Enhanced CO2/CH4 separation properties of asymmetric mixed matrix membrane by incorporating nano-porous ZSM-5 and MIL-53 particles into Matrimid®5218

Asymmetric Matrimid/fillers mixed matrix membranes, composed of a metal organic framework (MIL-53; with CO2 sorption properties) and a zeolite (ZSM-5; with size selective properties) as porous fillers, were used in CO2/CH4 separation. Cross-sectional SEM images of membranes showed a complete porous structure with finger-like pores. The presence of 6 wt. % of ZSM-5 in membrane matrix led to the CO2/CH4 selectivity enhancement. Conversely, results obtained from gas permeance tests (i.e., pure and mixed gas test) conducted over those membranes which contain higher loading percentage, showed the increase of permeation along with selectivity decline. Creation of interfacial voids between polymer and particles at higher loading of ZSM-5 caused the performance failure of membrane and selectivity was decreased, too. Alternatively, those membranes incorporated with MIL-53 particles, compared to pure Matrimid, showed significant enhancement in permeance of gases and CO2/CH4 selectivity. Organic linkers of MIL-53 improve the quality of polymer-filler interfaces and decrease the probability of the formation of interfacial voids as much as possible, which resulted in membrane performance enhancement. In pure permeation, CO2 permeance showed 270% growth and CO2/CH4 selectivity increased from 14.8 to 23.6 in membranes containing 15 wt. % MIL-53 compared to pure asymmetric Matrimid. MMMs filled with MIL-53 particles were suggested more proper separation factor compared to those embedded by ZSM-5 particles. The superior performance of Matrimid/MIL-53 MMM was attributed to the quality of polymer/filler interfaces as well as selective CO2 adsorption with embedded MIL-53. The best CO2 permeance and CO2/CH4 selectivity gained by Matrimide/MIL-53 at 3 bar were 46 GPU and 23.6 respectively; where Matrimid/ZSM-5 exhibited a CO2 permeance of 14.5 GPU and CO2/CH4 selectivity of 15.6. As the feed pressure increased from 3 to 12 bar, the permeance of both gases in MMMs decreased and CO2/CH4 selectivity increased, too. The increase of operating temperature from 35 to 65 °C resulted in enhancement of gas permeance, while CO2/CH4 selectivity decreased. Various permeation models (i.e., Maxwell, Bruggeman and Lewis-Nielsen) were used to predict mixed matrix membranes' separation properties. All models showed appropriate compatibility with experimental data at lower particles loading.