In-situ synthesis of ZIF-90 in polyimide membranes for high-efficient gas separation

Metal organic frameworks (MOFs)-based mixed matrix membranes (MMMs) have been considered effective in improving gas separation performance of polymeric membranes. However, state-of-the-art MOFs-based MMMs prepared through physical blending method generally suffered from non-uniform filler agglomeration and compromised gas separation efficiency. To address this challenge, we developed an in-situ synthesized ZIF-90 / polyimide MMMs for efficient CO₂ separation. Firstly, aromatic polyimide (PI) was synthesized using dianhydride monomer 6FDA and diamine monomer HFBAPP as polymer matrix. Then, ZIF-90, serving as porous MOFs filler, was in-situ synthesized in polymer solutions based on imidazole-2-carboxaldehyde and zinc dihydrate acetate to form the in-situ synthesized ZIF-90/PI MMMs. Results showed that the in-situ incorporation significantly reduced the ZIF-90 agglomeration in MMMs. Based on abundant inner channels of ZIF-90 and molecular sieving effect, the in-situ synthesized ZIF-90/PI MMMs presented comparable CO₂ separation performance over Robeson upper bound of 2008. At 1.5 MPa, the in-situ synthesized ZIF-90/PI MMMs (15 wt% ZIF-90 content) reached optimal selectivity around 89.58 (CO₂/CH₄) and 88.86 (CO₂/N₂), which is 101% and 41% higher than that of pure PI membrane and 56% and 32% higher than conventional blended ZIF-90/PI MMMs. In addition, the in-situ synthesized MMMs showed an anti-aging property over 120 days, with CO₂ permeability maintained at 165.3 Barrer and 154.3 Barrer (over 90% compared with fresh membrane), and selectivity at 95.15 and 93.22 for CO₂/CH₄ and CO₂/N₂, respectively. Therefore, we developed an in-situ synthesized ZIF-90/PI MMM with improved MOFs dispersion for high-efficient CO₂ separation.