Method for producing catalyst, and method for producing α, β-unsaturated carboxylic acid and α, β-unsaturated carboxylic acid ester using said catalyst

Abstract

The present invention provides a method for producing a catalyst, with which it is possible to produce a catalyst of high purity by a simple method using only a starting material and a small amount of a solvent. This method for producing a catalyst includes: (i) a step for mixing a starting material powder using a first pulverizer so as to obtain a mixture; and (ii) a step for adding a solvent that contains water to the mixture and mixing the mixture using a second pulverizer. The starting material powder contains a molybdenum starting material.

Description

Method for producing catalyst, and method for producing α,β-unsaturated carboxylic acid and α,β-unsaturated carboxylic acid ester using said catalyst

[0001] The present invention relates to a method for producing a catalyst using a pulverizer, and a method for producing an α,β-unsaturated carboxylic acid and an α,β-unsaturated carboxylic acid ester using the catalyst.

[0002] Heteropolyacids are condensed oxygen acids composed of oxides of multiple coordinating atoms called polyatoms and oxides of a central atom called a heteroatom. Examples of heteropolyacids include proton-type heteropolyacids, in which the counter cation is a proton, and heteropolyacid salts, in which some of the protons are replaced by cations other than protons, such as ammonium cations.

[0003] Heteropolyacid salts are known to be used as industrial catalysts, and Patent Document 1 discloses a Keggin-type heteropolyacid salt as a catalyst for producing methacrylic acid. As described in Patent Document 1, one method for producing a Keggin-type heteropolyacid salt is to heat and mix raw materials in water to obtain an aqueous slurry, from which water is removed by drying.

[0004] Non-Patent Document 1 discloses a method for producing a Keggin-type heteropolyacid salt by mechanochemical synthesis using a vibration mill. Mechanochemical synthesis is a method for inducing a chemical reaction by applying physical energy such as impact, shear, or friction using a grinding machine such as a ball mill or a vibration mill.

[0005] Japanese Patent Application Laid-Open No. 2003-010691

[0006] Manuel Wilke and Nicola Casati, Chemical Science, 2022, Vol. 13, p. 1146-1151

[0007] The method disclosed in Patent Document 1, in which raw materials are heated and mixed in water and then dried to remove moisture, uses a large amount of water and consumes a large amount of energy for heating and drying. Therefore, this method is undesirable from the standpoint of resources and energy. On the other hand, the mechanochemical synthesis method disclosed in Non-Patent Document 1 requires the addition of an aqueous ethanol solution (ethanol:water (volume ratio) = 1:1), which is a hazardous substance, and is therefore undesirable from an industrial standpoint. Furthermore, the addition of water alone promotes the production of unidentifiable by-products, making it difficult to obtain a high-purity Keggin-type heteropolyacid salt.

[0008] Therefore, an object of the present invention is to provide a method for producing a catalyst that is capable of producing a high-purity catalyst in a simple manner using only raw materials and a small amount of solvent.

[0009] The present inventors have conducted extensive research in view of the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by performing mechanochemical synthesis including a step of mixing only powders of raw material compounds in a grinder as a pre-step of adding a solvent containing at least water and mixing the raw material compounds, thereby completing the present invention.

[0010] That is, the present invention has the following technical features. [1] A method for producing a catalyst, comprising: (i) mixing raw material powders using a first pulverizer to obtain a mixture; and (ii) adding a solvent containing water to the mixture and mixing the mixture using a second pulverizer, wherein the raw material powder contains a molybdenum raw material. [2] A method for producing a catalyst according to [1], wherein, in the step (i), the raw material powders are charged into the first pulverizer and mixed in the presence of a grinding medium. [3] A method for producing a catalyst according to [1] or [2], wherein, in the step (i), a flow aid or an anti-caking agent is added to the raw material powder and mixed. [4] A method for producing a catalyst according to any of [1] to [3], wherein, in the step (i), a gravitational acceleration of 0.5 G or more is applied to the raw material powder. [5] A method for producing a catalyst according to any of [1] to [4], wherein the treatment time in the step (i) is 5 minutes to 60 minutes and the treatment time in the step (ii) is 5 minutes to 60 minutes. [6] The method for producing a catalyst according to any one of [1] to [5], wherein the amount of the water-containing solvent added is 1% by mass or more and 60% by mass or less based on the total mass of the raw material powder. [7] The method for producing a catalyst according to any one of [1] to [6], wherein the second pulverizer is a pulverizer different from the first pulverizer. [8] The method for producing a catalyst according to any one of [1] to [7], wherein the raw material powder further contains a phosphorus source and an ammonium source. [9] The method for producing a catalyst according to any one of [1] to [8], wherein the catalyst contains a Keggin-type heteropolyacid salt.

[10] The method for producing a catalyst according to any one of [1] to [9], wherein the catalyst is a catalyst for producing an α,β-unsaturated carboxylic acid.

[11] The method for producing a catalyst according to any one of [1] to

[10] , wherein the mixture is obtained in step (i) substantially without adding a solvent.

[12] The method for producing a catalyst according to any one of [1] to

[11] , wherein the molybdenum source is selected from the group consisting of molybdenum oxide, ammonium molybdate, and molybdenum chloride.

[13] The method for producing a catalyst according to any one of [8] to

[12] , wherein the phosphorus raw material is selected from the group consisting of phosphoric acid, phosphorus pentoxide, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

[14] A method for producing an α,β-unsaturated carboxylic acid, comprising producing an α,β-unsaturated carboxylic acid from an α,β-unsaturated aldehyde using a catalyst produced by the production method according to any one of [1] to

[13] .

[15] A method for producing an α,β-unsaturated carboxylic acid ester from the α,β-unsaturated carboxylic acid produced by the production method according to

[14] .

[0011] According to the present invention, a high-purity catalyst can be produced by a simple method using only raw materials and a small amount of solvent. Furthermore, according to the present invention, an α,β-unsaturated carboxylic acid and an α,β-unsaturated carboxylic acid ester can be produced using the high-purity catalyst obtained by such a method.

[0012] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits, and "A to B" means A or more and B or less. When a numerical range is written in stages, the upper and lower limits of each numerical range and the numerical values ​​written in the examples can be combined in any way.

[0013] <Method for Producing Catalyst> The method for producing a catalyst according to the present invention includes at least the steps of (i) mixing raw material powders using a first pulverizer to obtain a mixture, and (ii) adding a solvent containing water to the mixture and mixing using a second pulverizer. That is, the method for producing a catalyst according to the present invention is characterized by carrying out (i) a step of mixing only powders (raw material powders) of the raw material compounds (to which optional additives may be added) using a pulverizer (hereinafter also referred to as the "dry pulverization step"), followed by (ii) a step of adding a solvent containing water to the obtained mixture and further mixing using a pulverizer (hereinafter also referred to as the "wet pulverization step") to produce a catalyst. Each step will be described in detail below.

[0014] [Step (i): Dry-milling step] The dry-milling step is a step of mixing and pulverizing raw material powders using a pulverizer (first pulverizer) to obtain a mixture. Specifically, in this step, it is preferable to feed the raw material powders into the first pulverizer and mix and pulverize them in the presence of a pulverizing medium. This step is performed without adding a liquid (solvent) such as water, and can be said to be a step of obtaining a raw material powder mixture substantially without adding a solvent.

[0015] (First Pulverizer) The first pulverizer (hereinafter simply referred to as "pulverizer") is not limited as long as it can mix and pulverize raw material powders and the like. Examples of pulverizers include, but are not limited to, planetary ball mills, rotary mills, vibration mills, bead mills, roller mills, jet mills, high-speed rotary pulverizers, container-driven mills, kneaders, and crushers. Examples of planetary ball mills include PULVERISETTE 7 (trade name, manufactured by FRITSCH). When using a planetary ball mill as the pulverizer, a specific pulverization method involves first loading the raw material powder to be pulverized and a pulverization medium into the pulverizer, specifically, into a pulverization vessel equipped with the pulverizer. Next, forces such as gravity, vibration, or centrifugal force are applied to the pulverizer, causing violent collisions between the raw material powder and the pulverization medium, or generating friction between the raw material powder, the pulverization medium, and the pulverization vessel, thereby pulverizing the raw material powder. The gravitational acceleration applied to the raw material powder in this pulverization process is not particularly limited. However, by applying a gravitational acceleration of 0.5 G or more, it becomes easier to grind the raw material powder uniformly.

[0016] (Crushing Media) In this process, the raw material powder is usually mixed and crushed in the presence of crushing media. When a planetary ball mill or the like is used as the crusher, the crushing media are placed in the crushing container together with the raw material powder, and the crushing container is rotated, causing the crushing media to move around in the container and mix and crush the raw material powder. On the other hand, when a crusher, kneader, high-speed rotary crusher, or the like is used as the crusher, the crushing media is a crushing rod or agitator blade, and the raw material powder is mixed and crushed by the rotation of the crushing rod or agitator blade. When a planetary ball mill or the like is used as the crusher, the shape of the crushing media is preferably spherical in terms of fluidity in the crushing container and crushing efficiency. The amount of crushing media used is preferably 10% by volume or more, more preferably 15% by volume or more, relative to the capacity of the crushing container. Increasing the amount of crushing media used can improve crushing efficiency and shorten the processing time. On the other hand, reducing the amount of crushing media used can increase the amount of raw material powder that can be crushed. Furthermore, by setting the amount of grinding media to 50% by volume or less relative to the capacity of the grinding container, wear of the grinding container can be reduced, and therefore the amount of grinding media used is preferably 50% by volume or less, more preferably 30% by volume or less, relative to the capacity of the grinding container.

[0017] The materials for the grinding media and grinding vessel are not particularly limited as long as they have chemical resistance to the raw materials and physical resistance to the grinding conditions. Preferred materials for the grinding media and grinding vessel include tungsten carbide, high-hardness stainless steel, alumina, silicon nitride, and zirconia, with tungsten carbide or high-hardness stainless steel being more preferred.

[0018] (Raw Powder and Additives) In the dry milling process, raw powder containing at least a molybdenum raw material is charged into a milling container. Preferably, additives such as a flow aid or an anti-caking agent are added to and mixed with the raw powder. Known flow aids and anti-caking agents can be appropriately selected and used. Specific examples of flow aids and anti-caking agents include stearic acid and its salts (e.g., calcium stearate and magnesium stearate), silicates (e.g., potassium silicate, sodium silicate, and magnesium silicate), and phosphates (e.g., calcium phosphate). Among these, stearic acid and its salts are preferred. Adding these flow aids or anti-caking agents reduces compaction of the raw powder during the milling process, thereby increasing the recovery rate of the milled product. The amount of flow aid or anti-caking agent added is preferably 10% by mass or less, more preferably 7% by mass or less, based on the total mass of the raw powder. The amount of flow aid or anti-caking agent added is preferably 3% by mass or more, more preferably 5% by mass or more, based on the total mass of the raw powder. By adding the flow aid or anti-caking agent in an amount of 3 mass % or more, the effect of inhibiting compaction of the raw material powder is effectively exhibited.

[0019] The raw material powder preferably further contains a phosphorus raw material and an ammonium raw material in addition to the molybdenum raw material. Furthermore, when the resulting catalyst is used industrially as a catalyst, raw material powders other than the molybdenum raw material, the phosphorus raw material, and the ammonium raw material may be mixed as additional catalytically active components. The additional catalytically active components are preferably raw material powders selected from lithium, sodium, potassium, rubidium, cesium, antimony, bismuth, arsenic, germanium, tellurium, selenium, silicon, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, niobium, tantalum, tungsten, cerium, zirconium, silver, magnesium, barium, lanthanum, and the like.

[0020] The raw material powder is not particularly limited and can be selected from nitrates, carbonates, acetates, ammonium salts, oxides, halides, oxoacids, oxoacid salts, etc. of each element. These may be used alone or in combination of two or more.

[0021] Examples of phosphorus raw materials include phosphoric acid, phosphorus pentoxide, and phosphates such as ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate. Examples of molybdenum raw materials include molybdenum oxides such as molybdenum trioxide, ammonium molybdates such as ammonium paramolybdate and ammonium dimolybdate, and molybdenum chloride. Examples of ammonium raw materials include ammonium phosphate and ammonium molybdate, as well as ammonium carbonates such as ammonium hydrogen carbonate and ammonium carbonate, and ammonium chloride.

[0022] A pulverized product (mixture) of the raw material powder can be obtained by placing a pulverization container containing the raw material powder and any additives in a pulverizer and mixing them in the presence of pulverization media. The processing time for the dry pulverization step is preferably short, taking into account wear of the container. Specifically, the processing time is preferably 60 minutes or less, more preferably 30 minutes or less, and even more preferably 15 minutes or less. The lower limit of the processing time is not particularly limited as long as the raw material powder is sufficiently pulverized, and is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 15 minutes or more. The revolution speed of the pulverizer in the dry pulverization step can be set appropriately, and can be, for example, 100 rpm to 800 rpm.

[0023] [Step (ii): Wet-milling step] In the wet-milling step, a solvent containing water is added to a milling vessel containing the mixture obtained after the dry-milling step, and the milling vessel is then placed in a second mill for mixing, thereby obtaining a catalyst. Although this step is referred to as the "wet-milling step," it may also be referred to as a "wet mixing step" as long as it can at least mix the mixture obtained after the dry-milling step with the solvent. The second mill can be the same as the first mill used in the dry-milling step. The second mill used in the wet-milling step may be the same as the first mill used in the dry-milling step, or a different mill. Furthermore, the milling vessel may be the same as or different from the one used in the dry-milling step. However, from the standpoint of operational efficiency, it is preferable to use the milling vessel used in the dry-milling step as is in the wet-milling step.

[0024] (Solvent) In the wet-milling step, a solvent containing at least water is added and mixed with the mixture obtained after the dry-milling step. The solvent may be water alone, or two or more solvents containing at least water may be used. Examples of solvents other than water include methanol, ethanol, phosphoric acid, and aqueous ammonia. The proportion of water in the entire solvent is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The amount of solvent added is preferably 60% by mass or less, more preferably 30% by mass or less, relative to the total mass of the raw material powder. The smaller the amount of liquid (solvent) added in the wet-milling step, the less liquid needs to be removed in the drying step described below. On the other hand, when a large amount of liquid is added in the wet-milling step, the mechanochemical synthesis tends to proceed more quickly. Therefore, the amount of solvent added is preferably 1% by mass or more, more preferably 10% by mass or more, relative to the total mass of the raw material powder. The "mass of the entire raw material powder" means the mass of the entire raw material powder used in the dry pulverization step, and does not include the mass of additives.

[0025] As described above, the catalyst production method according to the present invention can be applied even when only a small amount of water is used as a solvent. Even when a solvent other than water is used in combination as a solvent, the proportion of water in the total solvent is preferably 70 mass% or more, and the amount of solvent other than water used can be reduced.

[0026] In the wet-pulverization step, it is sufficient that the mixture and the solvent can be uniformly mixed. Therefore, as in the dry-pulverization step, forces such as gravity, vibration, or centrifugal force may be applied in the pulverizer, but they are not required to be applied. The processing time in the wet-pulverization step is preferably short, taking into account wear of the container. Specifically, the processing time is preferably 60 minutes or less, more preferably 30 minutes or less, and even more preferably 15 minutes or less. There is no particular restriction on the lower limit of the processing time, as long as the raw material powder is sufficiently mixed, and it is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 15 minutes or more. The revolution speed of the pulverizer in the wet-pulverization step may be set appropriately, and can be, for example, 100 rpm to 800 rpm.

[0027] [Drying Step] The catalyst production method according to the present invention may include a drying step after the wet-pulverization step (ii) in which the wet powder, clay-like, or cake-like product (catalyst) obtained in the wet-pulverization step (ii) is dried. By carrying out the drying step, the solvent contained in the catalyst can be removed. The drying method is not particularly limited, and known methods such as natural drying, forced air drying, and hot air drying can be used. The drying temperature can be, for example, room temperature (20±5°C) to 90°C. In the present invention, the product obtained in the wet-pulverization step (ii) and the dried product obtained by drying the product are collectively referred to as the "catalyst."

[0028] [Catalyst] The catalyst obtained by the catalyst production method according to the present invention preferably contains a Keggin-type heteropolyacid salt, and may be a Keggin-type heteropolyacid salt. A Keggin-type heteropolyacid salt is a compound having a specific structure containing a molybdenum atom, a phosphorus atom, and an ammonium cation. Whether or not a compound has a Keggin-type structure can be determined, for example, by analysis using an infrared spectrophotometer. That is, in the case of a phosphomolybdate, which is a type of Keggin-type heteropolyacid salt, the wavenumber of infrared absorption changes depending on the type and substitution number of the counter cation, and the infrared absorption attributable to the P—O antisymmetric stretching vibration of the phosphorus oxide of the heteroatom is observed at a wavenumber of 1062±10 cm. －１ In addition, infrared absorption due to the antisymmetric vibration of the polyatomic molybdenum oxide is observed at a wave number of 965±10 cm －１ , 870±10cm －１ , and 790±10 cm －１ Therefore, when a catalyst is analyzed using an infrared spectrophotometer and peaks are observed at the above four wavenumbers, the catalyst can be identified as a compound containing a Keggin-type heteropolyacid salt. Peaks observed at wavenumbers other than those above are infrared absorptions due to impurities such as unreacted raw materials and by-products, and can be used as an index of the purity of the product.

[0029] The present inventors speculate that the reason why a high-purity catalyst, preferably a Keggin-type heteropolyacid salt, can be obtained by performing a dry-milling step before a wet-milling step (or a wet-mixing step) in the present invention is as follows: In other words, in the dry-milling step, physically applied energy such as impact, shear, or friction causes phenomena such as pulverization of the raw material powder, exposure of crystal faces, and generation of lattice distortion and lattice defects. These phenomena mechanically activate the reactivity between the raw material powders, thereby efficiently promoting the main reaction of generating a Keggin-type heteropolyacid salt and suppressing the generation of by-products.

[0030] Furthermore, the catalyst obtained by the catalyst production method according to the present invention is preferably a catalyst for producing an α,β-unsaturated carboxylic acid. That is, the catalyst obtained by the catalyst production method according to the present invention can be suitably used for producing an α,β-unsaturated carboxylic acid. When the catalyst obtained by the catalyst production method according to the present invention is a catalyst for producing an α,β-unsaturated carboxylic acid, the catalyst preferably has a composition represented by the following formula (I). In the present invention, when the catalyst is formed using a carrier, the catalyst means one that includes the carrier, and the composition represented by the following formula (I) is a composition that takes into account the carrier. P ａ Mo ｂ V ｃ Cu ｄ X ｅ Y ｆ Z ｇ (NH ４ ) ｈ O ｉ (I)

[0031] In formula (I), P, Mo, V, Cu, NH ４ , and O represent phosphorus, molybdenum, vanadium, copper, ammonium, and oxygen, respectively. X represents at least one element selected from the group consisting of silicon, titanium, germanium, arsenic, antimony, and bismuth. Y represents at least one element selected from the group consisting of niobium, tantalum, tungsten, cerium, zirconium, silver, iron, zinc, chromium, magnesium, cobalt, manganese, barium, and lanthanum. Z represents at least one element selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium. a to i represent the molar ratio of each component, and when b = 12, a = 0.5 to 3, c = 0.01 to 3, d = 0.01 to 2, e = 0 to 3, f = 0 to 3, g = 0.01 to 3, and h = 0.01 to 30, and i represents the molar ratio of oxygen necessary to satisfy the valence of each component.

[0032] The molar ratio of each element is a value determined by analyzing a solution in which the catalyst is dissolved in ammonia water by ICP emission spectrometry. The molar ratio of ammonium radical is a value determined by analyzing the catalyst by Kjeldahl method. In the present invention, "ammonium radical" refers to ammonium ion (NH ４ Ammonia (NH ３ ) and ammonium contained in ammonium-containing compounds such as ammonium salts.

[0033] <Method for Producing α,β-Unsaturated Carboxylic Acid> In the method for producing an α,β-unsaturated carboxylic acid according to the present invention, a catalyst obtained by the method for producing a catalyst according to the present invention is used to produce the corresponding α,β-unsaturated carboxylic acid from an α,β-unsaturated aldehyde. Specifically, an α,β-unsaturated aldehyde is subjected to gas-phase catalytic oxidation with molecular oxygen in the presence of the catalyst obtained by the method for producing a catalyst according to the present invention to produce an α,β-unsaturated carboxylic acid. Alternatively, the method for producing an α,β-unsaturated carboxylic acid according to the present invention can be described as a method in which a catalyst is produced by the method for producing a catalyst according to the present invention, and an α,β-unsaturated aldehyde is subjected to gas-phase catalytic oxidation with molecular oxygen using the catalyst to produce an α,β-unsaturated carboxylic acid. These methods enable the production of an α,β-unsaturated carboxylic acid in high yield by performing a gas-phase catalytic oxidation reaction using a highly pure catalyst.

[0034] Examples of the α,β-unsaturated aldehyde raw material include (meth)acrolein, crotonaldehyde (β-methylacrolein), and cinnamaldehyde (β-phenylacrolein). Among these, from the viewpoint of the yield of the target product, the α,β-unsaturated aldehyde is preferably (meth)acrolein, and more preferably methacrolein. The resulting α,β-unsaturated carboxylic acid is an α,β-unsaturated carboxylic acid in which the aldehyde group of the α,β-unsaturated aldehyde has been converted to a carboxyl group. Specifically, when the α,β-unsaturated aldehyde is (meth)acrolein, (meth)acrylic acid is obtained. Note that "(meth)acrolein" refers to acrolein and methacrolein, and "(meth)acrylic acid" refers to acrylic acid and methacrylic acid.

[0035] As a representative example, a method for producing methacrylic acid by gas-phase catalytic oxidation of methacrolein using molecular oxygen in the presence of a catalyst produced by the catalyst production method according to the present invention will be described below. The method described below is also applicable to the case where an α,β-unsaturated aldehyde other than methacrolein is used. In this method, methacrylic acid is produced by contacting a feed gas containing methacrolein and molecular oxygen with the catalyst according to the present invention. A fixed-bed reactor can be used in this reaction. The catalyst is packed into a reaction tube, and the feed gas is supplied to the reactor to carry out the reaction. The catalyst may be packed in a single layer, or multiple catalysts with different activities may be packed separately in multiple layers. Furthermore, the catalyst may be diluted with an inert carrier and packed to control activity.

[0036] The concentration of methacrolein in the raw material gas is not particularly limited, but is preferably 1% by volume to 20% by volume, more preferably 3% by volume as the lower limit, and more preferably 10% by volume as the upper limit. Methacrolein as a raw material may contain small amounts of impurities such as lower saturated aldehydes that do not substantially affect the reaction.

[0037] The concentration of molecular oxygen in the raw material gas is preferably 0.4 mol to 4 mol per mol of methacrolein, with the lower limit being more preferably 0.5 mol and the upper limit being more preferably 3 mol. From the viewpoint of economic efficiency, air is preferred as the molecular oxygen source. If necessary, a gas enriched in molecular oxygen by adding pure oxygen to air may be used.

[0038] The raw material gas may be prepared by diluting methacrolein and molecular oxygen with an inert gas such as nitrogen or carbon dioxide. Furthermore, water vapor may be added to the raw material gas. By carrying out the reaction in the presence of water vapor, methacrylic acid can be obtained in a higher yield. The concentration of water vapor in the raw material gas is preferably 0.1% by volume to 50% by volume, more preferably 1% by volume at the lower limit, and more preferably 40% by volume at the upper limit.

[0039] The contact time between the raw material gas and the catalyst is preferably 1.5 to 15 seconds. The reaction pressure is preferably 0.1 MPa (G) to 1 MPa (G), where (G) means gauge pressure. The reaction temperature is preferably 200 to 450°C, with the lower limit being more preferably 250°C and the upper limit being more preferably 400°C.

[0040] <Method for Producing α,β-Unsaturated Carboxylic Acid Ester> In the method for producing an α,β-unsaturated carboxylic acid ester according to the present invention, an α,β-unsaturated carboxylic acid ester is produced using the α,β-unsaturated carboxylic acid obtained by the method for producing an α,β-unsaturated carboxylic acid according to the present invention. The alcohol to be reacted with the α,β-unsaturated carboxylic acid is not particularly limited, and examples thereof include methanol, ethanol, isopropanol, n-butanol, and isobutanol. Examples of the resulting α,β-unsaturated carboxylic acid ester include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate. The esterification reaction can be carried out in the presence of an acidic catalyst such as a sulfonic acid-type cation exchange resin. The reaction temperature for the esterification reaction is preferably 50°C to 200°C.

[0041] Hereinafter, examples of producing a catalyst (Keggin-type heteropolyacid salt) according to the present invention will be described together with comparative examples. In the following examples and comparative examples, "parts" means parts by mass.

[0042] [Analysis of the product] The analysis of the product was carried out using an infrared spectrophotometer (trade name: NICOLET 6700FT-IR, manufactured by Thermo Electron Corporation). 1 mg of a sample of the product was mixed with 100 mg of potassium bromide, and the mixture was molded using a micro tablet molder (trade name: MP-1, manufactured by JASCO Corporation). The transmittance of the molded product was measured. The measurement conditions were: measurement range: 400 cm －１ ~4000cm －１ , resolution: 4cm －１ The number of scans was 128. First, to reduce noise, the obtained measurement data was converted into an average value of 10 data points before and after the measurement. Next, the converted data was converted into a wave number of 700 cm. －１ ~1200cm －１ The first-order differentiation was performed for the region, and the point where the differential value changed from a positive value to a negative value was regarded as a maximum value, that is, a peak of the spectrum, and the peak was detected.

[0043] [Example 1] (Dry Milling Process) 100 parts of molybdenum trioxide, 10.7 parts of ammonium dihydrogen phosphate, and 5.5 parts of ammonium bicarbonate were mixed in a mortar with 2.7 parts of ammonium metavanadate, 11.2 parts of cesium bicarbonate, and 0.4 parts of copper oxide as additional components to obtain a raw material powder mixture. Subsequently, high-hardness stainless steel milling balls with a ball diameter of 10 mm were added as milling media to a milling container (high-hardness stainless steel, capacity: 12 mL) so as to account for 26.2 volume % of the raw material powder mixture. Subsequently, 6 parts of the raw material powder mixture and 0.4 parts of stearic acid were added to the milling container, and the container was then covered with a packing. The milling container in this state was placed in a planetary ball mill (trade name: PULVERISETTE 7, manufactured by FRITSCH) and milled at a revolution speed of 500 rpm for 15 minutes to obtain a mixture. The gravitational acceleration in this step was 19.1 G. (Wet Milling Step) After the dry milling step, the milling container was temporarily removed from the apparatus, the lid was opened, and 30% by mass of water was added to the total mass of the raw material powder. After the addition, the milling container with the lid closed and a packing was placed in the planetary ball mill, and a milling process (mixing process) was carried out for 15 minutes at a revolution speed of 500 rpm. The powder (catalyst, composition: P １．６ Mo １２ V ０．４ Cu ０．１ Cs １．０ (NH ４ ) ３．２ The results are shown in Tables 1 and 2.

[0044] [Example 2] Powder was obtained in the same manner as in Example 1, except that the processing times for the dry milling step and the wet milling step were each 30 minutes. The catalyst composition was the same as in Example 1 (the same applies to the catalysts obtained in the following Examples and Comparative Examples). The obtained powder was analyzed using an infrared spectrophotometer. The results are shown in Tables 1 and 2.

[0045] [Example 3] A powder was obtained in the same manner as in Example 1, except that the processing times in the dry milling step and the wet milling step were each 60 minutes. The obtained powder was analyzed using an infrared spectrophotometer. The results are shown in Tables 1 and 2.

[0046] [Comparative Example 1] A powder was obtained in the same manner as in Example 2, except that the dry grinding step was not performed. The obtained powder was analyzed using an infrared spectrophotometer. The results are shown in Tables 1 and 2.

[0047] [Comparative Example 2] A powder was obtained in the same manner as in Example 3, except that the dry grinding step was not performed. The obtained powder was analyzed using an infrared spectrophotometer. The results are shown in Tables 1 and 2.

[0048] Comparative Example 3: A powder was obtained in the same manner as in Example 1, except that in the dry-milling and wet-milling steps, the raw material powder and stearic acid were mixed using a mortar and pestle instead of a mill. The gravitational acceleration in each step was approximately 0.2 G. The obtained powder was analyzed using an infrared spectrophotometer. The results are shown in Tables 1 and 2.

[0049] Comparative Example 4 A powder was obtained in the same manner as in Example 3, except that the wet-pulverization step was not performed. The obtained powder was analyzed using an infrared spectrophotometer. The results are shown in Tables 1 and 2. Note that the five detected peaks coincided with the peaks of the raw materials, and therefore, these peaks were determined to be due to unreacted raw materials.

[0050]

[0051]

[0052] As shown in Tables 1 and 2, the production method according to the present invention, which includes a dry-pulverization step and a wet-pulverization step, can produce a high-purity Keggin-type heteropolyacid salt with reduced unreacted raw materials and by-products. Furthermore, an α,β-unsaturated carboxylic acid can be produced by subjecting an α,β-unsaturated aldehyde to gas-phase catalytic oxidation with molecular oxygen using the catalyst obtained in the above examples. Furthermore, an α,β-unsaturated carboxylic acid ester can be produced by esterifying the resulting α,β-unsaturated carboxylic acid.

[0053] According to the present invention, a simple method for producing a catalyst (preferably a Keggin-type heteropolyacid salt) can be provided.

Claims

1. A method for producing a catalyst, comprising: (i) mixing raw material powders using a first pulverizer to obtain a mixture; and (ii) adding a solvent containing water to the mixture and mixing the mixture using a second pulverizer, wherein the raw material powder contains a molybdenum raw material.

2. The method for producing a catalyst according to claim 1, wherein in step (i), the raw material powder is charged into the first mill and mixed in the presence of a milling medium.

3. The method for producing a catalyst according to claim 1 or 2, wherein in step (i), a flow aid or an anti-caking agent is added to and mixed with the raw material powder.

4. The method for producing a catalyst according to any one of claims 1 to 3, wherein in the step (i), a gravitational acceleration of 0.5 G or more is applied to the raw material powder.

5. The method for producing a catalyst according to any one of claims 1 to 4, wherein the treatment time of the step (i) is from 5 minutes to 60 minutes, and the treatment time of the step (ii) is from 5 minutes to 60 minutes.

6. A method for producing a catalyst according to any one of claims 1 to 5, wherein the amount of the water-containing solvent added is 1 mass % or more and 60 mass % or less with respect to the total mass of the raw material powder.

7. The method for producing a catalyst according to any one of claims 1 to 6, wherein the second crusher is a crusher different from the first crusher.

8. The method for producing a catalyst according to any one of claims 1 to 7, wherein the raw material powder further contains a phosphorus raw material and an ammonium raw material.

9. The method for producing a catalyst according to any one of claims 1 to 8, wherein the catalyst comprises a Keggin type heteropolyacid salt.

10. The method for producing a catalyst according to any one of claims 1 to 9, wherein the catalyst is a catalyst for producing an α,β-unsaturated carboxylic acid.

11. The method for producing a catalyst according to any one of claims 1 to 10, wherein in step (i), the mixture is obtained substantially without adding a solvent.

12. The method for producing a catalyst according to any one of claims 1 to 11, wherein the molybdenum source is selected from the group consisting of molybdenum oxide, ammonium molybdate, and molybdenum chloride.

13. The method for producing a catalyst according to any one of claims 8 to 12, wherein the phosphorus source is selected from the group consisting of phosphoric acid, phosphorus pentoxide, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

14. A method for producing an α,β-unsaturated carboxylic acid, comprising producing an α,β-unsaturated carboxylic acid from an α,β-unsaturated aldehyde using a catalyst produced by the production method according to any one of claims 1 to 13.

15. A method for producing an α,β-unsaturated carboxylic acid ester, comprising producing an α,β-unsaturated carboxylic acid ester from the α,β-unsaturated carboxylic acid produced by the production method according to claim 14.

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