Gas permeability properties of Matrimid® membranes containing the metal-organic framework Cu–BPY–HFS

A microporous metal-organic framework Cu–4,4′-bipyridine–hexafluorosilicate (Cu–BPY–HFS), having a surface area of 2000 m2/g, was combined with Matrimid® polymer to form free standing films. The permeability properties of Cu–BPY–HFS–Matrimid® mixed-matrix membranes were tested for the pure gases H2, N2, O2, CH4, and CO2 and the gas mixtures CO2/CH4, H2/CO2 and CH4/N2. The ideal selectivity of CH4/N2 increased from 0.95 to 1.21, which suggests that Cu–BPY–HFS has a strong affinity towards CH4 and favors its permeation. The higher solubility of CH4 in the membranes leads to higher selectivity for CH4/N2. The enhanced CH4 transport is also apparent in the case of ideal selectivity for CO2/CH4 and H2/CH4. For CH4/N2 gas mixtures, the selectivity increased from 0.95 to 1.7. The Cu–BPY–HFS's affinity towards CH4, and its large surface area increased the solubility of CH4 in the mixed-matrix membranes, which led to higher selectivity towards CH4.