EP0046235A1

EP0046235A1 - A novel vertical type separator electrolytic cell

Info

Publication number: EP0046235A1
Application number: EP81106107A
Authority: EP
Inventors: Tokuzo Iijima; Yasushi Samejima; Kazuo Kishimoto; Kimihiko Kono
Original assignee: Kanegafuchi Chemical Industry Co Ltd
Current assignee: Kanegafuchi Chemical Industry Co Ltd
Priority date: 1980-08-16
Filing date: 1981-08-05
Publication date: 1982-02-24
Also published as: JPS5739183A

Abstract

Disclosed is a novel vertical type separator electrolytic cell which is comprised of a box-shaped structure (1) in which a plurarity of cathode structures are provided, a bottom plate (15) on which anodes (14) are mounted, a separator (11) such as a cation exchange membrane positioned between the cathode structure and the anode (14) and a cell top cover (20), said cathode structure comprising a cathode electroconductor (3) and a cathode (5) positioned along at least one lateral surface of the cathode electroconductor (3) by electroconductive ribs (4) located thereto, thus forming an independent vertical cathode working surface.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a separator electrolytic cell, more specifically to an electrolytic cell suitable especially in use for the preparation of an aqueous alkali metal hydroxide by the electrolysis of an aqueous alkali metal halide solution

2. Description of the Prior Art

Conventionally, asbestos has been mainly served as a separator when an alkali metal hydroxide, above all, caustic alkali is produced by the electrolysis of an aqueous alkali metal chloride solution using a separator electrolytic cell. Notwithstanding, the caustic alkali prepared by the asbestos electrolysis process contains impurities in greater amounts than that produced by a mercurial electrolysis process as a typical process of other processes and is therefore said to be unsuited to the rayon industry. On the other hand, the mercurial electrolysis process is now being forced.to be converted to the other processes due to contamination problems, while producing a high purity caustic alkali.
In the light of this situation, usefulness of a cation exchange membrane has been recognized recently as a separator in place of asbestos and various kinds of ion exchange membrane electrolytic cells are being developed. Most of the ion exchange membrane electrolytic cells supplied for the practical use are so-called filter press type electrolytic cells. The filter press type electrolytic cells, however, have numerous drawbacks as set forth below;

(1) Leakage of electrolyte solutions is apt to occur from the pressed portion of the membrane to the compartment frame.
(2) Titanium has to be used in greater amounts as an anolyte solution-resistant material of the compartment frame, thus resulting in an increase in cost of manufacture.
(3) To prevent leakage of electrolyte solutions, mechanical tolerance at the time of manufacture has to be made small, thereby increasing cost of manufacture.
(4) To every compartment frame, a supply inlet for an electrolyte solution and a removal outlet for an electrolysed liquor have to be provided and thus the assembly of the cell becomes complicated because of connecting the inlets and the outlets to outside pipe lines.

Under these circumstances, the present inventors have made an extensive series of study in an attempt to develop an electrolytic cell to which an ion exchange membrane, in particulary, is preferably provided as a separator, making use of advantages of the conventional separator electrolytic cells,and the present invention having been completed.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a vertical type separator electrolytic ceil which is less expensive in manufacture, permits substantially no leakage of electrolyte solutions and possesses high electrolytic efficiency.
It is another object of the present invention to provide a vertical type separator electrolytic cell which enables assembly or disassembly more feasibly.
It is a further object of the present invention to provide a vertical type separator electrolytic cell which improves passage of a catholyte solution as well as removal of a cathode gas evolved.
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 vertical type separator electrolytic cell comprising a box-shaped structure, a bottom plate and a cell top cover and providing in the box-shaped structure equipped with a cathode bus bar,

(1) cathode structure, positioned between a pair of opposite lateral walls of said box-shaped structure, which comprise a plurality of cathode electroconductors connected electrically to said cathode bus bur and cathodes positioned along at least one lateral surface of each cathode electroconductor by electroconductive ribs located across the horizontal axis of said cathode electroconductor and constituting independent vertical cathode working surfaces,
(2) anodes positioned between adjacent cathode structures, having vertical working surfaces parallel to said cathode working surfaces, and
(3) separators positioned between vertical working surfaces of said anodes and cathodes.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of a box-shaped structure including a cathode structure of an electrolytic cell illustrating a typical embodiment of the present invention.
Fig. 2 is a vertical sectional view taken in the direction of the arrows substantially along the line A-A of Fig. 1.
Fig. 3 is a vertical sectional view taken in the direction of the arrows substantially along the line B-B of Fig. 2.
Fig. 4-a, Fig. 4-b and Fig. 5 are partially omitted vertical sectional views and a top plan view of a conventional diaphragm electrolytic cell shown as a comparative example.
Fig. 6 is a partially cutaway perspective view illustrating a state that a separator was installed to a cathode structure.
Fig. 7 is a partially omitted vertical sectional view illustrating a cell assembled.

DETAILED DESCRIPTION OF THE INVENTION

In Fig. 1 to Fig. 3, to a side of a box-shaped structure (1) forming an outer wall of a cathode compartment, is a bus bar (2) located.
To inner walls of the side to which the cathode bus bar (2) is located, an end of a plurality of cathode electroconductors are respectively secured in parallel to one another by a suitable means such as welding, and connected electrically to the cathode bus bar (2), and the other end is also secured to an opposite inner wall in a similar fashion. To the cathode electroconductor (3), electroconductive ribs (4) are located across the horizontal axis of the cathode electroconductor, preferably vertical thereto. The electroconductive rib (4) has passage holes (9) for an electrolyte solution and a generated gas.
To the electroconductive ribs (4) are cathodes (5) positioned forming cathode working surface, the cathodes (5) constituting independent vertical cathode working surfaces along at least one side of each of the cathode electroconductors (3).
That is, when positioned to the outermost cathode electroconductor adjacent to the side wall of the box-shaped structure, a sheet of cathode is provided to the opposite side alone of the side wall, and when positioned to the intermediate cathode electroconductor two sheets of cathodes (5) (5) are provided independent of each other to and along the both sides of it.
Hence, a plurality of the cathode structures, each comprising a cathode electroconductor (3), electroconductive ribs (4) and cathodes (5) are thus provided parallel to one another at uniform intervals in the inside of the box-shaped structure (1). The box-shaped structure (1) is provided with a catholyte solution supply inlet (6), a catholyte electrolysed liquor. removal outlet (7) and a cathodic gas removal outlet (8).
_'Fig. 4-a, Fig. 4-b and Fig. 5 are vertical sectional views and a top plan view of a conventional, typical vertical type asbestos diaphragm electrolytic cell, i.e., a flattened tube type electrolytic cell (CHLORINE - Its Manufacture, Properties And Uses, at page 93, edited by J. S. Sconce, issued by REINHOLD PUBLISHING CORPORATION, NEW YORK, 1962). Fig. 4-a corresponds to Fig. 2 of the present invention and Fig. 4-b is a vertical sectional view taken in the direction of the arrows substantially along the line. C-C. As is evident from these drawings, in the conventional and known asbestos diaphragm electrolytic cell a cathode (5') is in the form of cylinder by being connected to an adjacent cathode (5) at the upper and the lower ends of its vertical working surface, otherwise a cathode (5") adjacent to the side wall of the cell is connected to the box-shaped structure (1'), thus forming a continuous inner wall comprising the cathode (5") in the inside of the side wall of the cell.
In contrast, in the electrolytic cell of the present invention illustrated in Fig. 1 to Fig. 3, a cathode (5) is substantially independent of an adjacent cathode and thus the periphery of the cathode (5) being net connected to the periphery of the adjacent cathode. Hence, the present electrolytic cell naturally possesses no inner walls of the box-shaped structure.
Here, what the cathodes are substantially independent of each other means that adjacent cathodes are not connected to each other at least full length of the one periphery and hence the connecting at a part of the periphery for the convenience of manufacture or for increasing the mechanical strength or the like is not departing from the scope of the present invention.
As the cathode material, there are preferably included soft steel, stainless steel, nickel and the like or those treated on their surface for reducing cathode overvoltage, which are resistant to electrolyte solutions. The cathode may preferably be in the form of a perforated plate such as a punching metal having numerous perforations, an expanded metal produced by making kerfs and then stretching so as to form a net, a knitted net of a linear metallic material. A flat plate may also be used which comprises only a portion acting substantially as a vertical cathode working surface, but it is practically preferred to provide an angled portion to the periphery of a flat plate to increase mechanical strength.
Between the cathode structures provided in the foregoing fashion in the inside of the box-shaped structure (1), the anodes are positioned respectively having vertical working surfaces in parallel to the vertical cathode working surfaces. These anodes are normally mounted on a bottom plate of the cell.
Fig. 6 is a partially cutaway perspective view illustrating a state that a separator was installed to a cathode structure.
In the figure, the upper and the lower horizontal surfaces of the cathode structure are covered with a pair of opposite upper and lower separator installation frames (10) having open portions over and under the anodes, a separator (11) formed in a cylindrical shape is positioned I substantially parallel to the cathode vertical surfaces and the end of the separator is located between a press plate (12) and an angled brim of the separator installation frame (10), then being fastened tightly by a securing means of bolts (13) with a gasket (not shown) inserted.
Meanwhile, a separator installation as described above only illustrates a typical embodiment and accordingly there may also be suitably available 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 set forth in Japanese Utility Model Application Nos. 178,714/1977, 107,197/1978, 57,341/1979 and 91,756/1979. Further, other securing means such as bonding and welding are also available.
Notwithstanding, when a cation exchange membrane is employed in particular as a separator, a mechanical securing means is superior to bonding or welding for the following reasons. That is, it is required to position a separator as tight as possible between cathodes and 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 a hologen 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 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 prolonged period of time. In such cases, when the membrane is installed by a mechanical means, slack and wrinkles can be easily removed by doing over again, thus operation being further continued without slack and wrinkles.
The separator installation frame (10) 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 the like. When an electroconductive material such as titanium is used, insulation has to be made between the cathodes (5) and the membrane installation frames.
As the separator used in the present invention, any sheet-like separator such as a cation exchange membrane and a microporous membrane may be employed, above all, the cation exchange membrane is more preferable. _Thecat- ion exchange membrane may preferably be made of a polymer having a fluorine-containing backbone with pendent cation exchange groups such as sulfonic acid groups, carboxylic acid groups and phosphoric acid groups, singly or in combination of two or more.
A cation exchange membrane, to one surface of which a porous anode is contacted and to the other surface of which a porous cathode is contacted by means of bonding or pressing, may also be available. In this case current collectors which are capable of pressing against the electrodes on the surfaces of the membrane are used in place of anodes and cathodes as aforesaid.
It is preferred to employ a cylindrically formed separator having circumferential length corresponding to that of an open portion of a separator installation frame. The cylindrically formed separator may be produced by joining the ends of one or two sheets of separator of a desired size by means of pressing, bonding, welding and the like, or may be processed directly at the time of preparing the separator.
As the 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. The anode is preferably constructed such that it contracts the thickness upon assembly of the cell to prevent the separator from being damaged, while expanding the thickness during the electrolysis to reduce a distance between the anode and the cathode.
Fig. 7 is a vertical sectional view of the present electrolytic cell assembled, which was described in detail earlier.
Anodes (14) are mounted substantially vertical on a bottom plate (15) with a gasket (16) interposed, separator installation frames (10)(10) are positioned, with gaskets (17)(18) interplaced, so as to cover upper and lower surfaces of a box-shaped structure (1), to which frames (10)(10) separators (11) are positioned to thereby separate cathode working surfaces from anode working surfaces. On the upper separator installation frame a cell top cover (20) is located with a gasket (19) interplaced, to which an anolyte solution supply inlet (21), an anolyte liquor removal outlet (22) and an anode gas removal outlet (23) are provided.
Hereinabove, an embodiment of the present invention was explained by referring to the accompanying drawings but it illustrates only one typical example and thus numerous modifications and applications are possible without being limited thereto.
The separator electrolytic cell of the present invention is drastically different from a conventional one, having such numerous advantages as stated below.

(1) The cathode structure of the present invention is fabricated such that a flat perforated cathode is just positioned to ribs located across a cathode electroconductor, not necessitating connection of adjacent perforated cathodes. Hence the cell is manufactured easily and the manufacture cost is reduced.
(2) The passage of a cathode electrolyte solution and a cathode gas generated is improved because there are no inner walls connecting the peripheries of the perforated cathodes.
(3) When the necessity of partially exchanging the cathode- structures takes place, it is accomplished without placing any influence on adjacent cathode structures, whereas in the conventional separator electrolytic cell it is impossible without damaging adjacent cathode structures.

As is apparent from the foregoing, the electrolytic cell of the present invention has numerous advantages that it does not have so many joints as a filter press type cell has, that the production quantity is greater per unit installation area, that efficiency per unit volume of the cell is greater, that an expensive material is not required for each part including cathodes and anodes, and that no strict mechanical tolerance is needed. In addition, the manufacture cost is exceedingly reduced. Furthermore, the assembly and disassembly are easy and simple, further sealing is also easy so that labor is 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 anode-cathode spacing, through which cell' voltage is lowered, maintains high current efficiency by keeping concentrations of anolyte and catholyte solutions uniform, but also achieves the scale-up of the cell with a decreased cost in maintenance as well as operation.

Claims

1. A vertical type separator electrolytic cell comprising a box-shaped structure, a bottom plate and a cell top cover and providing in the box-shaped structure equipped with a cathode bus bar,

(1) cathode structures,positioned between a pair of opposite lateral walls of said box-shaped structure, which comprise a plurality of cathode electroconductors connected electrically to said cathode bus bar and cathodes positioned along at least one lateral surface of each cathode electroconductor by electroconductive ribs located across the horizontal axis of said cathode electroconductor and constituting independent vertical cathode working surfaces,

(2) anodes positioned between adjacent cathode structures, having vertical working surfaces parallel to said cathode working surfaces, and

(3) separators positioned between vertical working surfaces of said anodes and cathodes.

2. The novel vertical type separator electrolytic cell of Claim 1, wherein the separators are positioned substantially parallel to the vertical cathode working surfaces between the opposite separator installation frames in such a shape as covering, at least, the upper and lower horizontal surfaces of the cathode structures leaving open portions over and under the anodes, and secured to the separator installation frames.

3. The novel vertical type separator electrolytic cell of Claim 2, wherein the separator is in the cylindrical form having the circumferential length equal to the inner circumference of the open portion.