How the perfect blend of tyres and plastic led to a sulfur-free oil

When tyres are broken down, the liquid oil that is formed normally contains hazardous sulfur-containing compounds, presenting a challenge for the safe upcycling of tyre waste.

Now, a team of scientists from Monash University appear to have solved this problem, using a coffee grinder, a freezer and a furnace. Their study is believed to be the first of its kind.

The chemical engineers found that there were strong synergies between tyre scrap and plastics, including low-density polyethylene (LDPE) and polystyrene, when all of these materials were treated together in a system using a process known as rapid pyrolysis, which subjects them to high temperatures over a short time.

The team found that blending either polystyrene or LDPE with tyre scrap for pyrolysis effectively eliminated the production of sulfur-containing compounds.

The team’s leader Professor Lian Zhang, from the Department of Chemical and Biological Engineering, said LDPE and polystyrene are both commonly used across a range of consumer goods including packaging, plastic bags and films, bottles and containers, and even medical disposables.

“Adding these plastics and using this process to break down tyres can substantially reduce the risk of releasing hazardous materials into the environment,” Zhang said.

“We believe our findings provide a very solid foundation and justification for using co-pyrolysis as an effective and value-added technology for upcycling potentially troublesome waste products.”

PhD student Wahyu Narulita Dewi, first author of the team’s study, said further analysis allowed the mechanisms underpinning the interactions between the chemical components in the system to be identified in detail. The study has been published in the journal Waste Management.

The Monash team is now working to develop and optimise the technology with the aim of enhancing the yield and the quality of the sulfur-free light oil produced by the process.

Their research is being supported by Tyre Stewardship Australia, a tyre industry organisation that promotes the development of viable markets for end-of-life tyres.

Further related research will also be a focus of a new Australian Research Council (ARC) Industrial Transformation Research Hub for Value-Added Processing of Underutilised Carbon Waste. Led by Zhang, the Hub will be launched later in 2024.

Image caption: Scrap tyre chips were frozen with liquid nitrogen and ground using a coffee grinder, blended with plastics and placed in a furnace at 600°C. Image courtesy of Monash University.