Mixed-metal approach towards assembling highly stable metal organic framework based adsorbent for simultaneous capture of CO2 and H2S

Abstract

The common method employed to capture CO₂/H₂S, liquid amine scrubbing, is associated with high energy penalty and some other drawbacks. Adsorption based technology, using physisorbent solids, is considered economically viable option. This work presented the assembly of H₂S stable metal-organic framework (MOF) sorbent, Tb-Cu-bqdc MOF, with underlying fluorite net that showed huge potential to be deployed for simultaneous capture of CO₂ and H₂S. The 8-coordinated rectangular cuboid and the 4-coordinated tetrahedral molecular building units required to assemble the targeted MOF were generated in situ from terbium nitrate, copper nitrate and 2,2′-biquinoline-4,4′-dicarboxylic acid under suitable solvothermal reactions. The structure, porosity, H₂S stability and other properties of the synthesized MOF were confirmed by XRD, ICP-OES, TGA, gas sorption, etc. The MOF’s high H₂S stability was evidenced in PXRD and cyclic CO₂ sorption studies with no loss of crystallinity, no phase change and no alteration in CO₂ uptake being observed upon exposure to H₂S. To realize the potential of the MOF for CO₂/H₂S removal, single gas and mixed gas sorption tests were performed. Appreciable breakthrough uptakes for H₂S and CO₂ (≈1.42 and ≈0.24 mmol g-1, respectively, at room temperature and 1 bar) with negligible sorption of the common gases (CH₄ and N) by the MOF, showed potential of the material for the purification of variety of gas streams containing CO₂ and H₂S. The preferential sorption of H₂S over CO₂ (selectivity ≈6.0) is also a merit in further processing of the captured acid gas to produce pure H₂S, raw material in Claus process.