Method for producing carbonate of group 2 elements and carbon dioxide fixation system

Abstract

To provide a method for producing a carbonate of a group II element by converting carbon dioxide into a carbonate with excellent conversion efficiency and immobilizing the same, and a carbon dioxide immobilization system.SOLUTION: A method for producing a carbonate of a group II element comprises: a first step of introducing carbon dioxide into an alkali adsorbent containing an alkali to adsorb the carbon dioxide; and a second step of adding a salt of the group II element to the alkali adsorbent with a pH of the alkali adsorbent having adsorbed the carbon dioxide having been adjusted to 10 or more to produce the carbonate of the group II element.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing a carbonate of a Group 2 element and a carbon dioxide fixation system. [Background technology]

[0002] Due to problems such as global warming and the depletion of fossil fuels, there is a need for the development of technologies to fix greenhouse gases such as carbon dioxide and to use them as renewable energy.

[0003] Therefore, a technology is being considered that involves adsorbing carbon dioxide in an alkaline solution and then precipitating carbonate to fix the carbon dioxide. For example, Patent Document 1 describes a carbon dioxide fixation device in which an electrodialysis cell receives a sodium nitrate solution to generate nitric acid and sodium hydroxide, nitric acid is supplied to a dissolution cell to dissolve a material containing a Group 2 element and generate a nitrate solution of the Group 2 element, sodium hydroxide is supplied to a gas absorption tower to absorb carbon dioxide and generate a sodium carbonate solution, the nitrate solution of the Group 2 element and the sodium carbonate solution are supplied to a reaction cell to generate a carbonate of the Group 2 element, carbon dioxide is fixed, and the sodium nitrate solution produced by the reaction is circulated to the electrodialysis cell.

[0004] Patent Document 2 describes a system and a method for recovering carbon dioxide in flue gas, the system and method comprising: a carbon dioxide absorption tower having an exhaust gas inlet, an alkaline absorbing solution inlet, an insoluble exhaust gas outlet, and an alkaline absorbing solution outlet, and bringing the introduced exhaust gas into gas-liquid contact with the alkaline absorbing solution to cause the alkaline absorbing solution to absorb carbon dioxide in the exhaust gas; an alkaline absorbing solution reflux line for refluxing the alkaline absorbing solution discharged from the alkaline absorbing solution outlet of the carbon dioxide absorption tower to the alkaline absorbing solution inlet; and a settling tank capable of accommodating the alkaline absorbing solution, which is inserted in the alkaline absorbing solution reflux line or is connected by a pipe branching off from the alkaline absorbing solution reflux line.

[0005] Patent Document 3 describes a system for recovering carbon dioxide in flue gas, which includes an electrolysis device that electrolyzes salt water to separate it into hydrogen, chlorine, and sodium hydroxide water, a carbon dioxide recovery device that brings flue gas and an alkaline solution into gas-liquid contact to recover carbon dioxide in the flue gas and generates the alkaline solution from a predetermined component generated by absorption of carbon dioxide and the sodium hydroxide water generated by the electrolysis device, and a calcium recovery device that recovers calcium from incineration ash using hypochlorous acid water generated using chlorine separated by the electrolysis device, and generates calcium carbonate using the solution from which the calcium was recovered and a part of the alkaline solution. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2012-96975 A [Patent Document 2] JP 2004-352587 A [Patent Document 3] JP 2006-137620 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in conventional techniques, the efficiency of carbon dioxide adsorption into alkaline solutions is insufficient, and losses occur when the carbon dioxide adsorbed into the alkaline solution is converted into carbonates. Therefore, a method for immobilizing carbon dioxide with higher conversion efficiency is desired.

[0008] Therefore, an object of the present invention is to provide a method for producing a carbonate of a Group 2 element, which converts carbon dioxide into a carbonate with excellent conversion efficiency and immobilizes the carbonate, and a carbon dioxide immobilization system. [Means for solving the problem]

[0009] As a result of extensive investigations aimed at solving the above problems, the present inventors discovered that carbon dioxide can be converted to a carbonate with excellent conversion efficiency and immobilized by adjusting the pH of an alkaline adsorption solution that has adsorbed carbon dioxide to 10 or more and then using a salt of a Group 2 element, thereby completing the present invention.

[0010] That is, the present invention is as follows. [1] A first step of introducing carbon dioxide into an alkali adsorption solution containing an alkali to adsorb it; a second step of adjusting the pH of the alkaline adsorption solution having adsorbed the carbon dioxide to 10 or more, and then adding a salt of a Group 2 element to the alkaline adsorption solution to produce a carbonate of a Group 2 element. [2] The method for producing a carbonate of a Group 2 element according to [1], wherein in the first step, the amount of the carbon dioxide introduced into the alkaline adsorption solution is 50% to 90% of the amount of the alkali in the alkaline adsorption solution. [3] The method for producing a carbonate of a Group 2 element according to [1] or [2], wherein in the first step, a pressure when carbon dioxide is introduced as the mixed gas is such that (partial pressure of carbon dioxide / total pressure of the mixed gas)×100 is 10% to 80%. [4] a third step of producing an acid and an alkali by electrodialysis of the liquid obtained after separating the carbonate of the Group II element produced in the second step; The alkali is reused in the first step. A method for producing a carbonate of a Group 2 element according to any one of [1] to [3]. [5] The method for producing a carbonate of a Group 2 element according to any one of [1] to [4], wherein the alkali is at least one selected from the group consisting of NaOH, KOH, Na2CO3, and K2CO3. [6] The method for producing a carbonate of a Group 2 element according to any one of [1] to [5], wherein the salt of the Group 2 element is at least one selected from CaCl2, Ca(NO3)2, CaSO4, MgCl2, Mg(NO3)2, and MgSO4. [7] a carbon dioxide adsorption device for introducing carbon dioxide into an alkali adsorption solution containing an alkali to adsorb the carbon dioxide; and a carbon dioxide fixation device for adjusting the pH of the alkaline adsorption solution having the carbon dioxide adsorbed therein to 10 or more, and then adding a chloride of a group II element to the alkaline adsorption solution to obtain a carbonate of the group II element. Carbon dioxide fixation system. [8] The carbon dioxide fixation system according to [7], further comprising an electrodialysis device that produces an acid and an alkali by electrodialysis of the liquid obtained after separating the carbonate of the Group II element, and a means for supplying the alkali to the carbon dioxide adsorption device. Effect of the Invention

[0011] According to the present invention, it is possible to provide a method for producing a carbonate of a Group 2 element, which converts carbon dioxide into a carbonate with excellent conversion efficiency and then immobilizes the carbonate, and a carbon dioxide immobilization system. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram for explaining an example of a method for producing a carbonate of a Group II element according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing an example of a carbon dioxide fixation system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described in detail. A method for producing a carbonate of a Group II element according to an embodiment of the present invention includes a first step of introducing carbon dioxide into an alkali adsorption solution containing an alkali to adsorb the carbon dioxide; and a second step of adjusting the pH of the alkaline adsorption solution having adsorbed the carbon dioxide to 10 or more, and then adding a salt of a Group 2 element to the alkaline adsorption solution to produce a carbonate of the Group 2 element. According to the method for producing a carbonate of a Group 2 element according to the embodiment of the present invention, carbon dioxide can be converted to a carbonate with excellent conversion efficiency and then immobilized.

[0014] Examples of Group 2 elements include beryllium, magnesium, calcium, strontium, barium, and radium, and among these, calcium or magnesium is preferred.

[0015] The method for producing a carbonate of a Group II element according to an embodiment of the present invention may further include a third step of producing an acid and an alkali by electrodialysis of a liquid remaining after separating the carbonate of the Group II element produced in the second step, and the alkali may be reused in the first step. In addition, the separated carbonate of the Group 2 element may be reacted with the acid to extract carbon dioxide and obtain a salt of the Group 2 element, and the salt of the Group 2 element may be reused in the second step.

[0016] [First step] In the method for producing a carbonate of a Group II element according to an embodiment of the present invention, the first step is a step of introducing carbon dioxide into an alkali adsorption solution containing an alkali to allow the carbon dioxide to be adsorbed. The adsorption conditions in the first step are not particularly limited and can be appropriately adjusted depending on the type and concentration of the alkali in the alkali adsorption solution, the concentration of carbon dioxide, etc. The adsorption conditions can also be appropriately changed during the carbon dioxide adsorption process. The shape of the reaction vessel used in the first step is also not particularly limited.

[0017] Examples of the alkali include sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium carbonate (Na2CO3), calcium carbonate (K2CO3), etc., which may be used alone or in combination. From the viewpoint of cost reduction, sodium hydroxide is preferred.

[0018] For example, when sodium hydroxide is used as the alkali, the reaction represented by the following reaction formula (1) proceeds by introducing carbon dioxide into the alkali adsorption solution, and carbon dioxide is adsorbed into the alkali adsorption solution to produce sodium carbonate.

[0019] 2NaOH + CO2→ Na2CO3+ H2O ···(1)

[0020] The alkali concentration in the alkali adsorption solution is preferably 0.5 mol / L or more, more preferably 1 mol / L or more, and even more preferably 1.5 mol / L or more in order to increase the amount of carbon dioxide adsorbed. Also, in order to prevent the precipitation of carbonates that are generated after carbon dioxide is adsorbed in the alkali adsorption solution, the alkali concentration is preferably 4 mol / L or less, and more preferably 2 mol / L or less. For example, when sodium hydroxide is used as the alkali, the alkali concentration is preferably 2 mol / L or less in order to prevent the precipitation of the generated sodium carbonate.

[0021] The solvent in the alkaline adsorption liquid according to the embodiment of the present invention is preferably a solvent capable of dissolving an alkali to form an alkaline adsorption liquid, and is not particularly limited, but examples of the solvent that can be used include water, ethylene glycol, polyethylene glycol, glycerin, methanol, ethanol, propanol, pentanol, tetrahydrofuran, dimethylformamide, etc. More preferably, water, ethylene glycol, polyethylene glycol, and glycerin can be used, and even more preferably, water can be used.

[0022] Carbon dioxide can be introduced, for example, by introducing a gas containing carbon dioxide into a carbon dioxide adsorption device in which an alkaline adsorption liquid has been charged.

[0023] The amount of carbon dioxide introduced is preferably 50% or more, more preferably 60% or more, and even more preferably 80% or more, relative to the amount of alkali in the alkaline adsorption solution. If the amount of carbon dioxide introduced is 50% or more relative to the amount of alkali in the alkaline adsorption solution, it becomes easier to adsorb almost all of the introduced carbon dioxide into the alkaline adsorption solution. The higher the amount of carbon dioxide introduced is relative to the amount of substance in the alkaline adsorption solution, the higher the carbon dioxide adsorption rate of the alkali, which is advantageous from the viewpoint of the cost of the alkali material. In addition, the amount of carbon dioxide introduced is preferably 90% or less relative to the amount of alkali in the alkaline adsorption solution. By setting the amount of carbon dioxide introduced to 90% or less relative to the amount of alkali in the alkaline adsorption solution, the introduced carbon dioxide can be adsorbed at a high adsorption rate. In addition, almost all of the introduced carbon dioxide can be adsorbed into the alkaline adsorption solution. This is because if the amount of carbon dioxide introduced is higher than 90% relative to the amount of alkali in the alkaline adsorption solution, a gas-liquid equilibrium state is reached between the introduced gaseous carbon dioxide and the carbon dioxide adsorbed in the alkaline adsorption solution, making it difficult to adsorb all of the introduced carbon dioxide. This is because when the amount of carbon dioxide introduced relative to the amount of alkali in the alkaline adsorption solution exceeds 90%, a gas-liquid equilibrium state is reached between the introduced gaseous carbon dioxide and the carbon dioxide adsorbed in the alkaline adsorption solution, making it difficult to adsorb all of the introduced carbon dioxide.

[0024] The gas containing carbon dioxide may be pure carbon dioxide gas or a mixed gas containing components other than carbon dioxide. Carbon dioxide gas and another gas may be introduced separately, or may be a mixed gas before being introduced. The carbon dioxide used in the embodiment of the present invention may be from a carbon dioxide gas cylinder, liquid carbon dioxide, supercritical carbon dioxide, dry ice, or the like.

[0025] Examples of gases containing carbon dioxide include air and exhaust gas. These may be used as they are, or may have an adjusted carbon dioxide concentration. Examples of components other than carbon dioxide include any other components contained in inert gases such as nitrogen and argon, water vapor, exhaust gas, and the like.

[0026] The partial pressure of the carbon dioxide when introduced as a mixed gas is preferably 10% or more, more preferably 30% or more, and even more preferably 50% or more, calculated as (partial pressure of carbon dioxide / total pressure of mixed gas) x 100. From the viewpoint of reducing the energy required for concentrating carbon dioxide gas, the partial pressure is preferably 80% or less, more preferably 70% or less, and even more preferably 50% or less. By setting the partial pressure condition of the carbon dioxide mixed gas to be introduced (partial pressure of carbon dioxide / total pressure of mixed gas) x 100 to 10% to 80%, the partial pressure of the gases introduced other than carbon dioxide will pressurize the gas, thereby enabling all of the carbon dioxide to be adsorbed into the alkaline adsorption liquid.

[0027] By setting the amount of carbon dioxide introduced to 90% or less of the amount of alkali in the alkaline adsorption solution and setting the partial pressure of the carbon dioxide mixed gas introduced, (partial pressure of carbon dioxide / total pressure of mixed gas) x 100, to 10% to 80%, the introduced carbon dioxide can be adsorbed in the alkaline adsorption solution with high efficiency. This is considered to be due to a synergistic effect resulting from satisfying the condition that all carbon dioxide is adsorbed without gas-liquid equilibrium being established between the introduced carbon dioxide and the carbon dioxide adsorbed in the alkaline adsorption solution, and the condition that all the introduced carbon dioxide is adsorbed in the alkaline adsorption solution due to the partial pressure of the introduced gas other than carbon dioxide.

[0028] From the viewpoint of the pressure resistance of the device, the pressure of the gas containing carbon dioxide is preferably 10 MPa or less, more preferably 5 MPa or less, and even more preferably 1 MPa or less. The carbon dioxide-containing gas may be bubbled (blowed) into the alkali adsorption liquid, or after the carbon dioxide-containing gas is introduced, the gas may be mixed with the alkali adsorption liquid by rotating the reaction vessel or the like.

[0029] The temperature in the first step is not particularly limited, but in order to efficiently proceed with the adsorption of carbon dioxide, for example, from the viewpoint of suppressing the efficiency of alkali adsorption energy in the first step, it is preferably 50° C. or less, more preferably 30° C. or less, and even more preferably 25° C. or less. From the viewpoint of suppressing the efficiency of heating energy, it is preferably 50° C. or less, more preferably 30° C. or less, and even more preferably 25° C. or less.

[0030] The carbon dioxide adsorption time in the first step is not particularly limited, but is preferably 0.25 hours or more, more preferably 10 hours or more, and even more preferably 3 hours or less, so as to allow as much carbon dioxide as possible to be adsorbed into the alkaline adsorption solution. From the viewpoint of shortening the process time, the time is preferably 10 hours or less, more preferably 5 hours or less, and even more preferably 3 hours or less.

[0031] The method of introducing the alkali adsorption liquid (alkali and solvent) and carbon dioxide used in the first step into the reaction vessel is not particularly limited, and may involve introducing all the raw materials at once, introducing some or all of the raw materials stepwise, or introducing some or all of the raw materials continuously. Also, these introduction methods may be combined.

[0032] In the first step, carbon dioxide can be adsorbed in the alkaline adsorption liquid, and the liquid can be handled as a liquid. This has the advantage of being easy to handle. The alkaline adsorption liquid that has adsorbed carbon dioxide in this step can be subjected to the second step.

[0033] [Second step] In the method for producing a carbonate of a Group 2 element according to the embodiment of the present invention, the second step is a step of adjusting the pH of the alkaline adsorption solution having adsorbed carbon dioxide to 10 or more, and then adding a salt of a Group 2 element to the alkaline adsorption solution, thereby producing a carbonate of a Group 2 element. In the first step, the carbon dioxide adsorbed in the alkaline adsorption solution exists as carbonate ions. In the second step, the carbonate ions react with the salt of the Group 2 element to produce the carbonate of the Group 2 element. The reaction conditions in the second step are not particularly limited, and can be appropriately adjusted depending on the carbonate ion concentration in the alkali adsorption solution and the type of salt of the group II element. The reaction conditions can also be appropriately changed during the reaction. The shape of the reaction vessel used in the second step is also not particularly limited.

[0034] The pH of the alkaline adsorption solution must be adjusted to 10 or higher, preferably 11 or higher, and more preferably 11.5 or higher. The pH can be adjusted by adding a solution containing an alkali as a pH adjusting solution. Examples of the alkali include inorganic basic compounds such as sodium hydroxide, potassium hydroxide, and ammonia, and organic basic compounds such as dimethylamine, trimethylamine, tetramethylammonium hydroxide, triethylamine, pyridine, aniline, and N,N-dimethylaniline. From the viewpoint of cost reduction, it is preferable to use sodium hydroxide.

[0035] Examples of salts of group 2 elements include calcium chloride (CaCl2), calcium nitrate (Ca(NO3)2), calcium sulfate (CaSO4), magnesium chloride (MgCl2), magnesium nitrate (Mg(NO3)2), magnesium sulfate (MgSO4), etc. Among them, calcium chloride is preferred because it has high solubility, can prepare a highly concentrated solution, can reduce the area of ​​the equipment, and is highly productive.

[0036] The reaction time in the second step is not particularly limited, but is preferably 1 minute or more, more preferably 3 minutes or more, and even more preferably 5 minutes or more in order to allow the reaction to proceed, and is preferably 10 hours or less, more preferably 4 hours or less, and even more preferably 3 hours or less in terms of shortening the process time.

[0037] The amount of the salt of the Group 2 element used is not particularly limited, but in order to convert all of the carbon dioxide adsorbed in the alkaline adsorption solution into carbonate, it is preferable that the amount of the salt of the Group 2 element used is greater than the amount of carbon dioxide adsorbed in the alkaline adsorption solution. In order to suppress loss of the salt of the Group 2 element that cannot be converted to a carbonate, it is preferable that the amount of the salt of the Group 2 element used is less than the amount of the alkali substance present in the alkali adsorption liquid.

[0038] When sodium hydroxide is used as the alkali in the first step, the reaction represented by reaction formula (1) proceeds by introducing carbon dioxide into the alkali adsorption solution as described above, and carbon dioxide is adsorbed into the alkali adsorption solution (aqueous sodium hydroxide solution) to produce sodium carbonate. By adding a salt of a group 2 element to the alkaline adsorption solution (aqueous sodium hydroxide solution), the reaction shown in the following reaction formula (2) proceeds, and a carbonate of the group 2 element is produced. Carbonates of group 2 elements have low solubility and precipitate as a solid from the alkaline adsorption solution. This makes them easy to separate, and carbon dioxide can be immobilized as a solid, which has the advantages of reducing transportation and storage costs and making them easy to handle. In the following reaction formula (2), an example is given in which sodium hydroxide is used as the alkaline adsorption solution and calcium chloride is used as the salt of the group 2 element.

[0039] Na2CO3+ CaCl2→ CaCO3↓ + 2NaCl ···(2)

[0040] According to the study by the present inventors, when a salt of a Group II element is added to the alkaline adsorption solution containing carbon dioxide adsorbed therein obtained in the first step without adjusting the pH, gas is generated. From the study of the generation of this gas, the following can be inferred. In the first step, in addition to the reaction shown in the above-mentioned reaction formula (1), it is presumed that a side reaction shown in the following reaction formula (3) occurs to produce sodium hydrogen carbonate. It is then considered that this sodium hydrogen carbonate reacts with a salt of a Group 2 element to produce carbon dioxide and generate gas by the reaction shown in the following reaction formula (4). The following reaction formula (4) shows an example in which calcium chloride is used as the salt of a Group 2 element.

[0041] 3NaOH + 2CO2→ Na2CO3+ NaHCO3+ H2O (3)

[0042] 2NaHCO3+ CaCl2→ CaCO3↓ + CO2↑ + 2NaCl + H2O···(4)

[0043] By adjusting the pH of the alkaline adsorption solution with adsorbed carbon dioxide to 10 or higher using a pH adjusting solution, the sodium bicarbonate produced in the side reaction represented by reaction formula (3) can be converted to sodium carbonate by the reaction represented by the following reaction formula (5). By subsequently adding calcium chloride, the sodium bicarbonate produced in the side reaction represented by reaction formula (3) can be converted to sodium carbonate and used in the reaction represented by reaction formula (2). As a result, it has become possible to suppress the loss of carbon dioxide adsorbed in the alkaline adsorption solution, which is discharged as carbon dioxide by the reaction represented by reaction formula (4), and to convert it to calcium carbonate at a high conversion rate and immobilize it.

[0044] NaHCO3+ NaOH→ Na2CO3+ H2O ···(5)

[0045] The method may further include a third step of producing an acid and an alkali by electrodialysis of the solution obtained after separating the carbonate of the Group II element produced in the second step, and the alkali may be reused in the first step. In the second step, after the reaction represented by reaction formula (2) is completed, the carbonate of the Group 2 element is precipitated and can be easily separated by a commonly used method. As the carbonate of a Group 2 element, sodium carbonate is preferred, because it has low solubility in water and can be easily precipitated as a solid, and also has low deliquescence as a solid, making it easy to handle.

[0046] There is no particular limitation on the method for separating the carbonate of the Group 2 element, and it can be separated by filtration, dehydration, or the like. Examples of the filtration method include natural filtration, reduced pressure filtration, pressure filtration, centrifugal filtration, etc. Examples of the filter medium include filter paper, membrane filters, and filter plates made by compression molding cellulose, glass fiber, etc.

[0047] The carbonate of the Group 2 element separated and recovered by filtration may be dried by natural drying, heat drying, drying under reduced pressure, or the like.

[0048] In an embodiment of the present invention, the liquid obtained after separating the carbonate salt of the Group II element produced in the second step contains an alkali salt, and by treating this liquid using an electrodialysis device in the third step, at least a part of the alkali salt contained in the liquid can be protonated by electrodialysis to produce an acid and an alkali.

[0049] In an electrodialysis device, for example, cation exchange membranes and anion exchange membranes are alternately arranged between an anode and a cathode, and a plurality of cells are formed by these cation exchange membranes and anion exchange membranes. A salt chamber is formed between each anion exchange membrane and a cation exchange membrane arranged on the cathode side thereof, and an alkaline chamber is formed between each anion exchange membrane and a cation exchange membrane arranged on the anode side thereof. By circulating and supplying the liquid from which the carbonate has been separated to the salt chambers while applying current, hydroxide (alkali) is generated in the alkaline chamber, and the alkali chloride salt circulated and supplied to the salt chambers is converted to hydrochloric acid.

[0050] As described above, the liquid obtained after separating the carbonate produced in the second step may be used as is for electrodialysis, or may be concentrated by adding pure water thereto, if necessary. The alkali produced by electrodialysis can be reused in the first step.

[0051] A method for producing a carbonate of a Group II element according to an embodiment of the present invention will be described with reference to FIG. 1, in which an aqueous sodium hydroxide solution is used as an alkaline adsorption liquid, the pH is adjusted with sodium hydroxide, and calcium chloride is used as a salt of the Group II element.

[0052] The carbon dioxide adsorption device 10 in FIG. 1 introduces carbon dioxide into an aqueous sodium hydroxide solution to cause adsorption. 1, by introducing carbon dioxide into the aqueous sodium hydroxide solution introduced into the carbon dioxide adsorption device 10, the carbon dioxide is adsorbed into the aqueous sodium hydroxide solution, the reaction represented by the above reaction formula (1) proceeds, and sodium carbonate is produced (first step). Sodium hydrogen carbonate produced as a side reaction by the above reaction formula (3) is converted into sodium carbonate by the reaction represented by the above reaction formula (5) by adjusting the pH using, for example, an aqueous sodium hydroxide solution as a pH adjusting solution, and the obtained sodium carbonate is introduced into the carbon dioxide fixation device 20, and by introducing calcium chloride, the above reaction formula (2) proceeds, and precipitated calcium carbonate can be obtained as a solid (second step). The aqueous sodium chloride solution obtained as a liquid after separating calcium carbonate can be subjected to electrodialysis using an electrodialysis device 30. By electrodialysis of the aqueous sodium chloride solution, hydrochloric acid and sodium hydroxide are produced, and the sodium hydroxide can be reused in the first step.

[0053] [Method for producing carbonate of Group 2 element] A method for producing a carbonate of a Group II element according to an embodiment of the present invention includes a first step of introducing carbon dioxide into an alkali adsorption solution containing an alkali to adsorb the carbon dioxide; and a second step of adjusting the pH of the alkaline adsorption solution having adsorbed the carbon dioxide to 10 or more, and then adding a salt of a Group 2 element to the alkaline adsorption solution to produce a carbonate of the Group 2 element. The method for producing a carbonate of a Group II element according to an embodiment of the present invention may further include a third step of producing an acid and an alkali by electrodialysis of a liquid remaining after separation of the carbonate of the Group II element produced in the second step, and the alkali may be reused in the first step. In the method for producing a carbonate of a Group 2 element according to the embodiment of the present invention, the conditions in the first step, the second step and the third step can be appropriately the same as those in the method for producing a carbonate of a Group 2 element.

[0054] [Carbon dioxide fixation system] The carbon dioxide fixation system according to an embodiment of the present invention includes: a carbon dioxide adsorption device that introduces carbon dioxide into an alkali adsorption liquid containing an alkali and adsorbs carbon dioxide therein; The alkaline adsorption solution having the carbon dioxide adsorbed therein is adjusted to a pH of 10 or more, and then a salt of a Group II element is added to the alkaline adsorption solution to obtain a carbonate of the Group II element.

[0055] The carbon dioxide fixation system according to the embodiment of the present invention may be any system that includes a carbon dioxide adsorption device and a carbon dioxide fixation device, and the products obtained by each device may be transported or stored and then supplied to another device.

[0056] The carbon dioxide fixation system according to the embodiment of the present invention may further include an electrodialysis device that produces an acid and an alkali by electrodialysis of the liquid remaining after separation of the carbonate of the Group II element, and a means for supplying the alkali to the carbon dioxide adsorption device.

[0057] The carbon dioxide fixation system according to the embodiment of the present invention may be any system that includes a carbon dioxide adsorption device and a carbon dioxide fixation device, and the products obtained by each device may be transported or stored and then supplied to another device.

[0058] FIG. 2 is a diagram showing an example of a carbon dioxide fixation system according to an embodiment of the present invention. The carbon dioxide fixation system 100 shown in FIG. 2 includes a carbon dioxide adsorption device 10 and a carbon dioxide fixation device 20.

[0059] 2 may further include an electrodialysis device 30. In addition, the system may further include a carbon dioxide cylinder 40 for introducing carbon dioxide into the carbon dioxide adsorption device 10, and a gas cylinder 50 for adjusting the carbon dioxide concentration as necessary. The carbon dioxide concentration and pressure can be adjusted by valves 1 and 2 provided in pipes L1 and L2.

[0060] The alkaline adsorption liquid may be charged in advance into the carbon dioxide adsorption device 10, and carbon dioxide can be introduced through a pipe L1. When carbon dioxide is introduced into the carbon dioxide adsorption device 10, the carbon dioxide comes into contact with the alkaline adsorption liquid inside the carbon dioxide adsorption device 10 and is adsorbed into the alkaline adsorption liquid. The carbon dioxide adsorption device 10 may be a pressure-resistant reactor or the like.

[0061] 2, a pH adjusting solution is supplied from a pH adjusting solution supply unit 60 via a pipe L3 to the alkaline adsorption liquid that has adsorbed carbon dioxide, thereby adjusting the pH of the alkaline adsorption liquid that has adsorbed carbon dioxide to 10 or more. The supply amount of the pH adjusting solution can be adjusted by a valve 3. The alkaline adsorption liquid that has been adjusted to a pH of 10 or more is supplied to a carbon dioxide fixation device 20 via a pipe L4.

[0062] In addition, the carbon dioxide fixation device 20 is supplied with a salt of the group 2 element from a group 2 element salt supply unit 70 via pipe L5. The amount of the salt of the group 2 element supplied can be adjusted by valve 4. The supplied salt of the group 2 element reacts with carbonate ions in the alkaline adsorption liquid that has adsorbed carbon dioxide in the carbon dioxide fixation device 20, generating a carbonate of the group 2 element in a solid state, which fixes the carbon dioxide. The generated carbonate of the group 2 element is separated into solid and liquid, and can be discharged via pipe L6.

[0063] Furthermore, the liquid obtained after separating the carbonates of the Group II elements is supplied to the electrodialysis device 30 via pipe L7, and acid and alkali can be produced by electrodialysis. The amount of the liquid supplied can be adjusted by the valve 5. The acid produced by electrodialysis can be discharged via pipe L8. Furthermore, the alkali produced by electrodialysis can be supplied to the carbon dioxide adsorption device 10 via pipe L9 and reused. The amount of the alkali produced by electrodialysis supplied to the carbon dioxide adsorption device 10 can be adjusted by the valve 6.

[0064] According to the method for producing a carbonate of a Group 2 element and the carbon dioxide fixation system of the present embodiment, it is possible to provide a method for producing a carbonate of a Group 2 element and a carbon dioxide fixation system which can convert carbon dioxide into a carbonate with excellent conversion efficiency and fix the carbon dioxide in a state where it is easy to handle. EXAMPLES

[0065] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples in any way.

[0066] [Examples 1 to 14] <First step (carbon dioxide adsorption step)> 20 ml of 2 mol / L aqueous sodium hydroxide solution was placed in a pressure reactor as an alkaline adsorption solution. A mixed gas of carbon dioxide and hydrogen was introduced into the pressure reactor so that (partial pressure of carbon dioxide / total pressure of mixed gas) x 100(%) was 10-100% at room temperature, as shown in Table 1, and the amount of carbon dioxide relative to the amount of sodium hydroxide, which is an alkali, ((amount of carbon dioxide introduced / amount of alkali) x 100(%)) was adjusted to 50-100%. The conditions in Examples 1-14 are shown in Table 1. After introducing the carbon dioxide mixed gas, the mixture was stirred at a rotation speed of 800 rpm, and the pressure gradually decreased. The carbon dioxide adsorption rate was calculated from the amount of pressure reduction and the volume of the pressure-resistant reactor. After confirming that the pressure was not decreasing, the pressure was released. The heat-resistant container was removed from the pressure-resistant reactor, and the alkaline adsorption liquid that had adsorbed carbon dioxide was collected. The adsorption rate (%) of carbon dioxide introduced into the alkaline adsorption solution was calculated by the following formula. Adsorption rate of carbon dioxide introduced into the alkaline adsorption solution (%) = (N2 / N1) x 100 N1: Amount of carbon dioxide introduced into the pressure reactor (mol) N2: Amount of carbon dioxide adsorbed in the alkaline adsorption solution (mol)

[0067] <Second step (carbonate fixation step)> The pH of the solution was adjusted by adding granular sodium hydrogen to the alkaline adsorption solutions of Examples 1 to 14, in which carbon dioxide was adsorbed to sodium hydroxide. LAQUAtwin-pH-11 (HORIBA Advanced Techno Co., Ltd.) (measurement accuracy pH ±0.1) was used to measure the pH. Calcium chloride was added as a salt of a group II element to each of the alkaline adsorption solutions of Examples 1 to 14 after pH adjustment so that the amount of substance was equal to the amount of carbon dioxide adsorbed in the carbon dioxide adsorption step, and a precipitate was formed when the solution was stirred for 15 minutes. The amount of gas generated when calcium chloride was added was quantified using the water displacement method. The rate (%) of carbon dioxide loss by adsorption in the alkaline adsorption solution during the carbonate fixation step was calculated by the following formula.

[0068] Adsorption carbon dioxide loss rate (%) = (1-V / 22.4 / N) x 100 V: Amount of gas generated when calcium chloride is added to the alkaline adsorption solution (L) N: The amount (mol) of carbon dioxide adsorbed in the alkaline adsorption solution during the carbon dioxide adsorption process The volume of 1 mol of carbon dioxide at standard conditions was set to 22.4 L. After stirring, the suspension was filtered, and the powder remaining on the filter paper was dried in an oven at 100°C and collected.

[0069] <Identification of calcium carbonate> The composition and purity of the powder were analyzed by X-ray diffraction (XRD). The equipment used for the analysis was a Rigaku SmartLab. The observed XRD peaks matched those of calcium carbonate, and the purity of calcium carbonate in the powder was 99.3%. Finally, the conversion rate (%) of the introduced carbon dioxide to calcium carbonate was calculated using the recovered mass of the powder.

[0070] [Comparative Example 1] In Comparative Example 1, carbon dioxide was adsorbed into the alkaline adsorption solution under the same conditions as in Example 1. Calcium chloride was added to the alkaline adsorption solution with carbon dioxide adsorbed therein without adjusting the pH, so that the amount of substance was equal to the absorbed carbon dioxide, and the solution was stirred for 15 minutes, resulting in the formation of a precipitate. The amount of gas generated when calcium chloride was added was quantified using the water displacement method. After stirring, the suspension was filtered, and the powder remaining on the filter paper was dried in an oven at 100°C and collected. The conversion rate (%) of introduced carbon dioxide to calcium carbonate was calculated using the collected mass of the powder. [Comparative Example 2] In Comparative Example 2, carbon dioxide was adsorbed into a 2 mol / L aqueous sodium carbonate solution under the same conditions as in Example 12. After carbon dioxide adsorption, the alkaline adsorption solution was filtered and the precipitate was removed. The filtrate was heated to 70°C, and sodium hydrogen carbonate was removed by thermal decomposition. The amount of gas generated by thermal decomposition was quantified using the water displacement method. Then, calcium chloride was added to the solution in an amount equivalent to the molar ratio of carbon dioxide absorbed, and the solution was stirred for 15 minutes to form a precipitate. After stirring, the suspension was filtered, and the powder remaining on the filter paper was dried and collected in an oven at 100°C. The conversion rate (%) of the introduced carbon dioxide to calcium carbonate was calculated using the recovered mass of the powder.

[0071] The results of Examples 1 to 14 and Comparative Examples 1 and 2 are shown in Table 1.

[0072] [Table 1]

[0073] As shown in Table 1, in Examples 1 to 14 in which the pH of the alkaline adsorption liquid that adsorbed carbon dioxide in the second step was adjusted to 10 or more, it was found that the conversion rate of the input carbon dioxide to calcium carbonate was high and carbon dioxide could be immobilized with high efficiency. On the other hand, in Comparative Examples 1 and 2 in which calcium carbonate was produced without adjusting the pH of the alkaline adsorption liquid that adsorbed carbon dioxide, there was a large loss of carbon dioxide in both the first step and the second step, the conversion rate of the input carbon dioxide to calcium carbonate was low, and the productivity was poor. In addition, in Examples 4 to 7 and 9 to 14 in which (partial pressure of carbon dioxide / total pressure of mixed gas)×100(%) was 80% or less in the first step, the carbon dioxide adsorption rate was 100%, which showed an extremely excellent carbon dioxide adsorption rate. Furthermore, in Examples 1 to 4 and 7 to 14 in which the pH of the alkaline adsorption solution that adsorbed carbon dioxide in the second step was adjusted to 11.5, the carbon dioxide loss rate was 0%, which showed that carbon dioxide can be converted and immobilized into carbonates with excellent conversion efficiency. [Explanation of symbols]

[0074] 1, 2, 3, 4, 5 Valves 10 Carbon dioxide adsorption device 20 Carbon dioxide fixation device 30 Electrodialysis equipment 40 Carbon Dioxide Cylinder 50 Gas Cylinder 60 pH adjustment solution supply section 70 Salt supply section for group 2 elements 100 Carbon Dioxide Fixation System L1, L2, L3, L4, L5, L6 piping

Claims

1. A first step of introducing carbon dioxide into an alkali adsorption solution containing an alkali to adsorb it; a second step of adjusting the pH of the alkaline adsorption solution having the carbon dioxide adsorbed therein to 10 or more, and then adding a salt of a Group II element to the alkaline adsorption solution to produce a carbonate of a Group II element; In the first step, the pressure when introducing the carbon dioxide as the mixed gas is such that (partial pressure of carbon dioxide / total pressure of the mixed gas)×100 is 10% to 80%, The salt of the second group element is CaCl ２ , Ca(NO ３ ) ２ , CaSO ４ At least one selected from the following: A method for producing carbonates of group 2 elements.

2. 2. The method for producing a carbonate of a Group 2 element according to claim 1, wherein in the first step, the amount of the carbon dioxide introduced into the alkaline adsorption solution is 50% to 90% of the amount of the alkali in the alkaline adsorption solution.

3. a third step of producing an acid and an alkali by electrodialysis of the liquid obtained after separating the carbonate of the Group II element produced in the second step; The alkali is reused in the first step. A method for producing the carbonate of Group 2 element according to claim 1 or 2.

4. The alkali is NaOH, KOH, Na ２ CO ３ , K ２ CO ３ The method for producing a carbonate of a Group 2 element according to any one of claims 1 to 3, wherein the carbonate is at least one selected from the following:

5. a carbon dioxide adsorption device for introducing carbon dioxide into an alkali adsorption solution containing an alkali to adsorb the carbon dioxide; a carbon dioxide fixation device for adjusting the pH of the alkaline adsorption solution having the carbon dioxide adsorbed therein to 10 or more, and then adding a salt of a Group II element to the alkaline adsorption solution to obtain a carbonate of the Group II element, In the introduction of the carbon dioxide, the pressure at which the carbon dioxide is introduced as a mixed gas is such that (partial pressure of carbon dioxide / total pressure of the mixed gas)×100 is 10% to 80%, The salt of the second group element is CaCl ２ , Ca(NO ３ ) ２ , CaSO ４ At least one selected from the following: Carbon dioxide fixation system.

6. 6. The carbon dioxide fixation system according to claim 5, further comprising: an electrodialysis device that produces an acid and an alkali by electrodialysis of the liquid obtained after separating the carbonate of the Group II element; and a means for supplying the alkali to the carbon dioxide adsorption device.

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