EP0029518A1 - Electrolysis apparatus with bipolar electrodes, in particular for the electrolysis of brine to produce hypochlorite - Google Patents

Abstract

This electrolysis device is characterized in that it comprises a plurality of electrolytic cells, each consisting of at least two successive layers of bipolar electrodes (A, C), all of the bipolar electrodes and of the monopolar terminal electrodes being enclosed between two extreme non-conductive support plates (b). In the successive layers of bipolar electrodes, the opposite parts of two consecutive electrodes are of opposite sign. The electrodes are arranged in electrode holders advantageously constituted by plates (f) having housings (g) for the electrodes and spaced from one another by intermediate pieces (h), the assembly thus formed being clamped on the plates - terminal supports (b). On each electrode holder (f), the latter are arranged in a "checkerboard" fashion, so that, in the succession of electrodes constituting the electrolytic cells, the anode part of an electrode is opposite the cathode part of the successor.

Description

The present invention relates to an electrolysis apparatus with bipolar electrodes, usable for carrying out electrochemical reactions, in particular the electrolysis of a saline solution with the production of an oxidizing solution containing chlorinated compounds, mainly in the form of sodium hypochlorite. . Such a solution having the same range of use as a commercial sodium hypochlorite solution, can be used for the chlorination of waters of all kinds, including waste waters, at any stage of the treatment of these waters. The oxidizing compounds present in such a solution are measured in "active chlorine equivalents".

Electrolysers using various types of bipolar electrode assembly have already been described and are industrially used for carrying out various electrochemical reactions. These known devices, when used to obtain a sodium hypochlorite solution from an alkali metal electrolyte such as: sea water, brackish water or sodium chloride solution, are the seat electrolytic redox reactions in the immediate vicinity of the electrodes and chemical reactions between the electrodes.

The active chlorine present in the oxidizing solution obtained is dissociated and is mainly found in the form of hypochlorous acid and ions hypochlorites, depending, among other things, on pH and temperature, with simultaneous production of hydrogen. When the electrolyte is constituted by sea water, the presence of calcium and magnesium salts gives rise to the formation at the cathode of a deposit making it less permeable to the flow of electrons and requiring periodic acid washes or short-term current reversals.

To avoid these drawbacks, it is advantageous on the one hand to limit the concentration of hydrogen formed, detrimental to the good behavior of the electrodes, by eliminating it during the treatment and, on the other hand, to operate at speeds of electrolyte circulation between the relatively high electrodes so as to reduce deposits at the cathode and space or eliminate washes or current inversions.

However, to achieve high conversion rates and therefore increase the concentration of active chlorine equivalent in the solution obtained, the current density can be increased; if you want to get-. n specific low consumption in kWh per kg of active chlorine equivalent produced, it is then necessary to reach low voltages, which can be obtained by reducing the interval between two electrodes.

Furthermore, during electrolysis, the chemical composition of the electrolyte changes, which requires different operating conditions, speed of the electrolyte between the electrodes, current density, etc.

The improvements brought about by the invention make it possible to obtain a electrolysis efficiency much higher than usual, therefore reducing the specific consumption in kWh / kg of active chlorine equivalent produced, allows operation at different current densities in the different chambers of the device and ensures efficient mixing of composed at the exit of these rooms.

The electrolysis apparatus with bipolar electrodes, provided with monopolar terminal electrodes, according to the invention, comprising a plurality of electrolytic cells, all of these electrodes. being sandwiched between two non-conductive end support plates, is characterized in that each of said electrolytic cells is constituted by at least two layers of bipolar electrodes arranged "in a checkerboard" fashion so that, in the succession of electrodes constituting the cells electrolytic, the anodic part of an electrode is located opposite the cathodic part of the one that follows it.

The various characteristics and advantages of the invention will emerge from the description which follows of some of its possible embodiments, given by way of nonlimiting examples.

• Fig. 1 une vue en perspective éclatée d'un appareil suivant l'invention ;
• Fig. la une vue en perspectiv,e d'une cellule ;
• Fig. 2 une vue extérieure en perspective de l'appareil suivant la fig. 1;
• Fig. 3 à 6, des vues respectivement des plaques terminales (fig. 3), des porte-électrodes (fig. 4 et 5) et des pièces intercalaires ou d'espacement (fig. 6) ;
• Fig. 7 à 10, des vues de "couches" d'électrodes bipolaires suivant divers arrangements ;
• Fig. Il à 13, des vues schématiques, dans un plan parallèle aux porte-électrodes des "chambres" créées dans l'appareil ;
• Fig. 14 à 15, des vues de "couches" d'électrodes bipolaires présentant des électrodes à surface inégale ;
• Fig. 16 et 17, des vues analogues aux Fig. 11 à 13 des chambres correspondant aux cellules électrolytiques constituées par des couches successives d'électrodes bipolaires à surfaces actives inégales, telles que montrées aux Fig. 14 et 15.

During this description, reference is made to the attached drawings which show:

• Fig. 1 an exploded perspective view of an apparatus according to the invention;
• Fig. a perspective view of a cell;
• Fig. 2 an external perspective view of the device according to FIG. 1;
• Fig. 3 to 6, views respectively of the end plates (fig. 3), of the electrode holders (fig. 4 and 5) and of the spacers or spacers (fig. 6);
• Fig. 7 to 10, views of "layers" of bipolar electrodes according to various arrangements;
• Fig. Il à 13, schematic views, in a plane parallel to the electrode holders of the "chambers" created in the device;
• Fig. 14 to 15, views of "layers" of bipolar electrodes having electrodes with uneven surface;
• Fig. 16 and 17, views similar to FIGS. 11 to 13 of the chambers corresponding to the electrolytic cells formed by successive layers of bipolar electrodes with uneven active surfaces, as shown in FIGS. 14 and 15.

In the example treated, the device is vertical and takes the form of a rectangular parallelepiped, in which successive layers of electrodes are arranged in successive parallel planes.

In general, an apparatus according to the invention has a framework constituted by lateral faces such as a and end plates, such. that b. Both have holes c.

At its lower part, the apparatus is provided with chambers d for supplying the electrolyte, and at its upper part with chambers e collecting the solution obtained.

In the housing thus formed, there are arranged electrode holders constituted, in the example treated, by flat plates f, provided with holes f ₁ , and which can affect various configurations, for the reasons which will be explained below.

In these plates are housed g receiving the electrodes, both monopolar and bipolar. These housings, generally rectangular or square, are also arranged in various configurations, depending on the arrangement provided for the electrodes of a "layer". Their dimensions correspond to that of the electrode they receive.

These electrode holder plates are, as shown in fig. 1, spaced apart by means of intermediate pieces h, also pierced with holes h _l , which coincide with those presented by the electrode holders f and the end plates b.

The electrode-carrying plates and the spacers are made of an insulating material and adapted to the particular operating conditions, such as temperature, aggressiveness of the solutions, etc. The housings have the same depth as the electrodes, generally between 1 and 3 mm if the electrodes are metallic, and between 4 and 5 mm if the electrodes are made of graphite for example. The intermediate pieces h preferably have a thickness of between 1.5 and 4 mm. These thicknesses depend on the operating conditions and the mechanical stability of the electrodes. The important thing is that, in the same device, all the housings have the same thickness; the same is true for the dividers.

The width of the spacers is slightly greater than the spacing between two housings, for example 3 to 6 mm, and such that it allows, by superposition and clamping, to rigidly fix the electrodes in their housings and to hide their edges.

During assembly, these various elements are assembled and tightened one on top of the other, like the filter plates of a filter press, by any system, for example by a screw-nut system, i.

The spacers h are, as shown in fig. 6 and, in particular, FIGS. 11 to 13, of a length such that they determine an internal partitioning delimiting the chambers k (FIG. 11) which will be discussed below.

The bipolar electrodes in any desired number, are arranged "in a checkerboard pattern" on an electrode holder, which thus constitutes a "layer" of electrodes and in such a way that, once the apparatus is assembled, each part of a bipolar electrode of one layer faces the bipolar part of opposite polarity of the electrode of the next layer.

FIGS. 7 and 8 show, by way of nonlimiting examples, respectively the first and the second layers of bipolar electrodes, arranged "in a checkerboard pattern". Each layer consists of four bipolar electrodes C - A, having a cathode part C and an anode part A, and by a terminal electrode (A in FIG. 7, C in FIG. 8). The monopolar terminal electrodes of several successive layers are connected to a source of direct current by the poles + and -.

When the successive layers of bipolar electrodes in FIG. 7, then in FIG. 8, then again in FIG. 7, then in FIG. 8, and so on, are assembled, successively C is obtained opposite A, then A opposite C, and so on. The anodes A and the cathodes C face the cathodes C and the anodes A respectively of the layers which. succeed them.

The succession, in a horizontal plane, of facing parts, of opposite sign, of at least two layers of bipolar electrodes, constitutes an elementary electrolytic cell 10, shown in perspective in FIG. the. The staging in the vertical plane, of a number of cells 10 thus formed, forms, with the intermediate pieces and as described above, electrolysis chambers.

The succession of layers 1, 2, 1, 2, etc. shown in FIGS. 7 and 8 can also be reversed, namely 2, 1, 2, 1, etc. The number of layers can be even or odd with a minimum of two coats.

The bipolar and monopolar electrodes of the extreme layers are electro-active only on the side of the surface facing the passage of the electrolyte.

The bipolar and monopolar electrodes of the intermediate layers are active on both sides.

FIGS. 9 and 10 show, by way of example, another possible arrangement with twelve elementary cells produced by means of superimposed layers of a set of five bipolar electrodes (fig. 9) and a set of six bipolar electrodes (fig. 10). In this case, the electrolyser also has three electrolysis chambers, but each chamber has four cells, ie twelve elementary cells in total, which is the case of the device shown in FIG. 1.

The anode ends (+) shown in FIG. 1 are joined together by connectors which are good conductors forming the pole (+) of the electrolyser. It is the same for the cathodes forming the pole (-).

The device is provided at its lower part with an enclosure d of distribution of the electrolyte and at its upper part of an enclosure e for taking up the solution produced.

These enclosures are connected, respectively, to the supply 14 of the electrolyte, and to the start 15 of the solution produced.

The course followed by the electrolyte in the chambers of the apparatus is different depending on the coupling of these chambers with one another.

FIGS. 11 to 13 represent, by way of example, three different couplings, by construction, of three chambers 11, 12, 13, FIG. 11 for example corresponding to an apparatus such as that shown in FIGS. 1 and 2.

In the example of FIG. 11, the internal arrangement of the apparatus is such that it determines a partitioning with baffles circulating the electrolyte, introduced at the base, of the upstream chamber 11 and distributed by a distribution device there, from this chamber 11 to the downstream chamber 13 passing through the intermediate chamber 12, the solution obtained being discharged at 13a. The pipes 20 for evacuating the hydrogen formed are advantageously provided with a gas-liquid separator 21.

FIG. 12 represents an internal arrangement of the apparatus according to which the electrolyte is distributed at the base of the apparatus at 16 between the three chambers without communication between them, and exits at the upper part at 17.

FIG. 13 represents an apparatus in which the electrolyte is also distributed between the chambers at its entry, but the solution obtained by electrolysis is collected in an enclosure 18 common to the chambers to be evacuated in 19.

In the case of FIGS. 12 and 13, the chambers 11, 12 and 13 can be supplied individually with electrolytes of various natures. This embodiment can also be envisaged when the products of the electrolysis of the chamber 11 must be mixed with the products obtained by the electrolysis carried out in the chamber 12, etc.

Up to now, it has been assumed that the active surfaces of the different electrodes are the same; however, they may be different.

FIGS. 14 and 15 represent, by way of example, an electrolyser whose active unit surface of the electrodes of the chamber It is less than the active unit surface of the electrodes of the chamber .12 and that of the chamber 12 less than that of room 13.

FIGS. 16 and 17 represent, by way of example, possible hydraulic circuits in chambers corresponding to the cases of FIGS. 14 and 15.

The chambers 13 then operate at a current density lower than that of the chambers 12, the latter operating at a current density lower than that of the chambers 11. It goes without saying that the chambers can occupy various positions in the electrolyser, in any order.

The internal electrical mounting of the electrodes in the same electrolyser is in parallel series.

The voltage across the pole (+) and pole (-) electrolyser is a function of the voltage per elementary cell multiplied by the number of cells.

The current intensity is a function of the current density at which the electrolysis takes place multiplied by the sum of the anodic or cathodic active surfaces of the electrodes constituting a cell.

The monopolar terminal electrodes, anode and cathode, are located opposite and at the same level at the top or at the same level at the bottom of the electrolyser, or at different levels, anode at the top and cathode at the bottom, or vice versa.

Several electrolysers can be mounted in hydraulic series or in parallel; the electrical mounting of several identical electrolysers is preferably carried out in series.

The electrolysis device according to the invention has many advantages compared to known devices.

The edges of the bipolar electrodes being protected by the housings in which the electrodes are received, there is no leakage of current from one electrode to the next located in the same plane; in addition, the destruction of the electrode at these edges, usually covered with difficulty by a noble metal (platinum, iridium), is avoided, the edges not being exposed to the phenomenon of electrolysis.

The possibility of using standard equipment produced in series, requiring no welding, facilitates the manufacture and assembly of a device according to the invention.

In addition, if we want to increase the production of the device, we can easily add additional layers of electrodes identical to the first or mask a number of layers by achieving this increase by using insulating plates solid instead of the electrode layers.

• - quelle que soit la ou les matières utilisées à leur fabrication, à condition qu'elles soient conductrices de courant et adaptées aux conditions électrochimiques d'utilisation ;
• - quelle que soit leur épaisseur, les plaques porte-électrodes non conductrices de courant et adaptées aux conditions de l'électrolyse envisagée devant avoir la même épaisseur que les électrodes;
• - quelle que soit la distance choisie entre deux couches successives, les intercalaires non conducteurs du courant et généralement de même matière que celle utilisée pour les logements devant être dimensionnés en conséquence ;
• - quel que soit le type d'électrodes choisi, c'est-à-dire surface pleine ou striée, etc... , à condition qu'elle soit plane ;
• - quelle que soit la surface des électrodes à condition de respecter les indications énumérées ci-dessus.

Furthermore, the configuration of the electrolyser described makes it possible to use planar electrodes, and this:

• - whatever the material or materials used in their manufacture, provided that they are current-carrying and adapted to the electrochemical conditions of use;
• - whatever their thickness, the non-current-carrying electrode plates adapted to the conditions of the envisaged electrolysis must have the same thickness as the electrodes;
• - whatever the distance chosen between two successive layers, the non-conductive inserts of the current and generally of the same material as that used for the housings to be sized accordingly;
• - whatever the type of electrodes chosen, that is to say solid or striated surface, etc., provided that it is flat;
• - whatever the surface of the electrodes provided that the indications listed above are observed.

In addition, the present invention has the advantage of increasing the overall yields of a complete installation because it allows on the one hand to improve the efficiency of the actual electrolysis by reducing the energy required at the terminals of the electrolyser. , and on the other hand, to decrease the losses of an electrotechnical nature concerning more particularly the losses by Joule effect in the bars, connections, cooling auxiliaries, etc ...

This is obtained by the use of bipolar electrodes constituting pluri-cells requiring an overall intensity significantly lower than that required by an electrolyzer of identical active surface but using monocells.

Similarly, the voltage applied to the terminals of a cell is infe lower than that applied to known devices, because the checkerboard arrangement with spacers makes it possible to reduce the distance between the electrodes and consequently the resistance of the electrolyte. This gives better resistance of the electrodes over time and in particular of the voltage-sensitive anodes.

For the same power consumed and assuming the same yields, the electrolyser which is the subject of the present invention has the advantage of operating at a low overall current and a higher voltage at the terminals. (V = v X number of cells). This results in a lower price for transformer-rectifier equipment, the price of the latter being for the same power lower when 1 is lower and V higher.

Claims (9)

1. Electrolysis apparatus with bipolar electrodes provided with monopolar terminal electrodes, comprising a plurality of electrolytic cells, the assembly of these electrodes being sandwiched between two is extreme non-conductive support plates, characterized in that each of said electrolytic cells by at least two layers of bipolar electrodes (A. C) arranged "in a checkerboard pattern" so that, in the succession of electrodes constituting the electrolytic cells, the anode part of an electrode is opposite the part cathodic of its successor. 2. Apparatus according to claim 1, characterized in that the electrodes are arranged in electrode holders advantageously constituted by plates (f) having housings (g) for the electrodes and spaced from each other by intermediate pieces (h ), the assembly thus formed being clamped on the end support plates (b). 3. Apparatus according to any one of the preceding claims, characterized in that the intermediate pieces, made of an insulating material, used for the spacing of the electrode holders, slightly cover the edges of the electrodes. 4. Apparatus according to any one of the preceding claims, characterized in that the electrode support plates determine, with their spacers, chambers each comprising at least two stepped electrolytic cells, these chambers communicating, or not, between them, being connected to the inlet of the electrolyte and to the outlet of the solution obtained, so as to be interconnected either in series, in parallel or in series-parallel. 5. Apparatus according to any one of the preceding claims, characterized in that the bipolar electrode holders are planar and of identical thickness. 6. Apparatus according to any one of the preceding claims, characterized in that the electrolytic cells formed are of rectangular or square section. 7. Apparatus according to any one of the preceding claims, characterized in that two neighboring chambers have electrodes whose active surface is identical. 8. Apparatus according to any one of the preceding claims, characterized in that two neighboring chambers have electrodes whose active surface is different so that the current density is different depending on the chambers. 9. Apparatus according to any one of the preceding claims, characterized in that it comprises an electrolyte distribution enclosure and an opposite enclosure for recovering the solution produced, these enclosures being respectively arranged at the base and at the top. of the device, or vice versa, and common or not to several rooms.

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