Catalyst filling method, method for producing (METH)acrylic acid, and reaction tube

Abstract

Provided is a catalyst filling method with which it is possible to improve the yield of a target product in a reaction using a catalyst without performing a special catalyst manufacturing process. Provided is a method for filling a reaction tube 1 provided to a fixed-bed reactor with a catalyst 2, wherein the catalyst contains a solid catalyst and a fine powder catalyst, and the fine powder catalyst satisfies the relationships 0.010 mass% ≤ X1 + X2 ≤ 2.300 mass% and X1 < X2 (X1 represents the amount (mass%) of the fine powder catalyst present in a reaction-gas-outlet-side region A1 with respect to 100 mass% of the total amount of the catalyst, and X2 represents the amount (mass%) of the fine powder catalyst present in a reaction-gas-inlet-side region A2 with respect to 100 mass% of the total amount of the catalyst, the reaction-gas-outlet-side region being a region in which 50 mass% of the total amount of 100 mass% of the solid catalyst is present by integrating from the reaction-gas-outlet 1B side, and the reaction-gas-inlet-side region being a region in which 50 mass% of the total amount of 100 mass% of the solid catalyst is present by integrating from the reaction-gas-inlet 1A side.

Description

Catalyst packing method, (meth)acrylic acid production method, and reaction tube

[0001] The present invention relates to a method for packing a catalyst, a method for producing (meth)acrylic acid using the catalyst, and a reaction tube packed with the catalyst.

[0002] Generally, a solid catalyst packed into a reaction tube of a fixed-bed reactor may be partially pulverized due to mechanical action or naturally during packaging after production, transportation from a production facility to a catalyst packing device, storage, weighing, and catalyst packing into a catalyst packing device. Conventionally, such pulverized catalyst with small particle size (fine catalyst) was packed into a reaction tube, and there was a risk of the pressure drop in the reaction tube increasing due to the inclusion of the fine catalyst. That is, the inclusion of the fine catalyst caused a decrease in reaction performance and an increase in pressure drop during the catalyst use period. Against this background, the following proposals have been made.

[0003] Patent Document 1 describes a method for selectively removing only finely powdered catalyst using a catalyst packing container when packing a solid catalyst into a reaction tube. Patent Document 2 describes a method for removing fine powder formed by powdering a portion of a stacked solid catalyst layer from the catalyst layer. Patent Document 3 describes a method for improving the mechanical strength of a solid catalyst by coating the surface of the solid catalyst with cellulose to prevent the catalyst from powdering during transportation and packing into a reactor. Furthermore, Patent Document 4 describes mixing a specified amount of catalyst into used packing material when reusing it to improve the yield of the target product.

[0004] JP 2003-275571 A JP 2014-62015 A JP 2007-111581 A WO 2015 / 166911

[0005] However, when (meth)acrylic acid is produced by packing a catalyst into a reaction tube using the methods described in Patent Document 1 or 2, a sufficient (meth)acrylic acid yield is not obtained, and further improvements are therefore required. Furthermore, the method described in Patent Document 3 requires a step of coating the catalyst surface with cellulose to prevent the catalyst from powdering, which increases the production cost. Furthermore, the method described in Patent Document 4 requires the use of a packing material in the reaction, and also requires the reuse of used packing material. Therefore, this method cannot be applied to reactions that do not use a packing material or reactions that use unused packing material.

[0006] In view of the above problems, an object of the present invention is to provide a method for packing a catalyst, which can improve the yield of a target product in a reaction using a catalyst without performing a special catalyst production process. Another object of the present invention is to provide a method for producing (meth)acrylic acid, which can produce (meth)acrylic acid in a high yield using a catalyst packed in this way. A further object of the present invention is to provide a reaction tube packed with a catalyst, which can improve the yield of a target product.

[0007] The present inventors have conducted extensive studies to solve the above-mentioned problems. As a result, they have found that the yield of a target product (e.g., (meth)acrylic acid) can be improved by setting the ratio of the powder catalyst to the catalyst contained in the entire reaction tube within a specific range and by packing the catalyst so that the ratio of the powder catalyst present on the reaction gas inlet side is increased and the ratio of the powder catalyst present on the reaction gas outlet side is decreased relative to the ratio of the powder catalyst contained in the entire reaction tube, and have thus achieved the present invention. That is, the gist of the present invention is as follows.

[0008] [1] A method for packing a catalyst into a reaction tube equipped with a fixed-bed reactor, wherein the catalyst comprises a solid catalyst that does not pass through a sieve with a nominal mesh size of 1 mm and a fine powder catalyst that passes through a sieve with a nominal mesh size of 1 mm, and the fine powder catalyst satisfies the following formulas (1) and (2): 0.010 mass%≦X １ +X ２ ≦2.300% by mass...(1); X １ <X２ ...(2), where X １ represents the amount (mass%) of the fine powder catalyst present in the reaction gas outlet side region relative to 100 mass% of the total amount of the catalyst, and X ２ represents the amount (mass%) of the fine powder catalyst present in the reaction gas inlet side region relative to 100 mass% of the total amount of the catalyst, provided that the reaction gas outlet side region is a region where 50 mass% of the solid catalyst is present out of 100 mass% of the total amount of the solid catalyst when integrated from the reaction gas outlet side of the reaction tube, and the reaction gas inlet side region is a region where 50 mass% of the solid catalyst is present out of 100 mass% of the total amount of the solid catalyst when integrated from the reaction gas inlet side of the reaction tube. [2] The solid catalyst is a catalyst that passes through a sieve with a nominal opening of 9.5 mm but not through a sieve with a nominal opening of 1 mm, and the average volume of the solid catalyst is 20 mm ３ / piece or more, 270mm ３ [3] The catalyst packing method according to [1], wherein the amount of fine catalyst powder present in the reaction gas inlet side region is X ２ (mass%) and the amount X of the fine powder catalyst present in the reaction gas outlet side region １ The method for packing a catalyst according to [1] or [2], wherein the ratio (mass %) of the fine catalyst and the solid catalyst is 60:40 to 100:0. [4] The method for packing a catalyst according to any one of [1] to [3], wherein the fine catalyst and the solid catalyst have substantially the same composition. [5] The method for packing a catalyst according to any one of [1] to [4], wherein a packing material is packed into at least one of a region on the reaction gas inlet side of the catalyst layer packed with the catalyst and a region on the reaction gas outlet side of the catalyst layer packed with the catalyst. [6] The method for packing a catalyst according to any one of [1] to [5], wherein a packing aid is packed together with the catalyst. [7] The method for packing a catalyst according to any one of [1] to [6], wherein the catalyst contains molybdenum and vanadium. [8] The method for packing a catalyst according to any one of [1] to [7], wherein the catalyst has a composition represented by the following formula (3): P ａ Mo ｂ V ｃ Cu ｄ X ｅ Y ｆ Z ｇ (NH ４ )ｈ O ｉ ...(3), In formula (3), P, Mo, V, Cu, NH ４ , and O represent phosphorus, molybdenum, vanadium, copper, ammonium, and oxygen, respectively; X represents at least one element selected from the group consisting of silicon, titanium, germanium, arsenic, antimony, and bismuth; Y represents at least one element selected from the group consisting of niobium, tantalum, tungsten, cerium, zirconium, silver, iron, zinc, chromium, magnesium, cobalt, manganese, barium, and lanthanum; Z represents at least one element selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium; a to i represent the molar ratio of each component, and when b = 12, a = 0.5 to 3, c = 0.01 to 3, d = 0.01 to 2, e = 0 to 3, f = 0 to 3, g = 0.01 to 3, and h = 0 to 30; and i is the molar ratio of oxygen necessary to satisfy the valence of each component. [9] The method for packing a catalyst according to any one of [1] to [8], wherein the catalyst is a catalyst for producing (meth)acrylic acid.

[10] A method for producing (meth)acrylic acid by a gas-phase catalytic oxidation reaction, comprising supplying (meth)acrolein and molecular oxygen to a reaction tube packed with the catalyst, the catalyst comprising a solid catalyst that does not pass through a sieve with a nominal mesh size of 1 mm and a fine powder catalyst that passes through a sieve with a nominal mesh size of 1 mm, and the fine powder catalyst satisfies the following formulas (1) and (2): 0.010 mass%≦X １ +X ２ ≦2.300% by mass...(1); X １ <X ２ ...(2), where X １ represents the amount (mass%) of the fine powder catalyst present in the reaction gas outlet side region relative to 100 mass% of the total amount of the catalyst, and X ２represents the amount (mass%) of the fine powder catalyst present in the reaction gas inlet side region relative to 100 mass% of the total amount of the catalyst, provided that the reaction gas outlet side region is a region where 50 mass% of the solid catalyst is present out of 100 mass% of the total amount of the solid catalyst, calculated from the reaction gas outlet side of the reaction tube, and the reaction gas inlet side region is a region where 50 mass% of the solid catalyst is present out of 100 mass% of the total amount of the solid catalyst, calculated from the reaction gas inlet side of the reaction tube.

[11] The solid catalyst is a catalyst that passes through a sieve with a nominal opening of 9.5 mm but not through a sieve with a nominal opening of 1 mm, and the average volume of the solid catalyst is 20 mm ３ / piece or more, 270mm ３

[12] The method for producing (meth)acrylic acid according to

[10] , wherein the amount of the fine powder catalyst present in the reaction gas inlet side region is X ２ (mass%) and the amount X of the fine powder catalyst present in the reaction gas outlet side region １ The method for producing (meth)acrylic acid according to

[10] or

[11] , wherein the ratio (mass %) of the fine powder catalyst and the solid catalyst is 60:40 to 100:0.

[13] The method for producing (meth)acrylic acid according to any of

[10] to

[12] , wherein the fine powder catalyst and the solid catalyst have substantially the same composition.

[14] The method for producing (meth)acrylic acid according to any of

[10] to

[13] , wherein a packing material is packed in at least one of a region on the reaction gas inlet side of the catalyst layer packed with the catalyst and a region on the reaction gas outlet side of the catalyst layer packed with the catalyst.

[15] The method for producing (meth)acrylic acid according to any of

[10] to

[14] , wherein a packing auxiliary material is packed together with the catalyst.

[16] The method for producing (meth)acrylic acid according to any of

[10] to

[15] , wherein the catalyst contains molybdenum and vanadium.

[17] The method for producing (meth)acrylic acid according to any of

[10] to

[16] , wherein the catalyst has a composition represented by the following formula (3): P ａ Mo ｂ V ｃ Cu ｄ X ｅ Y ｆ Z ｇ (NH ４ ) ｈ O ｉ...(3), In formula (3), P, Mo, V, Cu, NH ４ , and O represent phosphorus, molybdenum, vanadium, copper, ammonium, and oxygen, respectively; X represents at least one element selected from the group consisting of silicon, titanium, germanium, arsenic, antimony, and bismuth; Y represents at least one element selected from the group consisting of niobium, tantalum, tungsten, cerium, zirconium, silver, iron, zinc, chromium, magnesium, cobalt, manganese, barium, and lanthanum; Z represents at least one element selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium; a to i represent the molar ratio of each component, and when b = 12, a = 0.5 to 3, c = 0.01 to 3, d = 0.01 to 2, e = 0 to 3, f = 0 to 3, g = 0.01 to 3, and h = 0 to 30; and i is the molar ratio of oxygen necessary to satisfy the valence of each component.

[18] The method for producing (meth)acrylic acid according to any one of

[10] to

[17] , wherein the catalyst is a catalyst for producing (meth)acrylic acid.

[19] A reaction tube packed with a catalyst, wherein the catalyst comprises a solid catalyst that does not pass through a sieve with a nominal mesh size of 1 mm and a fine powder catalyst that passes through a sieve with a nominal mesh size of 1 mm, and the fine powder catalyst satisfies the following formulas (1) and (2): 0.010 mass%≦X １ +X ２ ≦2.300% by mass...(1); X １ <X ２ ...(2), where X １ represents the amount (mass%) of the fine powder catalyst present in the reaction gas outlet side region relative to 100 mass% of the total amount of the catalyst, and X ２represents the amount (mass%) of the fine powder catalyst present in the reaction gas inlet side region relative to 100 mass% of the total amount of the catalyst, provided that the reaction gas outlet side region is a region where 50 mass% of the solid catalyst is present out of 100 mass% of the total amount of the solid catalyst, calculated from the reaction gas outlet side of the reaction tube, and the reaction gas inlet side region is a region where 50 mass% of the solid catalyst is present out of 100 mass% of the total amount of the solid catalyst, calculated from the reaction gas inlet side of the reaction tube.

[20] The solid catalyst is a catalyst that passes through a sieve with a nominal opening of 9.5 mm but not through a sieve with a nominal opening of 1 mm, and the average volume of the solid catalyst is 20 mm ３ / piece or more, 270mm ３

[21] The amount of the fine catalyst powder present in the reaction gas inlet side region X ２ (mass%) and the amount X of the fine powder catalyst present in the reaction gas outlet side region １ The reaction tube according to

[19] or

[20] , wherein the ratio (mass %) of the fine catalyst and the solid catalyst to each other is 60:40 to 100:0.

[22] The reaction tube according to any of

[19] to

[21] , wherein the fine catalyst and the solid catalyst have substantially the same composition.

[23] The reaction tube according to any of

[19] to

[22] , wherein a packing material is packed in at least one of a region on the reaction gas inlet side of the catalyst layer packed with the catalyst and a region on the reaction gas outlet side of the catalyst layer packed with the catalyst.

[24] The reaction tube according to any of

[19] to

[23] , wherein a packing aid is packed together with the catalyst.

[25] The reaction tube according to any of

[19] to

[24] , wherein the catalyst contains molybdenum and vanadium.

[26] The reaction tube according to any of

[19] to

[25] , wherein the catalyst has a composition represented by the following formula (3): P ａ Mo ｂ V ｃ Cu ｄ X ｅ Y ｆ Z ｇ (NH ４ ) ｈ O ｉ ...(3), In formula (3), P, Mo, V, Cu, NH ４, and O represent phosphorus, molybdenum, vanadium, copper, ammonium, and oxygen, respectively; X represents at least one element selected from the group consisting of silicon, titanium, germanium, arsenic, antimony, and bismuth; Y represents at least one element selected from the group consisting of niobium, tantalum, tungsten, cerium, zirconium, silver, iron, zinc, chromium, magnesium, cobalt, manganese, barium, and lanthanum; Z represents at least one element selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium; a to i represent the molar ratio of each component, and when b = 12, a = 0.5 to 3, c = 0.01 to 3, d = 0.01 to 2, e = 0 to 3, f = 0 to 3, g = 0.01 to 3, and h = 0 to 30; and i is the molar ratio of oxygen necessary to satisfy the valence of each component.

[27] The reaction tube according to any one of

[19] to

[26] , wherein the catalyst is a catalyst for producing (meth)acrylic acid.

[0009] According to the present invention, a catalyst packing method can be provided that can improve the yield of the target product in a reaction using a catalyst without performing a special catalyst production process. Furthermore, according to the present invention, by using the catalyst packed in this way, (meth)acrylic acid can be produced with a high yield. Furthermore, according to the present invention, a reaction tube packed with a catalyst that can improve the yield of the target product can be provided.

[0010] FIG. 1 is a schematic diagram of a reaction tube used for packing a catalyst in one embodiment of the present invention.

[0011] A method for packing a catalyst according to one embodiment of the present invention, a method for producing (meth)acrylic acid using the catalyst, and a reaction tube packed with the catalyst will be described below, but the present invention is not limited to the following embodiment. In the present invention, (meth)acrylic acid refers to methacrylic acid or acrylic acid, and (meth)acrolein refers to methacrolein or acrolein. The preferred and more preferred aspects exemplified below can be used in appropriate combination with each other, regardless of expressions such as "preferred" or "more preferred." That is, regardless of expressions such as "preferred" or "more preferred," when an upper limit and a lower limit are specified for a certain numerical range, or when a numerical range is specified that combines an upper limit and a lower limit, the respective upper and lower limits described therein and the numerical values ​​described in the examples can be arbitrarily combined to form a new numerical range.

[0012] <Method for Packing Catalyst> The method for packing the catalyst according to this embodiment is a method for packing a catalyst containing a solid catalyst that does not pass through a sieve with a nominal mesh size of 1 mm and a fine powder catalyst that passes through a sieve with a nominal mesh size of 1 mm into a reaction tube of a fixed-bed reactor. In the method for packing the catalyst according to this embodiment, the reaction tube is packed with the fine powder catalyst so as to satisfy the following formulas (1) and (2) for the reasons described below, thereby forming a catalyst layer: 0.010 mass%≦X １ +X ２ ≦2.300% by mass...(1); X １ <X ２ ...(2).

[0013] Here, X １ represents the amount (mass%) of the fine catalyst present in the reaction gas outlet side region relative to 100 mass% of the total amount of the catalyst, and X ２ represents the amount (mass%) of fine powder catalyst present in the reaction gas inlet side region relative to 100 mass% of the total amount of catalyst. The "reaction gas outlet side region" is a region where 50 mass% of the total amount of solid catalyst is present, calculated from the reaction gas outlet side of the reaction tube. The "reaction gas inlet side region" is a region where 50 mass% of the total amount of solid catalyst is present, calculated from the reaction gas inlet side of the reaction tube.

[0014] In the present invention, "a finely divided catalyst that passes through a sieve with a nominal mesh size of 1 mm" refers to a catalyst that passes through a sieve with a nominal diameter of 200 mm and a nominal height of 45 mm, as specified in JIS Z8801-1, and falls into a receiver when the catalyst is vibrated for 10 minutes in a commercially available sieve shaker at a frequency of 50 times per minute and an amplitude of 2 mm. In the present invention, such a catalyst is also simply referred to as "finely divided catalyst." Furthermore, in the present invention, "a solid catalyst that does not pass through a sieve with a nominal mesh size of 1 mm" refers to a catalyst that does not pass through a sieve with a nominal mesh size of 1 mm, as specified in JIS Z8801-1, and a nominal diameter of 200 mm and a nominal height of 45 mm, as specified in JIS Z8801-1, when the catalyst is vibrated for 10 minutes in a commercially available sieve shaker at a frequency of 50 times per minute and an amplitude of 2 mm. In the present invention, such a catalyst is also simply referred to as a "solid catalyst." Therefore, in the present invention, a catalyst other than a fine powder catalyst can also be said to be a solid catalyst. That is, in the present invention, the catalyst satisfies the above formula (1) and is packed into the reaction tube so that the ratio of the solid catalyst after packing is 97.700 mass % or more and 99.990 mass % or less with respect to the total mass of the catalyst.

[0015] In the present invention, the "total amount of catalyst" means the total mass (100 mass%) of the catalyst (i.e., the fine powder catalyst and the solid catalyst) packed in the reaction tube. Since the mass of the catalyst remains the same before and after packing, the total amount of catalyst can also be said to be the total amount of catalyst present (packed) in the reaction tube after packing.

[0016] The reaction gas outlet side region (hereinafter also referred to as "first region") and the reaction gas inlet side region (hereinafter also referred to as "second region") will be described in more detail below with reference to Fig. 1. Fig. 1 is a schematic diagram of a reaction tube used for packing a catalyst in one embodiment of the present invention. By packing a catalyst (fine powder catalyst and solid catalyst) 2 into a reaction tube 1, a first region A, which is a reaction gas outlet side region, is formed in the reaction tube. １ (End Q on the reaction gas outlet 1B side １ a region from the boundary position P to the second region A, which is a reaction gas inlet side region; ２ (End Q on the reaction gas inlet 1A side ２The boundary position P is a region between the first region A and the boundary position P, where the solid catalyst is present in an amount of 50 mass % each. １ and the second region A ２ And, the X １ is the first region A relative to 100% by mass of the total amount of the catalyst １ represents the amount of finely divided catalyst present in the ２ is the second region A relative to 100% by mass of the total amount of the catalyst ２ The term "particle size" represents the amount of finely divided catalyst present in the reaction tube 1. The entire region in which the catalyst is present after packing is referred to as the catalyst layer 3. In FIG. 1, the first region and the second region are continuous via a boundary position P, but the first region and the second region do not have to be continuous regions. For example, there may be a region between the first region and the second region that consists only of the packing material described below. Furthermore, the first region and the second region may each contain, in addition to the catalyst, components required for forming a catalyst layer, such as a packing auxiliary material.

[0017] There may be a space in at least one of the upper part (the region closer to the reaction gas inlet than the catalyst layer) and the lower part (the region closer to the reaction gas outlet than the catalyst layer) of the catalyst layer in the reaction tube, and any packing material 4 may be filled in a part or all of the space. As the packing material, an auxiliary packing material described later may be appropriately selected and used. The flow direction of the reaction gas into the reaction tube may be either up or down. That is, in FIG. 1, the reaction gas is made to flow into the reaction tube from the upper part, but the reaction gas may also be made to flow into the reaction tube from the lower part. Depending on the flow direction of the reaction gas, the "reaction gas outlet side region A" may be used. １ " and "reaction gas inlet side region A ２ " will be replaced with ".

[0018] Generally, when (meth)acrylic acid is produced by the gas-phase catalytic oxidation reaction of (meth)acrolein, the reaction is carried out using a fixed-bed reactor equipped with a reaction tube filled with a catalyst. Here, as described in Patent Document 1, it has been conventionally believed that the presence of a fine powder catalyst having a particle size of 1 mm or less in the catalyst filled in the reaction tube reduces the yield of (meth)acrylic acid. However, the present inventors packed a solid catalyst formed for the gas-phase catalytic oxidation reaction of (meth)acrolein into a reaction tube and conducted an investigation to confirm the improvement of the reaction performance, and obtained the following findings. That is, when the ratio of the fine powder catalyst to the total amount (100 mass%) of catalyst filled in the reaction tube of the fixed-bed reactor is in the range of 0.010 mass% to 2.300 mass%, and １ Compared with the reaction gas inlet side region A of the reaction tube ２ It has been found that the presence of a larger amount of finely divided catalyst in the reaction mixture improves the yield of (meth)acrylic acid.

[0019] The reason why the presence of the above-mentioned fine powder catalyst improves the yield of (meth)acrylic acid in the gas-phase catalytic oxidation reaction of (meth)acrolein is not clear. However, when a larger amount of the fine powder catalyst is present in the reaction gas inlet region and the proportion of the fine powder catalyst is less than 0.010 mass%, it is thought that there is insufficient fine powder catalyst effective for improving the yield of (meth)acrylic acid. Furthermore, when the proportion of the fine powder catalyst exceeds 2.300 mass%, it is thought that the excessive amount of fine powder catalyst causes the successive reaction to proceed excessively.

[0020] The ratio of the fine catalyst to the total amount (100 mass%) of the catalyst present in the reaction tube after the catalyst is packed (X １ +X ２ From the viewpoint of further improving the (meth)acrylic acid yield, the proportion of the fine powder catalyst is preferably 0.040% by mass or more, and more preferably 0.100% by mass or more. On the other hand, from the viewpoint of preventing successive oxidation, the proportion of the fine powder catalyst is preferably 2.200% by mass or less, more preferably 2.100% by mass or less, and even more preferably 2.000% by mass or less.

[0021] As described above, in the present invention, the fine powder catalyst is present in a larger amount in the reaction gas inlet side region than in the reaction gas outlet side region of the reaction tube. １ <X ２ The finely divided catalyst is packed into the reaction tube so as to satisfy the following: １ (mass%) is 0 or greater than 0, and X ２ (mass%) is greater than 0. Specifically, X ２ and X １ The ratio (X ２ :X １ ) is preferably 60:40 to 100:0, more preferably 80:20 to 100:0, even more preferably 90:10 to 100:0, and most preferably 95:5 to 100:0.

[0022] The amount of the fine catalyst present in the first region and the second region (X １ and X ２ In calculating X ), unless there are special circumstances, it is assumed that the catalyst is uniformly packed in the reaction tube. Therefore, X at any point in the first region １ and X at any location within the second region ２ If the above formula (2) is satisfied, it can be determined that the above formula (2) is satisfied in the first region and the second region. However, the catalyst powdering rate, which will be described later, is to be taken into consideration separately.

[0023] The shape of the fine powder catalyst is not particularly limited, and examples thereof include spherical particles, cylindrical particles, pellets, granules, etc. The fine powder catalyst may also be an irregular shape formed by an aggregation of a plurality of granules, etc.

[0024] If the particle size of the solid catalyst is too large, the yield of (meth)acrylic acid may decrease. Therefore, from the viewpoint of further improving the yield of (meth)acrylic acid, the solid catalyst is preferably a catalyst that does not pass through a sieve with a nominal mesh size of 1 mm, but passes through a sieve with a nominal mesh size of 9.5 mm. Note that "a catalyst that passes through a sieve with a nominal mesh size of 9.5 mm" refers to a catalyst that passes through a sieve with a nominal mesh size of 200 mm and a nominal height of 45 mm, as specified in JIS Z8801-1, when the sieve is vibrated for 10 minutes at a frequency of 50 times / min and an amplitude of 2 mm in a commercially available sieve shaker. In addition to solid catalysts, "a catalyst that passes through a sieve with a nominal mesh size of 9.5 mm" also includes finely divided catalysts that pass through a sieve with a nominal mesh size of 1 mm. Therefore, in the present invention, it is preferred that 97.000 mass% or more of the catalyst passing through the sieve having a nominal mesh size of 9.5 mm accounts for 100 mass% of the total amount of catalyst packed into the reaction tube. The proportion of the catalyst passing through the sieve having a nominal mesh size of 9.5 mm is more preferably 99.000 mass% or more, and particularly preferably 100 mass%.

[0025] The shape of the solid catalyst is not particularly limited, and examples include spherical granules, cylindrical, pellet-like, and ring-like shapes. A solid catalyst is a catalyst powder containing catalytic components such as metal components, which is formed into a desired shape by a wet or dry process. Specific examples of solid catalysts include supported catalysts in which catalyst powder is supported on an inert carrier, tableted catalysts in which catalyst powder is tableted with a molding aid such as graphite, and extruded catalysts in which catalyst powder is extruded with water and a molding aid. Because the basic constituent of these molded solid catalysts is catalyst fine particles, the catalyst may be pulverized during packaging, transportation, storage, weighing, and catalyst loading, resulting in a finely divided catalyst. Therefore, to control the proportion of finely divided catalyst, it is preferable to classify and separate the finely divided catalyst contained in the solid catalyst before loading. The classified finely divided powder can be mixed with the solid catalyst to achieve a predetermined ratio. Furthermore, the degree of pulverization during catalyst loading can be adjusted by controlling the molding conditions.

[0026] Although there is no particular limitation on the number of solid catalysts in the reaction tube after packing, a plurality of solid catalysts are usually packed into the reaction tube. Here, among the solid catalysts, there is no particular limitation on the average volume of the solid catalysts that pass through a sieve with a nominal mesh size of 9.5 mm, i.e., the catalysts that pass through a sieve with a nominal mesh size of 9.5 mm but not through a sieve with a nominal mesh size of 1 mm. However, the average volume of the catalysts is not particularly limited before packing. ３ / piece or more, 270mm ３ It is preferable that the average volume of the catalyst is 20 mm ３ / or more, the pressure loss in the reaction tube can be further reduced. ３ When the number of particles is less than 30 mm, the catalytic activity tends to be improved. ３ More preferably, 170 mm ３ It is more preferable that the average volume of the solid catalyst is equal to or less than 1 / 1000. When the catalyst powder rate of the solid catalyst is 0% by mass (0.000% by mass), it can be considered that the average volume of the solid catalyst does not change before and after packing. When the catalyst powder rate of the solid catalyst is greater than 0.000% by mass, the average volume after packing changes slightly compared to before packing depending on the catalyst powder rate.

[0027] The total amount of catalyst packed into the reaction tube varies depending on the length and diameter of the reaction tube and the specific gravity of the catalyst, but is preferably 100 g or more, more preferably 200 g or more, while the total amount of catalyst is preferably 8000 g or less, more preferably 7000 g or less.

[0028] The method for filling the catalyst into the reaction tube is not particularly limited as long as the catalyst is filled into the reaction tube so as to simultaneously satisfy the above formulas (1) and (2). For example, the amounts of the solid catalyst and the fine powder catalyst may be adjusted and filled so that the ratio of the fine powder catalyst to the solid catalyst in the reaction tube after filling is a desired value. Alternatively, the catalyst to be filled into the reaction tube may be pre-pulverized, and the resulting fine powder catalyst may be mixed with the solid catalyst and filled into the reaction tube. Here, as described above, it can be assumed that the catalyst is uniformly filled in the reaction tube. However, the solid catalyst may be pulverized during filling or weighing, and a portion of the solid catalyst may become a fine powder catalyst. Therefore, it is preferable to measure in advance the ratio of the fine powder catalyst generated by pulverization of the solid catalyst during filling or weighing (also referred to as the "catalyst powder fraction"), and to adjust the filling amounts of the solid catalyst and the fine powder catalyst taking the catalyst powder fraction into consideration so that the desired ratio of the fine powder catalyst is obtained after filling. Note that, when the catalyst powder fraction is taken into consideration, it is also possible to fill only the solid catalyst without separately filling the fine powder catalyst, as long as the ratio of the fine powder catalyst in the reaction tube after filling is a desired value. The catalyst powdering rate can be measured by the method described in the Examples section below.

[0029] When packing the catalyst into the reaction tube, a known packing aid used in a catalyst layer may be packed together with the catalyst. The material of the packing aid is not particularly limited as long as it has heat resistance above the temperature used in the reaction. Examples of packing aids that can be used include silica, alumina, silica-alumina, magnesia, titania, and SUS (stainless steel). The shape of the packing aid is also not particularly limited, and examples include spherical, cylindrical, cylindrical, coiled, and plate-shaped shapes. Irregular packings such as cascade mini rings, terrarettes, pall rings, saddle-shaped, and medal packs can also be used as packing aids. The size of the packing aid is not particularly limited as long as it does not form bridges or significantly increase pressure loss when packed into the reaction tube, and is preferably approximately the same size as the solid catalyst. From an economical standpoint, ceramic balls and coil springs are preferred as packing aids, with silica-alumina ceramic balls and SUS coil springs being more preferred. These packing aids may be used alone or in combination of two or more. Furthermore, the extracted material after use in the reaction may be reused as the auxiliary packing material.

[0030] When a packing aid is used in the catalyst layer, there is no particular limitation on the amount of packing aid used in the catalyst layer relative to the total amount of catalyst present in the reaction tube after catalyst filling. However, from the viewpoint of suppressing heat generation, the amount of packing aid used is preferably 0.5% by mass or more and 60% by mass or less relative to the total amount of catalyst. The amount of packing aid used is more preferably 50% by mass or less, and even more preferably 40% by mass or less, relative to the total amount of catalyst. On the other hand, the amount of packing aid used is more preferably 1% by mass or more, and even more preferably 2% by mass or more, relative to the total amount of catalyst. In addition, the catalyst layer may include a region where only the packing aid is present.

[0031] In the catalyst packing method according to the present invention, the catalyst preferably contains at least molybdenum and vanadium. The catalyst preferably further contains phosphorus, and from the viewpoint of achieving a higher effect of the present invention, it is particularly preferable that the catalyst has a composition represented by the following formula (3). The composition represented by the following formula (3) is a value calculated from the amounts of raw materials charged: P ａ Mo ｂ V ｃ Cu ｄ X ｅ Y ｆ Z ｇ (NH ４ ) ｈ O ｉ ...(3)

[0032] In formula (3), P, Mo, V, Cu, NH ４ , and O represent phosphorus, molybdenum, vanadium, copper, ammonium, and oxygen, respectively. X represents at least one element selected from the group consisting of silicon, titanium, germanium, arsenic, antimony, and bismuth. Y represents at least one element selected from the group consisting of niobium, tantalum, tungsten, cerium, zirconium, silver, iron, zinc, chromium, magnesium, cobalt, manganese, barium, and lanthanum. Z represents at least one element selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium. a to i represent the molar ratio of each component, where when b = 12, a = 0.5 to 3, c = 0.01 to 3, d = 0.01 to 2, e = 0 to 3, f = 0 to 3, g = 0.01 to 3, and h = 0 to 30, and i represents the molar ratio of oxygen necessary to satisfy the valence of each component.

[0033] In the catalyst packing method according to the present invention, the catalyst is preferably a catalyst for producing (meth)acrylic acid. In this case, there are no particular limitations on the composition of the fine powder catalyst and the solid catalyst, as long as they are catalysts for producing (meth)acrylic acid by the gas-phase catalytic oxidation reaction of (meth)acrolein. However, as described above, a catalyst containing at least molybdenum and vanadium is preferred, a catalyst containing phosphorus is more preferred, and a catalyst having a composition represented by the above formula (3) is preferred.

[0034] There are no particular limitations on the composition of the solid catalyst and the fine powder catalyst. However, from the viewpoint of improving the yield of (meth)acrylic acid, the solid catalyst and the fine powder catalyst are preferably composed of the same constituent elements, and more preferably have substantially the same composition. In the present invention, the phrase "the solid catalyst and the fine powder catalyst have substantially the same composition" means, in principle, that the solid catalyst and the fine powder catalyst are composed of the same elements, and the difference in the ratio of each element relative to the main element (e.g., molybdenum) is within 50 mol%. The difference in the ratio of each element is preferably within 30 mol%, more preferably within 10 mol%, and even more preferably within 1 mol%. However, regardless of the ratio of each element, even if the fine powder catalyst is derived from the solid catalyst (molded body), the solid catalyst and the fine powder catalyst are considered to have substantially the same composition.

[0035] As described above, the solid catalyst and the fine powder catalyst preferably have substantially the same composition. However, in addition to these solid catalysts and fine powder catalysts having substantially the same composition, solid catalysts and / or fine powder catalysts not having substantially the same composition as these catalysts (when they contain different elements, or when they contain the same elements, the difference in the ratio of each element to the main element exceeds 50 mol%) may also be present, as long as the effects of the present invention are not impaired. There are no particular restrictions on the proportion of such catalysts relative to the total amount of catalyst present in the reaction tube after catalyst packing. However, from the viewpoint of preventing a decrease in the yield of (meth)acrylic acid, the proportion of the above catalyst is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 10% by mass or less, and particularly preferably 3% by mass or less.

[0036] The method for preparing the catalyst is not particularly limited as long as it does not result in significant uneven distribution of the catalyst components, and the catalyst can be prepared using a known method. Examples of such methods include precipitation, coprecipitation, and impregnation. Examples of raw materials used in preparing the catalyst include nitrates, carbonates, acetates, ammonium salts, oxides, and halides of each element. Specifically, the molybdenum raw material may be ammonium paramolybdate, molybdenum trioxide, molybdic acid, or molybdenum chloride. The phosphorus raw material may be orthophosphoric acid, phosphorus pentoxide, or ammonium phosphate. The vanadium raw material may be ammonium metavanadate or vanadium pentoxide. These may be used alone or in combination.

[0037] From the viewpoint of activating the catalyst, it is preferable to subject the catalyst to heat treatment. The heat treatment conditions are not particularly limited, and known heat treatment conditions can be applied. The heat treatment is preferably carried out under a flow of an oxygen-containing gas such as air and / or under a flow of an inert gas. From the viewpoint of further improving the (meth)acrylic acid yield, it is preferable to perform the heat treatment at a temperature of 300°C to 500°C for at least 0.5 hours. A heat treatment temperature of 300°C or higher sufficiently activates the catalyst. Furthermore, a heat treatment temperature of 500°C or lower can further suppress the collapse of the catalyst structure. The heat treatment temperature is more preferably 360°C or higher, and more preferably 390°C or lower. The heat treatment temperature is measured at a point within a radius of 1 m from the inlet for introducing the heat medium. Furthermore, from the viewpoint of improving the yield of (meth)acrylic acid and controlling the catalyst activity within a manageable range, the heat treatment time is more preferably 5 hours or longer, and more preferably 50 hours or shorter. The heat treatment for activating the catalyst may be carried out before or after the catalyst is packed into the reaction tube. In the present invention, the molded body before its activity is improved by the heat treatment is also referred to as the catalyst. That is, in the case where the catalyst is packed into the reaction tube and then the catalyst activity is improved by the heat treatment, the molded body before the heat treatment is also referred to as the catalyst. Note that even in the case where the catalyst is packed into the reaction tube and then the heat treatment is carried out to improve the catalyst activity, the catalyst is packed so that the catalyst after the heat treatment satisfies the above formulas (1) and (2). Usually, the ratio of the amount of the fine catalyst (X) to the total amount of the catalyst before and after the heat treatment is １ and X ２ Therefore, after the catalyst is filled so as to satisfy the above formulas (1) and (2), heat treatment can be carried out under appropriate conditions.

[0038] The type of fixed-bed reactor is not particularly limited, and examples thereof include a multi-tubular heat exchange type, a single-tubular heat exchange type, a self-heat exchange type, a multistage adiabatic type, and an adiabatic type. Industrially, a fixed-bed multi-tubular heat exchange type reactor is preferably used. There is no particular limitation on the number of reaction tubes that the fixed-bed reactor has, and a fixed-bed reactor having any number of reaction tubes can be used.

[0039] The length of the reaction tube of the fixed-bed reactor is not particularly limited, but is preferably 1 m or more, more preferably 3 m or more, and is preferably 15 m or less, more preferably 10 m or less. The inner diameter of the reaction tube of the fixed-bed reactor is not particularly limited, but is preferably 10 mm or more, more preferably 20 mm or more, and is preferably 40 mm or less, more preferably 30 mm or less.

[0040] There is no particular limitation on the volume of the reaction tube of the fixed bed reactor, but ３ It is preferable that the length is 300 cm or more. ３ More preferably, it is 900 cm or more. ３ On the other hand, the volume of the reaction tube is preferably 20,000 cm or more. ３ Preferably, it is 15,000 cm or less. ３ More preferably, it is 8000 cm or less. ３ It is even more preferable that:

[0041] <Method for Producing (Meth)acrylic Acid> In the present invention, (meth)acrylic acid can be produced by a gas-phase catalytic oxidation reaction of (meth)acrolein using a catalyst packed by the catalyst packing method according to the present invention. Specifically, the method for producing (meth)acrylic acid according to this embodiment is a method in which (meth)acrolein and molecular oxygen are supplied to a reaction tube equipped with a fixed-bed reactor packed with the catalyst, and (meth)acrylic acid is produced by a gas-phase catalytic oxidation reaction. Furthermore, in the method for producing (meth)acrylic acid according to this embodiment, the catalyst includes a solid catalyst that does not pass through a sieve with a nominal mesh size of 1 mm and a fine powder catalyst that passes through a sieve with a nominal mesh size of 1 mm, and the fine powder catalyst is packed into the reaction tube so as to satisfy the above formulas (1) and (2).

[0042] The reaction gas (also referred to as "feed gas") used in the gas-phase catalytic oxidation reaction of (meth)acrolein contains (meth)acrolein, an oxygen source gas, and an optional inert gas. The concentration of (meth)acrolein in the feed gas is not particularly limited, but is preferably 1% by volume to 20% by volume, and more preferably 3% by volume to 10% by volume. At the start-up of the gas-phase catalytic oxidation reaction, the concentration of (meth)acrolein in the feed gas may be increased stepwise to increase the reaction load stepwise. Furthermore, the feed (meth)acrolein may contain small amounts of impurities such as water and lower saturated aldehydes, and these impurities do not substantially affect the reaction.

[0043] It is economical to use air as the oxygen source gas, but if necessary, pure oxygen (O ２ ) can also be used. The concentration of molecular oxygen in the raw material gas is preferably 0.3 to 4, more preferably 0.4 to 2.5, in terms of molar ratio to (meth)acrolein. The raw material gas may also be diluted by adding an inert gas such as nitrogen, steam, or carbon dioxide. These inert gases can also be used as carrier gases when evaporating the raw material (meth)acrolein. (Meth)acrolein, the oxygen source gas, and the inert gas may be supplied separately to the reaction tube, or may be mixed before being supplied to the reaction tube and supplied as a mixed gas to the reaction tube.

[0044] The gas-phase catalytic oxidation reaction of (meth)acrolein is preferably carried out under atmospheric pressure to elevated pressure, and the reaction pressure is more preferably 0 kPaG to 200 kPaG. The reaction temperature is preferably 230°C to 450°C, more preferably 250°C to 400°C, and even more preferably 250°C to 350°C. Note that the reaction pressure [kPaG] means gauge pressure. The contact time between the raw material gas and the catalyst is preferably 1.5 seconds to 15 seconds, with the lower limit being more preferably 2 seconds and the upper limit being more preferably 10 seconds.

[0045] In the method for producing (meth)acrylic acid according to this embodiment, the fine powder catalyst packed into the reaction tube satisfies the above formulas (1) and (2). By packing the fine powder catalyst so as to satisfy the above formulas (1) and (2), the yield of (meth)acrylic acid can be improved, as described above. In addition, the above description of the method for packing the catalyst according to the present invention can also be applied to the method for producing (meth)acrylic acid according to the present invention.

[0046] <Reaction Tube> The reaction tube according to the present invention is a reaction tube filled with a catalyst by the catalyst filling method according to the present invention. That is, the reaction tube according to the present invention is a reaction tube filled with a catalyst, wherein the catalyst comprises a solid catalyst that does not pass through a sieve with a nominal mesh size of 1 mm and a fine powder catalyst that passes through a sieve with a nominal mesh size of 1 mm, and the reaction tube is filled with the fine powder catalyst so as to satisfy the formulas (1) and (2). By carrying out a reaction using the reaction tube according to the present invention, the yield of the target product can be improved. In addition, the above description of the catalyst filling method according to the present invention can also be applied to the reaction tube according to the present invention.

[0047] EXAMPLES 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.

[0048] (Yield of methacrylic acid) In the examples and comparative examples, the yield of methacrylic acid was calculated using the following formula (4): Yield of methacrylic acid [%] = B / A × 100 (4). In formula (4), A represents the number of moles of the raw material methacrolein supplied, and B represents the number of moles of methacrylic acid produced. The number of moles was calculated by gas chromatography.

[0049] (Catalyst Powdering Rate) The catalyst powdering rate refers to the proportion of finely divided catalyst particles generated by crushing the solid catalyst when the solid catalyst is packed into a reaction tube. As described above, the finely divided catalyst is a catalyst that falls into a receiver when the catalyst is vibrated for 10 minutes in a commercially available sieve shaker using a sieve with a nominal mesh size of 1 mm, a nominal diameter of 200 mm, and a nominal height of 45 mm, as specified in JIS Z8801-1, at a frequency of 50 times per minute and an amplitude of 2 mm. Specifically, the catalyst powdering rate was measured by the following method. 3,000 g of solid catalyst not containing finely divided catalyst particles was dropped from the top of a stainless steel cylindrical vessel having an inner diameter of 27 mm and a length of 6 m, which was placed perpendicular to the horizontal direction, to fill the vessel. Then, 10 portions (300 g each) of the packed catalyst were extracted from the bottom of the vessel. For each of the 10 separated and collected catalyst samples (mass represented as "D (g)"), the mass (represented as "E (g)") of the finely powdered catalyst that passed through a sieve with a nominal mesh size of 1 mm was measured. This drop test was repeated a total of five times, and the catalyst powdering rate was calculated from the average values ​​of the measured D and E using the following formula (5): Catalyst powdering rate (mass%) = E / D × 100 (5).

[0050] In the examples and comparative examples described below, the ratio of the fine catalyst to the total amount of catalyst (X １ and X ２ ) is not an actual measurement value, but a value estimated from the ratio of finely powdered catalyst and catalyst powdering rate when the catalyst is packed. In addition, taking into account the catalyst powdering rate, it is assumed that the catalyst is packed uniformly in the reaction tube, and X １ and X ２ was calculated.

[0051] [Catalyst Production Example 1: Production of Solid Catalyst Z1] A catalyst having an elemental composition excluding oxygen of P was produced by a production method similar to that described in Patent Document 4. １．５ Mo １２ V ０．８ Cu ０．１ K ０．７ Cs ０．４ Bi ０．３ Sb ０．３ Ce ０．２ As ０．２The powder catalyst was obtained. The elemental composition of the powder catalyst was calculated from the amounts of the raw materials charged. 3 parts by mass of graphite powder was added to 100 parts by mass of the powder catalyst and mixed thoroughly. The resulting mixture was placed in a container with an outer diameter of 5.0 mm, a height of 5.0 mm, and a catalyst volume of 98.2 mm. ３ The solid catalyst Z1 was obtained by tableting into a cylindrical shape with a crushing strength of 70 kgG and a particle size of 1000 μm. The catalyst powdering rate of the solid catalyst Z1 calculated using the above formula (5) was 0% by mass (0.000% by mass). The catalyst volume is the average volume of the solid catalyst passing through a sieve with a nominal mesh size of 9.5 mm before filling (the same applies hereinafter).

[0052] [Catalyst Production Example 2: Production of Solid Catalyst Z2] The mixture obtained in Catalyst Production Example 1 was mixed with a catalyst having an outer diameter of 3.0 mm, a height of 3.0 mm, a catalyst volume of 21.2 mm ３ Solid catalyst Z2 was obtained in the same manner as in Catalyst Production Example 1, except that the solid catalyst Z2 was tableted into a cylindrical shape with a crushing strength of 70 kgG and a particle size of 1 / 1000. The catalyst powder ratio of solid catalyst Z2 was 0% by mass (0.000% by mass).

[0053] [Catalyst Production Example 3: Production of Solid Catalyst Z3] The mixture obtained in Catalyst Production Example 1 was mixed with a catalyst having an outer diameter of 7.0 mm, a height of 7.0 mm, a catalyst volume of 269.4 mm ３ Solid catalyst Z3 was obtained in the same manner as in Catalyst Production Example 1, except that the solid catalyst Z3 was tableted into a cylindrical shape with a crushing strength of 40 kgG and a particle size of 1 / 1000. The catalyst powdering rate of solid catalyst Z3 was 0.020% by mass. In measuring the catalyst powdering rate, solid catalyst Z3 was dropped to form a catalyst layer, and the proportions of fine powder catalyst contained in each of the lower layer (1500 g) and the upper layer (1500 g) were measured. As a result, a greater amount of fine powder catalyst was found to be present in the lower layer, at a ratio of 9:1.

[0054] Example 1 1500 g of solid catalyst Z1 was packed into a stainless steel reaction tube with an inner diameter of 27 mm and a length of 6 m, which was equipped with a fixed-bed reactor. Next, a mixed catalyst prepared by thoroughly mixing 1500 g of solid catalyst Z1 with 67 g of a finely divided catalyst obtained by crushing solid catalyst Z1 and passing it through a sieve with a nominal mesh size of 1 mm was additionally packed from above the packed solid catalyst Z1 to form a catalyst layer (ratio of finely divided catalyst to total catalyst weight of 3067 g: 2.185 mass%). Note that 200 g of unused ceramic balls (6 mm diameter) were packed as packing material into the spaces below and above the catalyst layer in the reaction tube (see FIG. 1 ; the same applies to all subsequent Examples and Comparative Examples). As described above, the catalyst powdering rate of solid catalyst Z1 was 0 mass%, so the ratio of finely divided catalyst to the total catalyst weight after catalyst packing (X １ +X ２ ) remained at 2.185% by mass, the same as when the catalyst was packed (immediately before packing). Furthermore, the proportion of the catalyst present in the reaction tube after packing that passed through a sieve with a nominal mesh size of 9.5 mm relative to the total amount of catalyst was 100% by mass. Next, the temperature of the heat medium bath was raised to 380°C at a rate of 25°C / hr under air flow, and then the catalyst was heat-treated by maintaining it at 380°C for 12 hours. There was no change in the proportion of finely powdered catalyst before and after the heat treatment of the catalyst. Thereafter, the temperature of the heat medium bath was set to 290°C, and a mixed gas (reaction gas) consisting of 5% by volume of methacrolein, 12% by volume of oxygen, 10% by volume of steam, and 73% by volume of nitrogen was circulated from the top of the reaction tube under atmospheric pressure for a contact time of 3.6 seconds, to carry out a gas-phase catalytic oxidation reaction of methacrolein. The yield of methacrylic acid was calculated using the above formula (4). The results are shown in Table 1. As mentioned above, X １ +X ２ is 2.185 mass %, the fine powder catalyst packed in the reaction tube satisfies the above formula (1). In addition, the reaction gas is passed through the reaction tube from the top, and the fine powder catalyst is contained in a larger amount in the reaction gas inlet side region than in the reaction gas outlet side region, so that the fine powder catalyst satisfies the above formula (2) (hereinafter, in Examples 1 to 9 and Comparative Examples 1 to 4 and 6 using solid catalyst Z1, X １ is 0% by mass).

[0055] [Example 2] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z1 and 31 g of fine powder catalyst, which was thoroughly mixed together to be additionally filled from above solid catalyst Z1 (ratio of fine powder catalyst to total catalyst amount of 3031 g: 1.023 mass%). Except for the above, the catalyst was filled and heat-treated in the same manner as in Example 1, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z1 was 0 mass%, X after catalyst filling １ +X ２ The content of the fine powder catalyst remains at 1.023 mass%, the same as when the catalyst was packed. There was no change in the proportion of the fine powder catalyst before and after the heat treatment of the catalyst. In addition, since the reaction gas is circulated from the top of the reaction tube, the fine powder catalyst packed in the reaction tube satisfies the above formulas (1) and (2).

[0056] [Example 3] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z1 and 15 g of fine powder catalyst, which was thoroughly mixed and charged from above the solid catalyst Z1 (ratio of fine powder catalyst to total catalyst amount of 3015 g: 0.498 mass %). Except for the above, the catalyst was charged and heat-treated in the same manner as in Example 1, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z1 was 0 mass %, X after catalyst charging １ +X ２ The content of the fine powder catalyst remains at 0.498 mass%, the same as when the catalyst was packed. There was no change in the proportion of the fine powder catalyst before and after the heat treatment of the catalyst. In addition, since the reaction gas is circulated from the top of the reaction tube, the fine powder catalyst packed in the reaction tube satisfies the above formulas (1) and (2).

[0057] [Example 4] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z1 and 3 g of fine powder catalyst, which was thoroughly mixed together to be additionally packed from above the solid catalyst Z1 (ratio of fine powder catalyst to total catalyst amount of 3003 g: 0.100 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 1, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z1 was 0 mass%, X after the catalyst packing １ +X ２The content of the fine powder catalyst remains at 0.100 mass%, the same as when the catalyst was packed. There was no change in the proportion of the fine powder catalyst before and after the heat treatment of the catalyst. In addition, since the reaction gas is circulated from the top of the reaction tube, the fine powder catalyst packed in the reaction tube satisfies the above formulas (1) and (2).

[0058] [Example 5] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z1 and 0.4 g of fine powder catalyst, which was thoroughly mixed together to be additionally packed from above the solid catalyst Z1 (ratio of fine powder catalyst to total catalyst amount of 3000.4 g: 0.013 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 1, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z1 was 0 mass%, X after the catalyst packing １ +X ２ The content of the fine powder catalyst remains at 0.013 mass%, the same as when the catalyst was packed. There was no change in the proportion of the fine powder catalyst before and after the heat treatment of the catalyst. In addition, since the reaction gas is circulated from the top of the reaction tube, the fine powder catalyst packed in the reaction tube satisfies the above formulas (1) and (2).

[0059] [Comparative Example 1] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z1 and 105 g of fine powder catalyst, which was thoroughly mixed together to be additionally packed from above the solid catalyst Z1 (ratio of fine powder catalyst to total catalyst weight of 3105 g: 3.382 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 1, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of the solid catalyst Z1 was 0 mass%, X after the catalyst packing １ +X ２ The ratio of the fine powder catalyst remains at 3.382 mass%, the same as when the catalyst was packed. There is no change in the ratio of the fine powder catalyst before and after the heat treatment of the catalyst, and the fine powder catalyst packed in the reaction tube does not satisfy the above formula (1).

[0060] [Comparative Example 2] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z1 and 71 g of fine powder catalyst, which was thoroughly mixed and charged from above solid catalyst Z1 (ratio of fine powder catalyst to total catalyst amount of 3071 g: 2.312 mass%). Except for the above, the catalyst was charged and heat-treated in the same manner as in Example 1, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As described above, since the catalyst powdering rate of solid catalyst Z1 was 0 mass%, X after catalyst charging １ +X ２ The ratio of the fine powder catalyst remains at 2.312 mass%, the same as when the catalyst was packed. There is no change in the ratio of the fine powder catalyst before and after the heat treatment of the catalyst, and the fine powder catalyst packed in the reaction tube does not satisfy the above formula (1).

[0061] [Comparative Example 3] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z1 and 0.2 g of fine powder catalyst, which was thoroughly mixed together to be additionally packed from above solid catalyst Z1 (ratio of fine powder catalyst to total catalyst amount of 3000.2 g: 0.007 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 1, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z1 was 0 mass%, X after catalyst packing １ +X ２ The ratio of the fine powder catalyst remains at 0.007 mass %, which is the same as when the catalyst was packed. There is no change in the ratio of the fine powder catalyst before and after the heat treatment of the catalyst, and the fine powder catalyst packed in the reaction tube does not satisfy the above formula (1).

[0062] Comparative Example 4 The catalyst was packed and heat-treated in the same manner as in Example 1, except that 3,000 g of solid catalyst Z1 was packed into the reaction tube at once to form a catalyst layer (ratio of fine powder catalyst to the total amount of catalyst, 3,000 g: 0.000 mass%), and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As described above, since the catalyst powdering rate of solid catalyst Z1 was 0 mass%, X after the catalyst was packed １ +X ２ The ratio of the fine powder catalyst remains at 0.000 mass %, the same as when the catalyst was packed. There is no change in the ratio of the fine powder catalyst before and after the heat treatment of the catalyst, and the fine powder catalyst packed in the reaction tube does not satisfy the above formulas (1) and (2).

[0063] [Example 6] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z1, 200 g of unused 6 mmφ ceramic balls (filling aid, indicated as "CB" in the table), and 62 g of fine powder catalyst obtained by crushing solid catalyst Z1 in advance and passing through a sieve with a nominal mesh size of 1 mm (ratio of fine powder catalyst to total catalyst weight of 3062 g: 2.025 mass%) as a mixed catalyst to be additionally filled from above solid catalyst Z1 (ratio of fine powder catalyst to total catalyst weight of 3062 g: 2.025 mass%). Except for the above, the catalyst was filled and heat-treated in the same manner as in Example 1, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z1 was 0 mass%, X after catalyst filling was 0 mass%. １ +X ２ The content of the fine powder catalyst remains at 2.025 mass%, the same as when the catalyst was packed. There was no change in the proportion of the fine powder catalyst before and after the heat treatment of the catalyst. In addition, since the reaction gas is circulated from the top of the reaction tube, the fine powder catalyst packed in the reaction tube satisfies the above formulas (1) and (2).

[0064] [Example 7] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z1, 200 g of unused 6 mmφ ceramic balls, and 31 g of fine powder catalyst, which was thoroughly mixed together to be additionally packed from above solid catalyst Z1 (ratio of fine powder catalyst to total catalyst amount of 3031 g: 1.023 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 6, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z1 was 0 mass%, X after catalyst packing was 1.023 mass%. １ +X ２ The content of the fine powder catalyst remains at 1.023 mass%, the same as when the catalyst was packed. There was no change in the proportion of the fine powder catalyst before and after the heat treatment of the catalyst. In addition, since the reaction gas is circulated from the top of the reaction tube, the fine powder catalyst packed in the reaction tube satisfies the above formulas (1) and (2).

[0065] [Example 8] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z1, 200 g of unused 6 mmφ ceramic balls, and 3 g of fine powder catalyst, which was thoroughly mixed together to be additionally packed from above solid catalyst Z1 (ratio of fine powder catalyst to total catalyst amount of 3003 g: 0.100 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 6, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z1 was 0 mass%, X after catalyst packing １ +X ２ The content of the fine powder catalyst remains at 0.100 mass%, the same as when the catalyst was packed. There was no change in the proportion of the fine powder catalyst before and after the heat treatment of the catalyst. In addition, since the reaction gas is circulated from the top of the reaction tube, the fine powder catalyst packed in the reaction tube satisfies the above formulas (1) and (2).

[0066] [Example 9] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z1, 200 g of unused 6 mmφ ceramic balls, and 1.2 g of fine powder catalyst, which was thoroughly mixed together to be additionally packed from above solid catalyst Z1 (ratio of fine powder catalyst to total catalyst amount of 3001.2 g: 0.040 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 6, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z1 was 0 mass%, X after catalyst packing １ +X ２ The content of the fine powder catalyst remains at 0.040 mass%, the same as when the catalyst was packed. There was no change in the proportion of the fine powder catalyst before and after the heat treatment of the catalyst. In addition, since the reaction gas is circulated from the top of the reaction tube, the fine powder catalyst packed in the reaction tube satisfies the above formulas (1) and (2).

[0067] Comparative Example 5 1000 g of solid catalyst Z1 was packed into a reaction tube similar to that of Example 1. Next, a mixture of 500 g of solid catalyst Z1 and 74 g of fine powder catalyst was packed from above the packed solid catalyst Z1, and then a mixture of 1500 g of solid catalyst Z1 and 200 g of unused 6 mmφ ceramic balls was packed to form a catalyst layer (ratio of fine powder catalyst to total catalyst weight of 3074 g: 2.407 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 6, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z1 was 0 mass%, X after catalyst packing was 0 mass%. １ +X ２ The ratio of the fine powder catalyst remains at 2.407 mass%, which is the same as when the catalyst was packed. Note that there is no change in the ratio of the fine powder catalyst before and after the heat treatment of the catalyst, and the fine powder catalyst packed in the reaction tube does not satisfy the above formulas (1) and (2) (in Comparative Example 5, X ２ is 0% by mass).

[0068] [Comparative Example 6] A mixed catalyst, which was additionally packed from above the solid catalyst Z1, was prepared by thoroughly mixing 1500 g of the solid catalyst Z1, 200 g of unused 6 mmφ ceramic balls, and 0.1 g of a fine powder catalyst (ratio of fine powder catalyst to total catalyst amount of 3000.1 g: 0.003 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 6, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of the solid catalyst Z1 was 0 mass%, X after the catalyst packing １ +X ２ The content of the fine powder catalyst remains at 0.003 mass %, the same as when the catalyst was packed. There is no change in the proportion of the fine powder catalyst before and after the heat treatment of the catalyst, and the catalyst packed in the reaction tube does not satisfy the above formula (1).

[0069] Example 10 1500 g of solid catalyst Z2 was packed into a reaction tube similar to that used in Example 1. Next, a mixed catalyst prepared by thoroughly mixing 1500 g of solid catalyst Z2, 200 g of unused 3 mmφ ceramic balls, and 62 g of a fine powder catalyst obtained by crushing solid catalyst Z2 and passing it through a sieve with a nominal mesh size of 1 mm was additionally packed from above the packed solid catalyst Z2 to form a catalyst layer (ratio of fine powder catalyst to total catalyst weight of 3062 g: 2.025 mass%). The catalyst was then heat-treated in the same manner as in Example 1, and then subjected to a gas-phase catalytic oxidation reaction of methacrolein in the same manner as in Example 1, except that the temperature of the heat medium bath was changed to 280°C. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z2 was 0 mass%, the X after catalyst packing was 0%. １ +X ２ The ratio of the fine catalyst powder to the total catalyst mass remained at 2.025 mass%, the same as when the catalyst was packed. There was no change in the ratio of the fine catalyst powder before and after the heat treatment of the catalyst. In addition, since the reaction gas was passed through from the top of the reaction tube, the fine catalyst powder packed in the reaction tube satisfied the above formulas (1) and (2). １ is 0% by mass in all cases.) Furthermore, the ratio of the catalyst passing through a sieve with a nominal opening of 9.5 mm present in the reaction tube after the catalyst was packed to the total amount of the catalyst was 100% by mass.

[0070] [Example 11] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z2, 200 g of unused 3 mmφ ceramic balls, and 31 g of fine powder catalyst, which was thoroughly mixed together to be additionally packed from above solid catalyst Z2 (ratio of fine powder catalyst to total catalyst amount of 3031 g: 1.023 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 10, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z2 was 0 mass%, X after catalyst packing １ +X ２ The content of the fine powder catalyst remains at 1.023 mass%, the same as when the catalyst was packed. There was no change in the proportion of the fine powder catalyst before and after the heat treatment of the catalyst. In addition, since the reaction gas is circulated from the top of the reaction tube, the fine powder catalyst packed in the reaction tube satisfies the above formulas (1) and (2).

[0071] [Example 12] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z2, 200 g of unused 3 mmφ ceramic balls, and 3 g of fine powder catalyst, which was thoroughly mixed together to be additionally packed from above solid catalyst Z2 (ratio of fine powder catalyst to total catalyst amount of 3003 g: 0.100 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 10, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z2 was 0 mass%, X after catalyst packing １ +X ２ The content of the fine powder catalyst remains at 0.100 mass%, the same as when the catalyst was packed. There was no change in the proportion of the fine powder catalyst before and after the heat treatment of the catalyst. In addition, since the reaction gas is circulated from the top of the reaction tube, the fine powder catalyst packed in the reaction tube satisfies the above formulas (1) and (2).

[0072] [Example 13] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z2, 200 g of unused 3 mmφ ceramic balls, and 0.4 g of fine powder catalyst, which was thoroughly mixed together to be additionally packed from above solid catalyst Z2 (ratio of fine powder catalyst to total catalyst amount of 3000.4 g: 0.013 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 10, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z2 was 0 mass%, X after catalyst packing １ +X ２ The content of the fine powder catalyst remains at 0.013 mass%, the same as when the catalyst was packed. There was no change in the proportion of the fine powder catalyst before and after the heat treatment of the catalyst. In addition, since the reaction gas is circulated from the top of the reaction tube, the fine powder catalyst packed in the reaction tube satisfies the above formulas (1) and (2).

[0073] [Comparative Example 7] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z2, 200 g of unused 3 mmφ ceramic balls, and 74 g of fine powder catalyst, which was thoroughly mixed together to be additionally packed from above solid catalyst Z2 (ratio of fine powder catalyst to total catalyst amount of 3074 g: 2.407 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 10, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z2 was 0 mass%, X after catalyst packing was 0 mass%. １ +X ２ The ratio of the fine powder catalyst remains at 2.407 mass%, the same as when the catalyst was packed. There is no change in the ratio of the fine powder catalyst before and after the heat treatment of the catalyst, and the fine powder catalyst packed in the reaction tube does not satisfy the above formula (1).

[0074] [Comparative Example 8] A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z2, 200 g of unused 3 mmφ ceramic balls, and 0.02 g of fine powder catalyst, which was thoroughly mixed together to be additionally packed from above solid catalyst Z2 (ratio of fine powder catalyst to total catalyst amount of 3000.02 g: 0.0007 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 10, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As mentioned above, since the catalyst powdering rate of solid catalyst Z2 was 0 mass%, X after catalyst packing １ +X ２ The ratio of the fine powder catalyst remains at 0.0007% by mass, which is the same as when the catalyst was packed. There is no change in the ratio of the fine powder catalyst before and after the heat treatment of the catalyst, and the fine powder catalyst packed in the reaction tube does not satisfy the above formula (1).

[0075] Example 14 1500 g of solid catalyst Z3 was packed into a reaction tube similar to that used in Example 1. Next, from above the packed solid catalyst Z3, a mixed catalyst was added, prepared by thoroughly mixing 1500 g of solid catalyst Z3, 200 g of an unused stainless steel spring (SUS430, indicated as "SS" in the table) with a height of 6 mm, a wire diameter of 1 mm, and a gap of 0.5 mm, and 68 g of a fine powder catalyst obtained by crushing solid catalyst Z3 and passing it through a sieve with a nominal mesh size of 1 mm, to form a catalyst layer (ratio of fine powder catalyst to the total catalyst weight of 3068 g: 2.236 mass%). The catalyst was then heat-treated in the same manner as in Example 1, and a gas-phase catalytic oxidation reaction of methacrolein was carried out in the same manner as in Example 1, except that the temperature of the heat medium bath was set to 300°C. The results are shown in Table 1. Since the packing powder ratio of solid catalyst Z3 was 0.020% by mass, the amount of fine catalyst produced from a total of 3,000 g of solid catalyst Z3 was 0.6 g. Here, since the 68 g of fine catalyst was contained in the reaction gas inlet side region, the fine catalyst packed in the reaction tube satisfied the above formula (2). Furthermore, since the reaction gas was circulated from the top of the reaction tube, the fine catalyst packed in the reaction tube satisfied the above formula (1). Furthermore, the proportion of the catalyst that passed through a sieve with a nominal mesh size of 9.5 mm and was present in the reaction tube after the catalyst packing was 100% by mass relative to the total amount of catalyst.

[0076] Example 15: A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z3, 200 g of an unused stainless steel spring (SUS430) with a height of 6 mm, a wire diameter of 1 mm, and a gap of 0.5 mm, and 5 g of a fine powder catalyst, which was thoroughly mixed and additionally packed from above solid catalyst Z3 (ratio of fine powder catalyst to total catalyst weight of 3005 g: 0.186 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 14, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. Since the packing fraction of solid catalyst Z3 was 0.020 mass%, the amount of fine powder catalyst produced from a total of 3000 g of solid catalyst Z3 was 0.6 g. Since the 5 g of fine powder catalyst was included in the reaction gas inlet region, the fine powder catalyst packed in the reaction tube satisfied the above formula (2). Furthermore, since the reaction gas is passed through the upper part of the reaction tube, the finely divided catalyst packed in the reaction tube satisfies the above formula (1).

[0077] Comparative Example 9: A catalyst layer was formed using a mixture of 1500 g of solid catalyst Z3, 200 g of an unused stainless steel spring (SUS430) with a height of 6 mm, a wire diameter of 1 mm, and a gap of 0.5 mm, and 75 g of a fine powder catalyst, which was thoroughly mixed and additionally packed from above the solid catalyst Z3 (ratio of the fine powder catalyst to the total catalyst weight of 3075 g: 2.458 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 14, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. Since the packing fraction of solid catalyst Z3 was 0.020 mass%, the amount of fine powder catalyst produced from a total of 3000 g of solid catalyst Z3 was 0.6 g. Since the 75 g of fine powder catalyst was included in the reaction gas inlet region, the fine powder catalyst packed in the reaction tube satisfied the above formula (2). On the other hand, there is no change in the proportion of the fine powder catalyst before and after the heat treatment of the catalyst, and the fine powder catalyst packed in the reaction tube does not satisfy the above formula (1).

[0078] Comparative Example 10: 3,000 g of solid catalyst Z3 and 200 g of an unused stainless steel spring (SUS430) with a height of 6 mm, a wire diameter of 1 mm, and a gap of 0.5 mm were thoroughly mixed and packed into a reaction tube at once to form a catalyst layer (ratio of powder catalyst to total catalyst weight of 3,000 g: 0.020 mass%). Except for the above, the catalyst was packed and heat-treated in the same manner as in Example 14, and a gas-phase catalytic oxidation reaction of methacrolein was carried out. The results are shown in Table 1. As described above, the ratio of powder catalyst contained in the lower and upper layers of the catalyst layer formed by dropping solid catalyst Z3 was 9:1. Therefore, it can be said that the powder catalyst generated from solid catalyst Z3 was contained in a larger amount in the reaction gas outlet region than in the reaction gas inlet region. In other words, the catalyst packed into the reaction tube did not satisfy the above formula (2).

[0079] In all Examples and Comparative Examples, the proportion of the catalyst passing through a sieve with a nominal mesh size of 9.5 mm present in the reaction tube after the catalyst was packed relative to the total amount of the catalyst was 100 mass %.

[0080]

[0081] As shown in Table 1, in Comparative Examples 1 to 4, which do not satisfy at least one of the formulas (1) and (2), the ratio of the fine catalyst to the total amount of catalyst (X １ +X ２ ) in the range of formula (1) and by filling the powder catalyst so as to satisfy formula (2), the yield of methacrylic acid is improved. This tendency is also seen in a comparison between Examples 6 to 9 and Comparative Examples 5 and 6, in which ceramic balls were used as the filling auxiliary material, a comparison between Examples 10 to 13 and Comparative Examples 7 and 8, in which ceramic balls were used as the filling auxiliary material and the reaction temperature of the gas-phase catalytic oxidation reaction of methacrolein was changed to 280°C, and a comparison between Examples 14 to 15 and Comparative Examples 9 and 10, in which stainless steel springs were used as the filling auxiliary material and the reaction temperature was changed to 300°C.

[0082] While certain preferred embodiments of the present invention have been shown and described in detail above, it should be understood that the present invention is not limited to the above-described embodiments, but that various changes and modifications are possible without departing from the spirit or scope of the appended claims.

[0083] This application claims priority based on Japanese Patent Application No. 2024-014137, filed February 1, 2024, the entire contents of which are incorporated herein by reference.

[0084] 1: Reaction tube 1A: Reaction gas inlet 1B: Reaction gas outlet 2: Catalyst 3: Catalyst layer 4: Filler P: Boundary position Q １ : End portion on the reaction gas outlet side Q ２ : End portion on the reaction gas inlet side A １ A: Reactant gas outlet side region (first region) ２ : Reactant gas inlet side region (second region)

Claims

1. A method for packing a catalyst into a reaction tube of a fixed-bed reactor, the catalyst comprising a solid catalyst that does not pass through a sieve with a nominal mesh size of 1 mm and a fine powder catalyst that passes through a sieve with a nominal mesh size of 1 mm, the fine powder catalyst satisfying the following formulas (1) and (2): 0.010 mass%≦X １ +X ２ ≦2.300% by mass...(1); X １ <X ２ ...(2), where X １ represents the amount (mass%) of the fine powder catalyst present in the reaction gas outlet side region relative to 100 mass% of the total amount of the catalyst, and X ２ represents the amount (% by mass) of the fine powder catalyst present in the reaction gas inlet side region relative to 100% by mass of the total amount of the catalyst, provided that the reaction gas outlet side region is a region where 50% by mass of the solid catalyst is present out of 100% by mass of the total amount of the solid catalyst, calculated from the reaction gas outlet side of the reaction tube, and the reaction gas inlet side region is a region where 50% by mass of the solid catalyst is present out of 100% by mass of the total amount of the solid catalyst, calculated from the reaction gas inlet side of the reaction tube.

2. The solid catalyst is a catalyst that does not pass through a sieve with a nominal opening of 1 mm but passes through a sieve with a nominal opening of 9.5 mm, and the average volume of the solid catalyst is 20 mm ３ / piece or more, 270mm ３ 2. The method for loading a catalyst according to claim 1, wherein the number of particles is equal to or less than 1 / 10.

3. The amount X of the fine powder catalyst present in the reaction gas inlet side region ２ (mass%) and the amount X of the fine powder catalyst present in the reaction gas outlet side region １ The catalyst packing method according to claim 1, wherein the ratio of the catalyst to the catalyst (mass%) is 60:40 to 100:

0.

4. The catalyst packing method according to claim 1, wherein the finely divided catalyst and the solid catalyst have substantially the same composition.

5. A catalyst packing method according to claim 1, wherein packing material is packed into at least one of an area on the reaction gas inlet side of the catalyst layer packed with the catalyst and an area on the reaction gas outlet side of the catalyst layer packed with the catalyst.

6. The method for packing a catalyst according to claim 1, wherein a packing aid is packed together with the catalyst.

7. The method for loading a catalyst according to claim 1, wherein the catalyst contains molybdenum and vanadium.

8. The catalyst packing method according to claim 1, wherein the catalyst has a composition represented by the following formula (3): P ａ Mo ｂ V ｃ Cu ｄ X ｅ Y ｆ Z ｇ (NH ４ ) ｈ O ｉ ...(3), In formula (3), P, Mo, V, Cu, NH ４ , and O represent phosphorus, molybdenum, vanadium, copper, ammonium, and oxygen, respectively; X represents at least one element selected from the group consisting of silicon, titanium, germanium, arsenic, antimony, and bismuth; Y represents at least one element selected from the group consisting of niobium, tantalum, tungsten, cerium, zirconium, silver, iron, zinc, chromium, magnesium, cobalt, manganese, barium, and lanthanum; Z represents at least one element selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium; a to i represent the molar ratio of each component, and when b = 12, a = 0.5 to 3, c = 0.01 to 3, d = 0.01 to 2, e = 0 to 3, f = 0 to 3, g = 0.01 to 3, and h = 0 to 30; and i is the molar ratio of oxygen necessary to satisfy the valence of each component.

9. The catalyst packing method according to any one of claims 1 to 8, wherein the catalyst is a catalyst for producing (meth)acrylic acid.

10. A method for producing (meth)acrylic acid by a gas-phase catalytic oxidation reaction, comprising supplying (meth)acrolein and molecular oxygen to a reaction tube packed with a catalyst, the catalyst comprising a solid catalyst that does not pass through a sieve with a nominal mesh size of 1 mm and a fine powder catalyst that passes through a sieve with a nominal mesh size of 1 mm, the fine powder catalyst satisfying the following formulas (1) and (2): 0.010 mass%≦X １ +X ２ ≦2.300% by mass...(1); X １ <X ２ ...(2), where X １ represents the amount (mass%) of the fine powder catalyst present in the reaction gas outlet side region relative to 100 mass% of the total amount of the catalyst, and X ２ represents the amount (% by mass) of the fine powder catalyst present in the reaction gas inlet side region relative to 100% by mass of the total amount of the catalyst, provided that the reaction gas outlet side region is a region where 50% by mass of the solid catalyst is present out of 100% by mass of the total amount of the solid catalyst, calculated from the reaction gas outlet side of the reaction tube, and the reaction gas inlet side region is a region where 50% by mass of the solid catalyst is present out of 100% by mass of the total amount of the solid catalyst, calculated from the reaction gas inlet side of the reaction tube.

11. The solid catalyst is a catalyst that does not pass through a sieve with a nominal opening of 1 mm but passes through a sieve with a nominal opening of 9.5 mm, and the average volume of the solid catalyst is 20 mm ３ / piece or more, 270mm ３ The method for producing (meth)acrylic acid according to claim 10, wherein the number of the hydroxyl groups is 1 or less.

12. The amount X of the finely divided catalyst present in the reaction gas inlet side region ２ (mass%) and the amount X of the fine powder catalyst present in the reaction gas outlet side region １ The method for producing (meth)acrylic acid according to claim 10, wherein the ratio of (mass%) to (mass%) is 60:40 to 100:

0.

13. The method for producing (meth)acrylic acid according to claim 10, wherein the fine powder catalyst and the solid catalyst have substantially the same composition.

14. The method for producing (meth)acrylic acid according to claim 10, wherein a filler is filled in at least one of a region on the reaction gas inlet side of the catalyst layer filled with the catalyst and a region on the reaction gas outlet side of the catalyst layer filled with the catalyst.

15. The method for producing (meth)acrylic acid according to claim 10, wherein a packing aid is packed together with the catalyst.

16. The method for producing (meth)acrylic acid according to claim 10, wherein the catalyst contains molybdenum and vanadium.

17. The method for producing (meth)acrylic acid according to claim 10, wherein the catalyst has a composition represented by the following formula (3): P ａ Mo ｂ V ｃ Cu ｄ X ｅ Y ｆ Z ｇ (NH ４ ) ｈ O ｉ ...(3), In formula (3), P, Mo, V, Cu, NH ４ , and O represent phosphorus, molybdenum, vanadium, copper, ammonium, and oxygen, respectively; X represents at least one element selected from the group consisting of silicon, titanium, germanium, arsenic, antimony, and bismuth; Y represents at least one element selected from the group consisting of niobium, tantalum, tungsten, cerium, zirconium, silver, iron, zinc, chromium, magnesium, cobalt, manganese, barium, and lanthanum; Z represents at least one element selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium; a to i represent the molar ratio of each component, and when b = 12, a = 0.5 to 3, c = 0.01 to 3, d = 0.01 to 2, e = 0 to 3, f = 0 to 3, g = 0.01 to 3, and h = 0 to 30; and i is the molar ratio of oxygen necessary to satisfy the valence of each component.

18. The method for producing (meth)acrylic acid according to any one of claims 10 to 17, wherein the catalyst is a catalyst for producing (meth)acrylic acid.

19. A reaction tube packed with a catalyst, the catalyst comprising a solid catalyst that does not pass through a sieve with a nominal mesh size of 1 mm and a fine powder catalyst that passes through a sieve with a nominal mesh size of 1 mm, wherein the fine powder catalyst satisfies the following formulas (1) and (2): 0.010 mass%≦X １ +X ２ ≦2.300% by mass...(1); X １ <X ２ ...(2), where X １ represents the amount (mass%) of the fine powder catalyst present in the reaction gas outlet side region relative to 100 mass% of the total amount of the catalyst, and X ２ represents the amount (% by mass) of the fine powder catalyst present in the reaction gas inlet side region relative to 100% by mass of the total amount of the catalyst, provided that the reaction gas outlet side region is a region where 50% by mass of the solid catalyst is present out of 100% by mass of the total amount of the solid catalyst, calculated from the reaction gas outlet side of the reaction tube, and the reaction gas inlet side region is a region where 50% by mass of the solid catalyst is present out of 100% by mass of the total amount of the solid catalyst, calculated from the reaction gas inlet side of the reaction tube.

20. The solid catalyst is a catalyst that does not pass through a sieve with a nominal opening of 1 mm but passes through a sieve with a nominal opening of 9.5 mm, and the average volume of the solid catalyst is 20 mm ３ / piece or more, 270mm ３ The reaction tube according to claim 19, wherein the number of the reaction tubes is not more than 1 / 10.

21. The amount X of the finely divided catalyst present in the reaction gas inlet side region ２ (mass%) and the amount X of the fine powder catalyst present in the reaction gas outlet side region １ The reaction tube according to claim 19, wherein the ratio of the carbon black to the carbon dioxide (CO₂) (mass%) is 60:40 to 100:

0.

22. The reactor tube of claim 19, wherein the finely divided catalyst and the solid catalyst have substantially the same composition.

23. The reaction tube according to claim 19, wherein a packing material is packed in at least one of a region on the reaction gas inlet side of the catalyst layer packed with the catalyst and a region on the reaction gas outlet side of the catalyst layer packed with the catalyst.

24. The reactor tube according to claim 19, wherein a packing aid is packed together with the catalyst.

25. The reactor tube of claim 19, wherein the catalyst contains molybdenum and vanadium.

26. The reaction tube according to claim 19, wherein the catalyst has a composition represented by the following formula (3): P ａ Mo ｂ V ｃ Cu ｄ X ｅ Y ｆ Z ｇ (NH ４ ) ｈ O ｉ ...(3), In formula (3), P, Mo, V, Cu, NH ４ , and O represent phosphorus, molybdenum, vanadium, copper, ammonium, and oxygen, respectively; X represents at least one element selected from the group consisting of silicon, titanium, germanium, arsenic, antimony, and bismuth; Y represents at least one element selected from the group consisting of niobium, tantalum, tungsten, cerium, zirconium, silver, iron, zinc, chromium, magnesium, cobalt, manganese, barium, and lanthanum; Z represents at least one element selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium; a to i represent the molar ratio of each component, and when b = 12, a = 0.5 to 3, c = 0.01 to 3, d = 0.01 to 2, e = 0 to 3, f = 0 to 3, g = 0.01 to 3, and h = 0 to 30; and i is the molar ratio of oxygen necessary to satisfy the valence of each component.

27. The reaction tube according to any one of claims 19 to 26, wherein the catalyst is a catalyst for producing (meth)acrylic acid.

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