Increase In CO2 Permeability Research Articles

Reinforced facilitated transport PEBA membrane by 2D Fe-doped TiO2 macroporous nanosheets for CO2 separation: Utilizing cationic and non-ionic surfactants

In this study, macroporous nanosheets of 2D Fe-Doped TiO2 were synthesized, and subsequently, membranes composed of polyether block amide (PEBA) were prepared. These membranes were incorporated with the nanosheets mentioned above, as well as two distinct types of surfactant. The structure and gas separation properties of the membranes were studied using different methods, including atomic force microscopy (AFM), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), as well as gas permeation analyses and tensile test. The findings indicated that the nanosheets underwent a porous transformation following the doping process. This occurrence improved the bonding between the nanosheets and PEBA chains, consequently boosting the mechanical strength of the membranes embedded with these nanosheets. Incorporating these nanosheets into the membrane (4 wt%) established a more efficient facilitated transport mechanism via Lewis acid centers, resulting in a 12.5 % increase in CO2 permeability and a 136 % rise in the selectivity of CO2/N2 compared to the pure PEBA membrane. Two different surfactants were introduced to the PEBA/FeTiO2 matrix, resulting in varying impacts on membrane structure and performance. The Cetyl trimethyl ammonium bromide (CTAB) as a cationic surfactant led to membrane stiffening and a significant 241 % enhancement in CO2/N2 selectivity at 1 wt%. On the other hand, the Polysorbat (Tween) as a non-ionic surfactant softened the membrane and boosted CO2 permeability by 53 % at 6 wt% compared to the pure membrane.

Porous organic cage induced high CO2/CH4 separation efficiency of carbon molecular sieve membranes

Porous fillers have been incorporated into precursor membranes to fabricate carbon molecular sieve (CMS) membranes, where the interfacial compatibility between fillers and matrix significantly influences the separation performance of converted CMS membranes. To address this issue, we introduce molecular fillers of porous organic cages (POCs) into precursor membranes, the organic composition and discrete molecular characteristics of which can enhance the compatibility with the polymer matrix (PIM-1), bringing enhanced porosity and narrowed pore size distribution, especially in the ultra-micropore region, to the CMS membranes. The obtained CMS membrane shows simultaneously improved gas permeability and selectivity wherein the optimized CMS membrane pyrolyzed at 600 °C with 10 wt% POCs loading (CMS-10%-600) exhibits a CO2 permeability of 2002 Barrer and a CO2/CH4 selectivity of 221.6, surpassing the 2019 CO2/CH4 upper bound and superior to most of reported CMS membranes. Due to the incorporation of POC, the CMS-10%-600 membrane demonstrates a 147.5 % increase in CO2 permeability and a 297.1 % increase in CO2/CH4 selectivity compared to pristine PIM-1-based CMS membrane, along with the excellent aging resistance for over 30 days. This study provides new insights into the design of high-performance CMS membranes for gas separation.

De‐carboxylation of cross‐linkable triptycene‐based polyimides for CO2 separation

AbstractPolymer‐based membrane technology holds immense promise for CO2 separation. However, it faces persistent challenges, including the high CO2 pressure‐induced plasticization and permeability‐selectivity trade‐offs, which significantly hinder the development of polymeric membranes. To tackle this issue, we synthesized a novel polyimide 6FDA‐DAT:DABA(6FDD) containing triptycene and carboxylic groups. Upon de‐carboxylation induced cross‐linking, the membrane demonstrated a simultaneous enhancement of gas permeability and selectivity. Specifically, compared to the uncross‐linked 6FDD, the 400°C‐24 h cross‐linked membrane exhibited a remarkable increase in CO2 permeability by 177% (93.1 Barrer) and a significant rise in CO2/CH4 selectivity by 47% (57.5), reaching the CO2/CH4 upper bound. More importantly, the cross‐linked membrane displayed vastly improved CO2 plasticization resistance, withstanding up to 42 bar of CO2 feed pressure. The design of decarboxylated cross‐linked membranes in this work paves the way for creating high‐performing and plasticization‐resistant membranes with potential applications in high‐pressure CO2 separations.

Comparison of the effect of topology type and linker composition of zeolitic imidazolate framework fillers on the performance of mixed matrix membranes in CO2/N2 separation

Mixed matrix membranes (MMMs) combine the high separation performance of porous materials with the processibility of polymers and so possess potential for carbon capture from CO2-containing gas streams. Zeolitic imidazolate frameworks (ZIFs) are promising candidates as molecular-sieve fillers in MMMs due to their tunability and ease of synthesis. We have compared four ZIFs, all as nanoparticles of similar sizes (ca. 400 nm), as MMM fillers, to investigate the effects of ZIF structure and chemistry on MMM performance of pure gas (CO2, N2) permeation under the same conditions. The chosen ZIFs include two that exhibit strong CO2 adsorption (hybrid ZIF-7/COK-17 and ZIF-94) and two that have higher pore volumes but weaker CO2 interactions (ZIF-8 and a hybrid ZIF-11/ZIF-71). The hybrid ZIF-7/COK-17 and ZIF-94 are structurally related to ZIF-7 (rhombohedral sod topology) and ZIF-8 (cubic sod), respectively, via partial or complete substitution of benzimidazole or 2-methylimidazole by 4,5-dichloroimidazole or 4-methyl-5-imidazolecarboxaldehyde, while the hybrid ZIF-11/ZIF-71 has the rho topology but the same composition as the ZIF-7/COK-17 hybrid. In the first part of the comparative study, MMMs based on two types of commercial polymers, Matrimid®5218 and PEBAX-MH1657, were prepared containing the ZIF-7/COK-17 hybrid and also with ZIF-94. ZIF-94 shows much better compatibility with the polymers, forming homogeneous dispersions at all loadings attempted (≤35 % wt%) whereas the hybrid shows inhomogeneity above 12 wt% in each case. At 12 wt% loading, both fillers show an increase in CO2 permeability at 1.2 bar and 293 K compared to the pure membrane (in PEBAX, this increases from 49.5 to 60 and 68 Barrer) which is the result of increased solubility compensating for decreased diffusivity, and this improvement in permeability continues to increase at the higher levels of loading possible with ZIF-94. ZIF-7/COK-17 in PEBAX show higher selectivity, achieving a calculated CO2/N2 selectivity up to 70. Further investigation of CO2 and N2 permeation on MMMs with the four ZIFs at 12 wt% in PEBAX-MH1657 showed a clear distinction between the ZIF-94 and ZIF-7/COK-17 MMMs (which show higher membrane solubilities but lower diffusivities) compared to ZIF-8 and ZIF-11/ZIF-71 MMMs. At the loading chosen, the CO2 permeability increase achieved by the four ZIFs over PEBAX-MH1657 increases in the order ZIF-11/-71, ZIF-7-COK-17 (ca. 60 Barrer) < ZIF-94 (68) < ZIF-8 (81), reflecting the complex interplay between CO2 solubility (increasing with interaction strength) and diffusivity (increasing with available cage and window size). The calculated CO2/N2 selectivity is highest for the hybrid ZIF-7/COK-17 membrane (70), which is attributed to molecular sieving effects in the rhombohedral sod structure.

Controlling Microstructure-Transport Interplay in Poly(ether-block-amide) Multiblock Copolymer Gas Separation Membranes.

In this study, we investigated the effect of morphology on the gas-transport properties of a poly(ether-block-amide) (PEBA) multiblock copolymer. We annealed the copolymer samples and varied the annealing temperature to evaluate the influence of changes in the microstructure on the gas transport properties of PEBA. In addition, we used time-resolved attenuated total reflection Fourier transform infrared spectroscopy to evaluate the diffusion coefficient of CO2 in PEBA based on the Fickian model. The effect of the annealing temperature on the microphase-separated structure of the multiblock copolymer is discussed in detail. Furthermore, the gas diffusivity was significantly affected by the purity of the soft domains. The annealed sample demonstrated a 38% increase in CO2 permeability while maintaining a high CO2/N2 permselectivity of approximately 53. The findings of this study provide valuable insight into the design and optimization of PEBA membranes for gas separation applications.

The Functionalization of PES/SAPO-34 Mixed Matrix Membrane with [emim][Tf2N] Ionic Liquid to Improve CO2/N2 Separation Properties

The use of ionic liquid [emim][Tf2N] as an additive in polyethersulphone (PES) and nano-sized silico-aluminophosphate-34 (SAPO-34) mixed matrix membrane was studied through the incorporation of different amounts of [emim][Tf2N] in the membrane composition, as presented in this work, varying from 10 to 40 wt%. Through gas permeation tests using CO2 and N2, the membrane composition containing 20 wt% [emim][Tf2N] led to the highest increase in CO2 permeability and CO2/N2 selectivity. The use of low concentrations of additive (10–20 wt%) promoted a state called antiplasticization; in this state, the permeability was even more regulated by the kinetic diameter of the species which, in this work, permitted achieving a higher CO2/N2 selectivity while increasing the CO2 permeability until an optimal condition. [emim][Tf2N] also promoted a better dispersion of SAPO-34 particles and an increase in the flexibility of the polymeric matrix when compared to a film with the same composition without [emim][Tf2N]. Moreover, the characterizations corroborated that the inclusion of [emim][Tf2N] increased the zeolite dispersion and improved the polymer/zeolite compatibility and membrane flexibility, characterized by a decrease in glass transition temperature, which helped in the fabrication process while presenting a similar thermal resistance and hydrophilicity as neat PES membrane, without affecting the membrane structure, as indicated by FTIR and a contact angle analysis.

Pebax/poly(vinyl alcohol) mixed matrix membrane incorporated by amine‐functionalized graphene oxide for CO2 separation

AbstractGraphene oxide nanoparticles (GO) were firstly functionalized using p‐phenylenediamine and then utilized as nanofillers to prepare poly(ether‐block‐amide) (Pebax®‐1657)/poly(vinyl alcohol) (PVA‐60000)‐based mixed‐matrix membranes. The modified GO as well as the fabricated mixed matrix membranes underwent some characterization analyses, including FTIR, TGA, XRD, FESEM, and EDX. The influence of amine‐modified nanoparticles content (2, 4, and 6 wt%), and feed pressure on CO2, CH4, and N2 permeabilitis and ideal CO2/CH4 and CO2/N2 selectivities values of the MMMs were investigated. The permeation experiments demonstrated that Pebax/PVA (10 and 15 wt%) blend membranes caused an increase in CO2 permeability owing to the high affinity of polar CO2 molecules to polar PVA segments. Moreover, the incorporation of 6 wt% amine‐functionalized GO into the Pebax/PVA (10 wt%) and Pebax/PVA (15 wt%) blend polymer raised the CO2 permeability and CO2/CH4 and CO2/N2 selectivity by nearly 43%, 28%, and 37%, respectively, due to the higher CO2 adsorption capacity of the amine‐functionalized GO.

Mixed matrix membrane based on PEBAX® filled with layered double hydroxides

The effect of incorporating layered double hydroxide (LDH) nanoparticles containing different molar ratios of metals on the thermal, mechanical, and gas permeation properties of membranes based on PEBAX® was evaluated. The three nanoparticles were synthesized using molar x-ratios (x = Al/(Mg + Al)) equal to 0.20, 0.25 and 0.33. The dispersed nanoparticles changed thermal resistance, improved mechanical properties and CO2/CH4 separation performance of MMM when compared to the membranes of neat PEBAX®. The addition of 2 % of LDH in PEBAX® 1657 promoted an increase of about 17 % in the elastic modulus and 10 % in the stress at break. The best result of permeation tests (1657–0.33–5 % MMM at 0.5 bar), shows increase CO2 permeability by 44 % and CO2/CH4 selectivity by 115 % as compared to the neat material. Gas permeation results showed that LDH with more anions favors the facilitated transport of CO2.

Constructing double-faced CO2-capture domains by sandwich-like fillers in membranes for efficient CO2 separation

The sandwich-like composites were used as fillers, and prepared MMMs for effective CO2 separation by incorporating them into Pebax matrix. Zeolite imidazolate framework-8 (ZIF-8) was grown on two faces of a 2D amino-functionalized Al-metal organic framework (NH2-MIL-53(Al)) to fabricate the sandwich-like ZIF-8/NH2-MIL-53(Al) (ZM). Wherein, ZIF-8 in ZM was long-range ordered because ZIF-8 was evenly distributed throughout the double faces of NH2-MIL-53(Al). And the long-range ordered ZIF-8 constructed double-faced CO2-capture domains to quickly enrich CO2, contributing to improving CO2/CH4 selectivity of MMMs. The introduced NH2-MIL-53(Al) can endow MMMs with the increased CO2 permeability of MMMs. Therefore, the excellent CO2 separation performance was shown by using Pebax/ZM MMMs. The best CO2 separation performance was exhibited in Pebax/ZM MMM with the loading of 6 wt% ZIF-8/NH2-MIL-53(Al), which had a CO2 permeability of 488 ± 9 Barrer and a CO2/CH4 selectivity of 37.5 ± 0.6. It suggests that an efficient method for CO2 separation is the introduction of fillers that resemble sandwiches.

ZIF-8-based dual layer hollow fiber mixed matrix membrane for natural gas purification

To prevent pipe damage and lower operating costs, natural gas must be cleaned of pollutants like carbon dioxide (CO2) and hydrogen sulphide (H2S). High selectivity of the functional material in the mixed matrix membranes (MMMs) allows for a more efficient gas separation compared to traditional polymeric membranes. However, poor dispersion and compatibility between the functional material and the polymer matrix become one of the major problems of MMMs. The use of zeolite imidazole (ZIF-8) in MMMs has been explored for its ability to separate CO2/CH4 due to its versatile gas molecule diameter range and effective CO2 adsorption. In this study, the effects of ZIF-8 at various loadings were examined on the physical and chemical properties of dual layer hollow fiber MMMs and gas separation efficiency. Following the successful production of 86.25 nm ZIF-8 nanoparticles, ZIF-8-based DLHF MMMs were created. The results showed that 0.5 wt% ZIF-8 loading provided the best results, with excellent interaction between the polymer PSf and the inorganic filler ZIF-8, strong heat resistance, and chemical stability. Increased CO2 permeability and CO2/CH4 ideal selectivity by 72.5 % and 1196.2 % respectively, compared to the unmodified membrane. It was inferred through this study that minimal loading of 0.5 wt% ZIF-8 in the DLHF MMMs improved their ability to separate gases, making them a good option for capturing CO2.

Tailoring the CO2 permeation of Pebax1657/polyether imide thin film composite membrane via embedding Ag-based metal-organic framework

Thin-film composite/nanocomposite (TFC/TFN) membranes count as the latest version of carbon capture membranes characterized by their excellent gas permeance, great selectivity, cost-effectiveness, and the ability to separately manage and tune the constituents of the individual layer. In this regard, Pebax®1657 embedded with synthesized Ag-BTC metal-organic frameworks (MOFs) was coated on the polyether imide (PEI) support layer to produce TFNs. To assess the impacts of Ag-BTC particles (carboxyl-rich surface particles) on the features of the constructed TFC/TFN membranes and their gas permeation qualities, several CO2/N2 and CO2/CH4 separation experiments (mixed and pure gas testing) were carried out. Ag-BTC particles were distributed appropriately within the Pebax1657 matrix, improving the gas permeability (particularly for CO2) and enhancing CO2/N2 and CO2/CH4 separation factors. A simultaneous increase in CO2 permeability and gas pair selectivities was observed with rising feed pressure. A 394.97 Barrer CO2 permeability and 38.20 CO2/N2 and 21.25 CO2/CH4 selectivities were obtained for the TFN filled with 3 wt% Ag-BTC at 10 bar and 30 °C. A mixed gas test also showed a similar trend but lower values than a pure one. The results for the humidified conditions exhibited higher CO2 permselectivities in comparison with the dry gas given the water molecules facilitate the CO2 transportation through the Pebax®1657 matrix. Finally, enhancing Ag-BTC filler content and increasing the input pressure provided excellent conditions for approaching Robeson’s limit.

Utilization of plastic bottle waste of polyethylene terephthalate as a low-cost membrane and its modifications for gas separation

Polyethylene terephthalate (PET) is a widely used polymer in packaging products, leading to the daily disposal of millions of PET bottles as waste. 1.1 to 8.8 million tonnes of plastic waste enter the sea each year. The environmental challenge of non-biodegradable PET waste can be addressed by utilizing it as a thin-layer membrane for gas separation. This study modified the PET membrane by blending it with Pebax polymer and adding zeolite as a filler to enhance its performance. Characterization techniques, including FTIR, SEM, TGA, tensile strength testing, and contact angle measurements, were performed on all modified membranes. The membranes were prepared using phase inversion via immersion precipitation. The results showed that the PET waste membrane had a denser surface pore morphology and asymmetrical cross-sectional pores than other membranes. Adding Pebax and zeolite resulted in a more regular sponge-like pore structure. The PET, PET-Pebax, and PET-Zeolite NaY-Pebax membranes exhibited hydrophilic properties, as indicated by contact angle values ranging from 48-78°. Regarding CO2/CH4 separation, the 9% PET-Pebax membrane had the highest CO2 permeability, a 21% increase from the original PET waste membrane. Adding zeolite to the 9% PET-Pebax membrane increased CO2 permeability to 1044%.

Carbon nanotubes grown on ZIF-L(Zn@Co) surface improved CO2 permeability of mixed matrix membranes

Increasing CO2 permeability via tailoring CO2 diffusivity and selective absorption represents a critical endeavor toward achieving efficient CO2 separation. Herein, hierarchical structures composed of carbon nanotubes in-situ grown on carbonized ZIF-L (Zn@Co) (C-ZIF) were developed as nanofillers in a Pebax polymer to fabricate mixed matrix membranes (MMMs) with high CO2 permeability. The high volatility of zinc ions facilitated formation of a porous matrix in ZIF-L (Zn@Co) carbonization, while cobalt ions catalyzed in-situ growth of carbon nanotubes on C-ZIF surfaces due to their high carbon solubility at elevated temperatures (≥600 °C). This hierarchically structured C-ZIF with nanotubes increased perturbation of molecular chains of polymer membrane and thus improved its gas diffusivity toward CO2, evidenced by the decreased glassy transition temperature and crystallinity of MMMs with 10% C-ZIF-700 loadings. Meanwhile, C-ZIF facilitated transformation of saturated Me–N4 to unsaturated Me–N2 and imidazole-N to pyridine-N, thus providing abundant active sites for CO2 adsorption. Taken together, a largely increased CO2 permeability (161.3 Barrer) of MMMs with 10 wt% C-ZIF-700 was observed with a CO2/N2 selectivity of 51.4, representing a 62.1% increase compared to that of pure Pebax membrane (99.5 Barrer). This study demonstrates that carbonized-ZIF with hierarchical nanostructures may offer a great potential in constructing high-performance MMMs for various gas separations.

Cellulose Triacetate-Based Mixed-Matrix Membranes with MXene 2D Filler-CO2/CH4 Separation Performance and Comparison with TiO2-Based 1D and 0D Fillers.

Mixed-matrix membranes (MMMs) possess the unique properties and inherent characteristics of their component polymer and inorganic fillers, or other possible types of additives. However, the successful fabrication of compact and defect-free MMMs with a homogeneous filler distribution poses a major challenge, due to poor filler/polymer compatibility. In this study, we use two-dimensional multi-layered Ti3C2Tx MXene nanofillers to improve the compatibility and CO2/CH4 separation performance of cellulose triacetate (CTA)-based MMMs. CTA-based MMMs with TiO2-based 1D (nanotubes) and 0D (nanofillers) additives were also fabricated and tested for comparison. The high thermal stability, compact homogeneous structure, and stable long-term CO2/CH4 separation performance of the CTA-2D samples suggest the potential application of the membrane in bio/natural gas separation. The best results were obtained for the CTA-2D sample with a loading of 3 wt.%, which exhibited a 5-fold increase in CO2 permeability and 2-fold increase in CO2/CH4 selectivity, compared with the pristine CTA membrane, approaching the state-of-the-art Robeson 2008 upper bound. The dimensional (shape) effect on separation performance was determined as 2D > 1D > 0D. The use of lamellar stacked MXene with abundant surface-terminating groups not only prevents the aggregation of particles but also enhances the CO2 adsorption properties and provides additional transport channels, resulting in improved CO2 permeability and CO2/CH4 selectivity.

Plasticization of a novel polysulfone based mixed matrix membrane with high-performance CO[formula omitted] separation studied by positron annihilation

Plasticization is one of the challenges encountered by polymer membranes in the application of gas separation. In this paper, a novel Schiff base network/polysulfone mixed matrix membrane (SNW-3/PSF MMM) was synthesized. The CO2 adsorption, permeation and plasticization behaviors of the membrane were investigated. The SNW-3/PSF MMM shows an obviously enhanced carbon capture capacity, and a more than 400% increase in CO2 permeability, compared with the pristine PSF. The CO2 plasticization pressure of SNW-3/PSF MMM also increases from 23.8 atm to 31.8 atm. Innovatively, the variation of free volume of the membranes after plasticization was investigated by positron annihilation spectroscopy. The results show that both free volume size and fractional free volume (FFV) increase after plasticization of MMM and pristine PSF, with a larger increase in pristine PSF. During the subsequent relaxation after removing CO2 exposure, the free volume size and FFV both show rapid decrease with time. For SNW-3/PSF MMM, the FFV recovers more nearly to the value before plasticization, than pristine PSF. Our results show that positron is a superb probe for the precise information about the microstructural changes in plasticization of gas separation polymer membranes.

Nanocellulose Crystal-Enhanced Hybrid Membrane for CO2 Capture

Developing a membrane material with both high CO2 permeability and high CO2/N2 selectivity is always desired for CO2 capture, while improving the sustainability of the membrane preparation process is of equal importance. In the current work, a nanocellulose crystal (CNC) was blended with hydrophilic Pebax 1657 for CO2 separation application. The CO2/N2 separation performance of Pebax 1657/CNC hybrid membranes with up to 40 wt % CNC was evaluated by mixed-gas permeation tests under both dry and humid conditions. The humid test condition simultaneously increases CO2 permeability and CO2/N2 selectivity of all CNC/Pebax hybrid membranes compared to those under dry conditions. Introduction of only 5 wt % CNC into Pebax 1657 realizes 42 and 18% increments in CO2 permeability (305.7 Barrer) and CO2/N2 selectivity (41.6), respectively. However, further increasing the CNC loading increases the tortuosity of the membrane and results in the self-assembly of CNC in the Pebax matrix, which is observed by SEM, thus leading to both reduced gas permeability and CO2/N2 selectivity. The CO2/N2 separation results of 5 wt % CNC/Pebax locate close to Upper Bound 2008, showing its potential as a CO2/N2 separation membrane material.

CO2-Selective mixed matrix membranes of bimetallic Zn/Co-ZIF vs. ZIF-8 and ZIF-67

Bimetallic metal–organic frameworks (MOF) have received growing attention in several fields for gas separation/adsorption, energy storage and catalysis because of their synergic effect and enhanced properties compared to their parent structures. Here, we first report on a facile and low cost direct synthesis of solid solution of bimetallic Zn/Co-ZIF and its monometallic counterparts, ZIF-8 and ZIF-67 at room temperature. Zn/Co-ZIF showed higher pore volume and BET surface area than their parents, homogeneous distribution of metals within the framework and a slightly higher Zn-rich external surface. Next, mixed matrix membranes (MMM) of Zn/Co-ZIF, ZIF-8 and ZIF-67 based 6FDA-ODA polyimide were fabricated with different content (3–10 %wt) via a wet approach using undried MOF for CO2/CH4 single and mixed gas (10:90 vol%) separation application to determine the effect of the metal center on the gas transport properties. While Zn/Co-ZIF (10 wt%)/6FDA-ODA had the highest CO2/CH4 selectivity (39.8) and CO2 permeability (45.8 Barrer) compared to the MMM of ZIF-8 (PCO2 = 41.6 Barrer, SCO2/CH4 = 36.1) and ZIF-67 (PCO2 = 26.2 Barrer, SCO2/CH4 = 26.3) at the same concentration, the best performance was observed for Zn/Co (7.5 wt%)/6FDA-ODA MMM with 104% and 41% increase in CO2 permeability up to 44.2 Barrer and CO2/CH4 ideal selectivity to 45.1, compared to the neat polymer, respectively.

MOF/Polymer Mixed-Matrix Membranes Preparation: Effect of Main Synthesis Parameters on CO2/CH4 Separation Performance.

Design and preparation of mixed-matrix membranes (MMMs) with minimum defects and high performance for desired gas separations is still challenging as it depends on a variety of MMM synthesis parameters. In this study, 6FDA-DAM:DABA based MMMs using MOF-808 as filler were prepared to examine the impact of multiple variables on the preparation process of MMMs, including variation in polymer concentration, filler loading, volume of solution cast per membrane area, solvent type used and solvent evaporation rate, and to identify their impact on the CO2/CH4 separation performance of these membranes. Solvent evaporation rate proved to be the most critical synthesis parameter, directly influencing the performance and visual appearance of the membranes. Although less dominantly influencing the MMM performance, polymer concentration and solution volume also had an important role via control over the casting solution viscosity, particle agglomeration, and particle settling rate. Among all solvents studied, MMMs prepared with chloroform led to the best performance for this polymer-filler system. Chloroform-based MMMs containing 10 and 30 wt.% MOF-808 showed 73% and 62% increase in CO2 permeability, respectively, without a decrease in separation factor compared to unfilled membranes. The results indicate that enhanced gas separation performance of MMMs strongly depends on the cumulative effect of various synthesis parameters rather than individual impact, thus requiring a system-specific design and optimization.

Synthesis and Characterization of a Crystalline Imine-Based Covalent Organic Framework with Triazine Node and Biphenyl Linker and Its Fluorinated Derivate for CO2/CH4 Separation.

A catalyst-free Schiff base reaction was applied to synthesize two imine-linked covalent organic frameworks (COFs). The condensation reaction of 1,3,5-tris-(4-aminophenyl)triazine (TAPT) with 4,4′-biphenyldicarboxaldehyde led to the structure of HHU-COF-1 (HHU = Heinrich-Heine University). The fluorinated analog HHU-COF-2 was obtained with 2,2′,3,3′,5,5′,6,6′-octafluoro-4,4′-biphenyldicarboxaldehyde. Solid-state NMR, infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental analysis confirmed the successful formation of the two network structures. The crystalline materials are characterized by high Brunauer–Emmett–Teller surface areas of 2352 m2/g for HHU-COF-1 and 1356 m2/g for HHU-COF-2. The products of a larger-scale synthesis were applied to prepare mixed-matrix membranes (MMMs) with the polymer Matrimid. CO2/CH4 permeation tests revealed a moderate increase in CO2 permeability at constant selectivity for HHU-COF-1 as a dispersed phase, whereas application of the fluorinated COF led to a CO2/CH4 selectivity increase from 42 for the pure Matrimid membrane to 51 for 8 wt% of HHU-COF-2 and a permeability increase from 6.8 to 13.0 Barrer for the 24 wt% MMM.

Enhanced CO2-capture performance of polyimide-based mixed matrix membranes by incorporating ZnO@MOF nanocomposites

Mixed matrix membranes (MMMs) have received numerous interests as promising membrane configurations for dealing with the energy-intensive gas separation processes. In this study, MMMs were fabricated by incorporating novel ZnO@MOF nanocomposites (ZnO@ZnBDC) into Matrimid (PI) matrix. The physico-chemical properties and microstructures of ZnO@ZnBDC nanocomposites and ZnO@ZnBDC/PI MMMs were characterized. The CO2/CH4 separation performance of MMMs was evaluated and analyzed according to the solution-diffusion mechanism. ZnBDC in the nanocomposites increased CO2 permeability by providing mass transfer pathways with low resistance in the MMMs, while ZnO increased the CO2/CH4 selectivity via high CO2 affinity. Owing to the synergistic effect of the nanocomposites, MMMs with 0.75 wt% ZnO@ZnBDC showed CO2 permeability of 11.5 Barrer and CO2/CH4 selectivity of 39.5, which increased by 67% and 33%, respectively, by comparing with control PI membrane.