Effects of structural properties of fillers on performances of Matrimid® 5218 mixed matrix membranes

Matrimid® 5218 mixed matrix membrane (MMM) data reported in the literature were investigated. Correlations between filler structural properties, such as BET surface area, total pore volume, pore size, particle size and Matrimid® MMM performances, such as CO₂ permeability, CO₂/CH₄ ideal selectivity, CO₂/N₂ ideal selectivity, were determined. Regression was applied to the data and coefficient of determination values were calculated. A similar investigation was also performed for relating the diffusion and solubility coefficients of the MMMs to the structural properties of the fillers. It was determined that in most cases almost no correlation existed between the structural properties of the fillers and the permeability/ideal selectivity values of Matrimid® MMMs reported in the literature, when pure gas was used in the membrane measurements. The correlations increased to some extent when mixed gas was used. On the other hand, notable effects of the pore volumes and pore sizes of the fillers were observed on CO₂ and CH₄ diffusion coefficients of Matrimid® MMMs. Relatively high rate of adsorption and relatively strong interactions between fillers and CO₂/CH₄ gas molecules, during early stage membrane measurements, till the attainment of steady-state, was hypothesized to play significant role in these results. On the contrary, N₂ diffusion coefficients of Matrimid® MMMs did not seem to be so sensitive to the variations in the structural properties of fillers, possibly related to the more inert nature of this gas. The investigations performed in this study pointed that the simple relation between permeability, solubility and diffusivity may be questionable for MMMs.