JPS6040512B2 - Alkali metal sulfate electrolysis method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the electrolysis of alkali metal sulfates produced as by-products in, for example, flue gas desulfurization processes, and more specifically, the present invention relates to the electrolysis of alkali metal sulfates produced as by-products in flue gas desulfurization processes, etc. Specifically, the present invention relates to the electrolysis of alkali metal sulfates produced as by-products in flue gas desulfurization processes, etc. By introducing the alkali metal sulfate containing impurities into the central chamber sandwiched between the bellies, the migration of impurity anions to the anode is prevented, thereby preventing damage to the anode due to the impurity anions. The present invention relates to an electrolytic method and apparatus.

Conventional methods for treating alkali metal sulfates, such as trinitrate, which are produced as a by-product in the flue gas desulfurization process using soda-based absorbents, include chemical methods such as those found in Hakama Seki 49-114578 and Tokuseki 50- There are electrolytic methods as seen in the 809 solution. In order to prevent the loss of relatively expensive caustic alkali and economically recover useful products, or to promote closed systemization from the viewpoint of environmental conservation, the alkali metal sulfates produced by the above process are treated. An electrolytic method is preferred as the method. Accordingly, the alkali metal sulfate electrolysis equipment used in the flue gas desulfurization process has a single tank or multi-layered tank structure, but regardless of whether the electrode used is a single pole or two poles. First, the ion exchange membrane and diaphragm separating the anode and cathode were arranged as shown in FIGS. 1 and 2.

FIG. 1 shows the simplest electrolytic cell, in which a cation exchange membrane 3 provided at one location prevents mixing of ions.

A mixture of sulfuric acid and an alkali metal sulfate, such as moss nitrate, is obtained from the anode side. Although not shown, water is replenished into the cathode chamber after the caustic alkali is extracted.

FIG. 2 shows an improvement in the electrolytic current efficiency of FIG. 1.

The alkali metal sulfate solution passes through the diaphragm 4 into the central chamber 1.
Hydrogen ions are press-fitted into the anode chamber 15 from the anode 1 and generated at the anode 1, and are prevented from flowing back into the central chamber 17, and hydrogen ions are prevented from entering the cathode chamber 16, thereby improving current efficiency. In Figures 1 and 2, 2 is the cathode, 6 is the alkali metal sulfate liquid inlet, 7 is the anode gas-liquid separation tank, 8 is the cathode gas-liquid separation tank, 9 is the anolyte circulation pump, and 1 is the catholyte liquid. Circulation pump, 11 is an anolyte return port, 12 is a catholyte return port, 1
3 is an anolyte outlet, and 14 is a catholyte outlet. As mentioned above, the present invention is applied to a flue gas desulfurization device, and has the following features:
Although the present invention provides electrolytic bag counterfeiting of by-product molasses, for example, an electrolytic device for generating alkali metal sulfate in a flue gas desulfurization device has a problem of contamination with impurities, which is not seen in general electrolytic devices.

Conventionally, in order to prevent the contamination of these impurities, various pretreatment devices have been added to electrolysis devices for by-product alkali metal sulfates, such as sulfur.

However, there are harmful impurities that cannot be removed even with all conventional pretreatments. For example, in a flue gas desulfurization absorption tower, there are nitrate radicals caused by nitrogen oxides that are inevitably absorbed, fluorine that is continuously mixed into the raw alkali, or chlorine in the raw water.

Although these contaminants may be detected, as mentioned above, when promoting closed processing systems from the viewpoint of environmental conservation, there is a problem that these impurities accumulate in the system and flow into the electrolytic equipment. .

The inventors have discovered that the above-mentioned impurities cause the anode of an electrolyzer to wear out unexpectedly quickly.

Conventionally, efforts have been made only to improve the electrolytic efficiency in order to reduce the running cost of the electrolytic system as described above, and to this day, no measures have been taken to prevent depolarization of the electrodes, especially the anodes. The purpose of the present invention is to prevent the wear of the anode of an electrolyzer for alkali metal sulfates containing impurities, and it is clear that one of the causes of the wear of the anode is the contamination of impurities such as nitric acid wire, fluorine, or chlorine. As mentioned above.

However, for the anode of an electrolyzer for electrolyzing by-product alkali metal sulfate containing impurities, it is not always easy to select an anode material with a low oxygen overvoltage as in a normal electrolyzer due to corrosion resistance. . Therefore, when nitric acid, fluorine, chlorine, etc. are mixed into the oxidizing atmosphere in which an anode with a high oxygen overvoltage is used, the oxidizing property and reactivity become even greater, and the anode becomes more worn out.

In view of the above, the present invention provides an electrolysis device for an alkali metal sulfate containing impurities, including an anode, an anode chamber separated from the anode by a cation exchange membrane, a central chamber existing in the cation exchange gap, and a central chamber separated from the cation exchange membrane and the cathode. Using an electrolyzer having a cathode chamber and cathode, an alkali metal sulfate containing impurities is introduced into the central chamber, and the anode chamber is filled with dilute sulfuric acid containing no impurities and circulated, and sulfuric acid or Extracts acidic alkali sulfates and alkali metal sulfates,
The present invention provides a method and apparatus for extracting caustic alkali produced from a cathode chamber.

The principle is shown in Figure 4 and the following reaction formulas '1}, ■, [3'
As shown in the figure, sulfuric acid or acidic alkali sulfate and alkali metal sulfate are taken out from the central chamber, and caustic alkali is taken out from the cathode chamber.

Anodic reaction ratio 0-left-1 1/phantom 22H+ {1
'(Sun passes through the cation exchange membrane to the central chamber) Central chamber reaction Earth S04 → 2W + S024 ten [2
-2nd Juju S04 → Ratio S04 (M passes through the cation exchange membrane to the cathode chamber) Cathode reaction 2LO + Next one ratio Jugen H - '3' leg +
Jugen H-Ichihada H) Note that M represents an alkali metal.Next, regarding the method and apparatus for electrolyzing alkali metal sulfates of the present invention, we will explain the method for electrolyzing trinitrates containing impurities created by the flue gas desulfurization process. This will be explained in detail using an example of the device.

FIG. 3 shows one embodiment of the apparatus used in the present invention.

As is clear from FIG. 3, the most distinctive feature of the present invention is that the first
The anode chamber of the trinitrate electrolyzer shown in the figure is separated by a cation exchange membrane.

Since the cation exchange membrane is not completely impermeable to anions, impurity anions gradually flow into the anode chamber and accumulate.
In order to prevent the anode from being worn out, fresh dilute sulfuric acid containing no impurities is constantly supplied to the anode chamber, and sulfuric acid containing impurities is drawn out. Sulfuric acid or acidic sodium sulfate and trinitrate are transferred from the central chamber 22 and caustic soda is transferred to the cathode chamber 1.
The anode chamber 21 contains only pure S as an anion, and impurities such as nitrate, fluorine, and chlorine contained in the flowing reed sulfate are not accumulated in the anode chamber. The material of the anode used in the present invention is preferably a platinum-coated electrode based on titanium, aluminum or other composite material, or an electrode coated with an alloy oxide of platinum and platinum metal.

An alloy material containing 2% silver and 0.5 to 1% tellurium based on inexpensive lead can also be used.In particular, lead electrodes have a low oxygen overvoltage, so the electrolysis voltage can be lowered and costs can be reduced. It has the advantage of The cation exchange membrane used in the present invention may be of any known type, but it is preferable to use one that has excellent ion selectivity, low fin air resistance, high bursting strength, and excellent corrosion resistance; for example, one manufactured by DuPont, USA Nafion (
Nafion) etc. are suitable.

Also, the spacing between the anode chamber, central chamber, and cathode chamber is 1 to 1.
7 rails, preferably 2 to 4 sails, supporting the lower body with subbases or gaskets. In this embodiment, the external structure of the electrolytic cell may be a single structure or a multilayered structure in which several electrolytic cells are arranged in parallel.

In addition, the present invention applies not only to the by-product young salt from the above-mentioned flue gas desulfurization and other alkali metal sulfates, but also to Sosei Sannit from the piscose corporation fiber manufacturing process and other hatake from the chemical manufacturing process. It goes without saying that it can be used for the electrolysis of raw trinitrate or alkali metal sulfates containing other impurities. In the case of FIG. 3, the operating conditions of the present invention are 2.0 to 2. The state NaOH is 0.9 to 1. However, 2S04 or NaHS04 was obtained. In this case, the anode is a platinum-coated electrode, the cathode is a nickel-based electrode, and the electrolytic terminal voltage is 5. W,
Current density: 15-17A'dm2, temperature: 60-6y0, inlet molasses concentration: 1.7-1.9ho, dilute sulfuric acid for anode chamber circulation, 2.0-2. The electrolytic current efficiency was 75% or more with each chamber spaced between 3 and 5 legs.

The consumption condition of the anode material was good. A comparison of the degree of electrode wear between the present invention and a conventional ion exchange membrane method is as follows. Add 20% turf nitrate solution containing 100 pm of nitrate root to the second layer.
When electrolyzed in the conventional electrolytic cell shown in the figure, the platinum consumption rate of the platinum-coated anode used was 1.96 x 10-2
/AH, whereas when electrolyzed using the electrolytic cell according to the invention shown in FIG. 3, the consumption rate of platinum was 9'AH of 0.182 x 10-2.

The current density in this case is 17. Matsuno DM2, and the amount of platinum consumed per year in the former is 12.54", while that in the latter is 1.16", which is less than 1/10 of the amount consumed.The present invention The effects of this can be summarized as follows: (a) Creation of flue gas desulfurization process In the ramie electrolyzer, the anode is prevented from being consumed by eliminating impurities in the anode, and the flue gas desulfurization process is improved.

This makes it easy to create a fixed system, and reduces running costs and maintenance (repair) frequency. {o
) It is possible to use an inexpensive lead-based anode, which has been difficult to use due to its corrosion resistance, and to lower the electrolytic voltage in conjunction with its low oxygen overvoltage, thereby reducing costs.

An economical method and device for electrolyzing alkali metal sulfates has been established using a relatively simple structure of an electrolytic cell.

[Brief explanation of the drawing]

Figures 1 and 2 are conventional electrolyzers for alkali metal sulfates, Figure 3 is an embodiment of the electrolyzer for alkali metal sulfates containing impurities according to the present invention, and Figure 4 is the principle of the present invention. A schematic diagram illustrating this is shown. DESCRIPTION OF SYMBOLS 1... Anode, 2... Cathode, 3... Cation exchange membrane, 4... Diaphragm, 6... Alkali metal sulfate liquid inlet, 7... Anode gas-liquid separation tank, 8...・・Cathode gas-liquid separation tank,
9... Anolyte circulation pump, 10... Cathode solution circulation pump, 11... Anolyte return port, 12... Cathode solution return port, 13... Anolyte extraction port, 14... Cathode solution extraction mouth,
15,21... Anode chamber, 16... Cathode chamber, 17,2
2... Central chamber, 20... Central chamber circulation pump, 24.
...Extraction of electrolytic products. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1 Consists of an anode, an anode chamber separated by an anode and a cation exchange membrane, a central chamber separated by a pair of cation exchange membranes, a cathode chamber separated by a cation exchange membrane and a cathode, and a cathode. Using an electrolyzer, an alkali metal sulfate solution containing impurities is introduced from the central chamber, and the anode chamber is filled with dilute sulfuric acid containing no impurities and circulated. A method for electrolyzing impurity-containing alkali metal sulfates, which is characterized by extracting salt and extracting caustic alkali from a cathode chamber. 2. In an electrolyzer for alkali metal sulfate contained in impurities, an anode, an anode chamber separated by an anode and a cation exchange membrane, a central chamber separated by a pair of cation exchange membranes, and a cation exchange membrane separated by a cathode. The central chamber has an inlet for an alkali metal sulfate solution containing impurities, an outlet for the generated sulfuric acid or acidic sulfuric acid alkali and alkali metal sulfate, and a dilute sulfuric acid circulation in the anode chamber. An electrolyzer for an alkali metal sulfate containing impurities, characterized in that the cathode chamber is equipped with a caustic alkali outlet.