Polyethylene (PE) is one of the most common plastics due to its low price and simplicity in manufacturing. Some experts estimate that more than 80 million tons of this thermoplastic polymer are produced worldwide each year. An international team of experts has now presented a new proposal to address one of the main problems generated by the massive manufacturing and use of this type of plastic, the management of its waste. The authors present a system to use waste polyethylene (PE) as raw material and convert it into valuable chemicals using light-driven photocatalysis.
The study was led by Professor Shizhang Qiao, Professor of Nanotechnology and director of the Center for Materials in Energy and Catalysis at the Faculty of Chemical Engineering at the University of Adelaide, and the results have been published in the journal Science Advances.
The authors remind that the widespread use of plastic products requires proper end-of-life management to reduce environmental threats from landfills and recover value-added products from waste. As a possible partial solution to the problem, in their study they show a new alternative for waste treatment of one of the most common plastics and assure that they have achieved, “an atomic engineering strategy to modify a TiO 2 photocatalyst with reversible Pd species for the selective conversion of PE to ethylene (C2 H4) and propionic acid via dicarboxylic acid intermediates under mild conditions.”
In words that are easier to understand, they claim that they have achieved “the recycling of polyethylene plastic waste to convert them into ethylene and propionic acid with high selectivity using atomically dispersed metal catalysts,” explains Professor Qiao in a note released by his university.
“A coupled oxidation room temperature photocatalysis method was used to convert waste into valuable products with high selectivity. Nearly 99% of the liquid product is propionic acid, alleviating problems associated with complex products that then require separation. “Renewable solar energy was used instead of industrial processes that consume fossil fuels and emit greenhouse gases.”
“This waste recovery 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 palladium atoms isolated in its surface.”
Most of the plastics used today end up being discarded and accumulated in landfills. PE is the most used plastic in the world. Daily food packaging, shopping bags and reagent bottles are 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.
“Waste plastic 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 its early stages of development and is a practical challenge due to the chemical inertness of the polymers and secondary reactions arising from the structural complexities of the reactive molecules.”
Current chemical recycling of PE waste is carried out at high temperatures above 400° Celsius, resulting in complex product compositions.
Ethylene is an important chemical raw material that can be further processed into a variety of industrial and daily 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 in future 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.
“It will inspire the rational design of high-performance photocatalysts for solar energy utilization and benefit the development of solar-powered waste recycling technology.”
