Silver Membrane Research Articles

Effects of membrane surface chemistry on fouling investigated using self-assembled monolayers

Fouling is one of the key factors limiting the application of membrane processes. Recent studies have demonstrated that membrane fouling can be reduced by various surface modification techniques. However, the surface modification methods currently available often result in simultaneous changes in other membrane properties (e.g. reduction in pore size, damage to the base membrane, spatial non-uniformity in the degree of modification). These complications pose a challenge to quantitatively identify the key features in the surface modification that are needed to reduce fouling. Here a controlled surface modification technique without altering other membrane properties was applied to identify the surface chemistry required for developing fouling resistant membranes. We use self-assembled monolayers with various terminal functional groups including acid, alcohol, alkane, and tri(ethylene glycol) on silver membranes to investigate the effects of membrane surface chemistry on protein fouling. This method allows uniform coating of the internal pore structure with a monolayer of the modifier. The flux decline of the tri(ethylene glycol) terminated SAMs modified membrane is significantly reduced compared to the native membrane during bovine serum albumin (BSA) filtration. Other SAMs modified membranes also showed some minor effects on reducing the rate of flux decline. These results demonstrate a new approach to modify membrane surface chemistry for fouling investigation.

SOI-Supported Microdevice for Hydrogen Purification Using Palladium–Silver Membranes

High-purity hydrogen continues to receive attention as a promising energy source for fuel cells in portable power applications. On-demand hydrogen generation via fuel reforming offers a convenient alternative to hydrogen storage, but the concomitant CO generation is deleterious to the fuel cell catalyst. Of the possible hydrogen purification options, palladium membranes allow a compact design suitable for portable applications. We present a micromembrane device built in silicon-on-insulator wafers for hydrogen purification. The design imparts structural stability to a submicrometer-thick palladium-silver membrane, enabling hydrogen purification at higher pressures than were tolerated by previous devices with supported thin palladium membranes. The devices are manufactured using bulk micromachining techniques including photolithography, plasma, and wet etching. They are operated at pressures up to 2 atm with a correspondingly enhanced hydrogen flux. In particular, thin (200 nm) palladium-silver membrane yield high permeation rates of up to 50 mol/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /s at 350°C . The different transport resistances controlling hydrogen permeation in the micromembrane system are evaluated.

Enhanced Single-Molecule Detection using Porous Silver Membrane.

We evaluated a commercial porous silver membrane as a support substrate for direct localization and visualization of single molecule events. We characterized the fluorescence behaviors of fluorescently labeled DNA oligonucleotides on the silver membranes. The fluorescence from the fluorescent probes that were immobilized on the porous silver is greatly enhanced. Additionally, correlated to reflectance contour image, it appears that enhanced fluorescence came from location close to the "valley" of the pore channels (or in the voids). These results are of great interest to increase the effectiveness of fluorescence-based single molecule DNA analysis.

Hydrogen production for PEM fuel cell by gas phase reforming of glycerol as byproduct of bio-diesel. The use of a Pd–Ag membrane reactor at middle reaction temperature

Glycerol as a byproduct of biodiesel production represents a renewable energy source. In particular, glycerol can be used in the field of hydrogen production via gas phase reforming for proton exchange membrane fuel cell (PEMFC) applications. In this work, glycerol steam reforming (GSR) reaction was investigated using a dense palladium–silver membrane reactor (MR) in order to produce pure (or at least CO-free) hydrogen, using 0.5wt% Ru/Al2O3 as reforming catalyst. The experiments are performed at 400°C, water to glycerol molar feed ratio 6:1, reaction pressure ranging from 1 to 5bar and weight hourly space velocity (WHSV) from 0.1 to 1.0h−1. Moreover, a comparative study is given between the Pd–Ag MR and a traditional reactor (TR) working at the same MR operating conditions. The effect of the WHSV and reaction pressure on the performances of both the reactors in terms of glycerol conversion and hydrogen yield is also analyzed. The MR exhibits higher conversion than the TR (∼60% as best value for the MR against ∼40% for the TR, at WHSV=0.1h−1 and 5bar), and high CO-free hydrogen recovery (around 60% at WHSV=0.1h−1 and 5bar). During reaction, carbon coke is formed limiting the performances of the reactors and inhibiting, in particular, the hydrogen permeation through the membrane with a consequent reduction of hydrogen recovery in the permeate side.

Hydrogen production from urea wastewater using a combination of urea thermal hydrolyser–desorber loop and a hydrogen-permselective membrane reactor

This work presents novel application of palladium-based membrane in a wastewater treatment loop of urea plant for hydrogen production. Urea wastewater treatment loop is based on combined thermal hydrolysis–desorption operations. The wastewater of urea plant includes ammonia and urea which in the current treatment loop; urea decomposes to ammonia and carbon dioxide. The catalytic hydrogen-permselective membrane reactor is proposed for hydrogen production from desorbed ammonia of urea wastewater which much of it discharges to air and causes environmental pollution. Therefore hydrogen is produced from decomposition of ammonia on nickel–alumina catalyst bed simultaneously and permeates from reaction side to shell side through thin layer of palladium–silver membrane. Also a sweep gas is used in the shell side for increasing driving force. In this way, 4588 tons/yr hydrogen is produced and environmental problem of urea plant is solved. The membrane reactor and urea wastewater treatment loop are modeled mathematically and the predicted data of the model are consistent with the experimental and plant data that show validity of the model. Also the effects of key parameters on the performance of catalytic hydrogen-permselective membrane reactor such as the temperature, pressure, thickness of Pd–Ag layer, configuration of flow and sweep gas flow ratio were examined.

Gold-coated polycarbonate membrane filter for pathogen concentration and SERS-based detection

A SERS-based method for the concentration and detection of Giardia lamblia cysts in finished drinking water is reported. In this method, samples are concentrated with a membrane filter and then cysts captured on the filter surface are labeled with immunogold SERS labels and quantified via Raman spectroscopy. Anodisc((R)) membrane filters, silver membrane filters, and electroless gold-coated polycarbonate track etched (PCTE) membrane filters were investigated for their compatibility with the SERS based detection strategy. The largest pore size Anodisc((R)) membrane commercially available was too small for the proposed method because they led to physical retention of immunogold. When silver membrane filters were employed, cysts were difficult to distinguish from nonspecifically bound labels and cyst recovery from distilled water samples was only approximately 12.3%. With gold-coated PCTE membranes, however, cysts were readily detectable and cyst recovery was approximately 95%. This Raman based method simplifies Giardia detection and has potential to be extended to the simultaneous detection of numerous pathogenic organisms. To our knowledge, this is the first report coupling the use of membrane filters for the concentration and detection of organisms from water samples with a SERS based detection strategy.

A novel cathode for alkaline fuel cells based on a porous silver membrane

Porous silver membranes were investigated as potential substrates for alkaline fuel cell cathodes and as an approach for studying pore size effects in alkaline fuel cells. The silver membrane provides both the electrocatalytic function, mechanical support and a means of current collection. Relatively high active surface area (∼0.6 m 2 g −1) results in good electrochemical performance (∼200 mA cm −2 at 0.6 V and ∼400 mA cm −2 at 0.4 V) in the presence of 6.9 M KOH. The electrode fabrication technique is described and polarization curves and impedance measurements are used to investigate the performance. The regular structure of the electrodes allows parametric studies of the performance of electrodes as a function of pore size. Impedance spectra have been fitted with a proposed equivalent circuit which was obtained following the study of impedance measurements under different experimental conditions (electrolyte concentration, oxygen concentration, temperature, and pore size). The typical impedance spectra consisted of one high frequency depressed semi-circle related to porosity and KOH wettability and one low-frequency semi-circle related to kinetics. A passive air-breathing hydrogen–air fuel cell constructed from the membranes in which they act as mechanical support, current collector and electrocatalyst achieves a peak power density of 50 mW cm −2 at 0.40 V cell potential when operating at 25 °C.

Preparation of Platinum Catalyst on Silver Membranes for PEMFC with Green Electroless Deposition

As an alternative to platinum on carbon electrocatalysts for polymer electrolyte fuel cells, we have deposited platinum on silver membranes using electroless reduction of platinum salts with isopropanol. To speed discovery and optimization of the electroless chemistry, we developed two visual screening experiments to identify which formulations deposited active platinum catalysts. Once an environmentally friendly or green formulation was identified, we optimized the chemistry looking at catalyst activity and morphology as a function of temperature and reactant concentrations.

Production of ultrapure hydrogen in a PdAg membrane reactor using noble metal supported on La‐based oxides. Modeling for the dry reforming of methane reaction

AbstractA review is presented here of our previous contributions concerning the production of ultrapure hydrogen through the dry reforming of methane conducted in a membrane reactor. The reaction equilibration ratio is the criterion to compare the catalytic performance of the La‐based catalysts used in these studies. The solids were characterized by Laser Raman, X‐ ray photoelectron spectroscopy, X‐ray diffraction and temperature‐programmed reduction. The different behaviors are discussed taking into account the characterization results. To predict the influence of key process variables on conversion and product composition, a mathematical model is proposed to simulate the membrane reactor built around a palladium–silver membrane with 100% hydrogen selectivity. This study uses the kinetic equations developed for the dry reforming reaction on a Rh/La2O3 catalyst. Copyright © 2009 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Preparation of Platinum Catalyst on Silver Membranes for PEMFC with Green Electroless Deposition

not Available.

Production of hydrogen from purge gases of ammonia plants in a catalytic hydrogen-permselective membrane reactor

Abstract The present study investigates hydrogen production in a hydrogen-permselective membrane reactor from purge gases of an ammonia plant. Hydrogen which initially exists in the purge gases and hydrogen that is produced from decomposition of ammonia on nickel–Alumina catalyst bed simultaneously permeate from reaction side to shell side through a thin layer of palladium–silver membrane. A sweep gas can be used in the shell side for increasing driving force. The amount of hydrogen that can be gained annually and effect of pressure, temperature, thickness of Pd–Ag layer, configuration of flow in the membrane reactor and sweep gas flow ratio have been studied. This study shows that the countercurrent mode is better than co-current mode of operation. The rate of hydrogen permeation increases with increasing of temperature, pressure and sweep gas flow rate. This approach produces and separates large amounts of hydrogen and decreases environmental impacts owing to ammonia emission.

The mechanical strength of submicron porous silver foils

The tensile behavior of free-standing silver membranes with constituent micro-to-nanoscale porosity is measured as a function of strain rate to better understand operative deformation mechanisms across multiple length scales of structure. Composite structural features that can contribute to the rate-dependent strength behavior include the porosity, filament (or strut) size, and the constituent grain size. The strain-rate sensitivity of the porous silver specimens is found to increase with a functional decrease in the filament length scale and increase in porosity. This trend is similar to experimental results reported for bulk nanocrystalline metals.

Influence of the gas phase resistance on hydrogen flux through thin palladium–silver membranes

Pure and mixed gas permeation tests were performed on Pd-based hydrogen selective membranes at different experimental conditions. In particular the permeance of pure hydrogen as well as of binary and ternary mixtures containing hydrogen, nitrogen and methane was measured, at temperatures ranging from 673 to 773 K and at pressure differences up to 6 bar. The membranes, supplied by NGK Insulators Ltd., Japan, were formed by a selective Pd–Ag layer (20 wt% Ag) deposited on a tubular ceramic support, and showed very high hydrogen permeance and a practically infinite selectivity toward hydrogen. Interestingly, the permeance values measured in pure gas experiments resulted always higher than those obtained in permeation tests with gas mixtures; in the latter case, moreover, the permeate flux significantly deviates from Sieverts’ law based on the hydrogen partial pressure in the bulk gas phase. Both facts suggest the existence of non-negligible resistances to hydrogen transport in the gas phase itself, in addition to that offered by the metallic membrane. Experiments performed with increasing feed flow rates, showed also an increase in hydrogen permeance thus revealing the importance of the concentration polarization effects inside the module. Gas phase mass transport coefficients were calculated and used to determine the role of such a resistance in the overall mass transport process. The Sherwood number was also evaluated and was found to follow a boundary layer type of correlation. A general sensitivity analysis was performed in order to compare the effects on the transmembrane hydrogen flux of the two resistances, with different physical dimensions, offered by the gas phase and the metallic membrane. The concentration polarization number thus introduced allows for an a priori identification of the leading resistance at any operating conditions and gives clear indications on the actions required to improve the module performance.

Steam reforming of biogas mixtures with a palladium membrane reactor system

A fundamental study of the steam reforming of biogas and that derived from supercritical water gasification of glucose was conducted with a hydrogen-permeable palladium–silver membrane reactor. The hydrogen permeabilities for H 2 – H 2 O (4:1), H 2–CO 2 (4:1) and H 2 – N 2 (4:1) mixtures from 573 to 673 K were compared with those in the presence of hydrogen only. Water and nitrogen did not affect hydrogen permeability, whereas carbon dioxide tended to suppress its permeation in the high pressure region. Steam reforming of test gas 1 (moles H 2 : CH 4 : CO 2 = 50 : 10 : 40 ) and test gas 2 (moles H 2 : CH 4 : CO 2 = 10 : 40 : 50 ) mixtures having compositions expected from supercritical water gasification was carried out in the presence of 2 wt% Ru / Al 2 O 3 at 723 K and pressures up to 0.5 MPa. Methanation was dominant and slightly decreased as hydrogen permeated through the membrane in the steam reforming of the hydrogen rich mixture (test gas 1), whereas there was almost no effect of the membrane reactor for methane rich mixture (test gas 2). A new system combined the supercritical water gasification system and steam reforming system was developed and gas formation from glucose was carried out at 673 K and 10 MPa for supercritical gasification and from 0.1 to 0.5 MPa of reaction pressure. The experiments changing the order of catalytic bed and Pd–Ag membrane in the membrane reactor for steam reforming revealed that the elevated high pressures and hydrogen removal before catalytic steam reforming are advantageous for high hydrogen recovery.

Enhancement of carbon dioxide removal in a hydrogen-permselective methanol synthesis reactor

One of the major problems facing mankind in 21st century is the global warming which is induced by the increasing concentration of carbon dioxide and other greenhouse gases in the atmosphere. One of the most promising processes for controlling the atmospheric CO 2 level is conversion of CO 2 to methanol by catalytic hydrogenation. In this paper, the conversion of CO 2 in a membrane dual-type methanol synthesis reactor is investigated. A dynamic model for this methanol synthesis reactor was developed in the presence of long-term catalyst deactivation. This model is used to compare the removal of CO 2 in a membrane dual-type methanol synthesis reactor with a conventional dual-type methanol synthesis reactor. A conventional dual-type methanol synthesis reactor is a vertical shell and tube heat exchanger in which the first reactor is cooled with cooling water and the second one is cooled with synthesis gas. In a membrane dual-type methanol synthesis reactor, the wall of the tubes in the conventional gas-cooled reactor is covered with a palladium–silver membrane, which is only permeable to hydrogen. Hydrogen can penetrate from the feed synthesis gas side into the reaction side due to the hydrogen partial pressure driving force. Hydrogen permeation through the membrane shifts the reaction towards the product side according to the thermodynamic equilibrium. The proposed dynamic model was validated against measured daily process data of a methanol plant recorded for a period of 4 years and a good agreement was achieved.

Hydrogen permeability of 2.5 μm palladium–silver membranes deposited on ceramic supports

The permeability of hydrogen selective Pd-based membranes was tested in different experimental conditions. The membranes were obtained by depositing palladium–silver films onto ceramic porous supports, with film composition of about 20 wt% of silver and thicknesses of about 2.5 μm. Their permeance was measured at 400 °C at total trans-membrane pressures between 0.2 and 6 bar, using pure feeds of H 2 and N 2, as well as H 2/N 2 and H 2/CO mixtures; the temperature dependence of permeability was investigated using pure H 2 feeds at 300, 400 and 500 °C. The membranes exhibit a very attractive behavior, maintaining a virtually infinite selectivity throughout the testing, with permeance values among the highest values reported in literature for similar membranes. Permeation of pure hydrogen accurately follows Sieverts’ law and confirms the presence of a chemisorption–dissociation–diffusion mechanism, characterised by the transport of atomic hydrogen through the Pd–Ag layer as the limiting step. In the case of H 2/N 2 mixtures, the high membrane permeance originates also significant concentration polarization phenomena resulting in apparent deviations from Sieverts’ behavior; the presence of CO in the feed may reduce hydrogen permeability even by 75%, although this effect is shown to be fully reversible after a subsequent air treatment at 400 °C. The temperature dependence of the membrane permeability is of Arrhenius type, with an activation energy of about 17 kJ/mol, that is, close to what is reported for Pd–Ag membranes following Sieverts’ behavior.

HEEL ULCER IN HOSPICE PATIENT CLOSED QUICKLY USING POLYMERIC MEMBRANE DRESSINGS*

RATIONALE This patient was so debilitated that her heel ulcer was not expected to close. Her foot was cold, with poor capillary refill and an absent pedal pulse. Dressings were needed to prevent any infection from becoming systemic and to contain the wound exudate. Bordered polymeric membrane dressings conform well to heels and have a semipermeable membrane to protect wounds from contamination. They contain glycerol, a surfactant, and a super-absorbent starch. Polymeric membrane dressings’ ingredients draw and concentrate natural healing substances from the body into the wound bed to promote rapid healing while facilitating autolytic debridement directly by loosening the bonds between the slough and the wound bed. The liquefied slough is absorbed by the dressing, often eliminating the need for potentially damaging and painful manual wound bed cleansing during dressing changes. Together the dressing’s components reduce wound pain by inhibiting nociceptor activity at the wound site. In the absence of sufficient nutrients from the bloodstream, the glycerol in polymeric membrane dressings can be utilized by the body as an energy source and a component of new cells. The decision was made to use only silver or standard polymeric membrane dressings, depending upon the condition of the wound bed.

Ag/Cu layers grown on Si(111) substrates by thermal inducted chemical vapor deposition

Silver/copper thin layers were deposited on Si(111) substrates by thermal inducted chemical vapor deposition (CVD) method using [Cu(OOCC 2F 5)(VTMS)] (1), [Ag(OOCC 2F 5)] (2), and [Ag(OOCBu t)(PEt 3)] (3) as precursors. Analysis of grazing incidence X-ray diffraction (GIXRD) data confirms formation of silver/copper materials. The morphology studies, by scanning electron microscopy (SEM), exhibited that the type of Ag precursor, Ag(I)/Cu(I) precursors weight ratio, and the stability of metal containing species transported in vapors are the main factors, which influence the structure, size, and packed density of Ag/Cu layers. Depending on the weight ratio of precursors [Cu(OOCC 2F 5)(VTMS)] and [Ag(OOCBu t)(PEt 3)] the different type of silver/copper materials were prepared: the silver dispersed grains covered by the copper film composed of packed-density grains; the layer composes of Ag and Cu dense-packed grains; the copper layer consisted of large grains covered by silver one and the silver membrane containing copper grains located on the film surface. The low level of impurities adsorbed on the obtained surfaces was confirmed by diffuse reflectance FT IR (DRIFT) spectra. The investigations of electrical properties for fabricated Ag/Cu layers have been carried out using four-point probe technique. The highest conductivity [∼ 5.99 · 10 4 (Ω m) − 1 ] of films composed from Ag grain chains linked with the single Cu grains was noticed.

Study of hydrogen and deuterium permeation through Pd 77Ag 23 membrane: Analysis of stationary state

Permeation of interstitial components (hydrogen and deuterium) through Pd 77Ag 23 membrane was studied at stress conditions. Stresses were created in the process of metal lattice expansion after introduction of hydrogen or deuterium from gaseous phase into palladium–silver membrane. At T = 303.2 K the flows of hydrogen and deuterium in stationary states were determined for Pd 77Ag 23 membrane with initial contents of hydrogen and deuterium up to n 0 = 0.1 ( n 0, atomic ratio of hydrogen or deuterium to metal) and at different boundary conditions. The analysis of stationary state was done.

Raman spectroscopy and chemical imaging for quantification of filtered waterborne bacteria

Rapid and reliable assessment of pathogenic microbial contamination in water is critically important. In the present work we evaluated the suitability of Raman Spectroscopy and Chemical Imaging as enumeration techniques for waterborne pathogens. The prominent C–H stretching band observed between 2800–3000 cm − 1 of the spectrum is used for quantification purposes. This band provides the highest intensity of the bacterial-spectrum bands facilitating the detection of low number of microorganisms. The intensity of the Raman response correlates with number of cells present in drops of sample water on aluminum-coated slides. However, concentration of pathogens in drinking and recreational water is low, requiring a concentration step, i.e., filtering. Subsequent evaluation of filtering approaches for water sampling for Raman detection showed significant background signal from alumina and silver membranes that reduces method sensitivity. Samples concentrated by filtration show good correlation between Raman spectroscopy and other quantification methods including turbidity ( R 2 = 0.92), plate counts ( R 2 = 0.87) and dry weight ( R 2 = 0.97). Background interferences did not allow for evaluation of this relationship at low cell concentrations.