Catalyst Transforms Plastic Waste into Valuable Ingredients at Low Temperature

For the first time, researchers have used a novel catalyst process to recycle a type of plastic found in everything from grocery bags and food packaging to toys and electronics into liquid fuels and wax.

The team published their results on December 10 in the journal Applied Catalysis B: Environmental.

“Plastics are essential materials for our life because they bring safety and hygiene to our society,” said paper co-authors Masazumi Tamura, associate professor at the Research Center for Artificial Photosynthesis in the Advanced Research Institute for Natural Science and Technology in Osaka City University, and Keiichi Tomishige, professor at the Graduate School of Engineering in Tohoku University. “However, the growth of global plastic production and the rapid penetration of plastics into our society has brought mismanagement of waste plastics, causing serious environmental and biological issues such as ocean pollution.”

Polyolefinic plastics – the most common plastic – have physical properties that make it difficult for a catalyst, responsible for inducing chemical transformation, to interact directly with the molecular elements to cause a change. Current recycling efforts require temperatures of at least 573 Kelvin, and up to 1,173 Kelvin. For comparison, water boils at 373.15 Kelvin, and the surface of the Sun is 5,778 Kelvin.

The researchers looked to heterogeneous catalysts in an effort to find a reaction that might require a lower temperature to activate. By using a catalyst in a different state of matter than the plastics, they hypothesized that the reaction would be stronger at a lower temperature.

They combined ruthenium, a metal in the platinum family, with cerium dioxide, used to polish glass, to produce a catalyst that caused the plastics to react at 473 Kelvin. While still high for human sensibilities, it requires significantly less energy input compared to other catalyst systems.

According to Tamura and Tomishige, ruthenium-based catalysts have never been reported in the scientific literature as a way to directly recycle polyolefinic plastics.

“Our approach acted as an effective and reusable heterogeneous catalyst, showing much higher activity than other metal-supported catalysts, working even under mild reaction conditions,” Tamura and Tomishige said. “Furthermore, a plastic bag and waste plastics could be transformed into valuable chemicals in high yields.”

The researchers processed a plastic bag and waste plastics with the catalyst, producing a 92% yield of useful materials, including a 77% yield of liquid fuel and a 15% yield of wax.

“This catalyst system is expected to contribute to not only the suppression of plastic wastes but also to the utilization of plastic wastes as raw materials for the production of chemicals,” Tamura and Tomishige said.

Publication Details:

Title: Low-temperature catalytic upgrading of waste polyolefinic plastics into liquid fuels and waxes

Authors: YosukeNakaji, MasazumiTamura, ShuheiMiyaoka, ShogoKumagai, MifumiTanji, YoshinaoNakagawa, Toshiaki Yoshioka, KeiichiTomishige

Journal: Applied Catalysis B: Environmental

DOI: 10.1016/j.apcatb.2020.119805

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