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A successful collaboration involving a trio of research institutions has yielded a roadmap toward an for using enzymes to recycle plastics.

The researchers, from the National Renewable Energy Laboratory (NREL), the University of Massachusetts Lowell, and the University of Portsmouth in England, on the biological engineering of improved PETase enzymes that can break down polyethylene terephthalate (PET). With its low manufacturing cost and excellent material properties, PET is used extensively in single-use packaging, soda bottles, and textiles.

The new study, published in Nature Chemical Engineering, combines previous fundamental research with advanced chemical engineering, process development, and techno-economic analysis to lay the blueprints for enzyme-based PET recycling at an industrial scale.

While current methods exist for recycling PET, they are often incompatible with typical low-quality plastic waste. A potential solution lies with enzymes, which can selectively break down PET, even from contaminated and colored plastic waste streams.

The researchers' new design focuses on improvements at each stage of the process, from plastic deconstruction with enzymes, to efficient recovery of the resulting building blocks, or monomers. These monomers can be used to make new plastic or upcycled to generate higher value materials, saving energy and resources.

The key to making such a process viable is to reduce the energy and cost requirements, which in turn yields a cheaper product. The team has achieved this by innovations that change the reaction conditions and separations technologies to reduce expensive acid and base additions by more than 99%, reduce annual running costs by 74%, and reduce energy use by 65%.

"Despite the advantages of enzymatic recycling for complex plastic waste streams, the field has encountered multiple challenges for realistic implementation," said Gregg Beckham, a senior research fellow at NREL and co-lead of the study. "Here we have taken a multidisciplinary approach that incorporates multiple innovations to realize an economically viable and scalable process."

The modeled cost of the resulting enzyme-recycled PET are now below those of U.S. domestic virgin PET ($1.51/kg vs. $1.87/kg), making this an attractive option for industry investment and scale-up.

According to a 2022 NREL study, 86% of plastics were landfilled in the United States in 2019—materials with enough embodied energy to supply 5% of the power needs of the U.S. transportation sector. With global plastic production anticipated to increase between 2-4 times current levels by 2050, recovering and valorizing more postconsumer plastics is an opportunity to recapture that energy for domestic materials manufacturing.

"We see a significant opportunity to design, test, and optimize new recycling technologies to efficiently valorize postconsumer plastics into feedstock for new materials," said Natasha Murphy, a biochemist at NREL and co-first author of the new paper.