Definition :

Direct Air Capture is the fact to capture CO2 directly from the air. Different technologies and process can realize this task, such as amine scrubbing or calcium potassium scrubbing. This section is dedicated to calcium potassium scrubbing (amine gets its own section).

The full process is an addition of 4 chimical reactions as shown in the figure bellow, extracted from ^1.

The first reaction use potatium-oxide to capture CO2 from the air. $$CO_2 + 2KOH --> H_2O + K_2CO_3$$

The product K_2CO_3 will react with calcium hydroxide Ca(OH)_2. $$K_2CO_3 + Ca(OH)_2 --> 2KOH + CaCO_3$$ This second step allows to reuse the major part of the potatium oxide involde in the first reaction.

As a third step, CO2 is extracted from CaCO3, and a stream of concentrated CO2 gas is created through calciner, ready for storage. $$CaCO_3 --> CaO + CO_2$$

The fourth and last step is and hydratation of the CaO to create Ca(OH)2, used in the second reaction. $$CaO + H_2O --> Ca(OH)_2$$

As shown by the picture, this is process allows the re-use of its reactants by the major part.

Note : Datas extracted from ^1 concerns a study about a 1Mt CO2/year DAC plant.

Datas : Technical data was found in ^1, [^2], ^3 and ^4.

[^2]: Fasihi, M., Efimova, O. and Breyer, C., 2019. Techno-economic assessment of CO2 direct air capture plants. Journal of cleaner production, 224, pp.957-980. ^3: Keith, D.W., Holmes, G., Angelo, D.S. and Heidel, K., 2018. A process for capturing CO2 from the atmosphere. Joule, 2(8), pp.1573-1594. ^4: Vo, T.T., Wall, D.M., Ring, D., Rajendran, K. and Murphy, J.D., 2018. Techno-economic analysis of biogas upgrading via amine scrubber, carbon capture and ex-situ methanation. Applied energy, 212, pp.1191-1202.