Pd-Ru Membrane Research Articles

A CFD model of natural gas steam reforming in a catalytic membrane reactor: Effect of various operating parameters on the performance of CMR

The use of hydrogen as an energy carrier has increased for reasons related to its environmentally friendly characteristics. The most common and low-cost method of producing hydrogen from natural gas (or CH4) is the steam reforming process. The 2-D axisymmetric catalytic membrane reactor (CMR) model is developed for pure hydrogen production from real natural gas (NG) using a Pd–Ru membrane with a Ni/Al2O3 catalyst. In this paper, a CFD model is prepared to investigate the performance of a catalytic membrane reactor through natural gas conversion and hydrogen production under various operation parameters, i.e., temperature of reaction in the range of 600, 700, 800, 900, and 1000 K, gas hourly space velocity GHSV with a range of 500, 700, 1000, 2000, and 3000 h−1, and sweep gas flow rate (Re No.) 1, 50, 100, 150, and 250. The results of the simulation show that the CMR exhibits a high permeation rate of hydrogen on the permeate side (tube side) and achieves a high methane conversion rate of approximately 99.9 % at 1000 K on the retentate side. The hydrogen flux exhibits a decline as the temperature increases from 900 to 1000 K, despite the achievement of complete (NG) conversion. Hence, it can be concluded that the performance of the catalytic membrane reactor (CMR) process exhibits a pattern of increase when the other parameters, such as (GHSV) and (Re.No.), are increased.

Improved sulfur tolerance of Pd–Ru membranes: Influence of H2S concentration and exposure time on the hydrogen flux

The hydrogen flux of Pd–Ru membranes was investigated after they were exposed to H2S at different concentrations and over various period of time. The membranes were characterized by XPS, XRD, SEM, and hydrogen permeation tests. The Pd–Ru membrane exhibits excellent sulfur tolerance. The results show that when exposed to 10–80 ppm H2S at 723 K for 7 h, the hydrogen flux remains 57–73%. After removal of 10 ppm H2S, 100% recovery of flux is observed, and the flux recovers to 94% and 89% for membranes exposed to 30 ppm and 50 ppm H2S, respectively. Irreversible flux loss occurs when the membranes are exposed to 80 ppm H2S for 7 h or 30 ppm H2S for 72 h. The combination of SEM, XRD and XPS results shows that the presence of Ru on the surface significantly prevents the sulfidation of Pd. The initial rapid decrease in hydrogen flux appears to be mainly due to the blocking of surface sites, exacerbated by the subsequent formation of chemically adsorbed sulfur compounds. The high temperature annealing in H2 decomposes the chemically adsorbed species.

Investigation of steam methane reforming in a Pd–Ru membrane reactor with a counter-current configuration

Steam methane reforming (SMR) in a membrane reactor is a promising method to continuously produce high-purity hydrogen, which can directly supply to the proton exchange membrane fuel cell without complex CO purification processes. The performance of SMR in a Pd–Ru membrane reactor with a counter-current configuration for various operation parameters is investigated numerically in this work. In particular, the reverse hydrogen permeation is analyzed. The enhancement in the methane conversion by increasing the sweep ratio is ineffective for high sweep ratios. The hydrogen permeation rate increases with the membrane length, but the average hydrogen permeation flux decreases. The reverse permeation length increases with membrane length and feed gas flow rate. However, it decreases with sweep ratio and temperature. Replacing the membrane with the non-permeation material in the reverse permeate region achieves higher performance with less membrane area.

Effect of annealing process on the hydrogen permeation through Pd–Ru membrane

In this paper, we report the effect of the annealing process on the hydrogen permeation in/through Pd–Ru membranes. Pd–Ru membranes were deposited via sequential electroless plating method and annealed at different atmospheres and temperatures. The membranes were characterized by XRD, AES, SEM and hydrogen permeation test. The result shows that Ru is amorphous for the as-deposited Pd–Ru membrane. After annealing in H2, N2 atmospheres and vacuum at temperatures higher than 923 K, amorphous Ru transformed into crystalline Ru, and bubble-like cavities appear. The membrane annealed in H2 has larger and more bubble-like cavities compared with those annealed in N2 and vacuum. And the hydrogen permeabilities of Pd–Ru membranes annealed in H2, N2 atmospheres and vacuum decrease by 45–67% compared with that of the original as-deposited one. Furthermore, after annealed in hydrogen permeation process, the Pd–Ru membrane keeps compact and defect-free, and the Ru membrane remains in amorphous state. The hydrogen permeability of such Pd–Ru membrane is 1.2–1.3 times higher than that of the as-deposited one, which is mainly attributed to the dense structure and amorphous Ru in the membrane.

Ru-Containing Catalysts for Methanol and Ethanol Steam Reforming in Conventional and Membrane Reactors

We have carried out a comparative study of the catalytic activity of nanostructured M–Ru (M = Pt, Pd, Rh) bimetallic catalysts supported on detonation nanodiamond (DND) for methanol steam reforming (MSR) and ethanol steam reforming (ESR) processes in a conventional and a membrane reactor. The catalysts have been characterized by X-ray diffraction, transmission electron microscopy, and BET measurements. In the ESR process, the highest hydrogen yield is ensured by the Pt–Ru/DND catalyst, whereas the Ru–Rh/DND catalyst exhibits the highest activity for the MSR reaction. Our results demonstrate that, if the processes in question are run in a membrane reactor with a Pd–Ru membrane, there is a stable hydrogen flow, free of CO and other impurities, in the permeate zone even at temperatures on the order of 400°C.

Characteristics of hydrogen sorption/desorption for palladium foil doped by yttrium

Kinetics of hydrogen adsorption and desorption for palladium- 7% yttrium foil was studied using volume metrics measurements in oil free vacuum cell. Preliminary H2 was purified by diffusion from Pd-Ru membrane. Plots of the rate and constant rate of H2 adsorption/desorption versus temperature in interval 333-573 K were obtained. It was found that H2 sorption is the thermal activated process. The values of amount of H2 adsorbed, rate Ws, constant rate Ks and activation energy of sorption Ea,s of H2 sorption differs for initial foil surface and surface with preadsorbed hydrogen, which inhibits the repeated sorption. Due to preadsorbed hydrogen Ks decreases in 1,5 times (333 K) and Ea,s for molecular form of hydrogen adsorption increases in two times. Kinetics characteristics of hydrogen desorption depend on duration of the expose PdY foil in H2 at room temperature. Long saturation leads to sharply decrease of the hydrogen desorption rate and to some increase of activation energy of desorption varying from 56-68 and 85-108 kJ/mol for first and second kinetic order respectively. Isotherms of hydrogen adsorption were of anomalous shape and can be explained by the induced adsorption model. The results of isotherms analysis agree with kinetic data.

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.

Novel Electroless Plating of Ruthenium for Fabrication of Palladium-Ruthenium Composite Membrane on PSS Substrate and Its Characterization

Article history: This paper focused on a novel method of electroless plating ruthenium (Ru) on solid or porous substrates like porous stainless steel (PSS) discs or ceramic tubes. A novel complexing plating bath of Ru was developed. It is proven that Ru can be deposited directly on these substrates by the bath at a temperature of 328 K and strong alkaline environment. TGA, SEM, EDX and XRD confirmed the successful deposition of Ru. Relationships among plating rate, plating time, plating bath temperature and concentrations were also investigated. The Ru plating procedure was optimized. Based on the optimized procedure, a Ru layer was deposited by electroless plating of Ru onto the surface of pretreated aluminum-oxide modified PSS substrate. A 7.6 µm thick Pd-Ru membrane could be fabricated by electroless plating with a palladium (Pd) layer overlying the PSS substrate and a Ru layer overlying the Pd layer. Helium leakage and hydrogen permeation tests confirmed that the membrane was free of defects. Hydrogen diffusion through the Pd-Ru membrane was found to be the rate-controlling step in permeation. A new Pd-Ru composite membrane had the same features and permeation behavior as a previous one, indicating that electroless plating of both Ru and Pd is reliable and repeatable.

Application of a Pd–Ru composite membrane to hydrogen production in a high temperature membrane reactor

In this work, a ∼5.0μm thick Pd–Ru membrane (area∼13.3cm2), supported on a porous yttria-stabilized-zirconia/stainless steel substrate (ZrOD AccuSep®, Pall Corp.) was used to carry out steam methane reforming (SMR) over a commercial Ni-based reforming catalyst at a temperature of ∼580°C and pressures up to 2.9MPa. Methane conversions in the membrane reactor ranged from 65 to over 80%, depending on the reactor’s space velocity. The conversions obtained were significantly higher than the thermodynamic equilibrium predicted for the feed composition and process variables. The effect of parameters such as space velocity and reactor pressure on methane conversion and hydrogen recovery were investigated.The long term operation on this membrane revealed the potential suitability of this Pd-alloy to be a candidate for use in SMR membrane reactors at temperature as high as 580°C. The permeate hydrogen flux was very stable at 580°C, 2.9MPa feed pressure, and a steam-to-carbon ratio (SCR) of 3 for more than 1000h of continuous testing. The hydrogen permeate purity remained >93% over the course of testing. Stable methane conversions as high as ∼80% were obtained for the duration of the long term test which may be further improved by optimizing the fluid mechanics of the reactor design or geometry. 1-Dimensional process simulations were carried out and the results suggested that the methane conversion and hydrogen flux during the membrane reactor experiments were reduced by gas phase mass transfer due to concentration polarization effects. Ongoing work will focus on further optimization and testing of scaled-up Pd–Ru membranes in SMR reactor environments.

Structure and properties of Pd-Ru membrane alloy foil produced in the process of magnetron sputtering

The possibility of the formation of a thin foil in the process of magnetron sputtering of the membrane alloy Pd-Ru (6 wt %) is shown. Data on its structure, mechanical properties, and hydrogen permeability are obtained.

Preparation and characterization of palladium–ruthenium composite membrane on alumina‐modified PSS substrate

A new Ru/Pd/Al2O3/PSS layered membrane was fabricated by electroless plating of palladium and ruthenium for hydrogen separation. Pd and Ru were successively deposited on a pretreated PSS substrate using palladium and ruthenium plating baths at 333 and 358 K, respectively. EDX, XRD and XPS results confirmed the successful plating of ruthenium. Surface analysis showed that the palladium and ruthenium layers did not alloy significantly at temperatures of 723, 823 and 923 K over 100 h. The hydrogen permeation performance of the Pd–Ru composite membrane followed Sieverts' law, suggesting that diffusion of atomic hydrogen through the dense metal layer was rate‐limiting. The addition of ruthenium had a negligible effect on hydrogen permeability when the Ru weight content was ≤8 wt%. However, when the Ru content was increased to 11 wt%, H2 permeability decreased by 10 %. The Pd–Ru membrane exhibited good chemical stability and high H2/N2 selectivity in long‐term permeation testing.

Production of high purity hydrogen by ethanol steam reforming in membrane reactor

Production of hydrogen in the course of ethanol steam reforming (ESR) on bimetallic Pt-Ni and Pt-Ru nanocatalysts supported on detonation nanodiamonds (DND) was studied in conventional and membrane reactors. The highest hydrogen yield and purity were achieved in the case of Pt-Ru/DND catalysts at total metal content of 0.3% and atomic Pt/Ru ratio of 9/1. It is shown that realization of ESR process in the membrane reactor with simultaneous hydrogen removal through the Pd-Ru membrane produces hydrogen of high purity, free of any other gaseous products.

Structure, mechanical properties, and hydrogen permeability of Pd-Cu and Pd-Ru membrane foils prepared by magnetron sputtering

Magnetron sputtering is used to prepare thin (down to 7 μm) Pd-Cu and Pd-Ru membrane foils deposited on the surface of a SiO2/Si heterostructure at 300 and 700 K. Condensed foils (CFs) of an ordered Pd-Cu solid solution (β phase with a CsCl-type structure) and a Pd-Ru solid solution (fcc lattice) are synthesized for the first time. The foils of both alloys are characterized by a gradient granular structure due to selective development of 〈110〉 and 〈112〉 textures and a 〈111〉 texture in the Pd-Cu and Pd-Ru foils during their deposition, respectively. The hardness of the free surface of both foils removed from the substrate is determined by nanoindentation. The hardness is 3.0–3.6 GPa and is 20–50% lower than that of the contact surface (at the interface with the substrate) owing to the gradient structure. The hydrogen permeability of the Pd-Cu CF (β phase) is higher than that of the Pd CF by almost an order of magnitude (effect of a less dense crystal lattice) and is 5–7 times higher than those of the Pd-Ru CF and the Pd-Cu foil prepared by rolling.

Optimization and characterization of electroless co-deposited PdRu membranes: Effect of the plating variables on morphology

PdRu films were successfully synthesized on top of non-porous stainless steel supports by electroless co-deposition. The effect of synthesis variables on morphology, substrate adherence, bulk and surface composition was studied. The microstructure and morphology of the samples were analyzed by X-ray diffraction and scanning electron microscopy. Homogeneous and defect-free PdRu films were obtained employing baths at low pH, moderate to high agitation speeds, high concentration of hydrazine, using EDTA as a stabilizer and temperatures near 50 °C. Films characterized by X-ray photoelectron spectroscopy showed Pd segregation after annealing the sample at 400 °C in H 2 (5%)/Ar in the load-lock chamber of the spectrometer. The optimized conditions were employed to synthesize a PdRu composite membrane on top of a tubular porous stainless steel substrate (0.1 μm grade). Hydrogen permeation was measured over a 350–450 °C temperature range and a trans-membrane pressure up to 100 kPa. The PdRu membrane showed good performance with a hydrogen permeability of 6.5 × 10 −9 mol m −1 s −1 Pa −0.5 and a selectivity higher than 1700.

Methane steam reforming in a Pd-Ru membrane reactor

Methane steam reforming has been carried out in a Pd-Ru membrane reactor at 500–600 ‡C. The membrane reactor consisted of a Pd-6%Ru tube of 100 mm wall thickness and commercial catalysts packed outside of the membrane. The methane conversion was significantly enhanced in the membrane reactor in which reaction equilibrium was shifted by selective permeation of hydrogen through the membrane. The methane conversion at 500 ‡C was improved as high as 80% in the membrane reactor, while equilibrium conversion in a fixed-bed reactor was 57%. The effect of gas flow rate and temperature on the performance of the membrane reactor was investigated and the results were compared with the simulated result from the model. The model prediction is in good agreement with the experimental result. In order to apply the membrane in practice, however, the thickness of the membrane has to be reduced. Therefore, the effect of membrane thickness on performance of the membrane reactor was estimated using the model.

X‐ray photoelectron and Auger electron spectroscopies and surface segregations in Pd–Rh and Pd–Ru membrane catalysts

AbstractAuger electron and x‐ray photoelectron spectroscopies are used to estimate the segregation trends at the surface of Pd–Ru and Pd–Rh alloys. The measurements indicate Pd segregation in the studied systems that are in agreement with the Miedema criteria based on surface tensions of pure metals. Microscopic model calculations of the surface electronic structure of the relevant alloys show the same trend. Parameters associated with the electronic structure of the alloys are used in order to explain the experimental data for the hydrogenation reaction on a Pd–Ru alloy membrane catalyst.

Hydrogenation of ?-methylstyrene on membrane catalysts

The hydrogenation of α-methylstyrene on Pd-Ru and Pd-Ni membrane catalysts is zero-order relative to the starting substrate and close to 0.5 relative to H2. The use of the Pd-Ru catalyst is recommended for the hydrogenation of α-methylstyrene. Hydrogenation on this catalyst is superior in its mechanical strength to the Pd catalyst.

Hydrogenation of cyclopentadiene in the presence of isoprene and 1,3-pentadiene on a Pd-Ru membrane catalyst

1. The hydrogenation of cyclopentadiene, containing up to 25% of isoprene and 1.5% of 1,3-pentadiene, on a membrane catalyst composed of Pd alloy containing 9.8% Ru, proceeds at the same rate and selectivity in cyclopentene as does pure cyclopentadiene. 2. The relative adsorption coefficients of isoprene (0.6), 1,3-pentadiene (1.3), and cyclopentadiene (1) were determined.