Effect of the ZIF‐8 Distribution in Mixed‐Matrix Membranes Based on Matrimid® 5218‐PEG on CO2 Separation

In theory, the combination of inorganic materials and polymers may provide a synergistic performance for mixed‐matrix membranes (MMMs); however, the filler dispersion into the MMMs is a crucial technical parameter for obtaining compelling MMMs. The effect of the filler distribution on the gas separation performance of the MMMs based on Matrimid®‐PEG 200 and ZIF‐8 nanoparticles is demonstrated. The MMMs were prepared by two different membrane preparation procedures, namely, the traditional method and non‐dried metal‐organic framework (MOF) method. In CO₂/CH₄ binary mixtures, the MMMs were tested under fixed conditions and characterized by various methods. Finally, regardless of the MMM preparation procedure, the incorporation of 30 wt % ZIF‐8 nanoparticles allowed to increase the CO₂ permeability in MMMs. The ZIF‐8 dispersion influenced significantly the separation factor.     

Fabrication of mixed‐matrix membranes with MOF‐derived porous carbon for CO2 separation

Mixed‐matrix membranes (MMMs) have shown great advantages but still face some challenges, such as the trade‐off between permeability and selectivity, stability, and the lack of efficient ways to enhance them simultaneously. Here, the fabrication of MMMs with metal‐organic frameworks derived porous carbons (MOF‐PCs) as fillers which exhibit selective‐facilitating CO₂ transport passage originating from interactions between fillers and CO₂ is showed. With the aid of the developed multicalcination method, MOF‐PCs with variable N‐contents were prepared and incorporated into PPO‐PEG matrix for the first time to prepare MMMs, which show excellent separation performance for CO₂/CH₄ mixture with a tunable separation performance by combining different N‐contents and surface areas of MOF‐PCs. Moreover, the developed MMMs have hydrothermal and chemical stability. This work not only presents a series of MMMs with both good separation properties and stability, it also provides useful information for guiding the fabrication of high performance MMMs for practical application. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3400–3409, 2018     

Various Techniques for Preparation of Thin‐Film Composite Mixed‐Matrix Membranes for CO2 Separation

The application of thin‐film composite mixed‐matrix membranes (TFC‐MMMs) for gas separation is widely considered as an efficient separation technology. The principal methods for the preparation of TFC‐MMMs are dip‐coating, phase inversion, and interfacial polymerization comprising different types of support layers. These methods influence the CO₂ permeation over the selective and support layers. A comprehensive review is provided for capturing new details of progress achieved in developing TFC‐MMMs with detailed performance of gas separation in the previous few years. Various preparation techniques of TFC‐MMMs and their effect on the gas separation performance of the prepared membranes are described.     

Material Advancements in Fabrication of Mixed‐Matrix Membranes

The mixed‐matrix membrane (MMM) is a new membrane material for gas separation and plays a vital role for the advancement of current membrane‐based separation technology. Blending between inorganic fillers like carbon molecular sieves, zeolite, metal oxides, silica and silica nanoparticles, carbon nanotubes, zeolitic imidazolate framework, metal organic framework, and glassy and rubbery polymers etc. is possible. Due to mechanical, thermal, and chemical stability, these membranes achieve high permeability and selectivity as compared to pure polymeric materials. Despite of these advantages, the MMM performances are still below industrial expectations because of membrane defects and related processing problems as well as the nonuniform dispersion of fillers in MMMs. Material selection for organic and inorganic phases, preparation techniques, material advancements, and performance of MMMs are discussed. Issues and challenges faced during MMM synthesis as well as problem solutions are highlighted.     

改善无机填料混合基质膜气体分离性能的研究进展

混合基质膜（MMMs）是结合了无机填料和有机基质特点的一类膜材料,因其在气体分离应用上具有良好的渗透通量和分离性能被广泛关注。无机填料诸如二氧化硅纳米颗粒球、沸石分子筛、金属有机框架（MOF）、氧化石墨烯（GO）、碳纳米管（CNT）均被广泛应用于混合基质膜的制备,但是碍于无机填料在有机相中的分散性问题、两相相容性问题和界面缺陷问题,常会导致较差的气体分离性能。针对近年通过对无机填料进行表面官能化修饰、共价交联、多元填充、调控形貌等来改善混合基质膜气体分离性能的研究进行总结和阐述,并对其未来的发展趋势进行了展望。     

Effect of MIL‐53 (Al) MOF particles on the chain mobility and crystallization of poly(L‐lactic acid)

Polymer‐filler interactions significantly influence morphology, functionality, and various desirable properties of mixed matrix membranes (MMMs). In this study, chain mobility and crystallization of poly(l ‐lactic acid) (PLLA) MMM films prepared by solvent casting PLLA with 1, 5, 10, and 20% wt/wt of MIL‐53(Al) metal organic framework (MOF) were evaluated. The fabricated MMMs were characterized using differential scanning calorimetry, Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Differential scanning calorimetry studies indicated that the addition of MOF particles in the PLLA matrix reduces the polymeric chain mobility, which affects the crystallization process. The percent crystallinity of neat PLLA was found to decrease from 4% in neat PLLA to completely amorphous structures in PLLA‐10% and PLLA‐20% MMMs, as observed in the second heating cycle. Fourier transform infrared spectroscopy data supports these observations. Thermogravimetric analysis results showed that PLLA‐MOF films are thermally less stable than neat PLLA suggesting that MOF particles act as a depolymerization catalyst for PLLA. Partial agglomeration of MOF particles was observed in the samples using scanning electron microscopy studies. This study indicates strong PLLA‐MIL‐53(Al) MOF interactions. In addition, this study also provides insight into the effect of MOF particles on the segmental mobility and morphology of PLLA‐MIL‐53 (Al) composite films. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45690.     

Effect of different organic amino cations on SAPO‐34 for PES/SAPO‐34 mixed matrix membranes toward CO2/CH4 separation

Mixed matrix membranes (MMMs) embedded with functionalized SAPO‐34 were successfully synthesized and characterized. Two different types of organic amino cation, namely ethylenediamine (EDA) and hexylamine (HA), were used to functionalize SAPO‐34 particles prior to MMM synthesis. In this work, the effects of different functionalizing agents on the membrane morphology, pore size, and CO₂/CH₄ gas separation properties were investigated. Surface modification of SAPO‐34 was confirmed via X‐ray photoemission spectroscopy (XPS) where the presence of nitrogen atom was observed for the samples functionalized with amino cations. The dispersion of EDA‐functionalized SAPO‐34 particles was found to have better polymer/filler interface morphology as shown by field emission scanning electron microscopy (FESEM) analysis. The gas separation performance revealed that PES containing EDA‐functionalized SAPO‐34 exhibited better CO₂/CH₄ separation performance as compared to the MMMs containing HA‐functionalized SAPO‐34. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43387.     

Poly(vinyl alcohol)/ZIF‐8‐NH2 mixed matrix membranes for ethanol dehydration via pervaporation

Ethanediamine‐modified zeolitic imidazolate framework (ZIF)‐8 particles (ZIF‐8‐NH₂) is synthesized and incorporated in the poly(vinyl alcohol) (PVA) matrix to fabricate novel PVA/ZIF‐8‐NH₂ mixed matrix membranes (MMMs) for pervaporation dehydration of ethanol. The PVA/ZIF‐8‐NH₂ MMMs exhibit enhanced membrane homogeneity and separation performance because of the higher hydrophilicity and restricted agglomeration of the particles, as compared to corresponding MMMs loaded with unmodified particles. The effect of ZIF‐8‐NH₂ loading in the MMMs is studied and the MMM with a 7.5 wt % ZIF‐8‐NH₂ loading shows the best pervaporation performance for ethanol dehydration at 40°C. Various characterization techniques (Fourier transform infrared, scanning electron microscope, contact angle, sorption test, etc.) are used to investigate the MMMs loaded with ZIF‐8 and ZIF‐8‐NH₂ particles. The impact of operation conditions on pervaporation performance is also performed. The performance benchmarking shows that the MMMs have superior separation factors and comparable flux to most other PVA hybrid membranes. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1728–1739, 2016     

碳纳米管/环糊精金属有机骨架协同强化混合基质膜的CO2分离

为了实现混合基质膜中CO₂的高效分离,设计了羧基化多壁碳纳米管(CNT)和氨基化β-环糊精金属有机骨架(β-CD MOF)双填料(CM),并将其引入磺化聚醚醚酮(SPEEK)基质中,在膜内同时构建CO₂扩散通道和亲和位点,增强了混合基质膜的分离性能。采用FTIR和BET表征了CM的化学结构和孔结构,借助膜的SEM、FTIR和力学性能表征了填料-聚合物界面相互作用。研究了CM的合成比例、含量、压力、温度和混合气等因素对混合基质膜分离性能的影响。结果表明：CM与SPEEK之间具有良好的相容性并为气体分子提供了快速的传递通道。在改性CNT与MOF的质量比为5∶5、添加量为7%(质量)以及0.1 MPa和25℃的条件下,混合基质膜的分离性能最优,CO₂渗透性为844 Barrer,CO₂/N₂选择性为84,与纯SPEEK膜相比,分别提升了178%和163%,超过2019年上限。羧基化CNT的直孔通道缩短了CO₂的扩散路径,同时改性β-CD MOF表面的氨基载体提升了CO₂的溶解性,两者协同提高了混合基质膜的分离性能。此外,负载双填料的膜比单独负载相同含量的羧基化CNT或氨基化MOF的膜具有更好的分离性能。在360 h的测试过程中,混合基质膜保持较好的分离稳定性。     

碳纳米管/环糊精金属有机骨架协同强化混合基质膜的CO2分离

为了实现混合基质膜中CO₂的高效分离,设计了羧基化多壁碳纳米管(CNT)和氨基化β-环糊精金属有机骨架(β-CD MOF)双填料(CM),并将其引入磺化聚醚醚酮(SPEEK)基质中,在膜内同时构建CO₂扩散通道和亲和位点,增强了混合基质膜的分离性能。采用FTIR和BET表征了CM的化学结构和孔结构,借助膜的SEM、FTIR和力学性能表征了填料-聚合物界面相互作用。研究了CM的合成比例、含量、压力、温度和混合气等因素对混合基质膜分离性能的影响。结果表明：CM与SPEEK之间具有良好的相容性并为气体分子提供了快速的传递通道。在改性CNT与MOF的质量比为5∶5、添加量为7%(质量)以及0.1 MPa和25℃的条件下,混合基质膜的分离性能最优,CO₂渗透性为844 Barrer,CO₂/N₂选择性为84,与纯SPEEK膜相比,分别提升了178%和163%,超过2019年上限。羧基化CNT的直孔通道缩短了CO₂的扩散路径,同时改性β-CD MOF表面的氨基载体提升了CO₂的溶解性,两者协同提高了混合基质膜的分离性能。此外,负载双填料的膜比单独负载相同含量的羧基化CNT或氨基化MOF的膜具有更好的分离性能。在360 h的测试过程中,混合基质膜保持较好的分离稳定性。     

Fabrication of Homogenous Polymer‐Zeolite Nanocomposites as Mixed‐Matrix Membranes for Gas Separation

Interfacial void‐free mixed‐matrix membranes (MMMs) of polyimide (PI)/zeolite were developed using 13X and Linde type A nano‐zeolites and tested for gas separation purposes. Fabrication of a void‐free polymer‐zeolite interface was verified by the decreasing permeability developed by the MMMs for the examined gases, in comparison to the pure PI membrane. The molecular sieving effect introduced by zeolite 13X improved the CO₂/N₂ and CO₂/CH₄ selectivity of the MMMs. Separation tests indicated that the manufactured nanocomposite membrane with 30 % loading of 13X had the highest permselectivity for the gas pairs CO₂/CH₄ and CO₂/N₂ at the three examined feed pressures of 4, 8 and 12 atm.     

Enhanced compatibility and selectivity in mixed matrix membranes for propylene/propane separation

Mixed matrix membranes (MMMs) based on metal–organic framework (MOF) have great promising application in separation of gas mixtures. However, achieving a good interfacial compatibility between polymer and MOF is not straightforward. In this work, focusing on one of the most challenging olefin/paraffin separations: propylene/propane (C₃H₆/C₃H₈), we demonstrate that modification of the MOF filler via dopamine polymerization using a double solvent approach strongly improves interfacial compatibility. The resulting membranes show an outstanding separation performance and long-term stability with propylene permeability nearly 90 Barrer and propylene/propane selectivity close to 75. We anticipate that similar MOF modification strategies may help solve the problem of interface defects in the manufacture of MMMs and be extended to other porous fillers.     

Three‐component mixed matrix organic/inorganic hybrid membranes for pervaporation separation of ethanol–water mixture

Mixed matrix membranes (MMMs) were made by incorporating vinyltrimethoxysilane (VTMS)‐modified Silicalite‐1 zeolite nanoparticles (V‐Silicalite‐1 NPs) into fluorinated polybenzoxazine (F‐PBZ) modified polydimethylsiloxane (PDMS) polymer through in situ polymerization method. The membrane morphology, surface wettability, and pervaporation performance were systematically investigated. The addition of F‐PBZ into PDMS membranes resulted in substantially improved flux and marginal increase of separation factor, which is the result of higher free volume and higher hydrophobicity caused by the addition of F‐PBZ. The modification of Silicalite‐1 NPs improved the interfacial contact between zeolite crystals and polymer phase. The incorporation of hydrophobic V‐Silicalite‐1 zeolite NPs into the PDMS membranes led to much higher separation factor but reduced flux, which is the result of increased hydrophobicity and reduced free volume. The three‐component MMMs with V‐Silicalite‐1 zeolite NPs in the F‐PBZ fluorinated PDMS exhibited separation factor of 28.7 and flux of 0.207 kg m^?2 h^?1 for 5 wt % ethanol aqueous solution at 50 °C, while the pure PDMS membranes only had separation factor of 4.8 and flux of 0.088 kg m^?2 h^?1. The substantial increase of both flux and separation factor were attributed to the higher hydrophobicity and free volume caused by the incorporation of both hydrophobic zeolite crystals and F‐PBZ polymer into the PDMS membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44753.     

Preparation and Characterization of C60‐Filled Ethyl Cellulose Mixed‐Matrix Membranes for Gas Separation of Propylene/Propane

Mixed‐matrix membranes (MMMs) consisting of ethyl cellulose as continuous matrix and inorganic particle C₆₀ as dispersed phase were prepared for propylene/propane separation. The impact of the C₆₀ content on the separation properties of MMMs without and with ultraviolet cross‐linking was investigated. The increment of decomposition temperature and single glass temperature of ethyl cellulose/C₆₀ MMMs indicates a strong interfacial interaction between polymer and fullerenes. After UV irradiation, the gas permeability coefficient of propylene and ideal separation factor of propylene/propane decreased, and new features appeared in scanning electron microscopy and atomic force microscopy images, testifying the photopolymerization reaction of C₆₀ at a depth near to the surface. C₆₀ could be acted as a possible replaced carrier for the separation of olefin/paraffin using membrane separation technology.     

Improved gas transport properties of polyurethane–urea membranes through incorporating a cadmium-based metal organic framework

The increasing need for more efficient separation processes has motivated the development of polymer membranes that can provide fast and selective transport. In this work, cadmium-based metal–organic framework (MOF) nanoparticles and a polyurethane–urea (PUU) elastomer were synthesized. New mixed-matrix membranes (MMMs) were then fabricated from the nanoparticles and the PUU. SEM images verified that embedding the nanoparticles changes the morphology of the PUU and the nanoparticles disperse well in the PUU due to satisfactory compatibility of the polymer and nanoparticles. Fourier transform infrared spectroscopy and X-ray diffraction analysis confirmed the dispersion of the nanoparticles in the soft segment of the PUU. With increased temperature, gas permeabilities of the MMMs improved but their sieving ability deteriorated. An MMM incorporating 2.5 wt % of the MOF showed a CO₂ permeability of ~140 barrer and a CO₂/N₂ selectivity of ~30, which are 89 and 38% higher than those of the pristine membrane. Gas permeation tests showed that the higher CO₂/N₂ selectivity of the MMMs was due to improved solubility selectivity and the higher CO₂ permeability was a result of improved CO₂ diffusivity and solubility coefficients. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48704.     

Recent advances on mixed matrix membranes for CO2 separation

Recent advances on mixed matrix membrane for CO2 separation are reviewed in this paper. To improve CO2 separation performance of polymer membranes, mixedmatrixmembranes (MMMs) are developed. The concept of MMM is illustrated distinctly. Suitable polymer and inorganic or organic fillers for MMMs are summarized.Possible interface morphologies between polymer and filler, and the effect of interface morphologies on gas transport properties of MMMs are summarized. The methods to improve compatibility between polymer and filler are introduced. There are eightmethods including silane coupling, Grignard treatment, incorporation of additive,grafting, in situ polymerization, polydopamine coating, particle fusion approach and polymer functionalization. To achieve higher productivity for industrial application,mixed matrix composite membranes are developed. The recent development on hollow fiber and flat mixedmatrix composite membrane is reviewed in detail. Last, the future trend of MMM is forecasted.     

机械化学法合成小尺寸MOF填料助力高性能CO2分离

利用金属-有机骨架UTSA-280具有特定刚性尺寸的一维孔道可以筛分CO₂、CH₄、N₂的特性,采用机械化学研磨法减小其颗粒尺寸,将UTSA-280掺入聚砜（PSf）中制备MOF基混合基质膜,用于天然气提纯和烟道气CO₂捕获。结果表明,在PSf中掺入UTSA-280不仅可以增加聚合物的CO₂渗透通量而且提高了气体分离选择性。当UTSA-280掺杂量为30%（质量）时,混合基质膜对CO₂/CH₄、CO₂/N₂的分离因子分别为56.39和53.17,CO₂的渗透通量为18.61 Barrer,相对于PSf纯膜,选择性分别提高了47.3%和63.5%,CO₂渗透通量提高了128.9%,打破了“trade-off”效应。该工作通过引进具有分子筛分效应的MOF填料,能够增加气体通量的同时提高混合基质膜对含CO₂气体的分离性能,对天然气的提纯以及烟道气的CO₂的捕获有重要意义。     

Matrix effect of mixed‐matrix membrane containing CO2‐selective MOFs

Facilitated mixed‐matrix membranes (MMMs) containing Cu‐metal organic frameworks (Cu‐MOFs) with high CO₂ selectivity on an asymmetric polysulfone support were fabricated and examined the effect of gas separation performance using different matrices. An amorphous poly(2‐ethyl‐2‐oxazoline) (POZ) and semicrystalline poly(amide‐6‐b‐ethylene oxide) (PEBAX^®MH 1657) block copolymer were chosen as the polymeric matrix and the effect of the matrix on CO₂ separation for MMMs containing Cu‐MOFs was investigated. The interaction of CO₂ in different matrix was investigated theoretically using the density functional theory method, and it was found that the amide segment in PEBAX would contribute more to the CO₂ solubility than ether segment. The morphological changes were investigated by differential scanning calorimetry, field emission scanning electron microscope and X‐ray diffractometer. The ideal selectivity of CO₂/N₂ was enhanced significantly with the addition of a Cu‐MOF, and the values are higher in the Cu‐MOF/PEBAX MMM compared with that in a POZ based asymmetric MMM. Improvement in the CO₂/N₂ selectivity of a Cu‐MOF/PEBAX MMM was achieved via facilitated transport by the CO₂‐selective Cu‐MOFs due to both their high adsorption selectivity of CO₂ over N₂ and the decreased crystallinity of PEBAX due to the presence of the Cu‐MOFs, which would provide a synergic effect on the CO₂ separation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42853.     

Defektfreie Mixed‐Matrix‐Membranen aus Matrimid® und Aktivkohle für die Gastrennung

In this work the fabrication of new mixed‐matrix membranes (MMMs) of Matrimid® and activated carbon (AC) for gas separation is reported. The aim is the fabrication of membranes that have better gas permeation properties compared to the pristine Matrimid® membranes. The membranes were thermally and morphologically characterized, and the gas transport properties of single gases were estimated by a variety of methods. It has been found that with an increase of the AC content the selectivity remained stable for the different gases despite the marked increase in the effective permeability of the pure gases.     

ZIF‐8 SURMOF Membranes Synthesized by Au‐Assisted Liquid Phase Epitaxy for Application in Gas Separation

Metal‐organic frameworks (MOFs) exhibit a huge potential for gas separation. ZIF‐8 is an interesting candidate due to its high thermal stability and its pore properties. By liquid phase epitaxy, the growth of the highly oriented surface‐anchored MOF ZIF‐8 on non‐porous and porous surfaces has been proven. The preparation of monolithic ZIF‐8 thin films supported by porous α‐Al₂O₃ substrates modified by a thin layer of Au is investigated. The layer‐by‐layer deposition process accomplished via a dipping procedure results in the formation of defect‐ or crack‐free membranes, preliminary characterized by the determination of ethane and ethene permeance.