Method for producing catalyst, method for producing α,β-unsaturated carboxylic acid using said catalyst, and method for producing α,β-unsaturated carboxylic acid ester

Abstract

Provided is a method for producing a catalyst capable of producing an α,β-unsaturated carboxylic acid with high selectivity. A method for producing a catalyst to be used when producing an α,β-unsaturated carboxylic acid by oxidizing an α,β-unsaturated aldehyde, the method comprising: (i) a step for preparing a slurry (liquid A) that contains molybdenum, phosphorus, and ammonium radicals; (ii-1) a step for preparing a slurry (liquid B1) by mixing the liquid A and a raw material compound that contains an alkali metal; (ii-2) a step for preparing a slurry (liquid B2) by mixing the liquid B1 and a raw material compound that contains ammonium radicals; and (iii) a step for drying the liquid B2 to obtain a catalyst. The ratio N1 / N2 is at least 0.25 and less than 1.00, where N1 is the number of moles of ammonium radicals contained in the liquid A, and N2 is the number of moles of ammonium radicals contained in the liquid B2.

Description

Method for producing a catalyst, method for producing an α,β-unsaturated carboxylic acid using the catalyst, and method for producing an α,β-unsaturated carboxylic acid ester

[0001] The present invention relates to a method for producing a catalyst for the production of α,β-unsaturated carboxylic acids, and to a method for producing α,β-unsaturated carboxylic acids and α,β-unsaturated carboxylic acid esters using the catalyst.

[0002] When oxidizing α,β-unsaturated aldehydes to produce α,β-unsaturated carboxylic acids, heteropoly acid catalysts such as phosphomolybdate and phosphomolybdate salts are known to be used as catalysts for the production of α,β-unsaturated carboxylic acids (hereinafter also simply referred to as "catalysts"). Such heteropoly acid catalysts include proton-type heteropoly acids, in which the countercation is a proton, and heteropoly salts, in which some of the protons are replaced with cations other than protons (hereinafter, proton-type heteropoly acids will also be simply referred to as "heteropoly acids," and proton-type heteropoly acids and / or heteropoly salts will also be referred to as "heteropoly acids (salts)"). Known heteropoly salts include alkali metal salts, in which the cation is an alkali metal ion, and ammonium salts, in which the cation is an ammonium ion. Numerous studies have been conducted on methods for producing such catalysts, most of which involve preparing an aqueous solution or slurry containing each element constituting the catalyst, and then drying and calcining it to produce the catalyst.

[0003] Patent Document 1 discloses a method for producing a precursor for a catalyst used to produce α,β-unsaturated carboxylic acids, in which an ammonium compound is used as the ammonium compound in a step of adding an ammonium compound to an aqueous slurry or aqueous solution containing a molybdenum-containing heteropoly acid, wherein the ammonium compound is one that contains ammonium carbamate in a specific proportion.

[0004] International Publication No. 2018 / 110126

[0005] However, the catalyst obtained by the method described in Patent Document 1 does not necessarily provide sufficient selectivity for α,β-unsaturated carboxylic acids when used in their production. Therefore, there is a need for the development of a catalyst that can produce α,β-unsaturated carboxylic acids with higher selectivity.

[0006] The present invention aims to provide a method for producing a catalyst capable of producing α,β-unsaturated carboxylic acids with high selectivity. Furthermore, the present invention aims to provide a method for producing α,β-unsaturated carboxylic acids and α,β-unsaturated carboxylic acid esters with high selectivity using the catalyst.

[0007] The inventors diligently conducted research to achieve the above objectives. As a result, they discovered that the above problems could be solved by dividing and adding a raw material compound containing ammonium root in a specific ratio, and thus completed the present invention.

[0008] In other words, the present invention includes the following configurations: [1] A method for producing a catalyst used when oxidizing an α,β-unsaturated aldehyde to produce an α,β-unsaturated carboxylic acid, comprising: (i) a step of preparing a slurry (solution A) containing molybdenum, phosphorus, and ammonium root; (iii-1) a step of mixing solution A and a raw material compound containing an alkali metal to prepare a slurry (solution B1); (iii-2) a step of mixing solution B1 and a raw material compound containing ammonium root to prepare a slurry (solution B2); and (iii) a step of drying solution B2 to obtain a catalyst, wherein when the number of moles of ammonium root contained in solution A is N1 and the number of moles of ammonium root contained in solution B2 is N2, the ratio N1 / N2 is 0.25 or more and less than 1.00. [2] The method for producing a catalyst according to [1], wherein the ratio N1 / N2 is 0.40 or more and less than 1.00. [3] A method for producing a catalyst according to [1] or [2], wherein in step (i), a mixture obtained by mixing a raw material compound containing molybdenum, a raw material compound containing phosphorus, and a raw material compound containing ammonium root with a solvent is stirred and held at a temperature of 80°C or higher for 1 hour or more to prepare liquid A. [4] A method for producing a catalyst according to any one of [1] to [3] that satisfies the following formula (I-1): n1 = 0.01 to 4.50 (I-1), where n1 is the molar ratio of ammonium root contained in liquid A when the molar ratio of molybdenum in the catalyst is 12. [5] A method for producing a catalyst according to any one of [1] to [4] that satisfies the following formula (I-2): m1 = 6 to 12 (I-2), where m1 is the molar ratio of molybdenum contained in liquid B1 when the molar ratio of molybdenum in the catalyst is 12. [6] A method for producing the catalyst according to any one of [1] to [5], wherein the catalyst has a composition represented by the following formula (II): P ａ Mo ｂ V ｃ Cu ｄ G ｅ (NH ４ ) ｆ O ｇ (II) In equation (II), P, Mo, V, Cu, NH４ P, Mo, V, Cu, ammonium radical, and O represent phosphorus, molybdenum, vanadium, copper, ammonium radical, and oxygen, respectively, G represents at least one element selected from the group consisting of alkali metals, a to g represent the molar ratios of the respective components, when b = 12, a = 0.5 to 3, c = 0.01 to 3, d = 0.01 to 2, e = 0.01 to 3, and f = 0.01 to 10, and g is the molar ratio of oxygen necessary to satisfy the valences of the respective components. [7] The method for producing a catalyst according to any one of [1] to [6], wherein in the step (ii-1), the temperature of the liquid A mixed with the raw material compound containing the alkali metal is 30°C to 99°C. [8] The method for producing a catalyst according to any one of [1] to [7], wherein in the step (ii-2), the temperature of the liquid B1 mixed with the raw material compound containing the ammonium radical is 3°C to 99°C. [9] A method for producing an α,β-unsaturated carboxylic acid, which oxidizes an α,β-unsaturated aldehyde in the presence of a catalyst produced by the method according to any one of [1] to [8].

[10] A method for producing an α,β-unsaturated carboxylic acid ester, which esterifies the α,β-unsaturated carboxylic acid produced by the method according to [9].

[0009] According to the present invention, a catalyst capable of producing an α,β-unsaturated carboxylic acid with high selectivity can be obtained. Further, by using the catalyst, an α,β-unsaturated carboxylic acid and an α,β-unsaturated carboxylic acid ester can be produced with high selectivity. Furthermore, in a reaction where the selectivity of the α,β-unsaturated carboxylic acid is high, the sequential oxidation of the α,β-unsaturated aldehyde is suppressed, so the calorific value is suppressed and stable operation becomes possible.

[0010] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto. In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value, and "A~B" means A or more and B or less. Further, when the numerical range is described stepwise, the upper and lower limits of each numerical range, as well as the numerical values described in the examples, can be arbitrarily combined to form a new numerical range.

[0011] <Method for Producing the Catalyst> The method for producing the catalyst according to this embodiment is a method for producing a catalyst used when oxidizing an α,β-unsaturated aldehyde to produce an α,β-unsaturated carboxylic acid.

[0012] [Catalyst] The catalyst obtained by the catalyst production method according to this embodiment is used when oxidizing α,β-unsaturated aldehydes to produce α,β-unsaturated carboxylic acids. From the viewpoint of improving the selectivity of α,β-unsaturated carboxylic acids, the catalyst preferably has a composition represented by the following formula (II). Note that the catalyst may also contain small amounts of elements not listed in the following formula (II): P ａ Mo ｂ V ｃ Cu ｄ G ｅ (NH ４ ) ｆ O ｇ (II). In equation (II), P, Mo, V, Cu, NH ４ , and O represent phosphorus, molybdenum, vanadium, copper, ammonium ion, and oxygen, respectively. G represents at least one element selected from the group consisting of alkali metals. a to g represent the molar ratios of each component, where when b = 12, a = 0.5 to 3, c = 0.01 to 3, d = 0.01 to 2, e = 0.01 to 3, and f = 0.01 to 10, and g is the molar ratio of oxygen necessary to satisfy the valency of each component.

[0013] In formula (II) above, from the viewpoint of improving the selectivity of α,β-unsaturated carboxylic acids, when b is 12, a is preferably 0.6 or higher, more preferably 0.7 or higher. Also, a is preferably 2.5 or lower, more preferably 2 or lower. c is preferably 0.1 or higher, more preferably 0.15 or higher, and still preferably 0.2 or higher. Also, c is preferably 2.5 or lower, more preferably 2 or lower, and still preferably 1.5 or lower. d is preferably 0.03 or higher, more preferably 0.05 or higher. e is preferably 0.05 or higher, more preferably 0.1 or higher. Also, e is preferably 2.5 or lower, more preferably 2 or lower. Also, f is preferably 9 or lower, more preferably 8 or lower.

[0014] In formula (II) above, the molar ratio of each element is determined by analyzing a solution of the catalyst dissolved in ammonia water using ICP emission spectrometry. The molar ratio of ammonium rhizome is determined by analyzing the catalyst using the Kjeldahl method. In this invention, "ammonium rhizome" refers to ammonia (NH₃). ３ ) and ammonium ions (NH ４ ＋ This is a general term for ).

[0015] [Method for producing a catalyst] The method for producing a catalyst according to this embodiment includes at least the following steps (i) to (iii): (i) preparing a slurry (liquid A) containing molybdenum, phosphorus, and ammonium root; (iii-1) mixing liquid A with a raw material compound containing an alkali metal to prepare a slurry (liquid B1); (iii-2) mixing liquid B1 with a raw material compound containing ammonium root to prepare a slurry (liquid B2); and (iii) drying liquid B2 to obtain a catalyst.

[0016] Furthermore, in the catalyst manufacturing method according to this embodiment, when the number of moles of ammonium roots contained in solution A is N1 and the number of moles of ammonium roots contained in solution B2 is N2, the raw material compound containing ammonium roots is divided and added such that the ratio of N1 to N2 (N1 / N2) is 0.25 or more and less than 1.00. This makes it possible to manufacture a catalyst that has a high selectivity for α,β-unsaturated carboxylic acids and can suppress localized exothermic reactions when used in the oxidation reaction of α,β-unsaturated aldehydes. The following describes each step in detail.

[0017] (Step (i)) In step (i), a slurry (Solution A) containing at least molybdenum, phosphorus, and ammonium root is prepared by mixing a raw material compound containing molybdenum, a raw material compound containing phosphorus, a raw material compound containing ammonium root, and a solvent. The slurry (Solution A) may also be a solution. The preparation of Solution A is convenient and preferable to be carried out by adding some or all of the raw material compounds of each element constituting the catalyst to the solvent and stirring while heating. Solutions, slurries, or sols of the raw material compounds of each element constituting the catalyst may be added to the solvent. When producing a catalyst having the composition represented by formula (II), it is preferable in this step to prepare Solution A containing components other than element G included in the composition represented by formula (II). That is, Solution A preferably contains molybdenum, phosphorus, vanadium, copper, and ammonium root. Examples of solvents include water, ethanol, and acetone, but water is preferred.

[0018] The raw material compounds used are not particularly limited, and one or more of the following can be used individually or in combination: nitrates, carbonates, bicarbonates, acetates, ammonium salts, sulfates, oxides, hydroxides, halides, oxoacids, or oxoate salts of each element constituting the catalyst. Examples of molybdenum raw materials include ammonium paramolybdate, molybdenum trioxide, molybdic acid, and molybdenum chloride. Examples of phosphorus raw materials include phosphoric acid, phosphorus pentoxide, ammonium phosphate, and cesium phosphate. Examples of ammonium root raw materials include ammonium salts of each element, as well as ammonium bicarbonate, ammonium carbonate, ammonium nitrate, and aqueous ammonia. Examples of copper raw materials include copper sulfate, copper nitrate, copper oxide, copper carbonate, copper acetate, and copper chloride. Examples of vanadium raw materials include ammonium metavanadate, vanadium pentoxide, and vanadium chloride.

[0019] Furthermore, when an ammonium salt of an element constituting the catalyst is used as the ammonium root raw material, the ammonium salt is both a raw material compound containing ammonium roots and a raw material compound containing the element. Also, when the ammonium root raw material contains an ammonium salt of an element constituting the catalyst, for example, the number of moles of ammonium roots N1 contained in solution A is the number of moles of ammonium roots including the number of moles of ammonium ions contained in the ammonium salt.

[0020] As the starting material compound containing molybdenum, phosphorus, and vanadium, a heteropoly acid containing at least one element selected from molybdenum, phosphorus, and vanadium may be used. Examples of heteropoly acids include phosphomolybdic acid, phosphovanadomolybdic acid, and silicic acid. These may be used individually or in combination of two or more.

[0021] When N1 is the number of moles of ammonium roots contained in solution A, and N2 is the number of moles of ammonium roots contained in solution B2 (described later), the ratio N1 / N2 is 0.25 or greater and less than 1.00. That is, in step (i), first, solution A containing a portion of the ammonium root raw material is prepared. Subsequently, in steps (ii-1) and (ii-2) described later, the raw material compound containing the alkali metal and the raw material compound containing the remaining ammonium root are sequentially added to solution A, thereby achieving a suitable degree of supersaturation of the heteropoly acid complex salt. As a result, it is considered that a heteropoly acid complex salt suitable for the production of α,β-unsaturated carboxylic acids is stably formed. Note that a heteropoly acid complex salt refers to a salt in which the alkali metal salt and ammonium salt of a heteropoly acid are combined in a specific ratio. The lower limit of N1 / N2 is preferably 0.40, more preferably 0.41, even more preferably 0.45, even more preferably 0.50, even more preferably 0.60, and most preferably 0.70.

[0022] Furthermore, in the method for producing the catalyst according to this embodiment, it is preferable to prepare the catalyst so as to satisfy at least one of the following formulas (I-1) and (I-2) from the viewpoint of selectivity for α,β-unsaturated carboxylic acids. It is even more preferable to prepare the catalyst so as to satisfy both the following formulas (I-1) and (I-2): n1 = 0.01 to 4.50 (I-1); m1 = 6 to 12 (I-2). In formula (I-1), n1 represents the molar ratio of ammonium roots contained in solution A when the molar ratio of molybdenum in the catalyst is 12. In formula (I-2), m1 represents the molar ratio of molybdenum contained in solution B1 when the molar ratio of molybdenum in the catalyst is 12. For example, if the catalyst has the composition represented by formula (II) above, m1 is 12.

[0023] Solution A is preferably prepared by stirring and holding a mixture (solution or slurry) containing at least molybdenum, phosphorus, and ammonium root, obtained by mixing a raw material compound containing molybdenum, a raw material compound containing phosphorus, and a raw material compound containing ammonium root with a solvent, at a temperature of 80°C or higher for at least one hour. This allows for more stable formation of heteropoly acids (salts) in Solution A. Furthermore, in step (iii) described later, a catalyst with pores suitable for the production of α,β-unsaturated carboxylic acids can be easily produced. The lower limit of the heating temperature is preferably 90°C, and the upper limit is preferably 130°C. The lower limit of the holding time is preferably 1.5 hours, and more preferably 2 hours. There is no particular upper limit to the holding time, but from the viewpoint of shortening the time required for catalyst production, it is usually 5 hours or less.

[0024] (Step (ii-1)) In step (ii-1), the liquid A obtained in step (i) is mixed with a raw material compound containing an alkali metal to prepare a slurry (liquid B1). The slurry (liquid B1) may be a solution. The method of mixing liquid A and the raw material compound containing an alkali metal is not particularly limited, but it is preferable to dissolve or suspend the raw material compound containing an alkali metal in a solvent to make a solution or slurry, and then mix the solution or slurry with liquid A. The solvent may be the same as the solvent exemplified in the preparation of liquid A above. The solvent may be the same as the solvent used in the preparation of liquid A above, or it may be different. However, from the viewpoint of simplifying the production of the catalyst, it is preferable that the solvent is the same as the solvent used in the preparation of liquid A above.

[0025] As the alkali metal, it is preferable to use at least one element selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium, more preferably at least one element selected from the group consisting of potassium and cesium, and even more preferably cesium. Examples of raw material compounds containing alkali metals include nitrates, carbonates, bicarbonates, hydroxides, sulfates, acetates, or chlorides of each alkali metal element. Among these, it is preferable to use carbonates or bicarbonates. The raw material compounds containing alkali metals may be used individually or in combination of two or more.

[0026] The temperature of solution A, which is mixed with the alkali metal-containing raw material compound, is preferably 30°C to 99°C, and more preferably 70°C or higher, from the viewpoint of suppressing localized exothermic reactions in the reaction to produce α,β-unsaturated carboxylic acids using the resulting catalyst. This can further improve the activity of the resulting catalyst.

[0027] (Step (ii-2)) In step (ii-2), the B1 liquid obtained in step (ii-1) and the raw material compound containing ammonium root are mixed to prepare a slurry (B2 liquid). It is preferable to dissolve or suspend the raw material compound containing ammonium root in a solvent to make a solution or slurry, and then mix the solution or slurry with the B1 liquid. The solvent can be the same as the solvent exemplified in the preparation of the A liquid above. The solvent may be the same as the solvent used in the preparation of the A liquid above, or it may be different. However, from the viewpoint of simplifying the production of the catalyst, it is preferable that the solvent is the same as the solvent used in the preparation of the A liquid above. As the raw material compound containing ammonium root, the same compound as the ammonium root raw material described in step (i) above can be used. The raw material compound containing ammonium root mixed in this step may be the same as the raw material compound containing ammonium root mixed in step (i) above, or it may be different.

[0028] The temperature of liquid B1, which is mixed with the starting compound containing ammonium rhizome, is preferably 30°C to 99°C, and more preferably 70°C or higher, from the viewpoint of suppressing localized exothermic reactions in the reaction to produce α,β-unsaturated carboxylic acids using the resulting catalyst. This can further improve the activity of the resulting catalyst.

[0029] In step (ii-2), it is preferable to prepare solution B2 by mixing solution B1 with a raw material compound containing ammonium root, and then stirring the resulting mixture (solution or slurry) at a temperature of 90°C to 99°C for 15 minutes or more. This promotes the dissolution and reprecipitation of the heteropolyate, allowing for the formation of a crystalline structure suitable for the production of α,β-unsaturated carboxylic acids. From the viewpoint of promoting the dissolution and reprecipitation of the heteropolyate, a heating temperature of 95°C or higher is more preferable.

[0030] The pH of the B2 solution obtained in step (ii-2) is preferably 4 or less. Thereby, a Keggin-type heteropolyacid, which is a suitable structure in the production of α,β-unsaturated carboxylic acid, is stably formed. The pH of the B2 solution is more preferably 3.5 or less, and even more preferably 3 or less. The pH of the B2 solution can be adjusted by appropriately selecting the types and amounts of raw material compounds and adding nitric acid, oxalic acid, etc. as appropriate. The pH can be measured using, for example, a pH meter (trade name: D-21, manufactured by Horiba, Ltd.).

[0031] (Step (iii)) In step (iii), the B2 solution obtained in the above step (ii-2) is dried to obtain a catalyst. Examples of the drying method include a drum drying method, a fluidized bed drying method, an evaporation to dryness method, and a spray drying method. The drying temperature is preferably 120°C to 500°C, more preferably 140°C or higher for the lower limit, and more preferably 350°C or lower for the upper limit. Drying can be carried out until the B2 solution is dried to dryness. The water content of the obtained catalyst is preferably 0.1% by mass to 4.5% by mass. These drying conditions can be appropriately selected according to the desired shape and size of the catalyst.

[0032] This step (iii) can be carried out immediately on the B2 solution obtained after preparing the B2 solution at a temperature of 90°C to 99°C in step (ii-2). That is, after preparing the B2 solution, there is no need to lower the temperature (for example, to less than 50°C) before drying the B2 solution.

[0033] The catalyst obtained in step (iii) can be used in the production of α,β-unsaturated carboxylic acid. Furthermore, it is preferable to perform shaping and firing described later on the catalyst because the performance as a catalyst is improved. In the present invention, in addition to the catalyst obtained in step (iii), the shaped catalyst and the fired catalyst are collectively referred to as the catalyst.

[0034] (Molding Process) In the molding process, the catalyst obtained in step (iii) above is pulverized as necessary and then molded. The molding process may be performed after the calcination process described later. The molding method is not particularly limited, and known dry or wet molding methods can be applied. Examples of molding methods include tableting, extrusion, pressure molding, and rolling granulation. There are no particular restrictions on the shape of the molded product, and any shape can be used, such as spherical granules, rings, cylindrical pellets, star shapes, and granules obtained by pulverizing and classifying after molding. The catalyst size is preferably 0.1 mm to 10 mm in diameter. A catalyst diameter of 0.1 mm or more reduces the pressure loss in the reaction tube. Furthermore, a catalyst diameter of 10 mm or less improves catalytic activity. When molding the catalyst, the catalyst may be supported on a carrier. In addition, if necessary, known additives such as graphite or talc, or known binders derived from organic or inorganic materials may be added to the catalyst before molding.

[0035] (Castration Process) It is preferable to calcine the catalyst obtained in the above process (iii), or the catalyst obtained in the molding process, from the viewpoint of α,β-unsaturated carboxylic acid selectivity. The calcination conditions are not particularly limited, but can be carried out by heat treatment under the flow of at least one of an oxygen-containing gas such as air and an inert gas. Calcination is preferably carried out under the flow of an oxygen-containing gas. An "inert gas" means a gas that does not reduce catalytic activity, and examples include nitrogen, carbon dioxide, helium, and argon. These may be used individually or in mixtures of two or more. The calcination temperature is preferably 200°C to 500°C, with a lower limit of 300°C more preferably and an upper limit of 450°C more preferably. The lower limit of the calcination time is preferably 0.5 hours, with a higher limit of 1 hour. The upper limit of the calcination time is preferably 40 hours.

[0036] <Method for Producing α,β-Unsaturated Carboxylic Acid>In the method for producing an α,β-unsaturated carboxylic acid according to this embodiment, an α,β-unsaturated aldehyde is oxidized in the presence of a catalyst produced by the method for producing a catalyst according to this embodiment. Thereby, an α,β-unsaturated carboxylic acid can be produced with high selectivity.

[0037] Examples of the α,β-unsaturated aldehyde include (meth)acrolein, crotonaldehyde (β-methylacrolein), and cinnamaldehyde (β-phenylacrolein). Among these, from the viewpoint of the selectivity of the target product, (meth)acrolein is preferable, and methacrolein is more preferable. The obtained α,β-unsaturated carboxylic acid is an α,β-unsaturated carboxylic acid in which the aldehyde group of the α,β-unsaturated aldehyde is converted to a carboxyl group. Specifically, when the α,β-unsaturated aldehyde is (meth)acrolein, (meth)acrylic acid is obtained. Note that “(meth)acrolein” indicates acrolein and methacrolein, and “(meth)acrylic acid” indicates acrylic acid and methacrylic acid.

[0038] Hereinafter, as a representative example, a method for producing methacrylic acid by oxidizing methacrolein in the presence of a catalyst produced by the method according to this embodiment will be described. However, the following method is also applicable when other α,β-unsaturated aldehydes are used instead of methacrolein. In this method, methacrylic acid is produced by bringing a raw material gas containing methacrolein and oxygen into contact with a catalyst obtained by the method according to this embodiment in a reactor. A fixed bed reactor can be used as the reactor. The catalyst is filled in a reaction tube provided in the reactor, and the raw material gas is supplied to the reaction tube to perform an oxidation reaction. The catalyst layer may be a single layer, or a plurality of catalysts having different activities may be filled separately in a plurality of layers. Further, in order to control the activity, the catalyst may be diluted with an inert carrier and filled.

[0039] The concentration of methacrolein in the raw material gas is not particularly limited, but is preferably 1% to 20% by volume, more preferably 3% by volume at the lower limit and 10% by volume at the upper limit. The methacrolein used as a raw material may contain small amounts of impurities that do not substantially affect this reaction, such as lower saturated aldehydes. The oxygen concentration in the raw material gas is preferably 0.4 to 4 moles per mole of methacrolein, more preferably 0.5 moles at the lower limit and 3 moles at the upper limit. From an economic standpoint, air is preferred as the oxygen source. If necessary, an oxygen-enriched gas may be used by adding pure oxygen to air.

[0040] The raw material gas may be methacrolein and oxygen (or an oxygen source) diluted with an inert gas such as nitrogen or carbon dioxide. Furthermore, water vapor may be added to the raw material gas. By carrying out the reaction in the presence of water vapor, methacrylic acid can be obtained with higher selectivity. The concentration of water vapor in the raw material gas is preferably 0.1% to 50% by volume, more preferably 1% by volume at the lower limit and more preferably 40% by volume at the upper limit.

[0041] The contact time between the raw material gas and the catalyst is preferably 0.5 to 15 seconds. The reaction pressure is preferably 0.1 MPa(G) to 1 MPa(G), where (G) is the gauge pressure. The reaction temperature is preferably 200°C to 450°C, with a lower limit of 250°C being more preferable and an upper limit of 400°C being more preferable.

[0042] <Method for producing α,β-unsaturated carboxylic acid esters> In the method for producing α,β-unsaturated carboxylic acid esters according to this embodiment, the α,β-unsaturated carboxylic acid produced by the method according to this embodiment is esterified. According to this method, α,β-unsaturated carboxylic acid esters can be produced using α,β-unsaturated carboxylic acid obtained by oxidation of α,β-unsaturated aldehydes.

[0043] The alcohol reacted with the α,β-unsaturated carboxylic acid is not particularly limited and includes methanol, ethanol, propanol, isopropanol, n-butanol, and isobutanol. Examples of the resulting α,β-unsaturated carboxylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, and isobutyl (meth)acrylate. The esterification reaction can be carried out in the presence of an acidic catalyst such as a sulfonic acid type cation exchange resin. The reaction temperature is preferably 50°C to 200°C.

[0044] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" means parts by mass. The ammonium carbonate used in the examples and comparative examples is ammonium carbonate with an ammonium root content of 32.3% by mass.

[0045] (Analysis of raw material gas and products) The raw material gas and products were analyzed by gas chromatography (details are shown in Table 1). From the gas chromatography results, the selectivity of methacrylic acid was calculated using the following formula: Selectivity of methacrylic acid (%) = (P / R) × 100. In the formula, R represents the number of moles of methacrolein that reacted per unit time, and P represents the number of moles of methacrylic acid produced per unit time.

[0046]

[0047] [Example 1] (Step (i)) A slurry was obtained by adding 40 parts molybdenum trioxide to 160 parts pure water. Next, 1.68 parts vanadium pentoxide, 8.11 parts aqueous solution obtained by diluting 50.06 parts of 85% by mass phosphoric acid aqueous solution with 45 parts pure water, 4.16 parts aqueous solution obtained by dissolving 14 parts copper(II) nitrate trihydrate in 90 parts pure water, and 11.12 parts aqueous solution obtained by dissolving 9.35 parts ammonium carbonate in 53.76 parts pure water (hereinafter referred to as "aqueous solution containing ammonium nitrate 1") were added to the slurry. The resulting mixture (slurry) was then heated to 95°C while stirring, and the liquid temperature was maintained at 95°C while stirring for 2 hours to prepare solution A. (Step (iii-1)) Next, while stirring and maintaining the temperature of the obtained solution A at 95°C, 20.53 parts of an aqueous solution prepared by dissolving 28 parts of cesium bicarbonate in 100 parts of pure water were added dropwise to solution A, and the mixture was stirred for 15 minutes to prepare solution B1. (Step (iii-2)) Next, while stirring and maintaining the temperature of the obtained solution B1 at 95°C, 16.68 parts of an aqueous solution prepared by dissolving 9.35 parts of ammonium carbonate in 53.76 parts of pure water (hereinafter referred to as "aqueous solution 2 containing ammonium compounds") were added dropwise, and the mixture was stirred for 15 minutes to prepare solution B2. (Step (iii)) Next, the obtained solution B2 was heated with steam at 140°C and evaporated to dryness to obtain a catalyst.

[0048] Table 2 shows the ratio N1 / N2 of the number of moles of ammonium rhizoids in solution A to the number of moles of ammonium rhizoids in solution B2, and the molar ratio n1 of ammonium rhizoids in solution A and the molar ratio m1 of molybdenum in solution B1, given that the molar ratio of molybdenum in the catalyst is 12. For each raw material, the following molecular weights were used to calculate the values: Molybdenum trioxide: 143.94, Ammonium carbonate: 96.09 (Ammonium rhizoid content is 32.3% by mass), Ammonium rhizoids in ammonium carbonate (NH ４ ): 18.04.

[0049] Next, the obtained catalyst was pressure-molded and then pulverized. This pulverized catalyst was then calcined at 380°C for 5 hours under air circulation to obtain the calcined catalyst. The calcined catalyst was then packed into a reaction tube in a fixed-bed reactor, and a raw material gas consisting of 5% methacrolein, 10% oxygen, 10% water vapor, and 75% nitrogen was circulated through the reaction tube for a contact time of 3.5 seconds to carry out the methacrolein oxidation reaction. The reaction was carried out at atmospheric pressure, and the reaction temperature was 300°C. The results are shown in Table 2.

[0050] [Example 2] Solution A was prepared in the same manner as in Example 1, except that 19.46 parts of an aqueous solution prepared by dissolving 9.35 parts of ammonium carbonate in 53.76 parts of pure water was used as aqueous solution 1 containing ammonium rhizomes. Next, solution B1 was prepared using the obtained solution A in the same manner as in Example 1. Next, solution B2 was prepared using the obtained solution B1, except that 8.34 parts of an aqueous solution prepared by dissolving 9.35 parts of ammonium carbonate in 53.76 parts of pure water was added dropwise as aqueous solution 2 containing ammonium rhizomes, in the same manner as in Example 1. Next, a catalyst was obtained using the obtained solution B2 in the same manner as in Example 1. The values ​​of N1 / N2, n1, and m1 in catalyst production are shown in Table 2.

[0051] Next, using the obtained catalyst, a calcined catalyst was prepared in the same manner as in Example 1. Then, using the calcined catalyst, the oxidation reaction of methacrolein was carried out in the same manner as in Example 1. The results are shown in Table 2.

[0052] [Example 3] Solution A was prepared in the same manner as in Example 1, except that 25.02 parts of an aqueous solution prepared by dissolving 9.35 parts of ammonium carbonate in 53.76 parts of pure water was used as aqueous solution 1 containing ammonium rhizomes. Next, solution B1 was prepared using the obtained solution A in the same manner as in Example 1. Next, solution B2 was prepared using the obtained solution B1, except that 2.78 parts of an aqueous solution prepared by dissolving 9.35 parts of ammonium carbonate in 53.76 parts of pure water was added dropwise as aqueous solution 2 containing ammonium rhizomes, in the same manner as in Example 1. Next, a catalyst was obtained using the obtained solution B2 in the same manner as in Example 1. The values ​​of N1 / N2, n1, and m1 in catalyst production are shown in Table 2.

[0053] Next, using the obtained catalyst, a calcined catalyst was prepared in the same manner as in Example 1. Then, using the calcined catalyst, the oxidation reaction of methacrolein was carried out in the same manner as in Example 1. The results are shown in Table 2.

[0054] [Comparative Example 1] Solution A was prepared in the same manner as in Example 1, except that 2.78 parts of an aqueous solution prepared by dissolving 9.35 parts of ammonium carbonate in 53.76 parts of pure water was used as aqueous solution 1 containing ammonium rhizomes. Next, solution B1 was prepared using the obtained solution A in the same manner as in Example 1. Next, solution B2 was prepared using the obtained solution B1, except that 25.02 parts of an aqueous solution prepared by dissolving 9.35 parts of ammonium carbonate in 53.76 parts of pure water was added dropwise as aqueous solution 2 containing ammonium rhizomes, in the same manner as in Example 1. Next, a catalyst was obtained using the obtained solution B2 in the same manner as in Example 1. The values ​​of N1 / N2, n1, and m1 in catalyst production are shown in Table 2.

[0055] Next, using the obtained catalyst, a calcined catalyst was prepared in the same manner as in Example 1. Then, using the calcined catalyst, the oxidation reaction of methacrolein was carried out in the same manner as in Example 1. The results are shown in Table 2.

[0056] [Comparative Example 2] Solution A was prepared in the same manner as in Example 1, except that 5.56 parts of an aqueous solution prepared by dissolving 9.35 parts of ammonium carbonate in 53.76 parts of pure water was used as aqueous solution 1 containing ammonium rhizomes. Next, solution B1 was prepared using the obtained solution A in the same manner as in Example 1. Next, solution B2 was prepared using the obtained solution B1, except that 22.24 parts of an aqueous solution prepared by dissolving 9.35 parts of ammonium carbonate in 53.76 parts of pure water was added dropwise as aqueous solution 2 containing ammonium rhizomes, in the same manner as in Example 1. Next, a catalyst was obtained using the obtained solution B2 in the same manner as in Example 1. The values ​​of N1 / N2, n1, and m1 in catalyst production are shown in Table 2.

[0057] Next, using the obtained catalyst, a calcined catalyst was prepared in the same manner as in Example 1. Then, using the calcined catalyst, the oxidation reaction of methacrolein was carried out in the same manner as in Example 1. The results are shown in Table 2.

[0058]

[0059] As shown in Table 2, it was found that the methods according to Examples 1 to 3, which have steps (i) to (iii) and in which N1 / N2 is within the range defined in the present invention, yield a catalyst that can produce methacrylic acid with a higher selectivity compared to the methods according to Comparative Examples 1 and 2, in which N1 / N2 is outside the range. Furthermore, methacrylic acid esters can be obtained by esterifying the methacrylic acid obtained in these examples.

[0060] According to the present invention, a catalyst can be provided that can produce α,β-unsaturated carboxylic acids from α,β-unsaturated aldehydes with high selectivity, and that can suppress localized exothermic reactions during the production of α,β-unsaturated carboxylic acids, making it industrially useful.

Claims

1. A method for producing a catalyst used when oxidizing an α,β-unsaturated aldehyde to produce an α,β-unsaturated carboxylic acid, comprising: (i) a step of preparing a slurry (solution A) containing molybdenum, phosphorus, and ammonium root; (iii-1) a step of mixing solution A and a raw material compound containing an alkali metal to prepare a slurry (solution B1); (iii-2) a step of mixing solution B1 and a raw material compound containing ammonium root to prepare a slurry (solution B2); and (iii) a step of drying solution B2 to obtain a catalyst, wherein when N1 is the number of moles of ammonium root contained in solution A and N2 is the number of moles of ammonium root contained in solution B2, the ratio N1 / N2 is 0.25 or more and less than 1.

00.

2. The method for producing a catalyst according to claim 1, wherein the N1 / N2 ratio is 0.40 or more and less than 1.

00.

3. The method for producing a catalyst according to claim 1, wherein in step (i) above, a mixture obtained by mixing a raw material compound containing molybdenum, a raw material compound containing phosphorus, and a raw material compound containing ammonium root with a solvent is stirred and held at a temperature of 80°C or higher for 1 hour or more to prepare liquid A.

4. A method for producing the catalyst according to claim 1, satisfying the following formula (I-1): n1 = 0.01 to 4.50 (I-1), where n1 represents the molar ratio of ammonium roots contained in solution A when the molar ratio of molybdenum in the catalyst is 12.

5. A method for producing the catalyst according to claim 4, satisfying the following formula (I-2): m1 = 6 to 12 (I-2), where m1 represents the molar ratio of molybdenum contained in liquid B1 when the molar ratio of molybdenum in the catalyst is 12.

6. The method for producing the catalyst according to claim 1, wherein the catalyst has a composition represented by the following formula (II): P ａ Mo ｂ V ｃ Cu ｄ G ｅ (NH ４ ) ｆ O ｇ (II) In the formula (II), P, Mo, V, Cu, NH ４ , and O each represent phosphorus, molybdenum, vanadium, copper, ammonium radical, and oxygen, respectively, G represents at least one element selected from the group consisting of alkali metals, and a to g represent the molar ratios of the respective components. When b = 12, a = 0.5 to 3, c = 0.01 to 3, d = 0.01 to 2, e = 0.01 to 3, and f = 0.01 to 10, and g is the molar ratio of oxygen necessary to satisfy the valences of the respective components.

7. The method for producing a catalyst according to claim 1, wherein in step (ii-1), the temperature of the liquid A, which is mixed with the alkali metal-containing raw material compound, is 30°C to 99°C.

8. The method for producing a catalyst according to claim 1, wherein in step (ii-2), the temperature of the B1 liquid mixed with the raw material compound containing the ammonium root is 30°C to 99°C.

9. A method for producing an α,β-unsaturated carboxylic acid, comprising oxidizing an α,β-unsaturated aldehyde in the presence of a catalyst produced by any one of claims 1 to 8.

10. A method for producing an α,β-unsaturated carboxylic acid ester, comprising esterifying an α,β-unsaturated carboxylic acid produced by the method of claim 9.

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