Team converts polyethylene waste into valuable chemicals

Polyethylene waste (PE) is the most widely used plastic in the world, comprising daily food packaging, shopping bags and reagent bottles. It also makes up the largest proportion of all plastic waste and primarily ends up in landfill, posing a global ecological threat.

Now, an international team of scientists has developed a way of using PE as a feedstock and converting it into valuable chemicals via light-driven photocatalysis, with their findings published in the journal Science Advances. Leading the team was The University of Adelaide’s Professor Shizhang Qiao, Chair of Nanotechnology and Director of the Centre for Materials in Energy and Catalysis at the School of Chemical Engineering.

Qiao said an oxidation-coupled room-temperature photocatalysis method was used to convert the waste into valuable products. “We have upcycled polyethylene plastic waste into ethylene and propionic acid with high selectivity using atomically dispersed metal catalysts,” he said.

“Nearly 99% of the liquid product is propionic acid, alleviating the problems associated with complex products that then require separation.”

Ethylene is an important chemical feedstock that can be further processed into a variety of industrial and daily products, while propionic acid is in high demand due to its antiseptic and antibacterial properties. Qiao added that renewable solar energy was used instead of industrial processes that consume fossil fuels and emit greenhouse gases.

“This waste-to-value strategy is primarily implemented with four components, including plastic waste, water, sunlight, and non-toxic photocatalysts that harness solar energy and boost the reaction,” he said. “A typical photocatalyst is titanium dioxide with isolated palladium atoms on its surface.”

While the team’s finding was encouraging, Qiao said the catalytic recycling of PE waste is still in the early stages of development and presents challenges due to the chemical inertness of polymers and side reactions arising from structural complexities of reactant molecules. However, the team’s work will be of use in further scientific research, waste management and chemical manufacturing.

“Our fundamental research provides a green and sustainable solution to simultaneously reduce plastic pollution and produce valuable chemicals from waste for a circular economy,” Qiao said.

“It will inspire the rational design of high-performance photocatalysts for solar energy utilisation and benefit the development of solar-driven waste upcycling technology.”

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