IE52817B1

IE52817B1 - Bipolar electrolysis apparatus, particularly for the electrolysis of saline solutions

Info

Publication number: IE52817B1
Application number: IE1021/82A
Authority: IE
Original assignee: Degremont
Priority date: 1981-05-04
Filing date: 1982-04-30
Publication date: 1988-03-16
Also published as: JPS57185993A; ES511852A0; IE821021L; FR2504942B1; EP0065889B1; EP0065889A1; DE65889T1; ES8302800A1; FR2504942A1; DE3264871D1

Abstract

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.

Description

The present invention relates to an electrolysis apparatus, particularly for the electrolysis of saline solutions. More specifically, the present invention is directed to an electrolysis apparatus of the type including an enclosure of insulating material and having monopolar terminal electrodes for connection to current leads and a plurality of bipolar electrodes, such apparatus being particularly useful for the electrolysis .. of saline solutions to obtain sodium hypochlorite, a powerful oxidizing agent employable for disinfecting of all types of water.

There are known many electrolysis devices utilizing various types of bipolar electrode assemblies for industrial use to achieve various electrochemical reactions from pure electrolytes.

Such known electrolyzers however are poorly adapted to and have many serious disadvantages when the electrolyte is a natural, unpurified solution. This is particularly true in the case of unpurified sea water, brackish water or brine, by the electrolysis of which it is desired to obtain a diluted solution of sodium hypochlorite. In known electrolyzers employing unpurified electrolytes, the electrodes wear out more or less quickly and unevenly. It then becomes necessary to detect the failing electrodes and to replace them. However, the _ 3 _ design of such known electrolyzers is such that the changing of failing electrodes requires that the electrolyzers be completely dismantled.

The present invention provides electrolysis apparatus 5 having bipolar electrodes, in particular for the electrolysis of saline solutions, which apparatus is constituted by a parallelepiped container of insulating material enclosing bipolar electrodes removably arranged in compartments open towards one of the faces of the IO container, and single-pole terminal electrodes for the passage of current, wherein the double-pole electrodes are individually mounted to slide in said compartments or in drawers sliding in these compartments, the compartments and the drawers respectively being provided with means such as teeth or grooves of insulating material which receive and support the bipolar electrodes, the monopolar electrodes being secured to the side walls of each compartment or drawer.

Advantageously the teeth with which the compartments 2o are provided, are arranged on the compartments so as to support the bipolar electrodes while keeping them at the same distance from, and parallel to, the side walls of the container.

Preferably the front walls and the rear walls of the drawers are provided with grooves which are open at their upper ends and closed at their lower ends.

Conveniently the drawers are mounted to slide on tracks formed on the inner surface of the side walls of the container.

Advantageously the electrical connection between the monopolar terminal electrodes and each drawer and the corresponding current-supply bar is achieved with the aid of a shunt connected to the control cabinet and permitting continuous monitoring to ensure that each compartment or drawer is functioning correctly.

Preferably the bipolar 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.

Conveniently the margin provided on the cathode face of the bipolar electrodes is made of polyamide, polyurethane, polyethylene or epoxide.

Objects, features and advantages of the preseht invention will be apparent from the following detailed description of preferred embodiments, thereof, with reference to the accompanying drawings, wherein: Figure 1 is a perspective view from the front of an ' electrolysis apparatus in accordance with one embodiment of the present invention; Figure 2 is a view similar to Figure 1, but of a second embodiment of the present invention; Figure 3 is a perspective view of the apparatus of Figure 2, but viewed from the rear thereof; and Figure 4 is a perspective view, with portions broken away, of a box-shaped drawer structure employable in the embodiment of Figures 2 and 3.

DETAILED DESCRIPTION OF THE INVENTION All embodiments of the bipolar electrode electrolysis apparatus of the present invention include a vertically extending frame formed of an electrically insulating material, illustrated in the drawings as being a parallelepipedal enclosure 1 having a rectangular horizontal cross section.

The enclosure 1 includes conventional features such as a lower chamber 2 for supply of an electrolyte through an inlet 3 and an upper chamber 4 as an outlet through an outlet duct 5 for the sodium hypochlorite solution produced in the direction of the system for the elimination of gases, mainly hydrogen, formed during the electrolysis operation and being found in 2o supersaturation in such solution. Such system, not shown, is an air-stripping gas-liquid separator, advantageously equipped with a foam-damping vaporizer. Such features are conventional in this type of bipolar electrode electrolysis apparatus, and therefore such features are not described or illustrated herein in further detail, since those of ordinary skill in the art will readily understand such features.

In accordance with the apparatus of the present invention, monopolar terminal electrodes 6 are attached to 528 17 -6side walls of enclosure 1. Current leads to terminal electrodes 6 pass through the side walls of the enclosure and are connected to current lead bars 7 attached to the outer faces of the side walls of the enclosure.

This relationship is shown in the embodiment of Figure 1.

The enclosure 1 has therein at least one compartment 9, and preferably a plurality of vertically spaced compartments as shown in Figure 1. The compartments are adapted to be closed, for example in a hermetically sealed manner, by means of front covers 10 which may be formed of a non-current conducting transparent material, for example PVC.

A plurality of bipolar electrodes 8 are supported within each compartment 9 in a manner such that, upon removal of the respective cover 10, bipolar electrodes 8 may be easily and quickly removed from and/or inserted into the respective compartment 9. In the embodiment of Figure 1, the bipolar electrodes 8 are mounted in such fashion by members which are integral with front and rear walls of enclosure 1 and which have therein recesses into which the bipolar electrodes are removably slidable. The recesses are separated by projections 11 which space the bipolar electrodes 8 at equal intervals parallel to each other and to monopolar terminal electrodes 6. The members having the recesses and projections 11 are provided at the upper and lower portions of each compartment 9, as shown in Figure 1. Such members may be, as shown in Figure 1, integral with the respective walls of the enclosure 1, or may be separate elements fixed to such walls -7528 17 Furthermore, additional members may be provided between the front and rear walls of the enclosure 1, should the bipolar electrodes be of a size to require additional support.

As will be understood by those skilled in the art, the electrolyte circulates from the bottom of the device to the top thereof between the electrodes.

The recesses and projections 11 are of a size to maintain the intervals between the bipolar electrodes equidistant, preferably at distances of from 2.5 to 5 mm.

In a bipolar electrode electrolyzer, it is useful to maintain equal intervals between adjacent electrodes as small as possible. This may be achieved by installing on the bipolar electrodes a number of flanges, not shown, of an insulating material distributed so as not to interfere with the insertion or removal of the electrodes. For example, odd numbered bipolar electrodes 8 might be provided with such flanges, and even numbered bipolar electrodes may be without such flanges. Such flanges also have the advantage of preventing the deformation of the bipolar electrodes and causing a turbulent flow of the electrolyte between the adjacent electrodes.

By the above structural arrangement, replacement of a failing electrode is very easy, since it is necessary only to remove the cover 10 of the compartment in which the particular failing electrode is found and to remove such failing electrode from the respective compartment through its open side. The mobility of the bipolar electrodes 53817 -8is assured by their being simply inserted into the recesses between the projections 11.

One of the most important advantages of the apparatus of the present invention is the simplicity of changing electrodes when necessary and the accessibility of such electrodes through the front of the apparatus.

This makes it possible to limit the height of the overall electrolyzer. A defective or failing electrode easily may be detected through electronic monitoring of the operation of each compartment and the electrodes therein.

A second embodiment of the present invention is illustrated in Figures 2-4 of the drawings. In this embodiment, the structure supporting the bipolar electrodes in each compartment 9 in the enclosure 1 is in the form of a box-shaped drawer which is movably insertable into and removable from the respective compartment through the open side thereof. Each drawer 12 includes spaced front and rear walls 12a, 12b having therein vertically extending grooves 13 having lower ends closed, for example by abutments 14, and open upper ends. The bipolar electrodes are insertable intb and removable from the grooves 13 in drawer 12 through the open upper ends of the grooves when the drawer 12 is removed from the respective compartment 9.

Each drawer 12 may be slidably movable into and from the respective compartment 9 along grooves or rails, not shown, on the inner surfaces of the spaced side walls of enclosure 1. Each drawer 12 may have affixed thereto a respective cover 16, preferably formed of a transparent material. -982817 facilitating gripping and movement of the respective drawer into and from the .compartment. The cover 16 closes the respective compartment 9, for example by hermetic sealing, when the drawer is positioned within the compartment. The drawer 12 is formed of an electrically insulating material.

The current leads 7 in this embodiment of the invention may be attached to the rear wall of the enclosure 1. The current leads 7 may be connected to the terminal electrodes of each drawer 12 by means of a shunt 17, shown in Figure 3, which may be connected to a control cabinet allowing continuous monitoring of the proper operation of each compartment, in this case each drawer 12. Such arrangement constitutes an important advantage of this embodiment of the invention, since it makes it possible to quickly detect failure of any given bipolar electrode, thereby greatly facilitating operation of the electrolyzer.

Each drawer 12 is electrolytically autonomous within the electrolyzer and may be integrally replaced. The electrolyzer can be extended as necessary by superposition or juxtaposition of a plurality of additional drawers 12, the voltages at the posts of each drawer being identical.

In the case of failure of a particular electrode in a particular drawer, such electrode may be exchanged, or the entire drawer may be exchanged, or such drawer simply may be removed, thereby enabling operation of the electrolyzer with the remaining drawers. The required number of spare bipolar electrodes thereby is reduced. Additionally, the apparatus of the present invention offers a remarkable flexibility of operation, since the apparatus of the present -10invention may continue to operate even with one or more compartments going out of service. Failure of a particular electrode easily may be detected by electronic monitoring of each drawer. Electrodes of any type may be employed in a single compartment or box. In addition, the apparatus of the present invention provides the possibility of adjusting at will the concentration of the solution produced by the apparatus by varying the electrolyte feed flow rate at a constant current density or by varying the current density at a constant electrolyte flow rate. For a given power per apparatus, the apparatus of the present invention operates at an overall higher voltage and at a lower current density than in known devices, thus reducing the cost of a transformer-rectifier used.

When an electrolysis cell equipped with bipolar electrodes, each of which operates on one face as a cathode and on the opposite face as an anode, it is found that the specific current consumption expressed as kwh/kg of the product obtained is greater than that for a cell equipped 2o with monopolar electrodes. It is also found that there is relatively fast wear of such electrodes. This is particularly the case with titanium bipolar electrodes.

These disadvantages are avoided in accordance with the present invention by covering the central portion of the anode face of the bipolar electrode with platinum surrounded by a peripheral border portion of oxidized titanium, such peripheral border portion having a width perferably of 15 to 20 mm, and by providing the cathode face of the bipolar electrode with a peripheral border portion of the -1152817 same size as the peripheral border portion of the anode face and covered with a layer of electrically insulating material, such as polyamide, polyurethane, polyethylene, polytetrafluorethylene, epoxies, such layers preferably having a thickness of from 25 to 100 μ.

With this bipolar electrode configuration, a significant improvement is obtained in the specific consumption measured in kWh/kg of product, and the life of the bipolar electrode is substantially increased.

This is emphasized by the following examples illustrating the merits of the apparatus according to the invention.

Examples 1 and 2 A device generally according to the invention was employed to obtain sodium hypochlorite solution from sea water taken from a more or less polluted basin and having the following characteristics, which varied during the course of the tests: Concentration of Na: 7.90 to 10.00 g/i »1 Ca: 0.38 to 0.42 g/1 II Mg: 1.10 to 1.24 g/i II Cl: 17.40 to 18.90 g/i II SO4: 2.25 to 2.85 g/i PH : 7.6 to 8.1 The apparatus had two compartments in the form of drawers 12 which operated hydraulically serially and electrically parallel, each equipped with bipolar electrodes of titanium having a length of 320 mm and a thickness of 1 mm. The cathode face of each electrode was titanium, and the anode face of each electrode was platinum plated to the -12edges of the face. The unitary active surface was 1020 cm2. In example 1, the average distance between electrodes was 2.5 mm, and in example 2 the distance was raised to 5 mm.

The results obtained are given in the following table: Current density (A/cm2) Example 1 Example 2 kWh/kg (chlorine eq.) kWh/kg (chlorine eg.) 0.05 > 8 7 0.10 6.2 6.3 10 0.15 6.0 6.9 0.20 6.0 > 8 Examples 3 and 4 The same apparatus as employed in examples 1 and 2 was operated under the same conditions, but employing bipolar electrodes according to the specific features of the present invention, wherein the cathode face of each electrode was of titanium with the four edges thereof covered with a polytetrafluorethylene film having a thickness of about 50 μ and a width of about 15 mm. The anode side of each bipolar electrode was platinum plated in the central portion thereof, leaving a non-platinum plated peripheral border of a width of about 15 mm, i.e. identical to the peripheral border on the cathode side. The non-plated peripheral border portion of the anode side was oxidized titanium. The active cathode surface 2 and the anode platinum plated surface each were 840 cm . -1353817 The following table lists in example 3, with the spacing of 2 adjacent electrodes, and in example 5 mm between adjacent electrodes. the results obtained mm between the 4 with a spacing of Current density (A/cm2) Example 3 Example 4 -kWh/kg (chlorine eq.) kWh/kg (chlorine eq.) 0.05 5.3 5.2 0.10 4.8 4.9 0.15 4.7 5.3 0.20 4.7 6.1 Example 5 The same experiments were conducted employing a single drawer 12 instead of two drawers as in examples 1-4.

The same specific consumptions were obtained with one drawer, the concentrations of the solutions obtained being one half, allowing for measurement errors, as compared with solutions obtained employing two drawers operating hydraulically in series.

By comparing the results of the examples, it will be apparent that a substantial improvement in specific consumption is obtained when electrodes according to the present invention are employed.

Although the present invention has been described and illustrated with respect to preferred arrangements thereof, it is to be understood that such arrangements are intended to be exemplary only, and that various modifications of form, proportions and arrangements will be apparent to those skilled in the art, without departing from the scope of the present invention.

Claims

1. CLAIMS;

1. Electrolysis apparatus having bipolar electrodes, in particular for the electrolysis of saline solutions, which apparatus is constituted by a parallelepiped 5 container of insulating material enclosing bipolar electrodes removably arranged in compartments open towards one of the faces of the container, and monopolar terminal electrodes for the passage of current, wherein the bipolar electrodes are individually mounted to slide in said 10 compartments or in drawers sliding in these compartments, the compartments and the drawers respectively being provided with means such as teeth or grooves of insulating material which receive and support the bipolar electrodes, the monopolar electrodes being secured to the side walls 15 of each compartment or drawer.

2. Apparatus according to Claim 1 wherein the teeth, with which the compartments are provided, are arranged on the compartments so as to support the bipolar electrodes While keeping them at the same distance from one another, 20 and parallel to the side walls of the container.

3. Apparatus according to Claim 1, wherein the front walls and the rear walls of the drawers are provided with grooves which are open at their upper ends and closed at their lower ends. 25

4. Apparatus according to Claim 3, wherein the drawers -15 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, wherein the electrical connection between the 5 monopolar terminal electrodes and of each drawer and the corresponding current-supply bar is achieved with the aid of a shunt connected to the control cabinet and permitting continuous monitoring to ensure that each compartment or drawer is functioning correctly. 10

6. Apparatus according to any one of the preceding Claims, wherein the bipolar 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 15 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, wherein the margin provided on the cathode face of the bipolar electrodes is 20 made of polyamide, polyurethane, polyethylene or epoxide.

8. Electrolysis apparatus, substantially as herein described with reference to and as shown in Figure 1 or Figures 2 to 4 of the accompanying drawings.