CO2/N2 separations with mixed-matrix membranes containing Mg2(dobdc) nanocrystals

Nanocrystals of M2(dobdc) (M = Mg, Ni, Zn; dobdc4− = 1,4-dioxido-2,5-benzenedicarboxylate), also known as M-MOF-74 or CPO-27-M, with diameters of ∼100 nm or less were synthesized using a room-temperature reaction of 2 h duration. Adsorption data collected for CO2 and N2 show slightly lower surface areas but similar adsorption selectivites relative to the bulk materials. High-quality mixed-matrix membranes containing Mg2(dobdc) nanocrystals were fabricated using three different polymers for testing under conditions relevant to the removal of CO2 from flue gas. Significant enhancements in CO2 permeability and CO2/N2 selectivity over a pure polymer membrane were observed when a glassy polyimide was employed as the matrix, while membranes made with rubbery polymers showed decreased permeabilities, presumably due to the plugging of Mg2(dobdc) pores by polymer chains having a high mobility at room temperature.