RWTH Aachen University: Efficient removal of carbon dioxide from the atmosphere is already possible today

RWTH researchers publish in “Nature Energy” on negative emissions and other environmental impacts caused by the direct separation of carbon dioxide from the air.

Achieving the climate goals requires so-called negative emissions, i.e. the removal of carbon dioxide (CO2) from the atmosphere. A very promising technology for this is the direct separation of carbon dioxide from the air, English Direct Air Capture or DAC for short. At the same time, however, energy and materials are required, the generation and production of which lead to indirect CO2 emissions and other environmental impacts. The overall environmental benefit of DAC is therefore unclear.

In their research work as part of the Kopernikus project “Power-to-X”, RWTH scientist Sarah Deutz from the Chair of Technical Thermodynamics and Professor André Bardow, formerly RWTH and now ETH Zurich, showed that the first commercial DAC systems in Hinwil (Switzerland) and Hellisheiði (Iceland) can already provide negative emissions today. High efficiencies of 85.4 percent and 93.1 percent for carbon separation can be achieved. They published these results under the title “Life-cycle assessment of an industrial direct air capture process based on temperature-vacuum swing adsorption” in the journal “Nature Energy”.

Climate benefits depend on the energy source

Deutz and Bardow found that the climate benefits of DAC strongly depend on the energy source. The adsorbent used and the design of the system, on the other hand, only contribute 45 and 15 grams of CO2 per kilogram to the CO2 footprint of the capture. Only when using low-carbon energy, such as the geothermal energy in Hellisheiði, is this proportion of emissions significant. The large-scale use of DAC to capture one percent of annual CO2 emissions worldwide would probably not be limited by the availability of materials and energy and could be a possible step towards achieving the climate goals. Other environmental impacts would increase by less than 0.3 percent. The captured carbon dioxide could be stored to provide negative emissions, or serve as an alternative carbon component, for example for synthetic fuels. The energy sources used and energy efficiency are key to the environmental friendliness of these applications.

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