WO2025127065A1 - METHOD FOR PRODUCING CATALYST, AND METHOD FOR PRODUCING α, β-UNSATURATED CARBOXYLIC ACID AND α, β-UNSATURATED CARBOXYLIC ACID ESTER USING SAID CATALYST - Google Patents

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

The present invention relates to a method for producing a catalyst using a grinder, and a method for producing α,β-unsaturated carboxylic acids and α,β-unsaturated carboxylic acid esters using the catalyst.

Heteropolyacids are condensed oxygen acids composed of oxides of multiple coordinating atoms called polyatoms and oxides of a central atom called a heteroatom. 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.

Heteropolyacid salts are known to be used as industrial catalysts, and Patent Document 1 discloses a Keggin-type heteropolyacid salt as a catalyst for the production of methacrylic acid. As described in Patent Document 1, a method for producing a Keggin-type heteropolyacid salt includes a method of removing water by drying from an aqueous slurry obtained by heating and mixing raw materials in water.

Non-Patent Document 1 shows a method for producing Keggin-type heteropolyacid salts 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.

JP 2003-010691 A

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

In the method shown in Patent Document 1, in which raw materials are heated and mixed in water and then dried to remove moisture, a large amount of water is used and a large amount of energy is consumed for heating and drying. Therefore, this method is undesirable from the viewpoint of resources and energy. On the other hand, the mechanochemical synthesis method shown in Non-Patent Document 1 requires the addition of an aqueous ethanol solution (ethanol:water (volume ratio) = 1:1), which is a hazardous material, and is undesirable from an industrial point of view. Furthermore, the addition of only water promotes the production of unidentifiable by-products, making it difficult to obtain a high-purity Keggin-type heteropolyacid salt.

The present invention aims to provide a method for producing a catalyst that can produce a high-purity catalyst in a simple manner using only raw materials and a small amount of solvent.

The inventors of the present invention have conducted extensive research in light of the above problems. As a result, they have discovered that the above problems can be solved by performing mechanochemical synthesis that includes a process of mixing only the powders of the raw material compounds in a grinder, prior to the process of adding a solvent containing at least water and mixing the raw material compounds, and have thus completed the present invention.

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] The method for producing a catalyst according to [1], wherein in the step (i), the raw material powder is charged into the first pulverizer and mixed in the presence of a pulverizing medium.
[3] The 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 and mixed with the raw material powder.
[4] The method for producing a catalyst according to any one 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] The method for producing a catalyst according to any one of [1] to [4], wherein the treatment time of the step (i) is 5 minutes or more and 60 minutes or less, and the treatment time of the step (ii) is 5 minutes or more and 60 minutes or less.
[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 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 [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 raw material and an ammonium raw material.
[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 in the step (i), the mixture is obtained substantially without adding a solvent.
[12] The method for producing a catalyst according to any one of [1] to [11], wherein the molybdenum raw material 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 by 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, comprising producing an α,β-unsaturated carboxylic acid ester from an α,β-unsaturated carboxylic acid produced by the production method according to [14].

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

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

<Catalyst manufacturing method>
The method for producing a catalyst according to the present invention includes at least the steps of (i) mixing raw 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 in that after a step (i) of mixing only powders (raw powders) of the raw compound (optional additives may be added) using a pulverizer (hereinafter also referred to as a "dry pulverization step"), a solvent containing water is added to the obtained mixture and further mixed using a pulverizer (hereinafter also referred to as a "wet pulverization step") (ii) is carried out to produce a catalyst. Each step will be described in detail below.

[Step (i): Dry grinding step]
The dry grinding process is a process in which raw material powders are mixed and ground using a grinder (first grinder) to obtain a mixture. Specifically, in this process, it is preferable to feed the raw material powders into the first grinder and mix and grind the raw material powders in the presence of a grinding medium. This process is carried out without adding a liquid (solvent) such as water, and can be said to be a process in which a mixture of raw material powders is obtained substantially without adding a solvent.

(First Crusher)
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 a planetary ball mill is used as the pulverizer, a specific pulverization method is to first put the raw material powder to be pulverized and the pulverization medium into the pulverizer, specifically, into the pulverizer's pulverization vessel. Next, the raw material powder is pulverized by applying a force such as gravity, vibration, or centrifugal force to the pulverizer, causing the raw material powder to collide violently with the pulverization medium, or by generating friction between the raw material powder, the pulverization medium, and the pulverization vessel. 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 pulverize the raw material powder uniformly.

(Crushing media)
In this process, the mixing and grinding of the raw material powder is usually carried out in the presence of grinding media. When a planetary ball mill or the like is used as the grinder, as described above, the grinding media is placed in the grinding container together with the raw material powder, and the grinding container is rotated, so that the grinding media moves around in the container and the raw material powder is mixed and ground. On the other hand, when a crusher, kneader, high-speed rotary grinder, or the like is used as the grinder, the grinding media is a crushing rod or agitating blade, and the raw material powder is mixed and ground by the rotation of the crushing rod or agitating blade. When a planetary ball mill or the like is used as the grinder, the shape of the grinding media is preferably spherical in terms of fluidity and grinding efficiency in the grinding container. The amount of the grinding media used is preferably 10% by volume or more, more preferably 15% by volume or more, relative to the capacity of the grinding container. By increasing the amount of the grinding media used, the grinding efficiency can be increased and the processing time can be shortened. On the other hand, by reducing the amount of the grinding media used, the amount of raw material powder that can be ground can be increased. In addition, by setting the amount of grinding media to 50% or less by volume relative to the capacity of the grinding container, wear of the grinding container can be reduced. Therefore, the amount of grinding media used is preferably 50% or less by volume relative to the capacity of the grinding container, and more preferably 30% or less by volume.

There are no particular limitations on the materials for the grinding media and grinding vessel, so long as they are chemically resistant to the raw materials and physically resistant to the grinding conditions. Materials for the grinding media and grinding vessel are preferably tungsten carbide, high-hardness stainless steel, menthol, silicon nitride, zirconia, etc., and more preferably tungsten carbide or high-hardness stainless steel.

(Raw material powder and additives)
In the dry grinding process, raw powder containing at least a molybdenum raw material is charged into a grinding vessel. At this time, it is preferable to add a flow aid or an anti-caking agent as an additive to the raw powder and mix it. As the flow aid or anti-caking agent, a known one can be appropriately selected and used. Specific examples of the flow aid or anti-caking agent include stearic acid and its salts (calcium stearate, magnesium stearate, etc.), silicates (potassium silicate, sodium silicate, magnesium silicate, etc.), and phosphates (calcium phosphate, etc.). Among these, it is preferable to use stearic acid and its salts. By adding these flow aids or anti-caking agents, the raw powder during the grinding process is less likely to be compacted, and the recovery rate of the ground product can be increased. The amount of the flow aid or anti-caking agent added is preferably 10% by mass or less, more preferably 7% by mass or less, based on the mass of the entire raw powder. In addition, the amount of the flow aid or anti-caking agent added is preferably 3% by mass or more, more preferably 5% by mass or more, based on the mass of the entire 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 satisfactorily exhibited.

The raw material powder preferably further contains a phosphorus raw material and an ammonium raw material in addition to the molybdenum raw material. 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. As the additional catalytically active components, 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 are preferable.

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

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 carbonates such as ammonium hydrogen carbonate and ammonium carbonate, and ammonium chloride, in addition to the above-mentioned ammonium phosphate and ammonium molybdate.

In the presence of grinding media, a grinding container containing the raw powder and any additives is placed in a grinding machine and mixed to obtain a ground product (mixture) of the raw powder. The processing time for the dry grinding process is preferably short, taking into consideration wear on 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 lower limit to the processing time as long as the raw powder is sufficiently ground, 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 grinder in the dry grinding process can be set appropriately, and can be, for example, 100 rpm to 800 rpm.

[Step (ii): Wet grinding step]
In the wet grinding step, a solvent containing water is added to the grinding vessel containing the mixture after the dry grinding step, and then the grinding vessel is set in a second grinder to perform mixing, thereby obtaining a catalyst. Although this step is described as a "wet grinding step", it is sufficient to at least mix the mixture after the dry grinding step with the solvent, and it may also be a "wet mixing step". As the second grinder, one similar to the first grinder in the dry grinding step can be used. The second grinder used in the wet grinding step may be the same grinder as the first grinder used in the dry grinding step, or may be a different grinder. In addition, the grinding vessel may be the same as the grinding vessel used in the dry grinding step, or a different grinding vessel may be used. However, from the viewpoint of work efficiency, it is preferable to use the grinding vessel used in the dry grinding step as it is in the wet grinding step.

(solvent)
In the wet grinding step, a solvent containing at least water is added, and the mixture after the dry grinding step is mixed with the solvent. The solvent may be only water, 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, based on the mass of the entire raw material powder. The smaller the amount of liquid (solvent) added in the wet grinding step, the less the amount of liquid to be removed in the drying step described below, which is preferable. On the other hand, when the amount of liquid added in the wet grinding step is large, the mechanochemical synthesis tends to proceed faster. Therefore, the amount of solvent added is preferably 1% by mass or more, more preferably 10% by mass or more, based on the mass of the entire raw material powder. The "mass of the entire raw material powder" means the mass of the entire raw material powder used in the dry grinding step, and does not include the mass of additives.

As described above, the catalyst manufacturing method according to the present invention can be applied even when only a small amount of water is used as the solvent. Even when a combination of solvents other than water is used as the 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.

In the wet grinding process, it is sufficient that the mixture and the solvent can be mixed uniformly. Therefore, as in the dry grinding process, the grinder may apply forces such as gravity, vibration, or centrifugal force, but this is not essential. The processing time in the wet grinding process is preferably short, taking into consideration wear on 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 lower limit to the processing time, so long as the raw 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 grinder in the wet grinding process may be set appropriately, and can be, for example, 100 rpm to 800 rpm.

[Drying process]
The method for producing a catalyst according to the present invention may include a drying step of drying the wet powder, clay-like, or cake-like product (catalyst) obtained in the wet grinding step (ii) after the wet grinding step. 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, ventilation 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 grinding step (ii) and the dried product obtained by drying the product are collectively referred to as the "catalyst".

[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. The 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 one type of Keggin type heteropolyacid salt, the wave number of infrared absorption changes depending on the type and substitution number of the counter cation, and the infrared light absorption attributed to the P-O antisymmetric stretching vibration of the phosphorus oxide of the heteroatom is observed at a wave number of 1062±10 cm ^-1 . In addition, the infrared light absorption caused by the antisymmetric vibration of the molybdenum oxide of the polyatom is observed at wave numbers of 965±10 cm ^-1 , 870±10 cm ^-1 , and 790±10 cm ^-1 . Therefore, when a catalyst is analyzed using an infrared spectrophotometer and peaks are observed at the above four wave numbers, the catalyst can be identified as a compound containing a Keggin type heteropolyacid salt. Peaks observed at wave numbers other than the above are infrared absorptions caused by impurities such as unreacted raw materials and by-products, and can be used as an index of the purity of the product.

The inventors of the present invention speculate that the reason why a high-purity catalyst, preferably a Keggin-type heteropolyacid salt, can be obtained by adding a dry-milling step before the wet-milling step (or wet-mixing step) is as follows. That is, 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, which is believed to efficiently promote the main reaction, the generation of the Keggin-type heteropolyacid salt, and suppress the generation of by-products.

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 the carrier into consideration.
P _a Mo _b V _c Cu _d X _e Y _f Z _g (NH ₄ ) _h O _i (I)

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 indicate 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 is the molar ratio of oxygen necessary to satisfy the valence of each of the components.

The molar ratio of each element is a value obtained by analyzing a solution in which the catalyst is dissolved in ammonia water by ICP emission spectrometry. The molar ratio of ammonium root is a value obtained by analyzing the catalyst by Kjeldahl method. In the present invention, "ammonium root" refers to a general term for ammonia (NH ₃ ) that can become ammonium ion (NH ₄ +) and ammonium contained in ammonium-containing compounds such as ammonium salts.

<Method of 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 a 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 a catalyst obtained by the method for producing a catalyst according to the present invention to produce an α,β-unsaturated carboxylic acid. The method for producing an α,β-unsaturated carboxylic acid according to the present invention can also be said to be 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. According to these methods, an α,β-unsaturated carboxylic acid can be produced in a high yield by carrying out a gas-phase catalytic oxidation reaction using a catalyst with high purity.

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 is 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.

Below, 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. The method described below can also be applied to the case where an α,β-unsaturated aldehyde other than methacrolein is used. In this method, methacrylic acid is produced by contacting a raw material 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 in a reaction tube, and the raw material 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. The catalyst may also be diluted with an inert carrier and packed in order to control the activity.

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

The concentration of molecular oxygen in the raw gas is preferably 0.4 to 4 moles per mole of methacrolein, with a lower limit of 0.5 moles being more preferable and an upper limit of 3 moles being more preferable. From an economical standpoint, air is preferred as the source of molecular oxygen. If necessary, a gas enriched in molecular oxygen by adding pure oxygen to air may be used.

The raw material gas may be methacrolein and molecular oxygen diluted 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% to 50% by volume, more preferably with a lower limit of 1% by volume and an upper limit of 40% by volume.

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°C to 450°C, with a lower limit of 250°C being more preferable and an upper limit of 400°C being more preferable.

<Method of 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 α,β-unsaturated carboxylic acid ester obtained 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 acid catalyst such as a sulfonic acid type cation exchange resin. The reaction temperature of the esterification reaction is preferably 50°C to 200°C.

Below, a production example of the catalyst (Keggin-type heteropolyacid salt) according to the present invention will be described together with a comparative example. Note that "parts" in the following examples and comparative examples means parts by mass.

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

[Example 1]
(Dry grinding process)
100 parts of molybdenum trioxide, 10.7 parts of ammonium dihydrogen phosphate, and 5.5 parts of ammonium hydrogen carbonate were mixed in a mortar with 2.7 parts of ammonium metavanadate, 11.2 parts of cesium hydrogen carbonate, and 0.4 parts of copper oxide as additional components to obtain a mixture of raw material powders. Next, grinding balls made of high hardness stainless steel with a ball diameter of 10 mm were added as grinding media to a grinding container (made of high hardness stainless steel, capacity: 12 mL) so as to be 26.2 volume %. Next, 6 parts of the mixture of raw material powders and 0.4 parts of stearic acid were added to the grinding container, and then the container was covered with a packing. The grinding container in this state was set in a planetary ball mill (trade name: PULVERISETTE 7, manufactured by FRITSCH) and ground for 15 minutes at a revolution speed of 500 rpm to obtain a mixture. The gravitational acceleration in this process was 19.1 G.
(Wet grinding process)
The grinding container after the dry grinding process was once 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 grinding container with the lid and a packing was set in the planetary ball mill, and grinding (mixing) was performed for 15 minutes at a revolution speed of 500 rpm. The powder thus obtained (catalyst, composition: P _1.6 Mo ₁₂ V _0.4 Cu _0.1 Cs _1.0 (NH ₄ ) _3.2 ) was analyzed using an infrared spectrophotometer. The results are shown in Tables 1 and 2.

[Example 2]
A powder was obtained in the same manner as in Example 1, except that the processing time of the dry grinding step and the wet grinding step was 30 minutes each. The composition of the catalyst 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.

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

[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.

[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.

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

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

As shown in Tables 1 and 2, the manufacturing method according to the present invention, which has a dry grinding step and a wet grinding step, can produce a high-purity Keggin-type heteropolyacid salt with reduced amounts of unreacted raw materials and by-products. Using the catalyst obtained in the above example, an α,β-unsaturated aldehyde can be subjected to gas-phase catalytic oxidation with molecular oxygen to produce an α,β-unsaturated carboxylic acid. Furthermore, an α,β-unsaturated carboxylic acid ester can be obtained by esterifying the obtained α,β-unsaturated carboxylic acid.

The present invention provides a simple method for producing a catalyst (preferably a Keggin-type heteropolyacid salt).

Claims (15)

(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.
Including,
The method for producing a catalyst, wherein the raw material powder contains a molybdenum raw material. The method for producing a catalyst according to claim 1, wherein in step (i), the raw material powder is fed into the first grinder and mixed in the presence of a grinding medium. The method for producing a catalyst according to claim 1 or 2, wherein in step (i), a flow aid or anti-caking agent is added to and mixed with the raw material powder. The method for producing a catalyst according to any one of claims 1 to 3, wherein in step (i), a gravitational acceleration of 0.5 G or more is applied to the raw material powder. The treatment time of the step (i) is 5 minutes or more and 60 minutes or less,
The treatment time of the step (ii) is 5 minutes or more and 60 minutes or less.
A method for producing the catalyst according to any one of claims 1 to 4. The 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% by mass or more and 60% by mass or less with respect to the total mass of the raw material powder. 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. 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. The method for producing the catalyst according to any one of claims 1 to 8, wherein the catalyst comprises a Keggin-type heteropolyacid salt. 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. 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. The method for producing a catalyst according to any one of claims 1 to 11, wherein the molybdenum raw material is selected from the group consisting of molybdenum oxide, ammonium molybdate, and molybdenum chloride. The method for producing a catalyst according to any one of claims 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. A method for producing an α,β-unsaturated carboxylic acid, which produces an α,β-unsaturated carboxylic acid from an α,β-unsaturated aldehyde using a catalyst produced by the method according to any one of claims 1 to 13. 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.