CO2/N-2 separations with mixed-matrix membranes containing Mg-2(dobdc) nanocrystals

Abstract

Nanocrystals of M-2(dobdc) (M = Mg, Ni, Zn; dobdc(4-) = 1,4-dioxido-2,5- benzenedicarboxylate), also known as M-MOF-74 or CPO-27-M, with diameters of similar to 100 nm or less were synthesized using a room-temperature reaction of 2 h duration. Adsorption data collected for CO2 and N-2 show slightly lower surface areas but similar adsorption selectivites relative to the bulk materials. High-quality mixed-matrix membranes containing Mg-2(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/N-2 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 Mg-2(dobdc) pores by polymer chains having a high mobility at room temperature.