Comparison between ZIF-67 and ZIF-8 in Pebax® MH-1657 mixed matrix membranes for CO2 separation

In this study, mixed matrix membranes (MMM) based on poly(ether-b-amide) or Pebax® were prepared using a synthetized ZIF-67 and a commercial ZIF-8 (Basolite® Z1200) to determine the effect of particle content (0, 2, 3, 4 and 5 wt%) on CO2, CH4 and N2 single gas permeability as well as CO2/CH4 and CO2/N2 ideal selectivity. The MMM morphology was evaluated first by scanning electron microscopy (SEM) where excellent dispersion without aggregation was observed. The thermal properties were determined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) showing the disruptive role of fillers on polymer chain mobility. Fourier transform infrared spectroscopy (FTIR) showed that no significant chemical interaction between the polymer and ZIF particles occurred. Finally, gas permeation results at 35 °C and 11 bar revealed higher CO2 permeability for all MMM, but especially for Pebax/ZIF-67 with a 130% increase (162 Barrer) compared to the pristine Pebax membrane (70 Barrer), while the Pebax/ZIF-8 produced a lower (85%) increase (130 Barrer). Due to the smaller pore aperture of ZIF-67, CO2 selectivity over CH4 and N2 was higher compared to ZIF-8. Overall, the Pebax/ZIF-67 system was able to overcome the Robeson upper bound for the CO2/N2 separation.