The field of metal–organic framework based mixed matrix membranes (M4s) is critically reviewed, with special emphasis on their application in CO2 capture during energy generation.

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A R T I C L E I N F O Keywords:Metal organic frameworks ZIF-94 Mixed matrix membrane CO 2 capture A B S T R A C T Carbon capture and storage (CCS) using membranes for the separation of CO 2 holds great promise for the reduction of atmospheric CO 2 emissions from fuel combustion and industrial processes. Among the different process outlines, post-combustion CO 2 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 CO 2 /N 2 separation performance was evaluated by mixed gas tests (15CO 2 :85N 2 ) at 25°C and 1-4 bar transmembrane pressure difference. The CO 2 membrane permeability was increased by the addition of the ZIF-94 particles, maintaining a constant CO 2 /N 2 selectivity of~22. The largest increase in CO 2 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.

A zeolitic imidazolate framework two-layered membrane approach is simulated and experimentally validated to improve the pre-combustion gas separation.

Zeolitic imidazolate framework-93 (ZIF-93) continuous membranes were synthesized on the inner side of P84 co-polyimide hollow fiber supports by microfluidics. MOFs and polymers showed high compatibility and the membrane exhibited H2-CH4 and CO2-CH4 separation selectivities of 97 (100 °C) and 17 (35 °C), respectively.

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Zeolite A/poly (1‐trimethylsilyl‐1‐propyne) (zeoliteA/PTMSP) and [emim][Ac]/chitosan (IL/CS) are mixed‐matrix membrane (MMM) materials with enhanced CO2/N2 permselectivity even at higher temperature. The scalability to asymmetric flat and hollow‐fiber geometry by a simple dip‐coating method was analyzed. The CO2/N2 separation performance was evaluated at different temperatures. The resulting composite membranes exhibit a significantly enhanced CO2 permeation flux because the MMM layer thickness is reduced by 97 % from flat to hollow‐fiber geometries in IL‐CS composite membranes, while the selectivity is maintained similar to the self‐standing membranes, thus proving that compatibility between the membrane component materials leads to a defect‐free composite membrane, regardless the geometry and temperature.

Electronic supplementary information (ESI) available: TG analyses of the amine-functionalized SIM-1 powders and FTIR spectra of the P84 ® reaction with amines. AbstractA modification in the gas separation performance of zeolitic imidazolate framework (ZIF)-supported hollow fiber (HF) membranes by means of an imine-condensation functionalization reaction carried out by microfluidics is reported. The accommodation of voluminous amine molecules in the SIM-1, Zn(4-methyl-5imidazolcarboxaldehyde) 2 , also known as ZIF-94, sod structure during the functionalization reaction caused the ZIF atoms to be rearranged in a less dense rho structure, with a wider pore diameter and a diminished CO 2 affinity. These changes had effects on the membrane performance, resulting in an enhanced CO 2 permeance while maintaining a good permeance-selectivity balance. ZIF aldehyde-containing SIM-1 membranes were early prepared on the inner side of polymeric P84 ® HF using a microfluidic approach. The SIM-1 membranes displayed very interesting results in the separation of gas mixtures of great relevance in the natural gas field.High selectivities in the separation of He/CH 4 (160), H 2 /CH 4 (136) and CO 2 /CH 4 (38) mixtures were achieved, the first SIM-1 membranes with such a high separation performance to the best of our knowledge.These SIM-1 membranes were in situ stepwise functionalized with long-chain amine solutions, namely, hexyl-and nonylamine. Microfluidics allowed the easy sequential implementation of this post-reaction step in the membrane fabrication procedure. An imine-condensation reaction took place between the aldehyde groups in the 4-methyl-5-imidazolcarboxaldehyde ligand forming the SIM-1 and the corresponding amines. The extent of the reaction was analyzed by FTIR, TGA and XRD, together with the changes in the textural properties and the adsorption capacities. IntroductionMetal-organic frameworks (MOFs) offer novel chemical versatility as a result of the extensive supply of organic moieties in their forming ligands. 1,2 This versatility, which had not been previously observed in other inorganic microporous materials such as zeolites, 3 is potentially useful in numerous applications. These include gas separation 4 and adsorption, 1,5,6 catalysis 7,8 and controlled drug delivery. 9 A large number of studies have taken advantage of this MOF resourcefulness: among others, Thompson et al. 10,11 and Eum et al. 12 described the preparation of hybrid mixed-ligand MOFs and the resulting tune in their porosities, whereas Marti et al. 13 and Fei et al. 14 reported post-synthetic organic ligand and metal cluster exchanges from solution, respectively. Moreover, the covalent functionalization reaction is perhaps the most widespread strategy for MOF post-modification. 15,16 Most of these studies report gas adsorption equilibria, but nevertheless lack diffusion data through the MOF structures, which are needed for prediction of post-modified separation selectivities. 17 An interesting combination of narrow porosity and chemical versatil...