The field of metal–organic framework based mixed matrix membranes (M ⁴ s) is critically reviewed, with special emphasis on their application in CO ₂ capture during energy generation.

The authors acknowledge the financial support of the European Research Council under the European Union's Seventh Framework Programme (FP/2007–2013), under grant agreement no. 608490, M4CO2 project, and the Spanish Ministry of Economy and Competitiveness (national project MAT2015-65525-R). J.G. gratefully acknowledges support from the European Union Seventh Framework Programme (FP7/2007–2013), ERC Stg, Grant Agreement n. 335746, CrystEng-MOF-MMM.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 to 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.Publisher PDFPeer reviewe

Double-layered zeolitic imidazolate framework (ZIF) membranes were fabricated inside polyimide P84 hollow fibers by a step-synthesis conducted by microfluidic technology and applied to pre-combustion gas separation. Our hypothesis, based on the information provided by a combination of molecular simulation and experiments, is that a CO₂ adsorption reduction on the surface of the ZIF-9 would enhance the molecular sieving effect of this ZIF-9 layer and therefore the selectivity in the H₂/CO₂ mixture separation of the entire membrane. This reduction would be achieved by means of a less-CO₂-adsorptive methylimidazolate-based ZIF-67 or ZIF-8 layer coating the ZIF-9. ZIF-8/ZIF-9 and ZIF-67/ZIF-9 double-layered membranes were prepared and characterized by XRD, FTIR, SEM, FIB, TEM and EDS. This unprecedented strategy led to a H₂/CO₂ separation selectivity of 9.6 together with a 250 GPU H₂ permeance at 150 °C, showing a significant improvement with respect to the pure ZIF-9 membrane. Double-layered membranes also showed higher apparent CO₂ activation energies than single-layered membranes, attributable to a diminished adsorption.

Aldehyde-functionalized ZIF-93 and P84 copolyimide facilitated a hollow fiber supported membrane with enhanced permselective properties in H ₂ –CH ₄ and CO ₂ –CH ₄ separation processes.