(381z) An Efficient and Reliable Pre-Screening Method for Rapid Testing of Sorbents Under Steam Desorption Conditions for DAC Applications

DAC is defined as the process of removing carbon dioxide directly from the atmosphere [1]. There are various technologies for DAC and the most mature and developed ones are (1) liquid DAC (L-DAC), which utilizes chemical solvent to capture CO₂, and (2) solid DAC (S-DAC), which uses a solid adsorbent for CO₂ separation. Although using chemical solvents is a very mature and popular method to capture CO₂ from concentrated stream of CO₂, it is less suitable for capturing CO₂ through ambient air since it requires higher regeneration energy and there will be a solvent loss due to evaporation of solvent upon contact with massive amounts of air [2] [3]. In contrast, S-DAC has lower regeneration temperatures, faster sorption kinetics, and higher sorption capacity as supported by various publications [4] [5].

Considering adsorption processes, the adsorbent plays an important role in achieving the desired performance of the DAC unit. For instance, the used adsorbent should be optimized to multiple desirable characteristics such as high cyclic stability, high uptake capacity, high CO₂ selectivity, fast kinetics, high density and thermal conductivity, low manufacturing cost and scalability, and low environmental impact. While some sorbent characteristics particularly related to adsorption process such as uptake capacity, CO₂ selectivity, and kinetics are widely researched in literature [5] [6], it has been noticed that other important sorbent characteristics that are related to the desorption process are not researched much such as cyclic stability, desorption kinetics, high density and thermal conductivity, and low operating energy requirements. It is needless to mention that the desorption process is a critical one to achieve a process that is operationally and economically viable. Hence, a lot of efforts are needed to shed light on the desorption part of the process and particularly the cyclic stability of the sorbent to meet industrial standards to operate DAC units commercially.

There are various methods that could be used for desorption processes such as temperature vacuum swing adsorption (TVSA) with purge gas (utilizing N₂, air, or concentrated CO₂), TVSA with direct heating, or steam-assisted TVSA (s-TVSA). This project focuses on a s-TVSA method due to its merits compared to other methods for instance, leading to high CO₂ purity and faster desorption kinetics while the steam could be condensed downstream [7]. However, the main challenge that is associated with s-TVSA is the stability issues of adsorbents under steam.

Due to the rapidly increasing number of potential sorbents, an efficient and reliable method to pre-screen various sorbents, particularly under steam desorption is necessary. Various papers have studied the sorbent degradation upon exposure to steam to compare the sorbent capacity before and after steam exposure [8] [9]. However, most of these studies did not study the exposure of sorbents to steam for a duration that is equivalent to the sorbent’s lifetime in commercial DAC units. Additionally, most studies’ test rigs can test one sorbent at a time and the test is mechanically complex, which is not efficient to rapidly pre-screen multiple sorbents at the same time [10] [11].

Hence, the aim of this study is to provide a simple rapid screening methodology for testing the long-term steam stability of sorbents. The method includes an initial uptake capacity measurement through adsorption in ambient air followed by a TVSA desorption step in hot N₂. After the initial uptake measurement, each sorbent sample is exposed to continuous steam by replacing the ambient atmosphere in a sealed container containing the sorbent with steam and placing it in an oven for 1-60 days. The 60 days represents an expected duration that the sorbent shall be exposed to the steam upon desorption for a DAC unit running for 1 year. Upon removal from the oven another adsorption/desorption cycle is run, and the sorbent is desorbed again using the same process as described above. Comparing the uptake capacity initially and post-steam exposure shows the effect of long-term steam exposure on sorbent performance. The uptake capacity is plotted vs total time under steam exposure showing the curve of sorbent degradation. These methods can be used to identify sorbents that can withstand desorption under harsh steam conditions and to help predict a more informed potential lifetime of sorbents used in s-TVSA processes, providing invaluable data to be able to evaluate the use of a particular sorbent from an economic standpoint. Hence, leading to informed decision-making of DAC deployment utilizing a particular sorbent.

References:

[1] International Energy Agency, "Direct Air Capture - A key technology for net zero, 2022.

[2] A. Rao and E. Rubin, "A Technical, Economic, and Environmental Assessment of Amine-Based CO2 Capture Technology for Power Plant Greenhouse Gas Control," Environmental Science Technology, vol. 36, no. 20, pp. 4467-4475, 2002.

[3] K. Goto, K. Yogo and T. Higashii, "A review of efficiency penalty in a coal-fired power plant with post-combustion CO2 capture," Applied Energy, vol. 111, pp. 710-720, 2013.

[4] Y. Shi, R. Ni and Y. Zhao, "Review on Multidimensional Adsorbents for CO2 Capture from Ambient Air: Recent Advances and Future Perspectives," Energy Fuels, vol. 39, no. 9, pp. 6365-6381, 2023.

[5] L. Jiang, J. Yong, R. Xie, P. Xie, X. Zhang, Z. Chen and Z. Bao, "Screening, preparation, and prototyping of metal–organic frameworks for adsorptive carbon capture under humid conditions," Sustainable Materials, vol. 3, no. 5, pp. 609-638, 2023.

[6] J. Wang, H. Huang, M. Wang, L. Yao, W. Qiao, D. Long and L. Ling, "Direct Capture of Low-Concentration CO2 on Mesoporous Carbon-Supported Solid Amine Adsorbents at Ambient Temperature," Industrial and Engineering Chemical Research, vol. 54, no. 19, pp. 5319-5327, 2015.

[7] J. Young, F. Mcilwaine, B. Smit, S. Garcia and M. van der Spek, "Process-informed adsorbent design for direct air capture," Chemical Engineering Journal , vol. 456, p. 141035, 2023.

[8] M. A. Sakwa-Novak and C. W. Jones, "Steam Induced Structural Changes of a Poly(ethylenimine) Impregnated γ-Alumina Sorbent for CO2 Extraction from Ambient Air," ACS Applied Materials and Interfaces, vol. 6, no. 12, pp. 9245-9255, 2014.

[9] N. K. Sandhu, D. Pudasainee, P. Sarkar and R. Gupta, "Steam Regeneration of Polyethylenimine-Impregnated Silica Sorbent for Postcombustion CO2 Capture: A Multicyclic Study," Industrial and Engineering Chemistry Research, vol. 55, no. 7, pp. 2210-2220, 2016.

[10] M. Fayaz and A. Sayari, "Long-Term Effect of Steam Exposure on CO2 Capture Performance of Amine-Grafted Silica," ACS Applied Materials and Interfaces, vol. 9, no. 50, pp. 43747-43754, 2017.

[11] Q. Yu and D. Brilman, "Design strategy for CO2 adsorption from ambient air using a," in 13th International Conference on Greenhouse Gas Control Technologies, GHGT-13, Lausanne, 2016.