Direct air capture

Flow diagram of direct air capture process using sodium hydroxide as the absorbent and including solvent regeneration.
Flow diagram of direct air capture process using sodium hydroxide as the absorbent and including solvent regeneration
An example of what Direct Air Capture could look like and how the process works.

Direct air capture (DAC) is the use of chemical or physical processes to extract carbon dioxide directly from the ambient air.[1] If the extracted CO2 is then sequestered in safe long-term storage (called direct air carbon capture and sequestration (DACCS), the overall process will achieve carbon dioxide removal and be a "negative emissions technology" (NET).

The carbon dioxide (CO2) is captured directly from the ambient air; this is contrast to carbon capture and storage (CCS) which captures CO2 from point sources, such as a cement factory or a bioenergy plant.[2] After the capture, DAC generates a concentrated stream of CO2 for sequestration or utilization. Carbon dioxide removal is achieved when ambient air makes contact with chemical media, typically an aqueous alkaline solvent[3] or sorbents.[4] These chemical media are subsequently stripped of CO2 through the application of energy (namely heat), resulting in a CO2 stream that can undergo dehydration and compression, while simultaneously regenerating the chemical media for reuse.

When combined with long-term storage of CO2, DAC is known as direct air carbon capture and storage (DACCS or DACS[5]). DACCS can function as both a carbon dioxide removal mechanism or a carbon negative technology. As of 2023, DACCS has yet to be integrated into emissions trading because, at over US$1000,[6] the cost per ton of carbon dioxide is many times the carbon price on those markets.[7] For the end-to-end process to remain net carbon negative, DAC machines must be powered by renewable energy sources, since the process can be quite energy expensive. Future innovations may reduce the energy intensity of this process.

DAC was suggested in 1999 and is still in development.[8][9] Several commercial plants are planned or in operation in Europe and the US. Large-scale DAC deployment may be accelerated when connected with economical applications or policy incentives.

In contrast to carbon capture and storage (CCS) which captures emissions from a point source such as a factory, DAC reduces the carbon dioxide concentration in the atmosphere as a whole. Thus, DAC can be used to capture emissions that originated in non-stationary sources such as airplanes.[2]

  1. ^ Cite error: The named reference :4 was invoked but never defined (see the help page).
  2. ^ a b Erans, María; Sanz-Pérez, Eloy S.; Hanak, Dawid P.; Clulow, Zeynep; Reiner, David M.; Mutch, Greg A. (2022). "Direct air capture: process technology, techno-economic and socio-political challenges". Energy & Environmental Science. 15 (4): 1360–1405. doi:10.1039/D1EE03523A. hdl:10115/19074. S2CID 247178548.
  3. ^ Keith, David W.; Holmes, Geoffrey; St. Angelo, David; Heide, Kenton (7 June 2018). "A Process for Capturing CO2 from the Atmosphere". Joule. 2 (8): 1573–1594. doi:10.1016/j.joule.2018.05.006.
  4. ^ Beuttler, Christoph; Charles, Louise; Wurzbacher, Jan (21 November 2019). "The Role of Direct Air Capture in Mitigation of Anthropogenic Greenhouse Gas Emissions". Frontiers in Climate. 1: 10. doi:10.3389/fclim.2019.00010.
  5. ^ Quarton, Christopher J.; Samsatli, Sheila (1 January 2020). "The value of hydrogen and carbon capture, storage and utilisation in decarbonising energy: Insights from integrated value chain optimisation" (PDF). Applied Energy. 257: 113936. Bibcode:2020ApEn..25713936Q. doi:10.1016/j.apenergy.2019.113936. S2CID 208829001.
  6. ^ "Carbon-dioxide-removal options are multiplying". The Economist. 20 November 2023.
  7. ^ "The many prices of carbon dioxide". The Economist. 20 November 2023.
  8. ^ Sanz-Pérez, Eloy S.; Murdock, Christopher R.; Didas, Stephanie A.; Jones, Christopher W. (12 October 2016). "Direct Capture of carbon dioxide from Ambient Air". Chemical Reviews. 116 (19): 11840–11876. doi:10.1021/acs.chemrev.6b00173. PMID 27560307.
  9. ^ "Direct Air Capture (Technology Factsheet)" (PDF). Geoengineering Monitor. 24 May 2018. Archived (PDF) from the original on 26 August 2019. Retrieved 27 August 2019.