Liquid purification or separation – Filter – Material
Reexamination Certificate
2000-03-10
2002-05-07
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Filter
Material
C210S500260, C210S490000, C210S500270, C055S523000, C055S524000, C264S042000, C264S045500
Reexamination Certificate
active
06383386
ABSTRACT:
The invention relates to a permeable composite material having hydrophobic properties, to a process for making this permeable composite material and to use of the same.
Hydrophobic permeable materials have been known for many years. Membranes of Teflon (Gore-Tex®) can be cited in particular in this connection, although membranes of other organic polymers are also known. These are suitable for a broad scope of application, based on the principle that substances pass through the porous material exclusively in the form of gas or vapor, but not of fluid. Such materials are made, for example, by stretching Teflon sheets, whereby ultra-fine cracks are formed which subsequently allow the passage of vapor or gas. Water droplets are held back by the hydrophobic material, since high surface tension and the lack of wettability of the surfaces of the hydrophobic materials prevent them from penetrating into the pores.
Such hydrophobic materials are suitable not only for gas and vapor permeation but also for membrane distillation. Furthermore, they are used as inert filter materials in many applications.
A disadvantage of these materials, however, is always the limited temperature range in which they can be used. In contrast, inorganic filter materials are much more thermally stable, although they are often more hydrophilic as well.
Very many substances can be made hydrophobic by subsequent hydrophobing of the most diverse inorganic substrates by means of reactive components such as silanes or alkyl or fluoroalkyl compounds or by deposition of precursor products from the gas phase (CVD), but hydrophobing is possible only in a subsequent process step. To some extent this step is quite complex, and so hydrophobing during the actual process of production of inorganic filter materials would be advantageous. Furthermore, hydrophobing of large surfaces by the CVD technique is impossible or possible only with considerable expense.
The object Of the present invention was therefore to provide a permeable composite material which exhibits hydrophobic properties and has very much smaller pores and very much greater thermal stability than the known materials. Another object was to provide a simple process for making such a composite material.
It has been surprisingly found that it is possible in simple manner, by means of the sol-gel method, to hydrophobe a permeable composite material based on at least one porous and permeable support, which is provided on at least one side of the support and in the interior of the support with at least one inorganic component, which contains substantially at least one compound of a metal, a semi-metal or a mixed metal with at least one element of Group 3 to Group 7, and that such a composite material exhibits high thermal stability.
The subject matter of the present invention is therefore a permeable composite material based on at least one porous and permeable support, which is provided on at least one side of the support and in the interior of the support with an inorganic component, which contains substantially a compound of a metal, a semi-metal and/or a mixed metal with at least one element of Group 3 to Group 7, which material is characterized in that it exhibits hydrophobic properties.
Also subject matter of the present invention is a method for making a permeable composite material according to one of claims 1 to 9, in which at least one suspension which contains at least one inorganic component comprising at least one compound of at least one metal, one semi-metal or one mixed metal with at least one of the elements of Group 3 to Group 7 and a sol, is applied on at least one porous and permeable support, and this suspension is solidified on or in or on and in the support material by at least one heat treatment, which process is characterized in that at least one of the inorganic components used exhibits hydrophobic properties and/or at least one hydrophobic material and/or one hydrophobing agent is added to the sol and/or to the suspension.
Further subject matter of the present invention is the use of a composite material according to at least one of claims 1 to 9 as a membrane for membrane distillations.
The composite material according to the invention has the advantage that it can also be used at higher temperatures than in the case of the materials known heretofore. Consequently there are opened numerous possible applications in which the composite material according to the invention can be used.
The process according to the invention also has the advantage that hydrophobic composite materials can be made without the need to perform additional cost-intensive, time-consuming and/or energy-intensive process steps.
The composite material according to the invention will be described hereinafter by reference to an example, without limiting the composite material according to the invention to this type of embodiment.
The permeable composite material according to the invention, which material exhibits hydrophobic properties, is provided with at least one porous and permeable support as basis. On at least one side of the support and in the interior of the support the support is provided with at least one inorganic component, which substantially contains at least one compound of at least one metal, at least one semi-metal or at least one mixed metal with at least one element of Group 3 to Group 7. As used in the present invention, the term interior of a support refers to cavities or pores in a support.
Preferably the interior and exterior or the interior and the exterior surfaces of the composite material according to the invention are coated with hydrophobic layers. These layers can contain at least alkyl, fluoroalkyl and/or aryl groups. The interior and/or exterior surfaces of the composite material can also be coated, however, with wax and/or polymer layers. The polymer layers can contain hydrophobic materials chosen from polyethylene, polyvinyl chloride, polystyrene, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene chloride, polyisoprene, polybutadiene, heat-treated polyimide, heat-treated polyether imide, polysulfone, polyether sulfone, polyacrylate, polyimidazole or a mixture of these polymers. Preferably the hydrophobic material present in the hydrophobic layers has a melting and/or softening point below 500° C.
The composite material according to the invention, which material exhibits hydrophobic properties, preferably contains a proportion of hydrophobic material of from 0.0001 wt % to 40.0 wt %, especially preferably from 0.01 to 20 wt %.
Depending how the composite material according to the invention with hydrophobic characteristics is made, it is conceivable that the hydrophobic material will differ chemically and physically or chemically or physically from the material used to make the composite material.
According to the invention, the porous and permeable support can have interstices with a size of 1 nm to 500 &mgr;m. The interstices can be pores, meshes, holes, crystal lattice interstices or cavities The support can contain at least one material chosen from carbon, metals, alloys, glass, ceramics, minerals, plastics, amorphous substances, natural products, composite substances or from at least one combination of these materials. It is permissible for supports which can contain the said materials to have been modified by a chemical, thermal or mechanical treatment method or a combination of treatment methods. Preferably the composite material is provided with a support which contains at least one metal, one natural fiber or one plastic, which was modified by at least one mechanical forming technique or treatment method, such as drawing, upsetting, fulling, rolling, stretching or forging. Quite particularly preferably the composite material is provided with at least one support which contains at least woven, bonded, felted or ceramically bound fibers or at least sintered or bonded shapes, globules or particles. In a further preferred embodiment there can be used a perforated support. Permeable supports can also be such which become
Hörpel Gerhard
Hying Christian
Penth Bernd
Creavis Gesellschaft fuer Technologie und Innovation mbH
Fortuna Ana
LandOfFree
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