Ammonia adsorbent and ammonia adsorption device

Abstract

To provide an ammonia adsorbent that has high adsorption capacity for ammonia contained in exhaust gas from fuel cell using ammonia directly as fuel, and to provide an ammonia adsorption device.SOLUTION: Provided are an ammonia adsorbent and an ammonia adsorption device containing a zirconium phosphate-based compound, used for adsorbing ammonia contained in the exhaust gas of a fuel cell using ammonia as a direct fuel.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an ammonia adsorbent and an ammonia adsorption device.

Background Art

[0002] In recent years, fuel cells that do not emit carbon dioxide have attracted attention. Examples of fuels for fuel cells include hydrogen and ammonia. Ammonia is useful as a fuel because it can be liquefied at a relatively low pressure without being extremely cooled. However, in a fuel cell using ammonia directly as a fuel, unreacted ammonia may be contained in the exhaust gas. Measures for treating this unreacted ammonia are required.

[0003] For example, Patent Document 1 describes an ammonia storage and supply device including an ammonia adsorption / desorption material, and as the ammonia adsorption / desorption material, halogenated Ba compounds, halogenated Ca compounds, halogenated Sr compounds, halogenated Fe compounds, halogenated Co compounds, halogenated Mg compounds, etc. are described.

[0004] Patent Document 2 describes an ammonia fuel power generation system including an ammonia storage tank that houses an ammonia storage material that forms a complex with ammonia and adsorbs it, and desorbs ammonia in the adsorbed state when heated, and as the ammonia storage material, halogenated Ba compounds, halogenated Ca compounds, halogenated Sr compounds, halogenated Fe compounds, halogenated Co compounds, halogenated Mg compounds, etc. are described.

[0005] On the other hand, as a technique related to the adsorption of ammonia, Patent Document 3 describes a deodorizing mask including a deodorizing nonwoven fabric layer containing a chemisorption type deodorant, and it is described that ammonia is adsorbed by zirconium phosphate.

Prior Art Documents

Patent Documents

[0006] Patent Document 1 Japanese Unexamined Patent Application Publication No. 2017-166665 Patent Document 2 Japanese Unexamined Patent Application Publication No. 2018-160434 Patent Document 3 International Publication No. 2013 / 133195 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] However, in the ammonia adsorbent described in Patent Document 1 and the ammonia storage material described in Patent Document 2, the adsorption ability for ammonia is insufficient, and there is room for improvement. Further, in Patent Document 3, attention has not been paid to the removal of ammonia contained in the exhaust gas of a fuel cell using ammonia as a direct fuel.

[0008] In view of the above circumstances, the problem to be solved by the present invention is to provide an ammonia adsorbent and an ammonia adsorption device having excellent adsorption ability for ammonia contained in the exhaust gas of a fuel cell using ammonia as a direct fuel. MEANS FOR SOLVING THE PROBLEM

[0009] <1> An ammonia adsorbent containing a zirconium phosphate-based compound, which is used for adsorbing ammonia contained in the exhaust gas of a fuel cell using ammonia as a direct fuel. <2> The ammonia adsorbent according to <1>, wherein the zirconium phosphate-based compound is represented by the following formula (1). Zr 1―x Hf x H a (PO4) b ·nH2O (1) In formula (1), a and b are positive numbers satisfying 3b - a = 4, b is a positive number of 2.0 < b ≤ 2.1, x is a positive number of 0 ≤ x ≤ 0.2, and n is a positive number of 0 ≤ n ≤ 2.0. <3> The ammonia adsorbent according to <1> or <2>, wherein the crystal form of the zirconium phosphate-based compound is the α-form. <4>The fuel cell is a solid oxide fuel cell, and the ammonia adsorbent according to any one of <1> to <3>. <5>An ammonia adsorption device comprising means for introducing the exhaust gas of a fuel cell using ammonia as a direct fuel, and means for adsorbing the introduced exhaust gas to an ammonia adsorbent containing a zirconium phosphate-based compound. <6>The fuel cell is a solid oxide fuel cell, and the ammonia adsorption device according to <5>.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide an ammonia adsorbent and an ammonia adsorption device having a high adsorption ability for ammonia contained in the exhaust gas of a fuel cell using ammonia as a direct fuel.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the ammonia adsorbent and the ammonia adsorption device of the present invention will be described in detail. In this specification, the numerical range indicated by using "~" means a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described stepwise in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other stepwise descriptions. Also, in the numerical ranges described in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples. In this specification, the amount of each component in the composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified. Also, in this specification, a combination of two or more preferred embodiments is a more preferred embodiment.

[0012] <Ammonia Adsorbent> An ammonia adsorbent according to an embodiment of the present invention is an ammonia adsorbent containing a zirconium phosphate-based compound, which is used for adsorbing ammonia contained in the exhaust gas of a fuel cell using ammonia as a direct fuel.

[0013] In a fuel cell using ammonia as a direct fuel (hereinafter also referred to as a "direct ammonia fuel cell"), the exhaust gas may contain undecomposed ammonia. The zirconium phosphate-based compound has a pore structure and can take in and adsorb ammonia in the pores. The ammonia adsorbent according to an embodiment of the present invention contains a zirconium phosphate-based compound, so that it has a high adsorption capacity for ammonia contained in the exhaust gas of a direct ammonia fuel cell and can reduce the ammonia released outside the system of the direct ammonia fuel cell.

[0014] (zirconium phosphate-based compound) -Composition- The composition of the zirconium phosphate-based compound is not particularly limited. The zirconium phosphate-based compound may be crystalline or amorphous. When the zirconium phosphate-based compound is crystalline, its crystal form is not particularly limited, and examples include α-type, β-type, γ-type, etc. Among them, the α-type is preferred for the crystal form. That is, the zirconium phosphate-based compound is preferably α-zirconium phosphate. In particular, the zirconium phosphate-based compound is more preferably α-zirconium phosphate represented by the following formula (1). Zr 1―x Hf x H a (PO4) b ·nH2O (1) In formula (1), a and b are positive numbers satisfying 3b - a = 4, b is a positive number with 2.0 < b ≤ 2.1, x is a positive number with 0 ≤ x ≤ 0.2, and n is a positive number with 0 ≤ n ≤ 2.0.

[0015] In formula (1), hafnium (Hf) is derived from the raw zirconium compound. b is preferably a positive number of 2.05 or less, more preferably a positive number of 2.03 or less. x is preferably a positive number such that 0.005 ≦ x ≦ 0.1, more preferably a positive number such that 0.005 ≦ x < 0.03. n is preferably a positive number of 1.0 or less, more preferably a positive number of 0.5 or less, and even more preferably a positive number of 0.1 or less.

[0016] -Structure- The structure of the zirconium phosphate-based compound is not particularly limited and may be a three-dimensional network structure or a two-dimensional layered structure. Among them, from the viewpoint of the adsorption ability for ammonia contained in the exhaust gas of a direct ammonia fuel cell, the zirconium phosphate-based compound preferably has a two-dimensional layered structure.

[0017] Examples of the zirconium phosphate-based compound having a two-dimensional layered structure include α-type zirconium phosphate and γ-type zirconium phosphate. Among them, from the viewpoint of the adsorption ability for ammonia contained in the exhaust gas of a direct ammonia fuel cell, the zirconium phosphate-based compound is preferably α-type zirconium phosphate.

[0018] The structure of the zirconium phosphate-based compound is 31 confirmed by using phosphorus solid nuclear magnetic resonance ( 31 P solid NMR).

[0019] -Particle size- The zirconium phosphate-based compound preferably has a particulate shape. The average particle size of the zirconium phosphate-based compound is not particularly limited, but is preferably 0.1 μm to 100 μm, more preferably 0.2 μm to 10 μm, and even more preferably 0.5 μm to 2 μm.

[0020] The average particle size of the zirconium phosphate-based compound is measured using a laser diffraction particle size distribution measuring device.

[0021] -Content- In the ammonia adsorbent, the content of the zirconium phosphate-based compound is preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the total mass of the ammonia adsorbent. The content of the zirconium phosphate-based compound may be 100% by mass. That is, the ammonia adsorbent may consist only of the zirconium phosphate-based compound.

[0022] (Method for producing zirconium phosphate-based compound) The zirconium phosphate-based compound is produced, for example, by mixing a zirconium compound, an organic acid, an inorganic acid, and a phosphate compound. Examples of the method for producing the zirconium phosphate-based compound include the method described in JP-A-60-103008, but the method for producing the zirconium phosphate-based compound is not limited thereto.

[0023] Examples of the zirconium compound used in the production of the zirconium phosphate-based compound include zirconium nitrate, zirconium acetate, zirconium sulfate, zirconium carbonate, basic zirconium carbonate, basic zirconium sulfate, zirconium oxysulfate, and zirconium oxychloride. Among them, the zirconium compound is preferably zirconium nitrate, zirconium acetate, zirconium sulfate, zirconium carbonate, basic zirconium sulfate, zirconium oxysulfate, or zirconium oxychloride, and more preferably zirconium oxychloride.

[0024] The organic acid used in the production of the zirconium phosphate-based compound is preferably an aliphatic carboxylic acid, more preferably an aliphatic dibasic acid, still more preferably oxalic acid, maleic acid, malonic acid, or succinic acid, and particularly preferably oxalic acid. The organic acid may be a salt or a hydrate. Examples of the counter ion in the salt include ammonium ion, sodium ion, and potassium ion. Specific examples of the organic acid used in the production of the zirconium phosphate-based compound include oxalic acid dihydrate, ammonium oxalate, and ammonium hydrogen oxalate. Among them, oxalic acid dihydrate is preferred.

[0025] Examples of the inorganic acid used in the production of the zirconium phosphate-based compound include hydrochloric acid, sulfuric acid, nitric acid, hydroiodic acid, hydrobromic acid, chloric acid, bromic acid, iodic acid, permanganic acid, thiocyanic acid, perchloric acid, perbromic acid, tetrafluoroboric acid, and hexafluorophosphoric acid. Among them, from the viewpoint of availability, the inorganic acid is preferably hydrochloric acid, sulfuric acid, or nitric acid, and more preferably hydrochloric acid.

[0026] The phosphoric acid compound used in the production of the zirconium phosphate-based compound is preferably phosphoric acid or a phosphate, more preferably phosphoric acid, sodium phosphate, potassium phosphate, or ammonium phosphate, and still more preferably phosphoric acid.

[0027] After completion of the reaction, a solid-liquid separation treatment may be performed followed by a drying treatment, or the drying treatment may be performed without performing the solid-liquid separation treatment. The solid-liquid separation treatment can be performed using, for example, a filter press or a pressure filter. The drying treatment after the solid-liquid separation treatment can be performed using, for example, a paddle dryer (manufactured by Nara Machinery Co., Ltd.), a conical dryer, a vibrating dryer, or an inverted cone type stirring dryer. The drying treatment when the solid-liquid separation treatment is not performed can be performed using, for example, a spray dryer, a fluidized bed dryer with balls, or a jet turbo dryer (manufactured by Hiratori Iron Works Co., Ltd.). From the viewpoint of ease of handling, it is preferable to perform the drying treatment without performing the solid-liquid separation treatment.

[0028] After the drying treatment, the dried product may be subjected to a crushing or pulverizing treatment. In order to make the particles of the zirconium phosphate compound have a uniform particle size and to remove coarse particles, it is preferable to further perform a sieving treatment after the crushing or pulverizing treatment.

[0029] In order to remove coarse particles, it is preferable to further perform classification after the sieving process. The classification method may be either dry classification or wet classification, but dry classification is preferable from the viewpoint of simplifying the production process.

[0030] (form) The form of the ammonia adsorbent according to one embodiment of the present invention is not particularly limited, and may be any of powder, granules, pellets, and tablets.

[0031] Moreover, the ammonia adsorbent according to one embodiment of the present invention may be in the form of a slurry in which a zirconium phosphate-based compound is dispersed in water, an organic solvent, oils and fats having fluidity, or the like.

[0032] Furthermore, the ammonia adsorbent according to one embodiment of the present invention may be in a form in which a zirconium phosphate-based compound is applied or coated on a fibrous filter, or in a form in which a zirconium phosphate-based compound is supported on an inorganic molded body such as a honeycomb-shaped ceramic, an alumina ball, or a zirconia ball.

[0033] (Application) An ammonia adsorbent according to an embodiment of the present invention is used to adsorb ammonia contained in the exhaust gas of an ammonia direct fuel cell. The fuel cell is preferably a solid oxide fuel cell. The ammonia contained in the exhaust gas of the ammonia direct fuel cell is usually 1% to 100 ppm, and is 5,000 ppm to 10 ppm in a stable state. At the same time, the amount of inert gas introduced, at the start and stop of operation, may be higher or lower than the above concentration range. An ammonia adsorbent according to an embodiment of the present invention can remove ammonia contained in the exhaust gas of an ammonia direct fuel cell and suppress the discharge of ammonia outside the system.

[0034] An ammonia adsorbent according to an embodiment of the present invention is applicable to portable devices, automobiles, railways, etc. equipped with an ammonia direct fuel cell.

[0035] <Ammonia adsorption device> An ammonia adsorption device according to an embodiment of the present invention includes means for introducing the exhaust gas of a fuel cell using ammonia as a direct fuel, and means for adsorbing the introduced exhaust gas to an ammonia adsorbent containing a zirconium phosphate-based compound. The fuel cell is preferably a solid oxide fuel cell.

[0036] The means for introducing the exhaust gas of a fuel cell using ammonia as a direct fuel is not particularly limited, and known ones such as an introduction pipe connected to the fuel cell can be applied. The introduction pipe may be provided with a pump or the like.

[0037] Alternatively, the high-temperature exhaust gas discharged from a fuel cell using ammonia as a direct fuel may be introduced into a heat exchanger once for cooling, and then the low-temperature exhaust gas may be introduced into the ammonia adsorption device.

[0038] The means for adsorbing ammonia to the ammonia adsorbent containing a zirconium phosphate-based compound comprises an ammonia adsorbent containing a zirconium phosphate-based compound. The ammonia adsorbent containing a zirconium phosphate-based compound is preferably the ammonia adsorbent according to an embodiment of the present invention. The preferred embodiment of the ammonia adsorbent containing a zirconium phosphate-based compound is as described in the column of the above ammonia adsorbent.

[0039] The ammonia adsorption device according to an embodiment of the present invention may further comprise means for discharging the residual gas after ammonia in the introduced exhaust gas is adsorbed. The residual gas may be discharged into the atmosphere or introduced into another device.

Example

[0040] Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

[0041] <Example 1> -Production of zirconium phosphate-based compound- 6m 3 3,611 kg of deionized water and 363 kg of 35% hydrochloric acid were placed in a reactor. Further, 603 kg of a 20% by mass aqueous solution of zirconium oxychloride octahydrate containing 0.18% hafnium was added, and 250 kg of oxalic acid dihydrate was dissolved therein. While stirring this solution well, 275 kg of 75% phosphoric acid was added. The temperature of this solution was raised to 98 ° C. in 2 hours and refluxed with stirring for 12 hours. After cooling, the obtained precipitate was washed with water. Then, it was dried at 105 ° C. The dried product was crushed with a crusher. Then, sieving treatment was performed.

[0042] As a result of performing powder X-ray diffraction measurement and fluorescent X-ray analysis on the obtained powder, it was confirmed that it was α-zirconium phosphate. When fluorescent X-ray analysis and thermogravimetry-differential thermal simultaneous measurement (TG-DTA) of this α-zirconium phosphate were performed, the composition formula was Zr 0.99 Hf 0.01 H 2.03 (PO4)2.01 · It was 0.05H2O and had a median diameter of 0.89 μm.

[0043] The measurement conditions and methods for powder X-ray diffraction, X-ray fluorescence analysis, TG-DTA, and particle size (median diameter) are described below.

[0044] <Powder X-ray diffraction> As the X-ray diffractometer, D8 ADVANCE manufactured by BRUKER was used. Using a Cu-encapsulated X-ray source, a CuKα generated at an applied voltage of 40 kV and a current value of 40 mA was used to obtain an X-ray diffraction pattern. The detailed measurement conditions are as follows. X-ray source: Encapsulated X-ray source (Cu source), 0.4×12 mm 2 , Long Fine Focus Rated power: 2.2 kW Output used: 40 kV - 40 mA (1.6 kW) Goniometer radius: 280 mm Sample stage: FlipStick_Twin_Twin-XE Measurement range 2θ: 5° to 55° Step width: 0.02° Step time: 0.05 seconds / step Incident side soller slit: 2.5° Scattering prevention slit: 10.5 mm Curvature: 1.00 Detector: LYNXEYE XE Detector slit width: 5.758 mm Detector window width: 2.9°

[0045] <X-ray fluorescence analysis> X-ray fluorescence analysis was performed under the following conditions. Measuring instrument: ZSX Primus II manufactured by Rigaku Measurement conditions Elements to be measured: C to U (fixed angle measurement for F, Cl, Br, I, BG 4 sec, peak 8 sec) Analysis diameter: 20 mm Number of measurements: Measured with n2 Sample preparation: Using a tablet press, the sample was pressure-molded into pellets and used for measurement. Analysis Software: ZSX version7.49 Model: Bulk

[0046] <tg-dta> The TG-DTA measurement was carried out under the following conditions. Measuring instrument: TG / DTA 6300 manufactured by Hitachi High-Tech Science Measuring method: 7 - 8 mg of the sample was placed in an Al pan and set, and the temperature was raised to 600 °C at 20 °C / min. The weight loss from room temperature to 100 °C was regarded as the moisture content (adherent water), and the weight loss from 100 °C to 250 °C was estimated as the water of crystallization.

[0047] <Measurement of particle size (median diameter)> The particle size was measured with a laser diffraction particle size distribution measuring device "Mastersizer 2000" manufactured by Malvern, and the results were analyzed on a volume basis. The dispersion liquid added with zirconium phosphate was dispersed by ultrasonic waves and measured at a refractive index of 2.4.

[0048] The obtained α-zirconium phosphate was used as an ammonium adsorbent.

[0049] <Comparative Example 1> Anhydrous nickel chloride (manufactured by Fujifilm Wako Pure Chemical Corporation, Grade 1) was used as an ammonium adsorbent.

[0050] <Comparative Example 2> Anhydrous strontium chloride (manufactured by Fujifilm Wako Pure Chemical Corporation, Grade 1) was used as an ammonium adsorbent.

[0051] <Comparative Example 3> Anhydrous manganese chloride (manufactured by Fujifilm Wako Pure Chemical Corporation, Grade 1) was used as an ammonium adsorbent.

[0052] <Comparative Example 4> Calcium chloride dihydrate (manufactured by Fujifilm Wako Pure Chemical Corporation, Grade 1) was used as an ammonium adsorbent.

[0053] <Comparative Example 5> Magnesium chloride hexahydrate (manufactured by Fujifilm Wako Pure Chemical Corporation, Grade 1) was used as an ammonium adsorbent.

[0054] Using the above ammonia adsorbent, the ammonia adsorption capacity and the ammonia removal rate were calculated. The calculation method is as follows. Note that the ammonia adsorbent of Example 1 was in a non-deliquescent and free-flowing state. On the other hand, the ammonia adsorbents of Comparative Examples 1 to 5 were deliquescent and sticky.

[0055] [Ammonia adsorption capacity] First, a blank test without using the ammonia adsorbent was conducted. Specifically, assuming the ammonia concentration in the exhaust gas of a direct ammonia fuel cell, 3 L of ammonia adjusted to a concentration of 1000 ppm was put into a bag and sealed. The ammonia concentration after standing for 120 minutes was measured. The ammonia concentration after the blank test was 990 ppm. Next, tests using the ammonia adsorbents of the examples and comparative examples were conducted. First, about 10 mg of each ammonia adsorbent was weighed. Specifically, 10.2 mg of the ammonia adsorbent was weighed in Example 1 and Comparative Example 5, 10.3 mg in Comparative Examples 1 and 4, and 10.4 mg in Comparative Examples 2 and 3. 3 L of ammonia adjusted to a concentration of 1000 ppm and the ammonia adsorbent were put into a bag and sealed, and the ammonia concentration after standing for 120 minutes was measured. The ammonia adsorption capacity was calculated based on the following formula. Ammonia adsorption capacity (mL / g) = {Ammonia concentration after blank test (ppm) - Ammonia concentration after adsorption test (ppm)} × 3 (L) ÷ {Amount of ammonia adsorbent used (mg)} In the formula, the ammonia concentration after the blank test is 990 ppm. The ammonia concentration after the adsorption test is as shown in Table 1.

[0056] [Ammonia removal rate] First, about 10 mg of each ammonia adsorbent was weighed. Specifically, 10.2 mg of the ammonia adsorbent was weighed in Example 1 and Comparative Example 5, 10.3 mg in Comparative Examples 1 and 4, and 10.4 mg in Comparative Examples 2 and 3. Assuming the ammonia concentration in the exhaust gas of a direct ammonia fuel cell, 3 L of ammonia adjusted to a concentration of 1000 ppm and an ammonia adsorbent were placed in a bag and sealed. The ammonia concentration was measured after leaving it for 120 minutes. The ammonia removal rate was calculated based on the following formula. Ammonia removal rate (%) = {1000 (ppm) - ammonia concentration after adsorption test (ppm)} ÷ 1000 (ppm) × 100

[0057]

Table 1

[0058] As shown in Table 1, it was found that the ammonia adsorbent of Example 1 had a higher ammonia adsorption capacity compared to the ammonia adsorbents of Comparative Examples 1 to 5. Also, with the ammonia adsorbent of Example 1, 59% of the ammonia at a concentration of 1000 ppm, which was assumed to be the exhaust gas of a direct ammonia fuel cell, could be adsorbed. On the other hand, the ammonia adsorbents of Comparative Examples 1 to 5 were metal halides, and it was found that their ammonia removal rate was low. That is, it can be said that a large amount of the ammonia adsorbents of Comparative Examples 1 to 5 is required to completely adsorb the ammonia in the exhaust gas of a direct ammonia fuel cell.

[0059] Also, the ammonia adsorbent of Example 1 was not deliquescent and was easy to handle. On the other hand, the ammonia adsorbents of Comparative Examples 1 to 5 were deliquescent and difficult to handle in the atmosphere.

Industrial Applicability

[0060] The ammonia adsorbent according to one embodiment of the present invention can adsorb ammonia in a small amount. Therefore, it is possible to make the ammonia adsorption device equipped with the ammonia adsorbent according to one embodiment of the present invention compact and lightweight.

Claims

1. An ammonia adsorbent containing a zirconium phosphate-based compound, which is used for adsorbing ammonia contained in the exhaust gas of a fuel cell using ammonia as a direct fuel.

2. The ammonia adsorbent according to Claim 1, wherein the zirconium phosphate-based compound is represented by the following formula (1). Zr １―ｘ Hf ｘ H ａ (PO ４ ) ｂ ・nH ２ O (1) In formula (1), a and b are positive numbers satisfying 3b - a = 4, b is a positive number of 2.0 < b ≤ 2.1, x is a positive number of 0 ≤ x ≤ 0.2, and n is a positive number of 0 ≤ n ≤ 2.

0.

3. The ammonia adsorbent according to Claim 2, wherein in the formula (1), x is a positive number of 0.005 ≤ x ≤ 0.

2.

4. The ammonia adsorbent according to any one of Claims 1 to 3, wherein the crystal form of the zirconium phosphate-based compound is the α form.

5. The ammonia adsorbent according to any one of Claims 1 to 4, wherein the fuel cell is a solid oxide fuel cell.

6. Means for introducing the exhaust gas of a fuel cell using ammonia as a direct fuel, Means for adsorbing the introduced exhaust gas to an ammonia adsorbent containing a zirconium phosphate-based compound. An ammonia adsorption device comprising.

7. The ammonia adsorption device according to Claim 6, wherein the fuel cell is a solid oxide fuel cell.

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