H2 Permeance Research Articles

Self-catalytic nickel hollow fiber membrane reactor for hydrogen production via toluene steam reforming

Metal-nickel membrane exhibits good H2 separation performance and inherent catalytic activity, making it a promising candidate as a membrane reactor in the simultaneous catalytic reforming of hydrocarbons and H2 separation. In this work, nickel hollow fiber membranes were fabricated using a spinning/sintering technology and subsequently employed in a membrane reactor for toluene steam reforming and H2 separation. The catalytic H2 production and permeation performance of the toluene steam reforming (TSR) hollow fiber membrane reactor were investigated under varying conditions, such as temperature, feed flow rate, steam-to-carbon ratio (S/C). The results show that toluene can be fully converted with a toluene feed flow rate of 1.5 μL min−1. Increasing S/C can enhance the H2 production, but excessive steam will lead to a decrease of the H2 permeation flux. The H2 yield and H2 permeation flux are 24.2% and 4.35 mmol m−2 s−1, respectively, under the conditions of S/C = 3, Ar = 90 mL min−1 and N2 = 3 mL min−1 at a temperature of 950 °C. The H2 yield and H2 permeation flux of the TSR membrane reactor did not significantly decrease within 96 h. In addition, the membrane reactor can operate stably within 62 h in an atmosphere containing 1000 ppm H2S.

Homoelemental effect boosted stable ZIF-8 membrane with super high H2 permeance

Fabricating stable MOF membranes with high permeance for H2 separation and purification faces significant challenges primarily due to the heterogeneous nucleation of MOF on substrate. Herein, we propose a simple but effective homoelemental strategy by choosing the Zn-based ZIF-8 and Zn foam substrate. Without any chemical or physical modification, a serials of highly stable and compact ZIF-8 membranes are assembled on the Zn foam which exhibit high H2 permeance both for H2/CH4 and H2/CO2 separation. Especially, the 1-Zn-Foam/ZIF-8-24 membrane displays the high H2 permeance close to 104 GPU, surpassing most MOF membranes for H2/CH4 and H2/CO2 separation. Further, the excellent stability displays steady H2 permeance and selectivity, even after 96-hour test, high temperature of 100 °C, or high pressure. This is the first exploration by adopting Zn foam as a substrate for gas separation, not only demonstrating the Zn foam is an ideal carrier for assembling the Zn-based MOF membranes, but also implying the potential of the homoelemental strategy in fabricating other MOF membranes.

Catalytic membrane reactors for alkane dehydrogenation applications: an integration of catalysis and separation process

Abstract Catalytic dehydrogenation of saturated hydrocarbons to corresponding alkenes by the release of the stoichiometric amount of hydrogen is the paramount solution for safe storage of hydrogen. The utilization of a catalytic membrane reactor for this process enhances the reaction yield beyond thermodynamic equilibrium by selectively and simultaneously removing the produced H2 during the reaction. To this end, the present review is focused on the integration of H2 permeable membranes with the catalysts for dehydrogenation of lighter alkanes for coproduction of olefins and high-purity hydrogen in a single step. Besides, this review also covers dehydrogenation of liquid organic hydrogen carriers for safe storage of hydrogen. Herein, different types of H2 perm-selective membranes used for the dehydrogenation reaction are highlighted and the effect of hydrocarbon on H2 permeation through these membranes are discussed in detail. Furthermore, the simulation studies along with the experimental investigation performed on the membrane reactors for dehydrogenation of linear and cyclic alkanes are critically reviewed to find the coherence between simulation and experimental findings. Systematic discussion is done on the different types of alkane dehydrogenation reactions and the parameters affecting the reaction performance. Finally, directions are provided to prepare a cheaper and large industrial scale membrane reactor for dehydrogenation reaction. The concept of coupling an exothermic reaction with the endothermic dehydrogenation reaction is provided as a future direction study to enhance the overall yield and energy efficiency of the integrated membrane reactor.

Two morphology distinct fillers with chemical similarity incorporated into Tröger’ base polymers towards enhanced gas separation

Mixed matrix membranes (MMMs) with one class of fillers always require high loadings to maximize gas permeability. The incompatibility between polymers and high content fillers causes non-selective interfacial voids in the MMMs and poor mechanical properties of MMMs. This work adopts two morphology distinct fillers with chemical similarity to achieve improved gas separation performance of Tröger’ base membranes without sacrificing their mechanical properties. The three-dimensional ZIF-8 nanoparticles are beneficial for membrane gas permeability. The addition of low content ZIF-8 nanosheets can greatly improve H2/CH4 and CO2/CH4 selectivities of the membranes. ZIF-8 particles and ZIF-8 nanosheets with similar chemical properties can mix more homogeneously and disperse well in the polymer matrix with expected hydrogen bonding interaction compared to mixed ZIF-8 and CuBDC nanosheets. Eventually, the resulting dual filler MMMs doped with 4 wt% ZIF-8 nanosheets and 10 wt% ZIF-8 nanoparticles have H2/CH4 ideal selectivity of 60 with H2 permeability of 426 Barrer, which is an increase of 18% and 102% over pure membranes, respectively. Moreover, the membrane has a significantly enhanced CO2/CH4 mixed gas selectivity of 68 at sub-ambient temperature, accompanied by temperature-dependent CO2-induced plasticization behavior. Mixing morphology distinct fillers with chemical similarity is proved to be an effective method to prepare a robust MMM at low filler amounts, and the synergistic effect on gas permeability and selectivity endows these dual filler MMMs with great H2/CH4 and CO2/CH4 separation performance.

Zeolite imidazolate framework composite membranes prepared on amine/tannic acid cross-linked polymeric hollow fiber substrates for enhanced gas separation

In this work, a continuous dense zeolite imidazolate framework (ZIF) composite membranes for enhanced gas separation were successfully prepared on diethylenetriamine (DETA) and tannic acid (TA) cross-linked polymeric hollow fiber substrates via the in-situ solvothermal method for the first time. With strong reactivity and small molecular volume, DETA connected various TA molecules and anchored TA molecules on the organic hollow fiber substrate to form a relatively tight spatial network. The modified polyvinylidene fluoride(PVDF) support contained abundant phenolic hydroxyl, carbonyl, and amine groups, providing a large number of active sites for heterogeneous nucleation and promoting the forming of continuous and non-defect MOF film. The synergistic effect between TA and DETA not only enhanced the stiffness and durability of the MOF composite membrane, but also improved the performance of membrane on gas separation. The morphology of the amine/TA modified to support and the MOFs composite membrane was analyzed by SEM, XRD, FTIR, XPS, etc. The fabricated TA-DETA-PVDF/ZIF-8 composite membrane with a continuously dense layer and unique structural stability displayed excellent H2 permeance of 1.01 × 10-7 mol·m−2 s−1 Pa−1 and competitive H2/N2 and H2/CH4 selectivity of 24.0 and 24.4, respectively.

Enhanced H2/CO2 separation of ZIF-8/NPBI mixed matrix membranes by forming cross-linking networks and crystal defects via acid doping

Fabricating a membrane with high H2/CO2 separation performance at high temperatures is highly desired. Herein, a cross-linked zeolitic imidazolate framework 8/poly[2,2′-(1,4-naphthalene)-5,5′-bibenzimidazoles] (ZIF-8/NPBI) mixed matrix membranes (MMMs) with tiny defects in ZIF-8 is fabricated via a phosphoric acid doping approach. The cross-linked NPBI chains and partially etched ZIF-8 by the acid result in significantly improved H2 permeability and H2/CO2 mixed gas selectivity. At 150 °C, compared to pure PBI membrane, the H2 permeability of the acid-treated 10% ZIF-8/NPBI membrane is enhanced from 39.97 Barrer to 98.36 Barrer, and the H2/CO2 mixed gas selectivity increases from 4.6 to 8.9, eventually exceeding the Robeson's upper bound predicted for 150 °C. When tested with the gas mixtures of 50% H2/50% CO2 continuously, the resulting membrane exhibits a stable H2 permeability of around 74 Barrer and H2/CO2 mixed gas selectivity of ≈8.69 at 150 °C for 24 h. This simple approach of improving H2 permeability and H2/CO2 mixed gas selectivity through crosslinking and etching provides a new approach for designing MMMs for H2/CO2 separation at high temperatures.

Use of Pd-Ag Membrane Reactors for Low-Temperature Dry Reforming of Biogas-A Simulation Study.

Biogas is a valuable renewable energy source that can help mitigate greenhouse emissions. The dry reforming of methane (DRM) offers an alternative hydrogen production route with the advantage of using two main greenhouse gases, CO2 and CH4. However, its real application is limited mainly due to catalyst deactivation by coke formation and the reverse water gas shift (RWGS) reaction that can occur in parallel. Additionally, the typical dry reforming temperature range is 700-950 °C, often leading to catalyst sintering. A low-temperature DRM process could be in principle achieved using a membrane reactor (MR) to shift the dry reforming equilibrium forward and inhibit the RWGS reaction. In this work, biogas reforming was investigated through the simulation of MRs with thin (3.4 µm) and thick (50 µm) Pd-Ag membranes. The effects of the feed temperature (from 450 to 550 °C), pressure (in the range of 2-20 bar), and biogas composition (CH4/CO2 molar ratios from 1/1 to 7/3) were studied for the thin membrane through the calculation and comparison of several process indicators, namely CH4 and CO2 conversions, H2 yield, H2/CO ratio and H2 recovery. Estimation of the CO-inhibiting effect on the H2 molar flux through the membrane was assessed for a thick membrane. Simulations for a thin Pd-Ag MR show that (i) CO2 and CH4 conversions and H2 yield increase with the feed temperature; (ii) H2 yield and average rate of coke formation increase for higher pressures; and (iii) increasing CH4/CO2 feed molar ratio leads to higher H2/CO ratios, but lower H2 yields. Moreover, simulations for a thick Pd-Ag MR showed that the average H2 molar flux decreases due to the CO inhibiting effect (ca. 15%) in the temperature range considered. In conclusion, this work showed that for the considered simulation conditions, the use of an MR leads to the inhibition of the RWGS reaction and improves H2 yield, but coke formation and CO inhibition on H2 permeation may pose limitations on its practical feasibility, for which proper strategies must be explored.

Precise control on two‐dimensional nanochannels at sub‐nanometer level for customizable gas separation

AbstractMembranes with precise molecular sieving channels that break the permeability‐selectivity trade‐off are desirable for energy‐efficient gas separation. Two‐dimensional (2D) membranes sieve gas through their special interlayer channels between neighboring nanosheets. However, the regulation and precise control of the nanochannels that match well with the size of the gas molecules remains a big challenge. Herein, accurate tuning of the interlayer spacing of layered double hydroxide (LDH) membranes at sub‐nanometer level was achieved by intercalation of Cl−, Br−, I−, and NO3− ions. Such high‐precision control allows customizable gas separation by selecting specific LDH membranes with appropriate channels according to the size of the gas molecules. Two membranes were used for demonstration: Cl‐LDH membrane shows high H2 permeance of ∼1870 GPU and desirable selectivities for H2/CO2(81), H2/N2(197), H2/CH4(320), and H2/C3H8(603); while I‐LDH membrane displays CO2 permeance of ∼1780 GPU and CO2/N2, CO2/CH4 selectivities of 182 and 297, respectively. The simultaneously high permeabilities and selectivities surpass the 2008 Robeson upper bounds. Molecular dynamics simulations quantitatively support the experiment results, further confirming the significant role of interlayer anions in the regulation of gas‐sieving channels. Given the rich variability of layered spacing and interlayer microenvironment for LDH materials, this work provides a platform membrane for various molecular sieving, including gas separation, solvent purification, seawater desalination, and so on.

Zr‐Based Metal‐Organic Framework UiO‐66/Ultem® 1000 Membranes for Effective CO2/H2 Separation

AbstractMixed‐matrix membranes (MMMs) using UiO‐66 nanofillers as dispersing inorganic phase and polyetherimide (PEI) as continuous polymeric matrix were synthesized. Different UiO‐66 loadings of 10, 20, and 30 wt % were applied. The morphology and UiO‐66 dispersion over the prepared MMMs were examined. Gas separation measurements were performed for H2/CO2 gas mixture to evaluate the influence of UiO‐66 on the separation yield of resulting membranes. When compared with pristine PEI membranes, MMMs containing metal‐organic framework (MOF) nanoparticles revealed superior H2 permeability and H2/CO2 separation factor, e.g., maximum permeability values of 14.6 and 5.5 Barrer were observed for H2 and CO2 at a filler loading of 10 wt % and an applied pressure of 4.0 bar.

Selective gas permeation through polymer-hybridized graphene oxide nanoribbon nanochannels: Towards enhanced H2/CO2 selectivity

Two-dimensional materials have garnered significant attention as membrane building blocks for their tunability, which enables simultaneous enhancement of permeance and selectivity. This study investigates the impact of reduced nanosheet width on H2/CO2 separation by examining the gas permeation behavior of graphene oxide nanoribbon (GONR)/polymer hybrid membranes. Polymers are incorporated into the macroporous GONR scaffold to accelerate H2 transport due to the expansion of GONR nanochannels. The GONR/polymer scaffolds can be coated on porous support by using the scalable shear coating method, resulting in micrometer-scale selective layers. The carbon layers remain intact after polymer hybridization and inhibit polymer crystallization, allowing strong polymer-CO2 interactions to hinder CO2 permeation. However, the excessive polymer composition can compromise GONR-polymer hybridization and crystallization suppression. We also explore the effect of polymer charge on gas separation performance. A relatively small amount of cationic polymer enhances H2/CO2 selectivity, but the enhancement is limited due to strong electrostatic interactions. Anionic polymer-GONR hybridization also improves gas separation performance, but is less effective compared to neutral polymer, as repulsive interactions result in a looser structure. The gas separation performance of the optimized membrane (GONR/PEO 25 wt%) shows H2 permeability of 7,108 Barrer and H2/CO2 selectivity of 10.8, surpassing the Robeson upper bound for polymeric membranes and comparable to that of previous 2D-materials-based membranes. Our finding demonstrates that GONR nanochannels and their gas transport properties can be tuned by simply adding polymers depending on the quantity, molecular weight, and charge of the polymers.

Membrane Reactor Supported by MXene (Ti3C2TX) for Hydrogen Production by Ammonia Decomposition

Hydrogen (H2) production by ammonia (NH3) decomposition offers a solution to the energy problem. In this work, an MXene (titanium carbide, Ti3C2TX) membrane was successfully synthesized by depositing it onto the anodic aluminum oxide (AAO) substrate using vacuum-assisted filtration. Then, a membrane reactor supported by MXene was developed for H2 production by NH3 decomposition. The MXene membrane reactor could achieve an H2 permeance of 2.85 × 10–7 mol m–2 s–1 Pa–1 and an H2/N2 selectivity of 20 at 773.15 K. Next, a Ni-La/γ-Al2O3 catalyst prepared by impregnation and sintering was added to catalyze the NH3 decomposition process. The experimental results showed that the reactor could achieve a 99% NH3 conversion at 773.15 K, i.e., 9% higher than that of the packed catalytic reactor (without membrane). A mathematical model of the membrane reactor was developed to explain the experimental results. The calculated activation energies (Ead) of the MXene membrane for H2 and N2 permeances were 64.95 and 69.53 kJ mol–1, respectively. The activation energy (Ear) of NH3 decomposition was 147.8 kJ mol–1. Both the experimental and modeling results showed that the membrane reactor could enhance NH3 conversion and promote the production of high-purity H2.

Improved selectivity and anti-aging ability for 6FDA type carbon molecular sieve membranes by mixing silicon from macro-phase separation to molecule doping

Good gas separation performance and anti-aging ability are important for the applications of carbon molecular sieve membrane (CMSM). In this work, silicon atoms in the form of siloxane-Cl are introduced into 6FDA-DABA type polyimide (PI) precursor membrane, and benzimidazoles (BI) is copolymerized into PI to effectively improve the compatibility between PI and siloxane-Cl. By varying the content of siloxane-Cl, the composite membrane changes from macro-phase separation to molecule level miscibility, which leads to the formation of silicon-rich interface layer and silicon molecule doping after high temperature pyrolysis, respectively. The residual silicon content in CMSM could be as high as 1 wt%. The high content silicon doped CMSM exhibits much improved H2 permeability retention degree (3617 Barrer of H2 permeability, 62% higher) and H2/CH4 selectivity (138, 51% higher) as compared to control CMSM after 45 days of physical aging. This work proves that the incorporation of silicon in CMSMs in proper forms could significantly improve their molecular sieving and anti-aging performances; a higher content of residual silicon and molecule level doping are highly desired. The heteroatom doping is expected to pave a new way for finely tuning the micro-structures of CMSMs and improving gas separation performances.

Manipulating gas transport channels in graphene oxide membrane with swift heavy ion irradiation

Graphene oxide (GO), a prominent two-dimensional (2D) material, has established itself as an ideal building block for separation membranes, owing to its unique laminar structures and tunable physicochemical properties. While the ultrathin nature of GO membranes is anticipated to minimize transport resistance, the convoluted mass transport pathways within laminar GO membranes generally yield moderate permeance. Here, for the first time, we explored using swift heavy ion irradiation to incorporate through transport channels in GO membranes with highly enhanced gas permeation properties. After 129Xe irradiation, characteristic ion tracks were discerned within the GO membrane cross-section. The irradiation process created disorder regions and nanopores within the laminates, and meanwhile facilitated cross-linking between the oxygen-containing groups of GO, thereby reducing the interlayer spacing and enhancing molecular sieving capabilities. The irradiated GO membranes surpassed the H2/CO2 performance upper-bound, with H2 permeance exhibiting a remarkable three-order-of-magnitude increase. This work demonstrates the feasibility of applying heavy ion irradiation to create and tune interlayer channels based on physical and chemical interactions.

Palladium-Percolated Networks Enabled by Low Loadings of Branched Nanorods for Enhanced H2 Separations.

Nanoparticles (NPs) at high loadings are often used in mixed matrix membranes (MMMs) to improve gas separation properties, but they can lead to defects and poor processability that impede membrane fabrication. Herein, it is demonstrated that branched nanorods (NRs) with controlled aspect ratios can significantly reduce the required loading to achieve superior gas separation properties while maintaining excellent processability, as demonstrated by the dispersion of palladium (Pd) NRs in polybenzimidazole for H2 /CO2 separation. Increasing the aspect ratio from 1 for NPs to 40 for NRs decreases the percolation threshold volume fraction by a factor of 30, from 0.35 to 0.011. An MMM with percolated networks formed by Pd NRs at a volume fraction of 0.039 exhibits H2 permeability of 110Barrer and H2 /CO2 selectivity of 31 when challenged with simulated syngas at 200°C, surpassing Robeson's upper bound. This work highlights the advantage of NRs over NPs and nanowires and shows that right-sizing nanofillers in MMMs is critical to construct highly sieving pathways at minimal loadings. This work paves the way for this general feature to be applied across materials systems for a variety of chemical separations.

The effects of firing temperature and Ti/Si ratio on the H2 permeation characteristics of microporous TiO2-SiO2-organic chelating-ligand composite membranes

Titania-silica composite materials were synthesized and successfully employed in the preparation of microporous gas separation membranes via sol–gel processing. Acetylacetone (ACA), an organic-chelating ligand (OCL), was introduced as a reaction modulator to control the hydrolysis/condensation reactions of titan alkoxide, which resulted in formation of well combined titania and silica structures. The membrane material had a molar ratio of Ti/ACA = 1/1 and was coated onto an intermediate layer with an average pore diameter of about 1 nm. The effect of firing temperature on gas permeability was examined at 300 and 500 °C under a nitrogen atmosphere. As a result, for the case of Ti/Si/ACA = 1/1/1, the membrane fired at 300 °C under nitrogen (300 N) showed a molecular sieving permeation mechanism and a permeance that depended on molecular diameter. This membrane achieved H2 permeance of 0.63 × 10-6 mol/(m2 s Pa), H2/CH4 selectivity of 72.8, and H2/SF6 selectivity of 534.7. The membrane fired at 500 °C under nitrogen (500 N) showed a similar molecular sieving performance, albeit with smaller values for H2 permeance and H2/SF6 selectivity. For this study, the Ti/Si ratios were also altered and studied. Membranes with ratios of Ti/Si/ACA = 1/2/1 and 2/1/2 were prepared by firing under nitrogen at the optimal temperature of 300 °C, and the Ti/Si molar ratio effect on the gas permeance was examined. H2/SF6 selectivity was increased with an increase in the silica content (Ti/Si/ACA = 1/2/1 membrane: H2 permeance 1.26 × 10-6 mol/(m2 s Pa), H2/SF6 = 1350.7). On the other hand, H2/SF6 selectivity became smaller as the titania composite content was increased (Ti/Si/ACA = 2/1/2 membrane: H2 permeance 1.16 × 10-6 mol/(m2 s Pa, H2/SF6 = 53.0). Therefore, by optimizing the titania content, it is expected to achieve the H2 gas separation performance of the TiO2-SiO2-ACA membrane according to the application of the membrane.

Carbon molecular-sieve membranes developed from a Tröger’s base polymer and possessing superior gas-separation performance

Carbon molecular-sieve membranes possess tremendous practical advantages over unary polymer membranes by providing high gas-separation performance levels, coupled with excellent mechanical and chemical stability. Improving their overall effectiveness greatly expands the competitiveness of this class of membranes. In the present study, carbon membranes are fabricated from a Tröger’s base polymer as the precursor. By optimizing the carbonization conditions, the gas-separation performance of the resultant membranes are significantly enhanced. Under optimized conditions, a H2 permeability of up to 1135 Barrer is achieved, with a corresponding H2/CH4 selectivity of 1170 and a CO2/CH4 selectivity of 238. While increasing the operating temperature slightly reduces the selectivity, it still remains in the high-separation region. Overall, the measured separation performance levels for H2-related separations, i.e., H2/CH4, H2/N2 and H2/CO2, all substantially exceed the Robeson upper bound. Moreover, the CO2/CH4 separation efficacy also lies above the 2019 upper bound, indicating that the carbon membranes developed in the present work are versatile and promising for many different gas-separation applications.

Preparation, Characterization and Hydrothermal Stability of Hydrophobic TiO2/SiO2 Membrane

Hydrophobic TiO2/SiO2 (TiO2/HSiO2) membrane was fabricated by sol-gel method using methyltriethoxysilane as a precursor instead of partial tetraethylorthosilicate. The thermal stability of the composites was characterized by Fourier transform infrared spectra, X-ray diffraction, thermogravimetric-differential thermogravimetric analysis and N2 adsorption-desorption measurements. The H2 permeation and H2 permselectivity of TiO2/HSiO2 membrane were investigated by single gas permeance test. Calcination at about 350 ∼ 400 °C is suitable for preserving the hydrophobicity of the TiO2/HSiO2 membrane. The H2 permeance and H2 permselectivity in TiO2/HSiO2 membranes increased significantly with growing temperatures. At 200 °C and 0.4 MPa, the H2 permeance of TiO2/HSiO2 membrane is 7.27 × 10−6 mol·m−2·Pa−1·s−1 and the H2/CO2 and H2/N2 permselectivities are 7.68 and 10.09, respectively. In comparison to the HSiO2 membrane, the H2 permeances of TiO2/HSiO2 membrane increased by 71.56%, and the H2/CO2 and H2/N2 permselectivities increased by 23.07% and 24.11%, respectively. After steam treatment, the water absorption rate of TiO2/HSiO2 materials decreased by 33.17% relative to that of HSiO2 materials. TiO2/HSiO2 membrane has better hydrothermal stability and reproducibility than HSiO2 membrane.

Mild ultraviolet detemplation of SAPO-34 zeolite membranes toward pore structure control and highly selective gas separation

SAPO-34 zeolite membranes were activated by ultraviolet (UV) radiation at low temperatures to reduce grain boundary defects. The successful detemplation of SAPO-34 zeolite powders using UV radiation was confirmed by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and nitrogen adsorption-desorption. The irradiance exerted a significant impact on the quality of UV-detemplated SAPO-34 membranes. Under optimal UV detemplation conditions, SAPO-34 membranes showed a moderate H2 permeance of ∼10−7 mol Pa−1 m−2 s−1, with a H2/i-C4H10 permselectivity over 75 under room temperature. The membranes showed an exceptionally low CO2 permeance in comparison with N2 and CH4 despite the smaller molecular size of CO2, resulting in an unprecedentedly high H2/CO2 permselectivity over 50, which was ascribed mainly to the intense interaction between the CO2 molecules and confined organic structure directing agent (OSDA) residue in membrane channels. The temperature dependence of singe-gas permeance through SAPO-34 zeolite membranes showed that gases, including He, H2, CO2, CH4, C2H6, C3H8, and i-C4H10, markedly increased as the temperature increased, indicating an activated diffusion mechanism. The activation energies for H2 permeation through the SAPO-34 membranes were 17–23 kJ mol−1, which were reasonable based on the correlation between the activation energy for H2 permeation and the average pore size for reported membranes by assuming minimal grain boundary defects in the UV-detemplated SAPO-34 membranes.

Contemporary avenues of the Hydrogen industry: Opportunities and challenges in the eco-friendly approach

Hydrogen (H2) is a possible energy transporter and feedstock for energy decarbonization, transportation, and chemical sectors while reducing global warming's consequences. The predominant commercial method for producing H2 today is steam methane reforming (SMR). However, there is still room for development in process intensification, energy optimization, and environmental concerns related to CO2 emissions. Reactors using metallic membranes (MRs) can handle both problems. Compared to traditional reactors, MRs operates at substantially lower pressures and temperatures. As a result, capital and operational costs may be significantly cheaper than traditional reactors. Furthermore, metallic membranes (MMs), particularly Pd and its alloys, naturally permit only H2 permeability, enabling the production of a stream with a purity of up to 99.999%. This review describes several methods for H2 production based on the energy sources utilized. SRM with CO2 capture and storage (CCUS), pyrolysis of methane, and water electrolysis are all investigated as process technologies. A debate based on a color code was also created to classify the purity of H2 generation. Although producing H2 using fossil fuels is presently the least expensive method, green H2 generation has the potential to become an affordable alternative in the future. From 2030 onward, green H2 is anticipated to be less costly than blue hydrogen. Green H2 is more expensive than fossil-based H2 since it uses more energy. Blue H2 has several tempting qualities, but the CCUS technology is pricey, and blue H2 contains carbon. At this time, almost 80–95% of CO2 can be stored and captured by the CCUS technology. Nanomaterials are becoming more significant in solving problems with H2 generation and storage. Sustainable nanoparticles, such as photocatalysts and bio-derived particles, have been emphasized for H2 synthesis. New directions in H2 synthesis and nanomaterials for H2 storage have also been discussed. Further, an overview of the H2 value chain is provided at the end, emphasizing the financial implications and outlook for 2050, i.e., carbon-free H2 and zero-emission H2.

C-axis oriented ZIF-95 sheets intermixed with polyimide matrix with enhanced gas separation performance

The fabrication of mixed matrix membranes (MMMs) by intermixing suitable fillers with organic polymers is an effective strategy to surmount the well-known trade-off effect between gas permeability and selectivity, which can promote separation performance of membranes to a great extent. Two-dimensional (2D) metal-organic frameworks (MOFs) are considered as potential fillers for strengthening the separation performance of MMMs as they possess high aspect ratio and distinctive chemical characteristics. However, it remains challenging in engineering the morphology of the MOFs with desired pore structure and high aspect ratio. In this study, we firstly prepare c-axis oriented ZIF-95 sheets with lateral dimension exceeding 22 μm and thickness of around 3 μm by the solvothermal method. And then the ZIF-95 sheets are incorporated into the polyimide (PI) matrix to fabricate highly c-axis oriented ZIF-95@PI MMMs (denoted as COZIF-95@PI MMMs thereafter). Attributing to the straight permeation channel of ZIF-95 (3.6 Å) for gas permeation as well as its high compatibility with polyimide substrates, the COZIF-95@PI MMMs show a high gas separation capability. At 373 K and 100 kPa for the COZIF-95@PI MMM with 40 wt% loading, the mixture separation factors of H2/CH4 and H2/CO2 are 134 and 58, respectively, and the H2 permeability exceeds 967 barrer, which is hopeful for the separation and purification of hydrogen.