Effect of 2-MeIM/Zn Molar Ratio on CO2 Permeability of Pebax/ZIF-8 Mixed Matrix Membranes

The impact of controlling molar ratio of ZIF-8 precursors on Pebax 1657 and Pebax 2533 based Mixed Matrix Membranes (MMMs) on the CO2 permeability and CO2 /N2 ideal selectivity was investigated. Three types of ZIF-8 were synthesized by controlling molar ratio of 2-methylimidazole and zinc nitrate hexahydrate as 2/1, 8/1, and 32/1. The SEM images and XRD patterns of ZIF-8 showed that particle sizes and crystallinity peaks were decreased as molar ratio of ZIF-8 increased. The CO2 permeability of Pebax MMM was improved by filling with the ZIF-8 particles compared to the pure Pebax. At equivalent temperatures, the highest CO2 permeability was shown in Pebax 1657/ZIF-8 with the ZIF8 precursors’ molar ratio of 32/1 and Pebax 2533/ZIF-8 with the molar ratio of 2/1. As molar ratio of ZIF-8 precursors increases, CO2 permeability of Pebax 1657 was increased by excessive sorption of CO2 by imidazolium ions in ZIF-8, whereas CO2 permeability of Pebax 2533 was decreased by decreasing pore size and particle size of ZIF-8. The CO2 permeability was higher in Pebax 2533/ZIF-8 compared to Pebax 1657/ZIF-8, because Pebax 2533 has more concentrations of polar groups in the polymer matrix than Pebax 1657. However, the CO2 /N2 ideal selectivity was higher in Pebax 1657/ZIF-8 compared to Pebax 2533/ZIF-8 because diffusivity of Pebax 1657 compared to Pebax 2533 is lower for nonpolar gases, such as N2 , and the solubility is higher for polarizable gases like CO2 . As increasing temperature, Pebax/ZIF-8 MMMs showed enhancement of CO2 and N2 permeability but decreased in CO2 /N2 ideal selectivity.