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A Diaminopropane-Appended Metal-Organic Framework Enabling Efficient CO₂ Capture from Coal Flue Gas via a Mixed Adsorption Mechanism.

ABSTRACT: A new diamine-functionalized metal-organic framework comprised of 2,2-dimethyl-1,3-diaminopropane (dmpn) appended to the Mg²⁺ sites lining the channels of Mg₂(dobpdc) (dobpdc^4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) is characterized for the removal of CO₂ from the flue gas emissions of coal-fired power plants. Unique to members of this promising class of adsorbents, dmpn-Mg₂(dobpdc) displays facile step-shaped adsorption of CO₂ from coal flue gas at 40 °C and near complete CO₂ desorption upon heating to 100 °C, enabling a high CO₂ working capacity (2.42 mmol/g, 9.1 wt %) with a modest 60 °C temperature swing. Evaluation of the thermodynamic parameters of adsorption for dmpn-Mg₂(dobpdc) suggests that the narrow temperature swing of its CO₂ adsorption steps is due to the high magnitude of its differential enthalpy of adsorption (Δh_ads = -73 ± 1 kJ/mol), with a larger than expected entropic penalty for CO₂ adsorption (Δs_ads = -204 ± 4 J/mol·K) positioning the step in the optimal range for carbon capture from coal flue gas. In addition, thermogravimetric analysis and breakthrough experiments indicate that, in contrast to many adsorbents, dmpn-Mg₂(dobpdc) captures CO₂ effectively in the presence of water and can be subjected to 1000 humid adsorption/desorption cycles with minimal degradation. Solid-state ¹³C NMR spectra and single-crystal X-ray diffraction structures of the Zn analogue reveal that this material adsorbs CO₂ via formation of both ammonium carbamates and carbamic acid pairs, the latter of which are crystallographically verified for the first time in a porous material. Taken together, these properties render dmpn-Mg₂(dobpdc) one of the most promising adsorbents for carbon capture applications.

SUBMITTER: Milner PJ

PROVIDER: S-EPMC8221660 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Supported by increasingly available reserves, natural gas is achieving greater adoption as a cleaner-burning alternative to coal in the power sector. As a result, carbon capture and sequestration from natural gas-fired power plants is an attractive strategy to mitigate global anthropogenic CO2 emissions. However, the separation of CO2 from other components in the flue streams of gas-fired power plants is particularly challenging due to the low CO2 partial pressure (∼40 mbar), which necessitates that candidate separation materials bind CO2 strongly at low partial pressures (≤4 mbar) to capture ≥90% of the emitted CO2. High partial pressures of O2 (120 mbar) and water (80 mbar) in these flue streams have also presented significant barriers to the deployment of new technologies for CO2 capture from gas-fired power plants. Here, we demonstrate that functionalization of the metal-organic framework Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) with the cyclic diamine 2-(aminomethyl)piperidine (2-ampd) produces an adsorbent that is capable of ≥90% CO2 capture from a humid natural gas flue emission stream, as confirmed by breakthrough measurements. This material captures CO2 by a cooperative mechanism that enables access to a large CO2 cycling capacity with a small temperature swing (2.4 mmol CO2/g with ΔT = 100 °C). Significantly, multicomponent adsorption experiments, infrared spectroscopy, magic angle spinning solid-state NMR spectroscopy, and van der Waals-corrected density functional theory studies suggest that water enhances CO2 capture in 2-ampd-Mg2(dobpdc) through hydrogen-bonding interactions with the carbamate groups of the ammonium carbamate chains formed upon CO2 adsorption, thereby increasing the thermodynamic driving force for CO2 binding. In light of the exceptional thermal and oxidative stability of 2-ampd-Mg2(dobpdc), its high CO2 adsorption capacity, and its high CO2 capture rate from a simulated natural gas flue emission stream, this material is one of the most promising adsorbents to date for this important separation.

Project description:Carbon capture and sequestration is a key element of global initiatives to minimize anthropogenic greenhouse gas emissions. Although many investigations of new candidate CO2 capture materials focus on equilibrium adsorption properties, it is also critical to consider adsorption/desorption kinetics when evaluating adsorbent performance. Diamine-appended variants of the metal-organic framework Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) are promising materials for CO2 capture because of their cooperative chemisorption mechanism and associated step-shaped equilibrium isotherms, which enable large working capacities to be accessed with small temperature swings. However, the adsorption/desorption kinetics of these unique materials remain understudied. More generally, despite the necessity of kinetics characterization to advance adsorbents toward commercial separations, detailed kinetic studies of metal-organic framework-based gas separations remain rare. Here, we systematically investigate the CO2 adsorption kinetics of diamine-appended Mg2(dobpdc) variants using a thermogravimetric analysis (TGA) assay. In particular, we examine the effects of diamine structure, temperature, and partial pressure on CO2 adsorption and desorption kinetics. Importantly, most diamine-appended Mg2(dobpdc) variants exhibit an induction period prior to reaching the maximum rate of CO2 adsorption, which we attribute to their unique cooperative chemisorption mechanism. In addition, these materials exhibit inverse Arrhenius behavior, displaying faster adsorption kinetics and shorter induction periods at lower temperatures. Using the Avrami model for nucleation and growth kinetics, we determine rate constants for CO2 adsorption and quantitatively compare rate constants among different diamine-appended variants. Overall, these results provide guidelines for optimizing adsorbent design to facilitate CO2 capture from diverse target streams and highlight kinetic phenomena relevant for other materials in which cooperative chemisorption mechanisms are operative.

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A Diaminopropane-Appended Metal-Organic Framework Enabling Efficient CO₂ Capture from Coal Flue Gas via a Mixed Adsorption Mechanism.

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A Diaminopropane-Appended Metal-Organic Framework Enabling Efficient CO2 Capture from Coal Flue Gas via a Mixed Adsorption Mechanism.

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A Diaminopropane-Appended Metal-Organic Framework Enabling Efficient CO₂ Capture from Coal Flue Gas via a Mixed Adsorption Mechanism.