Boosting PET recycling with higher standards for laboratory experiments

In principle, PET molecules can be broken down into their basic building blocks using suitable enzymes. In practice, however, these approaches are difficult to transfer to an industrial scale. A new study shows how raising the bar in laboratory experiments could help identify promising enzymes for up-scaling and thus accelerate the development of industrial enzymatic plastics degradation.

In principle, PET molecules can be broken down into their basic building blocks using suitable enzymes. In practice, however, these approaches are difficult to transfer to an industrial scale. A new study shows how raising the bar in laboratory experiments could help identify promising enzymes for up-scaling and thus accelerate the development of industrial enzymatic plastics degradation. © HZB/Frank Lennartz, Gert Weber

Many enzymes promise to break down plastic. But what works well in the lab often fails on a large scale. Now a new study by Gert Weber, HZB, Uwe Bornscheuer, University of Greifswald, and Alain Marty, Chief Scientific Officer of Carbios, shows how raising the bar for laboratory experiments could help identify promising approaches more quickly. The team demonstrated the new standards on four newly discovered enzymes.

From time to time, media reports of major advances in the recycling of polyethylene terephthalate (PET). This is thanks to newly discovered enzymes, breaking down plastic into its constituent parts. However, the success story from the academic laboratory is usually followed by silence. PET accounts for 18% of the world’s plastic production, making it one of the most important plastics in terms of volume. Biotech company Carbios, for example, is building a plant in the north east of France by 2025. This plant will be able to recycle 50.000 tons of PET per year. They are interested to find the best possible enzymes for their industrial setup and have realised that many results from laboratory research cannot be transferred to a larger scale.

Upscaling experiments on PET recycling is difficult

“Some enzymes work great in laboratory experiments for a few hours, but they lose their activity very quickly and the substrate is not completely degraded,” says HZB expert Gert Weber. This is not a problem in the test tube in the laboratory, but it is when used in a large bioreactor. Together with the biotech company Carbios, Uwe Bornscheuer and Gert Weber show how new enzymes for PET degradation can be better compared with each other. “In order to allow upscaling later, many parameters must be within a narrow range even in laboratory experiments. The starting material must be precisely defined and the test protocols must be more standardised in order to better assess the performance of the enzymes and their application on an industrial scale,” explains Bornscheuer. The researchers have therefore developed a standardised PET hydrolysis protocol that defines reaction conditions relevant for hydrolysis on a larger scale. In particular, two PET materials were used, firstly a defined PET film and secondly PET granulate from waste bottles, as used by Carbios on a technical scale. They used these materials to test four recently discovered PET-decomposing enzymes: LCC-ICCG, FAST-PETase, HotPETase and PES-H1L92F/Q94Y.

When experimenting under this protocol, they found that two of these enzymes, FAST-PETase and HotPETase, were less suitable for large-scale use. This is mainly due to their relatively low depolymerisation rates. PES-H1L92F/Q94Y performed better. The fourth candidate, LCC-ICCG, outperformed the other enzymes by far: LCC-ICCG converts 98% of PET into the monomeric products terephthalic acid (TPA) and ethylene glycol (EG) in 24 hours. “In addition, we were able to reduce the amount of enzyme required for LCC-ICCG by a factor of 3 and the reaction temperature from 72 to 68 °C, which makes the use of this enzyme more economical,” says Bornscheuer.

Higher standards for experiments on PET recycling

“We should think about industrial applications already in our laboratory research,” says Gert Weber. After all, we are dealing with one of the really big problems of our time. Plastics are still being produced again and again from fossil raw materials, recycling rates are low and so far, it has mostly been a case of “downcycling” to inferior quality. Plastic waste can now be found in all bodies of water and soil and thus in the food chain. Progress is therefore urgent. “With these standards, we can do something to separate the wheat from the chaff more quickly.”

arö


You might also be interested in

  • BESSY II: How pulsed charging enhances the service time of batteries
    Science Highlight
    08.04.2024
    BESSY II: How pulsed charging enhances the service time of batteries
    An improved charging protocol might help lithium-ion batteries to last much longer. Charging with a high-frequency pulsed current reduces ageing effects, an international team demonstrated. The study was led by Philipp Adelhelm (HZB and Humboldt University) in collaboration with teams from the Technical University of Berlin and Aalborg University in Denmark. Experiments at the X-ray source BESSY II were particularly revealing.
  • Fuel Cells: Oxidation processes of phosphoric acid revealed by tender X-rays
    Science Highlight
    03.04.2024
    Fuel Cells: Oxidation processes of phosphoric acid revealed by tender X-rays
    The interactions between phosphoric acid and the platinum catalyst in high-temperature PEM fuel cells are more complex than previously assumed. Experiments at BESSY II with tender X-rays have decoded the multiple oxidation processes at the platinum-electrolyte interface. The results indicate that variations in humidity can influence some of these processes in order to increase the lifetime and efficiency of fuel cells. 
  • Fertilisation under the X-ray beam
    Science Highlight
    19.03.2024
    Fertilisation under the X-ray beam
    After the egg has been fertilized by a sperm, the surrounding egg coat tightens, mechanically preventing the entry of additional sperm and the ensuing death of the embryo. A team from the Karolinska Institutet has now gained this new insight through measurements at the X-ray light sources BESSY II, DLS and ESRF.