FR2585372A1 - ELECTRODE FOR ELECTROLYSIS CELL - Google Patents

Abstract

THE INVENTION CONCERNS THE ELECTRODES USED IN ELECTROLYSIS CELLS. IT RELATES TO AN ELECTRODE 1 FORMED BY A PLATE HAVING RECTANGULAR OPENINGS 5 WHICH INCLUDE BRIDGES 6. THE CURRENT TRANSMITTED BY SIDE TERMINALS 7 CIRCULATES HORIZONTALLY, SO ALTHOUGH THE RESISTANCE OF THE ELECTRODE IS PRACTICALLY NOT HIGHER OF A SOLID PLATE. ALL THE BRIDGES 6 ARE TURNED ON THE OPPOSITE SIDE OF DIAPHRAGM 2 WHICH IS PRACTICALLY ADJACENT TO THE OTHER SIDE OF PLATE 4. APPLICATION OF SODIUM CHLORIDE BY ELECTROLYSIS.

Description

The present invention relates to an electrode of

  intended for use in an electrolysis operation

  both a diaphragm and in particular an electrode for an electrolytic cell in which an electrode is placed near a diaphragm, such as a membrane exchange

  ion, etc., and a gas can be released at the level of the

  trode. Recently, in the electrolysis industry which produces chlorine or sodium hydroxide by electrolysis of an aqueous solution of sodium chloride, the process

  an ion exchange membrane, in which the elec-

  trolysis is performed by disposing an electrode near a membrane, was found to form an electrolytic system

  excellent, reducing pollution and saving energy.

  An excellent electrode suitable for this type of process

is therefore desirable.

  During the electrolysis of an aqueous solution of sodium chloride, chlorine and hydrogen gas are released at the anode and at the cathode respectively and

  sodium hydroxide is formed in the cathodic compartment

  than. In this case, when the electrode is placed near the ion exchange membrane, a reduction of the electrolysis voltage can be envisaged, but the circulation of the electrolysis solution or the extraction of the released gas

poses problems.

  For this reason, up to now, a member has been used in the form of a perforated plate, for example expanded metal as shown in FIG.

  perforated as shown in Figure 7, etc., as elec -

  trode. Thus, published and unexamined Japanese Patent Application No. 114,571 / 77 published Japanese Utility Model No. 83,756 / 80 and Japanese Unexamined Published Application No. 185,786 / 83 describe the use of expanded metal. . In addition, Japanese Unexamined Published Application No. 146,884 / 81 discloses the use of a

  electrode in the form of a perforated plate, as anode.

  In the manufacture of expanded metal, cutouts are formed in the original plate and the plate is deployed by applying a tensile force in a direction perpendicular to the cutting line and, when forming a perforated metal , circular, square or other holes are perforated in the plate

  of origin, and one thus obtains a plate forming an elec-

  trode having the openings necessary for the extraction of

off gases or the like.

  On the other hand, in the case of

  In the case of a trode, the opening ratio of the effective surface of the plate constituting the electrode should generally be between 30 and 60% approximately. For this reason, in

  conventional electrodes, the volume of the conductor of the electri-

  trode has been reduced from the volume corresponding to the ratio of the openings by a value between 30 and 60 - with respect to the volume of the original plate. Thus, the resulting increase in the resistance of the conductor of the plate poses a problem because of the increase in

the electrolysis voltage.

  In addition, Japanese Unexamined Published Application No. 67,882 / 83 discloses an electrode of which

  the plate has a number of curved-punched openings

  born in the form of ribbons. However, as the openings

  Punched curves in the form of ribbons are placed alternately

  on both sides of the plate, even when electricity

  trode is adjacent to the diaphragm, there is always a fixed distance between the main plane of the plate and the diaphragm so that a problem is posed by a

  such increase in anode-cathode distance.

  As indicated previously, in the electrolysis process in the presence of a diaphragm in which gas is formed at the electrode, it has been impossible, with regard to conventional electrodes, to prevent an increase in the resistance. conductors given the presence of the openings formed in the plate, with arrangement of the electrode near the diaphragm, and further to obtain sufficient circulation of the solution

  electrolysis and proper extraction of the gas formed.

  As a result, the increase of the electrolysis voltage causes an increase in the cost of electrical energy and therefore poses a problem. The invention relates to the resolution of the previous problems posed by conventional methods, and relates to

  an excellent electrode that is useful in electro-

  lysis. The invention overcomes the aforementioned drawbacks by using an electrode whose structure is such that, on the surface of the electrode plate used in the electrolysis, a number of rectangular elongated openings substantially in the horizontal direction are formed, each opening having bridges and / or gutter-shaped members formed at the same time as

  the plate by extrusion or folding on the opposite side to the

  contact face with the diaphragm, the lateral ends

having power terminals.

  Other features and advantages of the invention

  will be better understood by reading the description

  which will follow examples of embodiment, made with reference to the accompanying drawings in which: Figures 1 and 3 show prospects of an electrolysis cell using an ion exchange membrane, by use of an electrode according to the invention; Figures 2a and 2b on the one hand and 4a and 4b on the other

  share respectively represent a plan view of an elec-

  trode according to the invention and an enlarged partial section, in the case of the plates of Figures 1.and 3 respectively; Figures 5a to 5c are enlarged partial sections of an electrode according to the invention; Figure 6 is a schematic perspective of a conventional electrode made of expanded metal; and

  FIG. 7 is a diagrammatic elevation representing

  both a conventional electrode formed of perforated metal.

  FIG. 1 represents an exemplary implementation of the invention in which the electrode 1 according to the invention, used as anode, is placed near a diaphragm 2

  which may be an ion exchange membrane or the like.

  A cathode 3 is placed on the other side of the diaphragm, so that an elementary electrolysis cell is made and allows the implementation of an electrolysis using an ion exchange membrane. The anode 1 has a number of openings 5 of rectangular shape, on the plate 4, these openings having bridges 6 each corresponding to an opening 5 and formed with the plate 4 by extrusion in the opposite direction to that of the surface of contact with the diaphragm 2. Each opening and each trigger guard can be easily formed using cutouts made with

  two parallel knives, on the plate 4, and by extrusion.

  This operation requires a certain plasticity as well as a certain ductility of the material used. As the metals usually used as plate forming an anode or a cathode have these properties, for example metals for rectifiers such as titanium, tantalum, etc., iron, nickel and their alloys, any of these materials. can be used according to the invention. Rectangular openings are preferable because they facilitate the circulation of the electrolysis solution and the evolution of the gas created, the length preferably being

  horizontal, but a certain inclination is not harmful.

  The size and arrangement of the openings can be determined appropriately according to the quality and size

  the material of the plate as well as from the report required

  opening, and there are no particular restrictions

  culière. In the case of the electrolysis of sodium chloride by the process using an ion exchange membrane, as represented in FIG. 2b, the thickness t of the titanium plate 4 is usually between 0, About 5 and 2 mm, the longitudinal dimension a is between about 1.5 and 5 mm, the lateral dimension b is between about 5 and 100 mm, and the extrusion height c of the bridge 6 is greater than 1 mm. It is preferable that a number of openings 5 be disposed of

  the ratio of the openings in the effective surface

  electrode, which is between 30 and 60%.

  In addition, it is generally preferable for the longitudinal dimension to have an opening 5 greater than

  to the thickness t of the plate 4 and that the height c of extru-

  or stamping is greater than twice the thickness

  ture, so that the gas bubbles released can easily

  pass through the openings towards the rear face in the opposite direction to the contact surface with the membrane. The configuration of the bridge 6 corresponding to the openings 5 can be suitably determined from the thickness t, the longitudinal dimension a, the lateral dimension b, the extrusion height c and the ductility of the material, but as indicated by the reference 6 in Figures 1 and 2b, the bridge 6 usually has a trapezoidal shape in horizontal section, the largest part being parallel to the plate, and being connected to a base portion 8 of the bridge 6. When the lateral dimension b of the opening is weak, close to the edges or the like as indicated by the reference 6 'in FIG.

  have a shape of half-circle or half-ellipse.

  FIG. 3 represents another example of an electrode according to the invention; the electrode 1 acting as an anode is placed near the diaphragm 2, for example an ion exchange membrane, etc. One cathode 3 is placed on the other

  side of this diaphragm, and an elementary cell of electro-

  lysis by the ion exchange membrane method is thus performed. The anode electrode 1 has a number of

  pairs of openings 5 of rectangular shape, in the plate.

  Each pair of openings has a pair of gutter-shaped members 16 made with the plate 4 by folding on the opposite side to the contact surface with the diaphragm 2. Each opening 5 and the gutter can be easily formed by cutouts made with two parallel knives in the plate 4, then by folding the plate 4. In the

  rectangular shaped openings facilitating the circulation of

  the electrolysis solution and the evolution of the gas, it is preferable that the length be horizontal,

  but a certain inclination is not harmful. The size

  The arrangement and arrangement of the openings can be suitably determined according to the quality and size of the plate material and the required ratio.

  of opening, and no special restrictions apply.

  In the case of the electrolysis of sodium chloride using an ion exchange membrane, the thickness t, as indicated in FIG. 4b, of a titanium plate 4 is between approximately 0.degree. , 5 and 2 mm, the longitudinal dimension a is between about 1.5 and 5 mm, the lateral dimension b is between about 5 and 100 mm, and the bending angle of the gutter is between about 16 and more. It is preferable for a number of openings to be arranged in such a way that the ratio of openings in the effective area is between about

and 60%.

  In addition, it is generally preferable for the longitudinal dimension of the opening 5 to be greater than the thickness t of the plate so that the released gas bubbles can easily pass through the openings towards the rear face, on the opposite side to the the contact area

  with the membrane. The configuration of the gutter 16 corres-

  5 at the opening can be determined conveniently from the thickness t, the longitudinal dimension a, the lateral dimension b, the bending angle and the ductility of the material. However, as shown in Figures 3, 4a, 4b, 5a, 5b and 5c, it is usually preferable that the bending angle of the channel 16 and the plate 4 be between 30 and 45 C or more. The sectional shape of the channel 16 formed with the plate 4 may be in

  U or in the form of a semicircle, with a folding angle of about

  90 as shown in FIG. 5a, or with a confi-

  guring corresponding to an angle greater than about 90 "as shown in Figure 5b, the configuration may also correspond to a folding at an angle less than about 90 as shown in Figure 5c; other configurations are possible. Figures 3,

  4a and 4b indicate that the gutter 16 corresponding to the

  The opening 15 was cut along a length at both ends in the direction perpendicular to the electrode 4. However, depending on the ductility of the plate metal, the opening and the channel 16 can be formed by folding after cutting only. in the horizontal direction

and not in the vertical direction.

  In addition, as shown in Figures 2a, 2b,

  4a and 4b, it is preferable that a certain number of

  5 is arranged so that the adjacent openings are offset alternately by a distance d so that the gas evolved can easily escape. In this case, the offset can be advantageously determined from

  so that the distance d is between 0 and b.

  As in the case of conventional electrodes, the electrodes according to the invention can be manufactured by

  application of an active anodic or cathodic coating

  on the surface of the plate 4 at least which must be turned towards the membrane. The active coating may be applied before or after formation of the openings of the plate 4 by extrusion or stamping, or by folding. In addition, the circulation of the electrolyte solution and the outlet of the evolved gas can be further improved by forming a large number of vertical grooves at least on the surface of the plate 4 which must be in contact with the membrane,

  as disclosed in Japanese Patent Publication No. 38,432 / 80.

  In the electrode according to the invention, when the elec-

  trolysis is carried out by incorporation of the electrode to an electrolysis cell as shown in FIGS. 1 and 3, a plurality of supply terminals 7 are placed on the edges of the plate 4, laterally, so that

  that an electric current is transmitted laterally paral-

  same as the length of the bridge 6 or gutter 16 and this is advantageous for reducing the voltage increase due to the ohmic losses of the conductor forming the electrode. In the electrode according to the invention, the opening

  necessary for the electrode, in plate 4 (the ratio of

  usually between about 30 and 60%) can be obtained by producing a large number of the aforementioned openings of rectangular shape, so that the circulation of the electrolysis solution and the escape of the evolved gas are very regular. In addition, since the trigger guard 6 or the gutter 16 corresponding to each opening 5 is formed at the same time as the plate 4 by extrusion, stamping or bending, the original plate remains as it is without any loss of any part of the conductor or disappearance. one of his functions. So, although,

  in the case of the use of perforated metal (as

  7) or expanded metal (as shown in FIG.

  6), of the conventional type, the conductive part

  electrode is reduced from the portion removed from the original plate or the portion forming the openings in the plate and causes an increase in the resistance of the conductor, such an increase does not appear in the electrode according to the invention. In addition, in the electrode according to the invention, as several power supply terminals 7 are placed on the edges of the plate 4, laterally, so that an electric current is transmitted laterally, the electric current flows parallel to the bridge 6 or to the gutters 16 and the driver does not suffer effects

  due to folding following the cutting of the openings

  tures. Simultaneously, the electric current is distributed

  evenly on the surface of the plate.

  In addition, since the bridge 6 and the gutter are formed by extrusion, stamping or bending the side opposite to the contact surface of the electrode 4 with the diaphragm, the main working surface of the electrode can be

  placed close enough to the diaphragm to be

  tact. In the examples according to the invention and in the comparative examples illustrating the prior art, as indicated below, the electrodes are prepared in the following manner, and the tests are carried out in the form of

  of an anode in an electrolysis employing a mem-

  ion exchange brane. In all the electrodes, having

  a metal substrate made of titanium, a coating containing

  the oxide of the same precious metal obtained by an opera-

  thermal decomposition, was applied to the surface

  intended to be in contact with the diaphragm.

EXAMPLE 1

  An electrode whose plate had an effective surface of 30 cm x 25 cm and a thickness t equal to 1 mm, each opening had a longitudinal dimension a = 3 mm, a lateral dimension b = 45 mm, a height c of extrusion of 3 mm bridge and an opening ratio of about 40%,

with d = 0 (trigger guard).

EXAMPLE 2

  The electrode of Example 1, which also had a number of grooves of 0.5 mm wide and 0.3 mm deep, with a pitch of 1 mm in a vertical direction over the entire surface, was placed in contact with the diaphragm

(bridge equipped with throats).

EXAMPLE 3

  An electrode whose plate had a surface

  effective of 30 cm (width) x 25 cm (height) and thick

  t = 1 mm, was such that each opening had a longitudinal dimension a = 2 mm, a lateral dimension b = 45 mm, a gutter bend angle of 90 and a

  opening ratio of about 40% (gutter).

EXAMPLE 4

  The electrode of Example 3 also had a number of

  number of grooves 0.5 mm wide, 0.3 mm deep

  with a pitch of 1 mm, in the vertical direction over

  the surface intended to be in contact with the diaphragm (

with throat).

COMPARATIVE EXAMPLE 1

  The plate was 1 mm thick.

COMPARATIVE EXAMPLE 2

  The electrode was formed of expanded metal having an aperture ratio of about 35% having a length of 8 mm and a width of 3.6 mm, with a slit thickness of 1.2 mm and a thickness of 1 mm.

COMPARATIVE EXAMPLE 3

  The plate was made of thick perforated metal

  1 mm, having circular holes 2 mm in diameter, with a pitch of 3 mm, the opening ratio being approximately

40%.

  Tests were carried out under the following conditions, with each of these electrodes constituting an anode. In all the examples, an electric current

  was transmitted to the anode in the lateral direction.

  Anodic solution: aqueous solution of NaCl at 200 g / l Cathodic solution aqueous solution of NaOH at 35% by weight Cathode nickel deployed

  Diaphragm: ion exchange membrane (manufacture

by E.I. of the Pont de Nemours

and Co., under the brand name of

  than "Nafion" 902) Anode-cathode distance 2 mm

Electricity temperature

  trolysis: 90 C Current density 30 A / dm2 The results of the tests carried out are shown in the following table

BOARD

N Anode Obhmic Loss Voltage

in the electrolytic

  * 1) (mV) tick (V) Example 1 bridge 56 3.44 Example 2 throat bridge 78 3.46 Example 3 gutter 56 3.45 Example 4 groove trench 78 3.47

Example campa-

ratif 1 plate 56 - * 2)

Example caTapa-

ratif 2 expanded metal 108 3.53

Example ccapa-

  ratif 3 perforated metal 146 3.52 * 1) The ohmic losses of the conductor Vw were obtained by using the following equation V = i p22 / 3 t (V) w o

  in which i denotes the current density of elec-

  o trolysis (A / dm2), p denotes the specific resistance of the conductor (in S. cm), t denotes the electrically charged distance (in cm), and t denotes the thickness of the

the driver's plate (in cm).

  * 2) Electrolysis is impossible because the plate is not

perforated.

  As is clear from the results of the

  table, when using the electrode according to the invention

  the voltage corresponding to the ohmic loss of the

  is as low as that of a non-perforated plate and about half the losses of conventional expanded metal and perforated metal for the same thickness and

  the same opening report, so that the elec-

  trolysis can be reduced from 50 to 100 mV per use

of the electrode according to the invention.

  As described above, the electrode according to the invention

  vention has excellent characteristics as an electrode

  gas clearance near the diaphragm because not only

  the circulation of the electrolysis solution and the extrac-

  of the gas formed are very efficient but the electrolysis voltage can be reduced, so that the invention

  has a great industrial utility.

  Of course, various modifications can

  be brought by those skilled in the art to the electrodes which come

  to be described only as nonlimited examples.

  without departing from the scope of the invention.

Claims (5)

  1. Electrode for electrolysis, characterized   characterized in that it comprises, on a plate, a number of openings (5) of rectangular shape elongate substantially in the horizontal direction, each opening having a corresponding member in the form of a bridge (6), a gutter (16) or a bridge and a gutter, formed with the plate either by extrusion or stamping, or by folding on the opposite side to the surface to be in contact with a diaphragm, several terminals (7) of feeding being   placed on the edges of the plate, laterally.   2. Electrode according to claim 1, characterized in that the opening ratio of the effective surface of   the plate is between about 30- and 60%.   3. Electrode according to claim 1, characterized   in that the dimensions of the rectangular openings (5) are a length of about 1.5 to 5 mm, a width of about 5 to 100 mm, and   a plate thickness of between 0.5 and 2 mm approximately.   4. Electrode according to claim 1, characterized in that vertical grooves are formed at least on the surface of the plate which is intended to be in contact with the diaphragm. 5. Electrode according to claim 1, characterized in that the electrode carries an active coating at least on the surface of the plate which is intended to be in contact. of the diaphragm.