Direct air capture (DAC)

What Materials Work Well for DAC?

Ideal materials for extracting CO2 are those which strongly attract CO2, while not attracting other gases in the air like nitrogen, oxygen and water vapour. Other important characteristics of ideal capture materials include, but are not limited to:

• chemical stability, meaning they can withstand many cycles of regeneration;

• capture capacity, meaning a large amount of CO2 can be captured; and

• low cost to manufacture or procure.

It is usually the case that solid adsorbent materials for DAC also attract water vapor, while liquid absorbents are water based. Thus, DAC also requires thoughtful management of water — either water separated from the air, or the water used in solvents.

The choice of the DAC process and material will depend on the location of a project. The local climate – namely, the temperature, pressure and humidity – can alter how a material performs in a DAC system.

Real World Examples of DAC

‍Climeworks’ Orca plant in Iceland uses an amine-based adsorbent material. This material is a solid with a high surface area to which amine groups are chemically attached. These amine groups chemically react with CO2 in the air. In contrast, technology developed by Carbon Engineering for the STRATOS project in Texas uses a potassium hydroxide liquid absorbent to capture CO2. The potassium hydroxide reacts with CO2 in the air and, by using a liquid adsorbent. Many other capture materials are being developed and explored for large-scale deployment.

In both of these examples, heat is used to regenerate the material. For Climeworks’ amine-based sorbent system, the adsorbent material is heated to around 100°C, whereas for Carbon Engineering’s potassium hydroxide solvent system, the absorbent liquid is heated to around 900°C. In most DAC systems, the regeneration process is the most significant contributor to the total energy use. Other regeneration methods are being tested in hope of reducing this energy burden.

What makes DAC expensive?

DAC is one of the costliest CDR technologies. The primary reason for its cost is the amount of work it takes to separate CO2 from air, which is the equivalent of trying to find 4 special marbles mixed into a jar containing 10,000 marbles. This means that a large volume of air needs to be moved to collect a small amount of CO2, which requires electrical energy and relatively large equipment. Moreover, the adsorbent (or absorbent) must have a strong affinity for CO2, which means a relatively large amount of energy must be used in regeneration compared to many other similar separation processes. In addition, because this requires a lot of energy, it should also be from relatively low GHG emissions sources.

What is the role for DAC?

DAC is a useful tool to combat climate change because it can be used to offset the emissions from activities that are technically challenging to decarbonize (e.g., air transport), that we might want to continue to do despite the emissions (e.g., raising cattle), or address historical emissions. In addition, the infrastructure and operations needed for DAC are similar to other industrial processes, making it relatively easy for the existing workforce to be employed in a growing DAC industry. industry.

DAC has received policy support in Canada to both lower the cost of development and to establish project revenue streams. Through the federal Carbon Capture, Utilization, and Storage Investment Tax Credit, DAC projects can be eligible to receive 60 per cent of capital costs in tax credits. This lowers the initial cost of project development and reduces the barrier of getting a project financed.

In Alberta, DAC projects can generate carbon removal credits within the industrial carbon compliance market. This allows industrial facilities in Alberta to purchase carbon credits from participating DAC facilities to comply with emissions regulations. ‍