CO2 separation performance for PIM based mixed matrix membranes embedded by superbase ionic liquids

Abstract

• Superbase ionic liquid [HDBU][Im] has high affinity towards ZIF-67 and PIM-1. • The addition of [HDBU][Im]@ZIF-67 improves CO 2 separation performance of MMMs. • Reducing temperature increases the CO 2 selectivity by enhancing the CO 2 solubility. Mixed matrix membranes (MMMs) have drawn much interest in CO 2 separation due to their excellent separation performance, mechanical property, and desirable processability. However, obtaining highly compatible MMMs is a great challenge and is vital to avoid the loss of the separation selectivity of the MMMs. In this work, superbase ionic liquid (1,8-diazabicyclo[5,4,0]undec-7-ene imidazole ([HDBU][Im])) was used as a wetting agent to increase the interfacial compatibility between ZIF-67 and PIM-1, hence improving the membrane gas separation. [HDBU][Im] embeding into the MMMs could efficiently enhance the compatibility and diminish the interfacial voids. Furthermore, incorporating 5 wt% [HDBU][Im]@ZIF-67 nanocomposite into the PIM-1 matrix improves the gas permeability and CO 2 selectivity. The separation performances under the different temperatures were also conducted and showed that reducing temperature slightly decreases the gas permeability but significantly increases the CO 2 /CH 4 selectivity via enhancing the CO 2 solubility. The permeation active energies, diffusivities and solubilities were obtained to explain the gas permeate mechanism.