Molecular-level mixed matrix membranes comprising Pebax and POSS for hydrogen purification via preferential CO2 removal

The molecular-level mixed matrix membranes (MMMs) comprising Pebax^® and POSS have been developed by tuning the membrane preparation process in this work. They exhibit a simultaneous enhancement in CO₂ permeability and CO₂/H₂ selectivity by optimizing the POSS content at extremely low loadings. This is mainly attributed to the large cavity of POSS itself and its effect on the segmental-level polymeric chain packing. More interestingly, the Pebax^®/POSS MMMs reveal a much higher separation performance in the mixed gas test than that in the pure gas test. The highest CO₂/H₂ selectivity reaches 52.3 accompanied by CO₂ permeability of 136 Barrer at 8 atm and 35 °C. This is due to the CO₂-induced plasticization that improves the free volume and polymer chain mobility, hence benefiting the interaction between the polymer matrix and penetrant CO₂. These features may ensure the superiority of Pebax^®/POSS molecular-level MMMs as CO₂-selective membranes in the industrial application of hydrogen purification.     

Enhanced hydrogen purification by graphene - Poly(Dimethyl siloxane) membrane

In this study, a nanocomposite graphene oxide (GO) incorporated poly (dimethyl siloxane) (PDMS) membrane was produced and used for the purification of hydrogen (H₂₎ by separating the (CO₂). The produced membrane was characterized and the single-gas permeability test was performed. Effects of GO addition, trans-membrane pressure and membrane thickness on the gas separation performance of membrane were evaluated as a function of permeability and CO₂/H₂ selectivity. GO addition increased the CO₂/H₂ selectivity and H₂ purification performance. The highest CO2 permeability of 3670 Barrer and CO₂/H₂ selectivity of 11.7 were obtained when the GO loading was 0.5 wt% when the trans-membrane pressure was 0.2 Mpa.     

Hydrogen separation and purification with poly (4-methyl-1-pentyne)/MIL 53 mixed matrix membrane based on reverse selectivity

The effect of MIL 53 (Al) metal organic framework on gas transport properties of poly (4-methyl-1-pentyne) (PMP) was determined based on reverse selectivity. Mixed matrix membranes (MMMs) were fabricated considering various weight percent of MIL 53 particles. The reverse MMMs permselectivities were evaluated through measurement of pure CO₂ and H₂ permeation together with calculation of CO₂/H₂ selectivity. The PMP/MIL 53 (Al) MMMs exhibited privileged CO₂/H₂ permselectivity in comparison with the neat PMP. In addition, CO₂ solubility coefficient was significantly increased with increasing the MIL 53 loading, while the H₂ solubility coefficient was almost remained unchanged. Moreover with increasing the feed pressure the permeability of CO₂ and CO₂/H₂ selectivity were dramatically enhanced, especially at higher filler loadings. Therefore, it was observed that the reverse selectivity of MMMs was enhanced so that the Robeson upper bound was overcome. The best yielding membranes (PMP/30 wt.% MIL 53) represented the CO₂ permeability and CO₂/H₂ selectivity of 377.24 barrer and 24.91 for pure gas experiments respectively.     

Enhancing hydrogen gas separation performance of thin film composite membrane through facilely blended polyvinyl alcohol and PEBAX

Polymeric membranes offer economic separation processes but are less explored for H₂ separation application. This work aims to unveil the H₂ separation potential of polymeric membrane by developing PVA-based reverse selective composite membrane. CO₂-selective PEBAX was blended at different PVA:PEBAX ratio. The effect of PEBAX blending on membrane morphology, crystallinity and gas separation behavior was studied. Incorporation of PEBAX at <50 wt% resulted in composite with improved CO₂ permeability but selectivity loss. Blending of >60 wt% PEBAX enhanced both permeance and selectivity of the resulted composite as the host matrix was dominated by this PEO containing material thus greatly enhancing polymer chain mobility and promoting CO₂-solubility. The best composite which contains 60 wt% PEBAX exhibited CO₂ permeability of 20.0 Barrer and CO₂/H₂ selectivity of 7.6. This performance surpasses the Robeson's boundary and unleashes the potential of tailoring the properties of polymeric nanocomposite membrane for H₂ separation application through facile PVA/PEBAX blending.     

In situ fabrication of cross-linked PEO/silica reverse-selective membranes for hydrogen purification

Targeting at hydrogen purification, cross-linked organic–inorganic reverse-selective membranes containing poly(ethylene oxide) (PEO) are fabricated in situ by using functional oligomers (O,O′-bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol: Jeffamine^® ED-2003) with a high content of PEO and epoxy-functional silanes (3-glycidyloxypropyltrimethoxysilane: GOTMS). Changes in physicochemical properties due to varying silica content have been characterized; including a great decline in melting temperature; an improvement in glassy and degradation temperature, and the suppression of PEO crystallinity. The strong affinity between quadrupolar CO₂ and polar ethylene oxide (EO) groups enhances the CO₂/H₂ separation performance of hybrid membranes, which can be further tuned by controlling the organic/inorganic ratio. The organic–inorganic hybrid membrane with 90 wt% of ED-2003 demonstrates an appealing CO₂ permeability of 367 Barrer with an attractive CO₂/H₂ selectivity of 8.95 at 3.5 atm and 35 °C. The transport performance trend with composition variations is explained by analyzing the calculated solubility and diffusivity based on the solution-diffusion mechanism. Moreover, CO₂ permeability increases with applied pressure in pure gas tests because of CO₂ plasticization phenomena, which is beneficial for CO₂/H₂ separation. Attributing to CO₂ plasticization and CO₂ dominant sorption, the mixed gas test results of the membrane containing only 25 wt% ED-2003 show greatly improved CO₂/H₂ selectivity of 13.2 with CO₂ permeability of 148 Barrer at 35 °C compared to pure gas results. Interestingly, at a stipulated CO₂ pressure, the inherent tension in cross-linked networks maintains the CO₂ permeability stable with the time. The cross-linked organic–inorganic membranes with enhancements in mechanical and thermal properties are promising for industrial-scale hydrogen purification.     

Co-based zeolitic imidazolate framework ZIF-9 membranes prepared on α-Al2O3 tubes through covalent modification for hydrogen separation

Hydrogen has been regarded as the most promising clean and renewable energy. Beside the production of the hydrogen, the separation of hydrogen is also an import issue before it can be used in fuel cells. Membrane-based separation technologies have gained considerable attentions due to its high efficiency and low energy consumption. Zeolite imidazolate framework (ZIF) membranes have drawn intense interest due to their zeolite-like properties such as permanent porosity, uniform pore size and exceptional thermal and chemical stability. It is rather challenged to prepare well-intergrown Co-based zeolitic imidazolate frameworks (ZIFs) membranes on porous α-Al₂O₃ tubes since Co-based ZIFs prefer to form crystals in the synthesis solution rather than grow as membrane layer on the support surface. In this work, we report the preparation of high-quality ZIF-9 membrane with high H₂/CO₂ selectivity and excellent thermal stability by using 3-aminopropyltriethoxysilane (APTES) as a covalent linker to modify the α-Al₂O₃ tube. Due to the formation of covalent bonds between APTES and ZIF-9, ZIF-9 nutrients are bound to the support surface, thus promoting the growth of dense and phase-pure ZIF-9 membrane with a thin thickness of about 4.0 μm. The gas separation performances of the ZIF-9 membrane were evaluated by single gas permeation and mixture gas separation of H₂/CO₂, H₂/N₂ and H₂/CH₄, respectively. The mixture separation factors of H₂/CO₂, H₂/CH₄, and H₂/N₂ of the ZIF-9 membrane are 21.5, 8.2 and 14.7, respectively, which by far exceeds corresponding Knudsen coefficients. Moreover, the as-prepared ZIF-9 membrane exhibits excellent stability at a relatively broad range of operating temperature, which is beneficial for the industrial application of hydrogen separation or further membrane reactor.     

Preparation of mixed matrix composite membrane for hydrogen purification by incorporating ZIF-8 nanoparticles modified with tannic acid

The incompatibility between nanofillers and polymer, caused by the agglomeration of nanoparticles and their weak interaction with each other, is still a challenge to develop mixed matrix composite membrane. Herein, we introduced the ZIF-8-TA nanoparticles synthesized by in situ hydrophilic modification into the hydrophilic poly(vinylamine) (PVAm) matrix to prepare composite membranes for H₂ purification. The dispersion of ZIF-8 in water was improved by tannic acid modification, and the compatibility between ZIF-8 particles and PVAm matrix was enhanced by chemical crosslinking between the quinone groups in oxidized tannic acid (TA) and the amino groups in PVAm. Moreover, the compatibility between hydrophobic polydimethylsiloxane (PDMS) gutter layer and hydrophilic separation layer was achieved by the adhesion of TA-Fe³⁺ complex to the surface of PDMS layer during membrane preparation. The interlayer hydrophilic modification and the formation of separation layer were accomplished in one step, which simplified the preparation process. The experimental results indicated that when the TA addition used for modification was 0.5 g and the ZIF-8-TA_0.5 content in membrane was 12 wt%, the prepared membrane showed the best separation performance with the CO₂ permeance of 987 GPU and the CO₂/H₂ selectivity of 31, under the feed gas pressure of 0.12 MPa.     

Active block copolymer layer on carboxyl-functionalized PET film for hydrogen separation

To rationalize the energy requirements and environmental complications of the world, supply of pure hydrogen is the most promising as well best possible approach of such issues. Purified hydrogen gas is the necessity factor for the hydrogen-based economy. Hydrogen perm-selective membrane plays a crucial role for producing a large amount of hydrogen. Palladium is one of the best materials because of its excellent affinity to absorb hydrogen. In present work, our aim to improve selectivity as well permeability of the H₂ gas compare to N₂ and CO₂ gases of the block copolymer coated functionalized porous PET membrane. Porous polyethylene terephthalate (PET) membranes having pore size 0.2 μm, functionalized with a carboxyl group. The supramolecular assembly was prepared from PS (35500)-b- P4VP (4400) and 2-(4- Hydroxyphenylazo) benzoic acid (HABA) in 1, 4-dioxane. Chemically synthesized palladium nanoparticles were deposited on carboxylated block copolymer (BC) coated porous PET membrane. It is an appropriate way to use H₂ sensitive materials with block copolymer coated functionalized membranes to enhance the selectivity of H₂. It has been found that such membranes gain better permeability and selectivity towards H₂ as compared with N₂ and CO₂. Increment with the dipping time of these membranes in the palladium nanoparticle solution, permeability as well selectivity of H₂ over N₂, CO₂ increases as the more attachment of Palladium nanoparticles. A fine active layer of block copolymer on the carboxyl functionalized PET membrane play a crucial role for hydrogen based gas separation. The magnitude of the permeability of such membranes for different gases shows dependency on the pore size of the upper layer (BC coated) of the membrane in addition to the molecule size of the permeating gas. Block copolymer coating of the membranes established an effective responsibility for the selectivity of H₂ over CO₂ gas as well over N₂ gas.     

Evaluation of two gas membrane modules for fermentative hydrogen separation

The ability of (dimethyl siloxane) (PDMS) and SAPO 34 membrane modules to separate a H₂/CO₂ gas mixture was investigated in a continuous permeation system in order to decide if they were suitable to be coupled to a biological hydrogen production process. Permeation studies were carried out at relatively low feed pressures ranging from 110 to 180 kPa. The separation ability of SAPO 34 membrane module appeared to be overestimated since the effect concentration polarization phenomena was not taken into consideration in the permeation parameter estimation. On the other hand, the PDMS membrane was the most suitable to separate the binary gas mixture. This membrane reached a maximum CO₂/H₂ separation selectivity of 6.1 at 120 kPa of feed pressure. The pressure dependence of CO₂ and H₂ permeability was not considerable and only an apparent slight decrease was observed for CO₂ and H₂. The mean values of permeability coefficients for CO₂ and H₂ were 3285 ± 160 and 569 ± 65 Barrer, respectively. The operational feed pressure found to be more adequate to operate initially the PDMS membrane module coupled to the fermentation system was 180 kPa, at 296 K. In these conditions it was possible to achieve an acceptable CO₂/H₂ separation selectivity of 5.8 and a sufficient recovery of the CO₂ in the permeate stream.     

CO2-selective membranes for hydrogen purification and the effect of carbon monoxide (CO) on its gas separation performance

Industrial hydrogen production may prefer CO₂-selective membranes because high-pressure H₂ can therefore be produced without additional recompression. In this study, high performance CO₂-selective membranes are fabricated by modifying a polymer–silica hybrid matrix (PSHM) with a low molecular weight poly(ethylene glycol) dimethyl ether (PEGDME). The liquid state of PEGDME and its unique end groups eliminate the crystallization tendency of poly(ethylene glycol) (PEG). The methyl end groups in PEGDME hinder hydrogen bonding between the polymer chains and significantly enhance the gas diffusivity. In pure gas tests, the membrane containing 50 wt% additive shows CO₂ gas permeability and CO₂/H₂ selectivity of 1637 Barrers and 13 at 35 °C, respectively. In order to explore the effect of real industrial conditions, the gas separation performance of the newly developed membranes has been studied extensively using binary (CO₂/H₂) and ternary gas mixtures (CO₂/H₂/carbon monoxide (CO)). Compared to pure gas performance, the second component (H₂) in the binary mixed gas test reduces the CO₂ permeability. The presence of CO in the feed gas stream decreases both CO₂ and H₂ permeability as well as CO₂/H₂ selectivity as it reduces the concentration of CO₂ molecules in the polymer matrix. The mixed gas results affirm the promising applications of the newly developed membranes for H₂ purification.     

PVDF/ionic liquid polymer blends with superior separation performance for removing CO2 from hydrogen and flue gas

We have demonstrated, for the first time, a polymer blend comprising poly(vinylidene fluoride) (PVDF) and a room-temperature ionic liquid (RTIL) that shows a high CO₂ permeability of 1778 Barrer with CO₂/H₂ and CO₂/N₂ selectivity of 12.9 and 41.1, respectively. The low viscosity RTIL, 1-ethyl-3-methylimidazolium tetracyanoborate ([emim][B(CN)₄]) possesses a high CO₂ solubility, and plays a significant role in CO₂ separation, whereas PVDF provides the mechanical strength to the blend membranes. A series of PVDF/[emim][B(CN)₄] polymer blends with different compositions were tested for their gas separation performance involving H₂, N₂ and CO₂ in both pure gas and mixed gas conditions. Both optical observation and Maxwell predictions confirm the heterogeneous nature of the PVDF/[emim][B(CN)₄] system. However, compared to miscible ionic liquid based blends, where molecular level interactions may restrain chain flexibility and reduce gas permeability, heterogeneous PVDF/RTIL blend systems show far superior gas transport properties. Most of these blend membranes outperform most reported materials and their gas transport and separation capabilities fall within the attractive region bound by the “2008 Robeson Upper Limit” for CO₂/H₂ and CO₂/N₂ gas pairs, and are also very stable at trans-membrane pressure up to 5 atm. Therefore, they are potential materials for H₂ purification and CO₂ capture from hydrogen production and flue gas.     

Hydrogen separation and purification using crosslinkable PDMS/zeolite A nanoparticles mixed matrix membranes

The transport properties of gases in polydimethylsiloxane (PDMS)/zeolite A mixed matrix membranes (MMMs) were determined based on pure gas permeation experiments. MMMs were prepared by incorporating zeolite 4A nanoparticles into a PDMS matrix using a new procedure. The permeation rates of C₃H₈, CH₄, CO₂, and H₂ were evaluated through a dense homogeneous pure PDMS membrane and PDMS/4A MMMs to assess the viability of these membranes for natural gas sweetening and hydrogen purification. SEM investigations showed good adhesion of the polymer to the zeolite in MMMs. Permeation performance of the membranes was also investigated using a laboratory-scale gas separation apparatus and effects of feed pressure, zeolite loading and pore size of zeolite on the gas separation performance of the MMMs were evaluated. The MMMs exhibited both higher selectivity of H₂/CH₄ and H₂ permeability as compared with the neat PDMS membrane, suggesting that these membranes are very promising for gas separations such as H₂/CH₄ separation.     

GNs/MOF-based mixed matrix membranes for gas separations

NU-1000 and graphene nanosheet (GNs) with different loadings have been used as fillers to prepare mixed matrix membranes (MMMs) with polyethersulfone (PES). The high performance of the MMMs has been successfully fabricated for the evaluation of gas separation at 1 bar and various temperatures (20, 40, 60 °C). The successful fabrication of the MMMs were confirmed by using SEM, FTIR, AFM, and XRD. The crystalline nature of GNs and NU-1000 in the MMMs are evidenced by XRD, which confirms the successful fabrication of the MMMs. In addition, the thermal stability of the MMMs was enhanced with the increase of the GNs. Separation performance of H₂ was superior to CO₂, N₂ and CH₄ separation on the MMMs which is a critical for producing energy. The best gas separation results in terms of both permeability and selectivity were obtained with 0.03% GNs and 10% NU-1000. PG3N membrane presented maximum H₂/CO₂, H₂/N₂ and H₂/CH₄ selectivity of 5, 4.2, 3.3 at 20 C, respectively. With an increase in temperature, the permeability increased, while the selectivity of all the MMMs decreased. The MMMs exhibited excellent gas separation capability, which offers unique opportunities for potential large-scale practical applications.     

Development of hydrogen selective microporous PVDF membrane

Hydrogen is a sustainable clean and green energy source used to eliminate the problem of greenhouse effect. In the present work, the feasibility of gas permeability in separation of H₂ from CO₂ and N₂ have been examined using polyvinylidene fluoride (PVDF) membranes synthesised in our laboratory by the phase inversion process. Effect of various non-solvent additives, such as lithium chloride (LiCl) and Tetraethoxysilane (TEOS) in the PVDF dope solution, have been studied. The resulted asymmetric flat sheet microporous hydrophobic membrane, shows higher hydrogen permeability and selectivity over other gases (CO₂ & N₂). It has been observed that the MT5 membrane has shown the highest selectivity for hydrogen in comparison to CO₂ and N₂. The highest value of selectivity was obtained as 4.8 and 3.7 in case of H₂/CO₂ and H₂/N₂ respectively. The permeability of membrane has been obtained in the range of 2.3–4.2 mega barrer. SEM analysis is used for the investigation of membrane surface morphology.     

Effect of mesoporous silica modification on the structure of hybrid carbon membrane for hydrogen separation

An SBA-15/carbon molecular sieve (CMS) composite membrane, using polyetherimide as a precursor and mesoporous silica as filler, was fabricated for hydrogen separation. The effect of mesoporous SBA-15 on the gas transport properties of the composite membrane was evaluated. The permeability and selectivity coefficients of H₂, CO₂, O₂, N₂, and CH₄ were estimated for the pure CMS and SBA-15/CMS composite membranes at a feed pressure of 2-7 atm for 30 °C. The SBA-15/CMS composite membrane had a gas permeability higher than that of the pure CMS membrane, whereas its selectivity was the same. The permeability was found to be independent of pressure; this indicates that the gases are transported through the membrane by a molecular sieve mechanism. The membranes appeared to have a more microporous structure when the mesoporous silica SBA-15 was incorporated. These results concur with the hypothesis that SBA-15 improves gas diffusivity by increasing pore volume.     

Development of high performance amine functionalized zeolitic imidazolate framework (ZIF-8)/cellulose triacetate mixed matrix membranes for CO2/CH4 separation

High cost and complex fabrication process of inorganic membranes and lower position of pristine polymeric membranes in the Robeson upper bound curve urged the researchers to develop mixed matrix membranes (MMMs). Cellulose acetate being most commercially used polymer, dominates the market of CO₂ separation mainly because of low cost and environmental friendly resource. In the present study, MMMs consists of amine functionalized zeolitic imidazolate framework (NH₂-ZIF-8) and cellulose triacetate were fabricated for the first time. NH₂-ZIF-8 was used as a filler because the pore size of ZIF-8 is between the kinetic diameter of separating gases (CO₂ and CH₄). Moreover,  NH₂ group attached on the surface of ZIF-8 has affinity with condensable gases like CO₂. Morphology, crystallinity, tensile strength and functional groups of fabricated membranes were investigated using different analytical techniques. Results revealed that the increase of feed pressure has increased CO₂ permeability and decreased permselectivity. However, improvements in gas separation performance were observed with the addition of nanofiller. Best position in Robeson's upper bound curve at 4 bar was obtained with 10 wt% loading with CO₂ permeability and CO₂/CH₄ permselectivity of 218 barrer and 13.84, respectively. The improvement in the gas separation performance with loading is attributed to the increased diffusion coefficients as well as solubility coefficients, which was increased to 33% and 3.8%, respectively.     

Macrovoid-free high performance polybenzimidazole hollow fiber membranes for elevated temperature H2/CO2 separations

Thermally robust membranes are required for H₂ production and carbon capture from hydrocarbon fuel derived synthesis (syn) gas. Polybenzimidaole (PBI) materials have exceptional thermal, chemical and mechanical characteristics and high H₂ perm-selectivity for efficient syngas separations at process relevant conditions. The large gas volumes processed mandate the use of a high-throughput, small footprint hollow fiber membrane (HFM) platform. In this work, an industrially attractive spinning protocol is developed to fabricate PBI HFMs with unprecedented H₂/CO₂ separation performance. A unique dope composition incorporating an acetonitrile diluent is discovered enabling asymmetric macro-void free PBI HFM fabrication using a water coagulant. The influences of dope viscosity, coagulant chemistry, and air gap on HFM morphology are evaluated. Elevated temperature (up to 350 °C) H₂ permeances of 400 GPU with H₂/CO₂ selectivities > 20 are achieved. This unprecedented separation performance is a ground breaking achievement at temperatures traditionally considered out-of-reach for polymeric membranes.     

ZnO nanofiber skeleton induced robust zeolitic imidazolate framework membranes for gas separation

Rationally designing compact metal-organic framework (MOF) membrane is highly desired but challenging. Herein, we proposed a ZnO nanofiber skeleton induced zeolitic imidazolate framework (ZIF) membrane inspired by the reinforced concrete structure. In this process, the ZnO nanofiber skeleton was employed as active anchor sites to assist the heteroepitaxial growth of continuous membranes, like the reinforcing steel in structure. The formed ZIFs particles were tightly embedded in the skeleton like the concrete. With this approach, highly compact Co-based ZIF-9 membrane and Zn-based ZIF-8 membrane were successfully achieved and exhibit effective H₂ separation performance. For ZIF-9 membrane, the H₂ permeance and the ideal selectivity of H₂/CO₂ are 2.19 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ and 15.3, respectively. For ZIF-8 membrane, the H₂ permeance and the ideal selectivity of H₂/CH₄ are 2.26 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ and 9.7, respectively. More importantly, benefiting from the novel structure, the membrane showed a highly robust architecture under different pressures, good durability against rubbing, and separation stability of 100 h. This strategy provides a new approach toward other compact and robust MOF membrane.     

Palladium nanoparticle binding in functionalized track etched PET membrane for hydrogen gas separation

In this work, track-etched poly (ethylene terephthalate) (PET) membranes having different pore sizes were functionalized by the carboxylic groups and the amino groups. Palladium (Pd) nanoparticles of average diameter 5 nm were synthesized chemically and deposited onto pore walls as well as on the surface of these pristine and functionalized membranes. Effect of Pd nanoparticles binding on these membranes were explored and aminated membrane were found to bind more Pd nanoparticles due to its affinity. The morphology of these composite membranes is characterized by Scanning Electron Microscope (SEM) for confirmation of Pd nanoparticle deposition on pore wall as well as on the surface. Gas permeability of functionalized and non-functionalized membranes for hydrogen and carbon dioxide has been examined. From the gas permeability data of hydrogen (H₂) and carbon dioxide (CO₂) gases, it was observed that these membranes have higher permeability for H₂ as compared with CO₂. Due to absorption of hydrogen by Pd nanoparticles selectivity of H₂ over CO₂ was found higher as compared to without Pd embedded membranes. Such type of membranes can be used to develop hydrogen selective nanofilters for purification/separation technology.     

Developing cross-linked poly(ethylene oxide) membrane by the novel reaction system for H2 purification

In this study, a ‘green” method has been discovered by utilizing the amino functional poly(ethylene oxide) (PEO) and epoxy functional PEO with low molecular weights to synthesis cross-linked membranes for enhancing H₂ purification and CO₂ capture performance by retarding the crystallinity of semi-crystalline polymer of PEO. The cross-linking reaction can happen simply by mixing two materials without using any solvent. The reaction has been characterized by Fourier transform infrared-attenuated total reflectance (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), solid-state ¹³C nuclear magnetic resonance (NMR) and the gel content test. Furthermore, X-ray diffraction (XRD) and differential scanning calorimeter (DSC) confirm the amorphous structure of cross-linked PEO membranes, which should benefit the gas transport. The gas transport properties and the plasticizing phenomenon of CO₂ have been examined in detail. Interestingly, the investigation on CO₂ plasticization phenomenon reveals that the cross-linked PEO membrane should be plasticized immediately after the pressure load. The pressure dependence of CO₂ permeability in the pressure range from 0.25 atm to 30 atm can be separated into two stages based on the permeability increment although the CO₂ permeability continuously increases with the loading pressure. The gas transport results illustrate that CO₂ has much larger permeability than that of any tested gas (including H₂, N₂ and CH₄) attributing to the CO₂-philic characteristic of ethylene oxide (EO) groups in the cross-linked PEO membrane. The good permeability and selectivity make the developed PEO membrane promising for H₂ purification and CO₂ capture applications.