Metal-organic frameworks appended with cyclic diamines for carbon dioxide capture

摘要

Achieving the selective and reversible adsorption of CO₂ from humid, low partial pressures streams such as the flue gas resulting from the combustion of natural gas in combined cycle power plants (4% CO₂) is challenging due to the need for high thermal, oxidative, and hydrolytic stability as well as moderate regeneration conditions to reduce the energy of adsorption/desorption cycling. Appending cyclic primary, secondary diamines, exemplified by 2-(aminomethyl)piperidine (2-ampd), to the metal-organic frameworks Mg₂(dobpdc) (dobpdc⁴⁻=4,4-dioxidobiphenyl-3,3-dicarboxylate), Mg₂(dotpdc) (dotpdc⁴⁻=4,4″-dioxido-[1,1′:4′,1″-terphenyl]-3,3″-dicarboxylate) or Mg₂(pc-dobpdc) (pc-dobpdc⁴⁻=dioxidobiphenyl-4,4′-dicarboxylate) produces adsorbents of the classes EMM-44, EMM-45, and EMM-46, respectively, that display step-shaped adsorption of CO₂ at the partial pressures required for 90% capture from natural gas flue gas at temperatures up to or exceeding 60° C. Using a cyclic diamine in place of a diamine functionalized with bulky alkyl groups enables fast adsorption/desorption kinetics with sharp CO₂ adsorption and desorption steps.