New process to recycle polyolefinic plastics at low temperature

Photo Credit: Roman Milert/Adobe Stock

Researchers in Japan have used a novel catalyst process to recycle polyolefinic plastics into chemicals.

The problem being solved is that polyolefinic plastics 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 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,” said Masazumi Tamura, associate professor at the research centre 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.

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. Furthermore, a plastic bag and waste plastics could be transformed into valuable chemicals in high yields,” Tamura and Tomishige said.

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

The 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.