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.