Enhanced Gas Separation Performance Research Articles

Fluorine Incorporation for Enhanced Gas Separation Performance in Porous Organic Polymers: Investigating Reaction Pathways and Pore Structure Control.

The precise control of pore structures in porous organic polymer (POP) materials is of paramount importance in addressing a wide range of challenges associated with gas separation processes. In this study, we present a novel approach to optimize the gas separation performance of POPs through the introduction of fluorine groups and figure out an important factor of reaction decision that whether the AlCl3-catalyzed polymerization is Scholl reaction or Friedel-Crafts alkylation. In the chloroform system, the steric hindrance of function groups could make direct coupling between the benzene rings difficult, which would lead to part solvent knitting (Friedel-Crafts alkylation) instead. The fluorinated polymers show enhanced surface area and pore size characteristics. Notably, the fluorinated polymers exhibited significantly improved adsorption and separation performance for SF6, as evidenced by an ideal adsorbed solution theory selectivity (SF6/N2, v: v = 50:50, 273 K) increase of 75.0, 668.8, and 502.8% compared to the nonfluorinated POPs. These findings highlight the potential of fluorination as a strategy for tailoring the properties of POP materials for advanced gas separation applications.

Enhanced gas separation performance for H2 purification using MIL-68(ln)-nh2/PES mixed-matrix membranes

The growing demand for sustainable and efficient gas separation technologies has prompted the exploration of advanced materials to enhance the gas permeability and selectivity. Polyethersulfone (PES) membranes are widely used in gas separation, gas upgrading, and clean energy production owing to their environmental friendliness and low cost. However, their gas permeability and selectivity can be further improved for commercial application. This study explored the incorporation of 10 wt % of MIL-68(ln)-NH2 into PES membranes using a phase-inversion approach to enhance gas permeability and selectivity. The morphological, structural, and thermal properties of the resulting MOF/PES membrane were characterized using SEM, AFM, BET, XRD, FTIR, and TGA-DTG. Gas permeation experiments were conducted using different gases (CO2, N2, CH4, and H2) under different heating conditions (20–60 °C) to evaluate the gas permeability and selectivity of the MOF/PES membrane. The results showed that the incorporation of MOF into the mixed matrix membrane (MMMs) led to a 9% increase in porosity, 87% reduction in roughness, and 32% decrease in pore size compared to neat PES membranes. Significant changes in the morphology, crystallinity, and thermal stability were observed, with notable improvements of up to 22%. Moreover, the MOF/PES membrane exhibited high gas permeability (CO2 = 124656, N2 = 83650, CH4 = 159298, and H2 = 427075 Barrer) and selectivity (H2/N2 = 5.7, H2/CO2 = 4, CH4/N2 = 2, and CH4/CO2 = 1.7) for flammable gases. The optimal gas separation performance was observed at 20 °C and 60 °C for H2/N2 and H2/CO2 separation, respectively. These findings demonstrate the potential of MOF-based PES membranes for gas separation applications, particularly in H2 purification.

Effect of ZIF-78 metal-organic framework crystal morphology and defect in resulting polysulfone mixed matrix membranes

BackgroundMixed matrix membranes (MMMs) provide a new possibility for membranes to exceed the tradeoff between permeability and selectivity found in pure polymeric membranes. Factors that enhance gas separation performance in MMMs include filler morphology and aspect ratio. MethodsHigh aspect ratio microporous ZIF-78, a metal-organic framework (MOF) demonstrated in literature to have one of the highest carbon dioxide uptake capacities, was successfully synthesized using a solvothermal method. These particles were incorporated into MMMs in non-defective and systematically defective forms by using two common solvents – chloroform and DMF. Detailed characterization of the various membranes was performed using BET, XRD, SEM, EDS, DSC, TGA, FTIR, and a custom-built gas permeability measurement apparatus. Significant findingsIntroduction of crystals with no apparent defect results in a more tortuous pathway for permeating gas molecules, demonstrated by nitrogen permeation results. Conversely, for carbon dioxide, strong dipole-quadrupole interaction with ZIF-78 creates excellent permeation pathways through the crystal themselves. The defective system possesses more inter-filler free volume which allow all gas components to permeate more easily, in addition to the original mechanism. The gas separation performance of the resulting MMMs in this work displayed a 140 % improvement of CO2 permeability and 129 % improvement of CO2/N2 ideal selectivity over pure polysulfone membranes. This work shows the potential of using deliberately designed fillers to increase performance via special pathways for gas molecules.

Thermally rearranged OH-containing polyimide composite membranes with enhanced gas separation performance and physical aging resistance

Gas separation membranes play a pivotal role in various industrial processes, demanding continuous improvement in their efficiency and durability. This study focuses on thin-film composite (TFC) membranes based on polyimide, utilizing a hydroxyl-containing polyimide selective layer for its processability and selectivity. A complete and smooth surface for the selective layer in the composite membranes was achieved by exclusively selecting a 10% concentration of the polyimide spin-coating solution. Subsequent thermal rearrangement at 430°C induced the formation of a rigid polybenzoxazole structure, enhancing gas permeance. Optimal separation performance was achieved through a two-hour rearrangement, resulting in a more than 30-fold increase in gas permeance while preserving selectivity. The study also delved into anti-physical aging performance. The thermally treated PI-10 wt%−2 h membrane exhibited a 10% reduction in CO2 and O2 permeance over 90 days, with O2/N2 and CO2/N2 selectivities nearly maintaining their initial levels. This research provides valuable insights for the development of efficient and durable gas separation membranes.

Single and mixed gas permeability studies on mixed matrix membranes composed of MIL-101(Cr) or MIL-177(Ti) and highly permeable polymers of intrinsic microporosity

The gas transport properties of mixed matrix membranes (MMMs), prepared by dispersing nanoparticles of MOFs MIL-101(Cr) or MIL-177(Ti) into highly permeable Polymers of Intrinsic Microporosity PIM-EA-TB or PIM-TMN-Trip, were investigated. The homogeneity of the dispersion was confirmed by means of Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray (EDX) mapping analysis. Single gas time-lag measurements provided the permeability and ideal selectivity of different gas pairs, both after treatment of the MMMs with methanol and after natural aging over an extended period (up to 2000 days). This data demonstrated that the gas size-sieving pores of MIL-101(Cr) and MIL-177(Ti) and their good dispersion into the PIM matrix results in MMMs with enhanced gas separation performance, as compared to films composed solely of the polymer. The comparison of actual permeability with the Maxwell model for PIM-EA-TB with both MOFs confirmed the good dispersion and the absence of anomalies, whereas the inconsistency of permeability with prediction data for PIM-TMN-Trip suggests that the MOFs improved the polymer properties, stiffening or occupying the polymer free volume. In particular, the incorporation of MIL-101(Cr) into PIM-EA-TB significantly enhances the H2 permeability from ∼6000 to 13,000 Barrer, with a concurrent increase of the H2/N2 selectivity from 14 to 21. MIL-177(Ti) also enhances the H2/N2 selectivity to 20 due to a slight reduction of the N2 permeability. The addition of MIL-101(Cr) and MIL-177(Ti) into the ultra-permeable PIM-TMN-Trip showed more modest increases in H2 permeability and H2/N2 selectivity from 4.6 to ∼ 10. Hence the data for some of the MMMs surpass the 2008, and even approach the 2015/2019 Robeson’s upper bounds, particularly for gas pairs including H2.

Utilization of polyphenylene sulfide as an organic additive to enhance gas separation performance in polysulfone membranes.

Many studies have shown that sulfur-containing compounds significantly affect the solubility of carbon dioxide (CO2) in adsorption processes. However, limited attention has been devoted to incorporating organic fillers containing sulfur atoms into gas separation membrane matrices. This study addressed the gap by developing a new membrane using a polysulfone (PSf) polymer matrix and polyphenylene sulfide (PPs) filler material. This membrane could be used to separate mixtures of H2/CH4 and CO2/CH4 gases. Our study investigated the impact of various PPs loadings (1%, 5%, and 10% w/w) relative to PSf on membrane properties and gas separation efficiency. Comprehensive characterization techniques, including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM), were employed to understand how adding PPs and coating with polydimethylsiloxane (PDMS) changed the structure of our membranes. XRD and FTIR analysis revealed distinct morphological disparities and functional groups between pure PSf and PSf/PPs composite membranes. SEM results show an even distribution of PPs on the membrane surface. The impact of adding PPs on gas separation was significant. CO2 permeability increased by 376.19%, and H2 permeability improved by 191.25%. The membrane's gas selection ability significantly improved after coating the surface with PDMS. CO2/CH4 separation increased by 255.06% and H2/CH4 separation by 179.44%. We also considered the Findex to assess the overall performance of the membrane. The 5% and 10% PPs membranes were exceptional. Adding PPs to membrane technology may greatly enhance gas separation processes.

Improving gas separation performances of poly(furfuryl alcohol)-based carbon molecular sieve membrane by tuning furan ring opening and membrane structures

Carbon molecular sieve membranes (CMSMs) have exhibited significant potential in gas separation applications, particularly in the realm of hydrogen and carbon dioxide separation. Poly(furfuryl alcohol) (PFA) represents a cost-efficient and sustainable precursor utilized in the synthesis of CMSMs. Nonetheless, PFA-based CMSMs have exhibited suboptimal performance and frequently necessitate supplementary supporting layers. In the present investigation, we have explored various acids as catalysts for the in-situ self-polymerization of PFA. Our findings reveal that PFA membrane catalyzed by sulfuric acid exhibits the most favorable performance, yielding a hydrogen permeability of 1394.4 Barrer and a H2/CH4 selectivity of 404.1. These values exceed the Robeson upper limits established in 2019. The enhanced gas separation performance of the sulfuric acid catalyzed PFA-based CMSM could be attributed to the increased furan ring opening and higher polymerization degree achieved through this catalytic process. Furthermore, our investigation delved into the addition of poly(styrene-co-acrylonitrile) (SAN) into the PFA membrane, yielding a CMSM featuring both dense and porous layers. With the addition of 6 wt% SAN in PFA membrane, the resulting CMSM exhibited a hydrogen permeability of 3126.4 Barrer, underscoring the potential for high-performance CMSMs made from the economical PFA precursor. The optimization of the PFA polymerization process and the incorporation of SAN, hold the promise of further elevating the performance of PFA-based CMSMs, and these advancements will substantially contribute to the advancement of sustainable and efficient gas separation technologies.

ZIF-8 nanoplate/6FDA-DAM membrane for hydrogen extraction from propane dehydrogenation process

High-aspect ratio materials can enhance gas separation performance compared to low-aspect ratio materials when incorporated into a polymer matrix to form mixed matrix membranes (MMMs). However, the filler shape effect on various properties of MMMs was not thoroughly discussed. Herein, we fabricated a mixed matrix membrane with two different shapes of metal-organic framework (MOF) and examined the MOF filler shape effect on mechanical, thermal, and gas separation properties. Zeolitic imidazolate framework-8 nanoplates (NZIF-8) were synthesized by conversion method with an aspect ratio of 20. Isotropic ZIF-8 particles (IZIF-8) were also synthesized, and both fillers were hybridized with a 6FDA-DAM (PI) polymer. 20 wt% NZIF-8/PI membrane exhibited high mechanical properties of 0.282 GPa for hardness and 3.5 GPa for modulus, which is higher than that of IZIF-8/PI membranes. The membrane was stable in high temperatures which is comparable to the pristine PI membrane, showing long-term thermal stability at 300 °C. Furthermore, high aspect ratio fillers allowed significant enhancement in hydrogen separation performance, showing hydrogen permeability of around 1800 Barrer with hydrogen/propane selectivity of 260 at 20 wt% ZIF-8 nanoplate loading, which is much enhanced than the membrane with isotropic ZIF-8 particles. The separation performances were consistent in ternary mixture separation under different conditions. These highly stable and selective properties can be promising for hydrogen extraction from the propane dehydrogenation process.

Perovskite Membranes: Advancements and Challenges in Gas Separation, Production, and Capture.

Perovskite membranes have gained considerable attention in gas separation and production due to their unique properties such as high selectivity and permeability towards various gases. These membranes are composed of perovskite oxides, which have a crystalline structure that can be tailored to enhance gas separation performance. In oxygen enrichment, perovskite membranes are employed to separate oxygen from air, which is then utilized in a variety of applications such as combustion and medical devices. Moreover, perovskite membranes are investigated for carbon capture applications to reduce greenhouse gas emissions. Further, perovskite membranes are employed in hydrogen production, where they aid in the separation of hydrogen from other gases such as methane and carbon dioxide. This process is essential in the production of clean hydrogen fuel for various applications such as fuel cells and transportation. This paper provides a review on the utilization and role of perovskite membranes in various gas applications, including oxygen enrichment, carbon capture, and hydrogen production.

Tetramine-Based Hyperbranched Polyimide Membranes with Rigid Crosslinker for Improved Gas Permeability and Stability.

Triamine-based HBPI membranes are known for high gas separation selectivity and physical stability, but their permeabilities are still very low. In this study, we utilized a tetramine monomer called TPDA (N,N,N',N'-tetrakis(4-aminophenyl)-1,4-benzenediamine) as a crosslinking center and incorporated an additional diamine comonomer called DAM (2,4,6-trimethyl-1,3-diaminobenzene) to enhance gas separation performance, especially gas permeability. The findings demonstrated that the resultant 6FDA-DAM/TPDA membranes based on tetramine TPDA exhibited a greater amount of free volume compared to the triamine-based HBPI membranes, resulting in significantly higher gas permeabilities. Furthermore, the higher concentration of DAM component led to the generation of more fractional free volumes (FFV). Consequently, the gas permeabilities of the 6FDA-DAM/TPDA membranes increased with an increase in DAM content, with a minimal compromise on selectivity. The enhanced gas permeabilities of the 6FDA-DAM/TPDA membranes enabled them to minimize the footprint required for membrane installations in real-world applications. Moreover, the 6FDA-DAM/TPDA membranes exhibited remarkable durability against physical aging and plasticization, thanks to the incorporation of a hyperbranched network structure.

Preparation and characterization of asymmetric Kapton membranes for gas separation

It is a challenge to simultaneously achieve a high selectivity and permeance for the glassy polymeric membranes. Herein, the asymmetric Kapton membrane fabricated by pyromellitic dianhydride and 4,4′-oxydiphenylenediamine was prepared by the phase inversion method and characterized by rheometer, SEM, TGA, FT-IR and tensile testing. The aim of this work is to enhance gas separation performance of the membrane and its application value via optimizing the concentration of acetone additive, coagulation bath composition and evaporation time. After optimizing, results showed that the transition from the instantaneous coagulation to the delayed coagulation, and the inner membrane structure is gradually transferred from the finger-like shape to the sponge-like shape. The optimized gas separation performance of the resulting Kapton membrane has the permeance of 2.49 GPU and 1.10 GPU for H2 and CO2, respectively, as well as selectivity of 57.07 and 25.27 for H2/CH4 and CO2/CH4, respectively.

C-axis oriented ZIF-95 sheets intermixed with polyimide matrix with enhanced gas separation performance

The fabrication of mixed matrix membranes (MMMs) by intermixing suitable fillers with organic polymers is an effective strategy to surmount the well-known trade-off effect between gas permeability and selectivity, which can promote separation performance of membranes to a great extent. Two-dimensional (2D) metal-organic frameworks (MOFs) are considered as potential fillers for strengthening the separation performance of MMMs as they possess high aspect ratio and distinctive chemical characteristics. However, it remains challenging in engineering the morphology of the MOFs with desired pore structure and high aspect ratio. In this study, we firstly prepare c-axis oriented ZIF-95 sheets with lateral dimension exceeding 22 μm and thickness of around 3 μm by the solvothermal method. And then the ZIF-95 sheets are incorporated into the polyimide (PI) matrix to fabricate highly c-axis oriented ZIF-95@PI MMMs (denoted as COZIF-95@PI MMMs thereafter). Attributing to the straight permeation channel of ZIF-95 (3.6 Å) for gas permeation as well as its high compatibility with polyimide substrates, the COZIF-95@PI MMMs show a high gas separation capability. At 373 K and 100 kPa for the COZIF-95@PI MMM with 40 wt% loading, the mixture separation factors of H2/CH4 and H2/CO2 are 134 and 58, respectively, and the H2 permeability exceeds 967 barrer, which is hopeful for the separation and purification of hydrogen.

Constructing Gas Transmission Pathways in Two-Dimensional Composite Material ZIF-8@BNNS Mixed-Matrix Membranes to Enhance CO2/N2 Separation Performance

Two-dimensional (2D) nanomaterials, due to their high aspect ratio and high specific surface area, which provide a more tortuous pathway for larger gas molecules, are frequently used in membrane separation. However, in mixed-matrix membranes (MMMs), the high aspect ratio and high specific surface area of 2D fillers can increase transport resistance, thereby reducing the permeability of gas molecules. In this work, we combine boron nitride nanosheets (BNNS) with ZIF-8 nanoparticles to develop a novel material, ZIF-8@BNNS, to improve both CO2 permeability and CO2/N2 selectivity. Growth of ZIF-8 nanoparticles on the BNNS surface is achieved using an in-situ growth method where the amino groups of BNNS are complexed with Zn2+, creating gas transmission pathways that accelerate CO2 transmission. The 2D-BNNS material acts as a barrier in MMMs to improve CO2/N2 selectivity. The MMMs with a 20 wt.% ZIF-8@BNNS loading achieved a CO2 permeability of 106.5 Barrer and CO2/N2 selectivity of 83.2, surpassing the Robeson upper bound (2008) and demonstrating that MOF layers can efficiently reduce mass transfer resistance and enhance gas separation performance.

Computational Investigation of Dual Filler-Incorporated Polymer Membranes for Efficient CO2 and H2 Separation: MOF/COF/Polymer Mixed Matrix Membranes.

Mixed matrix membranes (MMMs) composed of two different fillers such as metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) embedded into polymers provide enhanced gas separation performance. Since it is not possible to experimentally consider all possible combinations of MOFs, COFs, and polymers, developing computational methods is urgent to identify the best performing MOF-COF pairs to be used as dual fillers in polymer membranes for target gas separations. With this motivation, we combined molecular simulations of gas adsorption and diffusion in MOFs and COFs with theoretical permeation models to calculate H2, N2, CH4, and CO2 permeabilities of almost a million types of MOF/COF/polymer MMMs. We focused on COF/polymer MMMs located below the upper bound due to their low gas selectivity for five industrially important gas separations, CO2/N2, CO2/CH4, H2/N2, H2/CH4, and H2/CO2. We further investigated whether these MMMs could exceed the upper bound when a second type of filler, a MOF, was introduced into the polymer. Many MOF/COF/polymer MMMs were found to exceed the upper bounds showing the promise of using two different fillers in polymers. Results showed that for polymers having a relatively high gas permeability (≥104 barrer) but low selectivity (≤2.5) such as PTMSP, addition of the MOF as the second filler can have a dramatic effect on the final gas permeability and selectivity of the MMM. Property-performance relations were analyzed to understand how the structural and chemical properties of the fillers affect the permeability of the resulting MMMs, and MOFs having Zn, Cu, and Cd metals were found to lead to the highest increase in gas permeability of MMMs. This work highlights the significant potential of using COF and MOF fillers in MMMs to achieve better gas separation performances than MMMs with one type of filler, especially for H2 purification and CO2 capture applications.

Mixed matrix membranes comprising 6FDA-based polyimide blends and UiO-66 with co-continuous structures for gas separations

Membrane gas separation is considered a highly promising alternative to conventional gas separation. Recently, mixed matrix membranes containing UiO-66 metal–organic frameworks (MOFs) have been demonstrated to achieve high gas separation performance, especially in CO2-related separation. To date, few studies have used morphological control strategies to enhance the gas transport properties of mixed matrix membranes. In this study, we fabricated mixed matrix membranes comprising porous UiO-66 nanoparticles and immiscible 6FDA-based polyimide blends with co-continuous structures. The selective location of UiO-66 nanoparticles within one polymer phase of the co-continuous polymer blend was observed. However, this co-continuous structure cannot be referred to as a double-percolative morphology since the percolative UiO-66 networks did not successfully form. The gas permeability and gas sorption properties of pure gases (H2, CO2, N2, O2, and CH4) in the dense membranes and mixed matrix membranes were measured using the constant-volume variable-pressure method and the dual-volume pressure decay method, respectively. On the basis of the solution–diffusion mechanism, the contributions of gas sorption and gas transport to the overall gas permeation properties were determined and examined. When the UiO-66 content reached 35 wt%, the CO2 permeability of the mixed matrix membranes was significantly increased from 16.5 Barrer to 104.7 Barrer (by 635 %) without scarifying the permeability selectivities of CO2/N2 (16.5 ± 1.5) and CO2/CH4 (31.7 ± 5.8). The results suggest that both the addition of porous UiO-66 nanoparticles and the co-continuous structures contributed to the strongly enhanced gas separation performance of the mixed matrix membranes.

Asymmetric membranes for gas separation: interfacial insights and manufacturing.

State-of-the-art gas separation membrane technologies combine the properties of polymers and other materials, such as metal-organic frameworks to yield mixed matrix membranes (MMM). Although, these membranes display an enhanced gas separation performance, when compared to pure polymer membranes; major challenges remain in their structure including, surface defects, uneven filler dispersion and incompatibility of constituting materials. Therefore, to avoid these structural issues posed by today's membrane manufacturing methodologies, we employed electrohydrodynamic emission and solution casting as a hybrid membrane manufacturing method, to produce ZIF-67/cellulose acetate asymmetric membranes with improved gas permeability and selectivity for CO2/N2, CO2/CH4, and O2/N2. Rigorous molecular simulations were used to reveal the key ZIF-67/cellulose acetate interfacial phenomena (e.g., higher density, chain rigidity, etc.) that must be considered when engineering optimum composite membranes. In particular, we demonstrated that the asymmetric configuration effectively leverages these interfacial features to generate membranes superior to MMM. These insights coupled with the proposed manufacturing technique can accelerate the deployment of membranes in sustainable processes such as carbon capture, hydrogen production, and natural gas upgrading.

Flexibility of Mixed Ligand Zeolitic Imidazolate Frameworks (ZIF-7-8) under CO2 Pressure: An Investigation Using Positron Annihilation Lifetime Spectroscopy.

Fine tuning of the pore architecture and flexibility of zeolitic imidazolate frameworks (ZIFs) is highly crucial for realizing their applications in molecular gas separation. Mixed ligand frameworks (ZIF-7-8) synthesized by mixing 2-methylimidazole (2meIm) and benzimidazole (bIm) ligands show enhanced gas separation performance, attributable to pore and flexibility tuning. In the present study, positron annihilation lifetime spectroscopy (PALS) measurements under CO2 pressure have been used to experimentally investigate the tuning of the pore architecture and flexibility of mixed ligand frameworks ZIF-7-8 having a ZIF-8 structure and similar morphology with varying bIm content up to 18.2%. The aperture and cavity of frameworks begin to open up with an increasing bIm ligand content followed by a decrease at a higher content. On the contrary, flexibility of the frameworks indexed from PALS measurements carried out under CO2 pressure shows a decreasing trend followed by an increase. The present study shows that mixed ligand frameworks having a larger aperture size are less flexible as a result of inherent open configurations of ligands in the framework lattice. On the other hand, frameworks having a comparatively smaller aperture size show higher flexibility as a result of a possibility of twisting of the ligands under CO2 pressure, resulting in aperture opening. The pore-opening phenomenon as a result of lattice flexibility under CO2 pressure is observed to be fully reversible for ZIF-7-8.

Polyurethane-based gas separation membranes: A review and perspectives

The membrane-based gas separation technique is considered one of the most environmentally benign approaches due to its low energy cost compared with conventional techniques. However, the permeability-selectivity trade-off has been the biggest challenge in the membrane gas separation field. A variety of membrane materials with enhanced gas separation performance, mechanical strength, thermal stability, etc., have been designed. Among them, polyurethane (PU) membranes have been drawing increasing attention. Compared with those high-performing membrane materials, PUs possess relatively lower gas separation performance. However, by careful design, the performance of PU membranes could be improved. This review article is the first report to summarize the gas separation performance of reported PU membranes. The gas separation performance of pure PUs and their mixed matrix membranes (MMMs) will be summarized. Current challenges in PU-based gas separation membranes will be discussed. Several novel design routes for PU membranes will also be proposed.

Carbon molecular sieve/ZSM-5 mixed matrix membranes with enhanced gas separation performance and the performance recovery of the aging membranes

Carbon molecular sieve (CMS)/ZSM-5 mixed matrix membranes (MMMs) were prepared by pyrolysis of PMDA-ODA polyimide/ZSM-5 precursors. The morphology and structure of the CMS/ZSM-5 MMMs were investigated by scanning electron microscope (SEM), X-ray diffractometer (XRD) and transmission electron microscope (TEM). The results indicated that ZSM-5 particles were well dispersed in the carbon matrix and maintained their microstructure during pyrolysis. The gas separation performance of the CMS/ZSM-5 MMMs was evaluated using single gases (H2, CO2, O2, N2, CH4) and mixed gases (21/79 mol.% O2/N2 and 50/50 mol.% CO2/H2). Compared with pure CMS membranes, the CMS/ZSM-5 MMMs exhibited outstanding permeability without significantly sacrificing selectivity. The gas permeabilities of the CMS/ZSM-5 MMMs increased with the increase of ZSM-5 loading and decreased with the increase of pyrolysis temperature. The aging of the CMS/ZSM-5 MMMs in a humid environment was also investigated. After simple thermal treatment, the pure gas permeabilities of the aging membrane were recovered to 39% (CH4), 66% (N2), 74% (H2), 77% (O2) and 83% (CO2) of the non-aging membrane, respectively, and the mixed gas permeabilities of the aging membrane were recovered to 63% (N2), 70% (O2), 82% (CO2) and 90% (H2) of the non-aging membrane, respectively.

Enhancing CO2 separation performance of mixed matrix membranes by incorporation of L-cysteine-functionalized MoS2

The incorporation of lamellar materials into polymer matrix can improve the gas separation performance of mixed matrix membranes (MMMs), which have great potential in chemical separation process. However, few intrinsic selectivity sites on MoS2 sheets suppress further employment in the membrane separation. In this work, the vacancies and defects-containing MoS2 sheets were prepared by high temperature oxidation and hydrothermal reaction in NaOH solution, and then L-cysteine-functionalized MoS2 (Cys-MoS2) was synthesized by a thiol-click chemistry reaction between S vacancies and thiol groups as confirmed by transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N2 absorption. After blending with polyether-block-amide (Pebax), the as-prepared MMMs showed outstanding mechanical properties as a result of the homogeneous dispersion of Cys-MoS2 and hydrogen bonding between two phases as evidenced by attenuated total reflectance-FTIR, scanning electron microscope (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The highest permeability of 297 Barrer accompanied with a CO2/N2 selectivity of 120 was obtained for MMMs loaded with 1.5 wt% Cys-MoS2, which were enhanced by 206.2 % and 124.7 % over the pristine Pebax membrane, respectively. Meanwhile, this value was superior to that of the previously reported Pebax-based MMMs, transcending 2019 upper bound. The enhanced gas separation performance is due to the improved CO2 adsorption selectivity by the vacancies and defects of Cys-MoS2, while the amine groups carrier enhanced CO2 reactivity selectivity.