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Superstructure Design of Solvent-Assisted Plastics Recycling Processes
Citation:
Jarrett, B., M. Mackley, L. Clarke, J. Stengel, A. Lehr, E. Aboagye, Gerardo J. Ruiz-Mercado, J. Stanzione, AND K. Yenkie. Superstructure Design of Solvent-Assisted Plastics Recycling Processes. 26th Annual Green Chemistry & Engineering Conference, Reston, VA, June 06 - 08, 2022.
Impact/Purpose:
The harmful effects of plastics on soil, air, and water ecosystems include releasing toxic chemical additives, interference with the food chain, spoiling oceans, and harming biodiversity. Also, 90% of spent plastics found in municipal solid waste (MSW) are either landfilled or incinerated. Plastics release chemical additives during their end-of-life (EoL) pathways. Some of these chemicals negatively affect the environment and human health. Therefore, drastic improvements to the existing EoL plastic stage are needed to minimize plastic waste and its chemical additive release and exposure resulting from MSW. This invited conference presentation describes a superstructure optimization approach for the recovery and recycling of plastic. This research supports decision-making steps to promote a safer EoL plastic stage and support sustainable materials management efforts.
Description:
Despite the extensive history of plastic manufacturing and widespread use, much of this industry's waste goes unrecycled. In 2018, the United States generated over 35.7 million tons of plastic waste, and only 8.4% of that waste was recycled. The remaining 91.6% was either incinerated or disposed of in a landfill. Recycling via conventional mechanical recycling, though cheaper, results in downgraded properties of recycled plastics. Alternatively, chemical recycling presents a promising alternative as it allows for plastics to regain their original properties. To that end, difficult problems posed by plastics entering their end-of-life stage need to be addressed through the investigation of feasible chemical recycling methods. To address this issue, we present a superstructure optimization approach for the recovery and recycling of plastic. With this framework, we categorize and compare different separation technologies based on driving forces, efficiencies, and feed properties, and group them into stages. Not only do we consider the technologies used but also the choice of solvent-types based on their physicochemical properties. Within the superstructure, stages are divided into four stages, namely, impurity removal, recovery, purification, and refinement. Technologies are mathematically modeled in the General Algebraic Modeling Systems (GAMS) software as a mixed-integer nonlinear program (MINLP). Through the implementation of binary variables, which are used for making a “yes” or “no” decision, we can select an optimal path that simultaneously quantifies the cost, recovery, and environmental impact of the recycling process as well as meet quality specifications. To validate the proposed framework, a case study of poly (ethylene terephthalate) (PET) recycling was developed and analyzed. In this case study, ethyl benzoate was used as a solvent for PET dissolution. We can simultaneously quantify the potential environmental advantages of the process along with the cost to obtain PET recovery of up to 80% in addition to solvent recyclability benefits.