Hierarchical metal–organic frameworks constructed from intergrowth for the adsorption of light hydrocarbons

Abstract

Hierarchical metal organic frameworks (MOFs) are a type of MOF material with both micropores and mesopores. In this work, we demonstrate heterometallic hierarchical MOF particles formed by intergrowth of pillared MOFs. Pillared MOF M^I₂(ndc)₂(dabco) (M^I = Co, Ni, Cu, Zn, ndc = naphthalenedicarboxylic acid, dabco = 1,4-diazabicyclo[2.2.2]octane) particles were synthesized with various morphologies, on which M^II₂(ndc)₂(dabco) (M^II = Co, Ni, Cu, Zn) particles were intergrown. The intergrown particles preserved the structure, crystallinity, and morphology of their respective primary particles, while creating additional mesoporosity for gas adsorption. Adsorption of hydrocarbons (CH₄, ethane, ethene, propane, and propene) at pressures up to 10 bar (absolute) was performed on the MOFs. Hierarchical MOFs have shown increased adsorption of hydrocarbons at low pressures, and IAST selectivity of propane/methane as high as 53 was observed (total pressure 1 bar, CH₄ mole fraction: 0.8), suggesting that the hierarchical materials can be used for adsorptive removal of natural gas liquids from crude natural gas.