Circular network design is an emergent approach amongst various sectors in achieving sustainability.Its applications range from food waste mitigation in the food sector to prolonging material life and reducing reliance on virgin resource utilization in the textiles industry. Studies in the literature highlight the positive environmental and economic impacts of implementing a circular design.In this work, we design circular networks for recycling polyethylene terephthalate (PET). PET is the primary plastic product used in single-use plastics and textiles, thus constituting a large share of created plastic and generated waste. The circular PET supply chain includes recycling by mechanical, chemical, and other physical processes; the vast amount of options makes it difficult to assess the best pathway and the extent of material circularity.
This work proposes a superstructure optimization approach to assess circular PET value chains.The superstructure considers fossil and biomass-based feedstocks for producing virgin PET via the two most common linear pathways. Additionally, we implement circularity with mechanical recycling and several chemical recycling options to recover monomers. The superstructure optimization problem is formulated as a mixed integer linear program (MILP). We obtain the Pareto optimal solutions that minimize the cost and consumption of new material. Preliminary results show that a combination of mechanical recycling and alcoholysis provides the circular network with the lowest operational cost.As expected, material circularity is improved by adding chemical recycling processes at the expense of higher costs.
The presentation will discuss the PET linear and circular superstructures, the proposed MILP model, and the Life cycle analysis of the economically-optimal PET circular value chain.
This work is funded by Carnegie Mellon University, the GEM fellowship, and the Thomas and Adrienne Klopack Graduate Fellowship in Engineering.
