Catalyst and method for producing unsaturated carboxylic acid using the same

Abstract

To provide a catalyst which is produced by a production method of the invention and can suppress variation of activity during use of the catalyst in a gas phase contact oxidation method, wherein, especially in a reaction for producing methacrylic acid from methacrolein as a raw material, the effect is remarkable and safe plant operation is enabled.SOLUTION: There is provided a catalyst which has, as catalyst active ingredients, molybdenum, copper, and vanadium, and in which water is used as a solvent, the catalyst having a maximum absorption wavelength in a wavelength range of 670 nm to 800 nm as measured by ultraviolet-visible spectroscopy (transmission system).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a catalyst for obtaining unsaturated carboxylic acids by oxidation reaction, which exhibits less fluctuation in activity from the initial stage of use than conventional catalysts and enables stable plant operation. [Background technology]

[0002] Methods for producing unsaturated aldehydes and unsaturated carboxylic acids, and vapor-phase catalytic oxidation methods for producing 1,3-butadiene from butenes are widely practiced industrially, and the use of composite metal oxide catalysts containing bismuth and molybdenum as main components is well known to those skilled in the art. In particular, many reports have been published on methods for improving the yield of unsaturated aldehydes and unsaturated carboxylic acids produced from raw materials such as propylene, isobutylene, and t-butyl alcohol. These reactions are exothermic, and the heat generated by the catalyst can activate the catalyst over time, easily causing the reaction to go out of control. Furthermore, catalysts tend to deteriorate and become inactivated with use. Therefore, there was a need for a catalyst that would exhibit stable catalytic activity with minimal fluctuations in activity from the beginning of use.

[0003] Among these, many catalysts for producing methacrylic acid have been proposed. Among these, there are some in which the microstructure of the catalyst, such as pore volume and pore distribution, is adjusted by the catalyst molding method and molding conditions. For example, Patent Document 1 proposes a catalyst for producing methacrylic acid in which the ratio of the pore volume of pores with a pore radius of 0.005 to 0.05 μm to the pore volume of pores with a pore radius of 0.005 to 10 μm is 20% or more.

[0004] Patent Document 2 proposes a catalyst for producing methacrylic acid, in which the pore volume of the catalyst is 0.1 cc / g or more and 0.9 cc / g or less, the pore volume occupied by pores having a pore diameter of less than 0.1 μm is 15% or less of the total pore volume, the pore volume occupied by pores having a pore diameter of 0.1 μm or more and less than 1 μm is less than 15% of the total pore volume, and the pore volume occupied by pores having a pore diameter of 1 μm or more and less than 10 μm is 65% or more of the total pore volume. Patent Document 3 proposes a catalyst for producing methacrylic acid, in which the volume of pores having a pore radius of 0.05 μm or less is 0.01 cc / g or less, and the volume of pores having a pore radius of more than 0.05 μm is 0.2 cc / g or more. Patent Document 4 proposes a method for producing a catalyst for methacrylic acid production, which comprises a heteropolyacid compound containing phosphorus and molybdenum, by drying an aqueous mixture of catalyst raw materials to obtain a dried product having a b value of 6.0 or more, molding this dried product, and then calcining it. Patent Document 5 proposes a catalyst for producing acrolein by catalytic gas-phase oxidation of propylene in the presence of molecular oxygen or a molecular oxygen-containing gas, which is an oxide catalyst containing molybdenum, bismuth, and iron as essential components, and in which the L*, a*, and b* values ​​of the catalyst components in the L*a*b* color system are within the ranges of 30≦L*≦60, 0≦a*≦5, and 5≦b*≦14, respectively. Regarding these known technologies, Patent Document 4 describes the dried product before undergoing the molding and calcination steps, while Patent Document 5 describes a catalyst with significantly different elements and structure constituting the catalyst, and is a technology used only when producing acrolein from propylene. In addition, these catalysts are described only in the visible light region in the solid state. Non-Patent Document 1 also describes the results of UV-Vis measurement in the wavelength range of 200 to 500 nm when the catalyst is dissolved in a solvent. Non-Patent Document 2 also describes the results of UV-Vis measurement in the wavelength range of 500 nm to 1900 nm when the catalyst is dissolved in a solvent. However, no literature has focused on the spectrum at high wavelengths above 600 nm in the results of UV-Vis measurement when the catalyst is dissolved in a solvent. The catalysts obtained as described in Patent Documents 1 to 3 have issues such as short catalyst life and large fluctuations in activity, and further improvements are desired for use as industrial catalysts. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent No. 3710944 [Patent Document 2] Japanese Patent Application Publication No. 2017-176932 [Patent Document 3] Japanese Patent Publication No. 2003-10690 [Patent Document 4] Japanese Patent Publication No. 2007-260588 [Patent Document 5] Japanese Patent Application Publication No. 2010-214217 [Non-patent literature]

[0006] [Non-Patent Document 1] Journal of Catalysis, 154, 275-292, 1995 [Non-patent document 2] Applied Catalysis A:General 222,2001, 63-77 [Non-patent document 3] Nakayo Yutaka and Yamashita Hiromi, "Practical aspects of solid surface characterization," Kodansha Scientific, February 10, 2005, pp. 56-63 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention relates to a catalyst for obtaining an unsaturated carboxylic acid by an oxidation reaction, and an object of the present invention is to provide a catalyst which exhibits less fluctuation in activity from the initial stage of use than conventional catalysts and enables stable plant operation. [Means for solving the problem]

[0008] As a result of extensive research into the current situation and problems described above, the inventors of the present application focused on the ultraviolet-visible spectrum of 600-1000 nm using water as a solvent, which had not been focused on in the prior art. They discovered that a catalyst containing molybdenum, copper, and vanadium as essential components and having specific absorption wavelengths in the ultraviolet-visible spectrum obtained by dissolving this in a water solvent has high stability in terms of catalytic activity, leading to the present invention.

[0009] The present invention relates to the following 1) to 9). 1) The catalyst contains molybdenum, copper, and vanadium as catalytically active components, Dissolve 0.40 ± 0.01 g of the catalyst in water to make a solution of 40.0 mL, and stir the solution at room temperature for 5 minutes or more. A catalyst having a maximum absorption wavelength at a wavelength of 670 nm to 800 nm measured by ultraviolet-visible spectroscopy (transmission system). 2) Having molybdenum, copper, and vanadium as catalyst active components. Dissolve 0.40 ± 0.01 g of the catalyst in water to make a solution of 40.0 mL, and stir the solution at room temperature for 5 minutes or more. A catalyst in which the ratio of the absorbance at 744 nm to the absorbance at 665 nm measured by ultraviolet-visible spectroscopy (transmission system) is 0.950 or more. 3) The catalyst according to any one of the above 1) to 3), having the composition represented by the following formula (1) as a catalyst active component. Mo , , , , V a1 P b1 Cu c1 As d1 X e1 Y f1 O g1 (1) <00​​​​​​​​​​The catalyst according to 3) or 4) above, wherein the catalytically active component having the composition represented by the formula (1) above satisfies the relationship of the following formula (II): 0 < b1 / c1< 5.5 (II) 6) The catalyst according to any one of the above 1) to 5), which is a catalyst in which a catalytically active component is supported on an inert carrier. 7) The catalyst according to 6) above, wherein the inert support is silica and / or alumina. 8) A method for producing an unsaturated carboxylic acid using the catalyst according to any one of 1) to 7) above. 9) The method according to the above 8), wherein the unsaturated carboxylic acid compound is methacrylic acid. [Effects of the Invention]

[0010] The catalyst produced by the production method of the present invention is highly active from the early stage of the reaction in a gas-phase catalytic oxidation process, and can reduce fluctuations in activity during the reaction. This effect is particularly significant in the reaction for producing methacrylic acid from methacrolein as a raw material, enabling safer plant operation. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing the ultraviolet-visible spectrum of the catalyst of Example 1. [Figure 2] FIG. 1 is a diagram showing the ultraviolet-visible spectrum of the catalyst of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0012] The catalyst of the present invention contains molybdenum, copper, and vanadium, and has a maximum absorption wavelength in the wavelength range of 670 nm to 800 nm measured by ultraviolet-visible spectroscopy (transmission system) using water as a solvent. In this specification, the numbers before and after "to" are inclusive of the upper and lower limits. [UV-visible spectroscopy (transmission system)] UV-visible spectroscopy (transmission system) is a method of determining the absorbance of a sample by irradiating the sample with light separated into wavelengths and measuring the intensity of the light transmitted through the sample, and can be measured using, for example, a U-2900 spectrophotometer (HITACHI). The measurement wavelength can be set arbitrarily within the range of 670 nm to 800 nm, as long as the presence or absence of a maximum absorption wavelength within this range can be confirmed, but a range of approximately 190 nm to 1100 nm is sufficient. For more details, see Non-Patent Document 3, etc.

[0013] [Maximum absorption wavelength in the wavelength range of 670nm to 800nm] The catalyst of the present invention has a maximum absorption wavelength in the wavelength range of 670 nm to 800 nm. This means that within this range, there is an inflection point where the absorbance changes from increasing to decreasing. The lower limit of the maximum absorption wavelength is, in order of preference, 670 nm, 675 nm, 685 nm, 695 nm, 700 nm, and 705 nm, with 720 nm being particularly preferred. The upper limit is, in order of preference, 785 nm, 775 nm, 765 nm, 755 nm, and 750 nm, with 743 nm being particularly preferred. Therefore, the range in which the maximum absorption wavelength exists is most preferably 720 nm to 743 nm.

[0014] [Absorbance ratio] Even if the catalyst of the present invention does not have the above-mentioned maximum absorption wavelength, it will similarly have high catalytic activity and stability as long as the ratio of the absorbance at 744 nm to the absorbance at 665 nm is 0.950 or more. More preferred values ​​for the lower limit of this ratio are 0.950, 0.960, 0.970, 0.980, and 0.990, respectively, and particularly preferably 1.000. The upper limits may be approximately 1.200, 1.115, 1.110, 1.100, 1.060, and 1.055, respectively. Therefore, the ratio of the absorbance at 744 nm to the absorbance at 665 nm is most preferably 1.000 or more and 1.055 or less.

[0015] <Preparation of measurement sample> For the sample preparation for the measurement of the catalyst by ultraviolet-visible spectroscopy (transmission system), 0.40 ± 0.01 g of the catalyst is dissolved in ion-exchanged water to make a solution of 40.0 mL, and the solution obtained by stirring at room temperature for 5 minutes or more is used for the measurement. In addition, when there are water-insoluble components such as an inert carrier in the catalyst, the solution obtained by filtering them is used as the measurement sample.

[0016] [Composition of Catalytic Active Component] The preferable composition of the catalytic active component of the catalyst of the present invention is represented by the following general formula (1). [Chemical Formula 1] Mo 10 V a1 P b1 Cu c1 As d1 X e1 Y f1 O g1 (1) Here, Mo, V, P, Cu, As and O represent molybdenum, vanadium, phosphorus, copper, arsenic and oxygen, respectively. X represents at least one element selected from the group consisting of Ag (silver), Mg (magnesium), Zn (zinc), Al (aluminum), B (boron), Ge (germanium), Sn (tin), Pb (lead), Ti (titanium), Zr (zirconium), Sb (antimony), Cr (chromium), Re (rhenium), Bi (bismuth), W (tungsten), Fe (iron), Co (cobalt), Ni (nickel), Ce (cerium) and Th (thorium). Y represents at least one element selected from the group consisting of K (potassium), Rb (rubidium), Cs (cesium) and Tl (thallium). a1, b1, c1, d1, e1, f1 and g1 represent the atomic ratios of the respective elements. a1 is 0 < a1 ≤ 6, b1 is 0 ≤ b1 ≤ 6, c1 is 0 < c1 ≤ 3, d1 is 0 ≤ d < 3, e1 is 0 ≤ e1 ≤ 3, f1 is 0 ≤ f1 ≤ 3, and g1 is a value determined by the valences and atomic ratios of other elements. In addition, the composition in the present invention means the active component, and as the inert carrier, silicon carbide, alumina, silica, silica-alumina, mullite, alundum, steatite, etc. can be used.

[0017] In the composition of the above formula (1), X is preferably Zn, Ag, Fe, or Sb, more preferably Ag, Fe, or Sb, particularly preferably Fe or Sb, and most preferably Sb.

[0018] In the composition of the above formula (1), Y is preferably K, Rb, or Cs, more preferably K or Cs, and most preferably Cs. However, the effects of the present invention tend to be particularly pronounced in catalysts that do not contain a Y component.

[0019] In the composition of the above formula (1), the preferred ranges of a1 to g1 are as follows. The lower limit of a1 is, in order of preference, 0.1, 0.15, and 0.2, and most preferably 0.25. The upper limit of a1 is, in order of preference, 5, 3, 2, 1, and 0.8, and most preferably 0.6. That is, the most preferred range of a1 is 0.25≦a1≦0.6. The lower limit of b1 is, in order of preference, 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0, and most preferably 1.1. The upper limit of b1 is, in order of preference, 5, 4, 3, and 2, and most preferably 1.5. That is, the most preferable range of b1 is 1.1≦b1≦1.5. The lower limit of c1 is, in order of preference, 0.1, 0.2, 0.25, and most preferably 0.3. The upper limit of c1 is, in order of preference, 2, 1.5, 1.2, 1.0, 0.8, and most preferably 0.6. That is, the most preferred range of c1 is 0.3≦c1≦0.6. The lower limit of d1 is, in order of preference, 0, 0.1, 0.2, and 0.3, and most preferably 0.35. The upper limit of d1 is, in order of preference, 2, 1.5, 1.2, 1.0, and 0.8, and most preferably 0.5. That is, the most preferred range of d1 is 0.35≦d1≦0.5. The lower limit of e1 is, in order of preference, 0.01, 0.02, and 0.03, and most preferably 0.04. The upper limit of e1 is, in order of preference, 2, 1.5, 1, 0.5, and 0.3, and most preferably 0.2. The lower limit of e1 is 0, and X is not contained; that is, the most preferred range of e1 is 0.04≦e1≦0.2. The upper limit of f1 is, in order of preference, 2, 1.5, 1, 0.5, 0.1, and most preferably 0.05. The lower limit of f1 is 0, and Y is not contained, that is, f1=0 is the most preferred composition of catalyst (A).

[0020] In the formula (1), when the relationship a1 / b1 is 0.1 or more and 0.6 or less, this is a particularly preferable catalyst composition for the catalyst of the present invention. The upper limit of a1 / b1 is preferably 0.65, 0.62, or 0.61, in that order, and particularly preferably 0.5. The lower limit is preferably 0.15, 0.18, 0.20, or 0.24, in that order, and particularly preferably 0.3. Therefore, the most preferable range of a1 / b1 is 0.3≦a1 / b1≦0.5.

[0021] In the formula (1), when the relationship b1 / c1 is 1.0 or more and 5.0 or less, this is a particularly preferable catalyst composition for the catalyst of the present invention. The upper limit of b1 / c1 is preferably 4.5 and 4.0, and particularly preferably 3.5. The lower limit is preferably 1.5 and 2.0, and particularly preferably 2.5. Therefore, the most preferable range of b1 / c1 is 2.5≦b1 / c1≦3.5.

[0022] In the formula (1), when the relationship a1 / c1 is 0.1 or more and 5.0 or less, this is a particularly preferable catalyst composition for the catalyst of the present invention. The upper limit of a1 / c1 is preferably 4, 3, 2, 1.8, and 1.5, in order of preference, and particularly preferably 1.3. The lower limit is preferably 0.2, 0.3, 0.4, and 0.5, in order of preference, and particularly preferably 0.7. Therefore, the most preferable range of a1 / c1 is 0.7≦a1 / c1≦1.3.

[0023] The method for producing a catalyst of the present invention comprises (A) a step of preparing a slurry by blending raw materials, (B) a step of drying the slurry, (C) a molding step, and (D) a calcination step. Typically, the process starts with step (A), and proceeds through steps (B) and (C) to step (D). However, steps other than (A) to (D) may be inserted, for example, a calcination step may be inserted between steps (B) and (C).

[0024] [(A) Step of blending raw materials to prepare slurry] Step (A) is a step of blending raw materials to prepare a slurry, more specifically, a step of dispersing compounds containing one or more of the constituent metals (hereinafter also referred to as active component elements) in water to prepare an aqueous solution or aqueous dispersion of these compounds (hereinafter both are collectively referred to as a slurry). Note that this step also includes a step of preparing compounds containing one or more of the constituent metals and a step of mixing these compounds with water. In step (A), a compound containing the essential active component elements of the catalyst of the present invention and any optional active component elements is used. Examples of such compounds include chlorides, sulfates, nitrates, oxides, or acetates of the active component elements. Specific examples of preferred compounds include, but are not limited to, nitrates such as cobalt nitrate, acetates such as copper acetate, oxides such as molybdenum oxide, vanadium pentoxide, copper oxide, antimony trioxide, cerium oxide, zinc oxide, or germanium oxide, and acids (or their salts) such as orthophosphoric acid, phosphoric acid, boric acid, aluminum phosphate, or 12-tungstophosphoric acid. These active component-containing compounds may be used alone or in combination. In step (A), each active component-containing compound and water are uniformly mixed to obtain a slurry. In the slurry, it is not necessary for all components to be dissolved in water; some or all of the components may be suspended in water. The amount of water used in the slurry is not particularly limited, as long as it is an amount that can completely dissolve all of the compounds used or allow them to be uniformly mixed. The amount of water to be used can be determined appropriately, taking into consideration the drying method and conditions in step (B). Typically, the amount of water is about 200 to 2,000 parts per 100 parts of the total mass of the raw materials. While the use of more water is better, too much water has many disadvantages, such as increasing the energy cost of the drying step in step (B) and sometimes preventing complete drying.

[0025] In the present invention, the shape of the stirring blades of the stirrer used in step (A) is not particularly limited, and any stirring blades such as propeller blades, turbine blades, paddle blades, inclined paddle blades, screw blades, anchor blades, ribbon blades, large lattice blades, etc. can be used in one stage or in two or more stages of the same or different blades arranged vertically. In addition, baffles (baffle plates) may be installed in the reaction vessel as necessary.

[0026] [(B) Step of drying the slurry liquid] In step (B), the slurry obtained in step (A) is completely dried. There are no particular limitations on the drying method, but examples include drum drying, freeze drying, spray drying, and evaporation to dryness. Among these, spray drying is preferred in the present invention, as it can dry the slurry into powder or granules in a short time. The drying temperature for spray drying varies depending on the concentration of the slurry, the liquid delivery speed, etc., but the temperature at the outlet of the dryer is generally 70 to 150°C.

[0027] [(C) Molding process] In step (C), the dried slurry obtained in step (B) (hereinafter referred to as "dry powder") is molded. Calcining the dry powder at approximately 250°C to 350°C before molding may improve mechanical strength and catalytic performance, so the dry powder may be calcined before molding (hereinafter, this step may be referred to as "pre-calcination"). There are no particular restrictions on the molding method. To reduce the pressure loss of the reaction gas in the oxidation reaction, the dry powder may be molded into pillars, tablets, rings, spheres, etc., or the dry powder may be coated on an inert carrier. Among these, coating the dry powder on an inert carrier to form a coated catalyst is preferred, as this is expected to improve selectivity and remove reaction heat. For this coating step, the rolling granulation method described below is preferred. This method involves, for example, rotating a flat or uneven disk at the bottom of a fixed container at high speed, vigorously agitating the support inside the container through repeated rotation and revolution. The support is then coated with a coating mixture containing the binder, the dry powder obtained in step (B), and, if necessary, other additives such as molding aids and strength improvers. The binder can be added in any of the following ways: 1) premixing with the coating mixture; 2) adding the binder simultaneously with the coating mixture being added to the fixed container; 3) adding the binder after the coating mixture is added to the fixed container; 4) adding the binder before the coating mixture is added to the fixed container; or 5) dividing the coating mixture and the binder into separate portions and adding the entire amount by combining steps 2) to 4). Of these, step 5 is preferably performed by adjusting the addition rate using an autofeeder or other device to ensure that the desired amount of the coating mixture is loaded onto the support without adhesion to the container wall or aggregation of the coating mixture.

[0028] Specific examples of the inert support used in the coating include silicon carbide, alumina, silica, silica-alumina, mullite, alundum, and steatite, preferably silicon carbide, alumina, silica, silica-alumina, and steatite, and more preferably alumina, silica, and silica-alumina. The diameter of the support may be 1 to 15 mm, preferably 2.5 to 10 mm, and may be a spherical support. The content of the component in the support is preferably 90 mass% or more, more preferably 95 mass% or more. These supports usually have a porosity of 10 to 70%. The ratio of the support to the coating mixture is usually 10 to 75 mass% of the coating mixture / (coating mixture + support), preferably 15 to 60 mass%. When the ratio of the coating mixture is high, the reactivity of the coated catalyst tends to be high, but the mechanical strength tends to be low. Conversely, when the ratio of the coating mixture is low, the mechanical strength tends to be high, but the reactivity tends to be low. Examples of molding aids that may be used as needed include silica gel, diatomaceous earth, and alumina powder. The amount of molding aid used is typically 1 to 60 parts by mass per 100 parts by mass of the solid catalytically active component. Furthermore, the use of inorganic fibers (e.g., ceramic fibers or whiskers) that are inert to the catalytically active component and reaction gas as a strength enhancer is useful for improving the mechanical strength of the catalyst. The amount of these fibers used is typically 1 to 30 parts by mass per 100 parts by mass of the solid catalytically active component. The inert support used in the present invention refers to a support that is inactive against the raw materials and products, and examples of such a support include a support that has a methacrolein conversion rate of 3.0% or less under commonly known reaction conditions. The binder used in step (C) is not particularly limited, but examples include water; linear or branched monoalcohols having 1 to 4 carbon atoms, such as methanol, ethanol, propanol, and butanol; polyhydric alcohols, such as ethylene glycol and glycerin; polymeric binders, such as polyvinyl alcohol; and celluloses, such as crystalline cellulose, methyl cellulose, and ethyl cellulose. Of these, linear monoalcohols having 1 to 4 carbon atoms are preferred, and ethanol is particularly preferred. The binder used may be used in combination with other binders.Other suitable binders include water, organic compounds with a boiling point of 150°C or less at 1 atmosphere or less, or their aqueous solutions, and inorganic binders such as silica sol aqueous solutions. Examples of organic compounds with a boiling point of 150°C or less include ethers such as ethyl ether, butyl ether, and dioxane, esters such as ethyl acetate and butyl acetate, and ketones such as acetone and methyl ethyl ketone. Among these, water is preferred; specifically, it is preferable to use a certain amount of water in combination with alcohol to form an alcohol-water solution. In this case, the ratio of alcohol to water is preferably 100 / 0 to 0 / 100 (by mass), more preferably 98 / 2 to 50 / 50, and particularly preferably 95 / 5 to 80 / 20.

[0029] [(D) About the firing process] The main purpose of step (D) is to remove the binder used in step (C). That is, the conditions are not particularly limited as long as this purpose is achieved, but an example of such a method is to place the catalyst molded body obtained by steps (A) to (C) in a vat in a calcination furnace and calcinate it by a batch method. As for firing conditions, for example, the binder component can be removed by firing under air flow at approximately 200°C to 1000°C, preferably 250°C to 700°C, and more preferably 250°C to 600°C. The firing time is preferably approximately 1 minute to 12 hours, and more preferably 5 minutes to 8 hours. The firing time here does not include the time required for the temperature increase and decrease steps, and refers to the time within ±5°C of the maximum set temperature in the firing step. The temperature increase rate is preferably 0.1 to 10°C / min, and more preferably 0.5 to 5°C / min. The gas atmosphere during firing is not particularly limited, but oxidizing gases such as air and inert gases such as nitrogen can be used.

[0030] [How to adjust absorption wavelength and absorbance ratio] Methods for adjusting the absorption wavelength and absorbance ratio of the catalyst of the present invention include changing the composition, the calcination time, the calcination atmosphere, the binder used when molding the dried slurry, and the addition of an organic substance during blending. In particular, methods for changing the composition and methods for increasing the calcination temperature or lengthening the calcination time are effective. <1. Changes in composition> When changing the composition, decreasing the amount of V relative to the amount of Mo shifts the maximum absorption wavelength to the longer wavelength side, and the ratio of the absorbance at 744 nm to the absorbance at 665 nm also tends to increase. <2. Firing temperature> In the method of changing the calcination temperature, increasing the calcination temperature shifts the maximum absorption wavelength to the longer wavelength side, and the ratio of the absorbance at 744 nm to the absorbance at 665 nm also tends to increase. <3. Baking time> In the method of changing the baking time, increasing the baking time shifts the maximum absorption wavelength to the longer wavelength side, and the ratio of the absorbance at 744 nm to the absorbance at 665 nm also tends to increase.

[0031] [Uses of the catalyst produced by the present invention] The catalyst obtained by the production method of the present invention can be applied to reactions for producing corresponding unsaturated aldehydes or unsaturated carboxylic acids using propylene, isobutylene, t-butyl alcohol, etc. as raw materials, and to the production of 1,3-butadiene from butenes, and enables stable operation with high selectivity. In particular, the effect can be more significantly confirmed when used in a reaction for producing methacrylic acid by gas-phase catalytic oxidation of methacrolein with molecular oxygen or a molecular oxygen-containing gas. In the method for producing methacrolein or methacrylic acid, the method for flowing the raw material gas may be a normal single flow method or a recycle method, and may be carried out under commonly used conditions, and is not particularly limited. For example, a mixed gas consisting of 1 to 10% by volume, preferably 4 to 9% by volume, of starting raw materials at room temperature, 3 to 20% by volume, preferably 4 to 18% by volume, of molecular oxygen, 0 to 60% by volume, preferably 4 to 50% by volume, of water vapor, and 20 to 80% by volume, preferably 30 to 60% by volume, of an inert gas such as carbon dioxide or nitrogen, is passed through a reaction tube filled with the catalyst of the present invention at 240 to 450°C under a pressure of normal pressure to 10 atmospheres at a space velocity of 300 to 5000 h -1 The volumes of all raw gases are calculated assuming that they are ideal gases. [Example]

[0032] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" means parts by weight, and "%" means % by weight.

[0033] [Measurement by UV-visible spectroscopy (transmission system)] The absorption wavelength and absorbance of the catalyst were measured using the following equipment and conditions. Equipment used: U-2900 spectrophotometer manufactured by Hitachi High-Tech Science Corporation Sample weight: 0.40±0.01g Measurement pretreatment: Approximately 5 g of the obtained catalyst was placed in an agate mortar, and the catalyst surface was peeled off using an agate pestle and crushed to 10 mesh or less. The crushed granules were then weighed and stirred for approximately 5 minutes with approximately 10 ml of ion-exchanged water at room temperature, and then allowed to stand for approximately 5 minutes. The entire liquid obtained was then transferred to a measuring flask, and ion-exchanged water was added to bring the total volume to 40.0 mL. Dissolving the catalyst in water may cause decomposition reactions or changes in the coordination structure, so the dissolution was carried out at room temperature. The obtained liquid was used for analysis after removing insoluble components using a Merck Millex VV Filter (pore size 0.1 μm). Measurement wavelength: 190nm~1100nm Sweep speed: 200 nm / min To ensure accurate measurements, baseline correction was performed during the measurements. Experimental conditions for UV-visible spectroscopy (transmission system) are set appropriately within scientifically reasonable conditions, taking into account the physical properties of the catalyst being measured and the characteristics of the measurement equipment. Baseline correction was performed using the program in the U-2900 spectrophotometer instruction manual, as follows: Prior to measurement, ion-exchanged water was placed in both cell holders, and zero correction was performed at a wavelength of 1100 nm. A blank measurement was then performed under the above measurement conditions to obtain baseline data. After this, the pretreated sample was placed in one of the cell holders, and the sample was measured under the above conditions, with the baseline subtracted.

[0034] [Example 1] 1) Preparation of catalyst Molybdenum oxide, vanadium pentoxide, cupric oxide, an aqueous solution of phosphoric acid, an aqueous solution of arsenic acid, and antimony trioxide were weighed out so that the solid catalytically active component had the following composition. Mo 10 V 0.5 P 1.2 As 0.5 Sb 0.04 Cu 0.4 O g (g is a value determined by the valence and atomic ratio of other elements.) Molybdenum oxide, vanadium pentoxide, cupric oxide, a phosphoric acid aqueous solution, and an arsenic acid aqueous solution were added to pure water (7 times the amount of molybdenum oxide by weight) and heated and stirred at 92°C for 4 hours to obtain a slurry. Antimony trioxide was then added to this solution, and the mixture was heated and stirred to obtain a slurry. This solution was then spray-dried to obtain a dried product. 214 parts of the resulting dried slurry and 29.8 parts of a strength improver (alumina-silica fiber) were then uniformly mixed, and the mixture was molded by coating 200 parts of a spherical porous alumina support (particle size 3.5 mm) with approximately 30 parts of a 90% aqueous ethanol solution as a binder. The molded product was then introduced into a furnace and calcined at 310°C for 6 hours while air was circulating to obtain a catalyst (coated catalyst) of the present invention.

[0035] 3) Production of methacrylic acid 10.3 ml of the obtained coated catalyst of the present invention was packed into a stainless steel reaction tube having an inner diameter of 18.4 mm. The feed gas (composition (molar ratio); methacrolein: oxygen: steam: nitrogen = 1:2:4:18.6), space velocity (SV) 1200 h -1 The oxidation reaction of methacrolein was carried out under the above conditions. The reaction bath temperature was adjusted between 290°C and 330°C, and the methacrylic acid selectivity at a methacrolein conversion rate of 77 mol% and the reaction bath temperature at a methacrolein conversion rate of 77 mol% were calculated. The lower the reaction bath temperature, the higher the activity, which is advantageous in terms of catalyst life and energy costs. The reaction was carried out in this manner for approximately 500 hours. During this reaction, the catalyst with the smaller change in reaction bath temperature at a methacrolein conversion rate of 77 mol% exhibited less activation and deactivation, which is advantageous in terms of catalyst life and catalyst safety. The conversion rate, selectivity, and reaction bath temperature fluctuation ranges are defined as follows: Conversion rate = moles of methacrolein reacted / moles of methacrolein supplied × 100 Selectivity = moles of methacrylic acid produced / moles of methacrolein reacted × 100 Fluctuation range of reaction bath temperature = (reaction bath temperature when reaction time is 400 hours and methacrolein conversion rate is 77 mol%) - (reaction bath temperature when reaction time is 200 hours and methacrolein conversion rate is 77 mol%) The fluctuation range of the reaction bath temperature is preferably within ±10°C, more preferably within ±7°C, particularly preferably within ±5°C, and most preferably within ±1°C.

[0036] [Example 2] In Example 1, A catalyst was prepared in the same manner as in Example 1, except that the composition of the catalytically active component solid was changed as follows: Mo 10 V 0.3 P 1.2 As 0.4 Sb 0.1 Cu 0.4 O g (g is a value determined by the valence and atomic ratio of other elements.)

[0037] [Example 3] In Example 1, A catalyst was prepared in the same manner as in Example 1, except that the composition of the catalytically active component solid was changed as follows: Mo 10 V 0.4 P 1.2 As 0.5 Cu 0.4 O g (g is a value determined by the valence and atomic ratio of other elements.)

[0038] [Example 4] In Example 1, A catalyst was prepared in the same manner as in Example 1, except that the composition of the catalytically active component solid was changed as follows: Mo 10 V 0.3 P 1.2 As 0.5 Sb 0.1 Cu 0.4 O g (g is a value determined by the valence and atomic ratio of other elements.)

[0039] [Example 5] In Example 1, A catalyst was prepared in the same manner as in Example 1, except that the composition of the catalytically active component solid was changed as follows and the calcination temperature was changed to 300°C. Mo 10 V 0.4 P 1.2 As 0.5 Cu 0.4 O g (g is a value determined by the valence and atomic ratio of other elements.)

[0040] [Example 6] In Example 1, A catalyst was prepared in the same manner as in Example 1, except that the composition of the catalytically active component solid was changed as follows: Mo 10 V 0.6 P 1.1 As 0.5 Cu 0.3 O g (g is a value determined by the valence and atomic ratio of other elements.)

[0041] [Example 7] In Example 1, A catalyst was prepared in the same manner as in Example 1, except that the composition of the catalytically active component solid was changed as follows and the calcination time was changed to 4 hours and 40 minutes. Mo 10 V 0.6 P 1.1 As 0.5 Cu 0.3 O g (g is a value determined by the valence and atomic ratio of other elements.)

[0042] [Comparative Example 1] A catalyst was prepared in the same manner as in Example 1, except that the composition of the catalytically active component solid was changed as follows: Mo 10 V 0.7 P 1.1 As 0.5 Cu 0.2 O g (g is a value determined by the valence and atomic ratio of other elements.)

[0043] The results of producing methacrylic acid using the catalysts of Examples 2 to 7 and Comparative Example 1 in the same manner as in Example 1 are shown in Table 1 together with the results for the catalyst of Example 1.

[0044] [Table 1]

[0045] As is clear from Table 1, it was confirmed that the catalyst of the present invention has higher initial activity and exhibits smaller fluctuations in activity during the reaction, making it more stable than conventional catalysts. [Industrial Applicability]

[0046] According to the present invention, it is possible to provide a catalyst that can safely and stably produce unsaturated aldehydes, unsaturated carboxylic acids, or conjugated dienes. Therefore, in a gas-phase catalytic oxidation reaction using the catalyst, the target compounds can be stably obtained.

Claims

1. The catalyst contains molybdenum, copper, and vanadium as catalytically active components, A catalyst having a maximum absorption wavelength in the wavelength range of 670 nm to 800 nm when the solution is prepared by dissolving 0.40±0.01 g of the catalyst in water to make 40.0 mL of solution and stirring at room temperature for 5 minutes or more using ultraviolet-visible spectroscopy (transmission system).

2. The catalyst contains molybdenum, copper, and vanadium as catalytically active components, 0.40±0.01 g of catalyst was dissolved in water to make 40.0 mL of solution, and the solution was stirred at room temperature for 5 minutes or more. A catalyst having a ratio of absorbance at 744 nm to absorbance at a wavelength of 665 nm measured by ultraviolet-visible spectroscopy (transmission system) of 0.950 or more.

3. 3. The catalyst according to claim 1, which has a composition represented by the following formula (1) as a catalytically active component: Mỏ １０ V ａ１ P ｂ１ Cổ ｃ１ A ｄ１ X ｅ１ Y ｆ１ O ｇ１ (1) (In the formula, Mo, V, P, Cu, As, and O represent molybdenum, vanadium, phosphorus, copper, arsenic, and oxygen, respectively. X represents at least one element selected from the group consisting of Ag, Mg, Zn, Al, B, Ge, Sn, Pb, Ti, Zr, Sb, Cr, Re, Bi, W, Fe, Co, Ni, Ce, and Th. Y represents at least one element selected from the group consisting of K, Rb, Cs, and Tl. a1, b1, c1, d1, e1, f1, and g1 represent atomic ratios of each element, where a1 is 0.1≦a1≦6, b1 is 0≦b1≦6, c1 is 0<c1≦3, d1 is 0<d1<3, e1 is 0≦e1≦3, f1 is 0≦f1≦3, and g1 is a value determined by the valences and atomic ratios of the other elements.)

4. 4. The catalyst according to claim 3, wherein the catalytically active component having the composition represented by the formula (1) satisfies the relationship of the following formula (I): 0 < a1 / b1 ≦ 0.6...(I)

5. The catalyst according to claim 3, wherein the catalytically active component having the composition represented by the formula (1) satisfies the relationship of the following formula (II): 0 < b1 / c1 < 5.5...(II)

6. 3. The catalyst according to claim 1, wherein the catalytically active component is supported on an inert carrier.

7. 7. The catalyst of claim 6, wherein the inert support is silica and / or alumina.

8. A method for producing an unsaturated carboxylic acid using the catalyst according to claim 1 or 2.

9. 9. The method according to claim 8, wherein the unsaturated carboxylic acid compound is methacrylic acid.

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