Regeneration and recyclability of amine-functionalized metal–organic framework (MOF), dmen-Mg2(dobpdc)

https://doi.org/10.1039/C5SC01191D

“Adsorbed CO₂ can be removed from the solid at 30 °C, lower than the uptake temperature of 40 °C, followed by a degree of CO₂ adsorption with a capacity identical to the first cycle’s (Fig. 3a). Fig. 3b presents the cycling behavior for the adsorption (40 °C)-activation (40 °C) protocols, showing a significant adsorption capacity as well as a facile desorption of the CO₂ adsorbed at low temperature (Fig. S13†); this is supported by in situ IR spectroscopy (Fig. S14†). A recyclability test using a TSA procedure was also run (Fig. 3c). CO₂ was adsorbed at 40 °C for 1 h and desorbed at 75 °C for 1 h under Ar. After 24 cycles, no capacity loss was observed, suggesting that the material is thermally stable under these experimental conditions. Thus, 1-dmen could be potentially applicable for capturing CO₂ from coal-fired power plant emissions, because its regeneration requires very low desorption temperatures, and it has a high adsorption capability and no capacity decay even after many TSA cycles. This finding is valuable in that our material requires a lower energy input to regenerate the capture material, which is one of the most essential objectives for current CCS technologies.”

“Fig. 3 (a) Adsorption–desorption cycling of CO₂ for 1-dmen, showing reversible uptake from simulated flue gas (0.15 bar CO₂ balanced with N₂). Adsorption temperature was 40 °C and desorption temperatures were 130 °C, 60 °C, 50 °C, 40 °C, and 30 °C under Ar. (b) Adsorption–desorption cycling of CO₂ at 40 °C by switching atmospheres between simulated flue gas and Ar. (c) Adsorption–desorption cycling of CO₂ at adsorption (40 °C) and desorption (75 °C) under Ar. (d) Vacuum-swing adsorption at 25 °C using a Micromeritics ASAP2020 instrument.”

“In another experiment, the desorption behavior of 1-dmen was further investigated via the vacuum-swing adsorption (VSA) method^52,53 using an ASAP2020 analyzer (Fig. 3d). At 25 °C, 1-dmen was saturated with CO₂ at 1.2 bar and then placed under high vacuum. The removal of adsorbed CO₂ from the solid was performed repeatedly by applying a vacuum to the adsorbent; this CO₂ desorption under vacuum was confirmed by IR data in which the peaks relating to CO₂ adsorption progressively vanish upon the application of a high vacuum (Fig. S15†). Thus, notably, even such a large amount of CO₂ as is adsorbed onto 1-dmen at 1.2 bar (∼4.5 mmol g⁻¹) can be completely desorbed only under vacuum, without heating. Such facile desorption of captured CO₂ under evacuation supports the hypothesis that the alkylammonium carbamate species is weakly bound, as was also found in amine-grafted SBA-15.⁴⁷“