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The cost of industrial hydrogen production and logistics, and the purity of hydrogen produced from different technologies are two critical aspects for the success of a future hydrogen economy. Here, we present a way to charge the Liquid Organic Hydrogen Carrier (LOHC) dibenzyltoluene (H0-DBT) with industrially relevant, CO 2 - and CO-containing gas mixtures. As only hydrogen binds to the hydrogen-lean carrier molecule, this process step extracts hydrogen from the gas mixture and binds it selectively to the carrier. Pd on alumina has been identified as the most promising catalyst system for successfully hydrogenating H0-DBT using model gas mixtures resembling the compositions produced in methane reforming and in industrial coke production (up to 50% CO 2 and 7% CO). Up to 80% of the hydrogen present in the feedstock mixture could be extracted during the LOHC hydrogenation process. 99.5% of the reacting hydrogen was selectively bound to the H0-DBT LOHC compound. The purity of hydrogen released from the resulting perhydro dibenzyltoluene previously charged with the hydrogen-rich gas mixture proved to be up to 99.99 mol%. Image 1 • Charging the LOHC compound dibenzyltoluene with H 2 from gas mixtures is feasible. • The process enables H 2 purification and storage in a single process step. • Pd is the catalyst of choice for this kind of mixed gas hydrogenation. • Hydrogen extraction is up to 80% with 99.5% selectivity for LOHC hydrogenation. • Purity of the released hydrogen is up to 99.99 mol%. [ABSTRACT FROM AUTHOR]

In this study, the various Sr(Ce 0.6 Zr 0.4) 0.9 Y 0.1 O 3-δ /YBaCo 2 O 5+δ (SCZY/YBCO) composite ceramic membranes were prepared by sintering at different temperatures and used as proton membranes for hydrogen permeation. SCZY and YBCO powders were prepared by the citrate-ethylenediaminetetraacetic acid sol-gel process and solid-state reaction method, respectively. The chemical reaction, structure, morphology, thermal expansion, and electrical conductivity of SCZY/YBCO were investigated through X-ray powder diffraction (XRD), scanning electron microscopy (SEM), thermal mechanical analyzer (TMA) and direct current four-probe method. The relative sintered density of SCZY/YBCO membrane sintered at 1250 °C was as high as 99.5%. The conductivity of the SCZY/YBCO increased with the sintering temperature. The SCZY/YBCO sample sintered at 1250 °C exhibited the highest conductivity of 13.44 S/cm at 800 °C. The H 2 permeability of the SCZY/YBCO membrane was 3.83 mL min−1 cm−2, much higher than that of SCZY at 800 °C (1.37 mL min−1 cm−2). • A composite high temperature proton ceramic membrane was prepared. • The electrical conductivity of samples is 13.44 S/cm at 800 °C. • A high hydrogen flux proton ceramic membrane was investigated. • A SCZY/YBCO film on the Ni-SCZY substrate was prepared and test for hydrogen permeation. [ABSTRACT FROM AUTHOR]

The main objective of this study is to determine the best intermediate layer for tubular carbon membranes for H 2 and He separation. Intermediate layer was applied to strengthen interfacial adhesion between selective carbon layers and tubular support. Three different intermediate layers (alumina powder, carbon molecular sieve (CMS), and carbon pencil) had been evaluated to compare their influence towards the performance of gas separation of the carbon membrane. Tubular carbon membrane was fabricated from PI/NCC-based polymer blends which had been carbonized under Argon atmosphere at 800 °C with a heating rate of 3 °C/min. Based on the scanning electron microscopic (SEM) observations, carbon membrane with alumina powder as an intermediate layer had formed a smoother surface compared to other types of intermediate layers. A high performance of tubular carbon membrane was obtained by employing alumina powder as an intermediate layer, which exhibited the best selectivity of H 2 /N 2 and He/N 2 of 447.31 ± 1.45 and 471.72 ± 2.19, respectively. • Three different intermediate layers were used to obtain high separation performance. • High performance of tubular carbon membrane was obtained by employing alumina powder as an intermediate. • Carbonization under Argon atmosphere at 800 °C with a heating rate of 3 °C/min were conducted. • Highest selectivity of H 2 /N 2 and He/N 2 of 447.31 ± 1.45 and 471.72 ± 2.19 was achieved. [ABSTRACT FROM AUTHOR]

These past few decades, the separation of various gas mixtures problems in order to obtain high purity gases can be overcome by the introduction of membrane-based technology. This current research was focusing on the development of tubular carbon membranes (TCMs) from polymeric precursors for the separation of hydrogen and nitrogen. The fabrication of TCMs involved the dip coating technique and was using P84 co-polyimide as the main precursor by blending of nanocrystaline cellulose (NCC) as an additive. It was believed a slight adjustment on time, temperature, or environment of the carbonization protocol for the commercially available PI/NCC membranes can alter the final properties of the carbons produced. The modifications on the carbonization parameters such as stabilization conditions and heating rates during fabrication of PI/NCC-based carbon membranes could also affect their gas separation performance. A large variety of TCMs for gas separation have been developed by simple carbonization of a PI/NCC deposited on a ceramic tubular support. Herein, in this study, the effect of different heating rates (1, 3, 5, and 7 °C/min) and stabilization environment (Argon, Nitrogen, and Helium) were investigated for all resultant TCMs. As a result, it was observed that stabilization under Argon environment with heating rate of 3 °C/min produced carbon membranes with the best H 2 /N 2 separation and the highest selectivity of 434.68 ± 1.39, respectively. • The effect of stabilization environment and heating rates was investigated. • The results showed that stabilization under Argon environment produced carbon membranes with better performance. • 3 °C/min heating rates improved the membrane selectivity and permeability. • The prepared tubular carbon membrane demonstrated high hydrogen separation performance. [ABSTRACT FROM AUTHOR]

Mixed matrix membranes (MMMs) with a thermally rearranged (TR) polymer and zeolitic imidazolate framework-8 (ZIF-8) were prepared in this study. ZIF-8 contributed to not only enhancing gas permeability, but also promoting thermal conversion of TR polymer membranes. As a result, TR ZIF-8 MMMs can be prepared at lower temperatures compared to the original TR polymers. The thermal rearrangement process also increased gas separation properties as it contributes to a tunable cavity size and hour-glass shape cavity distributions. Moreover, interfacial voids between the polymer phase and ZIF crystals which usually occur in most MMMs disappeared during thermal rearrangement of the TR polymer. As a result, the TR ZIF-8 MMMs showed excellent hydrogen separation properties with a H 2 permeability of 1,206 Barrer, H 2 /N 2 selectivity of 22.3, and H 2 /CH 4 selectivity of 25.7. TR conversion percent change of HPI and HPI ZF-8 MMMs with dwell time at 400 °C (left), conceptual images of HPI ZIF-8 MMMs (middle-top) TR ZIF-8 MMMs (middle-bottom), and the H 2 permeability H 2 /N 2 selectivity (right) of HPI ZIF-8 MMMs and TR ZIF-8 MMMs. Image 1 • Thermally stable ZIF-8 nanoparticles were introduced into TR polymers. • The introduction of ZIF-8 into TR polymers enabled TR conversion under mild conditions. • The interfacial voids between TR polymer and ZIF-8 were alleviated during the TR process. • The resulting membranes presented enhanced hydrogen permeability and selectivity. [ABSTRACT FROM AUTHOR]

A fluidized bed membrane reactor has its great advantage in the industrial application of hydrogen production owing to good mass and heat transfer characteristics compared to a fixed bed membrane reactor. However, the concentration polarization and the densification zone formation caused by membrane permeation will restrict mass and heat transfer as well as hydrogen membrane flux. In this work, a three-dimensional simulation is carried out to investigate the hydrogen separation process in a fluidized bed membrane reactor under the Euler-Euler framework. The effects of membrane arrangements with different eccentric distances and membrane sites including internal and external membranes on concentration polarization and densification zones are discussed. The results reveal that the enhancement of eccentric distances can weaken the concentration polarization, whereas the densification zone scope is enhanced. The arrangement of internal membranes can hinder the concentration polarization and promote the hydrogen separation, while external membranes significantly influence the hydrogen removal at the bottom of the reactor. • Hydrogen separation in a fluidized bed membrane reactor is numerically studied. • Effect of membrane arrangement with different eccentric distance is evaluated. • Concentration polarization with internal and external membrane is compared. [ABSTRACT FROM AUTHOR]

Multiphase Nb x Ti (100-x)/2 Co (100-x)/2 (x = 30–60) alloys are a promising material for hydrogen separating membranes. These alloy membranes exhibit a rapid decline in hydrogen permeation flux within ∼12 h when operated at 773 K. To address this issue, a dense oxide (e.g. Nb 2 O 5 , TiO 2 and CoO) layer was prepared between a Pd coating layer and an Nb–TiCo substrate by surface corrosion for improving their thermal stability, and the corrosion resistance of Nb–TiCo alloys was investigated. An increase in the Nb content (x) lowers the corrosion resistance of these alloys, but makes it easier to form the above oxide layer. Substantial enhancement of hydrogen permeability and thermal stability at 773 K was observed for the alloys (x = 30 and 40) after corrosion, which can be ascribed to an increase in hydrogen diffusivity. This improved permeability and stability are closely related to the formation of the above surface oxide layer that impeded interdiffusion between the Pd film and Nb–TiCo substrates. This study demonstrates that insertion of a diffusion barrier between the Pd and Nb-based substrates by surface corrosion is a viable approach to enhance the high-temperature stability of Pd-coated Nb–TiCo alloys, an aspect not widely explored in Nb-based hydrogen separation and purification membranes. • Dense intermediate oxide layer was prepared between Pd coating and the substrate. • Durability/permeability can be optimized by placing an inter-layer. • Nb 30 Ti 35 Co 35 with an oxide layer exhibits an excellent durability of ∼1053 min. • A high Φ value of 4.56 × 10−8 mol H 2 m−1s−1Pa−0.5 is derived for Nb 30 Ti 35 Co 35 at 773 K. • The variation of Φ is due to the change in D rather than K. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Graphene oxide (GO) nanocomposite membrane was synthesized by vacuum dip-coating method. • For preparation of GO membrane, the modified gamma-alumina support was used. • GO nanocomposite membrane indicated promising results for hydrogen separation. Abstract In the last five recent years, molecular-sieve Graphene Oxide (GO) membranes have shown a great potential to realize high-flux and high-selectivity mixture separation, at low energy cost. Hence, in this study, GO nanocomposite membranes were fabricated on modified γ-alumina tubes for hydrogen separation. As a high-performance process, H 2 -permselective GO membrane derived from graphite source was developed by using a modified hummer method. In fact, the GO nanocomposite membranes, referred to here as carbon membranes, were prepared via vacuum dip coating of the modified γ-alumina tubes using single-layer GO solution. Special attention was devoted to obtain high H 2 /CO 2 selectivity, high H 2 permeance, and good stability in separation process. Hence, the effects of the operating conditions (temperature, and pressure on quality and performance of the GO membranes) were investigated. At the best condition, the synthesized GO membrane exhibited good H 2 /CO 2 selectivity (>57) and high H 2 permeance (in the order of 7.9 × 10−7 mol Pa-1 m-2 s-1). Moreover, it was found that the GO membrane selectivities (H 2 /CO 2 and H 2 /N 2) were decreased by temperature increasing, while selectivity trends were improved by increasing pressure gradient. It should be noted that all permeation tests were reported after time durability of around 48 h. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The H 2 /N 2 ideal selectivity of the Pd-Au/Al 2 O 3 membrane was 500 at 400 °C. • The hydrogen permeating flux remained stable for more than 600 h under operation. • The absence of an intermediate layer does not affect the activation energy. Abstract The growing interest towards the hydrogen utilization as energy carrier placed a high demand on hydrogen permeable membranes as compact devices for hydrogen separation and purification. Many studies in this scientific field demonstrated that the composite Pd-based membranes are particularly effective for the aforementioned purposes, particularly if compared to the utilization of self-supported Pd-based membranes for their high cost and mechanical limitations. As a case study, a composite membrane based on a thin Pd-Au (8 μm of metallic layer and 12 wt% of Au) supported on α-Al 2 O 3 substrate was produced by electroless plating deposition. Permeation tests were performed with pure gases (H 2 , N 2 , CO 2 , CH 4) by varying the temperature between 300 °C and 400 °C and the feed pressure from 150 to 350 kPa. The exponential factor (n- value) in the equation describing the relationship between the hydrogen flux permeating through the membrane and its driving force was analyzed as a function of temperature and pressure variation. An apparent activation energy of 11 kJ/mol has been reached and it is comparable to other data present in the open literature. A H 2 /N 2 ideal selectivity of around 500 was reached at 400 °C and 50 kPa of transmembrane pressure and it remained stable up to 600 h under operation. The presence of defects on the metallic layer has affected the membrane performance in terms of H 2 perm-selectivity as testified by the post-mortem analysis on the exhausted membrane. [ABSTRACT FROM AUTHOR]

Abstract A new mixed protonic-electronic conducting material, Nd 5.5 W 0.35 Mo 0.5 Nb 0.15 O 11.25-δ (NWMN), was developed by Nb-doping to improve the hydrogen permeability of Nd 5.5 W 0.5 Mo 0.5 O 11.25-δ (NWM). The hydrogen permeation properties and stability of the NWMN were investigated in details. An enhanced hydrogen permeation flux through the NWMN membrane was achieved, which was about 2.5 times as high as that through the un-doped NWM membrane at 800 °C due to the increased ambipolar conductivity. Moreover, the phase structures of the NWMN powder and membrane remained unchanged after the treatment in pure CO 2 and H 2 -containing atmospheres, respectively, which reveals excellent stability of the NWMN powder in CO 2 and H 2 -containing atmospheres. The remarkable stability and improved hydrogen permeability make NWMN promising for the application of hydrogen separation. Highlights • A new H 2 permeable material, Nd 5.5 W 0.35 Mo 0.5 Nb 0.15 O 11.25-δ (NWMN), was developed. • Nb-doping is applied to enhance H 2 permeability of Nd 5.5 W 0.5 Mo 0.5 O 11.25-δ (NWM). • H 2 flux through NWMN membrane is ∼2.5 times as high as that through un-doped NWM. • The NWMN membrane shows excellent stability in CO 2 atmosphere. [ABSTRACT FROM AUTHOR]

Abstract Adding metal phase as the electronic transport channels in mixed protonic and electronic conductors is an effective method to enhance the conductivity and hydrogen permeability. Ceramic-metal (cermet) Ni-BaCe 0.85 Fe 0.15 O 3-δ (Ni-BCF8515) dual-phase membranes were successfully fabricated in this article, where BaCe 0.85 Fe 0.15 O 3-δ (BCF8515) served as the protonic conductor and Ni acted as the electronic conductor. The hydrogen permeability of Ni-BCF8515 dual-phase membrane was improved apparently, reaching 0.325 mL min−1 cm−2 at 1000 °C, which is four times higher than that of the single phase BCF8515 membrane. Hydrogen permeability of Ni-BCF8515 dual-phase membrane under different hydration conditions was studied here. Moreover, Ni-BCF8515 dual-phase membrane showed stable hydrogen permeability under the reducing atmosphere for 50 h. [ABSTRACT FROM AUTHOR]

Abstract High temperature H 2 -selective membranes can be applied as the membrane reactor for pure hydrogen production by catalytic reforming of alcohols or hydrocarbons. Conventional Pd-based membranes are limited for this purpose due to the low thermal stability, significant hydrogen embrittlement, quick poisoning by other impurity species and high material cost. In this work, metallic nickel (Ni) hollow fiber membranes with thin wall thickness and optimal microstructure were fabricated by the dry-wet spinning and sintering technique, and employed for H 2 separation from the model reformate mixtures containing CO 2 , CO, H 2 O and H 2 S at elevated temperatures up to 1000 °C. The prepared Ni hollow fiber membranes possess 100% H 2 -permselectivity, only allowing for the hydrogen in the reformate mixtures to permeate through under experimental conditions. In the presence of CO, CO 2 and H 2 O (vapor), the hydrogen recovery from reformate mixtures may be noticeably influenced due to the water gas shift reaction (WGS: CO + H 2 O ↔ CO 2 +H 2). Multiple cycling operation and long-term tests were conducted, indicating that the Ni hollow fiber membranes have good cycling operation performance and high resistance to CO, CO 2 , H 2 O and H 2 S poisoning at high temperatures. The excellent thermal and chemical stability as well as the high permeation performance make the Ni hollow fiber membranes great potentials in advanced applications such as the portable hydrogen sources or the large-scale hydrogen production from coal gasification. Highlights • Compact Ni hollow fiber membranes are fabricated by a dry-wet phase-inversion technique. • Pure H 2 separation from reformate mixtures is achieved using the Ni hollow fiber membrane. • The Ni membranes exhibit excellent thermal and chemical stability in reformate gases. • H 2 recovery is highly dependent on the CO and CO 2 concentrations due to the WGS reaction. [ABSTRACT FROM AUTHOR]

Two Pd-Cu alloy membrane modules were designed to recover high-purity hydrogen from a mixture at elevated temperature and pressure. Permeation and separation behavior were studied experimentally and theoretically using pure hydrogen gas and a binary mixture of H2/CO2 (58.2: 41.8 in vol%) at 250–350 °C and 800–1,200 kPa. The Pd-Cu membrane modules presented a maximum permeation flux at the highest temperature (350 °C) and pressure (1,200 kPa) both for pure H2 gas and the binary mixture. When the permeate and retentate flowed in the same direction in the membrane module (co-current flow), a temperature gradient and permeation flux variations were observed and the permeance of the H2/CO2 mixture was 2.263×10−4 mL/(cm2·s·Pa0.5) at 250 °C and 3.409×10−4 mL/(cm2·s·Pa0.5) at 350 °C. On the other hand, when the retentate flowed in the opposite direction to the permeate flow (counter-current flow), the temperature gradient and permeation flux variations were significantly reduced and the permeation flux improved by about 11% from that of the co-current flow module. The well-distributed temperature profile inside the module and increased hydrogen pressure difference through the membrane layer shortened the time to reach the steady state in the counter-current Pd-Cu membrane module, thus enhancing the membrane performance. The results of this study can contribute towards developing an efficient Pd-Cu membrane reactor. [ABSTRACT FROM AUTHOR]

Abstract A single phase, dense PdCu alloy film was prepared by one-step electroplating. The electroplated film was easily delaminated from the SUS electrode by cutting around the edge, and the single alloy film was thus collectable. The phase structure, surface morphologies, and alloy compositions were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). The plated film before and after hydrogen permeation tests consisted of a single face-centered cubic α phase and an ordered body-centered cubic β phase, respectively. The atomic ratios of Pd and Cu were 49 and 51 at%, respectively; the Pd and Cu contents were slightly higher and lower than Pd 47 Cu 53 , which shows the highest hydrogen permeability among Pd-Cu systems. The as-plated film exhibited high mechanical strength, and its load force at break point and displacement were 3 and 1.7 times those of the as-rolled Pd 47 Cu 53 films. The hydrogen permeability of the plated film with the β phase was almost the same as that of the rolled film and the values reported in literature. Highlights • Single phase, dense PdCu alloy film was prepared by one-step electroplating. • The as-plated film was delaminated from the SUS electrode by cutting around the edge, yielding a single alloy film easily. • XRD profile of the as-plated film showed a single FCC structure (α phase). • The as-plated film showed good flexibility and mechanical strength. • The obtained film is promising for use in hydrogen separation and membrane reactors. [ABSTRACT FROM AUTHOR]

Abstract Membrane thickness and structural type, which are closely related to the species diffusion in the membrane bulk and reactions at the gas-solid interfaces, have important influences on the performance of a dense ceramic membrane. Recently, oxygen-permeable dense ceramic membrane reactors have been suggested for hydrogen purification at elevated temperatures. Mixed conducting composite with composition of 75 wt% Ce 0.85 Sm 0.15 O 2-δ -25 wt% Sm 0.6 Sr 0.4 Al 0.3 Fe 0.7 O 3-δ (SDC-SSAF) was fabricated into oxygen-permeable membranes with different thicknesses and structural types. The effects of membrane thickness and structural type on the hydrogen separation performance were tested under different hydrogen concentrations and flow rates on side I, different flow rates of steam/He mixed gas on side II as well as different temperatures. The effect of concentration polarization on hydrogen separation rate and the rate determining steps were discussed by comparing the performances of the symmetric membranes and the asymmetric membranes. The apparent activation energies of the membrane reactors for hydrogen separation were analyzed. This study will give some constructive guides to the subsequent work on how to effectively improve the hydrogen separation performance. Graphical abstract Three oxygen-permeable ceramic membranes with different thicknesses and structural types were designed, prepared and tested to explore the effects of membrane thickness and structural type on the hydrogen separation performance. fx1 Highlights • Membranes with different thicknesses and structural types were prepared and tested. • Concentration polarization has weak effect on hydrogen separation process for asymmetric membranes. • Reducing the membrane thickness is effective to improve the hydrogen separation rate at high temperature. • Developing high activity catalysts is the key to enhance performance at low temperature. [ABSTRACT FROM AUTHOR]

Abstract The influences of solid-state reaction and sol-gel synthesis methods on the permeability through the La 5.5 W 0.6 Mo 0.4 O 11.25-δ membranes were investigated firstly. Then the superior sol-gel route was selected to synthesize chlorine-doped La 5.5 W 0.6 Mo 0.4 O 11.25-δ- x /2 Cl x (LWMCl x , x = 0–0.20) series membranes. The effects of chlorine doping on hydrogen separation performance through LWMCl x hydrogen permeable membranes were determined in detail. The developed LWMCl 0.1 membrane exhibited higher hydrogen permeability and better stability compared to its parent one, achieving 0.15 mL min−1 cm−2 at 1000 °C in dry atmosphere (50% H 2 in He), confirming the benefits of chlorine doping strategy. Highlights • Chlorine-doped La 5.5 W 0.6 Mo 0.4 O 11.25-δ Cl x (LWMCl x , x = 0–0.20) membranes were successfully prepared. • Enhanced hydrogen flux was achieved through the LWMCl x membranes. • Stable hydrogen permeation flux was obtained at 900 °C during the long-term test. • The distinctly difference of solid-state reaction and sol-gel methods were detail discussed. [ABSTRACT FROM AUTHOR]

Catalytic membrane reactors based on oxygen‐permeable membranes are recently studied for hydrogen separation because their hydrogen separation rates and separation factors are comparable to those of Pd‐based membranes. New membrane materials with high performance and good tolerance to CO2 and H2S impurities are highly desired. In this work, a new membrane material Ce0.85Sm0.15O1.925–Sr2Fe1.5Mo0.5O6‐δ (SDC–SFM) was prepared for hydrogen separation. It exhibits high conductivities at low oxygen partial pressures, which is benefit to electron transfer and ion diffusion. A high hydrogen separation rate of 6.6 mL cm−2 min−1 was obtained on a 0.5‐mm‐thick membrane coated with Ni/SDC catalyst at 900°C. The membrane reactor was operated steadily for 532 h under atmospheres containing CO2 and H2S impurities. Various characterizations reveal that SDC–SFM has good stability in the membrane reactor for hydrogen separation. All facts confirm that SDC–SFM is promising for hydrogen separation in practical applications. © 2018 American Institute of Chemical Engineers AIChE J, 65: 1088–1096, 2019 [ABSTRACT FROM AUTHOR]

Abstract An investigation was carried out into Nb-Pd-Ti ternary system to determine possible body-centered cubic (b.c.c.) membranes that can be used for hydrogen separation. A library of thin films was produced covering the greater portion of Nb-Pd-Ti ternary diagram using a combinatorial approach. The library was screened both structurally and in terms of a reactivity index defined as the ratio of the resistivity measured in the films under hydrogen and argon. The study showed that a substantial portion of compositional field stretching from Nb to Ti yield thin films with b.c.c. structure. The evaluation based on the reactivity index showed a narrow region close to Nb corner as possible compositions for separation membranes. The b.c.c. field was also screened with regard to the lattice volume so as to identify regions of acceptable hydrogen solubility. The superposition of two maps; one reactivity index and the other lattice volume yield a field 32 < Nb < 41, 27 < Pd < 44, 20 < Ti < 38 as possible compositions for separation membranes. Highlights • Thin film membrane library was obtained in Nb-Pd-Ti via magnetron sputtering. • A greater portion of compositions in Nb-Pd-Ti yield b.c.c. membranes. • Membranes were mapped in terms of a reactivity index and the lattice volume. • The reactivity index was defined as the ratio of film resistivity under H 2 and Ar. • Compositions; 32 < Nb < 41, 27 < Pd < 44 20 < Ti < 38 were identified as possible membranes. [ABSTRACT FROM AUTHOR]

Highlights • Metalloid cation was firstly doped into mixed protonic and electronic conductors. • P-doped La 5.5 W 0.6 Mo 0.4−x P x O 11.25−δ (LWMPx, x = 0–0.20) membranes were prepared. • Enhanced hydrogen permeability was achieved through LWMP0.05 membranes. • Improved stability was attained at 950 °C during the long-term test. Abstract Metalloid element doping is a novel strategy to improve the properties of hydrogen permeable membranes. Herein, phosphorus doping was applied to enhance the hydrogen separation performance of lanthanum tungstate membrane for the first time. The effects of P content on the hydrogen permeability of La 5.5 W 0.6 Mo 0.4−x P x O 11.25−δ (x = 0, 0.05, 0.1, 0.2) membranes were firstly investigated under different temperatures. Among series of doped-membranes, La 5.5 W 0.6 Mo 0.35 P 0.05 O 11.25−δ exhibited increased hydrogen permeability and improved stability than the parent material due to higher protonic conductivity. The results showed that metalloid phosphorus element doping possesses a beneficial effect on the hydrogen separation performance, which could accelerate the development of the hydrogen permeable membranes and promote their practical applications. [ABSTRACT FROM AUTHOR]

Abstract Ammonia is of interest as a hydrogen storage and transport medium because it enables liquid-phase hydrogen storage under mild conditions. Although ammonia can be used directly for energy applications, its use in conventional fuel cell electric vehicles necessitates decomposition into nitrogen and hydrogen, and the purification of the hydrogen to the composition required for commercial proton exchange membrane fuel cells. This article provides a review of the material and process considerations for catalytic ammonia decomposition and shows that Ru-based catalysts on conductive support materials are active at < 500 °C, but further understanding around lifetimes and deactivation conditions is required. This review then explores materials and technologies for hydrogen purification from decomposed ammonia gas streams, and our experiments show that defect-free dense-metal membranes are uninhibited by ammonia and can achieve the required product purity. Highlights • Ammonia enables liquid-state transport and storage of hydrogen. • Catalysts for NH 3 decomposition are reviewed and tabulated for comparison. • Ru-based catalysts are active at < 500 °C; some lower cost alternatives show promise. • Metal membranes deliver high purity H 2 from decomposed NH 3 for PEM fuel cells. [ABSTRACT FROM AUTHOR]

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

The hydrogen separation and purification method based on metal hydride (MH) is viewed as one of the ideal methods for recycling industrial by-product hydrogen. Usually, self-produce hydrogen purging is conducted to remove the impurity. However, the mechanism of impurity transport and separation under the MH dehydrogenation process is still not clear so that the purity of produced hydrogen or the hydrogen recovery ratio is low. In this paper, a novel poisoning dehydrogenation kinetics considering the effect of passivation layer is proposed to accurately describe the dehydrogenation properties under the impurity poisoning conditions. The poisoning factor is introduced to describe the poisoning effect of impurities on MH materials. More active impurity or higher impurity concentration result in the larger poisoning factor. Based on the poisoning dehydrogenation kinetics, the MH dehydrogenation reaction model for self-produce hydrogen purging process is developed to describe the impurity transport and separation behaviours. The effects of operating parameters on the impurity transport and separation are further investigated for ultra-pure hydrogen. It is found that the low temperature and low outlet flow rate results in the low hydrogen loss for ultra-pure hydrogen. After the optimization, an efficient hydrogen separation and purification with both a hydrogen purity of 99.9999% and a hydrogen recovery ratio of more than 80% is achieved, which shows the potential in the hydrogen separation and purification of industrial by-product hydrogen. [Display omitted] • MH dehydrogenation reaction model for self-produce hydrogen purging process is developed. • The poisoning factor is introduced to describe the poisoning effect of impurities. • Various operating parameters are investigated for ultra-pure hydrogen. • Hydrogen purity of 99.9999% and hydrogen recovery ratio of up to 80% are achieved. [ABSTRACT FROM AUTHOR]

Carbon molecular sieve (CMS) membranes are emerging porous carbon membranes for chemical separation and purification. Polyamide-imide (PAI) copolymers have shown attractive separation performance for natural gas upgrading and organic solvent separations. However, PAIs are rarely used as precursors to derive CMS membranes. This work shows that CMS hollow fiber membranes made from a PAI (Torlon®) can provide highly competitive H 2 permeability and H 2 /CO 2 selectivity overcoming the 2008 Robeson upper bound under both single-gas and mixed-gas permeation. With imide and amide moieties, the PAI showed intermediate H 2 /CO 2 separation performance between a polyimide (PI) and a polyaramid (PA). Interestingly, the trend was translated to the CMS membranes, i.e., the PAI-derived CMS membrane showed intermediate H 2 /CO 2 separation performance between the PI-derived CMS membrane and PA-derived CMS membrane with an excellent balance of H 2 permeability and H 2 /CO 2 selectivity. Sorption studies indicate that the PAI-derived CMS membrane had intermediate H 2 diffusivity and H 2 /CO 2 diffusion selectivity, which was further attributed to its intermediate ultramicropore size. To our best knowledge, this was the first report of PAI-derived CMS hollow fiber membranes with competitive gas separation performance and the first investigation of the chemistry and pore structure of PAI-derived porous carbon. This study also underscores the role of precursor backbone chemistry in tailoring CMS membrane properties, further suggesting that CMS membranes derived from copolymers comprising mixed backbone chemistry can give simultaneously attractive permeability and selectivity. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Polyamide membranes were fabricated using an in-situ confinement strategy. • Alkane molecules with different alkyl chains were confined in polyamide network. • Membrane microstructure was dynamicly regulated upon thermal stimulation. • Membrane exhibited excellent H 2 separation performance and stability at 100 °C. Rational design of polyamide cross-linked network is of vital significance for fabricating advanced separation membranes. Herein, polyamide membranes with tunable free volume cavity are constructed utilizing an in-situ confinement strategy during interfacial polymerization process, where organic alkane molecules with different alkyl chain such as n-octane, n-dodecane, and n-hexadecane are confined in stiff polyamide skeleton and entangled with nearby polyamide chains. The efficient confinement of organic alkane molecules is confirmed by thermogravimetric coupled with mass spectrometry analysis, and corresponding variations in chain architecture of polyamide network are verified by X-ray diffraction and positron annihilation lifetime spectroscopy techniques. Upon thermal stimulation, the inherent flexibility of confined organic alkane molecules along with stiffness of polyamide skeleton, allow enlargement of chain d-spacing and dynamic regulation of membrane microstructure for fascinating H 2 permeation separation. The optimized modified membrane exhibits a H 2 permeance of 116.1 GPU and a H 2 /CH 4 selectivity of 70.8, which can be stably operated at 100 °C for over 400 h. This study provides a deep understanding of polyamide membranes with confinement of organic molecules and thermally induced separation performances, advancing the design of novel membranes with promising H 2 separation performances at elevated temperatures. [ABSTRACT FROM AUTHOR]

In this work, the concentration and purification of hydrogen from multicomponent gas mixtures, such as syngas and H 2 :CH 4 blends, were investigated by simulations of multi-stage membrane configurations. In particular, the separation performance of carbon, polymeric and Pd-alloy membranes were analyzed for obtaining a final H 2 stream completely pure with a recovery higher than 90%. Carbon and polymer membranes in multistage configuration confirmed their suitability to be used as concentration units able to increase the hydrogen content in the gas mixture. A further purification of these pre-concentrated streams was carried out adding Pd-alloy membranes that were able to recover more than 90% of hydrogen fully pure. The use of an integrated process constituted of a concentration stage based on polymer/carbon membranes followed by a purification stage based on a Pd-alloy membrane allowed to drastically reduce the operating pressure and, moreover, save Pd-alloy membrane area. [Display omitted] [ABSTRACT FROM AUTHOR]

High-aspect ratio materials can enhance gas separation performance compared to low-aspect ratio materials when incorporated into a polymer matrix to form mixed matrix membranes (MMMs). However, the filler shape effect on various properties of MMMs was not thoroughly discussed. Herein, we fabricated a mixed matrix membrane with two different shapes of metal-organic framework (MOF) and examined the MOF filler shape effect on mechanical, thermal, and gas separation properties. Zeolitic imidazolate framework-8 nanoplates (NZIF-8) were synthesized by conversion method with an aspect ratio of 20. Isotropic ZIF-8 particles (IZIF-8) were also synthesized, and both fillers were hybridized with a 6FDA-DAM (PI) polymer. 20 wt% NZIF-8/PI membrane exhibited high mechanical properties of 0.282 GPa for hardness and 3.5 GPa for modulus, which is higher than that of IZIF-8/PI membranes. The membrane was stable in high temperatures which is comparable to the pristine PI membrane, showing long-term thermal stability at 300 °C. Furthermore, high aspect ratio fillers allowed significant enhancement in hydrogen separation performance, showing hydrogen permeability of around 1800 Barrer with hydrogen/propane selectivity of 260 at 20 wt% ZIF-8 nanoplate loading, which is much enhanced than the membrane with isotropic ZIF-8 particles. The separation performances were consistent in ternary mixture separation under different conditions. These highly stable and selective properties can be promising for hydrogen extraction from the propane dehydrogenation process. [Display omitted] • Zeolitic Imidazolate Framework-8 nanoplates (NZIF-8) were synthesized by conversion method. • ZIF-8/6FDA-DAM (PI) mixed matrix membranes were fabricated with ZIF-8 fillers with different shapes. • Compared to IZIF-8, NZIF-8/PI MMM showed better mechanical properties with high thermal stability up to 300 °C. • Gas separation tests were performed under various proportions of the ternary gas mixture, which is similar to the PDH process. • 20 wt% NZIF-8/PI MMM showed excellent separation performance with H 2 permeability of 1451 Barrer and H 2 /C 3 H 8 separation factor of 283. [ABSTRACT FROM AUTHOR]

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

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

Abstract Palladium composite membrane with excellent stability was successfully prepared using the electroless plating (ELP) route on a porous stainless steel (PSS) support for hydrogen separation. In order to modify the average pore size of PSS support and to prevent inter-metallic diffusion, the NaY zeolite layer was coated on the PSS support with the seeding and secondary growth method. A high-temperature membrane module was designed by Solid work software and fabricated from 316 L stainless steel with a knife-edge seal. The microstructures and morphologies of the samples were analyzed using XRD, BET, AFM, FESEM and EDX techniques. Permeation experiments were carried out with binary mixtures of H 2 /N 2 with various ratios (90/10, 75/25 and 50/50) and pure H 2 and N 2 at different temperatures (350, 400 and 450 °C) and feed pressures (200–400 kPa). Hydrogen permeation tests showed that the membrane with a thickness of about 7 μm had a hydrogen permeance of 6.2 × 10−4 mol m−2 s−1 Pa−0.5 with an ideal H 2 /N 2 selectivity of 736, at 450 °C. In addition, the results of stability tests revealed that the membrane could remain stable during a long-term operation by varying temperature and feed gases. Graphical abstract Image 1 Highlights • Pd/NaY/PSS composite membrane was successfully prepared using ELP method. • A membrane module was made of 316 L stainless steel with a knife-edge seal. • The PSS surface was modified by NaY zeolite through the seeding and secondary growth method. • The membrane had a hydrogen permeance of 6.2 × 10−4 mol m−2 s−1 Pa−0.5 at 723 K. • The Pd/NaY/PSS membrane exhibited stable hydrogen flux during long-term permeation tests (280 h). [ABSTRACT FROM AUTHOR]

Abstract Ceramic hydrogen separation membranes are promising devices to be integrated in industrial hydrogen-based technologies using fossil fuel as feedstock. Among all, BaCe 0.65 Zr 0.20 Y 0.15 O 3-δ –Ce 0.8 Gd 0.20 O 2-δ composite membrane is the most promising ceramic-ceramic system for such application. However, one of the main issues in Ba-containing perovskites is related to Ba loss at the high sintering temperature needed for the complete densification of the material. This work reports the influence of the sintering atmosphere and temperature on the membrane's densification and phase purity. BaCeO 3 (BC), BaCe 0.65 Zr 0.20 Y 0.15 O 3-δ (BCZY) and a BaCe 0.65 Zr 0.20 Y 0.15 O 3-δ –Ce 0.8 Gd 0.20 O 2-δ (BCZY-GDC) mixture were used as Ba-sources to modify the sintering atmosphere. The more reactive BC and BCZY systems promoted a solid-state reaction between BCZY and GDC leading to an undesired single mix-phase enriched in barium on the membrane's surface. The desired asymmetric architecture with the correct stoichiometry was obtained using BCZY-GDC as Ba-source and sintering the membrane at 1550 °C. [ABSTRACT FROM AUTHOR]

Highlights • The ZIF-7-NH 2 polycrystalline membranes were first prepared. • The coating of Pebax®1657 layer effectively control the microstructure of membrane. • Improved separation performance for H 2 /CO 2 mixture on ZIF-7 membrane was reported. • ZIF-7-NH 2 crystals exhibit higher hydrothermal stability than mono-ligand ZIF-7. Abstract Membrane-based hydrogen purification has been considered to be a promising alternative because of its low energy consumption, ease of operation, and cost effectiveness. Amino-functionalized ZIF-7 (ZIF-7-NH 2) is an attractive candidate for membrane gas separation due to the maintenance of pore-opening structure after total removal of guest molecules (DMF). In this work, ZIF-7-NH 2 membrane with improved both H 2 permeance and H 2 /CO 2 selectivity than reported mono-ligand ZIF-7 membrane was first prepared. Several activation process for ZIF-7-NH 2 membranes to opening the pores were investigated. It was found that the coating of a Pebax®1657 layer on the surface of ZIF-7-NH 2 membrane is crucial for preventing the formation of cracks during pore-activation procedure. The permeance of H 2 and separation factor for H 2 /CO 2 binary mixtures were improved to ∼ 1 × 10−7 mol/m2 s Pa and ∼19, respectively. The separation performance was very close to the upper bound for inorganic microporous membranes. Furthermore, the improved hydrothermal stability on ZIF-7-NH 2 materials endows the membrane is highly potential for hydrogen purification. [ABSTRACT FROM AUTHOR]

Graphical abstract Different to doping strategy, herein, the membrane configurations was optimized with asymmetric structure which consists thinner dense layer and porous support. The successfully prepared La 5.5 W 0.6 Mo 0.4 O 11.25−δ F 0.05 (LWMF05) asymmetric membrane exhibited improved hydrogen permeability and enhanced stability compared to the symmetric membrane, which achieving a maximum values of 0.16 mL min−1 cm−2 at 975 °C. Highlights • Asymmetric La 5.5 W 0.6 Mo 0.4 O 11.25−δ F 0.05 (LWMF05) membrane was successfully prepared. • Enhanced hydrogen flux was achieved through the LWMF05 asymmetric membrane. • Stable hydrogen permeation flux was obtained at 900 °C during the long-term test. • Effect of asymmetric structure on permeability and stability were discussed in detail. Abstract Asymmetric membrane structure consisting thinner dense layer (decrease bulk diffusion resistance) and porous substrate (beneficial for the surface exchange) is an efficient approach to improve the hydrogen separation performance. Herein, the successfully prepared La 5.5 W 0.6 Mo 0.4 O 11.25−δ F 0.05 (LWMF05) asymmetric membrane exhibited improved hydrogen permeability and enhanced stability compared to the symmetric membrane, which achieving a maximum values of 0.16 mL min−1 cm−2 at 975 °C. The hydrogen permeation performance through the LWMF05 asymmetric membrane were investigated in detailed. And the influences of the asymmetric structure on interfacial processes during hydrogen separation were discussed, which verifies the predominance of the asymmetric structure. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Commercial-scale WGSMR model combined with IGCC was developed using a process simulator. • Impacts of H 2 separation, pressure drop, and flow direction of sweep gas was studied. • A counter-current membrane model gave 9.3% higher H 2 yield than a co-current model. • A high flow rate and low pressure of sweep gas are advantageous for H 2 recovery. • Catalyst loading and syngas inlet temperature should be high for higher CO conversion. Abstract In integrated gasification combined cycle (IGCC) systems, the water–gas shift reaction, which promotes the conversion of CO present in syngas mixtures into hydrogen, is an important step for hydrogen production. Application of the water–gas shift membrane reactor (WGSMR) in IGCC systems is an attractive option for CO 2 capture compared with conventional methods because of smaller heat loss in gas purification and high CO conversion by selectively removing hydrogen from the reaction zone through the membrane. In this study, we proposed and evaluated commercial-scale WGSMR models combined with IGCC using reported laboratory-scale experimental data to optimize their operational parameters. Various models were developed using the Aspen Plus ® Ver. 8.6 process simulator to investigate the impacts of hydrogen separation, pressure loss, and the flow direction between the sweep gas on the permeate side and syngas on the retentate side on the WGSMR performance with respect to CO conversion, H 2 yield, and reactor temperature. The membrane reactor model gave approximately 20% higher CO conversion than a reactor model without H 2 separation and approximately 4% lower CO conversion than a membrane reactor model with a pressure drop. A counter-current membrane reactor model gave approximately 2% higher CO conversion than a co-current model; the H 2 yield on the permeate side was 9.3% higher in the counter-current model by separation of H 2 through the membrane. A sensitivity analysis indicated that a high flow rate and low pressure of sweep gas are advantageous for H 2 recovery, and high catalyst loading and high syngas inlet temperature are preferable for higher CO conversion. [ABSTRACT FROM AUTHOR]

Abstract In this work mixed protonic-electronic conducting nanocomposites comprised of Mo or La doped Nd 5.5 WO 11.25-δ and Cu 0.5 Ni 0.5 O were prepared by mechanical mixing in a high energy mill and sintering at 1100 °C using either conventional thermal sintering in the furnace or hot pressing in argon atmosphere. Their structural features were characterized by XRD, SEM, TEM with EDX analysis, IR and Raman spectroscopy. Electrical conductivity was measured by Van der Pauw techniques varying the temperature in dry and wet atmospheres. The oxygen mobility was studied by the oxygen isotope heteroexchange with C18O 2. Successful test of membrane with permselective Nd 5.5 WO 11.25-δ + Cu 0.5 Ni 0.5 O layer supported on NiAl foam substrate and covered by a porous layer of Ru + Ni/ Sm 0.15 Pr 0.15 Ce 0.35 Zr 0.3 O 2−δ catalyst showing promising performance in hydrogen separation from products of ethanol steam reforming has been carried out. The results indicated that a maximum hydrogen permeation flux of 0.033 ml min−1 cm−2 was achieved at 900 °C using 10% ethanol with 40% of H 2 O/Ar as feed gas and dry high purity argon as sweep gas. [ABSTRACT FROM AUTHOR]

Thanks to its high hydrogen permeability and good chemical stability in moist CO 2 environments, BaCe 0.65 Zr 0.20 Y 0.15 O 3-δ -Ce 0.85 Gd 0.15 O 2-δ mixed conducting material is considered one of the most promising candidates for hydrogen separation ceramic membranes. In this work, its chemical stability under H 2 S-rich atmosphere was systematically investigated by in-situ electrochemical characterizations and ex-situ structural, chemical and morphological analyses. A performance degradation of the total conductivity depending on the H 2 S content was observed: at 700 °C and under 1500 and 700 ppm of H 2 S the conductivity drop was 15% and 2% respectively. The complementary information gathered by morphological and chemical analyses showed that the changes responsible for the total conductivity degradation are mainly confined to the surface of the membrane. Indeed, after the exposure to the H 2 S-containing atmosphere, some traces of sulfur-related compounds were detected only on the top of the membrane while the bulk preserved a fully dense structure with well-defined grain boundaries and no evidence of cracks. However, no evidence of S-based compounds were revealed by structural investigations, probably due to the detection limit of these techniques and/or to the low crystallinity of the secondary phases. Contrary to Pd-based membranes that are severely deteriorated by a few ppm of sulfur, this material shows an acceptable stability even under 700 ppm of H 2 S and could be attractive for tailored applications such as, for example, operations related to steam reforming of methane often containing 10–300 ppm of H 2 S. [ABSTRACT FROM AUTHOR]

Liquid Organic Hydrogen Carrier (LOHC) systems have attracted growing attention in recent years as efficient way to store and transport hydrogen in the existing infrastructures for liquid fuels. This contribution highlights the additional feature that hydrogenation of the LOHC compound dibenzyltoluene with technical relevant H2/CO2 gas mixtures (up to 30 % CO2) gives access to hydrogen purification and hydrogen storage in one single process step. Alumina supported Rh and Pd catalysts proved to be especially suitable for this task. The rhodium catalysts enabled efficient aromatics hydrogenation in the temperature range of 120 °C to 150 °C with moderate methane formation (CH4/CO2<0.1 at 150 °C). The palladium catalyst showed the lowest selectivity to methane formation (CH4/CO2<0.1 at 270 °C) and promising hydrogenation activity at temperatures above 200 °C even in the presence of CO and CO2. Separation and storage! The hydrogenation of the LOHC compound dibenzyltoluene with technical relevant H2/CO2 gas mixtures (up to 30 % CO2) gives access to hydrogen purification and hydrogen storage in one single process step. Rh and Pd catalysts supported on alumina are especially suitable for this task showing high selectivity for aromatics hydrogenation over CO2 hydrogenation. [ABSTRACT FROM AUTHOR]

In this study, we prepared a Pd composite membrane with high hydrogen permeance and thermal stability on a tubular porous stainless steel (PSS) support by ethylene diamine tetraacetic acid-free electroless plating. The conventional yttria-stabilized zirconia (YSZ) was replaced with a NiO/YSZ/NiO multilayer as the diffusion barrier, and the latter was introduced on a PSS tube (diameter of 12.7 mm, length of 450 mm, and surface area of 175 cm 2 ). A long-term thermal stability test revealed that the NiO/YSZ/NiO multilayer significantly reduced the growth rate of nitrogen leakage. The test was carried out for ~1150 h on a 2.5-µm thick Pd membrane deposited on a NiO/YSZ/NiO/PSS tube (diameter of 25.4 mm, length of 450 mm, and surface area of 350 cm 2 ). The hydrogen permeance obtained at the end of the test was 3.81 × 10 −3 mol m −2 s −1 Pa −0.5 , and the H 2 /N 2 selectivity was ~87 at a temperature of 773 K and pressure difference of 101.3 kPa. The rate of increase in nitrogen leakage during the test was 3.05 × 10 –11 mol m −2 s −1 Pa −0.5 h −1 , which demonstrated the ability of the NiO/YSZ/NiO multilayer to mitigate nitrogen leakage. To produce hydrogen using the Pd composite membrane reactor, steam methane reforming was conducted under the following operating conditions: pressure, 430–1114 kPa; temperature, 883 K; and gas hourly space velocity, 1000 h −1 . The reaction yielded a methane conversion and hydrogen recovery of 75.1% and 97.9%, respectively. The permeate stream was composed of 93.1 vol% H 2 , 0.6 vol% CO, 1.8 vol% CH 4 , and 4.5 vol% CO 2 . The gas composition of the permeate stream was suitable for use as fuel in a high-temperature polymer electrolyte membrane fuel cell. [ABSTRACT FROM AUTHOR]

Pd-Ag supported membranes have been prepared by coating a ceramic interdiffusion barrier onto a Hastelloy X (0.2 µm media grade) porous support followed by deposition of the hydrogen selective Pd-Ag (4–5 µm) layer by electroless plating. To one of the membranes an additional porous Al 2 O 3 -YSZ layer (protective layer with 50 wt% of YSZ) was deposited by dip-coating followed by calcination at 550 °C on top of the Pd-Ag layer, and this membrane is referred to as a double-skin membrane. Both membranes were integrated at the same time in a single reactor in order to assess and compare the performance of both membranes under identical conditions. The membranes have first been tested in an empty reactor with pure gases (H 2 and N 2 ) and afterwards in the presence of a catalyst (rhodium onto promoted alumina) fluidized in the bubbling regime. The membranes immersed in the bubbling bed were tested at 400 °C and 500 °C for 115 and 500 h, respectively. The effect of the protective layer on the permeation properties and stability of the membranes were studied. The double-skinned membraned showed a H 2 permeance of 1.55·10 −6 mol m −2 s −1 Pa −1 at 500 °C and 4 bar of pressure difference with an ideal perm-selectivity virtually infinite before incorporation of particles. This selectivity did not decay during the long term test under fluidization with catalyst particles. [ABSTRACT FROM AUTHOR]

Supported, thin-layered Pd membranes are promising tools for pre-combustion carbon capture because they can deliver simultaneously high-pressure CO 2 and H 2 streams as needed for sequestration and power generation, respectively. Moreover, the diluent required for the gas turbine fuel can be advantageously added as sweep gas in the membrane separator to boost H 2 permeation. A composite membrane has been prepared with Pd layers on both sides of a porous ceramic tube to eliminate the mass transfer resistance resulting from sweep gas diffusion into the support of conventional Pd/ceramic membranes. The H 2 permeability of the Pd/ceramic/Pd membrane (1.01 ×10 −8 mol m −1 s −1 Pa −0.5 at 773 K) is similar to that of a supported single Pd layer membrane but its H 2 /N 2 selectivity (18033) is enhanced by an order of magnitude at 773 K and Δ P  = 500 kPa. Intriguingly, the selectivity of the double Pd layer membrane improves with increasing pressure difference Δ P while that of Pd/ceramic membranes declines. This unusual pressure dependence originates from the elevated pressure within the ceramic of the double Pd layer membrane. The sweep gas-induced mass transfer resistance grows rapidly with increasing permeate pressure and sweep gas amount attenuating the single gas H 2 flux of the Pd/ceramic membrane by 67% at 1 MPa permeate pressure. This resistance remains significant under CO 2 capture conditions albeit concentration polarization on the feed side has an even stronger permeation-retarding effect in that situation. The CO 2 capture rate and purity benefit greatly from the enhanced high-pressure H 2 selectivity of Pd/ceramic/Pd membranes which renders them attractive tools for any kind of H 2 separation task. [ABSTRACT FROM AUTHOR]

Cost‐effective and robust nickel (Ni) membrane for H2 separation is a promising technology to upgrade the conventional H2 industries with improved economics and environmental benignity. In this work, Ni hollow fibers (HFs) with one closed end were fabricated and assembled into a membrane module for pure H2 separation by applying vacuum to the permeate side. The separation behavior of the HF module was investigated both experimentally and theoretically. Results indicate that H2 recovery can be improved significantly by changing the operation conditions (temperature or feed pressure). Ni HF is a promising membrane geometry, but the negative effect of pressure drop when H2 passes through the lumen cannot be ignored. Under the vacuum operation mode, there is little difference in term of H2 recovery efficiency whether the feed gas flow is controlled in countercurrent or recurrent operation. This work provides important insight to the development of superior membrane H2 separation system. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3662–3670, 2018 [ABSTRACT FROM AUTHOR]

The permeation characteristics of palladium pore filled (PF) membranes have been investigated with gas permeation and structural characterization of the membranes. PF membranes have been prepared by filling with Pd the nanoporous γ-Al 2 O 3 /YSZ (or pure YSZ) layer supported onto porous α-Al 2 O 3 and ZrO 2 . The number of nanoporous layers and the applied vacuum level during the electroless plating process have been studied. Gas permeation properties of the PF membranes have been determined in a temperature range of 300–550 °C. The measured hydrogen permeances have been found to be lower than previously reported for similar membranes. It has been found that the hydrogen fluxes do not depend on the thickness of the nanoporous layers (γ-Al 2 O 3 /YSZ or pure YSZ) or on the vacuum pump employed for filling with Pd. The physicochemical characterization performed showed that the palladium deposited does not form a percolated network across the mesoporous layer(s), leading to low hydrogen permeances and thus low H 2 /N 2 perm-selectivities. [ABSTRACT FROM AUTHOR]

In order to investigate the hydrogen separation enhancing effect on glycerol steam reforming performance, the simulation is carried out via a packed bed membrane reactor, where the porous media model is employed to model the distribution of catalyst and the non-isothermal environment in the reactor is considered. The reforming performances with and without membranes are compared. The results indicate that the membrane separation can promote the hydrogen production at a low temperature. The impacts of operating parameters including catalyst load, fuel gas temperature, sweep gas velocity and sweep gas temperature on the enhancement of the reforming performance are analyzed. The results reveal that the membrane separation is very sensitive to the temperature variation under different operating conditions. It is essential to properly control the operating parameter so as to achieve the promotion of hydrogen yield with low cost of energy. [ABSTRACT FROM AUTHOR]

Pressure swing adsorption (PSA) is an excellent way for separation and purification of gas mixtures. In this work, a process that separates hydrogen from mixtures with natural gas transported in the natural gas grid is present. The aim is to make a simulation and optimization of PSA for the hydrogen separation. The results show that Box-Behnken design provides sufficient data to fit the quadratic models for hydrogen production. And the target function is optimized by Minitab response optimiser. It is calculated that the optimised conditions are that temperature is 34°C, height ratio of activated carbon and zeolite layer is 1.73, and adsorption time is 382 s, the maximum hydrogen mole fraction is 0.8018. [ABSTRACT FROM AUTHOR]

Hydrogen is considered a fuel of the future due to its diversified supply and zero greenhouse gas emission. The application of advanced membrane technology for hydrogen separation within the larger hydrogen production process context can substitute the use of more expensive and energy intensive cryogenic distillation and pressure swing adsorption technologies. This review overviews the basic aspects and progresses in perovskite-based proton conducting hydrogen separation membranes. Different configurations such as symmetric, asymmetric, hollow fiber, and surface modified perovskite membranes with various compositions are discussed and summarized. The challenges and future directions of such membranes are also elaborated. [ABSTRACT FROM AUTHOR]

Because of poor heterogeneous nucleation of MOF on the ceramic support surface, it is usually difficult to prepare defect-free metal-organic framework (MOF) layers as shape-selective membrane on the native ceramic supports by a direct solvothermal synthesis route. In the present work, inspired by “like dissolves like” principle, a simple and facile synthesis strategy was developed to prepare highly reproducible and permselective zeolitic imidazolate framework ZIF-8 membranes on the 1H,1H,2H,2H-perfluoroalkyltriethoxysilanes (POTS) modified α-Al 2 O 3 disks. Attributing to the enhancement of surface hydrophobicity of the α-Al 2 O 3 supports after POTS modification, hydrophobic ZIF-8 membranes are tending to grow well on the hydrophobic surface following the “like grows like” principle. Thus a well-intergrown ZIF-8 membrane with a thickness of about 20 µm has formed on the POTS-modified α-Al 2 O 3 disks. The developed ZIF-8 membranes show high hydrogen selectivity and thermal stability. At 200 °C and 1 bar, the mixture separation factors of H 2 /CO 2 , H 2 /N 2 , H 2 /CH 4 , and H 2 /C 3 H 8 are 15.8, 22.6, 40.6, and 549.3, with H 2 permeances higher than 2.1 × 10 −7 mol·m −2 ·s −1 ·Pa −1 , which is promising for hydrogen separation and purification. [ABSTRACT FROM AUTHOR]

The membranes of vanadium alloys can be substantially more productive and much cheaper than the palladium alloy membranes which are widely used for hydrogen separation. However, the insufficient workability of vanadium alloys makes difficult producing the membranes of any shape, except for small thick flat samples, suitable only for laboratory studies, while membranes in the form of thin-walled tubes are most preferable for practical use. Such seamless thin-walled self-maintained membranes of tubular shape, made of V-Pd and V-Fe alloys with a thin Pd-coating on their inner and outer sides and with welded joints to stainless steel on both ends, were fabricated and tested for their throughput, service life, mechanical stability, and capability of hydrogen recovering from WGS mixtures. In view of reliable and highly productive operation of tubular V-alloy membranes as well as of their absolute selectiveness, the assembly from 18 membranes was fabricated to use it in the multi-fuel processor feeding a 1 kW PEM FC and providing up to 16 slpm of ultrapure hydrogen by the steam conversion of light and heavy hydrocarbons including diesel “Euro 5”. A similar assembly made of V-Fe alloy membranes was estimated for hydrogen purification in MOCVD applications. [ABSTRACT FROM AUTHOR]