JPS5896886A - Electrolyzing method for aqueous alkali metal salt solution - Google Patents

Abstract

PURPOSE:To decrease the voltage of an electrolytic cell without degrading electric current efficiency in an electrolytic cell for aq. alkali chloride solns. using a cation exchange membrane by bringing an anode into tight contact with one side of the exchange membrane and a cathode with the opposite side via a conductive member. CONSTITUTION:A diaphragm used for a diaphragm type electrolytic cell for aq. alkali chloride soln. of NaCl or the like is constituted of a porous cation exchange membrane 1 of metallic oxide or the like having no electrode activity on at least one side thereof, and an anode 2 of a perforated Ti plate, meshes, or the like is brought into tight contact with one surface thereof. Alloys or oxides of Ru, Pt, etc. are coated on the surface thereof. A cathode 3 consisting of a perforated plate of iron, stainless steel, etc. is brought into tight contact with the opposite side of the membrane 1 via an elastic non-metallic conductor 8 of a carbon fiber mat or the like. Since the spacing between the anode 2 and the cathode 3 is narrow and inter-electrode resistance is small, the lower cell voltage of the electrolytic cell is required and the electric power efficiency for electrolysis is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for electrolyzing an aqueous alkali metal salt solution using a cation exchange membrane. More specifically, when producing caustic alkali by electrolyzing an alkaline all-polar salt aqueous solution with an electrolytic tag that is divided into an anode chamber and a negative chamber by a cation exchange membrane, the cation exchange membrane is used at least on the surface. -i'+'i is a cation exchange membrane with a porous layer having no electrode activity, and the cation exchange membrane is used as a cathode.7. The present invention relates to a method for electrolyzing an aqueous alkali metal salt solution, which is characterized in that the present invention is made in close contact with a cathode via an elastic conductive member.

Conventionally, the electrolysis method of aqueous alkali metal salt solutions uses mercury or ? :The mercury-based electrolysis method used and the diaphragm method using mercury (
Asbestos diaphragm method).

In the mercury method, because mercury is used in the cathode, mercury is contained in the caustic powder and in the wastewater that comes into contact with mercury, so there is a tendency worldwide to adopt non-mercury methods due to environmental pollution issues. be.

Also, the mercury method is 'I3 solution' i51. Average force intensity is 3.2
00KWH/t-NaOH and poor power efficiency.

The asbestos diaphragm method does not use mercury, so
Although the problem of environmental pollution due to mercury does not occur, the problem of environmental pollution due to asbestos remains. In addition, although the electrolytic power unit is 2500 KWH/t-NaOH on average and the gravity efficiency is high, the concentration of the generated caustic soda is as low as 10 to 2%, so it takes about 2.5% to reach 50%. st
/1-NaOH evaporation is required and is worse than the mercury method in terms of overall energy efficiency. On the other hand, ion exchange, which has been developed and commercialized in recent years? In the ion exchange membrane method using AM as the separation IP, neither water fort nor asbestos is used.
There is no problem of environmental pollution, the concentration of caustic soda produced is generally 20-40%, and the average electrolytic power consumption is 2.5%.
At 00 KWH/1-NaOH, approximately o4t/1-NaOH of steam is required to concentrate to 50%, but the overall energy efficiency is the best.

In the ion exchange membrane method, the present inventor conducted various studies and experiments in order to reduce the electrolytic force, and developed a cation exchange method in which a porous layer having no vN electrode activity was provided on at least one surface. In an electrolytic cell with a membrane interposed between an anode and a cathode,
The cation exchange membrane and the anode are brought into substantially close contact with each other, and an elastic non-metallic conductor is interposed between the cation exchange membrane and the cathode, so that the cation exchange phase 4 and the non-metallic conductor having a tonality are formed. The inventors have discovered that by electrolyzing an aqueous alkali metal salt solution while bringing the metal conductor and cathode into close contact, the electrolytic sliding voltage can be reduced without impairing current efficiency.

That is, in an electrolytic cell divided into an anode chamber and a cathode chamber by a cation exchange membrane having a porous QG4 layer with no electrode activity on at least one surface of the cation exchange membrane, the anode is placed between a conductive rib and a cathode chamber. /or When the cation exchange membrane is fixed to the chamber frame and the porous layer is provided on only one side, the cation exchange membrane has the surface on which the porous layer having no electrode activity is provided as the cathode side. By inserting and tightening an elastic non-metallic conductor, such as carbon fiber mat, between the cation exchange membrane and the cathode, the anode, cation exchange membrane and elastic The nonmetallic conductor and the cathode are brought into complete contact and pressure contact. At this time, the contact pressure must be maintained at such a level that the cation exchange membrane is not damaged. For example, if the contact pressure is expressed as the value obtained by dividing the pressure by the effective electrolytic direction .
O] Kri/- to 1.0 Ni/- is desirable.

Preferably, it can be set to 0.05 to 97-0.60 to 9/d. Furthermore, a more preferable form for preventing the cation exchange membrane from being damaged is to interpose a conductive metal spring between the cathode and the cathode conductive rib (or partition wall). By doing this, this snow%: Using an alkaline φ7 area salt water bath #tube%, (then, a non-metallic conductor such as a carbon mat is formed between the ion exchanger 1 and the cathode. As a result, the cathode and the film maintain a nearly uniform distance, and the gas generated at the cathode that cannot escape to the back surface of the cathode can easily escape through this non-metallic conductor (in other words, it prevents scum from accumulating). ＜〈) and also the electrolytic current (
1) Since a portion of the electrolyte flows through the conductor, it is possible to slightly lower the electrolytic voltage as a whole. In fact, due to the synergistic effect with the large hydrophilicity of the porous layer with no electrode activity provided on the surface of the cation exchange membrane, the amount of residue remaining between the cation exchange membrane and the cathode can be extremely reduced. The object of the present invention can be achieved even more preferably.

For a better understanding, the present invention will be described with reference to the accompanying drawings, but the invention is not limited to the form shown in the drawings.

The figure shows the outline of an electrolytic cell used in the present invention. Reference numeral 1 denotes a cation exchange membrane, which is provided with a porous layer on at least one surface that does not impair electrode activity. As the cation exchange membrane, a fluorine-based cation exchange membrane having a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group as an ion exchange group can be used, and there is no electrode activity provided on the surface of this cation exchange membrane. Materials used for the porous layer include, for example, titanium, zirconium, niobium, tantalum, vanadium, manganese, molybdenum, tin, antimony, tungsten, hismuth, indium, cobalt, nickel, beryllium, aluminum, chromium, iron,
potassium, kermanium, selenium, yztrium, silver,
Oxides, nitrides, and carbides of lanthanum, cerium, nitrogen, lead, thorium, and metal elements, as well as solid solutions or mixtures thereof, are used. Among these, on the opening side, oxides, nitrides, and carbides of titanium, zirconium, niobium, tantalum, vanadium, manganese, molybdenum, tin, antimony, tungsten, bismuth, etc. alone, solid solutions, or mixtures thereof are used. be done. To form a porous layer from these materials, the above materials are used in powder or particulate form, preferably bonded with a suspension of a fluorine-containing polymer such as pholytetrafluoroethylene, and formed into a layer as appropriate. After that, by applying pressure and heat to the surface of the ion exchange membrane, it is bonded and preferably embedded.

2 is an anode, for example, a perforated plate-shaped, mesh-shaped, net-shaped, or rod-shaped anode made of titanium, and the surface thereof is coated with one of precious metals such as ruthenium, platinum, iridium, and rhodium.
A seed, an alloy of 2S or higher, or an oxide thereof coated is used. The anode 2 is electrically connected to the titanium conductive lip 4.

The titanium conductive lip 4 is electrically and mechanically fixed to the anode chamber frame 6.

3 is the cathode, which is made of iron or stainless steel in the shape of a porous plate, mesh, net, or rod, and can be plated with Rodan nickel or co-electrodeposited with Raney nickel and nickel. . The cathode 3 is electrically and mechanically fixed to a conductive rib 5 made of iron or stainless steel,
Further, a conductive lip 5 made of iron or stainless steel is electrically and H4 fixed to the cathode chamber frame 7.

8 is a non-metallic ψ electric body having elasticity inserted between the cation exchange membrane 1 and the cathode 3; for example, a mat-like body of 7J-bon fiber, a laminate of cloth, or a mesh-like body is used. be able to.

9 and 10 are openings for making the concentration distribution in the electrode chamber uniform, 11 and 12 are anolyte and catholyte supply nozzles, and 13 and 14 are anolyte and catholyte supply nozzles.
This is a gas discharge nozzle. Reference numerals 15 and 16 are gaskets, and the tank opening/disassembly of the present invention is constructed of these members, and the anode, the partition ion exchange membrane, the elastic nonmetallic conductor, and the cathode are almost completely in close contact and pressure-welded. Ru.

Fig. 2 shows another form of the frost 1 melting cypress used in the present invention, in which the cathode 3 and the cathode conductive rib 5 are made of steel, stainless steel, nickel, or nickel on their surface. This is an electrolytic cell equipped with a plated spring. By doing so, damage to the cation exchange membrane can be completely prevented.

To summarize the features of the electrolytic cell of the present invention, an elastic non-metallic conductor such as carbon fiber is interposed between the cation exchange membrane and the cathode, and the elastic non-metal conductor is connected to the anode and the cation exchange membrane. By bringing the body and cathode into almost complete contact and pressure contact, the cation exchange membrane is not damaged.
In addition, stable operation can be continued with low electric current efficiency and low sliding voltage without impairing current efficiency. Carbon fiber has (1) excellent electrical conductivity, (2) excellent corrosion resistance, (8) low friction coefficient, (4) easy release of air bubbles, and (5) film This is because it has characteristics such as being hard to damage the surface.Example 1 The electrolytic structure shown in FIG. 1 with a current-carrying surface of 10 crnW x 15 crnH was assembled. The cation exchange membrane uses an ion exchange membrane with a carboxylic acid group and a fluorocarbon resin, and titanium oxide is bonded to both surfaces with an Oka suspension of phoritetrafluoroethylene, forming a layered structure. The treated one was used.

The anode has a longitudinal dimension (LW) of 12.7 mm,
A titanium mesh with a width of 6.3 mm and a thickness of 157 mm, whose optical surface is completely coated with ruthenium oxide, is used for the cathode.
W) 20 m, transversal dimension (6 tW)] A stainless steel mesh with a thickness of 1.8 mm is used, and a thickness of approximately 0.7 mm with elasticity is used between the cathode and the cation exchange membrane.
A carbon fiber cloth of mm was inserted. 67f liquid 3.5N
Na (1!1, catholyte 35% NaOH, temperature 90°C
As a result of electrolysis at 20A/dyy/, the sliding voltage was 303V, the current efficiency was 95chi, and the power consumption was 2137 KWH/t-N.
It was aOH.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an electrolytic cell used in the present invention. FIG. 2 is a sectional view of another example of the electrolytic cell used in the present invention. 1: Cation exchange membrane provided with a porous layer that does not have electrode activity 2: Anode 3: Cathode 8: Elastic nonmetallic conductor

Claims (1)

[Scope of Claims] (1) A cation exchange membrane provided with a porous layer having no electrical contact activity on at least one surface, which in practice has at least one
In the ion exchange membrane method electrolysis of an aqueous alkali chloride salt solution divided into an anode chamber having two anodes and a cathode chamber having substantially at least one cathode, the cation exchange membrane and the anode are substantially separated. A non-metallic conductor having elasticity is interposed between the cation exchange membrane and the cathode, and the conductor and the cathode are closely attached to the cation exchange membrane and the elastic non-metallic conductor. A method for electrolyzing an aqueous alkali gold salt solution. (2) The electrolysis method according to claim (1), wherein the nonmetallic conductor is mainly carbon. (8) Claim (1) characterized in that the means for bringing the cation exchange membrane, the elastic nonmetallic conductor, and the cathode into close contact is a conductive metal spring disposed on the back surface of the cathode, (2j and the electrolytic method described in (8).