Highly stable Pebax® Renew® thin-film nanocomposite membranes with metal organic framework ZIF-94 and ionic liquid [Bmim][BF4] for CO2 capture

Abstract

Ionic liquid (IL) [Bmim][BF4] and metal organic framework (MOF) ZIF-8 and ZIF-94 nanoparticles were incorporated into polymer Pebax® Renew® 30R51 to obtain highly efficient thin-film nanocomposite (TFN) membranes, ca. 300 nm thick. ZIF-94 particles were synthesized via a solvent assisted ligand exchange (SALE) from nano ZIF-8. To fabricate the membranes, the weight percentage of [Bmim][BF4] was firstly varied from 5 to 20 wt% to find the optimal IL content (10 wt%). Besides, ZIF-8 and ZIF-94 nanoparticles were separately incorporated (from 10 to 20 wt%) into the Pebax®/IL matrix to enhance the CO2 separation performance. Compared with the pristine Pebax® thin film composite (TFC) membrane, the IL (10 wt%) increased the CO2 permeance by 27% to 629 GPU and the CO2/N2 separation selectivity by 7% to 29 due to the enhancement in CO2 mass transport. After the incorporation of ZIFs, the CO2 permeance increased by 51% to 751 GPU and by 65% to 819 GPU, with 15 wt% loadings of ZIF-8 and ZIF-94, respectively, although the CO2/N2 separation selectivity decreased by 7% to 25 in both cases. Additional characterization was also carried out by the calculation of the permeation apparent activation energies for CO2 and N2 as well as the study of the long-term stability for up to 18 days. This demonstrated that the incorporation of the MOF enhanced the stability of the IL in the membrane, rendering it 55% and 35% more permeable (611 GPU) than the bare polymer and the membrane with only IL, respectively, while maintaining a CO2/N2 separation selectivity of 25.