NSF Award
2317307
Polyethylene (PE) is one of the most commonly produced plastics, primarily used for plastic bags, containers, bottles, and toys. Currently, over 100 million tons of PE are produced annually, accounting for 34% of the total plastics market. Unfortunately, most PE products are single-use and discarded in landfills, and waste PE contributes to over 50% of the plastics waste stream. The projected 12% annual PE production rate growth combined with the lack of effective recycling options make PE a major environmental concern. To recycle or upcycle waste PE, mechanical disruption, thermochemical treatment, and biochemical conversion processes have been explored, but these methods all ultimately result in low product qualities, inefficient conversion rates to value-added products, and high processing costs. None of the existing PE recycling or upcycling methods alone will likely contribute to a circular plastics economy. The objective of this project is to explore a two-step hybrid oxidative catalytic pyrolysis–biochemical approach to upcycle waste PE into chemical products with significantly higher values. This concept takes advantage of the benefits of both thermochemical (oxidative catalytic pyrolysis) and biochemical (biomanufacturing) methods for plastics upcycling. The proposed technology will lead to reduced waste plastics disposal, mitigating its negative environmental impacts. As UML being one of the Minority Serving Institutions (MSI) in Massachusetts, the project team will recruit students from underrepresented groups from underserved communities of the state to conduct research. Outreach events targeting local high schools and learning-disabled students pursing STEM careers will also be planned via UML’s Biomanufacturing Center and Center for Autism Research and Education, respectively. <br/><br/>A novel hybrid process is proposed to upcycle waste polyethylene (PE) into a series of value-added products. The first step of the proposed hybrid process consists of an oxidative pyrolysis reactor to decompose PE over redox metal oxide or mixed oxide catalysts on porous supports into C5–C20 alkanes, alcohols, aldehydes, and carboxylic acids. The fundamental chemical kinetics associated with reaction pathways on the catalyst surfaces, as well as the effects of species diffusion in the pores, will be quantified. Oxidative pyrolysis will be followed by a biomanufacturing step using an engineered yeast Yarrowia lipolytica to produce value-added platform chemicals such as long-chain diacids (LCDAs) as nylon precursors and triacetic acid lactone (TAL) and phloroglucinol (PG) for a wide spectrum of industrial applications. The research team will identify metabolic pathways leading to high yields of various products and will use reaction engineering principles to overcome mass transfer limitations in bioreactors. The success of this project will pave the way to a new paradigm, enabling future manufacturing of a wide range of strategic platform chemicals, particularly the molecules derived from the omega-oxidation, beta-oxidation, and related metabolic pathways, leading to more energy efficient, economical, and robust valorization of not only waste PE but also other similar waste polyolefins, such as polypropylene (PP) and polystyrene (PS).<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
