JPWO2019163707A1 - Catalyst and direct-coupled two-stage catalytic gas phase oxidation method using the same - Google Patents

Abstract

Catalyst that enables long-term stable operation and high yield of final product by reducing by-products of aromatic compounds that are high-boiling compounds, and direct-coupled two-stage catalytic gas phase using the same An oxidation method is provided. The catalyst contains molybdenum, bismuth, iron, and an alkali metal as essential components, has an atomic ratio of alkali metal to 12 atoms of molybdenum of more than 0.3 and less than 1.0, and has a high temperature side by an ammonia thermal desorption method. Is not more than 0.026 mmol / g.

Description

  TECHNICAL FIELD The present invention relates to a catalyst containing molybdenum, bismuth, iron and an alkali metal, and a direct-coupled two-step catalytic gas-phase oxidation method using the same.

  As a method for producing the corresponding unsaturated aldehyde or unsaturated carboxylic acid using propylene, isobutylene, t-butyl alcohol or the like as a raw material or a method for producing 1,3-butadiene from butenes, a contact gas phase with molecular oxygen is used. Many oxidation methods have been proposed.

  For example, Patent Document 1 discloses a method for producing a composite oxide catalyst containing molybdenum and bismuth, wherein (1) an organic acid is added at least in a step of integrating a source compound of these component elements in an aqueous system, Ammonia thermal desorption method for the amount of catalyst acid on the high temperature side by the ammonia thermal desorption method, comprising the steps of: preparing a solution or slurry containing raw materials; and (2) drying and calcining the solution or slurry. Discloses a method for producing a composite oxide catalyst, wherein the ratio of the acid amount of the catalyst on the low temperature side is 0.14 or less.

  Patent Document 2 discloses a method of adding salts such as nitrates and ammonium salts to a catalyst precursor, Patent Document 3 a method of adding a chelating agent to a molybdenum-containing slurry, and Patent Document 4 discloses a method of adding a molybdenum compound and a bismuth compound. A method of adding aqueous ammonia at the time of integration is disclosed.

  These known techniques are designed to increase the yield of the obtained catalyst by devising various steps for adding the catalyst component.However, the simplicity and safety during the production of the catalyst, the reproducibility in the production of the catalyst, and the mechanical strength of the catalyst are improved. However, conventional catalysts are not yet sufficient in terms of environmental problems and the like, and improvement thereof has been desired.

  When at least one selected from isobutylene and t-butyl alcohol is subjected to a catalytic gas phase oxidation reaction, compounds having a relatively high boiling point, such as maleic acid and terephthalic acid, are added to the main product, in addition to methacrolein. At the same time, a polymer or tar-like substance is contained in the reaction product gas. When the reaction product gas containing such substances is subjected to the latter reaction as it is, these substances cause clogging in the piping and the latter catalyst packed bed, increasing the pressure loss, decreasing the catalytic activity, and causing methacrylic acid. Causes a decrease in the selectivity of the film. In addition, industrial production must be stopped in order to remove the blockage, which causes a great decrease in productivity. Such troubles often occur when the supply amount of isobutylene and / or t-butyl alcohol is increased or the concentration of isobutylene and / or t-butyl alcohol is increased in order to increase the productivity of methacrylic acid.

  In order to prevent such troubles, a commonly employed method is to stop the reaction periodically and fill the gas inlet side of the latter catalyst with a gas filled to prevent clogging in the catalyst layer and a decrease in the activity of the catalyst. Methods have been proposed for extracting and replacing the active substance. Alternatively, a method has been proposed in which methacrolein is once separated from a gas produced by a first-stage reaction, and the separated methacrolein is supplied to a second-stage reaction, thereby adopting a process for optimizing an oxidation reaction. Further, a method has been proposed in which the reaction is performed by diluting the raw material gas concentration more than necessary to lower the concentration of by-products. Patent Literature 5 discloses a method of keeping the temperature of a portion above the boiling point of maleic anhydride at a temperature higher than the boiling point of maleic anhydride in order to prevent clogging of a pipe or the like at an intermediate portion of the first and second stages of the reaction. A method for doing so is disclosed. Patent Literature 6 proposes a method of specifying the shape of a catalyst used in the latter-stage reaction, increasing the porosity between the catalysts, and suppressing blockage of solids from the former-stage reactor. However, these methods are also not sufficiently satisfactory as industrial methods. For long-term industrial production rather than a slight improvement in yield, it is desired to develop a catalyst with less by-products of high-boiling substances. ing.

Japanese Patent Application Laid-Open No. 2012-115825 Japanese Patent Application Laid-Open No. 2003-251183 Japanese Patent Application Laid-Open No. 2-214543 JP-A-2003-220335 Japanese Patent Application Laid-Open No. 50-126605 Japanese Patent Application Laid-Open No. 61-221149

  An object of the present invention is to provide a catalyst capable of providing long-term stable operation and a high yield of a final product by reducing by-products of an aromatic compound which is a high boiling point compound, and a catalyst using the catalyst. The present invention provides a direct-coupled two-stage catalytic gas phase oxidation method.

  In order to solve the above problems, the present inventors have proposed a catalyst comprising molybdenum, bismuth, iron and an alkali metal as essential components and having an atomic ratio of alkali metal to molybdenum of 12 atoms of more than 0.3 and less than 1.0. In, a catalyst having a specific acid amount and a direct-coupled two-step catalytic gas-phase oxidation method using the same suppress the by-product of aromatic compounds, which are high-boiling compounds, and provide long-term stable operation and high yield. They have found that they contribute to the production of final products, and have completed the present invention.

That is, the present invention
(1)
Molybdenum, bismuth, iron and an alkali metal are essential components, and the atomic ratio of the alkali metal to 12 atoms of molybdenum is greater than 0.3 and less than 1.0, and the acid of the catalyst on the high temperature side by the ammonia thermal desorption method A catalyst having an amount of 0.026 mmol / g or less,
(2)
The catalyst according to (1), wherein the acid amount of the catalyst on the high temperature side by the ammonia thermal desorption method is 0.024 mmol / g or less,
(3)
The catalyst according to (1) or (2), wherein the acid amount of the catalyst on the high-temperature side according to the ammonia thermal desorption method is 0.020 mmol / g or less.
(4)
The catalyst according to any one of (1) to (3), wherein the catalytically active component has a composition represented by the following formula (I):
_{Mo a1 Bi b1 Fe c1 A d1} B e1 C f1 D g1 E h1 O x1 (I)
(Where Mo is molybdenum, Bi is bismuth, Fe is iron, A is at least one element selected from cobalt and nickel, B is at least one element selected from lithium, sodium, potassium, rubidium and cesium, and C is At least one element selected from boron, phosphorus, chromium, manganese, zinc, arsenic, niobium, tin, antimony, tellurium, cerium and lead, D is at least one element selected from silicon, aluminum, titanium and zirconium, E is At least one element selected from alkaline earth metals, and O is oxygen, and a1, b1, c1, d1, e1, f1, g1, h1, and x1 are Mo, Bi, Fe, A, B, C, Represents the atomic ratio of D, E and O, and when a1 = 12, 0.1 ≦ b1 ≦ 10 0.1 ≦ c1 ≦ 20, 1 ≦ d1 ≦ 20, 0.3 <e1 <1.0, 0 ≦ f1 ≦ 10, 0 ≦ g1 ≦ 30, 0 ≦ h1 ≦ 5, and x1 is a value of each element. It is a value determined by the oxidation state.)
(5)
The catalyst according to any one of (1) to (4), wherein the alkali metal is cesium,
(6)
The catalyst according to any one of (1) to (5), which is a shaped catalyst.
(7)
A catalyst in which a catalytically active component is supported on a spherical carrier, the average particle size of the catalyst is 3.0 mm or more and 10.0 mm or less, and the ratio of the catalytically active component to the whole catalyst is 20% by mass or more and 80% by mass or less. A catalyst according to any one of (1) to (6),
(8)
A step of drying a slurry containing a metal component constituting the composition of the catalytically active component to obtain a dry powder, a step of pre-baking the dried powder at a temperature of 200 ° C. to 600 ° C. to obtain a pre-fired powder, The method for producing a catalyst according to any one of (1) to (7), including a step of forming a prefired powder and a step of again firing the obtained molded article at a temperature of 200 ° C to 600 ° C. ,
(9)
(1) using the catalyst according to any one of (1) to (7) (hereinafter referred to as catalyst (A)) to obtain an unsaturated carboxylic acid compound after passing through an unsaturated aldehyde compound; Gas phase oxidation method,
(10)
A first step in which an unsaturated aldehyde compound is obtained using the catalyst (A), and an unsaturation using a catalyst different from the catalyst used in the first step (hereinafter referred to as catalyst (B)). The direct-coupled two-stage catalytic gas phase oxidation method according to (9), including a second-stage process for producing a saturated carboxylic acid compound,
(11)
The direct-coupled two-stage catalytic gas phase oxidation method according to (10), wherein the catalytically active component of the catalyst (B) has a composition represented by the following formula (II).
_{Mo 10 V a2 P b2 Cu c2} As d2 X e2 O g2 (II)
(In the formula, Mo, V, P, Cu, As, and O represent molybdenum, vanadium, phosphorus, copper, arsenic, and oxygen, respectively, and X represents Ag, Mg, Zn, Al, B, Ge, Sn, Pb, and Ti. , Zr, Sb, Cr, Re, Bi, W, Fe, Co, Ni, Ce and Th represent at least one element selected from the group consisting of Mo, V, P, Cu and As, respectively. And a represents the atomic ratio of X, a2 is 0.1 ≦ a2 ≦ 6, b2 is 0.5 ≦ b2 ≦ 6, c2 is 0 <c2 ≦ 3, d2 is 0 ≦ d2 ≦ 3, and e2 is 0 ≦ e2 ≦ 3, and g2 is a value determined by the valence and atomic ratio of another element.)
(12)
The direct-coupled two-stage catalytic gas phase oxidation method according to any one of (9) to (11), wherein the unsaturated aldehyde is methacrolein, and the unsaturated carboxylic acid is methacrylic acid.
(13)
(9) A method for reducing an aromatic compound which is a by-product, using the direct-coupled two-stage catalytic gas phase oxidation method according to any one of (12) to (12).
(14)
The method for reducing an aromatic compound which is a by-product according to (13), wherein the aromatic compound is terephthalic acid,
(15)
(9) A method for producing an unsaturated aldehyde compound, an unsaturated carboxylic acid compound, or both, using the direct-coupled two-stage catalytic gas phase oxidation method according to any one of (9) to (12).

  The catalyst of the present invention contains molybdenum, bismuth, iron and an alkali metal as essential components, has an atomic ratio of alkali metal to molybdenum of 12 atoms of more than 0.3 and less than 1.0, and is prepared by an ammonia temperature-programmed desorption method. The acid amount of the catalyst on the high-temperature side is 0.026 mmol / g or less, and the direct-coupled two-stage catalytic gas-phase oxidation method using the catalyst is useful for reducing aromatic compounds, which are high-boiling by-products. It is valid. According to this method, it is possible to obtain a final product in a long-term stable operation and a high yield.

In particular, when at least one raw material selected from isobutylene and t-butyl alcohol is subjected to catalytic gas-phase oxidation using a molecular oxygen-containing gas, the production method of the present invention makes it possible to obtain an aromatic compound having a high boiling point. By-products of the compound can be reduced, and long-term stable operation and high production of methacrolein and / or methacrylic acid can be maintained.
Also, by reducing by-products, pipe blockage is less likely to occur, the number of shutdowns due to periodic cleaning can be reduced, and unsaturated aldehydes and / or unsaturated carboxylic acid compounds can be stably produced. is there.

  Hereinafter, embodiments of the present invention will be described in detail.

[About the catalyst (A)]
The catalyst of the present embodiment is a composite oxide catalyst containing molybdenum, bismuth, iron and an alkali metal, in which the atomic ratio of alkali metal to 12 atoms of molybdenum is greater than 0.3 and less than 1.0, and the temperature of ammonia increases. The acid amount of the catalyst on the high temperature side by the desorption method is 0.026 mmol / g or less. In the present specification, the catalyst having the above configuration is referred to as catalyst (A).

  In the catalyst (A), the acid amount of the catalyst on the high temperature side by the ammonia thermal desorption method is 0.026 mmol / g or less, preferably 0.024 mmol / g or less, more preferably 0.020 mmol / g or less. is there. With this acid amount, side reactions other than the oxidation reaction to the target compound are suppressed, and by-products other than the target compound are reduced. As a result, by-products of the high boiling point compound can be reduced. In particular, it is possible to stably obtain a final product such as an unsaturated aldehyde compound and / or an unsaturated carboxylic acid compound in a high yield. The lower limit is not particularly limited, but may be 0.0002 mmol / g or the like, and a preferable lower limit is 0.0012.

  When the catalyst (A) of the present embodiment is measured with an ammonia temperature-programmed desorption spectrum (for example, “BELCAT-B”, which can be measured by Nippon Bell Co., Ltd.), the range is 100 ° C. or more and 400 ° C. or less (low temperature side). Has one peak (the value of this acid amount is referred to as acid amount (L)), and one peak (the value of this acid amount is )). The peak of the peak in the range of 100 ° C. or more and 400 ° C. or less exists near 200 ° C., and the peak of the peak in the range of 400 ° C. or more exists near 600 ° C.

  The catalyst (A) is a composite oxide catalyst containing molybdenum, bismuth, iron, and an alkali metal, and has an atomic ratio of alkali metal to molybdenum of 12 atoms of more than 0.3 and less than 1.0. The lower limit of the atomic ratio of the alkali metal for more effectively suppressing the generation of the aromatic compound as a by-product is preferably 0.32, more preferably 0.34, and most preferably 0.36. The upper limit of the atomic ratio of the alkali metal is more preferably 0.8, still more preferably 0.6, and most preferably 0.5.

A preferred composition of the catalytically active component of the catalyst (A) is represented by the following general formula (I).
_{Mo a1 Bi b1 Fe c1 A d1} B e1 C f1 D g1 E h1 O x1 (I)
(Where Mo is molybdenum, Bi is bismuth, Fe is iron, A is at least one element selected from cobalt and nickel, B is at least one element selected from lithium, sodium, potassium, rubidium and cesium, and C is At least one element selected from boron, phosphorus, chromium, manganese, zinc, arsenic, niobium, tin, antimony, tellurium, cerium and lead, D is at least one element selected from silicon, aluminum, titanium and zirconium, E is At least one element selected from alkaline earth metals, and O is oxygen, and a1, b1, c1, d1, e1, f1, g1, h1, and x1 are Mo, Bi, Fe, A, B, C, Represents the atomic ratio of D, E and O, and when a1 = 12, 0.1 ≦ b1 ≦ 10 0.1 ≦ c1 ≦ 20, 1 ≦ d1 ≦ 20, 0.3 <e1 <1.0, 0 ≦ f1 ≦ 10, 0 ≦ g1 ≦ 30, 0 ≦ h1 ≦ 5, and x1 is a value of each element. It is a value determined by the oxidation state.)
The term "catalytically active component" used herein refers to a component that exhibits catalytic activity contained in the catalyst (A), the catalyst (B) described below, and the like. That is, when the catalyst contains an inert carrier, the inert carrier is not included in the catalytically active component.

  The starting material of each element constituting the catalyst (A) of the present embodiment is not particularly limited. For example, molybdenum oxide such as molybdenum trioxide, molybdenum acid, paramolybdate Molybdic acid or a salt thereof such as ammonium or ammonium metamolybdate, a heteropoly acid containing molybdenum such as phosphomolybdic acid or silico-molybdic acid or a salt thereof can be used.

  As a raw material of the bismuth component, bismuth salts such as bismuth nitrate, bismuth carbonate, bismuth sulfate, and bismuth acetate, bismuth trioxide, and metal bismuth can be used. These raw materials can be used as a solid or as an aqueous solution, a nitric acid solution, or a slurry of a bismuth compound generated from the aqueous solution. It is preferable to use a nitrate, a solution thereof, or a slurry generated from the solution. The lower limit of b1 in the composition of the above general formula (I) is more preferably 0.3, still more preferably 0.5, and particularly preferably 0.8. As the upper limit of b1, 8 is more preferable, 6 is further preferable, and 4 is particularly preferable.

  Examples of the raw material of the alkali metal as the component B represented by the general formula (I) include, but are not limited to, hydroxides, chlorides, and carbonates of component elements (lithium, sodium, potassium, rubidium, and cesium). , Sulfates, nitrates, oxides or acetates. Preferably, the compound is a compound containing cesium, for example, cesium hydroxide, cesium chloride, cesium carbonate, cesium sulfate, cesium oxide, and the like. Particularly, cesium nitrate is preferably used. In the composition of the general formula (I), e satisfies 0.3 <e1 <1.0, preferably 0.32 ≦ e1 ≦ 0.8, and more preferably 0.34 ≦ e1 ≦ 0.6. Further, the alkali metal in the catalyst (A) is preferably cesium, and the B component of the general formula (I) in the above preferred embodiment is preferably cesium.

  If the atomic ratio of the alkali metal raw material as the component B represented by the general formula (I) is too low, the acid amount (H) of the catalyst obtained by the ammonia temperature-programmed desorption method becomes high, and the by-product of the high boiling point compound is produced. Is undesirably increased. In addition, when the atomic ratio of the B component raw material is high, by-products of the high-boiling compounds are reduced and industrial production can be performed for a long period of time, but the conversion of the raw material decreases, and as a result, a satisfactory yield is obtained. Improvement cannot be expected.

  Starting materials for the other component elements include ammonium salts, nitrates, carbonates, chlorides, sulfates, hydroxides, organic acid salts, oxides, and mixtures thereof, which are generally used for this type of catalyst. May be used in combination, but ammonium salts and nitrates are preferably used. As a lower limit of c1 in the composition of the above-mentioned general formula (I), 0.3 is more preferred, 0.6 is still more preferred, and 1 is particularly preferred. As the upper limit of c1, 16 is more preferable, 12 is further preferable, and 8 is particularly preferable. As the lower limit of d1 in the composition of the general formula (I), 3 is more preferable, 5 is more preferable, and 6 is particularly preferable. As the upper limit of d1, 16 is more preferable, 14 is further preferable, and 12 is particularly preferable. As an upper limit of f1 in the composition of the general formula (I), 8 is more preferable, 6 is more preferable, and 4 is particularly preferable. As the upper limit of g1 in the composition of the general formula (I), 20 is more preferable, 15 is more preferable, and 10 is particularly preferable. As the upper limit of h1 in the composition of the general formula (I), 4 is more preferable, 3 is further preferable, and 2 is particularly preferable.

  In the production of the catalyst (A), these compounds containing an active ingredient may be used alone or in combination of two or more. The slurry liquid can be obtained by uniformly mixing each active ingredient-containing compound and water. The amount of water used in the slurry liquid is not particularly limited as long as the entire amount of the compound used can be completely dissolved or uniformly mixed. The amount of water used may be appropriately determined in consideration of the drying method and the drying conditions. Usually, it is 200 parts by mass or more and 2000 parts by mass or less based on 100 parts by mass of the total mass of the compound for slurry preparation. Although the amount of water may be large, if it is too large, there are many disadvantages such as an increase in energy cost in a drying step and a case where drying cannot be performed completely.

  The slurry liquid of the source compound of each component element is obtained by mixing the above source compounds together (a) collectively, (b) collectively mixing and then aging, (c) stepwise. It is preferable to prepare by a method of mixing, (d) a method of repeating the mixing and aging treatment stepwise, and a method of combining (a) to (d). Here, the ripening means that "an industrial raw material or a semi-finished product is processed under specific conditions such as a certain time and a certain temperature to obtain necessary physical properties and chemical properties, increase or advance a predetermined reaction. Operation ". In the present embodiment, the above-mentioned certain time refers to a range of 5 minutes to 24 hours, and the certain temperature refers to a range of room temperature or higher and the boiling point of an aqueous solution or water dispersion or lower.

  In the present embodiment, the shape of the stirring blade of the stirrer used when mixing the essential active ingredients is not particularly limited, and propeller blades, turbine blades, paddle blades, inclined paddle blades, screw blades, anchor blades, ribbon blades, large-sized Arbitrary stirring blades such as lattice blades can be used in one stage or the same blade or different blades in two or more stages in the vertical direction. Further, a baffle (baffle) may be provided in the reaction tank as needed.

  Next, the slurry liquid thus obtained is dried. The drying method is not particularly limited as long as the slurry liquid can be completely dried, and examples thereof include drum drying, freeze drying, spray drying, and evaporation to dryness. Of these, in the present embodiment, spray drying which can dry the slurry liquid into powder or granules in a short time is particularly preferable. The drying temperature of the spray drying varies depending on the concentration of the slurry liquid, the feeding speed, and the like, but the temperature at the outlet of the dryer is generally 70 ° C. or more and 150 ° C. or less. In this case, it is preferable to dry the obtained slurry liquid so that the average particle diameter of the dried slurry liquid is 10 μm or more and 700 μm or less.

  The catalyst precursor obtained as described above is preliminarily calcined, molded, and finally calcined, whereby the molded shape can be controlled and maintained, and a catalyst having particularly excellent mechanical strength for industrial use can be obtained. As a result, stable catalytic performance can be exhibited.

  For the molding, any of a molding method in which the carrier is supported on a carrier such as silica and a non-supporting molding in which the carrier is not used can be adopted. Specific molding methods include, for example, tablet molding, press molding, extrusion molding, granulation molding and the like. As the shape of the molded product, for example, a columnar shape, a ring shape, a spherical shape, or the like can be appropriately selected in consideration of operating conditions. A supported catalyst having an average particle size of 3.0 mm or more and 10.0 mm or less, preferably an average particle size of 3.0 mm or more and 8.0 mm or less, in which a catalytically active component is supported on a spherical carrier, particularly an inert carrier such as silica or alumina, is used. It is preferable. When supported on a carrier, the ratio of the catalytically active component to the entire catalyst is preferably 20% by mass or more and 80% by mass or less. At the time of molding, a small amount of a known additive such as graphite or talc may be added. Further, as the carrier, silicon carbide, alumina, silica alumina, mullite, alundum, or the like may be used.

  The pre-firing method and pre-firing conditions or the main firing method and main firing conditions are not particularly limited, and known processing methods and conditions can be applied. Optimum conditions for the pre-firing or main firing vary depending on the catalyst raw material used, the catalyst composition, the preparation method, and the like. Is performed at 300 ° C. or more and 550 ° C. or less for 0.5 hour or more, preferably for 1 hour or more and 40 hours or less. Here, the inert gas refers to a gas that does not decrease the reaction activity of the catalyst, and specific examples include nitrogen, carbon dioxide, helium, and argon.

Since the catalyst (A) has a specific composition and a specific acid amount, generation of an aromatic compound can be effectively reduced.
In addition, since this effect is particularly effective in suppressing the generation of an aromatic aldehyde compound, it is more effective to use it in the step of obtaining an unsaturated aldehyde compound (defined as the first step in this specification). . In addition, since the aromatic compound is often a precursor of terephthalic acid, the direct-coupled two-step catalytic gas phase oxidation method of the present embodiment is particularly effective in suppressing the by-product of terephthalic acid.

  The direct-coupled two-stage catalytic gas-phase oxidation method is different from the separation method in which the target product is separated from the first-stage product gas and then subjected to the second-stage reaction, and the first-stage product gas is directly transferred to the second-stage reaction gas. It is a method to be served on the stage. In addition, the direct-coupled two-stage catalytic gas phase oxidation method of the present embodiment uses at least one raw material selected from isobutylene and t-butyl alcohol using a molecular oxygen-containing gas in the presence of an oxidation catalyst composition. It is particularly preferably used in producing methacrolein and / or methacrylic acid by catalytic gas phase oxidation.

[About the catalyst (B)]
In the direct-coupled two-stage catalytic gas phase oxidation method of the present embodiment, in the step of producing an unsaturated carboxylic acid (hereinafter referred to as the second step), a catalyst different from the catalyst used in the first step is used. (Hereinafter referred to as catalyst (B)) is preferably used. Here, "different" means that the composition or the production method of the catalyst is different, and if the catalyst is produced by the same composition and the same production method, it is "different" even if there are some differences in physical property values. Not something.
The catalyst (B) is not particularly limited as long as it is different from the catalyst used in the first step, and may or may not satisfy the conditions of the catalyst (A).

A preferred composition of the catalytically active component of the catalyst (B) is represented by the following general formula (II).
_{Mo 10 V a2 P b2 Cu c2} As d2 X e2 O g2 (II)
(In the formula, Mo, V, P, Cu, As, and O represent molybdenum, vanadium, phosphorus, copper, arsenic, and oxygen, respectively, and X represents Ag, Mg, Zn, Al, B, Ge, Sn, Pb, and Ti. , Zr, Sb, Cr, Re, Bi, W, Fe, Co, Ni, Ce and Th represent at least one element selected from the group consisting of Mo, V, P, Cu and As, respectively. And a represents the atomic ratio of X, a2 is 0.1 ≦ a2 ≦ 6, b2 is 0.5 ≦ b2 ≦ 6, c2 is 0 <c2 ≦ 3, d2 is 0 ≦ d2 ≦ 3, and e2 is 0 ≦ e2 ≦ 3, and g2 is a value determined by the valence and atomic ratio of another element.)

  In producing the catalyst (B) containing the catalytically active component having the preferred composition, a method generally known as a method for preparing this kind of catalyst, for example, an oxide catalyst, a catalyst having a heteropolyacid or a salt structure thereof, is employed. it can. Raw materials that can be used in producing the catalyst are not particularly limited, and various materials can be used. For example, as a molybdenum compound, ammonium molybdate, molybdic acid, molybdenum oxide and the like can be used, as a vanadium compound, ammonium metavanadate, vanadium pentoxide and the like can be used, and as a phosphorus compound, phosphoric acid or a salt thereof, polymerization Phosphoric acid or a salt thereof can be used, and as the copper compound, copper oxide, copper phosphate, copper sulfate, copper nitrate, copper molybdate, copper metal, etc. can be used, and antimony, arsenic, silver, magnesium, zinc, aluminum, Boron, germanium, tin, lead, titanium, zirconium, chromium, rhenium, bismuth, tungsten, iron, cobalt, nickel, cerium, thorium, potassium and rubidium compounds include nitrates, sulfates, carbonates and phosphates, respectively. , Organic acid salts, halides, hydroxides, oxidation , Metal or the like can be used.

  In the production of the catalyst (B), these compounds containing an active ingredient may be used alone or in combination of two or more. A slurry liquid can be prepared according to the same method as that described for the catalyst (A). The obtained slurry liquid is dried to obtain a catalytically active component solid. The drying method is not particularly limited as long as the slurry liquid can be completely dried, and includes, for example, drum drying, freeze drying, spray drying, and evaporation to dryness. Spray drying, which can be dried, is preferred. The drying temperature of the spray drying varies depending on the concentration of the slurry liquid, the liquid sending speed, and the like, but the temperature at the outlet of the dryer is generally 70 to 150 ° C. Further, it is preferable that the dried slurry liquid obtained at this time is dried so that the average particle diameter thereof is 10 to 700 μm.

  Particularly preferred among the catalytically active component solids of the present embodiment are catalysts having a heteropolyacid structure. The catalyst having the heteropolyacid structure has phosphorus banadomolybdic acid as a basic skeleton, and other constituent elements are incorporated into the heteropolyacid structure, thereby contributing to improvement in catalytic activity and selectivity and thermal stability of the structure. It is thought that it also contributed to the improvement of the performance. The catalyst having the heteropolyacid structure is a catalyst having a particularly long life. A catalyst having a heteropolyacid structure can be easily prepared by a general method for preparing a heteropolyacid.

  The catalytically active component solid obtained as described above can be used as it is for a coating mixture, but when calcined, moldability may be improved, which is preferable. The firing method and firing conditions are not particularly limited, and known processing methods and conditions can be applied. The optimum conditions for the calcination vary depending on the catalyst raw material, catalyst composition, preparation method and the like to be used, but the calcination temperature is usually 100 to 350 ° C, preferably 150 to 300 ° C, and the calcination time is 1 to 20 hours. The firing is usually performed in an air atmosphere, but may be performed in an inert gas atmosphere such as nitrogen, carbon dioxide, helium, or argon, or may be further performed as necessary after firing in an inert gas atmosphere. The firing may be performed in an air atmosphere.

  Further, in the present embodiment, the compound containing an active ingredient in preparing the slurry does not necessarily need to contain all the active ingredients, and some of the ingredients may be used before the coating step described below. .

  The shape of the catalyst (B) of the present embodiment is not particularly limited, and is used by molding into a column, a tablet, a ring, a sphere or the like in order to reduce the pressure loss of the reaction gas in the oxidation reaction. Among these, it is particularly preferable to coat the inert carrier with the solid of the catalytically active component to obtain a coated catalyst since selectivity and removal of heat of reaction can be expected.

  This coating step is preferably a rolling granulation method described below. In this method, for example, in a device having a flat or uneven disk at the bottom of a fixed container, by rotating the disk at a high speed, the carrier in the container is vigorously stirred by repetition of rotation and revolving motion. This is a method in which a carrier is coated with a coating mixture in which a binder, a catalytically active component solid, and, if necessary, other additives such as a molding aid and a strength improver are added thereto.

  The method of adding the binder is as follows: 1) preliminarily mixing with the coating mixture, 2) adding the coating mixture into the fixed container at the same time, and 3) adding the coating mixture into the fixed container and then adding it. 4) Addition before adding the coating mixture into the fixed container, 5) Separate the coating mixture and the binder, and appropriately combine 2) to 4) to add all of them. . Of these, in 5), for example, the addition rate is adjusted using an auto feeder or the like so that the coating mixture does not adhere to the fixed container wall, and the coating mixture does not agglomerate and a predetermined amount is supported on the carrier. Is preferred.

  The binder is not particularly limited as long as it is at least one selected from the group consisting of water and organic compounds having a boiling point at 150 ° C. or less at 1 atm or less. Specific examples of binders other than water include alcohols such as methanol, ethanol, propanols and butanols, preferably alcohols having 1 to 4 carbon atoms, ethers such as ethyl ether, butyl ether or dioxane, and esters such as ethyl acetate or butyl acetate. , Acetone or ketones such as methyl ethyl ketone, and aqueous solutions thereof, with ethanol being particularly preferred. When ethanol is used as the binder, it is preferable that ethanol / water = 10/0 to 0/10 (mass ratio), preferably 9/1 to 1/9 (mass ratio) by mixing with water. The amount of the binder to be used is generally 2 to 60 parts by mass, preferably 10 to 50 parts by mass, per 100 parts by mass of the coating mixture.

  Specific examples of the carrier in the coating include a spherical carrier having a diameter of 1 to 15 mm, preferably 2.5 to 10 mm, such as silicon carbide, alumina, silica alumina, mullite, and alundum. These carriers usually have a porosity of 10 to 70%. The ratio of the carrier and the coating mixture is usually such that the coating mixture / (coating mixture + carrier) = 10 to 75% by mass, preferably 15 to 60% by mass. When the proportion of the coating mixture is large, the reaction activity of the coated catalyst increases, but the mechanical strength tends to decrease. Conversely, when the proportion of the coating mixture is small, the mechanical strength is large, but the reaction activity tends to be small. In the above, as a molding aid used as necessary, silica gel, diatomaceous earth, alumina powder and the like can be mentioned. The amount of the molding aid used is usually 1 to 60 parts by mass with respect to 100 parts by mass of the catalytically active component solid. Further, if necessary, the use of an inorganic fiber (for example, a ceramic fiber or a whisker) that is inert to the catalytically active component solid and the reaction gas as a strength improver is useful for improving the mechanical strength of the catalyst, Glass fibers are preferred. The amount of these fibers to be used is generally 1 to 30 parts by mass based on 100 parts by mass of the catalytically active component solid.

  The coated catalyst obtained as described above can be directly used as a catalyst in a catalytic gas-phase oxidation reaction, but calcining is preferred because the catalytic activity may be improved in some cases. The firing method and firing conditions are not particularly limited, and known processing methods and conditions can be applied. Optimum conditions for the calcination vary depending on the used catalyst raw material, catalyst composition, preparation method and the like, but the calcination temperature is usually 100 to 450 ° C, preferably 270 to 420 ° C, and the calcination time is 1 to 20 hours. The firing is usually performed in an air atmosphere, but may be performed in an inert gas atmosphere such as nitrogen, carbon dioxide, helium, or argon, or may be further performed as necessary after firing in an inert gas atmosphere. The firing may be performed in an air atmosphere. By supporting the catalyst (B) used in the present embodiment on a carrier, favorable effects such as improved heat resistance, improved life, and increased reaction yield can be expected. As the material of the carrier, known materials such as alumina, silica, titania, zirconia, niobia, silica alumina, silicon carbide, carbide, and mixtures thereof can be used. The crystallinity and the mixing ratio of are not particularly limited, and an appropriate range should be selected in consideration of the performance, moldability, production efficiency, and the like of the final catalyst (B).

  The catalyst (A) of this embodiment is a method for producing the corresponding unsaturated aldehyde or unsaturated carboxylic acid using propylene, isobutylene, t-butyl alcohol or the like as a raw material, or producing 1,3-butadiene from butenes. It can be used in a method, in particular, a method for producing methacrolein or methacrylic acid by subjecting isobutylene or t-butyl alcohol to catalytic gas phase oxidation with molecular oxygen or a molecular oxygen-containing gas. By using the catalyst (A) in the above method, by-products of aromatic compounds (particularly terephthalic acid) can be effectively suppressed. In addition, the target product can be produced in a high yield by suppressing the temperature of the hot spot, and as a result, the price competitiveness of the product can be expected to be improved as compared with known methods.

The catalyst (A) is obtained by subjecting at least one kind of raw material selected from isobutylene and t-butyl alcohol to catalytic gas-phase oxidation using a molecular oxygen-containing gas in the presence of a catalyst to give methacrolein and / or It can be suitably used when producing methacrylic acid. The method of flowing the raw material gas in the production method of the present embodiment may be an ordinary single flow method or a recycling method, and can be carried out under generally used conditions, and is not particularly limited. For example, isobutylene as a starting material at room temperature is 1 to 10% by volume, preferably 4 to 9% by volume, molecular oxygen is 3 to 20% by volume, preferably 4 to 18% by volume, water vapor is 0 to 60% by volume, Preferably, 4 to 50% by volume, 20 to 80% by volume, preferably 30 to 60% by volume of a mixed gas containing an inert gas such as carbon dioxide and nitrogen is filled in the reaction tube in the catalyst of the present embodiment. The reaction is carried out by introducing at a space velocity of 300 to 5000 hr ^-1 at a pressure of normal pressure to 10 atm at -450 ° C.

Hereinafter, the present invention will be described more specifically with reference to examples.
In the examples, the conversion, yield, and selectivity are defined as follows.
Raw material conversion rate = (moles of t-butyl alcohol or isobutylene reacted in the first step) / (moles of t-butyl alcohol or isobutylene supplied to the first step) * 100
First-stage process methacrolein yield = (number of moles of methacrolein generated in first-stage process) / (number of moles of t-butyl alcohol or isobutylene supplied to first-stage process) * 100
-First-stage methacrylic acid yield = (moles of methacrylic acid generated in the first-stage process) / (moles of t-butyl alcohol or isobutylene supplied to the first-stage process) * 100
-Effective yield = first-stage step methacrolein yield + first-stage step methacrylic acid yield-Second-stage step methacrolein yield = (number of moles of methacrolein generated in the second-stage step) / (Molar number of t-butyl alcohol or isobutylene supplied to the first step) * 100
-Second-stage process methacrolein conversion = (first-stage process methacrolein yield-second-stage process methacrolein yield) / (first-stage process methacrolein yield) * 100
-Final methacrylic acid yield = (moles of methacrylic acid generated in the first step) + (moles of methacrylic acid generated in the second step) / (t-butyl supplied to the first step) The number of moles of alcohol or isobutylene) * 100

  The acid amount of the composite oxide catalyst containing molybdenum and bismuth by the ammonia thermal desorption method in this example was measured using a catalyst analyzer (trade name: "BELCAT-B", manufactured by Nippon Bell Co., Ltd.). did. After accurately weighing 0.3 g of the catalyst, the catalyst was filled in a measuring tube and subjected to a catalyst pretreatment at a treatment temperature of 500 ° C. for 1 hour in a helium atmosphere. Next, ammonia gas was adsorbed at an adsorption temperature of 100 ° C., evacuated for 30 minutes, heated up to 600 ° C. at a rate of 10 ° C./min, and the amount of ammonia desorbed per unit weight of the molded catalyst was measured.

The quantification of terephthalic acid was performed using liquid chromatography (trade name: “UltiMate 3000 HPLC system”, manufactured by Thermo Scientific). In the examples, the terephthalic acid yield was calculated according to the following equation.
Terephthalic acid yield (%) = (moles of terephthalic acid produced) / (moles of t-butanol or isobutylene supplied) * 100

[Evaluation on Catalyst (A)]
(Oxidation reaction test)
A stainless steel reactor having an inner diameter of 22.2 mm, in which a jacket for circulating a molten salt as a heat medium and a thermocouple for measuring the temperature of the catalyst layer were installed on a tube shaft, was filled with the formed catalyst. A mixed gas having a starting material molar ratio of isobutylene: oxygen: nitrogen: water = 1: 2.2: 12.5: 1.0 was supplied to the reactor for a contact time of 2.4 seconds (NTP basis), and 0 The reaction was performed under a pressure of 0.05 kgf. Table 1 shows the reaction results, the acid amount of the molded catalyst and the terephthalic acid yield by the ammonia thermal desorption method.

[Example 1]
While heating and stirring 3040 ml of distilled water, 800 g of ammonium molybdate and 29 g of cesium nitrate were dissolved to obtain an aqueous solution (A). Separately, 791 g of cobalt nitrate, 267 g of ferric nitrate, and 88 g of nickel nitrate were dissolved in 607 ml of distilled water to prepare an aqueous solution (B). An aqueous solution (C) was prepared by dissolving 306 g of bismuth nitrate in 402 ml of acidified distilled water by adding 78 ml of concentrated nitric acid. The aqueous solution (A) was mixed with (B) and (C) in this order with vigorous stirring, and the resulting suspension was dried using a spray drier and preliminarily calcined at 440 ° C. for 5 hours. ) Got. At this time, the composition ratio excluding oxygen of the catalytically active component was represented by the following atomic ratio: Mo = 12, Bi = 1.7, Fe = 1.8, Co = 7.2, Ni = 0.8, Cs = 0.4. Met.

Thereafter, a powder obtained by mixing 5 parts by mass of crystalline cellulose with 100 parts by mass of the pre-fired powder (D) was supported on an inert carrier (particle size: 4.0 mm). The loading was performed so that the ratio of the pre-fired powder (D) to the entire catalyst after molding was 40% by mass.
The molded product thus obtained was fully fired at 520 ° C. for 5 hours to obtain a molded catalyst (E). When the ammonia temperature-programmed desorption spectrum of the obtained molded catalyst was measured, it had one peak in the range of 100 ° C. or more and 400 ° C. or less, and had one peak in the range of 400 ° C. or more. . The peak of the peak in the range of 100 ° C. or more and 400 ° C. or less exists near 200 ° C. (the value of this acid amount is described as acid amount (L) in Table 1), and the peak of the peak in the range of 400 ° C. or more is 600 ° C. ° C (the value of this acid amount is indicated as acid amount (H) in Table 1). Table 1 shows the obtained results.

[Comparative Example 1]
A catalyst was prepared in the same manner as in Example 1 except that 29 g of cesium nitrate was changed to 0 g. At this time, the composition ratio excluding oxygen of the catalytically active component was Mo = 12, Bi = 1.7, Fe = 1.8, Co = 7.2, Ni = 0.8, and Cs = 0 in atomic ratio. Was. The ammonia heated desorption spectrum of the obtained molded catalyst showed a shape similar to that of the catalyst of Example 1. Table 1 shows the obtained results.

[Comparative Example 2]
A catalyst was prepared in the same manner as in Example 1 except that 29 g of cesium nitrate was changed to 11 g. At this time, the composition ratio excluding oxygen of the catalytically active component was expressed as Mo = 12, Bi = 1.7, Fe = 1.8, Co = 7.2, Ni = 0.8, Cs = 0.2 in atomic ratio. Met. The ammonia heated desorption spectrum of the obtained molded catalyst showed a shape similar to that of the catalyst of Example 1. Table 1 shows the obtained results.

[Example 2]
While heating and stirring 3040 ml of distilled water, 800 g of ammonium molybdate and 29 g of cesium nitrate were dissolved to obtain an aqueous solution (A). Separately, 718 g of cobalt nitrate, 297 g of ferric nitrate, and 264 g of nickel nitrate were dissolved in 678 ml of distilled water to prepare an aqueous solution (B). An aqueous solution (C) was prepared by dissolving 170 g of bismuth nitrate in 224 ml of acidified distilled water by adding 43 ml of concentrated nitric acid. The aqueous solution (A) was mixed with (B) and (C) in this order with vigorous stirring, and the resulting suspension was dried using a spray drier and preliminarily calcined at 440 ° C. for 5 hours. ) Got. At this time, the composition ratio excluding oxygen of the catalytically active component was represented by the following atomic ratio: Mo = 12, Bi = 0.9, Fe = 2.0, Co = 6.5, Ni = 2.4, Cs = 0.4. Met.

Thereafter, a powder obtained by mixing 5 parts by mass of crystalline cellulose with 100 parts by mass of the pre-fired powder (D) was supported on an inert carrier (particle size: 4.0 mm). The loading was performed so that the ratio of the pre-fired powder (D) to the entire catalyst after molding was 40% by mass.
The molded product thus obtained was fully fired at 520 ° C. for 5 hours to obtain a molded catalyst (E). When the ammonia temperature-programmed desorption spectrum of the obtained molded catalyst was measured, it had one peak in the range of 100 ° C. or more and 400 ° C. or less, and had one peak in the range of 400 ° C. or more. . The peak of the peak in the range of 100 ° C to 400 ° C was around 200 ° C, and the peak of the peak in the range of 400 ° C or more was around 600 ° C. Table 1 shows the obtained results.

[Example 3]
A catalyst was prepared in the same manner as in Example 2, except that 29 g of cesium nitrate was changed to 37 g. At this time, the composition ratio of the catalytically active component excluding oxygen was represented by atomic ratios of Mo = 12, Bi = 0.9, Fe = 2.0, Co = 6.5, Ni = 2.4, and Cs = 0. It was 5. The ammonia temperature-programmed desorption spectrum of the obtained molded catalyst showed a shape similar to that of the catalyst of Example 2. Table 1 shows the obtained results.

[Comparative Example 3]
A catalyst was prepared in the same manner as in Example 2 except that 74 g of cesium nitrate was used in Example 2. At this time, the composition ratio excluding oxygen of the catalytically active component was Mo = 12, Bi = 0.9, Fe = 2.0, Co = 6.5, Ni = 2.4, and Cs = 1. It was 0. The ammonia temperature-programmed desorption spectrum of the obtained molded catalyst showed a shape similar to that of the catalyst of Example 2. Table 1 shows the obtained results. Since the atomic ratio of cesium to 12 atoms of molybdenum is large, by-products of terephthalic acid are reduced and long-term industrial production is possible, but a satisfactory yield cannot be achieved because the raw material conversion rate has decreased. The result was.

[Comparative Example 4]
A catalyst was prepared in the same manner as in Example 2, except that 29 g of cesium nitrate was changed to 3 g. At this time, the composition ratio of the catalytically active component excluding oxygen was represented by atomic ratios of Mo = 12, Bi = 0.9, Fe = 2.0, Co = 6.5, Ni = 2.4, and Cs = 0. 04. The ammonia heated desorption spectrum of the obtained molded catalyst showed a shape similar to that of the catalyst of Example 1. Table 1 shows the obtained results.

[Comparative Example 5]
A catalyst was prepared in the same manner as in Example 2, except that 29 g of cesium nitrate was changed to 22 g. At this time, the composition ratio of the catalytically active component excluding oxygen was represented by atomic ratios of Mo = 12, Bi = 0.9, Fe = 2.0, Co = 6.5, Ni = 2.4, and Cs = 0. It was 3. The ammonia temperature-programmed desorption spectrum of the obtained molded catalyst showed a shape similar to that of the catalyst of Example 2. Table 1 shows the obtained results.

  In the above oxidation reaction (the first step in the direct two-stage catalytic gas phase oxidation), if the terephthalic acid yield is 0.01% or less, there is no problem in practicality. In Examples 1 and 2, the terephthalic acid yield was 0.01% or less, and it was confirmed that there was no practical problem.

[Evaluation of direct-coupled two-stage catalytic gas phase oxidation method]
[Example 4]
In Example 1, a molded product obtained by supporting a powder obtained by mixing crystalline cellulose with the preliminarily calcined powder (D) on an inert carrier was fully calcined at 540 ° C. for 5 hours to obtain a molded catalyst. At this time, the acid amount of the catalyst on the high temperature side by the ammonia thermal desorption method was 0.011 mmol / g.
The catalyst prepared as described in Example 1 and above was provided with a jacket for circulating a molten salt as a heat medium, for measuring the temperature at the boundary between the gas-phase oxidation catalyst layer and the inert packing layer. Was filled in a stainless steel reaction tube having an inner diameter of 22.6 mm, which was installed on a tube shaft. The filling was performed so that the layer height of the gas phase oxidation catalyst layer was 313 cm (90 cm for the 540 ° C. main firing product from the reaction material gas inlet portion, and 223 cm for the 520 ° C. main firing product). In addition, the inlet of the reaction raw material gas was filled with a spherical body having an average particle size of 5 mm and made of an inert filler mainly composed of silica and alumina so as to have a layer height of 140 cm. Next, a reaction material gas (composition (molar ratio); isobutylene: oxygen: steam: nitrogen = 1: 2.0: 1.6: 11.9) obtained by oxidizing isobutylene using molecular oxygen is placed in the reaction tube. ) Was supplied at a space velocity of 1000 hr ^-1 , the bath temperature was set to 340 ° C., and the reaction in the first step was started.
In the second stage oxidation reactor, a Mo-VP heteropolyacid catalyst described in Example 1 of Japanese Patent No. 5570142 was used. The catalyst was charged 350 cm into a stainless steel reaction tube having an inner diameter of 29.4 mm, and the gas generated by the oxidation reaction in the first step was introduced to perform the oxidation reaction in the second step. The reaction tube outlet pressure was adjusted to 0.05 MPa. The reaction bath temperature in the second stage is adjusted so that the conversion of methacrolein is from 65% to 85%, and the conversion of methacrolein in the second stage is controlled by terephthalic acid, which is the main component of the clogged pipe. Measurements were made on how the amount of formation changed. Table 2 shows the results.

[Comparative Example 6]
The reaction was started in the same manner as in Example 4 except that the catalyst prepared in Comparative Example 2 was charged into the oxidation reactor in the first step so that the layer height of the gas phase oxidation catalyst layer became 313 cm.
Note that the same catalyst as that used in Example 4 was used in the oxidation reactor in the second step. Table 2 shows the results.

  From the results of Example 4 and Comparative Example 6, it was confirmed that when the direct-coupled two-stage catalytic gas phase oxidation method of the present invention was used, the by-product rate of terephthalic acid was significantly reduced. In addition, it can be seen that the yield is also improved accordingly.

Although the present invention has been described in detail with reference to particular embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on February 20, 2018 (Japanese Patent Application No. 2018-27498) and a Japanese patent application filed on June 26, 2018 (Japanese Patent Application No. 2018-120455). And is incorporated by reference in its entirety. Also, all references cited herein are incorporated in their entirety.

  The present invention relates to a catalyst capable of providing long-term stable operation and a high yield of a final product by reducing by-products of an aromatic compound which is a high boiling point compound, and an unsaturated carboxylic acid using the catalyst. An object of the present invention is to provide a method for producing an acid compound. In particular, it is possible to reduce by-products of aromatic compounds, which are high-boiling compounds, under conditions of catalytic gas-phase oxidation using isobutylene or t-butyl alcohol as a raw material, and a molecular oxygen-containing gas. Operation and methacrolein and / or methacrylic acid can be obtained in high yield.

Claims (15)

  Molybdenum, bismuth, iron and an alkali metal are essential components, and the atomic ratio of the alkali metal to 12 atoms of molybdenum is more than 0.3 and less than 1.0, and the acid of the catalyst on the high temperature side by the ammonia thermal desorption method. A catalyst having an amount of 0.026 mmol / g or less.   The catalyst according to claim 1, wherein the acid amount of the catalyst on the high temperature side by the ammonia temperature-programmed desorption method is 0.024 mmol / g or less.   The catalyst according to claim 1 or 2, wherein the amount of acid of the catalyst on the high temperature side by the ammonia thermal desorption method is 0.020 mmol / g or less. The catalyst according to any one of claims 1 to 3, wherein the catalytically active component has a composition represented by the following formula (I).
_{Mo a1 Bi b1 Fe c1 A d1} B e1 C f1 D g1 E h1 O x1 (I)
(Where Mo is molybdenum, Bi is bismuth, Fe is iron, A is at least one element selected from cobalt and nickel, B is at least one element selected from lithium, sodium, potassium, rubidium and cesium, and C is At least one element selected from boron, phosphorus, chromium, manganese, zinc, arsenic, niobium, tin, antimony, tellurium, cerium and lead, D is at least one element selected from silicon, aluminum, titanium and zirconium, E is At least one element selected from alkaline earth metals, and O is oxygen, and a1, b1, c1, d1, e1, f1, g1, h1, and x1 are Mo, Bi, Fe, A, B, C, Represents the atomic ratio of D, E and O, and when a1 = 12, 0.1 ≦ b1 ≦ 10 0.1 ≦ c1 ≦ 20, 1 ≦ d1 ≦ 20, 0.3 <e1 <1.0, 0 ≦ f1 ≦ 10, 0 ≦ g1 ≦ 30, 0 ≦ h1 ≦ 5, and x1 is a value of each element. It is a value determined by the oxidation state.)   The catalyst according to any one of claims 1 to 4, wherein the alkali metal is cesium.   The catalyst according to any one of claims 1 to 5, which is a shaped catalyst.   A catalyst in which a catalytically active component is supported on a spherical carrier, the average particle size of the catalyst is 3.0 mm or more and 10.0 mm or less, and the ratio of the catalytically active component to the whole catalyst is 20% by mass or more and 80% by mass or less. A catalyst according to any one of claims 1 to 6.   A step of drying a slurry containing a metal component constituting the composition of the catalytically active component to obtain a dry powder, a step of pre-baking the dried powder at a temperature of 200 ° C. to 600 ° C. to obtain a pre-fired powder, The method for producing a catalyst according to any one of claims 1 to 7, comprising a step of forming a pre-fired powder and a step of again firing the obtained molded article at a temperature of 200 ° C or higher and 600 ° C or lower. .   A direct-coupled two-stage contact gas phase in which an unsaturated carboxylic acid compound is obtained after passing through an unsaturated aldehyde compound using the catalyst according to any one of claims 1 to 7 (hereinafter referred to as catalyst (A)). Oxidation method.   A first step in which an unsaturated aldehyde compound is obtained using the catalyst (A), and an unsaturation using a catalyst different from the catalyst used in the first step (hereinafter referred to as catalyst (B)). The direct-coupled two-stage catalytic gas-phase oxidation method according to claim 9, comprising a second-stage process in which a saturated carboxylic acid compound is produced. The direct-coupled two-stage catalytic gas phase oxidation method according to claim 10, wherein the catalytically active component of the catalyst (B) has a composition represented by the following formula (II).
_{Mo 10 V a2 P b2 Cu c2} As d2 X e2 O g2 (II)
(In the formula, Mo, V, P, Cu, As, and O represent molybdenum, vanadium, phosphorus, copper, arsenic, and oxygen, respectively, and X represents Ag, Mg, Zn, Al, B, Ge, Sn, Pb, and Ti. , Zr, Sb, Cr, Re, Bi, W, Fe, Co, Ni, Ce and Th represent at least one element selected from the group consisting of Mo, V, P, Cu and As, respectively. And a represents the atomic ratio of X, a2 is 0.1 ≦ a2 ≦ 6, b2 is 0.5 ≦ b2 ≦ 6, c2 is 0 <c2 ≦ 3, d2 is 0 ≦ d2 ≦ 3, and e2 is 0 ≦ e2 ≦ 3, and g2 is a value determined by the valence and atomic ratio of another element.)   The direct-coupled two-stage catalytic gas phase oxidation method according to any one of claims 9 to 11, wherein the unsaturated aldehyde is methacrolein, and the unsaturated carboxylic acid is methacrylic acid.   A method for reducing an aromatic compound as a by-product, using the direct-coupled two-stage catalytic gas phase oxidation method according to claim 9.   14. The method according to claim 13, wherein the aromatic compound is terephthalic acid.   A method for producing an unsaturated aldehyde compound, an unsaturated carboxylic acid compound, or both, using the direct-coupled two-stage catalytic gas phase oxidation method according to any one of claims 9 to 12.