JPS6148587A - Method of adding hydrochloric acid to electrolytic cell - Google Patents

Abstract

PURPOSE:To decrease acid-resistant pipings for the purpose of hydrochloric acid addition in the stage of adding hydrochloric acid to the anode chamber of an ion exchange membrane method alkali electrolytic cell by providing a diffusing pipe for outflow of the hydrochloric acid to the center of a salt water piping and adding the hydrochloric acid together with the salt water to the anode chamber. CONSTITUTION:OH<-> diffuses in the anode chamber of the ion exchange membrane type salt water electrolytic cell through the ion exchange membrane from the cathode chamber and therefore the hydrochloric acid is added to an anolyte to maintain the pH thereof at a normal value. The hydrochloric acid diffusing pipe consisting of an acid resistant material is disposed to the central part of the piping for the salt water to the anode chamber in the stage of adding the hydrochloric acid to the salt water. Many small holes are provided to the side face of the hydrochloric acid diffusing pipe and the concd. hydrochloric acid is supplied together with the salt water and is added to the salt water flowing in the salt water piping through the small holes. The sectional area of the small holes is so adjusted that the flow rate of the hydrochloric acid flowing out of said holes attains the flow rate of the salt water in the salt water piping or below and the small holes are made straight without bending within at least 0.2m from the top end of the hydrochloric acid diffusing pipe. The direct contact of the hydrochloric acid with the salt water piping is averted and the need for costly acid resistant materials is eliminated except for the hydrochloric acid piping.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for adding hydrochloric acid to an electrolytic cell, and specifically for lowering the pH of an anolyte during electrolysis of an aqueous alkali chloride solution such as common salt. This relates to a method of adding hydrochloric acid to

[Prior Art] In the technical field of alkaline electrolysis of salt, etc., so-called ion exchange membrane alkaline electrolysis, which uses a cation exchange membrane as a diaphragm, is becoming mainstream due to various advantages.
It is necessary to quickly neutralize the hydroxide ions (OH-) that diffuse from the cathode chamber through the ion exchange membrane to the anode chamber, and therefore it is necessary to lower the pH of the anolyte by adding ζphosphoric acid. It's well done. Although hydrochloric acid is generally used as an acid, various methods have been considered for specifically adding this hydrochloric acid to the anolyte. The main methods include a method of supplying hydrochloric acid to a gas-liquid separator for the anolyte discharged from the electrolytic cell, and a method of directly injecting hydrochloric acid from a thin pipe into the piping that supplies salt water to the anode chamber. be.

The hydrochloric acid used here is usually concentrated hydrochloric acid, which has the disadvantage that it tends to corrode gas-liquid separators and piping in both cases.

[Problems to be Solved by the Present Invention] The present invention provides a method that can prevent corrosion of equipment materials due to hydrochloric acid, which has conventionally been a problem when adding hydrochloric acid to an electrolytic cell.

[Means for Solving the Problem] The inventors of the present invention have conducted various studies on specific methods to avoid the above-mentioned corrosion problem caused by hydrochloric acid when supplying hydrochloric acid into salt water supply piping, and have developed the present invention. The present invention provides a method for adding iha to an electrolysis tank by supplying hydrochloric acid to brine for electrolysis in a brine pipe, in which a dispersion pipe having pores through which a trickle of hydrochloric acid can flow out is connected to the brine pipe. The dispersion tube is placed approximately along the center line of the dispersion tube, and hydrochloric acid is poured into the dispersion tube.

The present invention will be explained below based on the drawings. FIG. 1 is a sketch showing one example of a dispersion tube that can be suitably used in the present invention. Figure 2 shows the salt water distribution for the 1st attack pipe in Figure 1? FIG. 3 is a cross-sectional view showing the state of the i-fish under running water of hydrochloric acid when the fish is placed in the water.

The dispersion tube shown in FIG. 1 is a tube with a closed conical tip and a large number of pores in the side wall. Hydrochloric acid supplied from above the dispersion tube flows out to the surrounding area through the pores. FIG. 2 shows the state of the outflow. Hydrochloric acid is supplied from above to the dispersion pipe arranged approximately along the center line of the salt water pipe, while salt water is supplied between the salt water pipe and the dispersion pipe. Hydrochloric acid supplied to the dispersion tube flows out through pores provided in its side wall into the salt water flowing through the salt water piping. The hydrochloric acid that has flowed into the salt water flows along the outer surface of the dispersion pipe, increasing its bulge slightly as it goes towards the end of the dispersion pipe, but it is kept on the center line of the salt water pipe so as not to come into contact with the inner wall of the salt water pipe. According to the method of the present invention, a small amount of material is dispersed! If a hydrochloric acid resistant material is used only for 6., salt water piping that requires a large amount of material will be possible.
It becomes possible to use inexpensive materials that do not require hydrochloric acid resistance.

In the present invention, the openings of the dispersion tube preferably have a cross-sectional area such that the flow rate of hydrochloric acid flowing out from the openings is equal to or lower than the flow rate of the electrolytic salt water. Here, the flow rate of hydrochloric acid flowing out from the dispersion tube means the volumetric velocity of hydrochloric acid supplied to the dispersion tube divided by the total area of the openings.

Also. The flow rate of salt water for electrolysis means the volumetric velocity of salt water flowing through the salt water pipe divided by the difference between the cross-sectional area of the salt water pipe and the cross-sectional area of the dispersion pipe.

It is more preferable if the cross-sectional area of the opening provided in the dispersion ft. satisfies the above limitations, since there is less possibility that the effluent hydrochloric acid will come into contact with the piping.

=ρ et al. 1 In the present invention, as mentioned above, the hydrochloric acid flowing out of the dispersion pipe flows approximately along the center line of the salt water pipe and gradually diffuses into the surrounding salt water. Therefore, it is undesirable to change the flow path while the hydrochloric acid concentration near the center line is still high, that is, to have vents, branches, etc. in the salt water pipe, and the salt water pipe must be straight for a certain distance from the tip of the dispersion pipe. is preferred.

This range is preferably at least 0.2 m, although it depends on the cross-sectional area of the openings provided in the above-mentioned dispersion tube and the ratio of the volume velocity of salt water to the volume velocity of hydrochloric acid.

Furthermore, if the length of the salt water piping from the tip of the dispersion tube to the electrolytic cell is not very long, it is safe to install a splitter blade for a distributor in the portion of the salt water piping immediately in front of the electrolytic cell.

Furthermore, in the present invention, hydrochloric acid is supplied to the dispersion tube and from there to the hydrochloric acid piping. This is a preferred method because a premix is performed.

[Effects of the Invention] Thus, when the present invention is employed, the problem of corrosion of piping due to hydrochloric acid does not occur, and the objective can be fully achieved.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Part 3 I)! 5 is an enlarged sectional view of the salt water supply portion of the electrolysis plant used in this example. The purified saturated salt aqueous solution is supplied to the brine box at a rate of 4 m''. On the other hand, hydrochloric acid (concentration 1ON) is supplied from the top of the brine box to a PTFE pipe with an inner diameter of 15 mm connected to the dispersion tube at a rate of 25 g/h. The brine supply pipe (made of Ti, inner diameter 125 mm) is attached to the bottom of the brine box as shown in the figure, and its opposite end connects to the bottom of the electrolytic cell from the side!
It is continued.

On the other hand, the dispersion tube is made of PTFE with an outer diameter of 60v and an inner diameter of 50mm.
A made pipe with a closed end.

On each side of the dispersion tube, 16 holes and 4 holes each having a diameter of 0 mm and a diameter of 20+ nm were uniformly provided over a length of 150 mm in the longitudinal direction of the dispersion tube. Furthermore, the distance from the lower end of the dispersion tube to the vent part of the salt water piping is 600 mm.

In addition, fresh salt water discharged from the electrolytic cell is supplied to the brine box at a rate of 15 m/h and to the horizontal portion of the salt water piping just before being supplied to the electrolytic cell as circulating salt water at a rate of 15 m/h. Therefore, a saltwater distribution system with a dispersion pipe? The velocity of the salt water flowing through the part i↑ is 18 m゛ha, but since a portion of the water also flows into the dispersion pipe, the flow velocity of the salt water flowing outside the dispersion pipe is approximately 0.
It is 55m/see. Further, the flow rate of diluted hydrochloric acid flowing out from the opening of the dispersion tube is about 0.05 m/sec.

When electrolysis was carried out using the following equipment and conditions, the electrolytic tank contained p.
Salt water for electrolysis of H1 and 7 was supplied, and the salt water piping shown in the figure was not corroded by hydrochloric acid at all, and electrolysis could be carried out safely for a long period of time.

Example 2 In the electrolysis plant shown in Fig. 3, as in Example 1, two salt water supply pipes (Ti'M, inner
1125am)←Outer diameter 25mm, inner diameter 15mm (7
) Insert the PTFE pipe into the top of the dispersion tube. The dispersion tube is a PTFE pipe with an outer diameter of 80 mm and an inner diameter of 70 mm, with the tip closed in a conical shape, and 24 holes with a diameter of 10 cm are provided on the side of the tube in a staggered arrangement 200 mm in the longitudinal direction of the dispersion tube. ing. Further, the distance from the lower end of the dispersion pipe to the vent part of the salt water piping was 550 mm. The method and amount of supply of saturated salt water and fresh salt water are the same as in Example 1. The flow rate of the salt water is about 0.7 ml sec. On the other hand, hydrochloric acid is supplied at a concentration of 1ON at a rate of 30 g/h from a PTFE pipe with an inner diameter of 15 mm via a dispersion station. Further, the flow rate of diluted hydrochloric acid is about 0.16 m/sec.

When electrolysis was carried out using the equipment and conditions shown above, the electrolytic cell was supplied with pHL and S salt water for electrolysis, and the salt water piping shown in the diagram showed no corrosion due to hydrochloric acid, and electrolysis was carried out stably for a long period of time. I was able to implement it.

Comparative Example 1 An electrolysis experiment was carried out in the same manner as in Example 1, except that the dispersion tube was not used and hydrochloric acid was supplied to the salt water piping from a pipe with an inner diameter of 15 mm.

The results showed that corrosion marks were observed on the inner surface of the salt water pipe in a spiral pattern starting from the hydrochloric acid supply end.

This seems to be due to the flow of hydrochloric acid being in the state shown in FIG. 4.

[Brief explanation of drawings]

FIG. 1 is a sketch showing one example of a dispersion tube that can be used in the present invention. FIG. 2 is a cross-sectional explanatory diagram showing the state of flow of hydrochloric acid when the dispersion pipe shown in FIG. 1 is connected to a salt water pipe. FIG. 3 is an enlarged sectional view of the salt water supply portion of the electrolysis plant used in Example 1. FIG. 4 is an explanatory cross-sectional diagram showing the state of flow of hydrochloric acid in Comparative Example 1. Purification of drawings! : (No change in content) y42 Diagram 4 @ Hand-selling amendment (method) % formula % 1. Indication of the case Patent Application No. 168881 of 1988 2. Name of the invention Method for adding hydrochloric acid to an electrolytic cell 3. Relationship with the case of the person making the amendment Patent applicant address 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Name
(004) Asahi Glass Co., Ltd. 4, Agent November 27, 1980 (Date of dispatch) 6. Number of inventions increased by the amendment None 7. Subject of the amendment Drawing 8. Contents of the amendment As per the attached appendix. that's all

Claims (4)

[Claims] (1) In a method of supplying hydrochloric acid to the electrolytic brine in the brine pipe and adding it to the electrolytic cell, a dispersion pipe with pores through which a trickle of hydrochloric acid can flow is placed approximately along the center line of the brine pipe. and supplying hydrochloric acid to the dispersion tube. (2) The center line of the salt water piping is at least 0.2 m straight from the tip of the dispersion pipe.
Method of adding hydrochloric acid to the electrolytic cell described in Section 1. (3) The electrolytic cell according to claim (1), wherein the pores of the dispersion tube have a cross-sectional area such that the flow rate of the hydrochloric acid flowing out from the pores is equal to or lower than the flow rate of the electrolytic brine. Hydrochloric acid addition method. (4) A method for adding hydrochloric acid to an electrolytic cell according to claim (1), wherein a part of salt water is also supplied to the dispersion tube along with hydrochloric acid.