Metal-Organic Frameworks as Adsorbents for Hydrogen Purification and Precombustion Carbon Dioxide Capture

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 CO2 from H-2 via pressure swing adsorption. Single-component CO2 and H-2 adsorption isotherms were measured at 313 K and pressures up to 40 bar for Zn4O(BTB)(2) (MOF-177, BTB3- = 1,3,5-benzenetriben-zoate), Be-12(OH)(12)(BTB)(4) (Be-BTB), Co(BDP) (BDP2- = 1,4-benzenediprazolate), H-3[(CU4Cl)(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/CO2 gas mixtures relevant to H-2 purification and precombustion CO2 capture, respectively. In the former case, the results afford CO2/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 CO2/H-2 separations.