network, built from the ground up, is favorable over a linear network for all three design objectives.

In the second part of the talk, we address the need for generic mathematical models for circular initiatives incorporating the time dimension and the combined effects of different SC actors. We use system dynamics (SD) to develop a generic framework for the dynamic modeling of CE networks. We divide the network into five agents: a manufacturer, a consumer, a material recovery facility (MRF), a recycling facility, and the Earth. We apply this framework to the case study of the PET SC. Given the current recycling infrastructure in the US, we find that “slow-down-the-loop” initiatives (i.e., those that extend product use time through demand reduction or reuse) are more effective than “close-the-loop” initiatives (i.e., those that reintroduce product to the supply chain through recycling) for improving circularity and minimizing environmental impact.