JP5659490B2 - Method for producing catalyst for producing methacrylic acid, and method for producing methacrylic acid - Google Patents

Description

  The present invention relates to a method for producing a catalyst for producing methacrylic acid (hereinafter also simply referred to as “catalyst”) for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen, and a catalyst produced by this method. And a method for producing methacrylic acid using the catalyst.

  As a methacrylic acid production catalyst for producing methacrylic acid by vapor phase catalytic oxidation of methacrolein with molecular oxygen, a heteropolyacid catalyst containing molybdenum and phosphorus is known. As such a heteropolyacid catalyst, a proton type heteropolyacid whose counter cation is a proton, and one obtained by substituting a part of the proton with an alkali metal such as cesium, rubidium, potassium, etc., are known. (Hereinafter, the proton type heteropolyacid is also simply referred to as “heteropolyacid”, and the proton type heteropolyacid and / or the heteropolyacid salt is also referred to as “heteropolyacid (salt)”). Proton type heteropolyacids are water-soluble, but heteropolyacid salts in which protons are substituted with alkali metals generally have poor solubility in water because of the ionic radius of these cations.

The structure of the heteropolyacid (salt) includes the following description.
(A) The heteropolyacid (salt) has a heterogeneous element (hereinafter referred to as a central element) at the center and has a mononuclear or binuclear complex ion formed by condensing condensed acid groups while sharing oxygen. Several types of condensation forms are known, and phosphorus, arsenic, silicon, germanium, titanium, and the like can be the central element (Non-Patent Document 1).

Further, as a catalyst for improving the selectivity of methacrylic acid from methacrolein using a heteropolyacid catalyst, for example, the following catalysts are disclosed.
(B) An oxide is used as a raw material for molybdenum and vanadium components at the time of catalyst preparation, and a mixture of catalyst raw material other than potassium, rubidium, cesium and thallium and water is heated to 85 ° C. or higher for 1 to 10 hours, and then mixed The liquid is cooled to 80 ° C. or lower, and at least one element selected from the group consisting of potassium, rubidium, cesium, and thallium is added, and then ammonium nitrate, ammonium carbonate, ammonium bicarbonate, A multicomponent methacrylic acid production catalyst containing phosphorus, molybdenum and vanadium, characterized by heat-treating at least one compound selected from the group consisting of ammonium sulfate and ammonium hydrogen sulfate (Patent Document 1).

On the other hand, as a catalyst for improving the selectivity of methacrylic acid from isobutane using a heteropolyacid catalyst, for example, the following catalysts are disclosed.
(C) A catalyst in which a heteropolyacid (salt) containing molybdenum or phosphorus and containing molybdenum as a central element is reduced by 1 to 6 electrons per molecule of the heteropolyacid (Patent Document 2).
(D) containing phosphorus, arsenic as a central element, molybdenum and vanadium as coordination elements, the ratio of which is 0.5-3 gram atom for the central element and 0.01-2 gram atom for vanadium with respect to 12 gram atom of molybdenum A catalyst containing a heteropolyacid (salt) that is
(E) A catalyst containing a poorly water-soluble salt of a heteropolyacid and a composite oxide containing phosphorus, molybdenum, and vanadium (Patent Document 4).

JP-A-4-7037 JP-A 63-145249 Japanese Patent Laid-Open No. 02-42032 JP 2001-114726 A

Masayuki Otake, Takeshi Onoda, Catalyst, vol. 18, no. 6 (1976)

  However, the catalysts (b) to (e) still have insufficient selectivity for methacrylic acid as an industrial catalyst, and further improvement in the selectivity of methacrylic acid is desired for use as an industrial catalyst. Yes.

An object of the present invention is to provide a method of manufacturing a catalyze for producing methacrylic acid can be produced methacrylic acid with high selectivity, and a method for producing methacrylic acid using the catalyst.

The present invention relates to a phosphorus element, a molybdenum element, an X element (a group consisting of silicon, titanium, germanium, arsenic, antimony and cerium) used in producing methacrylic acid by vapor phase catalytic oxidation of methacrolein with molecular oxygen. A method for producing a catalyst comprising at least one element selected from the group consisting of an alkali metal element,
(I) adding at least a molybdenum raw material and an X element raw material in water to prepare an aqueous slurry or aqueous solution containing a heteropolyacid;
(Ii) adding an alkali metal compound to the aqueous slurry or aqueous solution to precipitate a heteropolyacid salt that is at least a part of the alkali metal salt of the heteropolyacid;
(Iii) adding a phosphorus raw material that is at least one selected from the group consisting of normal phosphoric acid, phosphorus pentoxide and ammonium phosphate to the aqueous slurry or aqueous solution in which the heteropolyacid salt is deposited;
(Iv) drying an aqueous slurry or aqueous solution containing all raw materials to obtain a dried product;
(V) heat-treating the dried product.

Also, the present invention is the above method of manufacturing, and producing methacrylic acid catalyst for producing, manufacturing method for methacrylic acid to produce methacrylic acid by vapor phase catalytic oxidation of methacrolein with molecular oxygen using the catalyst It is.

According to the present invention, methacrylic acid using a method of manufacturing a catalyze for producing methacrylic acid which can be produced with high selectivity to methacrylic acid by the gas-phase catalytic oxidation of methacrolein with molecular oxygen, and the production of methacrylic acid catalyst The manufacturing method of can be provided.

<Catalyst for methacrylic acid production and production method thereof>
The present invention is a catalyst comprising a phosphorus element, a molybdenum element, an X element (at least one element selected from the group consisting of silicon, titanium, germanium, arsenic, antimony and cerium) and an alkali metal element. It is preferable to have the composition represented by 1).

_{Mo a P b V c Cu d} X e Y f Z g O h (1)
(In the formula, Mo, P, V, Cu and O are element symbols indicating molybdenum, phosphorus, vanadium, copper and oxygen, respectively. X is selected from the group consisting of silicon, titanium, germanium, arsenic, antimony and cerium. Y represents at least one element, Y represents at least one element selected from the group consisting of bismuth, zirconium, silver, iron, zinc, chromium, magnesium, cobalt, manganese, barium, cerium and lanthanum; Represents at least one element selected from the group consisting of potassium, rubidium and cesium, where a, b, c, d, e, f, g and h represent the atomic ratio of each element, and when a = 12. B = 0.5-3, c = 0.01-3, d = 0.01-2, e = 0.1-3, f = 0-3, g = 0.01-3, h Is Serial is an atomic ratio of oxygen required to satisfy the valence of each element.)
The catalyst of the present invention is produced by a production method having the following steps.
Step (i): At least a molybdenum raw material and an X element raw material are added in water to prepare an aqueous slurry or aqueous solution containing a heteropolyacid (preparation step).
Step (ii): An alkali metal compound is added to the aqueous slurry or aqueous solution to precipitate a heteropolyacid salt in which at least a part of the heteropolyacid is an alkali metal salt (precipitation step).
Step (iii): A phosphorus raw material is added to the aqueous slurry or aqueous solution in which the heteropolyacid salt is deposited (phosphorus addition step).
Step (iv): The aqueous slurry or aqueous solution containing all raw materials is dried to obtain a dried product (drying step).
Step (v): The dried product is heat treated (heat treatment step).

  Furthermore, you may have the process (molding process) of shaping the said dried material.

  The present inventors use X element and phosphorus element as the central elements of the heteropolyacid (salt) contained in the catalyst, add the raw material of X element before precipitation of the heteropolyacid salt, and deposit the phosphorus raw material as precipitation of the heteropolyacid salt. It was found that the catalyst performance is greatly improved by adding it later.

  The reason for this is that the X element present in the heteropolyacid (salt) contained in the catalyst affects the selectivity of methacrylic acid, and the raw material for the X element is added before precipitation of the heteropolyacid salt. It is presumed that the ratio of the X element present in the heteropolyacid (salt) is increased by adding after the precipitation of the heteropolyacid salt.

  The catalyst includes a proton-type heteropoly acid whose counter cation of the heteropoly acid is all hydrogen (proton), and a part or all of the proton substituted with an alkali metal such as cesium, rubidium, potassium, etc., to form a heteropoly acid salt Exists. Proton type heteropolyacid is an important chemical structure in which methacrolein is converted to methacrylic acid by the supply of oxygen of the heteropolyacid. Heteropolyacid salt is further oxidized after methacrolein is oxidized to methacrylic acid. This has the effect of suppressing the sequential oxidation reaction. On the other hand, in the completed catalyst, there are impurities other than the heteropolyacid (salt) that could not be the heteropolyacid (salt).

  Although the role of impurities that could not become this heteropolyacid (salt) is not clear, the element X contributes to the improvement of the selectivity of methacrylic acid by constituting the heteropolyacid (salt), and the ratio that exists as an impurity As the value increases, the selectivity of methacrylic acid decreases. Therefore, the selectivity of methacrylic acid can be improved by increasing the proportion of the X element present in the heteropolyacid (salt).

  In the present invention, as the raw material for the central element, an alkali metal is added in the presence of the raw material for the X element, and after depositing the heteropolyacid salt having the X element as the central element, the phosphorus raw material is added. As a result, the heteropoly acid salt having the X element as the central element is formed in preference to the heteropoly acid (salt) having the phosphorus element as the central element. The selectivity is estimated to improve.

[Preparation process]
In this step, at least a molybdenum raw material and an X element raw material are added to water to prepare an aqueous slurry or aqueous solution containing a heteropolyacid. The phosphorus raw material is preferably not added in this step, but may be added as long as the phosphorus raw material has an amount of supplying a phosphorus element having a mole number smaller than the mole number of the X element in the X element raw material. In addition, molybdenum raw material, phosphorus raw material, X element raw material and raw materials other than alkali metal compounds (in the case of producing a catalyst having a composition represented by the formula (1), vanadium raw material, copper raw material and Y element raw material) Etc. may be added at any stage of the preparation process, the precipitation process and the phosphorus addition process. What is necessary is just to determine the compounding quantity of the raw material to add suitably according to the composition of the target catalyst.

  Examples of the raw material used include nitrates, carbonates, acetates, ammonium salts, oxides, halides and the like of each element. Examples of the molybdenum raw material include ammonium paramolybdate, molybdenum trioxide, molybdic acid, and molybdenum chloride. Examples of the copper raw material include copper nitrate, copper oxide, copper carbonate, and copper acetate. Examples of the vanadium raw material include phosphovanadomolybdic acid, ammonium metavanadate, vanadium pentoxide, and the like. However, when phosphovanadomolybdic acid is used as the vanadium raw material, molybdenum is contained in the phosphovanadmolybdic acid at the same time. Therefore, it is necessary to adjust the addition amount of the molybdenum raw material and the phosphorus raw material according to the amount of phosphovanadmolybdic acid added. There is.

  For preparing the aqueous slurry or aqueous solution, a method of adding a raw material of each element to water and stirring while heating is simple and preferable. An aqueous solution, an aqueous slurry, or an aqueous sol of the raw material of each element can be added to water. The amount of water used in the preparation step is preferably (total mass of raw materials used in the preparation step) :( mass of water used in the preparation step) = 1: 0.5 to 1:15. The amount of 1.0 to 1: 4.0 is more preferable, and the amount of 1: 1.0 to 1: 2.0 is more preferable. In addition, when an aqueous solution, aqueous slurry or aqueous sol of raw materials for each element is used, only the raw materials are included in the “raw materials used in the preparation step”, and the water as the solvent is “water used in the preparation step”. Include. Crystal water in the case where the raw material of each element is a hydrate is included in the “raw material used in the preparation process”. By setting the amount of water used in the preparation step within this range, the selectivity of methacrylic acid is improved. The role of the amount of water used in the preparation process is not clear, but by improving the concentration of the aqueous slurry, the physical structure of the heteropolyacid salt formed in the next precipitation process suppresses the sequential oxidation reaction. It is estimated that the selectivity of methacrylic acid is improved. The heating temperature of the aqueous slurry or aqueous solution is preferably 80 to 130 ° C, more preferably 90 to 130 ° C.

  When the pH of the aqueous slurry or aqueous solution to be prepared is high, it is preferable to select each raw material so as to contain a large amount of nitrate radicals. The pH of the prepared aqueous slurry or aqueous solution is preferably 4 or less, and more preferably 2 or less.

[Precipitation process]
In this step, an alkali metal compound is added to the aqueous slurry or aqueous solution obtained in the preparation step to precipitate a heteropolyacid salt in which at least a part of the heteropolyacid is an alkali metal salt. It is preferred to cool the aqueous slurry or aqueous solution before adding the alkali metal compound. The cooling temperature is preferably 20 to 80 ° C, more preferably 40 to 70 ° C.

The heteropolyacid salt to be deposited may have a Keggin type structure or a structure other than Keggin type such as Dawson type, but preferably has a Keggin type structure. When the heteropoly acid salt to be precipitated is Keggin type, the selectivity of methacrylic acid is further improved. In order to precipitate the heteropolyacid salt having a Keggin type structure, for example, molybdenum trioxide is used as a molybdenum raw material, and the pH in the precipitation step is adjusted to 3 or less. The structure of the deposited heteropolyacid salt can be confirmed by measuring the heteropolyacid salt separated by filtration or the like and drying it by infrared absorption analysis. In the case of a heteropolyacid salt having a Keggin structure, for example, when the X element is arsenic, the obtained infrared absorption spectrum has characteristic peaks in the vicinity of 960, 890, 870, and 780 cm ⁻¹ . In the case of a heteropolyacid salt having a Dawson structure, the obtained infrared absorption spectrum has characteristic peaks in the vicinity of 930, 870, and 720 cm ⁻¹ .

  Examples of the alkali metal compound include a cesium compound, a potassium compound, and a rubidium compound. In the case of producing a catalyst having the composition represented by the formula (1), it becomes a raw material for the Z element. From the viewpoint of thermal stability, a cesium compound is preferable. Examples of the cesium compound include cesium bicarbonate, cesium nitrate, and cesium oxide. What is necessary is just to determine the addition amount of an alkali metal compound suitably according to the composition of the target catalyst.

  The alkali metal compound is preferably added in the form of a solution or slurry of an alkali metal compound dissolved or suspended in a solvent. Examples of the solvent include water, ethyl alcohol, acetone and the like, but it is preferable to use the same water as the aqueous slurry or aqueous solution.

  The addition rate of the alkali metal compound solution or slurry is a ratio of 0.1 to 80 parts by mass of the alkali metal compound solution or slurry per minute when the total amount of the alkali metal compound solution or slurry is 100 parts by mass. It is preferable to add at a ratio of 1 to 20 parts by mass.

  The aqueous slurry or aqueous solution to which the alkali metal compound has been added may be subsequently subjected to the phosphorus addition step or may be allowed to stand, but is preferably stirred. As the agitator, a rotary agitator such as a rotary blade agitator, a high-speed rotary shear agitator (homogenizer, etc.), a pendulum linear motion agitator, a shaker that shakes the whole container, an ultrasonic wave, or the like was used. A known stirring device such as a vibration type stirrer can be used. The rotational speed of the stirring blade or the rotary blade in the rotary stirring device may be appropriately adjusted in consideration of the shape of the container, stirring blade, baffle plate, etc., the amount of liquid, etc., to the extent that inconvenience such as liquid scattering does not occur. . Stirring may be performed either continuously or intermittently, but is preferably performed continuously.

  In order to adjust the pH of the aqueous slurry or aqueous solution to be prepared, nitric acid or a nitric acid compound, aqueous ammonia or an ammonia compound may be added. An example of the nitrate compound is ammonium nitrate. Examples of the ammonia compound include ammonium hydrogen carbonate, ammonium carbonate, and ammonium nitrate. The pH of the prepared aqueous slurry or aqueous solution is preferably 4 or less, and more preferably 2 or less.

  20-80 degreeC is preferable and, as for the temperature of the aqueous slurry or aqueous solution at the time of stirring, 40-70 degreeC is more preferable. Moreover, 5 to 60 minutes are preferable and, as for the stirring time after adding an alkali metal compound, 10 to 30 minutes are more preferable.

  Moreover, 20-80 degreeC is preferable and, as for the temperature of the aqueous slurry or aqueous solution at the time of standing, 40-70 degreeC is more preferable. The time for standing still is preferably 5 to 60 minutes, and more preferably 10 to 30 minutes.

[Phosphorus addition process]
In this step, the phosphorus raw material is added to the aqueous slurry or aqueous solution in which the heteropolyacid salt is precipitated. Examples of the phosphorus raw material include orthophosphoric acid, phosphorus pentoxide, and ammonium phosphate. What is necessary is just to determine the addition amount of a phosphorus raw material suitably according to the composition of the target catalyst. However, as described above, when phosphorus vanadomolybdic acid is used as the vanadium raw material, it is necessary to adjust the amount of phosphorus raw material added in accordance with the amount of phosphorus vanadmolybdic acid added since phosphorus is simultaneously contained in the phosphorus vanad molybdic acid. There is.

  The phosphorus raw material may be added as it is, or may be added in the form of a solution or slurry of the phosphorus raw material dissolved or suspended in a solvent. Examples of the solvent in the case of using a solvent include water, ethyl alcohol, acetone and the like, but it is preferable to use the same water as the aqueous slurry or aqueous solution. The concentration of the phosphorus raw material solution or slurry is preferably 5 to 85% by mass, and more preferably 15 to 35% by mass.

  The aqueous slurry or aqueous solution to which the phosphorus raw material is added may be subsequently subjected to a drying step or may be allowed to stand, but is preferably stirred. As the agitator, a rotary agitator such as a rotary blade agitator, a high-speed rotary shear agitator (homogenizer, etc.), a pendulum linear motion agitator, a shaker that shakes the whole container, an ultrasonic wave, or the like was used. A known stirring device such as a vibration type stirrer can be used. The rotational speed of the stirring blade or the rotary blade in the rotary stirring device may be appropriately adjusted in consideration of the shape of the container, stirring blade, baffle plate, etc., the amount of liquid, etc., to the extent that inconvenience such as liquid scattering does not occur. . Stirring may be performed either continuously or intermittently, but is preferably performed continuously.

  20-80 degreeC is preferable and, as for the temperature of the aqueous slurry or aqueous solution at the time of stirring, 40-70 degreeC is more preferable. Moreover, 5 to 60 minutes are preferable and, as for the stirring time after adding a phosphorus raw material, 10 to 30 minutes are more preferable.

  Moreover, 20-80 degreeC is preferable and, as for the temperature of the aqueous slurry or aqueous solution at the time of standing, 40-70 degreeC is more preferable. The time for standing still is preferably 5 to 60 minutes, and more preferably 10 to 30 minutes.

  The aqueous slurry or aqueous solution stirred or allowed to stand may be subsequently subjected to a drying step or may be further allowed to stand. 5-40 degreeC is preferable and, as for the temperature of the aqueous slurry or aqueous solution at the time of standing still, 20-30 degreeC is more preferable. The shorter the standing time, the better, but it is preferably within 2 days.

[Drying process]
In this step, a dry product can be obtained by heating and drying an aqueous slurry or an aqueous solution containing all raw materials. Examples of drying methods include known methods such as drum drying, airflow drying, evaporation to dryness, and spray drying. The drying is usually performed at 120 to 500 ° C., preferably 140 to 350 ° C. until the aqueous slurry or the aqueous solution is dried. The conditions such as the model of the dryer used at this time and the drying temperature are not particularly limited, and can be appropriately selected depending on the desired shape and size of the dried product.

The heteropolyacid (salt) in the dried product may have a Keggin type structure or a structure other than a Keggin type such as Dawson type, but preferably has a Keggin type structure. When the heteropolyacid (salt) in the dried product has a Keggin structure, the reaction rate of methacrolein is improved and the yield of methacrylic acid is increased. To obtain a dried product of Keggin-type heteropolyacid (salt), for example, the Keggin-type heteropolyacid salt is precipitated in the precipitation step by the above method, and the pH in the phosphorus addition step and the drying step is adjusted to 3 or less. The method of doing is mentioned. The structure of the heteropolyacid (salt) in the dried product can be confirmed by measurement by infrared absorption analysis. In the case of a heteropolyacid (salt) having a Keggin structure, the obtained infrared absorption spectrum has characteristic peaks in the vicinity of 1060, 960, 870, and 780 cm ⁻¹ . On the other hand, in the case of a heteropolyacid (salt) having a Dawson type structure, the obtained infrared absorption spectrum has characteristic peaks in the vicinity of 1040, 1020, 930, 720, and 680 cm ⁻¹ .

[Molding process]
The obtained dried product may be heat-treated as it is, but the dried product may be shaped and the obtained shaped product may be heat-treated. Moreover, you may shape what heat-processed the dried material by the heat processing process mentioned later. Examples of the apparatus used for shaping the dried product or the heat-treated dried product include known powder molding machines such as a tableting machine, an extrusion molding machine, and a rolling granulator. There is no restriction | limiting in particular as a shape of a molded article, Arbitrary shapes, such as spherical shape, ring shape, cylindrical shape, and star shape, are mentioned.

[Heat treatment process]
In this step, the catalyst can be obtained by heat-treating the dried product or the molded product of the dried product. The heat treatment conditions are not particularly limited, and known heat treatment conditions can be applied. The heat treatment is usually performed at 200 to 500 ° C., preferably 300 to 450 ° C., for 0.5 hours or more, preferably 1 to 40 hours under the flow of an oxygen-containing gas such as air and / or an inert gas. .

  The catalyst for producing methacrylic acid according to the present invention as described above is a catalyst capable of producing methacrylic acid in high yield by gas phase catalytic oxidation of methacrolein with molecular oxygen.

<Method for producing methacrylic acid>
The method for producing methacrylic acid of the present invention is characterized in that methacrylic acid is produced by gas phase catalytic oxidation of methacrolein with molecular oxygen using the methacrylic acid production catalyst of the present invention.

  Specifically, methacrylic acid is produced by bringing a raw material gas containing methacrolein and molecular oxygen into contact with the catalyst of the present invention. This reaction is usually carried out in a fixed bed. Further, the catalyst layer may be one layer or two or more layers. The catalyst for producing methacrylic acid may be supported on a carrier, or may be a mixture of other additive components.

  The concentration of methacrolein in the raw material gas can be varied within a wide range, preferably 1 to 20% by volume, more preferably 3 to 10% by volume. The methacrolein may contain a small amount of impurities such as water and lower saturated aldehyde that do not substantially affect this reaction.

  The concentration of molecular oxygen in the raw material gas is preferably 0.4 to 4 mol, more preferably 0.5 to 3 mol, per 1 mol of methacrolein. The molecular oxygen source is preferably air from the viewpoint of economy. If necessary, a gas or the like enriched with molecular oxygen by adding pure oxygen to air may be used.

  The source gas may be obtained by diluting methacrolein and a molecular oxygen source with an inert gas such as nitrogen or carbon dioxide. Further, water vapor may be added to the source gas. By performing the reaction in the presence of water, methacrylic acid can be obtained in a higher yield. The concentration of water vapor in the raw material gas is preferably from 0.1 to 50% by volume, particularly preferably from 1 to 40% by volume.

  The contact time between the raw material gas and the catalyst for producing methacrylic acid is preferably 1.5 to 15 seconds, and more preferably 2 to 5 seconds.

  The reaction pressure is preferably atmospheric pressure (0.1 MPa-G) to several atmospheres (for example, 1 MPa-G). The reaction temperature is preferably 200 to 450 ° C, particularly preferably 250 to 400 ° C.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention in detail, this invention is not limited to these Examples. “Parts” in Examples and Comparative Examples means parts by mass.

  The catalyst composition was calculated by analyzing components dissolved in aqueous ammonia by ICP emission analysis and atomic absorption spectrometry.

The analysis of the raw material gas and the product was performed using gas chromatography. From the results of gas chromatography, the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined by the following formula.
Reaction rate of methacrolein (%) = (B / A) × 100
Methacrylic acid selectivity (%) = (C / B) × 100
Methacrylic acid yield (%) = (C / A) × 100
In the formula, A is the number of moles of methacrolein supplied, B is the number of moles of reacted methacrolein, and C is the number of moles of methacrylic acid produced.

[Example 1]
In 680 parts of pure water, 101.2 parts of phosphovanadomolybdic acid, 100 parts of molybdenum trioxide, 12.8 parts of 60% by weight aqueous arsenic acid solution and 2.6 parts of copper (II) nitrate trihydrate were dissolved. The mixture was heated to 95 ° C. while stirring and stirred for 3 hours while maintaining the liquid temperature at 95 ° C. After cooling to 50 ° C., 21.0 parts of cesium bicarbonate dissolved in 34 parts of pure water and 19.7 parts of ammonium nitrate dissolved in 34 parts of pure water were added dropwise while stirring with a rotary blade stirrer. After the salt was precipitated, the mixture was stirred for 15 minutes. The precipitated heteropolyacid salt had a Keggin type structure. 7.4 parts of 85 mass% phosphoric acid aqueous solution was dripped at this solution, and also it stirred for 15 minutes.

  The resulting mixture was heated to 101 ° C. and evaporated to dryness with stirring. The heteropolyacid (salt) in the obtained dried product had a Keggin type structure. The dried product was further dried at 130 ° C. for 16 hours, and then shaped by pressure molding. The obtained shaped product was heat-treated at 380 ° C. for 5 hours under air flow. The elemental composition other than oxygen (hereinafter the same) of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
The catalyst was filled in a reaction tube, and a raw material gas containing 5% by volume of methacrolein, 10% by volume of oxygen, 30% by volume of steam, and 55% by volume of nitrogen was passed at a reaction temperature of 290 ° C. and a contact time of 3.6 seconds. The product was collected and analyzed by gas chromatography to determine methacrolein reaction rate, methacrylic acid selectivity, and methacrylic acid yield. The results are shown in Table 1.

[Comparative Example 1]
A catalyst was produced in the same manner as in Example 1 except that 7.4 parts of 85 mass% phosphoric acid aqueous solution was added in the preparation step, not after the precipitation step. That is, 680 parts of pure water, 101.2 parts of phosphovanadomolybdic acid, 100 parts of molybdenum trioxide, 7.4 parts of 85 mass% phosphoric acid aqueous solution, 12.8 parts of 60 mass% arsenic acid aqueous solution, and copper (II) nitrate 2.6 parts of trihydrate was dissolved, and this was heated to 95 ° C. while stirring, and stirred for 3 hours while maintaining the liquid temperature at 95 ° C. After cooling to 50 ° C., 21.0 parts of cesium bicarbonate dissolved in 34 parts of pure water and 19.7 parts of ammonium nitrate dissolved in 34 parts of pure water were added dropwise while stirring with a rotary blade stirrer. After the salt was precipitated, the mixture was stirred for 15 minutes. The precipitated heteropolyacid salt had a Keggin type structure.

  The resulting mixture was heated to 101 ° C. and evaporated to dryness with stirring. The heteropolyacid (salt) in the obtained dried product had a Keggin type structure. The dried product was shaped in the same manner as in Example 1 and heat treated to produce a catalyst. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

[Example 2]
In 400 parts of pure water, 100 parts of molybdenum trioxide, 3.1 parts of ammonium metavanadate, 7.5 parts of 60% by weight aqueous arsenic acid solution and 1.5 parts of copper (II) nitrate trihydrate were dissolved. The temperature was raised to 95 ° C. while stirring, and the mixture was stirred for 3 hours while maintaining the liquid temperature at 95 ° C. After cooling to 50 ° C., 12.4 parts of cesium bicarbonate dissolved in 20 parts of pure water and 11.6 parts of ammonium nitrate dissolved in 20 parts of pure water were added dropwise while stirring with a rotary blade stirrer, and the heteropolyacid After the salt was precipitated, the mixture was stirred for 15 minutes. The precipitated heteropolyacid salt had a Keggin type structure. To this solution, 7.3 parts of an 85 mass% phosphoric acid aqueous solution was dropped, and the mixture was further stirred for 15 minutes.

  The resulting mixture was heated to 101 ° C. and evaporated to dryness with stirring. The heteropolyacid (salt) in the obtained dried product had a Keggin type structure. The dried product was shaped in the same manner as in Example 1 and heat treated to produce a catalyst. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

[Comparative Example 2]
A catalyst was produced in the same manner as in Example 2 except that 7.3 parts of 85 mass% phosphoric acid aqueous solution was added in the preparation step, not after the precipitation step. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 3
A catalyst was prepared in the same manner as in Example 2 except that 3.1 parts of ammonium metavanadate was changed to 2.4 parts of vanadium pentoxide. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

[Comparative Example 3]
A catalyst was produced in the same manner as in Example 3 except that 7.3 parts of 85 mass% phosphoric acid aqueous solution was added in the preparation step, not after the precipitation step. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 4
In 340 parts of pure water, 101.2 parts of phosphovanadomolybdic acid, 100 parts of molybdenum trioxide and 12.8 parts of 60% by mass aqueous arsenic acid solution were dissolved, and the temperature was raised to 95 ° C. while stirring. The mixture was stirred for 3 hours while maintaining at 95 ° C. After cooling to 50 ° C., 21.1 parts of cesium nitrate dissolved in 34 parts of pure water was added while stirring with a rotary blade stirrer. Subsequently, the liquid temperature was raised to 70 ° C., 61.7 parts of aqueous ammonia was added to precipitate the heteropolyacid salt, and the mixture was stirred at 70 ° C. for 30 minutes. The precipitated heteropolyacid salt had a Dawson type structure. 7.4 parts of 85 mass% phosphoric acid aqueous solution was dripped at this solution, and also it stirred for 15 minutes, and added 2.6 parts of copper (II) nitrate trihydrate.

  The resulting mixture was heated to 101 ° C. and evaporated to dryness with stirring. The heteropolyacid (salt) in the obtained dried product had a Dawson type structure. The dried product was further dried at 130 ° C. for 16 hours, and then shaped by pressure molding. The obtained shaped product was heat-treated at 380 ° C. for 5 hours under air flow. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 5
200 parts of pure water, 100 parts of molybdenum trioxide, 6.1 parts of ammonium metavanadate, 11.0 parts of 60% by weight aqueous arsenic acid solution, 7.5 parts of cerium (III) nitrate hexahydrate and copper (II) nitrate 3.4 parts of the trihydrate was dissolved, heated to 95 ° C. while stirring, and stirred for 3 hours while maintaining the liquid temperature at 95 ° C. After cooling to 50 ° C., stirring with a rotary blade stirrer, 13.5 parts of cesium bicarbonate dissolved in 22 parts of pure water, 3.1 parts of rubidium nitrate dissolved in 6.0 parts of pure water, and pure water 16 After 7.2 parts of ammonium carbonate dissolved in the part was added dropwise to precipitate the heteropolyacid salt, the mixture was stirred for 15 minutes. The precipitated heteropolyacid salt had a Keggin type structure. To this solution, 4.0 parts of an 85 mass% phosphoric acid aqueous solution was added dropwise, and the mixture was further stirred for 15 minutes.

  The resulting mixture was heated to 101 ° C. and evaporated to dryness with stirring. The heteropolyacid (salt) in the obtained dried product had a Keggin type structure. The dried product was shaped in the same manner as in Example 1 and heat treated to produce a catalyst. The elemental composition of the obtained catalyst was as follows.

Mo ₁₂ V _0.9 P _0.6 As _0.8 Ce _0.3 Cu _0.24 Cs _1.2 Rb _0.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

[Comparative Example 4]
A catalyst was produced in the same manner as in Example 5, except that 4.0 parts of an 85 mass% phosphoric acid aqueous solution was added in the preparation step, not after the precipitation step. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

Mo ₁₂ V _0.9 P _0.6 As _0.8 Ce _0.3 Cu _0.24 Cs _1.2 Rb _0.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 6
200 parts of pure water, 100 parts of molybdenum trioxide, 0.68 parts of ammonium metavanadate, 8.4 parts of antimony trioxide, 3.4 parts of cobalt (II) nitrate hexahydrate and copper (II) nitrate trihydrate 0.84 parts of the product was dissolved, the temperature was raised to 95 ° C. while stirring, and the mixture was stirred for 3 hours while maintaining the liquid temperature at 95 ° C. After cooling to 50 ° C., 16.8 parts of cesium bicarbonate dissolved in 27 parts of pure water and 11.6 parts of ammonium nitrate dissolved in 20 parts of pure water were added dropwise while stirring with a rotary blade stirrer, and the heteropolyacid After the salt was precipitated, the mixture was stirred for 15 minutes. The precipitated heteropolyacid salt had a Keggin type structure. To this solution, 8.7 parts of an 85 mass% phosphoric acid aqueous solution was dropped, and the mixture was further stirred for 15 minutes.

  The resulting mixture was heated to 101 ° C. and evaporated to dryness with stirring. The heteropolyacid (salt) in the obtained dried product had a Keggin type structure. The dried product was shaped in the same manner as in Example 1 and heat treated to produce a catalyst. The elemental composition of the obtained catalyst was as follows.

Mo ₁₂ V _0.1 P _1.3 Sb _1.0 Cu _0.06 Co _0.2 Cs _1.5 Rb _0.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

[Comparative Example 5]
A catalyst was produced in the same manner as in Example 6 except that 8.7 parts of 85 mass% phosphoric acid aqueous solution was added in the preparation step, not after the precipitation step. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

Mo ₁₂ V _0.1 P _1.3 Sb _1.0 Cu _0.06 Co _0.2 Cs _1.5 Rb _0.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 7
In 200 parts of pure water, 100 parts of molybdenum trioxide, 6.1 parts of ammonium metavanadate, 10.4 parts of 20% by mass silica sol (solvent: water) and 4.2 parts of copper (II) nitrate trihydrate were dissolved. The mixture was heated to 95 ° C. while stirring, and stirred for 3 hours while maintaining the liquid temperature at 95 ° C. After cooling to 50 ° C., while stirring with a rotary blade stirrer, 6.7 parts of cesium bicarbonate dissolved in 11 parts of pure water and 11.6 parts of ammonium nitrate dissolved in 20 parts of pure water were added dropwise to form a heteropolyacid. After the salt was precipitated, the mixture was stirred for 15 minutes. The precipitated heteropolyacid salt had a Keggin type structure. To this solution, 4.7 parts of an 85 mass% phosphoric acid aqueous solution was added dropwise, and the mixture was further stirred for 15 minutes.

  The resulting mixture was heated to 101 ° C. and evaporated to dryness with stirring. The heteropolyacid (salt) in the obtained dried product had a Keggin type structure. The dried product was shaped in the same manner as in Example 1 and heat treated to produce a catalyst. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.9 P 0.7 Si 0.6} Cu 0.3 Cs 0.6
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

[Comparative Example 6]
A catalyst was produced in the same manner as in Example 7, except that 4.7 parts of 85 mass% phosphoric acid aqueous solution was added in the preparation step, not after the precipitation step. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.9 P 0.7 Si 0.6} Cu 0.3 Cs 0.6
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 8
200 parts pure water, 100 parts molybdenum trioxide, 7.5 parts ammonium metavanadate, 26.1 parts 20% silica sol (solvent: water), 2.3 parts iron (III) nitrate nonahydrate and copper nitrate (II) 4.2 parts of the trihydrate was dissolved, heated to 95 ° C. while stirring, and stirred for 3 hours while maintaining the liquid temperature at 95 ° C. After cooling to 50 ° C., 12.4 parts of cesium bicarbonate dissolved in 20 parts of pure water and 11.6 parts of ammonium nitrate dissolved in 20 parts of pure water were added dropwise while stirring with a rotary blade stirrer, and the heteropolyacid After the salt was precipitated, the mixture was stirred for 15 minutes. The precipitated heteropolyacid salt had a Keggin type structure. 11.4 parts of 85 mass% phosphoric acid aqueous solution was dripped at this solution, and also it stirred for 15 minutes.

  The resulting mixture was heated to 101 ° C. and evaporated to dryness with stirring. The heteropolyacid (salt) in the obtained dried product had a Keggin type structure. The dried product was shaped in the same manner as in Example 1 and heat treated to produce a catalyst. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 1.1 P 1.7 Si 1.5} Cu 0.3 Fe 0.1 Cs 1.1 Rb 0.3
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

[Comparative Example 7]
A catalyst was produced in the same manner as in Example 8, except that 11.4 parts of 85 mass% phosphoric acid aqueous solution was added in the preparation step, not after the precipitation step. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 1.1 P 1.7 Si 1.5} Cu 0.3 Fe 0.1 Cs 1.1 Rb 0.3
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 9
In 200 parts of pure water, 100 parts of molybdenum trioxide, 3.1 parts of ammonium metavanadate, 7.5 parts of 60% by weight aqueous arsenic acid solution and 1.5 parts of copper (II) nitrate trihydrate were dissolved. The temperature was raised to 95 ° C. while stirring, and the mixture was stirred for 3 hours while maintaining the liquid temperature at 95 ° C. After cooling to 50 ° C., while maintaining at 50 ° C., stirring with a rotary blade stirrer, 32.4 parts of a solution obtained by dissolving 12.4 parts of cesium bicarbonate in 20 parts of pure water was 1.62 per minute. Then, 11.6 parts of ammonium nitrate dissolved in 20 parts of pure water was added dropwise to precipitate the heteropolyacid salt, followed by stirring for 15 minutes. The precipitated heteropolyacid salt had a Keggin type structure. While maintaining this solution at 50 ° C. while stirring using a rotary blade stirrer, 7.3 parts of 85 mass% phosphoric acid aqueous solution was added dropwise, and the mixture was further stirred for 15 minutes. After cooling to 30 ° C., it was allowed to stand for 30 minutes.

  The resulting mixture was heated to 101 ° C. and evaporated to dryness with stirring. The heteropolyacid (salt) in the obtained dried product had a Keggin type structure. The dried product was shaped in the same manner as in Example 1 and heat treated to produce a catalyst. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 10
A catalyst was produced in the same manner as in Example 9, except that the aqueous slurry cooling temperature in the precipitation step was changed to 30 ° C and the aqueous slurry temperature until the phosphorus addition step was changed to 30 ° C. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 11
A catalyst was produced in the same manner as in Example 9, except that the aqueous slurry cooling temperature in the precipitation step was changed to 70 ° C and the aqueous slurry temperature until the phosphorus addition step was maintained at 70 ° C. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 12
Implementation was performed except that the solution added in the precipitation step was changed to 43.8 parts of a solution obtained by dissolving 16.8 parts of cesium bicarbonate in 27 parts of pure water and added at a rate of 0.876 parts per minute. A catalyst was prepared as in Example 9. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 13
Implementation was performed except that the solution added in the precipitation step was changed to 43.8 parts of a solution obtained by dissolving 16.8 parts of cesium bicarbonate in 27 parts of pure water and added at a rate of 26.3 parts per minute. A catalyst was prepared as in Example 9. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 14
A catalyst was produced in the same manner as in Example 9 except that 7.3 parts of 85 mass% phosphoric acid aqueous solution was dissolved in 20 parts of pure water and dropped. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 15
A catalyst was produced in the same manner as in Example 9, except that 7.3 parts of an 85 mass% phosphoric acid aqueous solution was dissolved in 100 parts of pure water and dropped. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 16
A catalyst was produced in the same manner as in Example 9, except that the standing time after cooling to 30 ° C was changed to 2 days. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

Example 17
A catalyst was produced in the same manner as in Example 9 except that the standing time after cooling to 30 ° C was changed to 7 days. In addition, the heteropolyacid salt precipitated in the precipitation step had a Keggin type structure, and the heteropolyacid (salt) in the dried product obtained in the drying step had a Keggin type structure. The elemental composition of the obtained catalyst was as follows.

_{Mo 12 V 0.45 P 1.1 As 0.55} Cu 0.11 Cs 1.1
Except for using this catalyst, methacrylic acid was produced in the same manner as in Example 1, and the reaction rate of methacrolein, the selectivity of methacrylic acid, and the yield of methacrylic acid were determined. The results are shown in Table 1.

  From the above results, after depositing the heteropolyacid salt, the phosphorus raw material was added, and then in Examples 1 to 3 and 5 to 17 in which the heteropolyacid (salt) in the dried product has a Keggin-type structure, Also, the selectivity of methacrylic acid was increased, and methacrylic acid could be produced with a high yield. On the other hand, in Comparative Examples 1 to 7 in which the phosphorus raw material was added before the heteropolyacid salt was precipitated, the selectivity for methacrylic acid was lowered. In addition, the phosphorus raw material was added after the heteropolyacid salt was precipitated, but in Example 4 where the heteropolyacid (salt) in the dried product had a Dawson-type structure, the selectivity of methacrylic acid increased, but the catalytic activity Had fallen.

  The catalyst for producing methacrylic acid of the present invention has high selectivity for methacrylic acid and is useful for producing methacrylic acid.

Claims (6)

Phosphorus element, molybdenum element, X element (selected from the group consisting of silicon, titanium, germanium, arsenic, antimony and cerium) used in the production of methacrylic acid by vapor phase catalytic oxidation of methacrolein with molecular oxygen A method for producing a catalyst comprising at least one element) and an alkali metal element,
(I) adding at least a molybdenum raw material and an X element raw material in water to prepare an aqueous slurry or aqueous solution containing a heteropolyacid;
(Ii) adding an alkali metal compound to the aqueous slurry or aqueous solution to precipitate a heteropolyacid salt in which at least a part of the heteropolyacid is an alkali metal salt;
(Iii) adding a phosphorus raw material that is at least one selected from the group consisting of normal phosphoric acid, phosphorus pentoxide and ammonium phosphate to the aqueous slurry or aqueous solution in which the heteropolyacid salt is deposited;
(Iv) drying an aqueous slurry or aqueous solution containing all raw materials to obtain a dried product;
(V) A method for producing a catalyst for producing methacrylic acid, comprising a step of heat-treating the dried product.   The total mass of the raw materials used in the step (i): (the mass of water used in the step (i)) is 1: 0.5 to 1:15. The manufacturing method of the catalyst for methacrylic acid manufacture of description.   The method for producing a methacrylic acid production catalyst according to claim 1 or 2, wherein the heteropolyacid salt precipitated in the step (ii) has a Keggin type structure.   The method for producing a methacrylic acid production catalyst according to any one of claims 1 to 3, wherein the heteropolyacid and the heteropolyacid salt in the dried product have a Keggin type structure.   The method for producing a catalyst for methacrylic acid production according to any one of claims 1 to 4, wherein the dried product is shaped, and the obtained shaped product is heat-treated. A methacrylic acid production catalyst is produced by the method for producing a methacrylic acid production catalyst according to any one of claims 1 to 5 , and methacrolein is vapor-phase catalytically oxidized with molecular oxygen using the catalyst to produce methacrylic acid. A process for producing methacrylic acid.