Absorber for carbon dioxide from the atmosphere

Abstract

The present invention addresses the problem of providing a carbon dioxide absorber agent which enables the highly efficient absorption and fixation of carbon dioxide from the atmosphere and the separation and collection of the carbon dioxide in a simple manner. The present invention relates to an absorber agent for carbon dioxide in the atmosphere, the absorber agent being characterized by comprising an amine selected from the group consisting of m-xylylenediamine, benzylamine, phenethylamine, p-methoxybenzylamine and p-trifluoromethylbenzylamine and water, in which the content of the amine relative to the whole amount is 1 to 50% by weight. The present invention also relates to a method for generating carbon dioxide in a simple manner and with excellent energy efficiency, in which the carbon dioxide absorber agent is used.

Description

Technical Field

[0001] The present invention relates to a carbon dioxide absorbent composed of m-xylenediamine and water. The present invention also relates to a method for recovering [3-(aminomethyl)benzyl]carbamic acid produced by allowing the carbon dioxide absorbent to absorb carbon dioxide in the atmosphere and then performing solid-liquid separation, and generating carbon dioxide by acid treatment or heat treatment. The present invention also relates to a carbon dioxide absorbent composed of benzylamine, phenethylamine, p-methoxybenzylamine or p-trifluoromethylbenzylamine, and water.

Background Art

[0002] In recent years, from the perspective of global environmental protection, there has been active discussion about reducing emissions of carbon dioxide, a greenhouse gas, but no truly effective solution has yet been found. As a solution, technologies for efficiently recovering high-concentration carbon dioxide from exhaust gases emitted from thermal power plants and the like and storing it underground or in the sea (CCS: Carbon dioxide Capture and Storage) have been actively studied in recent years (Non-Patent Document 1). However, since CCS requires a large investment in large-scale facilities and the like, it cannot be said to be a realistic solution at the private (individual) level. In addition, exhaust gases contain high concentrations of toxic gases such as nitrogen oxides and sulfur oxides in addition to carbon dioxide, and many problems remain in order to utilize the carbon dioxide recovered together with these toxic gases as a carbon source (Patent Documents 1 and 2).

[0003] On the other hand, if atmospheric carbon dioxide (the proportion of carbon dioxide in the atmosphere is usually only 0.04-0.05 v / v%) could be used simply and effectively as a carbon source, it could be a truly effective solution. In this regard, technologies for capturing carbon dioxide from the atmosphere (DAC: Direct Air Capture) are beginning to attract attention. To date, methods for collecting only atmospheric carbon dioxide have been known, including a method in which atmospheric carbon dioxide is absorbed into an aqueous sodium hydroxide solution to form an aqueous sodium carbonate solution, which is then reacted with a calcium hydroxide slurry to obtain solid calcium carbonate, and then heated to 900°C to generate carbon dioxide gas, and a method using an aqueous hydroxyethylamine solution as a carbon dioxide absorbent (Non-Patent Literature 2, Non-Patent Literature 3). However, the method using an aqueous sodium hydroxide solution has the problem that sodium hydroxide used as a carbon dioxide absorbent is a hazardous substance and that it requires four steps from carbon dioxide absorption to generation. Furthermore, in both methods, since the solution remains in an aqueous solution state after carbon dioxide absorption, extra energy is required for heating the water when generating carbon dioxide (for example, under high temperature conditions (around 900°C)), and reducing energy consumption has been a challenge.

[0004] Recently, the present inventors have discovered that certain substituted alkylamines can selectively absorb and release carbon dioxide from the atmosphere (Patent Documents 3, 4, and 5). This method has the advantage of efficiently generating carbon dioxide under mild temperature conditions because, by using the specific substituted alkylamine itself as a carbon dioxide absorbent rather than its aqueous solution, energy for heating water is not required when releasing the absorbed carbon dioxide. However, in order to efficiently recover and reuse low concentrations of carbon dioxide from the atmosphere, it is necessary to further improve the carbon dioxide absorption (recovery) performance of the carbon dioxide absorbent. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2003-53134 [Patent Document 2] Japanese Patent Publication No. 2005-40683 [Patent Document 3] Japanese Patent Publication No. 2017-31046 [Patent Document 4] Japanese Patent Publication No. 2017-31062 [Patent Document 5] Japanese Patent Publication No. 2019-127417 [Non-patent literature]

[0006] [Non-Patent Document 1] Iijima, M. and Nakatani, S., Kagaku Kogaku, 2013, Vol.77, pages 300-303 [Non-Patent Document 2] Baciocchi, R. Storti, G. and Mazzotti, M., Chemical Engineering and Processing, 2006, Vol.45, pages 1047-1058. [Non-Patent Document 3] Kiani, A. Jiang, K. and Feron, P., frontiers in Energy Research, 2020, Vol. 8, Article 92. [Overview of the project] [Problems that the invention aims to solve]

[0007] The object of the present invention is to provide a carbon dioxide absorbent that can efficiently absorb and fix carbon dioxide, which is present in the atmosphere at low concentrations under room temperature and atmospheric pressure, and to effectively utilize the carbon dioxide absorbent as a carbon source by releasing carbon dioxide from it in a timely and energy-efficient manner under mild conditions after carbon dioxide fixation. [Means for solving the problem]

[0008] Under these circumstances, the inventors conducted extensive research and found that a composition consisting of m-xylylenediamine and water, with a m-xylylenediamine content of 1 to 50% by weight relative to the total amount, is an excellent carbon dioxide absorbent capable of absorbing and immobilizing atmospheric carbon dioxide significantly more efficiently than m-xylylenediamine alone. Furthermore, the inventors discovered that [3-(aminomethyl)benzyl]carbamic acid, formed by the absorption and immobilization of carbon dioxide by this carbon dioxide absorbent, unexpectedly precipitates as a nonhydrated solid in the composition and can be easily and efficiently isolated by solid-liquid separation without containing water, thereby enabling the energy-efficient generation of the immobilized carbon dioxide. In addition, the inventors found that benzylamine, phenethylamine, p-methoxybenzylamine, and p-trifluoromethylbenzylamine can also absorb and immobilize atmospheric carbon dioxide significantly more efficiently than m-xylylenediamine, thus completing the present invention.

[0009] In other words, the present invention is as follows: [1] An air carbon dioxide absorbent comprising an amine selected from the group consisting of m-xylylenediamine, benzylamine, phenethylamine, p-methoxybenzylamine, and p-trifluoromethylbenzylamine, and water, characterized in that the amine content relative to the total amount is 1 to 50% by weight. [2] The carbon dioxide absorbent according to [1] above, wherein the amine is m-xylylenediamine. [3] The carbon dioxide absorbent according to [1] above, wherein the amine is benzylamine. [4] The carbon dioxide absorbent according to [1] above, wherein the amine is phenethylamine. [5] The carbon dioxide absorbent according to [1] above, wherein the amine is p-methoxybenzylamine. [6] The carbon dioxide absorbent according to [1] above, wherein the amine is p-trifluoromethylbenzylamine. [7] A carbon dioxide absorbent according to any of [1] to [6] above, wherein the amine content is 3 to 30% by weight. [8] A carbon dioxide absorbent according to any of [1] to [6] above, wherein the amine content is 3 to 15% by weight. [9] A carbon dioxide absorbent according to any of [1] to [6] above, wherein the amine content is 3 to 6% by weight.

[10] A method for generating carbon dioxide, comprising the steps of: recovering a carbamic acid derivative precipitated by leaving a carbon dioxide absorbent described in any of [1] to [9] above to absorb carbon dioxide from the atmosphere by solid-liquid separation; and generating carbon dioxide by reacting the recovered carbamic acid derivative with an acid or by heating it.

[11] The method for generating carbon dioxide according to

[10] above, wherein a carbon dioxide absorbent described in any of [2] or [7] to [9] above is used, and the carbamic acid derivative is [3-(aminomethyl)benzyl]carbamic acid.

[12] The method according to

[11] above, wherein the acid is selected from the group consisting of hydrochloric acid, perchloric acid, phosphoric acid, oxalic acid, malonic acid, malic acid, glycolic acid, and trifluoroacetic acid.

[13] The method according to

[11] above, wherein heating is carried out at approximately 120-140°C.

[14] The method according to any one of

[11] to

[13] above, characterized in that water is added to m-xylylenediamine recovered by the method according to any one of

[11] to

[13] above to regenerate the carbon dioxide absorbent described in [2] above, and the regenerated carbon dioxide absorbent is used. [Effects of the Invention]

[0010] The carbon dioxide absorbent of the present invention has a higher carbon dioxide absorption capacity compared to known carbon dioxide absorbents, and therefore has the advantage of being able to efficiently absorb and fix carbon dioxide even when it is present in the atmosphere at low concentrations, under room temperature and atmospheric pressure. Furthermore, the carbamic acid derivative or bicarbonate that is produced (precipitated) after carbon dioxide fixation is extremely hydrophobic, so it can be isolated without water by a simple operation (solid-liquid separation), and because it does not contain water, it can be released under mild conditions with energy efficiency and can be effectively utilized as a carbon source. Therefore, according to the present invention, it is possible to provide an environmentally friendly carbon dioxide absorbent and a method for effectively utilizing carbon dioxide by efficiently absorbing and fixing carbon dioxide from the atmosphere and releasing atmospheric carbon dioxide in a timely manner while minimizing the use of external energy (heating, pressurization, stirring, etc.). [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1-1 shows the change in carbon dioxide concentration (ppm) over time in a rectangular parallelepiped container (6cm long, 6cm wide, 13cm high) located at the outlet side of the reaction vessel. At room temperature, aqueous solutions of m-xylylenediamine (7.58 mmol) at various concentrations (1, 3, 6, 13, 23, 30, 50, and 75% by weight), as well as m-xylylenediamine itself (7.58 mmol; 100% by weight), were each placed separately in cylindrical reaction vessels (5.5cm in diameter, 9cm or 13cm in height). A nitrogen / carbon dioxide mixed gas (carbon dioxide concentration: approximately 1 vol%) was flowed into the reaction vessels at a flow rate of 25 mL / min using a mass flow controller (hereinafter referred to as "MFC"). Figure 1-2 shows a magnified view of a portion of Figure 1-1. [Figure 2] Figure 2 shows the change in carbon dioxide concentration (ppm) over time in a rectangular container (6cm long, 6cm wide, 13cm high) located at the outlet side of the reaction vessel. An aqueous solution of 6% by weight m-xylylenediamine (7.58 mmol) is placed in a cylindrical reaction vessel (5.5cm in diameter, 13cm in height) at room temperature, and air (carbon dioxide concentration: approximately 450 ppm) is flowed into the reaction vessel at a flow rate of 250 mL / min using an MFC. [Figure 3] Figure 3 shows the change in mass (increase in grams) over time of an aqueous solution of m-xylylenediamine (7.58 mmol) with a concentration of 6% by weight, placed in a petri dish with a diameter of 8 cm and left in the atmosphere at room temperature. [Figure 4] Figure 4 shows the change in carbon dioxide concentration (ppm) over time (0 - 10 hours) in a rectangular parallelepiped container (6 cm in length, 6 cm in width, 13 cm in height) provided on the outlet (outflow port) side, when aqueous solutions of 6% by weight of m-xylylenediamine, benzylamine, phenethylamine, p-methoxybenzylamine or p-trifluoromethylbenzylamine are placed in reaction vessels respectively, and air (carbon dioxide concentration: about 450 ppm) is flowed into the reaction vessels at a flow rate of 250 mL / min using an MFC.

Mode for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in detail.

[0013] (Definition) In this specification, "room temperature" means from about 10°C to about 25°C.

[0014] In this specification, "normal pressure" means 1 atmosphere (1013 hPa).

[0015] In this specification, "about" is defined as ±5°C in the case of temperature, ±10 minutes in the case of time, and ±10% in the case of weight, volume and concentration.

[0016] In this specification, "solid-liquid separation" means an operation of separating solids mixed in a liquid, and includes separation operations by filtration using a filter and separation operations using a centrifuge.

[0017] In this specification, "carbamic acid derivative" means substituted benzyl- or phenethyl-carbamic acid formed by the reaction of m-xylylenediamine, benzylamine, phenethylamine, p-methoxybenzylamine or p-trifluoromethylbenzylamine with carbon dioxide.

[0018] In this specification, “bicarbonate” means a salt of m-xylylenediamine, benzylamine, phenethylamine, p-methoxybenzylamine, or p-trifluoromethylbenzylamine with a substituted benzyl- or phenethyl-amine formed by the reaction of these with an excess of carbon dioxide.

[0019] (The carbon dioxide absorbent of the present invention) The carbon dioxide absorbent of the present invention is a composition comprising an amine selected from the group consisting of m-xylylenediamine, benzylamine, phenethylamine, p-methoxybenzylamine, and p-trifluoromethylbenzylamine, and water, wherein the amine content relative to the total amount is 1 to 50% by weight.

[0020] m-xylylenediamine, benzylamine, phenethylamine, p-methoxybenzylamine, and p-trifluoromethylbenzylamine are commercially available and readily obtainable, and are low in volatility, low in toxicity, and miscible with water. The inventors have previously reported that m-xylylenediamine itself is a hydrophobic carbon dioxide absorbent that does not absorb water (moisture in the atmosphere) when absorbing carbon dioxide (see Patent Document 3), but the carbon dioxide absorbent of the present invention can absorb only carbon dioxide with significantly greater efficiency than m-xylylenediamine itself. Furthermore, by using the carbon dioxide absorbent of the present invention, [3-(aminomethyl)benzyl]carbamic acid, which is formed by the absorption and immobilization of carbon dioxide by m-xylylenediamine, precipitates as a nonhydrated solid, so [3-(aminomethyl)benzyl]carbamic acid can be efficiently isolated by solid-liquid separation without the presence of water through a simple operation. On the other hand, when a composition consisting of p-xylylenediamine and water was used as a carbon dioxide absorbent, it efficiently absorbed carbon dioxide, but did not precipitate as a solid that could be separated into solid and liquid forms.

[0021] The carbon dioxide absorbent of the present invention has an amine content of 1 to 50% by weight relative to its total amount. If the amine content is less than 1% by weight, the recovery efficiency may be extremely low because the carbamic acid derivative (e.g., [3-(aminomethyl)benzyl]carbamic acid) or bicarbonate formed by the absorption and immobilization of carbon dioxide by the amine does not precipitate sufficiently. If the amine content exceeds 50% by weight, a significant decrease in carbon dioxide absorption efficiency is observed.

[0022] The amine content relative to the total amount of the carbon dioxide absorbent of the present invention is preferably 3 to 30% by weight, more preferably 3 to 15% by weight, and even more preferably 3 to 6% by weight.

[0023] By using the carbon dioxide absorbent of the present invention, it is possible to reduce the carbon dioxide concentration per unit volume in the atmosphere to a maximum of 1 / 100.

[0024] The carbon dioxide absorbent of the present invention may be used alone or as part of a composition with known stabilizers and additives.

[0025] The carbon dioxide absorbent of the present invention can be used not only in the atmosphere but also in a high-concentration carbon dioxide atmosphere.

[0026] (A method for absorbing and immobilizing carbon dioxide from the atmosphere using the carbon dioxide absorbent of the present invention, and a method for isolating the carbamic acid derivative or bicarbonate produced thereby (hereinafter, these will be collectively referred to as "the carbon dioxide absorption method of the present invention")) The carbon dioxide absorption method of the present invention includes a step (carbon dioxide absorption step) in which the carbon dioxide absorbent of the present invention is left at room temperature, normal pressure, and in the atmosphere (air atmosphere) to absorb and fix carbon dioxide from the atmosphere, thereby generating a carbamic acid derivative or bicarbonate, which is then precipitated as a solid, and the carbamic acid derivative or bicarbonate is recovered simply and efficiently by solid-liquid separation without containing water.

[0027] Specifically, for example, the carbon dioxide absorbent of the present invention is placed in a reaction vessel, and air (carbon dioxide concentration: approximately 450 ppm) is flowed into the reaction vessel using an MFC at room temperature and atmospheric pressure. A carbon dioxide concentration meter is attached to the outlet side to observe the change in carbon dioxide concentration (ppm) over time. When the carbon dioxide concentration stops changing (returns to the initial carbon dioxide concentration), it can be confirmed that the fixation of atmospheric carbon dioxide into the carbon dioxide absorbent of the present invention is complete.

[0028] As shown in the test examples described later, the carbon dioxide absorbent of the present invention can maintain an extremely high carbon dioxide absorption efficiency for 4 to 12 hours, depending on the amine content relative to the total amount.

[0029] Specifically, the m-xylylenediamine in the carbon dioxide absorbent of the present invention absorbs and fixes carbon dioxide from the atmosphere, converting it into [3-(aminomethyl)benzyl]carbamic acid, which is poorly soluble in water, and precipitating as a solid. By separating the precipitated solid from the liquid, [3-(aminomethyl)benzyl]carbamic acid can be easily recovered without the presence of water. The recovered [3-(aminomethyl)benzyl]carbamic acid can be subjected to the following carbon dioxide generation method to regenerate m-xylylenediamine.

[0030] (Method for generating carbon dioxide from carbamic acid derivatives or bicarbonates (hereinafter also referred to as "the carbon dioxide generation method of the present invention")) The carbon dioxide generation method of the present invention includes a step (carbon dioxide generation step) of generating carbon dioxide by reacting a carbamic acid derivative or bicarbonate obtained by the carbon dioxide absorption method of the present invention with an acid at room temperature and atmospheric pressure, or by heating it at approximately 120 to 140°C. The carbon dioxide generation method of the present invention can be carried out in accordance with or in accordance with the method described in the examples of Patent Document 3.

[0031] Specifically, for example, when using the generated carbon dioxide as a carbon source for an organic synthesis reaction, a reaction apparatus (of which the material is not particularly limited) that can be connected to the reaction vessel in which the organic synthesis reaction is carried out is prepared, and [3-(aminomethyl)benzyl]carbamic acid is weighed and added thereto. After dilution with a solvent as necessary, the generation of carbon dioxide can be visually confirmed by adding acid dropwise or by heating.

[0032] When using carbamic acid derivatives (e.g., [3-(aminomethyl)benzyl]carbamic acid) or bicarbonates in organic synthesis reactions, the amount of carbon dioxide generated depends more on the total volume of the reaction apparatus than on the amount of reaction substrate. Therefore, it is desirable to set the amount of carbamic acid derivative or bicarbonate, and / or acid used, so that approximately twice the total volume of the reaction apparatus is generated in carbon dioxide.

[0033] In the carbon dioxide generation method of the present invention, a solvent is not necessarily required, but examples of solvents that can be used include alcohols such as methanol, ethanol, and isopropanol.

[0034] The acid used in the carbon dioxide generation method of the present invention is not particularly limited, but specifically, examples include dilute hydrochloric acid (e.g., 10% hydrochloric acid), perchloric acid, phosphoric acid aqueous solution (e.g., 85% phosphoric acid aqueous solution), oxalic acid, malonic acid, malic acid, glycolic acid, trifluoroacetic acid, etc., among which dilute hydrochloric acid (e.g., 10% hydrochloric acid) is preferably used. The amount of acid used is typically 0.01 to 3 moles, preferably 0.1 to 2 moles, per mole of carbamic acid derivative or bicarbonate. It is also possible to adjust the amount of carbon dioxide generated by controlling the amount of acid used.

[0035] Furthermore, in the carbon dioxide generation method of the present invention by heating, carbon dioxide can be effectively generated simply by heating to approximately 120-140°C. Compared to conventional methods that require heating conditions of 900°C (specifically, conventional techniques that use an aqueous sodium hydroxide solution or an aqueous hydroxyethylamine solution as a carbon dioxide absorbent), the carbon dioxide generation method of the present invention does not require the energy for heating water, making it possible to generate carbon dioxide under extremely mild conditions.

[0036] The amine generated after carbon dioxide is produced by the carbon dioxide generation method of the present invention can be easily recovered and used as a carbon dioxide absorbent of the present invention by making it an aqueous solution again (regeneration process of the carbon dioxide absorbent of the present invention).

[0037] By repeatedly performing the above series of processes (carbon dioxide absorption process (carbon dioxide absorption method of the present invention), carbon dioxide generation process (carbon dioxide generation method of the present invention), and carbon dioxide absorbent regeneration process of the present invention), it is possible to dramatically improve the efficiency of carbon dioxide recovery from the atmosphere and to realize an environmentally friendly process that significantly reduces the amount of external energy used when utilizing the recovered carbon dioxide. [Examples]

[0038] The present invention will be described in more detail below with reference to examples, but this does not limit the present invention, and variations may be made without departing from the scope of the present invention. The amount of carbon dioxide (CO2) absorbed was measured using a CO2 adsorption / desorption device manufactured by Toyoko Chemical Co., Ltd. Elemental analysis was performed using J-SCIENCE LAB JM10. The carbon dioxide concentration was measured using a carbon dioxide concentration meter (GC-02) manufactured by God Ability (GA). The weight was measured using an electronic balance (EK-610i) manufactured by A&D Corporation. In the following examples, percentages refer to weight percentages unless otherwise specified.

[0039] m-Xylylenediamine (manufactured by Tokyo Chemical Industry Co., Ltd.), benzylamine (manufactured by Tokyo Chemical Industry Co., Ltd.), phenethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.), p-methoxybenzylamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and p-trifluoromethylbenzylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) can be used as commercially available products.

[0040] Example 1 Changes in carbon dioxide concentration (ppm) over time in the presence of an aqueous solution of m-xylylenediamine (m-xylylenediamine content: 1, 3, 6, 13, 23, 30, 50, or 75% by weight) or m-xylylenediamine itself (100% by weight) under a nitrogen / carbon dioxide mixed gas stream.

[0041] (Experimental procedure) At room temperature, aqueous solutions of m-xylylenediamine (7.58 mmol) at various concentrations (1, 3, 6, 13, 23, 30, 50, and 75% by weight), as well as m-xylylenediamine itself (7.58 mmol; m-xylylenediamine concentration 100% by weight), were each placed separately in cylindrical reaction vessels (5.5 cm in diameter, 9 cm or 13 cm in height) as carbon dioxide absorbers. A nitrogen / carbon dioxide mixed gas (carbon dioxide concentration: approximately 1 vol%) was flowed into the reaction vessels at a flow rate of 25 mL / min using a mass flow controller (MFC), and the carbon dioxide concentration (ppm) in a rectangular parallelepiped container (6 cm long, 6 cm wide, 13 cm high) located on the outlet side was measured over time using a carbon dioxide concentration meter. Furthermore, the rectangular container used to measure carbon dioxide concentration is designed to release gas as needed, resulting in a device configuration that avoids pressure fluctuations.

[0042] (Experimental results) The changes in carbon dioxide concentration (ppm) inside the rectangular container are shown in Table 1, Figure 1-1, and Figure 1-2.

[0043] [Table 1]

[0044] The results from Table 1, Figure 1-1, and Figure 1-2 confirm that when the m-xylylenediamine content exceeds 50% by weight (75% and 100% by weight), a significant decrease in carbon dioxide absorption efficiency is observed. Furthermore, it was confirmed that the carbon dioxide absorbent solidified after the reaction when the m-xylylenediamine concentration was in the range of 1 to 100% by weight.

[0045] Example 2 Changes in carbon dioxide concentration (ppm) over time in the presence of a 6 wt% m-xylylenediamine aqueous solution under atmospheric airflow (carbon dioxide concentration: approximately 450 ppm).

[0046] (Experimental procedure) At room temperature, an aqueous solution of 6% by weight m-xylylenediamine (7.58 mmol) was placed in a cylindrical reaction vessel (5.5 cm in diameter, 13 cm in height). Air (carbon dioxide concentration: approximately 450 ppm) was flowed into the reaction vessel at a flow rate of 250 mL / min using an MFC, and the carbon dioxide concentration (ppm) in a rectangular parallelepiped container (6 cm long, 6 cm wide, 13 cm high) placed on the outlet side was measured over time using a carbon dioxide concentration meter. Furthermore, the rectangular container used to measure carbon dioxide concentration is designed to release gas as needed, resulting in a device configuration that avoids pressure fluctuations.

[0047] (Experimental results) The changes in carbon dioxide concentration (ppm) inside the rectangular container are shown in Table 2 and Figure 2.

[0048] [Table 2]

[0049] The results in Table 2 and Figure 2 show that the carbon dioxide concentration could be maintained at 200 ppm or less for 18 hours after the start of the experiment, and that carbon dioxide adsorption activity was maintained for 40 hours after the start of the experiment. These results support the high carbon dioxide adsorption capacity of the carbon dioxide adsorbent of the present invention.

[0050] Example 3 Mass change of a 6 wt% m-xylylenediamine aqueous solution over time in an atmospheric environment (carbon dioxide concentration: approximately 450 ppm).

[0051] (Experimental procedure) An aqueous solution of m-xylylenediamine (7.58 mmol) at a concentration of 6 wt% (test solution) was placed in an 8 cm diameter petri dish and left in the air. The increase in its mass over time was measured. Furthermore, in order to account for water evaporation, a control experiment was conducted using the same amount of water under the same conditions. The amount of water evaporation over time was calculated, and this decrease was subtracted from the change (difference) from the initial value of the test solution to determine the mass increase (g).

[0052] (Experimental results) Table 3 and Figure 3 show the change in the mass (g) of the test solution over time.

[0053] [Table 3]

[0054] The results in Table 3 and Figure 3 confirm that the mass of the test solution increases in a time-dependent manner simply by being left in the atmosphere. These results support the fact that the carbon dioxide adsorbent of the present invention has high carbon dioxide adsorption capacity even in an atmospheric environment.

[0055] Example 4 The solid precipitated after the reaction in Example 2 was filtered, and the attached moisture was removed. Elemental analysis of the resulting solid was performed, and the result was [3-(aminomethyl)benzyl]carbamic acid [composition formula: C9H 12 It was determined to be N2O2 (941 mg; 7.58 mmol; yield: 69%). The results of three elemental analyses of the obtained solid are shown in Table 4.

[0056] [Table 4]

[0057] The results in Table 4 confirm that [3-(aminomethyl)benzyl]carbamic acid, obtained by solid-liquid separation, is not a hydrate but a highly hydrophobic solid, despite being isolated from water.

[0058] Example 5 Changes in carbon dioxide concentration (ppm) over time in the presence of a 6 wt% aqueous solution of m-xylylenediamine, benzylamine, phenethylamine, p-methoxybenzylamine, or p-trifluoromethylbenzylamine under atmospheric airflow (carbon dioxide concentration: approximately 450 ppm).

[0059] (Experimental procedure) Similar to Example 2, at room temperature, aqueous solutions of m-xylylenediamine (MXDA) (7.58 mmol), benzylamine (BZA) (7.58 mmol), phenethylamine (PEA) (7.58 mmol), p-methoxybenzylamine (PMBZA) (7.58 mmol), or p-trifluoromethylbenzylamine (PTFMBZA) (7.58 mmol) at a concentration of 6 wt% were placed in separate reaction vessels. Air (carbon dioxide concentration: approximately 450 ppm) was flowed into the reaction vessels at a flow rate of 250 mL / min using an MFC, and the carbon dioxide concentration (ppm) in a rectangular parallelepiped container (6 cm long, 6 cm wide, 13 cm high) placed on the outlet side was measured over time (0 to 10 hours) using a carbon dioxide concentration meter.

[0060] (Experimental results) Table 5 and Figure 4 show the changes in carbon dioxide concentration (ppm) in a rectangular container in the presence of aqueous solutions of each amine.

[0061] [Table 5]

[0062] The results in Table 5 and Figure 4 show that, up to 10 hours after the start of the experiment, all amines, similar to m-xylylenediamine, were able to maintain a carbon dioxide concentration of approximately 200 ppm, demonstrating good carbon dioxide adsorption activity. Furthermore, in the initial stages up to 6 hours after the start of the experiment, some amines (phenethylamine and p-methoxybenzylamine) showed higher carbon dioxide adsorption capacity than m-xylylenediamine. [Industrial applicability]

[0063] The carbon dioxide absorbent of the present invention has a higher carbon dioxide absorption capacity compared to known carbon dioxide absorbents, and therefore has the advantage of being able to efficiently absorb and fix carbon dioxide even when it is present in the atmosphere at low concentrations, under room temperature and atmospheric pressure. Furthermore, the carbamic acid derivative (e.g., [3-(aminomethyl)benzyl]carbamic acid) or bicarbonate that is produced (precipitated) after carbon dioxide fixation is extremely hydrophobic, so it can be isolated without water by simple operation (solid-liquid separation), and because it does not contain water, it can be released under mild conditions with energy efficiency and can be effectively utilized as a carbon source. Therefore, according to the present invention, it is possible to provide an environmentally friendly carbon dioxide absorbent and a method for effectively utilizing carbon dioxide by efficiently absorbing and fixing carbon dioxide from the atmosphere and releasing atmospheric carbon dioxide in a timely manner while minimizing the use of external energy (heating, pressurization, stirring, etc.).

[0064] This application is based on Japanese Patent Application No. 2021-026634, filed in Japan on February 22, 2021, the contents of which are fully incorporated herein.

Claims

1. A method for generating carbon dioxide, comprising the steps of: recovering a nonhydrate of [3-(aminomethyl)benzyl]carbamic acid precipitated by leaving a carbon dioxide absorbent, characterized in that it consists of m-xylylenediamine and water, with the m-xylylenediamine content being 3 to 6% by weight relative to the total amount, to absorb carbon dioxide from the atmosphere, by solid-liquid separation; and generating carbon dioxide by reacting the recovered nonhydrate of [3-(aminomethyl)benzyl]carbamic acid with an acid or by heating.

2. The method according to claim 1, wherein the acid is selected from the group consisting of hydrochloric acid, perchloric acid, phosphoric acid, oxalic acid, malonic acid, malic acid, glycolic acid, and trifluoroacetic acid.

3. The method according to claim 1, wherein the heating is performed at approximately 120 to 140°C.

4. The method according to any one of Claims 1 to 3, characterized in that water is added to m-xylylenediamine recovered by the method according to any one of Claims 1 to 3 to regenerate a carbon dioxide absorbent consisting of m-xylylenediamine and water, wherein the content of m-xylylenediamine relative to the total amount is 3 to 6% by weight, and this is used as a carbon dioxide absorbent.

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