As announced, the new German government has tightened its climate protection targets and has therefore enshrined in law the goal of greenhouse gas neutrality by 2045. Already by 2030, emissions are to be reduced by 65 percent compared to 1990. Germany is thus on its way to climate neutrality - and must close carbon cycles in industry as soon as possible to achieve this. But that alone will hardly be enough. In order to reach the 1.5-degree target at the same time, the Intergovernmental Panel on Climate Change recommends that CO2 that has already been emitted must be removed from the atmosphere and permanently stored.

Researchers are looking for new ways to store CO2

"In order for industrial production to remain possible despite this, we have to take completely new technological paths," says Dr Benjamin Dietrich from the Institute of Thermal Process Engineering (TVT) at the Karlsruhe Institute of Technology (KIT). "This also applies to the provision of carbon in industry. It is needed in the production of batteries, in the paint industry, in the agricultural sector or even in the production of building materials. Until now, it has mostly come from fossil sources." In the NECOC (NEgative CarbOn dioxide to Carbon) research project coordinated by Dietrich, KIT is therefore developing, together with its joint partners INERATEC and Climeworks, a process with which CO2 from the atmosphere can be processed into carbon. "If this then remains bound in the long term, we combine negative emissions with a building block of post-fossil raw material supply in the sense of a future carbon management strategy. This is a double contribution to a more sustainable future," Dietrich says. Currently, the research team has set up and commissioned a container-scale experimental plant, which can currently extract almost two kilogrammes of CO2 from the ambient air and convert it into 0.5 kilogrammes of solid carbon every day in continuous operation.

From greenhouse gas to recyclable material in three steps

The NECOC process combines three process steps. In the first step, CO2 is separated from the ambient air with the help of an adsorber (direct air capture). It is then reacted in a microstructured reactor with green hydrogen from a connected electrolyser. In the process, the components carbon and oxygen form a new bond: the CO2 now becomes methane and water. While the water flows back into the electrolyser, the methane with its carbon component flows into a reactor with liquid tin. In the third step of the process, a pyrolysis reaction takes place in rising bubbles, i.e. the methane molecules are split. This produces hydrogen, which is returned to the first step. What remains is pure carbon, which floats as a microgranular powder on the tin and is continuously actively separated from it. The process makes it possible to produce different carbon modifications such as graphite, carbon black or even graphene by changing process parameters such as the temperature level.

What's next?

The start of the experimental plant marks the end of the first funding phase of the NECOC project. The second phase envisages scaling up and optimising the NECOC process for an expanded expansion stage "We want to make the process even more energy-efficient by improving the recovery of process heat," says project leader Dr. Leonid Stoppel from the Karlsruhe Liquid Metals Laboratory KALLA. "We are also looking at the integration of high-temperature heat storage and the direct integration of solar heat." Furthermore, the integration of CO2 point sources, novel approaches to remove CO2 from the air and the influence of trace and accompanying components from the process compound on the carbon quality will be investigated.

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