Recently, I came across a project that captures carbon dioxide directly from the atmosphere, which was quite shocking. China’s annual carbon emissions reach 14 billion tons, and the concentration of carbon dioxide in the atmosphere is 0.04% (400 ppm). Who thought of this brilliant idea to capture carbon from the air instead of focusing on industrial carbon capture?

DAC Technology: Direct Air Capture (DAC) refers to the technology that captures carbon dioxide (CO₂) directly from the atmosphere. Direct air capture (DAC) is a technology that removes carbon dioxide from the atmosphere. It captures CO₂ through special filters or chemical solutions, which can then be concentrated and stored underground or used for various applications. In the context where achieving global climate goals solely through emission reductions is challenging, DAC is seen as a key tool for mitigating climate change.

Direct Air Carbon Capture (DAC)

1. Components of Air

Air is a mixture of gases in the Earth’s atmosphere, with stable main components that vary slightly with altitude and environmental conditions: Major components (99.96% by volume):Nitrogen (N₂): 78% – A fundamental element for biological amino acids, chemically stable.

Oxygen (O₂): 21% – Supports biological respiration and combustion, a strong oxidizer.

Rare Gases: 0.93% (argon, neon, etc.) – Used as industrial protective gases and lighting fill gases. Trace components:

Carbon Dioxide (CO₂): 0.03%-0.04% – A greenhouse gas and a raw material for photosynthesis.

Water vapor (H₂O): Variable (0-4%) – Key to cloud formation and precipitation, affecting climate.

Others: Ozone (O₃), Methane (CH₄), Nitrogen oxides (NOₓ), and other trace gases, some of which are pollutants.

2. Direct Air Capture Technology (DAC)

The DAC technology captures CO₂ directly from the air, achieving “negative emissions.” The technical approach is as follows:

• Working Principle: The DAC system uses large fans or “sponge” materials (liquid or solid) to draw in air and capture CO₂, which is then released through heating or other means for utilization or storage.

• Technical Routes: Mainly divided into solid DAC (using solid adsorbents) and liquid DAC (relying on liquid solutions).

• Carbon Processing: The captured CO₂ can be stored in geological formations, converted into building materials, or used to produce low-carbon fuels.

(Large fans or sponge materials consume a lot of electricity)

1. Technical Principles

• Liquid Solvent Method: Air passes through a potassium hydroxide solution, where CO₂ forms carbonates, which are then decomposed at high temperatures (900°C) to release pure CO₂.

• Solid Adsorption Method: Air contacts special resins or metal-organic frameworks (MOFs), adsorbing CO₂, which is then desorbed by heating (80–120°C) or vacuum.

2. Introduction of International Companies and Projects

Currently, there are some demonstration projects, but large-scale implementation has not yet occurred.

Company	Country	Technical Route	Project Scale	Core Technical Features
Climeworks	Switzerland	Solid Adsorption	Orca plant in Iceland (4000 tons/year)	Modular design, basalt layer storage
Carbon Engineering	Canada	Liquid Solvent	Texas million-ton project (operational in 2024)	CO₂ used for synthetic fuels or enhanced oil recovery
Global Thermostat	USA	Solid Adsorption	1500 tons/year facility	Low-temperature desorption (105–120°C)

There are also some demonstration projects in China, which will be followed up continuously.

3. Advantages and Disadvantages of DAC Technology

Core Advantages

1. Flexibility

• Not limited by emission sources (can be deployed in deserts/coasts)
• Capture rate >90%, CO₂ purity >99%

Resource Utilization

• Can be stored underground (geological mineralization) or converted into fuels/plastics

Land Efficiency

• Requires >90% less land than artificial forests (1 ton of CO₂ = 25 hectares of forest)

Key Challenges

1. High Cost and Energy Consumption: It is understandable that capturing carbon dioxide from such a low concentration in the air and then regenerating it requires significant investment costs. The price is expected to be much higher than conventional industrial flue gas wet decarbonization (MDEA carbon capture technology).

1. Low Technology Maturity: Currently, many projects are still in small-scale demonstration stages, making large-scale implementation difficult.

2. Energy Consumption Trap: Capturing 1 ton of CO₂ requires 1,500–2,500 kWh of electricity.

DAC Keywords

• Solid Adsorption (e.g., Climeworks): Materials: Amino resins or MOFs (metal-organic frameworks)

• Key Reaction: CO₂ + Adsorbent → Weak chemical bond, desorption at 80–120°C

• Liquid Solvent (e.g., Carbon Engineering):

• Materials: Potassium hydroxide (KOH) solution

• Key Reaction: 2KOH + CO₂ → K₂CO₃ + H₂O, thermal regeneration at 900°C

Conclusion

1. The DAC (Direct Air Capture) technology for direct atmospheric carbon capture currently sounds quite futuristic. After all, industrial flue gas can easily capture hundreds of thousands of tons per year, while DAC involves using large fans to blow air into an absorption liquid, consuming a lot of electricity while the stored carbon dioxide is negligible.

2. The DAC technology is currently mainly a demonstration function, providing a solution for carbon capture, indicating that even trace amounts of carbon dioxide can be captured, let alone in other scenarios, although the capture cost is extremely high.