WO2023181794A1 - Carbon dioxide fixation method and carbon dioxide fixation system - Google Patents

Carbon dioxide fixation method and carbon dioxide fixation system Download PDF

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Publication number
WO2023181794A1
WO2023181794A1 PCT/JP2023/007085 JP2023007085W WO2023181794A1 WO 2023181794 A1 WO2023181794 A1 WO 2023181794A1 JP 2023007085 W JP2023007085 W JP 2023007085W WO 2023181794 A1 WO2023181794 A1 WO 2023181794A1
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Prior art keywords
carbon dioxide
seawater
dioxide fixation
electrolysis
ions
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PCT/JP2023/007085
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French (fr)
Japanese (ja)
Inventor
友恵 井藤
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住友重機械工業株式会社
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Publication of WO2023181794A1 publication Critical patent/WO2023181794A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/18—Carbonates
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/02—Hydrogen or oxygen
    • C25B1/04—Hydrogen or oxygen by electrolysis of water
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms

Definitions

  • the present invention relates to a carbon dioxide fixation method and a carbon dioxide fixation system.
  • the present invention relates to a carbon dioxide fixation method and a carbon dioxide fixation system for fixing carbon dioxide using seawater.
  • methods for recovering carbon dioxide from carbon dioxide-containing gas include chemical absorption methods in which carbon dioxide is dissolved in an absorption liquid such as monoethanolamine, and physical adsorption methods in which carbon dioxide is adsorbed on an adsorbent that has gas adsorption ability.
  • membrane separation methods using membranes are also known.
  • an ocean-based method that stores carbon dioxide in the ocean and sequesters it from the atmosphere by supplying carbon dioxide to the ocean. Methods related to storage are being considered.
  • Patent Document 1 describes a carbon dioxide fixation system that pumps deep seawater to near the sea surface and causes the pumped seawater to absorb carbon dioxide.
  • Ocean acidification is involved in the growth and reproduction of various marine organisms, and there are concerns about its impact on the ecosystem.
  • a certain amount of carbon dioxide is normally absorbed by the ocean even in the natural environment, but due to ocean acidification, the amount of carbon dioxide that the ocean can absorb is decreasing, causing an increase in atmospheric carbon dioxide. It can also be.
  • concentration of carbon dioxide in the atmosphere increases, the concentration of carbon dioxide in contact with the ocean surface also increases, so ocean acidification will continue to progress without being resolved. As a result, there is a fear that the two problems of ocean acidification and increased atmospheric carbon dioxide concentrations will become more serious at the same time.
  • An object of the present invention is to provide a carbon dioxide fixation method and a carbon dioxide fixation system that can fix carbon dioxide with high efficiency and at low cost and low energy.
  • the present inventor has found that carbon dioxide fixation can be achieved with high efficiency, low cost, and low energy consumption by using seawater and by performing electrolysis after supplying carbon dioxide to seawater.
  • the present invention was completed by discovering that it is possible to fix carbon dioxide. That is, the present invention provides the following carbon dioxide fixation method and carbon dioxide fixation system.
  • the carbon dioxide fixation method of the present invention for solving the above problems is a method of fixing carbon dioxide using seawater, which uses an electrolytic section in which a cation exchanger is arranged between electrodes, and a cathode of the electrolytic section. It has the feature that electrolysis is performed after supplying carbon dioxide to the seawater introduced to the side.
  • the carbon dioxide fixation method of the present invention uses seawater as an electrolyte solution and a divalent ion source, thereby significantly reducing the cost and energy required to procure raw materials for divalent ions necessary for carbon dioxide fixation. be able to.
  • the carbon dioxide fixation method of the present invention is based on this knowledge, and uses an electrolytic section in which a cation exchanger is placed between the electrodes to supply carbon dioxide to seawater introduced to the cathode side, thereby removing dissolved carbon dioxide.
  • electrolysis By performing electrolysis after increasing the concentration, carbonate ions increase on the cathode side as the pH increases, improving the carbonate production efficiency, while the pH increases to the point where the magnesium hydroxide production reaction becomes dominant. This makes it possible to suppress the production reaction of magnesium hydroxide. This makes it possible to fix carbon dioxide with high efficiency, low cost, and low energy.
  • one embodiment of the carbon dioxide fixation method of the present invention is characterized in that an electrolytic solution containing no chloride ions is introduced to the anode side of the electrolytic section.
  • an electrolytic solution containing no chloride ions is introduced to the anode side of the electrolytic section.
  • chlorine gas is generated on the anode side due to chloride ions contained in the seawater.
  • This chlorine gas has a large environmental impact and cannot be directly released into the atmosphere, but must be recovered and detoxified, leading to increased costs for carbon dioxide fixation.
  • seawater is introduced into the cathode side of the electrolytic section in which a cation exchanger is arranged between the electrodes, while an electrolytic solution containing no chloride ions is introduced into the anode side, and electrolysis is performed.
  • the carbon dioxide fixation system of the present invention for solving the above problems is a system for fixing carbon dioxide using seawater, and includes an electrolytic section in which a cation exchanger is arranged between electrodes. Seawater and carbon dioxide are introduced into the cathode side of the electrolytic section, and an electrolytic solution containing no chloride ions is introduced into the anode side of the electrolytic section.
  • Seawater and carbon dioxide are introduced into the cathode side of the electrolytic section, and an electrolytic solution containing no chloride ions is introduced into the anode side of the electrolytic section.
  • seawater introduced into the cathode side of the electrolytic part as an electrolyte solution and a source of divalent ions, it is possible to procure raw materials for divalent ions necessary for fixing carbon dioxide. Such costs and energy can be significantly reduced.
  • the carbonate production reaction progresses as the pH increases on the cathode side during electrolysis, while the generation of chlorine gas, which has a large environmental impact, is prevented on the anode side during electrolysis. Can be suppressed. This makes it possible to fix carbon dioxide with high efficiency, low cost, and low energy.
  • FIG. 1 is a schematic explanatory diagram of a carbon dioxide fixation system in an embodiment of the present invention. It is a graph showing the relationship between the pH of seawater and the abundance ratio of carbonic substances in seawater. 1 is a graph showing the relationship between the content of each composition in a precipitate generated by an inorganic salt production reaction associated with alkalinization of seawater and pH.
  • FIG. 1 is a schematic explanatory diagram showing one step (first step) of a carbon dioxide fixation method in an embodiment of the present invention.
  • FIG. 2 is a schematic explanatory diagram showing another step (second step) of the carbon dioxide fixation method in the embodiment of the present invention.
  • 1 is a graph showing results of an example of carbon dioxide fixation treatment using a carbon dioxide fixation method and a carbon dioxide fixation system in an embodiment of the present invention.
  • the source (or source) of carbon dioxide to be fixed is not particularly limited.
  • specific sources of carbon dioxide include gas containing carbon dioxide emitted from various facilities (power generation facilities, factories, general households, etc.) and means of transportation during daily life and industrial activities;
  • Examples include naturally occurring gases containing carbon dioxide, such as volcanic gases and volcanic gases.
  • the carbon dioxide fixation system of the present invention uses seawater to fix carbon dioxide. More specifically, by electrolyzing seawater in which carbon dioxide has been dissolved in advance, carbonate ions are generated. This method promotes carbon dioxide and fixes carbon dioxide by reacting carbonate ions with divalent ions in seawater on the cathode side to convert them into carbonates.
  • the carbon dioxide fixation system of the present invention uses an electrolyte that does not contain chloride ions on the anode side, thereby suppressing the generation of chlorine gas that occurs in general seawater electrolysis. It performs immobilization.
  • FIG. 1 is a schematic explanatory diagram showing the structure of a carbon dioxide fixation system according to an embodiment of the present invention.
  • the carbon dioxide fixation system 10 in this embodiment includes an electrolysis section 20 into which seawater containing carbon dioxide is introduced and performs electrolysis of the seawater.
  • a seawater introduction section (line L1) that introduces seawater, a carbon dioxide supply section 30 that supplies carbon dioxide, and an electrolytic solution that does not contain chloride ions (hereinafter simply referred to as "electrolytic solution E”) ) is provided with an electrolyte introduction section (line L2) for introducing the electrolyte.
  • electrolytic solution E electrolytic solution that does not contain chloride ions
  • seawater source The supply source of seawater introduced into the electrolysis section 20 (hereinafter referred to as "seawater source”) is not particularly limited.
  • the natural environment may be used as a seawater source, and seawater may be introduced directly from the ocean into the electrolyzer 20, or seawater may be artificially stored temporarily, such as seawater used for ocean storage treatment of carbon dioxide or as ballast water for ships.
  • the seawater that has been removed may be used as a seawater source.
  • the cost of raw material procurement of seawater is mainly the cost of transporting seawater.
  • seawater can be used with minimal transportation costs.
  • the electrolysis section 20 in this embodiment includes a pair of electrodes (electrodes 22a, 22b) and a cation exchanger 23 in a processing tank 21.
  • the inside of the processing tank 21 forms two spaces (spaces 24a and 24b) via the cation exchanger 23.
  • the treatment tank 21 may be of any material or shape as long as it is formed so as to be able to stably store seawater or electrolyte.
  • materials and shapes used in structures known as electrolytic cells and electrodialysis cells may be used.
  • Electrodes 22a and 22b are provided in spaces 24a and 24b, respectively, and are connected using conductive wires. Note that the electrodes 22a, 22b may be provided on or near the surface of the cation exchanger 23, and the electrodes 22a, 22b and the cation exchanger 23 may be treated as an integrated unit.
  • the electrodes 22a and 22b may be of any type as long as they function as an anode or a cathode, and there are no particular limitations on the material and shape. In this embodiment, the following explanation will be given assuming that the electrode 22a functions as an anode and the electrode 22b functions as a cathode.
  • Examples of materials for the electrodes 22a and 22b include carbon and metals (stainless steel, platinum, copper, etc.) that are widely used as electrode materials in the electrochemical field.
  • examples of the shape of the electrodes 22a and 22b include, for example, a flat plate shape, a rod shape, a mesh shape, and the like. Note that when the electrodes 22a and 22b are provided on the surface of the cation exchanger 23 or in the vicinity thereof, it is preferable that they have a shape that can suppress inhibition of mass transfer to the cation exchanger 23. Examples of such a shape include a mesh shape and a thin rod shape such as a wire.
  • the electrodes 22a and 22b is one in which an electrode pattern is created directly on the surface of the cation exchanger 23 by a method such as plating.
  • the shape of the electrode pattern is not particularly limited, but it is preferable that the shape can suppress the inhibition of mass transfer to the cation exchanger 23.
  • the power supply means for the DC power supply connected to the pair of electrodes is not particularly limited, but may be one that uses power supply equipment that uses renewable energy such as solar, wind, or wave power, or surplus power from other facilities. It is preferable that This makes it possible to reduce the energy used during electrolysis of seawater in the electrolysis section 20. In particular, by adopting a power supply means that uses renewable energy that does not emit carbon dioxide during power generation, it is also effective in promoting the reduction of carbon dioxide emissions.
  • the cation exchanger 23 divides the treatment tank 21 into a space 24a (hereinafter also referred to as "anode side") where an anode (electrode 22a) is located and a space 24b (hereinafter also referred to as "anode side") where a cathode (electrode 22b) is located. It is a membrane that can selectively permeate cations to the cathode side (also called the cathode side).
  • the cation exchanger 23 in this embodiment is preferably a membrane that suppresses chloride ions on the cathode side from moving to the anode side and allows hydrogen ions (H + ) on the anode side to move to the cathode side. preferable.
  • the cation exchanger 23 is not particularly limited as long as it has the function of restricting the movement of anions and transmitting at least hydrogen ions, and there are no particular limitations on the specific components or structure. .
  • membranes treated to selectively allow monovalent cations to permeate so-called monovalent ion-selective membranes
  • known membranes that allow the transfer of divalent or higher cations in addition to monovalent cations can be used.
  • the treatment tank 21 has a line L1 as a seawater introduction section that introduces seawater from a seawater source to the cathode side (space 24b) of the electrolytic section 20, and an electrolyte E that is introduced to the anode side (space 24a) of the electrolytic section 20.
  • a line L2 as an electrolyte introduction part is connected.
  • the line L1 that introduces seawater to the cathode side of the electrolysis section 20 is not particularly limited as long as it is connected to the space 24b and has a material and structure that allows stable transfer of seawater. Note that it is preferable to provide a means for preventing contaminants and living organisms in the seawater from entering the treatment tank 21 on the line L1. For example, a filter or a net may be provided on the line L1 to trap impurities and living things in the seawater.
  • the line L2 that introduces the electrolytic solution E to the anode side of the electrolytic section 20 is not particularly limited as long as it is connected to the space 24a and has a material and structure that allows stable transfer of the electrolytic solution E.
  • the electrolytic solution E may be any solution that does not contain chloride ions and satisfies the requirements of having electrical conductivity, and can be prepared by dissolving the electrolyte (excluding substances containing chloride ions) in pure water. For example, using an existing electrolyte solution (such as seawater) from which chloride ions have been removed.
  • the processing tank 21 is provided with a carbon dioxide supply unit 30 that supplies carbon dioxide from a carbon dioxide supply source (or generation source) in addition to the lines L1 and L2.
  • the carbon dioxide supply unit 30 may be anything that can supply carbon dioxide into the seawater introduced to the cathode side.
  • a carbon dioxide supply source or generation source
  • the carbon dioxide supply unit 30 may be anything that can supply carbon dioxide into the seawater introduced to the cathode side.
  • FIG. One example is one that includes a quantity adjusting means 33.
  • the pipe 31 connects the supply source (or source) of carbon dioxide and the treatment tank 21 (space 24b), and the tip side of the pipe 31 enters seawater stored in the space 24b,
  • a blowing section 32 is provided for blowing carbon dioxide into seawater.
  • the structure of the blowing section 32 is not particularly limited.
  • the tube may have a tubular structure having a diameter similar to that of the pipe 31, or may have a nozzle-like structure where the diameter decreases toward the tip.
  • a supply amount adjusting means 33 is provided for adjusting the amount of carbon dioxide supplied through the blowing section 32.
  • a pressurizing mechanism for pressurizing carbon dioxide is provided, and carbon dioxide is supplied from the blowing part 32 into the seawater.
  • the treatment tank 21 may be provided with means for recovering gas generated by electrolytic treatment.
  • hydrogen is generated on the cathode side and oxygen is generated on the anode side by performing electrolytic treatment in the electrolysis unit 20. Therefore, it is preferable to provide the treatment tank 21 with a line L3 for recovering the gas (hydrogen) generated on the cathode side and a line L4 for recovering the gas (oxygen) generated on the anode side.
  • hydrogen is a substance that is attracting attention as a next-generation energy source, and it is preferable to be able to recover and utilize highly pure hydrogen. Therefore, a means for removing gases other than hydrogen (such as water vapor) may be provided on the line L3. This makes it possible to recover highly pure hydrogen and effectively utilize hydrogen as an energy source.
  • the line L3 may be connected to equipment for storing hydrogen or equipment for controlling the amount of hydrogen supplied. This allows the generated and recovered hydrogen to be used as an energy source as appropriate.
  • the carbon dioxide fixation method using seawater in this embodiment uses carbonate ions generated when carbon dioxide is dissolved in water (seawater) and divalent ions (calcium ions, magnesium ions, etc.) contained in seawater. It is based on a carbonate fixation process in which carbonates are reacted to form a form that can be recovered as carbonates.
  • the carbon dioxide fixation method in this embodiment includes a step of bringing carbon dioxide and seawater into contact (mixing) in advance, alkalizing the seawater and promoting carbonate ionization of carbon dioxide. This is the result.
  • the carbonate ions (CO 3 2- ) generated in Formula 1 react with divalent metal ions contained in seawater and become carbonate.
  • carbonate ions (CO 3 2 ⁇ ) react with calcium ions (Ca 2+ ) contained in seawater to generate carbonate (calcium carbonate). This progresses the carbon dioxide fixation process.
  • Equation 1 From Equations 1 and 2, it can be seen that by allowing the chemical equilibrium reaction to proceed in the direction of producing carbonate ions, it is possible to improve the efficiency of carbon dioxide fixation treatment. In other words, it can be seen that by advancing the chemical equilibrium in Equation 1 toward the right side and increasing the amount of carbonate ions in Equation 2, it is possible to improve the reaction efficiency of carbonation related to carbon dioxide fixation treatment.
  • FIG. 2 is a graph showing the relationship between the pH of seawater and the abundance ratio of carbonic substances (carbonic acid, bicarbonate ions, carbonate ions) in seawater (1 atmosphere, 25 degrees Celsius).
  • the horizontal axis represents the pH of seawater
  • the vertical axis represents the abundance ratio of each carbonate substance.
  • the abundance ratio of carbonate ions is the highest among the three types of carbonic substances in seawater.
  • carbonate ions present in seawater are 90% or more.
  • the conventional method is to alkalize seawater (pH 10 or higher) and then supply carbon dioxide to increase the abundance ratio of carbonate ions and advance the reaction with divalent ions, resulting in carbonation. things were being done.
  • seawater electrolysis is performed as a means to alkalize seawater.
  • Alkalinization of seawater by electrolysis of seawater is also related to the carbon dioxide fixation method in this embodiment, and will be described in detail later. Note that, as described above, while a higher pH makes it possible to increase the abundance ratio of carbonate ions, the electric power required to alkalize seawater increases.
  • divalent metal ions contained in seawater are not limited to calcium ions, and other divalent metal ions also exist.
  • magnesium ions present in seawater undergo a reaction to produce magnesium hydroxide as shown in Formula 3.
  • the calcium carbonate production reaction based on Formula 2 and the magnesium hydroxide production reaction based on Formula 3 are both inorganic salt production reactions promoted under an alkali. Therefore, the present inventors conducted a study regarding which of the reactions of Formula 2 and Formula 3 progresses more as seawater becomes alkaline.
  • FIG. 3 is a graph showing the relationship between the content (%) of each composition in the precipitate produced by the inorganic salt production reaction accompanying the alkalinization of seawater and the pH of seawater (artificial seawater). More specifically, FIG. 3 shows that among the compositions determined from the precipitate, calcium derived from calcium carbonate produced in the production reaction based on formula 2, and magnesium derived from magnesium hydroxide produced in the production reaction based on formula 3. This is a graph showing the relationship between its content and pH. In FIG. 3, calcium derived from calcium carbonate is indicated by a black triangle ( ⁇ ), and magnesium derived from magnesium hydroxide is indicated by an open square ( ⁇ ). As shown in FIG.
  • the present inventors determined that the alkalinization of seawater (pH 10) is lower than that of the conventional method, from the viewpoint of energy consumption required for alkalinization by electrolysis of seawater, and from the viewpoint of suppressing the magnesium hydroxide production reaction. It has been found that it is preferable to carry out carbonation at pH. As a result of further studies based on this knowledge, the present inventors arrived at the carbon dioxide fixation method of this embodiment.
  • the carbon dioxide fixation method in this embodiment is based on the findings from the study results of the present inventors, and more specifically, by electrolyzing seawater in which the dissolved carbon dioxide concentration has been increased in advance. This is based on the knowledge that in addition to improving the carbonate production efficiency due to the common ion effect, it is possible to suppress the magnesium hydroxide production reaction and make the carbonate production reaction dominant.
  • the carbon dioxide fixation method in this embodiment is to fix carbon dioxide by electrolytically treating seawater in which carbon dioxide is dissolved using the carbon dioxide fixation system 10 in this embodiment. be.
  • FIGS. 4 and 5 are schematic explanatory diagrams showing steps related to carbon dioxide fixation in the electrolysis unit 20 of the carbon dioxide fixation system 10 of this embodiment.
  • the configuration inside the processing tank 21 in FIGS. 4 and 5 is the same as the configuration shown in FIG. 1.
  • FIGS. 4 and 5 mainly illustrate configurations involved in each process, and illustration of some configurations is omitted.
  • FIG. 5 mainly shows the movement of ions and molecules related to fixation of carbon dioxide, and some ions and molecules are not shown.
  • FIG. 4 is a schematic explanatory diagram showing the first step.
  • seawater is introduced into the cathode side (space 24b) of the processing tank 21 via line L1
  • electrolyte E is introduced into the anode side (space 24a) of processing tank 21 via line L2.
  • carbon dioxide is blown into the seawater introduced to the cathode side by the carbon dioxide supply unit 30 to increase the concentration of dissolved carbon dioxide in the seawater.
  • FIG. 5 is a schematic explanatory diagram showing the second step. As shown in FIG. 5, a voltage (or constant current) is applied between the electrodes 22a and 22b using a DC power source to perform electrolysis. At this time, the reaction at the electrode 22a in the space 24a (reaction on the anode side) is expressed by the following equation 4.
  • the hydrogen ions generated according to Formula 4 move to the space 24b side via the cation exchanger 23, as shown in FIG. Further, the oxygen generated by Equation 4 may be recovered via the line L4, or may be discharged directly to the outside of the system.
  • an electrolytic solution electrolytic solution E
  • chloride is removed from the cathode side by the cation exchanger 23. The movement of physical ions to the anode side is suppressed. Therefore, unlike normal seawater electrolysis, the reaction in which chloride ions become chlorine gas does not proceed.
  • reaction at the electrode 22b in the space 24b (reaction on the cathode side) is expressed by the following equation 5.
  • Carbon dioxide fixation treatment was performed using the carbon dioxide fixation method and carbon dioxide fixation system 10 in this embodiment described above.
  • a constant current was applied between the electrodes 22a and 22b to perform electrolysis.
  • electrolysis was performed at a current value of 300 mA, 600 mA, or 900 mA. Then, the precipitate generated by electrolysis was collected, dried, and then subjected to component analysis to determine the composition and content of the precipitate.
  • FIG. 6 is a graph showing the results of an example of carbon dioxide fixation treatment using the carbon dioxide fixation method and carbon dioxide fixation system 10 in this embodiment. More specifically, FIG. 6 shows, among the compositions determined from the precipitate produced by electrolysis, calcium derived from calcium carbonate produced in the production reaction based on formula 2, and hydroxide produced in the production reaction based on formula 3. Regarding magnesium derived from magnesium, the relationship between the content (%) of each composition in the precipitate and the pH on the cathode side after electrolysis is made into a graph. Note that FIGS. 6(A) to 6(C) show graphs related to the results when the electrolytic conditions were current values of 300 mA, 600 mA, and 900 mA, respectively. In addition, in FIGS. 6(A) to 6(C), calcium derived from calcium carbonate is indicated by a black triangle ( ⁇ ), and magnesium derived from magnesium hydroxide is indicated by an open square ( ⁇ ).
  • the pH near the electrode 22b locally increases due to the reaction based on Formula 5. Therefore, as shown in FIG. 6C, it is considered that the higher the applied current value, the more alkaline the pH near the electrode 22b is than the pH of the entire cathode side. Therefore, in FIG. 6C, it is considered that the reaction for producing magnesium hydroxide progressed near the electrode 22b, and the reaction related to carbonation was suppressed. Therefore, by providing the carbon dioxide fixation system 10 of this embodiment with a means for forming a water flow (stirring flow) near the electrode 22b, local high alkalinization can be eliminated, thereby increasing the reaction efficiency related to carbonation. It becomes possible to suppress the influence of the applied current value on.
  • an electrolytic section in which a cation exchanger is arranged between the electrodes is used, and the cathode side
  • electrolysis is performed, and as the pH increases, carbonate ions increase on the cathode side, improving the carbonate production efficiency.
  • the pH does not rise to the point where the magnesium hydroxide production reaction becomes dominant, making it possible to suppress the magnesium hydroxide production reaction.
  • seawater as an electrolyte solution and a source of divalent ions
  • the embodiments described above are examples of a carbon dioxide fixation method and a carbon dioxide fixation system.
  • the carbon dioxide fixation method and carbon dioxide fixation system according to the present invention are not limited to the embodiments described above, and the carbon dioxide fixation method and carbon dioxide fixation system according to the embodiments described above are not limited to the embodiments described above. Variations in the method and carbon dioxide fixation system may be made.
  • various means for efficiently performing electrolysis may be added to the electrolysis unit 20 in the carbon dioxide fixation system 10 of this embodiment.
  • examples of such means include means for suppressing the formation of precipitates on the surfaces of the electrodes 22a and 22b, and means for suppressing reduction in the ion permeation efficiency of the cation exchanger 23. Examples include means.
  • the carbon dioxide fixation system 10 and the carbon dioxide fixation method use an electrolytic solution that does not contain chloride ions and suppress the generation of chlorine gas from the viewpoint of environmental impact.
  • the electrolytic solution E may be one containing chloride ions, such as seawater.
  • the reaction related to carbonation is promoted, and on the anode side, chlorine (Cl 2 ) generated at the electrode 22a (anode) and chlorine-containing components (Cl 2 ) generated when chlorine is dissolved in the electrolytic solution
  • Hypochlorous acid (HClO) and hypochlorite ions (ClO - )) may be recovered and utilized outside the system.
  • sterilization and biofouling control can be performed. Examples include.
  • the carbon dioxide fixation method and carbon dioxide fixation system of the present invention can be suitably used as a carbonate fixation treatment to carbonate carbon dioxide.

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Abstract

The present invention addresses the problem of providing a carbon dioxide fixation method and a carbon dioxide fixation system which are capable of fixing carbon dioxide at high efficiency, low cost, and low energy. To resolve the problem, provided are a carbon dioxide fixation method and a carbon dioxide fixation system for a carbon dioxide fixation treatment using seawater, wherein an electrolysis unit in which a cation exchanger is arranged between electrodes is used, and electrolysis is performed after supplying carbon dioxide to the seawater introduced to the cathode side of the electrolysis unit. According to the present invention, it is possible to suppress magnesium hydroxide production reactions and make carbonate production reactions dominant, in addition to improving the carbonate production efficiency by means of the common ion effect. In addition, according to the present invention, efficient carbonation can be performed at a lower pH than conventional methods. This makes it possible to fix carbon dioxide at high efficiency, low cost, and low energy.

Description

二酸化炭素固定化方法及び二酸化炭素固定化システムCarbon dioxide fixation method and carbon dioxide fixation system
　本発明は、二酸化炭素固定化方法及び二酸化炭素固定化システムに関するものである。特に、本発明は、海水を用いて二酸化炭素の固定化を行う二酸化炭素固定化方法及び二酸化炭素固定化システムに関するものである。 The present invention relates to a carbon dioxide fixation method and a carbon dioxide fixation system. In particular, the present invention relates to a carbon dioxide fixation method and a carbon dioxide fixation system for fixing carbon dioxide using seawater.
　近年、地球温暖化などの環境問題に対して大きな影響を与えるとされる二酸化炭素について、環境への排出を抑制することが早急に対応すべき課題となっている。この課題に対し、二酸化炭素の排出量自体を削減する技術や、排出された二酸化炭素を回収し、固定化する技術に係る研究が進められている。 In recent years, controlling carbon dioxide emissions into the environment, which is said to have a major impact on environmental problems such as global warming, has become an issue that must be addressed immediately. To address this issue, research is underway on technologies to reduce carbon dioxide emissions themselves and technologies to capture and fix emitted carbon dioxide.
　特に、二酸化炭素の回収・固定化に係る技術についても、様々な方法が検討されている。例えば、二酸化炭素含有ガスから二酸化炭素を回収する方法として、モノエタノールアミンなどの吸収液に二酸化炭素を溶解させる化学吸収法や、ガス吸着能を有する吸着剤に二酸化炭素を吸着させる物理吸着法のほか、膜を用いた膜分離法などが知られている。また、これらの方法以外に、大気中の二酸化炭素濃度を低減させるという観点から、海洋に二酸化炭素を供給することで、海洋中に二酸化炭素を貯留し、大気からは二酸化炭素を隔離するという海洋貯留に係る方法が検討されている。 In particular, various methods are being considered regarding technologies related to carbon dioxide capture and fixation. For example, methods for recovering carbon dioxide from carbon dioxide-containing gas include chemical absorption methods in which carbon dioxide is dissolved in an absorption liquid such as monoethanolamine, and physical adsorption methods in which carbon dioxide is adsorbed on an adsorbent that has gas adsorption ability. In addition, membrane separation methods using membranes are also known. In addition to these methods, from the perspective of reducing the concentration of carbon dioxide in the atmosphere, there is also an ocean-based method that stores carbon dioxide in the ocean and sequesters it from the atmosphere by supplying carbon dioxide to the ocean. Methods related to storage are being considered.
　例えば、特許文献１には、深層の海水を海面付近まで汲み上げ、汲み上げた海水に二酸化炭素を吸収させる二酸化炭素の固定化システムが記載されている。 For example, Patent Document 1 describes a carbon dioxide fixation system that pumps deep seawater to near the sea surface and causes the pumped seawater to absorb carbon dioxide.
特開２０００－２６２８８８号公報Japanese Patent Application Publication No. 2000-262888
　特許文献１に記載されるように、海水に二酸化炭素を吸収させる場合、大気中の二酸化炭素を一時的に海水中に溶存させることができるが、大気中の二酸化炭素分圧との差分により海水中に溶存した二酸化炭素は再び大気中に放散されてしまう。さらに、海水中に効果的に二酸化炭素を溶存させ、海洋における二酸化炭素の貯留量を高めることができたとしても、海洋中に二酸化炭素が溶存することにより、海洋のｐＨが低下するという海洋酸性化を引き起こす可能性がある。 As described in Patent Document 1, when carbon dioxide is absorbed into seawater, carbon dioxide in the atmosphere can be temporarily dissolved in the seawater, but due to the difference between the partial pressure of carbon dioxide in the atmosphere and the carbon dioxide in the seawater. The carbon dioxide dissolved in it is released back into the atmosphere. Furthermore, even if it were possible to effectively dissolve carbon dioxide in seawater and increase the amount of carbon dioxide stored in the ocean, the acidity of the ocean would lower the pH of the ocean due to the dissolution of carbon dioxide in the ocean. may cause oxidation.
　海洋酸性化は、様々な海洋生物の成長や繁殖等に関与し、生態系への影響が懸念されている。また、本来、自然環境下においても海洋には一定量の二酸化炭素が吸収されているが、海洋酸性化により、海洋が吸収できる二酸化炭素の量が減少し、大気中の二酸化炭素が増加する要因ともなり得る。そして、大気中の二酸化炭素濃度が増加すると、海洋表面に接触する二酸化炭素濃度が増加するため、海洋酸性化は解消されることなく進行し続けることになる。このため、海洋酸性化と大気中の二酸化炭素濃度増加という２つの問題が同時に深刻化していくというおそれがある。 Ocean acidification is involved in the growth and reproduction of various marine organisms, and there are concerns about its impact on the ecosystem. In addition, a certain amount of carbon dioxide is normally absorbed by the ocean even in the natural environment, but due to ocean acidification, the amount of carbon dioxide that the ocean can absorb is decreasing, causing an increase in atmospheric carbon dioxide. It can also be. As the concentration of carbon dioxide in the atmosphere increases, the concentration of carbon dioxide in contact with the ocean surface also increases, so ocean acidification will continue to progress without being resolved. As a result, there is a fear that the two problems of ocean acidification and increased atmospheric carbon dioxide concentrations will become more serious at the same time.
　二酸化炭素の固定化に関しては、海水を利用することで大量の二酸化炭素を安価に固定できることが期待されるが、海洋酸性化の解消を考慮した技術が必要となる。
　また、二酸化炭素の固定化に係る技術においては、二酸化炭素の固定化を高効率化することに加え、環境負荷低減の観点から、二酸化炭素の固定化に使用するエネルギーや薬品使用に伴うコストを低減することも大きな課題となる。 Regarding the fixation of carbon dioxide, it is expected that large amounts of carbon dioxide can be fixed at low cost by using seawater, but technology that takes into account the solution to ocean acidification will be needed.
In addition to improving the efficiency of carbon dioxide fixation, technologies related to carbon dioxide fixation also aim to reduce the costs associated with energy and chemical use for carbon dioxide fixation, from the perspective of reducing environmental impact. Reducing this is also a major challenge.
　本発明の課題は、高効率、かつ低コスト・低エネルギーで二酸化炭素を固定化することができる二酸化炭素固定化方法及び二酸化炭素固定化システムを提供することである。 An object of the present invention is to provide a carbon dioxide fixation method and a carbon dioxide fixation system that can fix carbon dioxide with high efficiency and at low cost and low energy.
　本発明者は、上記の課題について鋭意検討した結果、二酸化炭素の固定化において、海水を用いること及び海水に二酸化炭素を供給した後で電解を行うことにより、高効率、かつ低コスト・低エネルギーで二酸化炭素の固定化が可能となることを見出して、本発明を完成した。
　すなわち、本発明は、以下の二酸化炭素固定化方法及び二酸化炭素固定化システムである。 As a result of intensive study on the above-mentioned issues, the present inventor has found that carbon dioxide fixation can be achieved with high efficiency, low cost, and low energy consumption by using seawater and by performing electrolysis after supplying carbon dioxide to seawater. The present invention was completed by discovering that it is possible to fix carbon dioxide.
That is, the present invention provides the following carbon dioxide fixation method and carbon dioxide fixation system.
　上記課題を解決するための本発明の二酸化炭素固定化方法は、海水を用いて二酸化炭素を固定する方法であって、電極間に陽イオン交換体を配置した電解部を用い、電解部のカソード側に導入された海水に対して二酸化炭素を供給した後、電解を行うという特徴を有する。 The carbon dioxide fixation method of the present invention for solving the above problems is a method of fixing carbon dioxide using seawater, which uses an electrolytic section in which a cation exchanger is arranged between electrodes, and a cathode of the electrolytic section. It has the feature that electrolysis is performed after supplying carbon dioxide to the seawater introduced to the side.
　海水は、二酸化炭素の固定化における炭酸塩化の原料となる二価イオンが既にイオンの状態で存在し、かつ、一定量の二価イオンが含まれている。したがって、本発明の二酸化炭素固定化方法は、海水を電解質溶液及び二価イオン源として用いることで、二酸化炭素の固定化に必要な二価イオンの原料調達にかかるコスト及びエネルギーを大幅に低減させることができる。 In seawater, divalent ions, which are the raw materials for carbonation in the fixation of carbon dioxide, already exist in the ionic state, and contain a certain amount of divalent ions. Therefore, the carbon dioxide fixation method of the present invention uses seawater as an electrolyte solution and a divalent ion source, thereby significantly reducing the cost and energy required to procure raw materials for divalent ions necessary for carbon dioxide fixation. be able to.
　また、従来法として、水中に溶解した二酸化炭素の炭酸イオン化を促進し、炭酸塩生成効率を高めることを目的として、アルカリ化した溶液に二酸化炭素を供給することが行われているが、この場合、アルカリ化するためのエネルギーや薬品を要することに加え、海水を用いた場合には、炭酸塩の生成反応以外の反応（水酸化マグネシウムの生成反応など）が生じるため、結果として、炭酸塩生成効率向上や、低コスト・低エネルギーでの二酸化炭素固定化が困難となる。
　一方、本発明者は、あらかじめ溶存二酸化炭素濃度を高めた海水に対して電解を行うことにより、共通イオン効果による炭酸塩生成効率の向上に加え、水酸化マグネシウムの生成反応を抑制し、炭酸塩の生成反応を優勢化させることができるという知見を得た。
　本発明の二酸化炭素固定化方法は、この知見に基づくものであり、電極間に陽イオン交換体を配置した電解部を用い、カソード側に導入された海水に二酸化炭素を供給して溶存二酸化炭素濃度を高めた後、電解を行うことで、カソード側ではｐＨの上昇とともに炭酸イオンが増加して炭酸塩の生成効率が向上する一方、水酸化マグネシウムの生成反応が優勢となる条件までｐＨが上昇せず、水酸化マグネシウムの生成反応は抑制することが可能となる。これにより、高効率、かつ低コスト・低エネルギーで二酸化炭素の固定化を行うことが可能となる。 In addition, as a conventional method, carbon dioxide is supplied to an alkalized solution in order to promote the carbonate ionization of carbon dioxide dissolved in water and increase the carbonate production efficiency. In addition to requiring energy and chemicals for alkalization, when seawater is used, reactions other than carbonate production reactions (such as magnesium hydroxide production reactions) occur, resulting in carbonate production. It becomes difficult to improve efficiency and fix carbon dioxide at low cost and low energy.
On the other hand, by electrolyzing seawater with a high concentration of dissolved carbon dioxide in advance, the present inventor not only improved the carbonate production efficiency due to the common ion effect, but also inhibited the production reaction of magnesium hydroxide, resulting in carbonate formation. We obtained the knowledge that it is possible to make the production reaction dominant.
The carbon dioxide fixation method of the present invention is based on this knowledge, and uses an electrolytic section in which a cation exchanger is placed between the electrodes to supply carbon dioxide to seawater introduced to the cathode side, thereby removing dissolved carbon dioxide. By performing electrolysis after increasing the concentration, carbonate ions increase on the cathode side as the pH increases, improving the carbonate production efficiency, while the pH increases to the point where the magnesium hydroxide production reaction becomes dominant. This makes it possible to suppress the production reaction of magnesium hydroxide. This makes it possible to fix carbon dioxide with high efficiency, low cost, and low energy.
　また、本発明の二酸化炭素固定化方法の一実施態様としては、電解部のアノード側には、塩化物イオンを含まない電解液が導入されるという特徴を有する。
　一般的に、海水の電解を行う場合、海水に含まれる塩化物イオンに起因して、アノード側では塩素ガスが発生する。この塩素ガスについては環境負荷が大きく、大気に直接放出することはできず、回収して無害化処理を行う必要があるため、二酸化炭素固定化におけるコスト増につながってしまう。
　一方、この特徴によれば、電極間に陽イオン交換体を配置した電解部のカソード側には海水を導入する一方、アノード側には塩化物イオンを含まない電解液を導入し、電解を行うことで、カソード側から塩化物イオンがアノード側に移動することを陽イオン交換体によって抑制し、アノード側では塩素ガス発生の要因となる塩化物イオンが存在しない状態を維持したまま電解を行うことが可能となる。これにより、電解部において海水を用いた電解を行う際に、塩素ガスが発生することを抑制し、低コストかつ環境負荷の低減を可能とした二酸化炭素固定化を行うことができる。 Further, one embodiment of the carbon dioxide fixation method of the present invention is characterized in that an electrolytic solution containing no chloride ions is introduced to the anode side of the electrolytic section.
Generally, when electrolyzing seawater, chlorine gas is generated on the anode side due to chloride ions contained in the seawater. This chlorine gas has a large environmental impact and cannot be directly released into the atmosphere, but must be recovered and detoxified, leading to increased costs for carbon dioxide fixation.
On the other hand, according to this feature, seawater is introduced into the cathode side of the electrolytic section in which a cation exchanger is arranged between the electrodes, while an electrolytic solution containing no chloride ions is introduced into the anode side, and electrolysis is performed. By doing so, the movement of chloride ions from the cathode side to the anode side is suppressed by the cation exchanger, and electrolysis can be performed while maintaining the absence of chloride ions that cause chlorine gas generation on the anode side. becomes possible. Thereby, when performing electrolysis using seawater in the electrolysis section, generation of chlorine gas can be suppressed, and carbon dioxide fixation can be performed at low cost and with a reduced environmental load.
　また、上記課題を解決するための本発明の二酸化炭素固定化システムは、海水を用いて二酸化炭素を固定するシステムであって、電極間に陽イオン交換体を配置した電解部を備え、電解部のカソード側には海水及び二酸化炭素を導入し、電解部のアノード側には塩化物イオンを含まない電解液を導入するという特徴を有する。
　本発明の二酸化炭素固定化システムによれば、電解部のカソード側に導入される海水を電解質溶液及び二価イオン源として用いることで、二酸化炭素の固定化に必要な二価イオンの原料調達にかかるコスト及びエネルギーを大幅に低減させることができる。また、本発明の二酸化炭素固定化システムを用いることで、電解時のカソード側においてはｐＨ上昇に伴い炭酸塩の生成反応が進行する一方、電解時のアノード側では環境負荷の大きい塩素ガス発生を抑制することができる。これにより、高効率、かつ低コスト・低エネルギーで二酸化炭素の固定化を行うことが可能となる。 Further, the carbon dioxide fixation system of the present invention for solving the above problems is a system for fixing carbon dioxide using seawater, and includes an electrolytic section in which a cation exchanger is arranged between electrodes. Seawater and carbon dioxide are introduced into the cathode side of the electrolytic section, and an electrolytic solution containing no chloride ions is introduced into the anode side of the electrolytic section.
According to the carbon dioxide fixation system of the present invention, by using seawater introduced into the cathode side of the electrolytic part as an electrolyte solution and a source of divalent ions, it is possible to procure raw materials for divalent ions necessary for fixing carbon dioxide. Such costs and energy can be significantly reduced. In addition, by using the carbon dioxide fixation system of the present invention, the carbonate production reaction progresses as the pH increases on the cathode side during electrolysis, while the generation of chlorine gas, which has a large environmental impact, is prevented on the anode side during electrolysis. Can be suppressed. This makes it possible to fix carbon dioxide with high efficiency, low cost, and low energy.
　本発明によれば、高効率、かつ低コスト・低エネルギーで二酸化炭素を固定化することができる二酸化炭素固定化方法及び二酸化炭素固定化システムを提供することができる。 According to the present invention, it is possible to provide a carbon dioxide fixation method and a carbon dioxide fixation system that can fix carbon dioxide with high efficiency and at low cost and low energy.
本発明の実施態様における二酸化炭素固定化システムの概略説明図である。1 is a schematic explanatory diagram of a carbon dioxide fixation system in an embodiment of the present invention. 海水のｐＨと、海水中の炭酸物質の存在比の関係を示すグラフである。It is a graph showing the relationship between the pH of seawater and the abundance ratio of carbonic substances in seawater. 海水のアルカリ化に伴う無機塩生成反応により生成した沈殿物における各組成の含有率と、ｐＨの関係を示すグラフである。1 is a graph showing the relationship between the content of each composition in a precipitate generated by an inorganic salt production reaction associated with alkalinization of seawater and pH. 本発明の実施態様における二酸化炭素固定化方法の一工程（第１工程）を示す概略説明図である。FIG. 1 is a schematic explanatory diagram showing one step (first step) of a carbon dioxide fixation method in an embodiment of the present invention. 本発明の実施態様における二酸化炭素固定化方法の他の工程（第２工程）を示す概略説明図である。FIG. 2 is a schematic explanatory diagram showing another step (second step) of the carbon dioxide fixation method in the embodiment of the present invention. 本発明の実施態様における二酸化炭素固定化方法及び二酸化炭素固定化システムを用いた二酸化炭素固定化処理の実施例に係る結果を示すグラフである。1 is a graph showing results of an example of carbon dioxide fixation treatment using a carbon dioxide fixation method and a carbon dioxide fixation system in an embodiment of the present invention.
　以下、図面を参照しつつ本発明に係る二酸化炭素固定化方法及び二酸化炭素固定化システムの実施態様を詳細に説明する。
　なお、実施態様に記載する二酸化炭素固定化方法及び二酸化炭素固定化システムについては、本発明に係る二酸化炭素固定化方法及び二酸化炭素固定化システムを説明するために例示したにすぎず、これに限定されるものではない。 EMBODIMENT OF THE INVENTION Hereinafter, embodiments of the carbon dioxide fixation method and carbon dioxide fixation system according to the present invention will be described in detail with reference to the drawings.
The carbon dioxide fixation method and carbon dioxide fixation system described in the embodiments are merely exemplified to explain the carbon dioxide fixation method and carbon dioxide fixation system according to the present invention, and are not limited thereto. It is not something that will be done.
　本発明の二酸化炭素固定化方法及び二酸化炭素固定化システムにおいて、固定化を行う対象である二酸化炭素の供給源（又は発生源）については、特に限定されない。具体的な二酸化炭素の供給源の例としては、例えば、生活・産業活動に伴い、各種施設（発電施設・工場・一般家庭等）や運輸手段から排出される二酸化炭素を含むガスのほか、大気や火山ガス等、天然に存在する二酸化炭素を含むガスなどが挙げられる。 In the carbon dioxide fixation method and carbon dioxide fixation system of the present invention, the source (or source) of carbon dioxide to be fixed is not particularly limited. Examples of specific sources of carbon dioxide include gas containing carbon dioxide emitted from various facilities (power generation facilities, factories, general households, etc.) and means of transportation during daily life and industrial activities; Examples include naturally occurring gases containing carbon dioxide, such as volcanic gases and volcanic gases.
（二酸化炭素固定化システム）
　本発明の二酸化炭素固定化システムは、海水を用いて二酸化炭素の固定化を行うものであり、より具体的には、あらかじめ二酸化炭素を溶解させた海水の電解を行うことで、炭酸イオンの生成を促進し、カソード側において炭酸イオンと海水中の二価イオンとを反応させて炭酸塩化することで二酸化炭素の固定化を行うものである。
　また、本発明の二酸化炭素固定化システムは、アノード側に塩化物イオンを含まない電解液を用いることで、一般的な海水の電解では生じてしまう塩素ガスの発生を抑制した状態で二酸化炭素の固定化を行うものである。 (carbon dioxide fixation system)
The carbon dioxide fixation system of the present invention uses seawater to fix carbon dioxide. More specifically, by electrolyzing seawater in which carbon dioxide has been dissolved in advance, carbonate ions are generated. This method promotes carbon dioxide and fixes carbon dioxide by reacting carbonate ions with divalent ions in seawater on the cathode side to convert them into carbonates.
In addition, the carbon dioxide fixation system of the present invention uses an electrolyte that does not contain chloride ions on the anode side, thereby suppressing the generation of chlorine gas that occurs in general seawater electrolysis. It performs immobilization.
　図１は、本発明の実施態様に係る二酸化炭素固定化システムの構造を示す概略説明図である。
　本実施態様における二酸化炭素固定化システム１０は、図１に示すように、二酸化炭素を含む海水が導入され、海水の電解を行う電解部２０を有している。また、電解部２０に対し、海水を導入する海水導入部（ラインＬ１）、二酸化炭素を供給する二酸化炭素供給部３０、塩化物イオンを含まない電解液（以下、単に「電解液Ｅ」と呼ぶ）を導入する電解液導入部（ラインＬ２）を備えるものである。 FIG. 1 is a schematic explanatory diagram showing the structure of a carbon dioxide fixation system according to an embodiment of the present invention.
As shown in FIG. 1, the carbon dioxide fixation system 10 in this embodiment includes an electrolysis section 20 into which seawater containing carbon dioxide is introduced and performs electrolysis of the seawater. Further, to the electrolytic section 20, a seawater introduction section (line L1) that introduces seawater, a carbon dioxide supply section 30 that supplies carbon dioxide, and an electrolytic solution that does not contain chloride ions (hereinafter simply referred to as "electrolytic solution E") ) is provided with an electrolyte introduction section (line L2) for introducing the electrolyte.
　電解部２０に導入する海水の供給源（以下、「海水源」と呼ぶ）は、特に限定されない。例えば、自然環境（海洋）を海水源とし、電解部２０に海洋から直接海水を導入するものとしてもよく、二酸化炭素の海洋貯留処理や船舶のバラスト水として用いられる海水など、人為的に一時貯留された海水を海水源として用いるものとしてもよい。
　なお、海水の原料調達にかかるコストは、主として海水の搬送に係るコストとなる。例えば、本発明の二酸化炭素固定化システム１０を海に近い陸地あるいは海上（船舶等を含む）に設置することにより、最小限の搬送コストで海水を利用することが可能となる。 The supply source of seawater introduced into the electrolysis section 20 (hereinafter referred to as "seawater source") is not particularly limited. For example, the natural environment (ocean) may be used as a seawater source, and seawater may be introduced directly from the ocean into the electrolyzer 20, or seawater may be artificially stored temporarily, such as seawater used for ocean storage treatment of carbon dioxide or as ballast water for ships. The seawater that has been removed may be used as a seawater source.
Note that the cost of raw material procurement of seawater is mainly the cost of transporting seawater. For example, by installing the carbon dioxide fixation system 10 of the present invention on land near the sea or on the sea (including ships, etc.), seawater can be used with minimal transportation costs.
　図１に示すように、本実施態様における電解部２０は、処理槽２１内に、一対の電極（電極２２ａ、２２ｂ）と、陽イオン交換体２３が設けられている。なお、図１に示すように、処理槽２１内は、陽イオン交換体２３を介して、２つの空間を形成している（空間２４ａ、２４ｂ）。 As shown in FIG. 1, the electrolysis section 20 in this embodiment includes a pair of electrodes (electrodes 22a, 22b) and a cation exchanger 23 in a processing tank 21. In addition, as shown in FIG. 1, the inside of the processing tank 21 forms two spaces (spaces 24a and 24b) via the cation exchanger 23.
　処理槽２１は、海水や電解液を安定して貯留可能となるように形成されているものであればよく、特に素材や形状は問わない。例えば、電解槽や電気透析槽として知られている構造に用いられる素材や形状を使用すること等が挙げられる。 The treatment tank 21 may be of any material or shape as long as it is formed so as to be able to stably store seawater or electrolyte. For example, materials and shapes used in structures known as electrolytic cells and electrodialysis cells may be used.
　電極２２ａ、２２ｂは、それぞれ空間２４ａ、２４ｂ内に設けられ、導線を用いて接続されている。なお、電極２２ａ、２２ｂは、陽イオン交換体２３の表面あるいは近傍に設け、電極２２ａ、２２ｂ及び陽イオン交換体２３を一体化したユニットとして扱うものとしてもよい。
　電極２２ａ、２２ｂとしては、アノード又はカソードとして機能するものであればよく、材質及び形状については特に限定されない。本実施態様においては、電極２２ａがアノードとして機能し、電極２２ｂがカソードとして機能するものとして、以下の説明を行う。
　電極２２ａ、２２ｂの材質の例としては、例えば、電気化学分野で電極材料として広く用いられている炭素や金属（ステンレス、白金、銅等）が挙げられる。また、電極２２ａ、２２ｂの形状の例としては、例えば、平板状、棒状、メッシュ状などが挙げられる。なお、電極２２ａ、２２ｂを陽イオン交換体２３の表面あるいは近傍に設ける場合、陽イオン交換体２３に対する物質移動の阻害を抑制できる形状とすることが好ましい。このような形状としては、例えば、メッシュ状や針金等の細い棒状などが挙げられる。さらに、電極２２ａ、２２ｂの別の例としては、メッキ処理などの手法により、陽イオン交換体２３の表面に直接電極パターンを作成するもの等が挙げられる。このとき、電極パターンの形状は特に限定されないが、陽イオン交換体２３に対する物質移動の阻害を抑制できるものとすることが好ましい。 Electrodes 22a and 22b are provided in spaces 24a and 24b, respectively, and are connected using conductive wires. Note that the electrodes 22a, 22b may be provided on or near the surface of the cation exchanger 23, and the electrodes 22a, 22b and the cation exchanger 23 may be treated as an integrated unit.
The electrodes 22a and 22b may be of any type as long as they function as an anode or a cathode, and there are no particular limitations on the material and shape. In this embodiment, the following explanation will be given assuming that the electrode 22a functions as an anode and the electrode 22b functions as a cathode.
Examples of materials for the electrodes 22a and 22b include carbon and metals (stainless steel, platinum, copper, etc.) that are widely used as electrode materials in the electrochemical field. Further, examples of the shape of the electrodes 22a and 22b include, for example, a flat plate shape, a rod shape, a mesh shape, and the like. Note that when the electrodes 22a and 22b are provided on the surface of the cation exchanger 23 or in the vicinity thereof, it is preferable that they have a shape that can suppress inhibition of mass transfer to the cation exchanger 23. Examples of such a shape include a mesh shape and a thin rod shape such as a wire. Furthermore, another example of the electrodes 22a and 22b is one in which an electrode pattern is created directly on the surface of the cation exchanger 23 by a method such as plating. At this time, the shape of the electrode pattern is not particularly limited, but it is preferable that the shape can suppress the inhibition of mass transfer to the cation exchanger 23.
　また、電極２２ａ及び２２ｂを導線により接続する際、電極間に電気エネルギーを供給するための直流電源を設けることが好ましい。このとき、一対の電極に接続される直流電源に対する給電手段については特に限定されないが、太陽光、風力、波力などの再生可能エネルギーを利用した給電設備や他の施設における余剰電力を利用するものとすることが好ましい。これにより、電解部２０における海水の電解時に使用するエネルギーを低減させることが可能となる。特に、発電に際して二酸化炭素を排出しない再生可能エネルギーを用いた給電手段を採用することで、二酸化炭素の排出抑制を推進することができるという効果も奏する。 Furthermore, when connecting the electrodes 22a and 22b with a conductive wire, it is preferable to provide a DC power source for supplying electrical energy between the electrodes. At this time, the power supply means for the DC power supply connected to the pair of electrodes is not particularly limited, but may be one that uses power supply equipment that uses renewable energy such as solar, wind, or wave power, or surplus power from other facilities. It is preferable that This makes it possible to reduce the energy used during electrolysis of seawater in the electrolysis section 20. In particular, by adopting a power supply means that uses renewable energy that does not emit carbon dioxide during power generation, it is also effective in promoting the reduction of carbon dioxide emissions.
　陽イオン交換体２３は、処理槽２１を区画し、アノード（電極２２ａ）が配置された空間２４ａ（以下、「アノード側」とも呼ぶ）からカソード（電極２２ｂ）が配置された空間２４ｂ（以下、「カソード側」とも呼ぶ）へ、陽イオンを選択的に透過することができる膜である。本実施態様における陽イオン交換体２３としては、カソード側の塩化物イオンがアノード側に移動することを抑制するとともに、アノード側の水素イオン（Ｈ＋）がカソード側に移動できる膜であることが好ましい。これにより、アノード側で塩素ガスが発生することを抑制するとともに、アノード側で発生した水素イオンをカソード側に移動させ、カソード側において水素生成を伴う反応の反応効率を高めることが可能となる。
　本実施態様においては、陽イオン交換体２３としては、陰イオンの移動を制限し、かつ、少なくとも水素イオンを透過させる機能を有するものであればよく、具体的な成分や構造については特に限定されない。例えば、一価の陽イオンを選択的に透過できるように処理したもの（いわゆる一価イオン選択膜）や、一価の陽イオンに加え、二価以上の陽イオンの移動が可能である公知の陽イオン交換膜を用いることができる。 The cation exchanger 23 divides the treatment tank 21 into a space 24a (hereinafter also referred to as "anode side") where an anode (electrode 22a) is located and a space 24b (hereinafter also referred to as "anode side") where a cathode (electrode 22b) is located. It is a membrane that can selectively permeate cations to the cathode side (also called the cathode side). The cation exchanger 23 in this embodiment is preferably a membrane that suppresses chloride ions on the cathode side from moving to the anode side and allows hydrogen ions (H + ) on the anode side to move to the cathode side. preferable. This makes it possible to suppress the generation of chlorine gas on the anode side, move hydrogen ions generated on the anode side to the cathode side, and increase the reaction efficiency of the reaction involving hydrogen production on the cathode side.
In this embodiment, the cation exchanger 23 is not particularly limited as long as it has the function of restricting the movement of anions and transmitting at least hydrogen ions, and there are no particular limitations on the specific components or structure. . For example, membranes treated to selectively allow monovalent cations to permeate (so-called monovalent ion-selective membranes), and known membranes that allow the transfer of divalent or higher cations in addition to monovalent cations. A cation exchange membrane can be used.
　処理槽２１には、海水源から電解部２０のカソード側（空間２４ｂ）に海水を導入する海水導入部としてのラインＬ１と、電解部２０のアノード側（空間２４ａ）に電解液Ｅを導入する電解液導入部としてのラインＬ２が接続されている。 The treatment tank 21 has a line L1 as a seawater introduction section that introduces seawater from a seawater source to the cathode side (space 24b) of the electrolytic section 20, and an electrolyte E that is introduced to the anode side (space 24a) of the electrolytic section 20. A line L2 as an electrolyte introduction part is connected.
　電解部２０のカソード側に海水を導入するラインＬ１は、空間２４ｂと接続し、海水の安定した移送が可能な材質及び構造を有するものであればよく、特に限定されない。
　なお、ラインＬ１上には、海水中の夾雑物や生物が処理槽２１内に混入することを防ぐための手段を備えることが好ましい。例えば、海水中の夾雑物や生物を捕捉するためのフィルターやネットをラインＬ１上に設けることが挙げられる。 The line L1 that introduces seawater to the cathode side of the electrolysis section 20 is not particularly limited as long as it is connected to the space 24b and has a material and structure that allows stable transfer of seawater.
Note that it is preferable to provide a means for preventing contaminants and living organisms in the seawater from entering the treatment tank 21 on the line L1. For example, a filter or a net may be provided on the line L1 to trap impurities and living things in the seawater.
　また、電解部２０のアノード側に電解液Ｅを導入するラインＬ２は、空間２４ａと接続し、電解液Ｅの安定した移送が可能な材質及び構造を有するものであればよく、特に限定されない。
　なお、電解液Ｅは、塩化物イオンを含まず、かつ電気伝導性を有するという要件を満たす溶液であればよく、純水中に電解質（塩化物イオンを含む物質を除く）を溶解させて調製したものを用いることや、既存の電解質溶液（海水等）から塩化物イオンを除去したものを用いることなどが挙げられる。 Further, the line L2 that introduces the electrolytic solution E to the anode side of the electrolytic section 20 is not particularly limited as long as it is connected to the space 24a and has a material and structure that allows stable transfer of the electrolytic solution E.
The electrolytic solution E may be any solution that does not contain chloride ions and satisfies the requirements of having electrical conductivity, and can be prepared by dissolving the electrolyte (excluding substances containing chloride ions) in pure water. For example, using an existing electrolyte solution (such as seawater) from which chloride ions have been removed.
　処理槽２１には、ラインＬ１及びＬ２と併せて、二酸化炭素の供給源（又は発生源）から二酸化炭素を供給する二酸化炭素供給部３０が設けられている。
　二酸化炭素供給部３０としては、カソード側に導入された海水中に二酸化炭素を供給することができるものであればよく、例えば、図１に示すように、配管３１と、吹込部３２と、供給量調整手段３３とを備えるものが挙げられる。 The processing tank 21 is provided with a carbon dioxide supply unit 30 that supplies carbon dioxide from a carbon dioxide supply source (or generation source) in addition to the lines L1 and L2.
The carbon dioxide supply unit 30 may be anything that can supply carbon dioxide into the seawater introduced to the cathode side. For example, as shown in FIG. One example is one that includes a quantity adjusting means 33.
　配管３１は、二酸化炭素の供給源（又は発生源）と処理槽２１（空間２４ｂ）を接続するものであり、配管３１の先端側には、空間２４ｂ内に貯留された海水中に進入し、海水中に二酸化炭素を吹き込むための吹込部３２が設けられている。吹込部３２の構造としては特に限定されない。例えば、配管３１と同様の管径を有する管状構造からなるものや、先端部に向かって管径が小さくなるノズル状構造を有するものなどが挙げられる。吹込部３２により、海水中に直接二酸化炭素を吹き込むことで、海水中の溶存二酸化炭素濃度を効率的に高めることができ、これにより、二酸化炭素の固定化を高効率化することが可能となる。
　また、配管３１上には、吹込部３２を介して供給する二酸化炭素の供給量を調整するための供給量調整手段３３を設ける。供給量調整手段３３としては、流量調節弁のように吹込部３２から供給する二酸化炭素の供給量を調整するもののほか、二酸化炭素を加圧する加圧機構を設け、吹込部３２から海水中に二酸化炭素を供給する際に、二酸化炭素の海水中への溶解効率を高めるものとすること等が挙げられる。 The pipe 31 connects the supply source (or source) of carbon dioxide and the treatment tank 21 (space 24b), and the tip side of the pipe 31 enters seawater stored in the space 24b, A blowing section 32 is provided for blowing carbon dioxide into seawater. The structure of the blowing section 32 is not particularly limited. For example, the tube may have a tubular structure having a diameter similar to that of the pipe 31, or may have a nozzle-like structure where the diameter decreases toward the tip. By blowing carbon dioxide directly into the seawater using the blowing section 32, it is possible to efficiently increase the concentration of dissolved carbon dioxide in the seawater, thereby making it possible to improve the efficiency of carbon dioxide fixation. .
Further, on the pipe 31, a supply amount adjusting means 33 is provided for adjusting the amount of carbon dioxide supplied through the blowing section 32. As the supply amount adjusting means 33, in addition to adjusting the supply amount of carbon dioxide supplied from the blowing part 32, such as a flow rate control valve, a pressurizing mechanism for pressurizing carbon dioxide is provided, and carbon dioxide is supplied from the blowing part 32 into the seawater. When supplying carbon, the dissolution efficiency of carbon dioxide into seawater may be increased.
　さらに、処理槽２１には、電解処理によって生成した気体を回収する手段を設けるものとしてもよい。後述するように、本実施態様における二酸化炭素固定化システム１０では、電解部２０において電解処理を行うことにより、カソード側では水素が生成し、アノード側では酸素が生成する。したがって、処理槽２１にはカソード側で生成する気体（水素）を回収するラインＬ３と、アノード側で生成する気体（酸素）を回収するラインＬ４を設けることが好ましい。
　特に、水素については、次世代のエネルギー源としても注目される物質であり、純度の高い水素の回収・利用を可能とすることが好ましい。そのため、ラインＬ３上に、水素以外の気体（水蒸気など）を除去するための手段を設けるものとしてもよい。これにより、純度の高い水素の回収を行い、水素をエネルギー源として効果的に利用することが可能となる。また、ラインＬ３は、水素を貯留するための設備や水素の供給量を制御するための設備と接続するものとしてもよい。これにより、生成・回収した水素を適宜エネルギー源として利用することが可能となる。 Furthermore, the treatment tank 21 may be provided with means for recovering gas generated by electrolytic treatment. As will be described later, in the carbon dioxide fixation system 10 of this embodiment, hydrogen is generated on the cathode side and oxygen is generated on the anode side by performing electrolytic treatment in the electrolysis unit 20. Therefore, it is preferable to provide the treatment tank 21 with a line L3 for recovering the gas (hydrogen) generated on the cathode side and a line L4 for recovering the gas (oxygen) generated on the anode side.
In particular, hydrogen is a substance that is attracting attention as a next-generation energy source, and it is preferable to be able to recover and utilize highly pure hydrogen. Therefore, a means for removing gases other than hydrogen (such as water vapor) may be provided on the line L3. This makes it possible to recover highly pure hydrogen and effectively utilize hydrogen as an energy source. Further, the line L3 may be connected to equipment for storing hydrogen or equipment for controlling the amount of hydrogen supplied. This allows the generated and recovered hydrogen to be used as an energy source as appropriate.
（二酸化炭素固定化方法）
　本実施態様における海水を用いた二酸化炭素固定化方法は、水（海水）に二酸化炭素を溶解させたときに生成する炭酸イオンと、海水中に含まれる二価イオン（カルシウムイオンやマグネシウムイオン等）を反応させ、炭酸塩として回収可能な形態にするという炭酸塩固定処理に基づくものである。
　特に、本実施態様における二酸化炭素固定化方法は、二酸化炭素と海水をあらかじめ接触（混合）させた状態で、海水のアルカリ化を行い、二酸化炭素の炭酸イオン化を促進するという工程を含むことが重要となるものである。 (Carbon dioxide fixation method)
The carbon dioxide fixation method using seawater in this embodiment uses carbonate ions generated when carbon dioxide is dissolved in water (seawater) and divalent ions (calcium ions, magnesium ions, etc.) contained in seawater. It is based on a carbonate fixation process in which carbonates are reacted to form a form that can be recovered as carbonates.
In particular, it is important that the carbon dioxide fixation method in this embodiment includes a step of bringing carbon dioxide and seawater into contact (mixing) in advance, alkalizing the seawater and promoting carbonate ionization of carbon dioxide. This is the result.
　まず、海水を用いた二酸化炭素の固定化に係る従来法について説明する。
　一般に、二酸化炭素を水（海水）に溶解したとき、式１に示すように、炭酸（Ｈ２ＣＯ３）との平衡状態を経て、炭酸（Ｈ２ＣＯ３）の一部が電離することで生成する炭酸水素イオン（ＨＣＯ３ －）及び炭酸イオン（ＣＯ３ ２－）を含む化学平衡が成立する。
First, a conventional method for fixing carbon dioxide using seawater will be explained.
Generally, when carbon dioxide is dissolved in water (seawater), it reaches an equilibrium state with carbonic acid (H 2 CO 3 ) and then some of the carbonic acid (H 2 CO 3 ) is ionized, as shown in equation 1. A chemical equilibrium is established involving the generated bicarbonate ions (HCO 3 − ) and carbonate ions (CO 3 2− ).
　式１において生成した炭酸イオン（ＣＯ３ ２－）は、海水中に含まれる二価の金属イオンと反応し、炭酸塩化する。例えば、式２に示すように、炭酸イオン（ＣＯ３ ２－）と海水中に含まれるカルシウムイオン（Ｃａ２＋）と反応して炭酸塩（炭酸カルシウム）が生成する。これにより、二酸化炭素の固定化処理が進行する。
The carbonate ions (CO 3 2- ) generated in Formula 1 react with divalent metal ions contained in seawater and become carbonate. For example, as shown in Formula 2, carbonate ions (CO 3 2− ) react with calcium ions (Ca 2+ ) contained in seawater to generate carbonate (calcium carbonate). This progresses the carbon dioxide fixation process.
　式１及び式２から、炭酸イオンを生成する方向に化学平衡反応を進行させることで、二酸化炭素の固定化処理に係る高効率化が可能になることが分かる。つまり、式１の化学平衡を右側に向かって進行させ、式２における炭酸イオン量を増加させることで、二酸化炭素の固定化処理に係る炭酸塩化の反応効率の向上が可能となることが分かる。 From Equations 1 and 2, it can be seen that by allowing the chemical equilibrium reaction to proceed in the direction of producing carbonate ions, it is possible to improve the efficiency of carbon dioxide fixation treatment. In other words, it can be seen that by advancing the chemical equilibrium in Equation 1 toward the right side and increasing the amount of carbonate ions in Equation 2, it is possible to improve the reaction efficiency of carbonation related to carbon dioxide fixation treatment.
　図２は、海水のｐＨと、海水中の炭酸物質（炭酸、炭酸水素イオン、炭酸イオン）の存在比の関係を示すグラフである（１気圧、２５度）。図２において、横軸は海水のｐＨであり、縦軸は各炭酸物質の存在比（ratio）を示している。
　図２に示すように、ｐＨが高いほど炭酸イオンの存在比が増加することが分かる。ｐＨが９を超える範囲では、海水中の炭酸物質３種類のうち、炭酸イオンの存在比が最も高くなる。特に、ｐＨが１０以上では、海水中に存在する炭酸イオンが９０％以上となる。 FIG. 2 is a graph showing the relationship between the pH of seawater and the abundance ratio of carbonic substances (carbonic acid, bicarbonate ions, carbonate ions) in seawater (1 atmosphere, 25 degrees Celsius). In FIG. 2, the horizontal axis represents the pH of seawater, and the vertical axis represents the abundance ratio of each carbonate substance.
As shown in FIG. 2, it can be seen that the higher the pH, the higher the abundance ratio of carbonate ions. In a range where the pH exceeds 9, the abundance ratio of carbonate ions is the highest among the three types of carbonic substances in seawater. In particular, when the pH is 10 or more, carbonate ions present in seawater are 90% or more.
　これらのことから、従来法としては、海水をアルカリ化（ｐＨ１０以上）した後、二酸化炭素を供給することで、炭酸イオンの存在比を高めて、二価イオンとの反応を進行させ、炭酸塩化することが行われていた。
　このとき、海水をアルカリ化する手段として、海水の電解が行われている。海水の電解による海水のアルカリ化については、本実施態様における二酸化炭素固定化方法にも関連するため、詳細については後述する。
　なお、上述したように、ｐＨが高いほうが炭酸イオンの存在比を高めることが可能となる一方で、海水のアルカリ化に要する電力が増加することになる。 For these reasons, the conventional method is to alkalize seawater (pH 10 or higher) and then supply carbon dioxide to increase the abundance ratio of carbonate ions and advance the reaction with divalent ions, resulting in carbonation. things were being done.
At this time, seawater electrolysis is performed as a means to alkalize seawater. Alkalinization of seawater by electrolysis of seawater is also related to the carbon dioxide fixation method in this embodiment, and will be described in detail later.
Note that, as described above, while a higher pH makes it possible to increase the abundance ratio of carbonate ions, the electric power required to alkalize seawater increases.
　また、海水に含まれる二価の金属イオンはカルシウムイオンに限るものではなく、その他の二価の金属イオンも存在している。特に、海水中に存在するマグネシウムイオンは、アルカリ条件下では、式３に示した水酸化マグネシウムの生成反応が進行する。
Furthermore, the divalent metal ions contained in seawater are not limited to calcium ions, and other divalent metal ions also exist. In particular, under alkaline conditions, magnesium ions present in seawater undergo a reaction to produce magnesium hydroxide as shown in Formula 3.
　上述したように、式２に基づく炭酸カルシウム生成反応及び式３に基づく水酸化マグネシウム生成反応は、どちらもアルカリ下で促進される無機塩の生成反応である。そこで、本発明者らは、式２及び式３の反応について、海水のアルカリ化に伴い、どちらがより進行するかということに関する検討を行った。 As described above, the calcium carbonate production reaction based on Formula 2 and the magnesium hydroxide production reaction based on Formula 3 are both inorganic salt production reactions promoted under an alkali. Therefore, the present inventors conducted a study regarding which of the reactions of Formula 2 and Formula 3 progresses more as seawater becomes alkaline.
　以下、検討内容及び検討結果について説明する。
　まず、容器に人工海水５０ｍＬ（ｐＨ８）を入れ、二酸化炭素を吹き込む。このとき、人工海水のｐＨは低下し、ｐＨ５となった。その後、この容器に４％の水酸化ナトリウムを添加し、人工海水のアルカリ化を行う。このとき生成した沈殿物を濾過によって回収し、回収した沈殿物を乾燥させた後、成分分析を行うことで、沈殿物の組成及びその含有率を求めた。 The details and results of the study will be explained below.
First, 50 mL of artificial seawater (pH 8) is placed in a container, and carbon dioxide is blown into the container. At this time, the pH of the artificial seawater decreased to pH5. Thereafter, 4% sodium hydroxide is added to this container to alkalize the artificial seawater. The precipitate generated at this time was collected by filtration, the collected precipitate was dried, and then a component analysis was performed to determine the composition and content of the precipitate.
　図３は、海水のアルカリ化に伴う無機塩生成反応により生成した沈殿物における各組成の含有率（％）と、海水（人工海水）のｐＨの関係をグラフにしたものである。より具体的には、図３は、沈殿物から求めた組成のうち、式２に基づく生成反応で生成した炭酸カルシウム由来のカルシウムと、式３に基づく生成反応で生成した水酸化マグネシウム由来のマグネシウムについて、その含有率とｐＨの関係をグラフにしたものである。なお、図３中、炭酸カルシウム由来のカルシウムを黒塗りの三角（▲）、水酸化マグネシウム由来のマグネシウムを白抜きの四角（◇）で示している。
　図３に示すように、ｐＨが高くなるに従い、水酸化マグネシウム由来のマグネシウム含有率が増加し、それに伴い炭酸カルシウム由来のカルシウム含有率が低下していく。すなわち、海水を高アルカリ化するほど水酸化マグネシウムが生成し、炭酸カルシウムの生成反応が抑制されてしまい、二酸化炭素の固定化に係る反応効率が低下するということが分かった。 FIG. 3 is a graph showing the relationship between the content (%) of each composition in the precipitate produced by the inorganic salt production reaction accompanying the alkalinization of seawater and the pH of seawater (artificial seawater). More specifically, FIG. 3 shows that among the compositions determined from the precipitate, calcium derived from calcium carbonate produced in the production reaction based on formula 2, and magnesium derived from magnesium hydroxide produced in the production reaction based on formula 3. This is a graph showing the relationship between its content and pH. In FIG. 3, calcium derived from calcium carbonate is indicated by a black triangle (▲), and magnesium derived from magnesium hydroxide is indicated by an open square (◇).
As shown in FIG. 3, as the pH increases, the magnesium content derived from magnesium hydroxide increases, and the calcium content derived from calcium carbonate decreases accordingly. In other words, it has been found that the more alkaline the seawater is made, the more magnesium hydroxide is produced, the more the calcium carbonate production reaction is suppressed, and the reaction efficiency related to carbon dioxide fixation is reduced.
　上記検討の結果、本発明者らは、海水の電解によるアルカリ化に要するエネルギー消費の観点、及び、水酸化マグネシウム生成反応の抑制の観点から、従来法における海水のアルカリ化（ｐＨ１０）よりも低いｐＨで炭酸塩化を行うことが好ましいという知見を得た。そして、本発明者らは、この知見に基づきさらに検討を重ねた結果、本実施態様における二酸化炭素固定化方法に至った。 As a result of the above study, the present inventors determined that the alkalinization of seawater (pH 10) is lower than that of the conventional method, from the viewpoint of energy consumption required for alkalinization by electrolysis of seawater, and from the viewpoint of suppressing the magnesium hydroxide production reaction. It has been found that it is preferable to carry out carbonation at pH. As a result of further studies based on this knowledge, the present inventors arrived at the carbon dioxide fixation method of this embodiment.
　本実施態様における二酸化炭素固定化方法は、本発明者らの検討結果に係る知見に基づくものであり、より具体的には、あらかじめ溶存二酸化炭素濃度を高めた海水に対して電解を行うことにより、共通イオン効果による炭酸塩生成効率の向上に加え、水酸化マグネシウムの生成反応を抑制し、炭酸塩の生成反応を優勢化させることができるという知見に基づくものである。
　また、本実施態様における二酸化炭素固定化方法は、本実施態様における二酸化炭素固定化システム１０を用い、二酸化炭素を溶存させた海水の電解処理を行うことで、二酸化炭素の固定化を行うものである。 The carbon dioxide fixation method in this embodiment is based on the findings from the study results of the present inventors, and more specifically, by electrolyzing seawater in which the dissolved carbon dioxide concentration has been increased in advance. This is based on the knowledge that in addition to improving the carbonate production efficiency due to the common ion effect, it is possible to suppress the magnesium hydroxide production reaction and make the carbonate production reaction dominant.
In addition, the carbon dioxide fixation method in this embodiment is to fix carbon dioxide by electrolytically treating seawater in which carbon dioxide is dissolved using the carbon dioxide fixation system 10 in this embodiment. be.
　以下、本実施態様における二酸化炭素固定化システム１０を用い、本実施態様における二酸化炭素固定化方法に係る工程について、図４及び図５に基づき説明する。
　図４及び図５は、本実施態様の二酸化炭素固定化システム１０に係る電解部２０における二酸化炭素の固定化に係る工程を示す概略説明図である。図４及び図５における処理槽２１内の構成は、図１に示した構成と同じである。なお、図４及び図５は、各工程に関与する構成を主に図示しており、一部の構成については図示を省略している。また、図５は、主に二酸化炭素の固定化に関わるイオンや分子の移動について示しており、一部のイオンや分子については図示を省略している。 Hereinafter, steps related to the carbon dioxide fixation method in this embodiment will be explained using the carbon dioxide fixation system 10 in this embodiment based on FIGS. 4 and 5.
FIGS. 4 and 5 are schematic explanatory diagrams showing steps related to carbon dioxide fixation in the electrolysis unit 20 of the carbon dioxide fixation system 10 of this embodiment. The configuration inside the processing tank 21 in FIGS. 4 and 5 is the same as the configuration shown in FIG. 1. Note that FIGS. 4 and 5 mainly illustrate configurations involved in each process, and illustration of some configurations is omitted. Moreover, FIG. 5 mainly shows the movement of ions and molecules related to fixation of carbon dioxide, and some ions and molecules are not shown.
　まず、本実施態様における二酸化炭素固定化方法における第１工程として、電解部２０に海水及び電解液を導入し、導入した海水に対し、二酸化炭素の供給を行う。
　図４は、第１工程を示す概略説明図である。図４に示すように、まず、ラインＬ１を介して処理槽２１のカソード側（空間２４ｂ）に海水を導入し、ラインＬ２を介して処理槽２１のアノード側（空間２４ａ）に電解液Ｅを導入する。そして、二酸化炭素供給部３０によって、カソード側に導入された海水に対し、二酸化炭素を吹き込み、海水中の溶存二酸化炭素濃度を高める。このとき、式１の化学平衡に基づき、図４に示すように、二酸化炭素（気体）は炭酸（Ｈ２ＣＯ３）となる。さらに、炭酸（Ｈ２ＣＯ３）は他の炭酸物質（炭酸水素イオン（ＨＣＯ３ －）、炭酸イオン（ＣＯ３ ２－））となり、その過程で水素イオンが生じることで、カソード側の海水は酸性化（ｐＨ５程度）する。
　ここで、上述した式２に基づく炭酸カルシウム生成反応は、難溶性塩の生成反応である。したがって、海水中の溶存二酸化炭素濃度を高めることは、難溶性塩の構成イオン種を添加することに相当し、いわゆる共通イオン効果によって、難溶性塩（炭酸カルシウム）の溶解度が低下し、炭酸カルシウムの析出を促進することができる。これにより、炭酸塩化の効率を高めることが可能となる。 First, as the first step in the carbon dioxide fixation method in this embodiment, seawater and an electrolytic solution are introduced into the electrolysis section 20, and carbon dioxide is supplied to the introduced seawater.
FIG. 4 is a schematic explanatory diagram showing the first step. As shown in FIG. 4, first, seawater is introduced into the cathode side (space 24b) of the processing tank 21 via line L1, and electrolyte E is introduced into the anode side (space 24a) of processing tank 21 via line L2. Introduce. Then, carbon dioxide is blown into the seawater introduced to the cathode side by the carbon dioxide supply unit 30 to increase the concentration of dissolved carbon dioxide in the seawater. At this time, based on the chemical equilibrium of Equation 1, carbon dioxide (gas) becomes carbonic acid (H 2 CO 3 ) as shown in FIG. Furthermore, carbonic acid (H 2 CO 3 ) turns into other carbonic substances (bicarbonate ions (HCO 3 − ), carbonate ions (CO 3 2− )), and hydrogen ions are generated in the process, which causes the seawater on the cathode side to Acidify (pH around 5).
Here, the calcium carbonate production reaction based on Formula 2 described above is a production reaction of a poorly soluble salt. Therefore, increasing the concentration of dissolved carbon dioxide in seawater corresponds to adding ion species constituting poorly soluble salts, and due to the so-called common ion effect, the solubility of poorly soluble salts (calcium carbonate) decreases, and calcium carbonate can promote the precipitation of This makes it possible to increase the efficiency of carbonation.
　次いで、本実施態様における二酸化炭素固定化方法における第２工程として、海水のアルカリ化を行う。また、第２工程は、式１に基づき、炭酸イオンを生成する方向に化学平衡反応を進行させ、式２に基づく炭酸塩化を行うものである。より具体的には、第２工程は、電解部２０における電解を行うものである。
　図５は、第２工程を示す概略説明図である。図５に示すように、直流電源により電極２２ａ、２２ｂ間に電圧（又は定電流）を印加し、電解を行う。
　このとき、空間２４ａ内の電極２２ａにおける反応（アノード側の反応）は、以下の式４で示される。
Next, as the second step in the carbon dioxide fixation method in this embodiment, seawater is alkalized. Further, in the second step, based on Formula 1, a chemical equilibrium reaction is allowed to proceed in the direction of producing carbonate ions, and carbonation is performed based on Formula 2. More specifically, the second step is to perform electrolysis in the electrolysis section 20.
FIG. 5 is a schematic explanatory diagram showing the second step. As shown in FIG. 5, a voltage (or constant current) is applied between the electrodes 22a and 22b using a DC power source to perform electrolysis.
At this time, the reaction at the electrode 22a in the space 24a (reaction on the anode side) is expressed by the following equation 4.
　ここで、式４により発生した水素イオンは、図５に示すように、陽イオン交換体２３を介して空間２４ｂ側に移動する。また、式４により発生した酸素については、ラインＬ４を介し、回収するものとしてもよく、そのまま系外に排出するものとしてもよい。
　なお、本実施態様における二酸化炭素固定化システム１０を用いた場合、アノード側には塩化物イオンを含まない電解液（電解液Ｅ）が用いられるとともに、陽イオン交換体２３により、カソード側から塩化物イオンがアノード側に移動することが抑制される。このため、通常の海水電解とは異なり、塩化物イオンが塩素ガスとなる反応は進行しない。 Here, the hydrogen ions generated according to Formula 4 move to the space 24b side via the cation exchanger 23, as shown in FIG. Further, the oxygen generated by Equation 4 may be recovered via the line L4, or may be discharged directly to the outside of the system.
In addition, when using the carbon dioxide fixation system 10 in this embodiment, an electrolytic solution (electrolytic solution E) that does not contain chloride ions is used on the anode side, and chloride is removed from the cathode side by the cation exchanger 23. The movement of physical ions to the anode side is suppressed. Therefore, unlike normal seawater electrolysis, the reaction in which chloride ions become chlorine gas does not proceed.
　一方、空間２４ｂ内の電極２２ｂにおける反応（カソード側の反応）は、以下の式５で示される。
On the other hand, the reaction at the electrode 22b in the space 24b (reaction on the cathode side) is expressed by the following equation 5.
　また、空間２４ａから空間２４ｂに移動した水素イオンは、電極２２ｂにおける反応により水素が生成する（式６）。
Further, hydrogen ions that have moved from the space 24a to the space 24b undergo a reaction at the electrode 22b to generate hydrogen (Equation 6).
　式５に示すように、カソード側（空間２４ｂ）では、電解により水酸化物イオンが生成するとともに、水素が気体として海水から放出されることで、海水がアルカリ化する。このとき、海水中の溶存二酸化炭素に由来する炭酸物質については、電解によって系内（カソード側）の水素イオンが消費されるため、式１の化学平衡が炭酸イオンを生成する方向に促進され、その結果、式２の炭酸カルシウム生成反応が促進される。
　このとき、カソード側のｐＨは８程度となるように、印加する電圧（又は電流）の値、あるいは電解時間を調整することが好ましい。これにより、ｐＨの上昇とともに海水中の炭酸イオンを増加させて、炭酸カルシウム生成反応を促進する一方で、水酸化マグネシウムの生成反応が促進される条件（ｐＨ１０程度）までｐＨを上昇させないことで、水酸化マグネシウムの生成反応を抑制することができるとともに、海水のアルカリ化に係る消費エネルギーを少なくすることが可能となる。なお、生成した炭酸塩（炭酸カルシウム）は回収が容易であるとともに、回収した炭酸塩を資源として様々な用途に利用することが可能である。
　また、併せて、式５及び式６に示すように、カソード側では水素も発生する。このため、ラインＬ３を介して水素を回収することが可能となる。 As shown in Equation 5, on the cathode side (space 24b), hydroxide ions are generated by electrolysis, and hydrogen is released from the seawater as a gas, thereby making the seawater alkaline. At this time, for carbonic substances derived from dissolved carbon dioxide in seawater, hydrogen ions in the system (cathode side) are consumed by electrolysis, so the chemical equilibrium of formula 1 is promoted in the direction of generating carbonate ions, As a result, the calcium carbonate production reaction of Formula 2 is promoted.
At this time, it is preferable to adjust the value of the applied voltage (or current) or the electrolysis time so that the pH on the cathode side is about 8. This increases the carbonate ions in the seawater as the pH increases, promoting the calcium carbonate production reaction, while not increasing the pH to the condition (about pH 10) that promotes the magnesium hydroxide production reaction. The production reaction of magnesium hydroxide can be suppressed, and the energy consumption related to alkalization of seawater can be reduced. Note that the generated carbonate (calcium carbonate) is easy to recover, and the recovered carbonate can be used as a resource for various purposes.
Additionally, as shown in equations 5 and 6, hydrogen is also generated on the cathode side. Therefore, hydrogen can be recovered via line L3.
　上述した本実施態様における二酸化炭素固定化方法及び二酸化炭素固定化システム１０により、二酸化炭素の固定化処理を実施した。 Carbon dioxide fixation treatment was performed using the carbon dioxide fixation method and carbon dioxide fixation system 10 in this embodiment described above.
　電極２２ａ（アノード）としてグラファイトを用い、電極２２ｂ（カソード）としてＳＵＳメッシュを用いた電解部２０において、空間２４ａ（アノード側）に２％水酸化ナトリウム水溶液５０ｍＬを導入し、空間２４ｂ（カソード側）に海水５０ｍＬを導入した。
　そして、二酸化炭素供給部３０により空間２４ｂに対して二酸化炭素を吹き込み、カソード側のｐＨを５．５とした。 In the electrolytic section 20 using graphite as the electrode 22a (anode) and SUS mesh as the electrode 22b (cathode), 50 mL of a 2% aqueous sodium hydroxide solution was introduced into the space 24a (anode side), and the space 24b (cathode side) 50 mL of seawater was introduced into the tank.
Then, carbon dioxide was blown into the space 24b by the carbon dioxide supply unit 30, and the pH on the cathode side was set to 5.5.
　この電極２２ａ、２２ｂ間に定電流を印加し、電解を行った。電解条件としては、電流値３００ｍＡ、６００ｍＡ、又は９００ｍＡで電解を行った。そして、電解により生成した沈殿物を回収、乾燥後、成分分析を行い、沈殿物の組成及びその含有率を求めた。 A constant current was applied between the electrodes 22a and 22b to perform electrolysis. As for electrolysis conditions, electrolysis was performed at a current value of 300 mA, 600 mA, or 900 mA. Then, the precipitate generated by electrolysis was collected, dried, and then subjected to component analysis to determine the composition and content of the precipitate.
　図６は、本実施態様における二酸化炭素固定化方法及び二酸化炭素固定化システム１０を用いた二酸化炭素固定化処理の実施例に係る結果を示すグラフである。より具体的には、図６は、電解により生成した沈殿物から求めた組成のうち、式２に基づく生成反応で生成した炭酸カルシウム由来のカルシウムと、式３に基づく生成反応で生成した水酸化マグネシウム由来のマグネシウムについて、沈殿物における各組成の含有率（％）と、電解後のカソード側のｐＨとの関係をグラフにしたものである。
　なお、図６（Ａ）～図６（Ｃ）は、それぞれ電解条件が電流値３００ｍＡ、６００ｍＡ、９００ｍＡのときの結果に係るグラフを示すものである。また、図６（Ａ）～図６（Ｃ）中、炭酸カルシウム由来のカルシウムを黒塗りの三角（▲）、水酸化マグネシウム由来のマグネシウムを白抜きの四角（◇）で示している。 FIG. 6 is a graph showing the results of an example of carbon dioxide fixation treatment using the carbon dioxide fixation method and carbon dioxide fixation system 10 in this embodiment. More specifically, FIG. 6 shows, among the compositions determined from the precipitate produced by electrolysis, calcium derived from calcium carbonate produced in the production reaction based on formula 2, and hydroxide produced in the production reaction based on formula 3. Regarding magnesium derived from magnesium, the relationship between the content (%) of each composition in the precipitate and the pH on the cathode side after electrolysis is made into a graph.
Note that FIGS. 6(A) to 6(C) show graphs related to the results when the electrolytic conditions were current values of 300 mA, 600 mA, and 900 mA, respectively. In addition, in FIGS. 6(A) to 6(C), calcium derived from calcium carbonate is indicated by a black triangle (▲), and magnesium derived from magnesium hydroxide is indicated by an open square (◇).
　図６（Ａ）～図６（Ｃ）を比較すると、電解条件として印加する電流値が小さいほうが、沈殿物に含まれるカルシウム含有率が高くなる傾向にあることが分かる。
　特に、図６（Ｃ）に示すように、一定の電流値を超えると、沈殿物に含まれる成分として、水酸化マグネシウム由来のマグネシウム含有率のほうが、炭酸カルシウム由来のカルシウム含有率よりも多くなり、炭酸塩化が抑制されていることが分かる。
　また、図６（Ａ）及び図６（Ｂ）に示すように、電解後のカソード側のｐＨが８．５程度までは、炭酸カルシウム由来のカルシウム含有率が水酸化マグネシウム由来のマグネシウム含有率よりも高く、ｐＨが８．５を超えて高くなるに従い、炭酸カルシウム由来のカルシウム含有率が低下していくことが分かる。
　したがって、本実施態様における二酸化炭素固定化方法では、電解時の印加電流値を小さくし、かつ、電解後のカソード側のｐＨを低くする（ｐＨ８．５以下）ことで、炭酸カルシウム生成反応を優勢化することができることが示された。すなわち、あらかじめ海水中の溶存二酸化炭素濃度を高めた後、海水の電解を行うことで、海水のアルカリ化に係る消費エネルギーの削減及び炭酸塩化の促進が同時に成り立つことが示された。 Comparing FIGS. 6(A) to 6(C), it can be seen that the smaller the current value applied as the electrolysis condition, the higher the calcium content contained in the precipitate tends to be.
In particular, as shown in Figure 6(C), when the current value exceeds a certain value, the magnesium content derived from magnesium hydroxide becomes higher than the calcium content derived from calcium carbonate as a component contained in the precipitate. , it can be seen that carbonation is suppressed.
Furthermore, as shown in FIGS. 6(A) and 6(B), until the pH on the cathode side after electrolysis is approximately 8.5, the calcium content derived from calcium carbonate is lower than the magnesium content derived from magnesium hydroxide. It can be seen that as the pH increases beyond 8.5, the calcium content derived from calcium carbonate decreases.
Therefore, in the carbon dioxide fixation method in this embodiment, by reducing the applied current value during electrolysis and lowering the pH on the cathode side after electrolysis (pH 8.5 or less), the calcium carbonate production reaction is dominated. It was shown that it is possible to In other words, it has been shown that by increasing the dissolved carbon dioxide concentration in seawater in advance and then electrolyzing the seawater, it is possible to simultaneously reduce the energy consumption associated with alkalinization of seawater and promote carbonation.
　なお、本実施態様の二酸化炭素固定化方法においては、式５に基づく反応により、電極２２ｂ近傍のｐＨが局所的に高まるものとなる。したがって、図６（Ｃ）に示すように、印加電流値が高いほど、電極２２ｂ近傍のｐＨは、カソード側全体のｐＨよりも高アルカリ化していることが考えられる。そのため、図６（Ｃ）では、電極２２ｂ近傍で水酸化マグネシウムの生成反応が進行し、炭酸塩化に係る反応が抑制されたものと考えられる。したがって、本実施態様の二酸化炭素固定化システム１０に、電極２２ｂ近傍に水流（撹拌流）を形成する手段を設けることにより、局所的な高アルカリ化を解消することで、炭酸塩化に係る反応効率に対する印加電流値の影響を抑制することが可能となる。 In addition, in the carbon dioxide fixation method of this embodiment, the pH near the electrode 22b locally increases due to the reaction based on Formula 5. Therefore, as shown in FIG. 6C, it is considered that the higher the applied current value, the more alkaline the pH near the electrode 22b is than the pH of the entire cathode side. Therefore, in FIG. 6C, it is considered that the reaction for producing magnesium hydroxide progressed near the electrode 22b, and the reaction related to carbonation was suppressed. Therefore, by providing the carbon dioxide fixation system 10 of this embodiment with a means for forming a water flow (stirring flow) near the electrode 22b, local high alkalinization can be eliminated, thereby increasing the reaction efficiency related to carbonation. It becomes possible to suppress the influence of the applied current value on.
　以上のように、本実施態様の二酸化炭素固定化システム１０及びこの二酸化炭素固定化システム１０を用いた二酸化炭素固定化方法により、電極間に陽イオン交換体を配置した電解部を用い、カソード側に導入された海水に二酸化炭素を供給して溶存二酸化炭素濃度を高めた後、電解を行うことで、カソード側ではｐＨの上昇とともに炭酸イオンが増加して炭酸塩の生成効率が向上する一方、水酸化マグネシウムの生成反応が優勢となる条件までｐＨが上昇せず、水酸化マグネシウムの生成反応は抑制することが可能となる。また、海水を電解質溶液及び二価イオン源として用いることで、二酸化炭素の固定化に必要な二価イオンの原料調達にかかるコスト及びエネルギーを大幅に低減させることができる。これにより、高効率、かつ低コスト・低エネルギーで二酸化炭素の固定化を行うことが可能となる。 As described above, according to the carbon dioxide fixation system 10 of this embodiment and the carbon dioxide fixation method using this carbon dioxide fixation system 10, an electrolytic section in which a cation exchanger is arranged between the electrodes is used, and the cathode side After increasing the dissolved carbon dioxide concentration by supplying carbon dioxide to the seawater introduced into the seawater, electrolysis is performed, and as the pH increases, carbonate ions increase on the cathode side, improving the carbonate production efficiency. The pH does not rise to the point where the magnesium hydroxide production reaction becomes dominant, making it possible to suppress the magnesium hydroxide production reaction. Furthermore, by using seawater as an electrolyte solution and a source of divalent ions, it is possible to significantly reduce the cost and energy required to procure raw materials for divalent ions necessary for fixing carbon dioxide. This makes it possible to fix carbon dioxide with high efficiency, low cost, and low energy.
　また、本実施態様の二酸化炭素固定化システム１０及びこの二酸化炭素固定化システム１０を用いた二酸化炭素固定化方法では、アノード側において塩素ガス発生の要因となる塩化物イオンが存在しない状態を維持したまま、電解を行うことが可能となる。これにより、電解部において海水を用いた電解を行う際に、塩素ガスが発生することを抑制し、低コストかつ環境負荷の低減を可能とした二酸化炭素固定化を行うことができる。 In addition, in the carbon dioxide fixation system 10 of this embodiment and the carbon dioxide fixation method using this carbon dioxide fixation system 10, a state in which chloride ions, which are a cause of chlorine gas generation, are not present is maintained on the anode side. It becomes possible to perform electrolysis without any change. Thereby, when performing electrolysis using seawater in the electrolysis section, generation of chlorine gas can be suppressed, and carbon dioxide fixation can be performed at low cost and with a reduced environmental load.
　さらに、本実施態様の二酸化炭素固定化システム１０及びこの二酸化炭素固定化システム１０を用いた二酸化炭素固定化方法では、水素の回収・利用も可能となる。 Furthermore, in the carbon dioxide fixation system 10 of this embodiment and the carbon dioxide fixation method using this carbon dioxide fixation system 10, it is also possible to recover and utilize hydrogen.
　なお、上述した実施態様は、二酸化炭素固定化方法及び二酸化炭素固定化システムの一例を示すものである。本発明に係る二酸化炭素固定化方法及び二酸化炭素固定化システムは、上述した実施態様に限られるものではなく、請求項に記載した要旨を変更しない範囲で、上述した実施態様に係る二酸化炭素固定化方法及び二酸化炭素固定化システムを変形してもよい。 Note that the embodiments described above are examples of a carbon dioxide fixation method and a carbon dioxide fixation system. The carbon dioxide fixation method and carbon dioxide fixation system according to the present invention are not limited to the embodiments described above, and the carbon dioxide fixation method and carbon dioxide fixation system according to the embodiments described above are not limited to the embodiments described above. Variations in the method and carbon dioxide fixation system may be made.
　例えば、本実施態様の二酸化炭素固定化システム１０における電解部２０に対し、電解を効率的に行うための各種手段を追加するものとしてもよい。このような手段の一例としては、例えば、電極２２ａ、２２ｂの表面で析出物が生成することを抑制するための手段や、陽イオン交換体２３のイオン透過効率が低減することを抑制するための手段などが挙げられる。 For example, various means for efficiently performing electrolysis may be added to the electrolysis unit 20 in the carbon dioxide fixation system 10 of this embodiment. Examples of such means include means for suppressing the formation of precipitates on the surfaces of the electrodes 22a and 22b, and means for suppressing reduction in the ion permeation efficiency of the cation exchanger 23. Examples include means.
　また、本実施態様における二酸化炭素固定化システム１０及び二酸化炭素固定化方法としては、環境負荷への観点から、塩化物イオンを含まない電解液を用い、塩素ガスの発生を抑制するものを示したが、本発明の二酸化炭素固定化方法の別態様として、電解液Ｅとして海水などの塩化物イオンを含むものを用いるものとしてもよい。このとき、カソード側では、炭酸塩化に係る反応を促進するとともに、アノード側では、電極２２ａ（アノード）で生じる塩素（Ｃｌ２）や、塩素が電解液に溶解することで生成する塩素含有成分（次亜塩素酸（ＨＣｌＯ）や次亜塩素酸イオン（ＣｌＯ－））を回収し、系外で活用するものとしてもよい。例えば、この塩素含有成分が溶解した電解液を回収し、船舶のバラスト水タンク等、微生物、藻類の繁殖に伴う生物付着が問題となるところに供給することで、殺菌や生物付着抑制を行うことなどが挙げられる。 In addition, in the present embodiment, the carbon dioxide fixation system 10 and the carbon dioxide fixation method use an electrolytic solution that does not contain chloride ions and suppress the generation of chlorine gas from the viewpoint of environmental impact. However, as another embodiment of the carbon dioxide fixation method of the present invention, the electrolytic solution E may be one containing chloride ions, such as seawater. At this time, on the cathode side, the reaction related to carbonation is promoted, and on the anode side, chlorine (Cl 2 ) generated at the electrode 22a (anode) and chlorine-containing components (Cl 2 ) generated when chlorine is dissolved in the electrolytic solution Hypochlorous acid (HClO) and hypochlorite ions (ClO - )) may be recovered and utilized outside the system. For example, by collecting the electrolyte in which chlorine-containing components are dissolved and supplying it to areas where biofouling due to the proliferation of microorganisms and algae is a problem, such as ships' ballast water tanks, sterilization and biofouling control can be performed. Examples include.
　本発明の二酸化炭素固定化方法及び二酸化炭素固定化システムは、二酸化炭素を炭酸塩化する炭酸塩固定処理として、好適に用いることができる。 The carbon dioxide fixation method and carbon dioxide fixation system of the present invention can be suitably used as a carbonate fixation treatment to carbonate carbon dioxide.
１０　二酸化炭素固定化システム、２０　電解部、２１　処理槽、２２ａ，２２ｂ　電極、２３　陽イオン交換体、２４ａ，２４ｂ　空間、３０　二酸化炭素供給部、３１　配管、３２　吹込部、３３　供給量調整手段、Ｌ１～Ｌ４　ライン、Ｅ　塩化物イオンを含まない電解液 10 carbon dioxide fixation system, 20 electrolysis section, 21 processing tank, 22a, 22b electrodes, 23 cation exchanger, 24a, 24b space, 30 carbon dioxide supply section, 31 piping, 32 blowing section, 33 supply amount adjustment means, L1-L4 Line, E Electrolyte that does not contain chloride ions

Claims (3)

  1. 　海水を用いて二酸化炭素を固定する方法であって、
    　電極間に陽イオン交換体を配置した電解部を用い、
    　前記電解部のカソード側に導入された海水に対して二酸化炭素を供給した後、電解を行うことを特徴とする、二酸化炭素固定化方法。     A method of fixing carbon dioxide using seawater,
    Using an electrolytic section with a cation exchanger placed between the electrodes,
    A method for fixing carbon dioxide, comprising supplying carbon dioxide to seawater introduced into the cathode side of the electrolytic section, and then performing electrolysis.
  2. 　前記電解部のアノード側には、塩化物イオンを含まない電解液が導入されることを特徴とする、請求項１に記載の二酸化炭素固定化方法。 The carbon dioxide fixation method according to claim 1, characterized in that an electrolytic solution containing no chloride ions is introduced into the anode side of the electrolytic section.
  3. 　海水を用いて二酸化炭素を固定するシステムであって、
    　電極間に陽イオン交換体を配置した電解部を備え、
    　前記電解部のカソード側には海水及び二酸化炭素を導入し、前記電解部のアノード側には塩化物イオンを含まない電解液を導入することを特徴とする、二酸化炭素固定化システム。
          A system that fixes carbon dioxide using seawater,
    Equipped with an electrolytic section with a cation exchanger placed between the electrodes,
    A carbon dioxide fixation system, characterized in that seawater and carbon dioxide are introduced into the cathode side of the electrolytic section, and an electrolytic solution containing no chloride ions is introduced into the anode side of the electrolytic section.
PCT/JP2023/007085 2022-03-22 2023-02-27 Carbon dioxide fixation method and carbon dioxide fixation system WO2023181794A1 (en)

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