A research team at ETH Zurich is developing methods for the chemical breakdown of plastics using ruthenium.
Plastic pollution is one of the biggest environmental problems, with 400 million tons of plastic waste generated annually, according to the United Nations. Recycling and establishing a circular economy are considered important solutions, alongside preventing new plastic waste. A research team at the Swiss Federal Institute of Technology (ETH) Zurich may have now made a significant contribution in this direction.
Currently, plastic waste is recycled mechanically by shredding and then melting it. However, as explained by the team in a press release, the quality of the resulting plastic products decreases with each recycling step.
As an alternative, methods are being developed to chemically break down long-chain plastic molecules—polymers—into their building blocks, monomers. These shorter-chain molecules could, for example, be used to produce gasoline, kerosene, or motor oil or could be further processed into new, high-quality plastics.
Targeted Recycling: Metal Catalyst and Stirring Method Are Crucial
For the necessary breakdown of polymer chains, researchers led by Javier Pérez-Ramírez, Professor of Catalysis Engineering, have made important groundwork. They studied the breakdown of polyethylene and polypropylene, which together make up 60 percent of plastic waste, using hydrogen. This is introduced after the plastic is melted in a steel tank. The right powdered catalyst plays an important role, with the metal ruthenium proving suitable. According to the researchers, this allows them to control the formation of molecules of a specific desired chain length and minimize byproducts like methane or propane.
They also discovered that proper stirring—meaning the right tool and speed—is crucial to ensure that the catalyst powder and hydrogen can reach every part of the plastic melt, which is a thousand times more viscous than honey.
Their work resulted in a mathematical formula for the entire chemical recycling process with all its parameters, “the dream of every chemical engineer,” according to Pérez-Ramírez. This formula could now be used by the entire scientific community, for example, to optimize the choice of catalyst further. The ETH Zurich team plans to focus on this next. Additionally, the developed principles are suitable for scaling the technology from the lab scale to large recycling plants in the future.
More on the role of strategic raw materials in the fight against plastic waste: Rare earth elements have also provided valuable insights into research on tackling plastic pollution in the world’s oceans.
Photo: iStock/OperationShooting
