Thermochemical recycling can replace fossil raw materials, researchers find

Researchers at Chalmers University of Technology in Sweden have demonstrated that the carbon atoms in mixed waste can replace all fossil raw materials in the production of new plastic.

The recycling method is inspired by the natural carbon cycle and could eliminate the climate impact of plastic materials, or even clean the air of carbon dioxide.

Plastic pellets that can be used to produce new plastic products. The pellets are made from gas that in turn comes from the mixed combustible waste heated to 600-800 degrees Celsius.
Credit: Johan Bodell, Chalmers

“There are enough carbon atoms in waste to meet the needs of all global plastic production. Using these atoms, we can decouple new plastic products from the supply of virgin fossil raw materials,” said Henrik Thunman, professor of energy technology at Chalmers University.

“If the process is powered by renewable energy, we also get plastic products with more than 95% lower climate impact than those produced today, which effectively means negative emissions for the entire system.” Thunman is one one of the authors of the study that was recently published in the Journal of Cleaner Production.

Thunman and his research team are focused on an important resource that often goes up in smoke today: the carbon atoms in waste, which are currently incinerated or end up in landfills instead of being recycled.

Thermochemical tech

Current plastic recycling methods are able to replace no more than 15 to 20% of the fossil raw material needed to meet society’s demand for plastic. The advanced methods proposed by the researchers are based on thermochemical technologies and involve the waste being heated to 600-800 degrees Celsius.

The waste then turns into a gas, which after the addition of hydrogen, can replace the building blocks of plastics. Using this recycling method could decouple new plastic products from the supply of new fossil raw materials.

Different types of waste, such as old plastic products and paper cups, with or without food residues, are put into the reactors at the Chalmers Power Central.

“The key to more extensive recycling is to look at residual waste in a whole new way: as a raw material full of useful carbon atoms. The waste then acquires value, and you can create economic structures to collect and use the material as a raw material worldwide,” Thunman said.

Just like nature

The principle of the process is inspired by the natural carbon cycle. Plants are broken down into carbon dioxide when they wither, and carbon dioxide, using the sun as an energy source and photosynthesis, then creates new plants.

“Our technology differs from the way it works in nature because we don’t have to take the detour via the atmosphere to circulate the carbon in the form of carbon dioxide. All the carbon atoms we need for our plastic production can be found in our waste, and can be recycled using heat and electricity,” Thunman noted.

The researchers’ calculations show that the energy to power such processes can be taken from renewable sources such as solar, wind or hydro power or by burning biomass, and they will be more energy-efficient than the systems in use today. It is also possible to extract excess heat from recycling processes, which in a circular system would compensate for the heat production currently derived from waste incineration, while eliminating the carbon dioxide emissions associated with energy recovery.

Replace fossil raw materials

The researchers have proven that the process can work in collaboration with plastics manufacturer Borealis in Stenungsund, Sweden, where they have verified the results and shown that the raw material can be used to make plastic, replacing the fossil raw materials used today.