SE9600044A0 - Electrode - Google Patents

Abstract

ABSTRACT In electrolytic processes where use is made of an electrode, the electric current is in many cases a predominant item of expenditure. When production is carried out in for instance a diaphragm cell, the cathode is coated with a diaphragm. In time, if the surface of the cathode is mechanically yieldable (e.g. a mesh), it will be pressed-in and a concave surface is formed. Thus, the distance to the facing anode, over the cathode surface will be varying. Consequently, the result will be formation of oxygen due to an uneven distribution of pressure, higher voltage and energy consumption. The present invention solves the above problem by providing an electrode, where the surface of the electrode is fitted with at least one through cut, a method of producing an electrode, an electrolytic cell comprising an anode and a cathode according to the invention, and the use of such an electrode in electrolysis. The present invention constitutes a flexible electrode, more capable of allowing movement and to follow uneven surfaces of a diaphragm or membrane.

Description

BILAGOR !ff1 Beskrivning, patentkrav och sammandrag i ire exemplar i in3rimingar i 3 exemplar 1 0 overlatelsehandrng jJ Fullmakt AVGIFT iGrundavgift: 1(.1.1'kronor 1 . 600 g Tilliggsavgift, MO kr for vane patentkrav utover no; 3 0 Okr Avgift for kopior ay nyhetsbinvisning 0 Diariebevis. 15 kronor Stpq.Opml,janu On, datumPer ma 1996 UndersknftZaid Schold ci C.

No 7 4 2 5,14.

Betalningssitt: 0 postgiroEl checkU kontant POstinVesABesbksacnessI eleto,,1 Es,et —1t,fl.7Ii2iflfl1 ORC.I.?PA7 ORE Ci56 84 -41 1 Electrode The present invention relates to an electrode, where the surface of the electrode is fitted with at least one through cut, a method of producing an electrode, an electrolytic cell 5 comprising an anode and a cathode according to the invention, and the use of such an electrode in electrolysis.

In electrolytic processes, the electric power is in many cases a predominant item of expenditure, and therefore a reduction of every unnecessary resistance in the electrolytic 10 cell is desired. For example, the distance between the anode and the cathode should be as short as possible, without interfering with the flow of the electrolyte.

In many processes gas develops, which means that accumulation of gas bubbles between the anode and the cathode 15 must be prevented so as not to increase the cell resistance. In for instance the production of chlorine and alkali, chlorine gas forms at the anode, and to be able to fully utilise the front side of the anode for the electrolysis, the electrolyte should be able to flow freely along the anode 20 surface.

When production is carried out in a diaphragm cell, the cathode is normally coated with a diaphragm. The diaphragm material may for instance essentially consist of asbestos and the cathode can be a mesh, a perforated sheet or the similar. 25 The diaphragm is evenly applied on the surface of the cathode, which usually is a mechanically yieldable mesh-cathode. In time, the surface of the cathode will be pressed-in, forming a concave surface. Thus, the distance to the facing anode, over the cathode surface will be varying. Also the diaphragm 30 surface facing the anode is often rough or uneven. Consequently, the result will be an increasing formation of oxygen due to an uneven distribution of the pressure in the cell, higher voltage and energy consumption. At the same time in a membrane cell, the membrane is pressed against the anode 35 surface. If the surface is rough and uneven, the energy consumption will be higher due to the varying distances.

These problems are difficult to solve, since available membranes and diaphragms are mechanically yieldable, at the same time as they are most fragile and easily damaged when • •• : • ••• : • • : • • • • ••• .. ••• • • • ••• • • • • • :• • • •••• • ••• • e• 2 subjected to mechanical stress.

US-A-3674676 discloses an expandable electrode, particularly an anode for use in a diaphragm-type electrolytic cell for the production of chlorine and caustic. The anode surface 5 can be provided with a slight gap in the centre of the anode. The present invention aims at solving the mentioned problem by providing an electrode for electrolysis, where the surface of the electrode is provided with at least one through cut forming an angle with the horizontal plane which is less 10 than 90°.

The invention also provides a method of producing an electrode, an electrolytic cell comprising an anode and a cathode according to the invention, and the use of such an electrode in electrolysis.

The present invention constitutes a flexible electrode, more capable of allowing movement and to follow uneven surfaces of a diaphragm or membrane. With the use of a flexible electrode according to the present invention, the result will be decreasing formation of oxygen due to an even 20 distribution of the pressure in the cell, lower voltage and energy consumption.

The electrode surface is fitted with at least one through cut, thus dividing the surface in at least two electrode segments, preferably with substantially equally 25 large area. The surface is suitably divided in several segments by several through cuts, the cuts being substantially horizontal as well as substantially vertical. Preferably the surface is divided in six or more segments, substantially of an equally large area, by at least three cuts (i.e. at least 30 two horizontal cuts and one central vertical cut, or two vertical cuts and one horizontal cut).

The width of the cut, i.e. the distance between the segments, can be large enough in order to let the segments move properly relative each other. The upper limit is not 35 critical, but restricted due to decreasing inefficiency of the electrode with increasing width. Normally the width would be less than about 100 mm and over about 0.1 mm. Suitably the width is at least about 0.5 mm, preferably at least about 1 mm, and most preferably at least about 2 mm. The distance -6 0—• —• • S• ■■ • e• • •• • 411. • • • ••• ••• • • • • • • II • • • • ••• • : : ••• ••• •• •• •••• ••• • •••• 3 •• • • * • • • • • :• ••• :• ••• • • • • • i• • ••• 0• • • •• •••• • • • • • • ••• ••11 • • • • between the segments is preferably the same as the width of the cutting tool, e.g. the width of the water jet when a water cutting method is used.

The angle of the horizontal through cut on the surface 5 should be forming an angle with the horizontal plane less than 90°. Suitably the angle formed with the horizontal plane is in the range between about 0° up to about 45°, most preferably in the range between about 00 up to about 20° and particularly most preferably it is a substantially horizontal through cut 10 in the range between about 00 up to about 5°. It is preferred to have the substantially horizontal cut as close to the horizontal plane as possible. The electrode surface can be provided with a plurality of horizontal through cuts, preferably at least two through cuts per electrode surface.

The preferred vertical through cut should preferably be forming an angle with the vertical plane less than about 45°. Preferably the angle formed with the vertical plane is in the range between about 0° up to about 20° and most preferably a substantially vertical through cut in the range between about 20 0° up to about 5°. The electrode surface can be provided with a plurality of vertical through cuts, suitably at least one central vertical throulll --- and preferably two vertical through cuts.

The electrode surface is suitably fitted with the 26 vertical respectively the horizontal through cut over the hole width or length of the surface.

The internal extender in the anode may also be provided with the thrpuah cuts. At least a part of the extender arm, or all the way through to the conductive bar, Is preferably 30 provided with the through cuts. Similarly, the additional pressing means, according to one embodiment of the invention, may also be provided with the through cuts.

Expandable anodes are known as such. They are usually fitted with two opposite electrode surfaces, which constitutes 35 a box shaped anode. The internal of the anode comprises expandable means, i.e. an extender and suitably additional pressing means, which forces the electrode surfaces apart from each other and against an opposed cathode, and an intermediate diaphragm or membrane. In installation, use is suitably made ".."• •• • • • •• • • • • •••••: : i•• •• •• • •••••• ••••••• • ••• ••• 4 of clamping means connected to the respective ends of the extender, positioned to hold the electrode in a contracted position. After installation in the cell, the clamping means may be removed causing the electrode to assume an expanded 5 position.

Additional pressing means may also be placed inside the extender of the anode, or at the outermost parts inside the expandable box. The pressing means can have the cross sectional sh,re of, for instance, the capital letter of C or of 10 an omega, and extends preferably along the whole length of the electrode. An omega shape is preferred, due to the larger spring-tension and it also constitute a good "downcomer", i.e. a circulation conduit for the electrolyte internally of the electrode. Therefore, the main part of the preferably used 15 omega-shaped pressing means is suitably situated outside the end parts of the extender, as can be seen in fig. 1-3 and 6. Such a pressing device can be cut through at the same moment as when the electrode surfaces are provided with through cuts, and at the corresponding spots. The pressing means may also 20 constitute of a spring of conventional shape and function.

The cathode construction is also known as such, to those skilled in the art. The cathode has usually the shape of a box or a cage, provided with an internal support construction and wrapped in a mesh, a net, a gauze, a grid, a perforated sheet 25 or the similar.

In order to make the electrode construction with the segmented surfaces more riaid, the segments can be connected and fitted together by connecting means. Use is suitably made of a strip, a thread, a wire, a plate, a sheet or other b• 30 suitable connecting means, preferably use is made of metal and suitably of the same material as the electrode. The connecting means are in its shape suitably substantially perpendicular near the ends, in order to be able to allow a proper movement of the electrode surfaces and to ccnnect the ends of the 35 connecting means to the respective segment, for example by welding. The connecting means are therefore suitably bent near the ends, in for instance a shape of a semi circle. At least one connecting means is used or connecting to divided segments. However, a plurality of connecting means may be used ee • o fo•• ••• ••• • **:•••: i". • 0.O.04• • .0 SOSO ::•• ate .00 S when joining two segments.

The anode and cathode surfaces are preferably of the open structure type, thus provided with a net, a gauze, a grid or a perforated metal sheet, in order to let gas and electro5 lyte pass through the open structure. The surface may also comprise of a mesh of threads, woven or none-woven, where the threads forming the mesh have been welded to each other. The metal sheet has a preferred thickness in the range of about 0.5 mm up to about 5 mm, suitably from about 1 mm up to about 10 3 mm. Suitably, use is suitably made of channel-forming threads in accordance with the electrode described in EP-A0533237 (i.e. a none-woven mesh), having a thickness of from about 0.05 to about 3 mm, preferably from about 0.2 to about 1.5 mm, and most preferably from about 0.5 to about 1.0 mm.

The distance between the threads is suitably from about 0.1.d to about 4.d, preferably from about 0..d to about 2.d, d being the thread thickness. The distance is measured as the shortest distance between two threads. The formed square, rhombic or diamondshaped openings can have diagonals in the 20 range of 0.5 up to 5 mm.

The entire anode or cathode, i.e. both the threads and the underlying structure, is suitably made of the same material, for example Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Ag, Pt, Ta, Pb, Al or alloys thereof. Ti or Ti alloys are pre- 25 ferred. It is also preferred that both the threads and the underlying structure are activated by some suitable, catalytically active material. Also electrodes in which the threads only are activated may be used. Useful catalytic materials are metals, metal oxides or mixtures thereof from Group 8B in the 30 Periodic Table, i.e. Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, or Pt, among which Ir and Ru are especially preferred. Examples of suitable anodes are dimensionally stable anodes sold by Permascand AB of Sweden, e.g. DSA' and DSA-02.

The present invention also relates to a method of 35 producing an electrode comprising one or more through cuts in the electrode surface, wherein one or more cuts can be applied by water cutting. The use of water cutting is advantageous thanks to the slight effect on the material properties of the electrode due to no heat distribution. In water cutting, the : •• • ••• • Oa. • • • 0 :**•: •• • •• • • •• •• • :*** • • •• •• • : • •• • : • • : • : •• : ••• 6 water jet is suitably directed at an angle formed substantially perpendicular to the electrode surface.

The through cuts in the electrode surface can also be applied by other methods, such as by laser cutting or by the 5 use of an angle cutting machine.

The width of the cut, e.g. the width of the water jet when a water cutting method is used, is preferably in the range of about 0.5 up to about 5 mm, suitably about 1 up to about 3 mm, and most preferably about 1.5 up to 2.5 mm.

The electrode of the present invention is especially suitable for a diaphragm process. The diaphragm used can be an asbestos diaphragm, suitably mixed with polymers such as polytetrafluoroethylene. The diaphragm used may also be a polymer diaphragm, suitably based on polytetrafluoroethylene, 15 or preferably a polymer diaphragm reinforced or mixed with fibres of zirconium (Polyramix') or other suitable replaceable materials for asbestos.

If electrolysis is carried out with membranes or membrane-bags, they can be of conventional design.

Furthermore, the invention also relates to an electro- lytic cell comprising at least one expandable anode and a cathode according to the invention. Preferably it also comprises a diaphragm, a membrane-bag or a membrane arranged between the anode and the cathode. The anodes and cathodes are 25 preferably interleaved. If the cell is intended for electro- lysis of alkali metal chloride solution in order to produce chlorine gas and alkali, the anode may be an expandable electrode with an open structure, preferably a mesh or a perforated metal sheet electrode fitted with an additional mesh, more 30 close-meshed, while the cathode can be a mesh type of elec- trode. Most preferably the cell is included in a diaphragm cell, e.g. of "Hooker-Uhde"-type or "MDC"-type. Besides, the cell can be designed according to conventional techniques, well known to those skilled in the art.

The electrode above is especially suitable for electro- lysis in diaphragm cells, i.e. electrolytic cells where the anode chamber and the cathode chamber are separated by a diaphragm. The electrode is particularly advantageous in electrolytic production of chlorine and alkali in diaphragm 7 cells, but is also very useful in electrochemical recovery of metals or recovery of gases from diluted solutions.

One embodiment of the invention will now be described in more detail with reference to the accompanying drawings. 5 However, the invention is not restricted to the embodiments illustrated, but many other variants are feasible within the scope of the claims.

Fig. 1 is a slanted side view illustrating an expandable anode, while fig. 2 is a cross sectional view of the anode in 10 fig. 1 along the line A-A. Fig. 3 is the slanted side view of the anode in fig 1. where a part of the front facing surface has been removed along line B-B in fig. 2. Fig. 4 illustrates the expandable anode in expanded form and its relation to the opposed cathodes. Fig. 5 shows a meshed electrode surface 15 divided in segments and provided with connecting means. Fig. 6 is a cross sectional view of an expandable anode. Fig. 7 illustrates an additional pressing means. Fig. 8 A-C shows examples of embodiments of the connecting means (12) shown in figures 5 and 6. Fig. 9 illustrates a cathode.

Fig. 1 and 2 illustrate an expandable anode (1) compris- ing electn ie surfaces (2) with an open structure, internal extenders (3) with arms (4) extending along the electrode surfaces and in electrical contact with the electrode surface at least at one spot, the extenders being secured and in 25 electrical contact with the conductive bar (5). The open structure of the electrode surface may be made of a grid, a mesh, a net, a gauze or a perforated sheet, and preferably provided with a further mesh, more close-meshed (6). The surface is provided with through cuts (7;8) in the electrode 30 surface, horizontal (7) as well as vertical (8) cuts. Additional pressing means (9) can also be placed in the extender.

Fig. 3 shows the inside and the internal parts of the anode. As evident from the figure, the through cuts (7;8) in the electrode surface may also cut through the extender arm (4) and the additional p71-essing means (9).

Fig, 4 illustrates the expandable anode (1) in expanded form and in electrical contact with the conductive bar (5). The outer surfaces of the anode are in close vicinity with the surfaces (11) of the opposed cathodes (10). Between the anode P. G. •• • • It • • •• • •• • •• • 4• •• •••• 41. • •• • • • • • 111•• •• • • • • • • : .0. • •• • •• • • •• • • • •• •• • 8 and the cathode surface, applied on the cathode surface, a diaphragm is usually situated (not shown here).

Fig. 5 shows a meshed electrode surface divided in segments by horizontal (7) as well as vertical (8) through 5 cuts. The segments are connected to each other by connecting means (12), suitably connected at their ends to each segment. Fig. 6 shows in a cross sectional view an expandable anode additional pressing means (9) and connecting means (12). Fig. 7 illustrates an additional pressing means (9), 10 aimed at being placed in an extender in the internal of the expandable anode as shown in figures 1-3 and 6. The pressing device, here in form of an omega, may also be provided with through cuts (7), at the same spots and in correspondence with the through cuts of the surface of the anode.

Fig. 8A shows the connecting device (12) in the form of a strip. Fig. 8B illustrates the connecting device as a strip with folded ends, the ends being folded essentially in perpendicular direction. Fig. 8C shows in another mode a semicircular design of the connecting device.

Fig. 9 illustrates a cathode (10), here provided with a suitably open structure in form of a mesh, a support structure (13) internal of the cathode and a horizontal through cut (7).

••• • ••• • • • •• • •• • •• • • •• •••• :••• V ••II 11 • • ••• ••• • • • • • • • : • :•• II : • •• • •• • • •• • • •••• ••11. 9 0 • • • .. • • • • • 6,11" • ••• • •••• •• • • ••• ••• • •••• ••• • ••• • • ••• ••• 11 • 11 ABSTRACT In electrolytic processes where use is made of an electrode, the electric current is in many cases a predominant item of expenditure. When production is carried out in for 5 instance a diaphragm cell, the cathode is coated with a diaphragm. In time, if the surface of the cathode is mechanically yieldable (e.g. a mesh), it will be pressed-in and a concave surface is formed. Thus, the distance to the facing anode, over the cathode surface will be varying. Consequently, 10 the result will be formation of oxygen due to an uneven distribution of pressure, higher voltage and energy consumption. The present invention solves the above problem by providing an electrode, where the surface of the electrode is fitted with at least one through cut, a method of producing an 15 electrode, an electrolytic cell comprising an anode and a cathode according to the invention, and the use of such an electrode in electrolysis. The present invention constitutes a flexible electrode, more capable of allowing movement and to follow uneven surfaces of a diaphragm or membrane. • •• • ••• • ••• •• 0 ••• • ••• •• • • • •• • • • •• • • • •• • • • ••• • • • •• to • • e••• • i( 4: it• ••■•• •••• •••••: • • ■• iI (Ikl,:„;:r.,,....;‘1..;•...-,c■t \ . ,A,‘Atk1 i.:,; '!,...,' y ,\!kli,y;.1\fy \!,11.0;KI:k!':!'1,":"c/.:.,Lt.:4f,i;),i.(y.A,ty'''IA ...!!! .1:',,c!, -\,':' '',/j\,,`..,/\;\j!l',ik,,',.'.A;‘1(22.4):!,A0iLl■• . k A ,, 1, •i Cr-,'.,.:011,i1.4,c1;y.fil 9Y,4i1.1;vc IA,A k 1.4 . 4...,. ; '' ..•,' ‘,, t: , ,., ■ '.; .; .1,\ i.t.,■.vh„, A / \I \ r,../ ,11,/ v\y,, \ AA , v , .,,./A /A.,”A AA A ,'k 11% rs...",/‘:,/ \if \ 1!;,i ' \ i 'Li 1 Al ,11, \ is',./',. ‘,...

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Claims (13)

CLAIMS 1. An electrode (1;10) for electrolysis,characterised in that the surface (2;11) of the electrode is provided with at least one through cut (7;8), forming an angle 5 with the horizontal plane which is less than 900. 2. An electrode according to claim 1,characterised in that the electrode is an anode (1) of the expandable type, the surfaces (2) of the anode are attached to an internal extender (3) which is in electrical contact and secured to a conducting bar (5). 3. An anode according to claim 2,characteri se d in that the internal extender of the anode is provided with at least one through cut (7;8). 4. An anode according to claim 2 or 3,characte15 rised in that the internal extender of the anode is provided with additional pressing means (9) in the shape of an omega. 5. An electrode according to claim 1,characte rised in that the electrode isacathode (10). 6. An anode or a cathode according to claim 2 or 5, characterised in that the surfaces of the anode respective tne cathode, are provided with at least one through cut (7) forming an angle with the horizontal plane in the range between about 00 up to about 45°, and at least a through cut (8) forming an angle with the vertical plane less than about 45°. 6. An electrode according to claim 1, charac- terisedin that the electrode is provided with a diaphragm. 7. An anode or a cathode according to any of the preceding claims, characterised in that the surfaces (2;11) are of the open structure type, provided with a mesh, a gauze, a net, a grid or a perforated metal sheet. 8. An electrode according to claim 1 or 6,chara c- terised in that the through cut (7) forming an angle with the horizontal plane, is substantially horizontal. 9. An electrode according to claim 6, chara cterised in that the through cut (8) forming an angle with the vertical plane, is substantially vertical. ••• 1. • 2. 4 II 1• 3. •• •• • 41, • lb* • • • •• I •••• • 4. • ••• 5. • ••• 6. • 7. • • ••• • • 8. • • ••• • : : •• • ••■ • •• • : : •• : • • • • •• • to, 10 10. An electrolytic cell,characterised in that the surfaces of the anode and/or the cathode are provided with at least one through cut (7;8) forming an angle with the horizontal plane less than 90°, according to any one of claims 1-9. 11. An electrolytic cell according to claim 10, c h a - racterised in that the cell is provided with a diaphragm. 12. Method of producing an electrode, char ac t e r- ised in that the surfaces are provided with at least one through cut forming an angle with the horizontal plane less than 90°, where the cuts are applied by water cutting. 13. Method in electrolysis, characterised in that uce is made of an electrode according to any one of 15 claims 1-9. • • *• 1. • 2. • 3. 11I * • 4. Ill* • I • •• • I • 511. :" t: ":: • : :• : • 1. I • ••• •• "41 •• ••• 11 ABSTRACT In electrolytic processes where use is made of an electrode, the electric current is in many cases a predominant item of expenditure. When production is carried out in for instance a diaphragm cell, the cathode is coated with a diaphragm. In time, if the surface of the cathode is mechanically yieldable (e.g. a mesh), it will be pressed-in and a concave surface is formed. Thus, the distance to the facing anode, over the cathode surface will be varying. Consequently, the result will be formation of oxygen due to an uneven distribution of pressure, higher voltage and energy consumption. The present invention solves the above problem by providing an electrode, where the surface of the electrode is fitted with at least one through cut, a method of producing an electrode, an electrolytic cell comprising an anode and a cathode according to the invention, and the use of such an electrode in electrolysis. 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