Mixed matrix membranes based on silica nanoparticles and microcellular polymers for CO2/CH4 separation

Mixed matrix membranes made from silica nanoparticles and microcellular polymers were prepared from Matrimid (R) 5218 combined with tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane via the sol-gel method. The nanoparticles were prepared in situ during membrane casting yielding a homogeneous distribution inside a foamed polyimide structure. Mixed matrix membranes with SiO2 contents up to 16% wt. were treated at 60?, 100?, 150?, and 200?. Thermal gravimetric analysis and Fourier transform infrared spectroscopy analyses were performed providing information on chemical composition and thermal stability, while the porous structure (average cell diameter and cell density) was studied by scanning electron micrograph. Also, dynamic mechanical analysis was used to determine the glass transition temperature (Tg) and elastic modulus. Finally, the gas transport properties were studied in terms of treatment temperature, feed pressure, SiO2 loading, and testing temperature. CO2 permeability was found to increase by a factor of 3-4 at 3% SiO2 content using tetraethoxysilane in Matrimid, while ideal selectivity for CO2/CH4 separation was constant. Finally, the plasticization effect was practically eliminated by the introduction of SiO2 nanoparticles.