How KIT researchers, together with industrial partners INERATEC and Climeworks, are countering climate change with negative emissions, converting the greenhouse gas carbon dioxide into an industrially usable raw material.
"Five to twelve!" are the plaintive words of climate activists. They are becoming increasingly louder and more demanding. In order to stop climate change, the reduction and avoidance of carbon dioxide (CO2) in all areas of life and the economy has been a top priority so far. Despite global socio-political efforts, such as the Paris Climate Agreement of 2015 and most recently the UN Climate Change Conference in November 2022, the record is sobering. Climate targets that have been set remain unattained. On the one hand, this is due to the fact that measures cannot be implemented quickly enough. On the other hand, there is simply a lack of effective solutions.
At the turning point
The official climate statistics reveal the bitter truth: It is not enough to reduce emissions of CO2 and other greenhouse gases to limit global warming to a maximum of 1.5 degrees. This value marks the turning point at which progressive climate change becomes increasingly harmful to people and their habitat. Rethinking and action are required to recapture emissions already emitted. Against this background, KIT has been collaborating with the companies Climeworks Deutschland GmbH and INERATEC GmbH in the NECOC (Negative Carbondioxide to Carbon) project since 2019. Their globally unique approach: extracting CO2 from the air and converting it into solid carbon. Dr.-Ing. Benjamin Dietrich from the Institute of Thermal Process Engineering (TVT) of KIT coordinates the project and is convinced: "Our technical solution brings us a decisive step closer to the ambitious climate policy goals. Carbon dioxide, which is removed from the atmosphere as a negative emission, can no longer harm the climate."
Carbon dioxide (CO2) accounts for the lion's share of the greenhouse effect. To slow down the resulting global warming, greenhouse gas emissions must be massively reduced. This is a start, but it will not be enough to achieve the climate targets. That is why technical solutions are being developed to remove CO2 from the atmosphere. Since this is the opposite of emissions, the term "negative emissions" was coined for this. In addition to CO2 capture, which is the basis of NECOC, there are other approaches to negative emissions: for example, the (re)afforestation of forests or the fertilization of oceans to increase natural CO2 uptake.
The demonstration plant at KIT's Campus North, which has been commissioned in 2022, combines important process steps of the three project partners to form a significant process chain. The basis is the CO2 capture from ambient air developed by Climeworks, known as "Direct Air Capture". The air is drawn in from the environment by fans and the climate-damaging carbon dioxide is separated with the help of a selective filter. By heating, the CO2 is then released for the subsequent process of methanation. In INERATEC's methanation reactor, CO2 reacts at pressure and high temperatures to form methane and water with the addition of regenerative produced hydrogen. "In the final step, the methane produced is broken down into its components in a bubble column filled with liquid tin at high temperatures. Decomposition into hydrogen and carbon takes place in rising gas bubbles. The hydrogen is recycled for the methanation process. In the bubble column reactor, the resulting black powder floating on top can then be mechanically separated," Dietrich explains the so-called methane pyrolysis, which was developed at the Karlsruhe Liquid Metals Laboratory (KALLA) as a facility of the KIT Institute for Thermal Energy Technology and Safety (ITES). Methane pyrolysis produces solid carbon powder that can be used as a raw material for industrial applications. Conceivable uses would be as a building material in the construction industry, in electrode foils, in the agricultural industry, or for paints. Dietrich reports on the current status: "We have combined the know-how of all partners and created a coherent process on a container scale. In continuous operation, the pilot plant currently removes just under two kilograms of CO2 from the ambient air every day, depending on the design, and produces around 0.5 kilograms of solid carbon from it."
"Global CO2 reduction alone is not enough. Only by removing CO2 from the atmosphere, it would be possible to slow down effectively the greenhouse effect. With our plant, we convert the climate-damaging CO2 into an economically usable raw material that is otherwise still mainly obtained from fossil sources today."
From load to yield
With the commissioning of the plant, the project partners were able to demonstrate that carbon dioxide can be transformed for the better. "We have succeeded in demonstrating the NECOC process. The next few months will remain exciting. We are investigating how different carbon modifications can be produced with different process parameters. This could be carbon black or graphene-like carbon, for example. We are paying particular attention to how efficiently the gases are converted in the individual process steps in the overall process and how we can recover and use the process heat directly," says Dietrich. For use in the market, he says, the next stage of development must be reached and the quality requirements of the purchasing companies must be met. NECOC offers the opportunity to replace the conventional manufacturing process of black powder based on fossil raw materials, such as crude oil, with a sustainable manufacturing process combined with negative emissions. A double benefit for the environment. Project coordinator Dietrich provides another perspective: "In addition to air as a source of CO2 for generating negative emissions, other sources are also conceivable, such as high-emitting industrial plants that could be directly coupled to the process. Wherever CO2 avoidance is already exhausted or emissions are simply unavoidable, such as in cement production, direct tapping of carbon dioxide is a future solution."
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