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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]

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 MOF crystal-glass composites (CGC) membrane, comprising a MOF crystal and MOF glass matrix, represents a novel self-supported membrane that has been effectively applied in gas separation. Nevertheless, the typical MOF glass matrix requires a higher operating temperature (>400 °C), which constrains its combination with a multitude of MOF crystals characterized by high porosity and low decomposition. In this work, Zn–P-dmbIm (coordination polymer) was chosen as the glass matrix, and MIL-101 crystal with high porosity were integrated at an operating temperature of 190 °C. Furthermore, the intrinsic low porosity of a g Zn-P-dmbIm can be enhanced by the incorporation of higher porosity MIL-101, which possessed a high specific surface area (from ∼1.7 m2/g to 401 m2/g) and porosity (from ∼0.0014 cm³/g/nm to 0.5605 cm³/g/nm) of the CGC. The intimate combination of MIL-101 and a g Zn-P-dmbIm by in - situ melting to reduce the interfacial defects, which also provides a robust foundation for effective CO 2 /N 2 separation. In CO₂/N₂ (50/50, v/v) mixed gas conditions, the MIL-101/ a g Zn-P-dmbIm membrane demonstrated a impressively high CO₂ permeability of 18670 barrer and CO₂/N₂ selectivity of 61, exceeding the CO₂/N₂ upper bound. The variable pressure (1–12 bar) and long-term stability (120 h) of the CGC membrane exhibited enhancing separation stability. Hence, the self-supported MIL-101/ a g Zn-P-dmbIm membrane demonstrated effective CO₂/N₂ separation performance, which had the potential to significantly extend the scope of applications for MOF crystal-glass matrices. [Display omitted] • Highly porous MIL-101 integrated with Zn–P-dmbIm glass. • The operating temperature of crystal-glass composites was reduced to 190 °C. • MOF crystal-glass composites membrane were obtained by in - situ melting. • Significantly enhanced CO 2 diffusion in Zn–P-dmbIm composites glass membrane. • The membrane has CO 2 permeability of 18670 barrer and CO 2 /N 2 selectivity of 61. [ABSTRACT FROM AUTHOR]

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]

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.

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]

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]

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.

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.

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]

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.

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]

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]

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]

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]

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]

A novel triptycene-based diamine, 2,6-diaminotriptycene-14-carboxylic acid, was synthesized and used for preparing carboxylic acid containing triptycene-based Tröger's base copolymers, CoPIM-TB-1 and CoPIM-TB-2, with another diamine monomer, 2,6-diaminotriptycene. The copolymers were subsequently post - crosslinked by glycidol to form C-CoPIM-TB-1 and C-CoPIM-TB-2. Glycidol crosslinking greatly impeded inter-chain mobility of the triptycene-based copolymers and subsequently restricted both physical aging rate and CO 2 induced plasticization. Gas permeabilities of 40 days old C-CoPIM-TB-2 film decreased by 7%, 5%, and 9%, to gases H 2 , CO 2 , and O 2 , respectively, which were slower than those of the uncrosslinked PIM-Trip-TB polymer of which permeabilities decreased by 21%, 42%, and 30%, respectively. Mixed gas permeation results showed no CO 2 induced plasticization at a CO 2 partial pressure up to 20 atm. Moreover, separation performance of C-CoPIM-TB-1 and C-CoPIM-TB-2 went over the Robeson 2008 upper bounds for gas pairs including O 2 /N 2 , CO 2 /CH 4 , CO 2 /N 2 and H 2 /N 2 . All these results indicated a great potential for the post-crosslinked Triptycene-Based Tröger's Base polymers for natural gas sweetening. [ABSTRACT FROM AUTHOR]

Herein, a series of novel triptycene-containing thermally rearranged poly(benzoxazole- co -imide) membranes (TPI-PBOs) with enhanced mechanical properties and gas separation performance are reported. The effects of chemical structures and poly(benzoxazole- co -imide) composition on the fractional free volume, polymer chain packing, microcavity size and size distribution, mechanical properties, and gas transport properties have been comprehensively investigated. Due to the incorporation of triptycene-containing non-TR-able polyimide segments, the resulting poly(benzoxazole- co -imide) films exhibited good mechanical properties even after being treated at 450 °C. The incorporation of bulky and rigid triptycene units led to significantly improved fractional free volume and gas transport properties compared to previously reported poly(benzoxazole- co -imide)s. Several triptycene-containing poly(benzoxazole- co -imide) films displayed excellent gas separation performance for H 2 /CH 4 , H 2 /N 2 , and CO 2 /CH 4 gas pairs that exceeded the 2008 upper bounds. [ABSTRACT FROM AUTHOR]

This work reports on the preparation and gas transport performance of mixed matrix membranes (MMMs) based on the polymer of intrinsic microporosity (PIM-1) and potassium dodecahydrododecaborate (K2B12H12) as inorganic particles (IPs). The effect of IP loading on the gas separation performance of these MMMs was investigated by varying the IP content (2.5, 5, 10 and 20 wt %) in a PIM-1 polymer matrix. The derived MMMs were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), single gas permeation tests and sorption measurement. The PIM1/K2B12H12 MMMs show good dispersion of the IPs (from 2.5 to 10 wt %) in the polymer matrix. The gas permeability of PIM1/K2B12H12 MMMs increases as the loading of IPs increases (up to 10 wt %) without sacrificing permselectivity. The sorption isotherm in PIM-1 and PIM1/K2B12H12 MMMs demonstrate typical dual-mode sorption behaviors for the gases CO2 and CH4. [ABSTRACT FROM AUTHOR]

A proper increase of d -spacing after crosslinking is an effective strategy to enhance gas separation performance and anti-plasticization property of polymeric membranes. One way to achieve high chain distance is to design and prepare polymer precursors that have large side groups with crosslinkable functionality. Our previous research proved that the decarboxylation crosslinked polyimides connected by a biphenyl group showed enlarged d -spacing. However, the 100% crosslinking temperature is 425–450 °C that is higher than the glass transition temperature ( T g ) of most polymers and may cause problem for preparing asymmetric crosslink membranes. Here we proposed a thermal oxidative crosslinking method which had a lower crosslinking temperature than the decarboxylation crosslinking method. Specifically, we synthesized two phenolphthalein-based cardo diamines, MPP and PP, with or without CH 3 substituted groups and prepared the 6FDA-MPP and 6FDA-PP polyimides. The lactone ring in the cardo moiety decomposed and the crosslinking reaction took place by heating the polymer in an air purge atmosphere. A 100% conversion of the crosslinking reaction was obtained at 400 °C. In addition, the crosslinked polyimides showed increased d -spacing, high CO 2 permeability and CO 2 /CH 4 selectivity than before. The best result for pure gas test was achieved for 6FDA-MPP-400, which had a CO 2 permeability of 193.8 Barrer with a CO 2 /CH 4 ideal selectivity of 39.2. No plasticization was observed for the 6FDA-MPP-400 and 6FDA-PP-400 polyimides at a CO 2 pressure up to 450 psia. In addition, both 6FDA-MPP-400 and 6FDA-PP-400 showed excellent mixed gas selectivity of 35 at a partial CO 2 pressure of 147 psia. [ABSTRACT FROM AUTHOR]

Ion gel films were prepared by incorporating eight commercially available ionic liquids in two different cross-linked polymer matrices to evaluate their phase miscibility, gas permeability and ionic conductivity for potential applications as gas separation membranes and solid electrolyte materials. The ionic liquids cations were 1-ethyl-3-methylimidazolium, 1-ethyl-3-methylpyridinium, 1-butyl-1-methylpyrrolidinium, tributylmethylphosphonium, and butyltrimethylammonium with a common anion (bis(trifluoromethylsulfonyl)imide). In addition, ionic liquids with 1-ethyl-3-methylimidazolium cation with acetate, dicyanamide and tetrafluoroborate counterions were evaluated. The two polymers were cross-linked poly(ethylene oxide) and cross-linked poly(ethylene oxide)/siloxane copolymer. Differential scanning calorimetry, X-ray diffractometry and visual observations were performed to evaluate the ion gels’ miscibility, thermal stability and homogeneity. Ionic liquids with the least basic anion (bis(trifluoromethylsulfonyl)imide) and aromatic cations containing acidic proton (e.g. imidazolium and pyridinium) gave the most stable and miscible ion gels. Phase stability was shown to be a function of both ionic liquid content and temperature, with phase separation observed at elevated temperatures. Gas permeability testing with carbon dioxide and nitrogen and ionic conductivity measurements confirmed that these ionic liquids increased the gas permeability and ionic conductivity of the polymers. [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]

Carbon molecular sieve (CMS) membranes are ideal candidates for natural gas separation due to their rigid pore structures and stability. The chemical composite and spatial configuration of the used precursors for deriving CMS membranes can greatly influence the final microporous structure and separation performance of the membranes. Most CMS membranes are transformed from amorphous precursors such as polymers nowadays. Here, for the first time, we report a new type of CMS membrane derived from a crystalline porous hydrogen-bonded organic framework membrane (named HCMS). The conversion process has been studied with the characterization of TGA, FTIR, XRD, SEM, and pore size distribution. The effect of pyrolysis temperature on the membrane structure has been investigated to achieve optimized CO 2 /CH 4 separation performance. On the one hand, as the pyrolysis temperature increases from 550 to 650 °C, the pore size distribution of HCMS membrane is narrowed, which is conducive to improving the molecular sieving effect of the membrane. On the other hand, higher ratios of graphitic N and pyrrolic N, which show better affinity for CO 2 molecules than pyridinic N, are obtained on the HCMS membranes, leading to more favorable adsorption of CO 2. The optimized HCMS membrane pyrolyzed at 600 °C shows a remarkable CO 2 /CH 4 selectivity of 128 and excellent separation stability at varying temperatures and pressures. The HCMS membranes derived from the crystalline HOF precursor can also maintain a stable separation performance against physical aging. The results reported in this work may open the door to constructing CMS membranes with the precursor of crystalline porous membranes. Crystalline porous hydrogen-bonded organic framework membrane is employed as a new kind of precursor for the first time to derive carbon molecular sieve membrane with a narrow pore size distribution, which reveals good separation selectivity and stability for CO 2 /CH 4. [Display omitted] • For the first time, a HOF membrane is used as a precursor to derive HCMS membrane. • Ordered porosity of HOF leads to a narrow pore size distribution of HCMS membrane. • Effect of pyrolysis temperature on membrane structure and CO 2 affinity is studied. • The HCMS-600 membrane reveals the optimized CO 2 /CH 4 separation selectivity of 128. • The HCMS-600 membrane is long-term stable at variable temperatures and pressures. [ABSTRACT FROM AUTHOR]

The transport of small gases (H2, CO2, N2, O2) through a series of novel membranes based on necklace-shaped inorganic polymers (DMS@POSS), in which a polyhedral oligomeric silsesquioxane (POSS) cage unit and soft chains of oligo-dimethyl siloxane (DMS) were alternately connected, was investigated. The influence of the DMS chain length and crosslinking density of the DMS@POSS on membrane properties were studied. The membranes revealed characteristic structure-property relation towards both glass transition and gases transport. Specifically, clear dependence of properties from the length of DMS units (or overall siloxane content) was revealed. Gas transport properties, when compared to state-of-art polydimethylsiloxane and commercial silicone rubber, demonstrated significantly higher selectivity of DMS@POSS for carbon dioxide (in CO2/N2), hydrogen (in H2/N2) and oxygen (in O2/N2) but lowered permeability, proportional to the amount of POSS in the material. With a precise control over mechanical and thermal properties compared to conventional silicone rubbers, described materials could be considered as materials of choice in niche gas separation or other applications.

Two series of novel aromatic polyimides ( PIs ) containing three polymers each one were prepared using two new aromatic silylated-diamine monomers. These monomeric diamines contain biphenylsilane units and biphenyl moieties in their structures. All PIs were obtained in high yield and the inherent viscosities were in the range of 0.44 to 0.82 dL/g. Polyimides showed excellent solubility in a wide variety of aprotic polar solvents, including THF and chloroform and were thermally stable with thermal decomposition temperature (TDT 10% ) over 500 °C and high glass transition temperatures (Tg) between 230 and 270 °C. Additionally, two films were prepared and gas transport properties were determined. These films offered a reasonably acceptable balance of permeability and selectivity with values close to a commercial polyimide (Matrimid), in particular for the CO 2 /N 2 gases pair. Experimental density of the films was measured and the fractional free volume was calculated. [ABSTRACT FROM AUTHOR]

Three spirobichroman-based diamines, FSBC, SBC and MSBC, with different substituted groups (-CF 3, -H, and -CH 3 ) were synthesized. The diamines were reacted with 4,4′-hexafluoroisopropylidene bisphthalic dianhydride (6FDA) to form 6FDA-FSBC, 6FDA-SBC, and 6FDA-MSBC polyimides, respectively. The organosolubilities, molecular weights ( M n ), densities, glass transition temperature (T g ), thermal stabilities, fractional free volume (FFV), d -spacing and gas separation properties of the spirobichroman-based polyimides were systematically studied. The three spirobichroman-based polyimides had high M n and T g , excellent thermal stabilities, and good solubilities in a wide range of organic solvents. 6FDA-FSBC exhibited the highest gas permeability which could be attributed to its insufficient chain packing conditions rooting from the incorporation of spriobichroman backbone with the spiro and non-coplaner nature, and the bulky CF 3 substituting group that increased the polymer FFV and decreased the polymer chain flexibility. 6FDA-MSBC had the highest H 2 /CH 4 selectivity due to the present of the CH 3 group in the diamine moiety which had the turnstile-like rotary thermal motion that inhibited the diffusion of large molecules like CH 4 but had little effect on the diffusion of small molecules like H 2 . [ABSTRACT FROM AUTHOR]

The fundamental gas transport properties and physical aging behavior of a series of triptycene-based polyimides with various substitution groups were investigated. Wide-angle x-ray diffraction revealed that the 6FDA-1,4-triptycene polyimides exhibit two chain packing domains with d -spacing values of ~6.7 Å and ~5.3 Å, corresponding to triptycene-induced chain packing disruption and chain segments lacking the triptycene moiety, respectively. Positron annihilation lifetime spectroscopy (PALS) showed a bimodal distribution of microcavity size made up of triptycene cleft cavities that are ~3 Å diameter and larger interchain cavities with an average diameter of ~7 Å. Additionally, PALS confirmed 6FDA-1,4-trip_CH 3 has the lowest fractional free volume, primarily due to smaller contributions from the interchain cavities, and 6FDA-1,4-trip_CF 3 has the largest fractional free volume. It was also found that the addition of substituent groups had a unique and positive effect on the aging properties over nine months, in which the addition of CH 3 and CF 3 groups led to permeability increases of ~20% and ~40%, respectively. This is caused by the combination of the lowered driving force for physical aging, the substituent groups sterically hindering tighter packing with time, and the interconnectivity and/or unblocking of free volume over time through small-scale, local chain motion. [ABSTRACT FROM AUTHOR]

Mixed matrix membranes (MMMs) with easy scale-up architectures have shown great potential to achieve superior CO 2 permeance, while their performances are often restricted by the poor interfacial compatibility between fillers and the matrix, and also by blocking of the original channel for gas transmission. Here, a rational design and facile construction of highly permeable MMMs is presented by dispersing triphenyltriazine-based β-ketoenamine-linked covalent organic framework (TpTta-COF) within solution-processable polymer of intrinsic microporosity (PIM-1). An intimate mixing was achieved by improved compatibility of the components induced by the hydrogen bond interaction between -N-H in TpTta-COF and C N of PIM-1. The good adhesion avoids the formation of interface defects, preserving the original gas transmission channel. TpTta-COF particles with strong CO 2 affinity are evenly distributed in the matrix, forming a fast and continuous channel for CO 2 transmission. The physical properties of MMMs were easily tuned, and the as-prepared PIM-1/TpTta–COF–6wt% demonstrates extraordinary stability, high CO 2 permeability and CO 2 /N 2 selectivity, surpassing the β-ketoenamine-free MMM counterparts. This study provides a feasibly pathway for the development of efficient and high performances separation membranes. A facile strategy to improve the compatibility between the matrix and filler through hydrogen-bonded interaction was presented for the construction of high performance MMMs with extraordinary long-term stability. [Display omitted] • A facile strategy to improve matrix-filler compatibility was developed through hydrogen-bonded interaction. • The CO 2 -philic COF fillers and defect-less interface provided fast channels for CO 2 diffusion. • The MMMs exhibited superior CO 2 permeability and CO 2 /N 2 and CO 2 /CH 4 selectivity than the β-ketoenamine-free counterparts. [ABSTRACT FROM AUTHOR]

High-performance polymer membranes with well-defined microporosity and size-sieving ability are especially attractive for helium and hydrogen recovery. Here we report novel macromolecular engineering of polybenzimidazole (PBI) membranes that integrate hierarchical triptycene units for high permeability and polyprotic acid doping for size sieving via controllable manipulation of microporous architecture. The triptycene moieties disrupt chain packing and introduce additional configurational free volume, leading to significantly boosted He and H 2 permeabilities compared to previously reported PBI membranes. The acid doping resulted in crosslinked PBI membranes via hydrogen bonding and proton transfer with dramatically enhanced gas selectivities. Via adjusting the H 3 PO 4 -doping level, triptycene-based polybenzimidazole (TPBI) composite membranes (TPBI-(H 3 PO 4) x) exhibit the highest gas selectivities for He enrichment (i.e., α (He/CH 4) = 7052 ± 156) and H 2 purification (i.e., α (H 2 /CH 4) = 5128 ± 110) among existing polymeric gas separation membranes. Additionally, under mixed-gas conditions at 150 °C, the TPBI-(H 3 PO 4) 0.98 membrane displays a H 2 permeability of 46.7 Barrer and a H 2 /CO 2 selectivity of 16, far beyond the Robeson's 2008 upper bound for H 2 /CO 2 separation. The facile and diverse tunability and excellent gas separation performance make TPBI-(H 3 PO 4) x membranes highly attractive for helium and hydrogen separation. Scheme demonstrating novel macromolecular engineering of polybenzimidazole (PBI) membranes via controllable manipulation of microporous architecture. Hierarchical triptycene moieties disrupt chain packing and introduce additional configurational free volumes for high permeability. Phosphoric acid doping enhances molecule sieving via hydrogen bonding and proton transfer. [Display omitted] • Novel triptycene-based polybenzimidazole was fabricated for gas separation membranes. • H 3 PO 4 doping enhanced size-sieving ability for hydrogen and helium separations. • TPBI-(H 3 PO 4) x membranes displayed extraordinary gas separation performance far beyond Robeson upper bounds. • TPBI and TPBI-(H 3 PO4) 0.98 membranes exhibited outstanding H 2 /CO 2 separation performance at 150 °C. [ABSTRACT FROM AUTHOR]

This paper reports comprehensive characterization and detailed analyses of microporous structure and fundamental gas transport properties for a series of new pentiptycene-containing polyimide gas separation membranes prepared from custom-synthesized pentiptycene-based diamines and 4,4′-hexafluoroisopropylidene bisphthalic dianhydride (6FDA) to identify the molecular origins for fast and selective gas transport. Both experimental characterizations of inter-chain spacing and microporosity and molecular modeling analysis of chain conformations and rigidity suggested that rigid H-shape pentiptycene units effectively disrupted chain packing, resulting in large fractional free volume and consequent high gas permeabilities in these membranes. Atomic-level detection of free volume architecture by positron annihilation lifetime spectroscopy (PALS) analysis revealed a bimodal microcavity size distribution with cavity sizes of d 4 ~7–8 Å and d 3 ~3–4 Å in this series of membranes. The microcavity size and size distribution were found to be sensitively affected by the substituent groups in the pentiptycene monomer structure based on the mechanism of “partial filling” of internal molecular cavities defined by the shape of pentiptycene units. Analysis of fundamental gas transport properties in terms of diffusivity ( D ) and solubility ( S ) coefficients demonstrated that size sieving mechanism (diffusivity contribution) dominates the gas transport in these polymers and bimodal microcavity size distribution with ultrafine microporosity is responsible for the excellent H 2 -related gas separation performance. Superior resistance against physical aging was observed for these high-free-volume polymers, which is ascribed to the stable, configuration-induced microcavity structure constructed by the rigid pentiptycene units. [ABSTRACT FROM AUTHOR]

Polyoxyethylene (POE) exhibits great potential for selective CO 2 permeation and is tethered onto poly(methyl methacrylate) (PMMA) or poly(styrene- r -acrylonitrile) (PSt- r -PAN) by atom transfer radical polymerization (ATRP) of POE methacrylate (POEM) to endow preferential CO 2 permeability. The polymer backbones are first prepared from corresponding monomers and 4-(chloromethyl)styrene (Cl-St) with various mixture ratios by free radical polymerization. The POE grafting is then carried out by chain propagation of POEM from the Cl-St moiety by ATRP. The introduction of Cl-St to a polymer backbone is readily controlled when the monomer ratio was less than 2 mol%, and thus the average distance of POE graft chains can be tuned along the polymer backbone. ATRP also defines the length of the POE graft chains. CO 2 separation properties over N 2 of the well-defined hyper-branched polymers are investigated by comparing permeability of CO 2 and N 2 pure gases. The gas permeabilities increase with increase of POE content, and the resulting CO 2 /N 2 selectivity is also enhanced in comparison to the pristine polymers and 35 and 40 for PMMA-based and PSt- r -PAN-based hyper-branched copolymers, respectively. Higher POE content indeed gives higher diffusion coefficient for both of CO 2 and N 2 , but the CO 2 and N 2 diffusivities are almost the same. Thus the gas permeation progresses under solubility control. The CO 2 permeability is 135 Barrer with the CO 2 /N 2 selectivity 42, when the POE content is 76 wt% of PSt- r -PAN-based hyper-branched copolymer. [ABSTRACT FROM AUTHOR]

Thermally induced chemical crosslinking has attracted substantial attention for fabricating plasticization resistant membranes due to the facile structure tunability that enables the construction of robust and well-defined architecture for gas separation. In this study, we report a new series of dual thermally crosslinkable polyimides derived from 4,4′-diamino-2,2′-biphenyldicarboxylic acid (DCB) containing two carboxyl groups, and a systematic investigation of the thermal treatment above and below T g demonstrated the decarboxylation-induced crosslinking. The dual thermally crosslinked membranes were insoluble in common organic solvents and maintained excellent mechanical properties. Due to the evolution of CO 2 and collapse of chain segments during thermal treatment, the crosslinked membranes exhibited hierarchical microcavity size distribution featuring ultra-micropore size in the range of 2.0–6.0 Å and micropore size in the range of 6.5–10.0 Å. Gas transport properties of the crosslinked membranes were feasibly tuned through the chemical compositions and thermal treatment procedures. For instance, the CO 2 permeability of crosslinked 6FDA-DAM 0.7 -TFMB 0.1 -DCB 0.2 increased almost three-fold with only a slight decrease in CO 2 /CH 4 selectivity. The crosslinked membranes also demonstrated superior plasticization resistance with mixed-gas feed pressure up to 40 bar and excellent low-temperature gas separation performance at −30 °C, making them attractive for aggressive gas separations. [Display omitted] • Dual thermal crosslinking provides additional tunability toward membrane microporosity and gas separation performance. • Positron annihilation lifetime spectroscopy demonstrates hierarchical microcavity architecture of the crosslinked membranes. • Dual thermal crosslinking improves crosslinking efficiency and boosts the CO 2 permeability increment up to 444%. • Crosslinked membranes show superior anti-plasticization properties and excellent low-temperature gas separation performance. [ABSTRACT FROM AUTHOR]

An environmentally friendly magnesium fuel cell system using seawater electrolyte and atmospheric oxygen was tested under practical considerations for use as maritime power supply. The hydrogen rate and therefore the power density of the system were increased by a factor of two by using hydrogen evolution cathodes with a gas separation membrane instead of submerged cathodes without gas separation. Commercial magnesium AZ31 rolled sheet anodes can be dissolved in seawater for hydrogen production, down to a thickness below 100 μm thickness, resulting in hydrogen generation efficiency of the anode of over 80%. A practical specific energy/energy density of the alloy of more than 1200 Wh/kg/3000 Wh/l was achieved when coupled to a fuel cell with atmospheric air breathing cathode. The performance of several AZ31 alloy anodes was tested as well as the influence of temperature, electrolyte concentration and anode – cathode separation. The excess hydrogen produced by the magnesium hydrogen evolving cell, due to the negative difference effect, is proportional to the cell current in case of the AZ31 alloys, which simplifies system control considerably. Stable long-term operation of the system was demonstrated at low pressures which can be maintained in an open-seawater-submerged hydrogen generator. [ABSTRACT FROM AUTHOR]

A series of new pentiptycene-containing diamines with systematically varied substituent groups were designed and synthesized with high purity and high yields. These diamines were used to prepare a series of new polyimides with 4,4′-hexafluoroisopropylidene bisphthalic dianhydride (6FDA) by conventional condensation polymerization. The obtained pentiptycene-containing polyimides possessed high molecule weights, excellent thermal stability, good solubility in a wide range of organic solvents and thus excellent processability for membrane fabrication. Because of the excess amount of internal free volume associated with the molecular cavities in the pentiptycene moieties and the consequently disrupted chain packing, all the polyimides exhibited high fractional free volume (FFV) leading to high gas permeabilities as well as good selectivities that are highly desired for gas separation membranes. In addition, the comparisons between the pentiptycene-containing polyimides bearing various substituent groups indicated that free volume, the vital structural parameter for fast and selective molecular transport, was very sensitive to the size of the substituent groups. Large substituent groups such as CF 3 led to increased FFV, while relatively small substituent groups such as CH 3 resulted in reduced FFV, possibly due to the mechanism of “partial filling” of the molecular cavities of pentiptycene units by the substituent groups. Gas permeability data also supported this unusual trend of the dependence of free volume on the substituent groups. This finding provides a completely new and potentially novel means of molecular-level manipulations to predictably construct preferred free volume architecture that may maximize the separation performance of polymeric membranes. [ABSTRACT FROM AUTHOR]

Carbon molecular sieve (CMS) membrane with high CO 2 separation performance were fabricated by pyrolysis of a novel hydroxyl-containing polyetherimide (BAHPPF-6FDA type HPEI) precursor. The thermal reactive ortho-OH group in HPEI resulted in the structural conversion when thermal treated at 450 °C, which simultaneously improved the chain rigidity and FFV of the precursor membrane. The structural evolution from HPEI precursor to intermediate polymer till CMS membrane was detected via TGA-MS, Py-GC/MS, FT-IR and WAXD. The pore structure, CO 2 separation performance and aging behavior of CMS membranes were characterized and analyzed by physisorption and gas permeation measurements. Results indicated that the structural properties of the intermediate TR-polymers, which depend on the thermal treatment protocol, have an obvious influence on the CMS membrane performance. Increased thermal soak time of HPEI at 450 °C leads to the increased chain rigidity and FFV, resulting in a more open pore structure and higher CO 2 permeability of derived CMS membranes. In addition, the prolonged soak time at 450 °C or increased pyrolysis temperature would result in the shrinkage of pore structure in CMS membranes and the enhanced molecular sieving performance. The high permeation CMS membrane prepared at the optimal thermal treatment protocol shows good performance stability under the mixed gas (50:50 mixture of CO 2 /N 2 or CO 2 /CH 4) feeds. The relative high CO 2 permeability of about 10000 Barrer and CO 2 /N 2 (or CH 4) selectivity over 30 were obtained after 60 days aging under vacuum, which exhibits a good potential for CO 2 separation application. [Display omitted] • A novel HPEI precursor was synthesized and employed to prepare the CMS membranes for CO 2 separations. • The structural evolution from HPEI to intermediate TR-polymer till CMS was detailed analyzed. • The effects of structural properties of the intermediate TR-polymers on the CMS membrane performance were investigated. • The CMS membrane shows high CO 2 separation performance under the mixed gas feeds after 60 days aging. [ABSTRACT FROM AUTHOR]

Gas separation membranes, considered among one of the promising emerging capture technologies for post-combustion capture, requires a two-stage process with significant compression work for CO 2 capture from a coal fired power plant flue gas. A hybrid membrane–liquefaction process for post-combustion CO 2 capture from the power plant flue gas is developed to mitigate the deficiencies of the two-stage membrane process. The energy efficiency of the process depends on the permeate CO 2 composition from the membrane unit. The performance envelope of the hybrid process is evaluated and shows that the optimum CO 2 concentration in the permeate is 65%– 67% depending on the targeted CCR. A techno-economic analysis for 85% CCR was performed and the cost of CO 2 avoided is calculated to 48 €2008/tCO 2 ,avoided, that is, 9% more cost-efficient than the baseline MEA absorption process. [ABSTRACT FROM AUTHOR]