The storage and separation of H2 and CO2 are investigated in a highly porous ionic rht metal-organic framework (rht-MOF) using molecular simulation. The rht-MOF possesses a cationic framework and charge-balancing extraframework NO3(-) ions. Three types of unique open cages exist in the framework: rhombicuboctahedral, tetrahedral, and cuboctahedral cages. The NO3(-) ions exhibit small mobility and are located at the windows connecting the tetrahedral and cuboctahedral cages. At low pressures, H2 adsorption occurs near the NO3(-) ions that act as preferential sites. With increasing pressure, H2 molecules occupy the tetrahedral and cuboctahedral cages and the intersection regions. The predicted isotherm of H2 at 77 K agrees well with the experimental data. The H2 capacity is estimated to be 2.4 wt % at 1 bar and 6.2 wt % at 50 bar, among the highest in reported MOFs. In a four-component mixture (15:75:5:5 CO2/H2/CO/CH4) representing a typical effluent gas of H2 production, the selectivity of CO2/H2 in rht-MOF decreases slightly with increasing pressure, then increases because of cooperative interactions, and finally decreases as a consequence of entropy effect. By comparing three ionic MOFs (rht-MOF, soc-MOF, and rho-ZMOF), we find that the selectivity increases with increasing charge density or decreasing free volume. In the presence of a trace amount of H2O, the interactions between CO2 and NO3(-) ions are significantly shielded by H2O; consequently, the selectivity of CO2/H2 decreases substantially.
[Show abstract][Hide abstract] ABSTRACT: The development of more efficient processes for CO 2 capture from the flue streams of power plants is considered a key to the reduction of greenhouse gas emissions implicated in global warming. Indeed, several U.S. and international climate change initiatives have identified the urgent need for improved materials and methods for CO 2 capture. Conventional CO 2 capture processes employed in power plants world-wide are typically postcombustion "wet scrubbing" methods involving the absorption of CO 2 by amine-containing solvents such as methanolamine (MEA). These present several disadvantages, including the considerable heat required in regeneration of the solvent and the necessary use of inhibitors for corrosion control, which lead to reduced efficiencies and increased costs for electricity production. This perspective article seeks to highlight the most recent advances in new materials for CO 2 cap-ture from power plant flue streams, with particular emphasis on the rapidly expanding field of metal–organic frameworks. Ultimately, the development of new classes of efficient, cost-effective, and industrially viable capture materials for application in carbon capture and stor-age (CCS) systems offers an immense opportunity to reduce atmospheric emissions of green-house gases on a national and international scale.
Pure and Applied Chemistry 01/2010; 83(1). DOI:10.1351/PAC-CON-10-09-18 · 2.49 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Porous aromatic frameworks (PAFs) were recently synthesized with the highest surface area to date; one such PAF (PAF-1) has diamond-like structure with biphenyl building blocks and exhibits exceptional thermal and hydrothermal stabilities. Herein, we computationally design new PAFs by introducing polar organic groups to the biphenyl unit and then investigate their separating power toward CO(2) by using grand-canonical Monte Carlo (GCMC) simulations. Among these functional PAFs, we found that tetrahydrofuran-like ether-functionalized PAF-1 shows higher adsorption capacity for CO(2) at 1 bar and 298 K (10 mol per kilogram of adsorbent) and also much higher selectivities for CO(2)/CH(4), CO(2)/N(2), and CO(2)/H(2) mixtures when compared with the amine functionality. The electrostatic interactions are found to play a dominant role in the high CO(2) selectivities of functional PAFs, as switching off atomic charges would decrease the selectivity by an order of magnitude. This work suggests that functionalizing porous frameworks with tetrahydrofuran-like ether groups is a promising way to increase CO(2) adsorption capacity and selectivity, especially at ambient pressures.
[Show abstract][Hide abstract] ABSTRACT: Selected metal-organic frameworks exhibiting representative properties--high surface area, structural flexibility, or the presence of open metal cation sites--were tested for utility in the separation of CO(2) from H(2) via pressure swing adsorption. Single-component CO(2) and H(2) adsorption isotherms were measured at 313 K and pressures up to 40 bar for Zn(4)O(BTB)(2) (MOF-177, BTB(3-) = 1,3,5-benzenetribenzoate), Be(12)(OH)(12)(BTB)(4) (Be-BTB), Co(BDP) (BDP(2-) = 1,4-benzenedipyrazolate), H(3)[(Cu(4)Cl)(3)(BTTri)(8)] (Cu-BTTri, BTTri(3-) = 1,3,5-benzenetristriazolate), and Mg(2)(dobdc) (dobdc(4-) = 1,4-dioxido-2,5-benzenedicarboxylate). Ideal adsorbed solution theory was used to estimate realistic isotherms for the 80:20 and 60:40 H(2)/CO(2) gas mixtures relevant to H(2) purification and precombustion CO(2) capture, respectively. In the former case, the results afford CO(2)/H(2) selectivities between 2 and 860 and mixed-gas working capacities, assuming a 1 bar purge pressure, as high as 8.6 mol/kg and 7.4 mol/L. In particular, metal-organic frameworks with a high concentration of exposed metal cation sites, Mg(2)(dobdc) and Cu-BTTri, offer significant improvements over commonly used adsorbents, indicating the promise of such materials for applications in CO(2)/H(2) separations.
Journal of the American Chemical Society 03/2011; 133(15):5664-7. DOI:10.1021/ja111411q · 12.11 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.