Porous Metal Filters Research Articles

Development of selective Pd–Ag membranes on porous metal filters

Metallic supports with sufficient surface quality to achieve highly selective thin Pd–Ag membranes require specific pre-treatments, are not readily available on the market and are generally very expensive. To reduce costs, rough and large media grade Hastelloy X filters have been acquired and pre-treated via polishing and chemical etching. The loss in gas permeance given by the polishing treatment proved fully recovered after chemical etching. A method to fill the large pores of the filters via aspiration of α-Al2O3 water-powder suspension has been applied and characterized via imaging of the filled pores, inferential statistics, and capillary flow porometry measurements. The most suitable filler particle size for pore size distribution reduction has been identified as 18 μm, while a 5 μm filler proved optimal for further pore morphology improvement. The wide pore size distribution of the filters has thus been reduced up to 200 nm by filling with α-Al2O3 particles of decreasing size, similarly to the ceramic supports used for thin Pd–Ag membranes deposition. A boehmite based interdiffusion barrier has been deposited, achieving further surface roughness reduction. A highly H2 selective membrane has been obtained via simultaneous Pd–Ag plating on the pre-treated filter.

Kinetics of Spreading over Porous Substrates

The spreading of small liquid drops over thin and thick porous layers (dry or saturated with the same liquid) is discussed in the case of both complete wetting (silicone oils of different viscosities over nitrocellulose membranes and blood over a filter paper) and partial wetting (aqueous SDS (Sodium dodecyl sulfate) solutions of different concentrations and blood over partially wetted substrates). Filter paper and nitrocellulose membranes of different porosity and different average pore size were used as a model of thin porous layers, sponges, glass and metal filters were used as a model of thick porous substrates. Spreading of both Newtonian and non-Newtonian liquid are considered below. In the case of complete wetting, two spreading regimes were found (i) the fast spreading regime, when imbibition is not important and (ii) the second slow regime when imbibition dominates. As a result of these two competing processes, the radius of the drop goes through a maximum value over time. A system of two differential equations was derived in the case of complete wetting for both Newtonian and non-Newtonian liquids to describe the evolution with time of radii of both the drop base and the wetted region inside the porous layer. The deduced system of differential equations does not include any fitting parameter. Experiments were carried out by the spreading of silicone oil drops over various dry microfiltration membranes (permeable in both normal and tangential directions) and blood over dry filter paper. The time evolution of the radii of both the drop base and the wetted region inside the porous layer were monitored. All experimental data fell on two universal curves if appropriate scales are used with a plot of the dimensionless radii of the drop base and of the wetted region inside the porous layer on dimensionless time. The predicted theoretical relationships are two universal curves accounting quite satisfactorily for the experimental data. According to the theory prediction, (i) the dynamic contact angle dependence on the same dimensionless time as before should be a universal function and (ii) the dynamic contact angle should change rapidly over an initial short stage of spreading and should remain a constant value over the duration of the rest of the spreading process. The constancy of the contact angle on this stage has nothing to do with hysteresis of the contact angle: there is no hysteresis in the system under investigation in the case of complete wetting. These conclusions again are in good agreement with experimental observations in the case of complete wetting for both Newtonian and non-Newtonian liquids. Addition of surfactant to aqueous solutions, as expected, improve spreading over porous substrates and, in some cases, results in switching from partial to complete wetting. It was shown that for the spreading of surfactant solutions on thick porous substrates there is a minimum contact angle after which the droplet rapidly absorbs into the substrate. Unfortunately, a theory of spreading/imbibition over thick porous substrates is still to be developed. However, it was shown that the dimensionless time dependences of both contact angle and spreading radius of the droplet on thick porous material fall on to a universal curve in the case of complete wetting.

Mechanism Analysis and Dairy Filtration Experimental Research on Porous 1Cr18Ni9 Stainless Steel Components

Cool-drawn 1Cr18Ni9 stainless steel wires of 0.1~0.5 mm can be woven and punched to prepare porous metal filters. There is certain amount of connected micron pores in the transformable components. Filtration mechanism of this porous material is investigated and three series of samples with different diameter of wires, porosities and filtrating ranges are prepared. Filtration performances compares experiments are carried out on a kind of chocolate milk with the brand of Sanyuan. Three-dimensional microscopy, KEYENCE VHX-600, is applied to investigate the diaphragms before and after filtrating. Portable contamination analysis kit, HPCA-2, is chosen to identify the degree of contaminating. Results indicate that these kind of porous metal filters have valid solid/fluid separating effects. Wires diameters and other preparation parameters will identify the porosity. Thinner wires contribute to more and tinier porous and will block particles effectively. Thickness of filters plays the similar role of filtration layer. Higher porosity will increase the cleanliness of the passing fluid and decrease the filtering efficiency. The data in this paper provide technical support to the application in dairy filtration industry.

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

Low temperature steam reforming of methane mainly to hydrogen and carbon dioxide (CH 4 + 2H 2O → 4H 2 + CO 2) 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.

Effect of catalytic activity on methane steam reforming in hydrogen-permeable membrane reactor

Steam reforming of methane, mainly to hydrogen and carbon dioxide, proceeds over nickel catalysts at 800 K in an equilibrium-shift reactor with a thin palladium membrane 11 μm-thick supported on a stainless steel porous metal filter. The methane conversion greatly exceeds its equilibrium conversion due to the hydrogen separation with the membrane. The catalytic activity affects the conversion much more than in the cases using an equilibrium reactor. The conversion in the membrane reactor decreases with an increase in the space velocity of the reaction mixture, mainly because of a decrease in the hydrogen separation ratio (rate of hydrogen separation/total production rate of hydrogen). The rate of hydrogen separation depends basically on the hydrogen permeability of the membrane, but an active catalyst also increases the rate; that is, the hydrogen production rate depends on the catalytic activity. Thus, the higher rate causes the higher partial pressure of hydrogen in the reactor, while the hydrogen flux through the membrane depends on the pressure.

Preparation of high porous metal filter element for the fail-safety function

The fail-safe filter element is an assistant filter mounted in a filter unit to intercept particle leak when parts of the main filter elements are broken. The filter element should be plugged easily to meet the sealing purpose and should have high permeability to save the mounting space. This study focuses on the preparation of the high-permeability metal filter element. The filter elements were fabricated by using the cold isotropic press (CIP) method and the binding (BD) method. The permeability of the filter element was effectively controlled by the following factors: material size (54–840 μm), CIP pressure (1.2×10 8–2.0×10 8 Pa), sintering temperature (1423–1523 K) and time by CIP method. The high porous filter element of 9.2×10 −11 m 2 permeability was prepared in optimal conditions using 420–840 μm metal powder, fabricated at CIP pressure of 1.7×10 8 Pa, and sintered at 1473 K for 1 h. The pressure drop across this filter element was six times less than that of the commercial ceramic filter element used in the main filter element. The metal filter element with a higher permeability of 2.76×10 −10 m 2 was also prepared by BD method by using 540–840 μm metal powder.

Spreading of liquid drops over porous substrates

Spreading of liquid drops over porous substrates

K-2234 触媒付きディーゼルパティキュレートフィルターの開発(G09 & J15-1 環境工学&循環社会におけるゼロ・エミッション技術(1))(J15 & G09 循環社会におけるゼロ・エミッション技術および環境工学部門一般講演)

In order to reduce the amount of the particulate matter (PM) and NOx in the exhaust gas of diesel engines, we have developed the diesel particulate filter (DPF) made of porous metal. This device consists of three parts, a oxidation catalyst applied on a metal honeycomb, a filter made of porous metal, and a deoxidation catalyst applied on a porous metal filter. We confirmed the performance of this device by using a reactor.

Fossil energy applications of intermetallic alloys

This paper presents the history and results of the US Department of Energy, Office of Fossil Energy (FE), development effort on iron aluminide alloys and the status of research and development on ultrahigh temperature (well above 1000°C) intermetallic alloys. The outstanding (perhaps unequaled) sulfidation resistance of iron aluminide alloys, based on the Fe3Al composition, was the basis for initiation of an exploratory project to determine whether improvement in mechanical properties of iron aluminide alloys could be achieved. This was a high-risk venture but with significant payoff if successful, because sulfidation was a critical problem for applications of alloys in coal gasification systems. The exploratory project, which was conducted at Oak Ridge National Laborator (ORNL), was successful, and the program was expanded in both scope and participation. Several other national laboratories, industrial research organizations, and universities were involved. Iron aluminide development is now quite mature. Some of the research has transferred to line programs leading to product that will be used in advanced fossil energy systems. The first product to be commercialized for fossil energ applications was a porous metal filter developed jointly by ORNL and Pall Corporation. In addition to th coal gasification application, these filters are also being used in combustion systems. Several other commercial products are being pursued. Additional exploratory projects on intermetallic alloys have been initiated. These are also high risk activities, but, as with the iron aluminides, the payoff potential is great. The intermetallic alloys presently being investigated include a Cr2Ta-strengthened chromium alloy and a boron-modified molybdenum silicid based on Mo5Si3. The challenges with these alloys are to modify them to provide acceptable mechanical properties, including ductility and toughness, and corrosion resistance to allow them to be used in structure applications such as gas turbines.

EXPERIMENTAL INVESTIGATION OF SINTERED POROUS METAL FILTERS

The particle penetration characteristics and solid volume fractions of 1.57 and 0.99 mm thick stainless steel porous metal filters with pore sizes from 100 to 2 μm were determined experimentally. The penetration measurements were performed with monodisperse NaCl and latex particles at face velocities of 3.0, 6.1, and 12.1 cm s −1. The penetration data were fitted by non-linear regression with a simple equation that takes into account the diffusion and impaction mechanisms. The effective fiber diameters for the filters based on the measured pressure drops were also calculated, and they agreed with the effective single-collector diameters obtained from the fitted equations. Loading of filters was studied by sampling indoor air for one and two months in the laboratory and in an apartment. The penetration characteristics with monodisperse NaCl particles and the pressure drops of these filters were also measured. Loading of particularly the small pore size filters was shown to decrease penetration significantly with longer sampling times. The increase in pressure drop during sampling is a good indicator of mass loading. The filters have been used in a portable diffusion battery and the increased pressure drop was used as a determinant of a filter change or the end of sampling. The porous metal filters are cleanable and reusable, and electrostatic effects, that may cause errors when sampling with membrane filters, are avoided.

Prediction of the overall efficiency of the filtration of gaseous heterogeneous systems by porous-metal filters

Prediction of the overall efficiency of the filtration of gaseous heterogeneous systems by porous-metal filters

Production of fine tin and lead powders and porous filters

The subject of this paper is the production of fine lead and tin powders and their porous filters, making use of the solid-state tin phase transition and intermetallic compound decomposition. The multiple tin allotropic conversion allows the manufacture of 1 μm tin powder and filters which can filter particles of 5 μm diameter. The method of lead and tin alkalimetal compound decomposition allows production of a porous sponge metal filter in any prefabricated mould, while retaining a high level of purity in the metal. Such filters are of particular interest and use due to their large active surface and high purity.

Technology Status of Particulate Removal from High-Temperature High-Pressure Combustion Gases

The adoption of coal-fired pressurized fluidized-bed combined-cycle combustion systems by utilities for electric power generation depends to a large extent on the development of an efficient and economic cleanup system between the combustor and gas turbine. To accomplish particulate removal from a dust-laden gas stream, a number of separation devices have been developed. These include conventional and augmented cyclones; porous metal, fabric, and ceramic membrane filters; fixed-, continuously moving-, and fluidized-bed granular filters; electrostatic precipitators; as well as several other novel separation devices. The results of tests of these devices are discussed in relation to pressurized fluidized-bed combustion applications.

A probe method for soil water sampling and subsurface measurements

A technique employing lightweight driving and sampling equipment to obtain interstitial soil water samples is described. It can also be used for hydraulic conductivity, temperature, and water pressure measurements. The sampler consists of a probe, with a shield, a porous metal filter and a check valve which are connected to the surface by plastic tubing inside standard EW or A drill rod. The water sample is collected with a bailer lowered inside the tubing from the surface. The tubing can then be cleared and sealed without pulling the drill rod and the sampler driven to the next depth. A method of estimating the probe shape factor is given. Some of the difficulties unique to sampling interstitial water in thawed subsea permafrost are discussed.

Corrosion resistance of stainless chrome-nickel steels in sodium as a function of its oxygen content

The article describes an experimental apparatus for studying the corrosion resistance of construction materials in circulating liquid sodium, as well as methods for the continuous removal of oxides from the sodium by means of porous metal filters and for the determination of its oxygen content. It describes the results of corrosion experiments and measurements of mechanical properties performed on six brands of stainless steel, specimens of which were placed in sodium containing 3·10−3% and (4–5)·10−2% oxygen at a temperature of 550°. The flow rate was 1.5 m/sec. The results of the corrosion experiments indicate that the corrosion rate of Type 18CrSNi stainless steels in sodium containing as much as (4–5)·10−2% oxygen does not exceed 21.3 mg/dm2 per month; these steets are not subject to intergranular corrosion, and their mechanical properties remain virtually machanged.