Polyethylene waste could be a thing of the past

An international team of experts conducting fundamental research has developed a way to use waste polyethylene (PE) as a feedstock and convert it into valuable chemicals, via light-powered photocatalysis.

University of Adelaide Professor Shizhang Qiao, Chair of Nanotechnology and Director of the Center for Materials in Energy and Catalysis in the School of Chemical Engineering, led the team which published their results in the journal Scientists progress.

“We recycled polyethylene plastic waste into ethylene and propionic acid with high selectivity using atomic dispersion metal catalysts,” said Professor Qiao.

“A room temperature photocatalysis method coupled with oxidation was used to convert waste into valuable products with high selectivity. Nearly 99% of the liquid product is propionic acid, mitigating the problems associated with complex products which then require separation. Renewable solar energy has been rather than industrial processes that consume fossil fuels and emit greenhouse gases.”

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

Most plastics used today end up being thrown away and accumulating in landfills. PE is the most used plastic in the world. Daily food packaging, shopping bags and reagent bottles are all made of PE. It also accounts for the largest proportion of all plastic waste and mainly ends up in landfills, posing a threat to the environment and global ecology.

“Plastic waste is an untapped resource that can be recycled and transformed into new plastics and other commercial products,” said Professor Qiao.

“Catalytic recycling of PE waste is still in its infancy and is a practical challenge due to the chemical inertness of polymers and side reactions resulting from the structural complexity of the reacting molecules.”

Current chemical recycling of PE waste takes place at high temperatures above 400°C, resulting in complex product compositions.

Ethylene is an important chemical raw material that can be processed into a variety of industrial and everyday products, while propionic acid is also in high demand due to its antiseptic and antibacterial properties.

The team’s work aims to address contemporary environmental and energy challenges, contributing to a circular economy. It will be useful for other 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,” said Professor Qiao.

“This will inspire the rational design of high-performance photocatalysts for solar energy utilization and benefit the development of solar energy-based waste recycling technology.”