Capture of Carbon Dioxide from Air and Flue Gas in the Alkylamine-Appended Metal-Organic Framework mmen-Mg2(dobpdc)

摘要

Two new metal-organic frameworks, M_2(dobpdc) (M = Zn (l), Mg (2); dobpdc~(4-) = 4,4'-dioxido-3,3'-biphenyldicarboxylate), adopting an expanded MOF-74 structure type, were synthesized via solvothermal and microwave methods. Coordinatively unsaturated Mg~(2+) cations lining the 18.4-A-diameter channels of 2 were functionalized with N,N'-dimethylethylenediamine (mmen) to afford Mg_2(dobpdc)-(mmen)_(1.6)(H_2O)_(0.4) (mmen-Mg2(dobpdc)). This compound displays an exceptional capacity for CO_2 adsorption at low pressures, taking up 2.0 mmol/g (8.1 wt %) at 0.39 mbar and 25 ℃. conditions relevant to removal of CO_2 from air, and 3.14 mmol/g (12.1 wt %) at 0.15 bar and 40℃, conditions relevant to CO_2 capture from flue gas. Dynamic gas adsorption/desorption cycling experiments demonstrate that mmen-Mg_2(dobpdc) can be regenerated upon repeated exposures to simulated air and flue gas mixtures, with cycling capacities of 1.05 mmol/g (4.4 wt 96) after 1 h of exposure to flowing 390 ppm CO_2 in simulated air at 25℃ and 2.52 mmol/g (9.9 wt %) after 15 min of exposure to flowing 15% CO_2 in N_2 at 40℃. The purity of the CO_2 removed from dry air and flue gas in these processes was estimated to be 96% and 98%, respectively. As a flue gas adsorbent, the regeneration energy was estimated through differential scanning calorimetry experiments to be 2.34 MJ/kg CO_2 adsorbed. Overall, the performance characteristics of mmen-Mg_2(dobpdc) indicate it to be an exceptional new adsorbent for CO_2 capture, comparing favorably with both amine-grafted silicas and aqueous amine solutions.