Membranes For CO2 Separation Research Articles

A study of H2O opposite-direction permeation through a mixed ceramic-molten salt CO2 separation membrane

Ceramic-molten salt dual-phase CO2-permselective membrane is a promising technology to capture CO2 at high temperatures. The formation of hydroxide (OH−) phase in molten carbonate (CO32−) in the presence of steam leads to an increase in CO2 permeation flux. However, few works have paid attention to the H2O permeability. In this study, we find that there are two routes for H2O permeation through the molten hydroxide-based dual-phase membrane with a wet sweep gas; one route is permeated with CO2, but in the opposite direction; the other is a separate route for H2O permeation through the interaction of oxygen ions and hydroxide ions. The resulting H2O fluxes are 5.3 and 1.7 times the fluxes of CO2 at 600 and 800 °C, respectively. Stable CO2 and H2O fluxes are obtained over 100 h at 700 °C, making the dual-phase membrane promising for coupling CO2 capture with conversion processes.

Innovative thermal crosslinked polyimide gas separation membrane with highly selective and resistance to physical aging base on phenyl ethynyl

In this study, a high performance phenyl ethynyl thermal crosslinked 6FDA-based polyimide (CR-4ETA-x) was developed, which has high gas permeability and selectivity, resistance to physical aging. By introducing 4,4′-(Acetylene-1,2-diyl) diphthalic anhydride (4ETA) monomer into the polyimide structure, the thermal crosslinking precursor membrane was formed. The precursor membrane was heat treated at 440℃ to obtain CR-4ETA-x. After heat treatment, we detected the olefin radical in the crosslinked membrane by electron paramagnetic resonance, which proved that the polyimide network was formed. This allows the crosslinked membrane to have greater d-spacing, higher rigidity, and BET surface area. The CO2 permeability of CR-4ETA-5% is 4114 barrer and the CO2/CH4 selectivity is 19.22. Compared to 6FDA-DAM, the CO2 permeability increased by 477% while the selectivity decreased by only 17%. CR-4ETA-20% shows the CO2 permeability of 3560 Barrer and CO2/CH4 selectivity of 21.1 in CO2/CH4 mixed-gas. After 60 days of aging the permeability maintenance of CR-4ETA-20% were 88%, 84%, 83% and 91% for O2, N2, CO2 and CH4. In addition, in the long-term stability test of more than 100 h, the separation performance of CR-4ETA-20% did not decrease significantly. However, CR-4ETA-x also has limitations, such as poor stability in alkaline environments and lower gas permeability than some advanced carbon molecular sieve membranes. In general, the method of phenyl ethynyl thermal crosslinking provides an effective way for the development of CO2 separation membranes with possible applications.

Development of cost-effective cellulose-based bilayer hybrid composite membranes for CO2 separation in biogas purification

CO2 is the main pollutant in biogas, reducing its calorific value. Among various technological methods to eliminate carbon dioxide from biogas, membrane separation technology stands out for large-scale industrial biogas purification due to its advantages. The selection of membrane material and preparation process are key factors in membrane separation technology. In this study, a premixing process was initially used to blend different masses of packed molecular sieves TS-1 (or ZSM-5) and cellulose derivatives (ethyl cellulose, cellulose acetate) separately. These mixtures were then coated onto porous PVDF substrates using a coating process to create various bilayer hybrid composite membranes. Among these, PVDF/EC-ZSM-5 (containing 15 % ZSM-5) bilayer hybrid composite membrane is the most fitting. For CO2/CH4 gas mixtures, the gas selectivity of this membrane surpassed Robeson's 1991 standard line (the CO2 permeability was 597.48 Barrer, and the CO2/CH4 selectivity was 9.14). Overall, this composite membrane, made for the first time from PVDF, ZSM-5, and EC, is expected to be a promising CO2 selective separation membrane material for biogas purification in large-scale industrial processes due to its simple production process.

Constructing the positive electrostatic environments by nanosheet in mixed matrix membranes for efficient CO2 separation

Mixed Matrix Membranes (MMMs) have shown advantages in overcoming trade-off effects, but there is still an urgent need to enhance CO2 separation performance in the design of multifunctional fillers. To overcome the trade-off effects in MMMs, a rational design of fillers with selective recognition for CO2 molecules is an effective strategy. A microporous nanosheet Qc-5-Cu was synthesized and incorporated into a Pebax MH 1657 (Pebax) to prepare MMMs for efficiently separating CO2 from CH4. The H atoms of the aromatic rings on the surface of pores in Qc-5-Cu constructed positive electrostatic environments, which significantly improves the CO2/CH4 separation performance of MMMs. On one hand, the constructed positive electrostatic environments in the MMMs attracted the negatively charged O atoms of CO2 molecules through electrostatic attraction, which effectively accelerated CO2 transport. On the other hand, the positive electrostatic environments established a selective barrier for preventing CH4 transport, achieving high CO2/CH4 selectivity in MMMs. Compared to pure Pebax membrane, the Pebax/Qc-5-Cu-0.5 MMM exhibited a remarkable enhancement of 99.52 % in CO2 permeability (934.24 Barrer) and a significant increase of 37.64 % in CO2/CH4 selectivity (25.01). The constructed positive electrostatic environments of nanosheets in MMMs offers a potential prospect for efficient CO2/CH4 separation.

Building high-speed facilitated transport channels in Pebax membranes with montmorillonite for efficient CO2/N2 separation

ABSTRACT Development of high-performance mixed matrix membranes (MMMs) is of great significance for CO2 separation membrane technology, in order to improve the commercial competitiveness and practical applications. Montmorillonite (MMT) was developed as a dopant to fabricate Polyether block amide (Pebax1074)-based MMMs for strengthening the CO2/N2 separation. The morphology, chemical groups, microstructure, and thermal properties of MMMs were characterised by scanning electron microscope, FTIR spectroscopy, X-ray diffraction and thermal analysis, respectively. The effects of MMT contents, permeation pressure and permeation temperature on the gas separation performance of the Pebax/MMT MMMs were investigated. The results show that the uniformly dispersed dopants MMT in the membrane matrix significantly influence the thermal stability and the structural compactness of MMMs. Moreover, the CO2 permeability monotonously increases in spite of the CO2/N2 selectivity first increasing and then decreasing with the MMT content elevating from 0% to 10% in MMMs. The highest CO2/N2 selectivity could reach to 120.3, along with the CO2 permeability of 130.6 Barrer for the MMMs made by MMT content of 6%.

Highly selective CO2 permeable double-network ionogel membrane containing 1-ethyl-3-methylimidazolium dicyanamide

A double-network (DN) ionogel membrane containing 1-ethyl-3-methylimidazolium dicyanamide ([C2mim][DCA]) was developed and evaluated for its mechanical robustness and its CO2 permeation properties. Polyvinyl alcohol (PVA) was used as the initial network for the DN ionogel membrane. It forms a partially-crystalline physical crosslinking within [C2mim][DCA] and acts as a sacrificial bond to toughen the ionogel. A loosely crosslinked poly(N,N-dimethylacrylamide) (PDMAAm) network was formed by free-radical polymerization to interpenetrate with the physically crosslinked PVA network. The more the gel was elongated, the more the physical crosslinking in the PVA network were broken and the more energy was dissipated. As a result, the ion gel toughened. Owing to its excellent toughness, the developed DN ionogel membrane retained 93 wt% of [C2mim][DCA] and exhibited the CO2 permeability and the CO2 perm-selectivity over N2 of 2920 barrer and 61, respectively, the highest level of CO2 separation performance among the latest CO2 separation membranes. The DN ionogel membrane kept the CO2 separation performance required for CO2 capture from flue gases from coal-fired power plants even at 80 °C and 80 % relative humidity.

Joint experimental-computational: Revealing the role of sodium poly(heptazineimide) in the selective separation of CO2 in PEBAX-based mixed matrix membranes

Mixed matrix membranes (MMMs) with the dual properties of porous materials and polymer matrix membranes have become one of the most optimal solutions to the gas separation problem. However, the adapted porous material and the explicit transport mechanism of gases within the mixed matrix membrane hinder its further commercialization. Thanks to their porous nature and tunable gas adsorption properties, heteroatom-doped porous materials, especially nitrogen-doped porous materials, are widely used to design and prepare advanced CO2 separation membranes. Herein, a layered two-dimensional nano-sheet with a nitrogen content of 44.7 % was successfully synthesized via thermal polymerization. And nano-sheets were homogeneously dispersed in a Pebax matrix to make a composite film. Since the CO2 affinity of the nitrogen functional site and the PEO flexible chain, realizing the synergistic improvement of CO2 permeability and selectivity. A comprehensive combined permeation experimental/simulation characterization reveals the CO2 transport pathway within the membrane, indicating the mechanism of action of nitrogen-doped porous packing on CO2 diffusion. Among these, the CO2 permeability of the mixed matrix film containing 5 wt% sodium poly(heptazine imide) (NaPHI) reached 153 Barrer at a feed gas pressure of 9 bar, nearly 149 % compared to the pure Pebax film. The selectivity of CO2/N2 was enhanced to 105, exhibiting a remarkable increase of 159 % and exceeding the 2019 Robeson limit. Importantly, the present work further reveals and demonstrates the gas separation mechanism of nitrogen-doped porous filler/polymer hybrid matrix membranes, which provides new ideas for the design and application of heteroatom-doped porous fillers in the field of gas separation.

Constructing bio-inspired anion channels by dual-ligand MOF in membranes for efficient CO2 separation

One of the biggest challenges of Pebax-based membranes is how to simultaneously achieve high CO2 permeability and selectivity. Hence, three-dimensional L-histidine@zeolitic imidazole framework-8 (His@ZIF-8 (X)) was synthesized as dual-ligand metal-organic framework (MOF), and it was incorporated into the Pebax 1657 matrix to fabricate mixed matrix membranes (MMMs) for efficient CO2 separation. The three-dimensional His@ZIF-8 (X) with abundant His mimicked anion transport protein, and it constructed bio-inspired anion transport channels. His@ZIF-8 (X) played important functions when it was incorporated into the MMMs: the bio-inspired active sites of His@ZIF-8 with the Zn2+ bonded to three Hmim and one water molecule had similar function with the active sites in carbonic anhydrase (CA), which can catalyze CO2 into water-soluble bicarbonate (HCO3−). Subsequently, the bio-inspired anion transport channels allowed HCO3− to rapidly transport, because they had His residues that can form anion-dipole interactions with HCO3− in His@ZIF-8 (X). Therefore, Pebax 1657/His@ZIF-8 (X) MMMs were endowed with the excellent separation performance due to the bio-inspired anion transport channels constructed by His@ZIF-8 (X). In particularly, MMM contained 4 wt% His@ZIF-8 (12.5) achieved the optimal separation performance with a CO2 permeability of 541 ± 9 Barrer and CO2/CH4 selectivity of 35 ± 0.6. The work implies that the construction of the bio-inspired anion transport channels within MMMs was a potential strategy for efficient CO2 separation.

Polymerization-induced self-assembly amino acid ionic liquid/poly(ethylene oxide) thin-film composite membranes for CO2 separation

It is well known that crosslinking poly(ethylene oxide) (PEO) membranes exhibit high CO2/N2 solubility selectivity, and are suitable for separating CO2 from flue gas. However, the high CO2/N2 selectivity is temperature sensitive and decreases rapidly with increasing temperature. To overcome this deficiency, imidazolium-based amino acid ionic liquids (AAILs) are introduced into the PEO membranes. A series of (AAILs-PEO)/PAN thin-film composite (TFC) membranes were prepared by a polymerization-induced self-assembly process. Due to the hydrogen and Coulomb interactions between the imidazolium ring of AAILs and the ether groups of PEO monomers, the morphology of the selective layer changed from micellar to granular upon the introduction of the AAILs into the PEO membranes, while the chain-segment flexibility and interspacing of the PEO are also changed. Compared with the original PEO/PAN TFC membrane, the (AAILs-PEO)/PAN TFC membranes show much higher CO2/N2 selectivity, which increases from ∼41 to ∼ 74. In addition, the AAILs show strong hydrophilicity, which leads to a significant increase in CO2/N2 selectivity under the wet-gas feed, reaching ∼105. Compared with the original PEO/PAN TFC membranes with CO2/N2 selectivity of ∼10 at 70 °C, the (AAILs-PEO)/PAN TFC membranes show the selectivity of ∼30, coupled with CO2 permeance of ∼1300 GPU at 70 °C. Under the 40: 60 mixtures of CO2: N2, which is a common lime kiln exhaust gas, by using the (AAILs-PEO)/PAN TFC membrane, the CO2 concentration on the downstream side can reach over 90 % at 20 °C and over 70 % at 70 °C, respectively, under a pressure ratio of 5.

Metal-Organic-Frameworks Based Mixed-Matrix Membranes for CO2 Separation: An Applicable-Conceptual Approach.

A promising class of porous crystalline materials, metal-organic frameworks (MOFs), have recently emerged as a potential material in fabricating mixed matrix membranes (MMMs) for gas separation applications. Their unique chemistry and structural versatility offer substantial advantages over conventional fillers. This review gives an in-depth exploration of MOF chemistry, focusing on strategies to manipulate their adsorption behavior to enhance separation properties. We scrutinize the impact of various MOF-based MMM components, including polymer matrix, MOFs fillers and polymer/filler interface, on the overall gas separation performance. This involves a detailed analysis of key parameters associated with MMM preparation. Additionally, we offer a comprehensive overview of the determining factors in MOF-based MMM development for gas separation, including MOF structure, synthesis, and chemistry. Moreover, the most advances in modification strategies of MOF for CO2 separation, such as a wide variety of hybrid MOFs will be outlined, which opens the door to an improved CO2 separation process. Finally, the gas transport mechanisms of MMMs are thoroughly discussed to understand the factors affecting the gas permeation through the polymer matrix, MOFs and interface between them.

Defect-Engineered Metal-Organic Framework/Polyimide Mixed Matrix Membrane for CO2 Separation.

Defect-engineered metal-organic frameworks (MOFs) with outstanding structural and chemical features have become excellent candidates for specific separation applications. The introduction of structural defects in MOFs as an efficient approach to manipulate their functionality provides excellent opportunities for the preparation of MOF-based mixed matrix membranes (MMMs). However, the use of this strategy to adjust the properties and develop the separation performance of gas separation membranes is still in its early stages. Here, a novel defect-engineered MOF (quasi ZrFum or Q-ZrFum) was synthesized via a controlled thermal deligandation process and incorporated into a CO2-philic 6FDA-durene polyimide (PI) matrix to form Q-ZrFum loaded MMMs. Defect-engineered MOFs and fabricated MMMs were investigated regarding their characteristic properties and separation performance. The incorporation of defects into the MOF structure increases the pore size and provides unsaturated active metal sites that positively affect CO2 molecule transport. The interfacial compatibility between the Q-ZrFum particles and the PI matrix increases via the deligandation process, which improves the mechanical strength of Q-ZrFum loaded membranes. MMM containing 5 wt.% of defect-engineered Q-ZrFum exhibits excellent CO2 permeability of 1308 Barrer, which increased by 99 % compared to the pure PI membrane (656 Barrer) at a feed pressure of 2 bar. CO2/CH4 and CO2/N2 selectivity reached 44 and 26.6 which increased by about 70 and 16 %, respectively. This study emphasizes that defect-engineered MOFs can be promising candidates for use as fillers in the preparation of MMMs for the future development of membrane-based gas separation applications.

Fabrication of high-performance biochar incorporated Pebax®1657 membranes for CO2 separation

This study highlights the utilization of biobased material for developing high-performance membranes for gas separation applications. Biochar was synthesized by the pyrolysis of pine needles and further modified by silane functionalization. Thus obtained biochar was incorporated into a rubbery polymer, poly(ether-blockamide) (Pebax-1657), to synthesize mixed matrix membranes (MMMs). Morphologies of membranes and physio-chemical interactions of the biochar and polymer were evaluated using SEM, FTIR, DSC, and XRD. MMMs exhibit higher gas adsorption properties compared to the neat Pebax-1657 membrane. The effect of biochar incorporation on gas permeation properties was conducted in an indigenously designed setup using pure CH4, CO2, and N2 gases in the pressure range of 5–30 kg/cm2. 20 wt% Biochar loaded MMM achieved a higher CO2 permeability of 114 Barrer, signifying 79% higher permeability over the pristine Pebax membrane. Correspondingly, the highest selectivity values for CO2/CH4 and CO2/N2 achieved were 32 and 94, respectively, with increasing pressure. A regression model was developed to estimate the relation between biochar loading and gas permeability. The data revealed a strong positive correlation (0.7–0.9) between gas permeability and the percentage of biochar loaded. The developed MMMs are stable and exhibit superior performance for CO2 removal from natural gas and power plant off-gases. Pine needles derived MMMs represent a promising new approach for developing high-performance and environmentally sustainable membranes for gas separation applications.

Enhancing CO2 transport with plasma-functionalized ionic liquid membranes

The ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate treated with radiofrequency plasma is proposed for functionalization and immobilization on polyethersulfone supports to form supported ionic liquid membranes for CO2 separation. The effects of treatment time and transmembrane pressure difference on CO2 permeance were evaluated. The best gas permeation performance was obtained with a treatment time of 10 min and the transmembrane pressure difference was 0.25 MPa. Characterization of the materials by Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and nuclear magnetic resonance spectroscopy demonstrates that the IL is grafted with carboxyl groups and deprotonated through plasma treatment. A preliminary mechanism for the plasma treatment and facilitated transport of CO2 has been proposed on this basis.

Laser Patterning of Porous Support Membranes to Enhance the Effective Surface Area of Thin-Film Composite-Facilitated Transport Membranes for CO2 Separation.

Although thin-film composite membranes have achieved great success in CO2 separation, further improvements in the CO2 permeance are required to reduce the size and cost of the CO2 separation process. Herein, we report the fabrication of composite membranes with high CO2 permeability using a laser-patterned porous membrane as the support membrane. High-aspect-ratio micropatterns with well-defined micropores on their surface were carved on microporous polymer supports by a direct laser writing process using a short-pulsed laser. By using a Galvano scanner and optimizing the laser conditions and target materials, in-plane micropatterns, such as microhole arrays, microline grating, microlattices, and out-of-plane hierarchical micropatterns, were created on porous membranes. An aqueous suspension of hydrogel microparticles doped with an amine-based mobile carrier was sprayed onto the patterned surface to form a defect-free thin separation layer. The surface area of the separation layer on the patterned support is up to 80% larger than that of flat pristine membranes, resulting in a 52% higher CO2 permeance (1106 GPU) with a CO2/N2 selectivity of 172. The laser-patterned porous membranes allow the development of inexpensive and high-performance functional membranes not only for CO2 separation but also for other applications, such as water treatment, cell culture, micro-TAS, and membrane reactors.

Tailoring the Structure-Property Relationship of Ring-Opened Metathesis Copolymers for CO2-Selective Membranes.

In this work, we explore the use of ring-opening metathesis polymerization (ROMP) facilitated by a second-generation Grubbs catalyst (G2) for the development of advanced polymer membranes aimed at CO2 separation. By employing a novel copolymer blend incorporating 4,4'-oxidianiline (ODA), 1,6-hexanediamine (HDA), 1-adamantylamine (AA), and 3,6,9-trioxaundecylamine (TA), along with a CO2-selective poly(ethylene glycol)/poly(propylene glycol) copolymer (Jeffamine2003) and polydimethylsiloxane (PDMS) units, we have synthesized membranes under ambient conditions with exceptional CO2 separation capabilities. The strategic inclusion of PDMS, up to a 20% composition within the PEG/PPG matrix, has resulted in copolymer membranes that not only surpass the 2008 upper limit for CO2/N2 separation but also meet the commercial targets for CO2/H2 separation. Comprehensive analysis reveals that these membranes adhere to the mixing rule and exhibit percolation behavior across the entire range of compositions (0-100%), maintaining robust antiplasticization performance even under pressures up to 20 atm. Our findings underscore the potential of ROMP in creating precisely engineered membranes for efficient CO2 separation, paving the way for their application in large-scale environmental and industrial processes.

High performance Ce0.8Nd0.2O2-δ-carbonate hollow fiber membrane for high-temperature CO2 separation

Ceramic-carbonate dual phase (CCDP) membrane consisting of oxygen ionic conductor and molten carbonate has potential applications in clean energy delivery as it enabling the direct CO2 separation or capture at the elevated temperatures. The performance of previous CCDP membranes is not ideal either with a low CO2 flux or with a poor operational stability. In the present work, we looked at the CeO2-based oxygen ionic conductor (neodymium doped cerium (NDC)) as the porous ceramic hollow fiber support to form NDC-carbonate hollow fiber membranes. The NDC hollow fiber was fabricated by the combined phase inversion and sintering techniques and the preparation conditions were optimized to better accommodate the carbonate phase and maintain the mechanical stability. The NDC hollow fibers possessed good bending strength, reaching 91.5 MPa upon sintering at 1500 °C. The effects of feed gas composition and sweep flow rates on the CO2 separation performance were carefully investigated. The resultant dual phase hollow fiber membranes exhibited appreciably high CO2 permeation fluxes at temperatures exceeding 800 °C, which was required to activate both conductions of oxygen and carbonate ions. The achieved maximum CO2 flux of the optimized NDC-carbonate hollow fiber membranes was up to 5.08 mL min−1 cm−2 with 50%CO2–50%N2 as the feed gas at 900 °C. At 700 °C, the membrane exhibited a relatively stable CO2 permeation behavior over 120 h and the spent membrane maintained a stable structure. The high flux and good operational stability of the developed membrane make a huge step towards practical applications.

Research on triazine-based nitrogen-doped porous carbon/Pebax mixed-matrix membranes for CO2 separation and its gas transport mechanism

Research on triazine-based nitrogen-doped porous carbon/Pebax mixed-matrix membranes for CO2 separation and its gas transport mechanism

Manipulating the monomers supply of interfacial polymerization towards the ultrathin polyamide composite membrane for CO2 capture

Preparing polyamide (PA) composite membranes with high gas separation performance requires rational control for the interfacial polymerization (IP) process. In this study, the monomer supply of piperazine (PIP) and trimesoyl chloride (TMC) in the IP process was precisely manipulated to generate an ultrathin PA film on the polydimethylsiloxane (PDMS) gutter layer for CO2 separation. Concretely, the PIP supply was regulated from the homogeneous, slow, and excess mode to the inhomogeneous, fast, and small mode by constructing a sodium dodecyl sulfate (SDS) array at the phase interface; subsequently, the TMC supply was increased by elevating the TMC concentration. Therefore, the amine-to-acid chloride concentration ratio in the reaction zone was optimized and, as a consequence, the IP reaction rate was significantly increased. As a result, the thickness of the PA film was reduced from ∼92 nm to ∼37 nm through the optimization of SDS and TMC concentrations, and accordingly, the CO2 permeance was increased from 501 GPU to 1498 GPU under 0.1 MPa without sacrificing selectivity. Moreover, the membrane preparation efficiency was greatly improved with an IP reaction time of less than 30 s. The insights provided could promote the industrial application of interfacial polymerization in the scale-up preparation of high-performance CO2 separation membranes.

Preparation of Polysilsesquioxane-Based CO2 Separation Membranes with Thermally Degradable Succinic Anhydride and Urea Units

New polysilsesquioxane (PSQ)-based CO2 separation membranes with succinic anhydride and monoalkylurea units as thermally degradable CO2-philic units were prepared by the copolymerization of a 1:1 mixture of [3-(triethoxysilyl)propyl]succinic anhydride (TESPS) or [3-(triethoxysilyl)propyl]urea (TESPU) and bis(triethoxysilyl)ethane (BTESE). The succinic anhydride and monoalkylurea units underwent thermal degradation to form ester and dialkylurea units, respectively, with the liberation of small molecules (e.g., CO2 and NH3) under N2 atmosphere. The effects of thermal degradation on the performance of the obtained membranes were investigated. The TESPS-BTESE- and TESPU-BTESE-based membranes calcined at 250 °C and 200 °C exhibited good CO2/N2 permselectivities of 20.2 and 14.4, respectively, with CO2 permeances of 7.7 × 10−8 and 7.9 × 10−8 mol m−2·s−1·Pa−1, respectively. When the membranes were further calcined at elevated temperatures of 350 °C and 300 °C, respectively, to promote the thermal degradation of the organic units, the CO2 permeances increased to 1.3 × 10−7 and 1.2 × 10−6 mol m−2·s−1·Pa−1 (3.9 × 102 and 3.6 × 103 GPU), although the CO2/N2 permselectivities decreased to 19.5 and 8.4, respectively. These data indicate that the controlled thermal degradation of the organic units provides a new methodology for possible tuning of the CO2 separation performance of PSQ membranes.

Graphene Oxide/Melamine/Ionic liquid membranes for selective CO2 separation

Highly permeable and selective membranes with long-term stability are needed to reduce operating and capital costs of industrial gas-separation units. In this study, we fabricate new membranes made of melamine (M)- and imidazolium-based ionic liquid (IL)-modified graphene oxide (GO) deposited on a porous support and buried with a polydimethylsiloxane (PDMS) layer. The CO2/N2 and CO2/CH4 ideal selectivities of the composite membranes are respectively 65 % and 70 % higher than those of the membranes containing only the IL. This significant improvement in ideal selectivity is attributed to synergic effects of nanochannels created by GO, fixed facilitated transport provided by the IL and numerous amine groups in the melamine structure, and the increased polarity of the membrane caused by the presence of the IL. The composite membrane has a pure CO2 permeance of 47 GPU with a high CO2/N2 ideal selectivity of 109 and a satisfactory CO2/CH4 ideal selectivity of 39. The composite membrane maintains stable performance over a 60-hour operation, highlighting its long-term reliability. The outstanding performance, coupled with the ease of fabrication, underscores the potential of these composite membranes for practical and efficient CO2 removal from both natural and flue gas streams in real-world applications.