Polythylene waste could soon be a thing of the past according to The University of Adelaide’s Professor Shizhang Qiao, chair of Nanotechnology and director, Centre for Materials in Energy and Catalysis, at the School of Chemical Engineering.
Professor Qiao’s international team of experts has developed a method of using polyethylene waste (PE) as a feedstock, converting it into valuable chemicals via light-driven photocatalysis.
“We have upcycled polyethylene plastic waste into ethylene and propionic acid with high selectivity using atomically dispersed metal catalysts,” said Professor Qiao.
“Nearly 99% of the liquid product is propionic acid, alleviating the problems associated with complex products that then require separation.
“Renewable solar energy was used rather than industrial processes that consume fossil fuel and emit greenhouse gases.
“This waste-to-value strategy is primarily implemented with four components, including plastic waste, water, sunlight and nontoxic photocatalysts that harness solar energy and boost the reaction.”
Most widely used plastic in the world
PE is the most commonly used plastic in the world, accounting for the largest proportion of all plastic waste – we produce about 350 million tonnes of total plastic waste per year, to put it into perspective.
The material takes more than 500 years to decompose naturally and while it can easily be recycled, only about 31% of it is recycled at present.
Daily food packaging, shopping bags and reagent bottles are all made from PE, the waste from which primarily ends up in landfills and poses a distinct threat to the world’s oceans.
“Plastic waste is an untapped resource that can be recycled and processed into new plastics and other commercial products,” said Professor Qiao.
“Catalytic recycling of PE waste is still in early development and is practically challenging because of chemical inertness of polymers and side reactions arising from structural complexities of reactant molecules.”
Improved processing
Current recycling processes for PE require very high energy inputs and temperatures up to 400 degrees Celsius, yielding complex product compositions that include added separation costs.
This new method is more energy efficient and produces two distinct chemicals – ethylene and propionic acid.
Ethylene is an important chemical feedstock that can be further processed into a variety of industrial and daily products while propionic acid is also in high demand owing to its antiseptic and antibacterial properties.
The University of Adelaide’s team is working to build a circular economy with this new processing methodology, seeking to address current environmental and energy challenges around plastic waste.
The team believes its research will be particularly useful in 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.
“It will inspire the rational design of high-performance photocatalysts for solar energy utilisation and benefit the development of solar-driven waste upcycling technology.”