Membranes For Hydrogen Purification Research Articles

Oriented Titanium‐MOF Membrane for Hydrogen Purification

Precise hydrogen sorting from purge gas (H2/N2) and coke gas (H2/CH4), commonly carried out by cryogenic distillation, still suffers from low separation efficiency, high energy consumption, and considerable capital cost. Though still in its infancy, membrane technology offers a potential to achieve more efficient hydrogen purification. In this study, an optimum separation of hydrogen towards both methane and nitrogen via a kinetically‐driven mechanism is realized through preferred orientation control of a MOF membrane. Relying on the 0.3 nm‐sized window aligned vertical to the substrate, b‐oriented Ti‐MOF membrane exhibits ultra‐high hydrogen selectivity, surpassing the upper bound limit of separating H2/N2 and H2/CH4 gas pairs attained so far by inorganic membranes. This spectacular selectivity is combined with a high H2 permeability owing to the synergistic effect of the 1 nm‐sized MOF channel.

Oriented Titanium-MOF Membrane for Hydrogen Purification.

Precise hydrogen sorting from purge gas (H2/N2) and coke gas (H2/CH4), commonly carried out by cryogenic distillation, still suffers from low separation efficiency, high energy consumption, and considerable capital cost. Though still in its infancy, membrane technology offers a potential to achieve more efficient hydrogen purification. In this study, an optimum separation of hydrogen towards both methane and nitrogen via a kinetically-driven mechanism is realized through preferred orientation control of a MOF membrane. Relying on the 0.3 nm-sized window aligned vertical to the substrate, b-oriented Ti-MOF membrane exhibits ultra-high hydrogen selectivity, surpassing the upper bound limit of separating H2/N2 and H2/CH4 gas pairs attained so far by inorganic membranes. This spectacular selectivity is combined with a high H2 permeability owing to the synergistic effect of the 1 nm-sized MOF channel.

Theoretical investigation of supramolecular organic framework membranes for hydrogen purification

Given that SOF materials have both inorganic and organic properties and are easy to prepare and structurally designable, this paper carries out the microbehavioral analysis and membrane design of SOF-8, SOF-9, and SOF-10 membranes for the hydrogen purification process of RMFCs. Since three materials have complementary performance characteristics for hydrogen purification, this paper focuses on the gas separation behavior of these three composite membranes using molecular dynamics simulations. Results showed that the SOF-9a+10a composite membranes could 100% block CO2 and CO, and displayed an excellent H2 permeability of 6.118 × 105 GPU during H2/CO2 separation, which exceeded the industry standard by nearly 105 times. Additionally, the SOF-9a+8 and SOF-10a+8 composite membranes improved gas selectivity and maintained high H2 permeability. Moreover, microdiffusion analyses revealed that the small pore sizes and irregular-shaped pore channels effectively hindered CO2 and CO transport. Microscopic analysis shows the potential of SOF composite membranes for gas separation.

Hydrogen (H2)/Toluene (TOL) Separation via One and Two Stages of the Bis(triethoxysily)ethane (BTESE) Membranes.

The separation ability of bis(triethoxysilyl)ethane (BTESE) membranes for hydrogen (H2) purification from hydrogen (H2)/toluene (TOL) gas mixtures after a methylcyclohexane (MCH) dehydrogenation process was investigated via one-stage and two-stage membrane processes. This study revealed that BTESE membranes of varied pore sizes (0.4, 0.5, and 0.7 nm) in a one-stage configuration can manage to achieve a H2 purity ~99.9%. However, the TOL concentrations fell within a wide range, ranging from 280 to 5441 ppm. A primary goal of this research was to lower the TOL concentration in the permeate stream below 200 ppm. Hence, by applying the two-stage membrane, it was demonstrated that the TOL concentration in the permeate stream could be lowered below 200 ppm.

Ultrathin and Self-Supporting MOF/COF-Based Composite Membranes for Hydrogen Separation and Purification from Coke Oven Gas.

Coke oven gas (COG) is considered to be one of the most likely raw materials for large-scale H2 production in the near or medium term, with membrane separation technologies standing out from traditional technologies due to their less energy-intensive structures as well as simple operation and occupation. Based on the "MOF-in/on-COF" pore modification strategy, the COF membrane (named the PBD membrane) and ZIF-67 were used as assembly elements to design advanced molecular sieving membranes for hydrogen separation. The composition and microstructure of membranes before and after ZIF-67 loading as well as ZIF-67-in-PBD membranes under different preparation conditions (metal ion concentration, metal-ligand ratio, and reaction time) were investigated by various characterizations to reveal the synthesis regularity and microstructure regulation. Furthermore, H2/CH4 separation performances and separation mechanisms were also analyzed and compared. Finally, a dense, continuous, ultrathin, and self-supporting ZIF-67-in-PBD membrane with a Co2+ concentration of 0.02 mol/L, a metal-ligand ratio of 1:4, and a reaction time of 6 h exhibited the largest specific surface area, micropore proportion, and the best H2/CH4 separation selectivity (α = 33.48), which was significantly higher than the Robeson upper limit and was in a leading position among reported MOF membranes. The separation mechanism was mainly size screening, and adsorption selectivity also contributed a little.

Preparation and Gas Separation of Amorphous Silicon Oxycarbide Membrane Supported on Silicon Nitride Membrane.

An amorphous silicon oxycarbide membrane supported on a silicon nitride membrane substrate was prepared. A starting suspension containing polyhydromethylsiloxane (PHMS), tetramethyltetravinyl-cyclotetrasiloxane (TMTVS) and a platinum catalyst was first prepared and spin-coated on a silicon nitride membrane, and then the suspension was cross-linked and cured, followed by pyrolyzing at 1000 °C under a flowing Ar atmosphere. A dense amorphous silicon oxycarbon ceramic membrane with a thickness of about 1.8 µm was strongly bonded to the Si3N4 membrane substrate. The single gas permeation of H2 and CO2 indicated that the ideal permeation selectivity of H2/CO2 was up to 20 at 25 °C and 0.5 MPa with good long-term stability, indicating the potential application of the obtained membrane for hydrogen purification.

Effect of high and low Nb content in multicomponent Nb–Ni–Ti–Zr–Co alloy on its structure, hardness and hydrogen permeability

In the present work, novel multicomponent Nb–Ni–Ti–Zr–Co alloys were synthesized by arc melting. Two alloys with low and high Nb contents and an equimolar high-entropy alloy (HEA) were produced and compared. The influence of the elemental composition on their microstructure, phase composition, lattice constants, hardness and hydrogen permeability was investigated. The synthesized Nb–Ni–Ti–Zr–Co alloys are characterized by near-equimolar BCC-(Nb, Ni, Ti, Zr, Co) and Nb-rich BCC-Nb(Ni, Ti, Zr, Co) phases. The equimolar Nb20Ni20Ti20Zr20Co20 alloy had the highest concentration of BCC-(Nb, Ni, Ti, Zr, Co) phase (84 vol %), while the Nb74Ni6Ti9Zr5Co6 alloy had the highest concentration of Nb-rich BCC phase (95 vol %). First-principles study of the lattice parameters for the Nb–Ni–Ti–Zr–Co alloy revealed that the lattice parameter of the BCC phase decreases with Ni and Co addition and increases with Nb, Zr addition. Titanium does not significantly affect the lattice constant of BCC phase for compositions close to equimolar (10–30 at. %). The microhardness of the alloys decreases with increasing Nb content, which is mainly due to the proportion of softer Nb-rich BCC phase and microstructural changes. The synthesized Nb15Ni20Ti15Zr30Co20 and Nb20Ni20Ti20Zr20Co20 alloys demonstrate high hydrogen permeability at 400 °C that makes them promising for hydrogen purification membranes. It is shown high-entropy Nb20Ni20Ti20Zr20Co20 alloy exhibit highest resistance to hydrogen embrittlement, while high Nb content alloys are strongly susceptible to embrittlement.

A high selective and permeable C7N6 monolayer membrane for H2 purification: First-principles and molecular dynamics simulations

Designing efficient membranes for hydrogen purification and separation is highly desired because of the development of the hydrogen economy. Using the combination methods of density functional theory (DFT) calculations and molecular dynamics (MD) simulations, we theoretically investigated the performance of the C7N6 monolayer for H2 purification and separation. Our DFT calculations indicate that H2 molecules would permeate through the C7N6 monolayer with a relatively low energy barrier (0.689 eV), and the C7N6 monolayer has an ultra-high selectivity of 7.47 × 106, 5.71 × 109, 1.19 × 1011, and 1.08 × 1012 for H2/O2, H2/CO2, H2/CO, and H2/N2 at even high temperature of 500 K, respectively. The MD simulations confirmed that the high selectivity and permeability of the H2 gas above 500 K. Even at higher temperatures of 800 to 1000 K, almost all of H2 gas can be separated by the C7N6 membrane without any other foreign gases passing through the membrane, indicating that the C7N6 monolayer can be used as an ultra-high performance H2 purification and separation membrane on the practical conditions as the C7N6 monolayers are dynamically, thermodynamically, and mechanically stable.

The defective C3N monolayers as high-efficient hydrogen purification membranes: DFT calculations and MD simulations

The design of new high-performance membranes for separation and purification of hydrogen remains highly desirable for industrial applications. Herein, using the density functional theory calculations along with MD simulations, we demonstrated firstly a new 2D membrane based C3N monolayer (D-C3N) with intrinsic pores and then investigated its potential as gas separation membranes for H2 purification. The cohesive energy and ab initio MD simulations confirmed that the D-C3N monolayer is structurally and thermodynamically stable under 1800 K. All considered gas molecules are physisorbed on the D-C3N monolayer with small interaction energy. At room temperature, the D-C3N membrane for H2 gas has high selectivity over other gases such as 1.5 × 103, 1.8 × 105, 8.8 × 109, 1.4 × 1012, and 1.3 × 1019 for H2/N2, H2/CO2, H2/O2, H2/H2O, and H2/CH4 at 300 K, respectively, and the H2 permeance is as high as 2.2 × 10−5 mol·m−2·s−1·Pa−1, exceeding the industrially acceptable value and most of the carbon-based separation membranes. In addition, MD simulations further confirmed that the defective porous C3N monolayer has ideal selectivity and permeation as a promising separation membrane for H2 purification from other gases for industrial applications.

Zirconium nitride intermetallic diffusion barriers enable stable hydrogen permeation in palladium–vanadium composite membranes

Zirconium nitride (ZrN) is explored as a hydrogen permeable, intermetallic diffusion barrier for stable, high temperature operation of composite palladium-vanadium membranes for hydrogen purification. ZrN was deposited by reactive sputtering, and the properties and performance of films deposited in the metallic and compound mode were compared. Screening experiments using Pd-based sandwich structures showed that ZrN does not significantly impede H permeation until its thickness is increased above 40 nm. Stable hydrogen permeabilities up to >6 × 10−8 mol H2 m−1 s−1 Pa−0.5 were obtained in Pd|ZrN|V|ZrN|Pd composite membranes at operating temperatures of T = 400–450 °C, with superior performance obtained from ZrN deposited in the metallic mode. Long term stability (>200 h) was obtained and the structural integrity post-testing was confirmed by XRD and TEM imaging. Compositional profiling showed that oxygen originating in the V foil segregates to the ZrN–V interface but does not impede flux, and the transient behavior observed is attributed to this. Zirconium nitride decomposes at T > 450 °C, leading to rapid Pd–V interdiffusion and loss of permeability. However, with perfect selectivity and permeabilities up to 4X greater than Pd, these membranes are a promising cost effective alternative for hydrogen purification operations at 350–450 °C.

Interplay of hydrogen and point defects in B2-type PdCu: A density functional theory study

To improve the performance of hydrogen-permeable alloys, quantitatively elucidating the metal–hydrogen interactions and identifying the controlling factors that govern the bottleneck step of the hydrogen permeation process are essential. In this study, based on the density functional theory, we characterized the interactions of hydrogen with point defects (such as antisite atoms and vacancies) in B2-type non-stoichiometric PdCu alloys, which are promising candidate materials for low-temperature working membranes for hydrogen purification. We proposed a “double defect” mechanism that produces a new type of defect complex with an atomic configuration similar to the Cu vacancy in B2-type PdCu alloys. We found that both Cu vacancies and double defects can act as strong hydrogen-trapping sites and are thus responsible for the marked decrease in hydrogen diffusivity. In contrast, antisite Cu atoms only repel H atoms and do not significantly hinder hydrogen diffusion. Whereas the binding energy of hydrogen to Cu vacancies and double defects exceeded 0.3 eV when relatively few (one or two) H atoms were trapped, the binding energy of hydrogen to Pd vacancies was substantially smaller (0.02 eV at most). Therefore, in Cu-rich non-stoichiometric PdCu alloys, the double defects may be the major hydrogen trapping sites. Furthermore, the effects of hydrogen on the formation of Pd vacancies, Cu vacancies, and double defects in B2-type PdCu alloys were clarified. Notably, double-defect formation from Pd vacancies in B2-type PdCu was significantly enhanced by the presence of nearby H atoms. This phenomenon, in which vacancies in B2-type intermetallic compounds transform into defect complexes in the presence of hydrogen, is postulated for the first time in this study. The findings of this study contribute to further understanding the driving forces for the formation of vacancy-hydrogen complexes in PdCu alloys at the atomic level and provide theoretical support for identifying the lattice defects that inhibit hydrogen permeability in Pd-based membranes.

Effect of flux direction through supported metal membranes: Golden ratio as maximum benefit in pure hydrogen and concept of swap point in mixture

In this paper, the role of the flux direction in composite supported metal membranes for hydrogen purification is elucidated from both mathematical and physical point of view under pure-hydrogen and mixture conditions considering a double-layer supported Pd-based membrane. A definitive mathematical proof is given to demonstrate that, in pure-hydrogen conditions, if the metal layer obeys Sieverts’ law and the diffusion in the support is controlled by the Knudsen mechanism, the permeating flux measured by feeding hydrogen from the support to the metal layer is always higher than the flux measured in the opposite direction at the same operating conditions and for whatever values of layer permeances, extending the state-of-the-art findings of the specialized literature. As a further surprising result, it is found that the maximum benefit in switching the flux direction is equal to the mathematical number called golden ratio, this representing a notable general finding. Moreover, a partial generalization of these results is extended to other particular driving forces, which leads us to propose the non-demonstrated-yet general conjecture that the highest flux be the flux established from the layer with the highest driving force pressure exponent to the layer with the lowest one. Furthermore, observing that, in mixture conditions, the permeating flux from the support side is lower than the opposite one for a sufficiently high mixture composition of non-permeating species – especially in the presence of inhibiting species like CO – the novel concept of swap point is introduced, which represents the mixture composition at which the fluxes measured in the two directions are equal. The value of the swap point depends on membrane geometrical characteristics, temperature and non-permeating species. It is highlighted that the findings of the present work hold also for other types of composite ones (polymeric, ceramic, etc.) as well as for every physical system that whose behaviour can be modelled by a sequence of non-linear resistances.

Layered Zeolite for Assembly of Two-Dimensional Separation Membranes for Hydrogen Purification.

Membrane separation is an energy-efficient and environmentally friendly process. Two-dimensional (2D) molecular sieving membranes featuring unique nanopores and low transport resistance have the potential to achieve highly permeable and selective mixture separation with low energy consumption. High-aspect-ratio zeolite nanosheets with intrinsic molecular-sieving pores perpendicular to the layers are desirable building blocks for fabricating high-performance 2D zeolite membrane. However, a wider application of 2D zeolitic membranes is restricted by the limited number of recognized zeolite nanosheets. Herein, we report a swollen layered zeolite, ECNU-28, with SZR topology and eight-member ring (8-MR, 3.0 Å×4.8 Å) pores normal to the nanosheets. It can be easily exfoliated to construct 2D membrane, which shows a high hydrogen selectivity up to 130 from natural gas and is promising for hydrogen purification and greenhouse gas capture.

Layered Zeolite for Assembly of Two‐Dimensional Separation Membranes for Hydrogen Purification

AbstractMembrane separation is an energy‐efficient and environmentally friendly process. Two‐dimensional (2D) molecular sieving membranes featuring unique nanopores and low transport resistance have the potential to achieve highly permeable and selective mixture separation with low energy consumption. High‐aspect‐ratio zeolite nanosheets with intrinsic molecular‐sieving pores perpendicular to the layers are desirable building blocks for fabricating high‐performance 2D zeolite membrane. However, a wider application of 2D zeolitic membranes is restricted by the limited number of recognized zeolite nanosheets. Herein, we report a swollen layered zeolite, ECNU‐28, with SZR topology and eight‐member ring (8‐MR, 3.0 Å×4.8 Å) pores normal to the nanosheets. It can be easily exfoliated to construct 2D membrane, which shows a high hydrogen selectivity up to 130 from natural gas and is promising for hydrogen purification and greenhouse gas capture.

Hydrogen recovery from industrial waste streams using Matrimid®/ZIF mixed matrix membranes

This work reports the performance of Mixed Matrix Membranes (MMMs) for hydrogen purification. ZIF-8 and ZIF-90 Zeolitic Imidazole Frameworks (ZIFs) have been used as additives to improve the separation performance of the pristine Matrimid® polymeric membrane. The good interfacial contact and distribution of the filler along the membrane have been determined by electronic microscopy and the comparison of the membrane's performance is done in terms of hydrogen permeability and selectivity from industrial waste streams. The results showed that MMMs almost double H2 permeability (50 Barrer) and increase H2 selectivity (H2/CO2: ≈4.3, H2/N2: ≈35, H2/CO: ≈41, H2/CH4: ≈36) compared to the pristine polymeric membrane. Finally, the influence of the feed composition (by means of binary and multicomponent mixtures) and temperature (30, 50 and 80 °C) as operating variables has been analysed. The permeability was stable in the wide range of feed compositions while the increase in temperature resulted in lower selectivity and higher permeability.

Reactive magnetron sputtering to enhance the hydrogen permeation performance of NbC/V composite membranes

Niobium carbide (NbC) catalytic films were deposited on the surface of vanadium (V) substrates by reactive magnetron sputtering (RMS) using CH4 as the carbon source to form the NbC/V composite membranes for hydrogen separation and purification. The effects of CH4 gas flow ratio (FCH4 = CH4/(CH4+Ar)) on the phase structure, surface microstructure and catalytic properties of NbC films and the hydrogen permeation performance of the NbC/V composite membranes were investigated. The results showed that the structure of the NbC catalytic film changed from the dual-phase of NbC and Nb2C to the single-phase of cubic NbC after the addition of CH4 gas. Furthermore, with the increase of FCH4, the carbon content in the NbC catalytic films increases, but the crystallinity decreases. When FCH4 is 5%, the hydrogen permeation performance of the NbC/V composite membrane is the highest, which is attributed to the appropriate carbon content and crystallinity of the NbC phase. Typically, the hydrogen permeability is 7.0 × 10−8 mol H2 m−1 s−1 Pa−0.5 at 650 °C, which is 2.4 times that of pure Pd.

Effect of EB treatment on permeation enhancement of palladium-free hydrogen purification membrane of SUS316L

Effect of EB treatment on permeation enhancement of palladium-free hydrogen purification membrane of SUS316L

An autonomous fuel cell: Methanol and dimethyl ether steam reforming direct fed to fuel cell

Studies of reforming systems integrated with Fuel Cells are interesting for energy production in remote regions, especially to develop multi-fuel processors, which can be fed by more than one fuel with no need to modify the unit. In this work, an Autonomous Fuel Cell (AFC) system with methanol and/or Dimethyl Ether Steam Reforming (SR) was modeled and simulated in Aspen Plus, evaluating process variables, appropriate operational conditions, and the need for additional processes. The maximum hydrogen formed is H2/C = 3.0 (yield of 99.9%) and occurs generally with S/C ≥ 2 for several temperatures. The presence of a WGS reactor and a membrane for hydrogen purification was identified as vital to develop an AFC. In six situations that were studied with different operating conditions that meet the AFC operation, it was observed that the lowest temperature is preferable since it will consume the least amount of utility to maintain the SR.

Orientation of the microstructure of free-standing carbon hollow fiber membranes modulated by carbonization condition triggers aging-resistant properties

The aim of this study is to determine the optimal carbonization conditions for carbon hollow fiber membranes for hydrogen purification. To this end, it is a prerequisite to obtain the best permselectivity of the resultant membrane. Three different carbonization atmospheres (vacuum, helium flow, and argon flow) were examined, while their effects on the changes in the microstructure and gas permeation properties of the as-synthesized carbon membranes were elucidated using a pure gas permeation test, coupled with an array of characterizations, including Raman spectroscopy and XPS. Moreover, the issue of vacuum degree was addressed to maintain the best reproducibility of the carbon membrane. The results revealed that CHFM-HV exhibited the best separation capability for H2/CH4 of 516.90, thereby indicating distinct hydrogen purification characteristics. Such good performance was driven by the attractive synergism of the ordered microstructure and larger pore volume. Notably, the recovery of permselectivity for CHFM-HV reached 90% after four months, thus suggesting its aging resistance. Hence, the demonstrated approach is efficient for altering the microstructure of the carbon membrane, thereby strengthening the separation performance and long-term stability. Overall, it is suitable for broad applications of diverse polymer precursors and prolonged the lifespan of the as-prepared carbon membrane.

Polyimide-derived carbon molecular sieve membranes for high-efficient hydrogen purification: The development of a novel phthalide-containing polyimide precursor

Hydrogen-based economy has been considered as a potential solution for energy security and sustainability in the future. And the ever-increasing demand for high-purity hydrogen (H2) provides an urgent force for the H2 purification technologies. Herein, a novel polyimide (BATPPP-6FDA) with rigid and contorted structure was synthesized and used as a precursor to fabricate the carbon molecular sieve membranes (CMSMs) for H2 purification. The structural changes from precursor to CMS were detected and the H2 separation performance of the membranes was optimized by the pyrolysis temperature. The CMSM pyrolyzed at 550 °C exhibited the highest H2 permeability of 10054.1 Barrer and moderate H2 permselectivity due to its highly disordered and turbostratic carbon structure originated from the generally decomposition of thermally labile -CF3 groups and the lactone rings of phthalide structure in the early stages (<550 °C) of pyrolysis. As the pyrolysis temperature raised, the H2 permeability of the derived CMSM decreased, and the H2 permselectivity enhanced greatly. The CMSM pyrolyzed at 800 °C demonstrated a high H2 permeability of 2622.4 Barrer and superior selectivity with H2/N2 of 524.48, H2/CH4 of 1248.76 and H2/CO2 of 7.51, respectively, which was attributed to the low densification of carbon structure resulting from the rigid and contorted structure of the BATPPP-6FDA precursor. The excellent H2 separation performance showed a great potential in hydrogen purification application.