(401e) Operation of Direct Air Capture Unit Under Degradation Effects

Recently, Direct air capture (DAC) has been a significant pathway to achieve negative emissions, and solid sorbent processes stand out thanks to relatively lower energy required for regeneration. Most active research has assumed constant behavior throughout the sorbent operational life. However, many sorbents under consideration for DAC degrade over operation time, which affects the equilibrium and kinetics under both the adsorption and desorption condition and causes reduction in the swing capacity over cycles if the operating conditions are constant [1][2]. Therefore, taking the degradation of materials into account is essential to simulate real DAC unit operation and to design effective long term operating strategies and material replacement timing.

Materials might have multiple degradation mechanisms, such as physical, thermal, and oxidative degradation, and dissolution leading to physical loss of adsorbent capacity [3] [4]. The degradation mechanisms are classified as reversible and irreversible, and by how the state trajectory of the adsorption or desorption impacts the rate of degradation. In addition, there may be changes in the support material properties such as loss of porosity which could impact the overall sorbent performance even without the sorbent itself degrading [5]. All classifications of degradation will cause cyclic productivity reduction, either permanently, reversibly, or partially reversibly, but have different forms of degradation over time.

In this work, mathematical models of material degradation for different degradation mechanisms have been constructed, and these models are embedded in the simulation model as a lumped degradation multiplier of the kinetic model or the equilibrium model respect to the effects. Then, the cycle parameters are adjusted based on predictions and state observations to account for the degradation. The final goal is to schedule optimally material regeneration for reversible degradation mechanisms, and schedule material replacement for irreversible and partially reversible degradation mechanisms.

Reference:

1. Shi, H. Xiao, H. Azarabadi, J. Song, X. Wu, X. Chen, and K. S. Lackner, "Sorbents for the Direct Capture of CO2 from Ambient Air," *Angew. Chem. Int. Ed.*, first published on 05 August 2019, doi: 10.1002/anie.201906756.
2. E. Holmes, S. Banerjee, A. Vallace, R. P. Lively, C. W. Jones, and M. J. Realff, "Tuning sorbent properties to reduce the cost of direct air capture," March 08, 2024, doi: 10.26434/chemrxiv-2024-8sc71.
3. Rosu, S. H. Pang, A. R. Sujan, M. A. Sakwa-Novak, E. W. Ping, and C. W. Jones, "Effect of Extended Aging and Oxidation on Linear Poly(propylenimine)-Mesoporous Silica Composites for CO2 Capture from Simulated Air and Flue Gas Streams," *ACS Applied Materials & Interfaces*, vol. 12, no. 34, 2020, doi: 10.1021/acsami.0c11185.
4. Miao, Y. Wang, X. Zhu, W. Chen, Z. He, L. Yu, and J. Li, "Minimizing the effect of oxygen on supported polyamine for direct air capture," *Separ. Purif. Technol.*, vol. 298, 121583, Oct. 2022, doi: 10.1016/j.seppur.2022.121583.
5. A. Saenz Cavazos, E. Hunter-Sellars, P. Iacomi, S. R. McIntyre, D. Danaci, and D. R. Williams, "Evaluating solid sorbents for CO2 capture: linking material properties and process efficiency via adsorption performance," *Front. Energy Res.*, vol. 11, July 2023, doi: 10.3389/fenrg.2023.1167043.