Breakthrough made in chemical plastics recycling
By ETH Zurich scientists
Scientists at ETH Zurich, a public research university in Zurich, Switzerland, have significantly advanced chemical plastics recycling, potentially transforming how the world handles plastic waste. The research team, led by Professor Javier Pérez-Ramírez, has unveiled critical insights into recycling, emphasising the pivotal role of stirring techniques.
Plastic waste, particularly polyethylene and polypropylene, makes up a large portion of global pollution, with millions of tonnes generated annually.
Traditional recycling methods, which involve shredding and melting plastics, often produce degraded material quality. Chemical recycling, however, offers a promising alternative: breaking down plastics into their basic monomers, allowing for the creation of high-quality new products.
ETH Zurich’s latest research focuses on a novel aspect of this process—enhancing the efficiency of breaking down long polymer chains into shorter molecules that can be converted into valuable fuels and lubricants.
The team’s work involves using hydrogen to decompose these plastics, which are first melted and then exposed to gaseous hydrogen and a powdered catalyst. By optimising the catalyst and the mixing process, the researchers aim to improve the quality and yield of the recycled products.
Stirring role
A breakthrough finding from the research is the crucial role of stirring in the chemical reaction.
The team discovered that an impeller with parallel blades provides the most effective mixing of the viscous plastic melt compared to other stirring methods. This approach ensures better integration of the catalyst and hydrogen, minimising the formation of undesirable byproducts like methane and propane. The ideal stirring speed was identified as approximately 1,000 revolutions per minute.
The researchers have developed a mathematical formula to model this process, which will be invaluable for future experiments and scaling up from laboratory to industrial applications.
“Having a precise formula for chemical engineers is a game-changer,” said Pérez-Ramírez. This formula will help researchers optimise catalysts and mixing conditions, paving the way for more efficient and scalable chemical recycling technologies.
Antonio José Martín, a research team member, emphasised the potential impact of this work. “Our focus now is on advancing the development of better catalysts and applying these principles to larger-scale recycling operations,” he said.
This research, supported by the National Centre of Competence in Research (NCCR) Catalysis, marks a significant step forward in addressing the global plastic waste crisis.
With these new insights, scientists worldwide are better equipped to develop innovative solutions for a genuinely sustainable recycling system.
Featured image: Most drink bottle caps are made of polypropylene, which, along with polyethylene, accounts for 60% of all plastic waste. Credit: Shibashish Jaydev/ETH Zurich
