Direct air capture

There are the three stages of capture in DAC: the contacting stage, the capture stage, and the separation stage. In the contacting stage, the DAC system transports atmospheric air containing to the equipment using large-scale fans. Subsequently, in the capture stage, rapidly and effectively binds with liquid solvents in chemical reactors or solid sorbents in filters, which must possess binding energies equivalent to that of . Later in the separation stage, external energy sources facilitate the separation of from the solvents or sorbents, yielding pure and regenerated solvents or sorbents. Following the completion of these three stages, the separated pure is either utilized or stored, while the recovered solvents or sorbents are recycled for reuse in the capture process. Generally, solid sorbents DAC (S-DAC) uses low temperature process DAC, while liquid (amine or metallic hydroxides) sorbents DAC (L-DAC) uses low or high temperature process. S-DAC and L-DAC feature different properties in terms of kinetics and heat transfers. Currently, L-DAC and S-DAC represent two mature technologies for industrial deployment. Additionally, several emerging DAC technologies, including electro-swing adsorption (ESA), moisture-swing adsorption (MSA), and membrane-based DAC (m-DAC), are in different stages of development, testing, or limited practical application. has developed the MechanicalTree™ which simply stands in the wind to capture . The company claims this 'passive capture' of significantly reduces the energy cost of Direct Air Capture, and that its geometry lends itself to scaling for gigaton capture. Most commercial techniques use a liquid solvent—usually amine-based or caustic—to absorb from a gas. For example, a common caustic solvent: sodium hydroxide reacts with and precipitates a stable sodium carbonate. This carbonate is heated to produce a highly pure gaseous stream. Sodium hydroxide can be recycled from sodium carbonate in a process of causticizing. Alternatively, the binds to solid sorbent in the process of chemisorption. Among the specific chemical processes that are being explored, three stand out: causticization with alkali and alkali-earth hydroxides, carbonation, and organic−inorganic hybrid sorbents consisting of amines supported in porous adsorbents. Moisture swing sorbent In a cyclical process designed in 2012 by professor Klaus Lackner, the director of the Center for Negative Carbon Emissions (CNCE), dilute can be efficiently separated using an anionic exchange polymer resin called Marathon MSA, which absorbs air when dry, and releases it when exposed to moisture. A large part of the energy for the process is supplied by the latent heat of phase change of water. The technology requires further research to determine its cost-effectiveness. Metal–organic frameworks are crystalline porous materials composed of metal ion clusters linked by organic molecules, resulting in highly ordered three-dimensional structures with exceptionally large internal surface areas. Compared to conventional solid sorbents such as activated carbons and zeolites, MOFs offer greater tunability: their pore size, geometry, and surface chemistry can be systematically varied by changing the metal centers or organic linkers, enabling materials to be designed with specific CO₂ binding properties. The dataset contains results from approximately 400 million CPU hours of quantum chemistry calculations screening MOF candidates for CO₂ adsorption properties, making it one of the largest open computational datasets in the field. employs semi-permeable membranes. This method requires little water and has a smaller footprint. Electro-Swing Adsorption Electro-swing adsorption (ESA) has also been proposed. Rock flour Rock flour, soil ground into nanoparticles by glacier ice, has potential both as a soil conditioner and for carbon capture. Glacier melting deposits one billion tons of rock flour annually, and one ton of Greenlandic rock flour can capture of carbon. == Environmental impact ==

DAC is a carbon negative technology, with its greenhouse gas emissions (GHG) estimated to range from 0.01 t emitted per t captured when renewable electricity is used to 0.65 t emitted per t captured when grid electricity and natural gas (NG) heating are used. The energy source emission factor of DAC is the primary driver of DAC's GHG emissions. 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). The IEA estimates that capture of at least 85 million tonnes and 980 million tonnes of CO2 annually by 2030 and 2050, respectively, are needed to achieve net zero. However, others claim that relying on this technology is risky and might postpone emission reduction under the notion that it will be possible to fix the problem later, and suggest that reducing emissions may be a better solution. It is important to see DAC as a complementary solution that is necessary in helping to achieve climate targets. Opponents of DAC argue that the resources required to operate DAC technologies, are an immense burden that may outweigh the goal of the technology itself. A 2020 analysis revealed that DAC 2 technology may be an unsuitable option to capture the projected 30 Gt- 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) However, the material demand of DAC is mostly from common materials, such as steel, concrete and earth minerals (like zeolites and metallic hydroxides). The use of electric vehicle may require substantial accessibility to critical materials, and this limited availability of critical materials may not be able to sustain the demand needed for net zero. Some DAC technologies, especially liquid systems, require both high temperature heat and electricity. In these systems the electrical demand is made using natural gas, imported electricity from the grid, and oxyfuel combustion of natural gas. This means that many DAC technologies are powered by fossil fuels, the very thing the technology is meant to eliminate reliance on. However, from GHG emissions standpoint, DAC would generally be carbon-negative even if natural gas was used for heating, with emission factors of 0.3–0.65 t emitted per t captured. DAC also requires higher energy input in comparison to traditional capture from point sources, like flue gas, due to the low concentration of . Some authors give the theoretical minimum energy required to extract from ambient air as 250 kWh per tonne of , while capture from natural gas and coal power plants requires, respectively, about 100 and 65 kWh per tonne of . The additional penalty from the use of fans to pump air could add a 10% to 30% energy penalty if DAC energy demand is 10 to 4 MJ/t, respectively. == Applications ==

Practical applications of DAC include • enhanced oil recovery, • carbon sequestration,''' DAC is not an alternative to traditional, point-source carbon capture and storage (CCS), rather it is a complementary technology that could be utilized to manage carbon emissions from distributed sources, fugitive emissions from the CCS network, and leakage from geological formations. However, the majority of existing DAC facilities are small scale, DAC facilities that sell CO2 for beverage production operate with low recovery rates of around 4.7% and produces 58-tCO2 per day. The use of DAC facilities for commercial purposes, reemphasizes the opinion of naysayers, that DAC is a ploy used by corporations to protect and promote financial interest. == Operational/developing DAC facilities ==

DAC Projects and their respective processes for carbon removal and/or storage'''''' International DAC development • 53 DAC plants are expected to be operational by the end of 2024 • 93 DAC plants to be operating in 2030 with a combined capacity of 6.4-11.4 MtCO2/yr • By the end of 2024, 18 plants are scheduled to be operational in North America and 24 in Europe China DAC technologies have been proposed to help China in its pursuit for carbon neutrality by 2060. Following the 2021 Glasgow Climate Conference, as the leading GHG emitter, China has begun the development of various low-emission strategies. With China's commitment to DAC alone, global warming could decrease by approximately 0.2 °C–0.3 °C. China has developed its own direct air capture (DAC) technology, called "CarbonBox," developed by Shanghai Jiao Tong University and China Energy Engineering Corporation. Each module can extract over 100 tonnes of carbon dioxide (CO2) annually, resulting in a 99% pure CO2 product. 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. Iceland The Orca, pioneered by Zurich-based Climeworks with support from Microsoft in 2021, was the first large-scale DAC plant, claimed to be able to remove 4000 tons of CO2 annually this amount corresponds to approximately 1.75 million liters of gasoline. Howvever the actual performance has averaged 600 tonnes per year since it started operating, and fails to even extract sufficient CO2 to compensate for its own emissions. The DAC facility is located in Iceland, Hellisheidi, and is powered by the Hellisheidi Geothermal Power Plant. Orca consists of 12 amine-holding containers that collect a total of around 600 kg of CO2 per hour. This facility operates in conjunction with CarbFix, an Icelandic technology firm. CarbFix takes the captured CO2 from the DAC facility and injects the CO2 into the Earth's crust (through mineralization) 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. 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. In collaboration with Carbonfuture, Octavia Carbon now seeks to implement a breakthrough digital Monitoring, Reporting, and Verification (dMRV) system for DAC. dMRV systems allow real-time data tracking across the entire carbon removal process. Project Hummingbird will utilize the mineralization process by injecting the stored CO2 into the basalt rock formations native to the Rift Valley == Cost ==

File:The_cost_of_CO2_capture_using_direct_air_capture.jpg|thumb|399x399px|The impact of plant capacity on key solid sorbent direct air capture technologies Although DAC implementation was initially and optimistically estimated to cost around $100–300 per tonne, as of 2023 it is estimated that the total system cost is over $1,000 per tonne of . The Department of Energy estimated costs per tonne to be under $100, while other sources have estimated the cost to be much larger. , it is estimated that the total system cost is over $1,000 per tonne of . Under the Bipartisan Infrastructure Law, the U.S. Department of Energy will invest $3.5 billion in four direct air capture hubs. According to the agency, the hubs have the potential to capture at least 1 million metric tonnes of carbon dioxide (CO2) annually from the atmosphere. Once captured, the CO2 will be permanently stored in a geologic formation. The Department of Energy invested $1.2 billion to further developments of direct air capture facilities in Texas and Louisiana. These projects are the result of initial selections from President Biden's Bipartisan Infrastructure Law == Development ==

Carbon engineering Carbon Engineering is a commercial DAC company founded in 2009 and backed, among others, by Bill Gates and Murray Edwards. The company stated that it costs around $600 to capture one tonne of from the air. and received funding from EuropeanUnion's Horizon2020 research program. The CarbFix2 pilot plant project runs alongside a geothermal power plant in Hellisheidi, Iceland. In this approach, is injected 700 meters under the ground and mineralizes into basaltic bedrock forming carbonate minerals. The DAC plant uses low-grade waste heat from the plant, effectively eliminating more than they both produce. On May 8, 2024, Climeworks activated the world's largest DAC plant named Mammoth in Iceland. It will be able to pull 36,000 tons of carbon from the atmosphere a year at full capacity, according to Climeworks, equivalent to taking around 7,800 gas-powered cars off the road for a year. This plant is reported to capture at a cost of $1,000 (£774) per t. This high cost is primarily due to the size of the plant as product cost generally decreases with economy of scale. It is reported that for a 1 Mtpa plant, DAC cost would generally be within $94–232 per tonne of atmospheric removed. The company claims to remove for $120 per tonne at its facility in Huntsville. for Dubai Expo 2020, that can produce synthetic methane from captured from buildings. Prometheus Fuels Prometheus Fuels is a start-up company based in Santa Cruz which launched out of Y Combinator in 2019 to remove CO2 from the air and turn it into zero-net-carbon gasoline and jet fuel. The company uses a DAC technology, adsorbing CO2 from the air directly into process electrolytes, where it is converted into alcohols by electrocatalysis. The alcohols are then separated from the electrolytes using carbon nanotube membranes, and upgraded to gasoline and jet fuels. Since the process uses only electricity from renewable sources, the fuels are carbon neutral when used, emitting no net CO2 to the atmosphere. Heirloom Carbon Technologies Heirloom's first direct air capture facility opened in Tracy, California, in November 2023. The facility can remove up to 1,000 U.S. tons of annually, which is then mixed into concrete using technologies from CarbonCure. Heirloom also has a contract with Microsoft in which the latter will purchase 315,000 metric tons of removal. Other companies • Center for Negative Carbon Emissions of Arizona State University • Carbfix – a subsidiary of Reykjavik Energy, Iceland • Energy Impact Center – a research institute that advocates for the use nuclear energy to power direct air capture technologies • Mission Zero Technologies — a startup in London, UK • Carbyon – a startup in Eindhoven, the Netherlands • EDIBON - A Madrid, Spain based initiative advancing education and research in emission capture technologies. Innovations in research Within the research domain, the ETH Zurich team's development of a photoacid solution for direct air capture marks a significant innovation. This technology, still under refinement, stands out for its minimal energy requirements and its novel chemical process that enables efficient CO2 capture and release. 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.Recent research suggests that integrating warehouse automation systems into DAC facilities can reduce operational costs and improve scalability by streamlining equipment handling and system maintenance. == Political discourse ==

Environmentalist opposition 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 The Stratos Project, was purchased by Occidental Petroleum for $1.1 billion. This investment is regarded by some as an attempt to extend the longevity of the fossil fuel industry. The Stratos project is ultimately owned by Occidental Petroleum, an American oil company that bought Carbon Engineering on November 3, 2023 for $1.1bn and views carbon removal as a sort of future-proofing for its industry. Jonathan Foley, executive director of Project Drawdown (a research-based plan to reverse global warming and stop climate change) regards DAC technology as a greenwashing exercise, that mitigates climate change issues but does not seek to solve them. A study conducted in 2024, analyzed the conditional support of DAC technologies in the United States. The study revealed that most of the participants who were familiar with DAC technology and had concerns about climate change had questions regarding the moral hazards of DAC technology. Complications associated with the impact DAC may have on air quality in specific communities are called into question as well. Another study focusing on perceptions of DAC technology from climate concerned persons from the United States and the United Kingdom found similar results. A theme across all groups was the perception of DAC as a technology that is incongrous with the vision for a sustainable society. These technologies have also been characterized by multiple failures and aborted projects, contributing to the already persistent doubt regarding the credibility of DAC projects. Biden's Bipartisan Infrastructure Law Some environmentalists believe that the 3.5 billion investment in DAC is a "dangerous gamble" that puts the lives of frontline communities at risk. 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". Additionally, the IRS decision to not release information about which companies are benefiting from these new investments in DAC increases uncertainty among people who are concerned how their taxes are paying for DAC development. The reason for bipartisan support for DAC seems to be due to two merits, the environmental benefit of DAC and the potential economic advantages. Republicans argue that DAC can provide economic advantages to the countries and local areas hosting these facilities through job creation, increase tax revenue and economic diversification. The economic utility DAC also provides is protection for fossil fuel industries as many including ExxonMobil have donated generously to DAC research and development. Some view DAC as a feasible solution to combat global warming (primarily Democrats), whereas Republicans support for DAC lies in the way the technology will not interfere with the economic interests of fossil fuel companies. == Direct air capture shortcomings ==

BECCS project Bioenergy with carbon capture and storage (BECCS) has come under scrutiny for a variety of reasons but primarily because the technology is energy intensive, requires large land changes/usage and has the potential to leak carbon dioxide back into the atmosphere. Environmentalists argued that BECCS was an infeasible option because of the emissions that the project would produce. "Atmospheric CO2 levels could spike significantly, especially if a leak were to occur from a major storage site." The carbon intensity of most electrical grids is high, eg Australia recorded an intensity of 0.45 tonnes of CO2 per MWh. So the Icelandic plant would release more than 2 tonnes of CO2 for every tonne captured, if it was operating in Australia, whereas in the UK it would capture as much CO2 as was emitted, and in Iceland, where the grid is almost 100% renewable, there would be very little CO2 emitted. == See also ==