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Hydrogen (H2) production and demand have steadily increased, leading to a rise in carbon dioxide (CO2) emissions since fossil fuels are the current raw material for H2 production. Thin film composite (TFC) hollow fiber membranes have become significant in H2 purification and CO2 capture, playing a critical role in developing next-generation fuels and supporting the United Nations Sustainable Development Goal 7 (SDG 7) – Affordable and Clean Energy, with the goal of providing universal access to clean, advanced, and renewable energy for all. However, the polymeric selective layer of TFC membranes faces a trade-off between permeability and selectivity, as well as challenges including CO2 plasticization and physical aging. Additionally, H2/CO2 separation remains particularly challenging because H2, being diffusivity-selective, permeates more quickly through the membrane due to its smaller molecular size and higher kinetic energy, while CO2, being solubility-selective, has a high affinity for dissolving in most polymeric membranes. Herein, this review provides an in-depth exploration of innovative modification strategies designed to overcome these challenges in glassy polymeric membranes and enhance H2 separation performance in the recent 10 years. Various nanofillers, such as metal-organic frameworks (MOFs) such as University of Oslo (UiO), Materials Institute Lavoisier (MILs), and Zeolitic Imidazolate Frameworks (ZIFs), have shown remarkable potential in boosting gas separation capabilities due to their superior compatibility with polymer matrices and tunable properties. The review also explores different types of hollow fiber membranes, including single layer, dual-layer, and TFC, alongside fabrication techniques like interfacial polymerization and dip-coating. Critically, the analysis highlights cutting-edge strategies to improve membrane performance, such as (i) thermal cross-linking, (ii) chemical cross-linking, (iii) ultraviolet (UV) cross-linking, (iv) polymer blends, and (v) modified fillers, along with their objectives and expected outcome. Furthermore, the review spotlights breakthroughs in H2/CO2, H2/CH4, and H2/N2 separation technologies, emphasizing the critical need for continued innovation to drive sustainable H2 production and meet the growing clean energy demand.

The influence of vacuum pressure applied on H2 separation from a palladium membrane is explored in this study. Three factors with three levels are considered, including the membrane chamber temperature with levels 320 °C, 350 °C, and 380 °C; the retentate-side total pressure with levels 1, 2, and 3 atm; and the permeation-side vacuum pressure with levels 0, 25, and 50 kPa. The Taguchi, response surface methodology (RSM), and multivariate adaptive regression splines (MARS) methods are employed to analyze the effects of the three parameters on hydrogen separation and predict their optimal combination. The retentate-side total pressure exhibits the highest impact on H2 permeation, following the permeation-side vacuum pressure and then the membrane chamber temperature. The maximum H2 flux is 0.226 mol∙s−1∙m−2, with H2 recovery of 91 % obtained at the optimal conditions with a temperature of 380 °C, a total pressure of 3 atm, and a vacuum pressure of 50 kPa. The improvement in H2 flux reaches 21.6 % compared with the case without the imposed vacuum pressure at the same temperature and total pressure. This result shows the imposed vacuum pressure is an efficient way to enhance H2 permeation. The maximum relative errors between the experimental data and the predictions from the Taguchi, RSM, and MARS methods are 6.74 %, 3.37 %, and 8.08 %, respectively. The RSM method presents higher accuracy than Taguchi and MARS, perhaps due to a more precise analysis of the interaction terms. The smaller amount of input data and ignoring the temperature effect in MARS could be the reason for the lower accuracy. Nevertheless, the MARS method still demonstrates acceptable results. The cost of the Taguchi method is lower than that of the RSM method since it requires fewer experimental cases. In a word, the choice of the prediction method depends on the desired accuracy and the experimental cost.

Depleting energy resources, global warming and environmental problems associated with conventional fuels are serious global challenges of the modern world. The substitution of conventional energy resources with more efficient and sustainable resources is inevitable. In this scenario, hydrogen (H2) has emerged as the ultimate choice due to its superior characteristics such as low carbon emissions, cleanliness, and efficiency. However, for the successful implementation of making H2as the next-generation fuel source, the hurdles of production, separation, and storage of H2should be resolved. This paper summarizes the issues and challenges in the separation of H2gas from various production streams by using available separation technologies. Different types of H2separation technologies, including membranes, adsorption processes, metal hydrides, and cryogenic separation technologies, have been considered and discussed. The review encompasses the types, advantages, and disadvantages of each technology, followed by a detailed account of issues and challenges observed in each separation method. More attention has been given to membrane technology because it is the most promising technology for the production of high-purity H2. Finally, this review provides an outlook for future directions and developments in H2separation technologies.

Experimental findings to contribute to the preliminary design of a metal foil pump for fuel separation in the Direct Internal Recycling loop of the DEMO fusion device are presented. In parametric studies on a small-scale superpermeation experiment with a microwave plasma source and two different metal foil materials, niobium Nb and vanadium V, a substantial increase in permeation with plasma power and with a decrease in pressure was observed. To ease operation in the typical fusion environment, in-situ heating procedures were developed to recover from impurity contamination. The temperature independence of plasma-driven permeation from 600 to 900 °C metal foil temperature was demonstrated. No proof of an isotopic effect for plasma-driven permeation of protium and deuterium could be found. The highest repeatable permeation flux achieved was 6.7 Pa∙m3/(m2∙s) or ~5.5 × 10−3 mol H/(m2∙s). The found compression ratios do safely allow the operation of the metal foil pump using ejector pumps as backing stages for the permeate. In a dedicated experimental setup, the operation of the plasma source in a strong magnetic field was tested. Parametric studies of pressure, power input, magnetic flux density, field gradient and field angle are presented.

Membrane separation technology provides an alternative to traditional thermally driven separations, owing to its advantages including low cost, energy-savings and environmental friendliness. However, the current membrane technology for gas separations using polymeric materials suffers the challenge of gas permeability-selectivity trade-offs. To overcome this hurdle, high-separation performance hybrid membranes are developed herein using microporous UiO-66-(OH)2 and PIM-1. Due to the stable interfacial hydrogen bonding, the MOF loading crosses the percolation threshold in hybrid membranes, and dual-path transport mechanisms govern the gas diffusion. Accordingly, the hybrid membranes with 40 wt% MOF loading exhibit a H2 permeability up to 9167.6 Barrer, transcending the 2008 H2/CH4 and H2/N2 Robeson upper bounds. Compared to neat PIM-1 membranes with a H2 permeability of 2378.3 Barrer, the H2 permeability of hybrid membranes increases over 285%, demonstrating ultra-high gas permeability. The design approach of hybrid membranes provides a viable pathway for the manufacture of hydrogen-bonded hybrid membranes with potential applications for hydrogen separation and CO2 capture.

This work investigates numerically the characteristics of the two process, hydrogen separation and steam methane reforming (SMR), in a palladium-based (Inconel-supported Pd–Ag film) membrane reactor (MR) of porous reformer (30% Ni/Al2O3) shell and multi-tube design. Still parameters like reactor design and temperature, feed gas concentration and pressure, and flow configuration need more investigation to figure out their impact on hydrogen production rate at lower energy cost and minimum possible volume. This work targets optimization of reactor performance for higher hydrogen yield and coming up with a scalable optimized reactor design for industrial applications. First, an optimization study is performed under non-reforming (separation-only) conditions to optimize the MR design and operating parameters for higher hydrogen production. Then, the study is extended to consider hydrogen separation under SMR conditions to come up with a MR design for hydrogen production at the industrial scale. Hydrogen permeation is limited to small zone near the membrane surface with no effect of feed pressure, inlet gas temperature, and feed hydrogen concentration on widening such zone that necessitates reducing the pitch distance between membrane tubes below 22 mm. The results showed reduced hydrogen permeation rate under SMR conditions compared to the separation-only cases.

In this paper, the capability of the Computational Fluid Dynamics (CFD) approach is evaluated to reliably predict the fluid dynamic and the separation performance of Pd membranes modules for gas mixture separation. In this approach, the flow fields of the pressure and velocity for the gas mixture and the species concentration distribution in the selected three-dimensional domains are obtained by simultaneous and numerical solution of continuity, momentum, and species transport (especially, gas-through-gas diffusion term that derived from the Stefan–Maxwell formulation) equations. Therefore, the calculation of the hydrogen permeation depends on the local determination of the mass transfer resistance caused by the gas phase and membrane, which is modeled as a permeable surface of known characteristics. The applicability of the model to properly predict the separation process under a wide range of pressure, feed flow rate, temperature, and gas mixtures composition is assessed through a strict comparison with experimental data. Moreover, in this work, the influence of inhibitor species on the module performance is discussed, which is obtained by implementing the CFD model. The results of the simulation showed that increasing the pressure on the feed side increases the molar fraction of hydrogen gas, the feed inlet flow on the shell side, and the hydrogen permeation through the membrane in the tube side. Comparison of simulation results with laboratory data showed good agreement. The model was obtained with an error of less than 3% at 450K and below 6% for 475K and 500K.

Pd membranes can play an important role in H2 separation and purification for the development of sustainable and renewable energies. By supporting on porous substrates, Pd layer thickness can be reduced to several micrometers, thus improving the H2 permeance by several orders of magnitude. However, the supported thin Pd membranes are concomitant with pinhole formation due to either fabrication (e.g., electroless-plating) or thermal treatment, which exist as a remarkable challenge for its widespread applications. This study presents a novel and facile approach for self-repair of Pd membrane defects by immersing the stainless-steel supported Pd membranes in PdCl2 solution. Three membranes were deliberately selected with a low selectivity of 152–1687 (400 ​°C, 0.1Mpa), for which disproportionation reactions between Pd2+ and Fe/Cr/Ni at the defect sites spontaneously occur leading to the formation of Pd particles at the exact point of defects. This self-repair process can be enhanced when applying a high pressure of 30–50 ​bar in the PdCl2 solution for 30 ​min, by overcoming the capillary resistance and penetrating through the pinholes. Interestingly, densely distributed hillocks were observed on the membrane surface probably due to reduction of PdCl2 under following H2 treatment, thus increasing the H2 permeance with a higher effective surface area. The H2/N2 selectivity can be improved by more than one order of magnitude (in the best case from 1687 to 8768) and a long-term stability test of 300 ​h was achieved for the repaired membranes, corroborating the application potential of this approach.

Membrane technology is an advanced hydrogen separation method that is of great significance in achieving hydrogen economy. Rare earth tungstate membranes have both high hydrogen permeability and remarkable mechanical/chemical stability, exhibiting good application prospects in hydrogen separation. This review provides the basic aspects and research progress on rare earth tungstate hydrogen separation membranes. The crystal structure, proton transport properties, and membrane stability under a chemical atmosphere are introduced. Different membrane construction designs, such as single-phase, dual-phase, and asymmetric rare earth tungstate membranes, are summarized. Lastly, the existing problems and development suggestions for tungstate membranes are discussed.

Hydrogen separation through oxygen transport membranes (OTMs) has attracted much attention. Asymmetric membranes with thin dense layers provide low bulk diffusion resistances and high overall hydrogen separation performances. However, the resistance in the porous support layer (PSL) limits the overall separation performance significantly. Engineering the structure of the PSL is an appropriate way to enable fast gas transport and increase the separation performance. There is no relevant research on studying the influence of the PSL on hydrogen separation performance so far. Herein, we prepared Ce0.85Sm0.15O1.925 – Sm0.6Sr0.4Cr0.3Fe0.7O3-δ (SDC-SSCF) asymmetric membranes with straight grooves in PSL by tape-casting and laser grooving. A ~30% improvement in the hydrogen separation rate was achieved by grooving in the PSLs. It indicates that the grooves may reduce the concentration polarization resistance in PSL for the hydrogen separation process. This work provides a straight evidence on optimizing the structures of PSL for improving the hydrogen separation performance of the membrane reactors.

This paper reports the fabrication of asymmetric tubular geometry lanthanum tungstate-based membranes for high temperature H2 separation applications. As starting materials, powders with the compositions La28-yW4+yO54+δ (y = 0.848), La28-yW4+yO54+δ (y = 1) and La28-y(W1-xMox)4+yO54+δ (x = 0.3, y = 1) were synthesized by solid state reaction method. Porous, thick-wall tubes made of lanthanum tungstate-based powders with high gas permeability (7–8 x10-15 m2 at 2 bar overpressure) and homogeneous porous microstructure were made by combining a cost-effective solid-state synthesis and thermoplastic extrusion method. Deposition of lanthanum tungstate-based dense thin film (∼20 μm) was achieved on top of porous supports through dip coating technique. The influence of conformation routes, thermal debindering and sintering processes were investigated in detail to achieve defect free H2 transport membranes. Asymmetric geometry membranes with ∼20 μm dense layer thickness supported on porous tubular (∼ 7.5 mm diameter and ∼0.8 mm thick) supports.As a result, a procedure for proton conducting ceramics manufacture was established which can be deployed to fabricate high temperature catalytic membrane reactors for synthetic fuel from gas-to-liquid (GTL) processes.

As an alternative route for aromatics and hydrogen production, methane dehydroaromatization (MDA) is of significant academic and industrial interest due to the abundance of natural gas resources and the intensive demand for aromatics and COx-free hydrogen. In the present work, a simulation study on MDA in membrane reactors (MRs) was performed with the aim of co-producing aromatics and COx-free hydrogen with a highly improved efficiency. The effects of various parameters, including catalytic activity, membrane flux and selectivity, as well as the operating conditions on the MR performance were discussed with respect to methane conversion, hydrogen yield, and hydrogen purity. The results show that catalytic activity and membrane flux and selectivity have significant impacts on CH4 conversion and H2 yield, whereas H2 purity is mainly dominated by membrane selectivity. A highly improved MDA is confirmed to be feasible at a relatively low temperature and a high feed pressure because of the hydrogen extraction effect. To further improve MDA in MRs by intensifying H2 extraction, a simple configuration combining a fixed-bed reactor (FBR) and an MR together is proposed for MDA, which demonstrates good potential for the high-efficiency co-production of aromatics and COx-free hydrogen.

Palladium doped silica membranes were synthesized by the sol-gel method using two different procedures. The first palladium-doped silica membrane (M1) was synthesized with a coating of four layers of silica-palladium sol. The second membrane (M2) was synthesized with a coating of two silica layers followed by a coating of two silica-palladium layers. Scanning electron microscopy (SEM) proved the formation of uniform γ-alumina interlayers on the supports. SEM results for M1 showed that synthesis of a membrane with this procedure leads to the formation of crack on the membrane selective layer. Single gas permeation measurements of H2 and N2 were carried out at room temperature, 100 °C and 550 °C. Gas permeation results revealed that Knudsen diffusion was dominant in permeation of these gases through membrane M1 while the dominant mechanism in permeation of gases through membrane M2 was activated transport which has exhibited different behavior in comparison with M1. This result is due to the activated sublayers of membrane M2. In this case, H2 permeance increases and N2 permeance decreases with increasing temperature, leading to better separation perforamce of membrane M2 over M1 in separation of H2. Therefore, using the activated silica sublayer in the synthesis of M2 can be used as a high potential method to synthesize a selective palladium-doped silica membrane.

The aim of this work is a theoretical study of multistage silica membrane configurations for hydrogen purification by methanol steam reforming (MSR) products. Four membrane schemes including single permeator, CMC (continuous membrane column), ISMC ("in series" membrane cascade), and CRC (countercurrent recycle membrane cascade) were considered for this purpose. The modeling results showed that silica membranes have a high potential for high purity (more than 99.9%) hydrogen production. The lowest amounts of compressor duty and the required total membrane area were considered as the objective functions to select the optimal design and amount of hydrogen purification. A comparison of our simulation results of the different multistage membrane schemes showed the CRC configuration was more efficient than the other configurations. The modeling results show that that increasing the retentate side pressure from 2 to 5 bar reduced the total silica membrane area for the CRC scheme by almost 13 times (30.67 and 2.37 cm2 silica membrane area for a retentate side pressure of 2 and 5 bar, respectively).

A higher density of large-angle grain boundaries in palladium membranes promotes hydrogen diffusion whereas small-angle grain boundaries suppress it. In this paper, the microstructure formation in 10 µm thick palladium membranes is tuned to achieve a submicronic grain size above 100 nm with a high density of large-angle grain boundaries. Moreover, changes in the grain boundaries’ structure is investigated after exposure to hydrogen at 300 and 500 °C. To attain large-angle grain boundaries in Pd, the coating was performed on yttria-stabilized zirconia/porous Crofer 22 APU substrates (intended for use later in an ultracompact membrane reactor). Two techniques of plasma sprayings were used: suspension plasma spraying using liquid nano-sized powder suspension and vacuum plasma spraying using microsized powder as feedstock. By controlling the process parameters in these two techniques, membranes with a comparable density of large-angle grain boundaries could be developed despite the differences in the fabrication methods and feedstocks. Analyses showed that a randomly oriented submicronic structure could be attained with a very similar grain sizes between 100 and 500 nm which could enhance hydrogen permeation. Exposure to hydrogen for 72 h at high temperatures revealed that the samples maintained their large-angle grain boundaries despite the increase in average grain size to around 536 and 720 nm for vacuum plasma spraying and suspension plasma spraying, respectively.

Owing to the excellent properties of high selectivity, high thermal stability, and low cost, in the past twenty years, mixed protonic-electronic conducting hydrogen separation membranes have received extensive attention. In particular, dual-phase mixed protonic-electronic conducting membranes with high ambipolar conductivity are more attractive because of the high hydrogen permeability. This paper aimed to present a review of research activities on the dual-phase membranes, in which the components, the characteristics, and the performances of different dual-phase membranes are introduced. The key issues that affect the membrane performance such as the elimination of the inter-phase reaction, the combination mode of the phases, the phase ratio, and the membrane configuration were discussed. The current problems and future trends were simply recommended.

Direct H2 separation using hydrogen adsorption materials has been gaining research attention for several decades. Rare-earth-metal-based alloys have proved to be feasible hydrogen adsorbents; however, their applications are restricted because of the presence of poisonous impurities, especially CO. Herein, we demonstrate the utilization of fluorinated LaNi5-based materials in elevated temperature pressure swing adsorption (ET-PSA) method for H2 separation is feasible. The adsorbent, fluorinated LaNi4.3Al0.7, maintained satisfactory working capacity at 453 K in poisonous mixed gas, which contained up to 30% CO or 0.5% H2S. During the breakthrough tests performed on a fixed bed reactor packed with, clean separations of H2/CO2+CO+N2+CH4 were observed when the feed gas component was N2/CH4/CO2/CO/H2 (45/10/10/5/30), indicating hydrogen was efficiently separated from the mixed gas in only one step, thereby simplifying the H2 separation process and the device. The mechanism of poisoning of LaNi5 by CO, and the effect of the working temperature on the CO resistance of LaNi5, were investigated using the density functional theory and ab initio molecular dynamics simulation, whose outcomes showed that the presence of CO significantly reduces the adsorption energy of H atoms. Nevertheless, at elevated temperatures (over 453 K), CO molecules was easier to escape from LaNi5 surface and less likely to completely cover the adsorbent surface, resulting in more possibility of H adsorbing on LaNi5 surface.

High stability Pd/ceramic/Ti-Al alloy composite membranes were prepared by electroless plating. Ceramic membranes fabricated by an in situ oxidation method were used as an inter-diffusion barrier between the Pd layer and the Ti-Al alloy support of the membranes to prevent intermetallic diffusion. The stabilities of the ceramic membranes at high temperatures in an H2 atmosphere were investigated. The permeation performances and stabilities of the Pd/ceramic/Ti-Al alloy composite membranes were also studied. The results showed that the thickness, pore size, and microstructure of the ceramic membranes did not change significantly after the treatment in an H2 atmosphere at high temperatures, indicating that the ceramic membranes prepared by the in situ oxidation method were stable in an H2 atmosphere at high temperatures. The thickness of the Pd layer was ~13 μm. The hydrogen permeability and H2/N2 selectivity of the Pd composite membranes at 773 K were 2.13 × 10−3 mol m−2 s−1 Pa−0.5 and 600, respectively. In addition, the H2 flux, N2 flux, and H2/N2 selectivity of the composite membranes remained nearly constant over three heat cycles (under the same conditions), indicating that the structures of the Pd/ceramic/Ti-Al alloy composite membranes were stable.

Mixed-matrix membranes (MMMs) consisting of an ortho-hydroxy polyamide (HPA) matrix, and variable loads of a porous polymer network (PPN) were thermally treated to induce the transformation of HPA to polybenzoxazole (β-TR-PBO). Two different HPAs were synthesized to be used as a matrix, 6FCl-APAF and tBTpCl-APAF, while the PPN used as a filler was prepared by reacting triptycene and trifluoroacetophenone. The permeability of He, H2, N2, O2, CH4 and CO2 gases through these MMMs are analyzed as a function of the fraction of free volume (FFV) of the membrane and the kinetic diameter of the gas, allowing for the evaluation of the free volume. Thermal rearrangement entails an increase in the FFV. Both before and after thermal rearrangement, the free volume increases with the PPN content very similarly for both polymeric matrices. It is shown that there is a portion of free volume that is inaccessible to permeation (occluded volume), probably due to it being trapped within the filler. In fact, permeability and selectivity change below what could be expected according to densities, when the fraction of occluded volume increases. A higher filler load increases the percentage of inaccessible or trapped free volume, probably due to the increasing agglomeration of the filler. On the other hand, the phenomenon is slightly affected by thermal rearrangement. The fraction of trapped free volume seems to be lower for membranes in which the tBTpCl-APAF is used as a matrix than for those with a 6FCl-APAF matrix, possibly because tBTpCl-APAF could approach the PPN better. The application of an effective medium theory for permeability allowed us to extrapolate for a 100% filler, giving the same value for both thermally rearranged and non-rearranged MMMs. The pure filler could also be extrapolated by assuming the same tendency as in the Robeson’s plots for MMMs with low filler content.

Due to high energy consumption and pollution rate caused by fossil fuels, in the world, hydrogen has been considered by many researchers as a clean fuel. Therefore, process of hydrogen separation can also be very important in this regard. Among various methods of hydrogen separation, membrane processes have been proposed as one of the promising methods for hydrogen purification. One the other hand, among several hydrogen selective membranes, inorganic membranes have also been considered more applicable owing to their high temperature tolerance. Meanwhile, in 2014, graphene membrane was first introduced for hydrogen separation, which showed a high selectivity over other inorganic membranes. Therefore, in this research, the performance of graphene membrane is evaluated using a CFD based model and the impact of important operating parameters such as pressure, temperature, membrane surface area and membrane selectivity on its performance have been investigated. According to the model results, the graphene membrane (with a 7% error) has the best performance at 293 K, while by increasing temperature up 373 K, H2 / CO2 selectivity is decreased from 2800 to 200 and permeances of hydrogen and carbon dioxide are indicated 2*10-7 mole /m2.Pa.s and 1.5*10-10 mole / m2.Pa.s, respectively. On the other hand, increasing the pressure and surface area values also show negative effects on hydrogen selectivity of graphene membranes.

The present study deals with the combination of ethanol steam reforming over a monolithic catalyst and hydrogen separation by membrane in a lab-scale catalytic membrane reactor (CMR). The catalyst was comprised of honeycomb thin-walled Fechralloy substrate loaded with Ni + Ru/Pr0.35Ce0.35Zr0.35O2 active component. The asymmetric supported membrane consisted of a thin Ni-Cu alloy–Nd tungstate nanocomposite dense permselective layer deposited on a hierarchically structured asymmetric support. It has been shown that the monolithic catalyst-assisted CMR is capable of increasing the driving potential for hydrogen permeation through the same membrane as compared with that of the packed bed catalyst by increasing the retentate hydrogen concentration. Important operating parameters responsible for the low carbon deposition rate as well as the amount of hydrogen produced from 1 mol of ethanol, such as the temperature range of 700–900 °C, the water/ethanol molar ratio of 4 in the feed, have been determined. Regarding the choice of the reagent concentration (ethanol and steam in Ar), its magnitude may directly interfere with the effectiveness of the reaction-separation process in the CMR.

Membrane separation is a compelling technology for hydrogen separation. Among the different types of membranes used to date, the mixed-matrix membranes (MMMs) are one of the most widely used approaches for enhancing separation performances and surpassing the Robeson upper bound limits for polymeric membranes. In this review, we focus on the recent progress in MMMs for hydrogen separation. The discussion first starts with a background introduction of the current hydrogen generation technologies, followed by a comparison between the membrane technology and other hydrogen purification technologies. Thereafter, state-of-the-art MMMs, comprising emerging filler materials that include zeolites, metal-organic frameworks, covalent organic frameworks, and graphene-based materials, are highlighted. The binary filler strategy, which uses two filler materials to create synergistic enhancements in MMMs, is also described. A critical evaluation on the performances of the MMMs is then considered in context, before we conclude with our perspectives on how MMMs for hydrogen separation can advance moving forward.

3D modeling of Pd/α-Al2O3 hollow fiber membrane by using computational fluid dynamic for hydrogen separation from H2/N2 mixture was considered in steady and unsteady states by using the concept of characteristic time. Characteristic time concept could help us to design and calculate surface to volume ratio and membrane thickness, and adjust the feed conditions. The contribution of resistance between the membrane and the gas phase could be analyzed by considering characteristic times. The effect of temperature on quasi-steady time was examined at constant feed flow rate and pressure. As a result, when thickness of membrane was less than the critical amount, the surface resistance was important. According to the results, about 50% mass separation was obtained in the initial 8% period of permeation time. By enhancing temperature, membrane permeation and, consequently, hydrogen separation increased. The CFD results showed good agreement with experimental data.

3D modeling of Pd/α-Al2O3 hollow fiber membrane by using computational fluid dynamic for hydrogen separation from H2/N2 mixture was considered in steady and unsteady states by using the concept of characteristic time. Characteristic time concept could help us to design and calculate surface to volume ratio and membrane thickness, and adjust the feed conditions. The contribution of resistance between the membrane and the gas phase could be analyzed by considering characteristic times. The effect of temperature on quasi-steady time was examined at constant feed flow rate and pressure. As a result, when thickness of membrane was less than the critical amount, the surface resistance was important. According to the results, about 50% mass separation was obtained in the initial 8% period of permeation time. By enhancing temperature, membrane permeation and, consequently, hydrogen separation increased. The CFD results showed good agreement with experimental data.

Extraction of hydrogen from hydrocarbons is a logical intermediate-term solution for the escalating worldwide demand for hydrogen. This work explores the possibility of using a single membrane to accomplish both the catalytic dehydrogenation and physical separation of hydrogen gas as a possible way to improve the efficiency of hydrogen production from hydrocarbon sources. The present analysis shows that regions of pressure/temperature space exist for which the overall process is thermodynamically spontaneous (ΔG < 0). Each step in the process is based on known physics. The rate of hydrogen production is likely to be controlled by the barrier to hydrogen abstraction, with the density of H-binding sites also playing a role. A critical materials issue will be the strength of the oxide/metal interface.

Solar hydrogen production via the photoelectrochemical water-splitting reaction is attractive as one of the environmental-friendly approaches for producing H2. Since the reaction simultaneously generates H2 and O2, this method requires immediate H2 recovery from the syngas including O2 under high-humidity conditions around 50 °C. In this study, a supported mesoporous γ-Al2O3 membrane was modified with allyl-hydrido-polycarbosilane as a preceramic polymer and subsequently heat-treated in Ar to deliver a ternary SiCH organic–inorganic hybrid/γ-Al2O3 composite membrane. Relations between the polymer/hybrid conversion temperature, hydrophobicity, and H2 affinity of the polymer-derived SiCH hybrids were studied to functionalize the composite membranes as H2-selective under saturated water vapor partial pressure at 50 °C. As a result, the composite membranes synthesized at temperatures as low as 300–500 °C showed a H2 permeance of 1.0–4.3 × 10−7 mol m−2 s−1 Pa−1 with a H2/N2 selectivity of 6.0–11.3 under a mixed H2-N2 (2:1) feed gas flow. Further modification by the 120 °C-melt impregnation of low molecular weight polycarbosilane successfully improved the H2-permselectivity of the 500 °C-synthesized composite membrane by maintaining the H2 permeance combined with improved H2/N2 selectivity as 3.5 × 10−7 mol m−2 s−1 Pa−1 with 36. These results revealed a great potential of the polymer-derived SiCH hybrids as novel hydrophobic membranes for purification of solar hydrogen.

The main goal of this work was to synthesize and evaluate the effect of dehydration temperature on the potential application of hydroxy sodalite zeolite membrane. Hydroxy sodalite zeolite membranes were synthesized via direct hydrothermal method onto a tubular alumina support without seeding in a hot air oven. The synthesized membranes were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Permeation tests of H2 and CO2 were carried out in order to investige the applied dehydration temperature effect on the performance of the synthesized membranes. The performance of the synthesized membrane dehydrated at 100 ºC tended to high selectivity compared to that of the rest samples and the maximum separation factor (~21) was achieved with acceptable permeances about 3.810-8 and 1.8*10-9 mol.m-2.Pa-1.s-1 for H2 and CO2, respectively. The low selectivities observed for two other synthesized membranes (dehydrated at 150 and 200 ºC), indicating the formation of defects during the dehydration of these membranes at high temperatures.

The present work is focused on the investigation of the performance and long-term stability of two composite palladium membranes under different operating conditions. One membrane (Pd/porous stainless steel (PSS)) is characterized by a ~10 µm-thick palladium layer on a porous stainless steel substrate, which is pretreated by means of surface modification and oxidation; the other membrane (Pd/Al2O3) is constituted by a ~7 µm-thick palladium layer on an asymmetric microporous Al2O3 substrate. The operating temperature and pressure ranges, used for studying the performance of these two kinds of membranes, are 350–450 °C and 200–800 kPa, respectively. The H2 permeances and the H2/N2 selectivities of both membranes were investigated and compared with literature data. At 400 °C and 200 kPa as pressure difference, Pd/PSS and Pd/Al2O3 membranes exhibited an H2/N2 ideal selectivity equal to 11700 and 6200, respectively, showing stability for 600 h. Thereafter, H2/N2 selectivity of both membranes progressively decreased and after around 2000 h, dropped dramatically to 55 and 310 for the Pd/PSS and Pd/Al2O3 membranes, respectively. As evidenced by Scanning Electron Microscope (SEM) analyses, the pinholes appear on the whole surface of the Pd/PSS membrane and this is probably due to release of sulphur from the graphite seal rings.

The effect on the gas permeance properties and structural morphology of the presence of methyl functional groups in a silica membrane was studied. Membranes were synthesized via chemical vapor deposition (CVD) at 650 °C and atmospheric pressure using three silicon compounds with differing numbers of methyl- and methoxy-functional groups: tetramethyl orthosilicate (TMOS), methyltrimethoxysilane (MTMOS), and dimethyldimethoxysilane (DMDMOS). The residence time of the silica precursors in the CVD process was adjusted for each precursor and optimized in terms of gas permeance and ideal gas selectivity criteria. Final H2 permeances at 600 °C for the TMOS-, MTMOS-, and DMDMOS-derived membranes were respectively 1.7 × 10−7, 2.4 × 10−7, and 4.4 × 10−8 mol∙m−2∙s−1∙Pa−1 and H2/N2 selectivities were 990, 740, and 410. The presence of methyl groups in the membranes fabricated with the MTMOS and DMDMOS precursors was confirmed via Fourier-transform infrared (FTIR) spectroscopy. From FTIR analysis, an increasing methyl signal in the silica structure was correlated with both an improvement in the hydrothermal stability and an increase in the apparent activation energy for hydrogen permeation. In addition, the permeation mechanism for several gas species (He, H2, Ne, CO2, N2, and CH4) was determined by fitting the gas permeance temperature dependence to one of three models: solid state, gas-translational, or surface diffusion.

Gas separation membranes were fabricated with varying trimethylmethoxysilane (TMMOS)/tetraethoxy orthosilicate (TEOS) ratios by a chemical vapor deposition (CVD) method at 650 °C and atmospheric pressure. The membrane had a high H2 permeance of 8.3 × 10−7 mol m−2 s−1 Pa−1 with H2/CH4 selectivity of 140 and H2/C2H6 selectivity of 180 at 300 °C. Fourier transform infrared (FTIR) measurements indicated existence of methyl groups at high preparation temperature (650 °C), which led to a higher hydrothermal stability of the TMMOS-derived membranes than of a pure TEOS-derived membrane. Temperature-dependence measurements of the permeance of various gas species were used to establish a permeation mechanism. It was found that smaller species (He, H2, and Ne) followed a solid-state diffusion model while larger species (N2, CO2, and CH4) followed a gas translational diffusion model.

The main purposes of this study are to evaluate the performance of graphene membranes in the separation/purification of hydrogen from nitrogen from a theoretical point of view using the molecular dynamic (MD) simulation method, and to present details about molecular mechanisms of selective gas diffusion through nanoscale pores of graphene membranes at the simulated set conditions. On the other hand, permeance and perm-selectivity are two significant parameters of such a membrane that can be controlled by several variables such as pressure gradient, pore density, pore layer angles etc. Hence, in this work, the hydrogen and nitrogen permeating fluxes as well as the H2/N2 ideal perm-selectivity are investigated from a theoretical point of view in a two-layer nanoporous graphene (NPG) membrane through classical MD simulations, wherein the effects of pressure gradient, pore density, and pore angle on the NPG membrane performance are evaluated and discussed. Simulation outcomes suggest that hydrogen and nitrogen permeating fluxes increase as a consequence of an increment of pressure gradient across the membrane and pore density.

In the present work, for the first time, a palladium-silver membrane has been prepared by electroless plating on the surface of a porous stainless steel disk by using ethylene glycol as a new reducing agent and polyol process. The reducing action of ethylene-glycol in the presence of PVP as a protecting surface agent produces a membrane with finely divided powder and nano-sized pores. Furthermore, the hydrogen separation ability of the membrane confirmed that the membrane with Pd77Ag23 is highly selective towards hydrogen compared to other prepared membranes. This is mainly related to the formation of dense and homogenous microstructure of the coating. Moreover, according to Graham’s law, the tests showed that hydrogen purity rises by increasing the applying temperature.

The Soret effect is a phenomenon in which a temperature gradient gives rise to a concentration gradient. In this study, we attempted a simple technique for the separation of hydrogen from a gas mixture by utilizing the Soret effect. A gas mixture of hydrogen and carbon dioxide was introduced into a metal mini tube in which a temperature gradient was established in the direction normal to the flow. The experiment demonstrated that hydrogen was actually separated from the gas mixture, although the separation was very small with the present apparatus. From results of the experiments and computational fluid dynamics (CFD) analysis, we believe that the layer of high hydrogen concentration that moved toward the heating wall was very thin. It would be necessary to extract the high concentration of hydrogen flowing near the wall to increase the separation efficiency.

In the last years, hydrogen has been considered as a promising energy vector for the oncoming modification of the current energy sector, mainly based on fossil fuels. Hydrogen can be produced from water with no significant pollutant emissions but in the nearest future its production from different hydrocarbon raw materials by thermochemical processes seems to be more feasible. In any case, a mixture of gaseous compounds containing hydrogen is produced, so a further purification step is needed to purify the hydrogen up to required levels accordingly to the final application, i.e., PEM fuel cells. In this mean, membrane technology is one of the available separation options, providing an efficient solution at reasonable cost. Particularly, dense palladium-based membranes have been proposed as an ideal chance in hydrogen purification due to the nearly complete hydrogen selectivity (ideally 100%), high thermal stability and mechanical resistance. Moreover, these membranes can be used in a membrane reactor, offering the possibility to combine both the chemical reaction for hydrogen production and the purification step in a unique device. There are many papers in the literature regarding the preparation of Pd-based membranes, trying to improve the properties of these materials in terms of permeability, thermal and mechanical resistance, poisoning and cost-efficiency. In this review, the most relevant advances in the preparation of supported Pd-based membranes for hydrogen production in recent years are presented. The work is mainly focused in the incorporation of the hydrogen selective layer (palladium or palladium-based alloy) by the electroless plating, since it is one of the most promising alternatives for a real industrial application of these membranes. The information is organized in different sections including: (i) a general introduction; (ii) raw commercial and modified membrane supports; (iii) metal deposition insights by electroless-plating; (iv) trends in preparation of Pd-based alloys, and, finally; (v) some essential concluding remarks in addition to futures perspectives.

Energy sources independent of fossil fuels or atomic power are of great importance to achieve a sustainable society from the viewpoint of environmental conservation and benefits. Hydrogen is considered as one of the main candidates for new sources. The steam reforming method is a major contemporary process for manufacturing hydrogen, during which carbon dioxide is simultaneously generated. Therefore, an additional process that can separate hydrogen from carbon dioxide is necessary. For this reason, we proposed the use of a new method based on the Soret effect for the separation of hydrogen and carbon dioxide. The Soret effect is capable of producing a concentration difference only by imposing a temperature difference. However, in previous studies, our group found that a single-step separation process could increase the concentration by only a few percent. Thus, a multi-step separation process is necessary for obtaining high gas concentration. In this study, we adopted micro-electromechanical system (MEMS) fabrication technology to develop a separation device and performed single-step hydrogen-separation experiments. The MEMS technology applied in this study has shown potential for the miniaturization of the device and enhancement of separation cycle number for future experiments.