The influence of fumed silica content and particle size in poly (amide 6-b-ethylene oxide) mixed matrix membranes for gas separation

Mixed-matrix membranes (MMMs) comprised of poly (amide 6-b-ethylene oxide) (PEBAX) as continuous phase and fumed silica (FS) as dispersed phase were prepared to separate CO2 and CH4. The influences of FS nanoparticle size and weight percentage on the phase behavior and microstructure of the prepared MMMs were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA), differential scanning calorimeter (DSC) and tensile testing. The performance of the prepared MMMs was characterized by single gas permeation measurement of CO2, N2 and CH4 (at 25 °C). The effects of feed pressure on the gas separation performance of the membranes were also investigated. Generally, PEBAX-FS MMMs showed higher CO2 permeability and selectivity (α) than the pure PEBAX membrane. Adding 10 wt% of 7 nm FS nanoparticles to the PEBAX matrix led to significant improvement in the CO2 permeability (∼4 times), CO2/CH4 and CO2/N2 selectivity (∼2 times) compared to the pure PEBAX membrane. The CO2/CH4 and CO2/N2 selectivity for these membranes were also about 64.8% and 45.3% higher than those of MMMs containing 10 wt% of larger FS nanoparticles (16 nm). This was attributed to the higher surface to volume ratio of smaller FS nanoparticles which can provide higher interactions with polymeric matrix and CO2 gas.