GB2103658A

GB2103658A - Ion-exchange membrane electrolytic apparatus and process for producing the same

Info

Publication number: GB2103658A
Application number: GB08220604A
Authority: GB
Inventors: Hiroshi Asano; Takayuki Shimamune; Kazuhiro Hirao; Toshiki Goto; Masaki Eguchi; Katsuhiki Date; Tutomu Suzuki
Original assignee: Permelec Electrode Ltd
Current assignee: De Nora Permelec Ltd
Priority date: 1981-07-21
Filing date: 1982-07-15
Publication date: 1983-02-23
Also published as: CA1218959A; IT1189321B; GB2103658B; SE8204406L; JPS5816082A; PH17767A; KR850001181B1; DE3226347A1; DE3226347C2; JPS614915B2; MY8600256A; SE8204406D0; FR2510143A1; KR840000671A; IT8248840A0; FR2510143B1; SE453203B

Abstract

An electrolytic apparatus comprises a cathode and an anode with an ion-exchange membrane positioned therebetween and at least one of the cathode and anode comprises a gas-liquid permeable porous plate electrode adhered closely with the ion-exchange membrane using a powdery ion-exchange resin. In a process for making such an electrode the porous plate is impregnated with the powdery ion- exchange resin and the ion-exchange membrane is bonded thereto under heat and pressure.

Description

SPECIFICATION lon-exchange membrane electrolytic apparatus and process for producing the same The present invention relates to an electrolytic apparatus using an ion-exchange membrane and a process for producing the same.

In greater detail, the present invention relates to an electrolytic apparatus having an ionexchange membrane as a solid polymer electrolyte diaphragm, wherein at least one of the cathode and the anode composed of a gas-liquid permeable porous plate is adhered closely to the ion-exchange membrane by means of a powdery ion-exchange resin, and a process for producing the same.

Recently achieving energy economy or resource economy, such as reduction of electric power consumption or minimization of apparatus size, etc. due to rapid increases in energy cost, has become an important problem.

In electrolysis of aqueous solutions of sodium chloride, etc., a cathode and an anode, in the past, have been separated by a space from a diaphragm therebetween. As an improvement, it has been proposed to adhere closely the cathode and anode to the cation-exchange membrane, by which electric resistance due to gas generation is reduced to decrease the electrolytic voltage (e.g., as disclosed in Japanese Patent Applications (OPI) 47877/79 and 60295/79).

Further, various kinds of the so-called solid polymer electrolyte (SPE) electrolytic processes are known hitherto. For example, Japanese Patent Publication 45557/76 (corresponding to U.S.

Patent 3,489,670) and Japanese Patent Application (OPI) 78788/77 (corresponding to U.S. Patent 4,039,409) on electrolysis of water, Japanese- Patent Application (OPI) 52297/78 on electrolysis of Glauber's salt, Japanese Patent Applications (OPI) 95996/79 and 97581/79 on hydrolysis of hydrochloric acid, and Japanese Patent Applications (OPI) 102278/78, 93690/79, 107493/79, 112398/79, 115982/80 and 1 311 87/80 on hydrolysis of sodium chloride, etc., are known.

in the electrolytic apparatus for the SPE process, an ion-exchange membrane is used as the electrolyte diaphragm, and stratified cathode and anode catalyst materials are held on the both sides of the diaphragm by being directly bonded thereto, by which electrolysis is carried out. In such cases an electric current is supplied by contacting a feeder with the electrode catalyst layer. Accordingly, they have characteristics that the distance between electrodes is reduced to the thickness of the diaphragm and theoretically the electrolytic solution is not present between the electrodes. Accordingly, it is possible to reduce the size of the apparatus to a great extent.Further, since loss of electric resistance due to the electrolytic solution between the electrodes and generation of bubbles can be disregarded, at least the corresponding value of the electrolytic voltage can be reduced. Accordingly, the SPE process is en excellent electrolytic system for energy economy.

However, in the prior electrode close adhesion processes and SPE processes, since bending or creases gradually occur with the ion-exchange membrane used when electrolysis is continued, a gas such as hydrogen or chlorine, etc., caused by separation or unevenness of the ion-exchange membrane, accumulates resulting in an inferior contact of the feeder with the electrode catalyst layer or irregular distribution of electric current on the electrolytic surface results. Consequently, a problem arises because the electrolytic voltage rapidly increases.

A technique for solving such a problem involves insertion of metal wires or a mesh or a porous plate as a reinforcing member into the inner part of the ion-exchange membrane, and a polytetrafluoroethylene dispersion is used as an adhesive (for example, as disclosed in Japanese Patents (OPI) 138088/80, 139842/80 and 141580/80). However, insertion of a reinforcing member into the thin ion-exchange membrane gives rise to problems in the production and properties thereof. Further, since adhesion of the electrode to the ion-exchange membrane is still insufficient, there is the possibility of the separation of the two of them during electrolysis for a long time, and this resistance due to the adhesive increases.

The present invention provides the ability to overcome the above described problems.

An object of the present invention is to provide an electrolytic apparatus using an ion-exchange membrane, wherein the adhesion between the ion-exchange membrane and the cathode is excellent and operation can be carried out in a stable manner for a long time without deformation of the ion-exchange membrane occurring, and a process for producing the same.

In one embodiment, this invention provides an electrolytic apparatus comprising a cathode and an anode on both sides of an ion-exchange membrane with at least one of the cathode and the anode being composed of a gas-liquid permeable porous plate electrode with the porous plate electrode adhering closely to the ionexchange membrane using a powdery ionexchange resin and, in a second embodiment, a process for producing the electrolytic apparatus.

Since the present invention has such a construction, the above-described object of the present invention is attained and excellent effects are exhibited as described in detail in the following.

Namely, the present invention is based on the discovery that, in producing an electrolytic apparatus by attaching a porous plate electrode to an ion-exchange membrane as described in Japanese Patent Application 1 69406/79 of the present inventors or Japanese Patent Applications (OPI) 131187/80 and 138088/80, the ionexchange membrane is firmly bonded to the electrode, if a powdery ion-exchange resin is used as a bonding agent for the ion-exchange membrane and the electrode.

Thus, according to the present invention, the ion-exchange membrane easily adheres closely and firmly to the porous plate electrode with dimensional stability arising. As the result, separation of the ion-exchange membrane does not occur even if electrolysis is carried out for a long time. Further remarkable effects occur in that occurrence of bending or creases can be prevented without using the above-described reinforcing member and it becomes possible to operate in a stable manner at a low electric voltage for a long time.

The ion exchange resin used as the bonding agent is similar to the resin used for ion-exchange membrane and is one, which does not deteriorate properties of the ion-exchange membrane as an electrolyte. Further, it has an advantage of increasing the electric resistance to a lesser extent.

The ion-exchange membrane used in the present invention is not restricted, and it is possible to use various kinds of ion-exchange membranes alone or as a combination thereof depending on the kind of electrolytic reaction.

Fluorine containing cation-exchange membranes having ion-exchange groups such as carboxylic acid groups, sulfonic acid groups, phosphoric acid groups or phenolic hydroxyl groups, etc., as described in the above-described Japanese Patent Applications (OPI) 1 31187/80 and 138088/80 are preferred for carrying out electrolysis of saline solutions, and other suitable ion-exchange membranes which can be used are described in U.S. Patents 3,134,697, 3,297,482, 3,341,366,3,432,353, 3,442,825,3,489,670 and 4,039,409, the disclosures of which are herein incorporated by reference.

The electrode used in the present invention should be composed of a gas-liquid permeable porous plate so that it can adhere closely to the ion-exchange membrane. It is preferred for both the cathode and the anode to adhere closely to the ion-exchange membrane, but only one of the cathode and the anode may be adhered closely thereto. The porous plate electrode may have various shapes. For example, nets, woven materials, lattices, perforated plates, sintered porous materials, spray coated porous materials and porous materials obtained by leaching out metal portions thereof, etc., can be used as they are or as electrode substrates, which are coated with an electrode active substance.Further, it is preferred for the porous plate electrode to have a porosity of about 10 to 99% and an opening size of about 1 i to 5 mm, preferably 100,u to 1 mm, so as to facilitate passage of the electrolytic solution and removal of gases generated but so as not to cause deformation of the ion-exchange membrane by projection into the openings.

Suitable porous plate electrodes can be produced using various known materials by various known processes depending to the electrolytic reaction for which the electrodes are to be used, and the processes described in the above-described Japanese Patent Application (OPI) 131187/80 and Japanese Patent Application 169406/79 (corresponding to U.S.

Patent Application Serial No. 217,608, filed December 1 8, 1 980), can be utilized, too.

For example, in electrolysis of a saline solution, it is possible to use, as the cathodes, porous plates composed of iron, nickel, titanium, zirconium, niobium or alloys comprising them as a main component, such as Ti-Ta, Ti-Ta-Nb etc., alloys; platinum metals such as Pt, Ru, Ir, Rh or Pd, or oxides thereof such as Ru02, IrO2, etc.; other metals or metal compounds such as WO3, MoO2, etc.; and carbon or combinations thereof; or porous plates composed of iron, nickel or titanium, etc., which are covered with a cathode active material using known means such as a thermal decomposition process, a powder sintering process, a plating process or a spray coating process, etc. For example, flame plasma spraying as described in Japanese Patent Application (OPI) Nos. 40676/73 and 46581/76 can be used.

Further, it is possible to use, as the anodes.

porous plates composed of platinum metals such as platinum, ruthenium, palladium, iridium, rhodium, etc., or oxides there of such as Ru02, PdO, Irk2, Rh203, etc.; other metals such as titanium, tantalum, tin or cobalt, etc., or oxides thereof such as TiO2, Ta205. SnO2, etc.; or combinations thereof, such as Ru02-Ti02, Ru02-Ir02-Ta20 , Ru0 2-Sn02-ri02, Pt-Sn02, etc.; or porous plates composed of titanium, tantalum, zirconium or electrically conductive oxides thereof such as TiO2~X where O < x < 0.5, which are covered with an anode active substance using known means such as a thermal decomposition process, a sintering process, a plating process or a spray coating process, etc., as described in U.S.Patents 3,711,385, 3,632,498, etc.

The resulting porous plate electrode is adhered closely to the above-described ion-exchange membrane using a powdery ion-exchange resin.

Examples of powdery ion-exchange resins which can be used include known resins having sulfonic acid groups, sulfonamide groups or carboxylic acid groups, etc. as ion-exchange groups, and the resins used in producing the membranes in the hereinbefore incorporated documents can be employed in a powdery form.

However, it is preferred to use the same ionexchange resin as the ion-exchange membrane having an ion-exchange capacity of about 0.1 to 3 milli-equivalents per gram of the dry resin, in order to improve the close adhesion of the ion-exchange membrane to the electrode without deteriorating the electrolytic ability thereof. For example, in case of using Nafion &num;120 or #110 (Nafion is a trademark of E. I. du Pont de Nemours co., Inc.) as the ion-exchange membrane, it is preferred to use a powder of the same resin as described above or available powdery ion-exchange resin such as Nafion &num;501 and #511. Although the particle size of the powdery ion-exchange resin may be suitably selected, it is preferred for the average particle size to be equal to or less than the average opening size of the porous plate electrode.

Generally, powdery ion-exchange resins having an average particle size of about 0.5 to 1 mm are used. When the ion-exchange resin powder with such a particle size is used as the bonding agent, it easily permeates into openings of the porous plate electrode upon heat treatment under pressure and becomes impregnated therein or fused therein by which the ion-exchange membrane is adhered firmly and closely to the porous plate electrode.

Various means can be utilized for bonding the porous plate electrode to the ion-exchange membrane using the powdery ion-exchange resin.

The simplest process comprises applying a powder of the ion-exchange resin to a surface of the porous plate electrode or the ion-exchange membrane in a uniform thickness, and pressing both of them simultaneously along with a heating of the bonding faces from, preferably, the electrode side to fuse the ion-exchange resin. It is preferred for the heating temperature to be about 80 to 3800C and the bonding pressure to be about 10 to 1000 kg/cm2. The heat treatment under pressure can be carried out in the air or, if desired, in an inert atmosphere such as of nitrogen or argon, etc.Further, it is also possible to use a process which comprises previously impregnating the surface to be bonded of the porous plate electrode with the powdery ion-exchange resin by mechanical introduction under pressure or by applying a liquid dispersion of a powdery ionexchange resin and, if desired, fusing by heating to form a bonding agent layer on the surface of the porous plate electrode, and bonding the ionexchange membrane thereto under pressure with heat. Further, it is possible to use a process which comprises attaching a powdery ion-exchange resin as a bonding agent to a side or both sides of the ion-exchange membrane during production thereof, and bonding the porous plate electrode to the ion-exchange membrane under pressure with heat.This latter process provides the advantage that the adhesion of the ion-exchange resin to the ion-exchange membrane and the adhesion of the ion-exchange resin to the porous plate electrode can be carried out under optimum conditions, respectively.

Where a porous plate electrode which is covered with an electrode active substance is used as an electrically conductive porous electrode substrate, it is possible to use a process which comprises bonding closely the ionexchange membrane to the electrically conductive porous electrode substrate using the powdery ionexchange resin employing the above-described process, and thereafter coating the electrode substrate with the electrode active substance. In this process, coating with the electrode catalyst substance must be conducted under conditions where the ion-exchange membrane is not broken, such as by using a sputtering process, a plating process or an evaporation process, etc.Further, the process according to the present invention can be employed not only in the case of providing a porous inactive layer between the ion-exchange membrane and the electrode as described in Japanese Patent Application 169406/79 and Japanese Patent Application (OPI) 75583/81, but also in production of other analogous electrolytic cells.

The present invention is illustrated below by reference to the following examples, but the present invention is not to be construed to be limited by these examples.

EXAMPLE 1 To a 20 mesh (mesh spacing: about 0.7 mm) nickel net having a wire diameter of 0.5 mm and an area of about 50 cm2, a nickel powder having an average particle size of 100y was applied by sintering for 10 minutes at 9000C in a H2 atmosphere to produce a porous plate cathode wherein a porous layer having a thickness of about 200 u and a porosity of about 80% was formed on a face to which an ion-exchange membrane was adhered.

On the other hand, a commercially available ion-exchange resin (ion-exchange capacity: about 0.8 milli-equivalent/1 g of dry resin) (Nafion &num;501) was powdered to an average particle size of 70y. The above-described cathode porous layer was sufficiently impregnated with the resulting powder, and further a small amount, e.g. about 5 g/m2, of the same powder was applied thereto.

A cation-exchange membrane of Nafion &num;120 was put on the processed layer, and adhesion of the ion-exchange membrane and the nickel porous cathode was carried out by pressing at a temperature of 2500C under a pressure of 10 kg/cm2. Using an expansion mesh having a thickness of 2 mm as an anode, an electrolytic cell was constructed by placing the anode at a distance of 3 mm from the ion-exchange membrane. For the purpose of comparison, an electrolytic cell was used wherein the abovedescribed cathode without the ion-exchange membrane bonded thereto was placed at a distance of 1.5 mm.As a result of electrolysis at 400C by supplying a 10% aqueous solution of NaOH to the cathode chamber and the anode chamber, respectively, the electrolytic voltage with the cathode bonded to the ion-exchange membrane according to the present invention was about 200 mV lower than that with the cathode not bonded to the ion-exchange membrane.

Further, separation of the ion-exchange membrane from the cathode was not observed after electrolysis had been carried out for about 1000 hours, and thus operation can be continued in a stable manner.

EXAMPLE 2 To a roiled titanium mesh having a thickness of 0.1 mm and an opening ratio of 60%, a titanium powder having an average particle size of about 50 y was applied to form a porous layer, and the layer was sintered at 11 000C for 20 minutes in a vacuum (10-5 Torr) to produce a porous plate having a thickness of about 50 u and a porosity of about 80%. This porous plate was covered with a compound oxide of Ru and Ti in a metal ratio of 60:40 by weight using a conventional thermal decomposition process to produce a porous plate anode.

Next, the surface of the above described porous anode was impregnated with powdered Nafion &num;500 (ion-exchange capacity of about 0.8 milliequivalents/1 g of dry resin) having an average particle size of 20 u or less, and a Nafion &num;315 ion-exchange membrane was bonded to the above-described surface at 2500C by pressing at a pressure of 20 kg/cm2.

Platinum black (specific surface area 30 m2/g) and a polytetrafluoroethylene dispersion were blended in a ratio by weight of 100:30. The mixture was applied to the other surface of the above-described ion-exchange membrane to form a cathode layer, and an electrolytic cell was constructed using it.

For the purpose of comparison, an electrolytic cell which was constructed in the same manner, except that the anode was bonded directly to the ion-exchange membrane without used the ionexchange resin powder was used.

As a result of electrolysis at 800C by supplying a 4 N aqueous solution of NaCI to the anode chamber and a 20% aqueous solution of NaOH to the cathode chamber, operation in a stable manner can be carried out according to the present invention at an average electrolytic voltage of 3.3 V for 1000 hours or more, and separation of the anode from the ion-exchange membrane was not observed at all. In the comparison electrolysis, separation of the anode from the ion-exchange membrane occurred to result in a rapid increase of the electrolytic voltage of 1.0 V or more after 1 5 minutes from the electrolysis operation was started.

EXAMPLE 3 A nickel porous plate having a thickness of about 1 mm (Cermet No. 5, produced by Sumitomo Electric Ind. Ltd.) was rolled to prepare a porous plate having a thickness of 0.3 mm and a porosity of 90%. It was coated with platinum in a thickness of about 1 u using a thermal decomposition process to produce a cathode.

Then the surface thereof was impregnated with a powder of an ion-exchange resin (Nafion &num;501) having an average particle size of 50 L in a thickness of about 0.2 mm. An aluminium foil was put on the resulting porous cathode, and the assembly pressed at a temperature of 3000C under a pressure of 200 kg/m2 in a nitrogen atmosphere. When the aluminum foil was removed, a uniform layer of the ion-exchange resin which adhered closely to one side of the nickel porous cathode plate was formed.

Then, to the resulting membrane layer, an ionexchange membrane (Nafion &num;315) was adhered by pressing at 2500C under 150 kg/m2.

A Ti mesh coated with a compound oxide of Ru02 :Ti02 - 1:1 by weight was used as an anode, which was placed at a distance of 2 mm from the ion-exchange membrane to construct an electrolytic cell. When electrolysis was carried out under the same condition as in Example 2, operation in a stable manner can be carried out at an electrolytic voltage of about 3.3 V for 1000 hours or more, and separation of the nickel porous cathode from the ion-exchange membrane was not observed.

While the invention has been described in detail and with reference to specific embodiments thereof, it wili be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims

1. An electrolytic apparatus comprising a cathode and an anode with an ion-exchange membrane position therebetween and further wherein at least one of said cathode and anode comprises a gas-liquid permeable porous plate electrode adhered closely with said ion-exchange membrane using a powdery ion-exchange resin.

2. The electrolytic apparatus according to Claim 1, wherein the ion-exchange membrane and the ion-exchange resin powder each have an ionexchange capacity of about 0.1 to 3 milliequivalents per gram of dry resin.

3. The electrolytic apparatus according to Claim 1, wherein the apparatus comprises a porous plate cathode adhered closely to the ion-exchange membrane using the powdery ion-exchange resin.

4. The electrolytic apparatus according to Claim 1 or 3, wherein the cathode is a porous plate prepared by (a) sintering a nickel powder or (2) applying a nickel powder to a nickel porous material by sintering.

5. The electrolytic apparatus according to Claim 1 or 3, wherein the cathode is a porous plate prepared by plating (1) a nickel porous material with a platinum metal or (2) a nickel powder sintered product with a platinum metal.

6. The electrolytic apparatus according to Claim 4, wherein the cathode is a porous plate prepared by plating (1) a nickel porous material with a platinum metal or (2) a nickel powder sintered product with a platinum metal.

7. The electrolytic apparatus according to Claim 1, wherein the apparatus comprises a porous plate anode adhered closely to the ion-exchange membrane by using the powdery ion-exchange resin.

8. The electrolytic apparatus according to Claim 1 or 7, wherein the anode is a porous plate prepared by sintering a titanium powder or by applying a titanium powder to a titanium porous material by sintering, and wherein said porous plate further is coated with a metal oxide electrode catalyst.

9. A process for producing an electrolytic apparatus having a cathode and an anode with an ion-exchange membrane positioned therebetween, which comprises forming a gas-liquid permeable porous plate electrode as at least one of the cathode or the anode, and adhering said porous plate electrode to the ionexchange membrane by using a powdery ionexchange resin under pressure with heat.

10. A process according to Claim 9, wherein said process comprises adhering an ion-exchange membrane to an electrically conductive porous material as an electrode substrate using said powdery ionexchange resin by pressing with heat, and coating said electrode substrate with a gasliquid permeable electrode active material.

11. A process according to Claim 9, wherein said process comprises applying the powdery ionexchange resin to at least one side of the ionexchange membrane during the formation of the ion-exchange membrane.

12. An electrolytic apparatus as claimed in Claim 1, substantially as described herein.

13. A process as claimed in Claim 9, substantially as described herein.

14. The features as herein described, or their equivalents, in any novel selection.