New Way to Transform Used Plastic into Carbon Nanotubes

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

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

Lead researcher associate professor Kalpit Shah said upcycling two massive waste streams through one circular economy approach could deliver significant financial and environmental benefits.

Cost-effective Way to Upcycle Used Plastic

The new method starts with converting agricultural or organic waste to biochar – a carbon-rich form of charcoal. The biochar is used to eliminate toxic contaminants – such as poly-cyclic aromatic hydrocarbons — as the waste plastic is broken down into its components of gas and oil. The process eliminates those contaminants and convert 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.

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,” Shah 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.”

Fluidized Bed Technology for the Study

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 fluidized 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 optimize the methodology, followed by pilot trials in the reactor. The research was supported through an Australian research council DECRA fellowship.

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