Effect of Amine Functionalization of MOF Adsorbents for Enhanced CO2 Capture and Separation: A Molecular Simulation Study

Abstract

Different types of amine-functionalized MOF structures were analyzed in this work using molecular simulations in order to determine their potential for post-combustion carbon dioxide capture and separation. Six amine models -of different chain lengths and degree of substitution- grafted to the unsaturated metal sites of the M2(dobdc) MOF [and its expanded version, M2(dobpdc)] were evaluated, in terms of adsorption isotherms, selectivity, cyclic working capacity and regenerability. Good agreement between simulation results and available experimental data was obtained. Moreover, results show two potential structures with high cyclic working capacities if used for Temperature Swing Adsorption processes: mmen/Mg/DOBPDC and mda-Zn/DOBPDC. Among them, the -mmen functionalized structure has higher CO2 uptake and better cyclability (regenerability) for the flue gas mixtures and conditions studied. Furthermore, it is shown that more amine functional groups grafted on the MOFs and/or full functionalization of the metal centers do not lead to better CO2 separation capabilities due to steric hindrances. In addition, multiple alkyl groups bonded to the amino group yield a shift in the step-like adsorption isotherms in the larger pore structures, at a given temperature. Our calculations shed light on how functionalization can enhance gas adsorption via the cooperative chemi-physisorption mechanism of these materials, and how the materials can be tuned for desired adsorption characteristics.

Transport tuning strategies in MOF film synthesis – a perspective

“…Amine functionalisation is one of the more widely studied functionalisation routes in many MOF structures, typically for CO 2 -targeted separations. 38,39 This is due to the favourable interaction of CO 2 with amine groups, allowing for enhanced CO 2 selectivity. Polar -OH and -NO 2 groups have also been used to help selectively adsorb/separate CO 2 from other gas molecules via active diffusion.…”

Pore Environment Optimization of Microporous Metal–Organic Frameworks with Huddled Pyrazine Pillars for C2H2/CO2 Separation

“…Generally, alkaline −NH 2 site should have a stronger affinity toward weakly acidic CO 2 . 11,46,53 In the case of DZU-11, however, a reversed preferential adsorption of C 2 H 2 was observed, which is rarely reported in literature studies. 54,55 The alkynyl and two H atoms of C 2 H 2 provide multiple host−guest interactions with the framework of DZU-11, especially the strong interaction between the alkynyl and −NH 2 functionality with a short distance.…”

A Cluster Based Cooperative Kinetic Model for CO2 Adsorption on Amine Functionalized Metal–Organic Frameworks

“…The equilibrium adsorption of CO 2 on amine functionalized mmen-Mg 2 (dobpdc) has been well studied. ,,− When modeling adsorption processes, authors often use empirical isotherms to correlate equilibrium adsorption data. − More advanced methodologies such as lattice theory, , density functional theory, and molecular simulations have also been applied to gain a better understanding of the adsorption physics.…”

“…4,6,9−11 isotherms to correlate equilibrium adsorption data. 12−15 More advanced methodologies such as lattice theory, 9,16 density functional theory, 17 and molecular simulations 18 have also been applied to gain a better understanding of the adsorption physics.…”