Composite Membranes For Hydrogen Separation Research Articles

Preparation of a zeolite-palladium composite membrane for hydrogen separation: Influence of zeolite film on membrane stability

With the development of hydrogen energy, palladium-based membranes have been widely used in hydrogen separation and purification. However, the poor chemical stability of palladium composite membranes limits their commercial applications. In this study, a zeolite-palladium composite membrane with sandwich-like structure was obtained by using a TS-1 zeolite film grown on the surface of palladium membrane. The membrane microstructure was characterized by SEM and EDX. The effects of the the TS-1 film on the hydrogen permeability and stability of palladium composite membrane were investigated in details. Benefited from the protection of the TS-1 zeolite film, the stability of palladium composite membrane was enhanced. The results indicate that the TS-1-Pd composite membrane was stable after 8 cycles of the temperature exchanging cycles between 773 K and 623 K. Especially, the loss of hydrogen permeance for TS-1-Pd composite membrane was much smaller than that of the pure palladium membrane when the membrane was tested in the presence of C3H6 atmosphere. It indicated that the TS-1-Pd composite membrane had better chemical stability in comparison with pure palladium membrane, owing to its sandwich-like structure. This work provides an efficient way for the deposition of zeolite film on palladium membrane to enhance the membrane stability.

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.

Substantial enhancement of hydrogen permeability of Mo2C/V composite membranes by ion beam sputtering

Ion beam sputtering (IBS) was used to deposit Mo 2 C catalytic layers on vanadium (V) foils and to prepare Mo 2 C/V composite membranes for hydrogen separation and purification. It is found that the sputtering temperature during IBS largely affects the structure and catalytic activity of the as-deposited Mo 2 C films. A high sputtering temperature facilitates the growth of cubic Mo 2 C along the catalytically dominant crystal plane, which substantially enhances the hydrogen permeability of Mo 2 C/V. Typically, the Mo 2 C/V membranes prepared by IBS at a sputtering temperature of 600 °C exhibit a significantly high hydrogen permeability of ∼ 6.7 × 10 −8 mol H 2 m −1 s −1 Pa −0.5 at a hydrogen permeation temperature of 600 °C. This is 2.4 times that of Pd and 2.0 times that of Mo 2 C/V membranes prepared by conventional magnetron sputtering. The present work demonstrates that IBS is a promising technique to prepare highly permeable and cost-effective Mo 2 C/V membranes for high temperature hydrogen separation. • Ion beam sputtering is a potential method to prepare Mo 2 C/V for H 2 separation. • The sputtering temperatures largely affect the microstructures of Mo 2 C films. • The cubic Mo 2 C by ion beam sputtering exhibits a preferred growth of (220) plane. • Enhancement of catalytic activity of Mo 2 C leads to high H 2 permeability of Mo 2 C/V. • The highest H 2 permeability of Mo 2 C/V membranes is ∼2.4 times that of pure Pd.

BaCe0.5Zr0.3Y0.2O3-La0.8Sr0.2Cr0.75Mn0.25O3 Composite Membrane for Hydrogen Separation

A dual-phase membrane was developed for hydrogen separation. A BaCe0.5Zr0.3Y0.2O3 (BCZY) phase provided a proton conduction pathway while A La0.8Sr0.2Cr0.75Mn0.25O3 (LSCrMn) phase provided an electronic conduction pathway for effective hydrogen permeation. Once each perovskite phase had formed, the powder mixture was attrition-milled and dry-pressed. After sintering a porous–dense–porous trilayer, the phase purity was confirmed by x-ray diffraction. Usage of a powder blanket was critical to avoid undesired phase formation in addition to LSCrMn and BCZY. Total conductivity of the composite was measured to confirm the 3D connectivity of the LSCrMn phase. The hydrogen flux was larger than 2 mL min−1 cm−2, demonstrating the effectiveness of the dual-phase design.

Mechanical spectroscopy of metal/polymer composite membranes for hydrogen separation

In the present work, mechanical properties of metal-polymer composite membranes for hydrogen separation have been investigated by tensile test and mechanical spectroscopy methods. The membranes were prepared by high-energy ball milling and subsequent thermal pressing of a powder mixture of polyethylene with 10 wt% hydride-forming intermetallic compound LaNi2.5Co2.4Mn0.1. The membranes were then subjected to activation by long exposure in a hydrogen atmosphere. The static tensile test showed a slight decrease in membrane tensile strength after hydrogen activation that may be explained by intermetallic particle embrittlement. Mechanical spectroscopy study reveals a shift of the internal friction peak of the activated membrane by 22 K towards lower temperatures and a small decrease of the activation energy of polyethylene viscoelastic transformation from 144 kJ/mol to 138 kJ/mol.

NaA zeolite membranes on modified porous stainless steel supports: a comparative study of different SiO2 sources

The deposition of a NaA zeolite layer on porous stainless steel substrates was optimized in order to obtain composite membranes for hydrogen separation. The effect of the silica source on NaA zeolite crystallinity and morphology was studied using two synthesis routes: concentrated gel and clear solution. The optimized synthesis conditions were applied for the synthesis of NaA zeolite layers on top of porous stainless steel disks or on the outer surface of tubular supports. SEM and XRD measurements confirmed that the use of rice husk allowed obtaining defect free and pure phase NaA zeolite membranes. Selectivity values similar to those published for NaA zeolite membranes based on ceramic substrates were obtained using zeolite layers deposited on porous stainless steel tubes. From the curve fitting of the experimental data, the contribution of zeolitic and non-zeolitic flux was estimated. For the membranes synthesized from a concentrated gel, H2 showed a predominated contribution of the zeolitic flux.

Preparation of Pd/SAPO-34/PSS composite membranes for hydrogen separation: Effect of crystallization time on the zeolite growth on PSS support

In this study, palladium composite membranes were fabricated on porous stainless steel (PSS) supports using silicoaluminophosphate (SAPO) zeolite (SAPO-34) as a diffusion barrier and substrate modifier. The vacuum-assisted seeding and secondary growth method was used to coat the SAPO-34 zeolite layer on the PSS substrates. The morphologies and microstructures of the membranes were analyzed by AFM, XRD, BET, ICP–AES, FESEM and EDX techniques. The effect of crystallization time (24, 48 and 72h) on the morphology and quality of SAPO-34 modified supports was studied. A continuous palladium layer with a thickness of about 9μm was deposited on the SAPO-34 modified PSS support (72h crystallization time) by electroless plating (ELP) route. The hydrogen permeation tests were carried out in the feed pressures range of 2–4bar and various temperatures (623, 673 and 723K). The values of the hydrogen permeance and ideal selectivity of H2/N2 for the PSM3 membrane were achieved 7.1×10–7molm–2s–1Pa–1 and 866, respectively a feed pressure of 2bar and 723K. In addition, the PSM3 membrane showed perfect stability during 260h hydrogen permeation experiment at a feed pressure of 2bar and 623K.

Surface modification of macroporous Al2O3 tubes with carbon-doped TiO2 intermediate layer and preparation of highly permeable palladium composite membranes for hydrogen separation

ABSTRACTTo prepare H2-permeable palladium composite membranes, a novel carbon-doped microporous TiO2 intermediate layer was introduced to modify the surface of macroporous Al2O3 substrates. The Pd/TiO2–C/Al2O3 membrane was prepared via electroless plating, and thereafter, carbon residue in the intermediate layer was removed by calcination in air, yielding a Pd/TiO2/Al2O3 membrane. Experimental results indicate that the carbon residue shrinks the pore size of the intermediate layer and facilitates a decrease of membrane defects. Additionally, carbon removal induces a higher effective membrane area at the permeate side, which enhances hydrogen permeability. Furthermore, the apparent activation energy (EA) and stability of the as-prepared Pd/TiO2/Al2O3 membrane were investigated.

Novel process for preparation of metal-polymer composite membranes for hydrogen separation

In the present work, a new preparation method for metal-polymer composite materials for hydrogen separation which consist of hydride-forming intermetallic compound LaNi5 and polyethylene was developed. According to this technique, the mechanical activation of the initial powder mixtures was employed to provide good interface between the phases. A series of composite membranes with various filler concentrations was synthesized and characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. The gas transport properties of the obtained materials in relation to H2, O2, N2, CO2 and CH4 were tested. The results indicate that the addition of the hydride-forming intermetallic compound to the barrier polymer leads to significantly improved selectivity with respect to hydrogen. The proposed method can be considered as a promising approach to producing of high performance composite membranes for hydrogen separation.

Contaminant-resistant MOF–Pd composite for H2 separation

Working principle of a contaminant-resistant MOF-on-Pd composite membrane for hydrogen separation.

Bifunctional palladium composite membrane for hydrogen separation and catalytic CO methanation

NiO was introduced into the porous Al 2 O 3 substrate by impregnation, and the resulting NiO/Al 2 O 3 was coated with the lead of a 2B pencil to modify its surface. A palladium layer with a thickness of 5 μm was deposited by electroless plating on the Pencil/NiO/Al 2 O 3 substrate, and a Pd/Pencil/Ni/Al 2 O 3 membrane was obtained after reduction with hydrogen. For reference, a Ni-free Pd/Pencil/Al 2 O 3 membrane was also fabricated. The surface and cross-sectional morphologies of the membranes were studied by scanning electron microscopy and metallographic microscopy. The hydrogen permeation kinetics was investigated by single gas tests, and the hydrogen separation performances of the Pd/Pencil/Al 2 O 3 and Pd/Pencil/NiO/Al 2 O 3 membranes were tested with a hydrogen feed composed of H 2 77.8%, CO 5.2%, CO 2 13.5%, and CH 4 3.5%. The Ni-free Pd/Pencil/Al 2 O 3 membrane only shows function of hydrogen separation, while the Pd/Pencil/Ni/Al 2 O 3 is also catalytically effective for methanation of CO and CO 2 in hydrogen, forming a bifunctional palladium membrane concept. Since the amount of CO and CO 2 in the hydrogen after membrane separation is very low, the consumption of hydrogen by the methanation reactions is negligible. The bifunctional membrane is promising for proton exchange membrane fuel cells because the catalytic methanation treatment solves the CO poisoning problem of the fuel cell electrodes and consequently allows the palladium membrane to tolerate more membrane defects and to achieve longer life. Aiming at the hydrogen purification for proton exchange membrane fuel cells, a bifunctional Pd/Pencil/Ni/Al 2 O 3 membrane that is capable of hydrogen separation and catalytic CO methanation was developed. It was compared with the Pd/Pencil/Al 2 O 3 membrane without the nickel methanation catalyst.

Development of CMS/Al2O3-supported PPO composite membrane for hydrogen separation

A novel composite membrane consisting of a poly(phenylene oxide) (PPO) selective layer and a CMS/Al2O3 substrate was fabricated by a spin-coating method. This new class of PPO/CMS/Al2O3 multilayer composite membranes showed an H2 permeability of 134 Barrer, two times greater than that for the corresponding self-supported PPO polymeric membrane. High selectivities for H2/CH4 and H2/N2 of 31.8 and 37.1, respectively, were also obtained with this composite membrane. According to field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) observations, using the CMS/Al2O3 material as the substrate provided a smooth surface for the support of the PPO selective layer and increased the roughness from the top to bottom surfaces. The effects of the substrate materials on the permselectivity of the resulting membrane were also investigated.

Toward low-cost Pd/ceramic composite membranes for hydrogen separation: A case study on reuse of the recycled porous Al 2O 3 substrates in membrane fabrication

The development of hydrogen energy systems has placed a high demand on hydrogen-permeable membranes as compact hydrogen separators and purifiers. Although Pd/Ceramic composite membranes are particularly effective in this role, the high cost of these membranes has greatly limited their applications; this high cost stems largely from the use of expensive substrate material. This problem may be solved by substrate recycling and the use of lower cost substrates. As a case study, we employed expensive asymmetric microporous Al 2O 3 and low-cost macroporous symmetric Al 2O 3 as membrane substrates (average pore sizes are 0.2 and 3.3 μm, respectively). The palladium membranes were fabricated by electroless plating, and substrate recycling was carried out by palladium dissolution with a hot HNO 3 solution. The functional surface layer of the microporous Al 2O 3 was damaged during substrate recycling, and the reuse of the substrate led to poor membrane selectivity. With the assistance of pencil coating as a facile and environmentally benign surface treatment, the macroporous Al 2O 3 can be successfully utilized. Furthermore, the macroporous Al 2O 3 can be also recycled and reused as membrane substrate, yielding highly permeable, selective and stable palladium membranes. Consequently, the substrate cost can be further decreased, and the applications of this kind of membranes would expand.

Preparation of Pd-TS-1 Composite Membrane for Hydrogen Separation

Palladium composite membranes have been prepared by improved electroless plating on macroporous α-Al2O3 tubes. TS-1 zeolite layer was introduced in the palladium composite membrane to modify macroporous α-Al2O3 tubes and prevent the diffusion between Pd and alumina. The detailed microstructure and morphology of the Pd-TS-1 composite membrane were examined by SEM and XRD. Moreover, gas permeation performance was tested at the temperature range of 623~773K. Results showed that the H2 permeance and H2/N2 ideal selectivity for Pd-TS-1 composite membrane could be up to 3.7×10-7 mol·m-2·s-1·Pa-1 and 310 at 773K, respectively.

Improvement of high temperature stability of Pd coating on Ta by HfN intermediate layer

Hafnium nitride (HfN) was chosen as a material for non-porous intermediate layer to improve the high temperature stability of Pd–Ta composite membranes for hydrogen separation. A layer of dense HfN (70 nm) was prepared between Ta substrate and thin Pd film (300 nm), and the high temperature stability of Pd coating was examined by hydrogen absorption experiments at 573 K after the heat treatments at 873 and 973 K. The HfN layer showed obvious hydrogen permeability, though the permeation rate in HfN appeared to be smaller than that in Pd and Ta. In addition, the degradation in coating effects of Pd at elevated temperatures was substantially retarded by HfN layer. Such improved stability was ascribed to retardation of open porosity development in Pd films and interdiffusion between Pd and Ta. It was concluded that HfN is a potential candidate material for intermediate layer to improve high temperature stability of Pd-group 5 metal composite hydrogen separation membranes.

Characteristic of Palladium Coated Tubular Alumina Composite Membrane for Hydrogen Separation

The palladium membrane has been developed for high temperature separation of hydrogen from other syngas molecules. In this study, tubular α-alumina substrate was used as a support for increase mechanical strength for thin palladium membrane. Prior depositing of palladium film, a dip-coating of palladium nuclei was performed to cover the substrate. Afterward, surface of activated support was modified with a thin intermediate layer for improving adhesion between support and Pd membrane. Electroless plating of dense palladium membrane was achieved from the plating bath containing EDTA stabilized palladium complex and hydrazine. The microstructural characteristics of palladium membranes were analyzed.

Fabrication and characterization of Pd/Nb 40Ti 30Ni 30/Pd/porous nickel support composite membrane for hydrogen separation and purification

A porous nickel support was successfully prepared by uniaxial compression of nickel powders. Microstructures and mechanical properties of Nb 40Ti 30Ni 30 membranes fabricated by magnetron sputtering were investigated. Deposited and annealed Nb 40Ti 30Ni 30 membranes consisted of amorphous and crystalline phases, respectively. Higher base temperature was shown to increase the hardness and elastic modulus of the Nb 40Ti 30Ni 30 membrane. Pd/Nb 40Ti 30Ni 30/Pd/porous nickel support composite membranes were then fabricated using a multilayer magnetron sputtering method. The hydrogen permeability of the composite membranes with amorphous and crystallized Nb 40Ti 30Ni 30 metal layer was measured and compared with that of self-supported Nb 40Ti 30Ni 30 and Pd alloys. Solid-state diffusion was shown to be the rate-controlling factor when the thickness of the Nb 40Ti 30Ni 30 layer was about 12 μm or greater, while other factors were in effect for thinner layers (such as 6 μm). The Pd/Nb 40Ti 30Ni 30/Pd/porous nickel support composite membrane exhibited excellent permeation capability and satisfactory mechanical properties. It is a promising new permeation membrane that could replace Pd and PdAg alloys for hydrogen separation and purification.

A novel Pd/silicalite-1 composite membrane for hydrogen separation

A novel Pd/silicalite-1 composite membrane supported on the macroporous tubular stainless steel substrate was successfully fabricated by electroless plating at 303 K. The structure, morphology and gaseous permeability of the membrane were detected by X-ray diffractiometry (XRD), scanning electron microscopy (SEM) and single-gas permeation test, respectively. Results confirm the formation of a thin, smooth, and continuous Pd/silicalite-1 composite membrane. The obtained composite membrane shows a high H2 permeance of 1.15×10−6 mol·m−2·s−1·Pa−1 with moderate H2 selectivity of 250 for H2/N2 at 773 K, at 0.1 MPa pressure drop, suggesting the potential application for H2 separation.

Preparation of highly stable palladium alloy composite membranes for hydrogen separation

Palladium alloy composite membranes for hydrogen separation have been fabricated on a porous stainless steel (SS) support by the vacuum electrodeposition and laminating procedure of thin palladium alloy film less than 25 μm. In spite of the formation of an alloy with copper, the brittleness of the palladium-based membrane due to palladium hydride in the presence of hydrogen diffusing through the membrane was a major problem, which causes a failure of the membrane with formation of pinholes. By preparing the composite membrane without microstructural change, it is possible to obtain both high performance and stable membrane. The permeation behavior for the prepared composite membranes was measured in long-term. During permeation testing, the physical and morphological stability of the composite membranes have been observed and the long-term tests have shown very high performances above 3 months of operation. Furthermore, these composite membranes had the capability to separate hydrogen from gas mixture with complete hydrogen selectivity and can be used to produce ultra-pure hydrogen for applications in membrane reactor and so on.

Improvement in high temperature stability of Pd coating on Nb by Nb 2C intermediate layer

Niobium subcarbide (Nb 2C) was chosen as a material for non-porous intermediate layer to improve the high temperature durability of Pd–Nb composite membranes for hydrogen separation. A layer of Nb 2C was prepared between Nb substrate and thin Pd films (100 nm), and the stability of Pd coating at elevated temperatures (573–773 K) was examined by hydrogen absorption experiments. Hydrogen permeability through the Nb 2C layer appeared to be sufficiently high, and no noticeable deterioration was observed in hydrogen absorption rate under as-prepared conditions. The degradation in coating effect of Pd at elevated temperatures was substantially mitigated by Nb 2C layer. Such improved durability was ascribed to retardation of open porosity development by Nb 2C caused as a consequence of impeded interdiffusion between Pd and Nb.