JPS6057515B2 - Production method of potassium bicarbonate - Google Patents

Description

Detailed Description of the Invention The present invention relates to a method for producing potassium bicarbonate, and in particular electrolyzes an aqueous solution of potassium chloride in an electrolytic cell using a cation exchange membrane, generates chlorine in the anode chamber, and generates hydrogen in the cathode chamber. This invention relates to a method for producing potassium bicarbonate using an electrolysis method that generates potassium hydroxide.

Potassium bicarbonate is produced by reacting caustic potassium obtained by various electrolytic methods with carbon dioxide gas to convert most of it into potassium bicarbonate, and the remainder into potassium carbonate, which is then cooled to precipitate and separate the potassium bicarbonate. The separated mother liquor is concentrated and returned to the carbon dioxide absorption process.

Concentration of the separated mother liquor is carried out primarily for the purpose of evaporating the moisture brought in by the caustic potassium raw material, but the addition of such a concentration step is not considered to be technically or economically advantageous.

On the other hand, a method of directly producing carbonates such as potassium carbonate in an electrolytic cell using a cation exchange membrane has been proposed for some time, and one side of this method is to electrolyze an aqueous solution of potassium chloride in the electrolytic cell as described above. One example is a method in which carbon dioxide gas is blown into the aqueous potassium hydroxide solution produced in the cathode chamber to convert substantially all of the solution into potassium carbonate.

Although this method can obtain potassium carbonate, it is not suitable at all for producing potassium bicarbonate. Even if you try to obtain potassium bicarbonate by blowing carbon dioxide gas into the caustic potassium produced in the cathode chamber, the reaction to reach potassium bicarbonate will not proceed sufficiently unless the partial pressure of carbon dioxide gas is increased, and in a general electrolytic cell, the pressure will be high. Because it is difficult to do this, unreacted carbon dioxide gas increases, making it not an efficient method. Normally, potassium bicarbonate is produced using caustic potassium as a raw material, so in many cases, a portion of the caustic potassium obtained by electrolysis of an aqueous potassium chloride solution is used for producing potassium bicarbonate.

The present invention improves the above-mentioned drawbacks in the production of potassium bicarbonate,
In addition, the aim is to advantageously obtain potassium bicarbonate by incorporating potassium bicarbonate production into the caustic potash production process using potassium chloride aqueous solution electrolysis. An electrolytic cell group consisting of a large number of unit electrolytic cells that can perform electrolysis (forming a cathode chamber and supplying purified potassium chloride aqueous solution to the anode chamber) is used, and some of them are used as an electrolytic cell for producing potassium carbonate. In addition, the remaining part is used as an electrolytic cell for producing caustic potash by conventional electrolysis, and a liquid containing potassium carbonate as a main component extracted from the cathode chamber of the electrolytic cell for producing potassium carbonate is reacted with carbon dioxide gas to produce potassium bicarbonate. The separated mother liquor after separating the produced potassium bicarbonate is supplied to the cathode chamber of the electrolytic cell for producing potassium carbonate, and at this time, the hydrogen gas discharged from the cathode chamber of the electrolytic cell group and the anode chamber are A method for producing potassium bicarbonate, characterized in that at least one of the discharged chlorine gas and the returned salt water is used to exchange heat with the liquid supplied to at least one electrode chamber of the electrolytic cell for producing potassium carbonate. be.

One embodiment of the method of the present invention will be described above with reference to the drawings.

FIG. 1 is a process diagram showing an example of producing potassium bicarbonate according to the present invention, and 1 and 1'' are electrolytic cells using cation exchange membranes C and C'', respectively. It is divided into chambers A, A'' and cathodes B, B''.

Among these electrolytic cells, 1 is intended for the production of potassium bicarbonate. It is an electrolytic cell for producing potassium carbonate, which is the raw material for the production of potassium carbonate.
1'' is an electrolytic cell for producing caustic potash.

A purified potassium chloride aqueous solution from the salt water purification system is supplied to these Denmachi tanks 1 and 1''. ，
The salt water is heat exchanged with the return salt water which exits from the anode chamber 1'' and passes through the path 10 in the heat exchanger 9, and then is supplied.

On the other hand, the returned salt water passes through this heat exchanger 9 and then undergoes dechlorination in step 2.
The raw salt is dechlorinated in the raw salt feed route 4, and then sent to the raw salt dissolution step 3 for dissolving the raw salt from the raw salt supply route 4, where it is mixed with the dissolved salt water 4,
Sent to brine precipitation step 5.

At this time, phosphoric acid or a salt thereof is added through route 6 at the entrance of this precipitation step. In the precipitation step 5, a commonly used precipitation agent (for example, potassium carbonate, caustic potash, or other precipitation accelerator) is added to remove the precipitate, and in the filtering step 7, calcium and magnesium components are removed.

Next, the pH of the liquid is adjusted to a range of 7 to 11, and the liquid is further passed through a chelate ion exchange resin tower 8 to almost completely remove these impurities, and then heat exchanged with the returned brine in the heat exchanger 9. The liquid is raised in temperature and then supplied to an electrolytic cell where it is subjected to electrolysis, thus forming a salt water purification system. In this case, the phosphoric acid or its salt added in route 6 is added so that the maximum allowable value is 5WL9/e1, ideally zero, after the filtration process, so that electrolysis can be achieved in combination with the impurity removal effect mentioned above. It prevents fluctuations in sliding voltage and current efficiency during operation, allowing stable operation over a long period of time.

On the other hand, in the cathode chamber B of the electrolytic cell 1, caustic potassium is produced by electrolysis of the potassium chloride aqueous solution, and this reacts with the cathode chamber supply liquid, which will be described later, to produce a solution whose main component is potassium carbonate. .

This cathode chamber produced solution is taken out of the electrolytic cell and introduced into the potassium bicarbonate production step 14 via route 11, where it is converted into potassium bicarbonate with carbon dioxide gas from route 15, which is then cooled and becomes heavier due to the difference in solubility. Potassium carbonate is precipitated, and this precipitate is separated in a filtering step 16 and taken out as a target product through a route 17. In addition, the mother liquor separated by overnight passing passes through a path 18 to a heat exchanger 1.
9, the temperature is raised by heat exchange with the hydrogen gas generated from each cathode chamber B, B'' and introduced into the heat exchanger 19 through path 12, and then into cathode chamber B of electrolytic cell 1 through path 20. Supplied.

On the other hand, as described above, in the electrolytic cell 1'', purified potassium chloride aqueous solution is supplied to the anode chamber, and water or dilute caustic potassium solution is supplied to the cathode chamber from route 21, and ion-exchange membrane electrolysis is carried out by a conventional method. The caustic potash produced in B'' is taken out as a product.

As described above, the method of the present invention combines an electrolytic cell group consisting of at least one electrolytic cell for producing potassium carbonate and at least one electrolytic cell for producing caustic potash to simultaneously produce potassium bicarbonate. At this time, the heat retained in the liquid and gas generated from each electrolytic cell is exchanged with the liquid supplied to the electrolytic cell to achieve effective operation.

Then, as mentioned above, the solution containing potassium carbonate as the main component obtained in the cathode chamber of the cation exchange membrane electrolytic cell 1 is sent to the potassium bicarbonate production process, and in this step, most of it is converted to potassium bicarbonate by reaction with carbon dioxide gas. The concentration step is almost unnecessary by converting the solution, cooling it, precipitating and separating potassium bicarbonate due to the difference in solubility, and returning the mother liquor to the electrolysis step.

In this case, a part of the cathode chamber product liquid is used for producing potassium bicarbonate, and the remaining liquid is mixed with the heated separated mother liquor after exiting the heat exchanger 19 in the path 20 and circulated to the cathode chamber. May be supplied. In these configurations for producing potassium bicarbonate, the cathode chamber produced liquid is essentially recycled as the cathode chamber feed liquid, and as a result, there is almost no room for water to enter from outside the system, and the water concentration throughout the process is approximately constant. It can be operated while being maintained at

Due to the water balance in the system including the St electrolytic cell, it is possible to prevent some concentration or the accumulation of impurities (such as when potassium chloride diffused from the anode chamber of the electrolytic cell accumulates as an impurity in the cathode production solution). Therefore, it may be necessary to draw out a part of the liquid, but it is economically very advantageous that there is almost no need to concentrate the liquid.

It is preferable to operate the electrolytic cell for producing potassium carbonate so that potassium carbonate containing caustic potassium is preferably 15% (weight %; the same applies hereinafter) or less, more preferably 5% or less, from the cathode chamber.

This is because when the concentration of caustic potassium exceeds 15%, the cathode current efficiency decreases depending on the type of cation exchange membrane, so it is desirable to maintain the concentration of caustic potassium below 5% in order to operate efficiently. be. When a portion of the liquid containing potassium carbonate as the main component discharged from cathode chamber B is used in the bicarbonate production process, the ratio of the liquid volume to be separated for the production of potassium bicarbonate to the total liquid volume can be set arbitrarily. It is desirable to operate this as appropriate, taking into account the potassium concentration at the electrolyzer outlet, the degree of carbon dioxide reaction in the potassium bicarbonate production process, the potassium bicarbonate concentration before cooling, the cooling temperature, etc. A particularly preferred ratio is cathode chamber outlet flow rate: separation liquid flow rate of 1:0.5~
0. It is about %.

The temperature of the liquid leaving the cathode chamber varies depending on the electrolytic operation, but is approximately 70°C.
-1100C, and therefore the temperature of the liquid extracted into the process of producing potassium bicarbonate is also 70-110C. This is sent to the potassium bicarbonate manufacturing process, and the mother liquor produced by the reaction after separation of potassium bicarbonate has a temperature of approximately 40 to 10°C, but this liquid is directly returned to the circulation system as the cathode chamber supply liquid. This causes the temperature of the electrolytic cell to drop and hinder operation, so heat exchange is performed between this mother liquor and the hydrogen gas generated in the cathode chamber of the electrolytic cell group, and the temperature of the liquid supplied to the cathode chamber is kept within the range of 70 to 110°C. maintain. In this case, as the supply heat source, in addition to the above-mentioned hydrogen gas, chlorine gas generated in the anode chamber of each electrolytic cell and the heat retained in returned salt water containing undecomposed potassium chloride may be used. In the method of the present invention,
The aqueous potassium chloride solution to be supplied to the electrolytic cell may be obtained by normal purification in which the returned brine is subjected to a raw salt dissolution process, then precipitated and filtered. It is desirable that the liquid be purified through the purification process described above in which a liquid is added. In particular, phosphoric acid or its salt added at the entrance of the precipitation process is added so that it becomes zero after the filtration process, and the pH of the brine after the filtration process is adjusted to remove impurities such as calcium and magnesium using a chelate ion exchange resin. This not only significantly accelerates the removal of these impurities, but also allows operation with good performance without fluctuations in both sliding voltage and current efficiency, and also extends the life of the cation exchange membrane. It can be maintained over time. In the above method, as mentioned above, the purified potassium chloride aqueous solution supplied to the anode chamber of the electrolytic cell for producing potassium carbonate is subjected to heat exchange with the returned brine produced in each electrolytic cell.
In place of the returned salt water, the salt water gas generated in the anode chamber or the above-mentioned hydrogen gas generated in the cathode chamber may be used.

The purpose of preheating and supplying the liquid to the anode chamber and cathode chamber of the electrolytic cell for producing potassium carbonate is to bring the entire electrolytic cell into a temperature state suitable for the electrolytic reaction. ) preheating is practical for either solution if the electrolytic reaction can be maintained properly. All you have to do is apply.

Among the liquids and gases that serve as heat carriers for this heat exchange, the return salt water and chlorine gas discharged from the anode chamber should be avoided from being heat exchanged with the cathode chamber supply liquid due to equipment corrosion caused by chlorine. It is desirable to use it for heat exchange with purified potassium chloride aqueous solution, which is usually treated with anti-corrosion measures in this system.

The electrolytic operation conditions of the electrolytic cell for producing caustic potash in the present invention are not particularly limited, and a conventional operation can be adopted. The cation exchange membrane of the electrolytic cell used in the method of the present invention is acid-resistant,
It is preferable that the membrane is alkali-resistant and resistant to chlorine gas, and in particular, a fluorine-containing membrane with sulfonic acid groups as ion exchange groups is preferable. There are some membranes that do this.

As described above, the present invention can advantageously obtain the desired product by cleverly combining the systems of the electrolytic cell for producing caustic potash and the electrolytic cell for producing potassium carbonate, and utilizing the heat.

The present invention will be explained below with reference to Examples.

Example 1 Potassium bicarbonate was produced as follows according to the method of the present invention using four ion-exchange membrane electrolyzers for producing potassium carbonate and one ion-exchange membrane electrolyzer for producing caustic potash. .

The flow of each liquid and gas in this operation is roughly as shown in Figure 1. Heat source 2 for heat exchange of the purified potassium chloride aqueous solution supplied to the anode chamber of the electrolytic cell for producing potassium carbonate is generated in the electrolytic cell for producing caustic potash. In addition, the hydrogen gas generated in the electrolytic cell for producing caustic potash was used as the heat source for heat exchange of the cathode chamber supply liquid of the electrolytic cell for producing potassium carbonate.

The equipment specifications and operating conditions for the main components and results 2 are as follows.

(1) Supply potassium chloride aqueous solution (a) Chelate ion exchange resin CR-10 (Mitsubishi Kasei Co., Ltd.
Co., Ltd. (Product name) ((口)～(F) are three items for electrolytic cells for producing potassium carbonate.

)2) Electrolytic cell and heavy duty manufacturing process -ーー゛-(
B) Electrolytic cell for producing potassium carbonate (1) Four 100 d bipolar cells are used, the anode chamber is made of titanium lining, and the cathode chamber is made of SUS.
3O dust, the anode uses a titanium mesh coated with a material containing ruthenium oxide, the cathode uses SUS3O4 mesh, and the cation exchange membrane is DuPont N-415.
(Product name Nafyon) is used.

(x1) Mother liquor temperature after producing potassium bicarbonate (before heat exchange) 31℃ (X
ii) Potassium bicarbonate production amount 36.3 kg/Hr (b)
Electrolytic cell for producing caustic potash (1) One 40KA electrolytic cell used,
Other specifications are the same as electrolytic cells for producing potassium carbonate.

(!i) Produced caustic potash concentration 25%-

[Brief Description of the Drawings] Fig. 1 is a process diagram showing an example of producing potassium bicarbonate by the method of the present invention. 1... Electrolytic cell for producing potassium carbonate, 1''...
Electrolytic cell for producing caustic force J, 3... raw salt dissolution process,
5... 2nd precipitation step, 7... filtration step, 9
, 19... Heat exchange; , 14... Potassium bicarbonate generation step.

Claims (1)

[Claims] 1. Using an electrolytic cell group consisting of a large number of unit electrolytic cells that can be separated by a cation exchange membrane to form an anode chamber and a cathode chamber, and can perform electrolysis while supplying purified potassium chloride aqueous solution to the anode chamber,
A part of it is used as an electrolytic cell for producing potassium carbonate, and the rest is used as an electrolytic cell for producing caustic potash by conventional electrolysis. The method consists of reacting with carbon dioxide gas to obtain potassium bicarbonate, and supplying the separated mother liquor after separating the generated potassium bicarbonate to the cathode chamber of the electrolytic cell for producing potassium carbonate; At least one of the hydrogen gas discharged from the anode chamber, the chlorine gas discharged from the anode chamber, and the returned salt water is used to exchange heat with the liquid supplied to at least one electrode chamber of the electrolytic cell for producing potassium carbonate. Characteristic method for producing potassium bicarbonate.