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Understanding environmental trade-offs and resource demand of direct air capture technologies through comparative life-cycle assessment

Abstract

Direct air capture (DAC) technologies remove carbon dioxide (CO2) from ambient air through chemical sorbents. Their scale-up is a backstop in many climate policy scenarios, but their environmental implications are debated. Here we present a comparative life-cycle assessment of the current demonstration plants of two main DAC technologies coupled with carbon storage: temperature swing adsorption (TSA) and high-temperature aqueous solution (HT-Aq) DAC. Our results show that TSA DAC outperforms HT-Aq DAC by a factor of 1.3–10 in all environmental impact categories studied. With a low-carbon energy supply, HT-Aq and TSA DAC have a net carbon removal of up to 73% and 86% per ton of CO2 captured and stored. For the same climate change mitigation effect, TSA DAC needs about as much renewable energy and land occupation as a switch from gasoline to electric vehicles, but with approximately five times higher material consumption. Input requirements for chemical absorbents do not limit DAC scale-up.

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Fig. 1: Comparative environmental analysis of the reference case (current technology) for HT-Aq and TSA DAC technologies, respectively.
Fig. 2: Sensitivity analysis of main environmental pressure indicators as a consequence of plausible changes in crucial process parameters.
Fig. 3: Scale-up scenario for 1 Mt CO2 captured per year for the two DAC technologies.
Fig. 4: Technology scale-up comparison.

Data availability

The complete process inventories for the two DAC technologies studied are available and documented in Supplementary Data 1 and 2. The data and assumptions behind the 1 Gt scale-up analysis are documented in Supplementary Data 3, as well as all numerical values plotted in the figures.

Code availability

The OpenLCA process models for different cases of HT-Aq DAC and TSA DAC are provided on Zenodo at https://doi.org/10.5281/zenodo.5500477. To rerun the LCA calculations, OpenLCA (freeware) and the Ecoinvent 3.5 database (license required) need to be installed on a standard desktop computer or laptop with at least 8 GB RAM.

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Acknowledgements

K.M. was supported by a grant from the Eva Mayr-Stihl Foundation under the PROSET project. We thank G. Realmonte for providing additional references for DAC material consumption.

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Authors

Contributions

K.M., S.P. and F.C. co-designed the research and jointly wrote the paper. S.D. compiled the process inventories for the TSA DAC plant and conducted the LCA for this technology. K.M. compiled the process inventories for the HT-Aq DAC, conducted the comparative LCA, prepared the figures and compiled the supplementary material. S.P. developed the 1 Gt scale-up comparison with other technology pathways.

Corresponding author

Correspondence to Kavya Madhu.

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The authors declare no competing interests.

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Peer review information Nature Energy thanks Derrick Carlson and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Notes 1–5, Figs. 1–11, Discussion and Tables 1–7.

Supplementary Data 1

Ancillary calculations and numerical values for HT-Aq DAC.

Supplementary Data 2

Ancillary calculations and numerical values for TSA DAC.

Supplementary Data 3

Ancillary calculations and numerical values shown in plots and Table 3.

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Madhu, K., Pauliuk, S., Dhathri, S. et al. Understanding environmental trade-offs and resource demand of direct air capture technologies through comparative life-cycle assessment. Nat Energy 6, 1035–1044 (2021). https://doi.org/10.1038/s41560-021-00922-6

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