钯复合膜的制备及其在氢气氮气分离中的应用

Thin palladium composite membranes were prepared by modified electroless plating method on a-alumina supports and a dense Pd/α-Al2O3 composite membrane with high hydrogen flux, good selectivity for hydrogen was obtained. It was tested in a single gas permeation system for hydrogen permeance and hydrogen selectivity over mtrogen. The hydrogen permeance of the corresponding membrane was ashigh as 2.45×10^-6mol·m^-2·s^-1.Pa^-1 and H2/N2 selectivityover700 at 623K and a pressure difference of 0.1MPa. The-main resistance of the composite membrane to H2 permeation lies in the aluminum ceramic support rather than the thin Pd layer.     

Pd-Cu alloy membrane deposited on alumina modified porous nickel support (PNS) for hydrogen separation at high pressure

This study reports on the hydrogen permeation properties of Pd-Cu alloy membranes at high pressures. A 7 μm thick Pd-Cu alloy membrane was prepared on an alumina-modified porous nickel support (PNS) by our developed magnetron sputtering and Cu-reflow method at 700 °C for 2 hours. The membrane was mounted in a stainless steel permeation cell with a gold-plated stainless steel O-ring. Helium leak testing confirmed that the membrane and membrane module were free of defects. Permeation tests were then conducted using hydrogen at temperatures in the range from 678 to 816 K with a transmembrane pressure difference of 1–20 bars, which showed that the membrane had a hydrogen permeation flux of 1.06 mol m⁻² s⁻¹ at a temperature of 816 K and a pressure difference of 20 bars. EDX analysis was carried out after hydrogen permeation test at 816 K and showed that there was no intermetallic diffusion between the Pd-Cu layer and PNS because the alumina layer inhibited it effectively.     

Preparation of supported palladium membrane and separation of hydrogen

Palladium acetate was sublimed at a reduced pressure at 400°C., carried into the macropores of the porous wall of an α-alumina support tube and was decomposed there. A thin palladium membrane which was thus formed showed a hydrogen permeance of 10⁶ mol·m²·s¹.-Pa¹ and a hydrogen/nitrogen permselectivity higher than 1000. The membrane was stable against hydrogen embrittlement even when the permeation temperature was varied between 100 and 300°C., and it was stable to sulfur or chlorine. To test the ability of this system for the separation of hydrogen and deuterium, a palladium disk was used instead of the prepared membrane since a definite membrane thickness was necessary for calculation. When H₂ and D₂ permeated through the membrane independently, the H/D permselectivity was approximately 7 at 150–200°C under a feed side pressure of 0.4 MPa and a permeate side pressure of 0.1 MPa. When a mixture of H₂ and D₂ was fed, the H/D permselectivity was reduced to 1.2–1.6.     

Stable equilibrium shift of methane steam reforming in membrane reactors with hydrogen‐selective silica membranes

Equilibrium shifts of methane steam reforming in membrane reactors consisting of either tetramethoxysilane‐derived amorphous hydrogen‐selective silica membrane and rhodium catalysts, or hexamethyldisiloxane‐derived membrane and nickel catalysts is experimentally demonstrated. The hexamethyldisiloxane‐derived silica membrane showed stable permeance as high as 8 × 10^?8 mol m^?2 s^?1 Pa^?1 of H₂ after exposure to 76 kPa of vapor pressure at 773 K for 60 h, which was a much better performance than that from the tetramethoxysilane‐derived silica membrane. Furthermore, the better silica membrane also maintained selectivity of H₂/N₂ as high as 10³ under the above hydrothermal conditions. The degree of the equilibrium shifts under various feedrate and pressure conditions coincided with the order of H₂ permeance. In addition, the equilibrium shift of methane steam reforming was stable for 30 h with an S/C ratio of 2.5 at 773 K using a membrane reactor integrated with hexamethyldisiloxane‐derived membrane and nickel catalyst. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Constant concentration method of measuring hydrogen permeation from a hydrogen mixture with Pd membrane

The conventional flow method of measuring hydrogen permeation flux was found to be inaccurate and inadequate to obtain a consistent value of hydrogen flux and permeance because of changing hydrogen concentration along the palladium membrane tube in a hydrogen mixture. We designed a new method in which the hydrogen concentration was kept constant in the retentate. This constant concentration method was a more accurate measurement of hydrogen permeation flux in all of the possible hydrogen mixtures: H₂ + Y with Y = Ar, N₂ and CH₄ and various hydrogen concentrations under different pressure. Permselectivity of the hydrogen mixture was measured under this constant concentration method and was compared with both the conventional flow-through method and separate flow measurement of pure component gases. All three methods gave a different value of permselectivity for the same composite mixture.This method enables us to measure hydrogen flux and permeance accurately in the corresponding composition of the mixture. We found that even with the same partial hydrogen pressure differential for Sieverts’ equation, the hydrogen flux and permeance decreased dramatically with the lowering of hydrogen concentration in the feed.     

The use of a rotating cylinder electrode to selective recover palladium from acid solutions used to manufacture automotive catalytic converters

The reduction of palladium, rhodium and neodymium ions at concentrations of 0.94, 0.97 and 0.69 mol dm⁻³, respectively was studied in 1 mol dm⁻³ HNO₃ or 1 mol dm⁻³ HCl, at a stainless steel and a vitreous carbon electrode, at 25 °C. At a vitreous carbon electrode in a solution containing rhodium and palladium ions in 1 mol dm⁻³ HCl electrolyte, the reduction of metal ions occurred at a similar potential to the formation of hydrogen gas, which impeded the selective separation of the two metals. At a stainless steel cathode in 1 mol dm⁻³ HNO₃, palladium deposition occurred at a potential ≈0.35 V less negative than that of rhodium allowing the selective recovery of palladium. Neodymium ions were not electroactive in acidic chloride or nitrate media at pH 0. Using a solution obtained from a catalytic converter manufacturer containing palladium, rhodium and neodymium ions in 1 mol dm⁻³ HNO₃, palladium ions were preferentially removed at 0.15 V versus SHE at an average cumulative current efficiency of 57%.     

Preparation of microporous silica membranes for gas separation

Microporous silica membranes for hydrogen separation were prepared on a γ-alumina coated α-alumina tube by sol-gel method. The reactants of sol-gel chemistry were tetraethoxysilane (TEOS) and methacryloxypropyl-trimethoxysilane (MOTMS). The silane coupling agent, MOTMS, was added as a template in order to control the pore structure to the silicon alkoxide, TEOS. In particular, the microporous membranes were prepared by changing the molar ratio of MOTMS with respect to other substances, and their pore characteristics were analyzed. Then, the effects of thermal treatment on the micropore structure of the resulting silica membranes were investigated. The pore size of the silica membrane prepared after calcination at 400–700 ‡C was in the range of 0.6–0.7 nm. In addition, permeation rates through the membranes were measured in the range of 100–300 dgC using H₂, CO₂, N₂, CH₄, C₂H₆, C₃H₆ and SF₆. The membrane calcined at 600 ‡C showed a H₂ permeance of 2×10^-7-7×10^-7 molm^-2s^-1Pa^-1 at permeation temperature 300 ‡C, and the separation factors for equimolar gas mixtures were 11 and 36 for a H₂/CO₂ mixture and 54 and 132 for a H₂/CH₄ mixture at permeation temperatures of 100 ‡C and 300 ‡C, respectively.     

The effect of humidity on the durability of inorganic membranes

Porous oxide membranes of γ-alumina, zirconia and silica were prepared on porous α-alumina tubes by sol-gel processes. γ-Alumina and zirconia membranes impregnated with platinum were also prepared. The permeation properties of these membranes were investigated by using unary and binary feeds of H₂ and CO₂ at 423 K. After permeation for 5 h with humidification at a concentration of 3 mol%, no large changes were found for the zirconia and γ-alumina membranes, but the permeances to H₂ and CO₂ for the silica membrane were decreased by 10–20%. A 70-h exposure to humidified feeds showed that the zircomaand γ-alumina-based membranes were more resistant than the silica membrane. The decrease in H₂ permeance was only 5% for the zirconia-based membranes and 17.4% for the silica membrane. The Pt-loaded gg-alumina membrane remained defect-free after one-month of exposure to the humidified feeds at 423 K.     

Oxygen permeability and structural stability of La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>Co<Subscript>0.2</Subscript>Fe<Subscript>0.8</Subscript>O<Subscript>3−<Emphasis Type="Italic">δ</Emphasis></Subscript> membrane

La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ oxides were synthesized by citrate method and hydrothermal method. The oxides prepared by citrate method are perovskite type structure, while the oxides by hydrothermal method have a small amount of secondary phase in the powder. Pyrex glass seal and Ag melting seal provided reliable gas-tight sealing of disk type dense membrane in the range of operation temperature, but commercial ceramic binder could not be removed from the support tube without damage to the tube or membrane. Though the degree of gas tightness increases in the order of glass>Ag>ceramic binder, in the case of glass seal, the undesired spreading of glass leads to an interfacial reaction between it and the membrane and reduction of effective permeation area. The oxygen flux of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ membrane increases with increasing temperature and decreasing thickness, and the oxygen permeation flux through 1.0 mm membrane exposed to flowing air (P _h =0.21 atm) and helium (P₁=0.037 atm) is ca. 0.33 ml/cm²·min at 950 °C. X-ray diffraction analysis for the membrane after permeation test over 160 h revealed that La₂O₃ and unknown compound were formed on the surface of membrane. The segregation compounds of surface elements formed on both surfaces of membrane irrespective of spreading of glass sealing material. This paper was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

GAS PERMEANCE BEHAVIOR AT ELEVATED TEMPERATURE IN MESOPOROUS ANODIC OXIDIZED ALUMINA SYNTHESIZED BY PULSE-SEQUENTIAL VOLTAGE METHOD

Mesoporous anodic oxidized alumina (MAOA) capillary tubes with and without a barrier layer have been synthesized by applying a pulse-sequential voltage. The single gas permeances at an elevated temperature and the thermal and hydrothermal stabilities of MAOA were investigated. A highly oriented radial mesopore channel with pore sizes from 40 to 4 nm was formed in the MAOA tubes. Micropores with sizes from 0.4 to 0.8 nm were formed in the barrier layer. The H₂ permeance of MAOA with a barrier layer (barrier type) was approximately 540 times lower than that of MAOA without a barrier layer (block type) at 773 K. The H₂/N₂ permselectivity of the barrier type in the temperature range from 333 to 673 K was 3.4; those of the barrier type at 773 and 823 K were 4.4 and 11, respectively. On the other hand, the H₂/N₂ permselectivities of the block type were from 3.1 to 3.6 in the temperature range from 333 to 773 K. The H₂ permeance and the H₂/N₂ permselectivity of the amorphous silica membrane on the block type were 1.1 × 10^?7 mol/m² · s · Pa and 40 at 773 K, respectively. MAOA synthesized by the pulse-sequential voltage method can be applied to the mesoporous support of the gas separation membrane at elevated temperatures.     

Hydrogen permeance and the effect of H2O and CO on the permeability of Pd0.75Ag0.25 membranes under gas-driven permeation and plasma-driven permeation

The hydrogen permeance of Pd_0.75Ag_0.25 membranes was measured in the presence of pure H₂ or mixtures of H₂ with CO and H₂O at temperatures in the range of 300–773 K and at atmospheric pressure under gas-driven permeation (GDP) and plasma-driven permeation (PDP). The Arrhenius plots of the permeability through these membranes versus the inverse temperature showed a small peak in the intermediate temperature range and different activation energies in the low and high temperature ranges. The experimental data also indicated a more pronounced effect of CO on the permeability than H₂O, and a similar effect of GDP and PDP. The stronger inhibition by CO was due to the strong interaction between CO and Pd, and this effect was eliminated at temperatures higher than 623 K.     

Palladium Membrane Formed in Macropores of Support Tube by Chemical Vapor Deposition with Crossflow through a Porous Wall

Abstract

Palladium acetate vapor was sublimed at a reduced pressure and was evacuated through the porous wall of an α-alumina support tube of 1.8 mm i.d. and 2.4 mm o.d. Due to chemical vapor deposition (CVD), a thin palladium membrane was formed in macropores of the support. The membrane part was about 50 mm in length and was used without any pretreatment. The palladium membrane, prepared at a maximum CVD temperature of 400°C, showed hydrogen permeance and selectivity to nitrogen higher than 10^?6 mol·m^?2·s^?1·Pa^?1 and 1000 at 300–500°C, respectively. Even after the permeation temperature was repeatedly varied between 100 and 300°C in a hydrogen atmosphere, the membrane exhibited no hydrogen embrittlement. The amount of palladium deposited in pores of the support tube was 22 g/m² of the outer surface of the tube. The thickness of the palladium membrane calculated from this value was 4.4 μm.     

Development of an All-ceramic Module with Silica Membrane Tubes for High Temperature Hydrogen Separation

Abstract

Heat resistant hydrogen selective membranes are desired for use as membrane reactors in low-temperature hydrogen production via the steam reforming of hydrocarbons, which are usually operated over 1000 K. In addition, developing a multi-tubular type of membrane unit that can process more reactants is becoming more and more important in order to realize the practical use of membrane reactors.

In this study, an all-ceramic module consisting of 6 silica membrane tubes with a comparatively large membrane area of around 0.04 m² was fabricated by a counter-diffusion chemical vapor deposition technique. As a result, the H₂/N₂ ideal separation factor and the H₂ permeance of the module were 1300 and 1.9 × 10^?7 mol·m^?2s^?1Pa^?1 at 873 K, respectively. In a 1000-hour thermal stability test for the silica membrane module, it was found that the H₂ permeance initially decreased by about 30% and then became steady under ΔP = 0.95 MPa at 773 K.     

Ethanol Steam Reforming for Hydrogen Production over Bimetallic Pt–Ni/Al2O3

Ethanol steam reforming was studied at 673–823 K over Pt–Ni/δ-Al₂O₃. Results indicate that bimetallic catalyst is resistant to coke deposition at steam-to-carbon ratios as low as 1.5 and higher ratios are beneficial for both ethanol conversion and hydrogen formation. About 773 K is the optimum since high H₂ production rates are accompanied by low CO and CH₄ production rates. A power-function rate expression obtained on the basis of intrinsic rates at 673 K gives reaction orders of 1.25 (±0.05) and −0.215 (±0.015) for ethanol and steam, respectively; the apparent activation energy is calculated as 39.3 (±2) kJ mol⁻¹ between 673 and 723 K.     

Pure hydrogen production by methane steam reforming with hydrogen-permeable membrane reactor

Low temperature steam reforming of methane mainly to hydrogen and carbon dioxide (CH₄ + 2H₂O → 4H₂ + CO₂) has been performed at 773 and 823 K over a commercial nickel catalyst in an equilibrium-shift reactor with an 11-μm thick palladium membrane (Mem-L) on a stainless steel porous metal filter. The methane conversion with the reactor is significantly higher than its equilibrium value without membrane due to the equilibrium-shift combined with separation of pure hydrogen through the membrane. The methane conversion in a reactor with an 8-μm membrane (Mem-H) is similar to that with Mem-L, although the hydrogen permeance through Mem-H is almost double of that through Mem-L. The amount of hydrogen separated in the reaction with Mem-H is significantly large, showing that the hydrogen separation overwhelms the hydrogen production because of the insufficient catalytic activity.     

Sorption of palladium on carbon adsorbents from nitric acid solutions

Sorption recovery of palladium from nitric acid solutions on carbon adsorbents BAU, LKAU-7, ABG and UC has been investigated using model solutions with concentrations 8 × 10⁻⁴–8 × 10⁻³ mol/l for palladium and 1, 2 and 5 mol/l for nitric acid. The recovery degrees of Pd(II) depend on the concentration of palladium in contacting solutions as well as on the type of sorbent used. On average, they reach 60%–100% with the maximum in 1 M HNO₃ The palladium desorption by 10% thiocarbamide solution in 1M H₂SO₄ proceeds completely for the sorbent LKAU-7. The use of thiocarbamide solutions in 0.1 M NaOH increases the desorption of palladium from the sorbents BAU and UC up to 80%–85%     

Permeation properties of hydrogen and water vapor through porous silica membranes at high temperatures

Silica and cobalt‐doped silica membranes that showed a high permeance of 1.8 × 10^?7 mol m^?2 s^?1 Pa^?1 and a H₂/N₂ permeance ratio of ～730, with excellent hydrothermal stability under steam pressure of 300 kPa, were successfully prepared. The permeation mechanism of gas molecules, focusing particularly on hydrogen and water vapor, was investigated in the 300–500°C range and is discussed based on the activation energy of permeation and the selectivity of gaseous molecules. The activation energy of H₂ permeation correlated well with the permeance ratio of He/H₂ for porous silica membranes prepared by sol–gel processing, chemical vapor deposition (CVD), and vitreous glasses, indicating that similar amorphous silica network structures were formed. The permeance ratios of H₂/H₂O were found to range from 5 to 40, that is, hydrogen (kinetic diameter: 0.289 nm) was always more permeable than water (0.265 nm). © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Experimental demonstration of enhanced hydrogen permeation in palladium via a composite catalytic‐permselective membrane

A composite catalytic‐permselective (CCP) membrane comprised of a 500‐μm Cu(II)O/Al₂O₃ catalyst film washcoated overtop a 27‐μm electroless‐plated dense palladium thin film was constructed on a porous less‐steel substrate. Hydrogen purification experiments performed under ideal (H₂–Ar) nonreactive mixtures and simulated reformate (5% CO, 7.5% H₂O, 15% H₂, 1.5% CO₂, and balance Ar) over a range of residence times at 623–773 K confirm up to 30% enhancement in observed hydrogen permeance of the palladium film, achieved using the CCP membrane design in which the catalyst layer modifies the gas‐phase composition in direct contact with the permselective Pd film. Scanning electron microscopy analysis of the palladium film after ～10‐h exposure to reaction conditions and Cu(II)O catalyst confirm no corrosion of the film, while observed hydrogen permselectivities remained in excess of 10,000:1. These experimental results confirm that the CCP membrane design is capable of significantly improving palladium membrane performance. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1627–1634, 2013     

Characteristics of ammonia permeation through porous silica membranes

A sol–gel method was applied for the preparation of silica membranes with different average pore sizes. Ammonia (NH₃) permeation/separation characteristics of the silica membranes were examined in a wide temperature range (50–400°C) by measurement of both single and binary component separation. The order of gas permeance through the silica membranes, which was independent of membrane average pore size, was as follows: He > H₂ > NH₃ > N₂. These results suggest that, for permeation through silica membranes, the molecular size of NH₃ is larger than that of H₂, despite previous reports that the kinetic diameter of NH₃ is smaller than that of H₂. At high temperatures, there was no effect of NH₃ adsorption on H₂ permeation characteristics, and silica membranes were highly stable in NH₃ at 400°C (i.e., gas permeance remained unchanged). On the other hand, at 50°C NH₃ molecules adsorbed on the silica improved NH₃‐permselectivity by blocking permeation of H₂ molecules without decreasing NH₃ permeance. The maximal NH₃/H₂ permeance ratio obtained during binary component separation was ～30 with an NH₃ permeance of ～10^?7 mol m^?2 s^?1 Pa^?1 at an H₂ permeation activation energy of ～6 kJ mol^?1. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Preparations of metal impregnated porous inorganic membranes for hydrogen separation by multi-step pore modifications

In this research, porous inorganic membranes for hydrogen separation were prepared with α-alumina support by multi-step pore modification method. Porous inorganic membranes were made by three consecutive steps: sol-gel method,in-situ hydrolysis of tetraethylorthosilicate (TEOS) and soaking and vapor deposition (SVD) method. In order to enhance the hydrogen selectivity, we used nickel (Ni) and palladium (Pd) particles in the first and final pore modification steps. Although both nickel and palladium induced surface diffusion, palladium was shown more effective for hydrogen selective adsorption than nickel. This multi-step method produced porous membranes with a moderate hydrogen selectivity and excellent hydrogen permeability at high temperature up to 773 K and at transmembrane pressure (ΔP) as high as 310 kPa. The separation factor of hydrogen relative to nitrogen was maintained at about 7 even when the transmembrane pressure was 70 kPa, and the hydrogen permeability was still much higher than that of non-porous polymeric membranes. Furthermore, the distributions of nickel and palladium within the intermediate layer formed at the membrane cross-section were examined by scanning electron microscopy (SEM) and energy dispersive X-ray analysis.