(289a) Multi-Scale Modeling of Novel Amine-Based Solvents for CO2 Capture

Among the different available options for combating climate change and global warming, carbon capture and storage (CCS) is positioned as the most feasible for short- and medium-terms, with post-combustion capture (PCC) considered more suitable for direct integration with power generation facilities reliant on fossil fuels. Aqueous alkanolamines have been the long-standing benchmark solvents for this application, however, the limiting factor in their commercialization is the parasitic energy load associated with the regeneration of the solvent. This can be attributed to either the enthalpy of absorption associated with the chemical solvent, or the latent and sensible heat requirements associated with the physical co-solvent. Efforts over the past decades have been directed towards reducing the regeneration energy requirements by either proposing alternative novel amines with lower absorption enthalpy, or the use of alternative organic diluents with lower thermal properties than water, formulating water-free or water-lean solvents [1, 2].

However, demonstration of the potentiality of these solvents remains limited to lab-scale application, focused on a limited set of performance criteria such as absorption capacity, and energy of regeneration. Additionally, the limited availability of experimental data required for detailed process modeling and simulation, hinders the techno-economic evaluation of these solvents to accurately assess their potential over their aqueous counterparts. Therefore, devising a consistent and reliable thermodynamic model capable of accurately describing the CO₂ solubility, thermophysical and transport properties of alternative amine-based solvents for representative techno-economic evaluation is highly needed.

In this contribution, we demonstrate the application of a multi-scale modeling framework to assess the potentiality of alternative amine-based solvents for CO₂ capture examining novel aqueous amines, water-free, and water-lean solvents. The multi-scale framework is built in a consistent manner establishing a direct link between the molecular structure of the solvent and its performance on industry-scale. The core of the multi-scale modeling framework relies on the application of a robust molecular-based equation of state (EoS), namely, soft-SAFT EoS [1,2], to provide all required thermodynamic information needed for an accurate process model and techno-economic evaluation, such as CO₂ solubility, solvent viscosity, density, surface tension, etc. Investigated solvents include novel aqueous amines from novel families such as alkyl-ethanolamines, amino-alcohols, dialkylamino-alcohols, and multiamines. Additionally, water-free and water-lean solvents formulated from the chemical solvent monoethanolamine (MEA), with a wide array of organic diluents such as alcohols, glycols, glymes, and polar aprotic solvents were also examined. Molecular parameters of all the investigated substances are either taken from previous contributions or developed in this work and used in a transferable manner for describing the solubility of CO₂ in the selected solvents at conditions of relevance for industrial applications. The CO₂ chemisorption process in the examined solvents is done by using a scheme of implicit reactions to describe the formation of carbamate resulting from the chemical reactions between CO₂ and the examined amines [3,4]. This approach eliminates the need to specify detailed equilibrium reactions, while significantly reducing the number of parameters required to capture the CO₂ solubility, allowing the application of the model in a predictive manner over a broad range of conditions unavailable from experimental data.

Once these solvents were fully characterized using available experimental data, the thermodynamic model was used in a predictive manner to provide required thermodynamic information for detailed process model and simulation for a post-combustion capture unit. This enabled the assessment of the performance of these solvents in terms of technical indicators such as absorption capacity, and energy consumption, along with economic indicators inclusive of capital, operating costs, and total annualized costs, providing a direct link between micro-level features and industry-level performance [5].

This work is funded by Khalifa University of Science and Technology (RC2-2019-007). Computational resources from the Research and Innovation Center on CO₂ and H₂ (RICH Center) are gratefully acknowledged.

References

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[2] F.J. Blas, L.F. Vega, Prediction of Binary and Ternary Diagrams Using the Statistical Associating Fluid Theory (SAFT) Equation of State, Ind. Eng. Chem. Res. 37 (1998) 660–674. https://doi.org/10.1021/ie970449+.

[3] L.M.C. Pereira, L.F. Vega, A systematic approach for the thermodynamic modelling of CO2-amine absorption process using molecular-based models, Appl. Energy. 232 (2018) 273–291. https://doi.org/10.1016/j.apenergy.2018.09.189.

[4] I.I.I. Alkhatib, L.M.C. Pereira, A. Alhajaj, L.F. Vega, Performance of non-aqueous amine hybrid solvents mixtures for CO2 capture: A study using a molecular-based model, J. CO2 Util. 35 (2020) 126–144. https://doi.org/10.1016/j.jcou.2019.09.010.

[5] H.A. Balogun, D. Bahamon, S. Almenhali, L.F. Vega, A. Alhajaj, Are we missing something when evaluating adsorbents for CO2 capture at the system level?, Energy Environ. Sci. 14 (2021) 6360–6380. https://doi.org/10.1039/D1EE01677F.