(479g) Selective Dynamic CO2 Separations On Mg-MOF-74 Pellets At Low Pressures: A Detailed Comparison With 13X

Selective separation of CO₂ from various gas streams is typically carried out via chemical absorption with amine solutions in the (petro-) chemical industry. Adsorption with porous solids such as metal-organic frameworks (MOFs) is an interesting alternative because this technique could be more energy efficient and thus cost reducing.

Different MOFs from the MOF-74 or MDOBDC family have large CO₂ capacities when exposed to pure CO₂ streams (M = Ni or Mg / DOBDC = 2,5 dioxido-1,4-benzenedicarboxylate). These MOFs contain open metal sites and experiments with small amounts of material indicate a large selectivity and capacity for CO₂ [1-2].

In this work, the potential of the promising Mg-MOF-74 material was studied in closer detail and compared to the benchmark zeolite 13X. Adsorption isotherms of CO₂, CH₄ and N₂ were recorded on MOF powder using the gravimetric technique at different temperatures (273 – 373 K). The uptake measurements indicate much lower affinity for CH₄ and N₂ and suggest a larger capacity and selectivity for the MOF in relevant low-pressure CO₂ separations.

To assess the dynamic separation potential we developed a new pellet preparation technique to ensure a minor capacity loss upon shaping of the powder. Breakthrough experiments with mixtures of CO₂ and CH₄ on a column packed with Mg-MOF-74 pellets at 308 K and 1 bar indicated a higher CO₂ capacity and separation efficiency for the MOF with respect to the benchmark 13X zeolite. The MOF regains 81% of its original capacity when purging with helium at 308 K during 10 minutes and can be fully regenerated at 353 K, which indicates the facile desorption of CO₂ on this material. However, the performance of Mg-MOF-74 severely deteriorates upon long-term exposure to relevant impurities in CO₂ separations at low pressures such as water and oxygen.

[1] P.D.C. Dietzel, V. Besikiotis, R. Blom, J. Mater. Chem., 19, (2009). 

[2] R. Krishna, J.M. van Baten, J. Membr. Sci., 377, (2011).