Globally only about 20% of waste plastics are recycled. Boosting that figure remains a challenge as recycling plastic cleanly can be expensive and usually produces lower-value products, often making it financially unviable.

The new method from researchers at RMIT University can produce high-value products from plastic – carbon nanotubes (CNTs) and clean liquid fuel – while simultaneously upcycling agricultural and organic waste.

The team’s two-step process converts organic waste into a carbon-rich and high-value form of charcoal, and then uses this as a catalyst to upcycle the plastic.

The new plastic upcycling approach offers a sustainable alternative for the production of carbon nanotubes. These hollow, cylindrical structures have very good electronic and mechanical properties, with applications across a broad range of sectors including hydrogen storage, composite materials, electronics, fuel cells and biomedical technologies.

Examples of carbon nanotubes produced with the new approach, at different magnifications.

The new method 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 Poly-cyclic Aromatic Hydrocarbons, known as 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.

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

Kalpit Shah, the Deputy Director (Academic) of the ARC Training Centre for Transformation of Australia’s Biosolids Resource at RMIT, said while the study only investigated one type of plastic the approach would be applicable to a range of plastic types.

“We focused on polypropylene as this is widely used in the packaging industry,” he said. “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 modeling to optimize the methodology, followed by pilot trials in the reactor. The research was supported through an Australian Research Council DECRA Fellowship.

"Conversion of pyrolytic non-condensable gases from polypropylene co-polymer into bamboo-type carbon nanotubes and high-quality oil using biochar as catalyst", with RMIT co-authors Dr Savankumar Patel, Pobitra Halder, Dr Sazal Kundu, Mojtaba Hedayati Marzbali, Ibrahim Gbolahan Hakeem, Dr Biplob Kumar Pramanik, Dr Ken Chiang and Tejas Patel, is published in the Journal of Environmental Management.

Globally only about 20% of waste plastics are recycled. Boosting that figure remains a challenge as recycling plastic cleanly can be expensive and usually produces lower-value products, often making it financially unviable.

The new method from researchers at RMIT University can produce high-value products from plastic – carbon nanotubes (CNTs) and clean liquid fuel – while simultaneously upcycling agricultural and organic waste.

The team’s two-step process converts organic waste into a carbon-rich and high-value form of charcoal, and then uses this as a catalyst to upcycle the plastic.

The new plastic upcycling approach offers a sustainable alternative for the production of carbon nanotubes. These hollow, cylindrical structures have very good electronic and mechanical properties, with applications across a broad range of sectors including hydrogen storage, composite materials, electronics, fuel cells and biomedical technologies.

Examples of carbon nanotubes produced with the new approach, at different magnifications.

The new method 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 Poly-cyclic Aromatic Hydrocarbons, known as 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.

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

Kalpit Shah, the Deputy Director (Academic) of the ARC Training Centre for Transformation of Australia’s Biosolids Resource at RMIT, said while the study only investigated one type of plastic the approach would be applicable to a range of plastic types.

“We focused on polypropylene as this is widely used in the packaging industry,” he said. “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 modeling to optimize the methodology, followed by pilot trials in the reactor. The research was supported through an Australian Research Council DECRA Fellowship.

"Conversion of pyrolytic non-condensable gases from polypropylene co-polymer into bamboo-type carbon nanotubes and high-quality oil using biochar as catalyst", with RMIT co-authors Dr Savankumar Patel, Pobitra Halder, Dr Sazal Kundu, Mojtaba Hedayati Marzbali, Ibrahim Gbolahan Hakeem, Dr Biplob Kumar Pramanik, Dr Ken Chiang and Tejas Patel, is published in the Journal of Environmental Management.