Cryogenic Phase Separation (Vapor-Solid)

Capture Mechanism

Cryogenic

Furthest Progress*

TRL 4

Highest Risks

Energy
Cost
Environment

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Method Overview

Definition:

Cryogenic separation in which very low temperatures enable a phase separation of CO2 from other gases by deposition (a phase transition of CO2 from vapor to solid).*

Example:

At very low temperatures, CO2 in air solidifies as dry ice on the surface of heat exchangers and then is removed through sublimation, resulting in concentrated CO2 for storage.*

Advantages:

Cryogenic methods are precedented in carbon capture from more concentrated industrial waste streams.
CO2 can be recovered from air at very high purity (99.99%) using this method.
Because of its operating temperature, this method can integrate well with production of liquid CO2, which is favorable for transportation and storage.

Disadvantages:

While it is competitive in post-combustion capture where CO2 is more concentrated, the estimated energy requirements of cryogenic DAC are only competitive with other methods when operated in arctic regions. Seasonal challenges limit operating times in these regions to 6–9 months per year. These estimates also assume advances in cryogenic refrigereration efficiencies. Other estimates project energy consumption as high as 50–102 GJ/tCO2.
Water must be removed from air prior to CO2 capture or it will solidify along with CO2 and affect the purity of the product.

* 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: Cryogenic separation is very energy intensive.

Energy needs meet our DAC criteria for “high risk” (>5 GJ/tCO2). Contacting and cooling alone require approximately 5 GJ/tCO₂.

Material Requirements

Low risk: No rare materials are required.

Apart from basic construction materials (e.g., steel, cement), this solution does not require the use of physical or chemical solvents or sorbents. If applicable, cryogenic liquids will be required.

Cost Requirements

Very high risk: Incomplete cost data.

We base our rating on cost estimates for FOAK plants and the quality of these estimates. We apply different cut-offs for modular / non-modular technologies, as iteration is easy and comparatively inexpensive for modular technologies. This technology meets our criteria for “very high risk” (FOAK <10 ktCO2; >$500 with incomplete data).

Land Requirements

Medium risk: Deployment may be limited to very cold regions to avoid massive energy requirements.

No information is available, but it is expected that cryogenic DAC plants will have a larger footprint than other DAC approaches due to the number of precooling units, separation units, compressors, and condensers that will be required. The footprint will be greater if land use for energy production is considered. Also, in the case of deployment in remote regions, dedicated energy infrastructure will be difficult to access.

Water Requirements

Low risk: Water is not expected to be required in significant quantities.

No information is available, but water is not expected to be an issue.

Environmental Impact

High risk: No / incomplete LCA data available.

No LCA is currently available. Beyond impacts associated with energy and material requirements, no other impacts are anticipated.

Co-Location of DAC and Storage

Medium risk: Co-location may be challenging.

Remote regions can make co-location challenging, although the technology can produce CO2 outputs suitable for long-term storage.

Secure Storage for 100+ Years

Low risk: Storage is durable.

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

Path to MRV at Scale

Low risk: Measurement is straightforward.

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

Key Innovations

While this method relies on well-developed equipment used in other cryogenic seperations, it must be significantly optimized to become energy-efficient enough for DAC. To address this, Atmosfuture proposes to incorporate substantial heat recovery in its upcoming pilot project.

To the best of our knowledge, only Atmosfuture has completed a prototype of a cryogenic DAC system and related companies are still in a concept-development stage, based on public information. Thus, Atmosfuture's material, process, and equipment design encompasses current innovation in the industry. Selected characteristics of the company are outlined below.

Material Design:

Refrigerants - This DAC approach does not rely on conventional liquid, solid or membrane-based sorbents, however, innovations in refrigerant materials and alternatives to heat exchangers like cryogenic liquids should be explored to help minimize the energy requirements of this method.

Process Design:

Water recovery - Whereas some DAC approaches choose to tailor material properties to capture water as a co-product, pre-drying air is necessary in cryogenic DAC to deliver pure CO2. Atmosfuture reports that it can produce up to 960 liters of clean water per MWh of electricity.
Energy production - After de-sublimation of CO2, Atmosfuture uses cooled, CO2-lean air to drive a thermal turbine and generate electricity that supports power cooling. The cold air is also used to pre-cool CO2-rich air before de-sublimation.
Energy source - Atmosfuture plans to integrate with data centers to utilize waste heat in its process.

Equipment:

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. Atmosfuture uses passive air contacting to reduce associated energy and cost requirements.