JPS5816081A - Electrolyzing method for aqueous solution of alkali metal chloride - Google Patents

Abstract

PURPOSE:To decrease the electric resistance on an anode chamber side and to prevent the degradation in the durability of a cation exchange membrane by maintaining the spacing between the cation exchange membrane and an anode in a specific range, and maintaining the corresponding diameter in the spacing part on the rear surface of the anode and the linear ascending speed of liquid under specific conditions. CONSTITUTION:In the stage of electrolyzing an aq. soln. of alkali metal chloride by the use of a vertical type electrolytic cell of an ion exchange membrane method, the spacing (t) between a cation exchange membrane 2 and an anode 5 is adjusted to 0.5-3mm., more preferably to about 0.5-2mm., and electrolysis is performed under the conditions under which the relation between the corresponding diameter De(mm.) in the space part 4 on the rear surface of the anode 1 and the linear ascending speed U(cm/sec) of liquid in the part 4 assumes U/De>=0.15. If (t)<0.5mm. in said relation, the foam of gaseous chlorine stagnates and contributes to deterioration of the cation exchange membrane, and if (t)>3mm., the electric resistance increases. If U/De exceeds 0.15, it is evident from experiment that the electric resistace on the anode chamber side decreases sharply.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses an ion-exchange membrane method to electrolyze an alkali metal chloride aqueous solution using an electrolytic cell, particularly for the purpose of reducing the electrical resistance on the anode chamber side. This invention relates to a method for electrolyzing an aqueous solution.

Much research has been carried out on methods of electrolyzing aqueous solutions of alkali metal chloride (1), such as sodium chloride, potassium chloride, etc., using an ion-exchange membrane vertical electrolytic cell, and this is becoming established as a new electrolytic technology. In this electrolysis method, reducing the electrical resistance on the anode chamber side and improving the power consumption rate is a very big l1ffl in economically implementing this electrolysis method, and various attempts have been made to date. is being done. For example, JP-A No. 55-58381 describes a technique for reducing the electrical resistance on the anode chamber side by adding special innovations to the shape of the anode, increasing the thickness of the anode chamber, and improving gas release. It's being done.

In addition, breaking the close contact with the anode surface of a cation exchange membrane is widely practiced as a means of lowering the electrical resistance on the anode chamber side.

However, with these methods, the degree of reduction in electrical resistance on the anode chamber side is far from sufficient and is not satisfactory. In addition, when the cation exchange membrane is brought into close contact with the anode surface, the durability of the cation exchange membrane decreases, resulting in the disadvantage of cracking.

The present inventors have conducted experiments and studies for many years in order to establish an electrolysis method that can eliminate the above-mentioned drawbacks and also achieve a reduction in the electrical resistance on the positive side chamber side. As a result, the following findings were obtained. That is, the chlorine gas generated at the anode tends to adhere to metals such as the anode, and usually remains on the surface of the anode until it grows into bubbles of 0.5 to several nanometers. The electrical resistance due to the bubbles accounts for a considerable portion of the electrical resistance on the anode chamber side. When the cation exchange membrane is brought into close contact with the anode, the amount of air bubbles adhering to the anode surface further increases, and the reduction in fluid resistance due to the cation exchange membrane being brought into close contact with the anode is due to the amount of air bubbles adhering to the anode surface. almost canceled out by the increase in electrical resistance due to

In addition, air bubbles remaining on the anode surface generate localized high current areas and excessive desalination areas, which can cause deterioration of the cation exchange membrane when it is placed in close contact with the anode. What to do. Based on these findings, we conducted many more experiments and found that the distance between the cation exchange membrane and the anode was maintained within a specific range, and the equivalent diameter of the space on the back of the anode and the rise of the liquid in the space were determined. They discovered that the desired objective could be achieved by maintaining the linear velocity under specific conditions, and thus completed the present invention.That is, the present invention utilizes an ion exchange farming vertical electrolytic cell to produce alkali metal chloride. When electrolyzing an aqueous solution, the gap between the cation exchange membrane and the anode is adjusted to 0.5 to 3af, and the equivalent diameter D e (11+1) of the space on the back of the anode and the rise of the liquid flowing into the space are adjusted. The relationship with speed U (cm/s@a) is U/D e≧
This is a method for electrolyzing an aqueous alkali metal chloride solution, which is characterized in that electrolysis is carried out under conditions such that the electrolysis temperature is 0.15.

In the electrolysis method of the present invention, the anode is made of a porous electrode such as an expanded metal or a metal porous plate.The electrode acid is formed by vertically arranging rod-like bodies, a so-called interdigital electrode, and the anode is made of a porous electrode such as an expanded metal or metal porous plate. The present invention can be applied to the electrolysis of an aqueous alkali metal chloride solution using an ion-exchange membrane vertical electrolytic cylinder in which a W wall exists without particular limitation.

In the present invention, the gap between the cation exchange membrane and the anode, E, and the gap between the cation exchange membrane Q) and the anode (1) in the partial sectional view of the vertical electrolytic cell for ion exchange farming shown in FIG. Interval a(t
) It is important to adjust it to 3tx, preferably 0.5 to 2. In addition, in Figure 1, (
3) is a partition wall, and (4) is a space behind the anode.

If the gap is smaller than the above range, bubbles are likely to grow on the anode surface, causing an increase in electrical resistance and deterioration of the cation exchange membrane. , the electrical resistance increases due to the bubbles and solution existing between the cation exchange membrane and the anode, and the electrical resistance is reduced by adjusting the liquid flow in the space on the back of the anode to specific conditions, which will be described later. The method of adjusting the gap between the cation exchange membrane and the anode within the above range is not particularly limited.For example, FIGS. 2 and 3 show the filter press type cation exchange membrane method. FIG. 2 is a partial cross-sectional view showing a typical mode of adjusting the gap within the above range in an electrolytic cell.The mode shown in FIG. A spacer (6) having continuous voids in the vertical direction is interposed, and the cation exchange membrane is held by the spacer.The shape of the spacer is particularly limited as long as it has continuous voids in the vertical direction. Preferably, a spacer in the form of a blind is used for the porous electrode, and a spacer in the form of a net is used for the electrode in the shape of a blind.The material of the spacer is Resins that have corrosion resistance against the liquid and gas in the anode chamber are generally used. For example, fluorine-based resins are preferred. In Fig. 2, (5) is the cathode, (7) is the liquid supply port, (8) is a gas/liquid outlet.

In the embodiment shown in FIG. 3, the cation exchange membrane (2)) is connected to the cathode (
5) to adjust the gap between the cation exchange membrane C) and the cation 1k(1). In this case, in order to prevent hydrogen gas generated at the cathode from adhering to the cation exchange membrane and increasing the electrical resistance on the cathode side, there is a gap between the cation exchange membrane (support) and the cathode (5). Preferably, a porous metal spacer 〇) is used. As the material of the metal spacer, a metal having a higher hydrogen overvoltage than that of the cathode is generally used. Further, the shape of the metal spacer is not particularly limited, such as a wire mesh shape, a net shape, a film shape, etc.

In the electrolysis method of the present invention, the gap between the cation exchange membrane and the anode is adjusted to the specified range, and the equivalent diameter D e (IM) of the space on the back of the anode and the rise of the liquid in the space are adjusted. The relationship with linear velocity U (e1m/sea) is U/
It is extremely important to perform electrolysis under conditions such that Do≧0.15. Note that the equivalent diameter Da of the space on the back surface of the anode can be determined by a known method.

For example, when the cross section of the space is rectangular.

In addition, the rising speed U (cm/8ec
) can be determined by dividing the amount of liquid supplied to the anode chamber by the cross-sectional area of the anode chamber excluding the anode portion.

Conventionally, the thickness of the back surface of the anode is generally 30 to 601111, and the equivalent diameter of the space on the positive 11f surface is:
It was in the range of 60-120m. In addition, the rising speed of the liquid in the space is 0.05 to 0, s ctx
/ sea. Follow me, 17/
D6 is operated in the range of 0.0004 to 0.01. It was believed that reducing the equivalent diameter of the space on the back of the anode would increase the bubble density on the anode chamber side and increase the electrical resistance. It had never been driven. As a result of repeated numerous experiments, the present inventors maintained the gap between the cation exchange membrane and the lli electrode at the specific interval,
In addition, if the flow rate is kept constant, the equivalent diameter De of the space on the back of the anode is reduced, and the rising speed υ of the liquid is increased to φ, the electrical resistance on the anode chamber side will gradually rise, but %v/ It has been found that a very peculiar phenomenon occurs when the electrical resistance on the anode chamber side suddenly decreases when no exceeds a certain value. This unique phenomenon occurs when IT/De exceeds a certain value when the gap between the specific cation exchange membrane and the anode is set as described above, regardless of the flow rate of liquid sent to the anode chamber. confirmed. The U/D41
The value of is not particularly limited as long as it is 0.15 or more, but if the value is too large, a large-capacity pump is required, which is uneconomical. Therefore, the upper limit of the value of TJ/D・ is 3
G, especially 2o to 50 ell/B'aOe preferably from the range 2 to 40 Cal/860 U/
It is preferable to determine the value of De so that it falls within the above range. In particular, it is preferable to carry out electrolysis with the equivalent diameter De within the above range, since the effects of the present invention are significantly exhibited.

In the present invention, the ion exchange farming vertical electrolyzer used is:
There is no particular restriction as long as the structure satisfies each condition of the present invention. For example, FIG. 4 is a sectional view showing one embodiment of a vertical electrolytic cell for ion exchange farming suitable for carrying out the method of the present invention. 4th v! In the ion exchange farming vertical electrolyzer shown in J, the partition wall (3) of the anode chamber is replaced with a cation exchange membrane (
2), and an enlarged space (lO) having a liquid supply port (7) and a gas/liquid discharge port (8) above and below, respectively, is formed. The above electrolytic cell can handle U/I) with a small supply amount of one liquid.
・It is possible to increase . In addition, the present invention-
As for other electrolytic conditions, known conditions are followed without any particular restrictions.

As understood from the above explanation, the electrolysis method of the present invention includes:
The electrical resistance on the anode side of a vertical electrolytic cell using ion exchange farming can be significantly reduced, and its economic benefits are immeasurable. Furthermore, the deterioration phenomenon of the cation exchange membrane, which is caused by the conventional method of bringing the cation exchange membrane into close contact with the anode, can be completely prevented. Furthermore, as described above, the method of the present invention is particularly effective in a range where the thickness of the electrode chamber is small, and is effective for compacting the electrolytic cell. However, the present invention is not limited to these embodiments.
.

Example 1 As a cation exchange membrane, Par7g1n carbon-based cation exchange membrane Neo Shichibuta YO-1000 (trade name).

(manufactured by Tokuyama Soda) -1 The anode is a titanium lath material coated with ruthenium oxide, the cathode is a bipolar electrode with a 9° mild steel mesh, and between the WIk electrode and the cation exchange membrane,
Width: 2001 ff, height: 90 mm, interposed with a fluororesin blind-shaped spacer having nine vertically continuous lines
Experiments were conducted using a 0 m battery container. Salt water (sodium chloride aqueous solution) was supplied to the anode chamber from the bottom, and drained brine along with chlorine was taken out from the top. A part of the drained salt water is circulated externally, and by changing the amount of liquid circulating externally, the rate of rise of the liquid in the space behind the anode can be changed.

The cathode was installed so that the distance from the cation exchange membrane was 2fi, and a pure water supply port was provided at the bottom, and a hydrogen and caustic soda aqueous solution outlet was provided at the top. A part of the obtained caustic soda aqueous solution was circulated externally, and a heat exchanger was installed in the middle of the circulation, so that the temperature of the solution in the cathode chamber could be controlled to 80°C. The thickness of the space on the back of the anode is 20111, 10a+, etc. with such a structure.
We prepared four types: 5H and 2sm. In addition, three types of spacers with thicknesses of 11101, 2111W and 5101 were used with various thicknesses as the spacer interposed between the anode and the cation exchange membrane.

Electrolysis was carried out at a current density of 30 A/III'', and the amounts of brine and pure water to be supplied were adjusted so that the anode chamber waste brine was 3.511 T, and the caustic concentration at the cathode chamber outlet was 7 N. The thickness of the space on the back of the anode, the gap between the cation exchange membrane and the anode, and the rising linear velocity of the liquid in the space on the back of the anode were varied as shown in Table 1.
The interelectrode voltage was measured 5 days after the start of operation. The results were as shown in Table-1.

Table-1 Nao Hata A 1.6.11.15.18.23.24.2
5.30.31.36 are comparative examples. In addition, the symbols in each column are as follows.

t; Gap between the cation exchange membrane and the anode surface d; Thickness of the anode back space De; Equivalent diameter of the anode back space M; Supply flow rate to the anode chamber υ; Rising linear velocity 0 V;
Electrode voltage comparison example 1 In the method of Example 1, a fluororesin spaghetti-shaped spacer was not interposed between the anode and the cation exchange membrane, and the pressure on the cathode chamber side was lowered to about 35Q*Aq anode chamber side pressure. Electrolysis was carried out under the conditions shown in Table 2 with the S cation exchange membrane brought into close contact with the anode surface by increasing the dyeing height. Start of operation 5
The interelectrode voltage after 1 day was 9 as shown in Table 2.

Table 2 Example 2 Electrolysis was carried out in A3 of Example 1 continuously for 6 months. After stopping electrolysis, the battery case was disassembled and the cation exchange membrane was examined, but no pinholes were found, and no signs of deterioration of the cation exchange membrane were found.

[Brief explanation of the drawing]

Figure 1 is a partial cross-sectional view of a vertical electrolyzer for ion exchange farming, Figure 2
3 and 3 are partial cross-sectional views showing typical embodiments of adjusting the gap between the cation exchange membrane and the anode in a filter press type ion exchange membrane method electrolytic cell, and FIG. 4 is a partial sectional view showing the method of the present invention being carried out. 1 is a partial sectional view showing one aspect of a vertical electrolytic cell suitable for ion exchange farming. In the figure, (1) is the anode, (2) is the cation exchange membrane, (3) is the partition wall, and (4) is the anode.
) is the space on the back of the anode, (5) is the cathode, (6) is the spacer, and (7) is the liquid supply port. (8) indicates the gas-liquid outlet, (9) indicates the metal spacer, and (1 indicates the expanded space. Patent applicant: Tokuyama Soda Co., Ltd.)

Claims (1)

[Claims] 1. When electrolyzing an alkali metal chloride aqueous solution using a vertical electrolytic cell in ion exchange farming, the gap between the cation exchange membrane and the anode is adjusted to 0.5 to 3 H, and the anode The relationship between the equivalent diameter De (W) of the space on the back surface and the rising linear velocity tr (am/%IO) of the liquid in the space is U/D@≧0.1
5. A method for electrolyzing an aqueous alkali metal chloride solution, characterized by carrying out electrolysis under conditions of 5. 2. The method according to claim 1, wherein the equivalent diameter D of the space on the back surface of the anode is 1 to 500.