JP2002317286A - Method of preparing aqueous potassium hydroxide solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of preparing an aqueous potassium hydroxide solution having a low sodium content for medicament, food and semiconductor field, etc. SOLUTION: A crude aqueous solution of a concentration of 22 to 28% is prepared by mixing an aqueous potassium chloride solution of a sodium content <=1,500 ppm or water with a raw material potassium chloride of a sodium content 300 to 5,000 ppm. This solution is cooled to -5 to 10 deg.C to allow the solid potassium chloride to deposit and is subjected to separation of solid from the liquid to dissolve the potassium chloride in the water and thereafter the aqueous saturated potassium chloride solution of the sodium content below 60 ppm is prepared. The aqueous potassium hydroxide solution of the sodium content below 100 ppm when converted to the aqueous potassium hydroxide solution of a concentration 48% is obtained by electrolyzing the solution by an ion exchange membrane electrolysis method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing an aqueous solution of potassium hydroxide.

[0002]

2. Description of the Related Art Generally, an aqueous potassium hydroxide solution is produced by electrolysis of an aqueous solution of potassium chloride, and a standard potassium hydroxide aqueous solution for industrial use has a concentration of 48%. Potassium chloride used as a raw material contains sodium in the form of sodium chloride or the like as an impurity. The sodium content in the raw material potassium chloride (converted to sodium element; the same in this specification) is 300 to 5;
Therefore, unless the sodium in the raw material potassium chloride is removed, the sodium content is 100 ppm.
It is difficult to obtain an aqueous solution of potassium hydroxide having a concentration of 48% or less at a concentration of 48 ppm or less.

As a method for removing impurity sodium from an aqueous potassium chloride solution for producing potassium hydroxide by electrolysis, a conventional method has been to add sodium antimony to an aqueous potassium chloride solution to remove sodium (Japanese Patent Application Laid-Open No. 61-1986).
A method for removing sodium by adding zirconium phosphate to an aqueous potassium chloride solution (see Japanese Patent Application Laid-Open No. 9-25117) is known.

[0004] In these methods, the process is complicated,
There was a problem that energy consumption was large. In particular, when antimonic acid, zirconium phosphate, etc. are added to an aqueous potassium chloride solution, these additives tend to be mixed into the potassium hydroxide, and it is difficult to remove them. It was not suitable for the food, semiconductor or other fields.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to efficiently remove sodium from a starting potassium chloride to obtain a potassium hydroxide aqueous solution having a low sodium content.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a raw material potassium chloride having a sodium content of 300 to 5000 ppm,
A potassium chloride aqueous solution or water having a sodium content of 1500 ppm or less is mixed to form a crude aqueous solution having a concentration of 22 to 28%, and the crude aqueous solution is cooled to a temperature of -5 to 10 ° C to precipitate solid potassium chloride. Separate potassium chloride and redissolve in water, sodium content 60ppm
A method for producing an aqueous solution of potassium hydroxide which obtains an aqueous solution of potassium hydroxide having a sodium content of 100 ppm or less when converted into an aqueous solution of potassium hydroxide having a concentration of 48% by converting the following saturated aqueous solution of potassium chloride into an aqueous solution of potassium hydroxide having a concentration of 48% by electrolysis using an ion exchange membrane electrolytic method I will provide a.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a raw material potassium chloride and a potassium chloride aqueous solution or water are mixed to form a mixture having a concentration of 22 to 28.
% Of a crude aqueous solution, and cooled to a temperature of −5 to 10 ° C. to precipitate potassium chloride in a solid state (hereinafter, referred to as solid potassium chloride). This crude aqueous solution contains sodium ions eluted from the raw material potassium chloride and sodium ions contained in the aqueous potassium chloride solution or water. The sodium content in the raw material potassium chloride is 300
5,000 ppm, and the sodium content of the aqueous potassium chloride solution or water is 1500 ppm or less. Therefore, when the temperature of the crude aqueous solution is cooled to -5 to 10 ° C., potassium chloride reaches a saturation concentration and forms solid potassium chloride. ,
Sodium chloride has a concentration lower than the saturation concentration. As a result, the impurity sodium remains in the aqueous solution as ions. In addition, in this specification, all of%, ppm, and ppb are mass conversion values.

In the present invention, potassium chloride having a sodium content of 300 to 5000 ppm is used as a raw material.
Raw material potassium chloride having a sodium content of less than 300 ppm is not preferable because the production method is difficult and expensive.
If the content is more than 5000 ppm, the sodium content is 100%.
It is difficult to produce a 48% aqueous potassium hydroxide solution of less than ppm. It is particularly preferable that the sodium content in the raw material potassium chloride is 300 to 1400 ppm.

In the present invention, a crude aqueous solution of potassium chloride having a concentration of 22 to 28% is prepared. If the concentration is less than 22%, the temperature for depositing solid potassium chloride in the aqueous potassium chloride solution becomes low, and the power required for cooling or the like increases, which is not preferable. If the concentration exceeds 28%, solid potassium chloride is difficult to dissolve, which is not preferable. The concentration of the crude aqueous solution of potassium chloride is particularly preferably from 26 to 28%.

In the present invention, the temperature of the aqueous potassium chloride solution or water to be mixed is preferably 0 ° C. to 80 ° C. Temperature is 0 ° C
If the temperature is lower than 80 ° C., the progress of dissolution of the raw material potassium chloride will be slow. The temperature is 50-6
0 ° C. is particularly preferred.

[0011] In the present invention, the cooling temperature is from -5 to -5.
Bring to 10 ° C. If the cooling temperature is lower than −5 ° C., not only potassium chloride but also sodium chloride tends to precipitate,
The sodium content in potassium chloride increases and the purity decreases. In addition, the energy for cooling is large and cannot be cost-effective. If the cooling temperature is higher than 10 ° C., the solubility of potassium chloride does not decrease and potassium chloride cannot be efficiently precipitated. The cooling temperature is particularly preferably from 0 ° C to 5 ° C.

In the present invention, as means for solid-liquid separation, for example, a method using a device such as a centrifugal separator, a horizontal belt filter, or the use of the fact that the specific gravity of precipitated solid potassium chloride is heavier than an aqueous solution of potassium chloride is used. Then, the cooling tank has a structure in which the precipitated solid potassium chloride is extracted from the lower portion, and an aqueous potassium chloride solution is extracted from the upper portion.

In the present invention, the content of calcium, magnesium or strontium in the potassium chloride crude aqueous solution supplied to the cold precipitation step is 50 ppb or less in terms of the elemental value of calcium, magnesium or strontium (hereinafter the same). Preferably, there is. When the content of these elements exceeds the above-mentioned value, before supplying to the cold precipitation step, an aqueous potassium chloride solution is passed through a cation exchange resin to convert calcium ions, magnesium ions or divalent cations of strontium ions. It is preferable to remove them. The content of calcium ion, magnesium ion or strontium ion is 20 pp each.
b or less is particularly preferred.

As for the cation exchange resin, it is possible to use a cation exchange resin in which divalent cations such as calcium ions, magnesium ions or strontium ions are significantly more selective than monovalent ions such as potassium ions. preferable. As the cation exchange resin, for example,
Cation exchange resin CR-11 manufactured by Mitsubishi Chemical Corporation and the like are included.

In the present invention, the aqueous potassium chloride solution supplied to the cold precipitation step is adjusted to pH 1 by adding hydrochloric acid.
It is preferably from 3 to 3. If the pH is higher than 3, the obtained crystals of solid potassium chloride contain water of crystallization, and it is difficult to control the concentration for preparing a saturated aqueous solution of potassium chloride, which is not preferable. If the pH is lower than 1, a large amount of hydrochloric acid must be used. However, it is not preferable because an expensive material such as a fluororesin lining is required for the material of the apparatus.

In the present invention, solid potassium chloride is dissolved in water to form a saturated potassium chloride aqueous solution having a sodium content of 60 ppm or less, and electrolyzed by ion exchange membrane electrolysis to produce a potassium hydroxide aqueous solution. If the sodium content of the aqueous potassium chloride solution exceeds 60 ppm, the effects of the present invention cannot be obtained, which is not preferable. The concentration of the aqueous potassium hydroxide solution obtained directly from the electrolytic cell is 28-54.
% Is preferred. The concentration of the aqueous potassium hydroxide solution is 48 to 5
0% is particularly preferred. Potassium hydroxide solution has a concentration of 48
Those having a sodium content of 100 ppm or less in terms of% are obtained.

In the present invention, before the step of dissolving the solid potassium chloride obtained in the cold precipitation step in water and conducting electrolysis, if the following treatment is further performed, the sodium concentration of the aqueous potassium hydroxide solution is further increased. Can be reduced. Hereinafter, this method is referred to as a second embodiment of the present invention.

Preferably, the solid potassium chloride is mixed with an aqueous potassium chloride solution or water having a sodium content of 60 ppm or less to form a slurry containing purified solid potassium chloride. The aqueous solution of potassium chloride used may be of any concentration. If the sodium content of the aqueous potassium chloride solution or water exceeds 60 ppm, the effects of the present invention cannot be obtained, which is not preferable.

The aqueous phase of the obtained slurry contains sodium ions eluted from solid potassium chloride and sodium ions contained in the aqueous potassium chloride solution or water. By this slurry operation, sodium chloride contained in solid potassium chloride elutes into the aqueous phase. In the aqueous phase of the slurry, potassium chloride reaches the saturation concentration, but the sodium content of the aqueous solution of potassium chloride or water is 60 ppm.
From the following, sodium chloride becomes a concentration lower than the saturation concentration, sodium chloride in solid potassium chloride elutes into the aqueous phase, and the sodium component in solid potassium chloride can be further removed.

The slurry preferably has a solid concentration of 10 to 90%. If the solid concentration is less than 10%, the production efficiency is extremely poor, which is not preferable. If the solids concentration is above 90%,
Since the contact between the solid phase and the liquid phase is insufficient, a satisfactory cleaning effect cannot be obtained, which is not preferable. The solid concentration is particularly preferably from 70 to 90%. In addition, the solid concentration is a concentration as a solid existing in the slurry, and does not include the amount of solute dissolved in the aqueous phase of the slurry.

It is preferable that purified potassium chloride is obtained as a solid by solid-liquid separation of the slurry (hereinafter referred to as purified potassium chloride solid). As for the sodium content in the purified potassium chloride solid, it is preferable that 50% or more of the sodium content in the solid potassium chloride is removed. The solid-liquid separation is preferably performed using a centrifuge, a horizontal belt filter, or the like.

In the second embodiment of the present invention, when a potassium chloride aqueous solution or water is mixed and subjected to solid-liquid separation as a slurry, the temperature is set to 0 ° C. to 50 ° C. to further increase the sodium content in the raw material potassium chloride. It is preferable because it can be removed.
It is particularly preferable to mix the aqueous potassium chloride solution or water at a temperature of 0 ° C to 30 ° C. The temperature at which the slurry is mixed is 30 ° C
If the temperature is higher than that, the solubility of sodium chloride in the mother liquor is increased, which is not preferable. The temperature at which the slurry is mixed is particularly preferably from 0C to 10C.

In the second embodiment of the present invention, the purified potassium chloride solid is further mixed with an aqueous solution of potassium chloride or water to form a slurry, and the operation of solid-liquid separation is repeated a plurality of times to further reduce the sodium content. It is more preferable because it is possible.

After dissolving the purified potassium chloride solid in water,
It is preferable to produce an aqueous solution of potassium hydroxide by subjecting a saturated aqueous solution of potassium chloride having a sodium content of 45 ppm or less to electrolysis by an ion exchange membrane electrolysis method. The aqueous potassium hydroxide solution has a sodium content of 7 when converted to a concentration of 48%.
It is preferable to obtain those of 5 ppm or less.

In the second embodiment of the present invention, the separated mother liquor after the slurry is subjected to solid-liquid separation is mixed with a potassium chloride aqueous solution or water having a sodium content of 2000 ppm or less before dissolving the raw material potassium chloride, and further with the raw material chloride. Contains sodium eluted from potassium. This separated mother liquor is preferably used as a raw material for dissolving a slurry or an aqueous potassium hydroxide solution for general industry.

[0026]

EXAMPLES Examples of the present invention (Examples 1, 2, and 3) and comparative examples (Example 4) are shown below. The results are summarized in Table 1. In each case, the sodium content in the aqueous potassium hydroxide solution was measured by atomic absorption spectrometry (standard addition method). When the sodium content of the aqueous solution of potassium hydroxide having a concentration of C% is Appm, the sodium content Bppm converted into the aqueous solution of potassium hydroxide having a concentration of 48% is expressed by the formula (B
= A x 48 / C).

Example 1 10 kg of a raw material potassium chloride having a sodium content of 4260 ppm was added with a sodium content of 0 p
28 kg of water at pm were added, and the temperature of the aqueous solution was raised to 50 ° C. to obtain 30 L of a 26% concentration crude aqueous potassium chloride solution. The crude aqueous solution is subjected to ion exchange resin (trade name: cation exchange resin CR-11, manufactured by Mitsubishi Chemical Corporation; the same applies hereinafter) to remove divalent cations such as calcium ions, magnesium ions, and strontium ions.
After the pressure was reduced to pb or less, the temperature of the aqueous solution was cooled to 5 ° C., and solid potassium chloride was precipitated and separated into solid and liquid to obtain 1100 g of solid potassium chloride. The obtained solid potassium chloride was dissolved in pure water to obtain a 26% aqueous potassium chloride solution, and the obtained aqueous potassium chloride solution was subjected to electrolysis (ion exchange membrane electrolysis, current density 4 kA / m ² , electrolytic bath temperature). 90
C., fresh salt water concentration 18%, the same applies hereinafter) to obtain a potassium hydroxide aqueous solution having a concentration of 32%.

Example 2 The same crude sodium chloride solution as in Example 1 was subjected to removal of divalent cations with an ion-exchange resin in the same manner as in Example 1, and then 17% hydrochloric acid was added to adjust the pH of the aqueous solution to 2%. And Next, the temperature of the aqueous solution was cooled to 5 ° C., and solid potassium chloride was precipitated, and separated into solid and liquid to obtain 1100 g of solid potassium chloride. The obtained solid potassium chloride was mixed with pure water having a sodium content of 0 ppm and stirred to obtain a slurry having a solid concentration of 80%, followed by solid-liquid separation to obtain 1100 g of purified sodium chloride solid. The obtained purified potassium chloride was dissolved in pure water to obtain an aqueous solution of potassium chloride having a concentration of 26%.
% Potassium hydroxide aqueous solution was obtained.

EXAMPLE 3 10 kg of a raw material potassium chloride having a sodium content of 1220 ppm was added with a sodium content of 0 pp
Then, 28 kg of water was added, and the temperature of the aqueous solution was raised to 50 ° C. to obtain 30 L of a 26% concentration crude aqueous potassium chloride solution. After removing divalent cations from the crude aqueous solution using an ion exchange resin in the same manner as in Example 1, 17% hydrochloric acid was added to adjust the pH of the aqueous solution to 2. Next, the temperature of the aqueous solution was cooled to 5 ° C., and solid potassium chloride was precipitated and separated into solid and liquid to obtain 1100 g of solid potassium chloride. The obtained solid potassium chloride was mixed with pure water having a sodium content of 0 ppm and stirred to form a slurry having a solid concentration of 80%, followed by solid-liquid separation to obtain 930 g of purified sodium chloride solid. The obtained purified potassium chloride was dissolved in pure water, and the concentration was 26%.
, And electrolyzed in the same manner as in Example 1 to obtain a 32% aqueous solution of potassium hydroxide.

Example 4 (Comparative Example) Sodium Content 426
To 10 kg of 0 ppm raw material potassium chloride, 28 kg of water having a sodium content of 0 ppm was added, and the temperature of the aqueous solution was lowered to 5 kg.
The temperature was raised to 0 ° C.,
0 L was obtained. Thereafter, in the same manner as in Example 1, after removing cations with an ion exchange resin, the concentration was 32%
Was obtained.

Example 5 (Comparative Example) Sodium content of 430
28 kg of water having a sodium content of 0 ppm was added to 10 kg of a raw material potassium chloride at a temperature of 50 ppm.
To 30 ° C. and a 30% crude aqueous solution of potassium chloride 30%.
L was obtained. Thereafter, in the same manner as in Example 1, cations were removed with an ion exchange resin, and a 32% aqueous solution of potassium hydroxide was obtained by an electrolytic method.

[0032]

[Table 1]

The units in the table are ppm, and the symbols are as follows. However, only the unit of e is%. a: sodium content in raw potassium chloride, b: sodium content in purified potassium chloride, c: sodium content in saturated potassium chloride aqueous solution after purification by cation exchange resin, d: obtained potassium hydroxide E: concentration of the obtained aqueous potassium hydroxide solution, f: sodium content in the aqueous potassium hydroxide solution when converted to a concentration of 48%.

[0034]

According to the present invention, a potassium hydroxide aqueous solution having a low sodium content can be produced. Further, the aqueous potassium hydroxide solution obtained by the method of the present invention is
It can also be suitably used for applications in the food and semiconductor fields.

Claims (4)

[Claims] 1. A sodium content of 300 to 5000 pp
m raw material potassium chloride has a sodium content of 1500
ppm or less of potassium chloride aqueous solution or water is mixed to obtain a crude aqueous solution having a concentration of 22 to 28%,
The solid potassium chloride was precipitated by cooling to -10 ° C, and the precipitated solid potassium chloride was separated and redissolved in water to obtain a saturated potassium chloride aqueous solution having a sodium content of 60 ppm or less. 48% concentration
A method for producing an aqueous potassium hydroxide solution, wherein an aqueous potassium hydroxide solution having a sodium content of 100 ppm or less when converted to an aqueous potassium hydroxide solution is obtained. 2. A sodium content of 300 to 5000 pp.
m raw material potassium chloride has a sodium content of 1500
ppm or less of potassium chloride aqueous solution or water is mixed to obtain a crude aqueous solution having a concentration of 22 to 28%,
After cooling to −10 ° C. to precipitate solid potassium chloride and separating the precipitated solid potassium chloride, the solid potassium chloride is mixed with a potassium chloride aqueous solution or water having a sodium content of 60 ppm or less to obtain a solid concentration of 10 to 90%. % Of the slurry, and the slurry is subjected to solid-liquid separation to remove 50% or more of sodium in solid potassium chloride in a state of being dissolved in the separated mother liquor. Then, purified potassium chloride separated as a solid is dissolved in water. And the sodium content is 45p
pm or less as a saturated potassium chloride aqueous solution, and electrolyzed by an ion exchange membrane electrolysis method, and when converted to a 48% aqueous solution of potassium hydroxide, the sodium content is 75 ppm.
A method for producing an aqueous potassium hydroxide solution to obtain the following aqueous potassium hydroxide solution. 3. The method according to claim 1, wherein the crude aqueous solution is brought into contact with a cation exchange resin to remove calcium ions, magnesium ions or strontium ions and then cooled.
Or the method for producing a potassium hydroxide aqueous solution according to 2 above. 4. The method for producing a potassium hydroxide aqueous solution according to claim 3, wherein the crude aqueous solution is brought into contact with a cation exchange resin, then adjusted to pH 1 to 3 by adding hydrochloric acid, and cooled.