JPS59190377A - Electrolyzing method - Google Patents

Abstract

PURPOSE:To obtain efficiently and stably alkali hydroxide of high quality for a long term by electrolyzing an aqueous soln. of alkali chloride in a horizontal electrolytic cell having a cation exchange membrane as a diaphragm while specifying the linear velocity of a catholyte in the cathode chamber and the gaseous partial ratio. CONSTITUTION:A horizontal electrolytic cell provided with an anode chamber on a horizontally stretched cation exchange membrane and a cathode chamber under the membrane is used. A cathode plate in the cathode chamber is impermeable to gas and liq. Electrolysis is carried out while regulating the initial linear velocity of a catholyte fed to the cathode chamber in the chamber to >=8cm/sec and the gaseous partial ratio at a position close to the catholyte discharging outlet to <=0.6. Low electrolytic voltage can be maintained by said initial linear velocity, and stable electrolysis can be continued for a long period by said gaseous partial ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention primarily relates to an electrolytic cell for an aqueous alkali metal halide solution, in particular an alkali chloride salt aqueous solution. More specifically, the present invention relates to an electrolytic method for efficiently producing high quality caustic alkali stably over a long period of time in a horizontal electrolytic cell using a cation exchange membrane as an electrolytic diaphragm.

A horizontal electrolytic cell is divided into an upper anode chamber and a lower cathode chamber by a horizontally stretched diaphragm. The most typical type of horizontal electrolyzer is the mercury method electrolyzer, which has been widely used because it produces a relatively high concentration of hydroxide bath solution.

However, since the mercury used in the cathode is an environmental pollutant, there is one possibility that it will have to be discontinued in the near future. By the way, scrapping all of the mercury electrolytic cells and phase-resistant devices that have been widely used in the past is not at all desirable from an economic or industrial policy standpoint, but it is also an extremely serious problem for the industry. Under such circumstances, it is highly desirable to convert mercury-based electrolytic cells and auxiliary equipment to other safer electrolytic cells without scrapping them.

From this perspective, the applicant has conducted extensive research and developed a technology that can advantageously convert a mercury-based electrolytic cell into a cation-exchange membrane electrolytic cell, and has previously filed a patent application (Japanese Patent Application No. 57-131).
377 etc.). That is, Japanese Patent Application No. 5'7-1.31377 is divided into an upper anode chamber and a lower cathode chamber by a cation exchange membrane stretched substantially horizontally, and the anode chamber is substantially horizontally stretched. The anode is surrounded by a lid body, a fixed anode chamber side wall surrounding the anode, and the upper surface of the cation exchange membrane, and has an anolyte inlet and a discharge date. anode gas discharge 1], the cathode chamber comprises a cathode plate having a substantially flat surface, a side wall of the cathode chamber surrounding the cathode plate, and a side wall of the cation exchange membrane. The electrolytic cell is surrounded by a lower surface and includes an inlet for a catholyte and an outlet for a mixed phase liquid of cathode gas and catholyte. sword)〃
) In order to perform electrolysis using an electrolytic cell with a structure of This is a great point. Therefore, in this regard, the present applicant has proposed that the initial linear velocity of the electrolyte supplied to the cathode chamber is closely related to gas retention and electrolysis voltage, and that the initial linear velocity in the cathode chamber is approximately 8 ovSeC or higher. It was discovered that by electrolyzing with
No. 7-16'0438).

However, even if the initial linear velocity is maintained at 8 Cm/sec or higher, as the gas amount increases, gas microbubbles will somehow come together, causing gas-liquid separation in the cathode chamber, and the separated gas will be transferred to the cation exchange membrane. Cover the bottom surface of the electrode and increase the electrolytic voltage. Furthermore, it causes vibration of the membrane (-1), which impedes long-term stable operation and eventually leads to membrane damage.

In view of the above circumstances, the present inventors conducted extensive research and found that by controlling the gas-liquid fraction between the cathode gas and the catholyte below a certain value, it is possible to prevent the above-mentioned gas 9M bubbles from meeting each other. Therefore, it was discovered that vibration of the membrane and damage to the membrane caused by this can be prevented, and the present invention was completed.

That is, the present invention includes an anode chamber in the upper part and a cathode chamber in the lower part of the cation exchange membrane which is installed substantially horizontally,
A horizontal electrolytic cell in which the cathode plate of the cathode chamber is gas/liquid permeable is used, and the initial linear velocity in the cathode chamber of the catholyte supplied to the cathode chamber is B' on7 sec or more, and the cathode The content is an electrolysis method characterized in that electrolysis is carried out at a gas fraction of 0.6 or less near the liquid outlet.

In the present invention, the initial linear velocity has the following meaning. That is, since the catholyte supplied to the cathode chamber entrains gas generated by electrolysis while flowing within the cathode chamber, the flow rate generally increases as it approaches the outlet. The linear velocity of the catholyte near the catholyte inlet when it does not contain any gas or contains only a small amount of gas is called the initial linear velocity. That is, the initial linear velocity means the linear velocity of the catholyte when there is substantially no gas generation. When the cross-sectional area of the catholyte flow path is substantially the same throughout the flow path, the initial linear velocity is equal to the linear velocity near the catholyte inlet. However, when the cross-sectional areas of the catholyte flow passages are different, it is expressed by the average linear velocity of the catholyte in the absence of gas generation.

FIG. 1 is a graph showing the relationship between the initial linear velocity of the catholyte and the electrolytic voltage.

It is clear from FIG. 1 that as the amount of electrolyte supplied increases, the voltage drops rapidly, then shows a gradual drop, and then roughly reaches equilibrium.

The bending point of the curve seen in the first graph has almost no relation to the current density, and the current density (
It is clear from the inventors that the flow rate range is approximately the same as 10 to 70 A/(ini') T. It is presumed that the rapid voltage drop at the first bending point 1 occurs because the accumulation of gas at the lower surface of the cation exchange membrane rapidly decreases as the flow rate increases. 1st bending point force)
It is presumed that the gradual drop in voltage from 1 to 2 to the second bending point is due to the fact that the adhesion of the generated gas to the electrode surface and the cation exchange membrane surface decreases as the flow rate increases.

According to the research results of the present inventors, the first bending point appears at an initial linear velocity of about 81 seconds or more, and the second bending point appears at about 29 seconds.
Appears above cm/BeC.

That is, in order to maintain a low electrolytic voltage, it is first necessary to operate at an initial linear velocity for supplying the catholyte to the catholyte chamber at about 8 cTvSec or higher, preferably at about 20 cTvsec or higher.

Furthermore, the second condition for continuing electrolysis stably for a long period of time is that it is necessary to operate at a gas fraction R of 0.6 or less near the catholyte outlet in the cathode chamber.

Here, the gas fraction R (for example, when electrolyzing at 85°C)
is expressed by the following equation.

R= G/(L+G) However, G is the cathode yt y, a yield (yyl/Hr)
Te, 0.4I8 (electrochemical equivalent) x KAH (kiloampere hour) x 358/273 (temperature compensation). L is the catholyte circulation flow rate (y)l/Hr).

In this way, the initial linear velocity of the catholyte in the cathode chamber is B a5
sec or more and the gas fraction near the cathode chamber exit is 0.6
By performing the electrolysis below, the specific resistance of the catholyte and the voltage drop are reduced, and long-term stable operation is possible at low voltage without damaging the membrane. Also, the current density at this time is 1
0 to 70 A/dtyf.

When the gas fraction R exceeds 0.6, the initial linear velocity is 8a/sec.
Even with the above, the amount of gas in the unit catholyte increases and the current-carrying area decreases, so not only does the electrolytic voltage rise, but the gas bubbles come together, causing gas-liquid separation in the cathode chamber.
The separated gas covers the lower surface of the cation exchange membrane and increases the electrolysis voltage. Furthermore, the flow of the separated gas and catholyte causes pulsation, which causes vibrations in the membrane near the cathode chamber outlet, causing damage to the membrane and making long-term operation impossible. Also, the vibration of the membrane is transmitted to the anode in contact with it,
Since vibration is generated in the cell cover via the conductive rod, a situation arises in which the cell itself must also be reinforced. Additionally, the gas fraction R near the cathode chamber exit
If the voltage is large, the electrical resistance to the catholyte near the entrance to the cathode chamber becomes large, which causes current distribution in the electrolytic cell, resulting in unfavorable results in terms of electrolytic performance.

Cation exchange membranes suitable for the present invention include, for example, Par71 rheolocarbon polymer f) having cation exchange groups.
).

As mentioned above, a membrane made of a perfluorocarbon polymer having a sulfonic acid group as an exchange group is manufactured by E.I.
Du Pont de Nemours &comp
Any) is commercially available under the trade name "Nafion", and its chemical structure is as shown in the following formula.

A suitable equivalent weight of such a cation exchange membrane is 1. .

00 to 2. O'00, preferably 1.100 to 1.500, where the equivalent weight is the weight (f) of the dry membrane per equivalent of exchange group. Alternatively, cation exchange membranes in which all of the cation exchange membranes are substituted with carboxylic acid groups and other commonly used cation exchange membranes can also be applied to the present invention. 3 water molecules without passing through
~4) It only passes IJium ions. In the present invention, in addition to the above-mentioned membrane, one so-called SPE
(5olj-d Po engineering Electrod
e) May be in April.

The shape of the gas/liquid permeable electrode used in the present invention is not particularly limited as long as it does not interfere with the flow of the electrolyte.

It may have a substantially flat surface, or it may have an uneven structure with convex striations along the flow of the electrolyte. Furthermore, small protrusions may be provided at appropriate intervals.

The uneven structure can be obtained by, for example, scraping out parallel miso on a flat plate, attaching a thin rod-shaped body such as a round bar or square bar to the flat plate by welding, or by integrally protruding it. Furthermore, the cathode plate itself can be made using a corrugated plate. There are no particular restrictions on the shape of the unevenness, such as rectangular wave,
75 beads can be used individually or in combination with trapezoidal, sinusoidal, circular, zykroid, etc. shapes.

Further, the unevenness does not necessarily have to be continuous along the flow direction of the liquid, and may be cut in the middle.

When using a gas/liquid permeable cathode plate having a concavo-convex structure, it is a preferred embodiment that the convex portions and the ion exchange membrane are in force≦adjacent to or in contact with each other.

The material of the above gas/liquid valve permeable electrode! Iron, stainless steel, nickel, Ni-Sokel alloy, etc. can be suitably used. Also, high-grade platinum group metals, their conductive oxides, or iron group metals, etc., which reduce hydrogen overvoltage, can be used on the surface of these electrodes. It is also preferred to apply a coating.

The anode placed above the cation exchange membrane (in order to quickly remove the generated gas from the upper part) is a porous electrode, such as an electrode, a mesh electrode, a louvered electrode, a round electrode, etc. It is also possible to use a wire-like electrode with rods lined up, or to supply and circulate the electrolyte between the electrode and the cation exchange membrane using a non-porous electrode. A substrate made of a single metal or an alloy of metals such as titanium, niobium, tantalum, etc., whose surface is coated with a platinum group metal, a conductive oxide thereof, etc. can be suitably used.

As mentioned above, according to the present invention, gas-liquid separation in the cathode chamber can be prevented, and as a result, vibration and damage of the membrane can be prevented.
It becomes possible to stably obtain high quality caustic alkali over a long period of time at low voltage.

The present invention will be explained below with reference to Experimental Example 1, but the present invention is not limited thereto.

As an example cation exchange membrane, “Nafion 901 (Du Po
(manufactured by nt)" with a length of 1. , g m x width 70C) nO
:) A horizontal bar was installed between the positive and negative poles of a horizontal electrolytic cell.

As the anode, a titanium expanded metal sheet whose surface was coated with Ru02 and TiO2 was used, and the distance between the electrodes was 2 mm. Part of the fresh salt water was circulated in the anode chamber, and the fresh salt water was drawn out to a concentration of 3.5 N. In the cathode chamber, the catholyte was circulated in the longitudinal direction so that the caustic concentration was 32%, and electrolysis was carried out at 85°C. The relationships among the current density, catholyte flow rate, and initial linear velocity in Experimental Examples 1 to 3 are as follows.

Experimental example 1 10 0.5-7 10-14
0 Experimental Example 2 40 0°9~9 18~180
Experimental example 8 70 1.6~9,8 32~
194 The relationship between the gas fraction and the catholyte specific resistance in this case is shown by a solid line in the second □□□. The specific resistance of the catholyte is 0.
It is clear that the value decreases when the value is 6 or less, and it is almost balanced when it is 0.4 or less.

EXAMPLE Experiments were carried out in the same manner as in Experimental Examples 1 to 3, except that a horizontal electrolytic cell with a length of 10 m and a width of 10 Ql+ was used, the distance between the electrodes was set to 4, and the flow rate was varied as described below.

Experimental example 4, 10 0.3-5.5 21
~380 Experimental Example 5 80 0.4~5. Q
28-350 Experimental Example 6 50 0.7-8,
8 49-580 The relationship between the voltage drop of the catholyte and the gas fraction at this time is shown in FIG. Cathode g! It can be seen that the voltage drop decreases when the gas fraction is 0.6 or less, and almost reaches equilibrium when the gas fraction is 0.4 or less.

EXAMPLE The above-mentioned "Nafion 901" was stretched between the negative and positive electrodes of a horizontal electrolytic cell measuring 11 m long x 1.8 m wide in a substantially horizontal manner. The anode used in Experimental Example 1 was used, and the distance between the electrodes was 3 mm. The current density is 8 o A/dyd,
The liquid circulation and concentration in the anode and cathode chambers were both under the same conditions as in Experimental Example 1, and the catholyte was circulated in the width direction. Circulation flow rate: 15-310 nf/Hr, initial linear velocity: 18-2
The relationship between the gas fraction and the electrolysis voltage when the temperature was changed to 50 an/1eec is shown in the fourth □□□. From FIG. 4, it is recognized that the electrolytic voltage decreases when the gas fraction is 0.6 or less, and almost reaches equilibrium when the gas fraction is 0.4 or less. Furthermore, the current density is 30
Long-term operation was performed for 5 months at A/dnf and circulation flow rate of 70 ni/Hr. The gas fraction at this time was 0.32. The voltage was 3.12 V and the current efficiency was 96%. Almost no vibration of the membrane was observed during operation, and after the operation was stopped, the electrolytic cell was disassembled and the membrane was observed, but no damage to the membrane was observed.

Example The distance between electrodes was 4 mm, and the current density was 10 Ladn7.
The same operation as in Experimental Example 1 was repeated except that .

The relationship between the gas fraction and the specific resistance of the catholyte at this time is shown by a broken line in FIG. As is clear from Figure 2, the gas fraction is 0.
．． Even when the initial linear velocity of the catholyte was less than 8Cr/VSeC, the specific resistance of the catholyte increased.

The present invention will be described below with reference to Examples and Comparative Examples.

Example 1 “Nafion 901(J)uP” as a cation exchange membrane
Ont Co., Ltd.] was stretched substantially horizontally between the negative and positive electrodes of a horizontal electrolytic cell with a length of 11.1 m and a width of 1.8 m. The anode used was a titanium expandable 7' metal sheet coated with RuO2 and TiO2, and the cathode was an iron plate coated with Ni.

The cathode had grooves with a depth of 8 mm and a width of 8 mm at a pitch of 16 mm in parallel with the longitudinal direction, and the convex portion was configured to face the cation exchange membrane while maintaining a distance of about 1 πm. The catholyte was circulated in the longitudinal direction.

The NaCl concentration in the anode chamber was 3.5N, the NaOH concentration in the cathode chamber was 32%, and the temperature was controlled at 85±2°C.

The vibration of the anode was measured with a dial gauge attached to the anode power supply rod. That is, the distance between the bar having a constant height and the upper end of the anode power supply rod as shown in FIG. 5 was measured with a gauge, and the vibration of the anode was observed from the vibration.

Current density 20 A/(circulating fluid volume 20 y at 1 m) I/
Hr (Initial linear velocity 6 Q Cm/BeC) f) h et al. 5
The speed was changed to 0 y no f/Hr' (150 m/sec). No anode vibration was observed. The gas fraction at the outlet at this time was 0.53 to 0.30.

Continuous operation was carried out for one month within the above range of circulating fluid amount, but the operation could be continued without any abnormality.

Comparative Example 1 Same electrolytic conditions as Iso Example 1, current density 3°A/d,
The m-c circulating fluid amount was increased to 2o, 3o, 5 onf/Hr.

At 30.50 yyi'/Hr, no vibration of the anode was observed, but at 2 Onf/Hr, the anode at the exit of the cathode chamber was observed to vibrate. The gas fraction at the outlet at this time was 0.62.

When the electrolytic cell was disassembled after one month of continuous operation and the membrane was inspected, small pinholes were found near the exit of the cathode chamber.

Comparative Example 2 Same electrolytic conditions as Example 1, current density 40A/dn
? Circulate 'e fA 20 yyi'/Hr T t
Solution fx fc.

Vibration of the anode was observed from a position 9 m from the cathode chamber entrance toward the exit.The closer the cathode chamber was to Hatakeguchi, the more intense the vibrations were. The gas fraction at a position 9 m away from the cathode chamber entrance is o, 64, and the gas fraction at the cathode chamber outlet is 0.69.
Met.

On the 20th day of continuous operation, the hydrogen concentration in the chlorine gas rose to 0.7%, so when we stopped the operation and inspected the membrane, we found pinholes from 9 m from the catholyte inlet to the catholyte outlet. In particular, a crack of 1.5 cm had occurred at the catholyte outlet.

Example 2 In Comparative Example 2, the amount of circulating fluid was set to 20 yy? /Hr to 83 ypi', /H°. No vibration of the anode was observed at all. At this time, the gas fraction at the outlet is 0
．． It was 57.

Comparative Example 3 The same conditions as in Example 1 were used except that the cathode was a flat plate and the distance between the electrodes was 4 mm.

Current density 40 A/dn? −? ? Circulating fluid volume 2077r'
When electrolysis was carried out at /Hr (initial linear velocity 78 cyn/SeC), vibration of the anode was observed from a position 9.5 m from the catholyte inlet to the outlet. The gas fraction at this point was 0.65.

Example 3 In Comparative Example 3, electrolysis was performed by increasing the amount of circulating fluid from 2' Onf/Hr to 85 m/Hr. No vibration of the anode was observed. At this time, the gas fraction at the outlet is 0.
It was 56.

[Brief explanation of drawings]

Figure 10 is a graph showing the relationship between the initial linear velocity of the catholyte and the electrolytic voltage, Figure 2 is a graph showing the relationship between the gas fraction and the specific resistance of the catholyte, and Figure 3 (2) is a graph showing the relationship between the gas fraction and the catholyte. FIG. 4 is a graph showing the relationship between gas fraction and electrolysis voltage. FIG. 5 is a schematic diagram of attaching a dial gauge to the electrolytic cell and measuring the vibration of the anode. l...Anode chamber 2...Cathode chamber 3...
Cation exchange membrane 4... Anode 5... Cathode
6...Cathode liquid inlet lower...Cathode liquid outlet
8...Gauge installation is rod 9...Dial gauge 10...Anode power supply rod Figure 1 11 @ Fine drawing summer? SZ power ratio G/(G or L) power ratio G/(G, L)

Claims (1)

[Claims] 1. An anode chamber is provided in the upper part of a cation exchange membrane stretched horizontally, and a cathode chamber is provided in the lower part of the cation exchange membrane, and the cathode plate of the cathode chamber is connected to gas or liquid. Using a horizontal electrolytic cell that is a permeation type electrolytic cell, the initial linear velocity of the catholyte supplied to the catholyte chamber is 8 CwVSeC or more, and the gas fraction near the catholyte outlet is 0.6 or less. An electrolysis method characterized by performing electrolysis. 2. The electrolysis method according to claim 1, wherein the current density is in the range of 10 to 70 A/d772'.