Matrix Membranes For Gas Separation Research Articles

Highly Permeable Mixed Matrix Membranes for Gas Separation via Dual Defect-Engineered Zeolitic Imidazolate Framework-8.

Defect engineering of metal-organic frameworks (MOFs) is a promising strategy for tailoring the interfacial characteristics between MOFs and polymers, aiming to create high-performance mixed matrix membranes (MMMs). This study introducesa new approach using dual defective alkylamine (AA)-modulated zeolitic imidazolate framework-8 (DAZIF-8), to develop high-flux MMMs. Tributylamine (TBA) and triethylamine (TEA) monodentate ligands coordinate with zinc ions in varying compositions. A mixture of Zn(CH3COO)2·2H2O:2-methylimidazole (Mim):AA in a 1:1.75:5 molar ratio facilitates high-yield coordination between Zn and multiple organic ligands, including Zn-Mim, Zn-TEA, and Zn-TBA (>80%). Remarkably, DAZIF-8 containing 3 mol% TBA and 2 mol% TEA exhibits exceptional characteristics, such as a Brunauer-Emmett-Teller surface area of 1745m2 g-1 and enhanced framework rigidity. Furthermore, dual Zn-AA coordination sites on the framework's outer surface enhance compatibility with the polyimide (PI) matrix through electron donor-acceptor interactions, enabling the fabrication of high-loading MMMs with excellent mechanical durability. Importantly, the PI/DAZIF-8 (60/40 w/w) MMM demonstrates an unprecedented 759% enhancement in ethylene (C2H4) permeability (281 Barrer) with a moderate ethylene/ethane (C2H4/C2H6) selectivity of 2.95 compared to the PI, surpassing the polymeric upper limit for C2H4/C2H6 separation.

Recent advances in the interfacial engineering of MOF-based mixed matrix membranes for gas separation.

The membrane process stands as a promising and transformative technology for efficient gas separation due to its high energy efficiency, operational simplicity, low environmental impact, and easy up-and-down scaling. Metal-organic framework (MOF)-polymer mixed matrix membranes (MMMs) combine MOFs' superior gas-separation performance with polymers' processing versatility, offering the opportunity to address the limitations of pure polymer or inorganic membranes for large-scale integration. However, the incompatibility between the rigid MOFs and flexible polymer chains poses a challenge in MOF MMM fabrication, which can cause issues such as MOF agglomeration, sedimentation, and interfacial defects, substantially weakening membrane separation efficiency and mechanical properties, particularly gas separation. This review focuses on engineering MMMs' interfaces, detailing recent strategies for reducing interfacial defects, improving MOF dispersion, and enhancing MOF loading. Advanced characterisation techniques for understanding membrane properties, specifically the MOF-polymer interface, are outlined. Lastly, it explores the remaining challenges in MMM research and outlines potential future research directions.

Mixed matrix membrane with amorphous metal-based complexes displays high CO2 separation performance

Design and exploration of advanced nanofillers that can be highly compatible with the existing polymeric membrane materials remain a subject of future study for mixed matrix membranes for gas separation. In this study, we propose the use of the newly synthesized metal-based complex (Zn-SiF6-py) as a promising filler to prepare high-performance PIM-1 based mixed matrix membranes for efficient CO2 separation. Results demonstrated that the as-synthesized Zn-SiF6-py features an amorphous mesoporous structure, and the inclusion of Zn-SiF6-py in the PIM-1 matrix can concurrently elevate the CO2 permeability and CO2/N2 selectivity. The significant improvements in membrane separation performance can be ascribed to the combined effects of additional gas transport channels and abundant active sites to CO2 molecules provided by Zn-SiF6-py fillers as well as a rigidified polymer region at the filler/matrix interface. Consequently, the optimized mixed matrix membrane at only 5 wt% filler loading achieves a CO2 permeability of 6268 Barrer and a CO2/N2 selectivity of 26.3, surpassing the 2008 Robeson upper bound.

Metal-organic framework-based mixed matrix membranes for gas separation: Recent advances and opportunities

The demand for carbon dioxide (CO2) emission mitigation has driven the scientific community to develop a viable strategy. Gas separation technology are considered as the most promising and effective carbon capture approach. The utility of mixed-matrix membranes (MMMs) for selective gas separation has prompted a paradigm shift from conventional methods towards more efficient and sustainable processes. Metal-organic frameworks (MOFs), with high porosity, surface area, and structural tunability, are identified as suitable fillers in MMMs. Their application in carbon capture and gas separation processes could significantly reduce greenhouse gas emissions while maintain cost-effectiveness. Herein, this review presents the latest scientific and technological advancements in several types of representative MOF fillers, including Zeolitic Imidazolate Frameworks (ZIFs), Materials of Institute Lavoisier (MILs), University of Oslo (UiO), and Hong Kong University of Science and Technology (HKUST-1). It also highlights the current challenges associated with MOF fillers and outlines potential research opportunities for future improvements in the performance of MOF-based MMMs.

The Difference in Performance and Compatibility between Crystalline and Amorphous Fillers in Mixed Matrix Membranes for Gas Separation (MMMs).

An increasing number of high-performing gas separation membranes is reported almost on a daily basis, yet only a few of them have reached commercialisation while the rest are still considered pure research outcomes. This is often attributable to a rapid change in the performance of these separation systems over a relatively short time. A common approach to address this issue is the development of mixed matrix membranes (MMMs). These hybrid systems typically utilise either crystalline or amorphous additives, so-called fillers, which are incorporated into polymeric membranes at different loadings, with the aim to improve and stabilise the final gas separation performance. After a general introduction to the most relevant models to describe the transport properties in MMMs, this review intends to investigate and discuss the main advantages and disadvantages derived from the inclusion of fillers of different morphologies. Particular emphasis will be given to the study of the compatibility at the interface between the filler and the matrix created by the two different classes of additives, the inorganic and crystalline fillers vs. their organic and amorphous counterparts. It will conclude with a brief summary of the main findings.

Organically modified clay as an enhancement filler in novel polyimide mixed matrix membranes for gas separation

Organically modified clay as an enhancement filler in novel polyimide mixed matrix membranes for gas separation

GNs/MOF-based mixed matrix membranes for gas separations

NU-1000 and graphene nanosheet (GNs) with different loadings have been used as fillers to prepare mixed matrix membranes (MMMs) with polyethersulfone (PES). The high performance of the MMMs has been successfully fabricated for the evaluation of gas separation at 1 bar and various temperatures (20, 40, 60 °C). The successful fabrication of the MMMs were confirmed by using SEM, FTIR, AFM, and XRD. The crystalline nature of GNs and NU-1000 in the MMMs are evidenced by XRD, which confirms the successful fabrication of the MMMs. In addition, the thermal stability of the MMMs was enhanced with the increase of the GNs. Separation performance of H2 was superior to CO2, N2 and CH4 separation on the MMMs which is a critical for producing energy. The best gas separation results in terms of both permeability and selectivity were obtained with 0.03% GNs and 10% NU-1000. PG3N membrane presented maximum H2/CO2, H2/N2 and H2/CH4 selectivity of 5, 4.2, 3.3 at 20 C, respectively. With an increase in temperature, the permeability increased, while the selectivity of all the MMMs decreased. The MMMs exhibited excellent gas separation capability, which offers unique opportunities for potential large-scale practical applications.

Synthesis and Characterization of PES/Pebax-MWCNTs Mixed Matrix Membranes for Gas Separation

The development of MWCNT mixed matrix membranes (MWCNT-MMMs) has shown good performance for gas separation. Interfacial interactions between the CNTs and the polymer and the dispersion of the MWCNTs in the polymeric matrix affects the overall performance of CNT mixed matrix membranes. Although CNTs properties are superior to other inorganic fillers but due to their chemically inert properties and inability to disperse in typical organic solvents, their applicability in industry is still uncertain. Typically, nanotubes are bound together by strong van der Waals interactions and form tight bundles. Therefore, MWCNTs tend to accumulate to each other in polymer matrix. This has been the biggest challenge in development of MWCNT-MMMs in producing defect free membranes. In this research, PES/Pebax-MWCNTs mixed matrix membraness were fabricated to capture carbon for natural gas. Sorbitol has been utilized in the fabrication of membranes to break the agglomeration of MWCNTs. In this study, the effect of MWCNTs loading and addition of sorbitol on the structure of synthesized membranes was analyzed using FESEM, DSC and FTIR. The incorporation of MWCNTs in the polymer matrix allows more active path for small molecules to flow across the membranes. The agglomeration of MWCNTs is more significant with the increase of fillers loading. Addition of sorbitol improved the morphology of membranes. Smooth surface of membranes with no agglomeration are observed for all MWCNTs loading (2-6 wt%). Glass transition temperature (Tg) was shifted to lower temperature with the addition of both MWCNTs and sorbitol.

Engineering CAU-10-H in the preparation of mixed matrix membranes for gas separation

Metal-organic frameworks (MOFs) are highly compatible with polymers and can be used to create mixed matrix membranes (MMMs) for gas separation. Herein, we engineered the particle size as well as the number of missing linkers in CAU-10-H MOFs via either applying the plasma treatment (CAU-10-H_Plasma) or varying the water/N,N-dimethylformamide (H2O/DMF) co-solvent ratios (CAU-10-H_Micro and CAU-10-H_Nano). The CAU-10-H_Nano showed the largest number of missing linkers, but the lowest adsorption uptake of CO2 and CH4 albeit the largest BET surface area. In contrast, both CAU-10-H_Plasma and CAU-10-H_Micro exhibited relatively high adsorption uptakes of CO2 and CH4. In addition, all the MMMs fabricated using 6FDA-mPDA:DABA (3:2) exhibited a good interaction between Al2+ metal ions of CAU-10-H and carboxylic groups of 6FDA-mPDA:DABA (3:2). Importantly, the 6FDA-mPDA:DABA (3:2)/CAU-10-H_Plasma (75/25 w/w) MMM exhibited more attractive selectivities of CO2/CH4 and H2/CH4 (e.g., 68 and 184, respectively) compared to those of the other two MMMs under single-gas conditions. It also showed the highest CO2/CH4 selectivity of 67 under equimolar CO2/CH4 mixed-gas conditions. As CAU-10-H_Plasma possessed the lowest quantity of defective sites among the three CAU-10-H samples, our results suggest that suppressing defective sites in MOFs could be an effective approach for enhancing the CO2 separation efficiency.

Recent development in polymer/montmorillonite clay mixed matrix membranes for gas separation: a short review

Recent development in polymer/montmorillonite clay mixed matrix membranes for gas separation: a short review

Functionalized two-dimensional g-C3N4 nanosheets in PIM-1 mixed matrix membranes for gas separation

The virtuous of two-dimensional (2D) nanomaterials in high aspect ratio and tunable surface functionality have geared towards their implementation in mixed matrix membranes (MMMs) for advanced gas separation. In this study, the effects of functionalized 2D nanosheets in the MMMs for gas separation were investigated. The graphitic carbon nitride (g-C3N4) nanosheets were modified with various functional groups namely sulfuric acid group, aliphatic amino group, aromatic amino group, and sulfonic group via four different synthesis approaches. Polymers of intrinsic microporosity (PIMs, e.g., PIM-1) was selected as the continuous polymer phase due to its intrinsic high permeability and comparable selectivity towards different gas pair. The sulfonic acid functionalized g-C3N4 MMMs (e.g., PIM-1/g-C3N4-D) imparted high separation properties ascribed to the great CO2 affinity induced by the sulfonic acid groups. In particular, PIM-1/g-C3N4-D (99:1) MMM demonstrated promising CO2 separation performance, with CO2 permeability of 3740 Barrer and CO2/N2 selectivity of 19.8. Moreover, at 5 wt% loading of g-C3N4-D, the H2/N2 and O2/N2 separation of the MMMs had exceeded the 2008 Robeson upper bound, thanks to the periodic triangular ultramicropores in g-C3N4 that favor precise sieving of small gases. These results pave the way in using the developed membranes in practical H2 purification, air separation and CO2 capture.

Hyper cross‐linked polymers containing amino group functionalized polyimide mixed matrix membranes for gas separation

AbstractThe design and synthesis of porous materials with novel structures and functional groups to prepare mixed matrix membranes (MMMs) is an effective way to break through trade‐off effect of membrane technology. Here, hyper cross‐linked polymers containing amino groups (HCPs‐NH2) with philic‐CO2 frame were successfully prepared for the fabrication of polyimide (PI)/HCPs‐NH2 MMMs. The separation performance of pure gas is studied in order to explore NH2 groups facilitating CO2 diffusion and transmission and enhancing CO2 permeability. Consequently, the permeability of the PI/HCPs‐NH2 MMMs toward CO2 and O2 are 77.56 Barrer and 17.91 Barrer versus pure PI film toward CO2 and O2 (62.42 Barrer and 13.85 Barrer). The selectivity for CO2/CH4 and O2/N2 pairs is 24.44 and 4.01, and the selectivity of pure PI film toward CO2/CH4 and O2/N2 pairs is 20.76 and 3.29, respectively. The permeability and selectivity of PI/HCPs‐NH2 MMMs are higher than pure PI film breaking through the trade‐off effect. Moreover, the PI/HCPs‐NH2 MMMs show better separation performance on the CO2/CH4 pair than the O2/N2 pair, indicating HCPs‐NH2 with philic‐CO2 frame plays a very important role in promoting CO2 permeability. Thus, the PI/HCPs‐NH2 MMMs have potential applications in the field of natural gas purification.

PIM-1/Holey Graphene Oxide Mixed Matrix Membranes for Gas Separation: Unveiling the Role of Holes.

PIM-1/holey graphene oxide (GO) mixed matrix membranes (MMMs) have been prepared and their gas separation performance for CO2/CH4 mixtures assessed. Nanopores have been created in the basal plane of gas-impermeable GO by chemical etching reactions, and the resulting holey flakes have been further chemically functionalized, either with octadecylamine (ODA) or with PIM-1 moieties, to aid their dispersion in PIM-1. It is found that nanopores barely promote gas transport through the graphene-like nanofiller for fresh membranes (tested right after preparation); however, the prepared hybrid PIM-1/holey GO membranes exhibit higher CO2 permeability and CO2/CH4 selectivity than the pure polymer membrane 150 days after preparation and 13 and 15% higher CO2 permeability for filler contents of 0.1% of octadecylamine-functionalized holey GO and 1% of (PIM-1)-functionalized holey GO, respectively. The most significant improvement is observed for the mitigation of physical aging, as MMMs using 10% of (PIM-1)-functionalized holey GO nanofillers are capable of maintaining up to 70% of their initial CO2 permeability after 150 days, whereas only 53% is kept for pure PIM-1 after the same period. The gas permeability of the nanofiller has been rationalized with the aid of the Maxwell-Wagner-Sillars equation.

Constructing Strong Interfacial Interactions under Mild Conditions in MOF-Incorporated Mixed Matrix Membranes for Gas Separation.

Although mixed matrix membranes (MMM) possess remarkably improved gas separation performance compared to traditional polymeric membranes, membrane stability including CO2 plasticization and aging is still a serious issue due to the existence of interfacial defects. In this work, we report an efficient and less destructive route to cross-link the MOFs/polyimide (PI) MMM, where amine group-functionalized MOF (NH2-UiO-66) nanoparticles are thermally cross-linked with a carboxylic acid-functionalized PI (COOH-PI) matrix to form an amide bond at the interface at 150 °C under vacuum condition. Such a chemical cross-linking strategy conducted at a relatively mild condition improves membrane stability greatly while ensuring that the membrane structure is not destroyed. The resulting cross-linked MMM achieves enhanced mechanical strength with higher Young's modulus than a pristine polymer membrane. The CO2 antiplasticization pressure of the MMM after cross-linking is enhanced by 200% from ∼10 to >30 bar and the CO2 permeability of MMM only drops slightly from 995 to 735 Barrer after 450 days. At the same time, the separation performance of H2/CH4 gas pair surpasses the 2008 upper bound and that of CO2/CH4 gas pair nearly approaches the 2008 upper bound. The cross-linking strategy used herein provides a feasible and effective route for improving membrane stability and membrane performance in the MMM system for gas separation.

Nano-porous Zeolite and MOF Filled Mixed Matrix Membranes for Gas Separation

The commercial SAPO-34 zeolite with 0.38 nm pore size and ZIF-8 particles with 0.34 nm aperture size were separately dispersed into different polymer matrix, to prepare the mixed matrix membranes (MMMs) for gas separation. The dispersed situation of the SAPO-34 and ZIF-8 particles in matrix and the influence of the fillers on the separation performance of the membrane had been investigated in this study. The as-synthesized MMMs showed a better trade-off between permeability and selectivity than the pure polymer membrane and the performance could exceed or close to the upper bound line of polymer membrane for CO2 and CH4 separation. The CO2 permeability and CO2/CH4 ideal selectivity of the 6FDA-mDAT MMM containing 40 wt% SAPO-34 zeolite was 190 barrer and ca. 60, respectively. The 6FDA-TrMPD based MMMs containing 20 wt% ZIF-8 provided a permeability of C3H6 and an ideal selectivity of C3H6/C3H8 at 24 barrer and ca. 17, respectively. These separation performances were in a suitable agreement of the theoretical value from Maxwell model.

Interfacial manipulation of MOFs/polymer mixed matrix membranes for gas separations: A review

Membrane-based separation technology holds great promise to effectively address separation needs in chemical industries due to advantages in energy efficiency, scalability, and small footprint. Mixed matrix membranes based on polymer/metal organic frameworks (MOFs), which combine the ease of processability of polymer materials with the excellent adsorption characteristics of MOFs, have been widely investigated for gas separations. The preparation of gas separation membrane materials with both high flux and gas selectivity is the key to achieving efficient gas separation. Recent research results show that the permeability coefficient and gas pair selectivity of mixed matrix membrane materials are hardly improved simultaneously by adding second phase materials such as MOFs. When the loading of MOFs increases, most membranes have common problems such as particle agglomeration and non-selective interfacial defective structures, which lead to a significant decrease in separation performance. To resolve these issues, research scientists are devoted to tailoring the interfacial microstructure of mixed matrix membranes with an aim to exceed the Robeson upper limit. Many novel characterization techniques coupled with simulation studies were carried out to probe the filler dispersion behavior and interfacial structure within membranes in order to provide rules for rationally designing mixed matrix membranes. A variety of approaches have been proposed to finely tune the interfacial interaction by constructing hydrogen bonding and covalent bonding in the membranes. For example, synthesizing functionalized MOFs via mixed-linker or ligand exchange methods provides a good option to enhance interfacial adhesion within membranes. The amino groups, hydroxyl groups and other organic functional groups in MOFs have the capability to create hydrogen bonding. Moreover, these groups can preferentially adsorb specific gas molecules (such as CO2 molecules) to improve gas selectivity. Some researchers post-functionalized MOFs to graft reactive groups on their surface, incorporating them with cross-linkable polymers. Then the light/heat induced crosslinking reaction occurred within the membrane to seal its defective structure, thereby achieving a substantial improvement in membrane separation performance. The past publications on mixed matrix membranes in the decade demonstrated that the researchers have much more in-depth understanding and insights on the fabrication process, membrane morphology, and structure-property relationship of mixed matrix membrane materials. With respect to fundamental research, research scientists are committed to investigating the MOFs properties including crystal morphology, coordinated metal ion, functional groups on membrane performance. To yield high performance mixed matrix membranes, highly permeable polymers were rationally designed as the polymer matrix. However, to complement their widespread industrial application, scale-up of hollow fiber mixed matrix membranes needs to be further investigated. The membrane stability in humid gas feeds is required to be improved. It is also of importance to develop stable, cost-effective and scalable MOFs fillers. With a specific focus on interfacial manipulation of MOFs/polymer mixed matrix membranes for gas separations, this paper mainly reviewed the research progress in the fields of MOFs/polymer-based hybrid matrix membranes for gas separations. It focuses on three aspects: (1) Research progress on optimizing and characterizing the interfacial structure; (2) fundamental understanding of the influences of MOFs and polymers properties on membrane performance; (3) research progress on scale-up of mixed matrix membranes. Finally, the future development direction of mixed matrix membrane materials is proposed in order to provide research ideas for the rational design of high-performance mixed matrix membranes.

Potential of adsorbents from agricultural wastes as alternative fillers in mixed matrix membrane for gas separation: A review

AbstractMixed matrix membrane (MMM), formed by dispersing fillers in polymer matrix, has attracted researchers’ attention due to its outstanding performance compared to polymeric membrane. However, its widespread use is limited due to high cost of the commercial filler which leads to the studies on alternative low-cost fillers. Recent works have focused on utilizing agricultural wastes as potential fillers in fabricating MMM. A membrane with good permeability and selectivity was able to be prepared at low cost. The objective of this review article is to compile all the available information on the potential agricultural wastes as fillers in fabricating MMM for gas separation application. The gas permeation mechanisms through polymeric and MMM as well as the chemical and physical properties of the agricultural waste fillers were also reviewed. Additionally, the economic study and future direction of MMM development especially in gas separation field were discussed.

Two-Dimensional Microporous Material-based Mixed Matrix Membranes for Gas Separation.

Since the discovery of graphene and its derivatives, the development and application of two-dimensional (2D) materials have attracted enormous attention. 2D microporous materials, such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), graphitic carbon nitride (g-C3 N4 ) and so on, hold great potential to be used in gas separation membranes because of their high aspect ratio and homogeneously distributed nanometer pores, which are beneficial for improving gas permeability and selectivity. This review briefly summarizes the recent design and fabrication of 2D microporous materials, as well as their applications in mixed matrix membranes (MMMs) for gas separation. The enhanced separation performances of the membranes and their long-term stability are also introduced. Challenges and the latest development of newly synthesized 2D microporous materials are finally discussed to foresee the potential opportunities for 2D microporous material-based MMMs.

Exploration of the Synergy Between 2D Nanosheets and a Non-2D Filler in Mixed Matrix Membranes for Gas Separation.

Dual-filler MMMs have attracted special interests in recent years because of the possibility of producing synergetic effect. This study is aimed at exploring the underlying synergy between two-dimensional (2D) nanosheets and a non-2D filler in mixed matrix membranes for gas separation. MXene or graphene oxide (GO) as typical nanosheet filler is selected to be in pair with a non-2D filler, SiO2 or halloysite nanotubes (HNTs), with Pebax as the polymer matrix. In this way, four pairs of binary fillers are designed and the corresponding four groups of MMMs are fabricated. By tuning the mass ratio of binary fillers, synergetic effect is found for each group of MMMs. However, the two 2D fillers found different preferential non-2D partners. GO works better with HNTs than SiO2, while MXene prefers SiO2 to HNTs. To be noted, GO/HNTs renders the membranes the maximum enhancement of CO2 permeability (153%) and CO2/N2 selectivity (72%) compared to Pebax control membrane, while each of them as single filler only brought about very limited enhancement of CO2 separation performance. The possible mechanisms are thoroughly discussed in terms of filler dispersion, nanosheet flexibility, and the tortuosity and connectivity of the surface diffusion pathways along nanosheets.

Highly selective filler–polymer gaps in situ fabricated in mixed matrix membranes for gas separation

We report an interface self-assembly strategy to build high speed gas transport channels throughout mixed matrix membranes in situ using the gaps between hydrophilic polymers and hydrophobic fillers (normally considered as defects that lower the gas separation performance).