A team of international scientists has unveiled a breakthrough recycling process that could dramatically reduce the financial and environmental toll of PET plastic, the most common material in bottles and food containers, potentially transforming how the world handles its plastic waste.
The new method, led by the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) and including Professor Andrew Pickford , the Director of the Centre for Enzyme Innovation (CEI) at the University of Portsmouth, introduces a series of innovations that charts a path to making future enzymatic recycling of PET not only environmentally sustainable but also cheaper than producing new plastic from fossil fuels.
The findings, published in Nature Chemical Engineering , show the new process cuts greenhouse gas emissions by nearly half and reduces operating costs by 74 per cent compared to previous techniques. One of the most significant advances in the study involves replacing the base sodium hydroxide with ammonium hydroxide, a subtle chemical switch that unlocked an important change.
Sometimes, the key to a global challenge lies in rethinking a single chemical. By choosing a different base, one that could be recycled within the process, we managed to close a loop and significantly improve both the sustainability and the economics of the system.
Professor Andrew Pickford, Director of the Centre for Enzyme Innovation (CEI)
"Sometimes, the key to a global challenge lies in rethinking a single chemical," explained Professor Pickford. "By choosing a different base, one that could be recycled within the process, we managed to close a loop and significantly improve both the sustainability and the economics of the system."
Ammonium hydroxide not only maintained the pH required for enzymatic PET breakdown, but allowed for in-process regeneration of the base via thermolysis of the breakdown product, nearly eliminating the use of fresh acid and base chemicals. The study found the process adjustments reduced expensive acid and base additions by over 99 per cent, reduced annual running costs by 74 per cent, and reduced energy use by 65 per cent.
The new process addresses long-standing challenges in enzymatic recycling. While mechanical recycling is energy efficient, much of the PET waste stream - such as coloured plastics, thermoforms, and textile fibres - is unsuitable for it. Enzymatic recycling offers a way to break PET down into its basic chemical components, but until now it has faced prohibitive costs and environmental downsides.
Professor John McGeehan, who recently joined the NREL team from the University of Portsmouth, said: "I am delighted to be part of a team that is dedicated to translate fundamental science towards real-world application and look forward to working closely between NREL and our industry partners to accelerate the design and construction of the first US enzymatic plastic recycling plants."
Dr Gregg Beckham, co-lead of this study from NREL added: "Despite the advantages of enzymatic recycling for complex plastic waste streams, the field has encountered multiple challenges for realistic implementation. Here we have taken a multidisciplinary approach that incorporates multiple innovations to realize an economically viable and scalable process."
In technical terms, using ammonium hydroxide allows for the production of diammonium terephthalate, which can then be broken down through a process called thermolysis to regenerate ammonia and produce pure terephthalic acid, one of the two key PET building blocks. This means the base can be reused indefinitely, vastly reducing waste and raw material input.
Alongside the ammonia-based innovation, the researchers optimised the pre-treatment of plastics via extrusion and quenching, enabling complete depolymerisation in 50 hours. It also improved the recovery of ethylene glycol, another core PET component, by increasing its concentration during fed-batch processing.
The result was a closed-loop PET recycling process with a minimum selling price of $1.51/kg, undercutting the $1.87/kg cost of virgin PET.
Professor Pickford added: "PET is one of the most widely used plastics in the world, and its current low recycling rates are a major environmental concern. This is the first-time enzymatic recycling of PET has looked not only environmentally preferable, but commercially viable. It's the sort of progress we need if we're serious about ending plastic pollution."
While the process has yet to be rolled out at industrial scale, the researchers are optimistic. This study brings that positive change a step closer.
The research team is made up of scientists from the National Renewable Energy Laboratory (NREL), the University of Massachusetts Lowell, and the University of Portsmouth in England.
The organisations previously partnered 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.
