GB2180556A

GB2180556A - Apertured electrode for electrolysis

Info

Publication number: GB2180556A
Application number: GB08618262A
Authority: GB
Inventors: Takayuki Shimamune; Shuji Nakamatsu; Yoshinori Nishiki; Tsuneto Furuta
Original assignee: Permelec Electrode Ltd
Current assignee: De Nora Permelec Ltd
Priority date: 1985-07-29
Filing date: 1986-07-25
Publication date: 1987-04-01
Also published as: KR870001331A; DE3625506A1; DE3625506C2; SE8603238L; IT8648307A0; SE464250B; AU6066486A; NL8601906A; SE8603238D0; FR2585372A1; AU577957B2; IT1195878B; GB8618262D0; FR2585372B1; KR890002058B1; GB2180556B

Abstract

An anode for electrolysis is a plate 1 having a plurality of openings 5 for the circulation of electrolyte and removal of gas formed, the openings being rectangular and elongated in the horizontal direction (the plate being used vertically) and each opening has a horizontal bridging strip 6 and/or a pair of horizontal flaps projecting from the top and bottom edges of the opening (Fig. 3), which strip or flaps were formed by extruding or bending the plate and they protect away from an adjacent semi-permeable diaphragm 2, on the other side of which is a cathode 3. The openings form 50 to 60% of the area of the cathode plate. Terminals 7 at the edge of the plate are for attachment of electric current supply. The anode is used in electrolysis of NaCl and NaOH. <IMAGE>

Description

SPECIFICATION Apertured electrode for electrolysis This invention relates to an electrode for electrolysis used in a diaphragm electrolytic process, and more particularly to an electrode for electrolysis adapted for an electrolytic process wherein an electrode is disposed adjacent a diaphragm such as an ion-exchange membrane, etc., and gas is allowed to be evolved from the electrode.

Recently, in the electrolytic industry wherein chlorine or sodium hydroxide is manufactured by the electrolysis of an aqueous solution of sodium chloride, the ion-exchange membrane process in which electrolysis is carried out by disposing the electrode adjacent a membrane has been developed as an excellent pollution-preventive, energy-saving electrolytic system. Thus an excellent electrode adapted for this type of process is desired.

In the electrolysis of an aqueous solution of sodium chloride, chlorine and hydrogen gases are evolved from the anode and from the cathode, respectively, and sodium hydroxide is produced in the cathode compartment. In this case, if the electrode is disposed adjacent the ion-exchange membrane, a reduction in the electrolytic voltage may be contemplated by problems arise in the circulation of the electrolytic solution or removal of the generated gas.

For this reason, heretofore, as the electrode a perforated tabular body such as a piece of expanded metal as shown in Fig. 6, or a punched metal as shown in Fig. 7, has been used. For example, disclosure of the use of expanded metal is found in Japanese Patent Application (OPI) No. 114571/77, Japanese Utility Model Publication No. 83756/80, and Japanese Patent Application (OPI) No. (185786/83 (the term "OPI" as used herein means an "unexamined published application").

Also, Japanese Patent Application (OPI) No. 146884/81 discloses use of a perforated tabular electrode as the anode.

In producing expanded metal, cuts are made in the original plate, and the plate is expanded by pulling the plate in a direction perpendicular to the cutting line, and in producing punched metal, circular, square, or other shaped holes are punched in the original plate, and thus there is obtained an electrode plate provided with openings necessary for the removal of the generated gases, or the like.

On the other hand, as for such openings of an electrode, the opening ratio in the effective electrode surface of the electrode plate generally must be in the range of from about 30 to about 60%. For this reason, in conventional electrodes the electrode conductor volume has been decreased by the volume corresponding to the opening ration of from about 30 to about 60% as compared with the volume of the original plate. Thus, the resulting increase in the conductor resistance of the electrode plate inevitably presents a problem due to the increase in the electrolytic voltage.

Also, Japanese Patent Application (OPI) No. 67882/83 describes an electrode whose plate is provided with a number of curved ribbon-shaped punched openings. However, because the curved ribbon-shaped punched openings are made alternatingly on both sides of the electrode plate, even when the electrode is adjacent the diaphragm, there is always a definite distance between the principal plane of the electrode plate and the diaphragm, so that a problem arises in that the anode-cathode distance increases so much.

As set forth above, in the diaphragm electrolytic process wherein generation of a gas occurs at the electrode, it was impossible, so far as conventional electrodes are concerned, to prevent an increase in the conductor resistance due to the opening in the electrode plate at the same time, while disposing the electrode adjacent the diaphragm and moreover ensuring sufficient circulation of the electrolytic solution and removal of the generating gas. Hence there is a problem in that the increase in the electrolytic voltage results in an increase in the electric power cost.

An object of this invention is to obviate these problems in the conventional process and to provide an excellent electrode for electrolysis.

This invention solves the above described problems by allowing the electrode to have a structure such that on the surface of the electrode plate of the electrode for electrolysis a number of openings having a rectangular shape elongated nearly in the horizontal direction are employed, wherein each of the openings having each of the corresponding bridge members and/or eaves shaped members are formed jointly with the electrode plate by extruding or bending in a direction opposite to the contact surface with the diaphragm, and at the lateral ends a plurality of feeding terminals are provided.

In the accompanying drawings: Figures 1 and 3 show, respectively, a partial oblique view illustrating the electrolytic cell in the ion-exchange membrane process, wherein two types of an electrode of this invention are disposed, and Figurer 2 and 4 show, respectively, a partially enlarged cross sectional view and a plan view illustrating the electrode of this invention, Figure 5 shows partially enlarged cross sectional views illustrating the electrode of this invention.

Figure 6 is a schematic view illustrating a conventional expanded metal electrode, and Figure 7 is a schematic illustration of a conventional punched metal electrode.

This invention is explained in greater detail below with reference to the drawings.

Fig. 1 illustrates an example, in which the electrode 1 of this invention, applied as an anode, is disposed adjacent diaphragm 2 which can be an ion-exchange membrane, or the like. A cathode 3 is disposed on the opposite side of this diaphragm, whereby a unit electrolytic cell for the ion-exchange membrane process electrolysis is constructed. The anode 1 is provided with a number of openings 5 rectangular in shape on the electrode plate 4, these openings having bridge member 6, each corresponding to one opening 5, which were formed jointly with the electrode plate 4 by extrusion in the direction opposite to the contact surface with the diaphragm 2. Each opening and bridge member can be readily formed by making two cuts using two parallel knives on the electrode plate 4 and extruding the strip between the cuts.Such processing requires that the material used possesses some degree of plasticity as well as ductility. As metal usually used as the electrode plate of an anode or a cathode, valve metals such as, for example, titanium, tantalum, iron, nickel or alloys thereof, possess these any of these materials can be used in this invention. Rectangular shaped openings are preferable for ease of the circulation of the electrolytic solution and for escape of the generated gas the direction of elongation preferably is horizontal, but some inclination to the horizon is acceptable.

The size and the arrangement of the openings can be suitably determined depending on the quality and dimension of the electrode plate material as well as the necessary opening ratio, and there is no particular limitation thereto. In the case of sodium chloride electrolysis by the ionexchange membrane process, as shown in Fig. 2 the thickness t of the electrode plate 4 made of titanium usually is from about 0.5 to about 2 mm, longitudinal dimension a is, about 1.5 to about 5 mm, laterally dimension b is from about 5 to about 100 mm, and the extrusion height c of bridge member 6 is from about 1 mm or more. It is preferable that a large number of openings 5 are disposed so that the opening ratio in the effective electrode surface is about 30 to about 60%.

Also, in order that the gas bubbles generated may easily pass through the openings to the back side in the direction opposite the contact surface with the membrane, in general it is preferable for the longitudinal dimension a of opening 5 be made larger than the thickness t of the electrode plate 4, and the extrusion height c be larger than double the thickness t. The shape of the bridge member 6 corresponding to the openings 5 may be suitably determined from the thickness t, longitudinal dimension a, lateral dimension b, extrusion height c, and the ductility of the material, but as shown by 6 in Figs. 1 and 2, usually the bridge member 6 is formed trapezoidal in horizontal cross section, with the main portion being parallel to the electrode plate, and is connected to a base portion 8 of the bridge member 6.Where the lateral dimension b of the opening 5 is short at the places near the edges, or the like, as shown by 6' in Fig. 1, the bridge member 6 may be a semicircular or semielliptical form.

Fig. 3 illustrates another example of the electrode of this invention, in which the electrode 1 of this invention, employed as an anode, is disposed adjacent the diaphragm 2 such as an ionexchange membrane. Cathode 3 is disposed on the opposite side of this diaphragm, whereby a unit electrolytic cell for the ion-exchange membrane process electrolysis is constructed. The anodic electrode 1 is provided with a number of pairs of openings 5 rectangular in shape in the electrode plate. Each pair of openings having each a pair of corresponding eaves-shaped members 16 which are formed jointly with the electrode plate 4 by bending in a direction opposite the contact surface with the diaphragm 2. Each opening 5 and the eaves-shaped member can be readily formed by making cuts using two parallel knives on the electrode plate 4 and then by bending the plate 4.As to the openings rectangular in shape, for the ease of the circulation of the electrolytic solution and the escape of the generating gas it is preferable for the direction of the elongation be horizontal, but some inclination to the horizontal is acceptable. The size and the arrangement of the openings can be suitably determined according to the quality and dimension of the electrode plate material as well as the necessary opening ratio, and there is no particular limitation thereto. In the case of sodium chloride electrolysis using the ion-exchange membrane process, as shown in Fig. 4, usually the thickness t of the electrode plate 4 made of titanium is from about 0.5 to about 2 mm, longitudinal dimension a is from about 1.5 to about 5 mm, lateral dimension b is from about 5 to about 100 mm, and the bending angle of the eaves-shaped member is about 16 to 30 or more. It is preferable that a large number of openings 5 be disposed so that the opening ratio in the effective electrode surface is from about 30 to about 60%.

Also, in order that the gas bubbles generated may easily pass through the openings to the back side in the direction opposite the contact surface with the membrane, in general it is preferable for the longitudinal dimension a of the opening 5 to be made larger than the thickness t of the electrode plate. The shape of the eaves-shaped member 16 corresponding to the opening 5 may be suitably determined from the thickness t, longitudinal dimension a, lateral dimension b, bending angle and the ductility of the material. However, as shown in Figs. 3, 4, and 5 (a), (b), and (c), usually it is preferable for the bending angle of the eaves-shaped member 16 and the electrode plate 4 to be from about 30 to about 45" or more.The cross sectional shape of the eaves-shaped member 16 formed jointly with the electrode plate 4 may be Ushaped or semicircular with a bending angle of about 90" as in Fig. 5 (a), or a shape bent at an angle larger than about 90" as in Fig. 5 (b), or a shape bent at an angle smaller than about 90" as in Fig. 5 (c), and so on. In addition, Figs. 3 and 4 show that the eaves-shaped member 6 corresponding to opening 5 has been cut by a length a at both ends in the direction perpendicular to the electrode 4. However, depending on the ductility of the electrode plate metal used, the opening 5 and the eaves-shaped member 16 may be formed by bending after making cuts only in the horizontal direction but not in the vertical direction.

Also, as shown in Figs. 2 and 4, in order to facilitate escape of the generated gas it is more feasible for a number of openings 5 to be disposed in such a relation that amoung those neighboring openings 5 the distance is alternatingly shifted by d. In this case the shift may be suitably determined in the range of d=O to b.

As in conventional electrodes, it goes without saying that electrodes can be produced by suitably applying an anodic or cathodic electrode active coating on at least the surface of the electrode plate 4 to contact with the membrane. The electrode active coating can be applied either before or after the openings of the electrode plate 4 are formed by extruding or bending.

Also, the circulation of the electrolytic solution and the escape of the generated gas can be further improved by making a large number of vertical grooves at least on the surface of the electrode plate 4 to contact the membrane, as described in Japanese Patent Publication No.

38432/80.

In the electrode of this invention, when electrolysis is carried out by incorporating the electrode in an electrolytic cell as shown in Figs. 1 and 3, a plurality of feeding terminals 7 are provided at the lateral edges of the electrode plate 4 so that an electric current is fed laterally in parallel with the elongated direction of the bridge member 6 or the eaves-shaped member 16, and this is preferable for the prevention of an increase in voltage due to the ohmic loss of the electrode conductor.

In the electrode of this invention, by providing a large number of the above described openings rectangular in shape, the requirement for the opening of the electrode plate 4 (opening ratio is usually from about 30 to about 60%), which is necessary as an electrode, can be fully achieved, so that the circulation of the electrolytic solution and the escape of the generated gas proceed very smoothly. Besides the above, since the bridge member 6 or the eaves-shaped member 16 corresponding to each opening 5 is formed jointly with the electrode plate 4 by extruding or bending, the original plate of the electrode plate remains as such without loss of any part of the whole electrode conductor or any function thereof.Thus, although in the case of the conventional punched metal (as shown in Fig. 7) or expanded metal (as shown in Fig. 6) a decrease in the electrode conductor portion corresponding to the portion removed from the original plate or the opening-formed portion of the original plate which always causes an increase in the conductor resistance, no such an increase is observed in the electrode of this invention.

Further, in the electrode of this invention, since a plurality of feeding terminals 7 are provided at the lateral edges of the electrode plate 4 for feeding an electric current laterally, the electric current flows in parallel with the bridge member 6 or the eaves-shaped member 16, and hence the electrode conductor undergoes no substantial effect of bending cut in providing the openings. At the same time uniform electric current distribution on the surface of the electrode plate occurs.

Moreover, since the bridge member 6 and the eaves-shaped member 16 are formed by extruding or bending in the direction opposite the contact surface between the electrode plate 4 and the diaphragm, the main functioning surface of the electrode can be brought sufficiently close contact to the diaphragm.

In the Examples of this invention and in the Comparative Examples illustrating the prior art shown below electrodes were prepared as follows, and tests were made using them as the anode for ion-exchange membrane process electrolysis. In all of the electrodes, using titanium as the metallic substrate, a coating containing the oxide of the same noble metal obtained by thermal decomposition process was applied on the surface to contact the diaphragm.

EXAMPLE I An electrode whose electrode plate has an effective electrode surface of 30 cm 25 cm and thickness t of 1 mm, each opening being of the size: longitudinal dimension a=3 mm, lateral dimension b=45 mm, extrusion height c of bridge=3 mm and the opening ratio being about 40% with d=O. (bridge) EXAMPLE 2 The electrode in Example 1, which was further provided with a number of grooves of 0.5 mm wide, 0.3 mm deep, and 1 mm in pitch in the vertical direction all over the surface to contact the diaphragm. (bridge with grooves).

EXAMPLE 3 An electrode whose electrode plate had an effective electrode surface of width 30 cm height 25 cm and a thickness of ti mm, each opening being of a longitudingal dimension a=2 mm, a lateral dimension b=45 mm, a bending angle of eaves-shaped member=900, and the opening ratio being about 40% (eaves-shaped).

EXAMPLE 4 The electrode in Example 3 which was further provided with a number of grooves of 0.5 mm wide, 0.3 mm deep, and 1 mm in pitch, in the vertical direction all over the surface to contact the diaphragm. (eaves-shaped with grooves) COMPARATIVE EXAMPLE 1 A plate of a thickness of 1 mm.

COMPARA TIVE EXAMPLE 2 Expanded metal of the size Lw 8xSw 3.6xSt 1.2xt 1 mm with an opening ratio of about 35%.

COMPARATIVE EXAMPLE 3 Punched metal of a size t=1 mm, opening=circular hole 2 mm in diameter, pitch=3 mm, with an opening ratio of about 40%.

Tests were made under the following conditions using each of these electrodes as the anode.

In each example, electric current was fed to the anode laterally.

Anodic Solution: 200 g/l aqueous solution of NaCI Cathodic Solution 35 wt% aqueous solution of NaOH Cathode; Ni expanded metal Diaphragm: lon-exchange membrane (manufactured by E.l. du Pont the Nemours & Co., trade name "Nafion" 902) Anode-Cathode Distance: 2 mm Electrolytic Temperature: 90"C Current Density: 30 A/dm2 The results of the above described tests are summarized in Table 1 below.

TABLE 1 * 1) Ohmic Loss of Electrolytic No. Anode Conductor Voltage Example 1 Bridge 56 3.44 Example 2 Bridge with grooves 78 3.46 Example 3 Eaves-shaped 56 3.45 Example 4 Eaves-shaped 78 3.47 with grooves Comparative Plate 56 - "2) Example 1 Comparative Expanded metal 108 3.53 Example 2 Comparative Punched metal 146 3.52 Example 3 '1) The ohmic loss of conductor Vw was obtained by the following equation.

V=i0pl2/3 t (V) i,: Electrolytic current density (A/dm2) p: Specific resistance of conductor (Q cm) I: Electrically charged distance (cm) t: Plate thickness of conductor (cm) "2) Electrolysis is impossible because of an imperforated plate.

As is clearly seen from the results shown in Table 1, with the electrode of this invention the voltage corresponding to the ohmic loss of the conductor is as low as that of the imperforated plate, and nearly one half of the losses of the conventional expanded metal and punched metal with the same thickness and opening ratio, so that the electrolytic voltage can be reduced by from about 50 to 100 mV by the application of the electrode of this invention.

As described above, the electrode of this invention provides excellent performance as a gasgenerating electrode which is disposed adjacent the diaphragm in that not only can both the circulation of the electrolytic solution and the removal of the generated gas be efficiently achieved, but also the electrolytic voltage can be produced, proving that it is extremely useful industrially.

Claims

1. An electrode for electrolysis, comprising a plate which is vertical in use in which are formed a plurality of openings having a rectangular shape elongated substantially in the horizontal direction, with each of said openings having corresponding bridge members and/or eaves-shaped members which were formed from the electrode plate either by extruding or by bending in the direction opposite the surface which is intended to contact a permeable diaphragm; and a plurality of feeding terminals are provided at the lateral edges of the electrode plate.

2. An electrode as claimed in Claim 1, wherein the proportion of the effective electrode surface of the plate which is occupied by said openings is from 30 to 60%.

3. An electrode as claimed in Claim 1 or 2, wherein the size of the rectangular openings is from 1.5 to 5 mm long and 5 to 100 mm wide, and the electrode plate is from 0.5 to 2 mm thick.

4. An electrode as claimed in Claim 1, 2 or 3, wherein vertical grooves are provided at least on the surface of the elctrode plate intended to contact the diaphragm.

5. An electrode for electrolysis as claimed in any preceding claim wherein at least the surface of the electrode plate intended to contact the diaphragm bears an electrode-active coating.

6. An electrode for electrolysis, substantially as hereinbefore described with reference to Figs. 1 and 2, or 3 and 4 of the accompanying drawings.

7. An electrode for electrolysis substantially as hereinbefore described with reference to any of Examples 1 to 4.

8. Electrolysis apparatus which includes an electrode as claimed in any preceding claim adjacent to a permeable diaphragm.

9. A process of electrolysis wherein electric current is supplied to the terminals of an electrode as claimed in any preceding claim which is placed in an electrolytic cell.