JP2023065761A - Production method of sodium carbonate - Google Patents

Abstract

To improve the production efficiency of sodium carbonate by industrially and stably producing sodium carbonate with low content of coarse and fine powder, and to provide a simple and economical sodium carbonate production method.SOLUTION: This invention provides a method for producing sodium carbonate by contacting carbon dioxide with an aqueous sodium hydroxide solution, wherein the pH of the aqueous solution containing sodium carbonate after contacting carbon dioxide with the aqueous sodium hydroxide solution is adjusted to 13.0 to 14.5 to precipitate a sodium carbonate monohydrate, then the sodium carbonate monohydrate is obtained by solid-liquid separation, the sodium carbonate monohydrate is then dispersed in water or an aqueous solution containing sodium carbonate to obtain a fluid dispersion of sodium carbonate monohydrate, and the dispersion is then brought into contact with carbon dioxide.SELECTED DRAWING: None

Description

The present invention relates to a method for producing sodium carbonate. Specifically, the present invention relates to a method for producing sodium carbonate that enables industrially stable production of sodium carbonate with a low content of fine powder and coarse powder.

Sodium carbonate is a compound that is widely used as an alkali agent in various industries or as a raw material for glass (see Patent Document 1). Sodium carbonate is produced, for example, by the ammonia-soda method. That is, in the ammonia-soda method, carbon dioxide gas generated by heating limestone is brought into contact with an aqueous solution containing ammonia and common salt (carbonation step) to obtain a slurry containing sodium hydrogen carbonate, and then the sodium hydrogen carbonate is obtained. Sodium carbonate is produced by solid-liquid separation of sodium hydrogen carbonate from a slurry containing and heating the obtained sodium hydrogen carbonate.

The sodium carbonate obtained by the above production method is so-called light ash having a small particle size and a low bulk density. This light ash can be difficult to handle depending on the application. Therefore, by spraying water on the light ash, sodium carbonate monohydrate having a large particle size and bulk density is generated, and by drying the sodium carbonate monohydrate, the particle size and bulk density are reduced. Large sodium carbonate (so-called dense ash) can be produced.

Alternatively, sodium carbonate is once dissolved in water to form an aqueous solution containing sodium carbonate, and then the water in the aqueous solution is evaporated to precipitate sodium carbonate monohydrate having a large particle size and bulk density, followed by solid-liquid separation. By drying sodium carbonate monohydrate isolated by, it is possible to produce sodium carbonate having a large particle size and bulk density (so-called dense ash).

As described above, it is known that the particle size, bulk density, etc. of sodium carbonate monohydrate affect the particle size, bulk density, etc. of the finally obtained sodium carbonate. It is also known that fine powders and coarse powders are precipitated during precipitation of substances. Therefore, various production methods have been proposed to reduce the precipitation of fine powder during the precipitation of sodium carbonate monohydrate. Specifically, when producing sodium carbonate monohydrate by bringing an aqueous sodium hydroxide solution and carbon dioxide gas into contact, the concentration of sodium hydroxide in the aqueous sodium hydroxide solution is adjusted to a predetermined temperature at a predetermined temperature. A method for producing sodium carbonate monohydrate having a large particle size and bulk density by adjusting the range is proposed (see Patent Document 2).

Japanese Patent Publication No. 46-033215 Japanese Patent Publication No. 46-012291 Japanese Patent Publication No. 55-049007

Although sodium carbonate monohydrate having a large particle size and bulk density can be produced by the method disclosed in Patent Document 2, the solid-liquid separated sodium carbonate monohydrate contains a liquid containing sodium hydroxide. Since it adheres, it was found that when drying to produce sodium carbonate, aggregated particles of sodium carbonate are by-produced, and corrosion occurs on the inner surface of the dryer. There is still room for improvement in terms of stable production. On the other hand, the sodium carbonate monohydrate adhering to sodium hydroxide is fluidized and dried using a carbon dioxide-containing gas, and after separating and removing fine sodium carbonate monohydrate, the sodium carbonate monohydrate is calcined. A method for obtaining sodium carbonate has also been proposed (see Patent Document 3).

However, in the method disclosed in Patent Document 3, fine sodium carbonate monohydrate, which is a by-product of adhering sodium hydroxide and carbon dioxide, tends to clog the inside of the fluidized dryer, and requires multi-stage drying processes. There was still room for improvement.

That is, the object of the present invention is to provide a simple and economical method for producing sodium carbonate by improving the production efficiency of sodium carbonate by industrially stably producing sodium carbonate with a low content of coarse powder and fine powder. to do.

In view of the above problems, the inventors of the present invention conducted intensive studies. As a result, in the reaction between sodium hydroxide solution and carbon dioxide, a solid precipitated until the reaction progressed to a certain extent, and it was found that this solid was sodium carbonate monohydrate with little coarse powder or fine powder. . However, it was also found that if the reaction was allowed to proceed further, the precipitated solids would re-dissolve and the precipitated solids would shrink.

Therefore, as a result of studying a method for precipitating sodium carbonate monohydrate while suppressing re-dissolution in the solution, an aqueous solution containing sodium carbonate monohydrate after contacting carbon dioxide with an aqueous sodium hydroxide solution It was found that by setting the pH of the solution to a predetermined range, sodium carbonate monohydrate having a large particle size and bulk density can be produced. Furthermore, even if the obtained sodium carbonate monohydrate is separated by solid-liquid separation, the sodium hydroxide contained in the aqueous solution that is not separated into crystals of sodium carbonate monohydrate remains. The inventors have found that sodium hydroxide can be removed by preparing a dispersion in which the hydrate is dispersed in water or an aqueous solution containing sodium carbonate, and bringing the dispersion into contact with carbon dioxide, thereby completing the present invention.

That is, the present invention is a production method for obtaining sodium carbonate by contacting carbon dioxide with an aqueous sodium hydroxide solution, wherein the pH of the aqueous solution containing sodium carbonate after contacting the carbon dioxide with the aqueous sodium hydroxide solution is is 13.0 to 14.5 to precipitate sodium carbonate monohydrate, then solid-liquid separation to obtain sodium carbonate monohydrate, then the obtained sodium carbonate monohydrate is mixed with water or sodium carbonate a sodium carbonate monohydrate dispersion by dispersing it in an aqueous solution containing sodium carbonate, and then bringing the dispersion into contact with carbon dioxide.

The present invention can preferably adopt the following aspects.

(1) From the dispersion of sodium carbonate monohydrate contacted with carbon dioxide, sodium carbonate monohydrate is obtained by solid-liquid separation, and then the obtained sodium carbonate monohydrate is dried to obtain carbonic acid. getting sodium.
(2) The concentration of the aqueous sodium hydroxide solution is higher than 25% by mass.
(3) The solid-liquid separation is a wet cyclone.
(4) Using the liquid separated by the solid-liquid separation as an aqueous sodium hydroxide solution to be brought into contact with carbon dioxide.
(5) The carbon dioxide to be brought into contact with the aqueous sodium hydroxide solution is an exhaust gas containing carbon dioxide.
(6) The exhaust gas containing carbon dioxide in (5) above is an exhaust gas generated in an ammonia-soda process.

The present invention is to precipitate sodium carbonate monohydrate with the pH of the aqueous solution after contacting carbon dioxide and sodium hydroxide aqueous solution within a predetermined range, and solid-liquid separation of the precipitated sodium carbonate monohydrate. After that, it is dispersed in water or an aqueous solution containing sodium carbonate, and the dispersion is brought into contact with carbon dioxide. By such a production method, it is possible to obtain sodium carbonate monohydrate with a low content of coarse powder and fine powder. By drying the obtained sodium carbonate monohydrate, it is possible to obtain sodium carbonate (dense ash) containing less coarse powder and fine powder.

Then, the sodium carbonate monohydrate separated by solid-liquid separation is dispersed in water or an aqueous solution of sodium carbonate to obtain a dispersion of sodium carbonate monohydrate, and then the dispersion is brought into contact with carbon dioxide. can remove the sodium hydroxide remaining in the aqueous solution that has not been separated from the separated sodium carbonate monohydrate, so that the resulting sodium carbonate monohydrate is dried to obtain an anhydrous sodium carbonate It is possible to prevent the by-production of sodium carbonate aggregate particles and the corrosion of the dryer when manufacturing the.

As described above, the sodium carbonate obtained by the production method of the present invention contains few coarse powders and fine powders. of sodium carbonate can be efficiently produced, and the industrial applicability is extremely high.

As described above, the present invention is to precipitate sodium carbonate monohydrate with the pH of the aqueous solution after contacting carbon dioxide and an aqueous sodium hydroxide solution within a predetermined range, and the precipitated sodium carbonate monohydrate After solid-liquid separation, it is dispersed in water or an aqueous solution containing sodium carbonate, and the dispersion is brought into contact with carbon dioxide. By such a production method, it is possible to obtain sodium carbonate with a low content of coarse powder and fine powder. The term "coarse powder" in the present invention refers to what remains on the sieve when sodium carbonate is sieved through a sieve with an opening of 1000 µm. Further, the term "fine powder" in the present invention refers to a substance that passes through a sieve with an opening of 125 µm when sodium carbonate is sieved.

Although the details of the reason why sodium carbonate with a low content of coarse powder and fine powder can be obtained by the production method of the present invention are unknown, the present inventors presume as follows. That is, after the reaction between carbon dioxide and an aqueous sodium hydroxide solution, an aqueous sodium carbonate solution can be obtained by reacting under conditions in which sodium hydroxide is completely consumed. The resulting sodium carbonate aqueous solution can precipitate sodium carbonate monohydrate by evaporating water by heating. be. On the other hand, in the reaction of blowing carbon dioxide gas into an aqueous sodium hydroxide solution, since the pH of the aqueous solution is high until the reaction progresses to some extent, sodium carbonate monohydrate with little coarse or fine powder is precipitated. The solubility of sodium carbonate monohydrate in an aqueous solution varies greatly depending on the pH of the aqueous solution, and as the reaction progresses, the pH of the aqueous solution decreases. It is assumed that the size will be reduced.

In the production method of the present invention, the pH of the aqueous solution is set to a predetermined range on the alkaline side, and sodium hydroxide monohydrate is precipitated in a state where sodium hydroxide remains, thereby suppressing the dissolution of sodium carbonate monohydrate. presumed to be possible. In addition, sodium carbonate monohydrate and sodium hydroxide can be separated by separating the precipitated sodium carbonate monohydrate and the aqueous solution in which sodium hydroxide remains by solid-liquid separation, and the separated carbonic acid By dispersing sodium monohydrate in water or an aqueous solution containing sodium carbonate, the pH change of the aqueous solution due to the reaction with carbon dioxide can be minimized, so dissolution of sodium carbonate monohydrate can be suppressed. It is assumed that Therefore, it is possible to obtain sodium carbonate monohydrate with a low content of coarse powder and fine powder, and by drying this sodium carbonate monohydrate, obtain sodium carbonate with a low content of coarse powder and fine powder. presumed to be possible.

Then, the sodium hydroxide adhering to the separated sodium carbonate monohydrate is removed by the reaction with carbon dioxide, and the sodium carbonate monohydrate separated by solid-liquid separation is removed from the dispersion liquid after contact with carbon dioxide. It is presumed that when the hydrate is dried to produce sodium carbonate, by-production of aggregated sodium carbonate particles and corrosion inside the dryer can be suppressed.

In this specification, unless otherwise specified, the notation "A to B" for numerical values A and B means "A or more and B or less". If a unit is attached only to the numerical value B in such notation, the unit is applied to the numerical value A as well. Hereinafter, the method for producing sodium carbonate of the present invention will be described in detail.

(carbon dioxide)
The carbon dioxide used in the production method of the present invention is not particularly limited, and industrially available forms can be used. Specifically, a gas containing carbon dioxide (so-called carbon dioxide gas) can be used. As the gas containing carbon dioxide, an exhaust gas containing carbon dioxide may be used. Exhaust gas discharged in various processes can be used as the exhaust gas containing carbon dioxide. Specifically, exhaust gas generated when fossil fuels such as petroleum and coal are burned in thermal power plants and combustion boilers, exhaust gas emitted by the ammonia-soda method, and generated when sludge is burned. exhaust gas, etc. In general, exhaust gas generated when fossil fuels such as petroleum and coal are burned in thermal power plants and combustion boilers is controlled within a certain range by the combustion conditions in the thermal power plants and combustion boilers. The amount of carbon dioxide in the discharged exhaust gas is also often within a certain range. On the other hand, the amount of carbon dioxide generated in the exhaust gas generated when sludge or the like is burned differs depending on the type of sludge, and the amount of carbon dioxide may vary depending on the combustion operation. In the ammonia-soda method, calcium chloride, ammonium chloride, etc. are produced in addition to sodium carbonate, and the amount of carbon dioxide discharged fluctuates according to the balance of these production amounts. In the production method of the present invention, any of the exhaust gases containing carbon dioxide can be suitably used. In particular, in the production method of the present invention, even when the amount of carbon dioxide to be discharged fluctuates, it is possible to produce while suppressing residual sodium hydroxide, and it is suitable to apply to such exhaust gas.

The exhaust gas may contain nitrogen oxides (NOx), sulfur oxides (SOx), and heavy metals. You can use it for the method.

(sodium hydroxide aqueous solution)
The sodium hydroxide aqueous solution in the production method of the present invention is not particularly limited, and aqueous solutions of various concentrations can be used. As described above, the solubility of sodium carbonate monohydrate is affected by the concentration, pH, etc. in the aqueous solution. Therefore, from the viewpoint of increasing the amount of sodium carbonate monohydrate precipitated, the concentration of sodium hydroxide in the sodium hydroxide aqueous solution is more preferably in a range exceeding 25% by mass, and 48 to 60% by mass. A range is particularly preferred.

(Contact between carbon dioxide and aqueous sodium hydroxide solution)
In the production method of the present invention, carbon dioxide and an aqueous sodium hydroxide solution are brought into contact. Carbon dioxide and sodium hydroxide react by the contact, and a slurry containing sodium carbonate monohydrate can be obtained. As a method for contacting the carbon dioxide and the aqueous sodium hydroxide solution in the production method of the present invention, a known method can be employed. Specifically, a method of blowing a gas containing carbon dioxide into a container filled with an aqueous sodium hydroxide solution and bringing the gas into contact with the aqueous sodium hydroxide solution can be used.

In the production method of the present invention, the temperature at which carbon dioxide and the aqueous sodium hydroxide solution are brought into contact may be any temperature at which sodium carbonate monohydrate is produced, and may generally be in the range of 35 to 108°C. When the temperature is lower than 35°C, the heptahydrate of sodium carbonate tends to precipitate, and when it is higher than 108°C, the anhydrous salt of sodium carbonate tends to precipitate. However, it tends to be difficult to control the particle size of the precipitated solids. From the viewpoint of efficiently precipitating the sodium carbonate monohydrate, the temperature at the time of contact between carbon dioxide and the aqueous sodium hydroxide solution is preferably in the range of 60 to 106°C, more preferably in the range of 80 to 106°C. is particularly preferred.

For the purpose of increasing the amount of sodium carbonate monohydrate precipitated, water may be distilled off by heating and concentrating the aqueous solution at the time of contact between the carbon dioxide and the aqueous sodium hydroxide solution.

(pH control of aqueous solution containing sodium carbonate)
In the production method of the present invention, it is necessary to adjust the pH of the aqueous solution containing sodium carbonate to 13.0 to 14.5 after contact between carbon dioxide and the aqueous sodium hydroxide solution. As described above, by setting the pH within the above range, it is possible to precipitate sodium carbonate monohydrate with a low content of coarse powder and fine powder. From the viewpoint of efficiently precipitating the sodium carbonate monohydrate, the pH of the aqueous solution containing sodium carbonate is preferably 14.0 to 14.4, more preferably 14.2 to 14.3. Especially preferred.

The method for adjusting the pH of the aqueous solution containing sodium carbonate to 13.0 to 14.5 is not particularly limited. can.

(Solid-liquid separation of sodium carbonate monohydrate)
A slurry containing sodium carbonate monohydrate can be obtained by the production method of the present invention. The obtained sodium carbonate monohydrate can be separated by a known method such as wet cyclone or filter press. Although sodium hydroxide remains in the slurry, most of the sodium hydroxide can be separated by solid-liquid separation.

It is preferable to perform solid-liquid separation by a wet cyclone because it has a high effect of reducing the water content in the separated sodium carbonate monohydrate and has a simple structure.

Further, the solution after solid-liquid separation contains sodium carbonate and sodium hydroxide dissolved in the solution. Therefore, the solution may be used as an aqueous sodium hydroxide solution to be brought into contact with carbon dioxide.

(Contact between separated sodium carbonate monohydrate and carbon dioxide)
About 0.5 to 5.0% by mass of sodium hydroxide remains in the sodium carbonate monohydrate isolated by the production method of the present invention. When this sodium carbonate monohydrate is dried as it is to obtain an anhydride of sodium carbonate, there is a risk of corrosion due to the by-product of aggregated sodium carbonate particles and the exposure of the inside of the dryer to high temperatures. . Therefore, in the production method of the present invention, the separated sodium carbonate monohydrate is dispersed in water or an aqueous solution containing sodium carbonate to prepare a dispersion of sodium carbonate monohydrate, and the dispersion is brought into contact with carbon dioxide. This causes the sodium hydroxide and carbon dioxide to react. By bringing carbon dioxide into contact with the dispersion, sodium hydroxide and carbon dioxide in the dispersion react to form sodium carbonate monohydrate, thereby removing sodium hydroxide.

The amount of water used for the dispersion is preferably as small as possible in order to dissolve the precipitate of sodium carbonate monohydrate. In order to suppress the dissolution of sodium carbonate monohydrate into the dispersion, it is preferable to dissolve sodium carbonate in advance in water and use an aqueous solution containing sodium carbonate as the dispersion medium. The concentration of sodium carbonate in the aqueous solution containing sodium carbonate may be appropriately determined according to the production conditions, but it is usually within the range of 25.0 to 30.5% by mass.

The sodium carbonate monohydrate slurry concentration when producing the sodium carbonate monohydrate dispersion is 20 from the viewpoint of the ability to efficiently remove sodium hydroxide and the solubility of sodium carbonate monohydrate. It may be appropriately set in the range of up to 50% by mass. As a method for contacting the dispersion of sodium carbonate monohydrate and carbon dioxide, specifically, a method of blowing a gas containing carbon dioxide into a container filled with the dispersion and bringing the gas into contact with an aqueous sodium hydroxide solution. are mentioned. Carbon dioxide may be contacted in an amount sufficient to consume the sodium hydroxide in the dispersion. When the dispersion medium is water, part of sodium carbonate monohydrate is dissolved in water, and when the dispersion medium is an aqueous solution containing sodium carbonate, sodium carbonate is dissolved in the dispersion medium. Therefore, when the sodium hydroxide in the dispersion liquid is consumed, the pH of the liquid becomes the pH of the sodium carbonate aqueous solution (11.9 to 12.2). Therefore, the pH of the dispersion liquid is confirmed, and the contact with carbon dioxide is carried out until it reaches the pH of the sodium carbonate aqueous solution.

The contact temperature is not particularly limited, and a range of 35 to 108° C. is usually sufficient. Moreover, for the purpose of increasing the amount of sodium carbonate monohydrate precipitated, the aqueous solution may be heated and concentrated to distill off water.

Sodium carbonate monohydrate after removing sodium hydroxide can be isolated by a known method such as filter press. The isolated sodium carbonate monohydrate contains about 1 to 10% by mass of water, and by drying it with a steam tube dryer or the like, the contained water is dried and the water of the hydrate is removed. Anhydride of sodium carbonate can be obtained by By such a production method, sodium carbonate with a low content of coarse powder and fine powder can be obtained. In addition, the solution after isolation contains sodium carbonate dissolved in the solution. Therefore, the solution may be used as a dispersion of sodium carbonate monohydrate.

The drying temperature in the above drying may be a temperature sufficient to form an anhydride, and may be appropriately set within the range of 150 to 180°C. As for the drying time, it may be sufficient to obtain an anhydride, and in the case of drying within the above temperature range, 0.5 to 2.0 hours is usually sufficient. When steam is used as a heat source when drying sodium carbonate monohydrate with a dryer such as a steam tube dryer, the steam discharged from the dryer is used as a mixture of the exhaust gas containing carbon dioxide and the aqueous sodium hydroxide solution. It can be used as a heat source during contact, or as a heat source when heating and concentrating an aqueous sodium carbonate solution and a dispersion to produce sodium carbonate monohydrate.

(Sodium carbonate obtained by the production method of the present invention)
By the production method of the present invention, it is possible to produce sodium carbonate with a low content of coarse powder and fine powder. Specifically, the resulting sodium carbonate has a bulk density of 1.1 to 1.3 kg/L as measured by JIS K1201-1, and coarse powder remaining on a 1 mm sieve is 3% by mass or less. The amount of fine powder that passes through a sieve with an opening of 125 μm is 6% by mass or less.

The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to these Examples. The physical properties of sodium carbonate obtained in the following examples and comparative examples were evaluated by the following methods.

<Physical property evaluation method>
The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to these Examples. In the following examples and comparative examples, the physical properties of an aqueous solution containing sodium carbonate, the physical properties of sodium carbonate, and the corrosion of a dryer were evaluated by the following methods.

<Method for analyzing aqueous solution containing sodium carbonate>
・pH
It was measured using a pH meter (SevenCompact S220 manufactured by Mettler Toledo).
・Analysis of aqueous solution (sodium carbonate concentration, sodium hydrogen carbonate concentration, sodium hydroxide concentration)
5 g of the obtained aqueous solution is precisely weighed in a 100 mL conical beaker, several drops of phenolphthalein are added, and the mixture is titrated with 1 mol/L hydrochloric acid while stirring well until the pink color disappears. A few drops of methyl orange are added to the solution, and the solution is titrated with 1 mol/L hydrochloric acid while stirring well until the yellow turns orange. Sodium carbonate concentration, sodium hydrogen carbonate concentration, and sodium hydroxide concentration were calculated from the titration amount.

<Physical property evaluation method>
- Particle size distribution 100 g of the obtained sodium carbonate was shaken and sieved for 5 minutes with a low-tap sieve shaker (without tap). The size of the sieve was as follows, and the mass of sodium carbonate remaining on the sieve was measured. The average particle size was calculated by taking the weighted average of the mass of sodium carbonate remaining on each sieve.
Sieves used in the sieve shaker: 1000 μm, 500 μm, 250 μm, 180 μm, 150 μm, 125 μm, and receiver Bulk density Measured according to the method described in JIS K1201-1.

<Dryer corrosion evaluation method>
Using a rotary dryer made of SUS304, the sodium carbonate monohydrate after centrifugation obtained in each example and comparative example was dried at 180° C. for a residence time of 1.0 hour. The dryer was operated continuously for 8 hours, and the state of corrosion before and after use was confirmed visually and by penetrant inspection.

<Example 1>
An aqueous sodium hydroxide solution adjusted to 48% by mass was charged into the reaction tank (10 L) at 1200 g / h, a gas containing carbon dioxide (carbon dioxide concentration 15% by volume) was charged at 3000 NL / h, and the stirrer was rotated. The number was 500 rpm. Sodium carbonate monohydrate was precipitated while reacting sodium hydroxide and carbon dioxide at a reaction temperature of 80°C. The resulting slurry containing sodium carbonate monohydrate was withdrawn from the reactor at a rate of 2400 g/h. The pH of the slurry containing sodium carbonate monohydrate was 14.1. Sodium carbonate monohydrate was separated from the slurry with a wet cyclone. The content of water in the separated sodium carbonate monohydrate was 31% by mass, and the content of sodium hydroxide was 1.5% by mass.

1,200 g of sodium carbonate monohydrate obtained by the wet cyclone is dispersed in 1,400 g of a dispersion having a sodium carbonate concentration of 30% by mass, and reacted with a gas containing carbon dioxide (carbon dioxide concentration: 15% by volume). to remove residual sodium hydroxide. The pH of the slurry after removing sodium hydroxide was 12.0.

After that, the obtained slurry of sodium carbonate monohydrate is separated into sodium carbonate monohydrate with a centrifuge, the crystals of sodium carbonate monohydrate are put into a rotary dryer, and the crystals in the dryer are dried. The residence time was adjusted to 1.0 hour and dried at 180° C. to obtain 750 g of anhydrous sodium carbonate crystals. As a result of evaluating the physical properties of the obtained crystals, it was found that the coarse powder was 2.2% by mass, the fine powder was 4.5% by mass, and the bulk density was 1.25 kg/L. No corrosion was found inside the dryer after the crystals were taken out.

Examples 2-4
Sodium carbonate (anhydrous) was produced under the same conditions as in Example 1 except that the conditions shown in Table 1 were used. Table 1 shows the physical property evaluation results of the obtained sodium carbonate crystals and the dryer corrosion evaluation results.

Comparative Examples 1-2
An aqueous sodium hydroxide solution and carbon dioxide were reacted under the conditions shown in Table 1. Except that the slurry containing sodium carbonate monohydrate extracted from the reaction tank was separated into sodium carbonate monohydrate as it was with a centrifuge, and the crystals of sodium carbonate monohydrate were dried with a rotary dryer. , to obtain sodium carbonate in the same manner as in Example 1. Table 1 shows the physical property evaluation results of the obtained sodium carbonate crystals.

Claims (7)

A production method for obtaining sodium carbonate by contacting carbon dioxide with an aqueous sodium hydroxide solution,
Precipitating sodium carbonate monohydrate by setting the pH of the aqueous solution containing sodium carbonate after contacting the carbon dioxide and the aqueous sodium hydroxide solution to 13.0 to 14.5,
Then, sodium carbonate monohydrate is obtained by solid-liquid separation,
Next, after dispersing the obtained sodium carbonate monohydrate in water or an aqueous solution containing sodium carbonate to obtain a dispersion of sodium carbonate monohydrate, the dispersion is brought into contact with carbon dioxide. A method for producing sodium carbonate. Obtaining sodium carbonate monohydrate by solid-liquid separation from the dispersion of sodium carbonate monohydrate contacted with carbon dioxide,
2. The method for producing sodium carbonate according to claim 1, wherein the obtained sodium carbonate monohydrate is then dried to obtain sodium carbonate. 2. The manufacturing method according to claim 1, wherein the concentration of the aqueous sodium hydroxide solution is higher than 25% by mass. 2. The method for producing sodium carbonate according to claim 1, wherein said solid-liquid separation is a wet cyclone. 2. The method for producing sodium carbonate according to claim 1, wherein the liquid separated by said solid-liquid separation is used as an aqueous sodium hydroxide solution to be brought into contact with carbon dioxide. 2. The method for producing sodium carbonate according to claim 1, wherein the carbon dioxide to be brought into contact with the aqueous sodium hydroxide solution is an exhaust gas containing carbon dioxide. 7. The method for producing sodium carbonate according to claim 6, wherein the exhaust gas containing carbon dioxide is exhaust gas generated in an ammonia-soda process.