Capillarity in fibrous filter media: Relationship to filter properties

This work examines the wetting of a range of low packing density (high porosity), porous, fibrous media by mineral oils. The fibrous media were suspended above a vessel of oil, and the rate of imbibation of oil was measured by means of a balance under the oil and a load cell above the media. It was found that the height of the oil column within the media over time generally resembled the classical capillary rise curve. Capillary rise models were fitted to the data to predict an equivalent capillary diameter, dynamic contact angle, and height of the liquid column as time approaches infinity, using the known filter and oil properties. Different capillary models were examined, and it was found that the modified Washburn equation was the simplest model to use and produced an acceptable agreement between theory and experiment. It was found that the adjustment phase of the curve from the fibrous media was generally more rapid than for a typical capillary, presumably since the fibrous media can be wetted not only from directly below (as with a capillary), but also through the meniscus at the sides of the media. It was found that a linear correlation existed between the effective capillary diameter of the media, and the packing density of the media divided by the fibre diameter. The results appear to be relatively independent of the material type. These results allow capillary diameters to be determined for fibrous media from easily measured parameters, without the requirement of conducting wetting experiments or ‘bubble-point’ tests.     

Biocatalytic oxidation of fuel as an alternative to biodesulfurization

A biotechnological method for fuel desulfurization is described. The method includes the steps of biocatalytic oxidation of organosulfides and thiophenes, contained in the fuel, with hemoproteins to form sulfoxides and sulfones, followed by a distillation step in which these oxidized compounds are removed from the fuel. Straight-run diesel fuel containing 1.6% sulfur was biocatalytically oxidized with chloroperoxidase from Caldariomyces fumago in the presence of 0.25 mM hydrogen peroxide. The reaction was carried out at room temperature and the organosulfur compounds were effectively transformed to their respective sulfoxides and sulfones which were then removed by distillation. The resulting fraction after distillation contained only 0.27% sulfur. Biocatalytic oxidation of fuels appears as an interesting alternative to biodesulfurization.     

Agglomerates and granules of nanoparticles as filter media for submicron particles

An experimental study on filtration of submicron solid and liquid aerosol particles by using a filter media composed of agglomerates or granules of nanoparticles is described. Fumed silica nanoagglomerates, carbon black granules, silica shells, activated carbon granules, glass beads and nanoporous hydrophobic aerogel were among the granular filter media tested and compared to a commercially available HEPA fiber-based filter. Other than the glass beads which were used for comparison purposes, the primary particle size of the agglomerates/granules is of nanometer scale, but they agglomerate to form porous structures of about several hundreds of microns which were customized as packed (deep bed) or fluidized bed filters and challenged against submicron solid and liquid aerosols. For packed bed filters, the size of the granules has been optimized to a range of 150-500 µm with a filter thickness of about 1-3 in. and superficial gas velocities of less than 4 cm/s. Fluidized beds required granules smaller than 150 µm and the height of the bed was in the range of 15-40 cm.The customized filters and a HEPA fiber-based filter were challenged simultaneously against the same aerosol at the same superficial gas velocities. When using carbon black or aerogel granules as filter media, collection efficiencies comparable or even higher than HEPA fiber-based filters are obtained, but with the advantage of extra filtration capacity due to the deep bed configuration and the absorption of liquids into the porosity of the media. A fluidized bed filter of aerogel granules not only provides higher collection efficiency and larger capacity than a HEPA fiber-based filter when challenged against both oil mist and solid aerosols but also has an extremely low pressure drop compared to a packed bed filter and can be operated continuously with respect to removing saturated granules and adding fresh ones.     

双金属催化滤料生物滤池处理效果及对膜污染影响研究

双金属催化滤料生物滤池替代传统生物滤池,作为超滤膜系统的预处理工艺,可提高三氮的去除效率,保证产水水质稳定,显著减缓超滤膜污染,延长膜使用寿命。生物催化滤池内催化还原反应促进反硝化系统的进行,保证了水中硝酸氮和亚硝酸氮的分解去除;研究表明,生物催化滤池预处理较常规生物滤池可将TOC的去除率由73.2%提高到81.5%,其增加部分的主要成分为可引起膜污染的芳香蛋白类和富里酸类有机污染物。此外,双金属催化滤料增加了滤池的过滤精度,其出水胶体平均粒径明显小于常规生物滤池。催化还原反应产生的铁离子在过滤紊流的环境中微絮凝,进一步去除了微污染水源水中的胶体和悬浮物,减轻了胶体颗粒对超滤膜的污染。除具有常规滤池的生物降解、过滤作用外,双金属催化滤料生物滤池还具有催化还原和微絮凝的协同作用,显著提高了水中有机污染物和胶体颗粒的去除率,超滤膜污染得到有效减缓。     

Preferential attachment of contaminants to filter media in oil

In oil filtration, particles must attach to the filter medium, typically fibres. Attachment is a function of the chemical and physical properties of both the contaminant and the filter medium. Cellulose and synthetic filter media are commonly used in oil filtration. The contaminants include wear metal particles, silica and soot. Because of differences in size and in physical and chemical characteristics, significant differences in contaminant attachment and removal are expected. Experiments were conducted in which filters were challenged with contaminants exhibiting different physical and chemical characteristics. It was found that contaminant shape, roughness and size distribution influence removal. Indirect evidence suggests that chemical interactions also influence removal. The structure of the filter medium mediates these effects.     

微孔过滤介质的进展

近２０年来用于固液分离的普通过滤介质除用化纤织物几乎取代了天然织物过滤介质外，微孔过滤介质有了突破性进展，相继出现了亲水微孔陶瓷；微孔复合薄膜，以及单丝纤维过滤介质等，本文综合介绍它们的特性及其出现的背景和重要意义。