Ammonia storage material

Abstract

This invention provides an ammonia storage material that can absorb and release ammonia through pressure manipulation and exhibits excellent reversible ammonia absorption and release characteristics. [Solution] The solution comprises a salt of at least one metal selected from alkali metals, alkaline earth metals, and transition metals, and a fluorocomplex.

Description

[Technical Field]

[0001] This invention relates to an ammonia storage material capable of absorbing and releasing ammonia. [Background technology]

[0002] In recent years, carbon dioxide emission regulations have necessitated a reduction in the use of fossil fuels. Hydrogen, which does not release carbon dioxide through oxidation or combustion, is attracting attention as a next-generation fuel to replace fossil fuels, and the use of ammonia (NH3) as a storage and transportation medium for this hydrogen is being considered.

[0003] The Haber-Bosch process, using hydrogen and nitrogen, has been the industrial method for synthesizing and producing ammonia. However, the synthesized ammonia needs to be separated and recovered from the unreacted hydrogen and nitrogen. Conventional separation and recovery processes for ammonia have included deep cooling recovery, which uses the difference in boiling points between the ammonia and the unreacted gases (hydrogen and nitrogen) for liquefaction, and water dissolution separation, which uses the difference in solubility in water for dissolution. However, these separation and recovery processes have problems such as energy costs and contamination by water vapor.

[0004] To solve these problems, development of ammonia storage materials using materials that exhibit selective ammonia storage characteristics is underway. For example, the ammonia storage material described in Patent Document 1 uses a combination of metal halides such as calcium chloride (CaCl2) and calcium bromide (CaBr2) to selectively absorb and release synthesized ammonia through pressure operation (PSA) or temperature operation (TSA). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 4745299 (page 4, Figure 8) [Overview of the project] [Problems that the invention aims to solve]

[0006] Although the ammonia storage material described in Patent Document 1 can increase the ammonia storage capacity by using metal halides, it is difficult to release ammonia under pressure at room temperature. Even at 200°C, where ammonia release is possible, the ratio of the release capacity to the ammonia storage capacity is low, at about 50%, which is a problem as it is not very practical.

[0007] This invention was made in view of these problems, and aims to provide an ammonia storage material that can absorb and release ammonia by pressure operation and has excellent reversible ammonia absorption and release characteristics. [Means for solving the problem]

[0008] The present inventors, while diligently studying the above-mentioned problems, discovered that by using a fluorocomplex salt of at least one metal selected from alkali metals, alkaline earth metals, and transition metals as a material exhibiting selective ammonia storage properties, an ammonia storage material can be obtained that can absorb and release ammonia by pressure manipulation and has excellent reversible ammonia storage and release properties, thus completing the present invention.

[0009] In other words, the ammonia storage material of the present invention contains a salt of a fluorocomplex with at least one metal selected from alkali metals, alkaline earth metals, and transition metals. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows an example of the three-dimensional structure of tetrafluoroborate (NaBF4) contained in the ammonia storage material of the embodiment. [Figure 2] This figure shows an example of the three-dimensional structure of hexafluorophosphate (KPF6) contained in the ammonia storage material of the embodiment. [Figure 3](a) is a diagram showing the ammonia absorption and desorption behavior of the ammonia storage material (NaBF4) at 27 °C in Example 1, and (b) is a diagram showing the ammonia absorption and desorption behavior of the ammonia storage material (KPF6) at 27 °C in Example 1. Hereinafter, in the diagrams showing the ammonia absorption and desorption behavior, the solid line graph represents the ammonia absorption capacity and the dotted line graph represents the ammonia pressure. [Figure 4] (a) is a diagram showing the ammonia absorption and desorption behavior of the conventional ammonia storage material (CaCl2) at 27 °C, and (b) is a diagram showing the ammonia absorption and desorption behavior of the conventional ammonia storage material (Na-Y zeolite) at 27 °C. [Figure 5] It is a diagram showing a comparison of the ammonia absorption and desorption characteristics of various fluoro complex salts (NaBF4, LiBF4, NaPF6, KPF6) which are ammonia storage materials in Example 1 and conventional ammonia storage materials (CaCl2, Na-Y zeolite). [Figure 6] (a) is a diagram showing the XRD patterns of the ammonia storage material (NaBF4) before and after ammonia absorption in Example 1, and (b) is a diagram showing the XRD patterns of the ammonia storage material (KPF6) before and after ammonia absorption in Example 1. [Figure 7] (a) is a diagram showing the FT-IR spectra of the ammonia storage material (NaBF4) before and after ammonia absorption in Example 1, and (b) is a diagram showing the FT-IR spectra of the ammonia storage material (KPF6) before and after ammonia absorption in Example 1. [Figure 8] (a) is a diagram showing the ammonia absorption and desorption behavior of the ammonia storage material (NaBF4) at 27 °C in Example 2, (b) is a diagram showing the ammonia absorption and desorption behavior at 50 °C, (c) is a diagram showing the ammonia absorption and desorption behavior at 100 °C, and (d) is a diagram showing the ammonia absorption and desorption behavior at 200 °C.

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described. However, the present invention can be implemented in many different forms and is not limited to the examples shown in the following embodiments and examples.

[0012] The ammonia storage material according to this embodiment contains a salt of at least one metal selected from alkali metals, alkaline earth metals, and transition metals and a fluoro complex.

[0013] The fluoro complex is tetrafluoroborate ion (BF4 - ), hexafluorophosphate ion (PF6 - ), hexafluoroaluminate ion (AlF6 3- ), hexafluorosilicate ion (SiF6 2- ), hexafluorotitanate ion (TiF6 2- ), hexafluorotungstate ion (WF6 2- ), etc., but from the viewpoint of increasing the ratio of the release capacity to the storage capacity of ammonia (NH3), tetrafluoroborate ion (BF4 - ) or hexafluorophosphate ion (PF6 - ) is preferable.

[0014] Also, the metal may be any of alkali metals, alkaline earth metals, and transition metals as long as it can form a salt with the fluoro complex. However, from the viewpoint of facilitating the formation of a stable salt, it is preferably an alkali metal or an alkaline earth metal, and particularly preferably sodium or potassium, which is an alkali metal.

[0015] Furthermore, the fluorocomplex salts used as ammonia storage materials according to this embodiment are capable of ammonia absorption and release in a solid state, and their melting points vary depending on the combination of metal and fluorocomplex. For example, the melting points of the fluorocomplex salts are 384°C for NaBF4, 297°C for LiBF4, 200°C for NaPF6, and 575°C for KPF6 (see Figure 5). In addition, although the ammonia absorption and release characteristics of the fluorocomplex salts differ depending on the combination of metal and fluorocomplex, the inventors have confirmed that they do not absorb ammonia at temperatures above 100°C, and that at temperatures below 100°C, particularly at room temperature, they exhibit large ammonia absorption and release capacity and high capacity reversibility with pressure operation (PSA) of 0.1 to 0.5 MPa.

[0016] Furthermore, the ammonia storage material of this embodiment exhibits high capacity reversibility, with a ratio of release capacity to ammonia storage capacity of 40% or more, preferably 50% or more, and more preferably 60% or more, when subjected to pressure operation of 0.1 to 0.5 MPa at room temperature, i.e., in the range of 5 to 35°C. In particular, NaBF4 and KPF6, as ammonia storage materials of this embodiment, exhibit extremely high capacity reversibility, with a ratio of release capacity to ammonia storage capacity of 97% or more.

[0017] Here, we will explain the three-dimensional structure of fluorocomplex salts. For example, the fluorocomplex salts NaBF4 and KPF6, as shown in Figures 1 and 2, have a large anion size and a three-dimensional structure in which a large space is formed around the adsorption site (metal cation). Furthermore, it has been confirmed that the three-dimensional structure of fluorocomplex salts expands and contracts almost uniformly in the a, b, and c axes (see Figures 1 and 2) due to the adsorption and release of ammonia, and it is presumed that ammonia is adsorbed into the large space formed around the adsorption site.

[0018] Thus, fluorocomplex salts can selectively and reversibly chemically adsorb ammonia in the space formed around the adsorption site, and large volumes of ammonia can be absorbed and released by pressure manipulation.

[0019] In this embodiment, the ammonia storage material is not limited to being composed solely of fluorocomplex salts; it is preferable that it contains fluorocomplex salts as the main component, and in this case, other materials such as binders may also be included. Furthermore, in this embodiment, the main component refers to the component that is present in the largest quantity among the constituent components of the ammonia storage material.

[0020] Furthermore, the ammonia storage material in this embodiment may be in powder or granular form, or it may be molded into pellets, tablets, or the like.

[0021] As described above, the ammonia storage material of this embodiment contains a salt of at least one metal selected from alkali metals, alkaline earth metals, or transition metals and a fluorocomplex, allowing for easy absorption and release of ammonia by pressure manipulation, and exhibiting excellent reversible ammonia absorption and release characteristics. [Examples]

[0022] Here, we actually fabricated the ammonia storage material according to the embodiment described above and confirmed its effects. These will be explained in detail below.

[0023] In this embodiment, the ammonia storage material is granular NaBF4 (manufactured by Tokyo Chemical Industry Co., Ltd., product code O0494) or granular KPF6 (manufactured by Tokyo Chemical Industry Co., Ltd., product code P1023) packed into a column, and ammonia is absorbed and released by operating the pressure at 0.1 to 0.5 MPa. Figures 3(a) and (b) show the ammonia absorption and release behavior of NaBF4 and KPF6 at room temperature (27°C). In this embodiment, ammonia absorption and release by pressure operation is performed for two cycles.

[0024] As shown in Fig. 3, for the ammonia storage materials (NaBF4 and KPF6) in this embodiment, at 27°C, as the ammonia pressure increases, the ammonia storage amount increases, and as the ammonia pressure decreases, the ammonia storage amount decreases. Therefore, it was confirmed that ammonia can be repeatedly stored and released by pressure operation.

[0025] Also, for the ammonia storage material (NaBF4) of this embodiment, at 27°C, as the ammonia pressure decreases, the ammonia storage amount decreases to around 0 mmol·g -1 It was confirmed that it shows reversible ammonia storage and release characteristics with the ratio of the release capacity to the storage capacity of ammonia being 97% or more (see Figs. 3(a) and 5). In the graph of Fig. 3(a), the ammonia storage capacity in the first cycle is 48.00 mmol·g -1 and the ammonia release capacity is 46.84 mmol·g -1 was.

[0026] Also, for the ammonia storage material (KPF6) of this embodiment, at 27°C, although the ammonia storage amount with the increase in ammonia pressure is about half of that of NaBF4 described above, as the ammonia pressure decreases, the ammonia storage amount decreases to around 0 mmol·g -1 It was confirmed that it shows reversible ammonia storage and release characteristics with the ratio of the release capacity to the storage capacity of ammonia being about 100% (see Figs. 3(b) and 5). In the graph of Fig. 3(b), the ammonia storage capacity in the first cycle is 25.93 mmol·g -1 and the ammonia release capacity is 25.92 mmol·g -1 was.

[0027] Furthermore, as shown in Figure 5, among the ammonia storage materials in this embodiment other than NaBF4 and KPF6 mentioned above, LiBF4 was found to have a higher ammonia storage capacity than NaBF4 at 27°C as the ammonia pressure increased, but the ratio of ammonia release capacity to ammonia storage capacity was slightly lower at approximately 40%. Similarly, NaPF6 was found to have a higher ammonia storage capacity than KPF6 at 27°C as the ammonia pressure increased, but the ratio of ammonia release capacity to ammonia storage capacity was slightly lower at approximately 45%.

[0028] Conventional ammonia storage materials made of metal halides (CaCl2) can store ammonia at 27°C as the ammonia pressure increases (ammonia storage capacity 56.07 mmol·g). -1 However, it was confirmed that ammonia release does not occur as the ammonia pressure decreases (see Figures 4(a) and 5).

[0029] Furthermore, conventional zeolite-based ammonia storage materials (Na-Y zeolite) can only slightly absorb ammonia at 27°C as the ammonia pressure increases (ammonia storage capacity: 2,246 mmol·g). -1 However, it was confirmed that ammonia release does not occur as the ammonia pressure decreases (see Figures 4(b) and 5). This is presumed to be because, in the case of zeolites, ammonia is adsorbed in the countless pores that are a characteristic structure of zeolites, making it difficult for ammonia to be released at room temperature. In contrast, in the ammonia storage material of this embodiment, ammonia is adsorbed in the space formed around the adsorption site (metal cation), so it is possible to adsorb and release ammonia by manipulating the pressure even at low temperatures such as room temperature.

[0030] From these findings, it was confirmed that the ammonia storage material of this embodiment exhibits excellent reversible ammonia storage and release characteristics at room temperature.

[0031] Furthermore, among the ammonia storage materials of this embodiment, KPF6 in particular was confirmed to exhibit reversible ammonia storage and release characteristics, with a ratio of ammonia release capacity to ammonia storage capacity of approximately 100% at 27°C.

[0032] Furthermore, it was confirmed that the ammonia storage and release characteristics differ depending on the metal (cationic species) used for BF4 salts (NaBF4, LiBF4) and PF6 salts (NaPF6, KPF6). It was also confirmed that BF4 salts generally have a larger ammonia storage capacity compared to PF6 salts.

[0033] Next, Figures 6 and 7 show the results of the durability evaluation of the ammonia storage materials (NaBF4 and KPF6) of this embodiment against ammonia storage at room temperature (27°C).

[0034] As shown in Figures 6(a) and 6(b), it was confirmed that the XRD patterns of the ammonia storage materials (NaBF4 and KPF6) in this embodiment remained unchanged before and after ammonia storage.

[0035] Furthermore, as shown in Figures 7(a) and (b), it was confirmed that the FT-IR spectra of the ammonia storage materials (NaBF4 and KPF6) in this embodiment remained unchanged before and after ammonia storage.

[0036] These results suggest that the ammonia storage materials (NaBF4 and KPF6) in this embodiment did not undergo any structural changes before and after ammonia storage, confirming their high durability against ammonia storage. [Examples]

[0037] Next, Figure 8 shows the results of evaluating the temperature dependence of ammonia storage and release for the ammonia storage material (NaBF4) of this embodiment. In this embodiment, the ammonia storage and release characteristics of the ammonia storage material (NaBF4) at 27°C, 50°C, 100°C, and 200°C are compared.

[0038] As shown in Figure 8(a), the ammonia storage material (NaBF4) in this embodiment has an ammonia storage capacity of 48.00 mmol·g in the first cycle at 27°C. -1 The ammonia release capacity is 46.84 mmol·g. -1 The ammonia storage capacity in the second cycle was 49.18 mmol·g. -1 The ammonia release capacity is 48.62 mmol·g. -1 Therefore, it was confirmed that the ratio of ammonia storage capacity to ammonia release capacity was 97% or more, indicating reversible ammonia storage and release characteristics.

[0039] Furthermore, as shown in Figure 8(b), the ammonia storage material (NaBF4) in this embodiment has an ammonia storage capacity of 27.22 mmol·g in the first cycle at 50°C. -1 The ammonia release capacity is 27.02 mmol·g. -1 The ammonia storage capacity in the second cycle was 27.22 mmol·g. -1 The ammonia release capacity is 26.98 mmol·g. -1 The ratio of ammonia storage capacity to ammonia release capacity is over 99%, indicating reversible ammonia storage and release characteristics. However, it was confirmed that the ammonia storage and release capacity decreased when the temperature was raised to 50°C.

[0040] Furthermore, as shown in Figures 8(c) and 8(d), it was confirmed that the ammonia storage material (NaBF4) of this embodiment could not absorb ammonia by pressure operation at 100°C and 200°C.

[0041] These results confirm that the ammonia storage material (NaBF4) of this embodiment cannot store ammonia at temperatures above 100°C, but exhibits a large ammonia storage and release capacity and high capacity reversibility at temperatures below 100°C, particularly at room temperature, under pressure conditions of 0.1 to 0.5 MPa.

[0042] Based on the embodiments and examples described above, it is possible to provide an ammonia storage material that can absorb and release ammonia by pressure operation and has excellent reversible ammonia absorption and release characteristics.

[0043] For example, in the above embodiment, a method of ammonia storage and release by pressure operation (PSA) was described, but the invention is not limited to this, and ammonia storage and release may also be performed by pressure-temperature operation (PTSA).

[0044] Furthermore, the pressure range in pressure operation is not limited to 0.1 to 0.5 MPa, but may be set appropriately according to the ammonia storage and release characteristics of the ammonia storage material. [Industrial applicability]

[0045] This invention provides an ammonia storage material that can absorb and release ammonia by pressure operation even at low temperatures such as room temperature, and has excellent reversible ammonia absorption and release characteristics, making it potentially useful in industry. Furthermore, because the absorption and release characteristics, such as the absorption and release rate and reversibility of ammonia, can be adjusted by combining the metal and fluorocomplex that constitute the fluorocomplex salt, which is the main component of the ammonia storage material, this invention enables highly efficient separation and recovery of ammonia depending on the operating conditions, and has a wide range of applications.

Claims

1. An ammonia storage material characterized by containing a salt of at least one metal selected from alkali metals, alkaline earth metals, and transition metals, and a fluorocomplex.

2. The ammonia storage material according to claim 1, characterized in that the fluorocomplex is a tetrafluoroborate ion.

3. The ammonia storage material according to claim 1, characterized in that the fluoro complex is a hexafluorophosphate ion.

4. The ammonia storage material according to any one of claims 1 to 3, characterized in that the aforementioned metal is sodium.

5. The ammonia storage material according to any one of claims 1 to 3, characterized in that the aforementioned metal is potassium.

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