Hydrogen production method, ammonia-containing gas treatment material, and method for producing the treatment material

Abstract

To provide a method for producing hydrogen which makes it possible to easily convert ammonia-containing gas into hydrogen without reducing catalytic activity despite a usage for a long time and at a high decomposition rate, a treatment material of ammonia-containing gas, and a method for producing a treatment material.SOLUTION: A method includes: a process of heating a catalyst layer to 200°C or higher and 700°C or lower; and a process of allowing ammonia-containing gas to pass through the heated catalyst layer to decompose ammonia into nitrogen gas and hydrogen gas, where a treatment material comprising at least one kind or more of γ-alumina and θ-alumina, and a composite including a sintered product of clay compound, and a metal carried by the composite is used for the catalyst layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing hydrogen, a material for treating ammonia-containing gas, and a method for producing the material. [Background technology]

[0002] Toward the realization of a decarbonized society, CO2-free hydrogen is attracting attention as a clean energy source. However, hydrogen's low density and melting point make it difficult to efficiently store and transport large amounts of hydrogen. To advance the use of hydrogen energy, solving these issues is essential, and active research is being conducted into materials that can serve as hydrogen energy carriers.

[0003] Ammonia is attracting attention as an excellent hydrogen energy carrier because it can be easily liquefied at about 10 atmospheres and contains three hydrogen atoms per molecule. In recent years, hydrogen stations that produce high-purity hydrogen using ammonia as a raw material have been developed both domestically and internationally, and this has led to an increasing demand for catalysts that can efficiently convert ammonia into hydrogen. Therefore, research is being conducted on catalysts for decomposing ammonia-containing gases that can be converted into hydrogen (see Patent Documents 1 to 3).

[0004] Furthermore, as a wastewater treatment technology, an ammonia-containing water treatment material containing alumina selected from γ-alumina or θ-alumina and aluminosilicates made from various clays as raw materials has been proposed, and it has also been proposed to support metals on the treatment material (see Patent Documents 4 to 6). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5380233 specification [Patent Document 2] International Publication No. 2019 / 188219 [Patent Document 3] Patent No. 6795804 specification [Patent Document 4] Japanese Patent Application Laid-Open No. 2017-164671 [Patent Document 5] Japanese Patent Application Publication No. 2019-171311 [Patent Document 6] Japanese Patent Application Publication No. 2020-049472 Summary of the Invention [Problem to be solved by the invention]

[0006] Catalysts with precious metals such as ruthenium supported on gamma-alumina or zeolite supports are widely known as catalysts for decomposing ammonia-containing gases to convert them into hydrogen. However, gamma-alumina-supported catalysts have poor alkali resistance, and when exposed to alkaline gases containing water vapor for long periods of time, they undergo hydration reactions and transform into boehmite, which has a small specific surface area. This can lead to a decrease in catalyst strength, which can lead to deterioration of the catalyst itself and a decrease in activity. Furthermore, zeolite-supported catalysts require pretreatment by passing an inert gas through them at approximately 100°C after loading the catalyst to reveal the acid sites of the zeolite support.

[0007] On the other hand, it is possible to repurpose existing ammonia-containing water treatment materials, but the density and the conditions surrounding the treatment target are different between liquid and gas, and in addition, the treatment conditions are significantly different because wastewater treatment requires the addition of hydrogen peroxide and a reaction under high pressure. Furthermore, Patent Documents 4 to 6 do not fully consider conversion to hydrogen.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a method for producing hydrogen, a treatment material for ammonia-containing gas, and a method for producing the treatment material, which are capable of easily converting an ammonia-containing gas into hydrogen at a high decomposition rate without reducing catalytic activity even when used for a long period of time. [Means for solving the problem]

[0009] (1) To achieve the above object, the hydrogen production method of the present invention includes a step of heating a catalyst layer to 200°C or higher and 700°C or lower, and a step of passing an ammonia-containing gas through the heated catalyst layer to decompose the ammonia into nitrogen gas and hydrogen gas, wherein the catalyst layer uses a treatment material comprising a composite containing at least one of γ-alumina and θ-alumina and a sintered clay compound, and a metal supported by the composite. Because the catalyst layer uses a treatment material comprising a composite containing at least one of γ-alumina and θ-alumina and a sintered clay compound, and a metal supported by the composite, the catalytic activity does not decrease even after long-term use, and the ammonia-containing gas can be decomposed at a high decomposition rate, and can be easily converted to hydrogen without the need for special operations such as pretreatment.

[0010] (2) The method for producing hydrogen of the present invention is characterized in that the composite contains 30% by mass or more and 70% by mass or less of the gamma-alumina, which allows the composite to maintain a sufficient specific surface area and is not altered even when exposed to a mist containing strongly alkaline wet gas or strongly alkaline water droplets.

[0011] (3) Furthermore, the method for producing hydrogen of the present invention is characterized in that the metal is one or a combination of two or more selected from the group consisting of ruthenium, platinum, and rhodium, thereby achieving ammonia decomposition at a high decomposition rate.

[0012] (4) The hydrogen production method of the present invention is characterized in that the metal is contained in an amount of 0.001% by mass or more and less than 10% by mass of the composite, thereby achieving a high ammonia decomposition rate at low cost.

[0013] (5) In the method for producing hydrogen of the present invention, the ammonia-containing gas is a wet gas that does not contain oxygen, thereby increasing the conversion rate of ammonia to hydrogen.

[0014] (6) The material for treating ammonia-containing gas of the present invention comprises a composite that is a sintered product of a molded body containing at least one of γ-alumina and θ-alumina and a clay compound, and a metal supported by the composite, wherein the content of the metal relative to the composite is 0.001% by mass or more and less than 10% by mass, thereby achieving a high ammonia decomposition rate at low cost.

[0015] (7) The method for producing a material for treating ammonia-containing gas according to the present invention includes the steps of: kneading at least one of γ-alumina and θ-alumina with a clay compound so that the total content of the γ-alumina and θ-alumina is 30% by mass or more and 70% by mass or less to obtain a kneaded mixture; molding the kneaded mixture; firing the molded body obtained by the molding at 900°C or more and 1200°C or less; and supporting 0.001% by mass or more and less than 10% by mass of metal on the fired body obtained by the firing. This allows the production of a treating material that can decompose ammonia-containing gas at a high decomposition rate without a decrease in catalytic activity even after long-term use and can easily convert the gas into hydrogen without requiring special operations such as pretreatment. [Effects of the Invention]

[0016] According to the present invention, the catalytic activity does not decrease even after long-term use, and it is possible to decompose an ammonia-containing gas at a high decomposition rate and easily convert it into hydrogen. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of an apparatus used in an ammonia decomposition test. [Figure 2] 1 is a graph showing the results of calculating the ammonia decomposition rate and the hydrogen composition ratio using gas chromatography for the gas after the ammonia decomposition reaction using a sample supporting 1 mass % ruthenium. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described. [Composition of treated material] The material for treating ammonia-containing gas contains at least one of γ-alumina and θ-alumina and a sintered clay compound. γ-alumina has a spinel-type crystal structure, and its particles have a larger specific surface area than α-alumina. A larger specific surface area of ​​the material can improve ammonia decomposition performance.

[0019] If the alumina content of the treatment material for ammonia-containing gas is too low, the specific surface area cannot be increased sufficiently. On the other hand, if the alumina content is too high, the alkali resistance decreases. For these reasons, the alumina content of the treatment material is 30 mass % to 70 mass %, preferably 35 mass % to 70 mass %, and more preferably 40 mass % to 60 mass %.

[0020] Sintered clay compounds can be obtained by sintering clay compounds. Examples of clay compounds include aluminosilicates such as kaolinite, mullite, and illite, as well as pottery clays containing a large amount of aluminosilicate, such as Gaime clay, Kasaoka clay, Kibushi clay, and Shigaraki clay. These can be used alone or in combination of two or more. Gaime clay is preferred because of its high ammonia decomposition ability. Sintered clay compounds can be obtained by firing these clay compounds at temperatures between 900°C and 1200°C. Sintered clay compounds are effective in promoting the sintering of γ-alumina and θ-alumina and inhibiting hydration by aqueous ammonia.

[0021] The treatment material for ammonia-containing gas may further contain silica. Silica is silicon dioxide (SiO2), and examples thereof include quartz contained in the clay compound used as the raw material, cristobalite produced by firing, and glassy silica formed by reaction of silica with an alkali component. One or more types of silica are contained in the treatment material. In the treatment material, at least one of γ-alumina and θ-alumina, a sintered clay compound, and silica form a composite, and the composite serves as a carrier for the metal.

[0022] The content of the sintered clay compound in the composite can be adjusted appropriately depending on the amount of alumina. For example, when the alumina content in the composite is 30% to 70% by mass, the content of the sintered clay compound (total amount including silica when silica is included) can be adjusted to 70% to 30% by mass. Note that the content of the sintered clay compound here refers to the mass of the clay compound after drying at 105°C during production.

[0023] The composite supports a metal as an active component. Examples of supported metals include platinum, palladium, ruthenium, rhodium, indium, iridium, gold, silver, cobalt, copper, nickel, tungsten, and water-insoluble or poorly water-soluble compounds of these metals. Specific examples include oxides such as cobalt monoxide, nickel monoxide, ruthenium dioxide, dirhodium trioxide, palladium monoxide, iridium dioxide, cupric oxide, and tungsten dioxide; chlorides such as ruthenium dichloride and platinum dichloride; sulfides such as ruthenium sulfide and rhodium sulfide; nitrates such as rhodium nitrate, nickel nitrate, ruthenium nitrate, copper nitrate, and silver nitrate; and complexes such as hexachloroplatinic acid hexahydrate, hexaammineruthenium chloride, ruthenium chloride, and diamminepalladium nitrite. The amount of metal supported is 0.001% by mass to 10% by mass, preferably 0.01% by mass to 10% by mass, more preferably 0.05% by mass to 10% by mass, and particularly preferably 0.5% by mass to 10% by mass, based on the weight of the carrier, in terms of the balance between ammonia decomposition performance and cost.

[0024] The ammonia-containing gas treating material can be formed into various shapes, including, but not limited to, a spherical shape, a pellet shape, a cylindrical shape, a rectangular parallelepiped shape, a tubular shape, a crushed piece shape, a honeycomb shape, and a powder shape.

[0025] [Manufacturing method of treated material] The ammonia-containing gas treatment material is produced by a production method including the steps of kneading a compound that provides at least one of γ-alumina and θ-alumina with a clay compound to obtain a kneaded mixture, shaping the kneaded mixture, and then firing the shaped body at a temperature of 900°C to 1200°C.

[0026] The term "compound that yields γ-alumina" refers to γ-alumina or a compound that generates γ-alumina upon calcination. Compounds that generate γ-alumina upon calcination are not particularly limited, but include hydroxides such as gibbsite, diaspore, and boehmite, nitrates such as aluminum nitrate, and chlorides such as aluminum chloride. The compound that generates γ-alumina can be used alone or in combination of two or more. Furthermore, the term "compound that yields θ-alumina" refers to θ-alumina or a compound that generates θ-alumina upon calcination. Compounds that generate θ-alumina upon calcination are not particularly limited, but include aluminum hydroxide.

[0027] When the above raw materials are kneaded to obtain a kneaded product, a solvent such as water or 1,3-butanediol may be added to the kneaded product in order to ensure kneadability and subsequent moldability. The kneading method can be carried out using a commonly used kneader or the like.

[0028] As for the blending ratio of the raw materials, in order to set the total content of γ-alumina and θ-alumina in the ammonia-containing gas treatment material to 30 mass% to 70 mass%, preferably 35 mass% to 70 mass%, more preferably 40 mass% to 70 mass%, the total content of compounds that provide γ-alumina and θ-alumina in the solid content of the kneaded product is set to 30 mass% to 70 mass%, preferably 35 mass% to 70 mass%, more preferably 40 mass% to 60 mass%.

[0029] The particle size of γ-alumina and θ-alumina is preferably an average particle size (D50) of 50 μm or less, more preferably 10 to 30 μm, in order to maintain the specific surface area and reduce loss of alumina due to sintering.

[0030] On the other hand, the content of the clay compound in the solid content of the kneaded product after drying at 105°C can be 30% by mass to 70% by mass, preferably 35% by mass to 65% by mass, and more preferably 40% by mass to 60% by mass, depending on the content of γ-alumina.

[0031] Furthermore, in order to maintain alkali resistance while maintaining ammonia decomposition performance, the clay compound preferably has an average particle size (D50) of 100 μm or less, more preferably 10 to 50 μm.

[0032] As a molding method for the kneaded material, an appropriate method can be selected depending on the shape of the treatment material to be produced. For example, when molding the kneaded material into a spherical molded body, molding can be performed using a granulator or the like. Furthermore, when molding the kneaded material into a cylindrical, rectangular, cylindrical, honeycomb, or other molded body, molding can be performed using an extrusion molding machine or the like. After molding the kneaded material, the molded body may be fired immediately, but from the viewpoint of preventing the occurrence of cracks, etc., drying may be performed before firing as necessary. In addition, since the raw material contains a clay compound, it has excellent moldability. Therefore, it can be easily molded without adding a binder.

[0033] The compact is fired at a temperature of 900° C. to 1200° C. By firing within this temperature range, it is possible to obtain a material for treating ammonia-containing gas that maintains the specific surface areas of γ-alumina and θ-alumina while increasing its strength.

[0034] If the firing temperature is less than 900°C, the strength of the material for treating ammonia-containing gas decreases and the shape is easily distorted. On the other hand, if the firing temperature exceeds 1200°C, γ-alumina and θ-alumina undergo a phase transition to form α-alumina with a corundum structure, and sintering of alumina progresses, resulting in a decrease in the specific surface area of ​​the material for treating ammonia-containing gas. The firing method is not particularly limited, and can be performed using a known firing device. As the firing device, a batch furnace, a tunnel kiln, a rotary kiln, etc. can be used.

[0035] The composite thus obtained may be used as is, or may be pulverized as necessary. Examples of pulverization methods include a jaw crusher and a ball mill. In order to maintain the specific surface area and breathability, the pulverized product preferably has a maximum particle size of 500 μm or less, more preferably 300 μm. Alternatively, the average particle size (D50) is preferably 300 μm or less, more preferably 50 μm to 200 μm.

[0036] Next, a metal is supported on the composite obtained in this manner. While any method for supporting the metal can be used, one example is impregnation with an aqueous metal solution. To impregnate the composite with an aqueous metal solution, the composite is first impregnated with an aqueous metal ion-containing solution. After impregnation, the water adhering to the composite is removed using an evaporator, a centrifugal separator (low speed rotation), or the like, and the composite is then calcined to support the metal. For example, to support ruthenium, the composite is impregnated with a hexaammineruthenium chloride solution, the water is removed, and the composite is calcined at approximately 300 to 500°C for 2 hours.

[0037] It is also effective to remove excess moisture from the surface of the material by air-drying it before firing, such as by exposing it to hot air or placing it in a dryer. In particular, when firing a composite without gradually increasing the firing temperature, pre-air drying allows for firing with high thermal efficiency.

[0038] The removed metal ion-containing aqueous solution can be recovered and reused. After calcination, the calcined body may be hydrogen-reduced. Hydrogen reduction can be performed, for example, by passing a 10% hydrogen-containing gas at 500°C through the calcined body. Hydrogen reduction can improve the activity of catalysts, especially those with reduced catalytic activity.

[0039] By passing an ammonia-containing gas through the treating material obtained by the above-described manufacturing method, the ammonia in the ammonia-containing gas can be decomposed.

[0040] [Hydrogen production methods] A method for producing hydrogen using a treatment material for an ammonia-containing gas will be described. First, the treatment material is held in the device as a catalyst layer. Then, the treatment material is heated to a predetermined temperature of 200 to 700°C, and an ammonia-containing gas is passed through the catalyst layer. The amount of treatment material is preferably adjusted according to the decomposition rate determined by the supported metal.

[0041] The ammonia concentration of the ammonia-containing gas is not particularly important. The amount of ammonia-containing gas fed is determined based on the space velocity SV of 5000 h -1 More than 10,000 hours is fine. -1 Above, maximum 15,000h -1 ~30,000h -1 Regardless of the input amount, a sufficient ammonia decomposition rate can be obtained when producing hydrogen industrially.

[0042] In this case, the ammonia-containing gas may be a wet gas that does not contain oxygen. Methods for generating such an ammonia-containing gas include bubbling an oxygen-free gas into ammonia-containing water, adding an alkali to ammonia-containing water, and spraying water vapor into ammonia gas. Here, the wet gas refers to a gas that contains moisture. In extreme cases, when the gas is added at a temperature below 100°C, it may be in the form of a mist containing strongly alkaline water droplets.

[0043] Furthermore, the ammonia-containing gas may contain a small amount of oxygen added to a portion of the ammonia. Hydrogen can also be produced by partial oxidation, which adds a small amount of oxygen. In a method for producing hydrogen using partial oxidation, the ammonia-containing gas is preferably a dry gas containing oxygen. Here, dry gas refers to a gas that does not contain moisture and has a dew point of about -47.5°C. In the partial oxidation method, water vapor is generated during the reaction process, but the treatment material of the present invention does not deteriorate.

[0044] The hydrogen produced by conversion from ammonia may be purified using known techniques such as adsorption or membrane separation. This allows high-purity hydrogen to be produced. In this way, ammonia-containing gas can be decomposed at a high decomposition rate even after long-term use. Furthermore, the ammonia-containing gas can be easily converted into hydrogen without the need for pretreatment.

[0045] [Example] 1.1 Experimental method (1) Sample preparation

[0046] (Preparation of powdered samples) A composite containing sintered γ-alumina and clay compounds was crushed to a size of 250 μm or less in a mortar. Approximately 0.3 g of this was precisely weighed and placed in an eggplant flask, and 5.94 ml of distilled water was added. After heating to 90°C, 1.26 × 10 -2 1.95 ml of a 1.0 mol / l hexaneammineruthenium chloride solution was added dropwise and stirred for 1 hour while maintaining the temperature at 90° C. After impregnation with the ruthenium solution, the water content was measured and the mixture was evaporated to dryness in an evaporator, and then calcined in air at 500° C for 2 hours to prepare a powdered 1 mass% ruthenium sample.

[0047] (2) Ammonia decomposition test FIG. 1 is a schematic diagram of an experimental apparatus 1 used in an ammonia decomposition test. A 0.5 g sample 13 sandwiched between quartz wool 15 was placed in a quartz glass tube 11 having an inner diameter of 10 mm and a length of 400 mm, and the tube was 80 mm long (volume 0.628 cm). 3 The quartz glass tube 11 was placed in a tubular electric furnace 17, and the temperature of the catalyst layer was adjusted.

[0048] The ammonia-containing gas was generated by placing 300 ml of 28% ammonia water in a 900 ml glass container 40 and supplying nitrogen gas using a nitrogen cylinder 20. The gas flow rate was adjusted to 100 ml / min using a mass flow controller 30. After one hour had passed since the catalyst bed was heated to 300 to 700°C, the nitrogen gas with the adjusted flow rate was bubbled through the ammonia water, causing the ammonia-containing gas to pass through the catalyst bed. At this time, the space velocity SV was 18,200 h -1 The gas that had passed through the catalyst layer was collected, and the ammonia concentration and hydrogen concentration of the reaction gas were measured by gas chromatography, and the ammonia decomposition rate and hydrogen composition ratio were calculated.

[0049] 1.2 Results and Discussion Ammonia-containing gas, generated by bubbling nitrogen gas through aqueous ammonia, was passed through the prepared 1% by mass ruthenium-supported sample in an attempt to generate hydrogen through the decomposition of ammonia. Generally, in the absence of oxygen, ammonia decomposes into hydrogen and nitrogen as follows: 2NH3 → N2 + 3H2…(1-1)

[0050] Furthermore, if all ammonia is converted to hydrogen and nitrogen according to the above formula, the theoretical hydrogen composition ratio will be 75%, as shown below. Therefore, using gas chromatography, the reaction gas after the ammonia decomposition reaction was recovered, and the ammonia concentration and hydrogen concentration were measured to calculate the ammonia decomposition rate and hydrogen composition ratio.

number

[0051] Figure 2 is a graph showing the ammonia decomposition rate and hydrogen composition ratio when the temperature of the catalyst layer is changed from 400 to 700°C. It was confirmed that the ammonia decomposition rate increases with increasing temperature, and an ammonia decomposition rate of 90% or more is achieved when the temperature of the catalyst layer is 500°C or higher. It was also revealed that the hydrogen composition ratio was approximately 75% regardless of temperature. In other words, the hydrogen composition ratio was almost consistent with the theoretical value, and it was confirmed that substantially all ammonia was converted to hydrogen.

[0052] 2.1 Experimental method (1) Sample preparation (Preparation of powdered samples)

[0053] A composite containing sintered γ-alumina or θ-alumina and a clay compound was crushed to a size of 250 μm or less in a mortar. Approximately 0.3 g of this was precisely weighed and placed in an eggplant flask, and 5.94 ml of distilled water was added. After heating to 90°C, 1.26 × 10 -2 1.95 ml of a 1.0 mol / l hexaneammineruthenium chloride solution was added dropwise and stirred for 1 hour while maintaining the temperature at 90° C. After impregnation with the ruthenium solution, the water content was measured and the mixture was evaporated to dryness in an evaporator, and then calcined in air at 500° C for 2 hours to prepare a powdered 1 mass% ruthenium sample.

[0054] Using the same method, 5.85 x 10 -2 The powdered sample was impregnated with 7.72×10-3 mol / L rhodium(III) nitrate and 7.72×10-3 mol / L hexachloroplatinic acid solution. The following γ-alumina or θ-alumina and clay compounds were used: (alumina) γ-alumina: Nippon Light Metal Co., Ltd. "C20" Average particle size (D50) 15-25 μm : Mizusawa Chemical Industries, Ltd. "Activated Alumina GB" spherical product, crushed in a mortar and used θ-alumina: Nippon Light Metal Co., Ltd. "C40" Average particle size (D50) 15-25 μm (clay compound) Frog-eye clay: Kawarin Ceramics Co., Ltd. Average particle size (D50) 20-50μm Kasaoka clay: Kanesan Industrial Co., Ltd., 250 mesh (62 μm), 95% passing

[0055] (2) Ammonia decomposition test FIG. 1 is a schematic diagram of an experimental apparatus 1 used in an ammonia decomposition test. A 0.5 g sample 13 sandwiched between quartz wool 15 was placed in a quartz glass tube 11 having an inner diameter of 10 mm and a length of 400 mm, and the tube was 80 mm long (volume 0.628 cm). 3 The quartz glass tube 11 was placed in a tubular electric furnace 17, and the temperature of the catalyst layer was adjusted.

[0056] The ammonia-containing gas was generated by placing 300 ml of 2.8% or 28% aqueous ammonia in a 900 ml glass container 40 and supplying nitrogen gas using a nitrogen cylinder 20. The gas flow rate was adjusted to 100 ml / min using a mass flow controller 30. After one hour had passed since the catalyst bed was heated to 100 to 700°C, the nitrogen gas with the adjusted flow rate was bubbled through the aqueous ammonia, causing the ammonia-containing gas to pass through the catalyst bed. At this time, the space velocity SV was 18,200 h -1 A three-way cock 50 was provided at the inlet of the catalyst layer and was used to evaluate the concentration at the inlet side of the catalyst layer (Inlet). The gas that had passed through the catalyst layer was bubbled for 10 minutes in a measuring cylinder 60 containing 250 ml of distilled water, and the ammonia concentration in the solution was analyzed (Outlet).

[0057] (3) Ammonia concentration evaluation The ammonia concentration was measured by the absorptiometry method according to JIS K 0400-42-60: 2000. The ammonia decomposition rate was calculated from the change in ammonia gas concentration before and after passing through the catalyst layer.

[0058] (a) Preparation of samples for absorbance measurement (Preparation of color-developing reagent) 13.0 g of sodium salicylate and 13.0 g of trisodium citrate dihydrate were dissolved in a small amount of distilled water, and then 0.097 g of sodium pentacyanonitrosylferrate(III) dihydrate that had been ground in a mortar was added, and the mixture was diluted to 100 ml using a measuring flask.

[0059] (Preparation of sodium dichloroisocyanurate solution) 3.2 g of sodium hydroxide was dissolved in a small amount of distilled water, and then 0.2 g of sodium dichloroisocyanurate dihydrate was added, followed by dilution to 100 ml using a measuring flask.

[0060] (Preparation of standard solution) 0.3819 g of ammonium chloride was dissolved in a small amount of distilled water and diluted to 100 ml using a measuring flask to prepare a 1000 ppm ammonium nitrogen standard solution. Using this prepared 1000 ppm ammonium nitrogen standard solution, a 100 ppm ammonium nitrogen standard solution and a 1 ppm ammonium nitrogen standard solution were prepared.

[0061] (b) Absorbance measurement 1 ml of the sample solution in which ammonia gas had been collected was diluted to 100 ml, and 40 ml of this solution was placed in a 50 ml measuring flask. 4 ml each of the color-developing reagent and sodium dichloroisocyanurate solution were added, and the total volume was adjusted to 50 ml. The mixture was left to stand for 10 minutes to develop color, and the ammonia concentration was measured using an absorption spectrophotometer.

[0062] The ammonia decomposition rate was calculated using the following formula.

number

[0063] 2.2 Results (1) Ammonia decomposition performance of samples made from various materials Table 1 shows the results of an ammonia decomposition test using samples in which 1% by mass of ruthenium was supported on catalyst supports made of various materials under set conditions of a catalyst layer temperature of 500°C and an ammonia water concentration of 2.8%. As shown in Table 1, samples 1 to 9 had an ammonia decomposition rate of 90% or more. Furthermore, samples 2 and 4, which used γ-alumina, had a higher ammonia decomposition rate than samples 8 and 9, which also used γ-alumina. Samples 1 to 5, which used Gaime clay, had a higher ammonia decomposition rate than samples 6 and 7, which used Kasaoka clay. From these results, it can be said that γ-alumina is the preferred alumina and Gaime clay is the preferred clay compound. [Table 1]

[0064] (2) Ammonia decomposition performance of various metal-loaded samples Table 2 shows the results of an ammonia decomposition test using samples with 1.0 mass% of each metal supported and samples with ruthenium supported in amounts ranging from 0.05 to 1.0 mass% under set conditions of a catalyst layer temperature of 500°C and an ammonia water concentration of 2.8%. The catalyst support for each sample was made with a mixture of 40% γ-alumina and 60% gamak clay. [Table 2]

[0065] As shown in Table 2, it was confirmed that an ammonia decomposition rate of 90% or more was achieved even with a ruthenium loading of 0.05% by mass. Furthermore, it was confirmed that, like the ruthenium-loaded sample, the rhodium-loaded sample also achieved an ammonia decomposition rate of 90% or more. It was also revealed that the platinum-loaded sample decomposed approximately 66% of ammonia.

[0066] Table 3 shows the ammonia decomposition rate (%) of samples supporting 1% by mass of ruthenium, rhodium, and platinum when the concentration of aqueous ammonia was fixed at 2.8% and the temperature of the catalyst layer was changed from 100 to 700°C. The catalyst support for each sample was made with a blend of 40% γ-alumina and 60% gamak clay. [Table 3]

[0067] In all samples, it was confirmed that 10% or more of ammonia could be decomposed by heating the catalyst layer to 200°C or higher. -1 This is set at a high value, which is thought to provide a sufficient ammonia decomposition rate for industrial hydrogen production. Furthermore, it was confirmed that an ammonia decomposition rate of 90% or more can be achieved by heating the catalyst layer to 500°C or higher for samples supporting 1% ruthenium and 1% rhodium by mass.

[0068] (3) Evaluation of ammonia decomposition performance of various catalyst supports Table 4 shows the ammonia decomposition rate (%) of samples in which 1 mass % of ruthenium is supported on various catalyst supports when the concentration of aqueous ammonia is fixed at 28% and the temperature of the catalyst layer is changed from 500 to 700°C. As an example, a sample prepared under the same conditions as sample 2 was used. Comparative Examples 1 to 3 were prepared under the same conditions as the example, except that the catalyst support was made of γ-alumina, magnesium oxide, and silica. [Table 4]

[0069] The following materials were used for the catalyst carrier in each comparative example. γ-Alumina (γ-Al2O3): Nippon Light Metal Co., Ltd., product name "C20" Magnesium oxide reagent (MgO): Fujifilm Wako Pure Chemical Industries, Ltd. Silicon dioxide reagent (SiO2): Kanto Chemical Co., Ltd.

[0070] As shown in Table 4, it was confirmed that the Examples achieved an ammonia decomposition rate of 95% or more by heating the catalyst layer to a temperature of 500 to 700° C. It was also revealed that the Examples exhibited a higher decomposition rate than the Comparative Examples at any temperature range.

[0071] (4) Durability evaluation Table 5 shows the ammonia decomposition rate (%) of samples in which 1 mass% of ruthenium is supported on various catalyst supports when an ammonia-containing gas is continuously passed through the catalyst layer under set conditions of a catalyst layer temperature of 500°C and an ammonia water concentration of 28% for 20 hours. [Table 5]

[0072] As shown in Table 5, it was confirmed that the ammonia decomposition rate did not decrease even when aeration was continued for 20 hours in the examples. On the other hand, it was revealed that the ammonia decomposition rate decreased when aeration was continued for 20 hours in the comparative examples. This is thought to be due to the progress of the hydration reaction of γ-alumina, resulting in the production of boehmite.

[0073] From the above, it has been confirmed that the hydrogen production method of the present invention can decompose an ammonia-containing gas at a high decomposition rate without reducing catalytic activity even when used for a long period of time, and can easily convert the gas into hydrogen without requiring any special operation such as pretreatment. [Explanation of symbols]

[0074] 1. Experimental equipment 11 Quartz glass tube 13 Sample 15 Quartz wool 17 Tubular electric furnace 20 Nitrogen Cylinder 30 Mass flow controller 40 glass containers 50 3-way cock 60 Measuring cylinder

Claims

1. heating the catalyst layer to 300°C or higher and 700°C or lower; and passing an ammonia-containing gas through the heated catalyst layer under oxygen-free conditions to decompose the ammonia into nitrogen gas and hydrogen gas, A method for producing hydrogen, characterized in that the catalyst layer uses a treatment material comprising a composite containing at least one of γ-alumina and θ-alumina and a sintered clay compound, and a metal supported by the composite.

2. 2. The method for producing hydrogen according to claim 1, wherein the composite contains 30% by mass or more and 70% by mass or less of the γ-alumina and the θ-alumina in total.

3. 3. The method for producing hydrogen according to claim 1, wherein the metal is one or a combination of two or more selected from the group consisting of ruthenium, platinum, and rhodium.

4. 4. The method for producing hydrogen according to claim 1, wherein the metal is present in an amount of 0.001 mass % or more and less than 10 mass % of the composite.

5. 5. The method for producing hydrogen according to claim 1, wherein the ammonia-containing gas is a wet gas that does not contain oxygen.

6. a composite which is a sintered product of a molded body containing at least one of γ-alumina and θ-alumina, and a clay compound; a metal supported by the composite; The metal is present in an amount of 0.001% by mass or more and less than 10% by mass of the composite, A treating material for decomposing ammonia in an ammonia-containing gas, characterized in that the composite has a pellet, cylindrical or honeycomb shape.

7. a step of kneading at least one of γ-alumina and θ-alumina with a clay compound so that the total content of the γ-alumina and the θ-alumina is 30% by mass or more and 70% by mass or less to obtain a kneaded product; A step of molding the kneaded product; a step of firing the molded body obtained by the molding at 900°C or higher and 1200°C or lower; and supporting 0.001% by mass or more and less than 10% by mass of metal on the fired body obtained by the firing. The method for producing a treating material for decomposing ammonia in an ammonia-containing gas, wherein the fired body has a pellet, cylindrical or honeycomb shape.

Images