Method for producing carbonate or bicarbonate of alkali metal

Abstract

The present invention provides a method for producing a carbonate or bicarbonate of an alkali metal, said method comprising supplying carbon-dioxide-containing bubbles, which are bubbles of a gas containing carbon dioxide, to an aqueous solution (a) of at least one alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal chlorides. When the aqueous solution (a) is an aqueous solution of an alkali metal chloride, carbon dioxide-containing bubbles are supplied after ammonia has been supplied to the aqueous solution (a). The carbon dioxide-containing bubbles have a d50 size of 100 μm or less and a d90 size of 150 μm or less.

Description

Method for producing alkali metal carbonates or hydrogen carbonates

[0001] The present invention relates to a method for producing an alkali metal carbonate or bicarbonate. This application claims priority to Japanese Patent Application No. 2024-040341, filed on March 14, 2024, the contents of which are incorporated herein by reference.

[0002] Alkali metal bicarbonates such as sodium bicarbonate are produced by crystallization from an aqueous solution. For example, the so-called ammonia-soda method has long been known, in which ammonia and carbon dioxide are blown into an aqueous solution containing sodium ions in this order to obtain sodium bicarbonate crystals. Another known method for obtaining alkali metal carbonates and / or bicarbonates is to supply a carbon dioxide-containing gas to an aqueous solution of an alkali metal hydroxide or alkali metal carbonate to carbonate and bicarbonate. For example, there is a method in which an aqueous sodium carbonate solution and a carbon dioxide-containing gas are continuously supplied to a tank in which sodium bicarbonate is suspended, causing a reaction and precipitating sodium bicarbonate. Patent Document 1 discloses a method for producing sodium bicarbonate, in which an aqueous sodium hydroxide solution or an aqueous sodium carbonate solution is reacted with carbon dioxide to obtain a sodium bicarbonate solution, and the solution is cooled to precipitate sodium bicarbonate crystals.

[0003] Patent Document 2 discloses a method in which an aqueous sodium hydroxide solution and a gas containing carbon dioxide are previously merged and then supplied into a reservoir tank containing an alkaline aqueous solution to precipitate sodium hydrogencarbonate.

[0004] On the other hand, Patent Document 3 discloses an apparatus for efficiently recovering carbon dioxide, which supplies carbon dioxide without electricity by supplying it through a perforated plate into a reaction tank in which an aqueous solution of an alkali metal hydroxide is stored.

[0005] Patent Document 4 discloses a method for producing sodium hydrogencarbonate slurry by supplying combustion exhaust gas containing carbon dioxide to an aqueous sodium carbonate solution generated in a caprolactam production process using a microbubbler, which is a high-pressure nozzle-type disperser.

[0006] Patent Document 5 discloses a method for producing sodium hydrogencarbonate by reacting an aqueous sodium carbonate solution with carbon dioxide, in which carbon dioxide is supplied in the form of fine bubbles having an average diameter of 0.1 mm or less using a swirling collision type mixer.

[0007] Japanese Patent Publication No. 3-275509 Japanese Patent Publication No. 2012-206872 Japanese Patent Publication No. 2023-65903 Korean Patent Publication No. 10-2205282 Korean Patent Publication No. 10-2313559

[0008] The present inventors considered that, since carbonates and hydrogencarbonates are produced by bringing a liquid aqueous solution of an alkali metal hydroxide or an alkali metal carbonate into contact with a gas containing carbon dioxide, and dissolving carbon dioxide in the aqueous solution, micronizing the carbon dioxide to increase the dissolution rate would increase the utilization rate of carbon dioxide, leading to an increase in the rate at which carbonates and hydrogencarbonates are produced.

[0009] However, in Patent Documents 1 and 2, this point is not taken into consideration, and the gas containing carbon dioxide is simply supplied through a tube. Therefore, only a portion of the supplied carbon dioxide reacts with the alkali metal hydroxide or alkali metal carbonate, that is, the utilization rate of carbon dioxide is low, and in some cases, equipment for recovering unreacted carbon dioxide is required.

[0010] In Patent Document 3, carbon dioxide is supplied through a perforated plate, and although the carbon dioxide absorption rate is improved, it is not sufficient. In addition, there is a risk that the perforated plate will become clogged if bicarbonate is precipitated.

[0011] In Patent Document 4, carbon dioxide is supplied using a device called a microbubbler, but the carbon dioxide conversion rate is only about 60%. This is thought to be because the carbon dioxide is not sufficiently atomized in the aqueous sodium carbonate solution.

[0012] In Patent Document 5, a reactor consisting of a bubble reactor and an adsorption tower maintained under a pressurized condition of 4 bar is used to supply pressurized carbon dioxide in the form of fine bubbles, but the utilization rate of carbon dioxide remains at about 90%. This is thought to be due to insufficient fineness of the carbon dioxide bubbles.

[0013] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a production method for producing an alkali metal carbonate or hydrogencarbonate, which can carry out a reaction such as carbonation of an alkali metal hydroxide or hydrogencarbonation of an alkali metal carbonate at a high speed, and which enables the effective use of gas with a low carbon dioxide concentration, thereby increasing the utilization rate of carbon dioxide.

[0014] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by supplying sufficiently fine carbon dioxide-containing bubbles to an aqueous solution (a) of at least one alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal chlorides, and have thus completed the present invention. The present invention encompasses the following aspects: [1] A method for producing an alkali metal carbonate or hydrogencarbonate, comprising supplying carbon dioxide-containing bubbles, which are bubbles of a gas containing carbon dioxide, to an aqueous solution (a) of at least one alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal chlorides, with the proviso that when the aqueous solution (a) is an aqueous solution of an alkali metal chloride, the carbon dioxide-containing bubbles are supplied after supplying ammonia to the aqueous solution (a), and the size of the carbon dioxide-containing bubbles is d50 or less and d90 or less. [2] The method for producing an alkali metal carbonate or bicarbonate according to [1], wherein the alkali metal carbonate or bicarbonate is lithium carbonate, sodium carbonate, potassium carbonate, lithium bicarbonate, sodium bicarbonate, or potassium bicarbonate. [3] The method for producing an alkali metal carbonate or bicarbonate according to [1] or [2], wherein the carbon dioxide-containing gas has a carbon dioxide concentration of 10% by volume or more. [4] The method for producing an alkali metal carbonate or bicarbonate according to any of [1] to [3], wherein the carbon dioxide-containing bubbles have a d50 size of 50 to 90 μm and a d90 size of 100 to 150 μm.[5] A method for producing an alkali metal bicarbonate, comprising: filtering a slurry containing an alkali metal bicarbonate precipitated therein, obtained by the method for producing an alkali metal carbonate or bicarbonate according to any one of [1] to [4]; adding a first aqueous solution (a) of at least one alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal chlorides to the obtained filtrate to obtain a second aqueous solution (a); supplying carbon dioxide-containing gas bubbles to the second aqueous solution (a) to obtain a third aqueous solution (a) of the alkali metal carbonate or bicarbonate; concentrating the third aqueous solution (a) by removing water from the third aqueous solution (a) to obtain a fourth aqueous solution (a); and supplying carbon dioxide-containing gas bubbles to the fourth aqueous solution (a) to precipitate the alkali metal bicarbonate. [6] A method for producing a powder of alkali metal bicarbonate, comprising obtaining an aqueous solution or slurry containing an alkali metal bicarbonate by the method according to any one of [1] to [5]; and subjecting the obtained aqueous solution or slurry to a dehydration treatment and a drying treatment to obtain a powder of alkali metal bicarbonate. [7] A method for producing an alkali metal bicarbonate powder, wherein the alkali metal bicarbonate powder has an average particle size (d50) of 100 μm or less.

[0015] According to the present invention, it is possible to provide a production method for producing an alkali metal carbonate or hydrogencarbonate, which can carry out a reaction such as carbonation of an alkali metal hydroxide or hydrogencarbonation of an alkali metal carbonate at a high speed, and which enables the effective use of gas with a low carbon dioxide concentration, thereby increasing the utilization rate of carbon dioxide.

[0016] 1 is a flow chart showing an example of the production method of the present invention. 2 is a flow chart showing another example of the production method of the present invention.

[0017] The meanings of terms used in this specification are as follows. A numerical range expressed as "to" means a numerical range with the numbers before and after "to" as the lower and upper limits. "d10," "d50," and "d90" respectively refer to the 10% diameter, 50% diameter (median diameter), and 90% diameter in a cumulative distribution curve of bubble (or particle) volume relative to bubble (or particle) size. "Carbon dioxide utilization rate" means the ratio, expressed as a percentage, of the calculated amount (B) of carbon dioxide gas required to convert all of the alkali metal compounds in the aqueous solution (a) used into alkali metal carbonates or bicarbonates, to the amount (A) of carbon dioxide gas supplied for producing alkali metal carbonates or bicarbonates.

[0018] The present invention will be described below, but is not limited to the examples in the following description. The method for producing an alkali metal carbonate or hydrogencarbonate of this embodiment includes supplying carbon dioxide-containing bubbles, which are bubbles of a gas containing carbon dioxide, to an aqueous solution (a) of at least one alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal chlorides. However, when the aqueous solution (a) is an aqueous solution of an alkali metal chloride, the carbon dioxide-containing bubbles are supplied after supplying ammonia to the aqueous solution (a).

[0019] <Aqueous Solution (a)> The aqueous solution (a) is an aqueous solution of at least one alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal chlorides. The upper limit of the concentration of the alkali metal compound in the aqueous solution (a) is the saturation concentration of the alkali metal compound. The concentration of the alkali metal compound in the aqueous solution (a) is preferably 3% or more, more preferably 5% or more. The lower limit of the concentration of the alkali metal compound in the aqueous solution (a) is preferably a concentration that exceeds the solubility of sodium bicarbonate at 0°C when the alkali metal compound reacts with carbon dioxide to produce sodium bicarbonate. In particular, the concentration of sodium carbonate in the aqueous solution (a) is preferably 6 to 25%, more preferably 10 to 20%. If the concentration is above the lower limit, when sodium bicarbonate is produced by reaction with carbon dioxide, the amount of sodium bicarbonate produced is likely to exceed the solubility of sodium bicarbonate, and sodium bicarbonate is likely to precipitate. Furthermore, if the concentration is below the upper limit, the amount of sodium bicarbonate in the produced sodium bicarbonate-containing slurry is appropriate, and the viscosity of the slurry does not become too high, making it easy to handle.

[0020] <Alkali Metal> Examples of alkali metals include lithium, sodium, and potassium. When these alkali metals are used, carbonates or bicarbonates such as lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate are obtained as target products of the method of the present embodiment.

[0021] <<Carbon dioxide-containing bubbles>> Carbon dioxide-containing bubbles are bubbles of a gas containing carbon dioxide. The gas containing carbon dioxide is not particularly limited as long as the carbon dioxide concentration is 10% by volume or more, and is not limited to a mixed gas of carbon dioxide with air or nitrogen gas, such as exhaust gas from a combustion furnace, exhaust gas from a glass melting furnace, or gas generated by neutralizing carbonate, but high-purity carbon dioxide gas can also be used. The preferred range of the carbon dioxide concentration is 30% by volume or more, more preferably 50% by volume or more. There is no particular limit on the upper limit of the carbon dioxide concentration, and it may be 100% by volume.

[0022] In the manufacturing method of this embodiment, carbon dioxide-containing bubbles, which are minute bubbles of a gas containing carbon dioxide, are formed and supplied to the aqueous solution of the alkali metal compound (a). The size of the carbon dioxide-containing bubbles is d50 or less and d90 or less, and carbon dioxide-containing bubbles of this size can be obtained by appropriately adjusting the conditions of a known fine bubble preparation method.

[0023] Fine bubbles are a general term for microbubbles with diameters of 1 to 100 μm and nanobubbles with diameters of less than 1 μm. When a large number of microbubbles are generated in water, they appear as cloudy white water. On the other hand, nanobubbles are so small that the water remains transparent. By converting a gas containing carbon dioxide into fine bubbles, the dissolution rate of carbon dioxide can be increased, and almost all of the supplied carbon dioxide can react with the alkali metal compound, allowing the carbon dioxide to react without loss. This not only eliminates the need for conventional equipment to recover unreacted carbon dioxide, but also enables the reaction to occur at a sufficient reaction rate even with a gas containing a low carbon dioxide concentration. Furthermore, the reaction apparatus does not require pressurization of the tank containing the aqueous solution of the alkali metal compound (a), and has the advantage of being able to use a simple, atmospheric-pressure apparatus.

[0024] Such fine bubble generating devices are not particularly limited, and examples include the following: (Example 1) A device that supplies gas to the suction side of a pressure pump and converts the gas into fine bubbles using a mixing blade rotating at high speed inside the pressure pump. A specific example is the "Vortex Turbo Mixer Pump" (product name) manufactured by Nikuni Co., Ltd. (Example 2) A device that creates a low-pressure area in a liquid flow by using the Venturi effect (narrowing the flow path of a pressurized liquid to increase the flow rate and create a low-pressure area), and then supplies gas to that area to generate fine bubbles. Specific examples include the "YJ Nozzle" (product name) manufactured by Envirovision Co., Ltd. and the "Aqua Transfer Nozzle" (product name) manufactured by Water Navi Co., Ltd. (Example 3) A device that creates a negative pressure area in the center by spraying water radially from a rapidly rotating disk, and then sucks in gas to generate fine bubbles. A specific example is the "Spinor" (product name) manufactured by Water Navi Co., Ltd.

[0025] The size of the carbon dioxide-containing bubbles can be measured, for example, by focused beam reflectance measurement. An example of an apparatus used for focused beam reflectance measurement is a particle size analyzer (product name: Particle Track) using FBRM (focused beam reflectance measurement) manufactured by Mettler Toledo K.K. In this specification, the size distribution of the carbon dioxide-containing bubbles is represented by the 10% diameter (d10), 50% diameter (median diameter, d50), and 90% diameter (d90) in a cumulative distribution curve of bubble volume versus bubble size. In this embodiment, by using carbon dioxide-containing bubbles having a d50 of 100 μm or less and a d90 of 150 μm or less, the utilization rate of carbon dioxide can be sufficiently increased in the carbonation reactions of alkali metal hydroxides and alkali metal carbonates or alkali metal chlorides. From the viewpoint of ensuring the effects of the present invention, d50 is preferably 50 to 90 μm, more preferably 60 to 80 μm, and d90 is preferably 100 to 150 μm, more preferably 100 to 130 μm. In the present invention, so-called fine bubbles with a bubble diameter of 1 μm or less do not need to be present. There are no particular restrictions on the minimum bubble diameter of the carbon dioxide-containing bubbles, but from the viewpoint of ease of adjusting the carbon dioxide-containing bubbles, it is preferable that the bubble diameter be greater than 1 μm or 10 μm or greater. According to the method of the present invention, the utilization rate of carbon dioxide can be sufficiently increased even without the presence of fine bubbles with a bubble diameter of 1 μm or less.

[0026] <<Supply of Carbon Dioxide-Containing Bubbles to Aqueous Solution (a)>> When the alkali metal compound is an alkali metal hydroxide, the temperature of the aqueous solution (a) when supplying the carbon dioxide-containing bubbles is not particularly limited, and is preferably 0°C to 80°C. The lower the temperature, the greater the solubility of carbon dioxide in the aqueous solution of alkali metal hydroxide (a), but temperatures of 0°C or higher are preferred because there is no risk of freezing. On the other hand, the higher the temperature, the less the solubility of carbon dioxide in the aqueous solution of alkali metal hydroxide (a), so temperatures of 80°C or lower are preferred because the rate of alkali metal carbonate production is less likely to slow down. The temperature of the aqueous solution (a) is more preferably 20 to 60°C, and even more preferably 30 to 50°C.

[0027] When the alkali metal compound is an alkali metal carbonate, the temperature of the aqueous solution (a) when carbon dioxide-containing bubbles are supplied is not particularly limited, but is preferably 0°C to 80°C. The lower the temperature, the greater the solubility of carbon dioxide in the aqueous solution of alkali metal carbonate. However, temperatures above 0°C are preferred because there is no risk of freezing. On the other hand, the higher the temperature, the less the solubility of carbon dioxide in the aqueous solution of alkali metal carbonate (a). Therefore, temperatures below 80°C are preferred because the rate of alkali metal carbonate production is less likely to slow down. Furthermore, the higher the temperature, the greater the solubility of the alkali metal bicarbonate produced. However, temperatures below 80°C are preferred because a greater amount of the alkali metal bicarbonate precipitates. The temperature of the aqueous solution (a) is more preferably 20°C to 70°C, and even more preferably 25°C to 50°C. The time for supplying carbon dioxide-containing bubbles to the aqueous solution (a) is not particularly limited as long as it allows the desired reaction to proceed sufficiently. However, it is generally 0.2 to 16 hours, and preferably 0.5 to 8 hours.

[0028] When the alkali metal compound is an alkali metal chloride such as sodium chloride, carbon dioxide-containing bubbles are supplied after ammonia is supplied to the aqueous solution (a). In this case, the procedure and conditions other than the use of carbon dioxide-containing bubbles can be carried out in accordance with the known ammonia-soda method.

[0029] One specific embodiment of the method of the present invention is described below. Carbon dioxide-containing bubbles are supplied to an aqueous solution (a) of an alkali metal carbonate (first aqueous solution (a)) to obtain a slurry in which an alkali metal bicarbonate has precipitated. This slurry is then filtered to obtain a filtrate (b), to which an aqueous solution of an alkali metal hydroxide (first aqueous solution (a)) is added to obtain a second aqueous solution (a). Carbon dioxide-containing bubbles are supplied to this second aqueous solution (a) to obtain an aqueous solution of an alkali metal carbonate, and the water is removed and concentrated to obtain a third aqueous solution (a). Carbon dioxide-containing bubbles are then supplied again to this concentrated aqueous solution of alkali metal carbonate (third aqueous solution (a)) to precipitate an alkali metal bicarbonate. The filtrate (b) obtained by filtering the slurry in which the alkali metal bicarbonate has precipitated is a saturated aqueous solution of alkali metal bicarbonate. Therefore, by employing this process, the present invention allows the saturated aqueous solution of alkali metal bicarbonate to be reused as a raw material for alkali metal bicarbonate, thereby eliminating the loss of the alkali metal and carbon dioxide used as raw materials and recovering all of the alkali metal bicarbonate. The reason for removing water from the aqueous solution of alkali metal carbonate to concentrate it is that as this series of operations is repeated, the volume of the slurry from which the alkali metal bicarbonate has precipitated gradually increases, necessitating the need for a large tank to accommodate this slurry. For example, when the alkali metal is sodium or potassium, only aqueous solutions of sodium hydroxide or potassium hydroxide with a maximum concentration of 48% can be obtained, and if water is not removed, the volume of the slurry from which sodium bicarbonate or potassium bicarbonate has precipitated gradually increases. If the concentration of the aqueous solution of alkali metal hydroxide can be increased to 66%, there is no need to remove water.

[0030] The method for removing and concentrating the aqueous solution of alkali metal carbonate is not particularly limited. However, the most preferred method is to supply fine bubbles of a gas with a low water vapor partial pressure to the aqueous solution, as this method requires minimal equipment. Examples of equipment for generating fine bubbles include the same equipment as described above. All that is required is a pump and piping for circulating the aqueous solution, as well as gas piping. Other methods include a method using a so-called packed tower. This method uses a packed tower equipped with packings such as pall rings, in which the aqueous solution is sprayed and allowed to flow downward from above while a gas with a low water vapor partial pressure is supplied upward from below, resulting in gas-liquid contact. However, this method requires a packed tower in addition to a pump and piping for circulating the aqueous solution and gas piping. Another method involves heating the aqueous solution to evaporate the water. Examples of heating methods include using a jacketed container containing the aqueous solution, or immersing a coiled tube in the aqueous solution, and passing steam or high-temperature hot water at or above atmospheric pressure through the jacket or coiled tube. However, this method requires not only a pump and piping for circulating the aqueous solution and gas piping, but also equipment for producing steam and high-temperature hot water and supplying them to the container containing the aqueous solution.

[0031] A first embodiment of the method of the present invention will be described below with reference to Fig. 1. However, this is merely one example of an embodiment of the present invention, and the present invention is not limited to this example. Fig. 1 is a flow chart showing an example of the production method of the present invention, and shows an example of the overall configuration of a sodium hydrogencarbonate production apparatus for carrying out the method of the present invention.

[0032] In FIG. 1 , concentration adjustment tank 1 for the sodium carbonate aqueous solution is an atmospheric pressure tank equipped with an agitator 2. Concentration adjustment tank 1 contains sodium carbonate aqueous solution 3. The sodium carbonate aqueous solution 3 is adjusted to a predetermined concentration by a method described below. This sodium carbonate aqueous solution 3 adjusted to the predetermined concentration is sent to sodium bicarbonate precipitation tank 6 through a feed pipe 5 using a vortex turbo mixer pump 4. The sodium bicarbonate precipitation tank 6 is also an atmospheric pressure tank equipped with an agitator 7. Liquid 8 in the sodium bicarbonate precipitation tank is initially a sodium carbonate aqueous solution with an adjusted concentration. This liquid is then circulated through circulation pipe 10 in sodium bicarbonate precipitation tank 6 using a vortex turbo mixer pump 9. Meanwhile, finely bubbled carbon dioxide-containing gas is introduced into the suction side of vortex turbo mixer pump 9 through a carbon dioxide-containing gas supply pipe 11 so that the d50 and d90 values ​​fall within the above-mentioned ranges. As the carbon dioxide-containing gas is introduced, the pH of liquid 8 in the sodium bicarbonate precipitation tank decreases, and sodium bicarbonate precipitates, causing the liquid to become cloudy. When the pH of the liquid 8 in the sodium bicarbonate precipitation tank finally reaches 8.5 or less, the supply of the carbon dioxide-containing gas is stopped, and sodium bicarbonate slurry is obtained.

[0033] This sodium bicarbonate slurry is extracted through a feed pipe 12 using a vortex turbo mixer pump 9. The extracted sodium bicarbonate slurry is then filtered in a centrifugal dehydrator 13. The sodium bicarbonate cake obtained by the centrifugal dehydration is sent through a feed pipe 14 to a drying facility 15, where it is dried to obtain sodium bicarbonate powder 16. During this centrifugal dehydration, a filtrate 17 is also produced. This filtrate 17 is saturated aqueous sodium bicarbonate, and is recovered in a filtrate recovery tank 18. After that, it is returned by a filtrate feed pump 19 through a filtrate feed pipe 20 to the concentration adjustment tank 1 for the aqueous sodium carbonate solution.

[0034] In the sodium carbonate aqueous solution concentration adjustment tank 1, sodium hydroxide is added to the filtrate 17 through the sodium hydroxide addition pipe 21. The addition of sodium hydroxide brings the pH of the aqueous solution to approximately 14. Subsequently, the filtrate is circulated through the circulation pipe 22 in the sodium carbonate aqueous solution concentration adjustment tank 1 using the vortex turbo mixer pump 4, while finely bubbled carbon dioxide is introduced through the carbon dioxide-containing gas supply pipe 23 to the suction side of the vortex turbo mixer pump 4 so that the d50 and d90 values ​​fall within the above ranges. As the carbon dioxide-containing gas is introduced, the pH of the liquid 8 in the sodium carbonate aqueous solution concentration adjustment tank 1 decreases. Finally, when the pH reaches that of the sodium carbonate aqueous solution (approximately 12), the supply of the carbon dioxide-containing gas is stopped, and the sodium carbonate aqueous solution is obtained. Subsequently, the sodium carbonate aqueous solution is circulated through the circulation pipe 22 in the sodium carbonate aqueous solution concentration adjustment tank 1 using the vortex turbo mixer pump 4, while finely bubbled air is introduced through the air supply pipe 24 to the suction side of the vortex turbo mixer pump 4. As air is introduced, the aqueous sodium carbonate solution is concentrated as water evaporates, and the solution is adjusted to a predetermined sodium carbonate concentration.

[0035] Next, a second embodiment of the method of the present invention will be described with reference to Fig. 2. However, this is merely one example of an embodiment of the present invention, and the present invention is not limited to this example. Fig. 2 is a flow chart showing another example of the production method of the present invention, and shows an example of the overall configuration of a sodium hydrogencarbonate production apparatus for carrying out the method of the present invention.

[0036] The second embodiment differs from the first embodiment in that a YJ nozzle is used instead of a vortex turbo mixer pump as a device for producing fine bubbles of gas containing carbon dioxide. In Figure 2, the liquid in the concentration-adjusting tank 1 for the aqueous sodium carbonate solution is supplied to the YJ nozzle 27 by a magnetic pump 25. The gas containing carbon dioxide is supplied to the center of the YJ nozzle 27 via a supply pipe 23 and is converted into fine bubbles within the YJ nozzle so that the d50 and d90 values ​​fall within the above-mentioned ranges. This results in an aqueous sodium carbonate solution 3 in the concentration-adjusting tank 1 for the aqueous sodium carbonate solution.

[0037] Similarly, the liquid in the sodium bicarbonate precipitation tank 6 is supplied to the YJ nozzle 28 by the magnetic pump 26. A gas containing carbon dioxide is supplied to the center of the YJ nozzle 28 by the supply pipe 11 and is converted into fine bubbles in the YJ nozzle so that the d50 and d90 fall within the above-mentioned ranges. As a result, sodium bicarbonate is precipitated in the sodium bicarbonate precipitation tank 6, and a sodium bicarbonate slurry is obtained.

[0038] According to the method for producing an alkali metal carbonate or bicarbonate of the present invention, the utilization rate of carbon dioxide can be increased. Here, the utilization rate of carbon dioxide is preferably 95% or more, more preferably 98% or more, and most preferably 100%. The method for producing an alkali metal carbonate or bicarbonate of the present invention has been described above, but the present invention is not limited to the configurations described in the above embodiments, and the configurations can be modified as appropriate within the scope of the invention.

[0039] Furthermore, according to this production method, the hydrogen carbonation reaction of an alkali metal carbonate can be carried out at a high speed to produce an alkali metal bicarbonate (e.g., sodium bicarbonate) having a small average particle size of 100 μm or less, and therefore this production method also has the advantage of facilitating pulverization to produce a fine powder of alkali metal bicarbonate having an average particle size of 8 to 15 μm (approximately 10 μm). The fine powder has a large specific surface area, making it suitable as an alkali metal bicarbonate (e.g., sodium bicarbonate) for treating exhaust gases generated at thermal power plants, waste incineration treatment facilities, biomass power plants, etc., i.e., for removing acidic gases contained in the exhaust gases. Here, "average particle size" refers to the cumulative 50% diameter (=median diameter, d50) based on volume, and small alkali metal bicarbonates are preferably 100 μm or less, more preferably 50 μm or less, more preferably 35 μm or less, even more preferably 25 μm or less, particularly preferably 20 μm or less, and most preferably 10 μm or less. That is, one aspect of the present invention provides a method for producing an alkali metal bicarbonate powder, comprising: obtaining an aqueous solution or slurry containing an alkali metal bicarbonate by the above-described production method; and subjecting the resulting aqueous solution or slurry to dehydration and drying treatments to obtain an alkali metal bicarbonate powder. The dehydration and drying treatments can be performed by known methods, for example, under conditions such that the moisture content of the resulting powder is 1.0% by mass or less, or 0.1% by mass or less. The moisture content can be measured by known methods, such as the method described in JP 2003-83947 A.

[0040] The present invention will be described in more detail below with reference to examples, but is not limited to these. Unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass", respectively.

[0041] Examples 1 to 5 and 9 are working examples, and Examples 6 to 8 and 10 are comparative examples.

[0042] <<Measurement Method / Evaluation Method>> (Size of Carbon Dioxide-Containing Bubbles) The size of the carbon dioxide-containing bubbles was measured using a particle size analyzer (product name: Particle Track G400) by FBRM (focused beam reflectance measurement) manufactured by Mettler Toledo K.K. Specifically, in Fig. 1 or 2, the bubble size was measured by immersing a measurement probe in the sodium carbonate aqueous solution 3 or the liquid 8 in the sodium bicarbonate precipitation tank. The bubble size distribution was expressed as the 10% diameter (d10), 50% diameter (median diameter, d50), and 90% diameter (d90) in a cumulative distribution curve of bubble volume versus bubble size.

[0043] (Carbon dioxide utilization rate) The carbon dioxide utilization rate (UR1) (%) during sodium bicarbonate precipitation was determined as the ratio, expressed as a percentage, of the calculated amount of carbon dioxide gas (B) required to convert all of the sodium carbonate in the aqueous sodium carbonate solution used to sodium bicarbonate to the amount of carbon dioxide gas (A) actually supplied for sodium bicarbonate precipitation. That is, the carbon dioxide utilization rate (UR1) can be calculated using the following formula (1): Carbon dioxide utilization rate (UR1) (%) during sodium bicarbonate precipitation = Calculated amount of carbon dioxide gas required to convert all of the sodium carbonate to sodium bicarbonate (B, unit: L) / Amount of carbon dioxide gas actually supplied (A, unit: L) × 100 Formula (1) Furthermore, the carbon dioxide utilization rate (UR2) (%) during the preparation of the aqueous sodium carbonate solution was determined as the ratio, expressed as a percentage, of the calculated amount of carbon dioxide gas (D) required to convert the filtrate and sodium hydroxide mixture obtained by centrifugal dehydration to the amount of carbon dioxide gas (C) supplied. That is, the carbon dioxide utilization rate (UR2) can be calculated by the following formula (2): Carbon dioxide utilization rate (UR2) (%) when preparing an aqueous sodium carbonate solution = Calculated value of the amount of carbon dioxide gas required to convert the filtrate and sodium hydroxide mixture into an aqueous sodium carbonate solution (D, unit: L) / Amount of carbon dioxide gas actually supplied (C, unit: L) × 100 Formula (2)

[0044] (Average particle diameter d50 of sodium hydrogencarbonate) Using a particle size distribution measuring device, Microtrac FRA type, manufactured by Nikkiso Co., Ltd., the particle size distribution of sodium hydrogencarbonate particles dispersed in a mixed solvent (methanol=11%, ethanol=88%, isopropanol=1%) was measured, and the cumulative 50% diameter on a volume basis (median diameter, d50) was determined.

[0045] Example 1: The apparatus of the first embodiment shown in FIG. 1 was used. First, 800 g of sodium carbonate powder and 4,000 g of ion-exchanged water were charged into an 8-L sodium carbonate aqueous solution concentration adjustment tank 1 and stirred to obtain 4,800 g of a 16.7% sodium carbonate aqueous solution. Next, this aqueous solution was transferred to an 8-L sodium bicarbonate precipitation tank 6, after which a vortex turbo mixer pump 9 was started and circulated through a circulation pipe 10. The vortex turbo mixer pump 9 was a KTM15ND02S model manufactured by Nikuni Co., Ltd. The circulation flow rate was 20 L / min. Immediately after starting circulation, carbon dioxide gas (carbon dioxide concentration 100% by volume) was supplied to the suction pipe of the vortex turbo mixer pump 9 at a rate of 1.0 L / min to introduce finely bubbled carbon dioxide. The carbon dioxide bubble sizes were d50 = 63 μm and d90 = 107 μm. The temperature of the aqueous solution during carbon dioxide introduction was 25 to 35°C. 169 minutes after the start of the supply of carbon dioxide-containing bubbles, the sodium hydrogencarbonate precipitation tank 6 became a cloudy sodium hydrogencarbonate slurry with a pH of 8.0. The carbon dioxide utilization rate (UR1) was 100%.

[0046] This sodium bicarbonate slurry was filtered using a centrifugal dehydrator 13, yielding 1,117 g of a centrifugal dehydrated cake and 4,015 g of a filtrate. A centrifugal dehydrator model H-110F manufactured by Kokusan Co., Ltd. was used as the centrifugal dehydrator 13. The centrifugal dehydrated cake was dried in a carbon dioxide atmosphere at 80°C, yielding 893 g of sodium bicarbonate powder. The resulting sodium bicarbonate powder had an average particle size d50 of 31 μm. 200 g of the resulting sodium bicarbonate powder was pulverized for 30 minutes using a pulverizer (model SP-3 manufactured by NY Lab LLC) at a blade rotation speed of 4,000 rpm, yielding a fine powder product with an average particle size d50 of 11 μm. Meanwhile, the filtrate, saturated sodium bicarbonate water (concentration 9.3%), was returned to the sodium carbonate aqueous solution concentration adjustment tank 1. After adding 886 g of 48% sodium hydroxide aqueous solution, the vortex turbo mixer pump 4 was started and circulated through the circulation pipe 22. The circulation flow rate was 20 L / min. The vortex turbo mixer pump used was a KTM15ND02S model manufactured by Nikuni Co., Ltd. Immediately after starting the circulation, carbon dioxide gas was supplied to the suction pipe of the vortex turbo mixer pump 4 at a rate of 1.0 L / min to introduce finely bubbled carbon dioxide. The carbon dioxide bubble sizes were d50 = 63 μm and d90 = 106 μm. After 69 minutes, the solution in the sodium carbonate aqueous solution concentration adjustment tank 1 had a pH of 12.0, a weight of 5037 g, and a sodium carbonate content of 800 g. The carbon dioxide utilization rate (UR2) was 100%.

[0047] Next, the vortex turbo mixer pump 4 was started, and while circulating the solution at a circulation flow rate of 20 L / min using the circulation pipe 22, air was supplied to the suction pipe of the vortex turbo mixer pump 4 at a rate of 1.0 L / min, and the air was introduced in the form of fine bubbles. The sodium carbonate aqueous solution in the sodium carbonate aqueous solution concentration adjustment tank 1 was gradually concentrated by evaporation of water, and after 9 hours, the weight of the sodium carbonate aqueous solution reached 4,800 g. The sodium carbonate content was 800 g, which was the same as the sodium carbonate aqueous solution initially prepared. Various conditions and results are shown in Tables 1 and 2.

[0048] (Example 2) The same procedure as in Example 1 was repeated, except that the gas added to the intake piping of the vortex turbo mixer pump 9 in the sodium bicarbonate precipitation tank 6 was changed to a mixed gas of carbon dioxide at 0.3 L / min and air at 0.7 L / min, which was then supplied in the form of fine bubbles. The bubble sizes of the carbon dioxide-containing mixed gas were d50 = 75 μm and d90 = 143 μm. The temperature of the aqueous solution during carbon dioxide introduction was 25 to 35°C. 563 minutes after the start of the carbon dioxide-containing bubble supply, the sodium bicarbonate precipitation tank contained a cloudy sodium bicarbonate slurry with a pH of 8.0. The carbon dioxide utilization rate (UR1) was 100%. Although the reaction time was prolonged because the carbon dioxide concentration in the carbon dioxide-containing gas was 30% by volume, the carbon dioxide utilization rate (UR1) was 100%. Various conditions and results are shown in Tables 1 and 2.

[0049] Example 3: The apparatus of the second embodiment shown in FIG. 2 was used. The procedure was the same as in Example 1, except that a YJ nozzle was used instead of a vortex turbo mixer pump as the apparatus for generating carbon dioxide-containing bubbles. The YJ nozzle used was a YJ-6 inline type (product name). First, 800 g of sodium carbonate powder and 4,000 g of ion-exchanged water were charged into an 8-L sodium carbonate aqueous solution concentration adjustment tank 1 and stirred, yielding 4,800 g of a 16.7% sodium carbonate aqueous solution. This aqueous solution was then transferred to an 8-L sodium bicarbonate precipitation tank 6, after which the magnetic pump 26 was started and circulated using the circulation piping 10. The magnetic pump used was a stainless steel motor pump, Model MM-254 (product name), manufactured by Maruhachi Pump Manufacturing Co., Ltd. The circulation flow rate was 20 L / min. Immediately after starting circulation, carbon dioxide gas was supplied to the YJ nozzle 28 at a rate of 1.0 L / min, and the carbon dioxide was introduced as fine bubbles. The sizes of the carbon dioxide bubbles were d50 = 63 μm and d90 = 102 μm. The temperature of the aqueous solution during the introduction of carbon dioxide was 25 to 35°C. 169 minutes after the start of the supply of carbon dioxide-containing bubbles, the sodium bicarbonate precipitation tank had a pH of 8.0 and a cloudy sodium bicarbonate slurry. The carbon dioxide utilization rate (UR1) was 100%.

[0050] This sodium hydrogen carbonate slurry was filtered using a centrifugal dehydrator 13 to obtain 1,117 g of a centrifugal dehydrated cake and 4,015 g of a filtrate. The centrifugal dehydrator used was Model H-110F manufactured by Kokusan Co., Ltd. The centrifugal dehydrated cake was dried at 80°C in a carbon dioxide atmosphere to obtain 893 g of sodium hydrogen carbonate powder.

[0051] Meanwhile, the filtrate, saturated sodium bicarbonate water (concentration 9.3%), was returned to the sodium carbonate aqueous solution concentration adjustment tank 1, and 886 g of 48% sodium hydroxide aqueous solution was added. The magnetic pump 25 was then started, and the solution was circulated using the circulation piping 22. The magnetic pump used was a stainless steel motor pump, Model MM-254 (product name), manufactured by Maruhachi Pump Mfg. Co., Ltd. The circulation flow rate was 20 L / min. Immediately after the start of circulation, carbon dioxide gas was supplied to the YJ nozzle 27 at a rate of 1.0 L / min to introduce finely bubbled carbon dioxide. The carbon dioxide bubble sizes were d50 = 63 μm and d90 = 103 μm. After 69 minutes, the solution in the sodium carbonate aqueous solution concentration adjustment tank 1 had a pH of 12.0, a weight of 5037 g, and a sodium carbonate content of 800 g. The carbon dioxide utilization rate (UR2) was 100%.

[0052] Next, the magnetic pump 25 was started, and while circulating the solution at a flow rate of 20 L / min using the circulation pipe 22, air was supplied to the YJ nozzle 27 at a rate of 1.0 L / min, and the air was introduced in the form of fine bubbles. The aqueous sodium carbonate solution in the concentration adjustment tank 1 for the aqueous sodium carbonate solution was gradually concentrated by evaporation of water, and after 9 hours, the weight of the aqueous sodium carbonate solution reached 4,800 g. The sodium carbonate content was 800 g, which was the same as the content of the initially prepared aqueous sodium carbonate solution. Various conditions and results are shown in Tables 1 and 2.

[0053] (Example 4) The same procedure as in Example 3 was repeated, except that the supply rate of carbon dioxide added to the YJ nozzle 28 in the sodium bicarbonate precipitation tank 6 was changed to 3.0 L / min. The carbon dioxide bubble sizes were d50 = 65 μm and d90 = 108 μm. The temperature of the aqueous solution during carbon dioxide introduction was 25 to 35°C. 56 minutes after the start of the supply of carbon dioxide-containing bubbles, the sodium bicarbonate precipitation tank contained a cloudy sodium bicarbonate slurry with a pH of 8.0. Even when the carbon dioxide supply flow rate was increased, the carbon dioxide utilization rate (UR2) was 100%, and a high-speed reaction was achieved. Various conditions and results are shown in Tables 1 and 2.

[0054] (Example 5) The same procedure as in Example 3 was repeated, except that the supply rate of carbon dioxide added to the YJ nozzle 28 in the sodium bicarbonate precipitation tank 6 was changed to 5.0 L / min. The sizes of the carbon dioxide bubbles were d50 = 72 μm and d90 = 124 μm. The temperature of the aqueous solution during carbon dioxide introduction was 25 to 35°C. 34 minutes after the start of the supply of carbon dioxide-containing bubbles, the sodium bicarbonate precipitation tank contained a cloudy sodium bicarbonate slurry with a pH of 8.0. Even when the carbon dioxide supply flow rate was increased, the carbon dioxide utilization rate (UR1) was 100%, and a high-speed reaction was achieved.

[0055] Example 6: 800 g of sodium carbonate powder and 4,000 g of ion-exchanged water were charged into an 8-L sodium bicarbonate precipitation tank 6 and stirred to obtain 4,800 g of a 16.7% sodium carbonate aqueous solution. Next, instead of using a vortex turbo mixer pump 9 or a YJ nozzle 28 to generate fine bubbles, carbon dioxide was added to the sodium bicarbonate precipitation tank 6 by spraying it at a rate of 1.0 L / min using a cylindrical gas injection tube (product name: Kerami Filter, pore size: 50 μm) manufactured by Koshin Chemical Manufacturing Co., Ltd. The carbon dioxide bubbles were large, with d50 = 168 μm and d90 = 306 μm. The temperature of the aqueous solution during carbon dioxide introduction was 25-35°C. It took a long time, 277 minutes, for the solution in the sodium bicarbonate precipitation tank to become a cloudy sodium bicarbonate slurry with a pH of 8.0, resulting in a carbon dioxide utilization rate (UR1) of 61%. The various conditions and results are shown in Tables 1 and 2.

[0056] Example 7: 800 g of sodium carbonate powder and 4,000 g of ion-exchanged water were charged into an 8-L sodium bicarbonate precipitation tank 6 and stirred to obtain 4,800 g of a 16.7% sodium carbonate aqueous solution. Next, instead of using a vortex turbo mixer pump 9 or a YJ nozzle 28 to generate fine bubbles, carbon dioxide was added to the sodium bicarbonate precipitation tank 6 by blowing it through a 4 mm diameter stainless steel tube installed in the sodium bicarbonate precipitation tank at a rate of 1.0 L / min. The size of the carbon dioxide bubbles in the aqueous sodium carbonate solution was visually observed to be several millimeters to several tens of millimeters. The temperature of the aqueous solution during carbon dioxide introduction was 25-35°C. Carbon dioxide was added for 169 minutes as in Example 1, but the solution in the sodium bicarbonate precipitation tank had a high pH of 10.0, was not cloudy, and sodium bicarbonate did not precipitate. Various conditions and results are shown in Tables 1 and 2.

[0057] (Example 8) The addition of carbon dioxide in Example 7 was continued after 169 minutes. The temperature of the aqueous solution during the introduction of carbon dioxide was 25 to 35°C. It took a very long time, 1,020 minutes, for the solution in the sodium bicarbonate precipitation tank to become a cloudy sodium bicarbonate slurry with a pH of 8.0. The carbon dioxide utilization rate (UR1) was 17%. Various conditions and results are shown in Tables 1 and 2.

[0058]

[0059]

[0060] Example 9: Using the apparatus of the first embodiment shown in Figure 1, potassium salt was used instead of sodium salt. First, 835 g of potassium carbonate and 1,600 g of ion-exchanged water were charged into an 8-L concentration adjustment tank 1 and stirred to obtain 2,435 g of a 34.3% potassium carbonate aqueous solution. This aqueous solution was then transferred to an 8-L precipitation tank 6, after which a vortex turbo mixer pump 9 was started and circulated through a circulation pipe 10. The vortex turbo mixer pump used was a KTM15ND02S model manufactured by Nikuni Co., Ltd. The circulation flow rate was 20 L / min. Immediately after starting circulation, carbon dioxide gas was supplied to the suction pipe of the vortex turbo mixer pump 9 at a rate of 1.0 L / min to introduce finely bubbled carbon dioxide. The carbon dioxide bubble sizes were d50 = 63 μm and d90 = 107 μm. The temperature of the aqueous solution during carbon dioxide introduction was 25-35°C. After 136 minutes, the sodium bicarbonate precipitation tank contained a cloudy potassium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR1) was 100%. This potassium bicarbonate slurry was filtered using a centrifugal dehydrator 13 to obtain 668 g of a centrifugal dehydrated cake and 2033 g of a filtrate. The centrifugal dehydrator used was Model H-110F manufactured by Kokusan Co., Ltd. The centrifugal dehydrated cake was dried at 80°C in a carbon dioxide atmosphere to obtain 605 g of potassium bicarbonate powder.

[0061] Meanwhile, the filtrate, a saturated potassium bicarbonate solution (concentration 29.8%), was returned to concentration adjustment tank 1, and 706 g of a 48% potassium hydroxide solution was added. Then, vortex turbo mixer pump 4 was started, and the solution was circulated at a flow rate of 20 L / min through circulation pipe 22. Air was supplied to the suction pipe of vortex turbo mixer pump 4 at a rate of 1.0 L / min to generate fine bubbles and introduce the air. The potassium carbonate solution in concentration adjustment tank 1 gradually concentrated due to evaporation of water, and after 12 hours, the weight of the potassium carbonate solution reached 2,435 g. The potassium carbonate content was 835 g, which was the same as the content in the initially prepared potassium carbonate solution. Various conditions and results are shown in Tables 3 and 4.

[0062]

[0063]

[0064] (Example 10) General-purpose industrial sodium bicarbonate (product name: KF) manufactured by AGC Inc. had an average particle size d50 of 150 μm. 200 g of this powder was pulverized for 30 minutes using the same pulverizer as in Example 1 at a blade rotation speed of 4,000 rpm, but the average particle size d50 could only be reduced to 33 μm. A second pulverization under the same conditions resulted in a 23 μm average particle size. A third pulverization under the same conditions finally yielded a fine powder with an average particle size d50 of 13 μm. This powder was more difficult to pulverize than the sodium bicarbonate powder of Example 1. The relationship between the pulverization conditions and average particle size for Examples 1 and 10 is shown in Table 5.

[0065]

[0066] REFERENCE SIGNS LIST 1 Sodium carbonate aqueous solution concentration adjustment tank 2, 7 Agitator 3 Sodium carbonate aqueous solution 4, 9 Vortex turbo mixer pump 5 Feed pipe 6 Sodium bicarbonate precipitation tank 8 Liquid in sodium bicarbonate precipitation tank 10, 22 Circulation pipe 11 Carbon dioxide-containing gas supply pipe 12 Withdrawal of sodium bicarbonate slurry 13 Centrifugal dehydrator 14 Sodium bicarbonate cake obtained by centrifugal dehydration 15 Drying equipment 16 Sodium bicarbonate powder 17 Filtrate 18 Filtrate recovery tank 19 Filtrate feed pump 20 Filtrate feed pipe 21 Sodium hydroxide addition pipe 23 Carbon dioxide-containing gas supply pipe 24 Air supply pipe 25, 26 Magnet pump 27, 28 YJ nozzle

Claims

1. A method for producing an alkali metal carbonate or hydrogencarbonate, comprising supplying carbon dioxide-containing bubbles, which are bubbles of a gas containing carbon dioxide, to an aqueous solution (a) of at least one alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal chlorides, provided that when the aqueous solution (a) is an aqueous solution of an alkali metal chloride, the carbon dioxide-containing bubbles are supplied after supplying ammonia to the aqueous solution (a), and the size of the carbon dioxide-containing bubbles is d50 or less of 100 μm and d90 or less of 150 μm.

2. The method for producing an alkali metal carbonate or bicarbonate according to claim 1, wherein the alkali metal carbonate or bicarbonate is lithium carbonate, sodium carbonate, potassium carbonate, lithium bicarbonate, sodium bicarbonate or potassium bicarbonate.

3. The method for producing an alkali metal carbonate or hydrogencarbonate according to claim 1 or 2, wherein the concentration of carbon dioxide in the carbon dioxide-containing gas is 10% by volume or more.

4. A method for producing an alkali metal carbonate or hydrogencarbonate according to claim 1 or 2, wherein the size of the bubbles containing carbon dioxide is d50 to 90 μm and d90 to 100 to 150 μm.

5. A method for producing an alkali metal bicarbonate, comprising: filtering a slurry in which an alkali metal bicarbonate has precipitated, obtained by the method for producing an alkali metal carbonate or bicarbonate according to claim 1 or 2; adding a first aqueous solution (a) of at least one alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal chlorides to the obtained filtrate to obtain a second aqueous solution (a); supplying carbon dioxide-containing bubbles to the second aqueous solution (a) to obtain a third aqueous solution (a) of an alkali metal carbonate or bicarbonate; concentrating the obtained third aqueous solution (a) by removing water to obtain a fourth aqueous solution (a); and supplying carbon dioxide-containing bubbles to the obtained fourth aqueous solution (a) to precipitate the alkali metal bicarbonate.

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