Porous Stainless Steel Tubes Research Articles

Life cycle assessment of H2-selective Pd membranes fabricated by electroless pore-plating

Pd-based membranes are attracting great attention to reach ultra-pure hydrogen in independent separators or combined with catalysts in membrane reactors. Many advances have been proposed for their fabrication over the last few years, reaching relatively thin Pd-films onto porous substrates with high permeation capacities and mechanical stability, although their commercialization and penetration in the industry are still scarce. At this point, it is important to complete all these technological advances with data about related economic and environmental implications during their fabrication to detect possible bottlenecks and select the best strategy. In this context, the current study presents for the first time a life cycle assessment focused on the preparation of Pd-based composite-membranes by Electroless Pore-Plating (ELP-PP). Two different types of composite membranes supported onto porous stainless steel tubes are analyzed, including or not an additional CeO2 intermediate layer between the support and the Pd-film. Precise experimental data of the fabrication process at laboratory-scale were considered to account for both materials and energy requirements. Thereafter, the environmental impacts were estimated through ReCiPe methodology by using the software Simapro 8.5. The results evidence that climate change (CC), human toxicity (HT), acidification (AC), freshwater ecotoxicity (FWE), metal depletion (MD) and fossil fuel resources depletion (FD) are the most relevant environmental impacts generated during the manufacturing of the Pd-based membrane. Under this perspective, palladium deposition appears as the manufacturing step with the highest impacts. It can be explained by the metal consumption and the high-energy consumption required for deposition cycles. Thus, the electricity mix of the country where the factory is located is critical to minimize the environmental impacts. For this reason, European countries are expected to be the most favorable ones for membrane fabrication. Finally, comparing both membrane types (with or without a CeO2 intermediate layer), it can be stated that the incorporation of the ceramic layer noticeably reduces the necessary amount of Pd to reach a fully dense membrane and therefore the associated environmental impacts.

Study of a stainless steel porous membrane for recovering tritium from Pb-Li alloys: Assessment of mass transfer coefficient

The eutectic Pb-Li alloy is used as liquid breeding blanket material in the concept design of future fusion nuclear reactors where the effective extraction of generated tritium is an important unit operation of the fusion fuel cycle. In this context, the adoption of porous stainless steel tubes working as Membrane Gas-Liquid Contactors (MGLCs) has been proposed for recovering hydrogen isotopes from liquid Pb-Li alloys. Taking into account the results achieved in a previous experimental campaign carried out at 370 °C, the hydrogen mass transfer coefficient has been evaluated and compared with data available in literature.The present study reveals that hydrogen extraction consists of diverse steps, although it is mainly controlled by recombination of hydrogen atoms and their desorption from the gas-liquid interface. The overall permeation exhibits mass transfer resistance values in the range 10−7 – 10-6 m2 s Pa mol-1, while hydrogen transport through the MGLC pores takes place with mass transfer resistances significantly smaller (around 10-4 m2 s Pa mol-1). These results make the use of MGLCs very promising for an effective extraction of tritium from liquid breeders in fusion reactors.

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.

Heat transfer and fouling characteristics during falling film evaporation in a vertical sintered tube

Heat transfer and fouling performance of water in a sintered porous stainless-steel tube were investigated experimentally. The test tube has a porous tube wall composed of stainless-steel powder with a typical diameter of 0.3 μm, and the special wall was designed to improve the thermal performance during falling film evaporation by increasing the nucleation site densities and relieve the foul processing through vapor transmission. Heat transfer tests were implemented at a saturation temperature of 373.2 K, over a mass velocity range of 0.42–1.47 kg/ (m s), with a subcooled degree of 0.5 K at inlet, and the temperature, pressure and mass flux of steam fixed, while the fouling tests were carried out using high-rigidity water as work fluid at a fixed mass velocity of 0.84 kg/ (m s). Heat transfer coefficient of the sintered tube is about 30% lower than that of the plain tube, and the inferior effect of the porous structure is caused by the weak thermal conductivity steam filled in the wall void and possible vapor film formed in the inner surface of tube. There is a flatten relationship between the heat transfer coefficient of the plain and the mass velocity, while that of the porous tube increases as the mass flux increases. As for the fouling process, the fouling resistance for the porous tube seems to make little difference on the overall thermal performance of the test section, contrary to the heat transfer deterioration for the smooth tube during the fouling deposition process.

Axial Distribution of Permeance and Selectivity of a Porous Cylindrical Tube for Binary Gas Mixtures (CO2/N2)

In previous studies, the selectivity property of a porous stainless steel cylindrical tube showed different filtration rates of pure carbon dioxide (CO2) and of pure nitrogen (N2) because of the effect of the dynamic boundary layer into the tube. In this study, a binary mixture of CO2 and N2 is considered under three different volumetric compositions (50/50%, 60/40%, and 70/30%) to evaluate the separation property of a porous stainless steel tube (membrane effect). The pure gas permeability, mixture permeability, ideal selectivity, and separation selectivity of this tube are determined for a total mass flow rate ranging from 1 to 2.5 g·s–1 and for an inlet pressure varying from 2 to 3.5 bar accordingly. The factors affecting the distribution of CO2 and N2 inside the porous tube are qualified. It is found that both the ideal and separation selectivity values are close to each other for a 50/50% composition, but the difference between the values increases for different compositions because of the effects of...

H2 permeation increase of electroless pore-plated Pd/PSS membranes with CeO2 intermediate barriers

This work presents the improvement of hydrogen permeance on electroless pore-plated Pd-composite membranes by the incorporation of ceria as intermediate barrier. This modification, in case of preparing a thick barrier, reduces both average pore size and external roughness of an oxidized Porous Stainless Steel (PSS) tube used as support. However, it also provokes a marked reduction of its permeance, turning more difficult the pass of the hydrazine through the modified support and, therefore, the palladium incorporation by electroless pore-plating. An optimization of this process leads to a Pd/CeO2/PSS composite membrane in which the initial roughness is halved, achieving a stable and selective Pd layer of around 15 μm. This composite membrane exhibits a hydrogen permeance of 5.37 · 10−4 mol m−2 s−1 Pa−0.5 at 400 °C, an ideal H2/N2 perm-selectivity ≥10,000 and an activation energy of 8.9 kJ mol−1. Moreover, the hydrogen flux increases around 400% with regard to previous results, in which no ceria was used as intermediate layer (measured range: 0.03–0.12 mol m−2 s−1 versus 0.01–0.03 mol m−2 s−1). This increase is derived from a high reduction, of around 30%, in the resistance to the permeation process when using electroless pore-plated membranes due to a lower penetration grade of the Pd external film into the support. In addition, it has been confirmed the successfully stability of the Pd membrane under thermal cycles and different operating conditions, including the variation of permeate flux direction from the inner to the outer of the membrane, where the Pd-layer is placed, or vice versa.

Superhydrophobic or Hydrophilic Porous Metallic/Ceramic Tubular Membranes for Continuous Separations of Biodiesel–Water W/O and O/W Emulsions

This paper reports the effective surface effect of porous inorganic membranes on improving the emulsion separations (i.e., perm-selective extraction of either oil phase or aqueous phase from the emulsions). A novel tubular form of superwetting, porous, stainless steel/ceramic membranes were demonstrated for enabling continuous separations of oil–water emulsions, extracting either oil phase or aqueous phase from the flowing emulsions. The superhydrophobic membranes consist of macroporous (4 μm) stainless-steel SS434 tube with inner wall surface modified with superhydrophobicity (>150° contact angle) via perfluoro-silane grafting functionalization. The (super)hydrophilic membranes consist of 4-μm porous stainless-steel SS434 tube without/with inner wall coated with nanoporous alumina (6 nm average pore size), the surface of which was further modified with superhydrophilicity via Hydrophil-S solution deposition. With the cross-flow membrane filtration setup, the surface-engineered tubular membranes were stud...

Oxy-combustion of coal in liquid-antimony-anode solid oxide fuel cell system

A novel system based on the indirect oxy-combustion of coal in a liquid Sb anode solid oxide fuel cell (SOFC) has been used to produce electricity for over 48 h. Pulverized anthracite was fed to the liquid-antimony-anode of the fuel cell, and a peak power density of 47 mW cm−2 was reached at 1023 K and 35 mW cm−2 at 973 K. The fuel cell was prepared using a porous stainless-steel tube as a support for an LSM cathode, antimony oxide (Sb2O3)/yittria stabilized zirconia (YSZ, Y0.08Z0.92O1.96) composite electrolyte (membrane), while liquid antimony acted as the anode. Liquid antimony/antimony oxide served as the intermediate medium for coal oxidation producing mainly carbon dioxide, which evolved as a separate gas stream. The fuel cell will facilitate carbon capture process, and simultaneously convert the chemical energy of coal directly to electricity. The experiment showed that while the fabricated electrolyte was porous, it became dense during the actual operation, preventing nitrogen leakage into the Sb/C side and producing reasonable open circuit voltage. Analysis of the experimental EIS data illustrates that the Ohmic resistance was the primary loss mechanism in the system. It further suggests approaches to improve the design. Continuous operation of this coal fueled oxy-combustion/fuel cell system achieved an overall efficiency of 28.2% despite of its tiny scale. Simple technologies can be employed to scale up this system at relatively low cost of fabrication and materials.

Hydrogen production by steam methane reforming in membrane reactor equipped with Pd membrane deposited on NiO/YSZ/NiO multilayer-treated porous stainless steel

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 cm2). 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 cm2). 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 H2/N2 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% H2, 0.6 vol% CO, 1.8 vol% CH4, and 4.5 vol% CO2. The gas composition of the permeate stream was suitable for use as fuel in a high-temperature polymer electrolyte membrane fuel cell.

Bonding Characterization Between 316L and Porous Stainless Steel Pipes by Vacuum Brazing

Vacuum brazing between porous stainless steel (PSS) tube and 316L stainless steel has been performed using BNi-7 brazing paste as a filler metal. And the interface microstructure of the joint was analyzed by SEM and EDS. The results show that Ni(Cr, Fe)-P intermetallic compounds and chromium-rich nickel-iron-based solid solutions phases are the main phases in the brazing seam. The wettability of the molten braze alloy to PSS is better than that to 316L. The molten braze filler is pulled into the pore of PSS by a capillary action during brazing. The highest tensile strength of 245 MPa is acquired from the joint brazed at 980°C for 15 min. Longer processing time or higher processing temperature does not improve the joint strength further.

Fluid flow analysis to describe the permeation process along the length of the porous tube

The use of a fuel Cell on board of an aircraft enforces the extraction of light species (such as Hydrogen and light hydrocarbons) from the liquid fuel which is stored and used, possibly at temperatures where fuel pyrolysis occurs. Natural porosity of composite material could be used to filtrate the selected species. Hence, the permeability and selectivity of the porous media becomes the key parameter to be measured accurately. This is often determined experimentally in laboratory using disc or cube samples and a perpendicular flow (outlet of the flow is achieved through the porous material). However in realistic configuration composed of tube, additional flow is found through the material tangential to main flow. Previous work has shown that the permeation is not constant all along the length of the porous channel. Permeance of a gas governs the permeation process along the length of the tube, which impacts the selectivity in case of a multispecies flow. In this study, a new permselectivity test bench is developed in order to study the permeance and selectivity all along the length of a porous tube with the help of isolated permeation cells. Pure N2 is used as a fluid at ambient temperature for evaluating the ability and accuracy of the test bench as a function of operating conditions. The effects of different inlet mass flowrate and pressure on the permeation along the tube have been studied. The obtained results of permeation along the length of a porous stainless steel tube are compared and discussed. The values of permeability obtained experimentally are in agreement with the literature data which guarantees the reliability of the test bench and of related measures. Comparison with analytical laws contribute to the investigation and explain the fundamental physics of the permeation process that will be later used to further study the selectivity of porous materials in case of multispecies flow.

Diffusion barrier coating using a newly developed blowing coating method for a thermally stable Pd membrane deposited on porous stainless-steel support

In this study, we present an intermetallic diffusion barrier coating using a newly developed blowing coating method for a thermally stable Pd-based composite membrane on porous stainless steel (PSS). A tubular PSS sample with 1/2 inch (12.7 mm) in diameter and 450 mm in length was used for the support. The support was welded with a stainless-steel cap and a 450-mm-long stainless-steel tube for each end. Before the diffusion barrier coating, the large-sized entrance pores were gradually blocked with sub-micron (∼500 nm) and nano (50–80 nm) yttria stabilized zirconia (YSZ). 8YSZ, i.e., 8wt.% YSZ, was used for the interdiffusion barrier material and dispersed on the surface of the pre-treated PSS using the blowing coating method. The blowing coating method has 4 steps: (i) spraying the 17 wt. % 8YSZ paste on the surface of the PSS tube, (ii) blowing the paste using compressed air, (iii) drying at room temperature, and (iv) heat treatment at 923 K for 2 h in air. Steps (i) and (ii) were repeated 3 times to have a ∼240 nm thick 8YSZ layer. A thin palladium layer (∼3 μm) was deposited on the pre-treated PSS using electroless plating, and the membrane stability was tested at 673–773 K for ∼ 200 h. A hydrogen permeation flux of 9.86 × 10−2 mol m−2 s−1 and an H2/N2 selectivity of 595 were obtained at 773 K and a transmembrane pressure difference of 20 kPa. The surface and cross-sectional SEM/EDX analysis confirmed that the 8YSZ layer sufficiently prevented the interdiffusion between Pd and PSS elements, such as Fe, Cr and Ni.

H2 separation using tubular stainless steel supported natural clinoptilolite membranes

AbstractDisk membranes generated from high‐purity natural clinoptilolite mineral rock have shown promising hydrogen separation performance. To scale up production of these types of membranes for industrial gas separation, a coating strategy was devised. A mixture of natural clinoptilolite and aluminum silicate was deposited on the inner surface of porous stainless steel tubes by the slip casting technique. Phase composition and morphology of the coating materials were investigated using X‐ray diffraction. The performance was evaluated for a range of gases using single gas permeation tests at different temperatures and pressures. Introduction of the second layer significantly improved the performance of the membrane system. The experiments on the double‐layered membranes measured a hydrogen permeance of 1.65 × 10−7 mol · m−2 · s−1 · Pa−1 at 300 °C. H2/CO2 and H2/C2H6 single gas selectivity was 10.2 and 8.45 respectively at 25 °C and feed pressure of 110 kPa. These results show that natural zeolite coated stainless steel tubular membranes have high potential for large‐scale gas separation at high temperature requirements.

Facile surface modification of porous stainless steel substrate with TiO2 intermediate layer for fabrication of H2-permeable composite palladium membranes

ABSTRACTThe increasing demand in compact hydrogen separators greatly stimulated the investigation and utilization of composite palladium membranes. Porous stainless steel (PSS) tubes were chosen as substrate material in this study, and a novel process of carbon-assisted solid-state sintering was introduced to modify the PSS surface with a TiO2 layer. A Pd/TiO2/PSS membrane with a Pd thickness of 6 µm was successfully fabricated via electroless plating. Scanning electron microscopy (SEM), metallographic microscopy, X-ray diffraction and pore-size analyses were performed for material characterizations. As measured by H2/N2 single-gas testing, the fabricated Pd/TiO2/PSS membrane is permeable and selective to hydrogen, and it was stable during a time-on-stream of 100 h under 450°C.

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.

In situ oxidized magnetite membranes from 316L porous stainless steel via a two-stage sintering process for hexavalent chromium [Cr(VI)] removal from aqueous solutions

Hexavalent chromium, Cr(VI), has seriously polluted groundwater and presents a great threat to human health. The efficient removal of the pollutant remains a high-priority challenge. In this experimental research, magnetite (Fe3O4) membranes were investigated for efficient removal of Cr(VI) from aqueous solutions. The Fe3O4 membranes were achieved via an in situ oxidization of 316L porous stainless steel (PSS) tubes by a two-stage sintering process. Compression tests showed that the elastic limits (σe) of the membrane tubes remained close to those of the unsintered tube. Cr(VI) adsorption on the membranes was highly pH dependent with a maximum adsorption percentage of 100% at pH 4.0. The adsorption kinetics followed the pseudo-second order model, and the adsorption isotherms data fitted the Langmuir isotherm equations. The concentration of Fe ions leached from the membranes was ∼0.01mg/L. The results verified that the two-stage in situ oxidization of PSS tubes endowed the resultant Fe3O4 membranes with an excellent adsorption potential for Cr(VI) while maintaining high mechanical strength and good chemical stability. The desorption ratio was ∼65% using 0.1mol/L Na2SO4 solution (pH 13). The membrane is quite promising for the efficient removal of Cr(VI) from aqueous solutions and is readily adaptable to industrial and environmental clean-up applications.

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.

Natural clinoptilolite composite membranes on tubular stainless steel supports for water softening

Disk membranes generated from high-purity natural clinoptilolite mineral rock have shown promising water desalination and de-oiling performance. In order to scale up production of these types of membranes for industrial wastewater treatment applications, a coating strategy was devised. A composite mixture of natural clinoptilolite from St. Cloud (Winston, NM, USA) and aluminum phosphate was deposited on the inner surface of porous stainless steel tubes by the slip casting technique. The commercial porous stainless steel tubes were pre-coated with a TiO2 layer of about 10 μm. Phase composition and morphology of the coating materials were investigated using X-ray diffraction and scanning electron microscopy. Water softening performance of the fabricated membranes was evaluated using Edmonton (Alberta, Canada) municipal tap water as feed source. Preliminary experimental results show a high water flux of 7.7 kg/(m(2) h) and 75% reduction of hardness and conductivity in a once-through membrane process at 95 °C and feed pressure of 780 kPa. These results show that natural zeolite coated, stainless steel tubular membranes have high potential for large-scale purification of oil sands steam-assisted gravity drainage water at high temperature and pressure requirements.

Aluminizing and oxidation treatments on the porous stainless steel substrate for preparation of H2-permeable composite palladium membranes

Composite palladium membranes based on porous stainless steel (PSS) substrate are idea hydrogen separators and purifiers for hydrogen energy systems, and the surface modification of the PSS is of key importance. In this work, the macroporous PSS tubes were aluminized through pack cementation at 850 °C in argon, followed by an oxidation with air at 600 °C. Palladium membranes were prepared by electroless plating. Their permeation performances were tested, and the hydrogen permeation kinetics was discussed. The substrate materials and the palladium membranes were characterized by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD). An Al2O3-enriched surface layer with small pore size was created through aluminizing and oxidation treatments, which greatly improves the membrane integrity. The intermetallic diffusion between the palladium membranes and the PSS substrate material was not observed after a heat-treatment at 500 °C under hydrogen for 200 h. However, the aluminizing and oxidation treatments still need to be further optimized in order to improve the membrane permeability and selectivity, and particularly, the high diffusion resistance of the substrate materials greatly limited the hydrogen flux.

Preparation of a novel Pd/layered double hydroxide composite membrane for hydrogen filtration and characterization by thermal cycling

A layered double hydroxide (LDH) layer was grown directly on a porous stainless steel (PSS) surface to reduce the pore opening of the PSS and to be a middle layer retarding Pd/Fe interdiffusion. A thin Pd film (∼7.85 μm) was plated on the modified PSS tube by an electroless plating method. A helium leak test proved that the thin Pd on the LDH-modified PSS substrate was free of defects. The membrane had a H2 flux of 28–36 m3/(m2 h) and H2/He selectivity larger than 2000 at a pressure difference of 1 bar. Thermal cycling between room temperature and 673 K was performed and showed that the membrane exhibited good permeance and selectivity. Long-term evaluation (1500 h) of the membrane at 673 K showed static results of H2 flux (∼30 m3/(m2 h)) and H2/He selectivity (∼2000) over the 1500 h test period.