The term “Direct Air Capture” (DAC) refers to chemical and engineering processes for capturing carbon dioxide (CO₂) from the ambient air. This technology plays an important role in climate protection strategies and the decarbonization of various economic sectors, but is still at a relatively early stage of technical development.
How It Works
DAC systems draw in ambient air and filter out CO₂, which makes up about 0.04% of the atmosphere. Two main processes are used for this:
- Chemical Absorption (Liquid process):
- Use of amine solutions or alkali hydroxides (e.g., sodium hydroxide or potassium hydroxide)
- CO₂ dissolves in the solution and forms carbonates
- Heating releases pure CO₂
- Solid-Phase Adsorption (Fixed-point method)
- Use of special materials such as amines on porous supports or metal-organic frameworks (MOFs)
- CO₂ adheres to the surface of materials
- Regeneration Through Heat and Vacuum
System Architecture
A DAC system consists of several components:
- Large fans for air intake
- Filter chambers containing absorption or adsorption material
- Regeneration unit for CO₂ recovery
- Compressors for compressing CO₂
- Control and Monitoring Systems
Application and Cost-Effectiveness
There are a wide variety of potential uses for the captured CO₂. Among the best-known are the production of synthetic fuels (e-fuels), its use as a raw material for the chemical industry (e.g., e-methanol), and its application in the food and fertilizer industries. Alternatively, the captured CO₂ can also be injected and stored underground (CCS).
Pioneering companies such as Carbon Engineering (2015), Climeworks (2017), and Zero Carbon Systemsare already operating their first commercial facilities, with more in the planning stages. One of the biggest challenges for DAC is the cost of capturing CO2 from the air. According to a study by ETH Zurich, Climeworks’ current costs range from about $1,000 to $1,300 per metric ton. However, it is expected that these costs could decline in the medium to long term due to economies of scale.
Point Source Capture vs. DAC
Unlike DAC, Point Source Capture targets CO₂ capture directly at emission sources such as industrial facilities or power plants. Because of the higher CO₂ concentration (5–15%), the energy required is significantly lower there. DAC, however, offers the advantage of flexibility in site selection and enables negative emissions.
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