JPH02259090A - Production of ozone by electrolysis - Google Patents

Abstract

PURPOSE:To prevent the application of the pressure of gas between a Pt coated electrode and membrane of a cation exchange resin and to increase the purity of ozone by pressing one side of the electrode against the membrane and electrolyzing water by zero-gap electrolysis. CONSTITUTION:When ozone is produced by electrolyzing water, a membrane 4 of a perfluorosulfonic acid type cation exchange resin and a specified electrode on the cathode side are used. The electrode is formed by coating one side of a porous sheet 6a of Ni (alloy steel) with Pt 5. The Pt 5 coating layer side of the electrode is pressed against the cathode side of the membrane 4 and zero-gap electrolysis is carried out. Since the pressure of gas is not applied between the electrode and the membrane 4, hydrogen does not enter into produced ozone and high purity ozone is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for the electrolytic production of ozone. More specifically, the present invention relates to an electrolytic ozone production method that can continuously supply ozone or ozone water useful for sterilization, preservation, etc. in the consumer fields such as food, medicine, and environmental hygiene, and for synthesis, processing, etc. in the industrial field.

A technique for producing ozone by electrolyzing water using a perfluorosulfonic acid type cation exchange membrane as a solid electrolyte is known.

A cell for carrying out this electrolysis is, for example, as shown in Figure 1, in which a platinum layer (5) serving as a cathode is bonded to one side of a cation exchange membrane (4), and an anode is attached to the other side. A porous titanium plate coated with a certain lead dioxide layer (3) (
Examples include cells formed by press-welding 2). The cell is equipped with a backup power source (not shown) that supplies a protective current at the same time as the current is interrupted, in order to prevent lead dioxide from being leached from the lead dioxide layer (3) when the current is interrupted, such as during a power outage.

By electrolyzing while sending pure water to the anode of the cell,
Ozone with a concentration of 200 g/m3 or more can be produced.

However, the above method has the following problems, for example. That is, since the one-sided bonding of platinum to a cation exchange membrane easily damages the cation exchange membrane, it requires many steps and increases costs. Moreover, the effective thickness (thickness effective to prevent hydrogen permeation) of the cation exchange membrane bonded with platinum is reduced, and the hydrogen pressure on the cathode side is high, so the amount of hydrogen diffusion within the membrane is reduced. As a result, hydrogen permeates to the anode side. However, since the lead dioxide of the anode does not have the catalytic ability to cause a hydrogen recombination reaction, the hydrogen that permeates to the anode side mixes with the ozone produced, reducing the purity of the ozone.

In addition, in the above conventional method, as is clear from Fig. 1, in consideration of the acid resistance and hydrogen embrittlement of the cation exchange membrane (4), powdery carbon, chopped carbon fiber, etc. are usually used as the power supply body on the cathode side. A porous carbon plate (6) such as a sintered body, carbon paper, felt, cloth, a molded product of carbon powder and PTFE resin, or a sintered body containing expanded graphite is used.

Porous carbon plates cause various problems if their porosity or opening diameter is not appropriate, or if their surface smoothness or cushioning properties are not sufficient. For example, if the porosity or opening diameter is too large, gas and liquid permeation will be good, but the mechanical strength of the plate will decrease and the electrical resistance will increase. On the other hand, if it is too small, gas and liquid permeation will be poor.
Contact resistance occurs between the plate and the platinum layer, causing a biased current distribution and making the cation exchange membrane more likely to be damaged. In addition, if the surface smoothness or cushioning properties are poor, excessive contact pressure is required, which may easily damage the membrane or impair gas release. However, it is extremely difficult to appropriately adjust the porosity, opening diameter, surface smoothness, and cushioning properties of a porous carbon plate.

Means for Solving the Problems The present inventor has conducted extensive research in view of the problems of the above-mentioned prior art. As a result, when producing ozone by water electrolysis using a perfluorosulfonic acid type cation exchange membrane,
An electrode coated with platinum on one side of a porous plate made of nickel or nickel alloy is placed on the cathode side of the ion exchange membrane.
When performing zero-gap electrolysis by placing a lead dioxide-coated porous titanium electrode on the anode side and pressure-welding it from both sides, 1)
Since no hydrogen pressure is applied between the cathode side electrode and the cation exchange membrane, almost no hydrogen is mixed into the generated ozone, making it possible to obtain ozone with higher purity than conventional methods. 2) Between the electrodes, stainless steel and platinum 3) As the material of the porous plate, nickel or nickel alloy is used, which allows easy adjustment of porosity, opening diameter, surface smoothness, and cushioning properties, so electrical resistance can be increased. It is possible to create an electrode with good gas and liquid drainage, and to achieve the highest ozone generation efficiency ever.
4) Since the catalyst electrode (platinum) is bonded to nickel or nickel alloy, which is hard to damage, the number of man-hours required for bonding is reduced. 5) Since metal material is used instead of porous carbon material, it is easier to assemble and disassemble the cell. 6) There is no need to create a platinum-cation exchange membrane assembly (
In addition, there is no need to use expensive porous carbon materials, resulting in a significant cost reduction. 7) Even if electrolysis is performed for a long time, the cathode side electrode placed in a hydrogen atmosphere will not corrode. Therefore, the inventors discovered that the cation exchange membrane is less likely to be damaged, and completed the present invention.

That is, when producing ozone by a water electrolysis method using a perfluorosulfonic acid type cation exchange resin membrane, the present invention provides an electrode made of a porous plate made of nickel or nickel alloy steel coated with platinum on one side on the cathode side. The present invention provides a method for electrolytically producing ozone, characterized in that the platinum coating layer side of the electrode is pressed against the cathode side of a cation exchange membrane to perform zero gap electrolysis.

In the present invention, the perfluorosulfonic acid type cation exchange resin membrane is not particularly limited as long as it acts as a solid electrolyte in a water electrolysis reaction and is resistant to ozone, and any known membrane can be used. Specifically, for example, DuPont's Nafion membrane 117 can be used.

In the present invention, a porous plate made of nickel or nickel alloy steel coated with platinum on one side is used as the cathode electrode.

Nickel and nickel alloy steel have superior strength, electrical conductivity, formability, and surface smoothness compared to carbon materials. Further, when manufacturing a porous plate using this, the porosity and the opening diameter can be easily adjusted by appropriately changing the manufacturing conditions. Furthermore, it also has the property of strongly bonding with platinum.

The nickel alloy steel is not particularly limited and any known material can be used, and among these, stainless steel is particularly preferred. Stainless steel is not particularly limited, but for example, 5U
Various types such as S304.5US316.5US316L can be mentioned.

The porous plate is made of the above nickel and nickel alloy steel,
It can be produced by molding and sintering a spherical metal powder by melt spraying, a rotating electrode method, etc., a short fiber by a chatter vibration cutting method, a long fiber by a die method, etc. according to a conventional method.

Further, as the porous plate, for example, a laminated plate such as an expanded plate, a punched plate, a photoetched plate, etc. made of nickel or a nickel alloy can be used.

The porosity of the porous plate is usually about 40 to 80%, preferably about 50 to 70%. In addition, the opening diameter is usually about 10 to 1000 μm, preferably 50 to 500 μm.
It is preferable that the thickness be on the order of μm. If the porosity is significantly less than 40% or the open area is significantly less than 10 μm, the water transported through the cation exchange membrane and the hydrogen generated during electrolysis will be
It becomes difficult to escape to the back side of the electrode, pressure increases at the electrode-cation exchange membrane interface, and there is a possibility that contact becomes poor, which is not preferable. Additionally, if the porosity significantly exceeds 80% or the pore diameter significantly exceeds 1000 μm, the number of contact points between the cation exchange membrane and the electrode will decrease, causing a localized current density that may damage the cation exchange membrane. There is.

Further, when performing zero gap electrolysis, it is preferable that the electrode and the cation exchange membrane are in good contact. For this reason, the porous plate preferably has cushioning properties. Specifically, the compression modulus is 5000 kg/c
It is preferable that the size is about m2 or less. In order to impart cushioning properties to the porous plate, manufacturing conditions such as the pressure during sintering may be adjusted.

The coating method for coating one side of the porous plate with platinum is not particularly limited, and any known method can be employed.

Specifically, examples include electroplating, electroless plating, pyrolysis plating, sputtering, and ion blating. Although the thickness of the platinum layer is not particularly limited, it may normally be about 1 to 5 μm.

Alternatively, a porous thin plate having a thickness of about 0.5 to 2.0 mm may be coated with platinum and integrally formed with another reinforcing porous plate.

Furthermore, a mixture of a conductive material and a binder is applied to a porous plate and fired, or a thin film with a thickness of about 50 to 200 μm is created using the above mixture, and this is thermally bonded to the porous plate. May be buried. Examples of the conductive material include carbon powder, nickel alloy powder, and the like coated with platinum by a known method such as vapor deposition, sputtering, and electroless plating. Examples of the binder include PTFE resin.

On the other hand, a porous titanium electrode coated with lead dioxide is used as the anode side electrode. The electrode is not particularly limited, and known electrodes can be used. Among them, for example, a two-layer structure lead dioxide-coated porous titanium electrode (Japanese Patent Application Laid-Open No. 63-23
No. 8293) can be preferably used.

FIG. 2 shows an example of an electrolytic cell for carrying out the method of the present invention. That is, a porous stainless steel plate (6a) having a platinum layer (5) on one side is placed on the cathode side of the cation exchange membrane (4), and a lead dioxide layer (3) is placed on the anode side of the membrane (4). A porous titanium plate (2) having a porous titanium plate (2) is arranged. (1) is a titanium end plate, and (7a) is a stainless steel end plate.

The platinum layer (5) and the lead dioxide layer (3) are each pressed against the cation exchange membrane (4). The contact pressure between each electrode and the cation exchange membrane is preferably approximately 50 to 200 kg/cm2.

Electrolysis is performed using a cell as described above and supplying water, preferably pure water, ion-exchanged water, or the like. Although the electrolysis conditions are not particularly limited, it is sufficient to normally set the temperature to about 20 to 40°C and the current density to about 50 to 100 A/dm2. Cell voltage is determined by temperature and current density. For example, in the case of 35℃ and 100A/dm2, 3.2~
The voltage will be about 3.3V. Further, the protective current from the backup power source when the operation is stopped may be about 0.1 to 0.5 A/dm''.

In the present invention, a monopolar or bipolar cell configured using one or more cells as described above is incorporated into a normal electrolysis device to perform electrolysis. FIG. 3 shows an example of an electrolysis device employing the method of the present invention.

Effects of the Invention According to the present invention, the following excellent effects can be achieved.

1) Since no gas pressure is applied between the electrode and the cation exchange membrane, almost no hydrogen is mixed into the generated ozone, making it possible to obtain ozone with higher purity than with conventional methods. In fact, the amount of hydrogen in the gas generated from the anode is lower than the conventional method (several 100 to several 10
It decreases to about 1/10 to 1/20 of 1000pp.

2) No contact resistance occurs between electrodes or between stainless steel and platinum.

3) Since nickel or nickel alloy is used as the material for the porous plate, the porosity and opening diameter can be easily adjusted, so an electrode with good gas and liquid drainage can be created without increasing electrical resistance.

In addition, since gas and liquid can be easily removed, the ozone generation efficiency can be the highest ever, and the current density during electrolysis can be lowered by about 0.1 to 0.2 V compared to conventional methods. Even in the case of multiple cells, the variation in voltage between each cell is 0.05V on average.

4) Since the catalyst electrode (platinum) is bonded to nickel or nickel alloy, which is hard to damage, the number of man-hours required for bonding is reduced.

5) Since a metal material is used instead of a porous carbon material, there is no risk of damage during assembly and disassembly of the cell, and the working time can be shortened.

6) There is no need to create a platinum-cation exchange membrane assembly, and there is no need to use expensive porous carbon materials, so costs can be significantly reduced.

7) Even if electrolysis is performed for a long time, the cathode side electrode placed in a hydrogen atmosphere will not corrode, and therefore the cation exchange membrane will not be easily damaged. Incidentally, according to the method of the present invention, no deterioration of the electrodes or cation exchange membrane or deterioration of cell performance was observed even after continuous operation for one year.

EXAMPLES Below, manufacturing examples, examples, and comparative examples of cathode side electrodes will be given to further clarify the present invention.

Production Example 1 Sintered SUS 316L short fibers [Toughmic Fiber, manufactured by Tokyo Rope Co., Ltd.] made using the chatter vibration cutting method
0°C x 1 hour) and 80 mm in diameter.

Thickness: 3mm, porosity: 80%, average opening diameter: 200μ
A porous plate of m was obtained.

After masking one side of this porous plate with insulating tape, the other side was subjected to alkaline degreasing, hydrochloric acid cleaning, and nickel strike plating, and then using an acidic platinum plating bath [Platanex, manufactured by Kuninaka Kikinzoku ■] at 75°C. ,3A/
The surface was plated with approximately 3 μm of platinum under conditions of dm2.

Production Example 2 A web of uniform thickness of SUS 316 fiber [Susmic Fiber, manufactured by Tokyo Rope Co., Ltd.] by the die method was annealed in a non-oxidizing and reducing atmosphere at 800°C for 2 hours) and pressed (press pressure = 800 kg). /cnY) and sintered (1
000°C x 1 hour) to a diameter of 80 mm and a thickness of 2.
A porous plate having a diameter of 5 mm, a porosity of 80%, and an average opening diameter of 100 μm was obtained.

This was degreased with alkali and washed with hydrochloric acid.

Tetraammineplatinum chloride (as pt) 0.3g Aqueous ammonia (28%) 2 Hydroxylamine (5%) 20 Dehydrazine (2
0%) 511Q water
A total amount of 300 mQ was then applied to electroplating one side of the porous plate with a portion of the above solution to form a catalyst layer, and after washing with water, the plate was immersed in the remaining solution and heated at 70°C for 3
Electroless plating was performed for several hours to plate platinum approximately 3 μm thick on one side.

Production Example 3 Sintering of nickel fiber web by melt spinning method 10
00°C x 1 hour), diameter 80mm, thickness 2.5mm,
A porous plate with a porosity of 60% and an average opening diameter of 200 μm was obtained.

After degreasing with alkali and washing with hydrochloric acid, Example 1
Approximately 3 μm of platinum was plated on one side using an acidic platinum plating bath.

Production example 4 Carbon black with 20% by weight platinum dispersed in PTF
Mix well using E-disversion, apply to one side of the porous plate of Example 2, dry, and then sinter at 280°C while applying gentle pressure (1 kg/cIiI) to the surface to form a porous plate. Platinum-supported carbon was embedded in the stainless steel surface.

Example 1 An ozone production experiment was conducted using the electrodes obtained in Production Examples 1 to 4 as cathodes. The electrolysis apparatus shown in Fig. 3 was used in the ozone production experiment. A power source with backup was used. The cell configuration and electrolysis conditions are as follows.

Cathode; Examples 1 to 4 each electrode, effective area 50 cm2 anode;
Lead dioxide coated porous titanium electrode (lead dioxide layer 200μm
), effective area 500 m2 Ion exchange membrane; Nafion 117 (manufactured by DuPont) anode plate; titanium cathode plate, SUS 304 Number of cells: 1 set electrolyte; ion exchange water current density: 100 A/dm2 Temperature: 28-30 ℃ Comparative Example 1 Cells with a conventional cathode configuration were assembled, connected in series, operated, and compared.

Cathode; platinum single-sided composite [platinum (3 μm)/Nafion 1
17 membrane) Cathode power feeder: Porous carbon (manufactured by Kobe Steel Corporation); Cathode end plate; graphite plate with ribs (manufactured by Toyo Tanso Corporation) Other conditions were the same as in Example 1.

The results of Examples and Comparative Examples are shown in Table 1.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a cell used in a conventional water electrolysis method. FIG. 2 is a schematic diagram of an example of a cell for carrying out the method of the invention. FIG. 3 is a schematic diagram of an example of an electrolysis device employing the method of the present invention. (1)...Titanium end plate (2)...Porous titanium plate (3)...Lead dioxide layer (4)...Cation exchange membrane (5)...Platinum layer (6)... Porous carbon plate (6a)...Porous stainless steel plate (7)...Carbon end plate (7a)...Stainless steel end plate (8)...0 ring (9)...Hydrogen outlet (10) ...Water supply port (11) ...Ozone + oxygen outlet ...Pure water reservoir and gas-liquid separator ...Liquid pump ...Electrolyzer ...Ozone/oxygen ...Ozone concentration meter ...・Hydrogen analyzer...Water seal...Hydrogen (or more) Fig. Fig. Fig.

Claims (1)

[Claims] (1) When producing ozone by a water electrolysis method using a perfluorosulfonic acid type cation exchange resin membrane, an electrode made of a porous plate made of nickel or nickel alloy steel coated with platinum on one side is used on the cathode side, and the A method for electrolytically producing ozone, characterized by carrying out zero-gap electrolysis by pressing the platinum coating layer side of an electrode against the cathode side of a cation exchange membrane.