JPS5837181A - Electrolytic cell for electrolysis of aqueous alkali metal chloride solution - Google Patents

Abstract

PURPOSE:To provide an electrolytic cell for electrolysis of aq. alkali metal chloride solns. which prevents damaging of cation exchange membranes and has improved electrolyzing efficiency by interposing a porous metallic membrane having hydrogen overvoltage larger than that of a porous cathode between the cation exchange membrane and the cathode. CONSTITUTION:In an electrolytic cell, a clearance of about 0.5-5mm. is provided between a cation exchange membrane 8 and a porous cathode 4, and a porous metallic membrane 8 having hydrogen overvoltage larger than that of the cathode 4 made of Fe, Ni or an alloy contg. these is interposed therein. By such interposition, the membrane 3 is pressed to the anode side and the pressure in the cathode chamber is maintained higher than the pressure in the anode chamber during operation. A sufficient clearance is provided between the membrane 3 and the cathode 4, and an aq. caustic alkali soln. is passed therein to conduct the gaseous hydrogen between the membrane 3 and the cathode 4 to the space behind the cathode 4. The electrolyzing effect of the aq. alkali metal chloride soln. is improved by such mechanism.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid electrolytic cell, particularly an electrolytic cell used for electrolyzing aqueous alkali metal chlorides such as sodium and potassium.

More specifically, it is a so-called two-chamber vertical electrolytic cell, and is characterized by having a metal diaphragm between the cation exchange membrane and the cathode.

Conventionally, the exchange membrane method has been known as a method for electrolyzing aqueous solutions of alkali metal salts. Furthermore, with the development of a more durable cation exchange membrane, a two-chamber electrolyzer was proposed. This type of electrolytic cell generally has a porous anode and a cathode, and they are placed relatively close to each other, with a cation exchange membrane between them, and an anode chamber space and a cathode chamber space behind each electrode. It is based on a structure with , and various design cost changes have been added to these.

Examples of various improvement proposals include lowering the electrolytic voltage by bringing the ion exchange membrane closer to the anode side or bringing it into close contact with the anode surface, and adding a net or strip between the ion exchange membrane and the anode and/or cathode. By interposing a wedge-shaped spacer, it is possible to prevent the accumulation of air bubbles, or to exchange the anode and cathode. [There are proposals to make the distance between the stain electrodes medium or small to make the electrical resistance of the solution as small as possible, as well as to bring them into close contact.

The present invention is characterized in that a metal porous membrane having a higher hydrogen overvoltage than the cathode is interposed between a cation exchange membrane and a porous cathode having a gas-liquid flow path behind the cathode. This is an electrolytic cell for exchange membrane method aqueous alkali metal chloride solution electrolysis.

The main feature of the present invention is the relationship between the cation exchange membrane and the cathode.
(Mosquito cathode) is also possible by interposing a metal porous membrane with a large hydrogen overvoltage.

As mentioned above, there have been proposals to interpose a cation exchange membrane and a cathode OMJK sweeper. Purpose #'i in this case
...To prevent the cation exchange membrane from coming into contact with the cathode and damage it, and by pushing the cation exchange membrane toward the anode side, the voltage between the electrodes during electrolysis can be reduced between the GA and the cation exchange membrane and the cathode. It is thought that a sufficient gap was provided between the membranes so that the caustic alkaline water bathing solution could flow into the gap, and hydrogen gas between the cation exchange membrane and the cathode was introduced into the space behind the cathode.

Therefore, the spacers used in the prior art are all made of non-conductive materials and have extremely large pore diameters, for example, mesh-like spacers with a mesh size of 701 or more.

Another technique is to create a metal mesh, also known as an auxiliary electrode, between the cation exchange membrane and the cathode, and when a potential is applied to it, the hydroxide ions generated on the cathode undergo cation exchange. Some methods use electrical repulsion to suppress diffusion toward the membrane side.

In this case there is a relatively large distance between the cathode and the auxiliary cathode, for example! The auxiliary cathode requires a spacing of about -10 wm, and the auxiliary cathode is made of a relatively large mesh metal, and furthermore, a potential smaller in absolute value than that of the cathode is separately added. This shape results in an increase in the thickness of the electrode chamber, and is not suitable for use as a multilayer electrolytic cell or the like.

In a preferred embodiment of the present invention, the distance between the anode and the cathode is 0.5 to S■
Furthermore, the narrow KFi is particularly one tatami mat size, and a metal membrane is interposed so as to be in contact with both the cation exchange membrane and the cathode.

The mosquito metal of the present invention has the same potential as the cathode when it comes into contact with the cathode. However, since the cathode also has a large hydrogen overvoltage, it does not function as a cathode itself.

In the present invention, the hydrogen gas generated on the cathode surface leaves the cathode surface very quickly, and in caustic alkali, it does not associate with each other relatively and becomes like an emulsified state. By elucidating the mechanism by which hydrogen gas adheres to the surface of the cation exchange membrane due to its good staining with hydrogen gas, reducing the current-carrying area causes an increase in voltage during electrolysis. We investigated ways to prevent the hydrogen generated on the cathode from coming into contact with the cation exchange membrane as much as possible. As a result, in the case of conventional non-conductive material spacers such as Thrilene, hydrogen bubbles tend to adhere to the cation exchange membrane in caustic alkali as well as the cation exchange membrane. 1 as in the case of
I learned that reducing the effective current-carrying area results in K.

However, strangely, metals do not stain well with hydrogen in aqueous caustic alkali solutions, and there is very little tendency for hydrogen gas to adhere to their surfaces. Furthermore, when considering the state of the pores of a porous metal that is suitable for preventing hydrogen gas generated at the cathode from passing through the porous metal membrane, reaching the cation exchange membrane, and adhering to the membrane surface, it is generally found that the pore size It is natural that the smaller the pore size, the better the performance, but when observed, the pore diameter is 0. A pore diameter of approximately s■ is sufficient, and even a pore diameter of approximately 1■ is observed to be sufficiently effective. Therefore, generally 10
A pore size of 00 μm or less is preferred. In addition, in order to obtain a very small pore diameter, the fast shielding part that constitutes this usually increases, so it is usually better to use a mesh membrane with a pore diameter of Sθ ~ 1000 s. The thickness of the porous metal film is not particularly determined, but is generally O, OS ~ 3.
- degree is sufficient. Also, the skeleton membrane vibrates during electrolysis,
If there is a risk of bending, it may be effective to fix it on the cathode by welding or other means.

Second, the material of the porous metal membrane of the present invention is determined by its relative relationship with the cathode, and it is essential that the material has a larger hydrogen overvoltage than the cathode. It is preferable that the material has a hydrogen overvoltage that is larger than the algebraic sum of the potential difference in the caustic alkaline aqueous solution and the cathode overvoltage, but in general, the potential difference in the #aqueous solution is 20~μ (7 m
It is only V/1u, and even if this is ignored and the material is selected, no superimposed problems will actually occur. Of course, if the thickness of the mosquito porous metal membrane is large, for example 2~. If it is as much as 7m1K,
It is desirable to consider the potential difference in the solution depending on the thickness K.
Examples of such materials are nickel alloys such as 2/Kel or stainless steel for mild steel cathodes, aluminum, etc., and secondary cathodes such as platinum, Fujiram, tungsten, gold, Alternatively, in the case of a cathode in which these are plated on a base metal as a cathode, or a nickel-plated cathode consisting of a sulfur-containing nickel layer, mild steel, nickel, or the like is used as the porous metal film.

Generally, iron, nickel, or stainless steel wire mesh is used.
As a cathode, it is preferable to use a cathode having a hydrogen overvoltage lower than that of iron, for example, a cathode substrate made of iron or the like, electroplated with or without copper plating in a plating bath containing rhodan nickel. This will be explained in more detail with reference to the drawings. Figure 1 is a sectional view of a part of a conventional ion-exchange membrane type rigid electrolytic cell, such as a filter breath type bipolar cell. Electrolytic tank frame 1.
1′ and bulkhead! 1 and 2', with a cation exchange membrane 8 sandwiched between them, 4 being a cathode and 6 being an anode. Further, 6 and 7 are conductive lips for supplying electricity to the cathode and the anode, respectively, and the spaces between the partition walls and the electrodes are a cathode chamber and an anode chamber, respectively, which serve as flow paths for the liquid and gas in the chambers.

Of course, the present invention is not limited to bipolar electrolytic cells, but any electrolytic cell that can basically constitute the unit cell shown in FIG. 1 may be used. FIG. 2 is a partial cross-sectional view of an example of the electrolytic cell of the present invention, and in this figure, which corresponds to FIG.
8 is a porous metal film. FIG. 3 shows this state more clearly. FIG. 3 is a diagram showing a part of a cross section taken in a direction perpendicular to the cross section of FIG. 2. FIG. In this embodiment, the porous metal membrane is present between the cation exchange membrane and the cathode in a narrow gap between the anode and the cathode, preferably between 005 and 5 m, and especially between the cation exchange membrane and the cathode. The invention shows its effectiveness. That is, the effect of pressing and fixing the cation exchange membrane on the anode side is also added. Furthermore, the electrolytic cell of the present invention is more effective if the pressure in the #1 electrode chamber is kept higher than the pressure in the anode chamber by 00 to 400 μm water column, or even 35'0 to 1750 μm water column, during operation.

Examples of use of the electrolytic cell of the present invention are shown below.

Example: An electrolytic cell with current-carrying area/g dm, the anode is a titanium lath coated with ruthenium oxide,
The nine cathodes were made of mild steel lath plated with copper by a conventional method, and further electroplated using a Rodan nickel bath. (The presence of sulfur in this plating layer was confirmed using an X-ray microanalyzer.) The structure had a distance of 3 wa between the electrodes and a space of 5 wa behind each electrode.

As a cation exchange membrane, the sulfonic acid group of Fion (trade name) manufactured by 7147 was converted to sulfonyl chloride by treating only one surface of the membrane with phosphorus pentoxide, and this was oxidized to exchange it with calgenic acid group. (EW=/10O) was used.

In salt electrolysis in the case where a porous metal membrane of stainless steel O-mesh plain woven mesh (wire diameter 0./Sum) was present between the cathode 2 cation exchange membrane and the case in which it was excluded. The respective data and electrolytic conditions are shown in Table/.

Table/Example Using the electrolytic cell of Example 1, similar experiments were conducted using mild steel plain-woven wire meshes with various openings. The results are shown in Table 2.

Figure 1 is a cross-sectional view of a conventional vertical ion exchange membrane electrolyzer, and Figure 2 is a cross-sectional view of a portion of the electrolytic cell of the present invention corresponding to Figure 1. FIG. 3 is a partial sectional view taken perpendicular to the cross section in FIG. 2.

' In the figure, 1.1' is the electrolytic cell frame, z, 2' are the partition walls, and 3
is a cation exchange membrane, 5 is a cathode, 5 is an anode, and 6 and 7 are ribs, respectively.

patent applicant Tokuyama Soda Co., Ltd. Shore 2a 312 years old Kata/Akira

Claims (1)

[Claims] 11+ A metal porous membrane having a higher hydrogen overvoltage than the cathode is interposed between the cation exchange membrane and the porous cathode having air and liquid flow paths behind the cathode. 4 electrolytic cells for aqueous electrolysis of alkali metal chloride using the ion-exchange membrane method.The metal porous membrane is made of one metal selected from iron, nickel, or an alloy containing these, and the cathode is made of iron, nickel, or an alloy containing these metals. , Claim 01 is characterized in that it has a low hydrogen overvoltage! Electrolytic cell described in @I, item (1) Patent claim OI1m, characterized in that it is plated with a compound and has nine surfaces! No. (2nd
) The gap between the anode and cathode is Q, j~
5- The electrolytic cell according to claim (1)