Catalyst for producing methacrolein and / or methacrylic acid

Abstract

To provide a catalyst which is used for producing the corresponding methacrolein and methacrylic acid from raw materials such as isobutylene or t-butyl alcohol, and which provides a high yield of the desired product.SOLUTION: A catalyst for producing methacrolein and / or methacrylic acid is a supported molded catalyst containing at least iron and an alkali metal as active components, where the content of iron in the active component layer is higher on the catalyst surface side and lower on the core side.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a catalyst that enables stable, high-yield production when methacrolein and / or methacrylic acid are oxidatively produced. [Background technology]

[0002] Methods for producing methacrolein and methacrylic acid from raw materials such as isobutylene and t-butyl alcohol are widely used industrially, and many reports have been published on means for improving the yield of these production methods (e.g., Patent Documents 1 and 2).

[0003] Despite the above-mentioned improvements, further yield improvements are needed in the production of methacrolein and / or methacrylic acid by the partial oxidation of isobutylene, t-butyl alcohol, etc. For example, the yield of the target product determines the amount of isobutylene, t-butyl alcohol, etc. required for production, significantly affecting production costs. Furthermore, continued operation at a low yield generates large amounts of by-products, which places a heavy burden on the purification process, increasing the time and operating costs required for the purification process. Furthermore, depending on the type of by-product, they may accumulate on the catalyst surface or in the gas flow path near the catalyst. These by-products reduce the catalyst's activity by covering necessary reactive active sites on the catalyst surface, forcing the need to increase the activity and necessitating an increase in the reaction bath temperature. This results in thermal stress on the catalyst, shortening its lifespan and further reducing selectivity, leading to a decrease in yield. Furthermore, by-products accumulated in the system can increase the system pressure, reducing selectivity and decreasing yield. In the worst case scenario, a sudden increase in internal pressure can cause temperature abnormalities and lead to a runaway reaction. If this happens, it is expected that operation will have to be suspended for an extended period of time, and that the system will need to be cleaned and the catalyst replaced.

[0004] Furthermore, Patent Document 3 reports a method for improving yield by controlling the composition of the support used when molding the catalyst into a supported catalyst and the catalyst particle size after molding. It has been found that the method of using such catalysts characterized by their shape is also important. In particular, when using a catalyst with a generally small catalyst particle size, a high space velocity causes an increase in the pressure within the system, which reduces the selectivity and leads to a decrease in yield. Therefore, it is clear that further development of a catalyst packing method that can maximize the catalyst's performance is necessary.

[0005] For example, Patent Document 4 discloses a method for producing methacrolein and / or methacrylic acid in which a plurality of catalyst layers are provided in a reaction tube, and a technique for improving the yield by specifying in detail the relationship between the density of catalytic active components and the average catalyst particle diameter and the volume occupied by them. However, even with this method, further improvement in terms of yield was required.

[0006] Furthermore, Patent Document 5 discloses a technology for suppressing hot spots by forming a catalyst for producing acrolein that does not contain alkali metals but contains molybdenum, bismuth, or iron as active components and supports granules having different composition ratios of bismuth and iron in two layers. However, this method is limited to the production of acrolein, and further improvement is required in terms of yield.

[0007] Furthermore, Patent Document 6 discloses a technology for suppressing hot spots by forming a catalyst for acrolein production containing an alkali metal and containing molybdenum, bismuth, or iron as an active component, and supporting granules with different iron composition ratios in two layers. This method focuses on reducing the hot spot temperature, and further improvement is needed in terms of yield. Furthermore, this method is limited to the production of acrolein and has not been applied to methacrolein. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2016 / 136882 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-024009 [Patent Document 3] Japanese Patent Publication No. 2020-171906 [Patent Document 4] Japanese Patent Publication No. 2023-141552 [Patent Document 5] Publication No. CN103769132A [Patent Document 6] Japanese Patent Application Laid-Open No. 2002-273228 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention proposes a catalyst that can be used to produce the corresponding methacrolein or methacrylic acid from isobutylene, t-butyl alcohol, or the like as raw materials, and that can produce the target product in high yield. [Means for solving the problem]

[0010] The present inventors have conducted extensive research under these circumstances and have completed the present invention.

[0011] That is, the present invention relates to the following 1) to 10). 1) A supported catalyst containing at least iron and an alkali metal as active components, A catalyst for producing methacrolein and / or methacrylic acid, characterized in that the iron content is high on the catalyst surface side and low on the core side. 2) The catalyst for producing methacrolein and / or methacrylic acid according to the above 1), characterized in that the content of the alkali metal is low on the catalyst surface side and high on the core side. 3) The catalyst for producing methacrolein and / or methacrylic acid according to 1) or 2) above, which satisfies the following formula (A), where A1 is the iron content on the catalyst surface side and A2 is the iron content on the core side. [Formula A] 1.1 ≦ A1 / A2 ··· (A) 4) When the content of the alkali metal on the catalyst surface side is B1 and the content of the alkali metal on the core side is B2, the catalyst for producing methacrolein and / or methacrylic acid according to any one of the above 1) to 3) that satisfies the following formula (B). [Formula B] B1 / B2 ≦ 0.95 ··· (B) 5) The catalyst for producing methacrolein and / or methacrylic acid according to any one of the above 1) to 4), which has a composition represented by the following formula (1) as a catalytic active component. [Formula 1] Mo Bi b1 Ni c1 Co d1 Fe e1 X f1 Y g1 Z h1 [[ID=F32]]O i1 ··· (1) (In the formula, Mo, Bi, Ni, Co, and Fe each represent molybdenum, bismuth, nickel, cobalt, and iron, X represents at least one element selected from tungsten, antimony, tin, zinc, chromium, manganese, magnesium, silicon, aluminum, cerium, and titanium, Y represents at least one element selected from sodium, potassium, cesium, rubidium, and thallium, Z belongs to Groups 1 to 16 of the periodic table and means at least one element selected from elements other than the above Mo, Bi, Ni, Co, Fe, X, and Y, and b1, c1, d1, e1, f1, g1, h1, and i1 each represent the number of atoms of bismuth, nickel, cobalt, iron, X, Y, Z, and oxygen, 0 < b1 ≦ 7.0, 0 ≦ c1 ≦ 10.0, 0 ≦ d1 ≦ 10.0, 0 < e1 < 5.0, 0 ≦ f1 ≦ 2.0, 0 < g1 ≦ 3.0, 0 ≦ h1 ≦ 5.0, and i1 = a value determined by the oxidation state of each element) 6) The method for producing methacrolein and / or methacrylic acid according to the above 5), wherein in the formula (1), 1.0 < e1 ≦ 2.5. 7) The method for producing methacrolein and / or methacrylic acid according to the above 5), wherein, in the formula (1), Y is cesium and 0.10≦g1≦1.0. 8) The catalyst for producing methacrolein and / or methacrylic acid according to any one of 1) to 7) above, which is supported on an inert carrier. 9) A method for producing methacrolein and / or methacrylic acid using the catalyst according to any one of 1) to 8) above. 10) The method for producing a catalyst for producing methacrolein and / or methacrylic acid according to any one of the above 1) to 8), wherein two catalytically active components having different compositions are sequentially supported on an inert carrier. [Effects of the Invention]

[0012] The catalyst of the present invention is very effective in improving the yield in a gas-phase catalytic oxidation reaction, and is useful when producing the corresponding methacrolein or methacrylic acid from isobutylene, t-butyl alcohol, or the like as a raw material. In particular, when isobutylene, t-butyl alcohol, etc. are used as raw materials to produce corresponding methacrolein, it is effectively used in the reaction to obtain methacrolein by the vapor-phase catalytic oxidation of isobutylene. When the catalyst of the present invention is used in the vapor-phase catalytic oxidation reaction of isobutylene, it contributes to improving the yield. This is a particularly effective feature in the direct oxidation method in which isobutylene becomes a poisonous substance in the subsequent reaction. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram showing a line analysis target area on the core side and a line analysis target area on the surface side of a catalyst of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Iron content] The supported shaped catalyst of the present invention contains iron and alkali metal as catalytically active components, characterized in that the iron content is high on the surface side of the catalyst and low on the core side. This may be a layered structure in which the iron component continuously decreases toward the core side, but a layered structure is preferred, a layered structure with two to three layers is more preferred, and a two-layered structure is particularly preferred. A two-layered structure is produced by placing a specific catalyst precursor (granules containing catalytically active components before molding) on ​​the core side, and then placing a catalyst precursor with a high iron content on the surface side, as will be described in detail later in the molding process. In the present invention, the catalyst surface side means the catalyst surface and / or its vicinity, and the core side means the center side, and detailed definitions in the analysis will be given later. The iron content can be measured using SEM-EDS (energy dispersive X-ray spectroscopy). As a pretreatment step, the catalyst is embedded in resin and polished to create a sample with an exposed cross section. Next, for the cross section of this sample, the analysis area for SEM analysis is defined as the shortest boundary of the ring-shaped cross section at the boundary of the active component containing iron and alkali metals, defining the inner periphery as the shortest boundary and the outer periphery as the longest boundary. Next, the smallest square with one side touching the inner periphery and two vertices touching the outer periphery is defined. The side touching the inner periphery is defined as the core side, and the line connecting the two vertices touching the outer periphery is defined as the catalyst surface side, and the elemental composition of each is measured by SEM-EDS line analysis. In the example shown in Figure 1, the thick line is measured. The measurement conditions are an acceleration voltage of 15 kV, 10 or more measurements, a pixel time of 200 ms, and three repeated measurements. The iron content is defined as the molar percentage of iron obtained from each measurement divided by the molar percentage of molybdenum. The iron content is calculated by arithmetically averaging the iron content obtained from at least three measurements in different analytical regions.

[0015] [Relationship between iron content A1 and A2] In the catalyst of the present invention, when the iron content on the catalyst surface side is A1 and the iron content on the core side is A2, it is preferable that the relationship between A1 and A2 be as expressed by (A) above. The lower limit of A1 / A2 is more preferably 1.15, 1.20, 1.25, 1.30, 1.35, 1.55, 1.60, 1.65, or 1.70, and most preferably 1.75. The upper limit may be about 2.50, more preferably 2.00, and even more preferably 1.90. That is, the most preferable ratio of A1 / A2 is 1.75 or more and 1.90 or less.

[0016] [Alkali metal content] The catalyst of the present invention contains an alkali metal as a catalytically active component, and the content thereof is preferably low on the surface side of the catalyst and high on the core side. The alkali metal is at least one element selected from sodium, potassium, cesium, rubidium, and thallium, and the content of the alkali metal is the total content of each element. The measurement method and catalyst manufacturing method are the same as those for iron.

[0017] [Relationship between alkali metal contents B1 and B2] In the catalyst of the present invention, when the alkali content on the catalyst surface side is B1 and the alkali metal content on the core side is B2, it is preferable that the relationship between B1 and B2 be as expressed by (B) above. The upper limit of B1 / B2 is more preferably 0.94, 0.93, and most preferably 0.92. The lower limit may be about 0.10, more preferably 0.20, 0.30, 0.40, 0.45, 0.50, 0.60, and 0.65, and particularly preferably 0.70. Therefore, B1 / B2 is most preferably 0.70 or more and 0.90 or less.

[0018] [Catalyst composition] The catalyst of the present invention has, as an active component, a composition represented by the following formula (1): A catalyst having this composition is also expected to have the effect of reducing by-products. [Formula 1] Mo a1 Bi b1 Ni c1 Co d1 Fe e1 X f1 Y g1 Z h1 O i1 ···(1) (In the formula, Mo, Bi, Ni, Co, and Fe represent molybdenum, bismuth, nickel, cobalt, and iron respectively, X represents at least one element selected from tungsten, antimony, tin, zinc, chromium, manganese, magnesium, silicon, aluminum, cerium, and titanium, Y represents at least one element selected from sodium, potassium, cesium, rubidium, and thallium, Z belongs to Groups 1 to 16 of the periodic table and means at least one element selected from elements other than the above Mo, Bi, Ni, Co, Fe, X, and Y, and a1, b1, c1, d1, e1, f1, g1, h1, and i1 represent the atomic numbers of molybdenum, bismuth, nickel, cobalt, iron, X, Y, Z, and oxygen respectively. When a1 = 12, 0 < b1 ≤ 7.0, 0 ≤ c1 ≤ 10.0, 0 ≤ d1 ≤ 10.0, 0 < e1 ≤ 5.0, 0 ≤ f1 ≤ 2.0, 0 < g1 ≤ 3.0, 0 ≤ h1 ≤ 5.0, and i1 is a value determined by the oxidation state of each element.)

[0019] In the above formula (1), when a1 = 12, the preferred ranges of b1 to h1 are as follows. The lower limits of b1 are preferably 0.2, 0.5, 0.8, 1.1, 1.3, 1.5 in order of preference, and particularly preferably 1.6. The upper limits are preferably 6, 5, 4, 3, 2.8, 2.6, 2.4, 2.2, 2.0, 1.9 in order of preference, and particularly preferably 1.8. That is, the most preferred range for b1 is 1.6 or more and 1.8 or less. The lower limits of c1 are preferably 0.2, 0.4, 0.5, 0.6 in order of preference, and particularly preferably 0.7. The upper limits are preferably 8.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.0, 1.0 in order of preference, and particularly preferably 0.9. That is, the most preferred range for c1 is 0.7 or more and 0.9 or less. The lower limit of d1 is, in order of preference, 1.0, 2.0, 3.0, 4.0, and 5.0, and the upper limit is, in order of preference, 9.5, 9.0, 8.5, and 8.0, and particularly preferably 7.5. That is, the most preferred range for d1 is 5.0 or more and 7.5 or less. Note that c1+d1 also has a preferred range, with the lower limit being 0.0, 2.0, 4.0, 6.0, 7.0, and 7.5, in order of preference, and the upper limit being 20.0, 15.0, 12.5, 11.0, 10.0, 9.0, and 8.5, in order of preference. In other words, the most preferred range for c1+d1 is 7.5 or more and 8.5 or less. The lower limit of e1 is, in order of preference, 0.10, 0.20, 0.50, 0.60, 0.80, and 1.00, and particularly preferably 1.10. The upper limit is, in order of preference, 4.80, 4.60, 4.40, 4.20, 4.00, 3.80, 3.60, and 3.40, and particularly preferably 3.20. In other words, the most preferred range for e1 is 1.10 or more and 3.20 or less. The upper limit of f1 is preferably 1.8, 1.5, 1.0, 0.8, and 0.5, in that order, and the lower limit is preferably 0. That is, the more preferable range for f1 is 0 or more and 0.5 or less, and 0 is most preferable. The lower limit of g1 is preferably 0.02, 0.04, 0.06, and 0.08, and particularly preferably 0.09. The upper limit is preferably 2.5, 2.0, 1.5, 1.0, 0.8, 0.6, 0.5, and 0.4, and particularly preferably 0.35. That is, the most preferable range for g1 is 0.09 or more and 0.35 or less. As Y, potassium, cesium, and rubidium are preferable, and cesium is most preferable. The upper limit of h1 is preferably 4.0, 3.0, 2.0, 1.8, 1.5, 1.0, 0.8, and 0.5, in that order, and the lower limit is preferably 0. That is, the more preferable range for h1 is 0 or more and 0.5 or less, and 0 is most preferable.

[0020] The catalyst of the present invention has different compositions of catalytically active components on the catalyst surface side and on the core side. For the catalytically active component on the catalyst surface side, e1 is preferably 1.20 to 3.20, more preferably 1.40 to 3.05, and particularly preferably 1.50 to 2.10. For the catalytically active component on the catalyst surface side, g1 is preferably 0.09 to 0.35, more preferably 0.09 to 0.25, and particularly preferably 0.09 to 0.20. For the catalytically active component on the catalyst core side, e1 is preferably 1.15 or more and 2.00 or less, more preferably 1.15 or more and 1.50 or less, and particularly preferably 1.15 or more and 1.30 or less. For the catalytically active component on the catalyst core side, g1 is preferably 0.10 or more and 0.34 or less, more preferably 0.20 or more and 0.33 or less, and particularly preferably 0.25 or more and 0.32 or less.

[0021] [Loading rate] The catalyst of the present invention is preferably a spherical catalyst supported on an inert carrier. As the material of the inert carrier, known materials such as alumina, silica, titania, zirconia, niobia, silica alumina, silicon carbide, carbide, steatite, and mixtures thereof can be used, but silica and / or alumina are preferred, and a mixture of silica and alumina is particularly preferred. When the catalyst of the present invention is used as a supported catalyst, the support ratio is preferably more than 30%. This support ratio is calculated using the following formula. The mixing ratio of the inert support and the pre-calcined powder depends on the charged mass of each raw material. Loading rate (mass%) = (mass of pre-calcined powder used for molding) / {(mass of pre-calcined powder used for molding) + (mass of support used for molding)} × 100 The lower limit of the loading rate is preferably 31%, 32%, 33%, 34%, 35%, 36%, and 37%, in that order, and particularly preferably 38%. The upper limit is preferably 60%, 55%, 50%, 45%, 44%, and 43%, in that order, and particularly preferably 42%. Therefore, the most preferred is 38% or more and 42% or less. It is preferable to use a binder for the support. Specific examples of binders that can be used include water, ethanol, methanol, propanol, polyhydric alcohols, polymeric binders such as polyvinyl alcohol, and inorganic binders such as silica sol aqueous solutions. Ethanol, methanol, propanol, and polyhydric alcohols are preferred, as are diols such as ethylene glycol and triols such as glycerin. An aqueous solution of glycerin with a concentration of 5% by mass or more is preferred. The use of an appropriate amount of aqueous glycerin solution improves moldability, resulting in a high-performance catalyst with high mechanical strength. The amount of these binders used is typically 2 to 60 parts by mass per 100 parts by mass of the pre-calcined powder, but 10 to 30 parts by mass is preferred for the glycerin aqueous solution. During the support process, the binder and the pre-calcined powder may be supplied alternately or simultaneously to the molding machine.

[0022] [About catalyst manufacturing methods] The starting materials for the elements constituting the catalyst precursor and catalyst of the present invention are not particularly limited. For example, as the starting material for the molybdenum component, molybdenum oxides such as molybdenum trioxide, molybdic acid or a salt thereof such as molybdic acid, ammonium paramolybdate, and ammonium metamolybdate, and molybdenum-containing heteropolyacids or a salt thereof such as phosphomolybdic acid and silicomolybdic acid can be used.

[0023] As the raw material of the bismuth component, bismuth salts such as bismuth nitrate, bismuth carbonate, bismuth sulfate, and bismuth acetate, bismuth trioxide, metallic bismuth, etc. These raw materials can be used as solids, or as an aqueous solution, a nitric acid solution, or a slurry of a bismuth compound produced from these aqueous solutions, but it is preferable to use the nitrate, or a solution thereof, or a slurry produced from the solution.

[0024] The raw material of the alkali metal, which is the Y component represented by the general formula (1), is not limited to these, but examples thereof include hydroxides, chlorides, carbonates, sulfates, nitrates, oxides, and acetates of the component elements (lithium, sodium, potassium, rubidium, and cesium).Preferably, it is a compound containing cesium, such as cesium hydroxide, cesium chloride, cesium carbonate, cesium sulfate, and cesium oxide, with cesium nitrate being particularly preferred.

[0025] As the starting materials for the other component elements, ammonium salts, nitrates, nitrites, carbonates, subcarbonates, acetates, chlorides, inorganic acids, salts of inorganic acids, heteropolyacids, salts of heteropolyacids, sulfates, hydroxides, organic acid salts, oxides, or mixtures thereof of metal elements generally used in this type of catalyst may be used in combination, with ammonium salts and nitrates being preferred.

[0026] These compounds containing catalytically active components may be used alone or in combination of two or more. The slurry can be obtained by uniformly mixing each active component-containing compound with water. There are no particular restrictions on the amount of water used in the slurry, as long as it can completely dissolve all of the compounds used or can be uniformly mixed. The amount of water used can be determined appropriately taking into account the drying method and drying conditions. Typically, the amount of water used is 200 to 2,000 parts by mass per 100 parts by mass of the total mass of the compounds used to prepare the slurry. While a larger amount of water is preferable, too much water has many disadvantages, such as increased energy costs in the drying process and incomplete drying. Furthermore, the nitrate ion concentration in the slurry liquid immediately before final drying is 8.0 mass% or more and 50 mass% or less, preferably 9.0 mass% or more and 45 mass% or less, more preferably 10.0 mass% or more and 40 mass% or less, and most preferably 11.0 mass% or more and 30 mass% or less. Similarly, the ammonium ion concentration in the slurry liquid immediately before drying is 1.0 mass% or more and 10 mass% or less, preferably 1.2 mass% or more and 8 mass% or less, more preferably 1.5 mass% or more and 6 mass% or less, and most preferably 1.7 mass% or more and 4 mass% or less.

[0027] The slurry of the source compounds of the above-mentioned component elements is preferably prepared by (a) mixing the source compounds all at once, (b) mixing them all at once followed by aging, (c) mixing them stepwise, (d) repeating the mixing and aging stepwise, or a combination of (a) to (d). Here, aging refers to "processing industrial raw materials or semi-finished products under specific conditions, such as a fixed time and a fixed temperature, to obtain or enhance required physical or chemical properties or to promote a desired reaction." In the present invention, the fixed time refers to a range of 5 minutes to 24 hours, and the fixed temperature refers to a range above room temperature and below the boiling point of the aqueous solution or dispersion. Among these, the stepwise mixing method (c) is preferred in terms of the activity and yield of the final catalyst. More preferred is a method in which the raw materials are mixed stepwise into a mother liquor in a completely dissolved state. Most preferred is a method in which an alkali metal solution and various mixtures of nitrates are mixed into a mother liquor prepared as a blend or slurry of the molybdenum raw material.

[0028] In the present invention, there are no particular restrictions on the shape of the stirring blades of the stirrer used when mixing the essential active ingredients, and any stirring blades such as propeller blades, turbine blades, paddle blades, inclined paddle blades, screw blades, anchor blades, ribbon blades, large lattice blades, etc. can be used in one stage or in two or more stages of the same or different blades in the vertical direction. In addition, baffles (baffle plates) may be installed in the reaction vessel as necessary.

[0029] The slurry thus obtained is then dried. The drying method is not particularly limited as long as it can completely dry the slurry, and examples thereof include drum drying, freeze drying, spray drying, and evaporation to dryness. Among these, spray drying is particularly preferred in the present invention, as it can dry the slurry into powder or granules in a short time. The drying temperature for spray drying varies depending on the concentration of the slurry, the liquid delivery speed, etc., but the temperature at the outlet of the dryer is generally between 70°C and 150°C.

[0030] The catalyst precursor obtained as described above can be molded and then calcined, thereby controlling and maintaining the molded shape, thereby obtaining a catalyst with particularly excellent mechanical strength for industrial applications and exhibiting stable catalytic performance. If necessary, a pre-calcination step may be carried out before molding.

[0031] For molding, supported molding can be employed in which the catalyst is supported on a carrier such as silica. Specific molding methods include, for example, tablet molding, press molding, extrusion molding, and granulation molding. The shape of the molded product can be selected appropriately, for example, from cylindrical, ring-shaped, spherical, etc., taking into account the operating conditions. Supported catalysts are used in which catalytically active components are supported on spherical carriers, particularly inert carriers such as silica or alumina, and have an average particle size of 1.0 mm to 10.0 mm, preferably 1.0 mm to 8.0 mm. During molding, small amounts of known additives, such as graphite and talc, may be added. The molding aids, pore-forming agents, and carriers added during molding are not considered as constituent elements of the active component in the present invention, regardless of whether they are active in converting raw materials into other products. To produce a catalyst having the configuration of the present invention, a molding method can be used in which two or more catalyst precursors are sequentially layered on the core side and the catalyst surface side in this molding process. For example, a catalytically active component is first supported in an amount equivalent to 5% by mass or more of the formed catalyst (hereinafter referred to as the first-stage support). Next, a catalytically active component with a different composition is supported in an amount equivalent to 5% by mass or more of the formed catalyst (hereinafter referred to as the second-stage support), thereby obtaining the desired catalyst of the present invention. The amount of the catalytically active component in the first stage is preferably 5% by mass or more to 50% by mass or less, more preferably 20% by mass or more to 33% by mass or less, of the formed catalyst. The amount of the catalytically active component in the second stage is preferably 5% by mass or more to 50% by mass or less, more preferably 20% by mass or more to 33% by mass or less, of the formed catalyst. After supporting the active component on the core side, air drying or calcination may be performed.

[0032] The pre-calcination (calcination of the catalyst precursor before molding) method and conditions, or the main calcination (calcination after molding) method and conditions are not particularly limited, and known processing methods and conditions can be applied. The optimal conditions for pre-calcination and main calcination vary depending on the catalyst raw material, catalyst composition, preparation method, etc., used. However, they are typically performed under a flow of oxygen-containing gas such as air or an inert gas at 200°C to 600°C, preferably 300°C to 550°C, for 0.5 hours or more, preferably 1 hour to 40 hours. Here, the term "inert gas" refers to a gas that does not reduce the catalytic activity, and specific examples include nitrogen, carbon dioxide, helium, and argon. The main calcination is particularly important in determining the catalytic activity of the present invention. However, when the catalytic activity is low or high, it is well known to those skilled in the art to adjust the activity by changing the process parameters of the main calcination step, such as the oxygen content in the atmosphere, the maximum temperature, and the calcination time, to maximize the yield of the composition. This is within the scope of the present invention. The firing step is carried out after the pre-firing step, and the maximum temperature reached in the firing step (firing temperature) is higher than the maximum temperature reached in the pre-firing step (pre-firing temperature). In the catalyst production method of the present invention, the main calcination temperature is preferably 540°C or lower, more preferably 530°C or lower, and particularly preferably 520°C or lower. In this specification, the catalytically active component that has been pre-calcined and has not yet been compacted is referred to as pre-calcined powder.

[0033] The catalyst of the present invention is preferably used as a catalyst for producing methacrolein and methacrylic acid compounds, and more preferably used as a catalyst for the first stage, i.e., for producing methacrolein.

[0034] In addition, when the catalyst of the present invention is used, it may be used alone or in one or more layers when a plurality of catalyst layers are provided in a reaction tube, but it is preferred that the catalyst be used as a catalyst in the second layer when two or more layers are packed.

[0035] <Catalyst particle size> The catalyst particle size of the catalyst of the present invention is preferably 4.1 mm or more and 5.0 mm or less. More preferred upper limits are 4.9 mm, 4.8 mm, 4.7 mm, and 4.6 mm, respectively, and particularly preferably 4.5 mm. The lower limits are 4.2 mm and 4.3 mm, respectively. That is, the most preferred range is 4.3 mm or more and 4.5 mm or less. The catalyst particle size is the number average of the three-axis mean diameter calculated from the average of the length (L), width (B), and thickness (T) of the catalyst. The three-axis mean diameter is calculated by the following formula (C). [Number C] Triaxial average (mm) = (L+B+T) / 3 (C) In the case of a spherical catalyst, the length (L), width (B), and thickness (T) of the catalyst used to calculate the three-axis mean diameter are the length (L), width (B), and thickness (T) of the three axes that pass through the center of gravity of the sample to be measured and are perpendicular to each other, in descending order of the diameter values. The details of the measurement do not matter as long as it is measured on a randomly sampled portion of the catalyst, but for example, it means the average value of measurements on 300 or more catalyst particles.

[0036] <About the second stage catalyst> When the catalyst of the present invention is used as a catalyst for producing methacrolein, a second-stage oxidation reaction can be carried out to obtain methacrylic acid. In this case, the second stage catalyst is preferably a catalyst represented by the following formula (2). Mo 10 V a2 P b2 Cu c2 Cs d2 (NH4) e2 X f2 O g2 (2) (In the formula, Mo represents molybdenum, V represents vanadium, P represents phosphorus, Cu represents copper, Cs represents cesium, (NH4) represents an ammonium group, X represents one or more elements selected from the group consisting of Sb, As, Ag, Mg, Zn, Al, B, Ge, Sn, Pb, Ti, Zr, Cr, Re, Bi, W, Fe, Co, Ni, Ce, Th, K, and Rb, a2 to g2 represent the atomic ratios of each element, a2 represents a positive number in the range of 0.1≦a2≦6.0, b2 represents a positive number in the range of 0.5≦b2≦6.0, c2 represents a positive number in the range of 0≦c2≦3.0, d2 represents a positive number in the range of 0≦d2≦3.0, e2 represents a positive number in the range of 0≦e2≦3.0, and f2 represents a positive number in the range of 0≦f2≦3.0. g2 is a value determined by the valence of each element.)

[0037] The catalyst of the present invention is used in reactions to produce the corresponding methacrolein or methacrylic acid from raw materials such as isobutylene or t-butyl alcohol, particularly in reactions to produce methacrolein or methacrylic acid by vapor-phase catalytic oxidation of isobutylene or t-butyl alcohol with molecular oxygen or a molecular oxygen-containing gas. This effectively suppresses the by-production of aromatic compounds (especially terephthalic acid), suppresses the hot spot temperature, and enables high yields of the target product in the region of high catalytic activity. As a result, compared with known methods, high yields can be achieved in the region of high catalytic activity, and improved product price competitiveness can be expected. Furthermore, the catalyst of the present invention is effective in improving yields even in regions where catalytic activity is not high. It also exhibits improved process stability in exothermic partial oxidation reactions, such as reducing ΔT (the difference between the hot spot temperature and the reaction bath temperature). Furthermore, the catalyst of the present invention is also effective in reducing by-products that adversely affect the environment and the quality of the final product, methyl methacrylate, such as carbon monoxide (CO), carbon dioxide (CO), acetaldehyde, acetic acid, acrolein, and formaldehyde.

[0038] The catalyst of the present invention thus obtained is used for producing methacrolein and / or methacrylic acid by gas-phase catalytic oxidation of at least one raw material selected from, for example, isobutylene and t-butyl alcohol using a molecular oxygen-containing gas, and is particularly effective when producing methacrolein and / or methacrylic acid. In the production method of the present invention, the method for flowing the raw material gas may be a normal single flow method or a recycle method, and can be carried out under commonly used conditions, without any particular limitation. For example, a mixed gas consisting of 1 to 10% by volume, preferably 4 to 9% by volume, more preferably 4 to 7.5% by volume, and most preferably 5 to 7% by volume of isobutylene as a starting material at room temperature, 3 to 20% by volume, preferably 4 to 18% by volume of molecular oxygen, 0 to 60% by volume, preferably 4 to 50% by volume of water vapor, and 20 to 80% by volume, preferably 30 to 60% by volume of an inert gas such as carbon dioxide or nitrogen, is filled in a reaction tube and then heated at 250 to 450°C under a pressure of normal pressure to 10 atmospheres at a space velocity of 300 to 5000 h -1 and the reaction is carried out. [Example]

[0039] The present invention will be described in more detail below with reference to examples. In the examples, the conversion rate, yield, selectivity and loading rate were calculated according to the following formulas. [Number D] TIFF2025153075000001.tif51170

[0040] [Example 1] (Preparation of Catalyst 1) (Manufacturing of core-side pre-fired powder) The composition ratio of catalytically active components excluding oxygen is Mo 12 Bi 1.7 Ni 0.8 Fe 1.2 Co 7.2 Cs 0.25 A catalyst was produced using the following procedure using the raw materials in the amounts shown below. Ammonium molybdate and cesium nitrate were dissolved in distilled water with heating and stirring to obtain aqueous solution (A). Separately, cobalt nitrate, nickel nitrate, and ferric nitrate were dissolved in distilled water to prepare aqueous solution (B). Bismuth nitrate was dissolved in distilled water acidified with concentrated nitric acid to prepare aqueous solution (C). Aqueous solution (A) was mixed with (B) and (C) in turn under vigorous stirring, and the resulting suspension was dried using a spray dryer. The resulting powder was calcined at 440°C for 4 hours to obtain pre-calcined powder (D). (Production of pre-fired powder for the surface side) The composition ratio of catalytically active components excluding oxygen is Mo 12 Bi 1.7 Ni 0.8 Fe 1.5 Co 7.2 Cs 0.2 A catalyst was produced using the following procedure using the raw materials in the amounts shown below. (Support treatment, etc.) Dissolve ammonium molybdate and cesium nitrate in distilled water while heating and stirring to obtain an aqueous solution. (E) was obtained. Separately, cobalt nitrate, nickel nitrate, and ferric nitrate were dissolved in distilled water to prepare an aqueous solution (F), and bismuth nitrate was dissolved in distilled water acidified with concentrated nitric acid to prepare an aqueous solution (G). (F) and (G) were sequentially mixed with the aqueous solution (E) under vigorous stirring, and the resulting suspension was dried using a spray dryer. The resulting powder was calcined at 440 °C for 4 hours to obtain pre-calcined powder (H). Pre-calcined powder (D) was then supported on an inert carrier (alumina, particle size 4.5 mm) using a tumbling granulator in a proportion of 20% by mass of the molded catalyst. A 25% by mass aqueous glycerin solution was used in an amount equivalent to 30% by mass of the total amount of the inert carrier and pre-calcined powder to perform the support process. Next, a quantity of pre-calcined powder (H) equivalent to 20% by mass of the molded catalyst was weighed, and the catalyst on which pre-calcined powder (D) was supported was subjected to the support process. Pre-calcined powders (D) and (H) contained crystalline cellulose as a strength improver at a concentration of 5% by mass relative to each pre-calcined powder. The molded product thus obtained was calcined at 510°C for 5 hours to obtain catalyst 1 of the present invention. The A1 / A2 ratio of the obtained catalyst 1 was 1.3, and the B1 / B2 ratio was 0.8.

[0041] [Example 2] (Preparation of Catalyst 2) In the same manner as in Example 1, the composition ratio of the catalytically active component on the core side, excluding oxygen, was changed to Mo in atomic ratio. 12 Bi 1.7 Ni 0.8 Fe 1.2 Co 7.2 Cs 0.3 The composition ratio excluding oxygen on the surface side is Mo 12 Bi 1.7 Ni 0.8 Fe 2.1 Co 7.2 Cs 0.1 Catalyst 2 was obtained by adjusting the A1 / A2 ratio to 1.8 and the B1 / B2 ratio to 0.3 for the obtained catalyst 2.

[0042] [Comparative Example 1] (Catalyst 3) Catalyst 3 was produced by supporting a pre-calcined powder containing one type of catalytically active component. The composition ratio of this catalytically active component, excluding oxygen, was Mo 12 Bi 1.7 Ni 0.8 Fe 1.8 Co 7.2 Cs 0.2 The amount of supported carbon was 40% by weight of the molded catalyst. The pre-calcined powder was prepared using the same procedure as described for (Catalyst 1). For Catalyst 3, A1 / A2 was 1.0 and B1 / B2 was 1.0.

[0043] Comparative Example 2 (Catalyst 4) In the same manner as in Example 1, the composition ratio of the catalytically active component on the core side, excluding oxygen, was changed to Mo in atomic ratio. 12 Bi 1.7 Ni 0.8 Fe 1.8 Co 7.2 Cs 0.4 The composition ratio excluding oxygen on the surface side is Mo 12 Bi 1.7 Ni 0.8 Fe 1.8 Co 7.2 Cs 0.1Catalyst 4 was obtained by adjusting the A1 / A2 ratio to 1.0 and the B1 / B2 ratio to 0.2 for the obtained catalyst 4.

[0044] Comparative Example 3 As in Comparative Example 1, one type of catalytically active component was supported in an amount that accounted for 40 mass % of the formed catalyst, to obtain catalysts 5 and 6. The composition ratio of catalyst 5 excluding oxygen was Mo in atomic ratio. 12 Bi 1.7 Ni 0.8 Fe 2.1 Co 7.2 Cs 0.1 The composition ratio of catalyst 6 excluding oxygen is Mo in atomic ratio. 12 Bi 1.7 Ni 0.8 Fe 1.0 Co 7.2 Cs 0.3 The pre-calcined powder was prepared using the same procedure as described for (Catalyst 1), and the treatments such as loading were also the same as described for (Catalyst 1). Catalyst 5 was packed at the gas inlet side of the reaction tube, and catalyst 6 was packed at the gas outlet side in a volume ratio of 1:1, and the same evaluation was carried out.

[0045] (Production of methacrolein and methacrylic acid) The catalyst obtained by the above preparation method was evaluated for reactivity by the following method. A total of 40.6 mL of catalyst, including inert diluents, was packed into a stainless steel reactor tube. The catalyst was then aged for at least 50 hours at a bath temperature of 360°C under conditions of an outlet pressure of 50 kPaG, a GHSV of 1000 hr-1, and a TOS of 345°C. The condensate and gas components were separated at the reactor outlet using a condenser. The gas and condensate components were quantitatively analyzed using a gas chromatograph equipped with a flame ionization detector and a thermal conductivity detector, respectively. The data obtained by gas chromatography were factor-corrected to calculate the feed conversion and effective yield.

[0046] [Table 1]

[0047] As shown in Table 1, the catalysts of Examples 1 and 2, in which the iron content is high on the catalyst surface side and low on the core side, have higher yields than the catalysts of Comparative Examples 1 to 3. Furthermore, Comparative Example 3, in which the amount of iron was loaded so that it was less on the outlet side than on the raw material gas inlet side, was unable to achieve the high yield of the present invention. In other words, the usefulness of catalysts loaded so that the composition varies on a catalyst-by-catalyst basis was also proven. [Industrial Applicability]

[0048] The catalyst of the present invention is useful when producing methacrolein using isobutylene or t-butyl alcohol as a raw material. [Explanation of symbols]

[0049] A: active ingredient layer, B: area to be analyzed by linear analysis on the core side, C: area to be analyzed by linear analysis on the surface side, D: carrier

Claims

1. A supported catalyst containing at least iron and an alkali metal as active components, A catalyst for producing methacrolein and / or methacrylic acid, characterized in that the iron content in the active component layer is high on the catalyst surface side and low on the core side.

2. 2. The catalyst for producing methacrolein and / or methacrylic acid according to claim 1, wherein the content of the alkali metal is low on the catalyst surface side and high on the core side.

3. 2. The catalyst for producing methacrolein and / or methacrylic acid according to claim 1, which satisfies the following formula (A), where A1 is the iron content on the catalyst surface side and A2 is the iron content on the core side. [Formula A] 1.1 ≦ A1 / A2...(A)

4. 2. The catalyst for producing methacrolein and / or methacrylic acid according to claim 1, wherein the content of the alkali metal on the catalyst surface side is B1 and the content of the alkali metal on the core side is B2, and the catalyst satisfies the following formula (B): [Formula B] B1 / B2 ≦ 0.95...(B)

5. The catalyst for producing methacrolein and / or methacrylic acid according to any one of claims 1 to 4, which has a composition represented by the following formula (1) as a catalytically active component: [Formula 1] Mo １２ Bi ｂ１ Ni ｃ１ Co ｄ１ Fe ｅ１ X ｆ１ Y ｇ１ Z ｈ１ O ｉ１ ・・・(1) (In the formula, Mo, Bi, Ni, Co, and Fe represent molybdenum, bismuth, nickel, cobalt, and iron, respectively; X represents at least one element selected from tungsten, antimony, tin, zinc, chromium, manganese, magnesium, silicon, aluminum, cerium, and titanium; Y represents at least one element selected from sodium, potassium, cesium, rubidium, and thallium; Z represents an element belonging to Groups 1 to 16 of the periodic table; and means at least one element selected from elements other than Ni, Co, Fe, X, and Y, and b1, c1, d1, e1, f1, g1, h1, and i1 represent the numbers of atoms of bismuth, nickel, cobalt, iron, X, Y, Z, and oxygen, respectively, and 0<b1≦7.0, 0≦c1≦10.0, 0≦d1≦10.0, 0<e1<5.0, 0≦f1≦2.0, 0<g1≦3.0, 0≦h1≦5.0, and i1=a value determined by the oxidation state of each element).

6. The method for producing methacrolein and / or methacrylic acid according to claim 5, wherein, in the formula (1), 1.0 < e1 ≦ 2.

5.

7. The method for producing methacrolein and / or methacrylic acid according to claim 5, wherein, in the formula (1), Y is cesium, and 0.10≦g1≦1.

0.

8. The catalyst for producing methacrolein and / or methacrylic acid according to any one of claims 1 to 4, which is supported on an inert carrier.

9. A method for producing methacrolein and / or methacrylic acid using the catalyst according to any one of claims 1 to 4.

10. 5. The method for producing a catalyst for producing methacrolein and / or methacrylic acid according to claim 1, wherein two types of catalyst precursors having different compositions are sequentially supported on an inert carrier.

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