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

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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 CO2 from H2 via pressure swing adsorption. Single-component CO2 and H2 adsorption isotherms were measured at 313 K and pressures up to 40 bar for Zn4O(BTB)2 (MOF-177, BTB3− = 1,3,5-benzenetribenzoate), Be12(OH)12(BTB)4 (Be-BTB), Co(BDP) (BDP2− = 1,4-benzenedipyrazolate), H3[(Cu4Cl)3(BTTri)8] (Cu-BTTri, BTTri3− = 1,3,5-benzenetristriazolate), and Mg2(dobdc) (dobdc4− = 1,4-dioxido-2,5-benzenedicarboxylate). Ideal adsorbed solution theory was used to estimate realistic isotherms for the 80:20 and 60:40 H2/CO2 gas mixtures relevant to H2 purification and precombustion CO2 capture, respectively. In the former case, the results afford CO2/H2 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, Mg2(dobdc) and Cu-BTTri, offer significant improvements over commonly used adsorbents, indicating the promise of such materials for applications in CO2/H2 separations.