Photocatalytic recycling: University of Adelaide researchers use light to upcycle PE into ethylene
22 Dec 2023 --- An international team of researchers, led by Professor Shizhang Qiao from the University of Adelaide, Australia, has developed a way to convert PE waste into ethylene (C2H4) and propionic acid, which has antiseptic and antibacterial properties, using a light-driven photocatalysis method.
The study outlines a method involving the atomic engineering of a titanium dioxide (TiO2) photocatalyst with reversible palladium (Pd) species. This modification enables the selective conversion of PE under mild conditions.
“We have upcycled polyethylene plastic waste into ethylene and propionic acid with high selectivity using atomically dispersed metal catalysts,” shares Qiao, chair of Nanotechnology and director of the Centre for Materials in Energy and Catalysis at the School of Chemical Engineering, University of Adelaide.
“Plastic waste is an untapped resource that can be recycled and processed into new plastics and other commercial products. Catalytic recycling of PE waste is still in early development. It is practically challenging because of the chemical inertness of polymers and side reactions arising from structural complexities of reactant molecules.”
The process involves room-temperature, oxidation-coupled photocatalysis. The team achieved a 98.8% selectivity in propionic acid, which can be used as preservatives to extend the shelf life in food packaging or as plasticizers in producing certain packaging materials.
Titled “Photocatalytic Production of Ethylene and Propionic Acid from Plastic Waste by Titania-Supported Atomically Dispersed Pd Species,” the research was published in the journal Science Advances.
Novel conversions
Qiao explains that what sets this method apart is its use of renewable solar energy instead of conventional industrial processes that rely on fossil fuels, contributing to a more sustainable and circular economy.
The waste-to-value strategy involves four components: plastic waste, water, sunlight and non-toxic photocatalysts, with TiO2 featuring isolated Pd atoms on its surface.
“Our fundamental research provides a green and sustainable solution to simultaneously reduce plastic pollution and produce valuable chemicals from waste for a circular economy,” states Qiao.
“It will inspire the rational design of high-performance photocatalysts for solar energy utilization and benefit the development of solar-driven waste upcycling technology.”
Routes for PE waste conversion (Image credit: Qiao et.al.).Contemporary environmental challenges
According to the researchers, the developed process addresses contemporary environmental and energy challenges and holds promise for further scientific research, waste management and chemical manufacturing.
“Most of the plastics used today are discarded and accumulated in landfills. PE is the most widely used plastic in the world. Daily food packaging, shopping bags and reagent bottles are all made from PE. It is also the largest proportion of all plastic waste and primarily ends up in landfills, posing a threat to the global environment and ecology,” states the University of Adelaide.
The study emphasizes that existing chemical recycling processes for bulk synthetic plastic, specifically PE, operate at high temperatures and pressures, resulting in a complex mixture of products. Achieving PE conversion under mild conditions with good selectivity toward value-added chemicals has proven to be a significant practical challenge.
“Current chemical recycling for PE waste is operated at temperatures greater than 400 degrees Celsius, yielding complex product compositions. Ethylene is an important chemical feedstock that can be further processed into various industrial and daily products. At the same time, propionic acid is also in high demand owing to its antiseptic and antibacterial properties,” underscores the university.
By Radhika Sikaria
