Researchers at Trinity College Dublin and the University of Manchester have made strides in improving how we recycle polyethylene terephthalate, the type of plastic most commonly found in beverage bottles and food containers. This research, led by Dr. Cristina Trujillo, and Professor Stephen Connon, was published in the journal RSC Sustainability. The team’s work focuses on using eco-friendly liquid salts based on cholinium for a process known as glycolysis, which breaks down plastics into their core components so they can be reused.
Plastic waste is a growing problem, and polyethylene terephthalate, a key material in many everyday products, is a major contributor. Unfortunately, much of this plastic can’t be efficiently recycled through standard mechanical methods due to contamination or wear from repeated use. When plastic is recycled this way, it often leads to lower-quality products. Glycolysis, on the other hand, offers a way to recycle plastic back into high-quality material, almost like new. Dr. Trujillo highlighted, “There is a growing interest in using cholinium-based liquid salt catalysts for the recycling of polyethylene terephthalate through glycolysis.” Their goal was to find more efficient and environmentally safe ways to do this.
Their research involved both computer simulations and lab experiments to better understand how cholinium, a key part of many liquid salts, helps break down plastics. Previous studies suggested that cholinium played an important role in the chemical reaction, helping to stabilize certain parts of the process. However, this new research showed that other factors, like the solvent ethylene glycol, are actually more important than previously thought. “Our findings show that while cholinium-based liquid salts have potential as catalysts for the chemical recycling of plastics, the role of the cholinium cation itself might have been exaggerated,” explained Professor Connon.
Through a variety of tests, the researchers compared different liquid salt catalysts, including new versions that did not include cholinium. Some of these alternative catalysts worked even better, using less material while achieving higher results. One particular type, using a phosphonium-based catalyst, stood out for its efficiency. The data demonstrated that these alternative catalysts significantly outperformed the cholinium-based ones. These findings are crucial because they show that there are more effective and sustainable ways to recycle plastics.
Cholinium’s appeal lies in the fact that it is biodegradable, meaning it breaks down naturally and is less harmful to the environment. However, the almost equal performance of alternative catalysts suggests that cholinium’s real advantage might be more about its environmental benefits than its ability to help in the recycling process. Dr. Cristina Trujillo noted, “This opens the door for future research to explore biodegradable catalysts without cholinium, offering a more efficient recycling process while still being environmentally friendly.”
This research has broader significance beyond just recycling plastic bottles. It emphasizes the need to revisit commonly accepted ideas in chemistry, especially when developing greener technologies. The team plans to continue looking at how different solvents and catalysts affect the recycling process, aiming to make it even more environmentally friendly. These ongoing efforts could lead to better, more sustainable methods of managing plastic waste and help meet global environmental goals.
In conclusion, the study represents a significant step forward in the search for greener recycling methods. It challenges the idea that cholinium is essential for the recycling process, showing that other liquid salt catalysts might work even better. However, whether cholinium-based or not, the continued development of these catalysts holds great promise for tackling the growing plastic waste problem.
Journal Reference
Bura D., Pedrini L., Trujillo C., Connon S.J. “Cholinium-based ionic liquid catalysts for polyethylene terephthalate glycolysis: understanding the role of solvent and a reappraisal of the cation contribution.” RSC Sustainability, 2023. DOI: https://doi.org/10.1039/d3su00336a
About the Authors
Dr. Cristina Trujillo obtained her Ph.D. in Theoretical and Computational Chemistry in 2008 at the Universidad Autónoma de Madrid (Spain). During the period 2008-2016, she held several Postdoctoral positions in Spain (CSIC), Prague (Academy of Sciences), and Ireland (Trinity College Dublin). From 2016 until 2018 she worked at TCD as a Research Fellow. After that, she worked as an Assistant Lecturer at TU-Dublin in the School of Chemical & Pharmaceutical Sciences. She has been awarded the very competitive SFI-Starting Investigator Research Grant (SIRG, 2018) and L’Oreal-Unesco Women in Science UK and Ireland Fellowship -Highly Commended (2019). She worked as an independent researcher leading her own research group at TCD from 2019 to 2022. Currently, she is a Lecturer in Computational & Theoretical Chemistry at The University of Manchester.
She has expertise in highly fundamental topics within Computational Organic Chemistry such as asymmetric catalysis, computationally-led catalysis design, mechanisms of reaction, and non-covalent interactions. Her research interests are focused on the asymmetric catalysis field, with particular emphasis on the application of computational techniques in the design of organocatalysts along with prediction and control of catalytic processes, with a direct impact on the development of products with different applications.
Diana Bura is a third-year PhD student under the supervision of Dr. Cristina Trujillo at the Trinity Biomedical Sciences Institute, Trinity College Dublin, Ireland. Her research journey began during her final year of undergraduate studies at Trinity College Dublin, where she conducted a theoretical investigation of phase transfer catalysts for the asymmetric conjugate cyanation of N-acylpyrroles within the Trujillo group. Currently, her PhD focuses on using Density Functional Theory (DFT) to perform mechanistic studies across diverse chemical fields, including PET depolymerisation, organocatalysis, and electroorganocatalysis. Her primary research interest lies in leveraging computational tools to enhance the efficiency and sustainability of chemical research.
Lorenzo Pedrini completed his M.Sc. degree in Pharmaceutical Chemistry and Technology at University of Genova, Italy, focusing his final project on the synthesis of imidazo-pyrazole derivatives under the direction of Prof. Chiara Brullo. He later moved to Dublin and is currently finishing his Ph.D. under the supervision of Prof. Stephen Connon at the Trinity Biomedical Science Institute, Trinity College Dublin, Ireland. His work focuses on the development of novel biodegradable ionic catalysts useful for plastics recycling. He has experience with depolymerization of PET, organic synthesis, ion-metathesis, ionic liquids and spectroscopic techniques.
