What is adsorbent-based direct air capture?
In adsorbent-based direct air capture (DAC), air is first blown through a solid material called adsorbent. The adsorbent has chemical groups on its surface, usually amines, that can selectively bind the carbon dioxide and humidity from air. This is called the adsorption step.
The adsorption step is followed by the desorption step, where the adsorbent needs to be regenerated, which means that the CO2 and water is removed from the adsorbent usually by heating. As a result, carbon dioxide can be captured directly from air, and produced as up to 100% pure gas stream.
Why is direct air capture costly?
The main cause of the cost is the very low concentration of CO2 in air of 0.04%. This results in enormous amounts of air required to be treated before reasonable amounts of CO2 can be produced. Consequently, the electricity required by air blowers is one of the major sources of the operating costs. However, these costs can be lowered by selecting adsorbent that causes a low pressure drop when air is blown over it.
Another implication of the low concentration of CO2 in air is that selectivity of the capture towards CO2 is paramount in the adsorbent. This is why specialized adsorbents are required for CO2 to be captured in any practically relevant amounts on the material. However, often this leads to high-cost of the material. Also, these materials require elevated temperatures, e.g. near 100 °C during the desorption step. As a result, the main energy consumption in the process is often the regeneration of the adsorbent via heating.
The cost of the process, operating costs and the investment cost, are therefore controlled largely by the properties of the adsorbent material. However, adsorbent chamber dimensions and optimization of different process parameters are also important. Finally, the early stage of the technology without mass production has a huge impact on the investment cost of the process.
How will DAC2.0 improve direct air capture?
The carrying idea in the project is to develop a new kind of adsorbent that couples a high CO2 capacity in atmospheric CO2 capture with a low pressure drop and good heat transfer properties. This requires the combination of several scientific disciplines. Adsorbent and process development are combined with techno-economic analysis (TEA) and life cycle assessment (LCA). Moreover, the potential and opportunities of DAC in carbon utilization and carbon storage are identified. The project also has an advisory panel that is consisted of companies that will provide industrially relevant targets and advice to help guide the DAC2.0 project to a meaningful direction. To find out more about the project, see the work package descriptions.
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