(401a) Towards Modelling and Structural Optimization of Adsorption-Based Direct Air Capture Technologies*

Efforts within the scientific community to counteract CO₂ emissions and curb global temperature rise below 1.5°C above pre-industrial levels are driving the development of Carbon Dioxide Removal (CDR) strategies. Within CDR, Carbon Capture and Sequestration (CCS) presents a promising framework, however, Direct Air Capture (DAC) is crucial for addressing hard-to-avoid emissions. Scaling up these approaches requires collaborative endeavors among industry, stakeholders, and policymakers. Challenges such as high energy consumption and scalability hinder the full potential of DAC. Hence, innovation in algorithm development and computational tools focused on optimizing adsorption-based systems becomes crucial. Computational Fluid Dynamics (CFD) is a powerful tool that can quantitatively predict the effects of design parametrization on device performance. Within this framework, we advocate for the utilization of topology optimization, a versatile, flexible, and potent mathematical tool. Together, Topology Optimization and CFD create a promising framework to enhance devices and get closer to commercial scale [1]. To make this connection possible, it is imperative to first obtain detailed CFD models that can describe a DAC process to make decisions.

Over the last few years, DAC research has been mainly focused on sorbent development. To contribute to this, there is a need for detailed simulation that opens the room for optimization techniques. A detailed DAC system considers complex kinetics, heat transfer, and temperature dependence. Another challenge in deriving optimal adsorption systems is the inherent dynamic nature of the process and the not well-understood mass transfer between solid material and fluid. Furthermore, it is imperative to account for interactions between the packing material (such as pellets) and bulk flow within the system. To model this, we rely on previous studies that model mass transfer as a linear driving force alongside the relevant governing and constitutive equations and make use of stepped isotherms to describe the proper behavior [2].

To achieve our objectives, we initially set up a 3D system to describe a DAC adsorption step and incorporate kinetics, obtained from the relevant literature on cutting-edge materials for DAC (e.g., [2, 3, 4] ). This dynamic model can be conceptualized as a pseudo-4D simulation where we describe the adsorption step in a 3D system and then add a 1D concentration profile along the packing pellet’s radius. This coupled model is carried out on COMSOL Multiphysics®. The model requires a coupled, three-dimensional implementation of heat, momentum and mass transfer, and is therefore computationally expensive. Furthermore, it includes stiff ODEs for the adsorption kinetics, imposing model convergence limitations. To address this issue, we get inspiration from previous work in analytical solutions for isotherm models [5]. According to this approach, a reformulation is proposed that substitutes stiff ODEs with 1D analytical expressions for adsorption. Once the model is validated, it is translated to a 2D approach that will be useful within a structural optimization framework. The designs derived from the topology optimization/CFD approach serve as a starting point towards the development of large-scale, intricately detailed systems optimized for scalability.

References

[1] F. Okkels and H. Bruus, "Scaling behavior of optimally structured catalytic microfluidic reactors," Physiscal Review E, 2007.

[2] L. A. Darunte, T. Sen, C. Bhawanani, K. S. Walton, D. S. Sholl, M. J. Realff and C. W. Jones, "Moving Beyond Adsorption Capacity in Design of Adsorbents for CO2 Capture from Ultradilute Feeds: Kinetics of CO2 Adsorption in Materials with Stepped Isotherms," Industrial & Engineering Chemistry Research, pp. 366-377, 2019.

[3] R. Hughes, G. Kotamreddy, A. Ostace, D. Bhattacharyya, R. L. Siegelman, S. T. Parker, S. A. Didas, J. R. Long, B. Omell and M. Matuszewski, "Isotherm, Kinetic, Process Modeling, and Techno-Economic Analysis of a Diamine-Appended Metal–Organic Framework for CO2 Capture Using Fixed Bed Contactors," Energy Fuels, vol. 35 , no. (7), p. 6040–6055. , 2021.

[4] S.-m. Kinm and G. Léonard, "Process modelling of Direct Air Capture (DAC) of CO2 using solid amine sorbents," Computer Aided Chemical Engineering, pp. 265-270, 2022.

[5] P. Roy, S. T. Castonguay, J. M. Knipe, Y. Sun, E. A. Glascoe and H. N. Sharma, "Multi-material modeling of sorption-desorption processes with experimental validation," Chemical Engineering Science, vol. 253, 2022.

*This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and was supported by Laboratory Directed Research and Development funding under project 22-SI-006. LLNL Release Number: LLNL-PROC-847581.