JPS5813632B2 - Method for purifying aqueous alkali chloride solution for electrolysis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a purification system for an aqueous alkali chloride solution for electrolysis,
More specifically, the present invention relates to a precise purification system for aqueous alkali chloride solutions used in ion-exchange membrane electrolysis.

It is well known that in alkali salt electrolysis for producing alkali metal hydroxide and chlorine, an aqueous alkali chloride solution used as a raw material must be sufficiently removed and purified, particularly for magnesium, calcium, etc. therein.

Especially in the case of ion exchange electrolysis, which has been proposed in recent years,
Since the aqueous alkali chloride solution and the aqueous alkali metal hydroxide solution come into contact with each other through the ion exchange membrane, the calcium ions and magnesium ions in the aqueous alkali chloride solution come into contact with the hydroxide ions inside the ion exchange membrane, forming poorly soluble salts. This causes the formation of fine precipitates within the membrane, which leads to fatal phenomena such as an increase in electrolytic voltage over time and destruction of the ion exchange membrane.

For this reason, in the case of ion-exchange membrane electrolysis, strict purification of the raw material aqueous alkali chloride solution is required compared to the conventional mercury method or asbestos diaphragm electrolysis.

Conventionally, a widely used method for purifying aqueous alkali chloride solutions has been to add caustic alkali or alkali carbonate to remove magnesium, calcium, etc. by precipitation as magnesium hydroxide and calcium carbonate, respectively. Although this method has the disadvantage of requiring a long time, the extent of calcium and magnesium removal by this method is not sufficient, especially for ion exchange electrolysis, because there is an economic limit to the amount of purifying agent added.

Instead of or after the sedimentation separation method, it has been proposed to remove impurities such as calcium and magnesium from an aqueous alkali chloride solution through an ion exchange method, particularly a chelate resin ion exchange layer, and its efficiency has been improved. Similarly, it is attracting attention because calcium and magnesium can be almost completely removed.

However, the purification method using such a chelate resin ion exchange layer requires regeneration of the resin.
In particular, in ion exchange membrane electrolysis, there is a practical problem due to the fact that it is essential to always supply an aqueous alkali chloride solution with as small an amount of impurities as possible.

The present invention solves the practical problems of aqueous alkali chloride solutions produced by the chelate resin ion exchange method and provides a system for purifying aqueous alkali chloride solutions for electrolysis, which can be carried out industrially very effectively.

That is, the present invention provides a first and a first pump connected in series by a liquid passage provided with a detector for detecting minute amounts of impurities to be removed, and in which the ion-exchangeable processing time of one can be longer than the regeneration-required processing time of the other. It consists of a second chelate resin ion exchange tower, and the aqueous alkali chloride solution for electrolysis to be treated is passed from the first chelate resin ion exchange tower through the detector to the second chelate resin ion exchange tower according to the concentration detected by the detector. (1) A method for purifying an aqueous alkali chloride solution for electrolysis, characterized in that the treatment is carried out in the process of passing it through a second chelate resin ion exchange tower, and a detector is provided for detecting trace amounts of impurities to be removed. It consists of a first and a second chelate resin ion exchange tower, which are connected in series through a liquid passageway, each with a processing time that allows for ion exchange to be longer than the regeneration processing time of the other, and which is capable of handling aqueous alkali chloride solutions for electrolysis. , according to the detected concentration of the detector, (a) passing from the first chelate resin ion exchange tower through the detector to the second chelate resin ion exchange tower, (b) passing through the second chelate resin ion exchange tower, (c) ) The treatment is carried out in a circulation process of passing from the second chelate resin ion exchange tower through the detector to the first chelate resin ion exchange tower, and (d) passing through the first chelate resin ion exchange tower. A method for purifying an aqueous alkali chloride solution for electrolysis, characterized by:

According to the system of the present invention, problems associated with resin regeneration that inevitably occur in ion exchange purification methods are largely eliminated, the purification process can be carried out virtually continuously, and each chelate resin can be used to the maximum extent according to its ion exchange capacity, and in the case of the present invention, even if the amount of impurities such as calcium and magnesium in the aqueous alkali chloride solution suddenly increases, the purified aqueous alkali chloride solution can always be used. It has the advantage that the amount of these impurities in it can be kept as small as possible.

Other advantages of the invention will become apparent from the more detailed description of the invention below.

FIG. 1 shows a representative example of the purification system of the present invention.

In the figure, 1 is a first chelate resin ion exchange tower;
2 is a second chelate resin ion exchange column, and these ion exchange columns, 1 and 2, are detectors for detecting impurities such as calcium and magnesium in the aqueous alkali chloride solution.
They are interconnected by a liquid path having 3.

The types and amounts of chelate resins used here are determined so that the ion exchange processing time of each of the first exchange tower and the second exchange tower can be longer than the processing time required for resin regeneration of the other resin. It is necessary to choose.

Thus, for example, ethylenediaminetetraacetic acid, which has a functional group having the general formula >N-CH2C00- in the molecule.
Trimethylenediaminetetraacetic acid, iminodiacetic acid, aminomethylphosphonic diacetic acid or their oligomers or alkali salts of these carboxylic acids can easily achieve the above objectives by controlling the concentration of impurities in the aqueous alkali chloride solution and the regeneration conditions. This is particularly preferable because it can be done.

Of course, an ion exchanger that forms an intramolecular complex of one or more of the impurity ions in the aqueous alkali chloride solution can also be used as long as it satisfies the above properties.

The chelate resin can be made of, for example, activated carbon, coal,
It can be used by being supported on silica gel or zeolite.

The ion exchange columns 1 and 2 do not necessarily need to use the same type of chelate resin, nor do they necessarily need to be filled with the same amount of chelate resin.

The type and amount of chelate resin can be changed as required, and an operating method can be adopted accordingly as described below.

The detectors for detecting impurities in the aqueous alkali chloride solution provided in the ion exchange towers 1 and 2 preferably have 1 to 2 p.
Any method can be used as long as it has the ability to detect trace amounts on the order of pm, and for example, EDTA titration, atomic absorption, or EDTA automatic titration can be used.

The purification system of the present invention has the following (a) to (d).
It is operated to purify an aqueous alkali chloride solution through a circulation process consisting of the steps of.

In addition, when supplying the system of the present invention, the aqueous alkali chloride solution is not essential, but in order to increase the ion exchangeable time of the chelate resin and reduce the number of times it can be regenerated,
It is appropriate to reduce the amount of impurities to preferably 30 ppm or less, more preferably 5 ppm or less, by the above-mentioned sedimentation removal method or the like.

(a) The aqueous alkali chloride solution to be treated is supplied from 4 to the ion exchange tower 1 through the valve 5, and after ion exchange, is supplied to the ion exchange tower 2 through the valve 6, the detector 3, and the valve 7, and then through the valve 8. It is extracted from 9 as a purified aqueous alkali chloride solution.

During this time, valves 10, 11, 12, 13 are closed and liquid flow through these valves is prevented.

In this process, the ion exchange capacity of the chelate resin in the ion exchange column 1 approaches saturation, and the amount of impurities detected by the detector 3 reaches a value that cannot be reduced below the allowable amount even after passing through the ion exchange column 2. When this is done, it is particularly preferable to continue the process until impurities start to be detected by the detector 3.

(Example) When the above point is reached, the opening valves 5, 6.7 are closed and the valve 12 is opened again.

Then, the aqueous alkali chloride solution to be treated passes through the valve 12.
After being supplied to the ion exchange tower 2 and ion-exchanged there, it passes through the valve 8 and becomes a purified aqueous solution.

During this time, the chelate resin in the ion exchange tower 1 is regenerated.

The playback process is performed using known operations. That is, after the adsorbed impurity ions are liberated with a mineral acid such as hydrochloric acid, they are regenerated into an alkali metal salt form using an alkali hydroxide of the same type as the alkali chloride to be purified.

In the figure, the regenerant is supplied from 14 and discharged from 15.

(c) After the regeneration of the chelate resin in the ion exchange column 1 is completed, the step (c) is carried out as necessary.

That is, here, the release valve 8 is closed and the valve 13 is newly opened.
, 10.11 will be held.

The aqueous alkali chloride solution ion-exchanged in the ion exchange tower 2 is supplied to the ion exchange tower 1 through the valve 13, the detector 3, and the valve 10.

The liquid leaving the ion exchange column 1 is taken out as a purified liquid 9 through a valve 11.

The process (c), which is carried out as needed, is performed when the ion exchange capacity of the chelate resin in the ion exchange column 2 approaches saturation, and the amount of impurities detected by the detector 3 increases after passing through the ion exchange column 1. Particularly preferably, this is continued until the impurities start to be detected by the detector 3, when the amount reaches a value that cannot be reduced below the allowable level.

(d) After the process in (b) above or after the process in (c),
Valves 8, 13, 10, 6 are closed and valves 5, 11 are opened.

The aqueous alkali chloride solution to be treated is supplied to the ion exchange column 1 through the valve 5, and after ion exchange, is taken out from the column 9 as a purified liquid through the valve 11.

During this time, the ion exchange column 21 is regenerated by being supplied with a regenerant from 16 and discharged from 17.

After the ion exchange column 2 has been regenerated, it is returned to the process (a) above and is subsequently recycled.

According to the purification system of the present invention consisting of the steps (a) to (d), as is clear from the above explanation, the regeneration process of the resin using the chelate resin ion exchange method The purification process can be carried out virtually continuously.

Furthermore, since the switching from the (a) process to the (x) process and the switching from the (c) process to the (d) process are performed using a detector installed between the two ion exchange columns,
Each ion exchange column can be operated to the maximum exchange capacity of the chelate resin without incurring the risk that an aqueous alkali chloride solution containing impurities exceeding the allowable amount will be taken out as a purified liquid.

In particular, by performing the above switching when impurities begin to be detected by the detector installed in the liquid path between the ion exchange towers, the above objectives can be achieved more reliably, and even if the Even when the amount of impurities in the aqueous alkali chloride solution suddenly increases, the impurities in the purified liquid obtained can always be kept at the lowest possible value.

In addition, when the first and second ion exchange columns having the same capacity are used, they are completely interchangeable, and the above explanations are also interchangeable.

On the other hand, it goes without saying that the first and second ion exchange columns can use different chelate resins and different capacities.

In addition, the number of the first and second ion exchange columns is not necessarily one each, but as shown in FIG. (one of which consists of two towers).

In such a case, it is necessary to configure the ion exchange tower so that the time required for regeneration of any one of the ion exchange towers is shorter than the ion exchange processing time of the other ion exchange towers.

The purification system shown in FIG. 2 is operated, for example, as follows.

In FIG. 2, the same numbers mean the same contents.

In the explanation, for convenience, it is assumed that the second ion exchange column in FIG. 1 is composed of two columns.

B) The aqueous alkali chloride solution to be treated is taken out from 9 as a purified liquid through valve 5, ion exchange tower 1, valve 6, detector 3, valve 7, ion exchange tower 2, and valve 8.

Alternatively, the liquid exiting the ion exchange column 2 can be taken out as a purified liquid from 9 through the valve 6', the detector 3', the valve 7, the ion exchange column 2', and the valve 8'.

(Port) When the ion exchange tower cannot be used due to the amount of impurities detected by the detector 3 or 3', the liquid to be treated is transferred to the valve 12, the ion exchange tower 2, the valve 6'1, and the detector 3'.
, valve 7', ion exchange column 2', and valve 8', the purified liquid is taken out as a purified liquid.

During this time, the ion exchange column 1 is regenerated.

(c) When the ion exchange tower 2 becomes unusable from the detector 311, the liquid to be treated is transferred to the valve 12', the ion exchange tower 2', the valve 6', the valve 13, the detector 3, the valve 10, the ion exchange tower 1, It is taken out as a purified liquid through a valve 11.

During this time, the ion exchange column 2 is regenerated.

(iv) When the ion exchange tower 21 becomes unusable due to the detector 3, the flow of the liquid to be treated becomes the same as in (a) above, and during this time the ion exchange tower 21 is regenerated.

Examples are shown below to more specifically illustrate the present invention, but the present invention is not limited to the above description and the following examples, and various changes can be made within the scope of the present invention. be.

Example 1 As shown in FIG. 1, two chelate resin ion exchange towers 1 and 2 are connected in series through a liquid path equipped with a detector 3 (Water Analyzer ■ type, manufactured by Nippon Technicon Co., Ltd.). Automatic switching valve, 5, 6, 7, 8, 10
, 11, 12, and 13.

As a chelate resin, 297 to 119 having a nominodiacetic acid group based on a styrene-divinylbenzene polymer is used.
0 μ granular ion exchanger 6 Diamond ion CR-10” (
(manufactured by Mitsubishi Kasei Corporation) was filled with 150 liters.

For such a system, by a previously known sedimentation separation method,
Calcium ion 7.8ppm, magnesium ion 1
Saturated salt solution made to 5 ppm (concentration approximately 300 g
/l, temperature of about 60°C) at a rate of about 4.1 m^/H, and the process was continued as follows.

g) Transfer the salt water to be treated from 4 to valve 5, ion exchange column 1, valve 6,
Detector 3, valve 7, ion exchange column 2, valve 8 through 9
The purified liquid was taken out.

Approximately 60 hours passed until detector 3 began to detect Ca and Mg ions in the liquid passing through it, but this time was approximately 75% of the theoretical capacity of the chelate resin in ion exchange column 1. Met.

I checked the ion concentrations of Ca, Mg, and Fe in the purified solution just to be sure, but I could not detect them at all.

(Example) As soon as impurity ions were detected by the detector 3, the valve was changed so that the liquid flowed through the valve 12, the ion exchange column 2, and the valve 8 to become a purified liquid.

On the other hand, in the ion exchange tower 1, after extruding the salt water with water,
of hydrochloric acid and then IN of caustic soda.
Playback completed on time.

(c) When the regeneration of the ion exchange column 1 is completed, the valve is switched and the liquid exiting the ion exchange column 2 is taken as a purified liquid through the valve 13, the detector 3, the valve 10, the ion exchange column 1, and the valve 11. I decided to put it out.

After switching from (a) to (b) above, detector 3
Therefore, 60 hours passed until impurity ions were detected, which was 75% of the theoretical capacity of the ion exchange column 2.

(iv) Immediately after impurity ions were detected by the detector 3, the valves were switched so that the flow of the liquid completed the valve 5, the ion exchange column 1, and the valve 11 and became a purified liquid.

During this time, the ion exchange column 2 was regenerated in the same manner as the ion exchange column 1 described above, and was carried out for 5 hours.

After the regeneration of the ion exchange column 2 was completed, the process was returned to the above step (a).

Example 2 In step (a) of Example 1, ion exchange column 1 and valve 6
The salt water was sampled every hour between the ion exchange tower 2 and the valve 8, and the Ca and Mg concentrations in the salt water were precisely analyzed.

The results are shown in Table 1. Table 1 also shows changes over time in the ratio of the chelate resin in the ion exchange tower 1 to the theoretical exchange capacity.

From the above results, it can be concluded that the usual single-column operation with two co-located columns has the following advantages compared to the system in which (i) the exchange capacity of one column is no longer sufficient and the exchange is switched to another co-located column; I understand.

(i) The dangers associated with single tower operation can be avoided.

That is, the Ca, M allowed in the ion-exchange membrane method electrolytic cell
The g concentration is at a very low level (e.g. 0.0 in terms of Ca).
8 ppm or 0.1 ppm), and this concentration level is difficult to measure without precise analysis, and cannot be measured continuously in conjunction with the operation of the ion exchange tower. Therefore, in the case of single tower operation, There is a great danger that salt water will be supplied to the electrolytic cell without knowing the Ca and Mg concentrations.

On the other hand, according to the system of the present invention, the ion exchange column in the previous stage is regenerated by detection by the detector (this concentration level may exceed the permissible concentration level for the ion exchange membrane method electrolytic cell). The Ca and Mg concentrations in the brine supplied to the ion-exchange membrane electrolytic cell can be safely brought below the permissible value while increasing the temperature.

(11) The ion exchange capacity of the chelate resin can be utilized to a greater extent than in the case of single column operation.

In order to avoid the danger in the case of single tower operation mentioned in (i), it is necessary to measure the Ca and Mg concentrations at the outlet of the ion exchange tower down to low concentrations simultaneously with the operation by some method. Even if it is possible, in that case, as can be seen from Table 1,
Approximately 26 to 27 hours after the start of operation, it is necessary to switch to another tower installed in parallel.

(In this case, the permissible concentration in the ion membrane method electrolytic cell was set to 0.08 to 0.09 ppm for a normal fluorine-containing ion exchange membrane.

) That is, only about 40 to 41.5% of the theoretical exchange capacity of the chelate resin in the ion exchange tower is utilized and it is necessary to regenerate it.

(According to the system of the present invention, this value is 75% from Example 1)

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one example of the purification system of the present invention, and FIG. 2 is a schematic diagram showing another example of the purification system of the present invention. 1, 2, 2'...Chelate resin ion exchange column, 3,3+...Detector, 5,6,7
, 8, 10, 11 , 1 2 , 1 3 . 6',
7', 8', 10', 12', 13'-...
··valve.

Claims (1)

[Scope of Claims] 1. A plurality of liquid passages connected in series with a liquid passage provided with a detector for detecting minute amounts of impurities to be removed, each having an ion-exchangeable processing time that can be longer than the regeneration required processing time of the other. Consisting of first and second chelate resin ion exchange towers, the aqueous alkali chloride solution for electrolysis to be treated is transferred from the first chelate resin ion exchange tower to the second chelate resin ion exchange tower via the detector according to the detected concentration of the detector. (b) a process of passing through a second chelate resin ion exchange column. 2. First and second chelates connected in series by a liquid passage provided with a detector for detecting minute amounts of impurities to be removed, each having an ion-exchangeable treatment time longer than the regeneration required treatment time of the other. A process in which the alkali chloride water bath temporary for electrolysis to be treated is passed from the first chelate resin ion exchange tower through the detector to the second chelate resin ion exchange tower according to the concentration detected by the detector; (1) Process of passing the second chelate resin ion exchange tower through the first chelate resin ion exchange tower, (c) Passing the first chelate resin ion exchange tower from the second chelate resin ion exchange tower through the detector, (d) First chelate resin ion exchange tower A method for purifying an aqueous alkali chloride solution for electrolysis, characterized in that the treatment is carried out in a circulation process through an ion exchange tower.