EP0065889B1 - Electrolysis apparatus with bipolar electrodes, especially useful in the electrolysis of brines - Google Patents

Description

The present invention relates to an electrolysis device of the type comprising, arranged in a generally rectangular-shaped enclosure made of insulating material, monopolar terminal electrodes for the current supply and a plurality of bipolar electrodes, such an apparatus being usable in particular for electrolysis of saline solutions, obtaining sodium hypochlorite, a powerful oxidizing agent, usable for the disinfection of water of all kinds.

Many electrolysis apparatuses using various types of assembly of bipolar electrodes have already been described and are industrially used for carrying out various electrochemical reactions from pure electrolytes.

These electrolysers are, however, ill-suited and have multiple and serious drawbacks when the electrolyte consists of unpurified natural solutions: in particular, seawater, brackish water or unpurified brine, for example electrolysis of which it is desired to obtain a dilute solution of sodium hypochlorite.

In these known devices, treating unpurified electrolytes, the electrodes wear more or less quickly and unevenly. It is then necessary to detect the faulty electrodes and to proceed with their replacement. However, the design of these known devices is such that the change of an electrode requires their total disassembly.

This is the case, for example, of the device according to European patent 0 013 215, in which the electrodes are stacked in compartments opening onto a front of the device and from which they are extracted as a whole, using removable means. such as plates provided under each stack of electrodes.

The present invention not only avoids any disassembly, but also allows quick and easy change of the electrodes. Thanks to this ease of replacement of the electrodes, the invention lends itself to the use of electrodes which are more consumable than others and therefore more economical.

In addition, the invention allows continuous monitoring of the operating conditions of the device.

The electrolysis apparatus with bipolar electrodes, in particular for the electrolysis of saline solutions, constituted by a rectangular enclosure made of insulating material comprising bipolar electrodes removably arranged in compartments opening on one of the faces of the enclosure and monopolar terminal electrodes for the current supply, is characterized in that the bipolar electrodes are individually mounted to slide in said compartments or in drawer-units sliding in these compartments, the compartments, respectively the drawer-units, being provided with means such as slots or grooves made of insulating material, receiving and supporting the bipolar electrodes, the monopolar electrodes being fixed on the side walls of each compartment or drawer-box.

The various characteristics and advantages of the invention will emerge from the description which follows of possible embodiments of the invention. It is clearly stated that these are only examples and that all other forms, proportions and arrangements could be adopted, without going beyond the ambit of the invention.

• - la figure 1 est une vue en prespective d'un appareil suivant l'invention, montrant particulièrement un compartiment autonome de l'appareil,
• - les figures 2 et 3 sont des vues analogues à la figure 1, d'un appareil suivant l'invention dans sa forme de réalisation où les compartiments autonomes sont constitués par des boîtiers-tiroirs,
• - et la figure 4 est une vue en perspective d'un de ces boîtiers-tiroirs.

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

• FIG. 1 is a perspective view of an apparatus according to the invention, showing in particular an autonomous compartment of the apparatus,
• FIGS. 2 and 3 are views similar to FIG. 1, of an apparatus according to the invention in its embodiment in which the autonomous compartments are constituted by boxes-drawers,
• - And Figure 4 is a perspective view of one of these drawer units.

Whatever its embodiment, the device is constituted by a vertical parallelepiped enclosure 1 of rectangular section. This enclosure comprises a lower chamber 2 for supplying electrolyte, via line 3, an upper starting chamber 4, via line 5 for output of the sodium hypochlorite solution produced towards a device for removing gases. , mainly hydrogen, formed during electrolysis and found in supersaturation in this sulution. This device (not shown) is a gas-liquid separator by air stripping; it is advantageously provided with a foam suppressant sprayer.

The monopolar terminal electrodes such as 6 are fixed on the side walls of the device. The current leads to these terminal electrodes pass through the side walls of the device to join the current feed bars 7 arranged on the side faces of the device.

According to the invention, the bipolar electrodes, such as 8, fitted to the apparatus are contained in compartments 9, the front wall of which is constituted by a cover 10, removable so as to allow direct access to the bipolar electrodes as well as to the terminal electrodes.

These compartments are provided with slots 11 made of insulating material intended to support the bipolar electrodes while keeping them equidistant from each other and allowing them to be pulled out of the compartments by the facade. The electrolyte flows from bottom to top of the device, between the electrodes.

The slots supporting the electrodes are arranged at the base and at the top of the boxes at the front and at the rear thereof; and possibly in the middle. The teeth of the slots keep the bipolar electrodes equidistant, preferably at distances of 2.5 to 5 mm.

The front wall of the compartments, constituted by the cover 10 is advantageously made of a transparent material which does not conduct current, PVC for example.

In a bipolar electrode chlorinator, it There is every interest in maintaining, between two successive electrodes, equal intervals and as reduced as possible. This object is achieved by the installation on the bipolar electrodes of several lugs (not shown) made of insulating material, and distributed so as not to hinder the insertion of the electrodes (for example the odd number electrodes with lugs, the others without cleats). These cleats also have the advantage of preventing the deformation of the bipolar electrodes and of causing the electrolyte to flow under turbulent regime between two electrodes.

Thanks to the arrangements according to the invention, the replacement of a faulty electrode is very easy since it suffices to remove the compartment cover 10 in which the retail electrode is located and to pull this electrode out of the compartment by its open front. , the removability of the electrodes being ensured by their simple insertion into the slots separating the slots 11.

One of the most important advantages of the device according to the invention essentially consists in the simplicity of changing the electrodes, if necessary and in the accessibility of these electrodes by the front of the device, which makes it possible to limit the height of the equipment.

The defection of an electrode is easy to detect by the electrical control of each compartment.

According to a particularly interesting embodiment of the invention shown in Figures 2 to 4, the bipolar electrodes 8 fitted to the device are contained in compartments made in the form of boxes 12 shown in detail in Figure 4. These boxes have their front 12a and rear 12b faces provided with grooves 13 open at their upper part, and limited, at their lower part, by a heel 14 which the considered faces of the housing have.

These housings are mounted on a drawer on the enclosure, for example by sliding on slides (not shown) formed on the internal faces of the side walls of the enclosure. They can be easily gripped and maneuvered by their cover 16.

The openings of the compartments receiving the drawer units 12 are hermetically closed by these covers 16, preferably made of a material, or of a transparent material.

The current leads 7 to the terminal electrodes of each box-drawer grouped together, as shown in FIG. 3, on the rear face of the enclosure 1.

The electrical connection between the terminal monopolar electrode of each box-drawer and the corresponding current supply bar 7 takes place, as shown in FIG. 3 using a shunt, such as 17, connected to the control cabinet and allowing continuous monitoring of the proper functioning of each compartment - in this case of each box-drawer 12 -. This arrangement constitutes an important advantage, since it makes it possible to quickly detect any possible failure, which greatly facilitates the operation of the installation.

Each box-drawer 12 being from an autonomous electrolytic point of view, can be replaced entirely. The device can be extended as required, by superimposing or juxtaposing a plurality of boxes, the voltage at the terminals of each box being identical. In the event of a failure on one electrode, you can either change this electrode, or change the complete housing, or remove it and operate on the other housings. The number of spare bipolar electrodes can therefore be reduced. In addition, the device offers a remarkable flexibility of operation because it can, without disadvantage, operate even in the case of the decommissioning of one or more compartments.

The defection of an electrode is, in this case also, easy to detect, by the electrical control of each box 12.

Electrodes of any kind can be used, and this in the same compartment or case. In addition, the device offers the possibility of adjusting the concentration of the solution produced by electrolysis at will by varying the flow rate of electrolyte supply at constant intensity or by varying the current density at electrolyte flow rate. constant. For the same power per device, it operates at a higher overall voltage and at a lower current density than in known devices, which reduces the price of the rectifier transformer used.

When an electrolysis cell is equipped with bipolar electrodes, operating as a cathode on one side and as an anode on the other, it is found that the specific current consumption, expressed in kWh / kg of the product obtained, is greater than that a cell equipped with monopolar electrodes. There is also a relatively rapid wear of such electrodes. This is particularly the case for bipolar titanium electrodes.

These drawbacks are avoided in accordance with the invention, by coating the central part of the anode face with platinum, surrounded by a border 15 to 20 mm wide in oxidized titanium, the cathode face of the electrode being covered with a border of the same dimension, made of an insulating material such as polyamide, polyurethane, polytetrafluoroethylene, etc., in the form of a layer, of thickness ranging from 25 to 100 μm.

There was obtained, with such an electrode according to the invention, a significant improvement in the specific consumption measured in kWh / kg of product and a significant extension of the duration of the electrode.

• On a utilisé un appareil suivant l'invention pour l'obtention d'une solution d'hypochlorite de sodium à partir d'une eau de mer prélevée dans-un bassin plus ou moins pollué et dont les caractéristiques, qui ont donc varié au cours des essais, étaient les suivantes:
  • - Concentration en Na : 7,9 à 10 g/I
  • - do. en Ca : 0,38 à 0,42 g/I
  • - Concentration en Mg : 1,1 à 1,24 g/I
  • - do. en CI :17,4 à 18,9 g/I
  • - do. en S04 2,25 à 2,85 g/I
  • - pH 7,6 à 8,1

A number of numerical examples have been given below showing the advantage of the device according to the invention:

• An apparatus according to the invention was used for obtaining a sodium hypochlorite solution from sea water taken from a more or less polluted basin, the characteristics of which have therefore varied during tests, were as follows:
  • - Na concentration: 7.9 to 10 g / I
  • - do. in Ca: 0.38 to 0.42 g / I
  • - Mg concentration: 1.1 to 1.24 g / I
  • - do. in CI: 17.4 to 18.9 g / I
  • - do. in S04 2.25 to 2.85 g / I
  • - pH 7.6 to 8.1

The apparatus consisted of two compartments in the form of boxes-drawers, operating hydraulically in series and electrically in parallel, provided with bipolar titanium electrodes with a side of 320 mm and 1 mm thick, platinized on one side.

The cathode face of each electrode was made of Titanium and the anode face platinized to the edge. The unit active area was 1.020 cm ² . In Example 1, the average distance between electrodes was 2.5 mm and in Example 2, the distance was increased to 5 mm.

The results obtained are given in the following table:

Examples 3 and 4

The same reactor as above operated under the same conditions but using bipolar electrodes, in accordance with the invention, the cathode face of which was made of titanium and the four edges were covered with a polytetrafluoroethylene film of approximately 50 µm over a width of 15 mm. The anode side was platinized over the entire central part, leaving a border of 15 mm in width not platinized on the whole. This non-platinum part, therefore made of Titanium, has been oxidized. The active cathode surface and the anode platinum surface were each 840 cm ² .

The table gives the results obtained in Example 3, with a spacing of 2.5 mm between electrodes, and Example 4 with 5 mm between electrodes.

Example 5

The same experiments were carried out using one drawer instead of two. The same specific consumption was obtained as with a drawer, the concentrations of the solutions obtained being half, to within the measurement errors, compared to those obtained with two drawers in hydraulic series.

By comparing the previous results, a marked improvement in the specific consumption is noted when the electrodes according to the invention are used.

Claims (7)

1. Electrolysis apparatus having a double-pole electrode, in particular for the electrolysis of saline solutions, which apparatus is constituted by a parallelopiped container (1) of insulating material enclosing double-pole electrodes removably arranged in the compartments open towards one of the faces of the container, and single-pole terminal electrodes for the passage of current, characterized in that the double-pole electrodes (8) are individually mounted to slide in said compartments (9) or in drawers (12) sliding in these compartments, the compartments (9) and the drawers (12) respectively being provided with means such as teeth (11) or grooves (13) of insulating material which receive and support the double-pole electrodes (8), the single-pole electrodes (6) being secured to the side walls of each compartment or drawer.

2. Apparatus according to Claim 1, characterized in that the teeth (11), with which the compartments (9) are provided, are arranged on the compartments so as to support the double-pole electrodes while keeping them at the same distance from, and parallel to, the side walls of the container.

3. Apparatus according to Claim 1, characterized in that the front walls (12a) and the rear walls (12b) of the drawers (12) are provided with grooves (13) which are open at their upper ends and closed at their lower ends.

4. Apparatus according to Claim 3, characterized in that the drawers (12) are mounted to slide on tracks formed on the inner surface of the side walls of the container.

5. Apparatus according to any one of the preceding Claims, characterized in that the electrical connection between the single-pole terminal electrodes and each drawer (12) and the corresponding current-supply bar (7) is achieved with the aid of a shunt (17) connected to the control cabinet and permitting continuous monitoring to ensure that each compartment or drawer is functioning correctly.

6. Apparatus according to any one of the preceding Claims, characterized in that the double-pole electrodes are constituted by a titanium body, the anode face of which is covered with platinum over its central part and has at its periphery a margin consisting of oxidized titanium, the cathode face of said body having a margin of the same width as the margin on the anode face and made of an insulating material.

7. Apparatus according to Claim 6, characterized in that the margin provided on the cathode face of the double-pole electrodes is made of polyamide, polyurethane, polyethylene or epoxide.

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