Nitrous oxide decomposition method and nitrous oxide decomposition device

Abstract

To provide a decomposition method and a decomposition device of a nitrous oxide which can efficiently decompose a nitrous oxide in a gas containing the nitrous oxide.SOLUTION: There are provided a decomposition method of a nitrous oxide which includes a step of bringing a catalyst carrying a component containing at least one selected from the group consisting of ruthenium and a ruthenium compound in a carrier containing a titanium oxide into contact with a nitrous oxide-containing gas containing a nitrous oxide, water vapor and ammonia; and a decomposition device of a nitrous oxide which includes a reactor filled with the catalyst, and a line which is connected to the reactor and supplies the nitrous oxide-containing gas to the reactor.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for decomposing nitrous oxide and an apparatus for decomposing nitrous oxide. [Background technology]

[0002] From the perspective of protecting the global environment and preventing air pollution, nitrogen oxides (NOx) in exhaust gases have become a problem, and their emissions are being strictly regulated. The nitrogen oxides that are particularly subject to emission regulations are nitrogen dioxide (NO2), which is harmful to humans and is believed to cause photochemical smog and acid rain. Various denitrification technologies have been developed and implemented to reduce emissions. However, nitrous oxide (NO2), a type of nitrogen oxide, is not currently subject to emission regulations and is typically released directly into the atmosphere. In fact, gases emitted from chemical manufacturing plants, such as nitric acid, epsilon-caprolactam, and adipic acid plants, undergo denitrification treatment to remove nitric oxide and nitrogen dioxide, but the by-product nitrous oxide is often released into the atmosphere without being decomposed.

[0003] However, when greenhouse gases such as nitrous oxide are released into the atmosphere, the greenhouse effect of the atmosphere increases due to an increase in greenhouse gas concentration, which is thought to be a cause of global warming. Nitrous oxide is said to have a warming effect approximately 300 times greater than that of carbon dioxide. Therefore, in recent years, there has been growing interest in reducing atmospheric emissions of nitrous oxide, along with carbon dioxide and methane. With growing awareness of sustainable environmental conservation, it is expected that nitrous oxide will be subject to emission control in the near future. Therefore, there is a need for technologies that decompose and remove nitrous oxide from exhaust gases to reduce its emissions into the atmosphere. Patent Document 1, for example, describes a nitrous oxide decomposition method that uses a catalyst carrying at least one noble metal selected from ruthenium (Ru), rhodium (Rh), palladium (Pd), rhenium (Re), osmium (Os), iridium (Ir), and platinum (Pt) to catalytically decompose a gas containing nitrous oxide in the presence of a reducing gas. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 06-218232 Summary of the Invention [Problem to be solved by the invention]

[0005] The nitrous oxide decomposition method described in Patent Document 1 is said to be able to decompose nitrous oxide in a nitrous oxide-containing gas by catalytically decomposing the gas containing nitrous oxide in the presence of a reducing gas such as carbon monoxide, a hydrocarbon gas, a mineral oil hydrocarbon gas, or an alcohol. However, the efficiency of decomposing nitrous oxide is insufficient, and further improvement in the efficiency of decomposing nitrous oxide is desired.

[0006] An object of the present invention is to provide a method and apparatus for decomposing nitrous oxide that can efficiently decompose nitrous oxide in a gas containing nitrous oxide, water vapor, and ammonia. [Means for solving the problem]

[0007] That is, the object of the present invention has been achieved by the following means. <1> a catalyst comprising a titanium oxide-containing carrier and a component containing at least one selected from the group consisting of ruthenium and ruthenium compounds; A method for decomposing nitrous oxide, comprising the step of contacting nitrous oxide with a nitrous oxide-containing gas containing water vapor and ammonia. <2> a molar ratio of the ammonia to the water vapor contained in the nitrous oxide-containing gas is 0.001 to 0.050; <1> The method for decomposing nitrous oxide according to claim 1. <3> the molar concentration of the nitrous oxide contained in the nitrous oxide-containing gas is 0.002 to 10%; <1> or <2> The method for decomposing nitrous oxide according to claim 1. <4> the molar concentration of the water vapor contained in the nitrous oxide-containing gas is 0.1 to 10%; <1> ~ <3> The method for decomposing nitrous oxide according to any one of the preceding claims. <5> the nitrous oxide-containing gas further comprises a saturated hydrocarbon gas; <1> ~ <4> The method for decomposing nitrous oxide according to any one of the preceding claims. <6> the nitrous oxide-containing gas further comprises a reducing gas; <1> ~ <5> The method for decomposing nitrous oxide according to any one of the preceding claims. <7> The reducing gas is carbon monoxide gas, an unsaturated hydrocarbon gas, or hydrogen gas. <6> The method for decomposing nitrous oxide according to claim 1. <8> The nitrous oxide-containing gas is a gas emitted from a chemical manufacturing plant. <1> ~ <7> The method for decomposing nitrous oxide according to any one of the preceding claims. <9> a reactor packed with a catalyst comprising a titanium oxide-containing carrier and a component containing at least one selected from the group consisting of ruthenium and ruthenium compounds; a line connected to the reactor for supplying a nitrous oxide-containing gas containing nitrous oxide, water vapor, and ammonia to the reactor. [Effects of the Invention]

[0008] The method and apparatus for decomposing nitrous oxide of the present invention can efficiently decompose nitrous oxide in a gas containing nitrous oxide, water vapor, and ammonia. DETAILED DESCRIPTION OF THE INVENTION

[0009] In the present invention and this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0010] [Method for decomposing nitrous oxide] The method for decomposing nitrous oxide of the present invention (hereinafter sometimes simply referred to as the decomposition method of the present invention) comprises a step (hereinafter sometimes referred to as the contacting step) of contacting a nitrous oxide-containing gas containing nitrous oxide, water vapor, and ammonia with a catalyst comprising a titanium oxide-containing carrier carrying a component containing at least one selected from the group consisting of ruthenium and ruthenium compounds. As will be described later, this contacting step enables the nitrous oxide in the nitrous oxide-containing gas to be efficiently decomposed into nitrogen molecules (usually nitrogen gas) and oxygen molecules (usually oxygen gas).

[0011] <Catalyst> The decomposition method of the present invention uses a catalyst in which a component containing at least one selected from the group consisting of ruthenium and ruthenium compounds is supported on a support containing titanium oxide. In the present invention, the term "a catalyst comprising a titanium oxide-containing carrier and a component containing at least one selected from the group consisting of ruthenium and ruthenium compounds" refers to a catalyst in which a component containing at least one selected from the group consisting of ruthenium and ruthenium compounds is attached to the surface and / or within the pores of a titanium oxide-containing carrier. In the decomposition method of the present invention, at least one selected from the group consisting of ruthenium and ruthenium compounds is selected as the component to be supported on the carrier in terms of the balance between catalytic activity and cost.

[0012] (Ruthenium compounds) The ruthenium compound is not particularly limited, and examples thereof include ruthenium oxide, ruthenium hydroxide, ruthenium nitrate, ruthenium chloride, chlororuthenate, chlororuthenate hydrate, salts of ruthenium acid, ruthenium oxychloride, salts of ruthenium oxychloride, ruthenium ammine complexes, chlorides of ruthenium ammine complexes, ruthenium bromide, ruthenium carbonyl complexes, ruthenium organic acid salts, and ruthenium nitrosyl complexes. Ruthenium oxides include RuO2. Ruthenium hydroxide includes Ru(OH)3. Ruthenium nitrate includes Ru(NO3)3. Ruthenium chloride includes RuCl3, RuCl3 hydrate, and the like. Examples of chlororuthenates include K3RuCl6, [RuCl6] 3- Salts with an anion such as K2RuCl6 and (NH4)2RuCl6, [RuCl6] 2- Examples of salts include those having the anion As the chlororuthenate hydrate, [RuCl5(H2O)4] 2- RuCl2(H2O)4 is a hydrated salt with the anion RuCl2(H2O)4. + Examples include salt hydrates with the cation Ruthenic acid salts include Na2RuO4 and K2RuO4. Ruthenium oxychlorides include Ru2OCl4, Ru2OCl5, and Ru2OCl6. Ruthenium oxychloride salts include K2Ru2OCl 10 , Cs2Ru2OCl4, etc. Ruthenium ammine complexes include [Ru(NH3)6] 2+ , [Ru(NH3)6] 3+ , [Ru(NH3)5H2O] 2+ Examples include complexes with complex ions such as The chloride of the ruthenium ammine complex is [Ru(NH3)5Cl] 2+ Examples of complexes with this ion include [Ru(NH3)6]Cl2, [Ru(NH3)6]Cl3, and [Ru(NH3)6]Br3. Ruthenium bromide includes RuBr3, RuBr3 hydrate, and the like. Ruthenium carbonyl complexes include Ru(CO)5 and Ru3(CO) 12 Examples include: Examples of ruthenium organic acid salts include [Ru3O(OCOCH3)6(H2O)3]OCOCH3 hydrate and Ru2(RCOO)4Cl (R=alkyl group having 1 to 3 carbon atoms). Ruthenium nitrosyl complexes include K2[RuCl5NO)], [Ru(NH3)5(NO)]Cl3, [Ru(OH)(NH3)4(NO)](NO3)2, and Ru(NO)(NO3)3. The ruthenium compound is preferably ruthenium oxide, ruthenium nitrate, ruthenium chloride, ruthenium bromide, a salt of ruthenium acid, or a ruthenium nitrosyl complex, and more preferably ruthenium oxide.

[0013] The component supported on the titanium oxide-containing carrier needs to contain at least one selected from the group consisting of ruthenium and ruthenium compounds, and may further contain metals other than ruthenium and metal compounds other than ruthenium compounds. In the present invention, for the purpose of inhibiting the adsorption of substances that cause catalyst poisoning onto the catalyst surface, preventing a decrease in catalyst performance, or preventing sintering of catalytic active sites, the catalyst is preferably a catalyst in which at least one selected from the group consisting of metals other than ruthenium and metal compounds other than ruthenium compounds is further supported on a support containing titanium oxide. The metal other than ruthenium is not particularly limited, and examples thereof include silicon, zirconium, aluminum, niobium, tin, copper, iron, cobalt, nickel, vanadium, chromium, molybdenum, tungsten, manganese, antimony, and tellurium. The metal compound other than the ruthenium compound is not particularly limited, and examples thereof include compounds containing the above-mentioned metals other than ruthenium, and oxides of the above-mentioned metals other than ruthenium are preferred. The metal oxide may be a composite oxide of multiple metal species. Furthermore, the catalyst may be a catalyst in which a carrier further supports an alloy of ruthenium and a metal other than ruthenium, or a composite oxide containing ruthenium and a metal other than ruthenium. The catalyst is more preferably a catalyst in which at least one oxide selected from the group consisting of silicon oxide, zirconium oxide, aluminum oxide, niobium oxide, manganese oxide, antimony oxide, tellurium oxide and tin oxide is further supported on a carrier containing rutile crystalline titanium oxide. The metal salt used to obtain the metal oxide is not particularly limited.

[0014] The content of at least one selected from the group consisting of ruthenium and ruthenium compounds in the catalyst is not particularly limited and may be set appropriately, but is, for example, preferably 0.1 to 20 mass%, more preferably 0.5 to 10 mass%, and even more preferably 1 to 5 mass%, based on metallic ruthenium. The content of at least one selected from the group consisting of ruthenium and ruthenium compounds is preferably 0.1 to 20 mass%, more preferably 0.5 to 10 mass%, and even more preferably 1 to 5 mass%, based on metallic ruthenium, assuming the total amount of the component containing at least one selected from the group consisting of ruthenium and ruthenium compounds and the carrier to be 100 mass%. The contents of metals other than ruthenium and metal compounds other than ruthenium compounds in the catalyst are not particularly limited and can be set appropriately depending on the above-mentioned purpose.

[0015] (Carrier) The carrier may contain titanium oxide, and may also contain other compounds as described below. The crystalline form of the titanium oxide constituting the carrier is not particularly limited, and may be any of rutile crystalline form, anatase crystalline form, and brookite crystalline form. In the present invention, the carrier is preferably composed of titanium oxide containing rutile crystalline titanium oxide. From the viewpoint of catalytic activity, the content of rutile crystalline titanium oxide in the titanium oxide contained in the carrier is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, where the total amount of titanium oxide contained in the carrier is 100% by mass.

[0016] In the present invention, titanium oxide containing rutile crystalline titanium oxide refers to titanium oxide containing rutile crystals, as determined by X-ray diffraction analysis to measure the ratio of rutile crystals to anatase crystals. Various X-ray sources are used, including copper Kα radiation. When copper Kα radiation is used, the ratios of rutile crystals and anatase crystals are determined using the diffraction peak intensity of the (110) plane at 2θ=27.5° and the diffraction peak intensity of the (101) plane at 2θ=25.3°, respectively. The support used in the present invention is a support having a rutile crystal peak intensity and an anatase crystal peak intensity, or a support having a rutile crystal peak intensity. That is, the support may have both a rutile crystal diffraction peak and an anatase crystal diffraction peak, or it may have only a rutile crystal diffraction peak.

[0017] Examples of other compounds that the support may contain include metal oxides other than titanium oxide, composite oxides of titanium oxide and other metal oxides, and mixtures of titanium oxide and other metal oxides. Examples of metal oxides other than titanium oxide include aluminum oxide, silicon oxide, and zirconium oxide.

[0018] Titanium oxide prepared by a known method can be used, or commercially available products can also be used. The following method can be used to prepare titanium oxide in the rutile crystal form. A method in which titanium tetrachloride is dissolved dropwise in ice-cold water, neutralized with an aqueous ammonia solution at a temperature of 20°C or higher to produce titanium hydroxide (orthotitanic acid), and the resulting precipitate is then washed with water to remove chloride ions and calcined at a temperature of 600°C or higher (Catalyst Preparation Chemistry, 1989, p. 211, Kodansha); A method in which a reactive gas is prepared by passing an oxygen-nitrogen mixed gas through a titanium tetrachloride evaporator, and then introduced into a reactor to react at 900°C or higher (Catalyst Preparation Chemistry, 1989, p. 89, Kodansha); A method of hydrolyzing titanium tetrachloride in the presence of ammonium sulfate and then calcining it (for example, Catalysis Engineering Lecture 10: Handbook of Elemental Catalysts, 1978, p. 254, Chijin Shokan); A method of calcining titanium oxide in anatase crystal form (e.g., Metal Oxides and Complex Oxides, 1980, p. 107, Kodansha); A method of thermally hydrolyzing an aqueous titanium chloride solution; and A method in which an aqueous solution of titanium compounds such as titanium sulfate or titanium chloride is mixed with rutile crystalline titanium oxide powder, followed by thermal hydrolysis or alkaline hydrolysis, and then calcination at a temperature of around 500°C.

[0019] The support can be obtained by molding titanium oxide or the like into a desired shape. When the support contains a compound other than titanium oxide, the support can be obtained by molding a mixture of titanium oxide and the other compound into a desired shape.

[0020] The shape of the catalyst (carrier) is not particularly limited, and examples thereof include spherical granules, cylindrical pellets, rings, honeycomb, monolith, and corrugated shapes, as well as granules and fine particles of appropriate size obtained by crushing and classifying the granules after molding. In the case of spherical granules, cylindrical pellets, and ring shapes, the catalyst diameter is preferably 10 mm or less from the viewpoint of catalytic activity. Here, the catalyst diameter means the diameter of the sphere for spherical granules, the diameter of the cross section for cylindrical pellets, and the maximum cross section diameter for other shapes.

[0021] The catalyst used in the decomposition method of the present invention can be prepared, for example, by impregnating a titanium oxide-containing carrier with a solution containing a component including at least one selected from the group consisting of ruthenium and ruthenium compounds, allowing the component including at least one selected from the group consisting of ruthenium and ruthenium compounds to adhere to the carrier, and then drying the carrier. The solvent in the solution containing the component including at least one selected from the group consisting of ruthenium and ruthenium compounds is not particularly limited, but water, ethanol, etc. can be used. After drying, the resulting mixture may be calcined. When the catalyst contains ruthenium oxide, it can be obtained, for example, by a method including a step of impregnating a support containing titanium oxide with a solution containing ruthenium halide to support the ruthenium halide on the support, a step of drying the support in which the ruthenium halide is supported on the support, and a step of calcining the dried product.

[0022] The catalyst may be used after diluting with an inert material.

[0023] <Nitrogen oxide-containing gas> The decomposition method of the present invention uses a nitrous oxide-containing gas that includes nitrous oxide, water vapor, and ammonia. The nitrous oxide-containing gas may contain one or more gases other than nitrous oxide, water vapor, and ammonia, as long as the gas contains these. Examples of such gases include various gases such as oxygen, helium, argon, nitrogen, and carbon dioxide, as well as reducing gases. The nitrous oxide-containing gas may also contain a liquid. In the decomposition method of the present invention, the nitrous oxide-containing gas needs to be in a gaseous state at least while in contact with the catalyst (under reaction conditions), and may be in a liquid state or a mixture of gas and liquid before contact.

[0024] The content (concentration) of each component in the nitrous oxide-containing gas is not particularly limited and can be set appropriately. However, except for components with special effects, it is usually efficient to use the nitrous oxide-containing gas at approximately the same concentration as the factory-specific value where the nitrous oxide-containing gas is emitted. Therefore, for example, the molar concentration of nitrous oxide in the nitrous oxide-containing gas is generally and preferably 0.002 to 10 mol %. The molar concentration of water vapor is generally and preferably 0.1 to 10 mol %. From the viewpoint of nitrous oxide decomposition efficiency, the molar concentration of ammonia in the nitrous oxide-containing gas is preferably 0.0002 mol % or more and preferably 1 mol % or less. The molar concentration of ammonia is more preferably 0.0002 to 0.5 mol %, and even more preferably 0.0002 to 0.2 mol %. The ratio of ammonia to water vapor contained in the nitrous oxide-containing gas [ammonia / water vapor] is not particularly limited and can be set as appropriate, but from the perspective of nitrous oxide decomposition efficiency, it is preferably 0.0010 or more in molar ratio. A molar ratio of 0.0010 to 0.050 is more preferred, and from the perspective of suppressing or avoiding problems with remaining ammonia (e.g., discharge into the atmosphere, removal work), it is more preferred to have a molar ratio of 0.0010 to 0.030, and even more preferred to have a molar ratio of 0.0010 to 0.010. Furthermore, the ratio of ammonia to nitrous oxide contained in the nitrous oxide-containing gas [ammonia / nitrous oxide] is not particularly limited and can be set as appropriate, but it is preferably a molar ratio of 0.005 to 10.

[0025] When the nitrous oxide-containing gas contains oxygen gas, the content of oxygen gas in the nitrous oxide-containing gas is not particularly limited and can be set appropriately, but it is preferably 0.01 to 10,000 molar times the content of ammonia in the nitrous oxide-containing gas. When the nitrous oxide-containing gas does not contain oxygen gas, it can be obtained, for example, by mixing the nitrous oxide-containing gas with an oxygen-containing gas. Examples of the oxygen-containing gas include air.

[0026] The nitrous oxide-containing gas can also contain a reducing gas to further enhance the decomposition efficiency of nitrous oxide. Similarly, to further enhance the decomposition efficiency of nitrous oxide, a saturated hydrocarbon gas can also be contained, which serves as a raw material for generating a reducing gas such as carbon monoxide upon reaction with oxygen contained in the nitrous oxide-containing gas or generated in the reactor. For the decomposition efficiency of nitrous oxide, a method in which a reducing gas is contained in the nitrous oxide-containing gas is preferred. The reducing gas may be any reducing gas other than ammonia, and any gas commonly used in a typical catalytic reduction method can be used without particular limitation. Examples of the reducing gas include unsaturated hydrocarbon gases such as ethylene, propylene, α-butylene, and β-butylene, carbon monoxide gas, hydrogen gas, and gases of alcohol compounds such as methanol, ethanol, propanol, and butanol. Among these, at least one of carbon monoxide gas, unsaturated hydrocarbon gas, and hydrogen gas is preferred. Examples of saturated hydrocarbon gases that serve as raw materials for generating a reducing gas such as carbon monoxide include methane, ethane, propane, and n-butane. Preferred saturated hydrocarbon gases include ethane, propane, and n-butane. The saturated hydrocarbon gas may be a mixture of natural gas, liquefied natural gas, or liquefied petroleum gas. The content of the reducing gas or saturated hydrocarbon gas in the nitrous oxide-containing gas is not particularly limited and can be set appropriately. For example, the molar concentration of the reducing gas or saturated hydrocarbon gas in the nitrous oxide-containing gas is 0.001 to 1 mol%. The molar ratio of the reducing gas or saturated hydrocarbon gas to the water vapor in the nitrous oxide-containing gas [reducing gas or saturated hydrocarbon gas / water vapor] is preferably 0.0003 to 0.03. Furthermore, the molar ratio of the reducing gas or saturated hydrocarbon gas to the nitrous oxide contained in the nitrous oxide-containing gas [reducing gas or saturated hydrocarbon gas / nitrous oxide] is preferably 0.01 to 100.

[0027] In the present invention, the nitrous oxide-containing gas can be prepared by appropriately mixing nitrous oxide, water vapor, ammonia, and other gases mentioned above. Various types of exhaust gases emitted from chemical manufacturing plants can also be used. For example, gases emitted from chemical manufacturing plants such as nitric acid manufacturing plants, ε-caprolactam manufacturing plants, and adipic acid manufacturing plants often contain water vapor, ammonia, and even oxygen gas in addition to nitrous oxide, and can be effectively utilized in the decomposition method of the present invention. In particular, exhaust gases satisfying the above-mentioned ranges of content, content ratio, and the like are preferred in that they can be directly applied to the decomposition method of the present invention without adjusting the content, etc.

[0028] <Contact process> In the decomposition method of the present invention, the catalyst is brought into contact with the nitrous oxide-containing gas. In this contact step, the nitrous oxide in the nitrous oxide-containing gas comes into contact with the catalyst, causing a decomposition reaction of nitrous oxide shown in the following formula, even in the presence of water vapor, and the nitrous oxide is efficiently decomposed into nitrogen molecules and oxygen molecules. Decomposition reaction of nitrous oxide: N2O → N2+ 1 / 2O2 Ammonia in the nitrous oxide-containing gas further accelerates the decomposition reaction of nitrous oxide. While the details of this mechanism are not yet clear, it is thought to be as follows. For example, in the presence of a catalyst that exhibits a reducing action, such as a ruthenium-supported catalyst, ammonia reacts with nitrous oxide on the catalyst surface, decomposing nitrous oxide into nitrogen molecules and water molecules, thereby further accelerating the decomposition reaction of nitrous oxide. On the other hand, in the presence of a catalyst that does not exhibit a reducing action, such as a ruthenium oxide-supported catalyst, ammonia reacts with oxygen atoms remaining on the catalyst surface, removing oxygen atoms from the catalyst surface and maintaining catalytic activity (suppressing catalyst deactivation), thereby accelerating the decomposition reaction.

[0029] In the contacting step, the nitrous oxide-containing gas is brought into contact with the catalyst. The contacting method is not particularly limited, and may be, for example, a batch system or a continuous system, with a continuous system being preferred in terms of reaction efficiency. Examples of continuous systems include a fixed bed system and a fluidized bed system. The contact temperature (reaction temperature) is determined appropriately, but is preferably 500°C or lower from the viewpoint of catalyst activity deterioration, and is preferably 100°C or higher from the viewpoint of reaction rate. The contact temperature is preferably 200 to 450°C, more preferably 250 to 400°C. In the continuous contact method, the supply rate of the nitrous oxide-containing gas relative to the weight of the catalyst is not particularly limited and may be determined appropriately. For example, the flow rate at 0°C and 0.1013 MPa (absolute) relative to 1 g of catalyst is 10 to 10,000 cm 3 / min, preferably 50 to 5000 cm 3 / min is more preferable. The reaction pressure varies depending on the contact temperature, the supply rate of the nitrous oxide-containing gas, the pressure of the outside air around the reactor, etc., but is preferably a pressure higher than the outside air, and is preferably 0.08 to 1 MPa (absolute) in absolute pressure, and more preferably 0.09 to 0.7 MPa (absolute) in absolute pressure.

[0030] <Other processes> The decomposition method of the present invention may include a step other than the contact step, such as a step of adjusting the component contents of the nitrous oxide-containing gas, or a step of introducing oxygen gas or a reducing gas into the nitrous oxide-containing gas.

[0031] [Nitrous oxide decomposition device] The nitrous oxide decomposition apparatus of the present invention (hereinafter sometimes simply referred to as the decomposition apparatus of the present invention) comprises a reactor packed with a catalyst comprising a titanium oxide-containing carrier supported with a component containing at least one selected from the group consisting of ruthenium and ruthenium compounds, and a line connected to the reactor for supplying a nitrous oxide-containing gas containing nitrous oxide, water vapor, and ammonia to the reactor. As will be described later, this decomposition apparatus can efficiently decompose the nitrous oxide in the nitrous oxide-containing gas into nitrogen molecules and oxygen molecules. The catalyst and nitrous oxide-containing gas in the decomposition apparatus of the present invention are as described above.

[0032] <Reactor> The reactor is a vessel in which the catalyst contained therein decomposes the nitrous oxide in the nitrous oxide-containing gas supplied to the catalyst, and its shape, dimensions, etc. are set as appropriate. For example, reactors used in continuous contact processes include tubular or tower-type reactors such as metal tubes and column towers, and specific examples include various fixed-bed reactors. The reactor has the catalyst contained in or filled in part or all of its internal space. This reactor may be any reactor as long as the surface of the internal space through which the nitrous oxide-containing gas flows is made of a material that is resistant to the nitrous oxide-containing gas, and examples include metal reactors whose main component is iron, such as stainless steel. The reactor may be equipped with a heater inside or outside to heat the internal space.

[0033] <line> The decomposition apparatus of the present invention is equipped with a line (supply pipe) connected to the reactor for supplying nitrous oxide-containing gas to the internal space of the reactor. The line may have any dimensions, etc., as long as the inner surface of the line through which the nitrous oxide-containing gas flows is made of a material that is resistant to the nitrous oxide-containing gas. The line may also be equipped with a pump for transporting the nitrous oxide-containing gas, a heater for heating the internal space, etc. Furthermore, the line may be directly or indirectly connected to a line for discharging nitrogen oxides (NOx) from a denitrification reactor.

[0034] The reactor may be equipped with a discharge line for discharging the nitrous oxide-containing gas after contacting the catalyst. The reactor or line may be connected to various gas introduction pipes for adjusting the content of each gas in the nitrous oxide-containing gas.

[0035] In the decomposition apparatus of the present invention, the nitrous oxide-containing gas is brought into contact with the catalyst packed in the internal space of the reactor, and preferably passed through the catalyst, thereby efficiently decomposing the nitrous oxide in the nitrous oxide-containing gas and suppressing emissions of nitrous oxide. In a preferred embodiment of the present invention, ammonia in the nitrous oxide-containing gas can also be efficiently decomposed and suppressed emissions of ammonia.

[0036] The decomposition method and decomposition apparatus of the present invention can be used in various fields and applications for decomposing and removing nitrous oxide, such as chemical manufacturing plants, and are particularly suitable for use in chemical manufacturing plants that emit gases containing nitrous oxide, ammonia, and water vapor, such as nitric acid manufacturing plants, ε-caprolactam manufacturing plants, and adipic acid manufacturing plants. When the decomposition apparatus of the present invention is applied to an existing production plant, the installation position of the decomposition apparatus of the present invention is not particularly limited, but it is usually installed at the last stage in the flow direction of the exhaust gas, for example, before the exhaust tower. Specifically, in the case of a nitric acid production plant, it is installed after the denitrification reactor. When the decomposition apparatus of the present invention is applied to an existing production plant, the production plant's exhaust pipe can be used as a line for the decomposition apparatus of the present invention, and the decomposition apparatus of the present invention can be installed alongside a nitrous oxide decomposition apparatus simply by installing a reactor in the existing production plant, allowing the existing production plant to be used effectively. [Example]

[0037] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0038] <Production Example 1> The RuO2 / TiO2 catalyst was prepared as follows. Titanium oxide powder (Showa Denko K.K.) was extruded into a titanium oxide compact (cylindrical pellet shape with a diameter of 3 mm and a length of 4 to 6 mm). The compact was then fired in a muffle furnace at 800°C for 3 hours to form a titanium oxide support (specific surface area: 5 m). 2 / g, 100% rutile crystal form) was obtained. The specific surface area of ​​the titanium oxide support was measured by the BET single-point method using nitrogen adsorption at 77K. 0.38 g of ruthenium chloride hydrate (Furuya Metals, RuCl3·nH2O, Ru content 40%) was dissolved in 2.0 g of ion-exchanged water. The resulting solution was impregnated into 9.7 g of a titanium oxide support using the incipient wetness method, and then air-dried overnight at room temperature (25°C) in an air atmosphere to obtain a titanium oxide solid supported with ruthenium chloride hydrate. The obtained solid was packed into a quartz glass tube equipped with a sheath tube for measuring the internal temperature, and then heated at 200 cm using an electric tubular furnace. 3 The furnace temperature was raised to 250°C under an air flow of (0°C, 0.1013 MPa (absolute)) / min, and then calcined by maintaining at that temperature for 2 hours. The temperature inside the quartz glass tube at an electric tubular furnace temperature of 250°C was 275°C. Calcination yielded 10 g of RuO2 / TiO2 catalyst containing 2.0 mass% of ruthenium oxide (Ru content 1.5 mass%).

[0039] Example 1 A quartz glass reaction tube (inner diameter 8 mm) equipped with a sheath tube for measuring the internal temperature was filled with 0.24 g of the RuO / TiO catalyst produced in the above Production Example 1. This reaction tube was placed in an electric furnace and heated at atmospheric pressure (0.1 MPa (absolute)) and 100 cm 3 The temperature inside the quartz glass tube was raised to 300°C under a helium flow at 0°C and 0.1013 MPa (absolute) / min. Next, at the same pressure and temperature, the gas to be contacted with the catalyst was changed from helium to a nitrous oxide-containing gas (flow rate: 100 cm3) having the composition shown in Table 1 below. 3 The pressure was switched to (0°C, 0.1013 MPa (absolute)) / min, and the decomposition reaction of nitrous oxide was carried out.

[0040] 0.5 hours after the start of the decomposition reaction of nitrous oxide, the reaction outlet gas (post-reaction gas) from the reaction tube was analyzed as follows. Nitrous oxide content in nitrous oxide-containing gas C B and the content of nitrous oxide in the reaction outlet gas, C AThe analysis was performed using gas chromatography (VARIAN Micro GC (detector: Micro TCD, column: CP-PoraPLOT Q 10m)). The reduction rate of nitrous oxide concentration was calculated from the analyzed nitrous oxide concentration using the following formula. The results are shown in Table 2. Nitrous oxide concentration reduction rate (%) = [(C B -C A ) / C B ] x 100

[0041] The ammonia concentration of the reaction outlet gas was analyzed using an ammonia gas detector tube (No. 3La, manufactured by Gastec Corporation) under the condition of single suction (measurement range 0.0005 to 0.0100%). The results are shown in Table 2.

[0042] <Examples 2 to 6 and Comparative Example 1> After carrying out the decomposition reaction and analysis of Example 1, the decomposition reaction and analysis of nitrous oxide were carried out in the same manner as in Example 1, except that the gas supplied to the reaction tube packed with the catalyst was sequentially switched to a nitrous oxide-containing gas having the composition shown in Table 1 below to start the decomposition reaction. Examples 2 to 6 and Comparative Example 1 were carried out in the following order: Example 2, Comparative Example 1, Example 3, Example 4, Example 5, and Example 6. The results obtained are shown in Table 2.

[0043] The composition of the nitrous oxide-containing gas is shown in Table 1. The remainder of the nitrous oxide-containing gas is helium gas. [Table 1]

[0044] [Table 2] In Examples 4 and 5, the ammonia concentration in the reaction outlet gas was not measured because it was estimated that the ammonia concentration was below the detection limit (denoted as "not measured" in Table 2).

[0045] <Production Example 2> The RuO2 / TiO2 used in Examples 1 to 6 and Comparative Example 1 was pre-reduced using hydrogen gas as follows to produce a Ru / TiO2 catalyst. A quartz glass tube (inner diameter 8 mm) equipped with a sheath tube for measuring the internal temperature was filled with 0.24 g of the RuO2 / TiO2 catalyst. This reaction tube was placed in an electric furnace and heated at atmospheric pressure and 50 cm 3 The furnace temperature was raised to 200°C at a rate of 5°C / min under a flow of argon / hydrogen mixed gas (hydrogen: 5 mol%, argon: 95 mol%) at (0°C, 0.1013 MPa (absolute)) / min, and then maintained at the same pressure and temperature for 0.5 hours to reduce the RuO2 / TiO2 catalyst with hydrogen, yielding a Ru / TiO2 catalyst. The internal temperature of the quartz glass tube at an electric tubular furnace temperature of 200°C was 206°C.

[0046] <Comparative Example 2> After the preparation of the Ru / TiO catalyst, the gas to be contacted with the catalyst was changed from argon / hydrogen mixed gas to 100 cm at the same pressure and temperature. 3 The gas was then changed from helium to a nitrous oxide-containing gas (flow rate: 100 cm3) with the composition shown in Table 3 below at the same pressure and temperature. 3 The pressure was switched to (0°C, 0.1013 MPa (absolute)) / min, and the decomposition reaction of nitrous oxide was carried out. 0.5 hours after the start of the decomposition reaction of nitrous oxide, the reaction outlet gas from the reaction tube was analyzed in the same manner as in Example 1. The results are shown in Table 4.

[0047] <Examples 7 and 8> After the reaction and analysis of Comparative Example 2 were carried out, the decomposition reaction and analysis of nitrous oxide were carried out in the same manner as in Comparative Example 2, except that the gas supplied to the reaction tube packed with the catalyst was sequentially switched to a nitrous oxide-containing gas having the composition shown in Table 3 below and the reaction was then started. Examples 7 and 8 were carried out in the order of Example 7, Example 8. The results obtained are shown in Table 4.

[0048] The composition of the nitrous oxide-containing gas is shown in Table 3. The remainder of the nitrous oxide-containing gas is helium gas. [Table 3]

[0049] [Table 4] In Examples 7 and 8, the ammonia concentration in the reaction outlet gas was not measured because it was estimated that the ammonia concentration was below the detection limit (denoted as "not measured" in Table 4).

[0050] As is clear from the results shown in Tables 1 to 4, when ammonia is not present during contact between the catalyst and nitrous oxide (Comparative Examples 1 and 2), the rate of decrease in nitrous oxide concentration is small and the decomposition efficiency of nitrous oxide is insufficient. In contrast, when ammonia is present during contact between the catalyst and nitrous oxide (Examples 1 to 8), the rate of decrease in nitrous oxide concentration is greater than that in the comparative example, and nitrous oxide can be decomposed efficiently. Furthermore, when the molar ratio of ammonia to water vapor [ammonia / water vapor] is set to 0.001 to 0.030 (Examples 2 to 8), the ammonia concentration in the reaction outlet gas can be reduced while maintaining good nitrous oxide decomposition efficiency, and ammonia can also be decomposed efficiently.

Claims

1. a catalyst comprising a titanium oxide-containing carrier and a component containing at least one selected from the group consisting of ruthenium and ruthenium compounds; contacting a nitrous oxide-containing gas containing nitrous oxide, water vapor, and ammonia; A method for decomposing nitrous oxide, wherein the molar concentration of ammonia in the nitrous oxide-containing gas is 0.0002 to 1 mol %, and the molar concentration ratio of the ammonia to the water vapor is 0.0010 to 0.

050.

2. A method for decomposing nitrous oxide as described in claim 1, wherein the molar concentration of nitrous oxide contained in the nitrous oxide-containing gas is 0.002 to 10%.

3. A method for decomposing nitrous oxide as described in claim 1 or 2, wherein the molar concentration of the water vapor contained in the nitrous oxide-containing gas is 0.1 to 10%.

4. A method for decomposing nitrous oxide described in any one of claims 1 to 3, wherein the nitrous oxide-containing gas further contains a saturated hydrocarbon gas.

5. A method for decomposing nitrous oxide according to any one of claims 1 to 4, wherein the nitrous oxide-containing gas further contains a reducing gas.

6. A method for decomposing nitrous oxide as described in claim 5, wherein the reducing gas is carbon monoxide gas, unsaturated hydrocarbon gas or hydrogen gas.

7. A method for decomposing nitrous oxide described in any one of claims 1 to 6, wherein the nitrous oxide-containing gas is a gas emitted from a chemical manufacturing plant.

8. A reactor packed with a catalyst comprising a titanium oxide-containing carrier and a component containing at least one selected from the group consisting of ruthenium and ruthenium compounds; and a line connected to the reactor for supplying to the reactor a nitrous oxide-containing gas containing nitrous oxide, water vapor, and ammonia, wherein the molar concentration of the ammonia is 0.0002 to 1 mol % and the molar concentration ratio of the ammonia to the water vapor is 0.0010 to 0.050.

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