Functionalized metal organic framework-polyimide mixed matrix membranes for CO2/CH4 separation

This work describes the preparation, characterization and CO2/CH4 gas separation properties of mixed matrix membranes (MMMs) made from five different as-synthesised metal organic frameworks (MOFs): UiO-66 (Zr-BDC), NH2-UiO-66 (Zr-ABDC), UiO-67 (Zr-BPDC), MOF-199 (Cu-BTC), and NH2-MOF-199 (containing 25% ABDC and 75% BTC mixed-linker) fillers and as-synthesized 6FDA–ODA polyimide as the polymeric matrix in order to investigate the ligand functionalization effect (–NH2) on MOFʹs adsorption properties and on the CO2/CH4 gas separation performance of the MMMs. The as-synthesized MOFs were carefully characterized by XRD, SEM, ATR-FTIR, and N2 adsorption at 77 K. MMMs were also characterized using ATR-FTIR, and SEM and CO2/CH4 pure and mixed gas separation measurements were carried out. Incorporation of the fillers in the MMMs resulted in an increase in perm-selectivity except for the UiO-67 filler. The presence of amine-functional groups in as-synthesized MOFs increased both the ideal selectivity and CO2 permeability. On the other hand, MMM made with UiO-66 increased significantly the CO2 permeability compared to the neat 6FDA–ODA membrane without any loss in ideal selectivity. Using mixed-linker NH2-MOF-199 enhanced the perm-selectivity of the MMM maybe because of the presence of some whisker-like roughness on their crystal surface as observed in SEM.