JP4601420B2 - Method for producing a catalyst for methacrylic acid production - Google Patents

Description

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

  In Patent Document 1, a solution or slurry containing at least molybdenum, phosphorus and vanadium and a solution or slurry containing an ammonia compound are mixed, and a solution or slurry containing Z element is mixed with the resulting mixed solution or slurry, A method for producing a catalyst for methacrylic acid production comprising a step of drying to obtain a dried product is disclosed.

  In addition, Patent Document 2 includes a step of adding water to an aqueous solution of a catalyst raw material and then removing water by a method such as heating after adding urea, a derivative of urea and / or ammonium nitrate, and heat treating the residue (dried product). A method for producing a catalyst for acid production is disclosed.

JP 2000-296336 A Japanese Patent Laid-Open No. 02-119942

  However, in such a conventional manufacturing method, there are cases where the dry matter obtained in the manufacturing process has poor fluidity and is difficult to handle. For example, when transporting dry powder, there is a problem that the dry powder forms a bridge with a hopper and does not flow easily, and the dry powder does not flow smoothly into a mold for tableting or press molding. . In addition, even when the flowability of the dried product is relatively good, there is a problem that the performance of the catalyst, particularly the yield of methacrylic acid, is not sufficient as an industrial catalyst.

  Therefore, an object of the present invention is a method for producing a catalyst used for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen, and the flowability of the dried product obtained in the production process is excellent. The present invention also provides a method for producing a catalyst capable of producing methacrylic acid in high yield, a catalyst obtained by the production method, and a method capable of producing methacrylic acid using the catalyst in high yield. .

The inventors of the present invention can improve the fluidity of the dried product by causing precipitation from a solution containing molybdenum, phosphorus and vanadium under specific conditions, and can improve the yield of the resulting catalyst. To solve the above problem.
That is, the present invention is a method for producing a catalyst having a composition represented by the following formula (1), which is used in producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen,
_{P a Mo b V c Cu d} X e Y f Z g O h (1)
(In the formula (1), P, Mo, V, Cu and O represent phosphorus, molybdenum, vanadium, copper and oxygen, respectively, and X represents antimony, bismuth, arsenic, germanium, zirconium, tellurium, silver, selenium and silicon. , At least one element selected from the group consisting of tungsten and boron, Y is at least selected from the group consisting of iron, zinc, chromium, magnesium, tantalum, cobalt, manganese, barium, gallium, cerium and lanthanum Z represents at least one element selected from the group consisting of potassium, rubidium and cesium, a, b, c, d, e, f, g and h are atomic ratios of the respective elements When b = 12, a = 0.5-3, c = 0.01-3, d = 0.01-2, e = 0-3, f = 0-3, = Is 0.01 to 3, h is an atomic ratio of oxygen required to satisfy the valence of each component.)
A production method comprising the following steps (i) to (iv):
(I) Prepare a solution or slurry (liquid a) containing at least molybdenum, phosphorus, vanadium and urea, each element of molybdenum, phosphorus and vanadium, and 90 mol% or more of urea being distributed to the solution side Process,
(Ii) The temperature of the liquid a is set to 60 ° C. or higher, does not exceed 100 ° C. during a period of 60 ° C. or higher, and the ammonium ion production coefficient defined by the following formula (2) is 0. A step of preparing a slurry (liquid A) by causing precipitation in the liquid under the conditions of 01 to 0.7 mol-NH ₄ ⁺ / (hr · L · mol-Mo);
Ammonium ion formation coefficient [mol-NH ₄ ⁺ / (hr · L · mol-Mo)] = x / (t × y × z) (2)
t: Period when the liquid temperature is 60 ° C. or higher (heating period) [hour]
x: Amount of ammonium ion generated during heating period [mol-NH ₄ ⁺ ]
y: Volume of liquid a [L]
z: Molybdenum atom content in liquid a [mol-Mo]
(Iii) A step of preparing a slurry (liquid C) by mixing liquid A or liquid derived from liquid A and a compound of element Z,
(Iv) Step of drying C liquid or liquid derived from C liquid

  The present invention is also a method for producing methacrylic acid, in which a catalyst is produced by the above-described method, and methacrolein is vapor-phase contact oxidized with molecular oxygen in the presence of the obtained catalyst.

  ADVANTAGE OF THE INVENTION According to this invention, the fluidity | liquidity of the dry matter obtained in a manufacturing process can be improved in the manufacturing method of the catalyst used when vapor-phase catalytic oxidation of methacrolein is carried out with molecular oxygen, and methacrylic acid is manufactured. . Moreover, according to this invention, the catalyst which can manufacture methacrylic acid with a high yield can be manufactured.

  Hereinafter, the method for producing a catalyst for producing methacrylic acid of the present invention (hereinafter sometimes simply referred to as a catalyst) will be described in more detail.

  The catalyst produced in the present invention has the composition of the above formula (1), and is composed of phosphorus, molybdenum, vanadium, copper, Z element and oxygen as essential components, and X element and Y element. Is an optional component. As the Z element, cesium is preferable. The atomic ratio (a and c to g) of each element in the target catalyst can be arbitrarily set within the above range by appropriately adjusting the blending ratio of each raw material to be described later. The atomic ratio (composition ratio) other than oxygen of the catalyst can be analyzed, for example, by analyzing the catalyst dissolved in aqueous ammonia by ICP emission spectrometry and atomic absorption spectrometry.

  The method for producing a catalyst of the present invention includes the steps (i) to (iv).

  In step (i), the solution a is prepared by dissolving at least each of a molybdenum compound, a vanadium compound, a phosphorus compound, and urea compounds in a solvent. In the liquid a, each element of molybdenum, phosphorus and vanadium, and 90 mol% or more of ureas must be distributed to the solution side (hereinafter referred to as condition 1), preferably 95 mol% or more, particularly preferably 100 mol%. That is, it is particularly preferable that the liquid a is dissolved in the total amount of each of these elements and compounds and is not contained on the solid side. The greater the proportion of each element and compound distributed to the solution side, the greater the amount of precipitate produced in the step (ii) described later, and the fluidity of the dry matter obtained in the process of (iv) step increases. The mixing method of each compound at the time of preparing this solution is not specifically limited. Examples of the mixing method include a method of dissolving the compounds in the solution simultaneously or sequentially, a method of dissolving the compounds separately and then mixing these solutions.

  Examples of the molybdenum compound that can be used include phosphomolybdic acid, ammonium molybdate, and molybdenum trioxide. Of these, phosphomolybdic acid and ammonium molybdate are preferred because of their high solubility.

  Examples of vanadium compounds that can be used include ammonium metavanadate, vanadyl oxalate, phosphovanadomolybdic acid, vanadium carbide, and vanadium pentoxide. Of these, ammonium metavanadate, vanadyl oxalate, and phosphovanadomolybdic acid are preferred because of their high solubility.

  Examples of the phosphorus compound that can be used include phosphomolybdic acid, phosphovanadomolybdic acid, phosphoric acid, diphenyl phosphate, triphenyl phosphate, and urea phosphate. A salt such as ammonium phosphate can also be used. Of these, phosphomolybdic acid, phosphovanadomolybdic acid and phosphoric acid are preferred because of their high solubility and low cost.

  Ureas that can be used are urea and urea derivatives. Here, the “urea derivative” is a general term for a substance in which at least one hydrogen atom bonded to the nitrogen atom of urea is replaced with another atomic group. Examples of such ureas include urea, methylurea, methylurea salt, N, N-dimethylurea, allylurea, N-benzylurea and the like. Of these, urea, methylurea, and N, N-dimethylurea are preferable because they are inexpensive.

  A molybdenum compound, a vanadium compound, a phosphorus compound, and ureas may be used alone or in combination of two or more.

  The combination and amount of each compound used as the raw material for the liquid a are appropriately selected so as to satisfy the condition 1. The liquid a may contain compounds other than molybdenum compounds, vanadium compounds, phosphorus compounds, and ureas. Examples of such compounds include X element (at least one element selected from the group consisting of antimony, bismuth, arsenic, germanium, zirconium, tellurium, silver, selenium, silicon, tungsten, and boron) and Y element (iron , Zinc, chromium, magnesium, tantalum, cobalt, manganese, barium, gallium, cerium and lanthanum), and salts and oxides.

  In addition, the solution a may contain at least one element selected from the group consisting of element Z, that is, potassium, rubidium and cesium. Therefore, there is a case where the condition 1 is not satisfied. For this reason, it is preferable that the amount of the Z element in the liquid a is small, and it is particularly preferable not to include it.

  What is necessary is just to set suitably the compounding ratio of these compounds so that it may become the composition of the target catalyst. Molybdenum compound, phosphorus compound and vanadium compound are preferably included in the liquid a because it is easy to prepare. However, only a part is included in the liquid a and the remainder is added at the same time as the compound of element Z described later. Or may be added to the precursor mixture.

  The solvent of the liquid a is not particularly limited as long as it is a compound that can dissolve a compound that becomes a solute. Examples of such a solvent include water and alcohol. Of these, water is preferred. Although the quantity of a solvent will not be specifically limited if it is the quantity which can melt | dissolve the compound used as a solute, 0.1-100 mass parts is preferable with respect to 1 mass part of molybdenum contained in a liquid.

  Although the temperature of the liquid at the time of preparing the liquid a is not particularly limited when ureas are not included, it is set to less than 60 ° C. at which the ureas are not substantially decomposed after the ureas are included. The temperature of the solution a after the preparation is such that 90 mol% or more of each element and compound of molybdenum, phosphorus, vanadium, and urea are distributed to the solution side.

In step (ii), the temperature of the liquid a is set to 60 ° C. or higher so that it does not exceed 100 ° C. during the period of 60 ° C. Is 0.01 to 0.7 mol-NH ₄ ⁺ / (hr · L · mol-Mo) (hereinafter referred to as condition 2), preferably 0.05 to 0.6 mol-NH ₄ ⁺ / (hr · Under the condition of (L · mol-Mo), ureas are decomposed and ammonium ions are generated in the liquid a, thereby forming a precipitate containing molybdenum and phosphorus. In this way, slurry A liquid is produced. The higher the ammonium ion production coefficient, the better the catalyst with excellent reaction results, and the lower the ammonium ion production coefficient, the more dry powder with excellent fluidity.

In the formula (2), t (heating period) is a period when the liquid temperature is 60 ° C. or more (unit: time), x is the amount of ammonium ions generated during the heating period (unit: mol-NH ₄ ⁺ ), y is a The volume of the liquid (unit: L), z is the amount of molybdenum atoms contained in the liquid a (unit: mol-Mo). x is calculated from the pH value of the liquid at the start of heating and the pH value of the liquid at the end of heating, assuming that all pH changes are due to ammonium ions. The pH is measured on a sample obtained by sampling a part of the liquid and cooling to 30 ° C. z can be obtained by calculation from the amount of the molybdenum compound used in the preparation of solution a.

  In this step, it is preferable to operate so that the liquid “a” of less than 60 ° C. is heated and kept at a temperature in the range of 60 to 100 ° C. for a certain period of time when the temperature of the solution becomes 60 ° C. or higher. . The holding temperature at that time is preferably 65 to 90 ° C. Moreover, after setting the temperature of a liquid to 60 degreeC or more, it can also be 60-100 degreeC intermittently so that it may be set to less than 60 degreeC and 60 degreeC or more again. In this case, the total period of the period in which the temperature of the liquid is in the range of 60 to 100 ° C. is set as the heating period. The higher the holding temperature, the better the catalyst with excellent reaction results, and the lower the temperature, the more dry powder with excellent fluidity. The heating period is preferably 1 to 30 hours, more preferably 1.5 to 18 hours. The longer the heating period, the more the reaction between the catalyst raw materials can proceed, and the shorter the heating period, the more agglomerated precipitated particles can be suppressed.

  The reason for improving the methacrylic acid yield of the catalyst obtained by improving the fluidity of the dried product obtained in the step (iv) by performing the step (ii) is not clear. However, it is estimated that the reason why the fluidity of the dry powder is improved is that, by treating the liquid “a” under the condition 2, the generation rate of ammonium ions is controlled and precipitation with a large median diameter is obtained. The reason why the methacrylic acid yield of the catalyst is improved is presumed that this precipitate contains a crystal structure preferable as a catalyst precursor.

  In step (iii), A liquid or a liquid derived from A liquid (these are collectively referred to as A liquid) and a compound of Z element are mixed to prepare a slurry (hereinafter referred to as C liquid). The compound of element Z (catalyst raw material) may be mixed with liquid A or the like, for example, in a powder state without being dissolved or suspended in the liquid, but the solution dissolved in the liquid or the suspended slurry (collectively It is preferable to mix with A liquid or the like as B liquid) in that a catalyst having excellent reaction results can be obtained, and B liquid is mixed with A liquid or the like in a solution state in that a catalyst with a uniform composition can be obtained. It is particularly preferred.

  Here, the liquid derived from the liquid A is a liquid obtained by adding various compounds to the liquid A or performing various treatments on the liquid A. Examples of compounds that can be added to the liquid A include copper compounds, antimony compounds, bismuth compounds, arsenic compounds, germanium compounds, zirconium compounds, tellurium compounds, silver compounds, selenium compounds, silicon compounds, tungsten compounds, boron compounds, irons. Examples thereof include compounds, zinc compounds, chromium compounds, magnesium compounds, tantalum compounds, cobalt compounds, manganese compounds, barium compounds, gallium compounds, cerium compounds, and lanthanum compounds. Any number of compounds may be added. The properties of the compound when added are not particularly limited, and examples thereof include solid powder and liquid. Moreover, you may add in the state melt | dissolved or suspended in liquids, such as water. Examples of the treatment that can be applied to the liquid A include heating, cooling, stirring, and aging.

  The mixing method is not particularly limited. For example, the method of adding the B solution to the container containing the A solution, the method of adding the heated A solution to the container containing the B solution, the A solution and the B solution in the container at the same time. Any method, such as an adding method, can be used. The mixing is preferably performed while stirring. The preparation temperature of the precursor mixed solution is not particularly limited, but may be prepared while heating to about 100 ° C. and stirring as necessary.

  Examples of Z element compounds that can be used include nitrates, carbonates, hydroxides, and the like. Specifically, when the Z element is cesium, they are cesium nitrate, cesium carbonate, cesium hydroxide, and the like. The compound of Z element may use 1 type, or may use 2 or more types together. Moreover, the kind of Z element may be one kind, or two or more kinds. When the element Z is cesium, a catalyst having a longer life can be obtained. What is necessary is just to set suitably the quantity of the compound of Z element so that it may become the composition of the target catalyst.

  When mixing the liquid A and the compound of the Z element, the compound of the element (excluding oxygen) included in the composition of the formula (1) may be mixed at the same time. In this case, these compounds can be contained in the B liquid, but it is preferable that the B liquid does not substantially contain any catalyst raw material other than the Z element compound.

  As a liquid used when preparing B liquid, water, alcohol, etc. are mentioned, for example. Of these, water is preferred. Although the quantity of a liquid is not specifically limited, It is preferable that it is 0.1-100 mass parts with respect to 1 mass part of all the catalyst raw materials contained in B liquid. Liquid B is preferably prepared by stirring at room temperature, but it may be prepared by appropriately heating to about 50 ° C.

  The liquid C thus obtained may further be mixed with a compound of an element (excluding oxygen) contained in the composition of the formula (1). In that case, it is preferable to mix with the solution or slurry of these compounds. The slurry and C liquid thus obtained are collectively referred to as C liquid and the like hereinafter.

  In step (iv), the liquid C obtained in this way is dried to obtain a dried product. The drying method is not particularly limited, and various drying methods such as an evaporation to dryness method, a spray drying method, a drum drying method, and an airflow drying method can be used. Of these, a drum drying method, a spray drying method, and an air flow drying method are preferable because a powdery dried product that is easy to handle is obtained, and a drum drying method and a spray drying method are particularly preferable. Moreover, conditions, such as temperature at the time of drying, time, are not specifically limited, The dried material according to the objective can be obtained by changing drying conditions suitably.

  The dried product thus obtained may be pulverized if necessary and then directly fired without being molded, but it is preferred to fire the molded product. The molding method is not particularly limited, and various known dry and wet molding methods can be applied. Specific examples of the molding method include tableting molding, press molding, extrusion molding, and granulation molding. The shape of the molded product is not particularly limited, and for example, a desired shape such as a columnar shape, a ring shape, or a spherical shape can be selected. The molding is preferably performed without including a carrier such as silica. In molding, known additives such as graphite and talc may be added.

  The obtained dried product or non-molded product is calcined to obtain the catalyst for producing methacrylic acid of the present invention. When a non-molded dried product is calcined, the obtained calcined product is preferably molded into a catalyst. The firing method and firing conditions are not particularly limited, and known treatment methods and conditions can be applied. Optimum conditions for calcination vary depending on the catalyst raw material, catalyst composition, preparation method, and the like, but are usually 200 to 500 ° C., preferably 300 to 450 under an oxygen-containing gas flow such as air and / or an inert gas flow. It is carried out at 0 ° C. for 0.5 hour or longer, preferably 1 to 40 hours. Here, the inert gas refers to a gas that does not decrease the reaction activity of the catalyst, and specifically includes nitrogen, carbon dioxide, helium, argon, and the like.

  Next, the manufacturing method of methacrylic acid of this invention is demonstrated. The method for producing methacrylic acid of the present invention is a method for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen in the presence of the catalyst of the present invention obtained as described above. The reaction is usually carried out in a fixed bed, and the catalyst layer in that case may be one layer or two or more layers, and the catalyst layer may be obtained by diluting the catalyst with an inert solid such as a diluent carrier. The reaction is carried out by bringing a raw material gas containing methacrolein and molecular oxygen into contact with the catalyst. The concentration of methacrolein in the raw material gas can be varied within a wide range, but is preferably 1 to 20% by volume, particularly 3 to 10% by volume. Although it is economical to use air as the molecular oxygen source, air or the like enriched with pure oxygen can also be used if necessary. The molecular oxygen concentration in the raw material gas is preferably 0.4 to 4 mol, particularly preferably 0.5 to 3 mol, relative to 1 mol of methacrolein. The contact time of the source gas is usually 1.5 to 15 seconds, preferably 2 to 5 seconds. The source gas may contain water vapor. When the reaction is carried out in the presence of water vapor, methacrylic acid is obtained in a higher yield. The concentration of water vapor in the raw material gas is preferably 0.1 to 50% by volume, particularly 1 to 40% by volume. The source gas may contain a small amount of impurities such as lower saturated aldehyde, but the amount is preferably as small as possible. The reaction pressure is from atmospheric pressure to several atmospheres. The reaction temperature is preferably 230 to 450 ° C, particularly preferably 250 to 400 ° C.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples. The amount x of ammonium ions generated during the heating period is based on the pH value of the liquid at the start of heating (when the temperature rises to 60 ° C.) and the pH value of the liquid at the end of the heating (when it reaches 60 ° C. when the temperature decreases). All pH changes were calculated based on ammonium ions. The pH was measured on a sample that was sampled from a portion of the liquid and cooled to 30 ° C. A laser diffraction / scattering method was used to measure the median diameter of the catalyst precursor, and a volume reference was used as the distribution reference. The flowability of the dried product is determined by Carr, R. L. , Chem. Eng. 72. Jan. 18 (1965). The larger the fluidity index, the better the fluidity. Moreover, the reaction rate of methacrolein, the selectivity of the produced | generated methacrylic acid, and the single flow yield of methacrylic acid are defined as follows.
Reaction rate (%) of methacrolein (MAL) = (B / A) × 100
Methacrylic acid (MAA) selectivity (%) = (C / B) × 100
Single flow yield (%) of methacrylic acid (MAA) = (C / A) × 100
Here, 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]
(Preparation of solution a) To 800 g of pure water, 63.2 g of phosphomolybdic acid, 38.5 g of phosphovanadomolybdic acid, 1.02 g of cupric nitrate, 0.85 g of ferric nitrate and 78.44 g of urea were added and stirred. A solution at 25 ° C. was prepared. Liquid a was a uniform solution.

(Preparation of liquid A) The temperature of the liquid a at 25 ° C. was increased while stirring and held at reflux at 80 ° C. for 4 hours to precipitate the catalyst precursor in the liquid. A liquid A was prepared. At this time, the heating period t is 4.2 hours, the amount x of ammonium ions generated during the heating period is 0.37 mol, the volume y of the liquid a is 0.81 L, and the amount z of molybdenum atoms contained in the liquid a is The ammonium ion production coefficient defined by the formula (2) was 0.215 mol-NH ₄ ⁺ / (hr · L · mol-Mo). Moreover, the median diameter of the solid substance in A liquid was 23.8 micrometers.

  (Preparation of Liquid B) Liquid B was prepared by dissolving 8.24 g of cesium nitrate at 25 ° C. in 100 g of pure water.

  (Preparation of Precursor Mixture) A liquid B was added while stirring the liquid A at 50 ° C. to prepare a slurry C liquid.

(Drying / Baking) The liquid C was dried with a drum dryer having a surface temperature of 130 ° C., and the obtained solid content was dried at 130 ° C. for 16 hours to obtain a dried product having a fluidity index of 76. The dried product was tablet-molded into a ring shape having an outer diameter of 4 mm, an inner diameter of 1 mm, and a height of 4 mm, and then calcined at 375 ° C. for 10 hours in an air stream to obtain a catalyst. The composition of the obtained catalyst was P _1.0 Mo ₁₂ V _0.65 Cu _0.15 Fe _0.1 Cs _1.0 .

  (Synthesis reaction of methacrylic acid) The catalyst was charged into a reaction tube, and a mixed gas of 5% methacrolein, 10% oxygen, 30% water vapor, 55% nitrogen (volume%) was reacted at 285 ° C. under atmospheric pressure, A one hour continuous reaction test was conducted with a contact time of 3.6 seconds. Table 2 shows the median diameter of the solid in the liquid A, the fluidity index of the dried product, the catalyst composition produced, and the reaction results of the continuous reaction test.

[Examples 2 to 6]
A catalyst having the same composition was prepared in the same manner as in Example 1 except that the preparation conditions were changed as shown in Table 1, and a continuous reaction test was performed. The results are shown in Table 2.

[Comparative Example 1]
A catalyst having the same composition was prepared in the same manner as in Example 1 except that the preparation conditions were changed as shown in Table 1, and a continuous reaction test was performed. The results are shown in Table 2.

[Comparative Example 2]
A catalyst having the same composition was prepared and subjected to a continuous reaction test in the same manner as in Example 1 except that the amount of pure water used for preparation of solution a was changed to 500 g and the preparation conditions were changed as shown in Table 1. The results are shown in Table 2.

[Comparative Examples 3 and 4]
Prepare a catalyst having the same composition as in Example 1 except that the liquid a was prepared using an autoclave, the amount of pure water used for preparing the liquid a was changed to 450 g, and the preparation conditions were changed as shown in Table 1. Prepared and subjected to continuous reaction test. The results are shown in Table 2.

[Comparative Example 5]
A catalyst having the same composition was prepared and subjected to a continuous reaction test in the same manner as in Example 1 except that the amount of pure water used for preparation of solution a was changed to 450 g and the preparation conditions were changed as shown in Table 1. The results are shown in Table 2.

[Comparative Example 6]
A catalyst having the same composition was prepared and subjected to a continuous reaction test in the same manner as in Example 1 except that the amount of pure water used for preparation of solution a was changed to 2000 g and the preparation conditions were changed as shown in Table 1. The results are shown in Table 2.

[Comparative Example 7]
A catalyst having the same composition was prepared in the same manner as in Example 1 except that the amount of pure water used for preparation of solution a was changed to 770 g and the preparation conditions were changed as shown in Table 1, and a continuous reaction test was performed. The results are shown in Table 2.

Claims (2)

A method for producing a catalyst having a composition represented by the following formula (1), which is used for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen,
_{P a Mo b V c Cu d} X e Y f Z g O h (1)
(In the formula (1), P, Mo, V, Cu and O represent phosphorus, molybdenum, vanadium, copper and oxygen, respectively, and X represents antimony, bismuth, arsenic, germanium, zirconium, tellurium, silver, selenium and silicon. , Y represents at least one element selected from the group consisting of tungsten and boron, Y is at least selected from the group consisting of iron, zinc, chromium, magnesium, tantalum, cobalt, manganese, barium, gallium, cerium and lanthanum Z represents at least one element selected from the group consisting of potassium, rubidium and cesium, a, b, c, d, e, f, g and h are atomic ratios of the respective elements When b = 12, a = 0.5-3, c = 0.01-3, d = 0.01-2, e = 0-3, f = 0-3, = Is 0.01 to 3, h is an atomic ratio of oxygen required to satisfy the valence of each component.)
A production method comprising the following steps (i) to (iv):
(I) Prepare a solution or slurry (liquid a) containing at least molybdenum, phosphorus, vanadium and urea, each element of molybdenum, phosphorus and vanadium, and 90 mol% or more of urea being distributed to the solution side Process,
(Ii) The temperature of the liquid a is set to 60 ° C. or higher, does not exceed 100 ° C. during a period of 60 ° C. or higher, and the ammonium ion production coefficient defined by the following formula (2) is 0. A step of preparing a slurry (liquid A) by causing precipitation in the liquid under the conditions of 01 to 0.7 mol-NH ₄ ⁺ / (hr · L · mol-Mo);
Ammonium ion formation coefficient [mol-NH ₄ ⁺ / (hr · L · mol-Mo)] = x / (t × y × z) (2)
t: Period when the liquid temperature is 60 ° C. or higher (heating period) [hour]
x: Amount of ammonium ion generated during the heating period [mol-NH ₄ ⁺ ]
y: Volume of liquid a [L]
z: Molybdenum atom content in liquid a [mol-Mo]
(Iii) A step of preparing a slurry (liquid C) by mixing liquid A or liquid derived from liquid A and a compound of element Z,
(Iv) Step of drying C liquid or C liquid-derived liquid   A method for producing methacrylic acid, comprising producing a catalyst by the method according to claim 1 and subjecting methacrolein to vapor phase catalytic oxidation with molecular oxygen in the presence of the obtained catalyst.