Plastic can be upcycled into nanomaterials and fuel

RMIT University researchers have developed a clean and cost-effective way to upcycle used plastic, transforming it into valuable nanomaterials and high-quality fuel. Their method has been described in the Journal of Environmental Management.

The export of unprocessed single resin/polymer plastics will be banned from 1 July 2022, under new Australian laws designed to phase out export of waste plastics, paper, glass and tyres. Australia’s national recycling target is for 70% of the country’s plastic packaging to be recycled or composted by 2025, but a recent report found just 9.4% of plastic was recycled in 2017–2018. Globally, that figure is around 20%.

Recycling plastic cleanly can be expensive and usually produces lower-value products, often making it financially unviable. The RMIT method, on the other hand, offers a sustainable alternative for the production of carbon nanotubes (CNTs) — hollow, cylindrical structures with exceptional electronic and mechanical properties and applications across a broad range of sectors including hydrogen storage, composite materials, electronics, fuel cells and biomedical technologies. With growing demand in the aerospace and defence industries, where they can facilitate the design of lightweight parts, the global market for CNTs has been projected to reach $5.8 billion by 2027.

RMIT’s two-step process starts with converting agricultural or organic waste to biochar — a carbon-rich form of charcoal often used for improving soil health. The biochar is used to eliminate toxic contaminants such as polycyclic aromatic hydrocarbons (PAHs), as the waste plastic is broken down into its components of gas and oil. The process eliminates those contaminants and converts plastics into high-quality liquid fuel; at the same time, the carbon in the plastic is converted into carbon nanotubes, which coat the biochar. These nanotubes can be exfoliated for use by various industries or the nano-enhanced biochar can be used directly for environmental remediation and boosting agricultural soils.

The study is the first to use low-cost and widely available biochar as a catalyst for making contaminant-free fuel and carbon nanomaterials from plastic. According to lead researcher Associate Professor Kalpit Shah, upcycling two massive waste streams through one circular economy approach could deliver significant financial and environmental benefits.

“Our method is clean, cost-effective and readily scaleable,” said Assoc Prof Shah, who serves as Deputy Director (Academic) of the ARC Training Centre for the Transformation of Australia’s Biosolids Resource at RMIT.

“It’s a smart solution for transforming both used plastic and organic waste — whether tonnes of biomass from a farm or food waste and garden clippings from household green bins.

“We hope this technology could be used in future by local councils and municipal governments to help turn this waste into genuine revenue streams.”

Assoc Prof Shah said the study focused on polypropylene as this is widely used in the packaging industry, but the approach would likely be applicable to a range of plastic types. He explained, “While we need to do further research to test different plastics, as the quality of the fuel produced will vary, the method we’ve developed is generally suitable for upcycling any polymers — the base ingredients for all plastic.”

The experimental study conducted at lab scale can also be replicated in a new type of hyper-efficient reactor that has been developed and patented by RMIT. The reactor is based on fluidised bed technology and offers significant improvement in heat and mass transfer, to reduce overall capital and operating costs.

The next steps for the upcycling research will involve detailed computer modelling to optimise the methodology, followed by pilot trials in the reactor. The team is keen to collaborate with plastic and waste industries to further the research and investigate other potential applications of the upcycling method.

“Upcycling plastic with home-grown tech would enable us to draw the greatest possible value out of our limited resources and bring us closer towards a true circular economy,” Assoc Prof Shah said.

Image caption: A carbon nanotube created through the new upcycling method. Image magnified 35,000 times.