EP0044472A1

EP0044472A1 - A separator electrolytic cell providing glove-shaped membranes

Info

Publication number: EP0044472A1
Application number: EP81105322A
Authority: EP
Inventors: Tokuzo Iijima; Yasushi Samijima; Kazuo Kishimoto; Kimihiko Kono
Original assignee: Kanegafuchi Chemical Industry Co Ltd
Current assignee: Kanegafuchi Chemical Industry Co Ltd
Priority date: 1980-07-17
Filing date: 1981-07-09
Publication date: 1982-01-27
Also published as: JPS5723078A; JPS6350435B2

Abstract

Disclosed is a separator electrolytic cell providing glove-shaped membranes (4) which is comprised of a first electrode compartment (20) surrounded with a releasable lateral plate (15) of a cell and a glove-shaped finger comprising a separator installation support (1) and glove-shaped membranes (4) and a second electrode compartment (21) surrounded with remainder cell walls and the glove-shaped finger. The glove-shaped membranes (4) processed by simplified steps are installed very feasibly to the cell, providing tight sealing.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a separator electrolytic cell. More particularly, it relates to a finger type electrolytic cell inexpensive in manufacture and suitable for a large capacity which facilitates installation or removal of a separator, especially a cation exchange membrane and further simplifies assemblage or disassemblage of anodes and cathodes.

2. Description of the Prior Art

As a process for production of an alkali metal hydroxide by the electrolysis of an aqueous alkali metal halide solution, above all, an aqueous alkali metal chloride solution, there has been heretofore proposed and practiced commercially electrolytic processes using a separator such as cation exchange membranes. In these days environmental pollution coming from mercurial processes has come to the fore and accordingly these processes are rapidly being substituted for the mercurial processes. Most of the electrolytic cells used for these processes are filter press type cells in which, for instance, a separator such as an ion exchange membrane and a microporous membrane is positioned between a cathode compartment frame and an anode compartment frame to give a unit and several or several tens of the units are assembled. The cells of such type are limited in a size of each compartment and a separator has to be positioned to every unit, so that it is difficult to assemble so many units. Moreover, to each compartment a supply inlet for a solution to be electrolysed and a removal outlet for a liquor after electrolysis have to be provided. A great number of supply inlets and removal outlets provided in the anode and the cathode compartments not only require voluminous and complicated operation of connecting many units to each other upon assemblage, but also inrease a risk of leakage of liquors produced by the electrolysis from connected portions. Furthermore a risk of leakage from connected portions between the compartment frames also increases inevitably as the number of compartment frames connected increases, which is said to be a fatal disadvantage to the filter press type cells. To prevent this disadvantage a strict mechanical tolerance in design as well as manufacture is needed, thereby inviting an increase in cost of manufacturing. In addition, as the number of compartment frames increases, a greater pressing force must be exerted to thus result in an increased risk of physical damages of the compartment frames and an increased cost.
For the foregoing reasons it is next to impossible to manufacture a filter press type cell of low cost and large capacity.
On the other hand, cation exchange membranes are normally produced in a form of thin sheet with the thickness of several hundred microns and limited dimensions because of making the most use of the performance thereof and of commercial factors in manufacture. That may be a reason why a filter press type cell is widely used as an electrolytic cell bearing a cation exchange membrane.
In order to eliminate the foregoing defects, Japanese Utility Model non-examined publication No. 51,333/1977 discloses an electrolytic cell which comprises anode and cathode compartments having continuously meandering concavo-convex anode and cathode, respectively, and a continuous film-like separator interposed between the anode and the cathode, the anode and cathode compartments are assembled in such a manner that the concave of the cathode or the anode and the convex of the anode or the cathode are interleaved with the separator intervened therebetween.
In the electrolytic cell of this type, however, to avoid physical damages of a separator, a gasket or a spacer must be employed to thereby maintain a clearance given between the cathode and the anode to prevent both electrodes from coming in contact with each other. Because of the clearance, cell voltage increases to thus interfere with the object of enlargement of scale.
In view of the above situation, there is a great need for an electrolytic cell to which a long size thin film-like cation exchange membrane or microporous membrane can be installed as it is and which enables the scale-up of the cell.
In the light of the foregoing problems and the present situation, the present inventors have made an extensive series of study on the development of an electrolytic cell of a large capacity bearing a long size of a separator such as a cation exchange membrane and have already proposed a novel separator electrolytic cell comprised of a plurality of anodes mounted at the bottom plate and a cathode box providing fingers interleaved between adjacent anodes, to the side surfaces of said fingers a sheet-like separator being installed by means of separator installation devices located above or below the fingers. This proposed invention provides a superior electrolytic cell which eliminates the foregoing problems the conventional arts have, it has still a drawback that a fairly lot of labor is needed in securing the sheet-like separator to the separator installation devices, and thus a measure for reduction of said labor is expected.
U.S. Pat. No. 4,175,024 discloses an electrolytic cell which is comprised of electrodes interleaved between electrodes of opposite polarity, to which cathode electrodes an enveloping synthetic separator is secured. While the electrolytic cell of this type is likely to save operation in securing the separator to the separator installation devices by intricate securing means, a lap expanding outwardly from the open end periphery of the separator has to be provided to the enveloping separator in order to ensure the tight sealing and has to be placed between an anode and a back screen, then fastened together. However, formation of the separator in such a shape is not necessarily easy and an anode plate of a complicated construction is required, thus leaving some problems on the practical usefulness.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a separator electrolytic cell bearing glove-shaped membranes, in which the glove-shaped membranes are feasibly installed.
It is another object of the present invention to provide a separator electrolytic cell bearing glove-shaped membranes which facilitates assembly and disassembly and provides tight sealing to thereby prevent leakage of electrolytes.
It is a further object of the present invention to provide a separator electrolytic cell bearing glove-shaped membranes which permits conversion of existing asbestos diaphragm electrolytic cells to ion exchange membrane electrolytic cells.
These and other objects of the present invention together with the advantages thereof will become apparent to those skilled in the art from the detailed disclosure of the present invention as set forth hereinbelow.
The present invention encompasses a novel separator electrolytic cell bearing glove-shaped membranes characterized in that on a releasable lateral plate one polar electrodes of either cathodes or anodes are mounted substantially vertical to the lateral plate and a bottom plate and on at least one wall plate comprising another lateral plate opposing the foregoing lateral plate, the bottom plate and a cell top cover the other polar electrodes are mounted substantially parallel to and facing close to the foregoing electrodes, said electrodes mounted on the releasable lateral plate being covered with glove-shaped separators secured to a separator installation support shading said lateral plate, said separator possessing an open end in which said electrode is inserted.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. la, Fig. lb and Fig. lc are a front view, a top plan view and a side view, respectively, of a separator installation support.
Fig. 2 is an illustrative view showing steps of forming a glove-shaped separator used in the electrolytic cell of the present invention.
Fig. 3 is a schematic illustration showing the securing of the separator to the separator installation support.
Fig. 4 is a horizontal schematic sectional view of the electrolytic cell of the present invention.
Fig. 5 is a schematic vertical sectional view of the electrolytic cell of the present invention in parallel to an electrode plate.

DETAILED DESCRIPTION OF THE INVENTION

In Fig. la to Fig. lc, the separator installation support (1) is basically of a flat plate shape having sufficient area to cover a releasable lateral palte of the electrolytic cell and is equipped with open portions (2), (2'), (2") --- which permit passage of electrodes mounted on the lateral plate. On the open portions (2), (2'), (2")_'--- collars (3) are protruded along their periphery substantially vertical to the separator installation support (1).
The separator installation support (1) as aforesaid may be made of an anti-corrosive and heat-resistant synthetic resin including polyvinyl chloride, chlorinated polyvinyl chloride, a fluorinated resin such as polytetrafluoroethylene, polyethylenetetrafluoroethylene and polyvinylidene fluoride, a material lined with the foregoing resins or rubbers, an anti-corrosive metal such as titanium, a titanium-paradium alloy and stainless steel, and the like. The separator installation support material is preferably an insulated material resistant to both anodic and cathodic solutions. The surface and the reverse side of the separator installation support may also be made of different materials resistant to each solution they are in contact with.
Fig. 2 illustrates steps of forming the separator (4) secured to the separator installation support (1) shown in Fig. la to Fig. lc, in which a sheet-like separator shown in the step (I) is folded down at a central fold (6) as shown in the step (72), then in the step (III) two end brims (7)(8) are bonded together. By those steps the glove-shaped separator (4), as depicted in the step (IV), having an open end is obtained.
As the separator, a cation exchange membrane or a microporous membrane may be suitably used and to the present electrolytic cell is a cation exchange membrane the most preferable.
The cation exchange membrane suitably used in the present electrolytic cell may preferably be made of a polymer having a fluorine-containing backbone with pendant cation exchange groups such as sulfonic acid groups, carboxylic acid groups and phosphoric acid groups, singly or in combination of two or more.
The glove-shaped separator (4) so formed as to possess the shape and the length equal to the inner peripheral length of the collar (3) protruded on the separator installation support (1) may be bonded or welded in its open end to and along the inner periphery of the collar (3), but may be secured more advantageously by a mechanical means which enables the exchanging of the separator. A practical example for the securing of the separator by a mechanical means will be explained relating to Fig. 3. The open end of the glove-shaped separator (4) is inserted in the open portion (2) of the separator installation support (1), then placed between the collar (3) and a pressing plate (9), and further a packing (10) is interposed between the separator (1) and the collar (3), these being secured together by the use of clips made of an anti-corrosive material such as titanium. The separator securing process depicted as above only illustrates a typical exemplification and accordingly there may be suitably applied a variety of securing means and instruments including bolts and nuts, clips, spring clips, clamps, springs, singly or in combination of two or more, which are suggested in Japanese Utility Model Application Nos. 178,714/1977, l07,l97/ 1978, 57,341/1979 and 91,756/1979.
As a material for the securing means, titanium is preferred for use in the anode compartment and ss, sus, etc. are preferred for use in the cathode compartment, but it is not particularly limited unless corrosive to anodic and cathodic solutione.
The packing (10) may be preferably in the form of a string, a flat sheet or.a protrusion-provided sheet made of a foamed article of polytetrafluoroethylene, a rubber or the like.
The pressing plate (9) may preferably be made of titanium, SS, SUS, a synthetic resin, a glassfibre reinforced resin or the like.
A separator installation apparatus by the use of a mechanical means as mentioned in detail earlier ensures and facilitates the installation of a separator (4) to and along the collar (3) on the separator installation support, so that changing of the separator damaged or blocked is possible very feasibly, thereby being by far superior as compared with bonding, welding or the like.
The installation of the separator by the mechanical securing means is in fact of exceeding importance even for the following reasons, especially when a cation exchange membrane is used as a separator. That is, it is required to position the separator as tight as possible between the cathodes and the anodes. The cation exchange membrane normally expands and contracts according to moisture contained in the circumstances, while a microporous membrane exhibits almost no such a phenomenon. Accordingly the cation exchange membrane, even when installed as tightly as possible in the air., is apt to expand to thereby produce slack and wrinkles during the operation since it comes into contact with an aqueous alkali metal halide solution and an aqueous alkali metal hydroxide liquor. Slack and wrinkles necessarily cause residence of halogen gas at the anode side of the membrane, thus resulting in low quality of the product. Inversely, at the cathode side of the membrane, release of hydrogen gas is prevented to produce gas-gap, thereby leading to an increase in the cell voltage.
Therefore, prior to the installation of the membrane to.the cell, it is at first wetted with water, brine or an aqueous alkali metal hydroxide liquor; then installed in a wet condition. In the installation of the membrane in a foregoing fashion, a mechanical securing is superior to welding, bonding or cementing, because the wetted membrane can not be welded and bonding of the wetted membrane, even when bonded, not only reduces bonding force, but also causes hydrolysis of adhesives. Furthermore, however tight the membrane may be installed, slack or wrinkles will occur during the course of operation over a long period of time. In such cases, when the membrane is installed by a mechanical means, slack and wrinkles can be easily removed by doing even again, thus operation being further continued without slack and wrinkles.
Next, description will be made by referring to Fig. 4 and Fig. 5 which show a state that a globe-shaped finger fabricated by securing the glove-shaped separator (4) to the separator installation support (1) is assembled together with the electrodes in the cell.
In these figures, electrodes (14) (for example, anodes) are mounted parallel on the bottom plate (13) and a lateral plate (15) positioned in parallel to a row of the electrodes (14) is releasable. On the lateral plate (15) are the other electrodes (16) (for example, cathodes) mounted parallel to and facing close to the electrodes (14). The glove-shaped finger comprising the separator installation support (1) and the glove-shaped separator (4) is placed between the lateral plate (15) and flanges (17), (17') and (17") provided at the edges of the cell (12) and fastened tight in such a way that the collar (3) is located near the lateral plate (15), i.e.., the separator (4) protrudes into the cell. Between the flanges (17), (17¹), (17") and the separator installation support (1) gaskets (18) are interposed and between the separator installation support (1) and the lateral plate (15) sheet-like packings (19) are interposed to provide tight sealing. The open portions (2) (2') --- and the glove-shaped separators (4) (4') --- are decided upon beforehand in dimensions and relative position so that the electrodes (16) (16¹) --- are inserted in the glove-shaped separators (4) (4') --- through the open portions (2) (2') --- of the separator installation support (1), when the glove-shaped finger is so assembled.
The so assembled cell is comprised of a first electrode compartment (20) (for example, cathode compartment) surrounded with the releasable lateral plate (15) and the glove-shaped finger, and a second electrode compartment (21) (for example, anode compartment) surrounded with the remaining cell walls and the glove-shaped finger. As is apparent from the foregoing description, the first electrode compartment (20) is provided with electrodes (16) (for example, cathodes) and the second electrode compartment (21) is provided with opposite polar electrodes (14) (for example, anodes). As a cathode, a lath, a foraminous plate and the like is preferable which is made of SS, SUS and the like. As an anode, an anti-corrosive anode is preferred which is made of a platinum group metal, an alloy thereof or a metal lined with oxides thereof.
In cases, as shown in Fig. 5, where the bottom plate (13) on which electrodes (14) are mounted is releasably secured using a packing (22) to a flange (23) located at the bottom of the cell, assembly or disassembly for exchange of electrodes (14) in the second electrode compartment (21) is markedly facilitated.
In an embodiment as mentioned above, there is depicted that the glove-shaped finger is secured to the lateral surface of the cell (12) by securing it to the lateral plate (15) on which the electrodes (16) are mounted and the other electrodes (14) are mounted on the bottom plate (13), but a variety of modifications are possible in a direction of mounting the electrodes (14). That is, the electrodes (14) may be mounted on a lateral plate opposing the lateral palte (15) or on the cell top cover (24), and likewise the glove-shaped finger and the electrodes (16) may also be inserted in the cell upwardly from the bottom plate (13) or downwardly from the top, provided that both electrodes oppose each other maintaining their parallel relationship. It is also one of significant improvements included in the present invention that opposite lateral plates of the cell (12) are allowed to be releasable respectively and either cathodes or anodes are mounted on one of the lateral plates substantially vertical to the lateral plate and the bottom plate and the other electrodes are mounted on at least one cell wall comprising the bottom plate and the cell top cover substantially parallel to and facing close to said electrodes, further the electrodes mounted on the lateral plate are covered with the glove-shaped separator secured to the separator installation support having open portions through which said electrodes are passed and shielding said lateral plate, i.e., the cell is fabricated so as to allow glove-shaped fingers extending from the opposite two lateral paltes interleave, thereby duplicating the capacity of the cell. Furthermore, it is also possible with ease by selecting a material in contact with a respective electrolyte to provide anodes in the first electrode compartment (20) and to provide cathodes in the second electrode compartment (21).
In the assemblage of the present electrolytic cell, it is preferred to position electrodes (14) in a slightly contracted form in their thickness so as not to damage the glove-shaped separator (4), then to expand them during electrolysis to thus reduce anodes-cathodes spacing.
The present invention not only provides an advantage of decreasing cell voltage exerted by enlarging the thickness of electrodes (14) upon electrolysis to bring anodes to cathodes as closely as possible, more preferably to bring anodes and cathodes into contact with both surfaces of the separator, but also realizes enlargement of scale by increasing the length or the number of fingers, while adding no essential difficulties in installation of the separator and assembly of the cell.
Although not shown in the accompanying drawings, there are provided, needlessly, to the cell an inlet for water or a diluted aqueous caustic alkali solution, an inlet for brine, an outlet for the product liquor i.e., an aqueous alkali metal hydroxide liquor, outlets for gases generated, i.e., hydrogen gas and a halogen gas, respectively, and an outlet for depleted brine, as is the case with the conventional separator type electrolytic cell. Notwithstanding, when the cell is so constructed that the glove-shaped finger is inserted upward from the bottom, a particular device has to be made as to the end portion of fingers with a view to removing gas generated in the first electrode compartment, which may disadvantageously lead to a complicated construction of the cell.
Hereinabove, embodiments of the present electrolytic cell were described with reference to the accompanying drawings, but to which embodiments the present invention is not limited and, of course, including a lot of modifications and applications without departure from the scope of the present invention.
The present electrolytic cell is constructed such that the glove-shaped separator can be prepared by exceedingly simple steps, the lap is no longer required to be provided at the open end, the glove-shaped separator can be secured in an exceedingly reduced time by simplified operations and instruments to the separator installation support to give the glove-shaped finger, and that a finger type electrolytic cell like a conventional diaphragm electrolytic cell can be provided very feasibly. Furthermore, as compared with a filter press type cell which is generally used when a sheet-like separator is employed, it is possible to supply a cell with a greater capacity per the same floor area. That is, a filter press type cell with a capacity of 150 KA at 20 A per dm² requires a floor area of 8 to 10 m², whereas the present electrolytic cell with the same capacity needs only 4 to 6 m 2 floor area. Moreover, the present electrolytic cell has numerous advantages that assembly or disassembly is by far easier than any other finger type electrolytic cell having ever been proposed before by the present inventors, and that more perfect sealing is provided to thus prevent leakage of electrolyte.
Furthermore the present electrolytic cell is suited to a construction of a mono-polar cell and it is also advantageous that it is possible to utilize the existing equipments including a current trnasformer effectively in conversion of a mercurial cell or an asbestos diaphragm cell to an ion exchange membrane cell.
As apparent from the foregoing, the present electrolytic cell has a lot of advantages over a filter press type cell. The present electrolytic cell has not so many joints and has a greater capacity per a unit installation area as well as a high efficiency per a unit volume of a cell. It further requires neither expensive materials for parts including cathodes and anodes nor strict mechanical tolerance, thereby resulting in an decrease in production cost. The assembly and disassembly are easy and simple, even if a glove-shaped separator is employed, further, sealing is easy so that labor is drastically saved. It not only enables a contact construction, in which anodes and cathodes are in contact with the respective surfaces of the separator, to thus reduce the anodes-cathodes spacing to the minimal distance, through which cell voltage is lowered, maintains high current efficiency by keeping concentration of anodic and cathodic solutions uniform, but also realizes the scale-up of the equipment with a decreased cost in maintenance as well as operation.

Claims

1. A separator electrolytic cell providing glove-shaped membranes for the production of an aqueous alkali metal hydroxide liquor by the electrolysis of an aqueous alkali metal halide solution in which one polar electrodes of either cathodes or anodes-are mounted on a releasable lateral. plate substantially vertical to the lateral plate and a bottom plate and the other polar electrodes are mounted on at least one wall plate comprising another lateral plate opposing the foregoing lateral plate, the bottom plate and a cell top cover substantially parallel to and facing close to the foregoing electrodes, said electrodes mounted on the releasable lateral plate being covered with glove-shaped separators secured to a separator installation support shading said lateral plate, said separator possessing an open end in which said electrode is inserted.

2. The separator electrolytic cell providing glove-shaped membranes of Claim 1, wherein the open portions of the separator installation support are provided with collars on and along the peripheral brim projecting toward the releasable lateral plate, to which collars the open ends of the glove-shaped separators are secured.

3. The separator electrolytic cell providing glove-shaped membranes of Claim 2, wherein the wall plate on which the other polar electrodes are mounted is also releasable.

4. The separator electrolytic cell providing glove-shaped membranes as claimed in any one of the preceding Claims 1 to 3, wherein the foregoing other polar electrodes are mounted on another lateral plate opposing the lateral plate on which the one polar electrodes are mounted.

5. The separator electrolytic cell providing glove-shaped membranes as claimed in any one of the preceding Claims 1 to 3, wherein the foregoing other polar electrodes are mounted at the bottom plate.

6. The separator electrolytic cell providing glove-shaped membranes as claimed in any one of the preceding Claims 1 to 3, wherein the foregoing other polar electrodes are mounted at the cell top cover.

7. A separator electrolytic cell providing glove-shaped membranes for the production of an aqueous alkali metal hydroxide liquor by the electrolysis of an aqueous alkali metal halide solution in which a pair of opposite lateral plates are releasable and on the either lateral plate one polar electrodes of either cathodes or anodes are mounted substantially vertical to the lateral plate and a bottom plate, and on at least one wall plate comprising another lateral plate, the bottom plate and a cell top cover the other polar electrodes are mounted substantially parallel to and facing close to the foregoing electrodes, said electrodes mounted on the foregoing lateral plate being covered with glove-shaped separator secured to a separator installation support shading said lateral plate, said separator possessing an open end in which said electrode is inserted.

8. The separator electrolytic cell providing glove-shaped membranes of Claim 7, wherein the open por- tionsof the separator installation support are provided with collars on and along the peripheral brim projecting toward the lateral plate, to which collars the open ends of the glove-shaped separators are secured.

9. The separator electrolytic cell providing glove-shaped membranes of Claim 8, wherein the wall plate on which the other polar electrodes are mounted is also releasable.

10. The separator electrolytic cell providing glove-shaped membranes as claimed in any one of the preceding Claims 7 to 9, wherein the foregoing other polar electrodes are mounted on the bottom plate.

11. The separator electrolytic cell providing glove-shaped membranes as claimed in any one of the preceding Claims 7 to 9, wherein the foregoing other polar electrodes are mounted on the cell top cover.