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An advanced steam cracking process developed by researchers at Chalmers University of Technology, Gothenburg, Sweden, can break down any plastic waste to its individual molecules. These gas-based molecules then can be transformed back into new plastics, which, say the researchers, have the same quality as virgin plastic.
The researchers, led by Henrik Thunman, professor of energy technology, have been experimenting with chemical recovery via steam cracking of plastic.
“Through finding the right temperature — which is around 850°C — and the right heating rate and residence time, we have been able to demonstrate the proposed method at a scale where we turn 200 kg/hr of plastic waste into a useful gas mixture. That can then be recycled at the molecular level to become new plastic materials of virgin quality,” he says.
An article in Sustainable Materials and Technologies outlines how such thermochemical recycling provides an opportunity to close the material cycle while using existing petrochemical infrastructure.
The researchers propose the following sequence: as a starting point, plastic waste partially replaces existing feedstock (up to 45% on a carbon basis); then, plastic waste supplants the feedstock totally; the process undergoes an electrification step — oxy-combustion and carbon capture and storage help to achieve 100% carbon recovery in the form of monomers or permanent storage.
An alternative transformation pathway includes introducing biomass.
The proposed implementation steps resolve energy and carbon balances, and present potential cost savings estimates related to the feedstock and required investments.
The researchers conclude that switching feedstock from virgin fossil fuels to plastic waste confers economic advantages — but with a caveat. The two transformation steps can only be justified if a value is assigned to the environmental benefits, for example carbon dioxide savings, increased share of biogenic carbon in plastic products, increasing recycling quotas, or the potential of the process to compensate for the intermittency of renewable power.
“We should not forget that plastic is a fantastic material — it gives us products we could otherwise only dream of. The problem is that it is manufactured at such low cost that it has been cheaper to produce new plastics from oil and fossil gas than from reusing plastic waste,” notes Thunman.
That plastics don’t degrade should be seen as a benefit, he believes, because it enables circular usage. This, in turn, creates true value for used plastic and, therefore, an economic impetus to collect it, Thunman says.
The researchers continue to work on the process. “We are now moving on from the initial trials, which aimed to demonstrate the feasibility of the process, to focusing on developing more detailed understanding. This knowledge is needed to scale up the process from a few tonnes of plastic a day, to hundreds of tonnes. That is when it becomes commercially interesting,” explains Thunman.
End-of-life bio-based materials such as paper, wood and clothes could also serve as raw material in the process. “This would mean we could gradually reduce the proportion of fossil materials in plastic. We could also create net negative emissions, if carbon dioxide is also captured in the process. The vision is to create a sustainable, circular system for carbon-based materials,” he concludes.
Meanwhile BASF, Ludwigshafen, Germany, has taken another step towards creating the circular economy envisaged by its ChemCyling initiative that was launched in 2018 to process recycled raw materials obtained from plastic waste in its production.
The company signed a €20-million ($22-million) deal with pyrolysis specialist Quantafuel, Oslo, Norway, which gives it first refusal for chemically derived pyrolysis oils and purified hydrocarbons from the company’s 16,000-mt/y plant in Skive, Denmark, for a minimum of four years after startup. Commissioning of that plant is now underway.
As part of the deal, the two companies will work together to further develop Quantafuel’s integrated pyrolysis and purification technology and optimize its output for use as a feedstock in chemical production.
At BASF’s Ludwigshafen site, the recycled raw materials will go into the production feedstock pool, thereby partially replacing fossil resources. Once the Quantafuel plant reaches full capacity, BASF aims to deliver first commercial supply volumes of products based on chemically recycled plastic waste to selected customers.
To increase the technology’s commercial opportunities, the firms plan to build jointly-owned plants to produce purified hydrocarbons via chemical recycling.
