Patent Application
20240042374
The present invention relates to carbon dioxide fixation methods, carbon dioxide recovery methods, carbon dioxide fixation devices and environmentally friendly industrial facilities.
As global warming has rapidly progressed in recent years, it is required to rapidly reduce carbon dioxide (CO2) in the atmosphere at a large scale. As one of the powerful methods for reducing carbon dioxide, a method of fixing (mineralizing) carbon dioxide as a poorly water-soluble carbonate mineral has been proposed for the purpose of long-term storage of carbon dioxide (see, for example, Non-Patent Literature 1).
Conventionally, as a carbon dioxide fixation method using mineralization, a so-called pH-swing method (pH-swing process) has been developed in which under low pH conditions (for example, pH<4) using a large amount of acid, rocks and industrial wastes are first dissolved to extract metal ions (Ca2+, Mg2+), and thereafter, under high pH conditions (for example, pH>9) with the addition of alkali, the extracted metal ions are carbonated to precipitate a carbonate mineral (see, for example, Non-Patent Literature 2).
It has been found by the present inventors and others that as a method with consideration given to a hydrothermal reaction in the ground, a high-concentration ligand NaHCO3 is utilized as a catalyst to greatly accelerate the dissolution of olivine [(Mg, Fe)2SiO4)] under temperature conditions of 225 to 300° C., and thus carbon dioxide can be fixed by the formation of magnesite (MgCO3) (see, for example. Non-Patent Literature 3).
Non Patent Literature 1: Sandra O. Snabjomsdottir, Bergur Sigfusson. Chiara Marieni, David Goldberg, Sigurdur R. Gislason and Eric H. Oelkers, “Carbon dioxide storage through mineral carbonation”, Nature Reviews Earth & Environment, February 2020, Volume 1, p. 90-102
However, the pH swing disclosed in Non-Patent Literature 2 uses a large amount of chemicals for pH adjustment, and thus material costs thereof are disadvantageously increased. Although the method disclosed in Non-Patent Literature 3 opens up a new field of carbon dioxide mineralization by hydrothermal alteration of rocks under alkaline conditions, the temperature at which olivine is dissolved is high, with the result that when the method is performed on a large scale industrially, facility costs may be increased.
The present invention is made in view of the problems as described above, and an object of the present invention is to provide a carbon dioxide fixation method, a carbon dioxide recovery method, a carbon dioxide fixation device and an environmentally friendly industrial facility which can reduce material costs and facility costs.
In order to achieve the object described above, a carbon dioxide fixation method according to the present invention includes: an aqueous solution formation step of forming an alkaline aqueous solution including: a raw material including metal elements that can combine with carbonate ions to form a carbonate mineral; and a chelating agent; a separation step of reacting the metal element with the chelating agent in the aqueous solution to separate the metal element from the raw material as metal ions; a mineral formation step of adding a compound that can generate carbonate ions in the aqueous solution to form a carbonate mineral by reacting the carbonate ions generated from the compound with the metal ions, into the aqueous solution after the separation step; a pH lowering step of injecting carbon dioxide gas into the aqueous solution after the mineral formation step to lower a pH to the pH of the aqueous solution formed in the aqueous solution formation step or a value near that; and a repetition step of adding a new raw material of the same type as the raw material into the aqueous solution after the pH lowering step and performing steps from the separation step to the pH lowering step.
In the carbon dioxide fixation method according to the present invention, the alkaline aqueous solution including the raw material and the chelating agent is first formed in the aqueous solution formation step, and thus in the separation step, the metal element is reacted with the chelating agent, with the result that the metal element can be separated from the raw material as metal ions. In the separation step, the pH of the aqueous solution can be increased by the separation of the metal element.
Then, in the mineral formation step, the compound that can generate carbonate ions in the aqueous solution is added into the aqueous solution after the separation step, and thus the carbonate ions generated from the compound reacts with the metal ions, with the result that a carbonate mineral can be formed. Here, since the pH of the aqueous solution is increased by the separation step, the reaction of the carbonate ions with the metal ions can be accelerated. In this way, carbon dioxide can be fixed as a carbonate mineral.
Then, in the pH lowering step, the carbon dioxide gas is injected into the aqueous solution after the mineral formation step, and thus the pH thereof can be lowered to the value of or a value near the pH of the aqueous solution formed in the aqueous solution formation step, and a carbonate ion concentration in the aqueous solution can be increased. By lowering the pH, a component unrelated to the mineral formation in the mineral formation step or a part thereof can be precipitated in the aqueous solution according to the type of raw material.
Then, in the repetition step, the new raw material is added into the aqueous solution after the pH lowering step, and thus the metal ions generated from the metal element included in the raw material and the metal ions which are not consumed in the first round of the mineral formation step are reacted with the carbonate ions the concentration of which has been increased in the pH lowering step, with the result that it is possible to form a carbonate mineral. In this way, carbon dioxide can be fixed as the carbonate mineral.
The new raw material is added such that a larger number of metal ions than the number consumed in the reaction with the carbonate ions are generated, and thus in the second round of the separation step, the metal element included in the new raw material reacts with the chelating agent left in the aqueous solution, with the result that the metal element can be separated from the raw material as the metal ions. Here, the chelating agent which is fed in the aqueous solution formation step is not consumed in the subsequent steps, and thus the chelating agent can be reused even in the second round of the separation step. As described above, the second round of the separation step can be performed under substantially the same conditions as the first round of the separation step, and the second rounds of the mineral formation step and the pH lowering step can be performed in the same manner as in the first rounds thereof. In this way, even in the second round of the mineral formation step, carbon dioxide can be fixed as the carbonate mineral.
As described above, in the carbon dioxide fixation method according to the present invention, in the first and second rounds of the mineral formation step and at the time of feeding of the new raw material in the repetition step, carbon dioxide can be fixed, with the result that the carbon dioxide fixation method can contribute to the reduction of carbon dioxide which attracts attention in the environmental problem. In the carbon dioxide fixation method according to the present invention, carbon dioxide can be fixed under alkaline conditions, and thus chemicals for pH adjustment as in the pH swing are not needed, with the result that the material cost thereof can be reduced. Since the chelating agent which has been fed once can be reused, the material cost thereof can be reduced. Carbon dioxide can be fixed at a relatively low temperature, and thus facility costs can be reduced.
In the carbon dioxide fixation method according to the present invention, the metal element included in the raw material is not limited as long as the metal element such as calcium, magnesium, iron, copper or manganese can form a carbonate (also called a carbonate mineral), and at least one of the elements described above are preferably included. The raw material is not limited as long as the raw material includes the metal elements, and the raw material preferably includes one or a plurality of relatively easily available materials derived from a silicate mineral, steel slag and waste. The chelating agent is not limited as long as the chelating agent can react with metal ions, and examples of the ligand element of the chelating agent include nitrogen, oxygen, sulfur, phosphorus, arsenic and the like. The chelating agent is a known material, and specifically, the chelating agent is preferably biodegradable GLDA (N,N-Dicarboxymethyl glutamic acid) or EDTA (ethylenediaminetetrancetic acid).
In the carbon dioxide fixation method according to the present invention, the compound which is added in the mineral formation step is not limited as long as the compound such as sodium carbonate, potassium carbonate, lithium carbonate or carbon dioxide can generate carbonate ions in the aqueous solution after the separation step, and the compound preferably includes at least one of these compounds.
In the carbon dioxide fixation method according to the present invention, in order to accelerate the reaction of the carbonate ions with the metal ions in the mineral formation step, the pH of the aqueous solution (aqueous solution used in the mineral formation step) after the separation step is preferably 10 to 14. Since the pH of the aqueous solution is increased in the separation step, the pH of the alkaline aqueous solution formed in the aqueous solution formation step is preferably 8 to 10 and particularly preferably equal to or greater than 8.5 so that the pH of the aqueous solution after the separation step is 10 to 14. In this case, the reaction in the separation step can also be accelerated.
In the carbon dioxide fixation method according to the present invention, in order to accelerate the reaction of the metal element in the raw material with the chelating agent, the separation step is preferably performed at a temperature equal to or greater than 5° C. and equal to or less than 80° C. or may be performed at room temperature. In order to accelerate the reaction of the carbonate ions with the metal ions, the mineral formation step is preferably performed at a temperature of 70° C. to 170° C. The pH lowering step is preferably performed at a temperature equal to or greater than 5° C. and equal to or less than 80° C. or may be performed at room temperature.
In the carbon dioxide fixation method according to the present invention, in the aqueous solution formation step, the aqueous solution is preferably formed by adding the raw material and the chelating agent into water. In the separation step, after the separation of the metal element, a solid component left undissolved in the aqueous solution may be recovered. In the mineral formation step, the carbonate mineral which has been formed is preferably recovered from the aqueous solution after the reaction. In the pH lowering step, a solid component which is precipitated after the pH is lowered may be recovered.
In the carbon dioxide fixation method according to the present invention, the repetition step may be repeated a plurality of times. In this case, at the time of feeding of the new raw material and in the mineral formation step in the repetition step, carbon dioxide can be continuously fixed. The chelating agent fed in the aqueous solution formation step can be repeatedly used in the separation step of the repetition step, and thus material costs can be further reduced.
Preferably, in the carbon dioxide fixation method according to the present invention, carbon dioxide which is used is emitted from an industry with a high environmental burden caused by carbon dioxide emission and is recovered. As a method for separating and recovering carbon dioxide from emission gas, a known method may be adopted. For example, in a “post-combustion recovery method” in which carbon dioxide is recovered after burning of fossil fuels, a “chemical absorption method” in which carbon dioxide is separated by utilization of an aqueous amine solution can be used. In this method, the property of the aqueous amine solution in which carbon dioxide is absorbed in a low temperature state whereas carbon dioxide is discharged at a high temperature is utilized. This method is utilized, and thus carbon dioxide can be separated and recovered.
In the carbon dioxide fixation method according to the present invention, carbon dioxide which is emitted from the industry with a high environmental burden caused by carbon dioxide emission can be utilized to be fixed. For example, in Japan, examples of industries with a high environmental burden based on carbon dioxide emission ratio (2018: International Energy Agency (IEA)) include cement (27%), steel (25%), petrochemicals (14%), pulp and paper (2%), aluminum (2%) and other industries (30%). Thermal power plants which use fossil fuels (such as petroleum, coal and natural gas) as raw materials, steel industries and petrochemical industries are also mentioned as industries with a high environmental burden caused by carbon dioxide emission.
In a carbon dioxide recovery method according to the present invention, carbon dioxide emitted from industries with a high environmental burden caused by carbon dioxide emission is recovered by the carbon dioxide fixation method according to the present invention.
In the carbon dioxide recovery method according to the present invention, the environmental burden caused by these industries can be reduced.
A carbon dioxide fixation device according to the present invention includes: an aqueous solution formation unit which forms an alkaline aqueous solution using: a raw material including a metal element which can combine with carbonate ions to form a carbonate mineral; and a chelating agent; a separation unit which reacts the metal element with the chelating agent in the aqueous solution to separate the metal element from the raw material as metal ions; a mineral formation unit which adds, into the aqueous solution after the separation of the metal ions in the separation unit, a compound that can generate carbonate ions in the aqueous solution to form a carbonate mineral by reacting the carbonate ions generated from the compound with the metal ions; a pH lowering unit which injects carbon dioxide gas into the aqueous solution after the formation of the carbonate mineral in the mineral formation unit to lower the pH thereof to a value of or a value near the pH of the aqueous solution formed in the aqueous solution formation unit; and a raw material addition unit which adds a new raw material of the same type into the aqueous solution whose pH has been lowered in the pH lowering unit, and the aqueous solution into which the new raw material has been added in the raw material addition unit is supplied to the separation unit, and is sequentially moved from the separation unit, to the mineral formation unit and then to the pH lowering unit.
The carbon dioxide fixation device according to the present invention can preferably perform the carbon dioxide fixation method according to the present invention. In the carbon dioxide fixation device and the carbon dioxide fixation method according to the present invention, it is possible to provide a carbonate mineral in which carbon dioxide is fixed. For example, the carbon dioxide fixation device according to the present invention is preferably used when carbon dioxide emitted in the industry with a high environmental burden caused by carbon dioxide emission is fixed, and is preferably incorporated as a part of an environmentally friendly industrial facility. In other words, an environmentally friendly industrial facility according to the present invention includes the carbon dioxide fixation device according to the present invention.
According to the present invention, it is possible to provide a carbon dioxide fixation method, a carbon dioxide recovery method, a carbon dioxide fixation device and an environmentally friendly industrial facility which can reduce material costs and facility costs.
Embodiments of the present invention will be described below based on drawings, Example and the like.
As shown in
In the carbon dioxide fixation method according to the embodiment of the present invention, as the aqueous solution formation step, a raw material including a metal element and a chelating agent are first added into water to form an alkaline aqueous solution having a pH of 8 to 10. The temperature of the aqueous solution is set in a range equal to or greater than room temperature and equal to or less than 80° C. In a specific example, the chelating agent is added into water to form the aqueous solution having a pH of 8 to 10, the temperature of the aqueous solution is set in the range equal to or greater than room temperature and equal to or less than 80° C. and thereafter the raw material is added into the aqueous solution.
In the aqueous solution formation step, the metal element included in the raw material is formed of an element which can combine with carbonate ions to form a carbonate mineral, and examples thereof include calcium, magnesium, iron, copper, manganese and the like. The raw material includes the metal elements described above, and is, for example, a silicate mineral, steel slag, waste or the like which is relatively easily available. The chelating agent includes a material which can react with metal ions, and is, for example, biodegradable GLDA-4Na, EDTA-4Na or the like. In a specific example shown in
When the aqueous solution is formed in the aqueous solution formation step, in the separation step, the metal element included in the raw material reacts with the chelating agent so as to be separated as metal ions in the aqueous solution. By the separation of the metal element, the pH of the aqueous solution is increased, and thus the pH of the aqueous solution after the separation step is 10 to 14. In the separation step, after the separation of the metal element, a solid component which is left without being dissolved in the aqueous solution may be recovered.
Then, after the separation step, as the mineral formation step, the temperature of the aqueous solution (having a pH of 10 to 14) after the separation step is increased to 70° C. or more, and a compound which can generate carbonate ions in the aqueous solution is added. In this way, the carbonate ions which are generated from the compound added into the aqueous solution reacts with the metal ions, and thus a carbonate mineral can be formed. Consequently, carbon dioxide can be fixed as the carbonate mineral. In the mineral formation step, the formed carbonate mineral is preferably recovered from the aqueous solution after the reaction. The recovered carbonate mineral can be effectively utilized. In the mineral formation step, the pH of the aqueous solution hardly changes.
The compound which is added into the aqueous solution in the mineral formation step can generate carbonate ions in the aqueous solution after the separation step, and examples thereof include sodium carbonate, potassium carbonate, lithium carbonate, carbon dioxide and the like. In the specific example shown in
Then, after the mineral formation step, as the pH lowering step, the temperature of the aqueous solution after the mineral formation step is set in the range equal to or greater than room temperature and equal to or less than 80° C., and carbon dioxide gas is injected to lower the pH thereof to a value of or a value near the pH of the aqueous solution formed in the aqueous solution formation step. Specifically, the pH is lowered to a value of 8 to 10, and is returned to the original value. In this way, the concentration of carbonate ions in the aqueous solution is increased. By lowering the pH, a component unrelated to the mineral formation in the mineral formation step or a part thereof can be precipitated in the aqueous solution. In the pH lowering step, a solid component which is precipitated may be recovered from the aqueous solution the pH of which has been lowered. The recovered solid component can be effectively utilized. In the specific example shown in
Then, after the pH lowering step, as the repetition step, a new raw material of the same type is first added into the aqueous solution after the pH lowering step. Here, metal ions which are generated from a metal element included in the new raw material or the metal ions which are not consumed in the first round of the mineral formation step react with the carbonate ions, and thus a carbonate mineral can be formed. In this way, carbon dioxide can be fixed as the carbonate mineral. In the repetition step, the carbonate mineral formed here is preferably recovered from the aqueous solution after the reaction. The recovered carbonate mineral can be effectively utilized.
In the repetition step, the new raw material is added such that a larger number of metal ions than the number consumed in the reaction with the carbonate ions are generated, and thus steps from the separation step to the pH lowering step are performed again. In the second round of the separation step, the metal element included in the new raw material reacts with the chelating agent left in the aqueous solution, and thus the metal element can be separated from the raw material as metal ions. The chelating agent which is fed in the aqueous solution formation step is not consumed in the subsequent steps, and thus the chelating agent can be reused even in the second round of the separation step. As described above, the second round of the separation step can be performed under substantially the same conditions as the first round of the separation step, and the second rounds of the mineral formation step and the pH lowering step can be performed in the same manner as in the first rounds thereof. In this way, even in the second round of the mineral formation step, carbon dioxide can be fixed as the carbonate mineral.
As described above, in the carbon dioxide fixation method according to the embodiment of the present invention, in the first and second rounds of the mineral formation step and at the time of feeding of the new raw material in the repetition step, carbon dioxide can be fixed, with the result that the carbon dioxide fixation method can contribute to the reduction of carbon dioxide to be emitted. In the carbon dioxide fixation method according to the embodiment of the present invention, carbon dioxide can be fixed under alkaline conditions, and thus chemicals for pH adjustment as in the pH swing are not needed, with the result that the material cost thereof can be reduced. Since the chelating agent which has been fed once can be reused, the material cost thereof can be reduced. Carbon dioxide can be fixed at a relatively low temperature, and thus facility costs can be reduced.
In the carbon dioxide fixation method according to the embodiment of the present invention, the repetition step may be repeated a plurality of times. In this case, at the time of feeding of the new raw material and in the mineral formation step in the repetition step, carbon dioxide can be continuously fixed. The chelating agent fed in the aqueous solution formation step can be repeatedly used in the separation step of the repetition step, and thus material costs can be further reduced.
As a raw material. CaSiO3 (made by FUJIFILM Wako Pure Chemical Corporation) was used, as a chelating agent, GLDA-4Na (N,N-Dicarboxymethyl glutamic acid, tetrasodium salt made by Tokyo Chemical Industry Co., Ltd.) was used and experiments on the carbon dioxide fixation method according to the embodiment of the present invention were performed. Experiments on an aqueous solution formation step and a separation step were first performed. In the experiments, as shown in
The experiments were performed as shown in Table 1 under conditions in which the pH (pH0) of the aqueous solution 2a, the temperature of the aqueous solution 2a, the amount of CaSiO3 fed and the concentration of GLDA-4Na serving as parameters were variously changed. In the experiments, in order to check a state where Ca serving as a metal element was separated from the raw material, the concentration of Ca (Ca ions) in an aqueous solution 2b which had been filtered and the like in experiments Nos. 1 to 12 shown in Table 1 were measured. In the following description, all the Ca in the aqueous solution indicates Ca ions.
In experiments Nos. 1 to 12 of Table 1, changes in the concentration of Ca in each of the aqueous solutions with time until the elapse of 20 minutes after the feeding of CaSiO3 into the aqueous solution 2a are shown in
As shown in
Then, experiments on a mineral formation step were performed. The aqueous solution 2b (pH of 11.9) in which the aqueous solution after the elapse of 20 minutes in experiment No. 4 of Table 1 had been filtered was used, as shown in
The residual ratios of Ca (Residual Ca ratios) in the aqueous solution at the temperatures after the elapse of 70 minute after the addition of Na2CO3 when the concentration of Na2CO3 was set to 0.3 mol/L are shown in
As shown in
As shown in
Then, experiments on a pH lowering step were performed. The amount of Ca was reduced to about 45%, the aqueous solution 2c shown in
A relationship between the pH and the Si concentration which were measured is shown in
Then, experiments on the repetition step were performed. The pH was lowered to 9, an aqueous solution 2d shown in
Consequently, it has been confirmed that Ca included in the newly added CaSiCO3 and Ca which was not consumed in the first round of the mineral formation step reacts with the carbonate ions the concentration of which had been increased in the pH lowering step, and thus CaCO3 is formed. It has also been confirmed that since the pH was increased. Ca included in the newly added CaSiO3 reacted with the chelating agent left in the aqueous solution and thus Ca was extracted from CaSiO3. It has been confirmed that the aqueous solution 2e obtained after filtering in the second round of the separation step shown in
Then, the aqueous solution 2e shown in
It has been mentioned from the experiments on the repetition step shown in
A carbon dioxide fixation device according to an embodiment of the present invention can easily be designed and produced by applying the carbon dioxide fixation method according to the embodiment of the present invention. Specifically, the carbon dioxide fixation device according to the embodiment of the present invention includes an aqueous solution formation unit, a separation unit, a mineral formation unit, a pH lowering unit and a raw material addition unit. The aqueous solution formation unit forms an alkaline aqueous solution including: a raw material including a metal element which can combine with carbonate ions to form a carbonate mineral; and a chelating agent, and can perform the aqueous solution formation step in the carbon dioxide fixation method according to the embodiment of the present invention. The separation unit reacts the metal element with the chelating agent in the aqueous solution to separate the metal element from the raw material as metal ions, and can perform the separation step in the carbon dioxide fixation method according to the embodiment of the present invention. The mineral formation unit adds, into the aqueous solution after the separation of the metal ions in the separation unit, a compound which can generate carbonate ions in the aqueous solution to react the carbonate ions generated from the compound with the metal ions so as to form a carbonate mineral, and can perform the mineral formation step in the carbon dioxide fixation method according to the embodiment of the present invention. The pH lowering unit injects carbon dioxide gas into the aqueous solution after the formation of the carbonate mineral in the mineral formation unit to lower the pH thereof to a value of or a value near the pH of the aqueous solution formed in the aqueous solution formation unit, and can perform the pH lowering step in the carbon dioxide fixation method according to the embodiment of the present invention. The raw material addition unit adds a new raw material of the same type as the raw material used in the aqueous solution formation unit into the aqueous solution the pH of which has been lowered in the pH lowering unit. Furthermore, in the carbon dioxide fixation device according to the embodiment of the present invention, the aqueous solution into which the new raw material has been added in the raw material addition unit is supplied to the separation unit, and is sequentially moved from the separation unit, to the mineral formation unit and then to the pH lowering unit, and can perform, together with the raw material addition unit, the repetition step in the carbon dioxide fixation method according to the embodiment of the present invention. In this way, the carbon dioxide fixation method and the carbon dioxide fixation device according to the embodiments of the present invention can provide a carbonate mineral in which carbon dioxide is fixed.
The carbon dioxide fixation device according to the embodiment of the present invention can fix carbon dioxide emitted from an industry with a high environmental burden caused by carbon dioxide emission. The carbon dioxide fixation device according to the embodiment of the present invention can be incorporated as an environmentally friendly industrial facility and a part thereof which fix carbon dioxide emitted in an industry with a high environmental burden caused by carbon dioxide emission. In other words, the environmentally friendly industrial facility according to an embodiment of the present invention includes the carbon dioxide fixation device according to the embodiment of the present invention.
In a carbon dioxide recovery method according to an embodiment of the present invention, carbon dioxide emitted in an industry with a high environmental burden caused by carbon dioxide emission is recovered by the carbon dioxide fixation method according to the embodiment of the present invention. In this way, in the carbon dioxide recovery method according to the embodiment of the present invention, it is possible to reduce environmental burdens caused by these industries.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-217738 | Dec 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/045014 | 12/7/2021 | WO |
