Porous Stainless Steel Support Research Articles

Methane steam reforming in a membrane reactor using high-permeable and low-selective Pd-Ru membrane

We performed a methane steam reforming (MSR) reaction through a membrane reactor packed with commercial Ni/Al2O3 catalyst and a tubular Pd-Ru membrane deposited on a YSZ modified porous stainless steel support under mild operating conditions: 773 K and a pressure difference range of 100-250 kPa. We prepared the Pd-Ru membrane with thickness of ~6 μm on a tubular stainless steel support (diameter 12.7mm, length 25 cm) using electroless plating, which was observed for the membrane performance using hydrogen and nitrogen. Gas permeation test carried out at 773 K and 31.4 kPa of pressure difference between retentate and permeate sides showed that the hydrogen permeation rate and nitrogen leakage were ~0.1050mol s−1 m−2 and ~0.0018 mol s−1 m−2, respectively. The MSR reaction was under the following conditions: temperature 773 K, pressure 100-250 kPa, gas hourly space velocity (GHSV) 837 h−1, and steam-to-carbon feed ratio (S/C) 3. The MSR reaction result showed that methane conversion was increased with increasing pressure difference and reached ~77.5% at 250 kPa. In this condition, the composition of carbon monoxide was ~2%, meaning that no two series of water gas shift reactors were needed in our membrane reactor system. Longterm stability test carried out for ~100 h showed that methane conversion and the hydrogen yield remained constant.

Atmospheric Plasma-Sprayed Metal-Supported Solid Oxide Fuel Cells with Varying Cathode Microstructures

Metal-supported solid oxide fuel cells were manufactured by plasma spraying the cell layers on porous ferritic stainless steel supports. Cathodes with four different microstructures were produced by varying the plasma spray parameters and mixing carbon or starch-based pore forming agents with the ceramic feedstock powders. At 750°C, the best-performing button cell contained a cathode made with a carbon pore forming agent. This cell had an open circuit potential of 1.057 V and peak power density of 562 mW/cm². The lowest cell polarization resistance was 0.29 Ωcm² at 750°C, measured at an operating point of 0.7 V.

Electroless Pd deposition on a planar porous stainless steel substrate using newly developed plating rig and agitating water bath

A new plating bath was developed to prevent palladium plating in the pores of the porous stainless steel support when using plate-type porous substrate. The plating bath, composed of a holder, a rubber O-ring and a bottom, provides very simple assembly and is very effective in preventing palladium plating in the pores of porous stainless steel. The agitation of the plating solution increases plating rate significantly because the agitation improves the external mass transfer of Pd ion and reducing agent to the membrane surface facilitating ~99.7% plating yield of palladium ion. This new plating method carried out at a temperature range of 293 to 298 K provides a very simple and economic membrane manufacturing process. Using a newly developed plating rig, an 88.9-mm diameter membrane was fabricated, and gas permeation tests showed that the hydrogen permeation flux reached ~0.9 mol s−1 m−2 at 873 K and a pressure difference of 300 kPa and selectivity (H2/N2) was ~1,850 at 873 K with a pressure difference of 100 kPa.

Natural gas steam reforming reaction at low temperature and pressure conditions for hydrogen production via Pd/PSS membrane reactor

The objective of this work is to analyze the performance of a composite palladium-based membrane reactor (MR) by performing the natural gas steam reforming reaction at low operating conditions for producing high-purity hydrogen. The MR comprises a composite membrane, having ~13µmPd layer deposited on a porous stainless steel support, fabricated via electroless plating and a commercial Ni-based catalyst.The composite membrane shows infinite ideal selectivity, H2/He and H2/Ar, at trans-membrane pressures less than 100kPa and T=400°C at the onset of experimental testing. The steam reforming reaction is performed at 400°C, by varying the reaction pressures and sweep gas flow rate between 150kPa and 300 kPa, and 0–100mL/min, respectively. The gas hourly space velocity (GHSV) and steam-to-carbon ratio (S/C) are kept constant at 2600h−1 and 3.5.The effect of CO2 as an impurity in the feed line is also analyzed at 400°C and 150kPa.The best performance of the Pd-based MR is obtained at 400°C, 300kPa and 100mL/min of sweep-gas, yielding a methane conversion of 84%, hydrogen recovery of 82%, and obtaining a pure hydrogen stream at the permeate side.The Pd/PSS MR worked for more than 700h under differing operating conditions. As a comparison, a conventional reactor operating at the same MR conditions is compared and discussed.

다공성 스테인리스 강 지지체의 표면개질에 따른 팔라듐-은 합금 수소 분리막의 수소 투과 선택도의 변화

다공성 스테인리스 강 지지체의 표면개질에 따른 팔라듐-은 합금 수소 분리막의 수소 투과 선택도의 변화

Stainless steel-supported solid oxide fuel cell with La0.2Sr0.8Ti0.9Ni0.1O3−δ/yttria-stabilized zirconia composite anode

A metal-supported solid oxide fuel cell (MS-SOFC) is fabricated by co-firing stainless steel (STS) support with a new reduction-resistant oxide-anode and yttria-stabilized zirconia electrolyte. La and Ni co-doped SrTiO3 (La0.2Sr0.8Ti0.9Ni0.1O3−δ, LSTN) which shows Ni exsolution capability is composited with Y0.16Zr0.84O2−δ (YSZ) electrolyte to form a new LSTN-YSZ anode. A cermet layer composed of STS and YSZ (STS-YSZ) is inserted between a porous STS support and a new LSTN-YSZ composite anode for stable contact. With La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathode and Ce0.8Gd0.2O2−δ (GDC) interlayer coated on top of co-fired half-cell, YSZ/LSTN-YSZ/STS-YSZ/STS, a newly designed and fabricated cell achieved maximum power density of 185 mW cm−2 at 650 °C. This power density is an improvement over many conventional co-fired MS-SOFCs that use a Ni-cermet anode.

NaA zeolite membranes synthesized on top of APTES-modified porous stainless steel substrates

NaA zeolite membranes were synthesized on top of both disk and tubular porous stainless steel substrates by the secondary growth method. The support seed stage was optimized, considering the seed synthesis conditions and the deposition method. The formation of the NaA zeolite on both the membrane and the residual powder collected at the bottom of the vessel after synthesis was corroborated by X-ray diffraction (XRD). Scanning electron microscopy (SEM) revealed the formation of a film with well-defined crystals with a cubic morphology characteristic of the NaA zeolite. The support modification with 3-aminopropyltriethoxysilane improved the morphology and stability of the NaA zeolite membranes synthesized on top of porous stainless steel substrates. When vacuum was applied only in the last hydrothermal synthesis stage, a smooth zeolite layer was obtained on top of porous stainless steel supports. The single gas (H2, N2, CO2 and CH4) and mixture (H2/N2 and H2/CH4) perm-selective properties of the tubular membranes were evaluated as a function of temperature and pressure. Separation factors higher than the Knudsen coefficient were obtained in all membranes. The single gas H2 and CO2 permeation flux of the membranes increased with temperature indicating a preponderance of the activated diffusion over the Knudsen diffusion. The higher H2/CO2 ideal separation factors were 7.6 and 5.6 for the more selective tubular membranes, at 453K and 100kPa.

Carbon molecular sieve membranes on porous composite tubular supports for high performance gas separations

Carbon molecular sieve (CMS) membranes on the inside of porous composite stainless steel supports were developed for gas separation in this research effort. The intermediate alumina layer was introduced to reduce the pore size of the porous stainless steel tube and subsequently provide uniform surface roughness. Viscosity of the phenolic polymer solution was varied from 10 to 30 centipoises (cP) to maximize performance of the CMS membranes. Pyrolysis temperature was also varied from 700 °C to 900 °C to optimize the fabrication of uniform CMS membranes on porous composite stainless steel supports. High performance CMS membranes were obtained from triple coatings and subsequent pyrolysis at 700 °C. The viscosity of precursor solutions played a critical role to determine the performance of CMS membranes in terms of gas permeance and ideal gas separation factor. The highest separation performance of the CMS membranes was shown with viscosity of 20 cP, resulting in gas separation factor of 462 for He/N2, 97 for CO2/N2, and 15.4 for O2/N2.

A tailor-made porous stainless steel support for a dense hydrogen separation membrane

A tailor-made DPSS (disc-shaped porous stainless steel substrate) for a thin and dense hydrogen membrane with high performance was fabricated by molding pre-treated metal powder, sintering an ingot and then slicing by electrical discharge machining. The sliced DPSS has a diameter of 50.8 mm and a thickness of 1.6 mm. In comparison with commercially produced support (DPSS-M), the sliced DPSS, having surface roughness of 2.7, maximum surface pore size of about 2 μm, porosity of 33.1% and average pore diameter of 0.58 μm, is more suitable as the support for the thinner Pd membrane. The hydrogen membrane with Pd layer of 4.4 μm was prepared and its performance was evaluated. It was shown that the Pd/DPSS membrane had a higher H2/N2 selectivity (3825) with a hydrogen flux of 24.7 ml/min/cm2, than that of Pd/DPSS-M (1821), at del-P = 1 and 400 °C, even though the surface morphologies of DPSS had been modified with less steps than DPSS-M. For CO2/H2 separation, the Pd/DPSS membrane enriched 40% CO2 to 90.8% and separated 60% H2 to 99.8% at 400 °C and del-P = 20 bar.

Preparation of palladium/NaX/PSS membrane for hydrogen separation

Abstract Palladium (Pd) membranes on porous stainless steel (PSS) were prepared by electroless plating. An intermediate layer of NaX nanozeolite was employed to modify the pore size of the PSS support and improve the hydrogen permeability. NaX nanozeolites were synthesized using convectional hydrothermal method. The NaX intermediate layer was coated by vacuum-assisted method on the PSS surface. The structure and morphology of the prepared membranes were characterized using SEM, XPS and XRD analysis. Permeation measurements were conducted using H 2 , N 2 and mixture of H 2 /N 2 at different temperatures (350–450 °C), and trans-membrane pressures (4–8 bar). The results indicated that the permeability and hydrogen selectivity were increased by enhancement in temperature and pressure. The hydrogen fluxes in H 2 /N 2 mixtures were lower than those corresponding to pure hydrogen at the same partial pressures and temperatures. The obtained results suggests that the use of NaX nanozolite is an effective intermediate layer in Pd/PSS membranes for hydrogen separation.

Development of a novel cell structure for low-temperature SOFC using porous stainless steel support combined with hydrogen permeable Pd layer and thin film proton conductor

A novel cell structure for low-temperature SOFC was proposed, using porous stainless steel support substrates combined with thin hydrogen permeable Pd layers, thin-film proton conductor, and thin-film cathode. Metallic supports consist of sintered ferritic stainless steel spherical powders whose thermal expansion coefficient is close to that of the hydrogen permeable layers and proton conductive electrolytes. To prepare the cell, both the 1.2-μm thick proton conductive Sr(Zr0.8Y0.2)O3−δ electrolyte layer and the 100-nm thick (La0.6Sr0.4)(Co0.2Fe0.8)O3−δ cathode layer were deposited by pulsed laser deposition (PLD) on a Pd-coated porous ferritic stainless steel substrate. The power generation performance at a low temperature of 400 °C was demonstrated in this proposed cell for the first time, while obtained power density is still low and improvements are required.

Atmospheric Plasma-Sprayed Metal-Supported Solid Oxide Fuel Cells with Varying Cathode Microstructures

Metal-supported solid oxide fuel cells (SOFCs) use less expensive materials than traditional anode-supported or electrolyte-supported SOFCs. The active layers of a metal-supported SOFC can be manufactured by plasma spraying without the need for high-temperature sintering. Plasma spraying is a rapid-fabrication process that is scalable for large cell areas and for mass production. Porous ferritic stainless steel (Sanergy HT, Sandvik, Sweden) supports were manufactured from powders by pressing and sintering pellets. The active cell layers consisted of a composite nickel - yttria-stabilized zirconia (YSZ) anode, a YSZ electrolyte, and a La0.6­Sr0.4Co0.2Fe0.8O3-δ (LSCF) – Ce0.8Sm0.2O1.9 (SDC) cathode. Plasma spraying produces unique microstructures, as the cell layers are built up by the rapid solidification of molten (or semi-molten) splats. These microstructures were tailored by adjusting the plasma spray process parameters and the ingredients in the feedstock. Dense electrolytes were made using a high-power plasma, a very high torch pass speed (to minimize the plasma heat impulse to the substrate), and a feedstock consisting of YSZ suspended in a mixture of water, ethanol, and ethylene glycol. Cathodes with four different microstructures were produced by varying the plasma spray parameters and mixing carbon or starch-based pore forming agents into the ceramic feedstock powders. Resultant microstructures are shown in Figure 1. Electrochemical performances of metal-supported button cells with varying cathode microstructures were measured. At 750°C, the cells had open circuit potentials of up to 1.057 V and peak power densities as high as 562 mW/cm². Electrochemical impedance spectra were measured at an operating point of 0.7 V, varying the cathode gas with different air-nitrogen mixtures. With 100% air as the cathode gas, the lowest cell polarization resistance was 0.29 Ωcm² at 750°C. Equivalent circuit modeling was performed to analyse how the cathode microstructure affected the cell performance. Figure 1

Atmospheric Plasma-Sprayed Metal-Supported Solid Oxide Fuel Cells with Varying Cathode Microstructures

Metal-supported solid oxide fuel cells were manufactured by plasma spraying the cell layers on porous ferritic stainless steel supports. Cathodes with four different microstructures were produced by varying the plasma spray parameters and mixing carbon or starch-based pore forming agents with the ceramic feedstock powders. At 750°C, the best-performing button cell contained cathodes made with a carbon pore forming agent. This cell had an open circuit potential of 1.057 V and peak power density of 562 mW/cm². The lowest cell polarization resistance was 0.29 Ωcm² at 750°C, measured at an operating point of 0.7 V.

Stability investigation of micro-configured Pd–Ag membrane modules – Effect of operating temperature and pressure

The long-term stability over a period of up to 50 days has been reported for various designs of microstructured Pd77Ag23 membrane modules for H2 production and purification. Even though microchannels provide sufficient mechanical support for moderate trans-membrane pressure difference and temperatures, i.e., 4–5 bars and 400–450 °C, long-term operation under these operating conditions results in a large deformative settling of the Pd77Ag23 film into the microchannel support. This settling leads to microstructural changes and pore formation on the feed surface of the membrane film that ultimately results in membrane failure. For pressures above approximately 5 bars, the application of microchannel-supported modules is thus not feasible, and for that purpose a continuous porous stainless steel support is introduced that allows for a sufficient stabilisation of the thin Pd77Ag23 films. For such a porous stainless steel supported microchannel module, a hydrogen flux of 195.3 mL cm−2 min−1 is obtained at 450 °C and 5 bars feed pressure, corresponding to a permeability of 3.4·10−8 mol m−1 s−1 Pa−0.5. During the complete operation of 1100 h at 450 °C, the module shows a very good stability up to the highest feed pressure applied of 15 bars. The N2 leakage flux has remained below the detection limit of the equipment, 5 μL cm−2 min−1, resulting in a minimum value for the H2/N2 permselectivity of 39.000 applying the pure H2 flux value obtained at 5 bars.

Control of silica-zirconia nanoparticles for uniform porous SiO2-ZrO2 membranes.

Silica-zirconia composite sols were prepared by means of a sol-gel method, using tetraethylorthosilicate (TEOS) and zirconium tetra-n-butoxide (ZrTB) precursors. TEOS, ZrTB, HCl, H2O and EtOH were mixed at 70 degrees C for 24 hours to give molar ratios of 1:1:8-80:0.2-1.0:100-300. The mean particle size of the silica-zirconia sol was controlled by the concentration of the alkoxides and catalyst, as well as the water molar ratio in the starting solution. The particle size of the SiO2-ZrO2 sol, which was analyzed by dynamic light scattering (DLS) and field emission scanning electron microscopy (FE-SEM), was in the range of 20 to 350 nm. The SiO2-ZrO2 sol solutions of different sol sizes were coated onto porous stainless steel supports (O.D. 10 mm, length: 20 mm, 316L SUS, Mott corp. USA) by a dipping-rolling-freezing-fast drying (DRFF) and soaking-rolling-freezing-fast drying (SRFF) method. After coating with SiO2-ZrO2 sol, the single gas permeation characteristics (He, H2 and N2) of the resulting SiO2-ZrO2 membranes were evaluated at room temperature. This produced a decrease in the mean flow diameter and H2/N2 permselectivity in the range of 2.0-3.5. Finally, following the results of gas permeation testing, the pore size of the membranes was controlled by changing their particle size.

Influence of the rotation rate of porous stainless steel tubes on electroless palladium deposition

Thin dense palladium (Pd) membranes (approximately 5μm) were fabricated on rotating porous stainless steel supports using electroless plating. During electroless Pd plating, the rate of Pd deposition increased as the support rotation rate increased. Compared with conventional electroless plating methods, the proposed modified electroless plating using a support rotation technique yielded Pd membranes that had considerably more uniform and smooth surface morphology, which substantially enhanced the membrane stability. The membranes exhibited a hydrogen permeance as high as 78m3/m2hbar0.5 (3.0×10−3mol/m2sPa0.5) and an ideal permselectivity exceeding 400 when the pressure difference was 4bar and the temperature was 400°C. Moreover, the membranes were stable during long-term temperature cycling performed between room temperature and 400°C over a period of 350h. These results indicated that the electroless plating combined with support rotation process was a simple, effective method for preparing thin dense Pd membranes featuring high hydrogen permeation flux and high thermal durability.

Development of thin palladium membranes supported on large porous 310L tubes for a steam reformer operated with gas-to-liquid fuel

Palladium membranes were prepared on large tubes (80mm diameter and 150mm length) of porous stainless steel supports (PSS) using a modified electroless plating technique. The morphology of the palladium layer was found to be depending on the container material of the coating apparatus. The use of PMMA resulted in compact palladium layers with smooth surfaces whereas PTFE led to inhomogeneous palladium coating with rough surface. Two different ceramic materials and coating methods were used to prepare an intermediate layer needed to prevent intermetallic diffusion between the palladium and the support at elevated temperatures. Wet powder spraying of TiO2 followed by sintering resulted in a smoother surface than atmospheric plasma spraying of YSZ, thus allowing for a thinner palladium coating. Pd/TiO2/PSS membranes showed about 4 times higher hydrogen permeances than Pd/YSZ/PSS membranes as a consequence of higher palladium thickness and lower porosity of the ceramic intermediate layer. The selectivity against nitrogen was comparable for both membranes. However, the YSZ intermediate layer showed better stability at elevated temperatures. Two membrane tubes were applied in the membrane reformer, which produced hydrogen successfully from a gas-to-liquid (GtL) fuel.

H2 production via water gas shift in a composite Pd membrane reactor prepared by the pore-plating method

In this work, H2 production via catalytic water gas shift reaction in a composite Pd membrane reactor prepared by the ELP “pore-plating” method has been carried out. A completely dense membrane with a Pd thickness of about 10.2 μm over oxidized porous stainless steel support has been prepared. Firstly, permeation measurements with pure gases (H2 and N2) and mixtures (H2 with N2, CO or CO2) at four different temperatures (ranging from 350 to 450 °C) and trans-membrane pressure differences up to 2.5 bar have been carried out. The hydrogen permeance when feeding pure hydrogen is within the range 2.68–3.96·10−4 mol m−2 s−1 Pa−0.5, while it decreases until 0.66–1.35·10−4 mol m−2 s−1 Pa−0.5 for gas mixtures. Furthermore, the membrane has been also tested in a WGS membrane reactor packed with a commercial oxide Fe–Cr catalyst by using a typical methane reformer outlet (dry basis: 70%H2–18%CO–12%CO2) and a stoichiometric H2O/CO ratio. The performance of the reactor was evaluated in terms of CO conversion at different temperatures (ranging from 350 °C to 400 °C) and trans-membrane pressures (from 2.0 to 3.0 bar), at fixed gas hourly space velocity (GHSV) of 5000 h−1. At these conditions, the membrane maintained its integrity and the membrane reactor was able to achieve up to the 59% of CO conversion as compared with 32% of CO conversion reached with conventional packed-bed reactor at the same operating conditions.

Sol–gel synthesis of thin alumina layers on porous stainless steel supports for high temperature palladium membranes

The synthesis of thin, defect-free and long lifetime Pd-based membranes for H2 separation is still a challenging task. A porous support is necessary in order to give mechanical stability to very thin layers. Sintered porous metal supports are very promising candidates having numerous advantages over the widely studied ceramic supports. The deposition of a non-metallic barrier between the stainless steel support and the Pd dense layer can prevent the intermetallic diffusion of elements from the support to the Pd-based layer and improve the characteristics (e.g. pore size, topography) of the support surface which actually limits the minimum Pd thickness required in order to obtain high selectivity membranes.In the present paper, the deposition of intermetallic barrier layers made of alumina obtained via sol gel technique was investigated using commercial porous stainless steel supports, both with their original roughness and after a mechanical smoothing treatment. The quality of the deposited alumina layer was related to the surface characteristics of the supports, sol composition (aluminium and additive content) and viscosity. Pd dense layers were grown via electroless plating technique on the alumina barrier by activation with an additional Pd doped thin alumina layer.

Performance and degradation of metal-supported solid oxide fuel cells with impregnated electrodes

Metal-supported solid oxide fuel cells (MS-SOFCs) containing porous 430L stainless steel supports, YSZ electrolytes and porous YSZ cathode backbones are fabricated by tape casting, laminating and co-firing in a reducing atmosphere. Nano-scale Ni and La0.6Sr0.4Fe0.9Sc0.1O3−δ (LSFSc) coatings are impregnated onto the internal surfaces of porous 430L and YSZ, acting as the anode and the cathode catalysts, respectively. The resulting MS-SOFCs exhibit maximum power densities of 193, 418, 636 and 907 mW cm−2 at 650, 700, 750 and 800 °C, respectively. Nevertheless, a continuous degradation in the fuel cell performance is observed at 650 °C and 0.7 V during a 200-h durability measurement. Possible degradation mechanisms were discussed in detail.