A Comparative Framework for Plastic-to-Plastic Recycling Technologies

The United States generates an estimated 42 million metric tons of plastic waste each year – the most of any country – resulting in pollution and lost chemical and energetic resources. Recycling strategies will play a pivotal role in recapturing this wasted material and ensuring resilient polymer life-cycles. Researchers are actively exploring chemical recycling techniques including pyrolysis, gasification, methanolysis, glycolysis, enzymatic depolymerization and more to supplement traditional mechanical recycling. As the plastic recycling landscape expands, it is crucial to implement these novel technologies in an environmentally and economically beneficial manner, yet there is currently no framework to guide the impartial and holistic making of such decisions.<br/>This work utilizes a rigorous modelling framework combining techno-economic, life cycle and material flows assessments to quantitatively compare current and next generation recycling technologies. The scope includes mechanical, pyrolysis, gasification, depolymerization and dissolution recycling for the top four most widely utilized polymers – high and low density polyethylene (HDPE, LDPE), polypropylene (PP) and polyethylene terephthalate (PET) – as well as biopolymers such as polylactic acid (PLA). The technologies are assessed based on a series of environmental (greenhouse gas emissions, energy use, water and land use, toxicity, waste production), economic (minimum selling price) and technical (technology readiness level, material quality, material retention, impurity and pigment tolerances) metrics to capture key benefits, disadvantages and trade-offs. Multi-criteria decision analysis is subsequently used to highlight preferential applications for the different recycling technologies, and sensitivity analysis allows for the identification of future research directions for improving the viability of these techniques. Through its broad scope, this work provides a baseline for decision-making in the current and upcoming plastic recycling landscape, with an added potential to encompass future recycling breakthroughs.