Method for direct capture of carbon dioxide from air

Abstract

The present invention relates to a method for directly capturing carbon dioxide from the air. The method for directly capturing carbon dioxide from the air according to the present invention is characterized by comprising the steps of: reacting seawater desalination concentrate with an alkali solution to form and separate magnesium hydroxide in a solid state; adding magnesium hydroxide to water to create a reaction solution and injecting carbon dioxide to precipitate hydromagnesite; heating the reaction solution to precipitate magnesium carbonate and basic magnesium carbonate and capturing carbon dioxide discharged from the reaction solution; injecting air containing carbon dioxide into the reaction solution to lower the pH; heating the reaction solution again to precipitate magnesium carbonate and basic magnesium carbonate and capturing carbon dioxide discharged from the reaction solution; and repeating the carbon dioxide injection step and the second capture step repeatedly and continuously after the second capture step.

Description

Technology Field

[0001] The present invention relates to a technology for capturing and removing carbon dioxide, a greenhouse gas, and in particular to a method for capturing carbon dioxide from the atmosphere. Background Technology

[0003] Efforts to reduce carbon dioxide emissions are underway worldwide. However, reducing emissions from industrial facilities such as power plants and factories alone cannot remove the carbon dioxide already accumulated in the atmosphere. Consequently, Direct Air Capture (DAC) technology, which directly captures and removes carbon dioxide from the atmosphere, is garnering attention.

[0004] The adsorbents (capturers) used in DAC technology include the liquid method (L-DAC) which uses a water-soluble alkaline solution and the solid method (S-DAC) which uses amines.

[0005] The solid method has the advantages of easy modularization and operation at low temperatures, but it has the disadvantages of high energy consumption at the level of 7.2–905 GJ / t_CO2 and a short lifespan of the adsorbent. The liquid method has the advantage of enabling large-scale carbon dioxide treatment, but it has the disadvantages of high initial equipment investment costs and the requirement of high temperatures of around 900°C for adsorbent regeneration. High-temperature process conditions not only reduce economic efficiency by consuming excessive energy, but also pose the problem of re-emitting carbon dioxide during the heating process that generates high temperatures. The problem to be solved

[0007] One objective of the present invention is to provide a method for effectively fixing and capturing carbon dioxide even at low temperatures of 70 to 100°C using magnesium hydroxide obtained from seawater desalination concentrate.

[0008] Meanwhile, other unspecified objects of the present invention will be further considered to the extent that they can be easily inferred from the following detailed description and effects. means of solving the problem

[0010] A method for directly capturing carbon dioxide from air according to the present invention for achieving the above objective comprises: a step of reacting seawater desalination concentrate with an alkali solution to form and separate magnesium hydroxide in a solid state; a step of adding the magnesium hydroxide to water to create a reaction solution and injecting carbon dioxide to precipitate hydromagnesite; a first capture step of heating the reaction solution to precipitate magnesium carbonate and basic magnesium carbonate and capturing carbon dioxide discharged from the reaction solution; a carbon dioxide injection step of injecting air containing carbon dioxide into the reaction solution to lower the pH; a second capture step of heating the reaction solution again to precipitate magnesium carbonate and basic magnesium carbonate and capturing carbon dioxide discharged from the reaction solution; and a repetition step of repeatedly and continuously performing the carbon dioxide injection step and the second capture step after the second capture step.

[0011] According to the present invention, the step of separating and recycling the precipitated hydromagnesite from the reaction solution may be further provided.

[0012] In one example of the present invention, magnesium hydroxide in the reaction solution is supplied at a concentration of 4.8 to 12 g / L, and it is preferable to supply additional magnesium hydroxide when the concentration of magnesium in the reaction solution becomes 200 mg / L or less.

[0013] In one example of the present invention, it is preferable to heat the reaction solution to a range of 50 to 100°C in the step of forming the hydromagnesite and in the first capture step and the second capture step.

[0014] In one example of the present invention, the magnesium carbonate and basic magnesium carbonate precipitated in the first collection step can be filtered and industrially recycled. Effects of the invention

[0016] A method for directly capturing carbon dioxide from the air according to one embodiment of the present invention fixes carbon from the atmosphere using magnesium carbonate and magnesium bicarbonate in a reaction solution. In particular, while the regeneration temperature in conventional calcium carbonate-based processes is high (600°C or higher), the present invention has the advantage of being able to significantly lower the temperature to 70°C to 100°C, thereby reducing energy consumption.

[0017] In addition, the present invention has the advantage of being able to separate hydromagnesite and magnesium carbonate and recycle them as industrial raw materials.

[0018] Meanwhile, it should be added that even if an effect is not explicitly mentioned here, the effects described in the following specification and the provisional effects expected by the technical features of the present invention are treated as described in the specification of the present invention. Brief explanation of the drawing

[0020] FIG. 1 is a schematic flowchart of a method for directly capturing carbon dioxide from air according to an example of the present invention. ※ It should be noted that the attached drawings are provided as examples for reference to help understand the technical concept of the present invention, and the scope of the rights of the present invention is not limited by them. Specific details for implementing the invention

[0021] In describing the present invention, detailed descriptions of related known functions are omitted if they are deemed obvious to a person skilled in the art and could unnecessarily obscure the essence of the invention.

[0022] A method for directly capturing carbon dioxide from the air according to an example of the present invention will be described in more detail below with reference to the attached drawings.

[0023] FIG. 1 is a schematic flowchart of a method for directly capturing carbon dioxide from air according to an example of the present invention.

[0024] The method for directly capturing carbon dioxide from the air according to the present invention first reacts seawater desalination concentrate with an alkaline solution to precipitate and separate solid magnesium hydroxide.

[0025] Concentrated seawater desalination water is rich in dissolved metal cations. For example, concentrated water discharged from a single domestic desalination plant contains sodium at levels of 18,298 mg / L, magnesium at 2,715 mg / L, calcium at 774 mg / L, and potassium at 711 mg / L. In addition, lithium, strontium, etc., are dissolved in the water, although at lower concentrations.

[0026] In this example, an alkaline solution (NaOH in this example) is first supplied to the concentrated water to raise the pH to approximately 10.5, thereby converting the magnesium in the concentrated water into solid magnesium hydroxide. That is, in this example, when a sodium hydroxide solution is supplied at a ratio of 1.8 to 2.2 times the molar amount of magnesium in the concentrated water, the pH rises and magnesium hydroxide precipitates. The precipitated magnesium hydroxide is separated from the concentrated water using a solid-liquid separator such as a centrifuge or a filter.

[0027] The separated magnesium hydroxide is mixed with water (preferably deionized water) in a mixing tank to form a reaction solution in the form of a suspension. Magnesium is included in the mixing tank at a concentration of 2 to 5 mg / L. Based on magnesium hydroxide, it is supplied at a concentration of 4.8 to 12 g / L. When carbon dioxide is injected into the reaction solution, hydromagnesite (Mg5(CO3)4(OH)2·4H2O) precipitates. In this example, the hydromagnesite is left in the reaction solution as is, but in other examples, the hydromagnesite may be separated from the reaction solution and utilized as an industrial material.

[0028] In the reaction solution under the above conditions, magnesium that has not been converted to hydromagnesite remains in an ionic state at a concentration of 300–600 mg / L. In addition, bicarbonate ions (HCO3) in the reaction solution -...also remains. That is, in addition to solid hydromagnesite, magnesium bicarbonate remains as a major component in the reaction solution.

[0029] Subsequently, when the reaction solution is heated to a range of 50 to 100°C, magnesium carbonate (MgCO3) precipitates into basic magnesium carbonate (mMgCO3·Mg(OH)2·nH2O) and carbon dioxide gas is released. The chemical reaction is represented by the following equation (1).

[0030] Mg(HCO3)2→ MgCO3, mMgCO3·Mg(OH)2·nH2O + CO2... Equation (1)

[0031] The released carbon dioxide is captured separately. The current state of carbon dioxide capture is called primary capture, and since the carbon dioxide captured in primary capture is injected separately when forming magnesium hydroxide into hydromagnesite, it does not reduce carbon dioxide.

[0032] As carbon dioxide is released from the reaction solution as shown in Equation (1) above, the reaction solution is composed in the pH range of 9 to 11.5. Now, when air from the atmosphere is injected into the reaction solution, the concentration of CO2 in the reaction solution increases, becoming saturated and the pH decreases. When the reaction solution is heated again to a range of 50 to 100°C while the pH is lowered by injecting air, carbon dioxide is released from the reaction solution and captured. This capture is called secondary capture, and carbon dioxide in the air can be separated and removed through secondary capture. When the reaction solution is heated during secondary capture, basic magnesium carbonate and magnesium carbonate are additionally produced and precipitated as shown in Equation (1) above.

[0033] In this example, the process of injecting air from the atmosphere into the reaction solution and the secondary capture process as described above are repeatedly performed.

[0034] That is, after the secondary capture of carbon dioxide is completed, air from the atmosphere is injected back into the reaction solution, and when the carbon dioxide in the reaction solution becomes saturated, the reaction solution is heated to capture carbon dioxide again.

[0035] Atmospheric carbon dioxide can be reduced by repeatedly performing secondary capture through the injection and heating of atmospheric carbon dioxide. However, if the magnesium concentration in the reaction solution decreases, the precipitation reaction of magnesium carbonate and alkaline magnesium carbonate no longer occurs. Therefore, if the magnesium concentration in the reaction solution falls below 200 mg / L, magnesium replenishment is required. In other words, the magnesium concentration can be increased by methods such as supplying additional reaction solution in which hydromagnesite has been precipitated.

[0036] Meanwhile, in another example of the present invention, magnesium carbonate and basic magnesium carbonate precipitated in the first collection step may be separated from the reaction solution and utilized as industrial materials.

[0037] In the method for directly capturing carbon dioxide from the atmosphere according to the present invention, air is injected into a magnesium-rich reaction solution to saturate the carbon dioxide in the reaction solution, and the solution is heated to degas only the carbon dioxide. The heating temperature is a very low temperature of 50 to 100°C. The process of degassing and capturing carbon dioxide and the regeneration process of lowering the concentration of carbon dioxide in the reaction solution are carried out together, and the process temperature is also at a relatively very low level.

[0038] Compared to the existing liquid-based carbon dioxide capture method (L-DAC), which requires temperatures of 600 to 900°C for carbon dioxide degassing and regeneration, this method is economical because the temperature range is very low.

[0039] In addition, the reaction solution used in this example has the advantage of being economical because it can be used repeatedly for carbon dioxide capture.

[0040] The scope of protection of the present invention is not limited to the description and expression of the embodiments explicitly described above. Furthermore, it is added once again that the scope of protection of the present invention cannot be limited by obvious changes or substitutions in the technical field to which the present invention belongs.

Claims

Claim 1 A method for directly capturing carbon dioxide from air, characterized by comprising: a step of reacting seawater desalination concentrate with an alkaline solution to form and separate solid magnesium hydroxide; a step of adding the magnesium hydroxide to water to create a reaction solution and injecting carbon dioxide to precipitate hydromagnesite; a first capture step of heating the reaction solution to precipitate magnesium carbonate and basic magnesium carbonate and capturing carbon dioxide discharged from the reaction solution; a carbon dioxide injection step of injecting air containing carbon dioxide into the reaction solution to lower the pH; a second capture step of heating the reaction solution again to precipitate magnesium carbonate and basic magnesium carbonate and capturing carbon dioxide discharged from the reaction solution; and a repetition step of repeatedly and continuously performing the carbon dioxide injection step and the second capture step after the second capture step. Claim 2 A method for directly capturing carbon dioxide from air, characterized by further comprising the step of separating and recycling the precipitated hydromagnesite from the reaction solution in claim 1. Claim 3 A method for directly capturing carbon dioxide from air according to claim 1, characterized in that magnesium hydroxide in the reaction solution is supplied at a concentration of 4.8 to 12 g / L. Claim 4 A method for directly capturing carbon dioxide from air according to claim 1, characterized by supplying additional magnesium when the concentration of magnesium in the reaction solution becomes 200 mg / L or less. Claim 5 A method for directly capturing carbon dioxide from air according to claim 1, characterized by heating the reaction solution to a range of 50 to 100°C when forming the hydromagnesite. Claim 6 A method for directly capturing carbon dioxide from air according to claim 1, characterized by heating the reaction solution to a range of 50 to 100°C in the first and second capture steps. Claim 7 A method for directly capturing carbon dioxide from air according to claim 1, characterized in that the magnesium carbonate and basic magnesium carbonate precipitated in the first capture step are filtered and industrially recycled.

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