Gas transport properties of poly(ether‐b‐amide) segmented block copolymers

The permeation properties of H₂, N₂, and CO₂ were determined at 35 °C and pressures up to 15 atm in phase‐separated polyether‐b‐polyamide segmented block copolymers. These polymers contain poly(ethylene oxide) [PEO] or poly(tetramethylene oxide) [PTMEO] as the rubbery polyether phase and nylon‐6 [PA6] or nylon‐12 [PA12] as the hard polyamide phase. Extremely high values of polar (or quadrupolar)/nonpolar gas selectivities, coupled with high CO₂ permeability coefficients, were observed. CO₂/H₂ selectivities as high as 9.8 and CO₂/N₂ selectivities as high as 56 were obtained in polymers with CO₂ permeability coefficients of approximately 220 × 10⁻¹⁰ cm³(STP) cm/(cm² s cmHg). As the amount of polyether increases, permeability increases. Gas permeability is higher in polymers with less polar constituents, PTMEO and PA12, than in those containing the more polar PEO and PA6 units. CO₂/N₂ and CO₂/H₂ selectivities are higher in polymers with higher concentrations of polar groups. These high selectivity values derive from large solubility selectivities in favor of CO₂. Because CO₂ is larger than H₂ and has, therefore, a lower diffusion coefficient than H₂, the weak size‐sieving ability of the rubbery polyether phase, which is the locus of most of the gas permeation, also contributes to high CO₂/H₂ selectivity. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2051–2062, 2000     

Gas sorption and characterization of poly(ether‐b‐amide) segmented block copolymers

The solubilities of He, H₂, N₂, O₂, CO₂, CH₄, C₂H₆, C₃H₈, and n‐C₄H₁₀ were determined at 35°C and pressures up to 27 atmospheres in a systematic series of phase separated polyether–polyamide segmented block copolymers containing either poly(ethylene oxide) [PEO] or poly(tetramethylene oxide) [PTMEO] as the rubbery polyether phase and nylon 6 [PA6] or nylon 12 [PA12] as the hard polyamide phase. Sorption isotherms are linear for the least soluble gases (He, H₂, N₂, O₂, and CH₄), convex to the pressure axis for more soluble penetrants (CO₂, C₃H₈, and n‐C₄H₁₀) and slightly concave to the pressure axis for ethane. These polymers exhibit high CO₂/N₂ and CO₂/H₂ solubility selectivity. This property appears to derive mainly from high carbon dioxide solubility, which is ascribed to the strong affinity of the polar ether linkages for CO₂. As the amount of the polyether phase in the copolymers increases, gas solubility increases. The solubility of all gases is higher in polymers with less polar constituents, PTMEO and PA12, than in polymers with more polar PEO and PA6 units. CO₂/N₂ and CO₂/H₂ solubility selectivity, however, are higher in polymers with higher concentrations of polar repeat units. The sorption data are complemented with physical characterization (differential scanning calorimetry, elemental analysis, and wide angle X‐ray diffraction) of the various block copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2463–2475, 1999     

Synthesis, characterization, and gas permeation properties of 6FDA-2,6-DAT/mPDA copolyimides

The goal of this work is to explore new polyimide materials that exhibit both high permeability and high selectivity for specific gases. Copolyimides offer the possibility of preparing membranes with gas permeabilities and selectivities not obtainable with homopolyimides. A series of novel fluorinated copolyimides were synthesized with various diamine compositions by chemical imidization in a two-pot procedure. Polyamic acids were prepared by stoichiometric addition of solid dianhydride in portions to the diamine(s). The gas permeation behavior of 2,2′-bis(3,4′-dicarboxyphenyl) hexafluoropropane dianhydride(6FDA)-2,6-diamine toluene (2,6-DAT)/1,3-phenylenediamine (mPDA) polyimides was investigated. The physical properties of the copolyimides were characterized by IR, DSC and TGA. The glass transition temperature increased with increase in 2,6-DAT content. All the copolyimides were soluble in most of the common solvents. The gas permeability coefficients decreased with increasing mPDA content. However, the permselectivity of gas pairs such as H₂/N₂, O₂/N₂, and CO₂/CH₄ was enhanced with the incorporation of mPDA moiety. The permeability coefficients of H₂, O₂, N₂, CO₂ and CH₄ were found to decrease with the increasing order of kinetic diameters of the penetrant gases. 6FDA-2,6-DAT/mPDA (3:1) copolyimide and 6FDA-2,6-DAT polyimide had high separation properties for H₂/N₂, O₂/N₂, CO₂/CH₄. Their H₂, O₂ and CO₂ permeability coefficients were 64.99 Barrer, 5.22 Barrer, 23.87 Barrer and 81.96 Barrer, 8.83 Barrer, 39.59 Barrer, respectively, at 35°C and 0.2 MPa (1 Barrer = 10⁻¹⁰ cm³ (STP)·cm·cm⁻²·s⁻¹·cmHg⁻¹) and their ideal permselectivities of H₂/N₂, O₂/N₂ and CO₂/CH₄ were 69.61, 6.09, 63.92 and 53.45, 5.76, 57.41, respectively. Moreover, all of the copolyimides studied in this work exhibited similar performance, lying on or above the existing upper bound trade-off lines between permselectivity and permeability. They may be utilized for commercial gas separation membrane materials. __________ Translated from Acta Polymerica Sinica, 2008, 8 (in Chinese)     

Mixed Metal–Organic Framework with Multiple Binding Sites for Efficient C2H2/CO2 Separation

The separation of C₂H₂/CO₂ is particularly challenging owing to their similarities in physical properties and molecular sizes. Reported here is a mixed metal–organic framework (M′MOF), [Fe(pyz)Ni(CN)₄] ( FeNi‐M′MOF , pyz=pyrazine), with multiple functional sites and compact one‐dimensional channels of about 4.0 Å for C₂H₂/CO₂ separation. This MOF shows not only a remarkable volumetric C₂H₂ uptake of 133 cm³ cm^?3, but also an excellent C₂H₂/CO₂ selectivity of 24 under ambient conditions, resulting in the second highest C₂H₂‐capture amount of 4.54 mol L^?1, thus outperforming most previous benchmark materials. The separation performance of this material is driven by π–π stacking and multiple intermolecular interactions between C₂H₂ molecules and the binding sites of FeNi‐M′MOF . This material can be facilely synthesized at room temperature and is water stable, highlighting FeNi‐M′MOF as a promising material for C₂H₂/CO₂ separation.     

Mixed Metal–Organic Framework with Multiple Binding Sites for Efficient C2H2/CO2 Separation

The separation of C₂H₂/CO₂ is particularly challenging owing to their similarities in physical properties and molecular sizes. Reported here is a mixed metal–organic framework (M′MOF), [Fe(pyz)Ni(CN)₄] ( FeNi-M′MOF , pyz=pyrazine), with multiple functional sites and compact one-dimensional channels of about 4.0 Å for C₂H₂/CO₂ separation. This MOF shows not only a remarkable volumetric C₂H₂ uptake of 133 cm³ cm⁻³, but also an excellent C₂H₂/CO₂ selectivity of 24 under ambient conditions, resulting in the second highest C₂H₂-capture amount of 4.54 mol L⁻¹, thus outperforming most previous benchmark materials. The separation performance of this material is driven by π–π stacking and multiple intermolecular interactions between C₂H₂ molecules and the binding sites of FeNi-M′MOF . This material can be facilely synthesized at room temperature and is water stable, highlighting FeNi-M′MOF as a promising material for C₂H₂/CO₂ separation.     

Continuous Porous Aromatic Framework Membranes with Modifiable Sites for Optimized Gas Separation

Continuous microporous membranes are widely studied for gas separation, due to their low energy premium and strong molecular specificity. Porous aromatic frameworks (PAFs) with their exceptional stability and structural flexibility are suited to a wide range of separations. Main-stream PAF-based membranes are usually prepared with polymeric matrices, but their discrete entities and boundary defects weaken their selectivity and permeability. The synthesis of continuous PAF membranes is still a major challenge because PAFs are insoluble. Herein, we successfully synthesized a continuous PAF membrane for gas separation. Both pore size and chemistry of the PAF membrane were modified by ion-exchange, resulting in good selectivity and permeance for the gas mixtures H₂/N₂ and CO₂/N₂. The membrane with Br^? as a counter ion in the framework exhibited a H₂/N₂ selectivity of 72.7 with a H₂ permeance of 51844 gas permeation units (GPU). When the counter ions were replaced by BF₄^?, the membrane showed a CO₂ permeance of 23058 GPU, and an optimized CO₂/N₂ selectivity of 60.0. Our results show that continuous PAF membranes with modifiable pores are promising for various gas separation situations.     

Overcoming the Trade-Off between C2H2 Sorption and Separation Performance by Regulating Metal-Alkyne Chemical Interaction in Metal-Organic Frameworks

Designing porous materials for C₂H₂ purification and safe storage is essential research for industrial utilization. We emphatically regulate the metal-alkyne interaction of Pd^II and Pt^II on C₂H₂ sorption and C₂H₂/CO₂ separation in two isostructural NbO metal–organic frameworks (MOFs), Pd/Cu-PDA and Pt/Cu-PDA . The experimental investigations and systematic theoretical calculations reveal that Pd^II in Pd/Cu-PDA undergoes spontaneous chemical reaction with C₂H₂, leading to irreversible structural collapse and loss of C₂H₂/CO₂ sorption and separation. Contrarily, Pt^II in Pt/Cu-PDA shows strong di-σ bond interaction with C₂H₂ to form specific π-complexation, contributing to high C₂H₂ capture (28.7 cm³ g⁻¹ at 0.01 bar and 153 cm³ g⁻¹ at 1 bar). The reusable Pt/Cu-PDA efficiently separates C₂H₂ from C₂H₂/CO₂ mixtures with satisfying selectivity and C₂H₂ capacity (37 min g⁻¹). This research provides valuable insight into designing high-performance MOFs for gas sorption and separation.     

High‐Performance Polymers for Membrane CO2/N2 Separation

This Concept examines strategies to design advanced polymers with high CO₂ permeability and high CO₂/N₂ selectivity, which are the key to the success of membrane technology for CO₂ capture from fossil fuel‐fired power plants. Specifically, polymers with enhanced CO₂ solubility and thus CO₂/N₂ selectivity are designed by incorporating CO₂‐philic groups in polymers such as poly(ethylene oxide)‐containing polymers and poly(ionic liquids); polymers with enhanced CO₂ diffusivity and thus CO₂ permeability are designed with contorted rigid polymer chains to obtain high free volume, such as polymers with intrinsic microporosity and thermally rearranged polymers. The underlying rationales for materials design are discussed and polymers with promising CO₂/N₂ separation properties for CO₂ capture from flue gas are highlighted.     

Synthesis,characterization, and gas permeation properties of adamantane‐containing polymers of intrinsic microporosity

A new bis(catechol) monomer, namely, 4,4′‐((1r,3r)‐adamantane‐2,2‐diyl)bis(benzene‐1,2diol) (THADM) was synthesized by condensation of 2‐adamantanone with veratrole followed by demethylation of the formed (1r,3r)‐2,2‐bis(3,4 dimethoxyphenyl)adamantane. Polycondensation of THADM and various compositions of THADM and 5,5,6′,6′‐tetrahydroxy‐3,3,3′,3′‐tetramethylspirobisindane was performed with 2,3,5,6‐tetrafluoroterephthalonitrile (TFTPN) to obtain the homopolymer and copolymers. These polymers demonstrated good solubility in common organic solvents such as dichloromethane, chloroform, and tetrahydrofuran and could be cast into tough films from their chloroform solutions. GPC analysis revealed that number average molecular weights of polymers were in the range 48,100–61,700 g mol⁻¹, suggesting the formation of reasonably high molecular weight polymers. They possessed intrinsic microporosity with Brunauer‐Emmett‐Teller (BET) surface area in the range 703–741 m² g⁻¹. Thermogravimetric analysis of polymers indicated that 10% weight loss temperature was in the range 513–518 °C demonstrating their excellent thermal stability. THADM‐based polymer of intrinsic microporosity (PIM) showed P(CO₂) = 1080, P(O₂) = 232 and appreciable selectivity [α(CO₂/CH₄) = 22.6, α(CO₂/N₂) = 26.7, and α(O₂/N₂)= 5.7]. The gas permeability measurements revealed that with increase in the content of adamantane units in PIMs, selectivity increased and permeability decreased, following the trade‐off relationship. The gas separation properties of PIMs containing adamantane units were located close to 2008 Robeson upper bound for gas pairs such as CO₂/CH₄, CO₂/N₂, H₂/N₂, and O₂/N₂. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 16–24     

Natural gas permeation in polyimide membranes

Polyimide membranes derived from 6FDA-DAM:DABA and 6FDA-6FpDA:DABA copolymers have been used to separate 50/50 CO₂/CH₄ mixtures and multicomponent synthetic natural gas mixtures at 35 °C and feed pressures up to 55 atm. For 6FDA-DAM:DABA 2:1 membranes the effects of thermal annealing and covalent crosslinking are decoupled with respect to effects on permeabilities and selectivity. Crosslinking at 295 °C with 1,4-butylene glycol and 1,4-cyclohexanedimethanol increases CO₂ permeabilities by factors of 4.1 and 2.4, respectively, at 20 atm feed pressure, without a loss in selectivity, relative to crosslinking at 220 °C. Thermal annealing and crosslinking also reduce CO₂ plasticization effects. Crosslinking of DABA-containing copolymers, therefore, can produce membranes with tunable transport properties that offer significantly higher performance with better plasticization-resistance than that reported in the literature for the commercial polymers Matrimid^® and cellulose acetate for CO₂ removal from natural gas mixtures. Separation of complex mixtures containing CO₂, CH₄, C₂H₆, C₃H₈, and C₄H₁₀ or toluene results in a significant decrease of the CO₂ permeability, but only a moderate decrease in the CO₂/CH₄ selectivity.     

Ultramicroporous Building Units as a Path to Bi‐microporous Metal–Organic Frameworks with High Acetylene Storage and Separation Performance

A strategy called ultramicroporous building unit (UBU) is introduced. It allows the creation of hierarchical bi‐porous features that work in tandem to enhance gas uptake capacity and separation. Smaller pores from UBUs promote selectivity, while larger inter‐UBU packing pores increase uptake capacity. The effectiveness of this UBU strategy is shown with a cobalt MOF (denoted SNNU‐45) in which octahedral cages with 4.5 Å pore size serve as UBUs. The C₂H₂ uptake capacity at 1 atm reaches 193.0 cm³ g^?1 (8.6 mmol g^?1) at 273 K and 134.0 cm³ g^?1 (6.0 mmol g^?1) at 298 K. Such high uptake capacity is accompanied by a high C₂H₂/CO₂ selectivity of up to 8.5 at 298 K. Dynamic breakthrough studies at room temperature and 1 atm show a C₂H₂/CO₂ breakthrough time up to 79 min g^?1, among top‐performing MOFs. Grand canonical Monte Carlo simulations agree that ultrahigh C₂H₂/CO₂ selectivity is mainly from UBU ultramicropores, while packing pores promote C₂H₂ uptake capacity.     

Effect of polyethyleneglycol (PEG) on gas permeabilities and permselectivities in its cellulose acetate (CA) blend membranes

The effect of polyethyleneglycol (PEG) on gas permeabilities and selectivities was investigated in a series of miscible cellulose acetate (CA) blend membranes. The permeabilities of CO₂, H₂, O₂, CH₄, N₂ were measured at temperatures from 30 to 80°C and pressures from 20 to 76 cmHg using a manometric permeation apparatus. It was determined that the blend membrane having 10 wt% PEG20000 exhibited higher permeability for CO₂ and higher permselectivity for CO₂ over N₂ and CH₄ than those of the membranes which contained 10% PEG of the molecular weight in the range 200–6000. The CA blend containing 60 wt% PEG20000 showed that its permeability coefficients of CO₂ and ideal separation factors for CO₂ over N₂ reached above 2 × 10⁻⁸ [cm³ (STP) cm/cm² s cmHg] and 22, respectively, at 70°C and 20 cmHg. Based on the data of gas permeability coefficients, time lags and characterization of the membranes, it is proposed that the apparent solubility coefficients of all CA and PEG blend membranes for CO₂ were lower than those of the CA membrane. However, almost all the blend membranes containing PEG20000 showed higher apparent diffusivity coefficients for CO₂, resulting in higher permeability coefficients of CO₂ with relation to those of the CA membrane. It is attributed to the high diffusivity selectivities of CA and PEG20000 blend membranes that their ideal separation factors for CO₂ over N₂ were higher than those of the CA membrane in the range 50–80°C, even though the ideal separation factors of almost all PEG blend membranes for CO₂ over CH₄ became lower than those of the CA membrane over nearly the full range from 30° to 80°C.     

De-Linker-Enabled Exceptional Volumetric Acetylene Storage Capacity and Benchmark C2H2/C2H4 and C2H2/CO2 Separations in Metal–Organic Frameworks

An ideal adsorbent for separation requires optimizing both storage capacity and selectivity, but maximizing both or achieving a desired balance remain challenging. Herein, a de-linker strategy is proposed to address this issue for metal–organic frameworks (MOFs). Broadly speaking, the de-linker idea targets a class of materials that may be viewed as being intermediate between zeolites and MOFs. Its feasibility is shown here by a series of ultra-microporous MOFs (SNNU-98-M, M=Mn, Co, Ni, Zn). SNNU-98 exhibit high volumetric C₂H₂ uptake capacity under low and ambient pressures (175.3 cm³ cm⁻³ @ 0.1 bar, 222.9 cm³ cm⁻³ @ 1 bar, 298 K), as well as extraordinary selectivity (2405.7 for C₂H₂/C₂H₄, 22.7 for C₂H₂/CO₂). Remarkably, SNNU-98-Mn can efficiently separate C₂H₂ from C₂H₂/CO₂ and C₂H₂/C₂H₄ mixtures with a benchmark C₂H₂/C₂H₄ (1/99) breakthrough time of 2325 min g⁻¹, and produce 99.9999 % C₂H₄ with a productivity up to 64.6 mmol g⁻¹, surpassing values of reported MOF adsorbents.     

Effects of tertiary amines and quaternary ammonium halides in polysulfone on membrane gas separation properties

Polymers containing CO₂‐philic groups are of great interest for CO₂/light gas separation membranes because the affinity toward CO₂ can effectively increase CO₂ solubility and thus permeability. In this study, polysulfones (PSUs) modified with different degrees of benzyldimethylamine (DMA), benzyltrimethylammonium fluoride (TMAF), and benzyltrimethylammonium iodide (TMAI) were synthesized using sequential post‐functionalization reactions and investigated for CO₂/N₂ and CO₂/CH₄ separation. The physical properties of these polymers were studied, including density, fractional free volume, and glass transition temperature. In contrast to the conventional wisdom that tertiary amines exhibit an affinity toward CO₂, this study convincingly shows that the DMA substituent has a minimal impact on CO₂ solubility and CO₂/light gas solubility selectivity in PSUs under dry condition. On the other hand, incorporating TMAF and TMAI in PSU significantly increases CO₂ solubility. Particularly, introducing TMAI with a molar ratio of 1.07 relative to PSU repeating units increases CO₂/CH₄ solubility from 4.4 to 5.2, CO₂/CH₄ permeability selectivity from 21 to 45, and CO₂/N₂ permeability selectivity from 24 to 33 at 35 °C, while the CO₂ permeability decreases from 5.6 to 1.7 Barrers. The effect of these functional groups in PSUs on gas diffusivity and diffusivity selectivity can be satisfactorily described by the free volume model. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1239–1250     

A Microporous Hydrogen Bonded Organic Framework for Highly Selective Separation of Carbon Dioxide over Acetylene

The separation of acetylene (C₂H₂) from carbon dioxide (CO₂) is a very important but challenging task due to their similar molecular dimensions and physical properties. In terms of porous adsorbents for this separation, the CO₂-selective porous materials are superior to the C₂H₂-selective ones because of the cost- and energy-efficiency but have been rarely achieved. Herein we report our unexpected discovery of the first hydrogen bonded organic framework (HOF) constructed from a simple organic linker 2,4,6-tri(1H-pyrazol-4-yl)pyridine (PYTPZ) (termed as HOF-FJU-88) as the highly CO₂-selective porous material. HOF-FJU-88 is a two-dimensional HOFs with a pore pocket of about 7.6 Å. The activated HOF-FJU-88 takes up a high amount of CO₂ (59.6 cm³ g⁻¹) at ambient conditions with the record IAST selectivity of 1894. Its high performance for the CO₂/C₂H₂ separation has been further confirmed through breakthrough experiments, in situ diffuse reflectance infrared spectroscopy and molecular simulations.     

Gas Permeation Properties of Organic-Inorganic Hybrid Membranes Prepared from Hydroxyl-Terminated Polyether and 3-isocyanatopropyltriethoxysilane

Organic-inorganic hybrid materials were prepared by reacting 3-isocyanatopropyltriethoxysilane (IPTS) with hydroxyl terminated poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG) and poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) (PEPG), followed by hydrolysis and condensation with acid catalysis. Composite membranes have been obtained by casting hybrid sol on the microporous polysulfone substrate. The membranes were characterized by Fourier transform infrared (FT-IR), ¹³C NMR and ²⁹Si NMR. The permeability coefficients of N₂, O₂, CH₄ and CO₂ were measured by variable volume method. The gas permeability coefficients increase with increasing molecular weight of the polyethers. For the membranes containing PEG and PEPG, the higher values of CO₂ permeability coefficients and CO₂/N₂ separation factors are due to the presence of ethylene oxide segments. In case of PEPG membranes, molecular weight has more influence on CO₂ permeability than the effect of facilitation by ethylene oxide. The addition of TEOS into hybrid sol results in the decrease of all the gas permeability and does not affect the gas selectivity. PEG2000 membrane display the most performance among the hybrid membranes investigated here. The best values observed are CO₂ permeability of 94.2 Barrer with selectivity of 38.3 for CO₂/N₂ and 15.6 for CO₂/CH₄.     

Preparation and characterization of a composite PDMS membrane on CA support

Polydimethylsiloxane (PDMS) is the most commonly used membrane material for the separation of condensable vapors from lighter gases. In this study, a composite PDMS membrane was prepared and its gas permeation properties were investigated at various upstream pressures. A microporous cellulose acetate (CA) support was initially prepared and characterized. Then, PDMS solution, containing crosslinker and catalyst, was cast over the support. Sorption and permeation of C₃H₈, CO₂, CH₄, and H₂ in the prepared composite membrane were measured. Using sorption and permeation data of gases, diffusion coefficients were calculated based on solution‐diffusion mechanism. Similar to other rubbery membranes, the prepared PDMS membrane advantageously exhibited less resistance to permeation of heavier gases, such as C₃H₈, compared to the lighter ones, such as CO₂, CH₄, and H₂. This result was attributed to the very high solubility of larger gas molecules in the hydrocarbon‐based PDMS membrane in spite of their lower diffusion coefficients relative to smaller molecules. Increasing feed pressure increased permeability, solubility, and diffusion coefficients of the heavier gases while decreased those of the lighter ones. At constant temperature (25°C), empirical linear relations were proposed for permeability, solubility, and diffusion coefficients as a function of transmembrane pressure. C₃H₈/gas solubility, diffusivity, and overall selectivities were found to increase with increasing feed pressure. Ideal selectivity values of 9, 30, and 82 for C₃H₈ over CO₂, CH₄, and H₂, respectively, at an upstream pressure of 8 atm, confirmed the outstanding separation performance of the prepared membrane. Copyright © 2009 John Wiley & Sons, Ltd.     

Molecular Sieving of Acetylene from Ethylene in a Rigid Ultra-microporous Metal Organic Framework.

Rigid molecular sieving materials are the ideal candidates for gas separation (e. g., C₂H₂/C₂H₄) due to their ultrahigh adsorption selectivity and the absence of gas co-adsorption. However, the absolute molecular sieving effect for C₂H₂/C₂H₄ separation has rarely been realized because of their similar physicochemical properties. Herein, we demonstrate the absolute molecular sieving of C₂H₂ from C₂H₄ by a rigid ultra-microporous metal-organic framework ( F−PYMO−Cu ) with 1D regular channels (pore size of ca. 3.4 Å). F−PYMO−Cu exhibited moderate acetylene uptake (35.5 cm³/cm³), but very low ethylene uptake (0.55 cm³/cm³) at 298 K and 1 bar, yielding the second highest C₂H₂/C₂H₄ uptake ratio of 63.6 up to now. One-step C₂H₄ production from a binary mixture of C₂H₂/C₂H₄ and a ternary mixture of C₂H₂/CO₂/C₂H₄ at 298 K was achieved and verified by dynamic breakthrough experiments. Coupled with excellent thermal and water stability, F−PYMO−Cu could be a promising candidate for industrial C₂ separation tasks.     

Structure-permeability relationships in silicone polymers

Permeability coefficients P for He, O₂, N₂, CO₂ CH₄, C₂H₄, C₂H₆, and C₃H₈ in 12 different silicone polymer membranes were determined at 35.0°C and pressures up to 9 atm. Values of P for CO₂, CH₄, and C₃H₈ were also determined at 10.0 and 55.0°C. In addition, mean diffusion coefficients D and solubility coefficients S were obtained for CO₂, CH₄, and C₃H₈ in 6 silicone polymers at 10.0, 35.0, and 55.0°C. Substitution of increasingly bulkier functional groups in the side and backbone chains of silicone polymers results in a significant decrease in P for a given penetrant gas. This is due mainly to a decrease in D , whereas S decreases to a much lesser extent. Backbone substitutions appear to have a somewhat lesser effect in depressing P than equivalent side-chain substitutions. The selectivity of a silicone membrane for a gas A relative to a gas B, i.e., the permeability ratio P (A)/P (B), may increase or decrease as a result of such substitutions, but only if the substituted groups are sufficiently bulky. The selectivity of the more highly permeable silicone membranes is controlled by the ratio S (A)/S (B), whereas the selectivity of the less permeable membranes depends on both the ratios D (A)/D (B) and S(A)/S(B). The permeability as well as the selectivity of one silicone membrane toward CO₂ were significantly enhanced by the substitution of a fluorine-containing side group that increased the solubility of CO₂ in that polymer.     

Thermal treatment of poly(ethylene oxide)-segmented copolyimide based membranes: An effective way to improve the gas separation properties

Copolyimide membranes with different poly(ethylene oxide) (PEO) content (from 28 to 68 wt percent, wt.%) have been thermally treated at different temperatures (from 200 to 300 °C) to evaluate the effect of the thermal protocol on the gas transport properties to O₂, N₂, CO₂ and CH₄. The permeability coefficients (P) for all gases increased after the thermal treatment of the membranes and were related to the PEO content, being this enhancement higher for membranes with lower PEO content. Thermal treatment at 300 °C of the membranes with 28 and 43 wt.% of PEO, yielded more productive materials for CO₂/N₂ separation since the permeability coefficients for CO₂ (PCO₂$P_{\text{C}{\text{O}}_2}$) increased 9.8 and 3.2 times, respectively, while the selectivity just suffered a small drop (less than 1.3 times in both cases). Overall, the membrane with 43 wt.% of PEO exhibited the best performance, with a PCO₂$P_{\text{C}{\text{O}}_2}$ of 78 Barrer and a CO₂/N₂ selectivity of 52. For CO₂/CH₄ separation, an increase on selectivity of 1.8 times was obtained in the copolyimide with 43 wt.% of PEO, reaching the selectivity a value of 18. This enhancement of productivity has been associated to an improvement of phase segregation.