Polysulfone/silica nanoparticle mixed-matrix membranes for gas separation

Mixed-matrix membranes (MMMs) are based on polymeric membranes filled with inorganic particles as a means to improve their gas separation performance. In this study, MMMs were prepared from polysulfone (PSf) containing embedded nonporous fumed silica nanoparticles and the gas permeation properties of the resulting membranes were investigated. Physical properties such as film density, thermal degradation and glass transition temperature of PSf/silica MMMs were characterized. The distribution of the silica nanoparticles in PSf was observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Furthermore, the interface between the polymer and silica agglomerates was studied in relation with the gas transport properties. The gas permeabilities of hydrogen, helium, oxygen, nitrogen, methane, and carbon dioxide were measured as a function of silica volume fraction and diffusion and solubility coefficients were determined by the time-lag method. The effect of silica nanoparticles in PSf membranes on gas permeability is in contrast with predictions based on the Maxwell model. The O2 permeability is approximately four times higher and CH4 permeability is over five times greater than in a pure PSf membrane. However, the performance comprising permeability versus selectivity of PSf/silica MMMs for O2/N2 and CO2/CH4 follows a similar slope to that of the trade-off upper bound with increasing silica content.