Pyrolysis Developing Alternative Carbon Sources

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In the "CarbonCycle" project, the German Center for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW), together with industrial partners, has developed a high-temperature process that makes it possible to thermochemically break down previously non-recyclable processing and production residues from the plastics industry into a hydrogen-rich gas and a solid carbon fraction, thus tapping into alternative carbon sources.

Today, plastic residues and waste are largely thermally recycled in Germany. The carbon contained in the plastics is converted into CO₂ during the incineration process, which is then released into the atmosphere and contributes to climate change.

At the same time, however, carbon, particularly in the form of graphite, is an essential component of today's batteries for electric vehicles. China accounts for around 80% of global graphite production. Graphite is listed as a critical raw material in the EU and demand will continue to increase: This is because, according to ZSW estimates, the annual demand for graphite alone will increase from just under 1 million tons recently to 3 to 4 million tons in 2030. The high-temperature rotary kiln thermolysis used in the CarbonCycle project is intended to help establish resilient, efficient raw material cycles - with the aim of reducing CO₂ emissions as much as possible.

With this project, we want to demonstrate that the recovery of carbon from existing industrial plastic waste is technically possible and economically feasible. We see this as an important contribution to the implementation of an EU-wide circular economy.

Dr. Jochen Brellochs

No Pyrolysis Oil, but Solid Carbon

In contrast to state-of-the-art plastic pyrolysis, the focus of high-temperature rotary kiln thermolysis is not on the production of pyrolysis oil, but on solid carbon. In the absence of oxygen, the scientists at ZSW want to convert plastics into a solid, pure carbon fraction and a hydrogen-rich gas at up to 900 °C for the first time. In the future, the hydrogen-rich gas can be used as a low-CO2 fuel gas in industrial processes in a similar way to so-called turquoise hydrogen from methane pyrolysis. Compared to methane pyrolysis, however, significantly lower temperatures, less energy and no fossil natural gas as a raw material are required for the same end products, hydrogen and solid carbon.

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In the course of the project, thermolysis tests will initially be carried out at ZSW with selected plastic fractions on a laboratory scale and the carbon samples produced will be characterized in electrochemical tests with regard to a battery application and processed and evaluated up to a battery half-cell. On this basis, the thermolysis process will then be implemented and validated at the ZSW on a pilot plant scale in the output range of up to 5 kg of plastic per hour. In various test campaigns, important findings on carbon yield and composition, hydrogen yield and energy requirements when using different residual material fractions as well as basic empirical values on process control and robustness of the components and materials used will be collected.

"With this project, we want to demonstrate that the recovery of carbon from existing industrial plastic waste is technically possible and economically feasible. We see this as an important contribution to the implementation of an EU-wide circular economy," says Dr. Jochen Brellochs, researcher in the Renewable Energy Sources and Processes department at ZSW. "At the same time, we are tapping into a new source of carbon that could at least partially replace the fossil carbon used to date," Brellochs continues.

Processing as a Secondary Raw Material in Battery Production

The project covers the entire process chain and involves all stakeholders: from the plastics industry as a raw material supplier to the innovative high-temperature technology used to produce the carbon product through to its direct refinement and processing as a secondary raw material in battery production. Other important aspects such as the development of recycling strategies, profitability analyses and the CO₂ footprint are also highlighted. The ZSW is working on the project together with its project partner Akkodis. The companies Südpack, GRAF, Alleima and Schwenk are participating as associated project partners. The aim is to build up long-term and comprehensive expertise and transfer technology to industry in order to implement the national circular economy strategy.