A method for producing alkali metal bicarbonates from exhaust gas produced by the neutralization reaction of an acidic aqueous solution with calcium carbonate.

Abstract

The present invention provides a method for producing high-purity alkali metal bicarbonates using a CO2-containing gas produced by the neutralization reaction of an acidic aqueous solution containing HF and / or HCl with calcium carbonate. [Solution] A method for producing an alkali metal bicarbonate, comprising: subjecting a first aqueous solution containing at least one acidic component selected from the group consisting of HF and HCl to calcium carbonate in a neutralization reaction to obtain a CO2-containing gas containing CO2 produced by the neutralization reaction; and performing a contact treatment in which the obtained CO2-containing gas is brought into contact with a second aqueous solution containing at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal carbonates to obtain an alkali metal bicarbonate.

Description

Technical Field

[0001] The present invention relates to a method for producing an alkali metal bicarbonate from a gas containing CO2 generated by a neutralization reaction between an acidic aqueous solution containing HF or HCl and calcium carbonate.

Background Art

[0002] Combustion exhaust gas generated in thermal power generation facilities, waste combustion treatment facilities, biomass power generation facilities, etc. contains a large amount of carbon dioxide. Since carbon dioxide is a greenhouse gas, methods for recovering it have been studied.

[0003] Patent Document 1 discloses an exhaust gas treatment facility that is a facility for treating exhaust gas generated by combustion, and includes an acidic gas removal device that removes acidic gas components contained in the exhaust gas by dry treatment, a temperature reduction device, and a device for separating and recovering carbon dioxide.

[0004] Patent Document 2 discloses a method for producing sodium bicarbonate using carbon dioxide derived from the combustion exhaust gas of a boiler diluted with an inert gas.

[0005] Patent Document 3 discloses a method for producing sodium bicarbonate from a product containing carbon dioxide generated by the treatment of a carbonaceous raw material.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] As described above, while conventional technologies have demonstrated the ability to recover carbon dioxide from combustion exhaust gases and produce sodium bicarbonate from carbon dioxide, there was still room for further consideration regarding the source of carbon dioxide. Therefore, the present inventors considered using a gas containing CO2 produced by the neutralization reaction between an acidic aqueous solution containing HF or HCl and calcium carbonate, in order to increase the purity of the resulting sodium bicarbonate.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a method for producing high-purity alkali metal bicarbonates using a gas containing CO2 produced by the neutralization reaction of an acidic aqueous solution containing HF and / or HCl with calcium carbonate. [Means for solving the problem]

[0009] As a result of diligent research, the inventors discovered that high-purity alkali metal bicarbonates can be produced by contacting a gas containing CO2, generated by the neutralization reaction of an acidic aqueous solution containing HF and / or HCl with calcium carbonate, with an aqueous solution of an alkali metal hydroxide or carbonate, thereby completing the present invention. The present invention encompasses the following embodiments. [1] A first aqueous solution containing at least one acidic component selected from the group consisting of HF and HCl is subjected to a neutralization reaction with calcium carbonate to obtain a CO2-containing gas containing CO2 produced by the neutralization reaction. A method for producing an alkali metal bicarbonate, comprising bringing the obtained CO2-containing gas into contact with a second aqueous solution containing at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal carbonates, thereby obtaining an alkali metal bicarbonate. [2] The method for producing alkali metal bicarbonate according to [1], wherein the first aqueous solution is HF-containing industrial wastewater discharged from a fluorine-containing compound manufacturing plant or a semiconductor manufacturing plant. [3] The method for producing an alkali metal bicarbonate according to [1], wherein the first aqueous solution is an aqueous solution containing HCl and is an aqueous solution for producing CaCl2. [4] A method for producing an alkali metal bicarbonate according to [1] or [2], wherein a preliminary treatment is performed to remove at least one acidic component selected from the group consisting of HF and HCl from the CO2-containing gas, and then the contact treatment is performed. [5] The method for producing alkali metal bicarbonate according to [4], wherein in the CO2-containing gas after the pretreatment, the molar ratio of HF to CO2 (HF / CO2) is 0.00023 or less, and the molar ratio of HCl to CO2 (HCl / CO2) is 0.00406 or less. [6] The method for producing an alkali metal bicarbonate according to [4] or [5], wherein the slurry containing the alkali metal bicarbonate obtained by the contact treatment has a fluorine concentration of 6.4 ppm or less and a chlorine concentration of 212 ppm or less, based on the mass of the slurry. [7] A method for producing an alkali metal bicarbonate according to any one of [4] to [6], wherein the alkali metal bicarbonate obtained by the contact treatment has a fluorine concentration of 6.0 ppm or less and a chlorine concentration of 200 ppm or less. [8] A method for producing an alkali metal bicarbonate according to any one of [4] to [7], wherein the preliminary treatment is performed by a wet method using a third aqueous solution containing at least one alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal bicarbonates, or by a dry method using powder of alkali metal bicarbonate. [9] A method for producing an alkali metal bicarbonate according to any one of [4] to [8], wherein the preliminary treatment is performed using the alkali metal bicarbonate obtained by the contact treatment.

[10] A method for producing an alkali metal bicarbonate according to any one of [1] to [9], wherein the contact treatment is carried out by supplying fine bubbles of the CO2-containing gas to the second aqueous solution. [Effects of the Invention]

[0010] According to the present invention, a method for producing a high-purity alkali metal hydrogen carbonate using a gas containing CO2 generated by a neutralization reaction between an acidic aqueous solution containing HF and / or HCl and calcium carbonate can be provided.

Brief Description of the Drawings

[0011] [Figure 1] In the present invention, it is a flowchart showing an example of a process for removing acidic components from a gas containing CO2 generated by a neutralization reaction between an acidic aqueous solution containing HF and / or HCl and calcium carbonate using a wet scrubber. [Figure 2] In the present invention, it is a flowchart showing an example of a process for removing acidic components from a gas containing CO2 generated by a neutralization reaction between an acidic aqueous solution containing HF and / or HCl and calcium carbonate by a dry method. [Figure 3] In the present invention, it is a flowchart showing an example of a process for producing an alkali metal hydrogen carbonate from a gas containing CO2 generated by a neutralization reaction between an acidic aqueous solution containing HF and / or HCl and calcium carbonate. [Figure 4] It is a schematic diagram showing an example of drying equipment used when drying a cake of an alkali metal hydrogen carbonate.

Embodiments for Carrying Out the Invention

[0012] The meanings of the terms in this specification are as follows. A numerical range represented by “~” means a numerical range having the numerical values before and after ~ as the lower limit value and the upper limit value. “d10”, “d50”, and “d90” respectively refer to the 10% diameter, 50% diameter (median diameter), and 90% diameter in the cumulative distribution curve of the volume of bubbles with respect to the size of the bubbles.

[0013] Hereinafter, the present invention will be described, but the present invention is not limited by the examples in the following description.

[0014] In the method of the present invention, a first aqueous solution containing at least one acidic component selected from the group consisting of HF (hydrogen fluoride) and HCl (hydrogen chloride) (hereinafter sometimes referred to as "acidic aqueous solution") is subjected to a neutralization reaction with calcium carbonate to obtain a CO##2## -containing gas containing CO##2## (carbon dioxide) generated by the neutralization reaction, and the obtained CO##2## -containing gas is brought into contact with a second aqueous solution containing at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal carbonates to produce an alkali metal hydrogen carbonate by performing a contacting treatment.

[0015] 《Adjustment of CO##2## -containing gas》 In the method of the present invention, first, a first aqueous solution (acidic aqueous solution) containing at least one acidic component selected from the group consisting of HF and HCl is subjected to a neutralization reaction with calcium carbonate to obtain a CO##2## -containing gas containing CO##2## generated by the neutralization reaction. The pH of the first aqueous solution is usually 3.0 or less, and the "neutralization reaction" means adding calcium carbonate to the first aqueous solution to make the pH of the first aqueous solution be 3.5 to 7.0. The CO##2## concentration in the CO##2## -containing gas is about 20 to 60% by volume. The concentration of the acidic component contained in this gas varies depending on the type of production plant and the like described later, but is approximately HF concentration = 0.1 to 1% by volume, HCl concentration = 1 to 5% by volume.

[0016] [[ID=→14]]<First aqueous solution> The first aqueous solution is an acid aqueous solution containing at least one acidic component selected from the group consisting of HF and HCl. Examples of the first aqueous solution include acidic industrial wastewater containing HF and / or HCl discharged from a production plant of a fluorine-containing compound, a semiconductor production plant, etc., and an aqueous HCl solution for producing CaCl##2##. Using such acidic industrial wastewater, etc. is not only advantageous in terms of environment and cost, but also has the advantage that the CO##2## concentration can be set relatively freely compared with the case of using combustion exhaust gas. The concentration of the acidic component in the first aqueous solution varies depending on the type of manufacturing plant, but is approximately HF concentration = 0.01-5% and HCl concentration = 0.1-35%. Furthermore, the first aqueous solution may contain other components besides the acidic component, as long as they do not interfere with the neutralization reaction. Examples of these other components include sulfuric acid and phosphoric acid. The concentration of these other components in the first aqueous solution is preferably 0.001-1%, and more preferably 0.005-0.5%. The acidic industrial wastewater typically contains hydrofluorosilicic acid as another component at a concentration of approximately 0.1-5%, and the HCl aqueous solution typically contains silica as another component at a concentration of approximately 0.01-1%. The method of the present invention may also include a step of recovering acidic industrial wastewater containing HF and / or HCl, discharged from a fluorine-containing compound manufacturing plant or a semiconductor manufacturing plant, as the first aqueous solution, prior to the step of obtaining the CO2-containing gas. Furthermore, the method of the present invention may include a step of producing CaCl2 using an aqueous HCl solution and a step of recovering a portion of the aqueous HCl solution as the first aqueous solution, prior to the step of obtaining a CO2-containing gas.

[0017] <Preliminary treatment> In the present invention, it is preferable to perform a preliminary treatment to remove at least one acidic component selected from the group consisting of HF and HCl from the CO2-containing gas before performing the contact treatment. In such a preliminary treatment, it is preferable to remove acidic components from the CO2-containing gas to such an extent that the gas composition after the preliminary treatment has an HF / CO2 molar ratio of 0.00023 or less and an HCl / CO2 molar ratio of 0.00406 or less, in order to obtain high-purity alkali metal bicarbonates. Using a gas from which acidic components have been removed within this range, the acidic component content in alkali metal bicarbonates can be reduced to a fluorine (F) concentration of 6.0 ppm or less and a chlorine (Cl) concentration of 200 ppm or less.

[0018] A preferred range for removing acidic components from the CO2-containing gas by pretreatment is a gas composition after pretreatment where the HF / CO2 molar ratio is 0.00011 or less and the HCl / CO2 molar ratio is 0.00205 or less. By using a gas from which acidic components have been removed within this range, the acidic component content in the produced alkali metal bicarbonate can be reduced to an F concentration of 3.0 ppm or less and a Cl concentration of 100 ppm or less.

[0019] A more preferable range for removing acidic components from the CO2-containing gas by pretreatment is a gas composition after removal of acidic components where the HF / CO2 molar ratio is 0.00003 or less and the HCl / CO2 molar ratio is 0.00084 or less. By using a gas from which acidic components have been removed within this range, the acidic component content in the produced alkali metal bicarbonate can be reduced to an F concentration of 1.0 ppm or less and a Cl concentration of 40 ppm or less.

[0020] In the present invention, the method for removing acidic components from the CO2-containing gas is not particularly limited and includes a wet method using an aqueous solution (third aqueous solution) of at least one alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal bicarbonates, or a dry method using slaked lime or alkali metal bicarbonate powder. Examples of alkali metals in the alkali metal compounds and alkali metal bicarbonates include lithium, sodium, and potassium. The concentration of the alkali metal compound in the third aqueous solution is not particularly limited as long as a predetermined amount of the acidic component is removed as described above, but it is typically in the range of 1 to 10% by mass.

[0021] Examples of wet methods include blowing the CO2-containing gas into the third aqueous solution, or supplying the CO2-containing gas while circulating the third aqueous solution within a tower using a scrubber as shown in Figure 1. In Figure 1, the scrubber 1 consists of a tower section 2 and a circulating liquid storage tank 3. The inside of the tower section 2 is filled with packing material 4 such as pole rings. The circulating liquid storage tank 3 contains circulating liquid 5, which is the third aqueous solution. In particular, the filtrate 29 in the apparatus for producing alkali metal bicarbonate shown in Figure 3, which will be described later, is a saturated aqueous solution of alkali metal bicarbonate, so using this is preferable from the viewpoint of resource recycling. By starting the circulating liquid pump 6, the circulating liquid is sent to a spray nozzle 7 installed in the upper part of the tower and sprayed into the tower. Meanwhile, the CO2-containing gas is introduced below the packing material 4 in the tower via the gas introduction pipe 8. The introduced gas comes into contact with the circulating liquid 5 on the surface of the packing material 4, removing the acidic components, and is discharged from the top of the tower via the gas outlet pipe 9.

[0022] In the dry method, as shown in Figure 2, a neutralizing agent powder 11, such as slaked lime or alkali metal bicarbonate, is added to the introduction pipe 10 of the CO2-containing gas. This neutralizing agent powder 11 reacts with the acidic components in the CO2-containing gas and is captured and removed by a dust collector 12, so that the gas from which the acidic components have been removed is discharged through the outlet pipe 13.

[0023] Regardless of whether the preliminary treatment method for removing acidic components from the CO2-containing gas is a wet or dry method, it is preferable from the standpoint of resource recycling if it uses alkali metal bicarbonates obtained by the contact treatment described later.

[0024] Contact Processing A method for obtaining alkali metal bicarbonate from the CO2-containing gas is to contact the CO2-containing gas with a second aqueous solution containing at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal carbonates, thereby precipitating alkali metal bicarbonate, filtering the slurry, and then drying it.

[0025] <Second aqueous solution> The second aqueous solution is an aqueous solution containing at least one alkali metal compound selected from the group consisting of an alkali metal hydroxide and an alkali metal carbonate. Examples of the alkali metal in the alkali metal compound include lithium, sodium, and potassium. When these alkali metals are used, hydrogen carbonate salts such as lithium hydrogen carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate can be obtained as the target product of the method of the present embodiment.

[0026] The upper limit of the concentration of the alkali metal compound in the second aqueous solution is the saturation concentration of the alkali metal compound. The concentration of the alkali metal compound in the second aqueous solution is preferably 3% or more, more preferably 5% or more. Regarding the lower limit of the concentration of the alkali metal compound in the second aqueous solution, when the alkali metal compound reacts with CO2 to form an alkali metal hydrogen carbonate, it is preferably a concentration exceeding the solubility of the alkali metal hydrogen carbonate at 0°C. In particular, when the alkali metal compound in the second aqueous solution is sodium carbonate, the concentration is preferably 6 to 25%, more preferably 10 to 20%. When it is above the above lower limit, when reacting with carbon dioxide to form sodium hydrogen carbonate, the amount is likely to exceed the solubility of sodium hydrogen carbonate, and sodium hydrogen carbonate is likely to precipitate. Also, when it is below the above upper limit, the amount of sodium hydrogen carbonate in the slurry containing the produced sodium hydrogen carbonate is appropriate, the viscosity of the slurry does not become too high, and it is easy to handle. The solid content concentration of the slurry is preferably 3 to 25%, more preferably 8 to 20%.

[0027] <Method for contacting a CO2-containing gas with a second aqueous solution of an alkali metal compound> The method for contacting the CO2-containing gas with the second aqueous solution is not particularly limited, and one method is to blow the CO2-containing gas into the second aqueous solution through a nozzle, but a method of supplying fine bubbles of CO2-containing gas is preferred. This is because the production of alkali metal bicarbonates is carried out by dissolving CO2 in the second aqueous solution, and by miniaturizing the CO2 and increasing the dissolution rate, the utilization rate of CO2 can be increased, and the production rate of carbonates and bicarbonates can be increased. The higher the utilization rate of CO2, the less exhaust gas containing CO2 can be used, so the amount of impurities mixed into the obtained alkali metal bicarbonate can be reduced, and a high-purity alkali metal bicarbonate can be obtained. The preferred range for the utilization rate of CO2 is 90% or more, more preferably 95% or more, and it is possible to achieve up to 100%.

[0028] When alkali metal bicarbonates are produced using a method of supplying fine bubbles of the CO2-containing gas to the second aqueous solution, the entire amount of acidic components contained in the CO2-containing gas is contained in the slurry containing the alkali metal bicarbonates. Therefore, the content of components derived from the acidic components relative to the mass of the slurry containing the alkali metal bicarbonates can be defined according to the degree of removal of the acidic components. In the gas composition after removing the acidic components from the CO2-containing gas, if the HF / CO2 molar ratio is 0.00023 or less and the HCl / CO2 molar ratio is 0.00406 or less, the content of components derived from the acidic components relative to the mass of the total slurry is F = 6.4 ppm or less and Cl = 212 ppm or less.

[0029] When the gas composition obtained by removing the acidic component from the CO2-containing gas is within the preferred range described above, with an HF / CO2 molar ratio of 0.00011 or less and an HCl / CO2 molar ratio of 0.00205 or less, the content of components derived from the acidic component relative to the mass of the total slurry is F = 3.1 ppm or less and Cl = 107 ppm or less.

[0030] When the gas composition obtained by removing the acidic component from the CO2-containing gas is within the more preferable range described above, where the HF / CO2 molar ratio is 0.00003 or less and the HCl / CO2 molar ratio is 0.00084 or less, the content of components derived from the acidic component relative to the mass of the total slurry is F = 0.8 ppm or less and Cl = 44 ppm or less.

[0031] The following describes a case in which the contact treatment is performed by supplying fine bubbles of the CO2-containing gas to the second aqueous solution. In this specification, "fine bubbles" refers to a general term encompassing microbubbles with a diameter of approximately 1 to 150 μm and nanobubbles with a diameter of less than 1 μm. When a large number of microbubbles are generated in water, it appears as turbidity. On the other hand, because nanobubbles are extremely small, the water remains clear. In this embodiment, it is preferable that the size (bubble diameter) of the fine bubbles in the pre-treated CO2-containing exhaust gas is such that d50 is 100 μm or less and d90 is 150 μm or less. By using fine bubbles with such a bubble diameter, the utilization rate of CO2 can be sufficiently increased. Furthermore, from the viewpoint of ensuring the effects of the present invention are more reliable, 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 this invention, so-called nanobubbles with a diameter of 1 μm or less are not required. The minimum value of the fine bubble diameter is not particularly limited, but from the viewpoint of ease of fine bubble preparation, it is preferable that it is greater than 1 μm or 10 μm or more. According to the method of this invention, the utilization rate of carbon dioxide can be sufficiently increased even without the presence of fine bubbles with a diameter of 1 μm or less.

[0032] The size (bubble diameter) of fine bubbles in CO2-containing gas can be measured, for example, using a particle size analyzer (product name: Particle Track G400) manufactured by Mettler Toledo, Inc., which employs FBRM (Focused Beam Reflectance Measurement).

[0033] The devices used to create such fine bubbles are not particularly limited, but include the following: (Example 1) A device that supplies gas to the suction side of a pressure pump and converts the inhaled gas into fine bubbles using mixing blades that rotate at high speed inside the pressure pump. An example is the "Vortex Turbo Mixer Pump" (product name) manufactured by Nikuni Co., Ltd. (Example 2) A device that creates a low-pressure region in a liquid flow by using the Venturi effect (narrowing the flow path of a pressurized liquid to increase the flow velocity and create a low-pressure region), and then supplies gas to that region to create fine bubbles. Examples include the "YJ Nozzle" (product name) manufactured by Envirovision Co., Ltd. and the "Aqua Transfer Nozzle" (product name) manufactured by Waternavi Co., Ltd. (Example 3) A device that creates a negative pressure zone in the center by ejecting water radially from a high-speed rotating disc, and then draws in gas to create fine bubbles. An example is "Spinor" (product name) manufactured by Waternavi Co., Ltd.

[0034] When the alkali metal compound is an alkali metal hydroxide, the temperature of the second aqueous solution when supplying the CO2-containing gas is not particularly limited, but is preferably 0°C to 80°C. The lower the temperature, the greater the solubility of CO2 in the second aqueous solution of the alkali metal hydroxide, but a temperature of 0°C or higher is preferable because there is no risk of freezing. On the other hand, the higher the temperature, the less the solubility of CO2 in the second aqueous solution of the alkali metal hydroxide, and a temperature of 80°C or lower is preferable because the rate of alkali metal carbonate formation is faster. The temperature of the second aqueous solution is more preferably 20 to 60°C, and even more preferably 30 to 50°C.

[0035] When the alkali metal compound is an alkali metal carbonate, the temperature of the second aqueous solution when supplying the CO2-containing gas is not particularly limited, but is preferably 0°C to 80°C. The lower the temperature, the greater the solubility of CO2 in the second aqueous solution of the alkali metal carbonate, but temperatures above 0°C are preferable because there is no risk of freezing. On the other hand, the higher the temperature, the less the solubility of CO2 in the second aqueous solution of the alkali metal carbonate, so temperatures below 80°C are preferable because the rate of alkali metal carbonate formation does not slow down. Also, the higher the temperature, the greater the solubility of the alkali metal bicarbonate formed, but temperatures below 80°C are preferable because the amount of alkali metal bicarbonate precipitated is greater. The temperature of the second aqueous solution is more preferably 20 to 70°C, and even more preferably 25 to 50°C. Regarding the time for supplying CO2-containing gas to the second aqueous solution, there are no particular restrictions as long as the desired reaction can proceed sufficiently, but it is generally 0.2 to 16 hours, and preferably 0.5 to 8 hours.

[0036] Next, with reference to Figure 3, an example of an apparatus for producing alkali metal bicarbonate from the CO2-containing gas will be described. The crystallization tank 20 contains liquid 22. Liquid 22 in the crystallization tank is an aqueous solution of alkali metal hydroxide or carbonate (the second aqueous solution). This liquid is sent to the YJ nozzle 24 using a circulation pump 23 and circulated through the circulation pipe 25. Meanwhile, CO2-containing gas is sent to the YJ nozzle 24 through the CO2-containing gas supply pipe 26 to create fine bubbles. As the CO2-containing gas is supplied, the aqueous solution of alkali metal hydroxide or carbonate in the crystallization tank is bicarbonated, and alkali metal bicarbonate precipitates. Once the alkali metal bicarbonate has precipitated, the supply of CO2-containing gas can be stopped.

[0037] Next, the liquid 22 in the crystallization tank, in which the alkali metal bicarbonate has precipitated, is sent through the supply pipe 27 to the filter 28 for filtration. The dewatered cake of alkali metal bicarbonate, separated from the filtrate 29 by the filter, is sent through the supply pipe 30 to the drying equipment 31, where it is dried to obtain alkali metal bicarbonate powder 32.

[0038] To obtain high-purity bicarbonates with a low content of components derived from acidic components in CO2-containing gas, it is advantageous to increase the solid content concentration in the dehydrated cake of alkali metal bicarbonates during this filtration process. This is because these impurity components tend to exist at a higher concentration in the mother liquor than in the solid alkali metal bicarbonates in the precipitated liquid. The dehydrated cake of alkali metal bicarbonates consists of solid alkali metal bicarbonates and a mother liquor, and impurities contained in the mother liquor in the dehydrated cake are carried over directly into the alkali metal bicarbonate powder after drying in the subsequent step. The solid content concentration in the dehydrated alkali metal bicarbonate cake is preferably 40% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. Methods of filtration to obtain such a dehydrated cake with a high solid content include, in addition to vacuum filtration, pressure filtration, methods using a centrifugal dehydrator, and methods using a filter press.

[0039] A common method for drying alkali metal bicarbonate cakes obtained by centrifugal dehydration is heating them to over 80°C in an atmosphere containing CO2 gas. Alkali metal bicarbonates undergo decomposition into alkali metal carbonates when exposed to high temperatures above 80°C in air for extended periods, as shown in equation (1). Therefore, drying in an atmosphere containing CO2 gas is necessary. However, this method has the problem of requiring equipment to recover the CO2 gas discharged from the drying facility. 2MHCО3→ M2CО3+ CО2+ H2О...Formula (1) (In the formula, M represents an alkali metal.)

[0040] Separately, drying can be done in air without using CO2 gas if the drying time is short. Examples of such equipment include airflow dryers and fluidized bed dryers. Examples of airflow dryers include the Flash Jet Dryer manufactured by Seishin Corporation and the Jet Turbo Dryer manufactured by Hiraiwa Iron Works Co., Ltd. Examples of fluidized bed dryers include the Slit Flow manufactured by Okawara Manufacturing Co., Ltd., the Fluidized Bed Dryer manufactured by Kurimoto Iron Works Co., Ltd., and the Tornesh Dryer manufactured by Nara Machine Works Co., Ltd.

[0041] Figure 4 shows the equipment for drying alkali metal bicarbonate cake using a flash jet dryer manufactured by Seishin Corporation. Hot air 41 is introduced into the flash jet dryer 40. When alkali metal bicarbonate cake 42 is supplied quantitatively to it, it is instantly dried and becomes an airflow containing alkali metal bicarbonate powder, which is introduced into the cyclone 43 and collected as powder in a recovery container 45 installed at its bottom. [Examples]

[0042] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0043] (Carbon dioxide utilization rate) The carbon dioxide utilization rate (UR) (%) during alkali metal bicarbonate precipitation was defined as the ratio (B) of the calculated amount of carbon dioxide gas required to convert all the carbonates in the alkali metal carbonate aqueous solution into bicarbonates to the actual amount of carbon dioxide gas supplied for alkali metal bicarbonate precipitation (A). That is, the carbon dioxide utilization rate (UR) can be calculated using the following formula (2). Carbon dioxide utilization rate (UR) (%) during alkali metal bicarbonate precipitation = Calculated amount of carbon dioxide gas required to convert all alkali metal carbonates into bicarbonates (B, unit: L) / Actual amount of carbon dioxide gas supplied (A, unit: L) × 100 Equation (2)

[0044] (Analysis method for determining the content of acidic components in CO2-containing gas in alkali metal bicarbonate powder) [Method for analyzing fluoride content] Measurement using a fluoride ion-selective electrode 5.0 g of alkali metal bicarbonate powder was dissolved in phenolphthalein solution, neutralized with (1:1) nitric acid, and the powder was dissolved. After confirming that the powder was dissolved, pure water was added to make a total volume of 50 ml, which was the sample solution. 20 ml of this sample solution was taken and placed in a beaker. 20 ml of TISAB buffer solution for measuring fluoride ion concentration was also collected and placed in a beaker. A fluoride ion-selective electrode was immersed in the sample solution, and the value was read once the potential stabilized. The potential was measured using four standard solutions with predetermined fluoride ion concentrations to create a calibration curve. The fluoride ion concentration in the sample solution was then determined from this calibration curve, and the concentration of alkali metal bicarbonate powder was calculated.

[0045] [Analysis method for Cl content] Analysis by turbidimetric method The analysis was performed according to JIS K 8001 5.7 [Chloride (Cl)] (1) (turbidimetric method). 5.0 g of alkali metal bicarbonate powder was added to approximately 10 ml of pure water, and (1:1) nitric acid was added to dissolve the powder. Then, distilled water was added again to make a total volume of 50 ml. Approximately 10 g of this solution was weighed out, and 1 ml of (1+2) nitric acid and 1 ml of 20 g / l silver nitrate aqueous solution were added, and the mixture was shaken. As a calibration curve, 0, 0.2, 0.4, 0.6, 0.8, and 1.0 ml of chloride standard solution with a concentration of 0.01 mg-Cl / ml were measured out, and the total volume was diluted to 10 ml with pure water. Then, 1 ml of (1+2) nitric acid and 1 ml of 20 g / l silver nitrate aqueous solution were added and shaken. After being left in the dark, the turbidity of the sample solution was compared with a chloride standard. From this turbidity, the chloride ion concentration in the sample solution was determined, and the concentration of alkali metal bicarbonate powder was calculated.

[0046] Tables 1 and 2 show the production conditions for alkali metal bicarbonates and the content of components derived from acidic components in the obtained alkali metal bicarbonate powder. Examples 1-5 and 8 are examples of producing alkali metal bicarbonate powder from CO2-containing gas produced by the neutralization reaction of HF-containing industrial wastewater discharged from a fluorine-containing compound manufacturing plant with calcium carbonate, while Examples 6 and 7 are examples of producing alkali metal bicarbonate powder from CO2-containing gas produced by the neutralization reaction of an aqueous HCl solution with calcium carbonate for the production of CaCl2.

[0047] (Example 1) Production of sodium bicarbonate from CO2 generated by the neutralization reaction of HF-containing industrial wastewater discharged from a fluorine-containing compound manufacturing plant with calcium carbonate (without removal of acidic components) Sodium bicarbonate powder was produced using the apparatus shown in Figure 3 from a CO2-containing gas generated by the neutralization reaction of HF-containing industrial wastewater discharged from a fluorine-containing compound manufacturing plant with calcium carbonate. The concentrations of each component in this CO2-containing gas were CO2 = 47 vol%, HF = 2250 vol ppm, and HCl = 650 vol ppm. Expressed as molar ratios to CO2, the HF / CO2 molar ratio was 0.00479 and the HCl / CO2 molar ratio was 0.00138. 400g of sodium carbonate powder and 2000g of deionized water were placed in a crystallization tank 20 with an internal volume of 5L, and stirred with a stirring device 21 to obtain 2400g of a 16.7% sodium carbonate aqueous solution. This aqueous solution was circulated at a flow rate of 20L / min through a circulation pipe 25 using a circulation pump 23. A YJ nozzle 24 was installed in the circulation pipe. The YJ nozzle used was a YJ-6 inline type (product name). Immediately after starting the circulation, a CO2-containing gas of the above composition was supplied to the YJ nozzle 24 at a rate of 4L / min in the form of fine bubbles. Here, the d50 of the fine bubbles was 70μm and the d90 was 135μm. The temperature of the aqueous solution when the CO2-containing gas was introduced was 25~35℃. Forty-five minutes after the start of supplying CO2-containing gas, and after supplying 180 L, the crystallization tank contained a turbid sodium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR) was 100%. At this time, the content of components derived from the acidic components in the CO2-containing gas added to the sodium bicarbonate slurry was F = 134 ppm and Cl = 72 ppm. The sodium bicarbonate slurry was filtered using a centrifugal dehydrator 28 to obtain 880 g of centrifugal dehydrated cake and 1686 g of filtrate 29. The centrifugal dehydrator 28 used was a H-110F model manufactured by Kokusan Co., Ltd. The centrifugal dehydrated cake was dried in a drying facility 31 under a carbon dioxide atmosphere at 80°C to obtain 440 g of sodium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 50%. The content of components derived from acidic components in the CO2-containing gas in the obtained sodium bicarbonate powder was high, at F=120 ppm and Cl=67 ppm.

[0048] (Example 2) Production of sodium bicarbonate after removing acidic components from the CO2-containing gas of Example 1. Acidic components were removed from the CO2-containing gas of Example 1 using the wet scrubber shown in Figure 1. The CO2-containing gas of Example 1 was supplied through the gas introduction pipe 8. A sodium bicarbonate aqueous solution was used as the circulating fluid. After the removal of the acidic components, the concentrations of each component were CO2 = 47 vol%, HF = 4.5 vol ppm, and HCl = 1.3 vol ppm. Expressed as molar ratios to CO2, the HF / CO2 molar ratio was 0.00001 and the HCl / CO2 molar ratio was 0.000003. Sodium bicarbonate powder was produced in the same manner as in Example 1, except that a CO2-containing gas from which the acidic components had been removed was used. Forty-five minutes after the start of supplying the CO2-containing gas from which the acidic components had been removed, after supplying 180 L, the crystallization tank contained a turbid sodium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR) was 100%. At this time, the content of components derived from the acidic components in the CO2-containing gas added to the sodium bicarbonate slurry was F = 0.3 ppm and Cl = 0.1 ppm. In the same manner as in Example 1, this sodium bicarbonate slurry was filtered using a centrifugal dehydrator 28 to obtain 880 g of centrifugal dehydrated cake and 1686 g of filtrate 29. The centrifugal dehydrated cake was dried in a carbon dioxide atmosphere at 80°C using a drying equipment 31 to obtain 440 g of sodium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 50%. The content of components derived from the acidic components in the CO2-containing gas in the obtained sodium bicarbonate powder was very low, at F=0.5 ppm and Cl=0.0 ppm, resulting in a high-purity sodium bicarbonate powder.

[0049] (Example 3) Production of sodium bicarbonate after removing acidic components from the CO2-containing gas of Example 1. A CO2-containing gas was prepared by mixing the CO2-containing gas used in Example 1 before the removal of acidic components with the CO2-containing gas used in Example 2 after the removal of acidic components using a wet scrubber, in a volume ratio of 2:98. The concentrations of each component in this mixed gas were CO2 = 47 vol%, HF = 45 vol ppm, and HCl = 13 vol ppm. Expressed as molar ratios to CO2, the HF / CO2 molar ratio was 0.00010 and the HCl / CO2 molar ratio was 0.00003. Sodium bicarbonate powder was produced in the same manner as in Example 1, except that a CO2-containing gas from which the acidic components had been removed was used. Forty-five minutes after the start of supplying the CO2-containing gas, after supplying 180 L, the crystallization tank contained a turbid sodium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR) was 100%. At this time, the content of components derived from the acidic components in the CO2-containing gas added to the sodium bicarbonate slurry was F = 2.7 ppm and Cl = 1.4 ppm. In the same manner as in Example 1, this sodium bicarbonate slurry was filtered using a centrifugal dehydrator 28 to obtain 880 g of centrifugal dehydrated cake and 1686 g of filtrate 29. The centrifugal dehydrated cake was dried in a carbon dioxide atmosphere at 80°C using a drying equipment 31 to obtain 440 g of sodium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 50%. The resulting sodium bicarbonate powder contained low levels of acidic components derived from the CO2-containing gas, with F=2.6 ppm and Cl=0.0 ppm, indicating that high-purity sodium bicarbonate powder was obtained.

[0050] (Example 4) Production of sodium bicarbonate after removing acidic components from the CO2-containing gas of Example 1. A CO2-containing gas was prepared by mixing the CO2-containing gas used in Example 1 before the removal of acidic components with the CO2-containing gas used in Example 2 after the removal of acidic components using a wet scrubber, in a volume ratio of 4:96. The concentrations of each component in this mixed gas were CO2 = 47 vol%, HF = 90 vol ppm, and HCl = 26 vol ppm. Expressed as molar ratios to CO2, the HF / CO2 molar ratio was 0.00019 and the HCl / CO2 molar ratio was 0.00006. Sodium bicarbonate powder was produced in the same manner as in Example 1, except that a CO2-containing gas from which the acidic components had been removed was used. Forty-five minutes after the start of supplying the CO2-containing gas from which the acidic components had been removed, after supplying 180 L, the crystallization tank contained a turbid sodium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR) was 100%. At this time, the content of components derived from the acidic components in the CO2-containing gas added to the sodium bicarbonate slurry was F = 5.4 ppm and Cl = 2.9 ppm. In the same manner as in Example 1, this sodium bicarbonate slurry was filtered using a centrifugal dehydrator 28 to obtain 880 g of centrifugal dehydrated cake and 1686 g of filtrate 29. The centrifugal dehydrated cake was dried in a carbon dioxide atmosphere at 80°C using a drying equipment 31 to obtain 440 g of sodium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 50%. The resulting sodium bicarbonate powder contained low levels of acidic components derived from the CO2-containing gas, with F=5.0 ppm and Cl=1.3 ppm, indicating that high-purity sodium bicarbonate powder was obtained.

[0051] (Example 5) Production of sodium bicarbonate after removing acidic components from the CO2-containing gas of Example 4 (increase in the solid content concentration of the dehydrated cake) In Example 4, the sodium bicarbonate slurry was filtered using a centrifugal dehydrator, but instead, it was filtered using a filter press, resulting in 550 g of centrifugal dehydrated cake and 2016 g of filtrate 29. The centrifugal dehydrated cake was dried in a carbon dioxide atmosphere at 80°C using a drying apparatus 31, yielding 440 g of sodium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 80%. The content of components derived from the acidic components in the CO2-containing gas in the obtained sodium bicarbonate powder was F=3.2 ppm and Cl=0.0 ppm, resulting in a sodium bicarbonate powder of higher purity than that obtained in Example 4.

[0052] (Example 6) Production of alkali metal sodium bicarbonate from CO2-containing gas produced by the neutralization reaction of aqueous HCl solution and calcium carbonate for the production of CaCl2 (without removal of acidic components) Sodium bicarbonate powder was produced from a CO2-containing gas generated by the neutralization reaction of an aqueous HCl solution with calcium carbonate to produce CaCl2, using the apparatus shown in Figure 3. The concentrations of each component in this CO2-containing gas were CO2 = 42.8% by volume and HCl = 1.4% by volume. Expressed as a molar ratio to CO2, the HCl / CO2 molar ratio was 0.033. Sodium bicarbonate powder was produced in the same manner as in Example 1, except that this CO2-containing gas was used. 49 minutes after the start of supplying the CO2-containing gas, after supplying 197 L, the crystallization tank contained a turbid sodium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR) was 100%. At this time, the content of components derived from the acidic components in the CO2-containing gas added to the sodium bicarbonate slurry was Cl = 1710 ppm. In the same manner as in Example 1, this sodium bicarbonate slurry was filtered using a centrifugal dehydrator 28 to obtain 880 g of centrifugal dehydrated cake and 1686 g of filtrate 29. The centrifugal dehydrated cake was dried in a carbon dioxide atmosphere at 80°C using a drying equipment 31 to obtain 440 g of sodium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 50%. The amount of components derived from the acidic components in the CO2-containing gas in the obtained sodium bicarbonate powder was high, at Cl = 1620 ppm.

[0053] (Example 7) Production of sodium bicarbonate after removing acidic components from the CO2-containing gas of Example 6. The acidic components were removed from the CO2-containing gas of Example 6 using the wet scrubber shown in Figure 1. The CO2-containing gas of Example 6 was supplied through the gas introduction pipe 8. A sodium bicarbonate aqueous solution was used as the circulating fluid. After the removal of the acidic components, the concentrations of each component were CO2 = 42.8 vol% and HCl = 28 vol ppm. Expressed as a molar ratio to CO2, the HCl / CO2 molar ratio was 0.00007. Sodium bicarbonate powder was produced in the same manner as in Example 6, except that a CO2-containing gas from which the acidic components had been removed was used. Forty-nine minutes after the start of supplying the CO2-containing gas from which the acidic components had been removed, after supplying 197 L, the crystallization tank became a turbid sodium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR) was 100%. At this time, the content of components derived from the acidic components in the CO2-containing gas added to the sodium bicarbonate slurry was Cl = 3.4 ppm. In the same manner as in Example 6, this sodium bicarbonate slurry was filtered using a centrifugal dehydrator 28 to obtain 880 g of centrifugal dehydrated cake and 1686 g of filtrate 29. The centrifugal dehydrated cake was dried in a carbon dioxide atmosphere at 80°C using a drying apparatus 31 to obtain 440 g of sodium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 50%. The amount of components derived from the acidic components in the CO2-containing gas in the obtained sodium bicarbonate powder was very low at Cl = 1.8 ppm, resulting in a high-purity sodium bicarbonate powder.

[0054] [Table 1]

[0055] (Example 8) Production of potassium bicarbonate Potassium bicarbonate powder was produced from the CO2-containing gas from which the acidic components of Example 2 had been removed, using the apparatus shown in Figure 3. The concentrations of each component after the removal of the acidic components were CO2 = 47 vol%, HF = 4.5 vol ppm, and HCl = 1.3 vol ppm. Expressed as molar ratios to CO2, the HF / CO2 molar ratio was 0.00001 and the HCl / CO2 molar ratio was 0.000003. In a crystallization tank 20 with an internal volume of 5 L, 635 g of potassium carbonate powder and 1217 g of deionized water were placed and stirred with a stirring device 21 to obtain 1852 g of a 34.3% potassium carbonate aqueous solution. This aqueous solution was circulated at a flow rate of 20 L / min through a circulation pipe 25 using a circulation pump 23. A YJ nozzle 24 was installed in the circulation pipe. The YJ nozzle used was a YJ-6 inline type (product name). Immediately after starting circulation, a CO2-containing gas of the above composition was supplied to the YJ nozzle 24 in the form of microbubbles at a rate of 4 L / min. The temperature of the aqueous solution when the CO2-containing gas was introduced was 25-35°C. 55 minutes after starting to supply the CO2-containing gas, after supplying 219 L, the inside of the crystallization tank became a cloudy potassium bicarbonate slurry with a pH of 8.3. The carbon dioxide utilization rate (UR) was 100%. The acidic components in the CO2-containing gas added to the potassium bicarbonate slurry at this time were F = 0.4 ppm and Cl = 0.2 ppm. The potassium bicarbonate slurry was filtered using a centrifugal dehydrator 28 to obtain 880 g of centrifugal dehydrated cake and 1174 g of filtrate 29. The centrifugal dehydrator 28 used was an H-110F model manufactured by Kokusan Co., Ltd. The centrifugal dehydrated cake was dried in a drying facility 31 under a carbon dioxide atmosphere at 80°C to obtain 440 g of potassium bicarbonate powder. The solid content concentration in the centrifugal dehydrated cake was calculated to be 50%. The content of components derived from the acidic components in the CO2-containing gas in the obtained potassium bicarbonate powder was F = 0.7 ppm and Cl = 0.0 ppm.

[0056] [Table 2] [Explanation of Symbols]

[0057] 1 Scrubber 2 Tower 3 Circulating fluid storage tank 4 Filling 5 Circulating fluid 6. Circulating fluid pump 7. Spray nozzle 8, 10 Gas introduction piping 9, 13 Gas outlet piping 11. Powdered alkaline neutralizing agent 12 Dust collector 20 Crystallization tank 21. Stirring device 22 Liquid in the crystallization tank 23 Circulation pump 24 YJ nozzles 25 Circulation piping 26. Supply piping for CO2-containing gas 27 Supply piping 28 Filter 29 Filtrate 30 Feeding pipe for dehydrated alkali metal bicarbonate cake 31 Drying equipment 32. Alkali metal bicarbonate powder 40 Flash Jet Dryer 41 Hot air 42. Alkali metal bicarbonate cake 43 Cyclone 44 Collection containers

Claims

1. A first aqueous solution containing at least one acidic component selected from the group consisting of HF and HCl is subjected to a neutralization reaction with calcium carbonate, and the CO produced by the neutralization reaction is... ２ Contains CO ２ Obtain the contained gas, The obtained CO ２ A method for producing an alkali metal bicarbonate, comprising bringing a contained gas into contact with a second aqueous solution containing at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal carbonates, thereby obtaining an alkali metal bicarbonate.

2. The method for producing an alkali metal bicarbonate according to claim 1, wherein the first aqueous solution is HF-containing industrial wastewater discharged from a fluorine-containing compound manufacturing plant, a semiconductor manufacturing plant, or the like.

3. The first aqueous solution is an aqueous solution containing HCl, and CaCl ２ A method for producing an alkali metal bicarbonate according to claim 1, which is an aqueous solution for producing the alkali metal bicarbonate.

4. The aforementioned CO ２ A method for producing an alkali metal bicarbonate according to claim 1 or 2, comprising performing a preliminary treatment to remove at least a portion of the acidic components from the contained gas, followed by the contact treatment.

5. The CO after the pretreatment ２ In the gas containing HF and CO ２ The molar ratio of HF to CO (HF / CO ２ ) is 0.00023 or less, and the molar ratio of HCl to CO ２ (HCl / CO ２ ) is 0.00406 or less. The method for producing an alkali metal hydrogen carbonate according to claim 4

6. A method for producing an alkali metal bicarbonate according to claim 4, wherein the slurry containing the alkali metal bicarbonate obtained by the contact treatment has a fluorine concentration of 6.4 ppm or less and a chlorine concentration of 212 ppm or less, based on the mass of the slurry.

7. The method for producing an alkali metal bicarbonate according to claim 4, wherein the alkali metal bicarbonate obtained by the contact treatment has a fluorine concentration of 6.0 ppm or less and a chlorine concentration of 200 ppm or less.

8. The method for producing an alkali metal bicarbonate according to claim 4, wherein the preliminary treatment is carried out by a wet method using a third aqueous solution containing at least one alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal bicarbonates, or by a dry method using powder of alkali metal bicarbonate.

9. The method for producing an alkali metal bicarbonate according to claim 4, wherein the preliminary treatment is performed using the alkali metal bicarbonate obtained by the contact treatment.

10. The above contact treatment is performed on the second aqueous solution, and the CO ２ A method for producing an alkali metal bicarbonate according to claim 1 or 2, comprising supplying fine bubbles of the contained gas.

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