Search Results (855)

The increasing concentration of atmospheric CO₂ has intensified the urgent need for efficient and sustainable carbon capture technologies. Covalent organic frameworks (COFs) have emerged as a highly promising class of porous crystalline materials for CO₂ adsorption and separation owing to their structural tunability, high surface area, and precisely designable pore environments. This review summarizes recent advances in COF-based CO₂ capture systems, covering pristine COFs, functionalized frameworks, composite materials, and membrane-based architectures. In pristine COFs, CO₂ adsorption is mainly governed by micropore confinement and physisorption within well-defined channels, where surface area and pore size distribution play key roles. Functionalized COFs introduce additional active sites, including amine groups, heteroatoms, ionic functionalities, and alkali metal centers, which significantly enhance CO₂ affinity through stronger electrostatic and acid–base interactions, often leading to mixed physisorption–chemisorption behavior. Composite COFs and mixed-matrix membranes further improve performance through synergistic effects, interfacial engineering, and enhanced mass transport. Despite these advantages, challenges remain in achieving an optimal balance between capacity, selectivity, and regenerability under realistic conditions such as humidity, low CO₂ partial pressure, and multicomponent gas streams. Issues related to scalable synthesis, structural stability, and processability also limit practical applications. Overall, this review highlights key structure–property relationships and outlines future directions, including humid-stable COFs, direct air capture, computational design strategies, and advanced membrane technologies, for next-generation CO₂ capture materials. Full article

Membrane separation is an efficient approach for volatile organic compound (VOC) recovery from industrial off-gases due to its low energy consumption, compact design, and operational simplicity. Membrane-based VOC recovery critically depends on the membrane material, which must exhibit high VOC permeability and selectivity under mixed-gas conditions. In this study, novel highly selective membranes for VOC removal based on polydecylmethylsiloxane (PAMS-10) were synthesized using both polydimethylsiloxane and various α,ω-dienes as cross-linkers: 1,7-octadiene (OD), 1,9-decadiene (DD), and 1,11-dodecadiene (DdD). The influence of cross-linker concentration and length on mechanical, structural, sorption, and transport properties was examined extensively. The combination of three independent experimental methods (time-lag, vapor permeation, and in situ spectroscopic ellipsometry) revealed that increasing α,ω-diene concentration and decreasing its length led to a reduction in the diffusivity and permeability of permanent gases, gaseous hydrocarbons, and VOC vapors. For VOC/N₂ separation, the slightly cross-linked OD-1 membrane and the DdD-5 membrane, cross-linked with long 1,11-dodecadiene, demonstrated outstanding mixed-gas selectivities of 950/921/314/840 and 940/1084/233/1106 for toluene/n-octane/i-octane/n-butyl acetate, respectively. Notably, the DD-5 membrane, cross-linked with 1,9-decadiene, matching the length of the PAMS-10 side chain substituent, exhibited the best mechanical properties and mixed-gas selectivity comparable to the ideal selectivity, a unique behavior attributed to optimal supramolecular organization. Full article

Hydrogen (H₂), produced from syngas and the Water–Gas Shift reaction, plays a vital role as both an energy carrier and an essential industrial feedstock. This preliminary study examines the effect of incorporating ionic liquids into PLA membranes for the separation of hydrogen (H₂) from carbon dioxide (CO₂), aiming to provide a more energy-efficient alternative to the conventional Pressure Swing Adsorption process. Specifically, neat PLA and composite membranes containing cholinium-based ionic liquids at concentrations of 3% and 10% were fabricated. Their thermal properties and microstructural characteristics were systematically analyzed, alongside their gas separation performance. The most promising membrane was further evaluated under humid conditions to assess the impact of water presence. The PLA membrane incorporating 3% cholinium glycinate ionic liquid demonstrated the best performance, achieving a hydrogen permeability of 111 Barrer and an H₂/CO₂ selectivity of 8.2, surpassing the Robeson Upper Bound reported in 2008. However, the presence of water led to a decline in separation performance, indicating that effective water removal is necessary prior to membrane application in hydrogen purification. Full article

Dual-layer membranes can offer significant advantages in desalination via membrane distillation (MD) compared to conventional single-layer designs. In this study, we report the development of a novel dual-layer nylon/polyvinylidene fluoride (PVDF) membrane with a Janus architecture, specifically engineered for application in sweeping gas membrane distillation (SGMD). The non-solvent induced phase separation (NIPS) method was used to cast PVDF solution on the top of a commercial nylon membrane. Water contact angle (WCA) measurements showed asymmetrical wettability. Scanning electron microscopy (SEM) confirmed that the PVDF layer was firmly anchored to the nylon support without signs of delamination. Desalination experiments were conducted using SGMD, where a significant flux enhancement as high as 81.2% was observed when the feed solution contacted the hydrophilic nylon surface while the hydrophobic PVDF surface faced the permeate side with gas flow. This enhancement was attributed to the high partitioning coefficient of the liquid–vapor mixture on the hydrophilic feed surface and the rapid vapor release across the hydrophobic permeate surface. Overall, these results demonstrate that hydrophilic membranes with small pore sizes (i.e., 0.22 µm) can serve effectively as supports when fabricated using the NIPS process, enabling new configurations for high-performance SGMD. Full article

Against the backdrop of the global energy transition, novel oxygen separation technologies that combine high selectivity, high permeability, and stability have become the key to overcoming industrial bottlenecks. Mixed ion–electron conductor (MIEC) ceramic oxygen transport membranes (OTMs), with their 100% oxygen selectivity, high oxygen permeability, and low energy consumption, are regarded as the most promising next-generation oxygen separation technology. Compared with traditional oxygen production approaches including cryogenic distillation and pressure swing adsorption (PSA), these solutions make up for their inherent defects. They have extensive application prospects in oxygen-enriched combustion, CCUS, high-efficiency hydrogen preparation and chemical synthesis processes. This paper systematically reviews the progress in the oxygen transport mechanisms, material systems, structural design, and fabrication processes of MIEC oxygen permeable membranes. Finally, we conducted an in-depth analysis of the key challenges OTMs face when applied to oxygen-enriched combustion including stability in high-temperature, complex flue gas environments and the optimization of oxygen permeability and offered insights into future research and industrialization directions. Full article

Research and development of novel CO₂-selective membranes, called molecular gate membranes (MGMs), has been conducted. Unlike conventional CO₂-selective membranes, MGMs show exceptionally high CO₂ separation over H₂. The membranes and the membrane modules were developed for CO₂ separation at low energy consumption and low cost in pre-combustion processes such as integrated gasification combined cycle (IGCC) and hydrogen production. To date, two candidate membrane materials—poly(ethylene glycol) (PEG)-based and poly(vinyl alcohol) (PVA)-based membranes—have been used. As for PEG-based membrane materials, the effect of operating conditions, such as relative humidity in feed gas and sweep gas and operating pressure, on CO₂ separation performance were investigated. Both CO₂ permeance and selectivity increased with increasing relative humidity on both the feed and permeate sides. The CO₂ permeance increased from the 10⁻¹² to the 10⁻¹¹ order, while the selectivity increased from 2.8 to 25. In addition, it was found that the water vapor permeates from the high to the low relative humidity side with a permeance typically on the order of 10⁻⁸ m³(STP)m⁻²·s⁻¹·Pa⁻¹, regardless of the total pressure difference between the feed side and the permeate side. This finding is important in the design of membrane systems. However, we found that PVA-based membranes exhibited superior thin-film coating ability and higher separation performance compared with PEG-based membranes. As for PVA-based materials, membranes that showed high CO₂ separation performance under high-pressure conditions of 2.4 MPa (the supposed pressure in the IGCC process) were successfully prepared. In addition, the technology to prepare MGMs with a large membrane area was developed by a continuous membrane-forming method, and the membrane elements (diameter: 10–20 cm; length: 20–60 cm) were also fabricated. Pre-combustion CO₂ capture tests of the membrane elements were conducted using coal-derived gasification gas, and it was confirmed that the membrane elements were durable against the real gas, which contained components such as H₂S (on the order of 100 ppm) and CO (32.4%). Full article

Mucic acid (MA) is used as a chelating agent or as a building block for bio-based polymers. MA can be produced by regioselective oxidation of D-galacturonic acid (GA). Gluconobacter oxydans is known for the partial oxidation of various substrates via membrane-bound dehydrogenases. As the wild-type strain shows only low oxidation activity towards GA, the engineered multideletion strain G. oxydans BP9.1 pta-mGDH, overexpressing a membrane-bound glucose dehydrogenase from Pseudomonas taetrolens, was used in buffered whole-cell batch biotransformations with GA as the sole substrate. Initial cell-specific MA formation rates elevated with rising educt concentrations up to 63 g L⁻¹. At pH 4, full GA conversion was only achieved with an initial GA concentration of 10 g L⁻¹. Complete conversion of 94 g L⁻¹ of GA was achieved at pH 5 with 3.4 g L⁻¹ of G. oxydans BP9.1 pta-mGDH within 48 h, resulting in >100 g L⁻¹ of MA, corresponding to a yield of >99% (mol/mol). Isolation of MA (purity > 90%) was achieved after cell separation, followed by cooling crystallization and drying, with a yield of 94%. Complete, full-yield GA conversion using non-growing cells of engineered G. oxydans in simple phosphate buffer yielded high product concentrations and enabled simple, high-yield product isolation, thus resulting in cost-effective and sustainable bioproduction of MA. Full article

Polymeric membranes are widely investigated for CO₂ separation; however, their performance is often limited by the permeability–selectivity trade-off. Incorporating metal–organic frameworks (MOFs) and designing composite membrane architectures are promising strategies to overcome these limitations. This study aims to evaluate the effect of incorporating MOF-74 (Cu and Ni variants) into a polydimethylsiloxane (PDMS) selective layer supported on a polysulfone (PSF) membrane for enhanced CO₂/N₂ separation performance. Dual-layer PDMS/PSF composite membranes were fabricated via phase inversion for the PSF support, followed by solution casting of the PDMS/MOF layer. The developed membrane architecture introduces a synergistic design that combines the mechanical robustness of PSF with the selective transport capability of PDMS and the strong CO₂ affinity of MOF-74, offering an effective strategy for improving gas separation efficiency. Gas permeation performance was assessed using single-gas CO₂ and N₂ measurements at feed pressures of 2–5 bar. The incorporation of MOF-74 improved CO₂ transport properties, with the 1 wt.% Cu-MOF-74 composite membrane achieving a CO₂ permeance of 912.5 GPU and a CO₂/N₂ ideal selectivity of 94.75. The dual-layer configuration significantly enhanced permeance compared with unsupported mixed-matrix membranes while maintaining selectivity. Additionally, the composite membranes exhibited improved mechanical strength due to the PSF support layer. The findings demonstrate that dual-layer PDMS/PSF composite membranes incorporating MOF-74 provide a promising proof-of-concept approach for improving CO₂ separation performance. Further studies involving mixed-gas testing and long-term stability are required to assess their practical applicability. Full article

Electrocatalytic CO₂ reduction reaction (CO₂RR) to ethylene (C₂H₄) has emerged as a promising approach for converting CO₂ into valuable chemicals while utilizing renewable electricity. To facilitate the commercialization of this technology, a process-level techno-economic assessment (TEA) is constructed for a plant producing 100 tons/day of C₂H₄ from coal-power flue gas CO₂ using a membrane electrode assembly (MEA) electrolyzer and downstream gas separations. The model integrates (i) flue gas CO₂ capture by chemical absorption, (ii) CO₂RR to C₂H₄ with H₂ as the only co-product, and (iii) cathode off-gas separation by pressure swing adsorption (PSA) plus anode off-gas CO₂ recovery and recycle. A Cu₁₀–Sn catalyst measured in an H-cell is projected to MEA operation by scaling current density by 10×, yielding a “Case Study in This Article” scenario of j = 246 mA·cm⁻² and FE(C₂H₄) = 48.74%. Under this scenario, the total cost is 592.61 thousand USD/day (5926 USD/ton), dominated by electricity (39.8%). Scenario analysis shows that the total cost can decrease to 76,755.0 USD/day (767.6 USD/ton) under a future-outlook case with improved electrolyzer performance and low-cost power, enabling a net profit of 19,945.0 USD/day at an ethylene selling price of 967 USD/ton. Sensitivity analysis identifies FE(C₂H₄), full-cell voltage, and electricity price as the most influential variables. The results translate laboratory catalyst metrics into industrial cost drivers and clarify quantitative performance targets for commercialization. Full article

Biogas produced from the anaerobic digestion of organic matter holds much promise as a renewable energy source for decentralized systems. However, raw biogas contains substantial volumes of carbon dioxide, hydrogen sulfide, water vapor, and other trace impurities. These impurities can reduce the calorific value of biogas and limit its direct use for household energy needs. Purifying biogas to high-grade biomethane (≥95%) is therefore important to improve methane (CH₄) content and combustion characteristics. This is a guarantee of its safe utilization in domestic appliances, including cooking, heating, lighting, and electricity generation. This article reviews and evaluates novel approaches for upgrading raw biogas into high-purity biomethane that can offset natural gas in domestic applications. It further examines recent developments in conventional and innovative upgrading technologies such as water scrubbing, chemical scrubbing, pressure swing adsorption, membrane separation, cryogenic separation, and biological upgrading. Particular emphasis is placed on low-cost and small-scale solutions suitable for off-grid or mini-grid rural energy systems. Moreover, the role of process optimization, intelligent monitoring, and data-driven control methods in increasing CH₄ recovery and process efficiency is discussed. Despite their relatively high capital costs and energy needs, conventional technologies such as water scrubbing, pressure swing adsorption, and membrane technology continue to dominate biogas purification systems. The findings show that coupling advanced separation technologies, including cryogenic separation, biological upgrading, and hybrid technologies, with optimized process control can significantly improve CH₄ purity, save energy use, and enhance the overall consistency of biogas purification systems. These innovative strategies have strong potential to promote the full-scale adoption of biomethane as a clean, sustainable, and affordable energy source for decentralized applications, particularly in the developing world. Full article

In this study, the task of integrating capture and conversion of CO₂ into a single material platform is realized by developing bifunctional membranes based on polymer ionic liquids (PILs). The novelty of this work lies in the fabrication and comprehensive evaluation of PIL-based membrane materials that combine catalytic activity toward CO₂ conversion with gas separation performance within one material system. In contrast to most previously reported imidazolium-based PILs, which have mainly been considered either as catalysts or as membrane materials, the present approach focuses on their dual functionality under both catalytic and gas transport conditions. A series of imidazolium-based PILs, including homopolymers and block copolymers with polystyrene, were synthesized. The materials were characterized to determine their catalytic activity during the cycloaddition of CO₂ to epichlorohydrin and to determine their gas transport properties using pure gases (N₂, O₂, CO₂) and a simulated dry flue gas mixture; membrane morphology was studied by scanning electron microscopy. Block copolymers exhibited higher catalytic conversions (up to 82.7%) than homopolymers, with selectivities above 93%. Chloride-containing block copolymers gave the best combination of CO₂ permeability (up to 7.5 Barrer) and CO₂/N₂ selectivity (18–22) under mixed-gas conditions. Iodide-containing analogs demonstrated higher selectivity (up to 30) but lower CO₂ permeability. Morphological analysis confirmed the presence of dense, defect-free structures in materials with the chloride anion, while materials with the iodide anion showed increased free volume and microheterogeneity. These results indicate that by altering the polymer and anion architecture, PIL-based membranes can effectively combine catalytic activity with selective CO₂ transport, providing a promising avenue for enhancing carbon capture and utilization processes. Full article

Large-scale and long-term hydrogen storage is one of the main obstacles to the wider use of hydrogen as a possible substitute for natural gas. A solution could be depleted natural gas fields, which have proven capacity and are already geologically prospected. However, part of this field remains occupied by residual natural gas, meaning that hydrogen is mixed with natural gas during storage and purification after extraction is therefore necessary. The aim of this study was to design and evaluate a hydrogen purification process for separating hydrogen from natural gas after extraction from a depleted natural gas field while maintaining the required hydrogen purity and recovery. Input data provided by Nafta a.s. were used for the mathematical simulation of hydrogen separation throughout a 150-day extraction period. A mathematical model of membrane separation and pressure swing adsorption (PSA) was developed. A single membrane stage was only able to operate effectively during the first 50 days of withdrawal while maintaining at least 80% hydrogen recovery. A two-stage membrane configuration achieved hydrogen purity above 98% with final recoveries above 80–85%, while the hybrid membrane–PSA system enabled hydrogen purity of 99.8% and total recovery of 82.5% on the last day of extraction. Full article

This study investigates the development of mixed matrix membranes based on polyethersulfone incorporated with attapulgite for gas separation applications, addressing the existing gap regarding the use of this mineral in dense membranes obtained exclusively by solvent evaporation and its combined effects on microstructure and transport. The membranes were prepared by phase inversion via solvent evaporation, using solvent/polymer ratios of 75/25 and 80/20 and a thickness of 0.25 mm. The solutions were evaluated in terms of viscosity, and the membranes were characterized by structural techniques such as X-ray diffraction (XRD), atomic force microscope (AFM), contact angle, mechanical properties (tensile testing), and water vapor permeation. The results showed that attapulgite incorporation promoted a reduction in surface roughness (up to ~40%) and a decrease in contact angle (from ~89° to ~68°), indicating increased hydrophilicity. In addition, water vapor permeability was influenced in a non-linear manner, with optimized performance observed at 3 wt% filler loading. Solution viscosities remained within ranges suitable for processing. Structural analyses indicated compatibility between the phases, while morphology changes dependent on filler content were decisive for transport behavior. It is concluded that attapulgite is a promising additive for fine-tuning membrane properties, enabling optimization of the sorption–diffusion balance and improvement of membrane performance in separation applications. Full article

The permeation of gases through membranes is a fundamental process with wide-ranging applications, from gas separation and fuel cell technology to respiratory physiology. Governed by Fick’s second law of diffusion, the mathematical modelling of such transport processes often becomes analytically and computationally challenging, especially in heterogeneous, mixed matrix, or multilayered systems. To navigate these complexities, this study revisits and expands upon the use of electrical analogies as an intuitive and powerful modelling approach rooted in mid-20th-century analog computing. By leveraging the mathematical equivalence between diffusion and electrical conduction, we construct an equivalent electrical network that mirrors the transient behaviour of gas permeation across membranes. In this framework, concentration gradients are represented as voltage differences, diffusive fluxes as electrical currents, and diffusional resistances as circuit resistances. While traditional applications of electrical analogies have largely focused on steady-state phenomena, our approach enables dynamic analysis, offering conceptual clarity and computational efficiency. This methodology not only simplifies the solution of Fick’s second law but also reinforces the enduring relevance of analogical thinking in modern engineering practice. Comparative results demonstrate that the equivalent electrical circuit closely aligns with both analytical and finite difference solutions, validating its effectiveness and accuracy. Full article

Perovskite mixed proton–electron hydrogen-permeable membranes have been widely applied in the field of membrane separation due to their 100% selectivity for hydrogen separation. La_5.5WO_11.25-δ-La_0.87Sr_0.13CrO_3-δ (LWO-LSF) four-channel hollow fiber membranes were prepared by the phase inversion and sintering technique using a one-step thermal processing (OSTP) approach. The effects of temperature, feed gas concentration, sweep gas flow, permeation mode, and water vapor on hydrogen flux were systematically investigated. At 900 °C, the hydrogen permeation flux of 50% H₂/N₂ feed from the shell side to the lumen side was 0.613 mL·min⁻¹·cm⁻², which was 62.59% higher than that from the lumen side to the shell side. The enhanced hydrogen permeation performance is attributed to the lower gas mass transfer resistance under shell-side feeding. Under humidified conditions on the sweep side, the hydrogen flux increased by an additional 3.42%. The presence of water vapor increased the number of proton carriers, effectively enhancing proton–electron-coupled transport and thereby increasing the hydrogen permeation flux. Full article