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

5 years ago

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

Jeffrey R. Long, Phillip J. Milner, Rebecca L. Siegelman, Jeffrey A. Reimer, Jeffrey D. Martell, Miguel I. Gonzalez, Alexander C. Forse, Tomče Runčevski

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.

Publisher URL: http://dx.doi.org/10.1021/jacs.7b07612

DOI: 10.1021/jacs.7b07612