(732f) Economic Optimization and Sensitivity Analysis of Ionic Liquid-Based Carbon Capture Plants

Carbon capture and sequestration (CCS) is an essential means to mitigate carbon emissions from power plants [1]. Current industrial-scale carbon capture systems rely on amine-based absorbents due to their high reactivity with CO₂. However, there are several disadvantages owing to the intrinsic properties of amine-based absorbents. Ionic liquids (ILs) have been proposed as potential absorbents for next-generation carbon capture processes. They are non-flammable, non-volatile, thermally stable, and non-corrosive relative to conventional amine solvents. In addition, ILs have a lower heat of absorption; consequently, energy requirements in the solvent regeneration step are lower compared to amine-based technologies. Aprotic heterocyclic anion ILs (AHAs) are particularly promising due to their ability to chemically absorb CO₂ without a significant increase in viscosity [2].

Although ILs have potential advantages at the molecular level, the process-level economics of IL-based carbon capture are not well studied. Developing process modeling and optimization tools for IL-based carbon capture plants is essential to elucidate their economic feasibility and scalability. However, robust simulation and optimization of the entire process flowsheet are challenging, particularly when rigorous models are used for key unit operations (e.g., absorber, stripper).

In this work, we present a novel framework for solving these flowsheet optimization problems, using a pseudo-transient modeling approach developed by our group [3,4]. The model is tailored to IL-based CCS: a Langmuir-type model that describes both chemical and physical uptake of CO₂ is used to describe the equilibrium absorption of CO₂ by the IL [5]. Further, a rigorous rate-based model for the absorption column is employed, that accounts for the effect of reversible chemical reactions on mass transfer. Detailed first-principles models of the other units in the plant flowsheet are used.

Economic optimization of the entire process flowsheet is performed. Sensitivity studies are then performed to elucidate the impact of the IL chemical absorption enthalpy and investigate the impact of other IL properties (viscosity, heat capacity, and molar volume) on process performance. We also present a comparison to amine-based processes, using recently published rigorous flowsheet optimization results for a modern amine-based CCS process [6].

References:

[1] J.-L. Fan. M. Xu, F. Li, L. Yang, X. Zhang, Carbon capture and storage (CCS) retrofit potential of coal-fired power plants in China: The technology lock-in and cost optimization perspective. Appl. Energy, 229 (2018), 326-334.

[2] S. Seo, M. Quiroz-Guzman, M.A. DeSilva, T. B. Lee, Y. Huang, B.F. Goodrich, W.F. Schneider, J.F. Brennecke, Chemically tunable ionic liquids with aprotic heterocyclic anion (AHA) for CO₂ capture. J. Phys. Chem. B, 118 (2014), 5740-5751.

[3] R.C. Pattison, M. Baldea, Equation-oriented flowsheet simulation and optimization using pseudo-transient models, AIChE J., 60 (2014), 4014-4123.

[4] R.C Pattison, C. Tsay, M. Baldea, Pseudo-transient models for multiscale, multiresolution simulation and optimization of intensified reaction/separation/recycle processes: Framework and a dimethyl ether production case study, Comput. Chem. Eng., 105 (2017), 161-172.

[5] B. Hong, L. D. Simoni, J. E. Bennett, J. F. Brennecke, M. A. Stadtherr, Simultaneous process and material design for aprotic n-heterocyclic anion ionic liquids in postcombustion CO₂ capture, Ind. Eng. Chem. Res., 55 (2016), 8432-8849.

[6] C. Tsay, R.C. Pattison, Y. Zhang, G.T. Rochelle, M. Baldea, Rate-based modeling and economic optimization of next-generation amine scrubbing carbon capture processes, Applied Energy, 252 (2019), 113379.

Acknowledgement – This work was supported by the University of Texas Energy Institute under the Fueling a Sustainable Energy Transition program. Additional support was provided by the U.S. Department of Energy under Award Number DE-FE0026465. Portions of this work were performed at the University of Notre Dame (B. H. and M. A. S.).