Direct air capture
Carbon dioxide removal is achieved when ambient air makes contact with chemical media, typically an aqueous alkaline solvent[4] or sorbents.
Following the completion of these three stages, the separated pure CO2 is either utilized or stored, while the recovered solvents or sorbents are recycled for reuse in the CO2 capture process.
[16][18] Among the specific chemical processes that are being explored, three stand out: causticization with alkali and alkali-earth hydroxides, carbonation,[19] and organic−inorganic hybrid sorbents consisting of amines supported in porous adsorbents.
The idea of using many small dispersed DAC scrubbers—analogous to live plants—to create environmentally significant reduction in CO2 levels, has earned the technology a name of artificial trees in popular media.
[20][21][22]In a cyclical process designed in 2012 by professor Klaus Lackner, the director of the Center for Negative Carbon Emissions (CNCE), dilute CO2 can be efficiently separated using an anionic exchange polymer resin called Marathon MSA, which absorbs air CO2 when dry, and releases it when exposed to moisture.
[1][18][26] Researchers posit that DAC could help contribute to the goals of the Paris Agreement (namely limiting the increase in global average temperature to well below 2 °C above pre-industrial levels).
[33] A 2020 analysis revealed that DAC 2 technology may be an unsuitable option to capture the projected 30 Gt-CO2 per year as it requires an enormous amount of materials (16.3–27.8 Gt of NH3 and 3.3–5.6 Gt of EO) [33] The same study found that DAC 1 technology requires at least 8.4–13.1 TW-yr (46–71% TGES), an estimate that was calculated with the exclusion of the associated energy costs for carbon storage.
[33] Energy cost concerns were explored in 2021 and found that In order for DAC technology to maintain a carbon removal of 73-86% per ton of CO2 captured, DAC would demand land occupation and renewable energy equivalent to what is needed for a global switch from gasoline to electric vehicles, with approximately five times higher material consumption.
A DAC system meant to combat six million metric tons of CO2 per year, may be sized at about 30 kilometers in length and 10 meters in height[37] Though using fossil fuel to generate electricity would release more CO2 than captured CO2, the minimum energy required for DAC technologies is estimated to be 250kWh per tonne of CO2m whereas capturing with natural gas and coal power plants requires about 100 and 65 kWh per ton of CO2 [38] This could lead to a new set of environmental impacts in the future.
[9] DAC also requires much greater energy input in comparison to traditional capture from point sources, like flue gas, due to the low concentration of CO2.
[9] When DAC is combined with a carbon capture and storage (CCS) system, it can produce a negative emissions plant, but it would require a carbon-free electricity source.
[42] However, the majority of existing DAC facilities are small scale,[28] And operate primarily to sell the captured CO2 for use in other products rather than permanently sequestering it.
CarbonBox DAC facilities are the size of a shipping container, can be installed on site and utilize low-carbon energy sources to remove CO2 from the atmosphere.
[75] The Orca, pioneered by Zurich-based Climeworks with support from Microsoft in 2021, was the first large-scale DAC plant, removing 4000 tons of CO2 annually[76] this amount corresponds to approximately 1.75 million liters of gasoline.
[80] The company plans to develop DAC technology in alignment with the country's renewable grid and rich geology, both of which are suitable for CO2 storage.
[81] This project is still in its development phase, however, following support from the Kenyan government and international DAC companies, the team has swelled to employ 53+ individuals.
[82] In collaboration with Carbonfuture, Octavia Carbon now seeks to implement a breakthrough digital Monitoring, Reporting, and Verification (dMRV) system for DAC.
[84] Project Hummingbird will utilize the mineralization process by injecting the stored CO2 into the basalt rock formations native to the Rift Valley[84] One of the largest hurdles to implementing DAC is the cost of separating CO2 and air.
These projects are the result of initial selections from President Biden's Bipartisan Infrastructure Law [89] Carbon Engineering is a commercial DAC company founded in 2009 and backed, among others, by Bill Gates and Murray Edwards.
[39] Climeworks's first industrial-scale DAC plant, which started operation in May 2017 in Hinwil, in the canton of Zurich, Switzerland, can capture 900 tonnes of CO2 per year.
[39] Soletair Power is a startup founded in 2016, located in Lappeenranta, Finland, operating in the fields of Direct Air Capture and Power-to-X.
[99] Within the research domain, the ETH Zurich team's development of a photoacid solution for direct air capture marks a significant innovation.
This method's potential for scalability and its environmental benefits align it with ongoing efforts by other companies listed in this section, contributing to the global pursuit of effective and sustainable carbon capture solutions.
[104] In the United States there is conflict between politicians and politically unaffiliated environmental advocates on Direct Air Capture as it relates to economic benefit and efficiency in improving climate change associated risks.
One of the main grievances climate campaigners have is in regards to how DAC is perceived to be at best, a costly irrelevance to the more pressing need to cut emissions and, is a ploy that is utilized to maintain the fossil fuel industry's status quo, and perpetuate pollution [105] The Stratos Project, was purchased by Occidental Petroleum for $1.1 billion.
[45] Participants expressed disdain for the possibility that DAC might allow companies to continue pollutive practices while greenwashing their public image was raised across all focus groups.
[45] Other participants worried that DAC technology would be used as a front by fossil fuel corporations, to create the illusion that something was being done to combat climate change without contributing real benefit to the environment.
"[42] The study revealed that the overall perception was that DAC is merely an intervention that fails to address the root cause of climate change and instead sustains the contributors to the crisis itself.
[113] The Institute of Policy studies regards this decision to be risky because "the promise of DAC may never materialize" and should the deployment of this technology fail, the result will be only harm on frontline communities in "new and unacceptable ways".
[120] Individuals concerned with protecting animal life also argue that increasing demand for land for BECCS would be an additional threat to biodiversity.
