JP2003171339A - Method for producing methacrylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing methacrylic acid by subjecting methacrolein to gas-phase catalytic oxidation with molecular oxygen to maintain methacrylic acid efficiently over a long period of time. A method for producing an acid is provided. SOLUTION: Each catalyst layer except for the catalyst layer on the most outlet side of the raw material gas is composed of a mixture containing at least two kinds of catalysts represented by the formula (1) and having different atomic ratios of the element X. The catalyst layer, which is the catalyst layer closest to the outlet of the raw material gas, is the catalyst represented by the formula (1), and the catalyst layer containing the catalyst having the same atomic ratio of the X element, or the catalyst layer having the same atomic ratio of the X element. A methacrylic catalyst layer comprising a mixture containing at least two different types of catalysts, wherein the X element-containing mass per unit mass of each catalyst layer decreases from the inlet side to the outlet side of the reactor. Method for producing acid. _{Mo a P b X c Y d} O e (1) ( wherein Mo, P, O are each molybdenum, phosphorus, represents oxygen, X is potassium, rubidium, cesium, represents thallium, Y is iron, cobalt and the like Represents.)

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen.

[0002]

2. Description of the Related Art It is known to use an alkali metal salt of a heteropolyacid containing molybdenum and phosphorus as a catalyst in the production of methacrylic acid by vapor-phase catalytic oxidation of methacrolein. For example, in Japanese Unexamined Patent Publication No. 4-210937, a plurality of catalysts having different activities with different alkali metal composition ratios are individually filled so that the activity becomes higher from the inlet side to the outlet side of the source gas. A method for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein in a catalyst layer is described. This method suppresses heat accumulation in the hot spot portion to prevent deterioration of the catalyst due to heat load, but has a problem that the catalytic activity greatly decreases with time. Further, if the content of the alkali metal in the catalyst is too large, there is a problem that the catalytic activity is lowered, so that further improvement is industrially desired.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen to efficiently maintain a high catalytic activity for a long period of time. Another object of the present invention is to provide a method for producing methacrylic acid.

[0004]

[Means for Solving the Problems] That is, the present invention uses a fixed bed tubular reactor having a catalyst packed portion composed of a plurality of catalyst layers divided from a raw material gas inlet side to a raw gas side, and methacrolein is converted into molecular oxygen. In the method for producing methacrylic acid in which vapor-phase catalytic oxidation is carried out, each catalyst layer except the catalyst layer on the most outlet side of the source gas is the catalyst represented by the formula (1), and at least the atomic ratio of X element is different. A catalyst layer composed of a mixture containing two kinds of catalysts, wherein the catalyst layer on the most outlet side of the source gas is the catalyst represented by the formula (1), and the catalyst contains the same atomic ratio of X elements. A layer, or a catalyst layer comprising a mixture containing at least two types of catalysts having different atomic ratios of X elements, wherein the X element-containing mass contained per unit mass of each catalyst layer is from the inlet side to the outlet side of the reactor. Characterized by less towards It is a manufacturing method of methacrylic acid. Mo _a P _b X _c Y _d O _e (1) (wherein Mo, P and O represent molybdenum, phosphorus and oxygen, respectively, and X is at least 1 selected from the group consisting of potassium, rubidium, cesium and thallium.
Represents a seed element, Y is iron, cobalt, nickel, copper, zinc, magnesium, calcium, strontium, barium, titanium, vanadium, chromium, tungsten, manganese, silver, boron, silicon, aluminum, gallium, germanium, tin, Lead, arsenic, antimony, bismuth, niobium, tantalum, zirconium, indium,
It represents at least one element selected from the group consisting of sulfur, selenium, tellurium, lanthanum and cerium. a,
b, c, d and e represent the atomic ratio of each element, and a = 12
, 0.1 ≦ b ≦ 3, 0.01 ≦ c ≦ 6, 0 ≦ d ≦
3, and e is the atomic ratio of oxygen required to satisfy the atomic ratio of each component. )

In the above invention, each catalyst layer except the catalyst layer on the most outlet side of the source gas is a catalyst layer comprising a mixture containing the catalyst represented by the formula (2) and the catalyst represented by the formula (3). The catalyst layer on the most outlet side of the source gas is a catalyst layer containing the catalyst represented by the formula (2) or a catalyst layer containing a mixture containing the catalyst represented by the formulas (2) and (3). Preferably there is. The mass mixing ratio of the catalysts represented by the equations (2) and (3) in each catalyst layer is 1: α (0.05 ≦ α ≦ 3) in the catalyst layer closest to the inlet side of the source gas, It is preferable that the catalyst layer on the most outlet side has a ratio of 1: β (0 ≦ β ≦ 1 and β <α). _{Mo f P g X h Y i} O j (2) ( wherein, Mo, P, X, Y and O are as defined formula (1).
f, g, h, i and j represent the atomic ratio of each element, and f =
When 12, 0.1 ≦ g ≦ 3, 0.01 ≦ h ≦ 3, 0 ≦
i ≦ 3, and j is the atomic ratio of oxygen required to satisfy the atomic ratio of each component. _{) Mo k P l X m Y} n O o (3) ( wherein, Mo, P, X, Y and O Equation (1) Same as.
k, l, m, n and o represent the atomic ratio of each element, and k =
In the case of 12, 0.1 ≦ l ≦ 3, 1.1 ≦ m ≦ 6 and 0.
1 ≦ (m−h) ≦ 5, 0 ≦ n ≦ 3, and o is the atomic ratio of oxygen required to satisfy the atomic ratio of each component. )

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, methacrolein is vaporized with molecular oxygen by using a fixed bed tubular reactor in which a catalyst packing portion is composed of a plurality of catalyst layers divided from a raw material gas inlet side to a gas outlet side. Catalytic oxidation produces methacrylic acid.

The fixed bed tube type reactor may be a single tube type having only one reaction tube or a multi tube type having a plurality of reaction tubes, but a fixed bed multi tube type reactor is usually used industrially. To be

The inside of the reaction tube is divided into a plurality of catalyst layers, and each of the catalyst layers except for the catalyst layer on the most outlet side of the source gas is the catalyst represented by the above formula (1), It is filled with a mixture containing at least two catalysts with different atomic ratios. In these catalyst layers, a catalyst having a low atomic ratio of X element and a high activity and a catalyst having a high atomic ratio of X element and a high thermal stability are filled in a mixed state. This is very important.

In the catalyst layer closest to the outlet of the source gas, the catalyst represented by the above formula (1) and containing the same X element atomic ratio, or the X element atomic ratio It is filled with a mixture containing at least two types of catalysts different from each other.

[0010] As the number of types of the catalyst to be filled in each catalyst layer becomes more complicated, the production and filling of the catalyst becomes more complicated. Therefore, two types are industrially preferable.

The number of catalyst layers is not particularly limited,
If the amount is too large, the catalyst filling becomes complicated, so industrially 2 to
Three layers are preferred.

Further, the X element-containing mass per unit mass of each catalyst layer is decreased from the inlet side to the outlet side of the reactor. For example, in the case of using two kinds of catalysts, the catalyst layer having a large content of X element is filled so that the catalyst layer on the inlet side of the raw material gas is larger and the catalyst layer on the outlet side is smaller to form the catalyst layer. Let When the catalyst layer contains a diluent carrier, the mass of the catalyst layer means the mass including the diluent carrier.

In the present invention, each catalyst layer except the catalyst layer on the most outlet side of the raw material gas is a catalyst comprising a mixture containing the catalyst represented by the formula (2) and the catalyst represented by the formula (3). It is preferably a layer. Further, the catalyst layer on the most outlet side of the source gas is a catalyst layer containing the catalyst represented by the formula (2),
Alternatively, the catalyst layer is preferably made of a mixture containing the catalysts represented by the formulas (2) and (3).

In this case, equations (2) and (3) of each catalyst layer are used.
The mass mixing ratio of the catalyst represented by is not particularly limited, but when the mixing ratio of the catalyst layer on the most inlet side of the source gas is 1: α, α is preferably 0.05 ≦ α ≦ 3, and particularly 0.1 ≤ α
≦ 1 is preferable. If the mixing ratio of the catalyst layer on the most outlet side of the source gas is 1: β (where β <α), β is 0 ≦
β ≦ 1 is preferable, and 0 ≦ β ≦ 0.5 is particularly preferable. When the number of catalyst layers is three or more, the mass mixing ratio of the catalyst layer on the most inlet side and the catalyst layer in the middle excluding the catalyst layer on the most outlet side is 1: γ.
(Β <γ <α).

The catalyst represented by the above formula (2) used in the present invention is preferably one represented by the formula (2 '). During _{Mo f P g X h Y '} i' Cu p V q O j (2 ') ( wherein, represents Mo, P, Cu, V and O represent molybdenum, phosphorus, copper, vanadium and oxygen, X is potassium Represents at least one element selected from the group consisting of, rubidium, cesium and thallium, Y'is iron, cobalt, nickel, zinc, magnesium, calcium, strontium, barium, titanium, chromium, tungsten, manganese, silver, Boron, silicon, aluminum, gallium, germanium, tin, lead, arsenic, antimony, bismuth, niobium, tantalum, zirconium,
It represents at least one element selected from the group consisting of indium, sulfur, selenium, tellurium, lanthanum and cerium. However, f, g, h, i ′, p, q and j represent the atomic ratio of each element, and when f = 12, g is 0.1 ≦
g ≦ 3, preferably 0.5 ≦ g ≦ 3. Similarly, h is 0.01 ≦ h ≦ 3, preferably 0.1 ≦ h ≦ 3.
Similarly, i ′ is 0 ≦ i ′ ≦ 2.98, preferably 0 ≦ i ′
≦ 2.5. Similarly, p is 0.01 ≦ p ≦ 2.99,
Preferably 0.01 ≦ p ≦ 2. Similarly, q is 0.0
1 ≦ q ≦ 2.99, preferably 0.01 ≦ q ≦ 2, and j is the atomic ratio of oxygen required to satisfy the atomic ratio of each component. However, i ′ + p + q is 0.02 ≦
(I ′ + p + q) ≦ 3. )

The catalyst represented by the formula (3) used in combination with the catalyst represented by the formula (2) is preferably one represented by the formula (3 '). During _{Mo k P l X m Y '} n' Cu r V s O o (3 ') ( wherein, Mo, represents P, Cu, V and O represent molybdenum, phosphorus, copper, vanadium and oxygen, X is potassium Represents at least one element selected from the group consisting of, rubidium, cesium and thallium, Y'is iron, cobalt, nickel, zinc, magnesium, calcium, strontium, barium, titanium, chromium, tungsten, manganese, silver, Boron, silicon, aluminum, gallium, germanium, tin, lead, arsenic, antimony, bismuth, niobium, tantalum, zirconium,
It represents at least one element selected from the group consisting of indium, sulfur, selenium, tellurium, lanthanum and cerium. However, k, l, m, n ′, r, s and o represent the atomic ratio of each element, and when k = 12, l is 0.1 ≦
1 ≦ 3, preferably 0.5 ≦ l ≦ 3. Similarly, m is 1.1 ≦ m ≦ 6, preferably 1.5 ≦ m ≦ 4 and 0.1
≦ (m−h) ≦ 5, preferably 0.5 ≦ (m−h) ≦ 3
Is. Similarly, n ′ is 0 ≦ n ′ ≦ 2.98, preferably 0 ≦ n ′ ≦ 2.5. Similarly, r is 0.01 ≦ r ≦
2.99, preferably 0.01 ≦ r ≦ 2.
Similarly, s is 0.01 ≦ s ≦ 2.99, preferably 0.01 ≦ s ≦ 2. o is the atomic ratio of oxygen required to satisfy the atomic ratio of each component. n ′ + r + s is 0.02 ≦ (n ′ + r + s) ≦ 3. )

The method for producing the catalyst used in the present invention is not particularly limited, and a coprecipitation method, an evaporation dryness method, an oxide mixing method and the like can be used. The raw material used for preparing the catalyst is not particularly limited, and nitrates, carbonates, acetates, ammonium salts, oxides, halides, oxyacids and the like of each element can be used in combination. For example, as a raw material of molybdenum, ammonium paramolybdate, molybdenum trioxide,
As a raw material of phosphorus such as molybdic acid and molybdenum chloride, phosphoric acid, phosphorus pentoxide, ammonium phosphate and the like can be used.

As a concrete method of preparing the catalyst, there is a method of calcining a dried aqueous slurry containing at least molybdenum, phosphorus and X. The method for drying the aqueous slurry is not particularly limited, and a drying method using a box dryer, a spray dryer, a drum dryer, a slurry dryer or the like can be used. The dried product (catalyst precursor) obtained at this time is preferably in powder form in consideration of molding. The dried product may be molded as it is, or may be molded after firing. The molding method is not particularly limited, and examples thereof include tablet molding, extrusion molding, granulation, and loading. Examples of the carrier of the supported catalyst include inert carriers such as silica, alumina, silica-alumina, and silicon carbide. At the time of molding, for the purpose of controlling the specific surface area, pore volume and pore distribution of the molded article or increasing the mechanical strength, for example, barium sulfate, inorganic salts such as ammonium nitrate, lubricants such as graphite, and celluloses. Additives such as starch, organic substances such as polyvinyl alcohol and stearic acid, hydroxide sols such as silica sol and alumina sol, whiskers, inorganic fibers such as glass fibers and carbon fibers may be appropriately added.

In the present invention, the at least two kinds of catalysts having different atomic ratios of the X element are at least two kinds of catalysts having different atomic ratios of the X element even if they are separate molded bodies having a single catalyst composition. It may be a molded product of a mixture of the precursors. In the case of the former, it is necessary to mix the catalyst or the molded body of the precursor before calcination and to fill the reaction tube, but in the case of the latter, two or more types of catalyst or the precursor before calcination thereof have already been mixed. Therefore, it suffices to only fill the molded body of this catalyst or its precursor before calcination. When the reaction tube is filled with the precursor, the precursor is fired in the reaction tube and then subjected to the reaction.

The calcination conditions are as follows: catalyst raw material used, catalyst composition,
Although it cannot be generally stated because it depends on the preparation conditions and the like, the firing is usually performed at 300 to 500 ° C., preferably 30 at 500 ° C. under an oxygen-containing gas flow such as air and / or an inert gas flow.
0 to 450 ° C., 0.5 hours or more, preferably 1 to 40
It is performed on the condition of time. It is preferable that the catalyst after calcination contains a structure of heteropolyacid and / or heteropolyacid salt.

In the method for producing methacrylic acid according to the present invention, the catalyst is filled so that the content of the element X contained in the catalyst per unit weight decreases from the inlet side of the raw material gas toward the outlet side thereof, that is, the inlet of the raw material gas. Fill from the side to the exit side with higher activity. As a result, the generation of hot spots in the catalyst layer is suppressed, and it is possible to prevent a decrease in selectivity due to sequential oxidation and deterioration of the catalyst due to heat storage. Furthermore, in each catalyst layer, catalysts having different X element contents are mixed and filled, that is, a catalyst having high activity and a catalyst having low activity are mixed and filled, and therefore, JP-A-4-210937. The production of methacrylic acid can be continued stably over a long period of time as compared with the invention described in the publication. It is not clear why mixing and packing two or more catalysts with different activities enables stable operation for a long period of time, but the reaction activity and the content of X component in the reactor during operation are not clear. It is thought that the difference may cause migration of components between two or more types of catalysts that are close to each other, or may have some effect on the prevention of deterioration of the catalyst as a whole due to the change in the ratio of active sites used over time. To be

The methacrolein concentration of the raw material gas used for the vapor phase catalytic oxidation can be varied over a wide range, but it is preferably 1 to 20% by volume, particularly preferably 3 to 10% by volume. The raw material methacrolein may contain a small amount of impurities such as water and lower saturated aldehydes that do not substantially affect the reaction, but the raw material gas contains such impurities derived from methacrolein. May be.

The source gas must contain molecular oxygen, but the amount of molecular oxygen in the source gas is preferably 0.4 to 4 times mol of methacrolein, particularly 0.5 to 3 times. Molar is preferred. It is industrially advantageous to use air as the molecular oxygen source of the raw material gas, but air enriched with pure oxygen can also be used if necessary. The raw material gas is preferably diluted with an inert gas such as nitrogen or carbon dioxide, or steam.

The reaction pressure for the vapor phase catalytic oxidation is from atmospheric pressure to several atmospheres. The reaction temperature is generally 200 to 450 ° C, preferably 250 to 400 ° C. The contact time between the raw material gas and the catalyst is usually 1.5 to 15 seconds, preferably 2 to 7 seconds.

[0025]

EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples. However, "parts" in Examples and Comparative Examples mean parts by weight. The reaction test analysis was performed by gas chromatography. The conversion of methacrolein as a raw material, the selectivity of methacrylic acid produced, and the yield are defined as follows. Methacrolein conversion rate (%) = (B / A) × 100 Methacrylic acid selectivity (%) = (C / B) × 100 Methacrylic acid single-flow yield (%) = (C / A) × 100 where: 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 catalyst 1) Ammonium paramolybdate 10
A solution prepared by dissolving 0 part in 200 parts of pure water, 2.8 parts of ammonium metavanadate and 8.2 parts of 85 wt% phosphoric acid in 30 parts of pure water, and 1.1 parts of copper nitrate in 30 parts of pure water. Solution dissolved in 10 parts of pure water and a solution of 3.8 parts of iron nitrate dissolved in 10 parts of pure water were sequentially added and heated to 90 ° C. with stirring, and then heated and stirred for 5 hours while maintaining the liquid temperature at 90 ° C. A solution prepared by dissolving 6.4 parts of cesium nitrate in 100 parts of pure water was added thereto, and the mixed liquid was evaporated to dryness while heating and stirring.
The obtained solid was dried at 130 ° C. for 16 hours and then pulverized. 3 parts of graphite was added to 100 parts of the powder obtained in this way, and then a tableting machine was used to give an outer diameter of 5 mm,
It was formed into a ring shape having an inner diameter of 2 mm and a length of 5 mm. The obtained molded product was calcined in air at 380 ° C. for 5 hours to obtain a catalyst. Table 1 shows the composition of elements other than oxygen in this catalyst.

(Preparation of catalyst 2) Catalyst 2 having the composition shown in Table 1 was prepared in the same manner as catalyst 1.

(Production of methacrylic acid) Methacrylic acid was produced using a fixed bed tubular reactor having one reaction tube having an inner diameter of 14 mm. The raw material gas inlet side of the reaction tube was filled with 10 g of a mixture of 8 g of catalyst 1 and 2 g of catalyst 2, and the outlet side was filled with 10 g of a mixture of 9.5 g of catalyst 1 and 0.5 g of catalyst 2 and methacrolein. 5% by volume, 10 oxygen
A raw material gas consisting of vol%, steam 20 vol% and nitrogen 65 vol% was passed through at a reaction temperature of 290 ° C. and a contact time of 3.6 seconds. The results are shown in Table 2.

Example 2 (Preparation of catalyst 3) Catalyst 3 having the composition shown in Table 1 was prepared in the same manner as catalyst 1.

(Production of Methacrylic Acid) Catalyst 1 and Catalyst 3
Methacrylic acid was produced in the same manner as in Example 1 except that the resin was charged as shown in Table 2. The results are shown in Table 2.

Example 3 (Preparation of catalysts 4 and 5) Catalysts 4 and 5 having the compositions shown in Table 1 were prepared in the same manner as catalyst 1.

(Production of Methacrylic Acid) Catalyst 4 and Catalyst 5
Methacrylic acid was produced in the same manner as in Example 1 except that the resin was charged as shown in Table 2. The results are shown in Table 2.

[Example 4] (Preparation of catalysts 6 and 7) Catalysts 6 and 7 having the compositions shown in Table 1 were prepared in the same manner as catalyst 1.

(Production of Methacrylic Acid) Catalyst 6 and Catalyst 7
Methacrylic acid was produced in the same manner as in Example 1 except that the resin was charged as shown in Table 2. The results are shown in Table 2.

[Example 5] (Production of methacrylic acid) Methacrylic acid was produced in the same manner as in Example 1 except that the catalysts 4 and 7 were charged as shown in Table 2. The results are shown in Table 2.

Comparative Example 1 (Preparation of catalyst 8) Catalyst 8 having the composition shown in Table 1 was prepared in the same manner as catalyst 1. The catalyst 8 had the average composition of all the catalysts of Example 1.

(Production of Methacrylic Acid) Methacrylic acid was produced in the same manner as in Example 1 except that only the catalyst 8 was charged as shown in Table 2. The results are shown in Table 2.

Comparative Example 2 (Production of Methacrylic Acid) Methacrylic acid was produced in the same manner as in Example 1 except that the catalyst 1 and the catalyst 2 were charged as shown in Table 2. The results are shown in Table 2.

[Comparative Example 3] (Production of methacrylic acid) Methacrylic acid was produced in the same manner as in Example 1 except that the catalyst 1 and the catalyst 2 were charged as shown in Table 2. The results are shown in Table 2.

[Comparative Example 4] (Production of methacrylic acid) Methacrylic acid was produced in the same manner as in Example 1 except that the catalysts 1 and 9 were charged as shown in Table 2. The results are shown in Table 2.

[Example 6] (Preparation of catalysts 9 and 10)
Catalysts 9 and 10 having the compositions shown in were prepared.

(Production of Methacrylic Acid) Catalyst 9 and Catalyst 1
Methacrylic acid was produced in the same manner as in Example 1 except that 0 was filled as shown in Table 2. The results are shown in Table 2.

[Comparative Example 5] (Preparation of catalyst 11) Catalyst 11 having the composition shown in Table 1 was prepared in the same manner as catalyst 1. In addition, the catalyst 11 is
In all, the average composition of the catalyst was used.

(Production of Methacrylic Acid) Methacrylic acid was produced in the same manner as in Example 1 except that only the catalyst 11 was charged as shown in Table 2. The results are shown in Table 2.

[0045]

[Table 1]

[0046]

[Table 2]

INDUSTRIAL APPLICABILITY According to the present invention, in a method for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen, high methacrylic acid can be efficiently produced by maintaining high catalytic activity for a long period of time. It can be manufactured.

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Claims (3)

[Claims] 1. A methacrylic acid that undergoes vapor phase catalytic oxidation of methacrolein with molecular oxygen using a fixed-bed tubular reactor having a catalyst filling section composed of a plurality of catalyst layers divided from a raw material gas inlet side to an outlet side. In the production method, each catalyst layer excluding the catalyst layer closest to the outlet of the raw material gas is a catalyst represented by the formula (1), and is composed of a mixture containing at least two kinds of catalysts having different atomic ratios of X elements. The catalyst layer is the catalyst layer on the most outlet side of the source gas, and the catalyst layer is the catalyst represented by the formula (1), and the catalyst layer contains the catalyst having the same atomic ratio of X elements, or the atomic ratio of X element is A methacrylic acid catalyst layer comprising a mixture containing at least two different types of catalysts, wherein the X element-containing mass per unit mass of each catalyst layer decreases from the inlet side to the outlet side of the reactor. Method for producing acid. Mo _a P _b X _c Y _d O _e (1) (wherein Mo, P and O represent molybdenum, phosphorus and oxygen, respectively, and X is at least 1 selected from the group consisting of potassium, rubidium, cesium and thallium.
Represents a seed element, Y is iron, cobalt, nickel, copper, zinc, magnesium, calcium, strontium, barium, titanium, vanadium, chromium, tungsten, manganese, silver, boron, silicon, aluminum, gallium, germanium, tin, Lead, arsenic, antimony, bismuth, niobium, tantalum, zirconium, indium,
It represents at least one element selected from the group consisting of sulfur, selenium, tellurium, lanthanum and cerium. a,
b, c, d and e represent the atomic ratio of each element, and a = 12
, 0.1 ≦ b ≦ 3, 0.01 ≦ c ≦ 6, 0 ≦ d ≦
3, and e is the atomic ratio of oxygen required to satisfy the atomic ratio of each component. ) 2. Each catalyst layer except the catalyst layer on the most outlet side of the raw material gas is a catalyst layer comprising a mixture containing the catalyst represented by formula (2) and the catalyst represented by formula (3), The catalyst layer closest to the outlet of the source gas is a catalyst layer containing the catalyst represented by the formula (2) or a catalyst layer containing a mixture containing the catalyst represented by the formulas (2) and (3). A method for producing methacrylic acid, which comprises: _{Mo f P g X h Y i} O j (2) ( wherein, Mo, P, X, Y and O are as defined formula (1).
f, g, h, i and j represent the atomic ratio of each element, and f =
When 12, 0.1 ≦ g ≦ 3, 0.01 ≦ h ≦ 3, 0 ≦
i ≦ 3, and j is the atomic ratio of oxygen required to satisfy the atomic ratio of each component. _{) Mo k P l X m Y} n O o (3) ( wherein, Mo, P, X, Y and O Equation (1) Same as.
k, l, m, n and o represent the atomic ratio of each element, and k =
In the case of 12, 0.1 ≦ l ≦ 3, 1.1 ≦ m ≦ 6 and 0.
1 ≦ (m−h) ≦ 5, 0 ≦ n ≦ 3, and o is the atomic ratio of oxygen required to satisfy the atomic ratio of each component. ) 3. The mass mixing ratio of the catalysts represented by the formulas (2) and (3) in each catalyst layer is 1: α (0.05 ≦ α ≦ 3 in the catalyst layer closest to the source gas). ), And 1: β (0 ≦ β ≦ 1 and β <α) in the catalyst layer at the most outlet side of the raw material gas, The method for producing methacrylic acid according to claim 2.