Study of Catalytic Filters for Soot Particulate Removal from Exhaust Gases

Two ceramic supports (sintered and foam) were employed for the preparation of catalytic filters for soot removal at diesel exhausts. Laboratory tests showed that while the foam filter is appropriate for small size and low engine backpressure, the sintered filter is more suitable for achieving high filtration efficiency. Tests carried out at the exhaust of a diesel engine showed that the catalytic filter can be continuously regenerated at operating conditions typical of diesel exhaust.     

The effect of the contact between platinum and soot particles on the catalytic oxidation of soot deposits on a diesel particle filter

Experiments were performed with two model soot aerosols brought into different forms of contact with Pt aerosol particles, to investigate the effectiveness of this contact in lowering the catalytic soot oxidation temperature. The contact was either generated between individual particles in the aerosol state (Pt-doped soot to simulate a fuel borne catalyst), or by sequential or simultaneous deposition of separately generated soot and Pt aerosols onto a sintered metal filter. (Formation of a soot cake on previously deposited Pt aerosol would simulate a catalyst coated diesel particle filter.) The catalytic activity was determined in all cases from temperature ramped oxidation in air of the filtered particles, and defined as the 50% conversion temperature.

It was found that Pt-doped soot and simultaneously filtered aerosols were both equally effective in reducing the oxidation temperature by up to 140–250 °C for the spark discharge soot (with 3–47 wt% Pt concentration in the soot cake), and by up to 140 °C for the pyrolysis soot (3 wt% Pt). Conversely, the deposition of a thin soot layer of 5–10 μm thickness onto Pt, or vice versa, produced only a slight temperature reduction on the order of about 13–42 °C. These results suggest that the distance between soot and Pt particles plays a key role in promoting an effective oxidation on the filter, which is consistent with the role of Pt particles as local generators of activated oxygen.     

Performances of a catalytic foam trap for soot abatement

A catalytic trap for soot particles was prepared by deposition of Cu–V–K–Cl catalyst on a ceramic foam. Catalytic trap performances were evaluated by treating the exhaust of a gas oil burner under different operating conditions. The results obtained showed that ceramic foam is a particularly suitable support for this application since it yields low gas pressure drop, good soot collection efficiency (“deep bed” filtration mechanism), high thermal shock resistance and good contact throughout the filter between soot particles and catalyst surface. In addition, the catalytic foam trap is able to spontaneously regenerate at operating conditions comparable to those typical of diesel engine exhaust and after more than 70 test hours it retains its activity towards soot oxidation.     

Molten Salts Are Promising Catalysts. How to Apply in Practice?

A diesel soot filter with a Cs₂SO₄V₂O₅ molten salt diesel soot oxidation catalyst has been developed. An engine test-bench was used to test it in diesel exhaust gas with ELPI analysis and to deposit diesel soot on filters for temperature programmed oxidation experiments. Molten salt (Cs₂SO₄V₂O₅) based catalytic foam has an onset temperature for catalytic oxidation of 320°C. This is a promising temperature for continuous filter-regeneration applications. Unfortunately the liquid state of the catalyst makes it unfit for the very effective wall-flow monolith filter, and necessitates the use of a foam filter as support. The onset temperature of the catalytic foam of 320°C is still too high to justify a change from wall-flow monolith to foam, as ceramic foam is a less effective filter than the wall-flow monolith. Foams are no absolute filters, and should be optimized for each application.     

Zeolite synthesised on copper foam for adsorption chillers: A mathematical model

In this work, a new adsorbent bed for adsorption chillers is proposed. Highly porous copper foams were directly sintered on the external surface of copper pipes. Afterwards, the foam surface was coated by several layers of zeolite 4A by in situ hydrothermal synthesis. The performance of an adsorbent bed based on the proposed configuration was then evaluated by a dynamic model. The results of simulations provided a cooling COP = 0.10–0.28, a specific cooling power ranging between 0.6 and 3.8 kW per kg of adsorbent material (77–123 W per kg of adsorber) and a volumetric cooling power of 103–214 kW per cubic meter of adsorber, depending on the copper foam thickness assumed (1–10 mm). A comparison with other “traditional” configurations based on loose pellets or consolidated layers of zeolite, demonstrated attractive performance – in terms of specific and volumetric powers – for the proposed adsorbent bed.     

A Novel Preparation Method for Foamed Silica Ceramics by Sol-Gel Reaction and Mechanical Foaming

A simple method for obtaining silica foam has been developed by combining sol-gel reaction and mechanical foaming without added organic pore formers, in order to reduce generation of CO₂ and harmful gases by decomposition of the organic compounds. The silica foam was prepared by mechanically foaming the silica sol and controlling the viscosity change and gelling. The gelation time of the silica sol can be varied from 10 minutes to 3 hours by changing the pH, temperature and concentration of the surfactant added as a foam stabilizer. The dried silica gel foam was calcined at 600°C then fired at 1000°C to obtain sintered silica foam. The porosity and average pore size of the silica foam was 84% and 140 m, respectively. The bending strength and gas permeability of the sintered silica foam was 2.4 MPa and 9.4 × 10^–11 m², respectively.     

Catalytic activation of ceramic filter elements for combined particle separation, NOx removal and VOC total oxidation

The development of a catalytically active filter element for combined particle separation and NO_x removal or VOC total oxidation, respectively, is presented. For NO_x removal by selective catalytic reduction (SCR) a catalytic coating based on a TiO₂–V₂O₅–WO₃ catalyst system was developed on a ceramic filter element. Different TiO₂ sols of tailor-made mean particle size between 40 and 190 nm were prepared by the sol–gel process and used for the impregnation of filter element cylinders by the incipient wetness technique. The obtained TiO₂-impregnated sintered filter element cylinders exhibit BET surface areas in the range between 0.5 and 1.3 m²/g. Selected TiO₂-impregnated filter element cylinders of high BET surface area were catalytically activated by impregnation with a V₂O₅ and WO₃ precursor solution. The obtained catalytic filter element cylinders show high SCR activity leading to 96% NO conversion at 300 °C, a filtration velocity of 2 cm/s and an NO inlet concentration of 500 vol.-ppm. The corresponding differential pressures fulfill the requirements for typical hot gas filtration applications. For VOC total oxidation, a TiO₂-impregnated filter element support was catalytically activated with a Pt/V₂O₅ system. Complete oxidation of propene with 100% selectivity to CO₂ was achieved at 300 °C, a filtration velocity of 2 cm/s and a propene inlet concentration of 300 vol.-ppm.     

The photocatalytic activity and kinetics of the degradation of an anionic azo-dye in a UV irradiated porous titania foam

A porous organic–inorganic hybrid titania foam, prepared from a long chain organic surfactant, hexadecylamine (HDA) and a semiconductor powder was characterized by microscopic and spectroscopic techniques and photocatalytically evaluated for the solution phase decomposition of methyl orange under alkaline conditions. Kinetic data obtained indicate conformity with Langmuir–Hinshelwood kinetic model at the initial stages of the degradation reaction. An attempt was made to study the effect of experimental parameters including catalyst loading and dye concentration on photocatalytic degradation of MO. Results indicate that the rate of reaction is governed by adsorption of azo-dye into the surface of the photocatalyst materials and suggests an optimum catalyst load and dye concentration for the degradation reaction. Light absorption and scattering within the substrate reaction zone and arising from differences in optical properties of catalyst material, made it impossible to interpret entire kinetic data on the basis of a simple Langmuir–Hinshelwood kinetics. However, kinetic data obtained at the initial stages of the reaction suggest conformity with first-order kinetics. The foam promises to be a versatile material in that it can be used for the treatment of low concentrations of pollutants of biological, organic and inorganic origins in water and air.     

高温高压飞灰过滤器的工作原理与优化

介绍了高温高压飞灰过滤器的工作原理,并将陶瓷滤芯和烧结金属滤芯进行对比,通过加装保安滤芯对陶瓷滤芯的保护,以对高温高压飞灰过滤器进行优化。     

Development of New Cu0–ZnII/Al2O3 Catalyst Supported on Copper Metallic Foam for the Production of Hydrogen by Methanol Steam Reforming

Copper metallic foam with thermal conductive properties, manufactured by S.C.P.S., has been investigated as a support for catalysts to improve thermal exchange inside the reactor for the endothermic steam reforming of methanol. Thus, we have developed a procedure for the in situ preparation of a Cu⁰–Zn^II/Al₂O₃ catalyst onto the copper metallic foam. The foam-based Cu⁰–Zn^II/Al₂O₃ catalyst shows an activity three times as high as commercial catalysts for a conversion of 74% of methanol into hydrogen.     

Experimental Techniques for the Development of the Turbulent Precipitator as a Diesel Particulate Filter

A novel type of diesel particulate filter is introduced: the turbulent precipitator. The aim is to develop a catalytically active filter, based on Cs₂SO₄V₂O₅ molten salt catalyst or cerium fuel-borne catalyst. The novel filter type is developed to circumvent obvious problems like plugging and high pressure drop. In addition to that, it should be flexible, robust and possible to tune for different diesel engines. Its main features are an open flow channel (to prevent plugging and high pressure drops) and soot collection plates (to trap diesel soot). Two filter geometries are described, one with metal collector plates and one with ceramic foam collector plates. Results show that different geometries have different capabilities, making tuning for different diesel engines possible. An engine test bench was designed to measure filter efficiencies, both by particle numbers and particle mass. The diesel soot aerosol is measured with an electrical low-pressure impactor (ELPI). These measurements are not straightforward. For evaluation purposes, the engine test bench was divided into three major components to test it for aerosol measurements: diesel setup, aerosol sampling setup, and ELPI. Each part is restricted by a maximum time on stream.     

Investigating the effectiveness of refining melts by filtration

Conclusions The filtration of Fe-Si-B melts through a loosely poured filter consisting of corundum granules of diameter 2–3 mm causes a four-fold reduction in the level of contamination from B₂O₃-SiO₂ inclusions with a filter layer height of 2 cm. The refined metal contains almost no inclusions measuring >5 um. A three-fold reduction in the content of solid-phase inclusions of magnesia occurs with the use of a combined filter, consisting of granules and corundum foam filter, but the effectiveness of the melt purification in removing coarse inclusions in this case is low.Translated from Ogneupory, No. 7, pp. 10–13, July, 1991.     

Prediction of Dimensionless Cutsize for Size‐Fractionated Measurements of Particles that Impact on a Sintered Stainless‐Steel Filter

Abstract

This investigation experimentally studied the penetration curve of particles that impact on a sintered stainless‐steel filter with various pore sizes, sampling flow rates and jet diameters. The penetration curves were compared to those with an aluminum foil substrate. Test data reveal that when the sintered stainless‐steel filter has larger pore sizes (100 µm or 40 µm), the particle penetration, P(%), is lower and the curve is less steep than that obtained from the aluminum foil substrate. The penetration curve of the sintered stainless‐steel filter with smaller pore size (5 µm) is close to that of the aluminum foil substrate. The dimensionless cutsize‐shift (the ratio of the dimensionless cutsize of sintered stainless‐steel filter to that of aluminum foil) falls as the pore sizes and the Reynolds number increase. Experimental data were then compared with theoretical results, and theory over‐predicted the dimensionless cutsize‐shift. Hence, a regression equation for the dimensionless cutsize‐shift is proposed by fitting the experimental data. The discrepancy between the experimental data and the regression prediction is within 4%. The regression equation can be used to predict the dimensionless cutsize for the size‐fractionated measurements of particles that impact on a sintered stainless‐steel filter with various sized pores and Reynolds numbers.     

Supported foam–copper catalysts for methanol selective oxidation

Structural, mechanical, gas-dynamic and catalytic properties of copper catalysts supported on foam ceramics have been studied. Due to the three-dimensional open-porous cellular structure the foam catalysts have high gas permeability, mechanical strength, and low density. Catalytic activity and selectivity of the foam catalysts in the process of oxidation of methanol to formaldehyde exceed the characteristics of the conventional crystalline and granulated catalysts of the same composition. Different electronic states (ions, charged clusters, nanoparticles and microcrystals) of copper on the catalyst surface have been studied by the method of UV–Vis spectroscopy.     

Preparation and application of mesocellular carbon foams to catalyst support in methanol electro-oxidation

A novel and simple preparation method for preparing a mesocellular carbon foam (MCF-C) is described. A silica–polymer composite as an amphi-templating material was synthesized by a sol–gel method using tetraethyoxy-orthosilicate (TEOS), P123 and divinylbezene (DVB) as a silica precursor, a template and a polymer precursor, respectively. The silica–polymer composite was subsequently transformed to either mesocellular carbon foam (MCF-C) or mesocellular silica foam (MCF-S). The prepared MCF-C exhibited well-developed mesocell pore structures with uniform windows. Compared to conventional methods, the method used for preparing MCF-C was economical and simple. MCF-C was used as a catalyst support in methanol electro-oxidation. The Pt/MCF-C-ETX (MCF-C-supported Pt catalyst which was prepared using sodium ethoxide) catalyst has smaller Pt nanoparticles and a larger electrochemically active surface area (EAS) value than the commercial Pt/C catalyst. In methanol electro-oxidation, the prepared Pt/MCF-C-ETX catalyst showed a higher catalytic performance than the commercial Pt/C catalyst.     

滤芯冒泡测试的原理及应用

PET装置所用过滤器的滤芯过滤层为金属烧结毡材质,价格昂贵。生产中一般用泡点测试判断滤芯金属烧结毡是否符合规格或是否破损。介绍了滤芯冒险泡测试的原理和应用步骤。     

煤气化装置烧结金属滤芯清洗再生技术

探讨了煤气化装置烧结金属滤芯的再生方法,采用空气吹扫、初步水冲洗、超声波清洗等步骤可使滤芯再生,对再生后的滤芯进行了透气性检验,结果满意。     

Sintering of Pt/Al2O3 reforming catalysts: EXAFS study of the behavior of metal particles under oxidizing atmosphere

The effect of an oxidative atmosphere (300 °C) is studied on fresh and sintered unchlorinated naphtha reforming catalysts containing 0.6–1% Pt. The TPR profiles show that only one species is formed using our experimental conditions, regardless of the mean crystallite size of the metal particles. The structural information supplied by EXAFS compared with cuboctahedral particle modeling, implies that such species is a surface platinum oxide, the structure of which is close to that of PtO₂, but largely distorted. This is true whether the catalyst is sintered or not.     

金属烧结毡滤芯过滤非牛顿料浆实验研究

分析了非牛顿料浆的过滤特性及相关理论,并选用金属烧结毡滤芯进行过滤实验,将实验数据与相关理论结合,分析证明了已有理论的指导意义,并为金属烧结毡滤芯过滤此类料浆提供相应实验参考。     

Microwave Regenerated Catalytic Foam: A More Effective Way for PM Reduction

In this work the effect of microwave irradiation on the regeneration of soot-loaded uncatalytic and catalytic ceramic foam filters was studied for two different catalytic filter formulations. Combining dielectric permittivity and catalytic activity of the foam filter components with microwave absorbing properties of soot allowed a more effective filter regeneration. Moreover, iron based catalysts, typically not active towards soot oxidation in case of electrical heating, showed a significant activity in the presence of microwave.