(700f) Revealing the Effect of Humidity on the Oxidative Stability of Solid Amine Sorbents for Direct CO2 Capture from Air

The rate of anthropogenic CO₂ emission for the past 100+ years has created a geo-scale problem that requires geo-scale solutions. To limit the associated increase of the average global surface temperature to below 2 ºC by the end of this century, fulfilling the ambitions of the Paris agreement,¹ CO₂ removal from the atmosphere at a gigaton level (~10 Gt/year by mid-century) must be deployed together with other mitigation technologies.² The development of adsorptive materials for the direct air capture (DAC) of atmospheric CO₂ is one response made by the scientific community which aims to create a suite of negative emissions technologies. However, the deployment of DAC technologies towards Gt-scale capture is still hindered by the nascency of the technology, and concerted R&D is targeted towards technology maturation and cost reduction. For DAC technologies based on solid adsorbents, the cost of the adsorbent is a significant component of the overall cost.^3-8 Some of the most promising adsorbents are supported amine materials, for which the chemical stability of sorbents can have a large impact on material and process costs. The stability of amine adsorbents depends on their chemical structure, as well as process parameters such as temperature, humidity, etc. The oxidative degradation of amine-based sorbents is an important potential mode of sorbent deactivation which must be protected against in commercial DAC processes. While the impact of temperature and oxygen concentration has been well-studied, the impact of ambient humidity on oxidative stability is not well understood. Furthermore, given that DAC is a technology that is likely to be deployed all over the world, in many different climates, understanding the role of humidity is a critical research gap that must be addressed.

In the present work, we explore the role of atmospheric humidity as an important stability parameter for DAC processes employing solid amine adsorbents. We demonstrate this via the use of prototypical class 1 aminopolymer-type solid sorbents that allows for flexibility in the support use. Sorbent deactivation was investigated by means of several complementary factors, including (i) the relative loss in amine efficiency determined via time-course CO₂ sorption, (ii) elemental analysis, and (iii) in situ IR spectroscopy to obtain an understanding of the role of water on the sorbent degradation process. Our findings provide important insights into the relevant parameters that impact the effective design of DAC sorbents & processes for different climatic environments, allowing tailoring of sorbent formulations to overcome the challenges associated with highly varied conditions in which a DAC process must operate.

References

1. FCCC, U. in United Nations Framework Convention on Climate Change.
2. Majumdar, A. & Deutch, J. Research opportunities for CO₂ utilization and negative emissions at the Gigatonne Scale. Joule 2, 805-809 (2018).
3. X. Shi, H. Xiao, H. Azarabadi, J. Song, X. Wu, X. Chen, K. S. Lackner, Angew. Chem. Int. Ed. 2020, 59, 6984-7006;
4. E. National Academies of Sciences, and Medicine, Negative Emissions Technologies and Reliable Sequestration: A Research Agenda, National Academies Press, 2019;
5. A. Sinha, L. A. Darunte, C. W. Jones, M. J. Realff, Y. Kawajiri, Ind. Eng. Chem. Res. 2020, 59, 503-505;
6. A. Sinha, L. A. Darunte, C. W. Jones, M. J. Realff, Y. Kawajiri, Ind. Eng. Chem. Res. 2017, 56, 750-764;
7. A. Sinha, M. J. Realff, AIChE J. 2019, 65, 16607;
8. Azarabadi, K. S. Lackner, Appl. Energy 2019, 250, 959-975.