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Converting Hard-To-Recycle Plastic Trash Into Clean Hydrogen Fuel

Another by-product of this innovative process offers a greener alternative for making carbon nanotubes needed in batteries and composite manufacturing.

Global plastic waste generation has more than doubled in the last two decades, the bulk of which has ended up in landfills, incinerated, or leaking into the environment. According to the Organisation for Economic Co-operation and Development, only 9 per cent of all plastic waste is successfully recycled. With growing populations and incomes driving a relentless rise in plastic consumption, many are looking for ways to curb plastic pollution by developing environmentally friendly alternatives or converting plastic waste into useful products.

Now, scientists at Nanyang Technological University, Singapore (NTU Singapore) have innovated a novel approach to convert plastic waste into hydrogen using a high-temperature chemical process known as pyrolysis. With 832 million kilograms of unrecycled plastic waste generated in Singapore annually, the energy generated from their pyrolysis-based method could potentially power up to 1,000 five-room apartments for a year. With 269 million kilograms of plastic waste currently floating in the oceans, the NTU team estimates that, if converted into energy, the waste could power an electric vehicle for 20 to 40 million kilometres, enough to go around the Earth 500 to 1,000 times.

Since most plastic litters contain contaminated food packaging, styrofoam, and plastic bags, all of which are challenging to recycle, most of them are incinerated or buried in landfills, which can lead to both water and ground pollution. Fortunately, pyrolysis can turn plastic litter into solid carbon nanotubes and hydrogen, the latter of which is useful for generating electricity and powering fuel cells in electric vehicles. Because clean water is the only by-product of hydrogen fuel, it has attracted attention as a greener alternative to fossil fuels.

“As part of NTU’s sustainability drive, in developing new ways to turn trash to treasure, we are looking to convert waste plastics that cannot be recycled into high-value chemicals and resources, such as hydrogen fuel, synthetic fuel that could replace petrol, and carbon nanotubes used for many industrial applications,” explained co-inventor Associate Professor Lisak, Director of the Residues, Resource and Reclamation Centre (R3C) at NEWRI, who is also a faculty at the School of Civil and Environmental Engineering.

Their approach first involves decomposing plastic waste by heating into gases that contain low concentrations of hydrogen molecules. The gases will then enter a reactor filled with a catalyst, where the technology enables the release of hydrogen fuel and the formation of carbon nanotubes.

Aiming to refine this novel conversion technique and to determine its commercial feasibility, researchers are test-bedding it on the NTU Smart Campus to treat local plastic waste, in partnership with Bluefield Renewable Energy, a local environmental firm that specialises in mobile waste to resources technologies. This project is also hoping to explore the potential of other emerging technologies for decentralised waste management such as the conversion of challenging waste streams into energy and valuable resources like syngas, biochar, activated carbon, and carbon nanotubes.

“During this pandemic, there has been an increase in plastic usage as most of us have been taking away our food in plastic containers and doing more grocery shopping. Current practices and efforts to recycle them have been challenging and require disposals in landfills and/or incineration plants leading to environmental contamination issues. In BRE, we pride ourselves in our ability to convert wastes into resources based on our flexi-pyrolysis system,” said Mr Craig Gavin, CTO, Bluefield Renewable Energy (BRE). “Collaborating with NTU NEWRI has allowed us to utilise these environmentally unfriendly plastic waste stream as a feedstock and converting them into valuable resources. With the market pivoting to a Hydrogen-powered economy, this collaboration allows us to expand our technological applications and commercialised locally created innovations, ultimately building a Singapore centred resource hub.”

Besides hydrogen fuel, the resultant solid carbon nanotubes can also be used for beneficial purposes. Compared to gaseous carbon dioxide emissions produced from plastic waste incineration, the solid carbon generated from the new conversion process is much easier to store. Therefore, the carbon can be easily sold as manufacturing feedstock for specialty chemicals or biofuels. According to NEWRI Senior Research Fellow Dr. Andrei Veksha, the co-inventor of the process who is piloting the technology, the solid carbon is a greener source for making carbon nanotubes, which are needed in batteries and composite manufacturing.

If successful, the initiative is expected to help Singapore decrease the amount of total waste disposed and prolong the lifespan of Singapore’s only landfill, Semakau Landfill, which is estimated to run out of space by 2035. [APBN]

Source: Nanyang Technological University