CO2 Permeability Coefficients Research Articles

Preparation of Pebax based ternary mixed matrix membranes for enhancing CO2 transport and separation

As a type of material for membrane separation in carbon capture technology, mixed matrix membranes (MMMs) have the advantages of simple processing and excellent gas separation performance and have great research prospects. However, the affinity between organic matrix and inorganic fillers is usually poor, and microphase separation occurs at the interface. At the same time, as the filler content increases, the filler particles will aggregate, leading to non-selective defects in the homogeneous membrane and reducing the gas separation performance of MMMs. Herein, the strategy of adding a third component was adopted. Small molecule polyethylene glycol dimethyl ether (PEGDME) was introduced into the Pebax/NH2-MIL-101 membrane to prepare a ternary mixed matrix membrane Pebax/PEGDME/NH2-MIL-101. Adding small molecules as the third component optimized the membrane structure by utilizing the interaction between the third component, inorganic fillers, and polymer matrix, effectively improving the physical microenvironment of gas separation. At the same time, NH2-MIL-101 was modified to PEI-MIL-101, further improving the performance of the mixed matrix membrane. The CO2 permeability of the Pebax/PEGDME/NH2-MIL-101 ternary mixed matrix membrane reached 313 Barrer, and the CO2/N2 selectivity reached 47.7. The CO2 permeability coefficient of Pebax/PEGDME/PEI-MIL-101 membrane reached 286 Barrer, and the CO2/N2 selectivity coefficient reached 54.2. This work provides new ideas for optimizing the gas separation performance of mixed matrix membranes.

Preparation of biodegradable poly(lactic acid)/poly[(butylene diglycolate)‐co‐furandicarboxylate] blends with excellent toughness and gas barrier performance

AbstractPoly(lactic acid) (PLA) is known as one of the most promising biodegradable polyesters, while inherent brittleness and insufficient gas barrier performance limit its potential application as a film material. Herein, poly[(butylene diglycolate)‐co‐furandicarboxylate] (PBDF) with excellent flexibility and good gas barrier properties was synthesized and then melt‐blended with PLA. Compared with neat PLA, the elongation at break of the PLA/PBDF20 blend increased more than 40 times and reached over 176.7%. In addition, its O2, CO2 and H2O permeability coefficients decreased by 21.3%, 50.8% and 46.3%, respectively. Moreover, the PLA/PBDF20 blend also exhibited better biodegradability, with a weight loss rate increasing from 2.7% of neat PLA to 19.0% after 5 weeks of composting. Notably, incorporation of a multifunctional epoxy compatibilizer (Joncryl ADR®‐4368) into the PLA/PBDF blends further enhanced their toughness and gas barrier performance, which could be attributed to the improvement of the miscibility between PLA and PBDF. © 2024 Society of Chemical Industry.

Investigating temperature-dependent gas permeation in PIM-1: Hysteresis, annealing effects, and thermal history impact

This study investigates the gas permeability, diffusion coefficients, and solubility coefficients of CO2 and N2 in PIM-1 over the temperature range of 35 °C–135 °C. During the first heating-cooling cycle, both gases' permeability exhibited hysteresis, which diminished during the second cycle. Thermal mechanical analysis confirmed volume relaxation occurring at temperatures above 95 °C, indicating physical aging. By calculating the relaxation time associated with volume relaxation, the influence of physical aging was minimized through measurements on samples annealed at 135 °C for 15 h. This approach enabled a successful evaluation of the temperature dependence of gas permeability under conditions where the impact of physical aging could be disregarded. The results revealed that the permeability of CO2 decreased, and that of N2 increased with increasing temperature. The diffusion coefficients showed positive temperature dependence, while the solubility coefficients decreased. Physical aging significantly affected the diffusion coefficients but had minimal impact on the solubility coefficients. Heat of sorption and activation energies for gas permeability and diffusion estimated, and it was found that the decrease in CO2 permeability with temperature was mainly attributed to the large heat of sorption for CO2.

Synergistic effect of combining UiO-66 nanoparticles and MXene nanosheets in Pebax mixed-matrix membranes for CO2 capture

The use of membrane-based gas separation has garnered significant interest owing to its cost-effectiveness, outstanding performance and positive environmental impact. The performance of gas separation membranes can be considerably enhanced by mixed-matrix membranes (MMMs), but poor interactions between additives and membrane matrix and the agglomeration of highly incorporated fillers in MMMs limit the benefits of overcoming tradeoff effect. Therefore, the regulation of the state of fillers in membrane matrix is a crucial indicator in the development of MMMs. In this study, MXene (Ti3C2Tx) nanosheets and UiO-66 nanoparticles were prepared and used as fillers, in combination with a Pepax-1657 matrix, to synthesize MMMs for CO2-gas separation. As-prepared MMMs were used for the separation; the large pores (0.5–0.6 nm) of UiO-66 served as a highway to enhance CO2 permeability, and MXene nanosheets were used as selective channels to achieve high selectivity via the terminal polar surface groups of MXene. The combination of UiO-66 and MXene not only enhanced the selectivity, but also increased the solubility and diffusivity via selective CO2 adsorption and the tortuous pathway provided by MXene nanosheets. As a result, adding MXene and UiO-66 to Pebax helped MMMs overcome the tradeoff effect. MMMs loaded with 10 wt% MXene/UiO-66 exhibited a CO2 permeability coefficient of 214.6 Barrer and an ideal CO2/N2 selectivity coefficient of 102. Dual filler-containing MMMs showed enhanced CO2 permeability coefficient and CO2/N2 selectivity in comparison to pristine Pebax and individual nanofiller-added membranes. In this study, the combination of 2D MXene and UiO-66 nanoparticles exerted a synergistic effect in improving the CO2 separation efficiency of MMMs. This research provides a novel route for fabricating high-performance MMMs in the separation of CO2.

Preparation and characterisation of heat‐resistant fluorinated co‐polyimides and their gas transport characteristics

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 Å, 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 co-polyimide membranes exhibited the most attractive separation performance for O2/N2 gas pairs, approaching the 1991 Roberson upper limit.

Towards ductile and high barrier poly(L-lactic acid) ultra-thin packaging film by regulating chain structures for efficient preservation of cherry tomatoes

The irreconcilable paradox between barrier performance and ductility is a “stumbling block” restricting the development of poly(L-lactic acid) (PLLA) films in the packaging industry. In this work, we reported the fabrication of an ultra-thin PLLA-based film with barrier properties and ductility by adjusting the polarity and conformational behavior of the polymer chains. Firstly, a novel unsaturated poly(L-lactic acid-co-butyrate itaconate) P(LA-BI) copolymer containing CC double bonds was synthesized using melt polycondensation. The results reveal that the addition of 60 % of P(LA-BI) enables PLLA film to achieve an elongation at a break of 83.6 % due to P(LA-BI) containing partially branched structures, which resulted in the polymer chains being arranged more in a high-energy gg conformer. Meanwhile, because of the large number of CO polar groups in P(LA-BI), PLLA/P(LA-BI)60 film show CO2 and O2 permeability coefficients (CDP and OP) of 1.8 and 0.45 × 10−8 g·m·m−2·h−1·Pa−1 respectively, which means that it has excellent gas barrier properties. Moreover, PLLA/P(LA-BI)60 film shows a 33.3 % increase in CO2/O2 ratio and an excellent ultraviolet (UV) barrier performance compared to neat PLLA. Preservation results suggested that the CO2 and O2 levels within the package could be regulated by varying the amount of P(LA-BI) added. Among them, PLLA/P(LA-BI)40 film generated a more desirable CO2 and O2 atmosphere for cherry tomatoes preservation, which was reflected by the delaying of senescence, discoloration, and decay, inhibition of oxidative cell damage through reduced malondialdehyde production, and maintenance of nutritional and flavor substances in cherry tomatoes. This PLLA-based film offers the advantages of operational simplicity, environmental friendliness, and inexpensive cost, making it great promising for food preservation and other applications requiring barrier properties and ductility.

Skinless Polyphenylene Sulfide Foam with Enhanced Thermal Insulation Properties Fabricated by Constructing Aligned Gas Barrier Layers for Surface-Constrained sc-CO2 Foaming.

A solid skin layer inevitably forms on the foam surface for supercritical carbon dioxide (sc-CO2) foaming technology, leading to deterioration of some inherent properties of polymeric foams. In this work, skinless polyphenylene sulfide (PPS) foam was fabricated with a surface-constrained sc-CO2 foaming method by innovatively constructing aligned epoxy resin/ferromagnetic graphene oxide composites (EP/GO@Fe3O4) as a CO2 barrier layer under a magnetic field. Introduction of GO@Fe3O4 and its ordered alignment led to an obvious decrease in the CO2 permeability coefficient of the barrier layer, a significant increase of the CO2 concentration in the PPS matrix, and a decrease of desorption diffusivity in the depressurization stage, suggesting that the composite layers effectively inhibited the escape of CO2 dissolved in the matrix. Meanwhile, the strong interfacial interaction between the composite layer and the PPS matrix remarkably enhanced the heterogeneous nucleation of cells at the interface, resulting in elimination of the solid skin layer and formation of an obvious cellular structure on the foam surface. Moreover, by the alignment of GO@Fe3O4 in EP, the CO2 permeability coefficient of the barrier layer became much lower, and the cell density on the foam surface further increased with decreasing cell size, which was even higher than that of the cross section of foam, attributed to stronger heterogeneous nucleation at the interface than the homogeneous nucleation in the core region of the sample. As a result, the thermal conductivity of the skinless PPS foam reached as low as 0.0365 W/m·k, decreasing by 49.5% compared with that of regular PPS foam, showing a remarkable improvement in the thermal insulation properties of PPS foam. This work provided a novel and effective method for fabricating skinless PPS foam with enhanced thermal insulation properties.

The Influence of Low-Temperature Plasma on the Structure of Surface Layers and Gas-Separating Properties of Polyvinyltrimethylsilane Membranes

New results of one-sided surface modification of polymeric films and composite membranes of polyvinyltrimethylsilane (PVTMS) using low-temperature plasma are presented. The treatment was carried out by direct current discharge at the cathode and anode, air was used as the working gas, the exposure time was from 10 to 60 s, and the working pressure in the chamber was 15–20 Pa. The structure of the surface layers was analyzed by XPS, AFM and SEM, and the contact properties of the surface were also studied. The effective permeability coefficients for O2, N2, CH4, CO2, He, and H2, as well as for gas diffusion, for cathode-treated PVTMS films are experimentally obtained, and the effective gas solubility coefficients are calculated. The permeability coefficients of the studied gases for composite membranes with a selective PVTMS layer modified at the cathode and anode were determined. It has been noted that the choice of electrode significantly affects not only the chemical structure of the surface and near-surface layers of PVTMS, but also the gas transport parameters of the modified samples. At the same time, during the treatment of PVTMS films at the cathode for 30 s, it was possible to achieve an increase in the O2/N2 selectivity by more than two times relative to the initial value. It has been established that the results of modification of composite membranes differ from those obtained for homogeneous films and it was possible to achieve O2/N2 selectivity in 2.5 times higher than the initial value. The potential of using surface modification of polymer films and membranes by low-temperature plasma to improve their gas separation properties is shown.

Modified CARDO-Based Copolyimides with Improved Sour Mixed-Gas Permeation Properties

Chemical modification is an interesting tool to introduce functional groups into polymers’ backbones to tailor their properties in a desired fashion. Polymers used in membrane-based gas separation applications need to possess high gas permeability and selectivity during mixed-gas separation under harsh operational conditions of pressure and temperature. Herein, we report the modification of three copolyimides containing the moiety 9,9-bis(4-aminophenyl)fluorine (CARDO) through Friedel–Crafts alkylation to introduce bulky tert-butyl groups into their backbones. Membranes prepared from the modified polymers were evaluated using pure- and sweet mixed-gas under aggressive feed pressures. Based on the promising results obtained, a selected copolyimide was subjected to sour mixed-gas separation under feed pressures up to 500 psi. Mixed-gas separation studies, especially those containing hydrogen sulfide, are of great interest to develop membranes for use in sour natural gas reserve treatment. For example, the H2S and CO2 permeability coefficients of 6FDA-Durene/6FDA-CARDO(t-Bu) at 500 psi were recorded as 456 and 238 Barrer, respectively, where the H2S/CH4 and CO2/CH4 are 20.4 and 10.6, respectively. The obtained results are very promising and even superior to many glassy polymers reported previously. This work represents an example of the benefit of chemical modification on polymers to tailor their structure–property relationship. Future works will be focused on the fabrication and testing of asymmetric or composite hollow fibers to imitate the membrane modules used industrially.

Mixed-Matrix Membranes Based on Polyetherimide, Metal-Organic Framework and Ionic Liquid: Influence of the Composition and Morphology on Gas Transport Properties.

In this work, membranes based on polyetherimide (PEI), a ZIF-8 metal–organic framework and 1-ethyl-methylimidazolium tetrafluoroborate ionic liquid (IL) were prepared. IL and ZIF-8 contents amounting to 7 wt% and 25 wt%, respectively, were investigated. CO2, He and H2 transport properties of PEI/IL/ZIF-8 membranes were compared to those obtained for the respective PEI/ZIF-8 and PEI/IL systems. Membranes’ gas permeability and selectivity are discussed as a function of the membrane composition and morphology, and they were assessed in relation to existing experimental and theoretical data from the literature. Promising gas transport properties were obtained using the appropriate combination of ZIF-8 and IL amounts in the PEI matrix. Indeed, an increase in the CO2 permeability coefficient by a factor of around 7.5 and the He and H2 permeability coefficients by a factor of around 4 was achieved by adding 7 wt% IL and 10 wt% ZIF-8 to the PEI matrix. Moreover, diffusion was evidenced as a governing factor in the studied membrane series.

Synthesis and Gas Separation Properties of Aromatic Polyimides Containing Noncoplanar Rigid Sites

Four aromatic polyimides were prepared using a conventional two-stage polymerization reaction of diamine monomers containing different noncoplanar rigid sites with commercially available dianhydride 6FDA. All polymers displayed high relative molecular masses, excellent solubilities, and outstanding thermal properties with Tg values higher than 260 °C, which ensured that they were able to be casted as dense films for gas permeation measurement. The comprehensive gas transport properties of four prepared polyimides were higher than conventional aromatic polyimides (e.g., Matrimid 5218 and Kapton), which suggested that the incorporation of the noncoplanar rigid groups into the polymer main chain was beneficial to prevent segment packing as well as to enhance the gas separation properties. The pure CO2 permeability coefficient of the spirobichroman-based polyimide (6FDA-BDA) was 2.9 times as high as that of Matrimid 5218, without sacrificing selectivity. Moreover, the effect of different noncoplanar rigid sites on the gas separation performance of aromatic polyimides was systematically investigated. By measurements of FFV, density, and d-spacing, it has been observed that the incorporation of different noncoplanar rigid sites significantly affected the microstructure, thus affecting the gas transport. For example, because the polyimide containing pendent phenyl groups (6FDA-BDM) had the lowest FFV and the densest segment packing, it exhibited the lowest permeability. Hence, the basic insights to the structure/property relationships of the four polyimides obtained in this work offer a meaningful guide for next-generation gas separation membranes.

Highly Selective Benzimidazole-Based Polyimide/Ionic Polyimide Membranes for Pure- and Mixed-Gas CO2/CH4 Separation

This paper reports two new series of benzimidazole functionalized polyimides and ionic polyimides for highly selective membranes with great potential for natural gas sweetening. It has been demonstrated that both the –NH groups in the benzimidazole moieties and the corresponding ionic groups after N-quaternization tighten the microporous structure and restrict polymer chain mobility through hydrogen bonding and electrostatic interaction. The BET surface areas and d-spacing values decrease with benzimidazole molar content or the degree of ionization. Consequently, a linear correlation between CO2 permeability coefficients with benzimidazole molar content or degree of ionization was observed due to the decrease of CO2 diffusivity, and the monotonic increase of CO2/CH4 selectivities is ascribed to the increase of both diffusivity selectivity and solubility selectivity. The benzimidazole-based copolyimide and the ionic copolyimide membranes exhibited high CO2/CH4 selectivity under high-pressure mixed-gas conditions. In particular, the copolyimide PI-0.75 membrane displayed a mixed-gas CO2 permeability of 27 Barrer and CO2/CH4 selectivity of 47 at 20 bar total pressure. The performance was much higher than those of the state-of-the-art commercial cellulose triacetate membranes for natural gas upgrading. The facile polymer synthesis and microporosity tunability, as well as the excellent mixed-gas separation performance, render the copolyimide membranes in this study promising towards economic membrane-mediated natural gas upgrading.

Novel bionanocomposite of polycaprolactone reinforced with steam-exploded microfibrillated cellulose modified with ZnO

Polycaprolactone (PCL) bionanocomposites reinforced with microfibrillated cellulose (MFC), either plain or modified with 2 wt% of zinc oxide (ZnO) nanoparticles, were first time developed for possible application as multifunctional packing. The MFC was obtained by an alkali treatment, a steam explosion process, and ZnO modification applied to parchment (PAR), a husk waste from the coffee industry. X-ray diffraction (XDR), thermogravimetric analysis (TGA/DTG), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), tensile tests, and CO2 permeability characterized the MFCs and the bionanocomposites. As for the MCFs, the crystallinity index of 50.6% measured by XRD for the plain PAR fiber increases with the combined alkaline treatment and steam explosion (CFA/EXP) to 68.2%, and further with ZnO modification (ZnO-CFA/EXP) to 80.1%. TGA/DTG displays a rising onset of thermal degradation from 214 to 306 °C, as well as maximum degradation rate from 330 to 350 °C, for PAR and ZnO-CFA/EXP, respectively. Regarding the nanocomposites, the addition of 3 wt% of alkali/steam explosion and ZnO-modified CFA/EXP contributes to enhancing thermal stability. Tensile tests disclosed improved mechanical properties of the novel nanocomposites as compared to the PCL matrix. In particular, Young's modulus rose from 88.5 to 169.5 MPa for the plain PCL and PCL reinforced with 3(ZnO-CFA/EXP), respectively. SEM images evidenced the participation of cellulose micro and nanofibrils in the PCL matrix. Approximately 20% reduction in the CO2 permeability coefficient of both PCL and its 3CFA/EXP nanocomposite compared with 3(ZnO-CFA/EXP) proved that the ZnO nanoparticles provide a gas barrier to the nanocomposite, a convenient property for food packing.

"All Polyimide" Mixed Matrix Membranes for High Performance Gas Separation.

To improve the interfacial compatibility of mixed matrix membranes (MMMs) for gas separation, microporous polyimide particle (AP) was designed, synthesized, and introduced into intrinsic microporous polyimide matrix (6FDA-Durene) to form “all polyimide” MMMs. The AP fillers showed the feature of thermal stability, similar density with polyimide matrix, high porosity, high fractional free volume, large microporous dimension, and interpenetrating network architecture. As expected, the excellent interfacial compatibility between 6FDA-Durene and AP without obvious agglomeration even at a high AP loading of 10 wt.% was observed. As a result, the CO2 permeability coefficient of MMM with AP loading as low as 5 wt.% reaches up to 1291.13 Barrer, which is 2.58 times that of the pristine 6FDA-Durene membrane without the significant sacrificing of ideal selectivity of CO2/CH4. The improvement of permeability properties is much better than that of the previously reported MMMs, where high filler content is required to achieve a high permeability increase but usually leads to significant agglomeration or phase separation of fillers. It is believed that the excellent interfacial compatibility between the PI fillers and the PI matrix induce the effective utilization of porosity and free volume of AP fillers during gas transport. Thus, a higher diffusion coefficient of MMMs has been observed than that of the pristine PI membrane. Furthermore, the rigid polyimide fillers also result in the excellent anti-plasticization ability for CO2. The MMMs with a 10 wt.% AP loading shows a CO2 plasticization pressure of 300 psi.

Effect of the CO2-philic ionic liquid [BMIM][Tf2N] on the single and mixed gas transport in PolyActive™ membranes

This study reports on the gas transport properties of four different grades of PolyActive™ polyether-co-polyester multi-block copolymer membranes containing different concentrations (4.8, 9.1, 16.7, 23.1 and 28.6 wt%) of the low-viscous CO2-philic ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N]). Single gas permeability, solubility and diffusion coefficients of He, H2, N2, O2, CH4 and CO2 were determined at 1 bar and 25 °C in a constant-volume time lag setup. Mixed gas permeability measurements of CO2/CH4 and CO2/N2 mixtures containing 35 and 15 vol% CO2, respectively, were carried out at 25 °C in the pressure range from 1 to 6 bar(a). The transport properties were correlated with the ionic liquid content of the samples, the specific PolyActive™ grade (i.e. chain length, copolymer composition), and previously determined microstructure, crystallinity, thermal and mechanical properties. For all PolyActive™ grades, the single gas permeability decreased in the order CO2 ≫ H2 > He > O2 ≈ CH4 > N2 and it typically increased with increasing IL content, whereas the ideal selectivity decreased with IL content for most gas pairs. None of the membranes revealed significant dependence on the feed pressure in both single and mixed gas permeation tests. Such behavior is typical for predominantly rubber-like materials. Samples based on PolyActive™ 4000PEOT77PBT23 had the strongest dependence on the IL concentration due to its higher weight fraction and higher crystallinity of the polyether phase.The specific behavior of the four polymers was illustrated via their different trends with increasing IL concentration in the Robeson diagrams. The study demonstrates how blending with ionic liquid can be used to tailor the permeability and selectivity of the membranes. It provides insight into the influence of ionic liquid and the weight percentages of the PEO blocks and the PBT blocks in the copolymers on the individual contributions of the solubility and diffusion coefficients on the permeability.

Gas-Transport Properties of Polyimides with Various Side Groups

Using one-step high-temperature polycyclocondensation organosoluble homo- and copolyimides containing various side groups, such as CF3‒, СOOН‒, Cl‒, and fluorene, and their certain combinations, are synthesized, and their effect on O2, N2, CO2, He, and CH4 permeability coefficients of films is studied. The synthesized polymers with a inherent viscosity of 0.41–0.76 dL/g are characterized by a high heat resistance (230°C ≤ Тg ≤ 380°C) and form strong films (60 MPa ≤ σ ≤ 140 MPa; 0.9 GPa ≤ E ≤ 1.6 GPa). It is shown that depending on the nature of side groups the polyimides under consideration demonstrate different gas-transport behavior. For example, for one of the polymers the selectivity factor for He/CH4 separation is 315 (a He permeability coefficient of 9.5 Barrer), while for another polymer the selectivity factor for CO2/CH4 separation is 34 (at a CO2 permeability coefficient of 37.3 Barrer). For crosslinked polyimide films the selectivity factor for He/CH4 separation attains 125 (at a He permeability coefficient of 19.7 Barrer) and the selectivity factor for CO2/CH4 separation is 43 (at a CO2 permeability coefficient of 7.0 Barrer).

An investigation on structural and gas transport properties of modified cross-linked PEG-PU membranes for CO2 separation

In this paper, modified poly(ethylene glycol)-polyurethane (PEG-PU) membranes were synthesized applying thiol-epoxy click polymerization to separate CO2 (the most important greenhouse gas) form light gases. PEG was initially reacted with isophorone diisocyanate (IPDI) and the NCO-terminated prepolymer was end-capped with glycidol to form epoxy-terminated prepolymer (EPU). The cross-linked membranes were eventually obtained through thiol-epoxy click polymerization reaction using a tetrathiol cross-linker (PETMP) in presence of poly(ethylene glycol) diglycidyl ether (PEGDE). The prepared membranes were characterized by ATR-FTIR, DSC, TGA and tensile analyses. The best fabricated membrane was chosen and named EMT2 which exhibited promising structural, thermal and mechanical properties. It was then employed for further gas transport properties studies. Permeability, solubility, and diffusion coefficients of CO2, N2, CH4, and O2 gases over wide ranges of temperature (308–348 K) and pressure (2–16 bar) were investigated. It was found that EMT2 membrane offers higher CO2 permeability coefficients, compared to some other PEG-PU membranes in the literature fabricated with a same length of soft segment.

Polymer with Intrinsic Microporosity PIM-1: New Methods of Synthesis and Gas Transport Properties

A ladder polymer with the intrinsic microporosity PIM-1 has been synthesized via precipitation polycondensation in dimethylsulfoxide and via polycondensation in N,N,N ',N '-tetramethylurea. The molecular weight characteristics of PIM-1 samples have been determined using gel permeation chromatography method. It has been shown that the synthesized polymers are characterized by a high molecular weight (~90 × 103) and by a bimodal molecular weight distribution; in this case, molecular weights of the high-molecular-weight fraction of polymer with the polydispersion coefficient of 2.1–2.4 are practically independent of the nature of the reaction medium. The weight content of the oligomer fraction in the obtained samples has been estimated from gel permeation chromatograms. Gas permeability coefficients of He, H2, O2, N2, CO2, and CH4 for the initial films of the synthesized polymers and the films treated with ethanol have been measured by the chromatographic method at 22 ± 2°С. It has been shown that, for all samples under investigation, the gas permeability coefficients are higher than for the PIM-1 samples described previously in the literature. In this case, the gas permeability and its increase during treatment with ethanol depend on the content of the low-molecular-weight fraction in the sample.

Fluorinated copolyimide membranes for sour mixed‐gas upgrading

ABSTRACTThree random and two block 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA)‐based copolyimides with different 6FpDA:Durene molar ratio varying from 25 to 80% were prepared and characterized. The pure‐gas permeation data of their membranes were investigated at 100 psi and 22 °C. The CO2/CH4 ideal selectivity coefficient increased to around 47 with the increase of the 6FpDA content to 80% in the copolymer backbone while the CO2 permeability coefficient found to be the highest (378 barrer) with highest Durene content copolymer. Based on its attractive pure‐gas permeation properties(CO2/CH4 = 47), 6FDA‐6FpDA/6FDA‐Durene (4:1) block copolyimide was selected for further analyses, where the effect of pressure and temperature on its gas transport properties was evaluated. Furthermore, the mixed‐gas permeation properties were investigated using multicomponent sweet and sour gas mixtures prepared from N2 (30% or 10%), CH4 (59%), C2H6 (1%), CO2 (10%), and H2S (0% or 20%)accordingly. The sweet mixed‐gas CO2/CH4 selectivity and CO2 permeability coefficients of 6FDA‐6FpDA/6FDA‐Durene (4:1) are around 39 and 45 barrer, respectively, at elevated pressure (800 psi). The polymer, however, showed nonideal behavior when subjected to high H2S‐content gas mixture (20 vol. % H2S), where the CO2/CH4 selectivity value dropped to around 21 and the H2S/CH4 selectivity coefficient is 13. The CO2 and H2S permeability coefficients are 42 and 26 barrer, respectively, at an upstream pressure up to 500 psi. When plotted on the combined acid gas permeability‐selectivity curve, the polymer separation efficiency was nearby the high‐performing polymers reported in the literature, and way superior to the industrial standard glassy polymer, cellulose acetate, used currently in gas separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48336.

Effect of pendent bulky groups on pure- and sour mixed-gas permeation properties of triphenylamine-based polyimides

Three diamine triphenylamine-based monomers, 4,4′-diaminotriphenylamine (TPA), 4,4′-diamino-4″-(dimethylamino)triphenylamine (TPA(NMe2)), and 4,4′-diamino-4″-(tert-butyl)triphenylamine (TPA(t-Bu)) were reproduced in preparation for their 6FDA-based homopolyimides: 6FDA-TPA, 6FDA-TPA(NMe2) and 6FDA-TPA(t-Bu). The bulkiness effect of two pendent groups (dimethylamino and tert-butyl) on the gas transport properties of the polymers was evaluated. Both bulky groups enhanced the fractional free volume (FFV) within the membranes matrices, thereby increasing gas diffusivity, which resulted in greater CO2 permeability of 6FDA-TPA(NMe2) by almost 32% and 6FDA-TPA(t-Bu) by 3 folds compared to their nonfunctionalized analog 6FDA-TPA. Moreover, introducing bulky groups had minimal effect on gas solubility, indicating that separation through these materials is a diffusion-driven process. Afterwards, sweet mixed-gas permeation properties where measured for 6FDA-TPA and 6FDA-TPA(t-Bu) membranes using a multicomponent gas mixture (N2, CH4, C2H6 and CO2) at various feed pressures up to 500 psi and a fixed temperature of 22 °C. Once again, the introduction of the bulky group (t-Bu) resulted in an increase in the mixed-gas CO2 permeability coefficient by 3 folds, while the CO2/CH4 selectivity coefficient dropped by around 33%. Moreover, the sour mixed-gas permeation properties using a high H2S-content multicomponent gas mixture (20 vol% H2S) were measured for 6FDA-TPA and 6FDA-TPA(t-Bu) membranes at feed pressures up to 500 psi and 22 °C. The membranes showed nonideal behavior in the presence of hydrogen sulfide, where both membranes performed similarly and the effect of the bulky group (t-Bu) was negligible.