Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
1999-07-26
2001-10-09
Chiesa, Richard L. (Department: 1724)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C055S282300, C055SDIG001, C095S074000, C095S278000, C095S283000, C204S157300
Reexamination Certificate
active
06299668
ABSTRACT:
A method is claimed of separating mixtures of substances by means of a substance-permeable material.
The separation of mixtures of substances is a problem which occurs often in the production of a variety of substances. In a particularly high frequency of cases, liquid phases containing solids are obtained. These solids, present partly as very small particles in the liquid phases, must frequently be removed from the liquids before the latter can be processed further. A separation task of this kind is encountered, for instance, in the beverage industry, where juices are to be separated from ultrafine solid components or where wastewaters require cleaning. Similarly, it may be the case that mixtures of two liquids of different molecular size need to be separated from one another. If this is not possible by distillation because, for example, an azeotrope is formed, the separation can be undertaken, for example, by means of pervaporation.
Membranes have long been used to ;separate mixtures of substances. In the case of synthetic membranes, a distinction is made between organic and inorganic membranes.
It is common to use membranes made of polymers or of inorganic components, such as oxides, for example. With the known methods in which these membranes are employed, such as electrolyses or filtrations, for example, there is always the problem that the membranes become blocked after a relatively short period of use, and the passage of substance through the membrane is considerably reduced. The membranes have to be changed and either laboriously cleaned or disposed of.
In the case of sufficiently stable ceramic membranes, the backwash principle has become established. At periodic intervals of time, the direction of flow is suddenly reversed for a short time by applying a pressure surge from the back side. This principle, however, has the disadvantages that it can be used effectively only in the case of liquid filtration, that, moreover, it subjects the membranes to high mechanical stress, and, finally, that, it is capable of removing only some of the caked-on material.
EP 0 165 744, EP 0 380 266 and EP 0 686 420 claim processes which, in order to clean a filter, cause gas bubbles to be formed by application of a voltage and performance of an electrolysis on the filter. The gas bubbles clean the filter surface, and so longer filter service times are achieved.
However, the abovementioned processes are unable to clean the inside of a filter. There is therefore a considerable reduction in the passage of substance through the filter in the course of filtration.
It is an object of the present invention to provide a method of separating mixtures of substances by means of a substance-permeable material which improves separation and makes it more economic by improving the passage of substance through the material.
It has surprisingly been found that the separation can be performed significantly better and more economically with a method of separating mixtures of substances by means of a substance-permeable material by applying to said material an electrical voltage for at least a short time.
The present invention therefore provides a method of separating mixtures of substances by means of a substance-permeable material, which comprises applying to said material an electrical voltage for at least a short time.
The method of the invention has the advantage that by applying a voltage to the material the latter can be heated. When the material is used as a membrane, separation is significantly accelerated by the higher temperature in the membrane. The heating of the material also makes it possible to achieve the thermal destruction of substances having become deposited in or on the material in the course of the separation process. This may take place either during separation or in a cleaning cycle.
A further advantage of the method of the invention is that by applying a voltage to a substance-permeable material it is possible to remove substances from and out of the material used as membrane by virtue of the fact that, on and in the membrane, gas bubbles are formed which loosen any blockage of the membrane.
The method of the invention has the advantage, in addition, that by applying a voltage to the material the latter becomes electrically charged. As a result, charged particles present in the mixture of substances to be separated and having the same charge as the material are kept away from the material; as a result, depending on the pore size of the membrane material, it is also possible to retain salts in the course of the separation.
The method of the invention is described by way of example below, without the method being restricted to the exemplary description.
In accordance with the invention, the novel method of separating mixtures of substances by means of a substance-permeable material applies to said material an electrical voltage for at least a short time.
The substance-permeable material employed can be a substance-permeable composite material.
By substance-permeable composite materials or supports are meant materials which are permeable to substances having a particle size of from 0.5 nm to 500 &mgr;m, depending on the configuration of the composite material or support. The substances can be gaseous, liquid or solid, or can be present in a mixed form of these aggregate states.
Said substance-permeable composite material has as its basis preferably at least one perforate and substance-permeable support. On at least one surface of the support and in its interior, the support has at least one inorganic component which essentially comprises at least one compound of a metal, a semimetal or a mixed metal with at least one element from main groups 3 to 7.
The substance-permeable composite material can be obtained by applying a suspension which comprises at least one inorganic component comprising a compound of at least one metal, semimetal or mixed metal with at least one element from main groups 3 to 7, and a sol, to a perforate and substance-permeable support and by subsequent heating at least once, in the course of which the suspension comprising at least one inorganic component is solidified on or in, or on and in, the support.
In accordance with the invention the composite material can be permeable to gases, solids or liquids, especially to particles having a size of from 0.5 nm to 10 &mgr;m.
As the perforate and substance-permeable support it is possible to use supports having interstices with a size of from 0.002 to 500 &mgr;m, preferably from 100 to 500 &mgr;m. The supports used are at least partly electrically conducting.
The interstices can be pores, meshes, holes, crystal lattice interstices or cavities. The support can comprise at least one material selected from carbon, metals, alloys, glass, ceramics, minerals, polymers, amorphous substances, natural products, composites, or from at least one combination of these materials. The supports which can comprise the abovementioned materials may have been modified by a chemical, thermal or mechanical method of treatment or a combination of these methods of treatment. The composite material preferably comprises a support, comprising at least one metal, natural fiber or polymer, which has been modified by at least one mechanical deformation technique or method of treatment, such as, for example, drawing, compressing, flexing, rolling, stretching or forging. Very preferably the composite material comprises at least one support which comprises at least woven, bonded, felted or ceramically bound fibers or at least sintered or bonded shaped articles, beads or particles. In a further preferred embodiment, a perforated support can be used. Substance-permeable supports can also be those which acquire their permeability or have been made permeable by laser treatment or ion beam treatment.
It can be advantageous for the support to comprise fibers of at least one material selected from carbon, metals, alloys, ceramics, glass, minerals, polymers, amorphous substances, composites and natural products or fibers of at least One combination of these
Hoerpel Gerhard
Hying Christian
Penth Bernd
Chiesa Richard L.
Creavis Gesellschaft fuer Technologie und Innovation mbH
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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