BOTTLE analysis shows enzyme-based PET recycling more energy efficient
Researchers in the Bio-Optimized Technologies to keep Thermoplastics out of Landfills and the Environment (BOTTLE) Consortium, including from the US Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL) and the University of Portsmouth in the UK, have identified using enzymes as a more sustainable approach for recycling polyethylene terephthalate (PET), a common plastic in single-use beverage bottles, clothing, and food packaging.
PET ranks among the most abundantly produced synthetic polymers in the world, with 82 million tonnes produced annually; roughly 54 percent of PET is used in the manufacture of textiles for clothing and fibers for carpets.
An analysis by researchers in the BOTTLE Consortium shows enzyme-recycled PET has potential improvement over conventional, fossil-based methods of PET production across a broad spectrum of energy, carbon, and socioeconomic impacts.
The concept, if further developed and implemented at scale, could lead to new opportunities for PET recycling and create a mechanism for recycling textiles and other materials also made from PET that is traditionally not recycled today.
From all the plastics that were produced since the 1950s, less than 10 percent of it has ever been recycled. Most waste plastics end up in landfills, said Avantika Singh, a chemical engineer at NREL and first author of a new paper outlining the path toward enzyme-based recycling
The paper, “Techno-economic, life-cycle, and socioeconomic impact analysis of enzymatic recycling of poly(ethylene terephthalate),” appears in the journal Joule. Her co-authors are Nicholas Rorrer, Scott Nicholson, Erika Erickson, Jason DesVeaux, Andre Avelino, Patrick Lamers, Arpit Bhatt, Yi Min Zhang, Greg Avery, Ling Tao, Alberta Carpenter, and Gregg Beckham, all from NREL; and John McGeehan and Andrew Pickford of the University of Portsmouth’s Centre for Enzyme Innovation in the United Kingdom, who are also members of BOTTLE.
BOTTLE is striving to address the problem of plastic pollution with two innovative approaches: (1) develop energy-efficient, cost-effective, and scalable recycling and upcycling technologies and (2) design modern plastics to be recyclable by design.
Enzymatic recycling concept
The new research paper addresses the challenge of plastic recyclability. The researchers modeled a conceptual recycling facility that would take in a fraction of the 3 million tonnes of PET consumed annually in the United States. The enzymatic recycling process breaks down PET into its two building blocks, terephthalic acid (TPA) and ethylene glycol.
Compared to conventional fossil-based production routes, the research team determined the enzymatic recycling process can reduce total supply-chain energy use by 69 percent–83 percent and greenhouse gas (GHG) emissions by 17 percent–43 percent per kilogram of TPA.
Additionally, an economy-wide comparison of virgin TPA and recycled TPA in the United States shows that the environmental and socioeconomic effects of the two processes are not distributed equally across their supply chain.
The proposed recycling process can reduce environmental impacts by up to 95 percent, while generating up to 45 percent more socioeconomic benefits, including local jobs at the material recovery facilities.
The study also predicts that enzymatic PET recycling can achieve cost parity with the production of virgin PET, thus highlighting the potential for this enzyme technology to decarbonize PET manufacturing, in addition to enabling the recycling of waste PET-rich feedstocks, such as clothing and carpets.
That’s one of the biggest opportunities. If we can capture that space—textiles, carpet fibers, and other PET waste plastics that are not currently recycled—that could be a true game-changer, Avantika Singh said.
This research is funded by DOE’s Advanced Manufacturing Office and the Bioenergy Technologies Office. The work was done as part of the Bio-Optimized Technologies to keep Thermoplastics out of Landfills and the Environment (BOTTLE) Consortium.
NREL is the DOE’s primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by the Alliance for Sustainable Energy, LLC.