JP4745653B2 - Method for producing methacrylic acid - Google Patents

Description

  The present invention relates to a method for obtaining methacrylic acid stably and in a high yield over a long period of time when producing methacrylic acid in gas phase catalytic oxidation of methacrolein with molecular oxygen using a fixed bed tubular reactor.

  It is widely known that a heteropolyacid catalyst containing at least molybdenum and phosphorus is effective for a catalyst for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen. Some are used in methacrylic acid production processes by direct oxidation.

  However, the greatest drawback of these heteropolyacid catalysts is short life as described in Patent Document 1 (Japanese Patent Laid-Open No. 59-20243), among which relatively stable alkalis. It has been reported that even if a metal salt is reacted for a long period of time, some of the constituent elements are decomposed or scattered in the form of oxides. This is because heteropolyacid compounds are generally thermally unstable.

  Therefore, in the industrial implementation of the oxidation reaction, in order to continue the reaction over a long period, (1) mild conditions such as lowering the starting material concentration and lowering the space velocity are adopted, or (2 ) The reaction temperature must be lowered by increasing the amount of catalyst filled in the reaction tube as much as possible.

  However, the method (1) is not preferable because it involves a decrease in methacrylic acid productivity and the operation is performed under conditions far from economic demands. Also in the method (2), since the oxidation reaction is a very exothermic reaction, the heat storage in the catalyst layer is large, and the yield is lowered due to an excessive oxidation reaction particularly in a local abnormally high temperature zone called a hot spot. In addition, the life is greatly affected by the deterioration of the catalyst due to heat load. For this reason, the present condition is also subject to considerable restrictions with respect to reaction conditions and catalyst filling conditions.

  As a method for suppressing heat storage in the hot spot section and continuing the reaction for a long period of time, for example, in Patent Document 2 (Japanese Patent Laid-Open No. Hei 4-210937), the inside of each reaction tube of a fixed-bed multitubular reactor is in the axial direction. A method is disclosed in which a plurality of catalysts having different activities are packed in a plurality of reaction zones divided into two or more layers in such a manner that the activity becomes higher from the inlet side to the outlet side of the raw material gas. Yes.

In Patent Document 2, the catalyst layer on the inlet side of the raw material gas is filled with a catalyst having lower activity than the catalyst layer on the outlet side, so that heat storage in the hot spot portion on the inlet side where the raw material concentration is high is suppressed and high. Methacrylic acid can be obtained in a yield. However, a catalyst having a low activity is deteriorated more quickly than a catalyst having a high activity, and at the same time, a raw material concentration is high and the catalyst is exposed to a high load. At present, the catalyst cannot be sufficiently prevented from deteriorating, and further improvements are required industrially.
JP 59-20243 JP-A-4-210937

  Accordingly, an object of the present invention is to provide a method for producing methacrylic acid in a high yield, which can continue the reaction stably over a long period of time.

The present invention comprises a plurality of catalyst layers in which the catalyst filling portion is divided from the inlet side to the outlet side of the raw material gas and filled with catalysts having different contents of ammonia and / or ammonium ions contained per catalyst unit mass part. In a method for producing methacrylic acid, in which methacrolein is vapor-phase catalytically oxidized with molecular oxygen using a fixed bed tubular reactor,
The reference position is a position where the amount of the catalyst filled in the catalyst filling portion is 50% by mass of the total filling amount per reaction tube along the tube axis direction,
The average value of the ammonia and / or ammonium ion content contained per unit mass part of the catalyst charged on the inlet side of the raw material gas from the reference position is 0.02 parts by mass or less,
The average value of the ammonia and / or ammonium ion content contained per unit mass part of the catalyst charged from the reference position to the outlet side of the raw material gas, and per unit mass part of the catalyst charged from the reference position to the inlet side of the raw material gas The ratio of the average value of the ammonia and / or ammonium ion content contained in is 1: α (1.3 ≦ α ≦ 10) in terms of mass ratio. The present invention relates to a method for producing an acid.

  According to the present invention, in a method for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen, methacrylic acid is effectively produced in a high yield while maintaining catalytic activity over a long period of time. Can do.

  In the present invention, methacrylic acid is obtained by subjecting methacrolein to gas phase catalytic oxidation with molecular oxygen using a fixed bed tubular reactor in which the catalyst filling part is composed of a plurality of catalyst layers divided from the inlet side to the outlet side of the raw material gas. Manufacturing.

  The fixed bed tube 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 reactor is usually used industrially.

  The reaction tube is divided into a plurality of catalyst layers, which are filled with catalysts having different contents of ammonia and / or ammonium ions (hereinafter collectively referred to as ammonia roots) contained per unit mass of the catalyst. ing. The number of catalyst layers having different contents of ammonia radicals may be any number, but if the amount is large, production and filling of the catalyst becomes complicated, and therefore, two to three layers are preferred industrially. The ratio of each catalyst layer is not particularly limited. For example, in the case of two layers, the catalyst packed in the catalyst layer on the inlet side of the raw material gas may be 10 to 70% by mass of the total catalyst loading. it can.

  In the present invention, the method for adjusting the content of ammonia radicals contained per catalyst unit mass packed in each catalyst layer is not particularly limited. For example, when adjusting according to the catalyst firing conditions, the firing temperature and / or Alternatively, by adjusting the baking time, when baking is performed under circulation, the baking can be performed by adjusting the flow rate of the baking gas and the moisture content in the baking gas in addition to the temperature and time. In the case of carrying out calcination under distribution, the calcination may be carried out after filling the catalyst precursor before calcination into the reaction tube, and there is no particular limitation. Moreover, as a method for adjusting the content of the ammonia radical other than the firing, a method for adjusting the content of the ammonia radical contained in the catalyst precursor in advance at the time of preparation of the catalyst may be mentioned.

  The content of ammonia radicals contained in the catalyst unit mass part filled in each catalyst layer is such that the amount of catalyst filled in the catalyst filling part is the total filling amount per reaction tube along the tube axis direction. The position where 50% by mass is taken as the reference position, the average value of the content of ammonia radicals contained per unit mass part of the catalyst charged from the reference position to the outlet side of the raw material gas, and the inlet side of the raw material gas was charged It is important to adjust the ammonia root content in the catalyst so that the ratio of the average value of the ammonia root content contained per catalyst unit mass part is 1: α by mass ratio. Here, α is 1.3 or more, preferably 1.4 or more, more preferably 1.5 or more. Α is 10 or less, more preferably 7 or less, and particularly preferably 5 or less.

  Further, the average value of the content of ammonia radicals contained per unit mass part of the catalyst charged on the raw material gas inlet side from the reference position is 0.02 parts by mass or less, preferably 0.015 parts by mass or less, More preferably, it is 0.01 mass part or less. The average value is preferably 0.0006 parts by mass or more, more preferably 0.001 parts by mass or more, and particularly preferably 0.002 parts by mass or more.

  Further, the average value of the content of ammonia radicals contained per unit part by mass of the catalyst charged on the outlet side of the raw material gas from the reference position is preferably 0.0005 parts by mass or more, more preferably 0. 0.001 part by mass or more. Moreover, it is preferable that this average value is 0.01 mass part or less, More preferably, it is 0.005 mass part or less.

  Further, in the present invention, catalysts having different contents of nitric acid and / or nitrate ions (hereinafter collectively referred to as nitrate radicals) are packed together with the contents of ammonia radicals contained per unit mass part of the catalyst layer. Preferably it is. The content of nitrate radicals contained in the catalyst unit mass part filled in each catalyst layer is the reference position at the position where 50% by mass of the total charge per reaction tube is the same as in the case of ammonia radicals. The average value of the content of nitrate radicals contained per catalyst unit mass part charged on the outlet side of the raw material gas, and the content of the nitrate radicals contained per catalyst unit mass part charged on the inlet side of the raw material gas It is preferable that the ratio of the average values is adjusted so that the mass ratio is 1: β. Here, β is 1.1 or more, preferably 1.2 or more, more preferably 1.3 or more. Β is 10 or less, more preferably 7 or less, and particularly preferably 5 or less.

  Further, the average value of the content of nitrate radicals contained per unit mass part of the catalyst charged on the raw material gas inlet side from the reference position is preferably 0.0003 parts by mass or less, more preferably 0.0002. It is below mass parts. Further, the average value is preferably 0.000002 parts by mass or more, more preferably 0.00001 parts by mass or more.

  Further, the average value of the content of nitrate radicals contained per unit mass part of the catalyst charged on the outlet side of the raw material gas from the reference position is preferably 0.000001 parts by mass or more, more preferably 0. 0.0005 part by mass or more. Moreover, it is preferable that this average value is 0.0001 mass part or less, More preferably, it is 0.00007 mass part or less.

  The method for adjusting the content of nitrate radicals contained per unit mass of the catalyst packed in each catalyst layer is not particularly limited, as in the case of adjusting the content of ammonia radicals, and the catalyst firing conditions and / or catalysts. Examples thereof include a method of adjusting the content of nitrate radicals contained in the catalyst precursor during preparation.

In the present invention, the catalyst filled in each catalyst layer may be diluted with an inert carrier or the like and is not particularly limited. However, in this case, the amount of ammonia radical or ammonia radical and nitrate radical per part by mass of the catalyst is the quantity of ammonia radical or ammonia radical and nitrate radical contained in the total amount of the inert carrier and the catalyst.
The amount of ammonia radicals in the catalyst is measured by the Kjeldahl method, and the amount of nitrate radicals is measured by ion chromatography.

  Further, the composition of the catalyst filled in each catalyst layer excluding the ammonia radical or ammonia radical and nitrate radical may be the same or different and is not particularly limited. When catalysts having different compositions are packed, the catalyst used in each catalyst layer is not greatly different in activity when having the same amount of ammonia or ammonia and nitrate. It is preferable to select the composition.

  In the present invention, methacrylic acid can be stably produced at a high yield over a long period of time by adjusting the content of the ammonia radicals contained per mass part of the catalyst packed in each catalyst layer. It becomes like this. This is because the generation of hot spot portions in the reaction tube is suppressed as described above.

  The reason why the generation of hot spots is suppressed is that the catalyst having a high content of ammonia radicals has an acid site at the initial stage of the reaction as ammonium ions, or an ammonia radical is adsorbed at the active site. For this reason, the number of active sites including acid sites is less than that of a catalyst having a low ammonia radical content, and the activity is low. Therefore, it is estimated that the oxidation reaction in the catalyst layer on the inlet side having a high raw material concentration can be moderately suppressed and the generation of excessive reaction heat can be suppressed.

  Further, in such a catalyst having a high content of ammonia radicals, the ammonia radicals are eliminated during the reaction operation period. As a result, new active sites such as acid sites appear in the catalyst. That is, apparently low activity is shown at the beginning of the reaction, and as the reaction proceeds, a new active site is expressed, and thus the activity is improved. At the same time, the degradation of the active sites existing from the start of the reaction proceeds. The present inventors will be able to produce methacrylic acid stably over a long period of time by balancing the improvement in activity due to the expression of the new active site and the decrease in activity due to the degradation of the active site existing from the start of the reaction. Guess.

  Also, in the present invention, the role of nitrate radicals is not clear, but the ammonia radical elimination rate when the ammonia radicals are eliminated during the operation period and a new active site is expressed is controlled. The present inventors have speculated that this is not the case. That is, the catalyst packed in the catalyst layer on the inlet side of the reaction gas, which is likely to generate hot spots, contains more nitrate radicals than the catalyst packed in the catalyst layer on the outlet side, so that the catalyst layer on the inlet side The present inventors presume that the ammonia radical is rapidly desorbed from the catalyst packed in the catalyst and the generation of a hot spot portion is suppressed.

  The present invention does not necessarily have to be carried out over the entire period from the start of the reaction until the end of the life of the catalyst, a hot spot is generated in the reaction tube, and the yield of methacrylic acid is reduced. Or it is preferable to carry out in the initial stage of the reaction where the thermal deterioration of the catalyst is likely to proceed.

  In the present invention, the catalyst filled in each catalyst layer may be a composite oxide containing molybdenum and phosphorus, and the composition of the catalyst excluding the ammonia and nitrate radicals is preferably that of the formula (1). Preferably it is Formula (1 ').

Mo _a P _b X _c Y _d O _e (1)
(In the formula, Mo, P and O represent molybdenum, phosphorus and oxygen, respectively, X represents at least one element selected from the group consisting of potassium, rubidium, cesium and thallium, and Y represents iron, cobalt and 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 Represents at least one element selected from the group consisting of aluminium, indium, sulfur, selenium, tellurium, lanthanum and cerium, wherein a, b, c, d and e represent the atomic ratio of each element, and when a = 12. 0.1 ≦ b ≦ 3, 0.01 ≦ c ≦ 3, 0 ≦ d ≦ 3, and e is An atomic ratio of oxygen required to satisfy the atomic ratio of the components.)

_{Mo a P b X c Y '} d' Cu f V g O e (1 ')
(Wherein Mo, P, Cu, V and O represent molybdenum, phosphorus, copper, vanadium and oxygen, respectively, and X represents at least one element selected from the group consisting of potassium, rubidium, cesium and thallium. Y ′ is iron, cobalt, nickel, zinc, magnesium, calcium, strontium, barium, titanium, chromium, tungsten, manganese, silver, boron, silicon, aluminum, gallium, germanium, preferably potassium, rubidium and cesium Represents at least one element selected from the group consisting of tin, lead, arsenic, antimony, bismuth, niobium, tantalum, zirconium, indium, sulfur, selenium, tellurium, lanthanum and cerium, preferably iron, zinc, germanium, Arsenic, antimony, lanthanum A, b, c, d ′, f, g and e represent the atomic ratio of each element, and when a = 12, b is 0.1 ≦ b ≦ 3, preferably 0.5 ≦. b ≦ 3 Similarly c is 0.01 ≦ c ≦ 3, preferably 0.1 ≦ c ≦ 3 Similarly d ′ is 0 ≦ d ′ ≦ 2.98, preferably 0 ≦ d ′. ≦ 2.5 Similarly f is 0.01 ≦ f ≦ 2.99, preferably 0.01 ≦ f ≦ 2, and similarly g is 0.01 ≦ g ≦ 2.99, preferably 0. .01 ≦ g ≦ 2, and e is an atomic ratio of oxygen necessary to satisfy the atomic ratio of each component, where d ′ + f + g is 0.02 ≦ (d ′ + f + g) ≦ 3. .)

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

  As a specific method for preparing the catalyst, a method in which an aqueous slurry containing at least molybdenum, phosphorus and X is dried is calcined. The drying method of 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 that time is preferably in the form of a powder in consideration of molding. The dried product may be molded as it is, or may be molded after firing. It does not specifically limit as a shaping | molding method, For example, tableting shaping | molding, extrusion molding, granulation, carrying | support etc. are mentioned. Examples of the supported catalyst carrier include inert carriers such as silica, alumina, silica / alumina, and silicon carbide. In the molding, for the purpose of controlling the specific surface area, pore volume and pore distribution of the molded product or increasing the mechanical strength, for example, inorganic salts such as barium sulfate and ammonium nitrate, lubricants such as graphite, celluloses, etc. Additives such as organic substances such as starch, polyvinyl alcohol and stearic acid, hydroxide sols such as silica sol and alumina sol, inorganic fibers such as whiskers, glass fibers and carbon fibers may be added as appropriate.

  When the molded body is fired, the firing may be performed before filling the reaction tube or in the reaction tube. The firing conditions vary depending on the raw material of the catalyst to be used, the catalyst composition, the preparation conditions, etc., and cannot generally be said, but usually 300 to 500 ° C., preferably under an oxygen-containing gas flow and / or an inert gas flow such as air. Is performed at 300 to 450 ° C. for 0.5 hour or longer, preferably 1 to 40 hours.

  In the present invention, in order to introduce ammonia radicals or ammonia radicals and nitrate radicals into the catalyst, at least one ammonia root or ammonia radical and nitrate radical precursor compound may be used during molding of the molded article.

  Note that a part of the catalyst layer filled in the reactor was filled with a catalyst not containing ammonia and / or nitrate as long as the relationship with respect to the content of ammonia and / or nitrate was satisfied. It may be a catalyst layer. However, since methacrylic acid can be produced stably over a longer period of time, it is preferable that the catalyst of all catalyst layers contains ammonia radicals or ammonia radicals and nitrate radicals.

  Conditions for carrying out the reaction in the method for producing methacrylic acid of the present invention are not particularly limited, and known reaction conditions can be applied. Below, reaction conditions are demonstrated.

  The raw material gas circulated in the catalyst filling part contains at least methacrolein and molecular oxygen.

  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 preferably 3 to 10% by volume. The raw material methacrolein may contain a small amount of impurities that do not substantially affect the reaction, such as water, lower saturated aldehydes, etc., but the raw material gas contains such an impurity derived from methacrolein. It may be.

  The concentration of molecular oxygen in the raw material gas is preferably 0.4 to 4 times mol, more preferably 0.5 to 3 times mol of methacrolein. Although it is industrially advantageous to use air as the molecular oxygen source of the source gas, air enriched with pure oxygen can also be used if necessary. The source gas is preferably diluted with an inert gas such as nitrogen or carbon dioxide, water vapor or the like.

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

Hereinafter, the present invention will be described using examples. “Parts” in Examples and Comparative Examples means parts by mass. In the production of methacrylic acid, the raw material gas and the product were analyzed by gas chromatography, the ammonia radical in the catalyst was measured by the Kjeldahl method, and the nitrate radical was measured by ion chromatography. Further, the conversion rate of the raw material methacrolein, the selectivity of the produced methacrylic acid and the yield are defined as follows.
Conversion rate of methacrolein (%) = (B / A) × 100
Methacrylic acid selectivity (%) = (C / B) × 100
Methacrylic acid single stream yield (%) = (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]
100 parts of ammonium paramolybdate, 4.4 parts of ammonium metavanadate and 9.2 parts of cesium nitrate were dissolved by heating in 300 parts of pure water. A solution obtained by dissolving 8.7 parts of 85% by mass phosphoric acid in 10 parts of pure water, then 5.5 parts of antimony trioxide was added, and the temperature was raised to 95 ° C. with stirring. A solution dissolved in 10 parts of pure water was added. The mixture was stirred at 95 ° C. for 15 minutes and then evaporated to dryness while stirring with heating. 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 thus obtained, and then formed into a ring shape having an outer diameter of 5 mm, an inner diameter of 2 mm, and a length of 5 mm by a tableting machine.

(Preparation of catalyst 1)
The molded body thus obtained was calcined at 370 ° C. for 5 hours under air calcining to obtain “Catalyst 1”. The composition of catalyst 1 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P _1.6 V _0.8 Cu _0.1 Sb _0.8 Cs ₁
The average value of ammonia radicals contained per part by mass of the catalyst was 0.0061 parts, and the average value of nitrate radicals was 0.000072 parts.

(Preparation of catalyst 2)
Similarly to the preparation of catalyst 1, the molded product obtained in the molding step was calcined at 390 ° C. for 5 hours under air calcining to obtain “catalyst 2”. The composition of catalyst 2 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P _1.6 V _0.8 Cu _0.1 Sb _0.8 Cs ₁
The average value of ammonia radicals contained per catalyst unit mass part was 0.0024 parts, and the average value of nitrate radicals was 0.000036 parts.

(Production of methacrylic acid)
Methacrylic acid was produced using a fixed bed tubular reactor having one reaction tube with an inner diameter of 14 mm. 10 g of catalyst 1 is filled in the raw material gas inlet side of the reaction tube, and 10 g of catalyst 2 is filled in the outlet side. The reaction temperature was 290 ° C., and the contact time was 3.6 seconds. The results are shown in Table 1. In addition, the maximum value (ΔTmax) of the difference between the temperature of the heat medium bath in the catalyst layer and the temperature of the catalyst layer in the period from the start of the reaction to 2000 hours was 19 ° C.

[Example 2]
(Preparation of catalyst 3)
A molded product obtained in the same manner as in Example 1 was calcined at 370 ° C. for 3 hours under air calcining to obtain “Catalyst 3”. The composition of catalyst 3 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P _1.6 V _0.8 Cu _0.1 Sb _0.8 Cs ₁
The average value of ammonia radicals contained per catalyst unit mass part was 0.0071 parts, and the average value of nitrate radicals was 0.000096 parts.

(Preparation of catalyst 4)
The molded body obtained in the same manner as in Example 1 was calcined at 390 ° C. for 7 hours under air calcining to obtain “Catalyst 4”. The composition of catalyst 4 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P _1.6 V _0.8 Cu _0.1 Sb _0.8 Cs ₁
The average value of ammonia radicals contained per catalyst unit mass part was 0.0014 parts, and the average value of nitrate radicals was 0.000012 parts.

(Production of methacrylic acid)
Methacrylic acid was produced in the same manner as in Example 1 except that 10 g of the catalyst 3 was charged on the raw material gas inlet side of the reaction tube and 10 g of the catalyst 4 was charged on the outlet side. The results are shown in Table 1. Further, ΔTmax in the catalyst layer at this time was 23 ° C.

Example 3
(Preparation of catalyst 5)
A molded body obtained in the same manner as in Example 1 was calcined at 380 ° C. for 3 hours under air calcining to obtain “Catalyst 5”. The composition of catalyst 5 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P _1.6 V _0.8 Cu _0.1 Sb _0.8 Cs ₁
The average value of ammonia radicals contained per catalyst unit mass part was 0.0049 parts, and the average value of nitrate radicals was 0.000063 parts.

(Preparation of catalyst 6)
A molded body obtained in the same manner as in Example 1 was calcined at 380 ° C. for 7 hours under air calcining to obtain “Catalyst 6”. The composition of catalyst 6 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P _1.6 V _0.8 Cu _0.1 Sb _0.8 Cs ₁
The average value of ammonia radicals contained per catalyst unit mass part was 0.0036 parts, and the average value of nitrate radicals was 0.000045 parts.

(Production of methacrylic acid)
Methacrylic acid was produced in the same manner as in Example 1 except that 10 g of the catalyst 5 was charged on the raw material gas inlet side of the reaction tube and 10 g of the catalyst 6 was charged on the outlet side. The results are shown in Table 1. Further, ΔTmax in the catalyst layer at this time was 21 ° C.

[Comparative Example 1]
(Preparation of catalyst 7)
A molded body obtained in the same manner as in Example 1 was calcined at 380 ° C. for 5 hours under air calcining to obtain “Catalyst 7”. The composition of catalyst 7, excluding oxygen atoms, ammonia radicals and nitrate radicals,
Mo ₁₂ P _1.6 V _0.8 Cu _0.1 Sb _0.8 Cs ₁
The average value of ammonia radicals contained per catalyst unit mass part was 0.0043 parts, and the average value of nitrate radicals was 0.000054 parts.

(Production of methacrylic acid)
Methacrylic acid was produced in the same manner as in Example 1 except that 20 g of catalyst 7 alone was charged in the reaction tube. The results are shown in Table 1. Further, ΔTmax in the catalyst layer at this time was 33 ° C.

[Comparative Example 2]
(Production of methacrylic acid)
Methacrylic acid was produced in the same manner as in Example 1 except that 10 g of catalyst 2 was charged on the raw material gas inlet side of the reaction tube and 10 g of catalyst 1 was charged on the outlet side. The results are shown in Table 1. Further, ΔTmax in the catalyst layer at this time was 38 ° C.

Example 4
(Preparation of catalyst 8)
100 parts of molybdenum trioxide, 2.6 parts of vanadium pentoxide, and 6.7 parts of 85 mass% phosphoric acid were added to 800 parts of pure water, and the mixture was heated and stirred for 3 hours under reflux. To this, 1.4 parts of copper oxide was added, and the mixture was further heated and stirred under reflux for 2 hours. The mixture after reflux is cooled to 50 ° C., a solution in which 7.1 parts of potassium nitrate is dissolved in 40 parts of pure water is added, a solution in which 14.7 parts of ammonium nitrate is dissolved in 60 parts of pure water is added, and the mixture is stirred with heating. While evaporating to dryness. The obtained solid was dried and molded in the same manner as in Example 1. The molded body thus obtained was calcined at 380 ° C. for 5 hours under air calcining to obtain “Catalyst 8”. The composition of catalyst 8 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P ₁ V _0.5 Cu _0.3 K _1.2
The average value of ammonia radicals contained per catalyst unit mass part was 0.0060 parts, and the average value of nitrate radicals was 0.000052 parts.

(Preparation of catalyst 9)
In the preparation of the catalyst 8, the same procedure as in the preparation of the catalyst 8 was performed except that a solution in which 14.7 parts of ammonium nitrate was dissolved in 60 parts of pure water was changed to a solution in which 9.8 parts of ammonium nitrate was dissolved in 40 parts of pure water. Thus, a molded body was obtained. The molded body thus obtained was calcined at 390 ° C. for 5 hours under air calcining to obtain “Catalyst 9”. The composition of catalyst 9 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P ₁ V _0.5 Cu _0.3 K _1.2
The average value of ammonia radicals contained per catalyst unit mass part was 0.0026 parts, and the average value of nitrate radicals was 0.000016 parts.

(Production of methacrylic acid)
Methacrylic acid was produced in the same manner as in Example 1 except that 8 g of catalyst 8 was charged on the raw material gas inlet side of the reaction tube and 12 g of catalyst 9 was charged on the outlet side, and the reaction temperature was changed from 290 ° C. to 285 ° C. . The results are shown in Table 1. Further, ΔTmax in the catalyst layer at this time was 21 ° C.

[Comparative Example 3]
(Preparation of catalyst 10)
A molded product obtained in the same manner as in the preparation of the catalyst 9 in Example 4 was calcined at 380 ° C. for 5 hours under air calcining to obtain “Catalyst 10”. The composition of the catalyst 12 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P ₁ V _0.5 Cu _0.3 K _1.2
The average value of the ammonia radicals contained per catalyst unit mass part was 0.0039 parts, and the average value of the nitrate radicals was 0.000034 parts.

(Production of methacrylic acid)
Methacrylic acid was produced in the same manner as in Example 4 except that 20 g of catalyst 10 alone was charged in the reaction tube. The results are shown in Table 1. Further, ΔTmax in the catalyst layer at this time was 32 ° C.

Example 5
100 parts of ammonium paramolybdate, 2.8 parts of ammonium metavanadate and 9.2 parts of cesium nitrate were dissolved in 400 parts of pure water. While stirring this, a solution prepared by dissolving 8.2 parts of 85% phosphoric acid in 10 parts of pure water was added, and the temperature was raised to 95 ° C. Next, a solution prepared by dissolving 3.4 parts of copper nitrate, 7.6 parts of ferric nitrate, 1.4 parts of zinc nitrate and 1.8 parts of magnesium nitrate in 80 parts of pure water was added. Further, this mixed solution was stirred at 100 ° C. for 30 minutes. The obtained aqueous slurry was dried by a co-current type spray dryer under the conditions of a dryer inlet temperature of 300 ° C. and a slurry spray rotating disk of 20000 rpm. The dried product thus obtained was dried and molded in the same manner as in Example 1.

(Preparation of catalyst 11)
The molded body thus obtained was calcined at 370 ° C. for 5 hours under air calcining to obtain “Catalyst 11”. The composition of catalyst 11 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P _1.5 V _0.5 Cu _0.3 Fe _0.4 Mg _0.15 Zn _0.1 Cs ₁
The average value of ammonia radicals contained per catalyst part by mass was 0.0051 parts, and the average value of nitrate radicals was 0.000046 parts.

(Preparation of catalyst 12)
Similar to the preparation of the catalyst 11, the molded body obtained in the molding step was calcined at 390 ° C. for 5 hours under air calcining to obtain “catalyst 12”. The composition of the catalyst 12 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P _1.5 V _0.5 Cu _0.3 Fe _0.4 Mg _0.15 Zn _0.1 Cs ₁
The average value of ammonia radicals contained per catalyst unit mass part was 0.0022 parts, and the average value of nitrate radicals was 0.000022 parts.

(Production of methacrylic acid)
Methacrylic acid was produced in the same manner as in Example 1 except that 12 g of the catalyst 11 was charged on the raw material gas inlet side of the reaction tube and 8 g of the catalyst 12 was charged on the outlet side. The results are shown in Table 1. Further, ΔTmax in the catalyst layer at this time was 18 ° C.

[Comparative Example 4]
(Preparation of catalyst 13)
A molded body obtained in the same manner as in Example 5 was calcined at 380 ° C. for 5 hours under air calcining to obtain “Catalyst 13”. The composition of catalyst 13 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P _1.5 V _0.5 Cu _0.3 Fe _0.4 Mg _0.15 Zn _0.1 Cs ₁
The average value of ammonia radicals contained per catalyst unit mass part was 0.0039 parts, and the average value of nitrate radicals was 0.000034 parts.

(Production of methacrylic acid)
Methacrylic acid was produced in the same manner as in Example 1 except that 20 g of catalyst 13 alone was charged in the reaction tube. The results are shown in Table 1. Further, ΔTmax in the catalyst layer at this time was 29 ° C.

Example 6
100 parts of ammonium paramolybdate was dissolved in 200 parts of pure water at 70 ° C. The solution which melt | dissolved 2.8 parts of ammonium metavanadate, 8.2 parts of 85 mass% phosphoric acid in 30 parts of pure water, the solution which melt | dissolved 1.1 parts of copper nitrate in 30 parts of pure water, and iron nitrate 3.8 there. A solution prepared by dissolving 10 parts of pure water in 10 parts was sequentially added and heated to 90 ° C. while stirring. After stirring for 5 hours while maintaining the liquid temperature at 90 ° C., 9.2 parts of cesium nitrate was added to 100 parts of pure water. The solution dissolved in was added and evaporated to dryness with heating and stirring. The obtained solid was dried at 130 ° C. for 16 hours and then pulverized. The powder thus obtained was molded in the same manner as in Example 1 to obtain a molded body.

(Preparation of catalyst 14)
The molded body thus obtained was calcined at 390 ° C. for 5 hours under air calcining to obtain “Catalyst 14”. The composition of catalyst 14 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P _1.5 V _0.5 Cu _0.1 Fe _0.2 Cs ₁
The average value of ammonia radicals contained per unit mass of catalyst layer was 0.0027 parts, and the average value of nitrate radicals was 0.000024 parts.

(Production of methacrylic acid)
Methacrylic acid was produced in the same manner as in Example 1 except that 10 g of catalyst 1 was charged on the inlet side of the raw material gas of the reaction tube and 10 g of catalyst 14 was charged on the outlet side. The results are shown in Table 1. Further, ΔTmax in the catalyst layer at this time was 20 ° C.

Example 7
(Preparation of catalyst 15)
A molded body obtained in the same manner as in Example 6 was calcined at 370 ° C. for 5 hours under air calcining to obtain “Catalyst 15”. The composition of catalyst 15 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P _1.5 V _0.5 Cu _0.1 Fe _0.2 Cs ₁
The average value of ammonia radicals contained per unit mass part of the catalyst layer was 0.0065 parts, and the average value of nitrate radicals was 0.000060 parts.

(Production of methacrylic acid)
Methacrylic acid was produced in the same manner as in Example 1 except that 10 g of the catalyst 15 was charged on the inlet side of the raw material gas of the reaction tube and 10 g of the catalyst 2 was charged on the outlet side. The results are shown in Table 1. Further, ΔTmax in the catalyst layer at this time was 18 ° C.

[Comparative Example 5]
(Preparation of catalyst 16)
A molded body obtained in the same manner as in Example 6 was calcined at 380 ° C. for 5 hours under air calcining to obtain “Catalyst 16”. The composition of catalyst 16 excluding oxygen atoms, ammonia radicals and nitrate radicals is
Mo ₁₂ P _1.5 V _0.5 Cu _0.1 Fe _0.2 Cs ₁
The average value of ammonia radicals contained per unit mass part of the catalyst layer was 0.0044 parts, and the average value of nitrate radicals was 0.000048 parts.

(Production of methacrylic acid)
Methacrylic acid was produced in the same manner as in Example 1 except that 20 g of catalyst 16 alone was charged in the reaction tube. The results are shown in Table 1. Further, ΔTmax in the catalyst layer at this time was 35 ° C.

Example 8
(Preparation of catalyst 17)
After 20 g of the molded body obtained in the same manner as in Example 1 was filled in the same reaction tube as in Example 1, the temperature was raised to 380 ° C. at 25 ° C./hr while supplying dry air at a contact time of 10 seconds, and left as it was. Calcination was performed for 5 hours to obtain “Catalyst 17”. The composition of the catalyst 17 excluding the ammonia and nitrate radicals is
Mo ₁₂ P _1.6 V _0.8 Cu _0.1 Sb _0.8 Cs ₁
Met.

(Production of methacrylic acid)
After the completion of the firing, the temperature of the reactor was lowered to 290 ° C., and then the same reaction gas as in Example 1 was passed in a contact time of 3.6 seconds in the opposite direction to the air supply during firing. The results are shown in Table 1. Further, ΔTmax in the catalyst layer at this time was 22 ° C.

(Quantification of ammonia and nitrate radicals)
The catalyst obtained in the same manner as in the preparation of the catalyst 17 was taken out from the reaction tube, and then the ammonia and nitrate radicals were quantified. As a result, the raw material gas was filled on the inlet side (firing gas outlet side) from the reference position. The average value of ammonia radicals contained per catalyst part by mass is 0.0054 parts, and the average value of nitrate radicals is 0.000068 parts, filling the outlet side of the raw material gas (firing gas inlet side) from the reference position. The average value of ammonia radicals contained per mass part of the catalyst unit was 0.0031 parts, and the average value of nitrate radicals was 0.000041 parts.

[Comparative Example 6]
(Preparation of catalyst 18)
10 g of the molded body obtained in the same manner as in Example 1 and 9.3 g of the molded body obtained in the same manner as in the preparation of the catalyst 8 in Example 4 were filled in a reaction tube similar to that in Example 1, and then dry air was added to the latter. While being fed in the direction in which the former molded body was filled from the molded body of No. 1 with a contact time of 10 seconds, the temperature was raised to 380 ° C. at 25 ° C./hr and calcined for 8 hours to obtain “Catalyst 18”. The composition of the catalyst 18 excluding the ammonia and nitrate radicals is such that the outlet side of the calcined gas (the inlet side of the raw material gas in the subsequent production of methacrylic acid) from the reference position,
Mo ₁₂ P _1.6 V _0.8 Cu _0.1 Sb _0.8 Cs ₁
The inlet side of the firing gas (the outlet side of the raw material gas in the subsequent methacrylic acid production)
Mo ₁₂ P ₁ V _0.5 Cu _0.3 K _1.2
Met.

(Production of methacrylic acid)
After the completion of the firing, the temperature of the reactor was lowered to 290 ° C., and then the same reaction gas as in Example 1 was passed in a contact time of 3.6 seconds in the opposite direction to the air supply during firing. The results are shown in Table 1. Further, ΔTmax in the catalyst layer at this time was 30 ° C.

(Quantification of ammonia and nitrate radicals)
The catalyst obtained in the same manner as in the preparation of the catalyst 18 was taken out of the reaction tube and then the ammonia and nitrate radicals were quantified. As a result, the catalyst was filled on the source gas inlet side (firing gas outlet side) from the reference position. The average value of ammonia radicals contained per catalyst unit mass is 0.0044 parts, and the average value of nitrate radicals is 0.000058 parts, filling the raw material gas outlet side (firing gas inlet side) from the reference position. The average value of ammonia radicals contained per mass part of the catalyst unit was 0.0041 parts, and the average value of nitrate radicals was 0.000036 parts.

Claims (5)

Fixed bed tube type consisting of a plurality of catalyst layers in which the catalyst filling part is divided from the inlet side to the outlet side of the raw material gas and filled with catalysts having different contents of ammonia and / or ammonium ions contained per unit mass part of the catalyst In a method for producing methacrylic acid, in which methacrolein is vapor-phase catalytically oxidized with molecular oxygen using a reactor,
The reference position is a position where the amount of the catalyst filled in the catalyst filling portion is 50% by mass of the total filling amount per reaction tube along the tube axis direction,
The average value of the ammonia and / or ammonium ion content contained per unit mass part of the catalyst charged on the inlet side of the raw material gas from the reference position is 0.02 parts by mass or less,
The average value of the ammonia and / or ammonium ion content contained per unit mass part of the catalyst charged from the reference position to the outlet side of the raw material gas, and per unit mass part of the catalyst charged from the reference position to the inlet side of the raw material gas The ratio of the average value of ammonia and / or ammonium ion content contained in the methacrylic acid is 1: α (1.3 ≦ α ≦ 10) by mass ratio.   The average value of the content of ammonia and / or ammonium ions contained per unit mass of the catalyst charged on the outlet side of the raw material gas from the reference position is 0.0005 to 0.01 parts by mass. The method for producing methacrylic acid according to claim 1. The reference position is a position where the amount of the catalyst filled in the catalyst filling portion is 50% by mass of the total filling amount per reaction tube along the tube axis direction,
The average value of nitric acid and / or nitrate ion content contained per unit mass part of the catalyst charged on the inlet side of the raw material gas from the reference position is 0.0003 parts by mass or less,
The average value of nitric acid and / or nitrate ion content contained per unit mass part of the catalyst charged from the reference position to the outlet side of the raw material gas, and per unit mass part of the catalyst charged from the reference position to the inlet side of the raw material gas The ratio of the average value of nitric acid and / or nitrate ion content contained in the methacrylic acid according to claim 1 or 2, wherein the mass ratio is 1: β (1.1 ≦ β ≦ 10). Production method.   The average value of the content of nitric acid and / or nitrate ions contained per unit mass part of the catalyst charged on the outlet side of the raw material gas from the reference position is 0.000001 to 0.0001 parts by mass. The manufacturing method of methacrylic acid in any one of Claims 1-3. The method for producing methacrylic acid according to any one of claims 1 to 4, wherein the catalyst is a composite oxide represented by the composition of the following formula (1).
Mo _a P _b X _c Y _d O _e (1)
(In the formula, Mo, P and O represent molybdenum, phosphorus and oxygen, respectively, X represents at least one element selected from the group consisting of potassium, rubidium, cesium and thallium, and Y represents iron, cobalt and 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, sulfur, selenium, tellurium, lanthanum, and cerium represent at least one element selected from the group consisting of a, b, c, and d , a = 12, 0.1 ≦ b ≦ 3, 0 .01 ≦ c ≦ 3, atomic ratio of each element satisfying 0 ≦ d ≦ 3, e is a, (This is the atomic ratio of oxygen necessary to satisfy the atomic ratio of each element represented by b, c, and d .)