Mixed matrix membranes comprising silica-(ZIF-8) core–shell spheres with ordered meso–microporosity for natural- and bio-gas upgrading

Mixed matrix membranes (MMMs) containing meso–microporous silica-(ZIF-8) spheres (MSS-Z8) were prepared using polysulfone (PSF) as polymeric matrix, with loadings varying between 0 and 32 wt%. The interaction between the filler and the polymer was studied by scanning electron microscopy and focused ion beam techniques, observing a good dispersion of the filler and an intimate contact between the ZIF-8 crystals shell and the polymeric matrix. X-ray diffraction indicated that the polymeric matrix did not alter the structure of the filler, and suggested the penetration of PSF chains into the flexible pores of the ZIF-8 crystals of the shell. MSS-Z8 MMMs were tested for the separation of CO2/CH4 and H2/CO2 mixtures at different temperatures (35–150 °C) and CO2/CH4 feed compositions. For all equimolar mixtures, the selectivity remained almost constant with the filler content while the permeability increased, the best performance being achieved for 32 wt% MSS-Z8 MMMs with an increase of almost 400% for H2 and 300% for CO2 in comparison with pure PSF. This enhancement in permselectivity resulted in Robesonʹs 2008 upper bound for H2/CO2 separation being reached when the temperature was increased up to 120 °C.