The Mechanism of Carbon Dioxide Adsorption in an Alkylamine-Functionalized Metal–Organic Framework

Abstract

The mechanism of CO 2 adsorption in the amine-functionalized metal−organic framework mmenMg 2 (dobpdc) (dobpdc 4− = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate; mmen = N,N′-dimethylethylenediamine) was characterized by quantum-chemical calculations. The material was calculated to demonstrate 2:2 amine:CO 2 stoichiometry with a higher capacity and weaker CO 2 binding energy than for the 2:1 stoichiometry observed in most amine-functionalized adsorbents. We explain this behavior in the form of a hydrogen-bonded complex involving two carbamic acid moieties resulting from the adsorption of CO 2 onto the secondary amines.T he predicted growth of the global economy and world population in the near future will lead to an increased demand for energy, 1 resulting in even further increases in the concentration of CO 2 in the atmosphere. The development and worldwide utilization of efficient carbon capture and sequestration (CCS) technologies could reduce the CO 2 emissions associated with the use of fossil fuels. 2 Current carbon capture technologies generally use aqueous solutions of alkanolamines to scrub the flue gases. 3 Amines are known to be very selective toward CO 2 capture from flue gases because of the strong chemical bonds formed in the chemisorption process. To overcome the energy penalty associated with the process, an important new development based on solid materials functionalized with amines has been proposed. 4−10 These materials have much lower heat capacities than aqueous amine solutions. 11 Of particular interest are amines grafted onto the open metal sites of metal−organic frameworks (MOFs). Indeed, recent experiments have shown that in the case of one particular MOF, Mg 2 (dobpdc) (dobpdc 4− = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate), N,N′-dimethylethylenediamine (mmen) can be bound to almost every open metal site lining the one-dimensional channels of the structure ( Figure 1). 4 The high adsorption enthalpy of mmen-Mg 2 (dobpdc) for CO 2 endows the adsorbent with a significant capacity for CO 2 down to very low pressures.The regeneration energy of the solid adsorbent is lower than that of aqueous amine solutions because of its large working capacity and low heat capacity. Understanding reactivity

Dynamic capture of low-concentration CO2 on amine hybrid silsesquioxane aerogel

“…Two peaks at 1432 and 1385 cm -1 are assigned to the organic moiety, corresponding with its stretching vibration observed at 2935 and 2882 cm -1 [60]. Peaks at 1092 and 1048 cm -1 should be assigned to the CO 2 adsorption performance of an amine-based adsorbent [64].…”

Structurally simple complexes of CO2

“…Interactions such as these have been observed in other CO2 complexes of nitrogen-containing porous materials, [56][57][58][59] and some have been studied computationally. 60 The stabilizing effect of nitrogen is not surprising considering the known reactivity of CO2 towards basic nitrogen atoms, primary and secondary amines in particular, which will be discussed in the next section. Interactions between the carbon atom of CO2 with oxygen atoms of host-guest complexes are also common, 56,61,62 as are similar interactions with halogen atoms.…”

Effect of Chain Topology of Polyethylenimine on Physisorption and Chemisorption of Carbon Dioxide

“…[12][13][14][15][16] In recent years, av ariety of amine supports and immobilizing techniques have been tested and the results are promising. [17][18][19][20] Amongp olymeric amines, polyethylenimine (PEI) contains an abundance of amines in the polymer backbone: tertiarya mines at branch points, secondary amines in the main chain, and primary amines at the end of each branch. [21] High-efficiency sorbents have been developed based on PEI-functionalized mesoporousmaterials.…”