(617f) Modeling and Techno-Economic Optimization of a Rotary Packed Bed for Post-Combustion CO2 Capture Using a Diamine-Appended Metal-Organic Framework

The amount of carbon dioxide in the atmosphere is currently rising globally by around six billion tons per year¹. Thus, it is essential to separate and recover carbon dioxide from the flue gases released by power plants to avoid surplus CO₂ emissions. Carbon capture and sequestration (CCS) technologies will continue to play a vital role in CO₂ capture until substantial changes are made to the energy infrastructure². Presently, carbon capture by amine absorption is the most widely used technology. Still, solvent regeneration is energy-intensive, and other significant drawbacks include solvent degradation and corrosion. Therefore, alternatives are being developed. The use of solid sorbents for post-combustion capture is considered one of the potential options, and design of the solids contactor plays a critical role for these sorbents to be economically viable. Presently, extensive research has been focused on fixed bed, moving bed, or fluidized-bed reactors. However, fixed beds exhibit difficulty processing large volumes of flue gas, and moving beds and fluidized beds suffer from particle attrition³. To that end, a rotary packed bed concept for carbon capture with integrated cooling and heating in between layers is designed and analyzed to eliminate the challenges of traditional contactor designs.

Metal-organic frameworks (MOF’s) have been recognized as promising candidates for CO₂ capture due to desirable characteristics such as high pore volume, surface area, and remarkable tunability⁴. This work utilizes a novel class of diamine-appended MOF’s that have strong potential in reducing the cost of carbon capture^5,6. In this study, we model these diamine-appended MOF’s to be impregnated on the surfaces provided by a rotary packed bed reactor. As the bed continuously rotates, CO₂ is adsorbed by exposing a portion of the bed to flue gas. In the regeneration portion of the bed, steam is used to regenerate the MOF and recover CO₂. Cooling water is used to decrease the temperature rise in the adsorption section, while regeneration occurs by direct injection of steam and indirect heating by an embedded heat exchanger.

The developed RPB model is a dynamic, pressure-driven, two-dimensional model. First-principles mass and energy balances coupled with internal and external mass transfer resistance and reaction kinetics are solved using a moving reference frame (MRF) to incorporate the effect of the rotational speed of the matrix and variation in the circumferential direction. Due to high heat of reaction for this specific MOF and due to the step-shaped isotherms coupled with a highly non-linear kinetics, there is considerable variation in the temperature and loading in the circumferential direction along with the axial direction motivating the development of the two-dimensional model. An increase in the rotation speed can improve the solids loading in the capture section for a given inlet lean solid loading. However, an increase in the rotation speed results in an increase in the lean solids loading from the regeneration section due to the lower residence time. Furthermore, as the rotation speed increases, the electric power requirement keeps increasing. The tradeoffs discussed above suggest that there is an optimum rotational speed, but would require to take into account both the capital and operating costs. Therefore, a techno-economic analysis is performed for obtaining the optimal operating conditions including the speed by minimizing the equivalent annual operating cost. Compared to the conventional MEA-based capture system, the optimal RPB using the diamine-appended MOF shows considerable decrease in the penalty of CO₂ capture.

References:

[1] Zhao, Z., et al. (2007). "Adsorption of carbon dioxide on alkali-modified zeolite 13X adsorbents." International Journal of Greenhouse Gas Control 1(3): 355-359.

[2] Sumida, K., et al. (2012). "Carbon dioxide capture in metal–organic frameworks." Chemical reviews 112(2): 724-781.

[3] Thiels, M., et al. (2016). "Modelling and design of carbon dioxide absorption in rotating packed bed and packed column." IFAC-PapersOnLine 49(7): 895

[4] D'Alessandro, D. M., et al. (2010). "Carbon dioxide capture: prospects for new materials." Angewandte Chemie International Edition 49(35): 6058-6082.

[5] McDonald, T. M., et al. (2015). "Cooperative insertion of CO 2 in diamine-appended metal-organic frameworks." Nature 519(7543): 303.

[6] Milner, P. J., et al. (2017). "A diaminopropane-appended metal–organic framework enabling efficient CO2 capture from coal flue gas via a mixed adsorption mechanism." Journal of the American Chemical Society 139(38): 13541-13553.