High performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer

Carbon capture and storage (CCS) using membranes for the separation of CO₂ holds great promise for the reduction of atmospheric CO₂ emissions from fuel combustion and industrial processes. Among the different process outlines, post-combustion CO₂ capture could be easily implemented in existing power plants. However, for this technology to become viable, new membrane materials have to be developed. In this article we present the development of high performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer matrix. The CO₂/N₂ separation performance was evaluated by mixed gas tests (15CO₂:85N₂) at 25 °C and 1–4 bar transmembrane pressure difference. The CO₂ membrane permeability was increased by the addition of the ZIF-94 particles, maintaining a constant CO₂/N₂ selectivity of ~22. The largest increase in CO₂ permeability of ~ 200% was observed for 40 wt% ZIF-94 loading, reaching the highest permeability (2310 Barrer) at similar selectivity among 6FDA-DAM MMMs reported in literature. For the first time, the ZIF-94 metal organic framework crystals with particle size smaller than 500 nm were synthesized using nonhazardous solvent (tetrahydrofuran and methanol) instead of dimethylformamide (DMF) in a scalable process. Membranes were characterized by three non-invasive image techniques, i.e. SEM, AFM and nanoscale infrared imaging by scattering-type scanning near-field optical microscopy (s-SNOM). The combination of these techniques demonstrates a very good dispersion and interaction of the filler in the polymer layer, even at very high loadings.