(617e) A Cluster Based Cooperative Kinetic Model for CO2 Adsorption on Amine Functionalized Metal Organic Frameworks

Amine functionalized metal organic frameworks Mg₂ (dobpdc) and Mn₂ (dobpdc) have shown promise as carbon capture adsorbents from streams with low CO₂ partial pressure, such as air. These materials have exhibited several anomalies in their adsorption kinetics. To evaluate the potential of these materials in cyclic adsorption processes, an accurate representation of both equilibrium adsorption and adsorption kinetics is required. A new model for the adsorption kinetics of CO₂ on amine functionalized metal organic frameworks Mg₂ (dobpdc) and Mn₂ (dobpdc) is proposed. The equilibrium adsorption is evaluated using the cooperative lattice theory of Kundu et. al. [1]. The lattice theory provides a microscopic interpretation of adsorption behavior on the basis of the state of adsorbed CO₂: singly adsorbed, chain ends, and chain interiors. On this basis, the proposed kinetic model accounts for the kinetics of non-cooperatively adsorbed CO₂, as well as the kinetics of adsorption into cooperative chains. These two kinetic paths have separate yet coupled rate laws. This allows for the accurate description of complex kinetic phenomena observed in low partial pressure CO₂ breakthrough curves on mmen-Mg₂ (dobpdc). In addition to good numerical agreement with measured data, the approach developed in this work provides a needed microscopic interpretation of measured kinetic data in these systems. This microscopic picture may allow for more targeted material design, and a pathway to include additional factors such as the effect of humidity on CO₂ adsorption and kinetics.

References:

1) Kundu, J.; Stilck, J. F.; Lee, J.H.; Neaton, J. B.; Prendergast, D.; Whitelam, S., Cooperative gas adsorption without a phase transition in metal-organic frameworks. Physical review letters 2018, 121 (1), 015701.