Search

Biogas is a type of biomass energy source, primarily composed of methane and carbon dioxide. It is generated through the controlled anaerobic digestion of manure or other organic residues. As a cleaner alternative to conventional fuels, fully purified biogas can produce approximately 36.68 MJ/m3 of en.ergy. As the separation of CO2/CH4 in biogas became an important part of the energy industry, we used membrane separation technique to study its separation methods. At first, 3,3′‐dihydroxy‐4,4′‐diamino‐biphenyl (HAB) and 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) were polymerized by open‐loop as polyamide acid macromolecules. Then it was divided into two research routes. One was condensation to polyimide (PI) membranes directly and then thermal rearrangement (TR); the other one was ionic liquid (IL) added before condensation and thermal rearrangement. Through adjusting the thermal rearrangement temperature, different modified polyimide membranes were obtained and tested their separation performance of CO2/CH4. For the result of the test, the best one, membrane HAB‐6FDA‐IL‐TR400, could reach a good separation performance as PCO2 = 403.80 Barrer, αCO2/CH4 = 82.35. It was beyond the Robeson's 2019 upper limit and proved that the modification by IL and thermal rearrangement was benefit for the separation performance of polyimide membranes. [ABSTRACT FROM AUTHOR]

A fluorescein‐based diamine, 2‐(3,6‐bis(4‐amino‐3‐hydroxyphenoxy)‐9H‐xanthen‐9‐yl) benzoic acid (CADA), was synthesized and copolymerized with Durene and 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA) to form a 6FDA‐Durene/CADA (3:2) copolyimide. The copolyimide was thermally cross‐linked at 300–425°C to form a series of decarboxylated cross‐linked polyimides. Compared with the 6FDA‐CADA polyimide, the incorporation of Durene diamine increased gas permeability of the pristine and the thermally cross‐linked polyimides greatly. The copolyimide cross‐linked at 375°C showed separation performance to the O2/N2 gas pair beyond the 1991 Robeson upper limit, while the CO2/CH4 separation property of the copolyimide cross‐linked at 425°C (PI‐425) was close to the 2008 Robeson upper limit. Moreover, the anti‐CO2‐induced plasticization property of the 6FDA‐Durene/CADA(3:2) copolyimides was improved by cross‐linking. The copolyimides cross‐linked at 350°C and above were not plasticized at a CO2 pressure up to 30 atm. This study showed that gas transport property of the decarboxylated cross‐linked polyimides could be improved significantly by the incorporation of bulky diamino moiety. The fluorescein‐based copolyimide had great potentials for gas separation applications. [ABSTRACT FROM AUTHOR]

Porous organic cages (POCs) with abundant porosity and interconnected cavities have garnered significant research attention as a distinct class of porous materials due to their potential applications in gas sorption and separation. However, the ordered arrangement of POCs to eliminate inter‐cage defects remains challenging in the assembly of molecular‐selective membranes, which greatly hinders the effectiveness of pore sieving. Here, amine‐rich molecular nodules (AMNs) are created by reduction of the porous organic cage CC2, in which the spatial structure incurs a vertex collapse into the interior of the original tetrahedral structure, which eliminates the large window of CC2. By an interfacial reaction with terephthaloyl chloride, the AMNs assemble into a cross‐linked topological network having angstrom‐scale channels for selective CO2/N2 separation. The AMN‐assembled membrane displays a high CO2 permeance of 752 GPU, a CO2/N2 selectivity of 67 at 1 bar, as well as high‐pressure resistance, operational stability, and scalable manufacture potential, which provides a cost‐effective and practical solution for developing membranes for capturing CO2 from industrial flue gas. [ABSTRACT FROM AUTHOR]

A series of fluorinated co-polyimide films based on the 6FDA-FTPPA/BAFL backbone were prepared from 4-(3-fluoro-4- (trifluoromethyl)phenyl)-2,6-bis(4-aminophenyl)pyridine (FTPPA), commercial 9,9-bis(4-aminophenyl)fluorene (BAFL), and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), with varying ratios of FTPPA:BAFL units (3:1, 2:1, 1:1, 1: 2, and 1:3). Co-polyimides not only exhibit high thermal stability (Tg > 357°C), good optical properties (λcutoff > 327 nm) and hydrophobicity (contact angle >91.4°), but also favorable solubility properties in both high and low boiling organic solvents. The fractional free volume of the polymers was simulated using molecular mechanics and molecular dynamics and correlated with experimental gas separation data. The presence of bulky groups led to high FFVs (>17.8%) and the formation of large microcavities with diameters ranging from 5.48 to 5.72 A°, which efficiently increased gas permeability. In pure gas permeation experiments, the permeability coefficients of CO2 and He for the 6FDA-FTPPA/BAFL (3:1) film were 41.48 and 79.38 bar, respectively, which were superior to those of commercial Matrimid and Kapton in terms of gas permeability. In especial, the 6FDA-FTPPA/BAFL (1:2) and 6FDA-FTPPA/BAFL (1:3) in copolyimide membranes exhibited the most attractive separation performance for O2/N2 gas pairs, approaching the 1991 Roberson upper limit. [ABSTRACT FROM AUTHOR]

Gas separation membranes offer a cost‐effective solution for capturing greenhouse gases, mitigating the global greenhouse effect. Ionic liquids (ILs) have emerged as one of the promising materials for greenhouse gas separation due to their strong affinity for CO2. In this study, we propose a laboratory‐scale method for preparing IL–PVDF blend membranes with high CO2/N2 selectivity. The separation performance of the membranes was evaluated using a custom gas permeation measurement system. The effects of casting solution composition, solidification method, and film‐forming processes on separation performance were experimental investigated, and the obtained experimental data were used to train a back propagation neural network (BPNN) optimized by the Gray Wolf Optimizer (GWO) algorithm. This hybrid GWO–BPNN model was utilized to predict separation membrane efficiency, optimize the film‐forming process, and identify the optimal range of process parameters. Notably, the GWO–BPNN model demonstrated a 2.76% higher prediction accuracy compared to a standalone BPNN. The results indicated that the GWO–BPNN algorithm has a great potential to accurately predict membrane separation efficiency and apply in optimal membrane process design (OMPD), and this method can significantly reduce the number of experimental trials required to achieve OMPD. [ABSTRACT FROM AUTHOR]

Imidazole ionic liquids (ILs) have good affinity and good solubility for carbon dioxide (CO2). Such ionic liquids, combined with polyimide membrane materials, can solve the problem that, today, CO2 is difficult to separate and recover. In this study, the ionic liquid (IL) of 1-ethyl-3-methylimidazolium tetrafluoroborate (IL1), 1-pentyl-3-methylimidazolium tetrafluoroborate (IL2), 1-octyl-3-methylimidazolium tetrafluoroborate (IL3), and 1-dodecylimidazolium tetrafluoroborate (IL4) with different contents were added to a polyimide matrix, and a series of polyimide membranes blended with ionic liquid were prepared using a high-speed mixer. The mechanical properties and gas separation permeability of the membranes were investigated. Among them, the selectivity of the PI/IL3 membrane for CO2/CH4 was 180.55, which was 2.5 times higher than the PI membrane, and its CO2 permeability was 16.25 Barrer, which exceeded the Robeson curve in 2008; the separation performance of the membrane was the best in this work. [ABSTRACT FROM AUTHOR]

The use of mixed matrix membranes (MMMs) comprising metal–organic frameworks (MOFs) for the separation of CO2 from flue gas has gained recognition as an effective strategy for enhancing gas separation efficiency. When incorporating porous materials like MOFs into a polymeric matrix to create MMMs, the combined characteristics of each constituent typically manifest. Nevertheless, the inadequate dispersion of an inorganic MOF filler within an organic polymer matrix can compromise the compatibility between the filler and matrix. In this context, the aspiration is to develop an MMM that not only exhibits optimal interfacial compatibility between the polymer and filler but also delivers superior gas separation performance, specifically in the efficient extraction of CO2 from flue gas. In this study, we introduce a modification technique involving the grafting of poly(ethylene glycol) diglycidyl ether (PEGDE) onto a UiO-66-NH2 MOF filler (referred to as PEG-MOF), aimed at enhancing its compatibility with the 6FDA-durene matrix. Moreover, the inherent CO2-philic nature of PEGDE is anticipated to enhance the selectivity of CO2 over N2 and CH4. The resultant MMM, incorporating 10 wt% of PEG-MOF loading, exhibits a CO2 permeability of 1671.00 Barrer and a CO2/CH4 selectivity of 22.40. Notably, these values surpass the upper bound reported by Robeson in 2008. [ABSTRACT FROM AUTHOR]

Oxygen-enriched combustion technology is an emerging incineration method suitable for waste treatment. In this study, we investigated an economical modular configuration method for oxygen-enriched air production using gas separation membrane technology. Various module configurations were examined based on input pressure, gas temperature, sweep, and multistage module arrangement, and an optimal economically viable configuration was proposed. Using a polysulfone-based polymer membrane module, oxygen-enriched air with an oxygen concentration of 40–65% was produced. Even in cases of low input pressures achieved using a vacuum pump at the permeate side, oxygen-enriched air with concentrations >40% was achieved, with an approximately 20% increase in the permeation flow rate. As the permeation rate increased with increasing temperature, the oxygen recovery efficiency decreased. When the membrane area was increased, the corresponding increase in the input pressure did not result in a proportional increase in the permeation rate compared with single-module setups. Through multistage module arrangements, oxygen-enriched air with a maximum oxygen concentration of 66% was produced. By employing sweep that recirculated a portion of input air to the permeate side, the production of oxygen-enriched air was enhanced by approximately 38%. Therefore, the proposed process involving low input pressure, vacuum pumps, and sweeping was optimal for oxygen-enriched air production. [ABSTRACT FROM AUTHOR]

Mixed-matrix membranes (MMMs) composed of suitable CO2-philic polymers and fillers can be attractive candidates for CO2/CH4 and CO2/N2 separation due to their high CO2 permeability, good thermochemical stability, low fabrication cost, and fast production process. In this research, a novel ternary MMM was fabricated via the blending of poly (amide 12-b-ethylene oxide) (PEBAX-1074) with polyethylene glycol (PEG-200) and magnesium oxide (MgO) nanoparticles mixture. The effects of various loadings of the fillers on CO2, N2, and CH4 permeability values through the membranes were studied. Permeation of CO2, N2, and CH4 gases through the resultant membranes at pressures of 2, 4, 6, 8, and 10 bar and temperatures of 25, 35, 45, and 55 °C revealed the superiority of the MMMs for CO2/CH4 and CO2/N2 separation in comparison with the pristine membranes. Particularly, at 25 °C and 2 bar, the CO2 permeability, as well as ideal CO2/CH4 and CO2/N2 selectivity of the optimized MMM containing 40 wt% of PEG-200 and 8 wt% of MgO nanoparticles, rose to 210.1 Barrer, 24.9 and 60.9, corresponding to enhancement of around 225%, 23% and 24% of the CO2 permeability and selectivity compared to the neat membrane, respectively. Thus, the fabricated MMM has a satisfying potential to separate CO2 from N2. [ABSTRACT FROM AUTHOR]

Imidazole ionic liquids (ILs) have good affinity and good solubility for carbon dioxide (CO2). Such ionic liquids, combined with polyimide membrane materials, can solve the problem that, today, CO2 is difficult to separate and recover. In this study, the ionic liquid (IL) of 1-ethyl-3-methylimidazolium tetrafluoroborate (IL1), 1-pentyl-3-methylimidazolium tetrafluoroborate (IL2), 1-octyl-3-methylimidazolium tetrafluoroborate (IL3), and 1-dodecylimidazolium tetrafluoroborate (IL4) with different contents were added to a polyimide matrix, and a series of polyimide membranes blended with ionic liquid were prepared using a high-speed mixer. The mechanical properties and gas separation permeability of the membranes were investigated. Among them, the selectivity of the PI/IL3 membrane for CO2/CH4 was 180.55, which was 2.5 times higher than the PI membrane, and its CO2 permeability was 16.25 Barrer, which exceeded the Robeson curve in 2008; the separation performance of the membrane was the best in this work.

Carbon molecular sieve (CMS) membranes show attractive potential for energy-efficient separation of C 2 H 4 /C 2 H 6 due to their unique slit-like pore structure. In this work, a novel precursor polymer of phenolphthalein-based poly(arylene ether ketone) (PEK-C) was introduced to prepare high-performance CMS membranes for C 2 H 4 /C 2 H 6 separation. Molecular insight into the effect of the sp 3/ sp 2 hybridized carbon ratio on the packing morphology of carbon layers, pore size and configuration, and C 2 H 4 /C 2 H 6 diffusion and separation properties of CMS membranes was investigated via using in-depth characterization techniques combined with molecular simulations. Results show that the carbon layers with more sp 3 hybridized carbons lead to forming a loose and disordered carbon structure and pore structure with large pore volume and micropore size (steric voids), resulting in low C 2 H 4 /C 2 H 6 permselectivity of CMS membrane. With the reduction of the sp 3/ sp 2 hybridized carbon ratio, a compact and graphite-like carbon structure with the two-dimensional slit-like ultramicropore structure is formed, and the C 2 H 4 /C 2 H 6 permselectivity is obviously enhanced. The CMS membranes derived from the novel precursor of PEK-C exhibit high C 2 H 4 permeability with superior C 2 H 4 /C 2 H 6 selectivity, which have surpassed the trade-off bounds of both polymeric membrane and CMS membrane, and reveal a great potential in the industrial applications of C 2 H 4 /C 2 H 6 separation. [Display omitted] • A novel precursor was introduced to prepare high-performance CMS membranes. • The structure-property relationships between microstructure and gas separation performance were investigated. • The sp3/ sp 2 hybridized carbon ratio obviously affects the C 2 H 4 /C 2 H 6 diffusion selectivity. • The C 2 H 4 /C 2 H 6 separation performance of CMS membranes exceed the trade-off bounds of polymeric and CMS membranes. [ABSTRACT FROM AUTHOR]

Zeolitic imidazolate frameworks (ZIFs) are promising for gas separation membrane, but their molecular cut‐off differs from that expected from its intrinsic aperture structure because of their flexibility. Herein, we introduced graphene nanoribbons (GNRs) to rigidify the ZIF framework. Because the sp2 edge of the GNRs induces strong anchoring effects, the modified layer can be rigidified. Particularly, when the GNRs were embedded and distributed in the ZIF‐8 layer, an intrinsic aperture size of 3.4 Å was observed, resulting in high H2/CO2 separation (H2 permeance: 5.2×10−6 mol/m2 Pa s, ideal selectivity: 142). The performance surpasses the upper bound of polycrystalline MOF membrane performance. In addition, the membrane can be applied to blue H2 production, as demonstrated with a simulated steam reformed gas containing H2/CO2/CH4. The separation performance was retained in the presence of water. The fundamentals of the molecular transport through the rigid ZIF‐8 framework were revealed using molecular dynamics simulations. [ABSTRACT FROM AUTHOR]

A set of ionic liquid capped polyimide membranes was prepared using 1-aminoethyl-3-methylimidazolium hexafluorophosphate (IL1) and 1-aminopropylimidazolium bis(trifluoromethylsulfonyl)imine (IL2) as the terminal groups. The products' molecular weights, mechanical properties, and separation permeability (CO2/CH4) were investigated. For CO2/CH4 separation, the selectivity of the ionic liquid capped polyimide membranes was higher than that of noncapped ones. Among them, the membrane synthesized by 4.4′- diaminodiphenyl ether and 4.4′-(hexafluoroisopropyl) diphthalic anhydride (6FDA) as monomer, with IL1 as terminal group, displayed the best selectivity. Its permeability was 7.47 Barrer and selectivity 102.42, which exceeded the 1991 Robeson curve. Polyimide membranes capped by ionic liquid showed high gas selectivity and good gas permeability as well as good physical and chemical properties. Consequently, it can be concluded that introducing an ionic liquid structure to polyimide chains could make attractive membrane materials for various gas separation and related applications. Graphical Abstract [ABSTRACT FROM AUTHOR]

Long-term thermal stability is one of the biggest challenges in the utilization of inorganic ceramic membranes in high-temperature separation and membrane reactor applications. This work demonstrated that yttrium doping into SiO2-ZrO2 enabled a membrane to maintain stable N2 permeance in a long-term permeation test at 850 °C. Characterization techniques such as DLS, FTIR, XRD, and N2 adsorption confirmed that doping with an yttrium/zirconium molar ratio of 1/9 was optimal. A comparison of the thermal stabilities of pristine SiO2-ZrO2 and Y-doped SiO2-ZrO2 samples calcined at 550–850 °C via XRD and N2 adsorptions revealed that doping with yttria significantly minimized phase segregation and microstructural densification. Furthermore, a membrane prepared at 550 °C from pristine SiO2-ZrO2 showed an immediate decline in N2 permeance from 6.0 × 10−6 to 0.75 × 10−6 mol m−2 s−1 Pa−1 during a 20-hour, long-term, thermal-stability test conducted at 850 °C. By contrast, after 24 h at 850 °C a Y-SiO2-ZrO2-derived membrane showed a reduction of only 5.5 × 10−6 to 5.0 × 10−6 mol m−2 s−1 Pa−1. Thus, the improved thermal stability of this SiO2-ZrO2 composite via yttrium doping heralds the opportunity for ceramic membranes that are more robust. Highlights: Yttrium was successfully doped into SiO2-ZrO2 via a sol-gel process The optimal doping molar ratio of Y/Zr was 1/9 Yttrium-doped SiO2-ZrO2 displayed better thermal stability than pristine SiO2-ZrO2 Membranes derived from yttrium-doped SiO2-ZrO2 maintained a stable long-term permeance at 850 °C [ABSTRACT FROM AUTHOR]

The use of mixed matrix membranes (MMMs) comprising metal–organic frameworks (MOFs) for the separation of CO2 from flue gas has gained recognition as an effective strategy for enhancing gas separation efficiency. When incorporating porous materials like MOFs into a polymeric matrix to create MMMs, the combined characteristics of each constituent typically manifest. Nevertheless, the inadequate dispersion of an inorganic MOF filler within an organic polymer matrix can compromise the compatibility between the filler and matrix. In this context, the aspiration is to develop an MMM that not only exhibits optimal interfacial compatibility between the polymer and filler but also delivers superior gas separation performance, specifically in the efficient extraction of CO2 from flue gas. In this study, we introduce a modification technique involving the grafting of poly(ethylene glycol) diglycidyl ether (PEGDE) onto a UiO-66-NH2 MOF filler (referred to as PEG-MOF), aimed at enhancing its compatibility with the 6FDA-durene matrix. Moreover, the inherent CO2-philic nature of PEGDE is anticipated to enhance the selectivity of CO2 over N2 and CH4. The resultant MMM, incorporating 10 wt% of PEG-MOF loading, exhibits a CO2 permeability of 1671.00 Barrer and a CO2/CH4 selectivity of 22.40. Notably, these values surpass the upper bound reported by Robeson in 2008.

Interfacial polymerization has emerged as a robust method for fabricating task-specific polyamide (PA) membranes. However, the limited microporosity of highly cross-linked PA membranes constrains their effectiveness in gas separation applications. Herein, we introduce an ionic liquid (IL)-regulated interfacial polymerization process to fabricate polyamide nanofilms incorporating kinked tetrakis (4-aminophenyl) methane monomers. In situ ultraviolet-visible spectroscopy demonstrates that the diffusion of 1,3,5-benzenetricarbonyl trichloride (TMC) toward the interface increases with the IL/H 2 O ratio, leading to the formation of a more compact membrane with a higher cross-linking degree. The PA-TAM7/3-60 min membrane exhibits a CO 2 permeance of 29.8 GPU and a CO 2 /CH 4 selectivity of 109, exceeding the 2008 Robeson upper bond. Additionally, the highly cross-linked structure imparts the membranes with notable plasticization resistance. Mixed-gas tests (CO 2 /CH 4 = 50/50, v/v) reveal that the PA-TAM7/3-60 min membrane experiences only a 2% reduction in CO 2 permeance and a 10% decrease in CO 2 /CH 4 selectivity at a CO 2 partial pressure of 300 PSIG, compared to its performance at 30 PSIG. The ease of tuning membrane structure and gas separation performance, along with its excellent plasticization resistance, underscores the potential of these PA membranes for task-specific gas separations.

Carbon molecular sieve (CMS) membranes demonstrate promising economic and environmental advantages in gas separation applications. In this work, we synthesized a novel polymer precursor of PEK-N and utilized it to fabricate a series of PEK-N derived CMS membranes. With varying carbonization temperature and time, the pore structures and gas separation performance were finely tuned. The gas separation properties of membranes with different carbonization temperature were comprehensively evaluated. In particular, by carbonizing the sample at 650 °C for 1 h, PEK-N derived CMS membranes (CMS-650-1) achieved the highest CO 2 permeability around 2176 Barrer, and selectivities of 48.2 for CO 2 /N 2 and 57.8 for CO 2 /CH 4 in their gas mixtures. Our study suggests that the use of rationally designed polymers has the potential to bring about high gas separation performance for polymer-derived carbon molecular sieve membranes. This study explores the use of a novel polymer of polyaryletherketone bearing tertiary amine group (PEK-N) for preparing carbon molecular sieve membranes through control of carbonization temperature and time. The optimized CMS membrane (CMS-650-1) exhibited a CO 2 permeability around 2176 Barrer, and CO 2 /N 2 and CO 2 /CH 4 gas selectivities of 48.2 and 57.8, respectively. [Display omitted] • Polyaryletherketone bearing tertiary amine group polymer was synthesized. • CMS membranes were fabricated using PEK-N polymer. • The structural features of CMS membranes could be tuned by adjusting the carbonization temperature and time. • The CMS membrane exhibited high separation performance for CO 2 /N 2 and CO 2 /CH 4. [ABSTRACT FROM AUTHOR]

• Pebax-based membranes containing different 2D materials for CO 2 capture. • The separation mechanism and properties of Pebax materials are discussed. • The transport mechanism of CO 2 in the membrane was explained. • The challenges and future directions of the Pebax gas separation field are presented. Since the onset of the industrial age, annual global CO 2 emissions have risen, significantly affecting the climate and natural ecosystems. Addressing this, the development of carbon capture, utilization, and storage (CCUS) technologies becomes crucial. Gas membrane separation, recognized for its efficiency, low energy consumption, and eco-friendly nature, is rapidly gaining prominence in global carbon capture efforts. Polyether-block-polyamide (Pebax), with its high CO 2 affinity and resilient mechanical properties (attributed to its elastic polyether and robust polyamide segments) is gaining traction in CO 2 separation research. Yet, the inherent trade-off effect poses challenges for its industrial application. This article delves into the current research landscape of gas separation membranes made of Pebax and assorted 2D nanomaterials for CO 2 separation. It outlines the separation mechanism of Pebax materials and elucidates the CO 2 separation membrane's transport mechanism. Further, the application of gas separation membranes formed by combining Pebax with various 2D nanomaterials for CO 2 capture is also described in detail. Relevant studies underscore that these gas separation membranes offer enhanced separation efficacy and stability, positioning them as potential leaders in CO 2 separation solutions. The paper concludes by highlighting challenges in Pebax-based research and suggesting future research avenues. [ABSTRACT FROM AUTHOR]

Crosslinked poly (ethylene oxide) (XLPEO) membranes are leading candidates for membrane post-combustion carbon capture, because of their high CO 2 /N 2 selectivity and CO 2 permeability. However, their crosslinked nature makes it difficult to process them into thin films through conventional coating techniques. In this study, interfacially initiated chain growth polymerization of epoxides is used to circumvent the XLPEO processing challenge whilst allowing in-situ crosslinking. The interfacial design strategy yields intrinsically crosslinked, epoxide-based PEO (eXLPEO) thin-film composite gas separation (GS) membranes consisting fully of CO 2 -philic ether bonds. An eXLPEO selective layer made from poly (ethylene glycol) diglycidyl ether was successfully deposited on a PAN support and, after introduction of densification steps and a PDMS sealing, gas selective membranes were obtained. Synthesis-structure-performance analysis revealed that multiple reaction condition combinations result in highly selective membranes with a tunable chemical structure. The best performing membranes showed CO 2 /N 2 separation factors of 58 at 35 °C, with a stable operation at pressures from 2 to 10 bar, and retaining a separation factor of 30 at 65 °C. However, all membranes had a low CO 2 permeance (<10 GPU), probably due to pore impregnation of the support layer. This work demonstrates for the first time the viability of interfacial polymerization for the synthesis of thin film eXLPEO GS membranes. [Display omitted] • Epoxide chemistry is a novel platform for thin-film composite (TFC) gas separation membrane synthesis. • Crosslinked poly (ethylene oxide) TFC were synthesized using epoxide interfacial polymerization. • The chemical structure of epoxide-TFC is controlled by the monomer/initatior ratio. • Membranes show high CO 2 /N 2 selectivity, even at elevated temperatures. • The hydrophilicity of the monomers caused pore impregnation. [ABSTRACT FROM AUTHOR]

Refinery gas contains abundant H2 and a small amount of C1--C4 hydrocarbons. Here, we propose a condensability sieving strategy to realize preferential permeation of hydrocarbons over H2 by developing halogen-induced porous coordination polymer (PCP) mixed matrix membranes (MMMs) that display condensability sieving gas transport. The 4-Cl-PCP, 5-Cl-PCP and 5-Br-PCP are synthesized by using Zr4+ and X-isophthalic acid (where X = 4-Cl or 5-Cl or 5-Br) exhibit increased gas adsorption capacity with the increase in carbon number of the feed gas, but with almost no H2 adsorption. MMMs containing the PCPs with different charge distributions enhance condensability sieving selectivity and inhibit diffusion selectivity. The permeances of the MMMs originated from condensability sieving are consistent with the polarizability-dependent adsorption of the PCP. The selectivity of the obtained MMMs for n-C4H10/H2, C3H8/H2, C2H6/H2, and CH4/H2 achieve ~40, ~15, ~5, and ~2, respectively, exhibiting promising applications in refinery gas purification owing to their lower energy consumption compared with H2-preferential permeation membranes. [ABSTRACT FROM AUTHOR]

Refinery gas contains abundant H2 and a small amount of C1--C4 hydrocarbons. Here, we propose a condensability sieving strategy to realize preferential permeation of hydrocarbons over H2 by developing halogen-induced porous coordination polymer (PCP) mixed matrix membranes (MMMs) that display condensability sieving gas transport. The 4-Cl-PCP, 5-Cl-PCP and 5-Br-PCP are synthesized by using Zr4+ and X-isophthalic acid (where X = 4-Cl or 5-Cl or 5-Br) exhibit increased gas adsorption capacity with the increase in carbon number of the feed gas, but with almost no H2 adsorption. MMMs containing the PCPs with different charge distributions enhance condensability sieving selectivity and inhibit diffusion selectivity. The permeances of the MMMs originated from condensability sieving are consistent with the polarizability-dependent adsorption of the PCP. The selectivity of the obtained MMMs for n-C4H10/H2, C3H8/H2, C2H6/H2, and CH4/H2 achieve ~40, ~15, ~5, and ~2, respectively, exhibiting promising applications in refinery gas purification owing to their lower energy consumption compared with H2-preferential permeation membranes. [ABSTRACT FROM AUTHOR]

In this study, graphene nanosheets (GNs) were incorporated into polyethersulfone (PES) by phase inversion approach for preparing PES-GNs mixed matrix membranes (MMMs). To investigate the impact of filler content on membrane surface morphology, thermal stability, chemical composition, porosity and mechanical properties, MMMs were constructed with various GNs loadings (0.01, 0.02, 0.03, and 0.04 wt%). ​The performance of prepared MMMs was tested for separation and selectivity of CO2, N2, H2 and CH4 gases at various pressures from 1 to 6 bar and temperature varying from 20 to 60 °C. It was observed that, compared to the pristine PES membrane, the prepared MMMs significantly improved the gas separation and selectivity performance with adequate mechanical stability. The permeability of CO2, N2, H2 and CH4 for the PES + 0.04 wt% GNs increases from 9 to 2246, 11 to 2235, 9 to 7151, and 3 to 4176 Barrer respectively, as compared with pure PES membrane at 1 bar and 20 °C due to improving the membrane absorption and porosity. In addition, by increasing the pressure, the permeability and selectivity of CO2, N2, H2 and CH4 are increased due to the increased driving force for the transport of gas via membranes. Furthermore, the permeability of CO2, N2, H2 and CH4 increased by increasing the temperature from 20 to 60 °C due to the plasticization in the membranes and the improvement in polymer chain movement. This result proved that the prepared membranes can be used for gas separation applications.

Refinery gas contains abundant H2 and a small amount of C1–C4 hydrocarbons. Here, we propose a condensability sieving strategy to realize preferential permeation of hydrocarbons over H2 by developing halogen-induced porous coordination polymer (PCP) mixed matrix membranes (MMMs) that display condensability sieving gas transport. The 4-Cl-PCP, 5-Cl-PCP and 5-Br-PCP are synthesized by using Zr4+ and X-isophthalic acid (where X ​= ​4-Cl or 5-Cl or 5-Br) exhibit increased gas adsorption capacity with the increase in carbon number of the feed gas, but with almost no H2 adsorption. MMMs containing the PCPs with different charge distributions enhance condensability sieving selectivity and inhibit diffusion selectivity. The permeances of the MMMs originated from condensability sieving are consistent with the polarizability-dependent adsorption of the PCP. The selectivity of the obtained MMMs for n-C4H10/H2, C3H8/H2, C2H6/H2, and CH4/H2 achieve ∼40, ∼15, ∼5, and ∼2, respectively, exhibiting promising applications in refinery gas purification owing to their lower energy consumption compared with H2-preferential permeation membranes.

Two-dimensional nanopores are very promising for high-permeance molecular sieving, but the molecular backflow from permeate-side to feed-side is not beneficial for improving molecular permeance. We study the quasi-unidirectional molecular transport through a graphene-hexagonal boron nitride bilayer nanopore, aiming to realize a high-permeance molecular sieving. Molecular dynamics simulations of CO2/CH4 separations show that the bilayer pore presents 3.7 times higher selectivity comparing to the single-layer graphene nanopore with the same size. The quasi-unidirectional molecular transport is attributed to the distinctive adsorption abilities of gas molecules on the two sides of bilayer nanopores and the inhibited molecular backflow from permeate-side to feed-side. This work provides a promising way to realize the ultra-permeable porous membranes with molecular permeance even higher than the single-layer atomic-thickness membranes.

Two-dimensional (2D) MXene materials have recently been the focus of membrane research due to their unique properties, such as their single-atomic-layer thickness, flexibility, molecular filtration abilities and microstructural similarities with graphene, which is currently the most efficient precursor material for gas separation applications. In addition, the potential to process nanoscale channels has motivated investigations of parameters which can improve membrane permeability and selectivity. Interlayer spacing and defects, which are still challenging to control, are among the most crucial parameters for membrane performance. Herein, the effect of heat treatment on the d-spacing of MXene nanosheets and the surface functionalization of nanolayers was shown regarding its impact on the gas diffusion mechanism. The distance of the layers was reduced by a factor of over 10 from 0.345 nm to 0.024 nm, the defects were reduced, and the surface functionalization was maintained upon treatment of the Ti3C2 membrane at 500 °C under an Ar/H2 atmosphere as compared to 80 °C under vacuum. This led to a change from Knudsen diffusion to molecular sieving, as demonstrated by single-gas permeation tests at room temperature. Overall, this work shows a simple and promising way to improve H2/CO2 selectivity via temperature treatment under a controlled atmosphere.

Composite membranes consisting of microporous tantalum-doped silica layers supported on mesoporous alumina substrates were fabricated using chemical vapor deposition (CVD) in both thermal decomposition and counter-flow oxidative deposition modes. Tetraethyl orthosilicate (TEOS) was used as the silica precursor and tantalum (V) ethoxide (TaEO) as the tantalum source. Amounts of TaEO from 0 mol% to 40 mol% were used in the CVD gas mixture and high H2 permeances above 10−7 mol m−2 s−1 Pa−1 were obtained for all conditions. Close examination was made of the H2/CH4 and O2/CH4 selectivities due to the potential use of these membranes in methane reforming or partial oxidation of methane applications. Increasing deposition temperature correlated with increasing H2/CH4 selectivity at the expense of O2/CH4 selectivity, suggesting a need to optimize membrane synthesis for a specific selectivity. Measured at 400 °C, the highest H2/CH4 selectivity of 530 resulted from thermal CVD at 650 °C, whereas the highest O2/CH4 selectivity of 6 resulted from thermal CVD at 600 °C. The analysis of the membranes attempted by elemental analysis, X-ray photoelectron spectroscopy, and X-ray absorption near-edge spectroscopy revealed that Ta was undetectable because of instrumental limitations. However, the physical properties of the membranes indicated that the Ta must have been present at least at dopant levels. It was found that the pore size of the resultant membranes increased from 0.35 nm for pure Si to 0.37 nm for a membrane prepared with 40 mol% Ta. Similarly, an increase in Ta in the feed resulted in an increase in O2/CH4 selectivity at the expense of H2/CH4 selectivity. Additionally, it resulted in a decrease in hydrothermal stability, with the membranes prepared with higher Ta suffering greater permeance and selectivity declines during 96 h of exposure to 16 mol% H2O in Ar at 650 °C.

• Review the macromolecular structures of microporous polymers for O 2 /N 2 separation. • Explore the aging behavior of innovative microporous materials. • Review the impacts of thermal treatments to reset microporosity and O 2 /N 2 separation. • Investigate the application of polymers and process design in membrane systems. This review summarizes the performance of recently developed microporous polymers for practical industrial O 2 /N 2 separations. The macromolecular design of innovative polymers of intrinsic porosity and derivatives is evaluated from the perspective of pore structure regulation for their outstanding O 2 /N 2 separation performance. The structural groups that could fine-tune the free volume elements are examined to discern the promising moiety and architectures to improve size-based sieving. The long-term aging behaviors of the state-of-the-art macromolecules are also screened to explore the impacts of improved pore/free volume configuration. The strategies using thermal treatments to reset the structure of microporosity are inspected for their potential to improve the gas permeability or enhance size-specific molecular sieving, including the thermal rearrangement of polymeric membranes and pyrolyzed carbon molecular membranes using pre-crosslinked precursors and PIM-derived precursors. Membrane process design and optimization are summarized to evaluate the prospects of these novel membrane materials for large-scale industrial applications. [ABSTRACT FROM AUTHOR]

Chemical structure and morphology of polymers are directly related with the membrane separation performance. Poly(imide)s (PIs) are the most widely used polymers in the preparation of membranes for gas separation applications; thus, research on the structural design of polymers is of great interest to develop new membranes. In the present work, we reported the synthesis, characterization, and measurement of the gas transport properties of a new co-poly(imide)s (PI-D2a-D2b-6FDA) prepared from a mixture of isomeric diamines. The co-poly(imide) synthetic route involved several steps, starting by a bromination reaction, followed by a double nucleophilic aromatic substitution giving an isomeric mixture of precursors, which suffered a Suzuki-Miyaura C–C cross-coupling reaction followed by the reduction of nitro groups to give two new isomeric diamines. Finally, diamines simultaneously reacted with the dianhydride 6FDA to obtain PI-D2a-D2b-6FDA. The co-poly(imide) had a M n of 47.7 kDa and a M w of 74.0 kDa with a PDI of 1.6. The sample exhibited a 10% weight loss at 540 °C, T g of 280 °C, BET surface area of 110 m2 g−1, and wide-angle X-ray diffraction (WAXD) interchain d- spacing at 9.5 Å and 6.3 Å. Tensile strength, elongation at break and Young's modulus were 109.6 MPa, 6.66% and 2.18 GPa, respectively. co-Poly(imide) was soluble in various polar aprotic organic solvents such as DMSO, NMP, DMF, DMAc, THF, and chloroform, forming a self-standing dense film whose gas transport properties were measured. Pure gas permeability coefficients for H 2 , CO 2 , O 2 , N 2 , and CH 4 , were 47.28, 24.04, 4.35, 1.02, and 0.76 (Barrer), respectively, which follows a decreasing order by the increasing kinetic diameters of the respective gases. Ideal gas selectivities H 2 /N 2 , O 2 /N 2 , CO 2 /CH 4 , and CO 2 /N 2 were 46.4, 4.3, 31.6, and 23.6, respectively. These gas transport properties were compared with the commercial polymer Matrimid®, showing higher gas permeability coefficients than Matrimid®. Synthetic route to obtain a new self-standing co-polyimide. [Display omitted] • A new co-poly(imide)s was prepared from a mixture of isomeric diamines (position monomers). • The co-poly(imide) was soluble even in low boiling point solvents like THF and chloroform, forming a self-standing dense film. • Isomeric structures in the polymer lead to irregular growth, achieving higher diffusion coefficients than Matrimid®. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COF) are deemed as disruptive membrane materials owing to their versatile functionalities, high stability and ordered nanochannels. However, the size mismatch between the COF intrinsic pore and gas molecules becomes a grand challenge when using COF membrane for carbon capture. Herein, we propose a new type of polymer-functionalized COF laminar membranes through grafting CO 2 -phlic polyethyleneimine (PEI) polymer onto carboxylic acid COF (cCOF) laminar membranes. The cCOF nanosheets with high density of carboxyl groups are prepared via modified single phase solution method and then assembled to fabricate membranes. Further, the cCOF membranes are functionalized with PEI using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-Hydroxysuccinimide (EDC/NHS) coupling chemistry. The introduction of abundant amino groups from PEI afford the affinity of membranes toward CO 2. Meanwhile, the graft of the PEI polymers reduces the defects or pinholes on the membrane surface. As a result, the PEI functionalized cCOF membranes exhibit a high CO 2 permeance of 1004 GPU and a CO 2 /N 2 selectivity of 33.7, which reach the carbon capture target performance and show great prospect for treating real flue gas. Our approach of functionalizing cCOF membranes with tailored functionalities may inspire the design of molecule-selective COF membranes. [Display omitted] • Carboxyl covalent organic framework (cCOF) nanosheets are assembled into membrane. • cCOF membranes are modified with CO 2 -philic PEI polymer under mild condition. • The membrane shows CO 2 permeance of 1004 GPU with CO 2 /N 2 selectivity of 33.7. • Our work will inspire the design and modification of diverse COF membranes. [ABSTRACT FROM AUTHOR]

• Demonstration of mixed matrix membrane using defective ZIF-78, a MOF with the highest CO 2 uptake reported in literature. • Different solvents used to prepare polysulfone lead to smooth or cracked fillers with different membrane free volume. • CO 2 permeability and CO 2 /N 2 selectivity enhanced by 140 % and 129 % with optimally loaded MMMs. Mixed 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. High 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. Introduction 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 CO 2 permeability and 129 % improvement of CO 2 /N 2 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. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, Amine-functionalized CNF/UiO-66 (CNF–NH 2 /UiO-66) composite membranes were fabricated by incorporating UiO-66 nanoparticles in the CNF–NH 2 matrix. The CO 2 -facilitated transfer channels can be constructed in the CNF–NH 2 /UiO-66 composite membrane. As a natural polymer material, CNF–NH 2 would absorb water and form a gel-like structure under humidification. The adsorbed water can convert CO 2 into bicarbonate ions (HCO 3 −) through the catalysis of amino groups on CNF–NH 2. Moreover, in CNF–NH 2 /UiO-66 composite membranes, HCO 3 − could quickly migrate to the permeate side promoted by the porous UiO-66, facilitating CO 2 transport. The optimum membrane gave a CO 2 permeability of 257.0 Barrer with a CO 2 /CH 4 ideal selectivity of 71.3. [Display omitted] • Hydrogel material CNF–NH 2 was selected as membrane matrix for gas separation. • Adsorbed water molecules can act as fast moving carriers of CO 2. • Porous UiO-66 was incorporated in CNF–NH 2 matrix as a highway for CO 2 transport. • Significantly higher CO 2 permeability was observed for membranes in a humid state. [ABSTRACT FROM AUTHOR]

We prepared a series of microporous network polyimides (MN‐PIs) derived from tris(4‐aminophenyl)amine (TAPA), and three commercial dianhydrides such as 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 3,3′,4,4′‐ benzophenonetetracarboxylic dianhydride (BTDA), and pyromellitic anhydride (PMDA). Particularly, in order to obtain these free‐standing membranes before forming insoluble gel products, the self‐crosslinking rate between dianhydride and triamine functional groups was controlled via reaction temperature changing. All MN‐PIs exhibited outstanding thermal stability with high glass transition temperatures (Tg) exceeding 305°C. Gas transport experiments demonstrated that 6FDA‐derived MN‐PI membrane showed the highest gas permeabilities and well‐maintained gas‐pair selectivities rooting from the bulky ‐C(CF3)2‐ linkage groups that inhibited efficient chain‐packing and the comparable backbone rigidity relative to that of PMDA‐derived MN‐PI. The comprehensive gas transport properties of 6FDA‐based MN‐PI membrane approached the 2008 Robeson upper bound for CO2/CH4, showing CO2 permeability of 37.4 Barrer and ideal selectivity of ~56.7. Physical aging monitored for 75 days lead to a decline in gas permeabilities (e.g., 7.8% and 18.4% drop for O2 and N2) and moderately enhanced selectivity (corresponding 14.3% rise for O2/N2). Additionally, 6FDA‐derived MN‐PI also possessed excellent mixed CO2/N2 gas selectivity of 32.9, roughly equaling to its pure gas transport behaviors, which are probably related to the Lewis acid‐base interactions between CO2 and N atoms of tertiary amine in TAPA segments. [ABSTRACT FROM AUTHOR]

Four spirobichroman-based polyimides (6FDA-F, 6FDA-O, 6FDA-P, and 6FDA-M) were successfully obtained via polyreaction between diamines of different substituents (-H, -OCH3, -N, and -CH3) and 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA). The molecular weights, thermophysical, dihedral angle of the molecules, fractional free volume, d-spacing, Brunauer–Emmett–Teller surface area, and gas separation performance were studied through a combination of experiments and molecular dynamics simulations. These polymers show high molecular weights, with number-average molecular weights (Mn) in the range of 5.0–15.3 × 104, and excellent thermal stability, with weight loss temperatures (T5%) of over 420 °C. The pure-gas (O2, N2, CO2, and CH4) permeation results indicated that the four polymers selectivity of CO2/CH4 over 31 and that 6FDA-F had the highest gas permeability among the four tested gases. Importantly, the dihedral angle from molecular simulation was used to clarify the phenomenon wherein the 6FDA-P gas permeability lower than 6FDA-F. A detailed analysis indicates that -CH3 increased the gas permeability of the polyimides, while the turnstile-like rotary thermal motion of -OCH3 formed channel obstacles and improved the gas selectivity. The polymers containing pyridine ring and those containing benzene ring follows different gas separation mechanisms, based on the gas solution-diffusion behaviour.

Mixed matrix membranes (MMMs) have attracted significant attention for overcoming the limitations of traditional polymeric membranes for gas separation through the improvement of both permeability and selectivity. However, the development of defect-free MMMs remains challenging due to the poor compatibility of the metal–organic framework (MOF) with the polymer matrix. Thus, we report a surface-modification strategy for a MOF through grafting of a polymer with intrinsic microporosity onto the surface of UiO-66-NH2. This method allows us to engineer the MOF–polymer interface in the MMMs using Pebax as a support. The insertion of a PIM structure onto the surface of UiO-66-NH2 provides additional molecular transport channels and enhances the CO2 transport by increasing the compatibility between the polymer and fillers for efficient gas separation. As a result, MMM with 1 wt% loading of PIM-grafted-MOF (PIM-g-MOF) exhibited very promising separation performance, with CO2 permeability of 247 Barrer and CO2/N2 selectivity of 56.1, which lies on the 2008 Robeson upper bound. Moreover, this MMM has excellent anti-aging properties for up to 240 days and improved mechanical properties (yield stress of 16.08 MPa, Young’s modulus of 1.61 GPa, and 596.5% elongation at break).

Designing hollow fiber (HF) membrane modules occupies one of the key positions in the development of efficient membrane processes for various purposes. In developing HF membrane modules, it is very important to have a uniform HF distribution and flow mixing in the shell side to significantly improve mass transfer and efficiency. This work suggests the application of different textile 3D HF structures (braided hoses and woven tape fabrics). The 3D structures consist of melt-spun, dense HFs based on poly(4-methyl-1-pentene) (PMP). Since the textile processing of HFs can damage the wall of the fiber or close the fiber bore, the membrane properties of the obtained structures are tested with a CO2/CH4 mixture in the temperature range of 0 to 40 °C. It is shown that HFs within the textile structure keep the same transport and separation characteristics compared to initial HFs. The mechanical properties of the PMP-based HFs allow their use in typical textile processes for the production of various membrane structures, even at a larger scale. PMP-based membranes can find application in separation processes, where other polymeric membranes are not stable. For example, they can be used for the separation of hydrocarbons or gas mixtures with volatile organic compounds.

New PIM-1 copolymers with 2,3,6,7-anthracenetetrayl moiety have been synthesized as fine powders from 2,3,6,7-tetrahydroxy-9,10-di(p -fluorophenyl)anthracene monomer in DMSO, with crystal structure of the monomer as well as its precursors and the product of its model side crosslinking reaction being determined using X-ray diffraction. The microporosity and surface characteristics of the copolymers powders have been measured. As-cast membrane from the copolymer with 5 mol% of the monomer synthesized revealed promising gas separation properties as compared with original PIM-1. [ABSTRACT FROM AUTHOR]

High‐flux nanoporous single‐layer graphene membranes are highly promising for energy‐efficient gas separation. Herein, in the context of carbon capture, a remarkable enhancement in the CO2 selectivity is demonstrated by uniquely masking nanoporous single‐layer graphene with polymer with intrinsic microporosity (PIM‐1). In the process, a major bottleneck of the state‐of‐the‐art pore‐incorporation techniques in graphene has been overcome, where in addition to the molecular sieving nanopores, larger nonselective nanopores are also incorporated, which so far, has restricted the realization of CO2‐sieving from graphene membranes. Overall, much higher CO2/N2 selectivity (33) is achieved from the composite film than that from the standalone nanoporous graphene (NG) (10) and the PIM‐1 membranes (15), crossing the selectivity target (20) for postcombustion carbon capture. The selectivity enhancement is explained by an analytical gas transport model for NG, which shows that the transport of the stronger‐adsorbing CO2 is dominated by the adsorbed phase transport pathway whereas the transport of N2 benefits significantly from the direct gas‐phase transport pathway. Further, slow positron annihilation Doppler broadening spectroscopy reveals that the interactions with graphene reduce the free volume of interfacial PIM‐1 chains which is expected to contribute to the selectivity. Overall, this approach brings graphene membrane a step closer to industrial deployment. [ABSTRACT FROM AUTHOR]

Metal‐organic frameworks (MOFs)‐based membranes have shown great potentials as applications in gas separation. In this work, a uniform membrane based on 2D MOF Ni3(HITP)2 (HITP=2,3,6,7,10,11‐hexaaminotriphenylene) was fabricated on ordered macroporous AAO via the filtration method. To fabricate the membrane, we obtained the Ni3(HITP)2 nanosheets as building blocks via a soft‐physical exfoliation method successfully that were confirmed by AFM and TEM. We also studied the H2, CO2 and N2 adsorption isotherms of Ni3(HITP)2 powder at room temperature, which shows Ni3(HITP)2 has high heats of adsorption for CO2 and high selectivity of CO2 over N2. Gas permeation tests indicate that the Ni3(HITP)2 membrane shows high permeance and selectivity of CO2 over N2, as well as good selectivity of H2 over N2. The ideal separation factors of CO2/N2 and H2/N2 from sing‐gas permeances are 13.6 and 7.8 respectively, with CO2 permeance of 3.15×10−6 mol⋅m−2⋅s−1⋅Pa−1. The membrane also showed good stability, durability and reproducibility, which are of potential interest for practical applications in the CO2 separations. [ABSTRACT FROM AUTHOR]

Summary: Spirobichroman‐based polymers have garnered considerable attention as promising gas separation membrane materials. Herein, two spirobichroman‐based diamines were synthesised using a pyridine heterocyclic ring with methyl substituents at different positions. The diamines were reacted with 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and bis‐(3‐phthalyl anhydride) ether (ODPA) to achieve four polyimides functionalised by pyridine. The polymers performances were characterised by experimentally and molecular dynamics simulations. They showed high molecular weights of Mn = 9.4 to 14.0 × 104, excellent thermal stability, good solubility in a series of common organic solvents, and easy processability to form membranes. The membrane showed high gas pair selectivities of αCO2/CH4>30 and αCO2/N2>24, which were attributed to turnstile‐like rotary motions of the methyl and basic group of pyridine. The gas permeability results suggested that the substituents position of the methyl has little effect on the rigid molecular chain, unlike the densely packed flexible molecules chains. [ABSTRACT FROM AUTHOR]

[Display omitted] • This article reviewed the preparation strategies for large MXene flakes. • A systematic summary was conducted based on the preparation methods of MXene gas separation membranes. • An analysis on the influence of the surface groups on gas adsorption process and the adsorption in gas sensing was carried out. • The potential relationship between gas adsorption and separation as well as the application of computational simulation were explored. Recently, MXene, a novel two-dimensional (2D) material, shows promising potential in many fields. Among these fields, gas separation and adsorption have emerged as new application areas for MXene. The number of studies relevant to the application of MXene in gas separation and adsorption is gradually increasing, making it a hot spot in scientific research. Therefore, timely and systematic reviews of the strengths and weaknesses of MXene are crucial to its further development. This article focused on the application of MXene in gas separation and adsorption. In this review paper, we presented some preparation methods of large MXene layers and practicable strategies for utilizing them to enhance the operational stability of MXene membranes, and the latest research advancements in the application of MXene in gas separation and adsorption. In terms of gas separation, we provided a systematic summary of the research progress based on the techniques used to prepare MXene membranes. As for gas adsorption, we discussed the research progress from both experimental and theoretical perspectives. This discussion was divided into three parts: (1) exploration of the impact of the surface groups on gas adsorption process; (2) analysis on the effect of gas adsorption in gas sensing; and (3) study on theoretical calculation pertaining to gas adsorption and separation. Finally, we evaluated the advantages and disadvantages of using MXene in gas separation and adsorption and then outlined the potential avenues for the future development of MXene. It is expected that this review may provide valuable insights and guidance for the researchers engaged in promoting the intensive study and the broad application of MXene. [ABSTRACT FROM AUTHOR]

Thermally rearranged (TR) polymers have shown a great potential for gas separation. However, the temperature of TR reaction often goes beyond the glass transition temperature (Tg) of polymer precursor and results in pore collapsing and low gas permeance to asymmetric membranes. To solve this problem, we prepared a series of crosslinked thermally rearranged (XTR) polybenzoxazoles (PBO) at sub-Tg. We synthesized crosslinkable phenolphthalein-based polyimides via chemical imidization (EPPI) and azeotropic distillation (HPPI). The two polyimides were crosslinked at 300–335 °C to increase their Tg so that the subsequent TR reaction were accomplished at sub-Tg. The HPPBO-425 exhibited the best separation performance with a CO 2 permeability of 122 barrer and a CO 2 /CH 4 selectivity of 40.4 for pure gases. Moreover, the XTR PBO was not plasticized at a CO 2 pressure of 30 atm. After aged for 60 days, the CO 2 permeability decreased to 100 barrer and the CO 2 /CH 4 selectivity increased to 44. When separating CO 2 /CH 4 (1:1) mixed gases, the CO 2 permeability gradually decreased from 120 to 74 barrer with a decrement in the CO 2 /CH 4 selectivity from 47 to 26 because of the progressively saturated Langmuir sorption sites and the competitive sorption by CH 4 decreasing the solubility of CO 2. The excellent and stable CO 2 /CH 4 separation property makes the sub-Tg XTR PBO an ideal material for fabricating hollow fiber gas separation membranes. [Display omitted] • Crosslinked thermally rearranged PBOs were synthesized at sub-Tg. • Gas permeability increased by 20 times while maintained selectivity after TR. • XTR-PBO resists plasticization and good for nature gas separation. • Phenolphthalein based diamine is good platform to XTR polymer. [ABSTRACT FROM AUTHOR]

A novel gas separation membrane was fabricated from a commercially available polymer of phenolphthalein-based cardo poly (arylene ether ketone) (PEK-C). Thermal treatment was employed to improve the gas permeability and anti-plasticization property of PEK-C polymeric membrane via inducing interchain crosslinking. The changes of chemical structure, thermal crosslinking reaction, interchain distance, gas separation performance and anti-plasticization properties of PEK-C membranes were investigated by the FT-IR, XPS, TG-MS, XRD and gas permeation tests. Results show that the gas separation performance and anti-plasticization properties of PEK-C membranes are significantly enhanced after the thermal crosslinking, which is induced by the decomposition of the lactone rings in cardo moieties and crosslinking with the formation of biphenyl linkages. The dramatic enhancement in gas permeability for the crosslinked membrane is attributed to the enlargement of the interchain distance and free volume cavity, and the great improvement on the anti-plasticization property is due to the formation of a rigid crosslinked network structure. Compared to PEK-C polymeric membrane, the CO 2 permeability of the crosslinked membrane increased by more than 110 times with an adequate CO 2 /CH 4 selectivity, especially for the separation of CO 2 /CH 4 mixed gas (50:50 mol%). The CO 2 plasticization pressure substantially increased from 2 atm to the highest tested pressure of 30 atm. The gas separation performance of the crosslinked membrane surpassed the 2008 upper bound for CO 2 /CH 4 , exhibiting that the thermal crosslinking membrane derived from PEK-C membrane material is an attractive candidate for the natural gas purification. • A novel gas separation membrane was fabricated from a commercially available polymer. • Thermal crosslinking greatly enhances the gas permeability and anti-plasticization. • The CO 2 permeability increased by more than 110 times after crosslinking. • The CO 2 plasticization pressure of cross-linked membrane increased up to 30 atm. [ABSTRACT FROM AUTHOR]

Compared with current conventional technologies, oxygen/nitrogen (O2/N2) separation using membrane offers numerous advantages, especially in terms of energy consumption, footprint, and capital cost. However, low product purity still becomes the major challenge for commercialization of membrane-based technologies. Therefore, numerous studies on membrane development have been conducted to improve both membrane properties and separation performance. Various materials have been developed to obtain membranes with high O2 permeability and high O2/N2 selectivity, including polymer, inorganic, and polymer-inorganic composite materials. The results showed that most of the polymer membranes are suitable for production of low to moderate purity O2 and for production of high-purity N2. Meanwhile, perovskite membrane can be used to produce a high-purity oxygen. Furthermore, the developments of O2/N2 separation using membrane broaden the applications of oxygen enrichment for oxy-combustion, gasification, desulfurization, and intensification of air oxidation reactions, while nitrogen enrichment is also important for manufacturing pressure-sensitive adhesive and storing and handling free-radical polymerization monomers. [ABSTRACT FROM AUTHOR]

Herein, the microporous structure and gas transport property of a new family of polyimides (PIs) containing bulky tetra- o -isopropyl and naphthalene groups prepared via a microwave-assisted polymerization process are reported. The polyimides were prepared from a naphthalene and isopropyl containing diamine, i.e., 4,4'-(naphthalen-1-ylmethylene)bis(2,6-diisopropylaniline)) (i.e., BAN-3) obtained via a one-step electrophilic substitution reaction, reacting with three commercial dianhydrides. Analysis of fractional free volume (FFV) in conjunction with positron annihilation lifetime spectroscopy (PALS) showed that the resultant BAN-3 based PIs had high FFV values of over 0.19 featuring a bimodal size distribution of microcavities with average diameters in the range of 8.0–9.0 Å and 5.6–6.3 Å, respectively. Wide angle X-ray diffraction (WXRD) further confirmed that the introduction of naphthalene and tetra- o -isopropyl groups effectively enhanced polymeric backbone rigidity and disrupted chain packing, leading to high gas permeabilities in all three PI films. For example, the PI-3F film had high H 2 and CO 2 permeability values of 722 and 849 barrer, respectively while maintaining comparable selectivities for H 2 /CH 4 and CO 2 /CH 4 gas pairs with other reported PIs of the same dianhydride. In addition, the PI-3B film displayed excellent gas separation performance for O 2 /N 2 gas pair approaching the 2008 Robeson upper bound. Image 1 • Robust and highly soluble polyimides containing isopropyl and naphthalene units were readily prepared. • The polyimides had high FFV values featuring a bimodal size distribution of microcavities. • The polyimides showed excellent gas selectivity for O2/N2, approaching the 2008 Robeson upper bound. [ABSTRACT FROM AUTHOR]

Polymer crosslinking via thermal oxidation is a well-established technique that enhances the gas selectivity of a polymer membrane, but usually at the expense of lower gas permeability. As thermal oxidation is typically performed at temperatures higher than the glass transition temperature (T g) of polymers, large energy footprints are incurred while pore structures in asymmetric membranes – the preferred physical configuration of polymer membranes are collapsed. To overcome these drawbacks, here we report a strategy to simultaneously enhance both gas permeability and selectivity via thermal oxidation at sub-T g temperatures. This was achieved with a copolymer consisting a component that enhanced T g , and another component with functional groups that decomposed and induced crosslinking at lower temperatures. We used a series of complementary characterization techniques to pinpoint the actual mechanism underpinning our sub-T g thermal oxidation approach. Crosslinking slightly reduced the d-space between polymer chains but increased polymer fractional free volume and most importantly, inhibited CO 2 -induced plasticization. The pure CO 2 permeability of the crosslinked polymer reached 88.5 Barrer with a CO 2 /CH 4 ideal selectivity of 38.8, while no plasticization behavior was detected at a CO 2 pressure up to 30 atm at 35 °C. When separating CO 2 :CH 4 (1:1) mixed gas at total pressures between 10 and 60 atm, the CO 2 permeability and CO 2 /CH 4 selectivity of this crosslinked polymer were reduced to 55 Barrer and 29 due to competitive permeation. Image 1 • Introducing Durene into 6FDA-MPP enhances T g and decreases crosslinking temperature. • Thermal oxidative crosslinking mechanism of the lactone ring based polyimide was elucidated. • Polyimide is crosslinked at 275 °C that is 75 °C lower than its T g. • Crosslinked polymer shows no plasticization at a CO 2 pressure of 30 atm. [ABSTRACT FROM AUTHOR]

Metal-organic framework (MOF) membranes have become promising candidates for gas separation due to their adjustable structure, high separation performance, and environmental friendliness. However, the emergence of grain boundary defects, and interface defects between the support layer and separation layer significantly decrease the gas separation performance of MOF membranes. Herein, a self-supported ZIF (zeolitic imidazolate framework) glass membrane is fabricated, eliminating grain boundary defects and cracks through the molten-liquid phase. The fluorine-based linkers with high electronegativity and polarizability are introduced to enhance a g ZIF-62(a and g denote amorphous and glass, respectively) interaction of CO 2 and CH 4. The CO 2 /N 2 and CH 4 /N 2 ideal selectivity of a g ZIF-UC-4 membrane (fluorine-based, UC-4 named by Cambridge University) reach 36 and 6.2, respectively. In addition, the CO 2 and CH 4 permeance of the a g ZIF-UC-4 membrane with an independent separation layer and the non-grain boundary has improved to 4752 and 818 GPU, respectively. Under the mixed gas condition, a g ZIF-UC-4 membrane exhibits good separation performance, exceeding the 2019 Mckeown upper bond of CO 2 /N 2. Moreover, a g ZIF-UC-4 membrane has good stability for CO 2 /N 2 and CH 4 /N 2 under continuous operation and variable pressure testing. Hence, the self-supported a g ZIF-UC-4 membrane is a potential candidate for preparing MOF glass membranes with good gas separation performance. [Display omitted] • A self-supported a g ZIF-UC-4 glass membrane is fabricated for gas separation. • The glass membrane can eliminate grain boundary defects by the molten-liquid phase. • The a g ZIF-UC-4 membrane has enhanced CO 2 and CH 4 permeance of 4752 and 818 GPU, respectively. • The a g ZIF-UC-4 membrane has good stability for CO 2 /N 2 and CH 4 /N 2. • The performance of a g ZIF-UC-4 membrane surpasses the corresponding upper bounds. [ABSTRACT FROM AUTHOR]

[Display omitted] • Triptycene-based highly crosslinked and microporous nanofilms were fabricated on PES substrate. • Triptycene enhanced the microporosity and interconnectivity of the polymer networks. • PA-Trip nanofilms displayed outstanding gas separation performance for several gas pairs. • Microporosity and gas separation properties were highly tailorable by reaction condition. Highly permeable and selective synthetic polymer membranes are attractive for energy-efficient gas separations, while fabricating such membranes with well-defined micropore architecture and interconnectivity remains a significant challenge. We report the design and fabrication of highly crosslinked and microporous polymer nanofilms via engineering the bridged-bicyclic triptycene triamine moieties into the interfacially polymerized networks. The integrated polyamide nanofilms exhibited hierarchical pore structures with finely tuned microporosity (pore size 0.7–1.0 nm), ultramicroporosity (pore size 0.4–0.7 nm), and submicroporosity (pore size < 0.4 nm) and enhanced micropore interconnectivity due to triptycene-induced non-coplanar orientation and configurational free volume in the networks. Consequently, the composite membranes comprising polyamide nanofilms display exceptional gas separation performance for He and H 2 recovery with enhanced permeances and selectivities as well as notable plasticization resistance compared to current state-of-the-art highly crosslinked TFC membranes. It is also proved that the microporosity and gas transport properties of the composite nanofilms are highly tailorable by regulating the reaction conditions. Incorporating hierarchical triptycene units with well-defined and interconnected microvoids provides the potential to fabricate highly permselective thin-film composite membranes applicable for various important gas separations. [ABSTRACT FROM AUTHOR]

A novel method to determine the individual diffusion coefficients of gases in a mixture during their permeation through polymeric membranes is described. The method was developed in two independent laboratories, using rubbery Pebax ® and glassy Hyflon ® AD60X membrane samples as standards, and validated using the Tröger's base containing Polymer of Intrinsic Microporosity, PIM-EA-TB. Monitoring of the permeate composition in real time by a quadrupole mass spectrometer allowed the analysis of the permeation transient for gas mixtures. Two operation modes, either with a vacuum in the permeate and a direct connection to the mass spectrometer via a heated restriction, or using a sweeping gas and a heated capillary sample inlet, give excellent agreement with the traditional time lag method for single gases. A complete overview of the method development, identification of the critical parameters, instruments calibration, data elaboration and estimation of the experimental accuracy are provided. Validation with PIM-EA-TB, shows that the method can also successfully detect anomalous phenomena, related to pressure and concentration dependency of the transport properties, physical aging or penetrant-induced dilation. Rapid online analysis of the permeate composition makes the method also very suitable for routine mixed gas permeability measurements. [ABSTRACT FROM AUTHOR]