Adsorption and Low-Grade Heat Regeneration

Capture Mechanism

Solid

Furthest Progress*

TRL 9

Highest Risks

Energy
Cost

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Method Overview

Definition:

CO2 adsorption onto the surface of a solid sorbent material (where CO2 is captured on the surface of a porous solid material), followed by a desorption process where mainly low-grade heat (<120 °C) is used to release the CO₂ from the sorbent.*

Example:

Fans pull air over solid particles with large surface area that is used to physically or chemically bind with CO₂ from air and release it in the presence of higher temperature and/or lower pressure.*

Advantages:

Sorbents of this type exhibit higher capture capacities per cycle than liquid DAC approaches (excluding continuous electrochemical DAC).
Lower regeneration temperatures enable the use of waste heat and renewable energy sources for regeneration more easily.
This technology is modular and requires little land area, making it easier to scale and more adaptable to a variety of installations.
This approach offers more choice in sorbent design than other approaches, which facilitates greater optimization for various conditions and material properties.

Disadvantages:

Sorbents of this type frequently co-adsorb water, which typically lowers the capacity form CO2 and requires additional energy to remove during sorbent regeneration, however, water can improve CO2 binding strength and adsorption kinetics so humidity is often controlled.
Specific material considerations like hydrolytic stability are needed based on plant location and climate conditions to control CO2 binding strength and selectivity.
Sorbent degradation over repeated capture cycles requires more frequent replacement.
This approach is commonly affected by pressure drop, which occurs as air is moved through the solid filter. Compensating for this drop requires additional energy to push air through the system.

* Reproduced from The Applied Innovation Roadmap for CDR (2023) by RMI.

Company Overview

Plot of estimated funding vs. deployment status of companies utilizing this approach. Select data points to view company details. Only companies for which funding information is publicly available are included. Companies without funding information are tabulated with related details where relevant.

Summary of Deployments

View DAC deployments within this approach that have achieved or surpassed prototype scale. Planned deployments are included. Sort DAC deployments by company, scale, start of operations, and more. Because DAC is a rapidly evolving industry, this list may not be exhaustive.*

* Due to uncertain funding, plans for most DOE-funded DAC Hubs are not included in this analysis.

Risk Assessment

RMI's Applied Innovation Roadmap for CDR (2023) categorizes the risks associated with different classes of DAC technologies. Their assessment of this method is reproduced here and contextualized with current self-reported company data, where available.

Energy Requirements

High risk: Sorbent regeneration by low grade heat is very energy intensive.

The required energy meets the DAC criteria for “high risk” (>5 GJ/tCO2). The capture and sorbent regeneration alone require approximately 5-11 GJ/tCO₂. The full removal pathway will also require additional energy (e.g., compression, transport, and storage).

Self-reported energy requirements of DAC companies (GJ/tCO2): Aircapture: 4, Carbyon: 9, CleanCaptureTech: 3.1, Climeworks: 7.2, DACLab: 6.5, NEG8 Carbon: 5.0, Spiritus: 3.6, Sustaera: 5.4.

Material Requirements

Low risk: No rare materials are required

Beyond basic construction materials (e.g., steel, cement), this solution requires chemicals (e.g., functionalized amine adsorbents, zeolites, MOFs) that need to be synthesized and purchased but are not rare.

Cost Requirements

High risk: The technology is modular; cost estimates are greater than $600/tCO2.

Ratings are based on cost estimates for FOAK plants and the quality of these estimates. Different cut-offs were applied for modular/non-modular technologies. For modular technologies, iteration is simpler and comparatively cheap. This technology meets the AIR criteria for “high” risk (FOAK <10 ktCO₂; >$600/tCO2 plus plant data available)

Self-reported cost requirements of DAC companies ($/tCO2): Clairity Technology: $700, Climeworks: $1000, Terrafixing: $1025, DACLab: $500.

Land Requirements

Low risk: Significant land areas are suitable for DAC siting.

These DAC plants have a small footprint (100 - 2000 km²/GtCO₂/y) compared to other CDR solutions and can be deployed on most types of land. The footprint is larger if land use for energy production is considered.

Self-reported estimates: Climeworks: 50 km²/GtCO₂/y

Water Requirements

Low risk: The volume of water needed for operation is insignificant.

Steam may be required for sorbent regeneration, but it is not expected to be a limiting consideration, especially since water may be recovered from ambient air.

Companies co-producing water: 280 Earth, Clairity Technology, NEG8 Carbon, Stathmos, ZeoDAC.

Environmental Impact

Low risk: No environmental impacts are anticipated beyond concerns from energy intensity.

Minimal to no environmental impacts are anticipated, apart from those associated with energy, water, and material requirements.

Co-Location of DAC and Storage

Low risk: Co-location of DAC and storage is relatively easy for this approach.

DAC performance might be affected by different climate conditions. However, these units can easily be deployed in favorable climates. Straightforward co-location with storage is also favorable given the high CO₂ purities from the DAC unit.

Secure Storage for 100+ Years

Low risk: Storage is durable.

Geological sequestration or in-situ mineralization (the primary storage options) are considered permanent storage approaches.

Path to MRV at Scale

Low risk: Measurement to inform MRV is straightforward.

Measurement and monitoring for DAC+S is straightforward. Capture occurs in a controlled environment and geological injection has established monitoring standards.

Key Innovations

DAC via adsorption and low-grade heat regeneration represents the largest portion of companies in the field, largely because it offers a high degree of flexibility to tailor the sorbent design and to optimize the capture cycle around many energy sources. As such, companies are pursuing a wide variety of solutions based on their conception of an ideal DAC system.

All companies share the goals of making DAC more cost and energy-efficient to remain competitive in a crowded field. Innovations by companies towards these goals can be broadly sorted as Material, Process, and Equipment design.

Material Design:

Novel Sorbent – This DAC approach typically involves amines-appended porous materials, metal-organic frameworks (MOFs), and zeolites. Some companies are pursuing new classes of sorbents, such as structured alkali carbonates and graphene-based materials, generally to reduce costs.
Water Production - The materials used to capture CO₂ in this DAC approach frequently co-capture water from air without a pre-drying step. Some companies are leveraging this feature to co-produce fresh water.
Manufacturing - These sorbents are not rare but must be mass-manufactured and structured. Both steps can strongly affect sorbent properties such as porosity. Several companies have formed partnerships with chemical manufacturers to support their deployments.

Process Design:

Energy Source - Reducing the energy requirements of sorbent regeneration by integrating renewable alternatives to direct heating (e.g., waste heat from data centers and other industries, steam-stripping, nuclear, geothermal, solar heat, etc.) is a major shared focus in the industry.
Energy Savings - Besides utilizing alternative energy sources, some companies have described ways in which their process design lowers energy consumption. A large focus is the development of more energy-efficient ways to regenerate sorbent materials using electricity (microwave, joule heating, etc.). In some cases, such as integration with HVAC, DAC can reduce the energy consumption of systems it is integrated with.

Equipment Design:

Air Contactor - DAC requires flowing enormous volumes of air through a contactor unit to capture CO₂ and that can come at a high energy penalty, especially due to pressure drop across the contactor. Innovations in contactor design, such as using passive air contactors, seek to lower the energy required to filter out CO2.
Process Intensification - Learning through deployment reduces energy and cost requirements as real-world insights drive innovations. Improvements in the performance, cost, and/or energy-efficiency of successive iterations of DAC prototypes/deployments are positive indications of productive learning.

This tool organizes several key characteristics of DAC companies for which public information is available based on these three categories. Search below by company name or search "Material", "Process", of "Equipment" to view all related company activities.