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

摘要

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_4O(BTB)_2 (MOF-177, BTB~(3-) = 1,3,5-benzenetriben-zoate), Be_12(OH)_12(BTB)_4 (Be-BTB), Co(BDP) (BDP~(2-) = 1,4-benzenedipyrazolate), H_3[(Cu_4Cl)_3(BTTri)_8] (Cu-BTTri, BTTri~(3-) = 1,3,5-benzenetristriazolate), and Mg_2-(dobdc) (dobdc~(4-)= l,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/Hv 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.