# Analysis of Technologies for Carbon Dioxide Capture from the Air
## 3 DAC Companies  
Several companies have developed direct air capture technology, such as Carbon Engineering, Climewords, Global Thermostat, Hydrocell, Skytree and Infinitree. Carbon Engineering is a Canadian company led since 2009 by [PERSON], a professor at Harvard University [3]. The company's approach is based on the use of absorption technology with KOH aqueous solution, as shown in Figure 4 and discussed in Section 2.1. It is the only solvent-based company in the market. Carbon Engineering constructed the first pilot plant in British Columbia (Canada) in 2015, and spent the years between 2019 and 2021 constructing and designing a demonstration DAC plant. Currently, they have a commercial plant under construction in Parmian Basin (TX, USA), as shown in Figure 14, which has a capture capacity of 1 MtonCO\({}_{2}\)/year, the captured CO\({}_{2}\) being used for enhanced oil recovery [128]. The main features of this process are the air contactor design (instead of the convectional absorption column) and the pellet reactor (instead of a convectional precipitator). The first is an open-air contactor with a cross-flow and slab geometry: the aqueous solution flows downward along the PVC structured packing, while air is pushed horizontally and orthogonally to the solution with a velocity of 1.3 m/s, in order to achieve a trade-off between the operative (fan power) and capital (size of absorber) costs. The overall configuration differs from that of traditional closed counter-flow towers and reduces the total cost. The pellet reactor is used instead of the traditional precipitator, and CaCO\({}_{3}\) pellets are suspended in a solution flowing upward, while a slurry made of 30% Ca(OH)\({}_{2}\) is fed at the bottom. In this way, CaCO\({}_{3}\) pellets, rather than lime mud, are able to precipitate, reducing energy consumption and increasing the thermal efficiency to 78% [3]. Since the process uses natural gas for heating (the regeneration temperature is set to 1173 K), 0.48 tons of CO\({}_{2}\) are released per ton of captured CO\({}_{2}\) and are captured in a following step. The purity of the obtained CO\({}_{2}\) is 97.1% [129]. Another process was proposed by Carbon Engineering; it is called \"thermo-catalysis\". In this process, which will be used in the future, the captured CO\({}_{2}\) reacts with renewable hydrogen obtained by water electrolysis to produce synthetic fuels, such as gasoline, diesel and jet fuel [130]. A pilot plant for this kind of process is located in Squamish, British Columbia (Canada). Moreover, the company is proposing a purely electrical process, in which high-temperature electrical heating will provide thermal energy for calcination [49]. Figure 14: Carbon Engineering plant in _Texus_. Reproduced under a Creative Commons license [34]. Another important company is Clineworks, a Swiss company that is a spin-off of ETH Zurich, founded by the engineers [PERSON] and [PERSON] in 2009 [3,49]. The company developed their first prototype in 2013. Currently, they have the first commercial plant in the world, located in Hinwil (Switzerland), with a capture capacity of 900 tonCO\({}_{2}\)/year. In contrast to that of Carbon Engineering, the plant is scalable and modular, and it consists of a single collector that is able to capture 135 kgCO\({}_{2}\)/day, as in Figure 15 [3,131]. Climeworks uses an amine-functionalized sorbent of class II, such as the 3-aminopropyl methyldiethoxysilane (APDES), loaded onto nanofibrillated cellulose (NFC) (APDES-NFC-FD) ([PERSON], 2015). Regeneration is achieved by temperature vacuum swing adsorption (TVSA) and at a temperature of 373 K, exploiting the waste heat from a local incinerator. A full cycle has a duration of 4-6 h [129]. The CO\({}_{2}\) obtained with a purity of 99.9% is used to supply a greenhouse. Another commercial plant of this company is located in Hellisheidi (Iceland), called Orca, and it is able to capture and store CO\({}_{2}\) at 700 m underground, with a capacity of 4000 tonCO\({}_{2}\)/year.