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

Abstract

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.