Economical and Green: Underground Storage of Carbon Captured Directly From Air


New research reveals that geological storage of low-purity carbon dioxide mixed with nitrogen and oxygen from direct air capture is an economically viable and environmentally friendly way to eliminate carbon from the atmosphere.

The threat of continuous climate change has one primary cause: carbon that was buried under the earth in the form of fossil fuels is being extracted and discharged into the atmosphere in the form of carbon dioxide (CO2). One promising way to approaching this problem is carbon capture and storage: adopting technology to capture CO2 out of the atmosphere to return it underground.

In new research issued in Greenhouse Gases Science and Technology, scientists from Kyushu University and the National Institute of Advanced Industrial Science and Technology, Japan, studied geological storage of low-purity CO2 mixed with oxygen (O2) and nitrogen (N2), produced by direct air capture (DAC) through membrane-based technology.

Several carbon capture projects are carried out at limited sources using concentrated CO2 emissions, such as coal-fired power plants, and require intense purification storage owing to the presence of hazardous gases such as sulfur oxide and nitrogen oxide. Furthermore, viable geological storage sites are typically far from the sources of CO2 which result in high transportation cost. 

Storage of Carbon
Schematic representation of low-purity CO2 storage with the membrane-based Direct Air Capture (DAC). Source: Takeshi Tsuji

In contrast, direct air capture of CO2 can be done anywhere, including at the storage site, and does not need intense purification because the pollutants, N2, and O2 are not hazardous. Hence, low-purity CO2 can be extracted from the atmosphere and inserted directly into geological formations, at least in theory. Understanding how the resulting mixture of CO2, N2, O2, acts when it is inserted and stored in geological formations is essential before underground storage of low-purity CO2 from direct air capture can be extensively adopted.

According to the study’s first author, Professor Takeshi Tsuji, “It is challenging to capture high-purity CO2 using DAC. We conducted molecular dynamics simulations as an introductory evaluation of the storage effectiveness of CO2-N2-O2 mixtures at three distinct pressure and temperature condition, corresponding to depths of 1,000 m, 1,500 m, and 2,500 m at the Tomakomai CO2 storage site in Japan.”

Although additional considerations such as studies of the chemical reactions of injected O2 and N2 at great depths are still required. The outcomes of these simulations propose that geological storage of CO2-N2-O2 mixtures generated by direct air capture is both economically viable and environmentally safe.

According to Professor Tsuji, “Because of the universality of ambient air, direct air capture has the potential to become a universal means of carbon capture and storage that can be executed in many remote areas, such as barrens and marine platforms. This is essential both for lessening transportation costs and securing social acceptance.”

Journal Reference: 

“Geological storage of CO2–N2–O2 mixtures produced by membrane-based direct air capture (DAC)” by Takeshi Tsuji, Shigenori Fujikawa, Masao Sorai, Masashige Shiga, Toyoki Kunitake, 1 June 2021, Greenhouse Gases: Science and Technology.

DOI: 10.1002/ghg.2099


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