Carbon dioxide fixation method, carbon dioxide fixation suspension, carbon dioxide fixation powder, and carbon dioxide fixation device

Abstract

To provide a carbon dioxide fixation method that is suitable for medium and small-sized exhausters because of its high absorption efficiency of CO2 and low facility cost.SOLUTION: Provided is a carbon dioxide fixation method for fixing carbon dioxide in a carbon dioxide fixation agent, including a step of supplying a carbon dioxide-containing gas from the outside of a porous pipe into the inside of the porous pipe while circulating a fixation-agent-containing composition containing the fixation agent in the porous pipe, thereby generating microbubbles of the carbon dioxide-containing gas inside the porous pipe.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide fixation method, a carbon dioxide fixation suspension, a carbon dioxide fixation powder, and a carbon dioxide fixation device. [Background technology]

[0002] In recent years, there has been a demand for reducing CO2 emissions in relation to the issue of global warming. As a method for reducing CO2 emissions, for example, a method has been disclosed in which an immobilization composition having a carbon dioxide immobilization agent attached thereto that immobilizes carbon dioxide is placed in a high-concentration carbon dioxide gas flow path, and carbon dioxide is immobilized on the surface and stored (see Patent Document 1).

[0003] However, the method described in Patent Document 1 has the problem that the efficiency of CO2 fixation is low and the amount of carbon dioxide fixed is insufficient.

[0004] Carbon dioxide Capture, Utilization and Storage (CCUS) is being adopted as a method of reducing CO2 emissions by businesses and other entities with large CO2 emissions. Specifically, the CO2 released into the atmosphere is reduced by absorbing the CO2 contained in exhaust gases from incinerators and other sources into a basic solution, and the basic solution is then concentrated to recapture the CO2 gas or liquefied CO2, which is then used as a resource.

[0005] However, the above method does not provide sufficient CO2 fixation efficiency and low CO2 absorption efficiency, and there is room for further improvement.

[0006] Another problem with the above methods is that the capture cost per unit weight of CO2 is very high. Furthermore, chemical absorption plants like CCUS require large-scale equipment costs due to the complex processes involved. Even if the capture cost were reduced, they would only be targeted at large-scale CO2-producing businesses, such as steelmakers and thermal power plants (oil and coal), that can absorb the initial investment. This means that they are not suitable for small- to medium-sized emitters of CO2, emitting a few tons or even thousands of tons per year.

[0007] A carbon dioxide fixation method suitable for small and medium-sized emitters, which has the advantages of high CO2 absorption efficiency and low equipment costs, especially a method that can be used for a wide variety of exhaust gases, has not yet been developed. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2023-22383 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide a carbon dioxide fixation method that is suitable for small and medium-sized emitters because it has high CO2 absorption efficiency and low equipment costs. [Means for solving the problem]

[0010] As a result of extensive research into achieving the above-mentioned object, the present inventors have found that the above-mentioned object can be achieved by a carbon dioxide fixation method comprising the steps of supplying a carbon dioxide-containing gas from the outside of a porous tube into the inside of the porous tube while circulating a fixation liquid containing a fixation agent inside the porous tube, thereby generating microbubbles of the carbon dioxide-containing gas inside the porous tube, and have thus completed the present invention.

[0011] That is, the present invention relates to the following carbon dioxide fixation method, carbon dioxide fixation suspension, carbon dioxide fixation powder, and carbon dioxide fixation device. 1. A carbon dioxide fixation method for fixing carbon dioxide in a carbon dioxide fixation agent, comprising: A carbon dioxide fixation method comprising the steps of: supplying a carbon dioxide-containing gas from outside the porous pipe into the porous pipe while circulating a fixation-agent-containing composition containing the fixation agent inside the porous pipe, thereby generating microbubbles of the carbon dioxide-containing gas inside the porous pipe. 2. The carbon dioxide fixation method according to Item 1, wherein the fixation agent contains a hydroxide of at least one metal selected from the group consisting of alkali metals, alkaline earth metals, and rare earths. 3. The carbon dioxide fixation method according to Item 1, wherein the fixation agent is a metal hydroxide of an alkaline earth metal. 4. The carbon dioxide fixation method according to any one of items 1 to 3, wherein the microbubbles have a bubble diameter distribution of 0.5 to 100 μm. 5. The carbon dioxide fixation method according to any one of Items 1 to 4, wherein the porous tube is a ceramic porous tube, a metal porous tube, or a resin porous tube. 6. The carbon dioxide fixation method according to any one of items 1 to 5, wherein the porous tube has a pore size of 0.1 to 50 μm. 7. The carbon dioxide fixation method according to any one of Items 1 to 6, wherein the flux of the fixation agent-containing composition inside the porous tube is 0.1 to 50 m / s. 8. The carbon dioxide fixation method according to any one of items 1 to 7, wherein the fixation agent-containing composition has a pH of 5 or higher. 9. A carbon dioxide fixation suspension containing a fixation agent in which carbon dioxide is fixed. 10. The carbon dioxide fixation suspension according to Item 9, wherein the fixation agent in which carbon dioxide is fixed contains a hydroxide of at least one metal selected from the group consisting of alkali metals, alkaline earth metals, and rare earths. 11. Carbon dioxide fixation powder containing a fixation agent in which carbon dioxide is fixed. 12. The carbon dioxide fixation powder according to Item 11, wherein the fixation agent in which carbon dioxide is fixed contains a hydroxide of at least one metal selected from the group consisting of alkali metals, alkaline earth metals, and rare earths. 13. A carbon dioxide fixation device for fixating carbon dioxide in a carbon dioxide fixation agent, the carbon dioxide fixation device having a fixation agent-containing composition containing the fixation agent within a porous tube. 14. The carbon dioxide fixation device according to Item 13, wherein the porous tube is a ceramic porous tube, a metal porous tube, or a resin porous tube. 15. The carbon dioxide fixation device according to item 13 or 14, wherein the porous tube has a pore size of 0.1 to 50 μm. [Effects of the Invention]

[0012] The carbon dioxide fixation method of the present invention is suitable for small and medium-sized emitters because it has high CO2 absorption efficiency and low equipment costs. Furthermore, the carbon dioxide fixation suspension of the present invention and the carbon dioxide fixation powder of the present invention fix a high amount of CO2 and are excellent in CO2 storage capacity. Furthermore, the carbon dioxide fixation device of the present invention can implement a carbon dioxide fixation method with high CO2 absorption efficiency and low equipment costs. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing a carbon dioxide fixation apparatus used in the carbon dioxide fixation method of the present invention. [Figure 2] 1 is a longitudinal cross-sectional view of an SPG module equipped with a porous ceramic tube, which is used in the carbon dioxide fixation method of the present invention. FIG. [Figure 3] 1 is a schematic cross-sectional view in the short direction of an SPG module equipped with a ceramic porous tube, which is used in the carbon dioxide fixation method of the present invention. FIG. [Figure 4] FIG. 1 is a graph showing the relationship between suspension pH and reaction time when the flow rate of carbon dioxide-containing gas, that is, the number of moles of CO2 supplied per unit time (carbon dioxide molar flow rate), is changed in various ways in the present invention. [Figure 5] FIG. 1 is a diagram showing thermodynamic principles in the solution chemistry of calcium carbonate, i.e., a diagram showing the relationship between the abundance ratio of CO3 2− and HCO3 − and pH in the present invention. [Figure 6] FIG. 1 is a diagram showing the relationship between the CO2 inflow rate (molar flow rate of carbon dioxide) and the reaction rate in the present invention. [Figure 7] FIG. 10 is a diagram showing the relationship between Ca2+ concentration and pH in Example 3. [Figure 8] FIG. 10 is a diagram showing the results of XRD analysis of the precipitate recovered after filtering the immobilizing agent-containing composition having a pH of 7 in Example 3. [Figure 9] FIG. 10 is a graph showing the particle size distribution of the precipitate (CaCO3) recovered by filtering the immobilizing agent-containing composition having a pH of 7 in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0014] 1. Carbon dioxide fixation method The carbon dioxide fixation method of the present invention is a method for fixating carbon dioxide in a carbon dioxide fixation agent, comprising the steps of: circulating a fixation agent-containing composition containing the fixation agent through a porous pipe; and supplying a carbon dioxide-containing gas from outside the porous pipe into the porous pipe to generate microbubbles of the carbon dioxide-containing gas within the porous pipe. The carbon dioxide fixation method of the present invention, characterized by the above-described features, comprises the steps of supplying a carbon dioxide-containing gas from outside the porous pipe into the porous pipe to generate microbubbles of the carbon dioxide-containing gas within the porous pipe. This allows the carbon dioxide to disperse in the fixation agent-containing composition flowing through the porous pipe in the form of microbubbles, increasing the contact area of the carbon dioxide, thereby increasing the opportunity for contact with the fixation agent and enabling efficient fixation of carbon dioxide in the fixation agent. Furthermore, the carbon dioxide fixation method of the present invention can be implemented using only a porous pipe, equipment for supplying a carbon dioxide-containing gas through the porous pipe, and equipment for flowing a fixation liquid containing a fixation agent through the porous pipe. Therefore, the equipment costs are lower than those of a plant with large-scale facilities. This carbon dioxide fixation method is suitable for small- to medium-sized carbon dioxide emitters.

[0015] The carbon dioxide fixation method of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a carbon dioxide fixation apparatus used in the carbon dioxide fixation method of the present invention. In FIG. 1, the carbon dioxide fixation apparatus has a reaction vessel containing a fixation agent-containing composition. The fixation agent-containing composition is pumped up and passed through a flow meter, causing the fixation agent-containing composition to circulate inside the SPG module, which is a porous tube. At the same time, 15% CO2 gas, a carbon dioxide-containing gas, is sent from a gas cylinder outside the porous tube into the porous tube, generating microbubbles of the carbon dioxide-containing gas inside the porous tube. In FIG. 1, the reaction vessel is placed in a thermostatic bath connected to a thermostatic water circulator, and the fixation agent-containing composition in the reaction vessel is prepared.

[0016] Fig. 2 is a longitudinal cross-sectional view of an SPG module, which is a porous pipe used in the carbon dioxide fixation method of the present invention, and Fig. 3 is a transverse cross-sectional view. In the carbon dioxide fixation method of the present invention, as shown in Figs. 2 and 3, a carbon dioxide-containing gas is sent from the outside of the porous pipe to the inside of the porous pipe, causing microbubbles of the carbon dioxide-containing gas to be generated in the immobilizing agent-containing composition inside the porous pipe.

[0017] Hereinafter, each element constituting the carbon dioxide fixation method of the present invention will be described.

[0018] (fixing agent) The carbon dioxide immobilization agent is not particularly limited, and known compounds capable of binding with and immobilizing carbon dioxide can be used. Examples of such compounds include hydroxides of metals such as alkali metals, alkaline earth metals, rare earth metals, and heavy metals. Among these, hydroxides of metals such as alkali metals, alkaline earth metals, and rare earth metals are preferred, with metal hydroxides of alkaline earth metals being more preferred, as they are more likely to immobilize carbon dioxide. Alternatively, a mixture containing a metal hydroxide of one of these metals as the main component and a soluble salt of the metal (such as a chloride, sulfate, or nitrate) may be used. The term "main component" as used herein means that the content of the metal hydroxide is 50% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, or 99% by mass or more, based on 100% by mass of the carbon dioxide immobilization agent.

[0019] Examples of alkali metals include Li, Na, K, Rb, Cs, etc. Among these, Li, Na, and K are preferred, and Li is more preferred, in terms of the amount of carbon dioxide that can be fixed.

[0020] Examples of alkaline earth metals include Be, Mg, Ca, Sr, and Ba. Among these, Be, Mg, and Ca are preferred, and Ca is more preferred. That is, calcium hydroxide (Ca(OH)2) is preferably used as a carbon dioxide fixation agent.

[0021] Examples of rare earth elements include lanthanoid elements of the sixth period, such as yttrium, lutetium, lanthanum, dysprosium, neodymium, and samarium, and actinoid elements of the seventh period.

[0022] Examples of metals include manganese, chromium, copper, cadmium, mercury, selenium, lead, arsenic, and cadmium.

[0023] The carbon dioxide immobilizing agent may be a mixture containing a metal hydroxide of one of the above metals as the main component, mixed with a soluble salt of the metal (chloride, sulfate, nitrate, etc.). An example of such a mixture is a mixture of calcium hydroxide and calcium chloride. The term "main component" means that the content of the metal hydroxide is 50% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, or 99% by mass or more, based on 100% by mass of the carbon dioxide immobilizing agent.

[0024] The carbon dioxide fixation agents can be used alone or in combination of two or more.

[0025] By using the above-mentioned fixation agent, carbon dioxide is fixed in the fixation agent. Specifically, the fixation agent reacts with carbon dioxide, and carbon dioxide is fixed in the reaction product. For example, when the fixation agent is calcium hydroxide (Ca(OH)2), it reacts with carbon dioxide to produce a product as shown in the following formula, and carbon dioxide is contained in the fixation agent-containing composition. In other words, carbon dioxide is fixed in the fixation agent. First step at pH above 12: Ca 2+ +CO3 2- →CaCO3 · Second step of the reaction at pH 7-12: CaCO3 + H2O + CO2 → Ca(HCO3)2 → Ca 2+ +2HCO3 -

[0026] (Fixing agent-containing composition) The fixative-containing composition is a composition containing the fixative and flows through the porous pipe. The fixative-containing composition may be in the form of a liquid or a suspension.

[0027] The solvent constituting the fixative-containing composition is not particularly limited as long as it can dissolve or uniformly disperse the fixative, and examples thereof include water, lower alcohols such as methanol, polar inorganic or organic liquids such as dimethyl sulfoxide, etc. Among these, water is preferred from the viewpoints of excellent fixative solubility and safety.

[0028] The content of the fixative in the fixative-containing composition is preferably 0.1 g / kg or more, more preferably 0.3 g / kg or more, even more preferably 0.5 g / kg or more, particularly preferably 0.7 g / kg or more, and most preferably 1 g / kg or more. The content of the fixative in the fixative-containing composition is preferably 900 g / kg or less, more preferably 750 g / kg or less, even more preferably 300 g / kg or less, particularly preferably 100 g / kg or less, and most preferably 10 g / kg or less. By setting the lower limit of the fixative content within the above range, carbon dioxide can be more fully fixed. By setting the upper limit of the fixative content within the above range, the carbon dioxide absorption rate can be further improved.

[0029] The pH of the immobilizing agent-containing composition is preferably 5 or higher, more preferably 7 or higher, more preferably 9 or higher, and even more preferably 10 or higher. The pH is also preferably 14 or lower, more preferably 13 or lower, even more preferably 12 or lower, and particularly preferably 11 or lower. When the lower limit of the pH is within the above range, for example, when the immobilizing agent is CaCO3, dissolution of CaCO3 is suppressed, and the amount of CaCO3 recovered is further improved. In particular, when carbon dioxide immobilization is completed at a pH range of 10 to 11, the yield of Ca is maximized (97% or higher), and therefore, CaCO3 can be recovered with the highest yield.

[0030] (porous tube) The porous pipe is not particularly limited as long as it can supply a carbon dioxide-containing gas from the outside of the porous pipe to the inside of the porous pipe and generate microbubbles of the carbon dioxide-containing gas in the immobilizing agent-containing composition inside the porous pipe. Examples of such porous pipes include ceramic porous pipes, metal porous pipes, and resin porous pipes. Among these, ceramic porous pipes are preferred because the pore size formed in the porous pipe can be easily adjusted to a pore size that allows microbubbles to be formed.

[0031] Examples of the ceramic porous tube include an SPG membrane, etc. In the carbon dioxide fixation device, an SPG module having an SPG membrane, etc. is preferably used.

[0032] Examples of the porous metal tube include porous metal tubes made of metals such as Fe, Cu, stainless steel, and noble metals.

[0033] Examples of the porous resin pipe include porous resin pipes made of resins such as polyvinyl chloride and polyethylene.

[0034] The wall of the porous tube has holes for supplying a carbon dioxide-containing gas from the outside of the porous tube to the inside of the porous tube. The pore size (diameter of the pores) of the porous tube is preferably 0.1 to 50 μm, more preferably 0.2 to 10 μm, more preferably 0.3 to 5 μm, and even more preferably 0.3 to 2 μm. When the pore size of the porous tube is within the above range, microbubbles can be more easily generated in the immobilizing agent-containing composition flowing inside the porous tube.

[0035] The bubble size distribution of the microbubbles generated in the immobilizing agent-containing composition in the porous tube is preferably 0.1 to 200 μm, more preferably 0.3 to 50 μm, even more preferably 0.5 to 20 μm, and particularly preferably 0.5 to 10 μm. When the lower limit of the bubble size distribution is within the above range, carbon dioxide can be immobilized more sufficiently. When the upper limit of the bubble size distribution is within the above range, carbon dioxide absorption efficiency is further improved.

[0036] (carbon dioxide containing gas) The carbon dioxide-containing gas is not particularly limited as long as it contains carbon dioxide, and a mixed gas of carbon dioxide and other gases can be used as such a carbon dioxide-containing gas.

[0037] The other gases are not particularly limited, and examples thereof include air, nitrogen, oxygen, argon, etc. Among these, air is preferred because it is easy to prepare, inexpensive, and has excellent stability.

[0038] The carbon dioxide content in the carbon dioxide-containing gas is preferably 0.01 to 50%, more preferably 1 to 30%, still more preferably 5 to 20%, and particularly preferably 10 to 20%. When the lower limit of the carbon dioxide content is within the above range, the carbon dioxide can be fixed more efficiently and sufficiently.

[0039] (Process) The carbon dioxide fixation method of the present invention includes a step of supplying a carbon dioxide-containing gas from the outside of the porous pipe to the inside of the porous pipe while circulating a fixation agent-containing composition containing a fixation agent in the porous pipe, thereby generating microbubbles of the carbon dioxide-containing gas inside the porous pipe.

[0040] The method for distributing the immobilizing agent-containing composition is not particularly limited as long as it allows the immobilizing agent-containing composition to move through a porous pipe and generates microbubbles of carbon dioxide-containing gas within the porous pipe. For example, as shown in Figure 1, a method in which the immobilizing agent-containing composition is drawn up from a reaction vessel using a pump and then distributed through a porous pipe under pressure is exemplified. The pump pressure is not particularly limited, but is preferably 0.1 to 20 MPa, more preferably 0.105 to 10 MPa.

[0041] The flow rate of the fixation-agent-containing composition during circulation may be adjusted appropriately depending on the scale of the facility. For example, when the total amount of fixation-agent-containing composition circulating through the facility is 10 L, the flow rate of the fixation-agent-containing composition during circulation is preferably 1 L / min or more, more preferably 5 L / min or more. When the flow rate of the fixation-agent-containing composition is within the above range, carbon dioxide can be more efficiently and sufficiently fixed. There is no particular upper limit to the flow rate, and the higher the flow rate, the more efficiently and sufficiently carbon dioxide can be fixed.

[0042] The flow rate of the immobilizing agent-containing composition per minute during circulation is preferably 1 / 10 or more, more preferably 1 / 2 or more, of the total amount of the immobilizing agent-containing composition in the facility. 3 In this case, the flow rate of the immobilizing agent-containing composition during distribution is 0.1 m 3 / min or more is preferable, and 0.5m 3 / min or more. In addition, the total amount of the immobilizing agent-containing composition flowing through the facility is preferably 1000 m 3 In this case, the flow rate of the immobilizing agent-containing composition during distribution is 100 m 3 / min or more is preferable, and 500m 3 / min or more. Furthermore, the total amount of the fixative-containing composition flowing through the facility is preferably 100,000 m 3 In this case, the flow rate of the immobilizing agent-containing composition during distribution is 10,000 m 3 / min or more is preferable, and 50,000m 3 / min or more is more preferable. By keeping the flow rate of the immobilizing agent-containing composition within the above range, carbon dioxide can be immobilized more efficiently and sufficiently. There is no particular upper limit to the flow rate, and the higher the flow rate, the more efficiently and sufficiently carbon dioxide can be immobilized.

[0043] The flux of the immobilizing agent-containing composition inside the porous tube is preferably 0.1 to 50 m / s. By keeping the flux within the above range, carbon dioxide can be immobilized more efficiently and sufficiently.

[0044] The flux can be determined by dividing the flow rate of the liquid by the cross-sectional area of the tube.

[0045] The temperature of the fixation-agent-containing composition in the step (the temperature of the fixation-agent-containing composition in the reaction tank in FIG. 1) is preferably 0 to 100°C, more preferably 2 to 30°C, and even more preferably 5 to 20°C. When the lower limit of the temperature is within the above range, the viscosity of the fixation-agent-containing composition decreases and the fixation-agent-containing composition becomes more fluid, allowing carbon dioxide to be fixed more efficiently and sufficiently. When the upper limit of the temperature is within the above range, evaporation of the solvent in the fixation-agent-containing composition is suppressed, making it easier to maintain a constant concentration of the fixation agent in the fixation-agent-containing composition.

[0046] The inflow rate of the carbon dioxide-containing gas when it is fed from the outside of the porous tube into the inside of the porous tube, i.e., the number of moles of CO2 fed per unit time (carbon dioxide molar flow rate), can be adjusted appropriately depending on the scale of the facility. For example, when the total amount of the immobilizing agent-containing composition circulating through the facility is 10 L, the inflow rate is preferably 0.0001 to 0.5 mol / min, more preferably 0.001 to 0.4 mol / min, and even more preferably 0.005 to 0.3 mol / min. By setting the lower limit of the inflow rate within the above range, carbon dioxide can be immobilized in the immobilizing agent in a shorter time. By setting the upper limit of the inflow rate within the above range, the reaction rate between the immobilizing agent and carbon dioxide can be further improved.

[0047] Through the steps described above, carbon dioxide can be immobilized in the carbon dioxide immobilization agent.

[0048] In the carbon dioxide fixation method of the present invention, after carbon dioxide is fixed in the carbon dioxide fixation agent, the fixation agent-containing composition can be filtered to recover the precipitate (for example, CaCO3).

[0049] 2. Carbon dioxide fixation suspension The carbon dioxide fixation suspension of the present invention (hereinafter sometimes simply referred to as "suspension") contains a fixation agent in which carbon dioxide is fixed. The carbon dioxide fixation suspension of the present invention is not particularly limited as long as it is a suspension containing a fixation agent in which carbon dioxide is fixed, but for example, it is a fixation agent-containing composition in the form of a suspension containing a fixation agent in which carbon dioxide has been fixed by the carbon dioxide fixation method of the present invention described above.

[0050] The immobilization agent in which carbon dioxide is immobilized is the same as that described in the carbon dioxide immobilization method above.

[0051] The carbon dioxide content in the suspension of the present invention is preferably 0.1% by mass or more, more preferably 10% by mass or more, and even more preferably 30% by mass or more, based on 100% by mass of the suspension of the present invention. The upper limit of the carbon dioxide content in the suspension of the present invention is preferably as high as possible, and may be 95% by mass or less, 90% by mass or less, 80% by mass or less, 75% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, or 40% by mass or less.

[0052] In the suspension of the present invention, the immobilizing agent in which carbon dioxide is immobilized is not particularly limited, and examples thereof include hydroxides of metals such as alkali metals, alkaline earth metals, rare earth metals, heavy metals, etc. Among these, hydroxides of metals such as alkali metals, alkaline earth metals, and rare earth metals are preferred, and metal hydroxides of alkaline earth metals are more preferred, in that they can more easily immobilize carbon dioxide.

[0053] The hydroxides of metals such as alkali metals, alkaline earth metals, rare earths, and heavy metals are the same as those explained in the carbon dioxide fixation method of the present invention.

[0054] The immobilizing agents in which carbon dioxide is immobilized may be used alone or in combination of two or more.

[0055] 3. Carbon dioxide fixation powder The carbon dioxide fixation powder of the present invention (hereinafter sometimes simply referred to as "powder") contains a fixation agent in which carbon dioxide is fixed. The carbon dioxide fixation powder of the present invention is not particularly limited as long as it is a powder containing a fixation agent in which carbon dioxide is fixed, but for example, it is a powder obtained by removing the solvent from a fixation agent-containing composition containing a fixation agent in which carbon dioxide has been fixed by the carbon dioxide fixation method of the present invention described above.

[0056] The immobilization agent in which carbon dioxide is immobilized is the same as that described in the carbon dioxide immobilization method above.

[0057] The carbon dioxide content in the powder of the present invention may be more than 0% by mass, assuming the suspension of the present invention to be 100% by mass. The upper limit of the carbon dioxide content in the suspension of the present invention is preferably as high as possible, and may be 80% by mass or less, 70% by mass or less, 60% by mass or less, or 50% by mass or less.

[0058] In the powder of the present invention, the immobilizing agent in which carbon dioxide is immobilized is not particularly limited, and examples thereof include hydroxides of metals such as alkali metals, alkaline earth metals, rare earth metals, heavy metals, etc. Among these, hydroxides of metals such as alkali metals, alkaline earth metals, and rare earth metals are preferred, and metal hydroxides of alkaline earth metals are more preferred, in that they more easily immobilize carbon dioxide.

[0059] The hydroxides of metals such as alkali metals, alkaline earth metals, rare earths, and heavy metals are the same as those explained in the carbon dioxide fixation method of the present invention.

[0060] The immobilizing agents in which carbon dioxide is immobilized may be used alone or in combination of two or more.

[0061] (Carbon dioxide fixation device) The carbon dioxide fixation device of the present invention is a carbon dioxide fixation device that fixes carbon dioxide in a carbon dioxide fixation agent, and has a fixation agent-containing composition containing a fixation agent in a porous pipe. The carbon dioxide fixation device of the present invention is capable of circulating the fixation agent-containing composition in the porous pipe. An example of such a carbon dioxide fixation device is the carbon dioxide fixation device shown in FIG. 1.

[0062] The components such as the porous pipe constituting the carbon dioxide fixation device shown in FIG. 1 and the porous pipe shown in FIG. 2 are the same as those described in the carbon dioxide fixation method above. [Example]

[0063] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0064] The raw materials, equipment, etc. used in the examples and comparative examples are as follows.

[0065] (porous tube) SPG (Shirasu Porous Glass) tube: manufactured by SPG Techno Co., Ltd. Product name: SPG membrane, pore size 0.5 μm, outer diameter 5 / 10 mm, length customizable up to 500 mm (carbon dioxide fixation agent) Calcium hydroxide (Fixing agent-containing composition) Calcium hydroxide 0.1-54% by mass, water 46-99.9% by mass

[0066] (Study on the relationship between the flow rate of carbon dioxide-containing gas and reaction time) Examples 1 to 4 A carbon dioxide fixation apparatus as shown in Figure 1 was prepared. A porous pipe, a carbon dioxide fixation agent, and a solvent for preparing the fixation agent-containing composition were prepared as shown in Table 1. The fixation agent-containing composition in the reaction vessel was sucked in by a pump, and while the fixation agent-containing composition containing the fixation agent was circulated in the porous pipe under the conditions shown in Table 1, a carbon dioxide-containing gas was sent from the outside of the porous pipe to the inside of the porous pipe, generating microbubbles of the carbon dioxide-containing gas inside the porous pipe.

[0067] [Table 1]

[0068] The results are shown in Figure 4.

[0069] The results in FIG. 4 show that the higher the molar flow rate of carbon dioxide, the shorter the reaction time.

[0070] (Examination of the relationship between CO2 inflow rate (carbon dioxide molar flow rate) and reaction rate) Figure 5 shows the CO3 2- and HCO3 - 5 shows the relationship between the abundance ratio and pH in the pH range of 8 to 13. In the first stage of the reaction in FIG. 5, where the pH exceeds 12, calcium carbonate is thought to be produced according to the following formula. Ca 2+ +CO3 2- →CaCO3 In the second stage of the reaction at a pH of 7 to 12, calcium carbonate dissolves into bicarbonate ions and calcium ions according to the following formula: CaCO3+H2O+CO2→Ca 2+ +2HCO3 - Here, since it is difficult to track how carbon dioxide is consumed, in Figure 5, 97.9% is CO3 2- The reaction rate was examined at pH 12 present in the solution.

[0071] From the above, the amount of carbon dioxide that reacted until 10 L of slaked lime suspension reached pH 12 is 2+ Considering the amount, it is 0.135 mol. Based on this, the reaction rate was calculated using the following formula. Reaction rate (%) = Amount of carbon dioxide (mol) that reacts with the added slaked lime without excess or deficiency = (0.135 mol / amount of carbon dioxide (mol) supplied until pH reaches 12) x 100 = {0.135 mol / [(CO2 inflow per unit time (mol / min)) × (time to supply carbon dioxide-containing gas until pH is reached (min))]} × 100

[0072] FIG. 6 shows the relationship between the reaction efficiency calculated by the above-mentioned method and the carbon dioxide molar flow rate (CO2 influx rate).

[0073] 6, the reaction rate was 62% in Example 4, where the CO2 inflow rate was 0.0057 mol / min, while the reaction rate was 11% in Example 1, where the CO2 inflow rate was 0.23 mol / min. This indicates that in the carbon dioxide fixation method of the present invention, the reaction rate decreases as the CO2 inflow rate increases. This is thought to be because the CO2 absorption rate is slower than the CaCO3 production rate and / or because the CaCO3 thin film formed at the gas-liquid interface inhibits CO2 absorption, resulting in the release of unreacted CO2 into the gas phase.

[0074] (Examination of the reaction end point) FIG. 7 shows the Ca 2+ The relationship between Ca concentration and pH is shown in Figure 7. 2+It was found that the yield of Ca was highest (97%) when the reaction was terminated at a pH of 10 to 11, where the concentration was at its lowest, and therefore the yield of CaCO3 was highest. This is thought to be because the CaCO3 dissolves when the reaction is continued until the pH reaches 10 or below, reducing the amount of CaCO3 recovered. Furthermore, when a fixative-containing composition containing Ca(HCO3)2 is dried, CaCO3 is obtained, but excess CO2 is thought to be released, as shown in the following formula. Ca(HCO3)2 → CaCO3 + H2O + CO2

[0075] (XRD analysis of precipitate) Fig. 8 shows the results of XRD analysis of the precipitate recovered after filtering the immobilizing agent-containing composition having a pH of 7 in Example 3. The results in Fig. 8 show that highly crystalline calcite was obtained.

[0076] (Particle size distribution of precipitate (CaCO3)) Figure 9 shows the particle size distribution of the precipitate (CaCO3) recovered by filtering the immobilizing agent-containing composition having a pH of 7 in Example 3. The results in Figure 9 show that the particle size of the precipitate (CaCO3) obtained by the carbon dioxide fixation method of the present invention is approximately 0.2 to 20 µm, and the average particle size D 50 was found to be 4.5 μm.

[0077] The particle size distribution of the recovered precipitate (CaCO3) was measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, product name SALD-2300) under conditions using a flow cell.

Claims

1. A carbon dioxide fixation method for fixating carbon dioxide in a carbon dioxide fixation agent, comprising the steps of: circulating a fixation agent-containing composition containing the fixation agent through a porous pipe; and supplying a carbon dioxide-containing gas from outside the porous pipe into the porous pipe; thereby generating microbubbles of the carbon dioxide-containing gas within the porous pipe.

2. 2. The carbon dioxide fixation method according to claim 1, wherein the fixation agent contains a hydroxide of at least one metal selected from the group consisting of alkali metals, alkaline earth metals, and rare earths.

3. 2. The carbon dioxide fixation method according to claim 1, wherein the fixation agent is a metal hydroxide of an alkaline earth metal.

4. 2. The carbon dioxide fixation method according to claim 1, wherein the microbubbles have a bubble diameter distribution of 0.1 to 200 μm.

5. 2. The carbon dioxide fixation method according to claim 1, wherein the porous tube is a ceramic porous tube, a metal porous tube, or a resin porous tube.

6. 2. The carbon dioxide fixation method according to claim 1, wherein the porous tube has a pore size of 0.1 to 50 μm.

7. 2. The method for fixation of carbon dioxide according to claim 1, wherein the flux of the fixation agent-containing composition inside the porous pipe is 0.1 to 50 m / s.

8. 2. The carbon dioxide fixation method according to claim 1, wherein the fixation agent-containing composition has a pH of 5 or higher.

9. A carbon dioxide fixation suspension containing a fixation agent in which carbon dioxide is fixed.

10. 10. The carbon dioxide fixation suspension according to claim 9, wherein the fixation agent in which carbon dioxide is fixed contains a hydroxide of at least one metal selected from the group consisting of alkali metals, alkaline earth metals, and rare earths.

11. A carbon dioxide fixation powder containing a fixation agent in which carbon dioxide is fixed.

12. 12. The carbon dioxide fixation powder according to claim 11, wherein the fixation agent in which the carbon dioxide is fixed contains a hydroxide of at least one metal selected from the group consisting of alkali metals, alkaline earth metals, and rare earths.

13. A carbon dioxide fixation device for fixating carbon dioxide in a carbon dioxide fixation agent, the carbon dioxide fixation device having a fixation agent-containing composition containing the fixation agent within a porous tube.

14. The carbon dioxide fixation device according to claim 13, wherein the porous pipe is a ceramic porous pipe, a metal porous pipe, or a resin porous pipe.

15. 14. The carbon dioxide fixation device according to claim 13, wherein the porous tube has a pore size of 0.1 to 50 μm.

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