Absorption and Low-Grade Heat Regeneration

Capture Mechanism

Liquid

Furthest Progress*

TRL 5

Highest Risks

Energy
Cost
Water
Environment

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Method Overview

Defintion:

CO2 absorption with a liquid solvent (e.g., amines or amino acids, where CO2 is dissolved or diffused in a liquid to form a solution), followed by a desorption process in which low-grade heat (120 °C or lower) is used to release the captured CO2 and regenerate the solvent.*

Example:

Fans pull air over an amino acid solution that chemically binds with CO2 in air. The resulting CO2-rich liquid is then processed at low temperatures (<120 °C) to release the CO2 for storage and regenerate the amino acid solution.*

Advantages:

Liquid amine scrubbing remains the most deployed method of CO2 capture in other industries where it is used to separate CO2 from more concentrated sources (12–15 %) than DAC (0.04%).
Amine sorbents are cheap and readily available, relative to other DAC approaches, however other equipment such as washing columns drive up the cost of this method.
Aqueous amine solutions strongly bind CO2 through chemical reactions forming carbamates and/or bicarbonate/carbonate species. Some amines show rapid capture rates comparable to aqueous hydroxide-based sorbents.
Lower regeneration temperatures and steam stripping can be used in this method.

Disadvantages:

High regeneration energy is required for sorbent regeneration despite utilizing low-grade heat, largely due to the large volume of liquid that must be heated.
This method requires high water consumption (~3-6 GtH₂O/GtCO₂) in the form of steam used to regenerate the sorbent.
Conventional amine sorbents suffer from oxidative degradation and volitility, and likewise are corrosive, which all affect operating costs. Alternative sorbents like amino acids have more favorable properties but generally exhibit slower absorption kinetics.

* 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

Very high risk: Low-grade heat solvent regeneration is very energy intensive.

Energy needs meet our DAC criteria for "very high risk“ (>10 GJ/tCO2). Capture and solvent regeneration alone require approximately 10-17 GJ/tCO₂. The full pathway will require additional energy (e.g., compression, transport, and storage).

Self-reported energy requirements of DAC companies (GJ/tCO2): MK Collect: 4.0.

Material Requirements

Low risk: No rare materials are required.

Apart from basic construction materials (e.g., steel, cement), this solution requires chemicals (e.g., amines or amino acids) that need to be synthesized and purchased. However, these materials are readily available.

Cost Requirements

High risk: The technology is non-modular and cost estimates are >$500/t.

Rating is based on the cost estimates for FOAK plants & the data quality used for these estimates. Different cut-offs for modular/non-modular technologies were applied, as modular approaches are comparatively cheaper and easier to scale. This technology meets our criteria for “high” risk (FOAK: >10 ktCO2; >$500/tCO2 plus available plant data).

Self-reported energy requirements of DAC companies ($/tCO2): MK Collect: $100 (100–150 AUD).

Land Requirements

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

This approach has a higher footprint per capture capacity than other DAC approaches, but optimal designs can reduce it. The footprint is larger if land use for energy production is considered.

Water Requirements

High risk: Large volumes of water are evaporated when operating the facility.

This DAC technology requires large amounts of water (~3-6 GtH₂O/GtCO₂), which restricts deployment to locations with low water stress indices.

Environmental Impact

High risk: No / incomplete data available. Risk due to amine volatility exists but is manageable.

No LCA exists for this technology. Impacts associated with energy, water, and material requirements are expected to be significant but manageable. Risks associated with amine volatility and toxicity should be easily controllable using a water washing column or nonvolatile and non-degradable solvents.

Co-Location of DAC and Storage

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

Performance of DAC can be affected by local conditions such as access water. However, CO2 storage is widely available, so co-location can be easily achieved.

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 is straightforward.

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

Key Innovations

Liquid amine scrubbers like monoethanolamine (MEA) are widely deployed in industry to capture CO2 from concentrated point sources (12-15 %) where it is efficient, but liquid amine perfomance in DAC applications is hindered by their substantial regeneration energy - despite using low-grade heat - and oxidative degratation. Conventional amines are further limited by their high toxicity, and their corrosiveness and volatility increase operating expenditures. While this technology is mature in other industries, DAC companies must make significant adaptations through innovative Material, Process, and Equipment design.

Material Design:

Material innovations in this method seek to reduce conventional amine degradation or optimize alternative sorbents, such as amino acids, with favorable properties (e.g., greater stability, lower volatility, lower corrosiveness) for DAC.

Process Design:

Some companies utilizing this DAC approach are integrating rewable geothermal heat to compensate for energy demand or are pursuing process innovations that avoid regenerating liquid amines in bulk - either operating on an amine mist or removing CO2 from amine solutions through crystallization.

Equipment Design:

Liquid amine-based CO2 scrubbing commonly uses large absorption towers to capture CO2, which limits modular deployments. Efficient air contactor design can enable more modularity and/or reduce the overall energy requirements of this DAC method.

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.