(239e) Sustainable Process Design for Valorization of PET Waste

The global plastic waste crisis has become an urgent environmental issue in recent years, with waste polyethylene terephthalate (PET) being a significant contributor. PET plastic is not only non-biodegradable, but it also has low recycling rates reported across the globe. The European Commission estimated in 2017 that only small fraction of PET plastic generated in the EU ends up in recycling. This ultimately leads to landfilling or incineration of the remaining of waste plastic resulting in increased GHG emissions, marine pollution, and human health risks. To tackle the pollution generated from PET plastic waste it is essential to find strategies to prevent PET from reaching landfills. A promising alternative is the use of upcycling technologies for the valorization of PET. This approach holds the promise of reducing the amount of waste by developing circular economies, and its advocates claim that economic benefits may be harnessed by carefully selecting the upcycling reactions. In recent years a significant amount of attention has been devoted to this problem by experimental groups, and different valorization strategies based on pyrolysis, gasification, and other catalytic reactions have been proposed by Khumthai in Energy Conversion and Management journal. However, in the case of PET little attention has been paid to the issue from the perspective of the process and systems engineering community. Most of the work has been done on a case-by-case basis. That is, for selected upcycling strategies some processes have been developed and their economic and environmental impacts analyzed. However, the current state of the art is much larger than a handful of alternatives, and we need to develop tools enabling the accurate and rapid surveying of this design space such that optimal upcycling strategies are identified based on their economic potential and environmental impacts. To overcome this challenge, in this work, we develop a comprehensive superstructure-based optimization framework for PET upcycling. The superstructure is comprehensive because (1) it considers a representative sample of current PET upcycling technologies and (2) it includes a varied set of possible products (monomers, fuels, and specialty chemicals). The problem is formulated as a multi-objective mixed integer nonlinear program to optimize the net present value and unit life cycle environmental impacts. In our work we discuss optimal upcycling strategies, and the trade-off between environmental and economic objectives.