JP2005021870A - Method for reducing carbon dioxide in the air, method for recovering and removing carbonic acid in sea water and its disposal method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the global warming problem itself by globally reducing CO<SB>2</SB>which is released into the air and is accumulated therein by utilizing the ocean with respect to the production source countermeasure and the global countermeasure of CO<SB>2</SB>which is not realized as a fundamental reduction technology until now. <P>SOLUTION: Surface seawater is electrolyzed, bicarbonate ions and carbonate ions included in sea water are combined with calcium and magnesium and insoluble carbonate salt is produced, is precipitated to deep sea by self weight and is deposited on the sea bottom. Because the sea water which is allowed to lower a carbonate concentration in the surface layer absorbs CO<SB>2</SB>in the air, the global warming problem can be solved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a method for globally reducing carbon dioxide (CO ₂ ), which has a large greenhouse effect among greenhouse gases, which are a problem of global warming, especially because the amount of anthropogenic emission is the largest.

As method of reducing CO ₂ emissions from thermal power plants and cement production plants a large number generation source of CO ₂ is injected, the chemical absorption method for recovering an amine compound, to the ocean in order to dispose of the recovered CO ₂ Methods of disposal, methods of chemically converting CO ₂ to methane and recycling it, and other methods of reducing atmospheric carbon dioxide have been studied. In addition, the use of natural CO ₂ fixation processes such as afforestation, algae growth, fertilization to the ocean (especially iron spraying), and coral reef growth are methods of globally reducing the CO ₂ released and accumulated in the atmosphere. Thinked and tried. However, CO ₂ reduction measures and global reduction measures at these conventional sources have cost and energy problems, adverse effects on the environment, concern that CO ₂ injected into the ocean will be released again in the future, or reduction effects There is a problem that it cannot be expected, and no specific solution has yet been found that can fundamentally solve the global warming problem caused by CO ₂ .
Japanese Patent Laid-Open No. 11-29314 Japanese Patent Laid-Open No. 200-262888

The present invention is, with respect to CO ₂ source measures and global measures hitherto not been realized as a reduction technologies fundamental CO _2, the CO ₂ that have accumulated is released to the atmosphere globally by utilizing ocean By reducing it, we try to fundamentally solve the global warming problem itself.

The present invention is a method for removing a global scale in the reduction can be practical CO ₂ for CO _2, it is possible to reduce the CO ₂ that is released accumulated yet future release far globally, CO ₂ can control the amount of removal, excess CO ₂ stored in the atmosphere can be stably isolated from the biosphere, is controllable and uncontrollable non technology, new CO ₂ and unnecessary waste by processing occurs It is a low-cost, energy-saving method, does not require chemical and biological additives to the environment, is environmentally friendly and does not disturb the balance of the environmental ecosystem. The present invention is a method that can eliminate social problems for reducing CO ₂ and has a low economic burden, and does not require the idea of suppressing economic development.

The present invention relates to a practical method for reducing carbon dioxide in the global atmosphere. According to the present invention, not only CO ₂ released in the past and accumulated in the atmosphere, but also in the future, without economic restraint. it is possible also to remove to growing CO _2, appropriately removed while controlling without CO ₂ that strong-arm biosphere, stably sequester atmospheric CO ₂ stored in the excess from the biosphere By doing so, it becomes possible to keep the global atmospheric environment appropriate.

  In the method for reducing atmospheric carbon dioxide according to the present invention, decarboxylated seawater having a reduced carbonic acid concentration generated by removing bicarbonate ions and carbonate ions contained in seawater of the ocean surface is in contact with the atmosphere. Thus, carbon dioxide in the atmosphere is absorbed and reduced from the atmosphere due to the chemical equilibrium effect between the atmosphere and the ocean surface layer.

In this way, the treatment method for removing carbonic acid from the ocean surface seawater that has absorbed carbon dioxide in the atmosphere generates carbonic acid contained in seawater as an insoluble carbonate, without adding any additive to the seawater, This is a combination of calcium and magnesium coexisting with seawater and carbonic acid.
Further, as a method for recovering carbonic acid dissolved in seawater, carbonic acid can be precipitated and separated as insoluble carbonates, and the carbonate precipitates can be settled in the deep sea and the seabed and deposited.

  Decarbonized seawater from which carbon dioxide contained in ocean surface seawater has been removed comes into contact with the atmosphere, absorbs carbon dioxide in the atmosphere due to the chemical equilibrium effect between the ocean and ocean surface layers, and calcium coexists with carbon dioxide in seawater. And a combination of magnesium and the like to precipitate and recover as an insoluble carbonate, and further, the insoluble carbonate is settled to a deep layer in a solid state and deposited on the seabed, which is a series of processes.

  In this case, carbon dioxide in the seawater is recovered as insoluble carbonate by the method of reducing carbon dioxide in the atmosphere, and the carbon dioxide concentration in the ocean surface seawater is reduced to reduce atmospheric carbon dioxide by the chemical equilibrium effect between the atmosphere and the ocean. For reduction, insoluble carbonate is produced by direct electrolysis without adding any additive to seawater.

  In the above-mentioned electrolytic treatment for removing carbon dioxide from the ocean surface seawater for the purpose of reducing carbon dioxide in the atmosphere, the hydrogen ion concentration in the seawater after the electrolytic treatment is lower than that in the seawater before the treatment, so that further Increases carbon absorption capacity. In addition, in the electrolytic treatment, hydrogen gas as a by-product generated simultaneously with the electrolytic treatment of seawater is recovered and recycled.

According to the present invention, since atmospheric CO ₂ can be reduced globally, a reduction measure at the source of CO ₂ that is threatened to be realized becomes unnecessary, which brings about a great social and economic effect. According to the global CO ₂ reduction measures according to the present invention, it is not necessary to think about suppressing the rapid increase of the population mainly in developing countries, the accompanying economic development, and the accompanying increase in CO ₂ emission. Therefore, the present invention does not require the idea of suppressing economic development. In addition, regarding the obligation to reduce the emitted CO ₂ in the Kyoto mechanism, it is necessary to obtain an international agreement to make the CO ₂ reduction amount the decarboxylation amount of seawater according to the present invention.

Hereinafter, examples of the present invention will be described in detail with specific examples with reference to the drawings.
As a method for reducing CO _{2 in} the atmosphere of the present invention on a global scale, an average of 2.0 to 2.2 mmol / kg of bicarbonate ions and carbonate ions (hereinafter referred to as “carbonic acid”) is contained in ocean surface seawater. Carbonic acid is reacted with calcium (Ca: contained in 10 mmol / kg) and magnesium (Mg: contained in 53 mmol / kg) coexisting in seawater to form insoluble Ca-Mg carbonate. This removes carbonic acid as a precipitate. The decarboxylated seawater absorbs and reduces atmospheric CO ₂ by the chemical equilibrium effect between the atmosphere and the ocean surface.

As a specific decarboxylation method, most of the salts dissolved in seawater exist in the form of ionization or ion pairs, and therefore seawater is an electrolyte solution with high electrical conductivity. Using this property of seawater, seawater is directly electrolyzed to convert the carbonic acid contained therein into an insoluble carbonate. The electrolysis reaction of seawater is carried out in a bipolar flow type (circulation type) electrolytic cell having a porous diaphragm, and at the cathode (cathode), first, by OH ⁻ generated by the reaction of water decomposition reaction formula (1). The reaction of the formula (2) proceeds, and carbonic acid dissolved in seawater is precipitated as insoluble calcium carbonate (CaCO ₃ ). The actual precipitate is a basic carbonate [CaCO ₃ · Mg (OH) ₂ ] containing Mg. At the cathode, hydrogen gas is simultaneously generated by the water splitting reaction formula (1) shown above. On the other hand, in the anode (anode), the reaction of the formula (3) mainly proceeds compared to the water splitting reaction, and the hydrolysis reaction of the formula (4) further proceeds. The total reaction of seawater electrolysis described above is expressed by equation (5), and from this reaction equation and experimental results, there is no generation of CO ₂ gas accompanying the electrolytic reaction. When the seawater after the above cathodic reaction and anodic reaction is mixed, the hydrogen ion concentration is alkalized compared to the seawater before the treatment, so the CO ₂ absorption capacity of the decarbonated seawater is higher than that of the seawater before the treatment. It has risen further.

(1) 2H ₂ O + 2e ⁻ → H ₂ + OH ⁻
(2) Ca ²⁺ + Mg ²⁺ + HCO ₃ ⁻ + OH ⁻ → Ca (Mg) CO ₃ ↓ + H ₂ O
(3) 2Cl ⁻ → Cl ₂ + 2e ⁻
(4) Cl ₂ + H ₂ O → 2H ⁺ + ClO ⁻ + Cl ⁻
(5) 2H ₂ O + 2Cl ⁻ + (2Na ⁺ + 4Cl ⁻ ) + Ca ² + xMg ²⁺ + 2HCO ₃ ⁻
→ 2H ₂ ↑ + CaCO ₃ · xMg (OH) ₂ ↓ + CO ₃ ²⁻ + 2HClO (+ 2NaCl)

Now, as carbon dioxide fixation reaction in coral reefs causes the same amount of CO ₂ to be released during the generation of CaCO ₃ as shown in equation (6), the CO ₂ gas in the atmosphere will be absorbed and reduced. It is said that coral reefs cannot be expected. On the other hand, in the case of the present invention, as shown in the formula (5), the release of CO ₂ gas accompanying the seawater electrolysis reaction does not occur, which is different from the carbon fixation reaction in the coral reef.
(6) Ca ²⁺ + 2HCO ₃ ⁻ → CaCO ₃ ↓ + CO ₂ + H ₂ O

Solid basic carbonate generated by seawater electrolysis is collected inside the flow-type electrolytic cell using the flow of the ocean current, and settled by its own weight in the solid state on the seabed as the disposal site. As a result, carbonic acid is removed from the ocean surface layer, and it becomes possible to increase the movement rate of the carbonic acid component from the surface layer to the deep layer, which was the rate-determining factor of the absorption rate of atmospheric CO _{2 into} the ocean.

Through the above process, carbonic acid dissolved in the ocean surface seawater becomes an insoluble carbonate compound and sinks to the deep sea by its own weight and deposits on the seabed. By this series of processes, decarboxylated seawater generated by electrolysis absorbs CO ₂ in the atmosphere, and as a result, the reduction of excess CO ₂ accumulated in the atmosphere causing the greenhouse effect is promoted. The principle of the present invention is shown in FIG.

As described above, the method for reducing surplus CO _{2 in} the atmosphere according to the present invention can be artificially controlled such that a chemical or biological additive is unnecessary and the amount of CO ₂ disposed of can be grasped. This is an environmentally friendly method because the seawater hydrogen ions are slightly reduced by seawater electrolysis. According to this method, unlike the conventional method of recovering CO ₂ from a large-scale source such as a thermal power plant or a cement manufacturing factory and disposing the CO ₂ as gaseous or dry ice, CO ₂ recovery In addition, there is no problem of acidification of seawater that occurs when disposal does not require a large amount of energy, and when the CO ₂ thus recovered is directly thrown into the ocean. When the power required for the decarbonation treatment of seawater according to the present invention is generated by power generation using non-fossil fuels such as solar power generation, solar thermal power generation, wind power generation, oxyhydrogen fuel cell, and deep sea water temperature difference power generation , the ratio of emission and the fixed reduction of the emissions is small CO ₂ new CO ₂ due to reduction disposal of CO ₂ is 1 / 10-1 / 20.

The invention is illustrated in more detail by the following examples.
For the electrolysis of seawater, two types of cylindrical electrodes with different diameters coated with platinum on a cylindrical titanium mesh in a cylindrical electrolytic cell (inner diameter 96 mm, length 500 mm) are set at a distance of about 20 mm between the electrodes. A cylindrical porous membrane (made of polypropylene, pore diameter 50-300 μm) having an outer diameter of 70 mmφ and an inner diameter of 55 mmφ is set between the electrodes, and 1 to 4 L / min. Then, seawater was allowed to flow at a constant flow rate within the range, and a direct current voltage was applied between the two electrodes to perform electrolytic treatment.

From the experimental results of the electrolytic treatment, carbonic acid in seawater was precipitated and removed as an insoluble carbonate, and the effectiveness of the present invention could be confirmed. In addition, as conditions for the electrolysis treatment of seawater, the generation of white precipitates started when the electrolysis current density was about 6 to 8 mA / cm ² or more, and the generation of precipitates became active under the electrolysis conditions of about 20 to 30 mA / cm ² . . This precipitate was a basic carbonate containing CaCO ₃ and Mg (OH) ₂ . In addition, by controlling the electrolytic current density during the electrolytic treatment, it was possible to convert the carbonic acid in the cathode-treated seawater into a carbonate with an efficiency of 20 to 70%. From these results, the insoluble carbonate formation reaction proceeded with only the components in the seawater without adding any additive to the seawater, and confirmation of the seawater decarboxylation treatment of the present invention was obtained. Since this solid carbonate has low solubility in seawater, surplus CO ₂ in the atmosphere can be completely isolated from the biosphere by sinking it to the deep sea and depositing it on the seabed, and it can be expected to be rocked by long-term deposition. . For this reason, the present invention has no concern about the re-release of CO ₂ into the atmosphere as compared with the CO ₂ gas injection disposal and the dry ice disposal proposed in the seawater.

  Seawater was electrolyzed under the same conditions as in Example 1, and the hydrogen gas produced from the cathode was recovered. As a result, a very fine gas is generated from the cathode by electrolysis. The gas is hydrogen, and the hydrogen gas is generated almost in proportion to the amount of coulomb of the electrolysis process. The amount produced was 2-4 mol / kWh. The produced hydrogen gas easily permeates the gas separation membrane and is easily recovered. The purity of the recovered hydrogen gas is as high as 95% or more, and it can be sufficiently used as a raw material gas for an oxyhydrogen fuel cell. .

The insoluble carbonate produced by seawater electrolytic treatment varies in composition and shape depending on the electrolytic treatment conditions. The tendency is that in the case of weak electrolytic treatment with low current density, carbonate with low basicity and high calcium carbonate content (low basic carbonate) is formed, and in the case of electrolytic treatment with high current density and strong A carbonate having a high basicity and a low calcium carbonate content (a highly basic carbonate) is produced. Although the physical properties of these carbonates vary depending on their form and particle size, the sedimentation rate of the produced carbonate in seawater at atmospheric pressure is approximately 1-10 m / hour, and the components in the surface seawater move to the deep sea. Much faster than the speed (on the order of 1 cm per year). In addition, as a result of pressurizing the produced carbonate with high-pressure seawater at 300 to 500 atmospheres, leaching of Mg (OH) ₂ contained in the carbonate occurs with time in the high-pressure seawater state. Since the content ratio of CaCO ₃ increases and the specific gravity increases, the subsidence due to its own weight in the deep sea further increases, and its petrification is likely to proceed.

About 20 to 30 ppm of ClO ^- is generated by the anodic electrolysis of seawater shown in the above formulas (3) to (4), but this substance is harmful to marine organisms, and therefore, decarbonated seawater containing it. Cannot be released. However, the ClO ^- is can be completely decomposed by contacting with activated carbon, there is no generation and release of carbon monoxide CO and CO ₂ due to decomposition treatment with activated carbon. When the decarbonated seawater containing ClO ⁻ is treated with activated carbon, alkalinization is further promoted by the reaction shown in the formula (7). This phenomenon is caused by the disappearance of hydrogen ions accompanying the decomposition reaction of ClO ⁻ .
Formula (7) ClO ⁻ + 2H ⁺ −2e ⁻ → activated carbon treatment → Cl ⁻ + H ₂ O

A process for separating and recovering carbonic acid in seawater as an insoluble carbonate and a specific measure for sinking the solid carbonate into the deep sea are required. Now, a large amount of surface seawater with a concentration of 2 mmol / kg of carbonic acid must be disposed. The flow-type electrolytic cell shown in FIG. 2 having the function is installed in a place where the ocean current always flows and the flow is used. Introducing into the electrolytic cell and processing. An insoluble carbonate is generated inside the electrolytic cell by this electrolytic treatment, and this is led to a pipe that sinks into the deep sea while flowing and gathering inside the electrolytic cell by the flow of the ocean current. If this system is installed, for example, in the Kuroshio current near Japan (with an average flow rate of 1 m / s), 1GtonC of carbon dioxide in the seawater (GtonC gigaton carbon G = 10 ⁹ ; 1GtonC is the consumption of fossil fuels. Is equivalent to 1/6 of the amount discharged into the atmosphere by the CO2 and 1/3 of the amount of CO ₂ emission to be reduced to prevent accumulation in the atmosphere). When the efficiency is 25 to 50%, 2.28 to 4.56 × 10 ⁶ m ² is necessary as an effective area for taking in the ocean current. When using an atmospheric ocean equilibrium layer up to a sea depth of 100 m, the size of the ocean current inlet corresponds to 100 m (depth) x 22,800 to 45,600 m (width). The seawater decarboxylation system is shown in FIG.

The main system is an electrolytic cell and a power generation facility for obtaining the power required for electrolysis, but the method for obtaining the power required by this system is generated by solar power generation, wind power generation, or electrolysis. Clean power generation with low CO ₂ emission, such as an oxyhydrogen fuel cell using hydrogen gas as a raw material gas or temperature difference power generation, is desirable. The amount of electric power for electrolytically converting carbonic acid in seawater into carbonate is about 1 to 4 × 10 ⁹ kW per 1 ton of carbonic acid treatment per year (assuming that the carbonation efficiency is 25 to 50%). Necessary. If the 3GtonC a year global warming due to CO ₂ as reduction of CO ₂ throughout the world to solve the global needs of the system having the above-mentioned dividing carbonate capability that may be at three Become. In addition, the system is constantly exposed to wind power, rain, and waves due to the strong currents of the ocean currents, and must be operated for a very long period of time. Is required.

It is a conceptual diagram illustrating the principle of a global reduction method of atmospheric CO ₂ by seawater electrostatic cancellation carbonate treated as an embodiment of the present invention. It is a conceptual diagram which shows the principle of the seawater electrolysis by a flow type electrolytic cell as embodiment of this invention. It is a conceptual diagram which shows the process of the seawater carbonic acid removal process by the seawater carbonic acid removal system as embodiment of this invention.

Claims (7)

  As a method of reducing carbon dioxide in the atmosphere, when decarbonated seawater with reduced carbonate concentration produced by removing bicarbonate ions and carbonate ions contained in seawater on the surface of the ocean is in contact with the atmosphere, A method for reducing carbon dioxide in the atmosphere, characterized in that atmospheric carbon dioxide is absorbed and reduced from the atmosphere by the chemical equilibrium effect between the ocean and the ocean surface layer.   As a method of decarbonation treatment of ocean surface seawater, in order to generate carbonic acid contained in seawater as insoluble carbonate, it is possible to combine calcium and magnesium coexisting in seawater with carbonic acid without adding any additive to seawater. A method for recovering and removing carbonic acid from seawater.   As a method for recovering carbonic acid dissolved in seawater, a method for disposing carbonic acid in seawater, comprising precipitating and separating carbonic acid as insoluble carbonates, and depositing the carbonated precipitates in the deep sea and the seabed and depositing them.   Decarbonized seawater from which carbon dioxide contained in ocean surface seawater has been removed comes into contact with the atmosphere to absorb atmospheric carbon dioxide by the chemical equilibrium effect between the atmosphere and the ocean surface layer, and calcium coexists with carbon dioxide in seawater. In the atmosphere characterized by combining and collecting magnesium and the like as an insoluble carbonate, and further precipitating the insoluble carbonate into a deep layer in a solid state and depositing it on the seabed, and making them a series of processes. How to reduce carbon dioxide.   The carbon dioxide in the seawater is recovered as an insoluble carbonate by the method for reducing carbon dioxide in the atmosphere according to claim 1 or 4, and the carbon concentration in the ocean surface seawater is lowered to reduce the atmospheric concentration by the chemical equilibrium effect between the atmosphere and the ocean. A method for reducing carbon dioxide in an atmosphere, characterized in that insoluble carbonate is generated by direct electrolytic treatment without adding any additive to seawater.   In the electrolytic treatment for removing carbon dioxide from the ocean surface seawater for the purpose of reducing carbon dioxide in the atmosphere, the hydrogen ion concentration in the seawater after the electrolytic treatment is lower than that in the seawater before the treatment. 6. The method for reducing carbon dioxide in the atmosphere according to claim 5, wherein the capacity increases.   In the electrolytic treatment according to claim 5 for removing carbon dioxide from marine surface seawater for the purpose of reducing carbon dioxide in the atmosphere, recovering and recycling hydrogen gas generated simultaneously with the electrolytic treatment of seawater. Disposal method of carbonic acid in seawater.

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