AT513929A1 - Salt water desalting process and apparatus - Google Patents

Abstract

The invention relates to a method and a device for desalting water by means of electrodialysis using semipermeable membranes between at least two edge electrodes for establishing an electric field, which are characterized in that i) as membranes electrically conductive, non-ionic, water and ion permeable membranes which are electrically connected in pairs for equipotential bonding to create a potential-free space between those in the membranes of a pair; andii) at the edge electrodes to prevent the formation of electrolysis gases held below the electrolysis voltage is applied; whereby the solution in the space between the two membranes of a pair is enriched with salt and those outside the membrane pairs depleted of salt.

Description

The invention relates to a method and a device for the desalination of salt water by means of electrodialysis.

BACKGROUND OF THE INVENTION

For a long time, desalination of e.g. Seawater separators used, which has a stack of alternating anion and cation exchange membranes between two electrodes. Each pair of ion exchange membranes forms a separate " cell ". Such stacks sometimes consist of more than two hundred membrane pairs. If a direct electrical voltage is applied to the electrodes, then the anions migrate to the anode. The anions can easily pass through the positively charged anion exchange membranes, but are stopped at the nearest negatively charged cation exchange membrane. Since the same thing happens with the cations with the opposite sign, the net effect of electrodialysis is to accumulate salts in the odd-numbered cells (anion exchange membrane / cation exchange membrane), while even-numbered cells (cation exchange membrane / anion exchange membrane) deplete salt. The solutions with increased salt concentration are combined to form a high-salt concentrate, while the low-salt solutions form the diluate. In Fig. 1, the principle of such a conventional separator is shown schematically (Source: German Wikipedia for keyword "dialysis (chemistry)".

The disadvantages of such sparers are high manufacturing costs, a high potential of the membranes due to their electrical resistance, a low life by membrane fouling, the use of a desiccation sensitive material, limited cleaning options, high energy consumption, especially when used for seawater desalination or similar applications, and losses Concentrate or Diluat at the Umpolung.

The aim of the invention was therefore to provide a method and a device with which the above disadvantages can be at least partially eliminated. 2/35 -1 - · · · · · · · · · · · · ♦ ♦

DISCLOSURE OF THE INVENTION

This object is achieved in a first aspect of the present invention by providing a process for desalting water by means of electrodialysis using semipermeable membranes between at least two edge electrodes for establishing an electric field, characterized in that i) as membranes are electrically conductive, non-conductive ion selective, water and ion permeable membranes are used, which are electrically connected in pairs for potential equalization in order to create a potential-free space between the two membranes of a pair; and ii) applying to the edge electrodes a voltage which is kept below the electrolysis voltage to prevent the formation of electrolysis gases; whereby the solution in the space between the two membranes of a pair is enriched with salt and those outside the membrane pairs depleted of salt.

By such a method using - in contrast to the prior art - electrically conductive and non-ion-selective, that is permeable to water and ions membranes, the efficiency of electrodialysis can be significantly increased. The pairs of interconnected membranes define a potential-free space in between, similar to a Faraday cage, in which, despite bipolar arrangement between the edge electrodes, no electrically induced ion transport takes place.

The salt ions also migrate to the electrodes in the electric field between the edge electrodes according to the method of the invention. However, as soon as they enter the potential-free space between the electrically conductive membranes, the migration stops because no electric field acts on them. Counter-charged ions enter the potential-free space from opposite sides, which is thus enriched in salt, while the space between the electrically connected membrane pairs, also referred to herein as " double membranes " or, in specific embodiments discussed later, also referred to as " double membrane elements " be referred to, steadily depleted of salt. The high-salt solutions are preferably combined to concentrates and the low-salt to diluents. In this way, depending on the number and dimensions of the membranes, it is sometimes possible to obtain high-purity concentrates and substantially salt-free diluents.

In the method according to the invention, however, the membranes are significantly less contaminated than in the prior art. The reason for this is - without wishing to be limited to a particular theory - assumed that it comes to the present invention to virtually no pH shifts on the separation membranes. When using ion-selective membranes by conventional separation methods, only one ion species can pass through the membrane at a time. Their counterion is replaced when passing through the membrane by fixed to and within the membrane counterions; Only after the complete passage of the ion does it recombine again with the original counterion, ie Na + or Cl ', respectively, and it is neutralized by it. This initial counterion, when its oppositely charged partner enters the membrane, initially remains outside the latter in the bilayer located there and migrates in the opposite direction in the electric field. However, before it can pass through the closest ion-selective membrane itself, a water molecule must be ionized to OH 'and H + for charge equalization (at least intermediate) of which only one type of ion is neutralized by the salt ion and the second the pH of the aqueous solution at the membrane surfaces changes. The same happens in the membrane interstices where the salt is enriched: the ions are held there by the membranes with opposite selectivity in their migration in the electric field, but accumulate in the vicinity of the membranes blocking them, causing it locally, i. near the membrane surfaces, there is a lack of associated counterions and again water must be ionized to balance the charges.

These local pH shifts lead to deposits on the membranes, also known as " membrane fouling " and reduces their durability and reduces the efficiency of the separation process. Although a reduction in the separation rate 4/35 -3- leads to weaker pH gradients and fewer deposits, the need for membrane surface and thus the cost increases.

In general, membranes resist the directional movement of ions in the electric field. One speaks of membrane potentials to be overcome during the separation processes. The reasons for the relatively high membrane potentials of the ion-selective, non-electrically conductive membranes lie on the one hand in their fine pores (ion-selective membranes are also referred to as "non-porous membranes" or membranes with "spurious micropores" or as solid electrolytes) be small enough that only the ions themselves, but no ion pairs can pass through, and on the other hand in the construction of concentration and pH gradients due to the above-described enrichment of the counterions, which can not be transported through the membrane due to the selectivity of the membranes.

When arranging the non-ion selective but electrically conductive double membranes in the process of the present invention between two electrodes supplied with power in a saline solution to the anode facing outer surfaces of the double membranes rich anions and at the cathode facing outer surfaces of the double membranes cations. The counter ions required for charge equalization according to the state of the art, fixed to the membrane surfaces and in the pores of the membranes, are replaced in the process of the invention by charges of the double membranes conducting on the outer surface. The charge separation, i. the separation of the anions from the cations takes place here already in the solution, ie before the entry of the ions into the double layer on the membrane, and not only in the pores. There is therefore no accumulation of the original counterions on the surface of the membranes, pH gradients due to the migration of the ions in the electric field arise outside of the double layer around the membranes are thereby less contaminated.

Recombinant ions or unseparated ion pairs, which accumulate in the vicinity of the electrodes outside the bilayer, can pass unhindered through the membrane in accordance with the invention, supported by the flow. This results in a higher yield compared to classical electrodialysis and less membrane fouling.

Furthermore, according to the present invention, identical membranes can be used instead of alternating cation-ion and anion-selective membranes, which significantly reduces the manufacturing costs of a suitably equipped separator.

To increase the separation efficiency, the pressure in the space between the double membranes is kept lower than that outside the membrane pairs, which accelerates the migration of the ions through the membranes. The water to be desalinated is preferably supplied with a slight overpressure into the space outside the membrane pairs.

In further preferred embodiments, the solution in the space between the membranes of a pair, that is, within the double membranes, is conducted in countercurrent to the solution outside the membrane pairs, i. the supply of the water to be desalinated and the discharge of the concentrate from the double membranes take place on opposite sides of a corresponding device. This reduces the osmotic potentials and increases the separation efficiency of the process according to the invention. Alternatively, the field-free space within the double membranes may be subdivided into several sections from which the respective concentrates may be separately separated, again reducing the osmotic potentials.

When large quantities of water to be desalinated are available, e.g. Seawater, and less attention is paid to high salt concentrations in the concentrates, i. if the mere desalination is in the foreground, the interior of the double membranes can also be performed transversely to the flow direction of the water to be desalinated outside of the double membranes. -5- 6/35

Anions or cations accumulate on the edge electrodes during the process. These may be depleted, for example, by electrolysis, i. consumed. By reducing the salt concentration in the outer space between the double membranes and the accumulation of acid or alkali at the two edge electrodes occurs at the edge electrodes a water separation, while at the bipolar double membranes no gas evolution is observed

In a preferred embodiment of the method according to the invention, however, the evolution of gas at the edge electrodes can be completely avoided by also using conductive, ion-permeable membranes as boundary electrodes whose outer sides are brought into contact with ions of respectively opposite charge continuously or at certain time intervals. These can pass through the membranes serving as electrodes and recombine with the counterions otherwise accumulating thereon. The ions required for the charging of the outer spaces of the edge electrodes, which are preferably acids or alkalis, can in preferred embodiments be drawn off from the space on the inside of the respective counterelectrode. That is to say, acidic or basic solutions formed on the insides of the edge electrodes are preferably mixed with one another or exchanged for one another continuously or at specific time intervals. It is important to ensure that an electrical separation of the anode and cathode space is maintained. This can be achieved in a simple manner by a discontinuous mode of operation, by storing the liquids in collecting containers, by brief power interruptions during the subsequent delivery of the respective electrolytes or by the installation of a drip path in the connection between the anode and cathode compartments. In this way, excessive pH shifts on the inner electrode surfaces can be avoided, which increases the life of the electrodes and increases the efficiency of the process.

Alternatively or additionally, for cleaning the membranes and electrodes, the electric field applied across the edge electrodes can be reversed at specific time intervals and / or the voltage can be applied briefly via the electrolysis voltage.

be lifted, as is known from the prior art. Due to the electrical conductivity of the double membranes, however, according to the present invention, in such a voltage increase, gas evolution may be caused not only at the edge electrodes but at all outer surfaces of the conductive membranes. This represents a significant advantage over the classical ion-selective membranes, and is particularly preferably carried out according to the invention at regular intervals as a purification step, preferably in addition to regular reversals.

In a second aspect, the present invention also provides an apparatus for carrying out a desalting process as described above which, in broad analogy to the method of the first aspect, comprises: a succession of a plurality of substantially closed chambers, their partitions of electrically conductive ones, not ion-selective, for water, ions and salts permeable membranes are formed, wherein the partitions are strictly alternately connected in pairs electrically conductive together; each at least one electrode on the lateral outer surface of the first chamber and the lateral outer surface of the last chamber for generating a succession of chambers penetrating electric field, the electrodes are provided with respective electrical terminals, the pairs of electrically conductively connected partition walls between each potential-free Define chambers that deal with potential combs, ie Alternating chambers penetrated by the electric field; and

Inlets for water to be desalinated, outlets for desalinated water and outlets for saline-enriched water, as well as inlets and outlets into and out of the first and last chambers.

Each potential chamber preferably has at least one inlet for water to be desalinated and at least one outlet for desalinated water and each potential-free chamber at least one outlet for saline-enriched water, wherein the solutions withdrawn through these outlets are preferably combined in turn into concentrate and diluate streams. -7- 8/35

The advantages of such a device according to the invention, also referred to as " separator " Of course, they are the same as for the process according to the first aspect: higher purities of the concentrates and diluents are achievable, the membranes are significantly less contaminated during operation, i.e., less so. &Quot; Membrane fouling " is suppressed, and the membrane areas can be reduced compared to conventional separators with constant performance.

The inlets for water to be desalinated and the desalted water outlets are preferably provided at or near opposite edges and / or in opposite side surfaces of the potential chambers in order for the salt water to flow entirely through the chambers in order to make optimum use of the existing membrane area.

Furthermore, the outlets for salt-enriched water from the potential-free chambers and the outlets for desalinated water from the potential chambers are preferably provided on opposite sides of the chambers, which is an already discussed countercurrent flow of the solutions on the two sides of a separation membrane and concomitantly lowering the osmotic potentials and increasing the separation efficiency of the inventive method causes.

In preferred embodiments, the two edge electrodes are also conductive, ion-permeable membranes, on the outer surfaces of which an additional chamber with at least one supply line and optionally at least one discharge are provided. This in turn allows the charging of the inner electrode surfaces with ions of opposite charge to the there due to the migration in the electric field accumulating ions, through the electro-den membranes through, as well as the mutual exchange of the acid or alkali-enriched solutions in the potential combs adjacent to the electrodes. -8- 9/35 • · • · • ·

Between the two serving as partitions of a potential-free chamber, electrically interconnected membranes, i. the double membranes, one or more spacers are preferably provided to more reliably define the space therebetween and also to be able to use, for example, thin films as material for the membranes, even if, as in preferred embodiments of the method according to the invention, the external pressure is higher than the pressure inside the double membranes. With sufficient strength of the membranes, however, no spacers are required.

The spacers can serve simultaneously as electrically conductive connections of the membrane pairs, although they are also a conductive, e.g. conductive coated material, but may also be electrical insulators. The materials of interest are not particularly limited, and e.g. various plastics, metals, ceramics and composite materials.

The shape of the spacers is also not particularly limited as long as they are able to serve their purpose. Preferably, they are selected from rods, meshes, woven fabrics, porous sheets, solid, open-celled foams, and mixtures thereof.

In particularly preferred embodiments of the invention, structures in the surface of the membranes themselves serve as spacers, so that the two membranes are referred to herein as " double membrane element " designated component are connected. Such double membrane elements may also comprise additional spacers between the two membranes, but preferably they are absent. This allows a cheaper production of double membranes.

The surface structures are particularly preferably formed by embedded in the membranes, more or less coarse-grained particles, which - as well as the other spacers - may or may not be electrically conductive. In the first case, no additional electrical connection between the two membranes needs to be provided. Due to the particle size, the distances between the two membranes and thus the volume of the potential-free chambers can be controlled - at least at punctual intervals. Particle sizes in the range of a few dozen microns to about 4 mm, e.g. from about 100 pm to 2 mm or from about 500 pm to 1 mm. For the dimensions of the chambers, it is generally true that the distances between the floating chambers, i. The double membranes should be small, since the strength of the electric field decreases with the distance and the migration speed of the ions with the electric field strength. If the distance is too short, however, the volume of the potential chambers may become too small to ensure sufficient throughput of the device according to the invention, so that an optimization between the migration speed of the ions and the chamber volume must take place. This can be determined by one of ordinary skill in the art for a desired number and length of chambers without undue experimentation. Currently, a distance between the floating chambers of &lt; 2 mm, more preferably, a distance &lt; 1 mm, in particular a distance of <100 pm.

If the same amount of water is to pass through the potential chambers and floating chambers and the pressure in the floating chambers is set slightly lower in preferred embodiments than in the potential chambers, the volume of the floating chambers should be higher than that of the potential chambers. If identical membranes are used with the same length, it follows that a greater distance is preferably to be selected between the pairs of electrically connected membranes than between the double membranes. Currently, a distance between the paired electrically interconnected membranes of &lt; 4 mm preferred. More preferably, a distance of &lt; 2 mm or also &lt; 1 mm.

The membranes are preferably two electrically conductive or conductively coated films, which are connected to one another via the embedded particles to form a double-membrane element, which reduces the manufacturing costs for an invention. ····· · # ········ ··

Device lowers. In this case, the particles are between the two membranes and are in direct contact with both. If it is electrically conductive particles, such. Grains or spheres (or globules) of metal, conductive or or conductive coated ceramic or conductive or conductive coated plastic, they may again serve simultaneously as a spacer and as an electrical connection between the membranes.

However, the membranes are particularly preferably electrically conductive or conductively coated films, of which a film comprises embedded particles which are embedded in depressions in the film, wherein the depressions on the opposite side of the film, ie on its underside form bulges, the structural spacers represent, with which the second film is glued or welded to form the double membrane element. In this case, the particles are in contact with only one of the two membranes and therefore need not be electrically conductive. The connection between the two membranes, however, tends to be stronger in these embodiments than in contact via the particles, since, for example, two metal foils or two conductive or conductive coated plastic foils can be welded or glued directly to each other. Of course, in the case of adhesive bonds, it is preferable to use an electrically conductive adhesive so as not to have to provide additional electroconductive bonds between the films, and one skilled in the art, without undue experimentation, will be able to select a suitable adhesive from a wide range.

The above statement that the surface structures are preferably formed by particles embedded in the membranes also applies in those last-mentioned cases where the particles are embedded in depressions of a first film and a second film is glued or welded to the underside of the depressions Namely, when the troughs are generated by the impressions of the particles in the first film, as is preferred according to the present invention and is apparent from the manufacturing process described below for double membrane elements. -11 - 12/35

To increase the passage speeds, the electrically conductive, non-ion-selective membranes preferably consist of a porous and / or perforated material. While not specifically limited, this material is preferably selected from electrically conductive plastic, electrically conductive coated plastic, graphite, carbon, carbon fiber fabric, electrically conductive ceramic, electrically conductive coated ceramic, porous metal foil, and mixtures thereof.

As previously mentioned, the two electrically interconnected membranes of a pair are preferably films whose edges are glued or welded together, e.g. Metal foils or films of conductive or conductive coated plastic. This ensures a permanent contact between the two membranes and thus a long durability of such a double membrane element.

As indicated above, in a third aspect, the invention relates to a process for preparing double membrane elements as defined above for use in a method or apparatus of the invention as described above. The method is characterized in that particles are embedded in a first electrically conductive or electrically conductive film and / or particles are adhered to the film, after which a second electrically conductive or electrically conductive coated film is welded or glued to the first film. The second film is either applied directly to the particles embedded in the first film and / or adhered to the first film and glued or welded thereto, or it will be before or during embedding or sticking of the particles on the first film wells in the first Produces film that form on the opposite side bulges on which the second film is applied and glued or welded.

To simplify the manufacturing process, the wells are generated in situ by pushing the particles into the first sheet. For this purpose, the film should be made of a deformable material, e.g. Metal or electrically conductive or electrically conductive coated plastic, optionally heated to an elevated temperature prior to or during the application of the particles to be deformable by the particles, and thereafter cooled again. The cooling preferably takes place after bonding or welding to the second film, so that only a single heating step has to be carried out both for the formation of the depressions in the first film and for the connection of the same to the second film.

If the particles are to serve as spacers at the same time, they are in turn preferably electrically conductive or electrically conductive coated, but may otherwise also consist of an electrical insulator. In the case of an adhesive bond between the two films of a double membrane element, an electrically conductive adhesive is preferably used again in order to improve the electrical contact between the films. The material of the films is preferably selected from electrically conductive or electrically conductive coated plastic and metal. During or after the bonding or welding of the two foils over the particles or the undersides of the troughs, preferably also the edges of the two foils are glued or welded together to form the space between the foils, i. to define the volume of the double-membrane element which is to form a potential-free space in the device according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in more detail below with reference to concrete exemplary embodiments, which are to be understood as an illustration and not as a restriction. Reference is made to the accompanying drawings, which show:

Fig. 1 shows schematically the operation of an electrodialysis separator according to the prior art;

Fig. 2 shows schematically the operation of an electrodialysis separator according to the invention; -13- 14/35

Fig. 3 shows schematically a preferred embodiment of the device according to the present invention; and

Fig. 4 shows schematically an embodiment of the manufacturing method for a double membrane element according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In Fig. 1, the operation of an electrodialysis separator according to the prior art is shown schematically. Between two edge electrodes is an alternating sequence of cation-selective and anion-reflective membranes. Cation-selective membranes are shown here in a thicker form and labeled with the negatively charged counter anions (-) fixed to the membrane, whereas anion-selective membranes are lighter and labeled with fixed counter cations (+). As indicated by arrows, the ions of an aqueous salt solution (&quot; Feed Solution &quot;) fed between the membranes migrate in the electric field according to their charge, i. to the oppositely charged electrode. Since all membranes are permeable only for one kind of ions, the ions can only pass a maximum of one membrane and are stopped at the latest by a membrane with opposite selectivity. In this way, the spaces between the membranes alternately accumulate with salt on and off. The high-salt solutions are combined to concentrate while low-salt diluate (s) are withdrawn.

Not shown in this drawing are the double layers on the membranes, which form in the field-free space due to the electrostatic attraction of the ions contained in the membranes, in a separator shown here, but mainly due to the effect of the applied electric field. Especially in those membrane spaces that are enriched with salt, the ions are attracted to the surface of the membrane with opposite selectivity, but they can not pass and therefore dwell in their immediate vicinity. However, the associated counterions stay near the surface of the next membrane for the same reason. Due to the local deficiency of counterions, pH shifts continuously occur at the membranes, since the * * * ♦. need to be ionized to compensate for this deficiency.

According to the present invention, as shown schematically in Fig. 2, this is through the use of non-ion-selective, but electrically conductive membranes which are connected in pairs with each other electrically conductive to so-called double membranes, so to speak, a sequence of Faraday cages in the electric field form between the edge electrodes, effectively avoided.

As soon as the ions, in the course of their migration in the electric field outside the double membranes, have entered the fieldless space inside, they are no longer subject to the attraction of the edge electrodes and can recombine with a counterion arriving from the opposite direction or be neutralized by it in their charge , The accumulation at the membrane surfaces takes place here only due to electrostatic attraction of the ions fixed to the membrane surfaces, which is many times lower than the effect of the applied electric field. In this way, membrane fouling according to the present invention can be largely suppressed.

In Fig. 3, an embodiment of the device according to the invention is shown. This comprises a sequence of a plurality of substantially closed chambers 8 and 10, the partitions of electrically conductive, non-ion-selective, permeable to water, ions and salts membranes are formed, wherein the partitions strictly alternately connected in pairs electrically conductive to form so-called double membranes are. On the lateral outer surface of the first chamber 10a and the lateral outer surface of the last chamber 10b, an electrode 9 is provided for generating the electric field, which are provided with electrical terminals 1 and 2, respectively. The pairs of partitions electrically connected to one another define in each case potential-free chambers 8, which communicate with potential chambers 10, i. Alternate chambers penetrated by the electric field. -15- 16/35 ····· ·········································

To the chambers are provided inlets 4 for water to be desalinated, outlets 6 for desalted water and outlets 7 for saline-enriched water, as well as inlets 3 and outlets 5 into and out of the first and last chambers 10a and 10b respectively, each potential chamber 10 preferably has at least one inlet 4 for water to be desalted and at least one outlet 6 for desalinated water and each potential-free chamber 8 has at least one outlet 7 for salt-enriched water. As mentioned above, multiple inlets and / or outlets may be provided for each chamber 8 and 10, respectively.

As can be seen in FIG. 3, the inlets 4 for water to be desalinated and the desalted water outlets 6 are provided near the opposite edges of the potential chambers 10 for transporting the solution to be desalinated past substantially the entire membrane surface and Sufficient salt ions to pass through the membrane.

The salt-enriched water outlets 7 from the floating chambers 8 and the desalted water outlets 6 from the potential chambers 10 are preferably provided on opposite sides of the chambers, which provides a countercurrent flow of the two solutions inside and outside the double membranes, i. the chambers 8, causes and increases the separation efficiency.

In Fig. 4, finally, a simple embodiment of a method for the production of membranes for use in the method according to the invention and in the device according to the invention is shown schematically. The membranes to be used are, as mentioned above, preferably connected to double membrane elements in which structures in the surface of the membranes serve as spacers to define the space within the double membrane and thus the volume of the chambers 8. These structures are produced according to the third aspect of the invention by a manufacturing method, the sequence of which is shown schematically in FIGS. 4a to 4c. -16- 17/35 • ·· ·

In Fig. 4a, a first film F1, which is preferably made of metal or electrically conductive or conductive coated plastic, as well as a number of particles to see P, which are to be joined together, preferably by heating or heating of the film to make it easier to deform close. The particles are then preferably pressed into the deformable or deformable film, which produces on its opposite side troughs M, as shown in Fig. 4b. The fixation of the particles in the wells can either be done by the fact that the film is melted by heating and solidifies again on cooling and thus holds the particles, or using an adhesive, which should be an electrically conductive adhesive, if the particles themselves are also electrically conductive to produce a uniform, electrically conductive surface of F1.

Fig. 4c finally shows how a second film F2 is bonded to the underside of the troughs M to give, together with film F1, the double-membrane element. This connection of the two films can preferably be done by gluing or fusing. If they are glued, again an electrically conductive adhesive should be used. Preferably, the embedding of the particles in film F1, the production of the wells by means of impressing the particles in F1 and the joining of the well bottoms with foil F2 by fusing in the course of a single heating step.

Depending on the pattern in which the particles are applied to the film F1, the stability of the double-membrane element can be controlled. Preferably, the particles are distributed in a regular pattern over the entire film surface to maintain the spacing between the films substantially constant.

The final steps of the method according to the invention, not shown in Fig. 4, consist of connecting the edges of the foils F1 and F2 together to define a closed chamber therebetween, as well as attaching saline-enriched water outlets 7. The bonding of the edges is preferably carried out again by gluing or welding or fusing, -17- 18/35 • ······················································································ And also a pipe or hose that serves as an outlet 7, can be inserted through an opening attached to the appropriate position and fixed by gluing or welding in the double membrane element. The tube or hose is preferably not electrically conductive, of course, to ensure safe handling of the device during operation. -18- 19/35

Claims (35)

♦ · ··· ··♦♦♦♦ · φφφφφφφφφφφ I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I·····························································································································································································································. Therefore, 1. A process for the desalting of water by means of electrodialysis using semipermeable membranes between at least two edge electrodes for establishing an electric field, characterized in that i) as membranes are electrically conductive, non-ion selective, for water and ion permeable membranes are used, which are electrically connected in pairs for potential equalization in order to create a potential-free space between the two membranes of a pair; and ii) a voltage is applied to the edge electrodes to keep the formation of electrolysis gases below the electrolysis voltage; whereby the solution in the space between the two membranes of a pair is enriched with salt and those outside the membrane pairs depleted of salt. 2. The method according to claim 1, characterized in that the pressure in the space between the membranes of a pair is kept lower than that outside the membrane pairs. 3. The method according to claim 1 or 2, characterized in that the water to be desalinated is supplied into the space outside the membrane pairs. 4. The method according to any one of claims 1 to 3, characterized in that the solution is conducted in the space between the membranes of a pair in countercurrent to the solution outside the membrane pairs. 5. The method according to any one of the preceding claims, characterized in that the space between the membranes of a pair is divided into a plurality of sections from which liquid is independently removable. 6. The method according to any one of the preceding claims, characterized in that as edge electrodes also conductive, ion-permeable membrane - 20- 20/35 ·············································· ············································································································································································································································ Charge be brought into contact. 7. The method according to claim 6, characterized in that the outer sides of the edge electrodes for neutralization in each case with an acid or alkali are brought into contact. 8. The method according to any one of the preceding claims, characterized in that on the insides of the edge electrodes resulting acidic or basic solutions are mixed continuously or at certain intervals or exchanged with each other. 9. The method according to any one of the preceding claims, characterized in that for cleaning the membranes and electrodes, the applied over the edge electrodes electric field is reversed in certain time intervals. 10. The method according to any one of the preceding claims, characterized in that for the cleaning of the membranes and electrodes, the voltage is briefly raised above the electrolysis voltage. The apparatus for performing a desalting process according to any one of claims 1 to 10, comprising: a series of a plurality of substantially closed chambers (8, 10) whose partitions are of electrically conductive, non-ionic, water, ionic, and salt permeable ones Membranes are formed, the partitions are strictly alternately connected in pairs electrically conductive together; in each case at least one electrode (9) on the lateral outer surface of the first chamber (10a) and the lateral outer surface of the last chamber (10b) for generating an electrical field penetrating the sequence of chambers, the electrodes (9) being connected to respective electrical terminals (1 , 2), wherein the pairs of interconnecting electrically interconnected partitions between them each define potential-free chambers (8), which correspond to potentials of the cells 21 - 21/35 ········································································. «· ······························································································································································ Alternating chambers penetrated by the electric field; and inlets (4) for water to be desalinated, desalted water outlets (6) and salt-enriched water outlets (7), and feeds (3) and drains (5) into and out of the first and last chambers (10a , 10b). 12. The device according to claim 11, characterized in that each potential chamber (10) has at least one inlet (4) for water to be desalinated and at least one outlet (6) for desalinated water and each potential-free chamber (8) at least one outlet (7). for salt-enriched water. 13. The apparatus according to claim 12, characterized in that the inlets (4) for desalzalzendes water and the outlets (6) for desalted water at or near opposite edges and / or in opposite side surfaces of the potential chambers (10) are provided. 14. Device according to one of claims 11 to 13, characterized in that the outlets (7) for salt-enriched water from the potential-free chambers (8) and the outlets (6) for desalinated water from the Potentialkammem (10) on opposite sides the chambers are provided. 15. Device according to one of claims 11 to 14, characterized in that the electrodes (9) are also conductive, ion-permeable membranes, on the outer surfaces of which an additional chamber is provided with at least one supply line and optionally at least one derivative. 16. Device according to one of claims 11 to 15, characterized in that between the two serving as partitions of a potential-free chamber (8), electrically interconnected interconnected membranes one or more spacers are provided. -22- 22/35 • · · · φ 99 9 99 9 99 9 99 9 99 9 9 • ··· ·· ···· ···· 9919 · ···· 9 9 9 9 · Φ · · ·· ··· ··· ·· 17. The apparatus according to claim 16, characterized in that the spacers serve as electrically conductive connections of the membrane pairs. 18. The apparatus according to claim 16, characterized in that the spacers are electrical insulators. 19. Device according to one of claims 16 to 19, characterized in that the spacers are selected from bars, grids, fabrics, porous plates, solid, open-cell foams and mixtures thereof. 20. Device according to one of claims 16 to 20, characterized in that structures in the surface of the membranes serve as spacers, wherein the two membranes are connected to form a double membrane element. 21. The device according to claim 20, characterized in that the surface structures of embedded in the membranes, more or less coarse-grained particles are formed. 22. The device according to claim 21, characterized in that the membranes are two electrically conductive or conductive coated films which are connected to each other via the embedded particles to form a double membrane element. 23. The device according to claim 21, characterized in that the membranes are electrically conductive or conductively coated films, of which a film comprises embedded particles embedded in hollows in the film, wherein the troughs on the opposite side of the film form bulges, the Represent structural spacers with which the second foil is glued or welded to form the double membrane element. 24. Method or device according to one of the preceding claims, characterized in that the electrically conductive, non-ion-selective membranes consist of a porous and / or perforated material. -23- 23/35 ························································································· · · · · · ············································· 25. The method or device according to any one of the preceding claims, characterized in that the material of the electrically conductive, non-ionensive membranes of electrically conductive plastic, electrically conductive coated plastic, graphite, carbon, carbon fiber fabric, electrically conductive ceramic, electrically conductive coated Ceramic, porous metal foils and mixtures thereof. 26. The method or device according to one of the preceding claims, characterized in that the two electrically conductive interconnected membranes of a pair of films whose edges are glued or welded together. 27. A process for the preparation of double membrane elements, as defined in any one of claims 20 to 26, for use in a method or apparatus according to one of the preceding claims, characterized in that in a first electrically conductive or electrically conductive coated film particles are embedded and / or particles are glued to the film, after which a second electrically conductive or electrically conductive coated film is welded or glued to the first film. 28. Method according to claim 27, characterized in that the second film is applied to the particles embedded in the first film and / or adhered to the first film and glued or welded thereto. 29. The method according to claim 27, characterized in that before or during the embedding or sticking of the particles on the first film troughs are produced in the first film, which form bulges on the opposite side, applied to the second film and glued or is welded. 30. The method according to any one of claims 27 to 29, characterized in that the particles are coated electrically conductive or electrically conductive. -24- 24/35 ··· ····························································································· · · · Φ · · · · · · · · · · · ΦΦ ·· ΦΦΦ ·· · »· 31. The method according to any one of claims 27 to 30, characterized in that the particles consist of an electrical insulator. 32. The method according to any one of claims 27 to 31, characterized in that an electrically conductive adhesive is used. 33. The method according to any one of claims 27 to 32, characterized in that the material of the films of electrically conductive or electrically conductive coated plastic and metal is selected. 34. The method according to any one of claims 27 to 33, characterized in that the films are heated to embed or stick the particles and / or for bonding or welding together. 35. The method according to any one of claims 27 to 34, characterized in that during or after the bonding or welding of the two films on the particles or wells, the edges of the two films are glued or welded together. VANOR GmbH through: HÄUPL &amp; ELLMEYER KG Vienna, on 05.02.2013 -25 25/35