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Membranes for Hydrogen Rainbow toward Industrial Decarbonization: Status, Challenges and Perspectives from Materials to Processes
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Hydrogen is a clean energy carrier that will allow the world to accomplish its strategic targets of zero-emission and the decarbonization of industry. The development of environmentally friendly, energy-efficient hydrogen production processes gains increased attention from both academia and industry. Blue hydrogen produced from the steam methane reforming process integrated with CO2 capture is considered the bridge for an energy transition from fossil fuels to a hydrogen economy. While green hydrogen production from water electrolysis using renewable energies of wind and solar power is becoming a hot topic, and several large-scale green hydrogen projects are under deployment. Membrane technology can be instrumental for hydrogen production and enrichment either in the blue or green form. The challenge of bringing down the costs for membrane materials such as hydrogen-selective membranes, polymer electrolyte membranes (PEM), and anion exchange membranes (AEM), etc. must be addressed to enhance their competitiveness compared to the grey hydrogen produced from fossil fuels. Other challenges including the aging phenomenon, long-time stability, performance enhancement, and upscaling should be also overcome for hydrogen rainbow towards industrial decarbonization. Furthermore, suitable process intensification techniques based on membranes can effectively enhance the energy efficiency of the whole process to enable the practical deployment of this technology. Herein, this work conducts a critical review of the status of membrane material performances and the challenges of membrane processes for hydrogen production, purification, and recovery. Some emerging materials like two-dimensional (2D) nanomaterials and carbon membranes show a particular interest in this field. However, to meet the requirements of different scenarios, further developments of materials and modules, combining membranes with other processes or technologies, and incorporating process simulation are necessary and urgent. 50 days' free access: https://authors.elsevier.com/a/1hK-Z4x7R2gOu%7E
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... The drive toward environmentally sustainable and energy-efficient hydrogen production gains momentum, spotlighting green hydrogen and blue hydrogen from water electrolysis and steam methane reforming (SMR), respectively. Blue hydrogen, integrating CO 2 capture with reforming, serves as a transitional solution in the shift from fossil fuels to a hydrogen economy, while green hydrogen, produced through electrolysis with renewable energies, takes the forefront in large-scale projects (Lei et al., 2021;Yuan et al., 2023). ...
... Additionally, the 30-year lifespan of solar panels necessitates careful management as special waste at the end of their life (Osman et al., 2022). Despite the dominance expected for green hydrogen in the sustainable energy system of the future, blue hydrogen remains a vital player in expediting the energy transition (Yuan et al., 2023). In addition, the transition to sustainable energy systems requires a comprehensive assessment of hydrogen energy and the hydrogen economy. ...
In the pursuit of sustainable energy solutions, hydrogen emerges as a promising candidate for decarbonization. The United States has the potential to sell wind energy at a record‐low price of 2.5 cents/kWh, making hydrogen production electricity up to four times cheaper than natural gas. Hydrogen's appeal stems from its highly exothermic reaction with oxygen, producing only water as a byproduct. With an energy content equivalent to 2.4 kg of methane or 2.8 kg of gasoline per kilogram, hydrogen boasts a superior energy‐to‐weight ratio compared to fossil fuels. However, its energy‐to‐volume ratio, exemplified by liquid hydrogen's 8.5 MJ.L ⁻¹ versus gasoline's 32.6 MJ.L ⁻¹ , presents a challenge, requiring a larger volume for equivalent energy. In addition, this review employs life cycle assessment (LCA) to evaluate hydrogen's full life cycle, including production, storage, and utilization. Through an examination of LCA methodologies and principles, the review underscores its importance in measuring hydrogen's environmental sustainability and energy consumption. Key findings reveal diverse hydrogen production pathways, such as blue, green, and purple hydrogen, offering a nuanced understanding of their life cycle inventories. The impact assessment of hydrogen production is explored, supported by case studies illustrating environmental implications. Comparative LCA analysis across different pathways provides crucial insights for decision‐making, shaping environmental and sustainability considerations. Ultimately, the review emphasizes LCA's pivotal role in guiding the hydrogen economy toward a low‐carbon future, positioning hydrogen as a versatile energy carrier with significant potential.
This article is categorized under: Emerging Technologies > Hydrogen and Fuel Cells
... Among the technologies employed for this capture, and in the case of CO 2 specifically, absorption, adsorption, and membrane technologies are the most widely proposed. Several recent reviews on the utilization of these technologies have been published, including the use of membranes [1]; MXene-based membranes [2]; composite membranes [3,4]; microporous membranes composed of nanopores [5]; nanomaterials [6][7][8][9][10][11], and more specifically, graphene and its 2D nanomaterial derivatives [12]; nanomaterials derived with support from artificial intelligence (AI) [13]; kaolinite-based nanomaterials [14]; MXene nanoderivatives [15]; azobenzene-based supramolecular materials [16]; carbon-bearing nanomaterials [17]; nanobiotechnology using microalgae [18]; nanomaterials for catalystassisted solvent regeneration in absorption processes using amine [19]; and finally, some general reviews on technologies for CO 2 removal from gas streams [20][21][22][23]. ...
Since CO2 is an important component of gas emissions, its removal from gas streams is of the utmost importance to fulfill various environmental requirements. The technologies used to accomplish this removal are based mainly on absorption, as well as adsorption and membrane processing. Among the materials used in the above separation processes, materials in nano forms offer a potential alternative to other commonly used macromaterials. The present work reviews the most recent publications (2023) about CO2 capture using different nanomaterials, and whilst most of these publications were dedicated to investigating the above, several presented data on the separation of CO2 from other gases, namely nitrogen and methane. Furthermore, a number of publications investigated the recyclability of nanomaterials under continuous use, and just three of the references were about computational modeling; all others were experimental papers, and only one reference used a real industrial gas.
Hydrogen is widely regarded as an ideal energy source, while the difficulties related to storage and transportation restricted its affordable employments. Ammonia, as a zero-carbon substance with properties of high hydrogen content, easy liquefaction and excellent safety, is recognized as a promising hydrogen carrier. In the past decades, much effort has been dedicated into the transformation from ammonia to hydrogen. Herein, this work provided some references for the future development of ammonia decomposition based hydrogen production systems under the theme of sustainable development. The ammonia decomposition technologies, including combustion/electric/solar heating, plasma, photo/electro catalysis, and the key materials including thermal/photo/electro catalysts for kinetics improvement, were presented and compared. Then, the hydrogen separation technologies including pressure swing adsorption and permeable membranes were introduced. Particularly, the recent progress of ammonia decomposition reactors and hydrogen production systems were discussed and summarized. Finally, the characteristics of diverse ammonia decomposition reactors and hydrogen production system were evaluated, followed with the recommendations and perspectives on their different application scenarios.
Polybenzimidazole (PBI) membranes show excellent chemical stability and low vanadium crossover in vanadium redox flow batteries (VRFBs), but their high resistance is challenging. This work introduces a concept, membrane assemblies of a highly selective 2 µm thin PBI membrane between two 60 µm thick highly conductive PBI gel membranes, which act as soft protective layers against external mechanical forces and astray carbon fibers from the electrode. The soft layers are produced by casting phosphoric acid solutions of commercial PBI powder into membranes and exchanging the absorbed acid into sulfuric acid. A conductivity of 565 mS cm⁻¹ is achieved. A stability test indicates that gel mPBI and dense PBI‐OO have higher stability than dense mPBI and dense py‐PBI, and gel/PBI‐OO/gel is successfully tested for 1070 cycles (ca. 1000 h) at 100 mA cm⁻² in the VRFB. The initial energy efficiency (EE) for the first 50 cycles is 90.5 ± 0.2%, and after a power outage stabilized at 86.3 ± 0.5% for the following 500 cycles. The initial EE is one of the highest published so far, and the materials cost for a membrane assembly is 12.35 U.S. dollars at a production volume of 5000 m², which makes these membranes very attractive for commercialization.
The development of sustainable energy technology has received considerable attention to meet the increasing energy demands and realize carbon neutrality. Hydrogen is a promising alternative energy source to replace fossil fuels and mitigate environmental issues. However, most hydrogen is produced by reforming fossil fuels, called gray hydrogen, and the production of gray hydrogen emits a large amount of carbon dioxide. As a sustainable approach, water electrolysis technology has been developed to produce high‐purity hydrogen, called green hydrogen. Among various technologies, water electrolysis equipped with an anion exchange membrane has been regarded as an attractive pathway for large‐scale H2 production at a low cost. The status of anion exchange membrane water electrolyzers is approaching toward megawatt‐scale H2 production by companies, which has the potential to become competitive technology for existing water electrolyzers (alkaline electrolyzer, proton exchange membrane electrolyser). This review article represents recent advances in the development of major components (membrane, catalyst, membrane electrode assembly) of anion exchange water electrolyzers. By recognizing the current water electrolysis performance and solving the remaining challenges, anion exchange membrane electrolysis can be a leading technology for green hydrogen production. Anion exchange membrane water electrolysis (AEMWE) is a technology that complements the disadvantages of alkaline water electrolysis and proton exchange membrane water electrolysis. However, AEMWE possesses several challenges to be overcome for sustainable large‐scale hydrogen production. Component development and optimization of cell operation are prerequisites for the practical AEMWEs with high stability and current density.
Anion‐exchange‐membrane water electrolyzers (AEMWEs) in principle operate without soluble electrolyte using earth‐abundant catalysts and cell materials and thus lower the cost of green H2. Current systems lack competitive performance and durability needed for commercialization. One critical issue is a poor understanding of catalyst‐specific degradation processes in the electrolyzer. While non‐platinum‐group‐metal (non‐PGM) oxygen‐evolution catalysts show excellent performance and durability in strongly alkaline electrolyte, this has not transferred directly to pure‐water AEMWEs. Here, AEMWEs with five non‐PGM anode catalysts are built and the catalysts’ structural stability and interactions with the alkaline ionomer are characterized during electrolyzer operation and post‐mortem. The results show catalyst electrical conductivity is one key to obtaining high‐performing systems and that many non‐PGM catalysts restructure during operation. Dynamic Fe sites correlate with enhanced degradation rates, as does the addition of soluble Fe impurities. In contrast, electronically conductive Co3O4 nanoparticles (without Fe in the crystal structure) yield AEMWEs from simple, standard preparation methods, with performance and stability comparable to IrO2. These results reveal the fundamental dynamic catalytic processes resulting in AEMWE device failure under relevant conditions, demonstrate a viable non‐PGM catalysts for AEMWE, and illustrate underlying design rules for engineering anode catalyst/ionomer layers with higher performance and durability. This article is protected by copyright. All rights reserved
Carbon nanotube (CNT) is a prominent material for gas separation due to its inherent smoothness of walls, allowing rapid transport of gases compared to other inorganic fillers. It also possesses high mechanical strength, enabling membranes to operate at high pressure. Although it has superior properties compared to other inorganic fillers, preparation of CNTs into a polymer matrix remains challenging due to the strong van der Waals forces of CNTs, which lead to agglomeration of CNTs. To utilize the full potential of CNTs, proper dispersion of CNTs must be addressed. In this paper, methods to improve the dispersion of CNTs using functionalization methods were discussed. Fabrication techniques for CNT mixed-matrix membrane (MMM) nanocomposites and their impact on gas separation performance were compared. This paper also reviewed the applications and potential of CNT MMMs in gas separation.
As highlighted by the recent roadmaps from the European Union and the United States, water electrolysis is the most valuable high‐intensity technology for producing green hydrogen. Currently, two commercial low‐temperature water electrolyzer technologies exist: alkaline water electrolyzer (A‐WE) and proton‐exchange membrane water electrolyzer (PEM‐WE). However, both have major drawbacks. A‐WE shows low productivity and efficiency, while PEM‐WE uses a significant amount of critical raw materials. Lately, the use of anion‐exchange membrane water electrolyzers (AEM‐WE) has been proposed to overcome the limitations of the current commercial systems. AEM‐WE could become the cornerstone to achieve an intense, safe, and resilient green hydrogen production to fulfill the hydrogen targets to achieve the 2050 decarbonization goals. Here, the status of AEM‐WE development is discussed, with a focus on the most critical aspects for research and highlighting the potential routes for overcoming the remaining issues. The Review closes with the future perspective on the AEM‐WE research indicating the targets to be achieved.
Anion-exchange membrane (AEM) fuel cells (AEMFCs) and water electrolyzers (AEMWEs) have gained strong attention of the scientific community as an alternative to expensive mainstream fuel cell and electrolysis technologies. However, in the high pH environment of the AEMFCs and AEMWEs, especially at low hydration levels, the molecular structure of most anion-conducting polymers breaks down because of the strong reactivity of the hydroxide anions with the quaternary ammonium (QA) cation functional groups that are commonly used in the AEMs and ionomers. Therefore, new highly stable QAs are needed to withstand the strong alkaline environment of these electrochemical devices. In this study, a series of isoindolinium salts with different substituents is prepared and investigated for their stability under dry alkaline conditions. We show that by modifying isoindolinium salts, steric effects could be added to change the degradation kinetics and impart significant improvement in the alkaline stability, reaching an order of magnitude improvement when all the aromatic positions are substituted. Density functional theory (DFT) calculations are provided in support of the high kinetic stability found in these substituted isoindolinium salts. This is the first time that this class of QAs has been investigated. We believe that these novel isoindolinium groups can be a good alternative in the chemical design of AEMs to overcome material stability challenges in advanced electrochemical systems.
Anion‐exchange membrane fuel cells (AEMFCs) are promising energy conversion devices due to their high efficiency. Nonetheless, AEMFC operation time is currently limited by the low chemical stability of their polymeric anion‐exchange membranes. In recent years, metallopolymers, where the metal centers assume the ion transport function, have been proposed as a chemically stable alternative. Here we present a systematic study using a polymer backbone with side‐chain N‐heterocyclic carbene (NHC) ligands complexed to various metals with low oxophilicity, such as copper, zinc, nickel, and gold. The golden metallopolymer, using the metal with the lowest oxophilicity, demonstrates exceptional alkaline stability, far superior to state‐of‐the‐art quaternary ammonium cations, as well as good in situ AEMFC results. These results demonstrate that judiciously designed metallopolymers may be superior to purely organic membranes and provides a scientific base for further developments in the field.
Membrane systems for CO2 capture have become increasingly attractive due to their higher energy efficiency, smaller footprint, and lower environmental impact. However, membrane systems should be operated at the optimal condition for a given separation scenario to achieve a significant cost-reduction benefit. This work paid particular attention to the insight of membrane system design and comparison of different membranes for various post-combustion CO2 capture scenarios. The four membranes demonstrated at pilot scale have been investigated for carbon capture in the cement factory and fossil fuel-fired power plants, and the specific cost of <20 $/tonne CO2 captured for both Polaris and PolyActive membranes were found in the scenarios where the flue gases contain high-content CO2 of >13 vol.%. The membrane units with an estimated footprint of fewer than 7 standard 40-foot containers can be realistically installed in a cement plant. It is recommended that the deployment of membrane systems for CO2 capture should be prioritized in the energy-intensive industries due to a relatively smaller gas volume to be processed compared to power plants. Moreover, membrane systems are better to be operated at a moderate CO2 capture ratio of 70-80 % and pursuing a very high capture ratio of 90 % will not be economically beneficial.
Metal–organic frameworks (MOFs) are found to be promising porous crystalline materials for application in gas separation. Considering that mixed matrix membranes usually increase the gas separation performance of a polymer by increasing selectivity, permeability, or both (i.e., perm-selectivity), the zeolitic imidazole framework-95 (ZIF-95) MOF was dispersed for the first time in polysulfone (PSF) polymer to form mixed matrix membranes (MMMs), namely, ZIF-95/PSF. The fabricated ZIF-95/PSF membranes were examined for the separation of various gases. The characterization of solvothermally synthesized ZIF-95 was carried out using different analyses such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), porosity measurements, etc. ZIF-95 was mixed with PSF at 8%, 16%, 24%, and 32% weight percent to form different loading MMMs. SEM analysis of membranes revealed good compatibility/adhesion between the MOF and polymer. The permeability of He, H2, O2, CO2, N2, and CH4 were measured for the pure and composite membranes. The ideal selectivity of different gas pairs were calculated and compared with reported mixed matrix membranes. The maximum increases in permeabilities were observed in 32% loaded membrane; nevertheless, these performance/permeability increases were at the expense of a slight decrease of selectivity. In the optimally loaded membrane (i.e., 24 wt% loaded membrane), the permeability of H2, O2, and CO2 increased by 80.2%, 78.0%, and 67.2%, respectively, as compared to the pure membrane. Moreover, the selectivity of H2/CH4, O2/N2, and H2/CO2 gas pairs also increased by 16%, 15%, and 8% in the 24% loaded membrane, respectively.
Polybenzimidazole (PBI) is a promising and suitable membrane polymer for the separation of the H 2 /CO 2 pre-combustion gas mixture due to its high performance in terms of chemical and thermal stability and intrinsic H 2 /CO 2 selectivity. However, there is a lack of long-term separation studies with this polymer, particularly when it is conformed as hollow fibre membrane. This work reports the continuous measurement of the H 2 /CO 2 separation properties of PBI hollow fibres, prepared as mixed matrix membranes with metal-organic framework (MOF) ZIF-8 as filler. To enhance the scope of the experimental approach, ZIF-8 was synthesized from the transformation of ZIF-L upon up-scaling the MOF synthesis into a 1 kg batch. The effects of membrane healing with poly(dimethylsiloxane), to avoid cracks and non-selective gaps, and operation conditions (use of sweep gas or not) were also examined at 200°C during approximately 51 days. In these conditions, for all the membrane samples studied, the H 2 permeance was in the 22–47 GPU range corresponding to 22–32 H 2 /CO 2 selectivity values. Finally, this work continues our previous report on this type of application (Etxeberria-Benavides et al . 2020 Sep. Purif. Technol. 237 , 116347 ( doi:10.1016/j.seppur.2019.116347 )) with important novelties dealing with the use of ZIF-8 for the mixed matrix membrane coming from a green methodology, the long-term gas separation testing for more than 50 days and the study on the membrane operation under more realistic conditions (e.g. without the use of sweep gas).
Carbon molecular sieve (CMS) membranes have been developed to replace or support energy-intensive cryogenic distillation for olefin/paraffin separation. Olefin and paraffin have similar molecular properties, but can be separated effectively by a CMS membrane with a rigid, slit-like pore structure. A variety of polymer precursors can give rise to different outcomes in terms of the structure and performance of CMS membranes. Herein, for olefin/paraffin separation, the CMS membranes derived from a number of polymer precursors (such as polyimides, phenolic resin, and polymers of intrinsic microporosity, PIM) are introduced, and olefin/paraffin separation properties of those membranes are summarized. The effects from incorporation of inorganic materials into polymer precursors and from a pyrolysis process on the properties of CMS membranes are also reviewed. Finally, the prospects and future directions of CMS membranes for olefin/paraffin separation and aging issues are discussed.
The increased demand for a reliable and sustainable renewable energy source encourages the hydrogen-based economy. For the same, membrane separation approaches were reviewed as an advantageous process over contemporary techniques due to the environmentally friendly nature, economically viable pathway, and easily adaptable technology. A comprehensive assessment for the advancements in the type of membranes namely, polymeric and mixed matrix membranes (MMMs) has been delineated in the present article with the fabrication methodologies and associated mechanism for hydrogen separation. In hydrogen separation mechanism of the membrane, depends on the morphology of the membrane (dense or porous). The existence of pores in membranes offers various gas transport mechanisms such as Knudsen diffusion, surface diffusion, capillary condensation, molecular sieving mechanisms were observed, depending on the pore size of membranes and in dense membrane gas transport through the solution-diffusion mechanism. In polymer membrane, hydrogen separation occurs mainly due to solubility and diffusivity of gases. The hydrogen separation mechanism in MMMs is very complex due to the combining effect of polymer and inorganic fillers. So, the gas separation performance of MMMs was evaluated using the modified Maxwell model. Moreover, adequate polymeric material and inorganic fillers have been summarised for MMMs synthesis and highlighting the mechanism for gas transport phenomena in the process. Several types of materials implemented with polymeric matrix examined in the literature, amongst these functionally aligned CNTs with Pd-nanoparticles dispersed in polymer matrix were observed to reveal the best outcome for the hydrogen separation membrane due to the uniform distribution of inorganic material in the matrix. Henceforth, the agglomeration gets reduced promoting hydrogen separation.
Catalytic membrane reactors have been widely used in different production industries around the world. Applying a catalytic membrane reactor (CMR) reduces waste generation from a cleaner process perspective and reduces energy consumption in line with the process intensification strategy. A CMR combines a chemical or biochemical reaction with a membrane separation process in a single unit by improving the performance of the process in terms of conversion and selectivity. The core of the CMR is the membrane which can be polymeric or inorganic depending on the operating conditions of the catalytic process. Besides, the membrane can be inert or catalytically active. The number of studies devoted to applying CMR with higher membrane area per unit volume in multi-phase reactions remains very limited for both catalytic polymeric and inorganic membranes. The various bio-based catalytic membrane system is also used in a different commercial application. The opportunities and advantages offered by applying catalytic membrane reactors to multi-phase systems need to be further explored. In this review, the preparation and the application of inorganic membrane reactors in the different catalytic processes as water gas shift (WGS), Fisher Tropsch synthesis (FTS), selective CO oxidation (CO SeLox), and so on, have been discussed.
Bipolar membrane|electrode interface water electrolyzers (BPEMWE) were found to outperform a proton exchange membrane (PEM) water electrolyzer reference in a similar membrane electrode assembly (MEA) design based on individual porous...
Nowadays, we face a series of global challenges, including the growing depletion of fossil energy, environmental pollution, and global warming. The replacement of coal, petroleum, and natural gas by secondary energy resources is vital for sustainable development. Hydrogen (H2) energy is considered the ultimate energy in the 21st century because of its diverse sources, cleanliness, low carbon emission, flexibility, and high efficiency. H2 fuel cell vehicles are commonly the end-point application of H2 energy. Owing to their zero carbon emission, they are gradually replacing traditional vehicles powered by fossil fuel. As the H2 fuel cell vehicle industry rapidly develops, H2 fuel supply, especially H2 quality, attracts increasing attention. Compared with H2 for industrial use, the H2 purity requirements for fuel cells are not high. Still, the impurity content is strictly controlled since even a low amount of some impurities may irreversibly damage fuel cells’ performance and running life. This paper reviews different versions of current standards concerning H2 for fuel cell vehicles in China and abroad. Furthermore, we analyze the causes and developing trends for the changes in these standards in detail. On the other hand, according to characteristics of H2 for fuel cell vehicles, standard H2 purification technologies, such as pressure swing adsorption (PSA), membrane separation and metal hydride separation, were analyzed, and the latest research progress was reviewed.
Asymmetric carbon molecular sieve (CMS) membranes prepared from cellulose hollow fiber precursors were investigated for H2/CO2 separation in this work. The prepared carbon membrane shows excellent separation performance with H2 permeance of 111 GPU and an H2/CO2 selectivity of 36.9 at 10 bar and 110 °C dry mixed gas. This membrane demonstrates high stability under a humidified gas condition at 90 °C and the pressure of up to 14 bar. A two-stage carbon membrane system was evaluated to be techno-economically feasible to produce high-purity H2 (>99.5 vol%) by HYSYS simulation, and the minimum specific H2 purification cost of 0.012 $/Nm3 H2 produced was achieved under the optimal operating condition. Sensitivity analysis on the H2 loss and H2 purity indicates that such membrane is still less cost-effective to achieve ultrapure hydrogen (e.g., >99.8 vol%) unless the higher operating temperatures for carbon membrane systems are applied.
https://www.sciencedirect.com/science/article/pii/S0376738821001915
Anthropogenic emissions have developed the environmental demands for proficient carbon dioxide (CO2) separation technologies. Adsorption and membrane technologies are widely used to separate CO2 from other light gases due to their multiple technological benefits, including but not limited to factors such as energy efficiency and low environmental footprint. In this context, zeolites are often used due to their intrinsic molecular sieving capacity. This review initially addresses recent technological advances to enhance the gas separation performance of zeolite materials. Current trends directed toward improving CO2 adsorption capacity of zeolites include amine, silica, and ion-exchange modifications. Other promising efforts to improve the adsorption performance of zeolites involve processing zeolite nanoparticles, nanofibers, and zeolite-based foams. The second part of the review deals with pristine and modified zeolites beneficial properties for designing polymer-based mixed matrix membranes (MMMs), which enable to adapt a desirable gas separation performance. The gas transport mechanisms and morphological properties of MMMs are essential. This review addresses the most current strategies used to improve interfacial adhesions between zeolite particulates and polymer matrices to overcome the trade-off between gas selectivity and permeability faced by pure polymeric membranes. Filler shape and size play vital roles in determining the filler and polymer matrix's interfacial adhesions. New structures of inorganic fillers have been designed to fabricate MMMs with excellent gas transport properties. Hollow zeolite spheres (HZSs) are particularly interesting as they effectively minimize agglomeration and improve filler dispersion in the polymer matrix. Furthermore, approaches that employ nanoporous layered fillers, including AMH-3 and Jilin-Davy-Faraday, layered solid No. 1 (JDF-L1), have been reviewed to overcome the limitation of incorporating high contents of zeolites, which are required to improve the gas transport properties of MMMs. Furthermore, this review explores implementing zeolitic imidazolate frameworks (ZIFs) in MMMs because of their tunable pore structure and remarkably high adsorption capacity and surface area as well as excellent chemical and thermal properties. Lastly, we address the prospects and future developments in gas separation applications.
To prove the usefulness and achieve penetration of microporous ceramic membranes in gas separation applications of industrial interest, their behavior needs to be validated and predicted at relatively realistic conditions. In this respect, the present study employed hybrid silica (HybSi) membranes, modified by chemical vapor infiltration (CVI) in order to render them more selective to hydrogen in hydrogen/carbon dioxide binary mixtures, which are representative to effluent streams of methane or biogas steam reforming/water gas shift processes. Experimental studies with a single modified membrane exhibited high hydrogen permeance (1.5.10⁻⁷ mol.m-2.s-1.Pa⁻¹, at 250 oC) and H2/CO2 permselectivity (H2/CO2=61.3, at 250 oC). Gas separation tests with binary gas mixtures revealed that high hydrogen purity values (>99%) can be reached at different process conditions. The mathematical model, also developed in this study in order to interpret the experimental results, can reliably predict hydrogen separation process performance over a wide range of operating conditions and also serve as a tool for subsequent optimum process engineering purposes.
Carbon molecular sieve (CMS) membranes with rigid and uniform pore structures are ideal candidates for high temperature- and pressure-demanded separations, such as hydrogen purification from the steam methane reforming process. Here, we report a facile and scalable method for the fabrication of cellulose-based asymmetric carbon hollow fiber membranes (CHFMs) with ultramicropores of 3–4 Å for superior H2 separation. The membrane fabrication process does not require complex pretreatments to avoid pore collapse before the carbonization of cellulose precursors. A H2/CO2 selectivity of 83.9 at 130 °C (H2/N2 selectivity of >800, H2/CH4 selectivity of >5700) demonstrates that the membrane provides a precise cutoff to discriminate between small gas molecules (H2) and larger gas molecules. In addition, the membrane exhibits superior mixed gas separation performances combined with water vapor- and high pressure-resistant stability. The present approach for the fabrication of high-performance CMS membranes derived from cellulose precursors opens a new avenue for H2-related separations.
https://www.nature.com/articles/s41467-020-20628-9
Covalent organic frameworks (COFs) are promising materials for advanced molecular-separation membranes, but their wide nanometer-sized pores prevent selective gas separation through molecular sieving. Herein, we propose a MOF-in-COF concept for the confined growth of metal-organic framework (MOFs) inside a supported COF layer to prepare MOF-in-COF membranes. These membranes feature a unique MOF-in-COF micro/nanopore network, presumably due to the formation of MOFs as a pearl string-like chain of unit cells in the 1D channel of 2D COFs. The MOF-in-COF membranes exhibit an excellent hydrogen permeance (>3000 GPU) together with a significant enhancement of separation selectivity of hydrogen over other gases. The superior separation performance for H 2 /CO 2 and H 2 /CH 4 surpasses the Robeson upper bounds, benefiting from the synergy combining precise size sieving and fast molecular transport through the MOF-in-COF channels. The synthesis of different combinations of MOFs and COFs in robust MOF-in-COF membranes demonstrates the versatility of our design strategy.
A novel hydroxyl-containing polyetherimide (named BAHPPF-ODPA) with highly aromatic backbone and contorted chain conformation was designed and synthesized as the precursor to fabricate carbon molecular sieve membranes (CMSMs) for H2/N2 separation. The structural evolution from polymeric precursor to carbon during pyrolysis was investigated using characterization techniques combined with pyrolysis simulation. And the relationship between membrane structure formation and their separation performance was explored here. Results indicate that the generation and evolution of pyrolysis products including formed fragments and gases, which depend on the precursor chemistry and pyrolysis conditions, exhibited a significant influence on microstructure and performance of derived CMSMs. Designing precursors with an aromatic backbone and contorted structure and precisely tuning pyrolysis temperature allows the fabrication of CMSMs with controllable micropore structure and excellent H2 separation performance. The BAHPPF-ODPA derived CMSM pyrolyzed at 600 °C exhibited the high H2 permeability of about 3500 Barrer and the superior H2/N2 selectivity of more than 400 were obtained after 750 h of long-term mixed gas (75:25 mixture of H2/N2) testing, showing promising application prospects. The experimental and simulation results obtained here would be beneficial to understand the CMS formation and reasonable to design the precursor molecular structure for fabrication of high-performance CMSMs.
Sulfur poisoning could result in fast deterioration of Pd-based membranes by the formation of metal sulfides and reduction of hydrogen purity. The introduction of an MoO2/TS-1 layer could provide an effective protection of the Pd layer. Therefore, in this paper a synthetic method is presented for preparation of sulfur-resistant MoO2/TS-1 zeolite modified PdCu alloy composite membranes and their application in hydrogen separation under H2S containing steam. According to the stability test results, the MoO2/TS-1 zeolite armored layer obviously prolonged the stability of Pd based membrane. After 50 h stability test with 100 ppm H2S, there were no obvious structural changes and metal sulfide formation detected in the PdCu bulk from SEM images and XRD patterns, indicating that MoO2/TS-1 armor structure was good enough for protecting the PdCu alloy bulk.
The construction of H2 infrastructure is crucial for accomplishing an H2 economy in the future, however, the current cost of H2 transportation is relatively expensive due to the lack of infrastructure. One of the alternatives is to inject H2 into the existing natural gas pipeline networks, which is subsequently recovered by membrane technology for end-users. In this work, the high-performance cellulose-derived asymmetric carbon hollow fiber membrane developed in previous work was tested for H2/CH4 separation. The experimental results demonstrated the outstanding separation performance and good stability of the developed carbon membrane with H2 permeance of up to 21.3 GPU and H2/CH4 separation factor of up to 96 at 50 ℃ under different feed pressures of 5-40 bar and H2 concentrations of 5-25 vol%. The techno-economic feasibility analysis for H2 recovery from the natural gas pipeline networks was conducted. A two-stage carbon membrane system was designed to produce high-purity H2 (>99.7 vol%) by UniSim simulation. Notably, the higher 1st-stage feed pressure (8-40 bar) and the higher feed H2 content (5-25 vol%) significantly lessened the required membrane areas, contributing to reducing the major expense on H2 recovery cost. Moreover, the influences of the process operating factors (e.g., feed H2 content, feed pressure, etc.) on H2 recovery cost were systematically explored, and the results indicated the considerable impact of process design on H2 recovery cost.
https://authors.elsevier.com/a/1gCQB4wbrT7oat
Hydrogen (H2) separation and purification is challenging because of the high purity and recovery requirements in particular applications, as well as the critical properties of H2 and its associated components. Unlike pressure swing adsorption, cryogenic- and membrane-based technologies are currently employed for H2 separation. Membrane-assisted (case-I) and cryogenic-assisted (case-II) separation and purification of H2 were evaluated in this study in terms of the energy, exergy, and economic aspects of the processes. In case-I and case-II, H2 was first produced from synthesis gas via the water-gas shift reaction and was then separated from other components using membrane and cryogenic systems, respectively. Additionally, an organic Rankine cycle was integrated with the water-gas shift reactors to recover the waste heat. A well-known commercial process simulation software, Aspen Hysys® v11, was employed to simulate both processes. Energy analysis revealed that case-I has a lower energy consumption (0.49 kWh/kg) than case-II (2.04 kWh/kg). However, low H2 purity and recovery rates are the main limitations of case-I. In terms of exergy, the H2 separation section in case-I exhibited a higher efficiency (28.4%) than case-II (9.9%). Furthermore, the economic evaluation showed that case-I was more expensive ($17.9 M) than case-II ($10.2 M) because of the high cost of the compressors required. In conclusion, this study could assist industry practitioners and academic researchers in selecting optimal H2 separation and purification technologies for improving the overall H2 economy.
We present a comprehensive theoretical and experimental study of the effect of membrane thickness on the anion-exchange membrane (AEM) fuel cell (AEMFC) performance. AEMFC tests are carried out with several AEMs with thickness in the range of 5 – 50 µm and assembled with a PtRu anode, and two different cathode catalysts (Pt/C or FeNC). Dramatic improvements in cell performance are observed as the membrane thickness decreases, which is mainly attributed to reduced ohmic losses and enhanced water transport between the electrodes. The simulated cell performance obtained using our previously developed AEMFC model qualitatively and quantitatively explains the experimental results in the entire range of current densities (0–4 Acm⁻²). Simulated results show that thinner membranes enhance water transport between the electrodes, mitigating the anode flooding, and resulting in increased local hydration in the membrane and cathode catalytic layer. These high hydration values enhance the anionic conductivity of the ionomeric materials, thereby improving cell performance. Furthermore, the enhanced water transport towards the cathode electrode provides sufficient water to participate in the oxygen reduction reaction, thus reducing the activation losses. Simulation modeling allows for a thorough understanding of cell behavior and aids in the development of the next generation of advanced AEMFCs.
The hydrogen economy becomes an important route in approaching carbon neutrality. Compared to conventional methods, membrane separation possesses combined merits, including energy-saving, convenience, and economic efficiency. In the past few years, significant progress has been made in hydrogen (H2)/methane (CH4) separation membranes, but a systematic review of membrane materials for this application is still lacking. Herein, the research progress of polymeric membranes, mixed matrix membranes (MMMs), and carbon molecule sieve (CMS) membranes has been critically reviewed and discussed. Research results from the latest literature are summarized and analyzed. It is found that polymeric membranes and CMS membranes exhibit outstanding H2/CH4 separation properties, while MMMs, although widely investigated, show lower performance. The perspectives and future research directions for H2/CH4 separation membranes were presented. This review provides an in-depth understanding of the latest research and offers valuable inspirations for theoretical research and practical applications for the H2/CH4 separation membranes.
Highly-asymmetric metallic Ni hollow fiber membranes (NHFMs) with a dense inner skin layer and an outer porous substrate were fabricated by a modified phase inversion and sintering technique. A triple-orifice spinneret was used for spinning the hollow fiber precursors with water as the internal coagulant and a solvent-ethanol mixture as the temporary external coagulant. The hollow fiber precursors were sintered in a H2-containing atmosphere at 1100–1400 °C to form dense metallic membranes. Effects of the external coagulant composition and air gap length as well as the sintering temperatures on the morphology of the resultant hollow fiber membranes were systematically investigated. Results indicate that the hollow fiber with an optimal microstructure has achieved a maximum hydrogen flux of 73.17 mmol m⁻² s⁻¹ (9.83mL cm⁻² min⁻¹) at 1000 °C, which is about 8 times higher than that obtained from the traditional hollow fiber membrane.
Hydrogen is a promising energy carrier and feedstock alike for decarbonizing the energy, transport, and chemical sector and mitigating the effects of global warming. Identifying and realizing environmentally friendly hydrogen production pathways is, however, significantly impeded by the need for step-wise transformation of national energy systems. This paper reviews the current level of hydrogen production technology development. Nine process configurations based on four different process technologies were considered comprising steam methane reforming, steam methane reforming with carbon capture and storage, methane pyrolysis and polymer electrolyte membrane electrolysis. Hydrogen from these technologies is often associated with the respective colors grey, blue, turquoise, and green. The critical comparison of the technologies is objectified and quantified based on the methodology of life cycle assessment. For this purpose, the environmental impacts of the hydrogen production technologies are gathered and the most promising solutions with respect to the progressing energy transition identified thereby differentiating the approaches for their short, medium-, and long-term benefit. By considering sixteen impact categories, both, environmental co-benefits and burden shifting resulting from the transition to more climate-friendly hydrogen production technologies were taken into account. The environmental impact of the hydrogen production technologies was found to be determined to large extend by the underlying electricity and natural gas supply chains. Anticipating technology shifts and taking regional differences and future advances in national supply chains into account, technology recommendations deviate substantially for the countries considered.
With increasing importance attached by the international community to global climate change and the pressing energy revolution, hydrogen energy, as a clean, efficient energy carrier, can serve as an important support for the establishment of a sustainable society. The United States and countries in Europe have already formulated relevant policies and plans for the use and development of hydrogen energy. While in China, aided by the “30·60” goal, the development of the hydrogen energy, production, transmission, and storage industries is steadily advancing. This article comprehensively considers the new energy revolution and the relevant plans of various countries, focuses on the principles, development status and research hot spots, and summarizes the different green hydrogen production technologies and paths. In addition, based on its assessment of current difficulties and bottlenecks in the production of green hydrogen and the overall global hydrogen energy development status, this article discusses the development of green hydrogen technologies.
The application of natural biopolymers such as polysaccharides for the fabrication of bio-based membranes has recently attracted attention for CO2 separation from gas mixtures. Here we review the types of natural polysaccharides that are used in membrane processes for CO2 separation. Various derivatives of polysaccharides including esters, ethers, silyls, amines have been synthesized and used in gas separation membranes as the main component of self-standing membranes, or in a blend with commercial polymers, or as a thin layer on the substrates. Nanoparticles of raw polysaccharides have been added to polymer matrices to form mixed matrix membranes with enhanced gas separation efficiency. The effect of the functionalization of polysaccharides on CO2 separation performance is detailed.
In the search for selective, productive and robust membranes for gas and other separations, highly permeable polymers, such as the prototypical polymer of intrinsic microporosity PIM-1, have been combined with a wide range of polymers, metal-organic frameworks, 2D materials and other fillers. Recent research has highlighted the importance of optimising the polymer used for the continuous phase, as well as achieving good compatibility between the different components. Many studies have focused on relatively thick films (>20 μm) and more work is needed to understand and control the behaviour of thin films (typically <1 μm) that are more relevant to real-life applications.
Porous asymmetric composite membranes (ACMs) have attracted intensive attentions in energy-efficient gas separations. However, fabricating ACMs with defect-free interface and enhanced selectivity without sacrificing permeability remains great challenge. Herein, a major step towards this goal is proposed by employing an efficient co-weaving strategy to regulate interfacial microstructure of ACMs with bilayer geometry on porous substrates. The double layers are constructed by in-situ growing zeolitic imidazolate frameworks-8 (ZIF-8) on the surface of amidoxime-functionalized polymer of intrinsic microporosity-1 (AO-PIM-1) layer (denoted as [email protected]). The pre-designed amidoxime groups on the AO-PIM-1 backbone provide abundant coordinate sites for Zn (ΙΙ) ions, offering advantages for building a continuous membrane. Consequently, the obtained [email protected] membrane demonstrates remarkable performance in H2/CO2 separations, with the H2/CO2 selectivity of 11.97 and the H2 permeability of up to 5688 Barrer at 298 K and 1 bar. Both the H2 permeability and H2/CO2 selectivity exceed most of reported ACMs, and far surpassed Robeson’s 2008 upper bound by taking advantage of the molecular sieving effect of interfacial layer formed by co-weaving of AO-PIM-1 chains with ZIF-8. This is contributed either by position-space renormalisation for AO-PIM-1 chains or pore space partition in ZIF-8 at the interface. The study reports herein offer an alternative route to develop high-performance composite membranes for improved gas separations.
The combination of catalytic decomposition of ammonia and in situ separation of hydrogen holds great promise for the use of ammonia as a clean energy carrier. However, finding the optimal catalyst – membrane pair and operation conditions have proved challenging. Here, we demonstrate that cobalt-based catalysts for ammonia decomposition can be efficiently used together with a Pd-Au based membrane to produce high purity hydrogen at elevated pressure. Compared to a conventional packed bed reactor, the membrane reactor offers several operational advantages that result in energetic and economic benefits. The robustness and durability of the combined system has been demonstrated for more than 1000 h on stream, yielding a very pure hydrogen stream (>99.97 % H2) and recovery (>90 %). When considering the required hydrogen compression for storage/utilization and environmental issues, the combined system offers the additional advantage of production of hydrogen at moderate pressures along with full ammonia conversion. Altogether, our results demonstrate the possibility of deploying high pressure (350 bar) hydrogen generators from ammonia with H2 efficiencies of circa 75% without any external energy input and/or derived CO2 emissions.
Hydrogen (H2) is the most promising alternative to fossil energy for zero-emission of CO2. However, the by-produced H2 from coking process was generally burned as fuel. It is highly desired to recycle the H2 from coke oven gas as the clean energy resource. Herein all-silica STT zeolite membranes were prepared from the fluorine-free precursor for H2/CH4 separation. The crystallization period was shortened by 75% at the elevated temperature. After hydrothermal synthesis of 2 days, the membrane showed H2 permeance up to 2.8 × 10⁻⁸ mol·m⁻²·s⁻¹·Pa⁻¹ and H2/CH4 selectivity up to 49.6 at 0.2 MPa and 298 K. More importantly, STT zeolite membrane was resistant to CO and H2S, which should be prevented from feeding to the commercial polymeric and Pd membranes. The membrane was stable up to 336 h in the simulated coke oven gas of 63 H2: 28 CH4: 7 CO: 2 C2H6 containing 100 ppm H2S. This would pave the way of zeolite membranes to H2 separation in practical applications.
This paper is devoted to the investigation of the thermochemical waste-heat recuperation system based on ammonia decomposition. Thermochemical waste-heat recuperation system consists of a reactor, an ammonia preheater, and a condenser. The thermodynamic analysis of the TCR system was performed via Aspen HYSYS software. The heat balance was calculated for the different operating parameters such as temperature (100–700°C) and pressure (1–20 bar). The heat balance showed that in the temperature range from 150–500°C there are heat deficits in the TCR system. To cover this deficit up to 15% of steam from flue gas have to be condensed. For compensating the heat deficit was suggested using a condenser after a preheater. The heat of H2O condensation is covered a significant part of the heat deficit. The heat recovery rate was determined and showed that the TCR system has a maximum efficiency in the temperature range above 500°C and pressure above 20 bar. The heat recuperated in the reactor is 2–5 times higher than the heat recuperated in the preheater. The heat transformation coefficient (ratio between the combustion heat of the ammonia decomposition products and ammonia) is about 1.16 for in the temperature range above 500°C.
Polysulfone (PES) membranes are among the rare membranes that are capable of double filtration: a pre-filter layer captures agglomerates and a thin-dense layer is responsible for the main separation process. This work aims to enhance the permeability and H2/N2 and CH4/N2 of the dense layer of PES by mixing it with low concentrations of carbon nanotubes (CNTs: 0.01-0.03 wt.%) using solution casting and doctor blade techniques. The pore topology, microstructure, chemical, thermal, and mechanical properties of the synthesized CNTs/PES membranes were investigated using FTIR, XRD, TGA, and a universal testing machine, while permeability of single CO2, H2, N2, and CH4 permeability of the CNTs/PES membranes were tested under different temperatures (20-60˚C) and pressures (1-6 bar). Also, the effect of added CNTs, separation temperature, and pressure on the gas separation mechanism were investigated. The results showed that adding of CNTs contributed to increase in porosity from 81.7% (PES) to 88.4% (CNTs/PES) and decrease in pore sizes from 84 nm (PES) to 50 nm (CNTS/PES). Meanwhile, the thermal and mechanical analysis showed that CNTs/PES membranes had higher thermal stability and somewhat lower strength compared with neat membranes. Also, the permeability measurements showed a big increase when only 0.01 wt.% of CNTs had been added, where H2, CH4, N2, CO2 permeabilities were increased up to 28553, 11358, 7540, 6720 Barrer, respectively, vs 10.4, 4.6, 13.7, and 12.3 Barrer in case of PES membranes. In addition, CO2/N2, CH4/N2, and H2/N2 selectivity of CNTs/PES membranes were enhanced by 29%, 396%, and 426%, respectively, as a result of pores refining and increasing of free space in the prepared CNTs/PES membranes. According to these results, CNTs/PES membranes with small loading of CNTs have a tremendous ability to deal with separation of H2/N2 and CH4/N2, what make them promising candidates for clean energy extraction applications.
Palladium (Pd) membranes are a crucial device for separating hydrogen and are usually operated at normal pressure on the permeate side with a single outlet. Instead of these common operating conditions, the difference between using a double outlet and a single outlet is studied. Four different vacuum degrees (15–60 kPa) are applied on the permeate side, and the results are compared with the non-vacuum operations. Situations under the vacuum and the effects of temperatures (300–400 °C) on H2 permeation are discussed. Finally, the influences of different feed gas mixtures (H2/N2, H2/CO2, and H2/CO) on the Pd membrane performance are investigated. The results show that there is no difference in H2 permeation impact the single outlet and the double outlet on the permeate side. When a vacuum is imposed on the permeate side, the H2 permeation rate and H2 recovery are efficiently intensified, that is, when the pressure difference is 9 atm, they increase from 73.21 to 84.51% and from 0.0035378 to 0.0040808 mol∙s⁻¹, respectively. Moreover, the H2 recovery can be improved to up to 68.44% under a vacuum degree of 60 kPa. At a given Reynolds number, an increase in temperature increases the H2 permeation rate but lowers its recovery, stemming from more H2 in the feed gas. This study also investigates the feed gas of H2/N2 under a vacuum to provide a useful insight into H2 production and separation from ammonia, and the results are compared with two different feed gases of H2/CO2 and H2/CO mixtures. The results suggest that the impurities (i.e., N2, CO2, and CO) have a negative influence on the Pd membrane, which causes the H2 permeation rate to decrease, and the effect of N2 is the least significant compared to the other two.
Metal organic frameworks (MOFs) are ideal fillers for preparing mixed matrix membranes (MMMs) because of their molecular sieving property. However, MOF nanoparticles are not easy to be dispersed, which limits their application in MMMs with high MOFs loading. In this study, highly dispersed ZIF-8 nanoparticles with diameter of around 50 nm were prepared by coating isophthalic dihydrazide (IPD) molecular layer onto their surfaces via coordination interaction (abbre. [email protected]). Benefiting from the highly stable and highly dispersed [email protected] solution, MMMs with high nanoparticles loading content and excellent uniformity are achieved. The modification of IPD on the surface of ZIF-8 nanoparticles greatly enhances the interfacial affinity between ZIF-8 as filler and 6FDA-Durene polyimide (PI) as polymer matrix under the interaction of strong hydrogen bond between them. Gas permeation results reveal that the H2 permeability of [email protected] mixed PI (PI/[email protected]) MMM with 45 wt% loading content is up to 8000 Barrer and the corresponding ideal selectivities of H2/CH4 and H2/N2 gas pairs are 15.1 and 13.0, which increase by 46.6% and 32.7%, respectively, comparing to those of ZIF-8 mixed PI (PI/ZIF-8) MMMs. The comprehensive separation performance of PI/[email protected] MMMs surpasses the 2008 Robeson’s upper bounds. The surface modification of IPD enhances the CO2 plasticization resistance property of PI/[email protected] MMMs from 21 bar to 30 bar. This study provides a facile and easy-operated strategy for the surface modification of MOF nanoparticles, and opens up a new way for the preparation of MMMs with high filler loading and good quality.
Biohydrogen production from biomass through dark fermentation provides a great potential to achieve a green hydrogen economy for sustainable energy development. However, the purification of fermentative biohydrogen usually contains 30-40 vol.% CO2 at small-scale plants requires advanced separation technologies. Carbon molecular sieving membranes are considered as an alternative solution in this application. This work focuses on the techno-economic feasibility analysis of H2-selective carbon membrane systems for biohydrogen enrichment by investigation of process design, optimization of operating parameters, and the selection of membrane materials. High vacuum operation on the permeate is favorable to reduce the specific cost as the membrane-related capital cost is dominating the total cost. While the operation with feed gas compression provides better separation performance, and the minimum specific cost of $ 0.026/Nm³ at 6 bar was identified to achieve the hydrogen recovery of 90 %. A two-stage carbon membrane system is technically feasible to reach the biohydrogen purity of >99.5 vol.% with the specific cost of $ 0.06/Nm³, which is lower than pressure swing adsorption. The sensitivity analysis indicates that the carbon membrane system is scalable and flexible in responding to the variation of plant capacity with the feed flow ranges from 500-2500 Nm³/h without significant changes in production cost. Compared to the enhancement of membrane selectivity, improving hydrogen permeance by developing submicrometer asymmetric carbon membranes is urgently needed to increase its competitiveness for biohydrogen purification.
Membrane-based technology has attracted considerable attention owing to its low energy consumption, mild operating conditions, and high efficiency. Polymeric membranes are widely utilized in different separation processes for their low cost and highly reproducible preparation. Fouling and the trade-off between permeability and selectivity represent the main drawbacks in the polymeric membrane field. These problems could be overcome by using inorganic membranes that are less prone to fouling due to their hydrophilic nature, high chemical stability, and high permeability and selectivity. Zeolite membranes, a type of inorganic membranes, can separate liquid and gas species (with very similar size and shape) thanks to their defined pore size at a molecular level and high adsorption property. They are studied in different separation processes as gas separation, pervaporation, and desalination. However, they find application, at the industrial level, only for alcohol dehydration by pervaporation process. Indeed, although 30 years are passed since the first scientific papers about the zeolite membrane preparation, many problems are still unsolved, as reproducibility of the synthesis, defects into the zeolite layer, and high manufacturing costs, which caused a limitation to their application on a large scale.
In this review, the main zeolite membrane preparation methods and the novelty in their developing and fabricating have been analyzed. Their application in pervaporation and desalination has been discussed. The effect of zeolite membrane topology and chemical composition on natural gas purification has been presented in detail. The application of zeolite membrane reactors in different interesting processes has been discussed. Concluding remarks and future perspective have been also suggested.
Speciality chemicals company Evonik Industries AG, and industrial gases and engineering firm Linde, have been working together to provide a way of extracting hydrogen from natural gas pipeline networks through which it can be conveyed. By combining different technologies, the aim is to enable existing natural gas infrastructure to be used more extensively to transport this gas – in particular green hydrogen – so that it can be used in industrial applications or as a source of energy.
One of the promising directions for accumulating hydrogen is its binding into a liquid organic hydrogen carrier (LOHC). In this concept, a LOHC is loaded with hydrogen (hydrogenation) during production and then discharged again (dehydrogenation) when the hydrogen is needed. Biphenyl is an interesting option as potential LOHC due to its reasonable storage capacity. This paper deals with the experimental chemical equilibrium study and a detailed analysis of the biphenyl hydrogenation reactions. We evaluated the consistent set of vapour pressures and standard molar thermodynamic properties of biphenyl derivatives with help of complementary vapour pressure measurements, and empirical and quantum-chemical calculations. The chemical equilibrium constants of hydrogenation-dehydrogenation and thermodynamic characteristics for the biphenyl system were determined.
In our study, the synthesis of zeolitic imidazolate framework (ZIF-12) crystals and the preparation of mixed matrix membranes (MMMs) with various ZIF-12 loadings were targeted. The characterization of ZIF-12 and MMMs were carried out by Fourier transform infrared spectroscopy analysis, thermogravimetric analysis, scanning electron microscopy (SEM), and thermomechanical analysis. The performance of MMMs was measured by the ability of binary gas separation. Commercial polyetherimide (PEI-Ultem ® 1000) polymer was used as the polymer matrix. The solution casting method was utilized to obtain dense MMMs. In the SEM images of ZIF-12 particles, the particles with a rhombic dodecahedron structure were identified. From SEM images, it was observed that the distribution of ZIF-12 particles in the MMMs was homogeneous and no agglomeration was present. Gas permeability experiments of MMMs were measured for H 2 , CO 2 , and CH 4 gases at steady state, at 4 bar and 35 °C by constant volume-variable pressure method. PEI/ZIF-12-30 wt% MMM exhibited high permeability and ideal selectivity values for H 2 /CH 4 and CO 2 /CH 4 were P H 2 / CH 4 = 331.41 ${P}_{{\text{H}}_{2}/{\text{CH}}_{4}}=331.41$ and P CO 2 / CH 4 = 53.75 ${P}_{{\text{CO}}_{2}/{\text{CH}}_{4}}=53.75$ gas pair.
Polybenzimidazole (PBI) with a strong size-sieving ability exhibits attractive H2/CO2 separation properties for blue H2 production and CO2 capture. Herein, we report that PBI can be facilely cross-linked with polycarboxylic acids, oxalic acid (OA), and trans-aconitic acid (TaA) to improve its separation performance. The acids react with the amines on the PBI chains, decreasing free volume and increasing size-sieving ability. The acid doping increases H2/CO2 selectivity from 12 to as high as 45 at 35 °C. The acid-doped samples demonstrate stable H2/CO2 separation performance when challenged with simulated syngas containing water vapor at 150 °C, which surpasses state-of-the-art polymers and Robeson's upper bound for H2/CO2 separation.
Although mixed matrix membranes (MMM) possess remarkably improved gas separation performance compared to traditional polymeric membranes, membrane stability including CO2 plasticization and aging is still a serious issue due to the existence of interfacial defects. In this work, we report an efficient and less destructive route to cross-link the MOFs/polyimide (PI) MMM, where amine group-functionalized MOF (NH2-UiO-66) nanoparticles are thermally cross-linked with a carboxylic acid-functionalized PI (COOH-PI) matrix to form an amide bond at the interface at 150 °C under vacuum condition. Such a chemical cross-linking strategy conducted at a relatively mild condition improves membrane stability greatly while ensuring that the membrane structure is not destroyed. The resulting cross-linked MMM achieves enhanced mechanical strength with higher Young's modulus than a pristine polymer membrane. The CO2 antiplasticization pressure of the MMM after cross-linking is enhanced by 200% from ∼10 to >30 bar and the CO2 permeability of MMM only drops slightly from 995 to 735 Barrer after 450 days. At the same time, the separation performance of H2/CH4 gas pair surpasses the 2008 upper bound and that of CO2/CH4 gas pair nearly approaches the 2008 upper bound. The cross-linking strategy used herein provides a feasible and effective route for improving membrane stability and membrane performance in the MMM system for gas separation.
The hydrogen economy is being pursued quite vigorously since hydrogen is an important and green energy source
with a variety of applications as fuel for transportation, fuel cell, feedstock, energy vector, reforming in refineries, carbon dioxide
valorization, biomass conversion, etc. Steam reforming of alcohols is a well-established technique to obtain syngas. Methanol is
viewed to be a lucrative alternative for fossil fuels, due to its flexibility in being generated from multiple sources, high energy density,
and low operating temperatures. The catalysts used for reforming govern the methanol conversion rate and the ratio of gaseous
products, i.e., H2, CO, and CO2. Group VIII−XII metals have been widely utilized for methanol steam reforming as they have a
higher hydrogen yield. Several other catalysts and novel techniques have been developed and used to date. Quite a few strategies to
enhance the performance of catalysts and reduce deactivation have been discussed. This review focuses on the metallic catalysts,
mainly Cu, Pd, Zn, with different formulations and compositions for steam reforming of methanol (SRM). Active catalyst
components, supports, and their interactions, along with different promoters, are reviewed, and their performances are critically
analyzed. The various reaction mechanisms and reaction pathways have been identified and elaborated. A fundamental
understanding of the functionality and structure of catalysts is required no matter which alcohol is used as a feedstock, and some
general inferences can be obtained from polyhydroxyl feed for the steam reforming of methanol, which is the subject matter of this
review. Particularly, the role of copper as a component in mono and multimetallic systems and the nature of support must be studied
fundamentally to get high hydrogen yields. It is important to determine how metal support interactions, including oxygen transfer
from reducible oxides to the metal site, influence the catalyst activity, selectivity, and stability. Further, the mechanism by which
alloying affects the selectivity in multimetallic catalysts must be understood by using high-end characterizations.
The global energy market is in a transition towards low carbon fuel systems to ensure the sustainable development of our society and economy. This can be achieved by converting the surplus renewable energy into hydrogen gas. The injection of hydrogen (⩽10% v/v) in the existing natural gas pipelines is demonstrated to have negligible effects on the pipelines and is a promising solution for hydrogen transportation and storage if the end-user purification technologies for hydrogen recovery from hydrogen enriched natural gas (HENG) are in place. In this review, promising membrane technologies for hydrogen separation is revisited and presented. Dense metallic membranes are highlighted with the ability of producing 99.9999999% (v/v) purity hydrogen product. However, high operating temperature (⩾300 °C) incurs high energy penalty, thus, limits its application to hydrogen purification in the power to hydrogen roadmap. Polymeric membranes are a promising candidate for hydrogen separation with its commercial readiness. However, further investigation in the enhancement of H2/CH4 selectivity is crucial to improve the separation performance. The potential impacts of impurities in HENG on membrane performance are also discussed. The research and development outlook are presented, highlighting the essence of upscaling the membrane separation processes and the integration of membrane technology with pressure swing adsorption technology.