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The use of immiscible polymer blends in gas separations is limited due to uncontrollable phase separation. In contrast, compatibilized immiscible polymer blends can be used as precursors with controlled morphologies that allow for a unique pore architecture. Herein, an immiscible polymer blend (1:1) comprising polybenzimidazole (PBI) and the copolyimide 6FDA-DAM:DABA [3:2], derived from reacting 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 2,4,6-trimethyl-1,3-phenylenediamine (DAM) and 3,5-diaminobenzoic acid (DABA), were combined with durene diamine as a compatibilizer. The compatibilizer helped reduce the 6FDD domain sizes from 5.6 µm down to 0.77 µm and induced a more even 6FDA distribution and the formation of continuous thin-selective PBI layers. The carbon–carbon composite membranes derived from the compatibilized immiscible polymer blends showed a 3-fold increase in both H2 permeability and H2/CO2 selectivity compared to the membranes derived from non-compatibilized polymer blends. The H2 permeability of the compatibilized immiscible polymer blends increased from 3.6 to 27 Barrer, and their H2/CO2 selectivity increased from 7.2 to 20. The graphitic domain size of the carbon–carbon composite membranes derived from the polymer blends also increased from 6.3 nm for the non-compatibilized blend to 10.0 nm for the compatibilized blend. [ABSTRACT FROM AUTHOR]

Carbon molecular sieve membranes (CMSMs) were prepared by carbonizing the high free volume polyimide BTDA-BAF that is obtained from the reaction of benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (BTDA) and 9,9-bis(4-aminophenyl) fluorene (BAF). The bulky cardo groups prevented a tight packing and rotation of the chains that leads to high permeabilities of their CMSMs. The incorporation of metal–organic polyhedra 18 (MOP-18, a copper-based MOP) in the BTDA-BAF polymer before pyrolysis at 550 °C prevented the collapse of the pores and the aging of the CMSMs. It was found that upon decomposition of MOP-18, a distribution of copper nanoparticles minimized the collapse of the graphitic sheets that formed the micropores and mesopores in the CMSM. The pillared CMSMs displayed CO2 and CH4 permeabilities of 12,729 and 659 Barrer, respectively, with a CO2/CH4 selectivity of 19.3 after 3 weeks of aging. The permselectivity properties of these membranes was determined to be at the 2019 Robeson upper bound. In contrast, the CMSMs from pure BTDA-BAF aged three times faster than the CMSMs from MOP-18/BTDA-BAF and exhibited lower CO2 and CH4 permeabilities of 5337 and 573 Barrer, respectively, with a CO2/CH4 selectivity of 9.3. The non-pillared CMSMs performed below the upper bound. [ABSTRACT FROM AUTHOR]

Gas separation for industrial, energy, and environmental applications requires low energy consumption and small footprint technology to minimize operating and capital costs for the processing of large volumes of gases. Among the separation methods currently being used, like distillation, amine scrubbing, and pressure and temperature swing adsorption, membrane-based gas separation has the potential to meet these demands. The key component, the membrane, must then be engineered to allow for high gas flux, high selectivity, and chemical and mechanical stability at the operating conditions of feed composition, pressure, and temperature. Among the new type of membranes studied that show promising results are the inorganic-based and the metal-organic framework-based mixed-matrix membranes (MOF-MMMs). A MOF is a unique material that offers the possibility of tuning the porosity of a membrane by introducing diffusional channels and forming a compatible interface with the polymer. This review details the origins of these membranes and their evolution since the first inorganic/polymer and MOF/polymer MMMs were reported in the open literature. The most significant advancements made in terms of materials, properties, and testing conditions are described in a chronological fashion. [ABSTRACT FROM AUTHOR]

Abstract: Zeolitic imidazolate frameworks (ZIFs), that have the potential for gas separation, were used as additives in mixed-matrix membranes (MMMs). ZIF-8, which exhibits the sodalite topology, is composed of zinc (II) ion clusters linked by imidazolate ligands. The ZIF-8 pore aperture is 3.4Å allowing it to readily absorb small molecules such as H2 and CO2. ZIF-8/Matrimid® MMMs were fabricated with loadings up to 80% (w/w), which are much higher than the typical loadings achieved with select zeolite materials. Only at the highest loading did the ZIF-8/Matrimid® MMM show a loss of mechanical strength, leading to a decrease in flexibility. The ZIF-8/Matrimid® MMMs permeability properties were tested for H2, CO2, O2, N2, CH4, C3H8, and gas mixtures of H2/CO2 and CO2/CH4. The permeability values increased as the ZIF-8 loading increased to 40% (w/w). However, at higher loadings of 50% and 60% (w/w), the permeability decreased for all gases, and the selectivities increased consistent with the influence of the ZIF-8 additive. The ideal selectivities of gas pairs containing small gases, such as H2/O2, H2/CO2, H2/CH4, CO2/CH4, CO2/C3H8, and H2/C3H8, showed improvement with the 50% (w/w) ZIF-8 loading, demonstrating a transition from a polymer-driven to a ZIF-8-controlled gas transport process. In control experiments using as-synthesized ZIF-8 with filled pores, there was no transition at 50% (w/w) loading. This may be the first example of an MMM wherein molecular sieving is evident and suggests that additive loadings >50% (w/w) may be required to observe this effect in MMMs. [Copyright &y& Elsevier]

The process of electrospinning has been applied for the first time in the production of mesoporous molecular sieve fibers. Different organic templates and silica sources were used to reproducibly obtain a high density of SBA-15 and DAM-1 fibers with diameters in the range of a micron to a few hundred nanometers. [Copyright &y& Elsevier]

Although propylene/propane separation remains a challenge for industrial processes, carbon molecular sieve membranes (CMSMs) have the potential to replace traditional separation methods. A high molecular weight crosslinkable polyimide was utilized to fabricate CMSMs, which showed pure gas permeabilities in excess of 400 barrers with propylene/propane selectivities as high as 25. Mixed gas (C 3 H 8 :C 3 H 6 50:50) measurements yielded a propylene permeability of 257 barrers and a selectivity of 20. CMSMs from thermally precrosslinked polymer precursors demonstrated a 98% propylene permeability retention after aging for 20 days under vacuum. Active gas flow conditions resulted in slightly lower permeability retention (92.5%) after 15 days of testing. • Deprotonation of carboxylic acid in DABA improves molecular weight of 6FDA-DABA. • 6FDA-DABA can be completely thermally crosslinked at 450 °C. • Precrosslinked carbon membranes showed a higher graphitic carbon content. • Higher graphitic carbon contents resulted in higher propylene solubility. • Precrosslinked carbon membrane exhibited superior aging resistance. [ABSTRACT FROM AUTHOR]