Sequential amine functionalization inducing structural transition in aldehyde-containing zeolitic imidazolate framework: application to gas separation membranes

A 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-5-imidazolecarboxaldehyde)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 CO2 affinity. These changes had effects on the membrane performance, resulting in an enhanced CO2 permeance while maintaining a good permeance–selectivity balance. ZIF aldehyde-containing SIM-1 membranes were earlier 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 to the natural gas field. High selectivities in the separation of He/CH4 (160), H2/CH4 (136) and CO2/CH4 (38) mixtures were achieved, and these are 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-imidazolecarboxaldehyde ligand forming 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.Financial support (MAT2013-40556-R, MAT2016-77290-R) from the Spanish MINECO, the Aragón Government (DGA, T05), the European Social Fund and FEDER is gratefully acknowledged

Ultrapermeable Thin Film ZIF-8/Polyamide Membrane for H-2/CO2 Separation at High Temperature without Using Sweep Gas

The use of thin film composites containing metal-organic frameworks (MOFs) as filler is of widespread interest for nanofiltration issues, since their thin selective layer allows a high permeation flow. The application of this kind of membranes for gas separation should provide a better permeance in comparison with other polymeric membranes and a reduction in the amount of MOF required for their fabrication. Here, the preparation of 50-100 nm thick polyamide flat membranes containing zeolitic imidazolate framework-8 (ZIF-8) nanoparticles is shown via interfacial polymerization, containing a lower amount of MOF (0.013 g m(-2) membrane) as compared to other membranes used for gas separation. The membranes are applied for H-2/CO2 separation at high temperatures and pressures, showing a stable performance at 180 degrees C for at least seven days. Outstanding separation values are 328 GPU of H-2 and a H-2/CO2 selectivity of 18.1 at 180 degrees C and 6 bar feed without transmembrane pressure. These membranes, also measurable without sweep gas, are highly suitable for industrial application

Interactive thermal effects on metal–organic framework Polymer composite membranes

Polymeric membranes are important tools for intensifying separation processes in chemical industries, concerning strategic tasks such as CO2 sequestration, H2 production, and water supply and disposal. Mixed-matrix and supported membranes have been widely developed; recently many of them have been based on metal–organic frameworks (MOFs). However, most of the impacts MOFs have within the polymer matrix have yet to be determined. The effects related to thermal behavior arising from the combination of MOF ZIF-8 and polysulfone have now been quantified. The catalyzed oxidation of the polymer is strongly affected by the MOF crystal size and distribution inside the membrane. A 16 wt¿% 140 nm-sized ZIF-8 loading causes a 40¿% decrease in the observed activation energy of the polysulfone oxidation that takes place at a temperature (545¿°C) 80¿°C lower than in the raw polymer (625¿°C)

Comparison of flat and hollow-fiber mixed-matrix composite membranes for CO2 separation with temperature

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 CO2permeation 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.Financial support from the Spanish Ministry of Economyand Competitiveness (MINECO) under project CTQ2012-31229 at the Universidad de Cantabria is gratefully acknowl-edged. A.F.B. and C.C.C. also thank the MINECO for theEarly Stage Researcher (BES2013-064266) and ‘‘Ramón yCajal’’ (RYC2011-0855) contracts, respectively. The authorsthank F. Noboru Ramirez-Matsumoto for his contribution inthe synthesis and permeation experiments of the CS andIL-CS composite flat membranes by the modified IP method

Metal-organic framework based mixed matrix membranes: a solution for highly efficient CO2 capture?

The field of metal-organic framework based mixed matrix membranes (M(4)s) is critically reviewed, with special emphasis on their application in CO2 capture during energy generation. After introducing the most relevant parameters affecting membrane performance, we define targets in terms of selectivity and productivity based on existing literature on process design for pre- and post-combustion CO2 capture. Subsequently, the state of the art in M(4)s is reviewed against these targets. Because final application of these membranes will only be possible if thin separation layers can be produced, the latest advances in the manufacture of M-4 hollow fibers are discussed. Finally, the recent efforts in understanding the separation performance of these complex composite materials and future research directions are outlined.European Commission FP7 608490 ERC 33574

New strategies based on microfluidics for the synthesis of metal-organic frameworks and their membranes

Metal-organic frameworks (MOFs) are highly porous crystalline materials formed by the coordination of organic ligands with metal clusters. Despite the significant progress in their development over the last few years and their applications in various classic and emerging fields, the control of their shape and size remains a challenge, in particular the search for more efficient and environmentally friendly syntheses. In this context, the microfluidics approach allows not only the continuous production of MOFs but also an accurate reaction parameter control in their synthesis, representing a step towards intensification, versatility and scalability in the use of MOFs. Microfluidics also offers the possibility of synthesizing effective and defect free MOF-based hollow fiber membranes saving reactants as compared to conventional methods. This review is devoted to highlighting the multitude of synergies appearing when dealing with MOFs and microfluidics, not only in the bare synthesis of MOFs and their hierarchical structures but also when fabricating hollow fiber membranes with important applications in the separation field

MOF-polymer enhanced compatibility: post-annealed zeolite imidazolate framework membranes inside polyimide hollow fibers

Thermal annealing, a commonly used procedure for improving the performance of polymeric membranes, is in this work exploited in the presence of a metal-organic framework (MOF) supported layer. MOFs and polymers are materials with a common organic character, suggesting an enhanced affinity between them when used together in membrane separation. Zeolite-like imidazolate frameworks (ZIFs) ZIF-8 and ZIF-93 with sod and rho structures and pore apertures of 0.34 and 0.36 nm, respectively, have been grown inside 356 mm OD co-polyimide P84 hollow fibers by microfluidics, leading to continuous supported membranes. When these membranes were thermally in situ annealed below the glass transition temperature, while monitoring both H-2 and CH4 permeances, the MOF-polymer adhesion was enhanced. Thus the gas separation selectivity increased without any significant reduction in the gas permeance, and H-2/CH4 and CO2/CH4 maximum selectivities of 103 and 18 (ZIF-8) and 101 and 20 (ZIF93) were respectively measured. The good compatibility between MOF and polymer made improvements possible in the annealing of the membrane once it was prepared. If the annealing of the polymer was carried out before the MOF synthesis, the polymer chain rearrangement and surface smoothing prevented an optimum MOF-polymer interaction and the separation performance worsened. These results proved the compatibility between both materials and their synergistic contribution to gas selective transportSpanish MINECO MAT2013-40556-R, Aragon Government (DGA), European Social Fund, DGA fellowshi