Plastic breakdown: Researchers discover faster, greener chemical method for upcycling waste
23 Aug 2022 --- Researchers have discovered an improved method of upcycling used plastic waste into valuable products. A team from Pacific Northwest National Laboratory (PNNL), says their findings have produced a more cost-efficient, fast-acting catalyst for the breakdown of polymers into usable chemicals.
Presented to the American Chemical Society (ACS) yesterday and published in ACS Catalysis, the results are also being touted for their ability to reduce greenhouse gas (GHG) emissions, like methane, a typical byproduct of the conversion process in other methods.
“It was very interesting to us that there had been nothing previously published showing this result,” says postdoctoral research scientist Linxiao Chen, who presented the research at ACS. “This research shows the opportunity to develop effective, selective and versatile catalysts for plastic upcycling.”
Less is more
Petroleum-based plastic waste presents an untapped source of carbon-based chemicals that can serve to create useful materials and fuels. Very little plastic is currently recycled, mainly due to a lack of infrastructure and investment.
The catalyst breaks down polymers in a far more speedy and efficient way than through traditional methods.Adding hydrogen to difficult-to-recycle plastics like PP and PE, a reaction known as hydrogenolysis, is a strategy that converts plastic waste into small value-added hydrocarbons. This process requires efficient and selective catalysts to make it economically feasible.
“The key discovery we report is the very low metal load,” remarks PNNL chemist Janos Szanyi, who led the research team. “This makes the catalyst much cheaper.”
The study authors found that reducing the amount of the precious metal ruthenium actually improved the polymer upcycling efficiency and selectivity.
Their findings show that the improvement in efficiency happened because the low ratio of metal to support structure caused the structure to shift from an orderly array of particles to disordered rafts of atoms.
Trapping atoms
The researchers observed the transition to disorder on the molecular level and then used established theory to show that single atoms are actually more effective catalysts in this experimental work.
“There has been a lot of effort from a material perspective to try to understand how single atoms or very small clusters can make effective catalysts,” says chemist Oliver Gutiérrez, an expert in industrial applications for catalysis.
At ACS, Chen also described new work that explores the support material’s role in improving the system’s efficiency.
“We have investigated cheaper and more easily available support materials to replace cerium oxide,” said Chen. “We found that a chemically modified titanium oxide may enable a more effective and selective pathway for polypropylene upcycling.”
Tolerating chlorine
To make the method practical for use with mixed plastic recycling streams, the research team is now exploring how chlorine’s presence affects the chemical conversion efficiency.
“We are looking into more demanding extraction conditions,” said chemist Oliver Y. Gutiérrez, an expert in industrial applications for catalysis.
“When you don’t have a clear plastic source, in an industrial upcycling process, you have chlorine from polyvinylchloride and other sources. Chlorine can contaminate the plastic upcycling reaction. We want to understand what effect chlorine has on our system.”
That fundamental understanding may help convert waste plastic that usually ends up as environmental pollution into useful products.
By Louis Gore-Langton
