DAC: Processes, types of DAC and Current state of DAC

What is DAC? 

Direct Air Capture (DAC) is an engineered CDR technology that uses chemical reactions to extract carbon dioxide (CO2) from the air. 

When air passes over these chemicals (sorbents/solvents), they selectively react with and trap CO2, allowing other components of air to pass through. The captured CO2 is then either stored underground in geological formations or mineralized or utilized. The estimated global removal potential by 2050 is 0.5–5 Gt CO2 annually.

DAC core processes

1. CO2 capture: CO2 from the air is selectively bound to the capture medium (leaving behind other molecules).
2. CO2 regeneration: The bound CO2 is released from the capture medium as a pure gas.

The methods of capture and regeneration affect energy efficiency, scalability, material usage, carbon intensity, ease of CO2 integration (for utilization or mineralization), CO2 purity, and maintenance needs.

Types of DAC

DACS can broadly be categorized into two types based on the medium of capture: solid and liquid DAC.

1. Solid-DAC (SDAC)

• Capture Medium: Solid sorbents
• Methodology: 
  • Air is passed through a filter containing a solid sorbent material.
  • The sorbent chemically binds with CO2 from the air.
  • Once saturated, the sorbent is heated to release concentrated CO2.
  • The sorbent cools and is reused in the next cycle.

2. Liquid-DAC (LDAC)

• Capture Medium: Liquid solvents

• Methodology

• Air is drawn into a contactor using large fans.
• The air passes through a chemical solution that selectively reacts with CO2.
• The CO2-rich solution is then processed and heated to concentrate the CO2 and regenerate the original solvent.

Why is CO2 regeneration the most important step in DACS?

The method of CO2 regeneration dictates the cost, energy efficiency, and scalability of a DAC plant. Here’s a breakdown of the 4 key regeneration methods:

• Low temperature regeneration 

1. Involves heating the capture medium to temperatures below 200°C to release CO2. 
2. Commonly used with liquid solvents like amine solutions, as they are particularly effective at low temperatures and provide CO2 capture with minimal material degradation.
3. Requires less energy compared to high temperature regeneration, Due to this energy costs decrease making it an economically attractive option.
4. Desorption tends to be slower at lower temperatures and may reduce the CO2 capture capacity.

• High temperature regeneration

1. Requires heating the capture medium to around 800°C, typically used for solid sorbents like metal oxides.
2. Requires significant energy, raising cost and dependence on renewable energy sources.
3. High efficiency in releasing CO2, as the intense heat ensures maximum CO2 desorption.
4. Repeated high-temperature cycles can reduce the lifespan of capture materials. 

• Moisture based regeneration

1. Uses moisture to release captured CO2 via moisture swing adsorption (a shift between dry and wet states).
2. Requires minimal energy compared to thermal methods
3. Desorption is slower compared to thermal methods

• Electrochemical regeneration

1. Uses an electric current to release CO2 through chemical reactions.
2. Heat-free and fully electrified with renewable energy integration.
3. Lower carbon footprint and higher energy efficiency

Current state of DAC in the CDR market

The DAC sector is experiencing rapid growth within the carbon dioxide removal (CDR) market, with approximately 161 projects globally in our database. Of these, only 30 projects are currently selling credits, while the rest are at various stages of development.The global distribution of these projects is visualized in our DAC deployment map, created in collaboration with the DAC Coalition.

From active DAC projects, it is observed that deployment is evenly split between SDAC and LDAC, with a few using novel electrochemical approaches.

Current landscape of the DAC market

• 30 suppliers have sold approximately 2.1 million tonnes of carbon removal credits, including both direct purchases and memorandums of understanding (MOUs).
• 1PointFive, Climeworks, and Heirloom collectively accounted for 87% of all the DAC credits sold to date.
• The average price of a DACS credit is $850. 
• Microsoft has contributed to 41% of the total DACS credits sold to date, making it the largest buyer in the market.
• Amazon and Airbus  accounted for 33% of the total credits sold to date, supporting 1PointFive’s efforts to scale.
• By late 2030s, the estimated price of DACS credits is projected to fall below $100 in real terms, based on survey data collected by AlliedOffsets.
• Geological storage is the most prevalent sequestration strategy, with the remaining projects favoring ex-situ mineralization, which yields cement and other building aggregates.