(674g) Process Modeling and Techno-Economic Optimization of a Moving Bed Contactor for CO2 Capture Using a Diamine-Appended Metal–Organic Framework

Aqueous solvents are the current leading commercial technologies for post-combustion CO₂ capture, but they suffer from several drawbacks that include degradation, large energy penalties, and low working capacities. Solid sorbents are viable alternatives to these aqueous solvents. Most notably, a novel class of functionalized metal-organic frameworks (MOF’s) have been shown to exhibit promising characteristics for post-combustion capture from the flue gas in the fossil-fired power plants^1–3. The MOF studied in this work, Mg₂(dobpdc) (dobpdc^4– = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate), contains one-dimensional hexagonal channels with unsaturated Mg²⁺ sites and is functionalized by binding the diamine 2,2-dimethyl-1,3-diaminopropane (dmpn) to these sites which then chemisorb CO₂ in cooperative mechanism to form carbamate and carbamic acid species. This MOF exhibits a step-shaped isotherm under low partial pressures of CO₂ which leads to higher working capacities under similar temperature and pressure intervals when compared to traditional sorbents. Along with high working capacities, this functionalized MOF also shows excellent long-term stability and maintains performance under humid conditions, both desirable attributes for flue gas CO₂ capture.¹

To realize the economic potential of this new class of MOFs, both the contactor technology and their operating conditions are crucial. While there has been much work on optimizing the design of the towers, their internals, and operating conditions for the solvent-based capture processes, there are very few publications in the open literature on optimal design of the contactor technology for solid-sorbent systems. Previous work has focused on economic analysis of a fixed bed process⁴, but a moving bed (MB) contactor can offer several advantages over other solid-gas contactors, such as a fixed bed or fluidized bed. The counter-current flow pattern exhibited in a MB results in larger driving forces when compared to a fixed bed contactor while the moderate hydrodynamics also will reduce particle attrition when compared to a fluidized bed. Since MOF particles typically do not process high attrition resistance characteristics, moving bed systems offer an excellent option for these materials.

In this work, a dynamic, one-dimensional, non-isothermal MB reactor model is developed and used to model a full scale temperature swing adsorption process using the functionalized MOF. The model simultaneously solves a set of partial differential equations for the mass and energy balances of the system, and accounts for internal and external mass transfer resistances, reaction kinetics, and heat transfer between the gas and solid phase. A hydrodynamic model is also developed. The model also accounts for heat transfer between the system and an embedded heat exchanger which can provide/remove a large amount of heat and facilitate operation close to the optimal temperature profile as the capture target change or the flue gas flowrate/composition changes. A cost model is also developed incorporating both capital and operating costs. A mathematical programming problem is then solved for simultaneous optimization of the design and operating variables of the MB process. The study shows that the MB system can considerably improve the economics of the MOF technology compared to the fixed bed processes.

References:

(1) Milner, P. J.; Siegelman, R. L.; Forse, A. C.; Gonzalez, M. I.; Runčevski, T.; Martell, J. D.; Reimer, J. A.; Long, J. R. A Diaminopropane-Appended Metal–Organic Framework Enabling Efficient CO₂ Capture from Coal Flue Gas via a Mixed Adsorption Mechanism. J. Am. Chem. Soc. 2017, 139 (38), 13541–13553. https://doi.org/10.1021/jacs.7b07612.

(2) McDonald, T. M.; Mason, J. A.; Kong, X.; Bloch, E. D.; Gygi, D.; Dani, A.; Crocellà, V.; Giordanino, F.; Odoh, S. O.; Drisdell, W. S.; Vlaisavljevich, B.; Dzubak, A. L.; Poloni, R.; Schnell, S. K.; Planas, N.; Lee, K.; Pascal, T.; Wan, L. F.; Prendergast, D.; Neaton, J. B.; Smit, B.; Kortright, J. B.; Gagliardi, L.; Bordiga, S.; Reimer, J. A.; Long, J. R. Cooperative Insertion of CO₂ in Diamine-Appended Metal-Organic Frameworks. Nature 2015, 519 (7543), 303–308. https://doi.org/10.1038/nature14327.

(3) Forse, A. C.; Milner, P. J.; Lee, J.-H.; Redfearn, H. N.; Oktawiec, J.; Siegelman, R. L.; Martell, J. D.; Dinakar, B.; Porter-Zasada, L. B.; Gonzalez, M. I.; Neaton, J. B.; Long, J. R.; Reimer, J. A. Elucidating CO₂ Chemisorption in Diamine-Appended Metal–Organic Frameworks. J. Am. Chem. Soc. 2018, 140 (51), 18016–18031. https://doi.org/10.1021/jacs.8b10203.

(4) Hughes, R.; Kotamreddy, G.; Ostace, A.; Bhattacharyya, D.; Siegelman, R. L.; Parker, S. T.; Didas, S. A.; Long, J. R.; Omell, B.; Matuszewski, M. Isotherm, Kinetic, Process Modeling, and Techno-Economic Analysis of a Diamine-Appended Metal–Organic Framework for CO ₂ Capture Using Fixed Bed Contactors. Energy Fuels 2021, 35 (7), 6040–6055. https://doi.org/10.1021/acs.energyfuels.0c04359.