Catalyst for the gas phase oxidation of 1,2,4,5-tetraalkylbenzene, its preparation method and use, and method for preparing 1,2,4,5-benzenetetracarboxylic anhydride

Abstract

The present invention discloses a catalyst for preparing 1,2,4,5-benzenetetracarboxylic anhydride by vapor phase oxidation of 1,2,4,5-tetraalkylbenzene, a preparation method thereof, and its use, as well as a preparation method thereof. The catalyst according to the present invention comprises a carrier and a catalytically active component coating deposited on the carrier, the catalytically active component coating comprising a first coating and a second coating, the first coating being close to the surface of the carrier and the second coating being distant from the surface of the carrier, and the mass ratio of titanium element calculated as Ti to vanadium element calculated as V in the first coating being Ti / V. 1 The mass ratio of titanium element (converted into Ti) to vanadium element (converted into V) in the second coating is Ti / V 2 Then, Ti / V 2 = Ti / V 1 +ΔTi / V, and ΔTi / V is within the range of 3 to 9. The catalyst according to the present invention exhibits improved catalytic activity and can effectively improve the yield of 1,2,4,5-benzenetetracarboxylic anhydride.

Description

Detailed Description of the Invention

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of Chinese Patent Application No. 202111282786.7, filed on November 1, 2021, the contents of which are incorporated herein by reference.

[0002] [Technical field] The present invention relates to a catalyst, in particular to a catalyst for preparing 1,2,4,5-benzenetetracarboxylic anhydride by vapor phase oxidation of 1,2,4,5-tetraalkylbenzene. The present invention also relates to a method for preparing and using said catalyst. The present invention further relates to a method for preparing 1,2,4,5-benzenetetracarboxylic anhydride.

[0003] [Background technology] Pyromellitic dianhydride (1,2,4,5-benzenetetracarboxylic dianhydride, hereafter referred to as pyromellitic dianhydride) is a very important chemical raw material. Pyromellitic dianhydride and its derivatives are very important and have a wide range of uses, and pyromellitic dianhydride in particular is useful as one of the main monomers for producing polyimides. Due to its comprehensive performance at high temperatures, polyimides have the widest range of use temperatures of any organic polymer material today. They are new engineering materials that offer excellent dimensional stability at high temperatures, radiation resistance, mechanical properties, electrical properties, and corrosion resistance.

[0004] Initially, the production of pyromellitic dianhydride using durene as a raw material mainly involved liquid-phase oxidation, in which the raw material was oxidized to produce an acid, which was then dehydrated to produce the anhydride. Currently, the most commonly used process is the gas-phase oxidation, in which 1,2,4,5-tetraalkylbenzene is used as a raw material to produce 1,2,4,5-benzenetetracarboxylic dianhydride in a single step by air oxidation. The gas-phase oxidation process is characterized by its simplicity, the elimination of the step of dehydrating the acid to produce the anhydride, and the use of air as the oxidant, which eliminates the need for the catalyst separation step required in the liquid-phase oxidation process. It also allows for continuous production and is easily automated.

[0005] The production of pyromellitic dianhydride by oxidation of 1,2,4,5-tetraalkylbenzene is a reaction process in which selective oxidation generates a relatively large amount of heat, so that the theoretical yield of pyromellitic dianhydride is high but the actual yield is low.

[0006] Controlling the elemental composition of the catalyst is one of the technical measures mainly adopted in the prior art to increase the yield of pyromellitic dianhydride. CN107866241A is a catalyst for producing pyromellitic dianhydride by oxidizing durene, which uses an inert support and contains at least one of vanadium, titanium, Group VA elements, and alkali metal elements as an active component. CN107866257A is a catalyst for producing pyromellitic dianhydride from durene, which uses α-Al2O3, silicon carbide, ceramic rings, or a mixture thereof as a support and contains at least one of vanadium, iron-based elements, Group IIB elements, and alkali metal elements as an active component.

[0007] Staged catalyst loading is another prior art means of increasing the yield of pyromellitic dianhydride. CN1116197A discloses a method for producing 1,2,4,5-benzenetetracarboxylic anhydride, in which catalysts are packed into a reactor in stages to form a multi-stage catalyst, and a first catalyst containing vanadium (a) and at least one metal (b) selected from molybdenum and tungsten, with the atomic ratio of the metal (b) to the vanadium (a) being 0.01 to 2, is packed on the product gas outlet side of the reactor, and at least one other catalyst selected from a second catalyst containing vanadium (a) and at least one metal (b) selected from molybdenum and tungsten, with the atomic ratio of the metal (b) to the vanadium (a) being smaller than that of the first catalyst, and a third catalyst containing vanadium (a) and an alkali metal (c), with the atomic ratio of the alkali metal (c) to the vanadium (a) being 0.2 to 2.5, is packed on the raw material mixed gas inlet side of the reactor.

[0008] Although controlling the elemental composition of the catalyst and loading the catalyst stepwise have had some effect on increasing the yield of pyromellitic dianhydride, there is still a relatively large difference between the actual yield and the theoretical yield of pyromellitic dianhydride, and how to further increase the actual yield of pyromellitic dianhydride remains a technical problem to be solved.

[0009] [Summary of the Invention] [Problem to be solved by the invention] Most conventional vanadium catalysts for producing pyromellitic dianhydride by the vapor-phase oxidation of 1,2,4,5-tetraalkylbenzene have a coating containing catalytically active components formed on the surface of a support. However, the present inventors have intensively investigated the problem of low product yields when producing pyromellitic dianhydride by the vapor-phase oxidation of durene. As a result, they have found that the yield of pyromellitic dianhydride can be effectively improved by forming a coating containing catalytically active components on the surface of a vanadium catalyst support, and controlling the titanium / vanadium mass ratio in the radial direction of the coating so that the titanium / vanadium mass ratio in the coating closest to the support is lower than the titanium / vanadium mass ratio in the coating farther from the support, and both differences are within a predetermined range. This finding led to the completion of the present invention.

[0010] [Means for solving the problem] According to a first aspect of the present invention, there is provided a method for manufacturing a semiconductor device comprising: The present invention comprises a support and a catalytically active component coating carried on the support, the catalytically active component coating comprising a first coating and a second coating, the first coating being close to a surface of the support and the second coating being distant from the surface of the support, the first coating and the second coating each independently containing vanadium element and titanium element, and a mass ratio of titanium element (calculated as Ti) to vanadium element (calculated as V) in the first coating being Ti / V. 1 the mass ratio of titanium element (calculated as Ti) to vanadium element (calculated as V) in the second coating is Ti / V2 Then, Ti / V 2 =Ti / V 1 +ΔTi / V, and ΔTi / V is in the range of 3 to 9.

[0011] According to a second aspect of the present invention, there is provided a method for manufacturing a semiconductor device comprising: (1) applying a first slurry containing a first dispersing medium, a first vanadium source, and a first titanium source to a surface of a support to form a first coating; (2) applying a second slurry containing a second dispersing medium, a second vanadium source, a second titanium source, and a pore expander onto the surface of the carrier on which the first coating has been formed to form a second coating; The mass of the vanadium source introduced into the first coating in terms of V is C V 12 , the mass of the titanium source introduced into the first coating in terms of Ti is C Ti 12 , the mass of the vanadium source introduced into the second coating in terms of V is C V 22 , the mass of the titanium source introduced into the second coating in terms of Ti is C Ti 22 Then, Ti / V 12 =C Ti 12 / C V 12 , Ti / V 22 =C Ti 22 / C V 22 , Ti / V 22 =Ti / V 12 +ΔTi / V 2 and ΔTi / V 2 The present invention provides a method for preparing a catalyst for the vapor phase oxidation of 1,2,4,5-tetraalkylbenzene, wherein the .sigma. of the catalyst is in the range of 3 to 9.

[0012] According to a third aspect of the present invention, there is provided a catalyst prepared by the method according to the second aspect of the present invention.

[0013] According to a fourth aspect of the present invention, there is provided the use of a catalyst according to the first or third aspect of the present invention as a catalyst for the reaction for preparing 1,2,4,5-benzenetetracarboxylic acid anhydride by oxidation of a 1,2,4,5-tetraalkylbenzene.

[0014] According to a fifth aspect of the present invention, there is provided a method for manufacturing a semiconductor device comprising: There is provided a method for preparing 1,2,4,5-benzenetetracarboxylic acid anhydride, comprising the step of contacting a gas comprising 1,2,4,5-tetraalkylbenzene and oxygen gas with a catalyst according to the first or third aspect of the present invention to obtain a product stream comprising 1,2,4,5-benzenetetracarboxylic acid anhydride.

[0015] When used as a catalyst for the reaction of preparing 1,2,4,5-benzenetetracarboxylic anhydride by oxidation of 1,2,4,5-tetraalkylbenzene, the catalyst of the present invention exhibits improved catalytic activity and can effectively improve the yield of 1,2,4,5-benzenetetracarboxylic anhydride.

[0016] [Mode for Carrying Out the Invention] The endpoints of the ranges and any values ​​disclosed herein are not intended to be limited to the exact ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. In the case of numerical ranges, the endpoints of each range, and the individual point values ​​and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0017] In the present invention, unless otherwise specified, the terms "first" and "second" appearing before the names of materials or steps do not indicate a sequence or limit the individual materials or steps, but are used simply to distinguish the names of the materials or steps. For example, in "first coating" and "second coating," the terms "first" and "second" are used to distinguish between two types of coating. In the present invention, the term "optional" means that the term following "optional" is not required, and can be understood as containing, not containing, or including or not including the term.

[0018] In the present invention, the 1,2,4,5-tetraalkylbenzene may be one or more selected from the compounds shown in formula I: [ka] In Formula I, R1, R2, R3, and R4 are the same or different and each independently represent a C1 to C5 alkyl. In the present invention, C1 to C5 alkyl includes C1 to C5 linear alkyl and C3 to C5 branched alkyl, and specific examples thereof include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, and vineopentyl.

[0019] Preferably, the 1,2,4,5-tetraalkylbenzene is 1,2,4,5-tetramethylbenzene (ie, durene).

[0020] According to a first aspect of the present invention, there is provided a catalyst for the vapor phase oxidation of 1,2,4,5-tetraalkylbenzene, comprising a support and a catalytically active component coating supported on the support, the catalytically active component coating comprising a first coating and a second coating, the first coating being close to the surface of the support and the second coating being distant from the surface of the support.

[0021] According to the catalyst of the present invention, the first coating and the second coating each independently contain vanadium and titanium. According to the catalyst of the present invention, the mass ratio of titanium to vanadium (i.e., the mass ratio of Ti / V) in the first coating and the second coating is different, and the mass ratio of Ti / V in the second coating is 2 The mass ratio of Ti / V in the first coating is 1 As a result of investigation, the inventors of the present invention found that the mass ratio of Ti / V in the first coating, which is the inner coating close to the surface of the support, is higher than that of Ti / V. 1 The mass ratio of Ti / V in the second coating, which is the outer coating away from the surface of the support, is 2 By controlling the difference between the two elements within a specific range, the activity of the catalyst can be effectively improved and a higher product yield can be obtained. According to the catalyst of the present invention, the mass ratio of titanium element (calculated as Ti) to vanadium element (calculated as V) in the first coating can be set to Ti / V 1 the mass ratio of titanium element (calculated as Ti) to vanadium element (calculated as V) in the second coating is Ti / V 2 Then, Ti / V 2 =Ti / V 1 +ΔTi / V, and ΔTi / V is in the range of 3 to 9. Specifically, ΔTi / V may be 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, or 9. Preferably, ΔTi / V is within the range of 3.5 to 8.5.

[0022] According to the catalyst of the present invention, the mass ratio Ti / V of titanium element in the first coating calculated as Ti to vanadium element in the first coating calculated as V is1 may be 7 to 8.5:1, for example, 7:1, 7.1:1, 7.2:1, 7.3:1, 7.4:1, 7.5:1, 7.6:1, 7.7:1, 7.8:1, 7.9:1, 8:1, 8.1:1, 8.2:1, 8.3:1, 8.4:1, or 8.5:1.

[0023] According to the catalyst of the present invention, the mass ratio Ti / V of titanium element in the second coating calculated as Ti to vanadium element in the second coating calculated as V is 2 is 12~15.5:1, for example, 12:1, 12.1:1, 12.2:1, 12.3:1, 12.4:1, 12.5:1, 12.6:1, 12.7:1, 12.8:1, 12.9:1, 13:1, 13.1:1, 13.2:1, 13.3:1, 13.4:1, 13.5:1, 13.6:1, 13. It may be 7:1, 13.8:1, 13.9:1, 14:1, 14.1:1, 14.2:1, 14.3:1, 14.4:1, 14.5:1, 14.6:1, 14.7:1, 14.8:1, 14.9:1, 15:1, 15.1:1, 15.2:1, 15.3:1, 15.4:1, or 15.5:1.

[0024] According to the catalyst of the present invention, the content C of titanium element in terms of Ti in the first coating Ti 1 may be in the range of 40 mass % to 60 mass %, for example, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, or 60%. Preferably, the content C of titanium element in terms of Ti in the first coating is Ti 1 is in the range of 45 to 55 mass %.

[0025] According to the catalyst of the present invention, the content C of titanium element in terms of Ti in the second coating Ti 2may be in the range of 45 to 65 mass %, for example, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, or 65%. Preferably, the content C of titanium element in terms of Ti in the second coating is Ti 2 may be in the range of 50 to 60 mass %.

[0026] In the present invention, the mass ratio of titanium to vanadium in the first and second coatings (i.e., the Ti / V mass ratio) is measured using a scanning electron microscope-energy spectrometer. The specific test method is as follows: After cooling the catalyst particles with liquid nitrogen, they are cut longitudinally from the side without the coating to obtain catalyst semi-particles with exposed cross sections. The catalyst semi-particles are then fixed to conductive tape and their surfaces are coated with gold, platinum, or carbon to improve their conductivity, obtaining test samples. The test samples are placed on the sample stage of a scanning electron microscope, and the cross sections of the catalyst semi-particles are observed using the scanning electron microscope. The Ti / V mass ratios at various coating thicknesses (also referred to as the "longitudinal direction") are measured using an energy spectrometer. The method for measuring the Ti / V mass ratio at the same coating thickness is as follows: Three adjacent points along the horizontal direction of the coating (i.e., perpendicular or nearly perpendicular to the thickness direction of the coating) are randomly selected, magnified by the same factor (typically 500 to 1000 times), and the Ti / V mass ratios at those points are measured using an energy spectrometer. The values ​​measured at the three points are averaged to determine the horizontal Ti / V mass ratio. In the present invention, the first and second coatings are distinguished based on the difference in the Ti / V mass ratios between two adjacent points along the thickness direction of the coating. If the difference in the Ti / V mass ratios between the two adjacent points is within the ΔTi / V range defined in the present invention, the two points belong to the first and second coatings, respectively. If the difference in the Ti / V mass ratios between the two adjacent points is below the ΔTi / V range defined in the present invention (including both endpoints), the two points belong to the same coating.

[0027] According to the catalyst of the present invention, the catalytically active component coating may further contain a trace amount of an adjusting element. In one preferred embodiment, the catalytically active component coating further contains at least one element selected from the group consisting of a Group VA non-metal element, an alkali metal element, and an auxiliary metal element, and the auxiliary metal element is at least one element selected from the group consisting of a rare earth element, a Group VIB element, a Group VIII element, a Group IIIA metal element, a Group VA metal element, and a Group IVB element other than titanium.

[0028] According to the catalyst of the present invention, the Group VA non-metallic element is preferably phosphorus (P). The content of the Group VA non-metallic element in the first coating is 0.1 to 0.5 mass %, preferably 0.3 to 0.4 mass % in terms of elements. According to the catalyst of the present invention, the second coating may contain the Group VA non-metallic element or may not contain the Group VA non-metallic element. Preferably, the second coating does not contain the Group VA non-metallic element.

[0029] According to the catalyst of the present invention, the alkali metal element is preferably cesium (Cs). The content of the alkali metal element in the first coating may be 0.1 to 0.3 mass%, preferably 0.15 to 0.2 mass% in terms of element. The content of the alkali metal element in the second coating may be 0.1 to 0.7 mass%, preferably 0.3 to 0.5 mass% in terms of element.

[0030] According to the catalyst of the present invention, specific examples of the auxiliary metal element include at least one selected from the group consisting of rubidium (Rb), cerium (Ce), niobium (Nb), chromium (Cr), tungsten (W), silver (Ag), cobalt (Co), gallium (Ga), indium (In), antimony (Sb), bismuth (Bi), zirconium (Zr), and erbium (Er), but are not limited thereto. In one preferred embodiment, the auxiliary metal element is at least one selected from the group consisting of niobium, zirconium, and antimony.

[0031] According to the catalyst of the present invention, the content of the auxiliary metal element in the first coating, calculated as an oxide, may be 1 to 6 mass%, preferably 1.5 to 5 mass%, more preferably 2 to 4.5 mass%, and even more preferably 3 to 4 mass%. In one preferred embodiment, the auxiliary metal elements in the first coating are niobium, zirconium, and antimony. In this preferred embodiment, the content of the niobium-containing compound in the first coating, calculated as Nb2O5, may be 0.15 to 0.2 mass%, the content of the zirconium-containing compound in the first coating, calculated as ZrO2, may be 0.4 to 0.45 mass%, and the content of the antimony-containing compound in the first coating, calculated as Sb2O3, may be 2.8 to 3.2 mass%.

[0032] In the second coating, the content of the auxiliary metal element, calculated as oxide, may be 1 to 6 mass%, preferably 1.2 to 5%, and more preferably 1.5 to 3%. In one preferred embodiment, the auxiliary metal elements in the second coating are niobium and antimony. In this preferred embodiment, the content of the niobium element-containing compound, calculated as Nb2O5, in the second coating may be 0.12 to 0.18 mass%, and the content of the antimony element-containing compound, calculated as Sb2O3, in the second coating may be 1.5 to 2 mass%.

[0033] In the present invention, the amounts of titanium element, Group VA non-metal element, alkali metal element, and auxiliary metal element in the coating are calculated as input amounts, and are calculated based on the total amount (in oxide terms) of the raw materials forming the coating, and the raw materials do not include the dispersion medium.

[0034] According to the catalyst of the present invention, the first coating is closer to the support surface than the second coating, i.e., the first coating is closer to the support surface than the second coating. In one preferred embodiment, the second coating is attached to the surface of the first coating. In one more preferred embodiment, the second coating is attached to the surface of the first coating, and the first coating is attached to the support surface. In this more preferred embodiment, the second coating is exposed to the environment as an outer coating, and the first coating is an inner coating that connects the support and the second coating.

[0035] According to the catalyst of the present invention, the weight ratio of the first coating, the second coating, and the support may be 5.5-6.8:1.9-3.5:100, but is preferably 5.8-6.7:1.9-2.9:100.

[0036] According to the catalyst of the present invention, the total pore volume of the catalyst is 0.03 to 0.08 mL / g.

[0037] In the present invention, the total catalytic pore volume is measured by the BET specific surface method.

[0038] According to the catalyst of the present invention, the support is used to support a catalytically active coating, and the support is an inert inorganic support, which may be at least one selected from the group consisting of alumina, talc, silicon carbide, aluminum silicate, quartz, and ceramics.

[0039] According to the catalyst of the present invention, the catalyst may have a cylindrical, spherical, annular, or granular shape. Preferably, the catalyst has an annular shape. In one preferred embodiment, the catalyst is annular, and the outer diameter of the catalyst (i.e., the diameter of the outer ring) may be 3 to 13 mm, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13 mm. Preferably, the outer diameter of the catalyst is 5 to 9 mm. In this preferred embodiment, the catalyst has a thickness (i.e., the difference between the diameter of the outer ring and the diameter of the inner ring / 2) of 0.1 to 10 mm, preferably 0.1 to 5 mm, and more preferably 1 to 3 mm. In this preferred embodiment, the catalyst has a height of 2 to 12 mm, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 mm, but is preferably 3 to 8 mm.

[0040] According to a second aspect of the present invention, there is provided a method for preparing a catalyst for the gas phase oxidation of 1,2,4,5-tetraalkylbenzenes, comprising the steps of: (1) applying a first slurry containing a first dispersing medium, a first vanadium source, and a first titanium source to a surface of a support to form a first coating; and (2) applying a second slurry containing a second dispersing medium, a second vanadium source, a second titanium source, and a pore expander onto the surface of the carrier on which the first coating has been formed to form a second coating.

[0041] According to the method of the present invention, the mass of the vanadium source introduced into the first coating in terms of V is C V 12 , the mass of the titanium source introduced into the first coating in terms of Ti is C Ti 12 , the mass of the vanadium source introduced into the second coating in terms of V is C V 22 , the mass of the titanium source introduced into the second coating in terms of Ti is C Ti 22 Then, Ti / V 12 =C Ti 12 / C V 12 , Ti / V22 =C Ti 22 / C V 22 , Ti / V 22 =Ti / V 12 +ΔTi / V 2 and ΔTi / V 2 is in the range of 3 to 9. Specifically, ΔTi / V 2 may be 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, or 9. Preferably, ΔTi / V 2 is in the range of 3.5 to 8.5.

[0042] According to the method for preparing the catalyst of the present invention, the content C of the titanium source introduced into the first coating in terms of Ti Ti 12 may be in the range of 40 mass % to 60 mass %, for example, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, or 60 mass %. Preferably, the content C of titanium element introduced into the first coating in terms of Ti Ti 12 is in the range of 45 to 55 mass %.

[0043] According to the catalyst of the present invention, the content C of the titanium source introduced into the second coating in terms of Ti Ti 22 may be in the range of 45 to 65 mass %, for example 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, or 65%. Preferably, the content C of titanium element introduced into the second coating in terms of Ti Ti22 is in the range of 50 to 60 mass %.

[0044] According to the catalyst preparation method of the present invention, the first vanadium source and the second vanadium source may be the same or different. The first vanadium source and the second vanadium source may each independently be at least one selected from the group consisting of ammonium metavanadate, vanadium pentoxide, and sodium vanadate. Preferably, the first vanadium source and the second vanadium source are ammonium metavanadate.

[0045] According to the catalyst preparation method of the present invention, the first titanium source and the second titanium source may be the same or different. The first titanium source and the second titanium source may each independently be titanium dioxide and / or a precursor of titanium dioxide. In one preferred embodiment, the first titanium source and the second titanium source each independently are at least one selected from the group consisting of titanium dioxide and metatitanic acid. The titanium dioxide is preferably anatase TiO2. The specific surface area of ​​the anatase TiO2 is 10 to 30 m 2 / g.

[0046] According to the method for preparing a catalyst of the present invention, the mass ratio of titanium element (calculated as Ti) introduced into the first coating to vanadium element (calculated as V) introduced into the first coating is Ti / V 12 may be 7 to 8.5:1, for example, 7:1, 7.1:1, 7.2:1, 7.3:1, 7.4:1, 7.5:1, 7.6:1, 7.7:1, 7.8:1, 7.9:1, 8:1, 8.1:1, 8.2:1, 8.3:1, 8.4:1, or 8.5:1.

[0047] According to the method for preparing a catalyst of the present invention, the mass ratio of titanium element (calculated as Ti) introduced into the second coating to vanadium element (calculated as V) introduced into the second coating is Ti / V 22is 12~15.5:1, for example, 12:1, 12.1:1, 12.2:1, 12.3:1, 12.4:1, 12.5:1, 12.6:1, 12.7:1, 12.8:1, 12.9:1, 13:1, 13.1:1, 13.2:1, 13.3:1, 13.4:1, 13.5:1, 13.6:1, 13. It may be 7:1, 13.8:1, 13.9:1, 14:1, 14.1:1, 14.2:1, 14.3:1, 14.4:1, 14.5:1, 14.6:1, 14.7:1, 14.8:1, 14.9:1, 15:1, 15.1:1, 15.2:1, 15.3:1, 15.4:1, or 15.5:1.

[0048] According to the catalyst preparation method of the present invention, the first slurry and the second slurry may each independently contain at least one compound selected from the group consisting of a compound containing a Group VA non-metallic element, a compound containing an alkali metal element, and a compound containing an auxiliary metal element, whereby the first coating and the second coating each independently contain at least one compound selected from the group consisting of a compound containing a Group VA non-metallic element, a compound containing an alkali metal element, and a compound containing an auxiliary metal element. The auxiliary metal element is at least one selected from the group consisting of a rare earth element, a Group VIB element, a Group VIII element, a Group IIIA metal element, a Group VA metal element, and a Group IVB element other than titanium. In one embodiment, the first slurry contains a compound containing a Group VA non-metallic element, a compound containing an alkali metal element, and a compound containing an auxiliary metal element. The second slurry contains a compound containing an alkali metal element, a compound containing an auxiliary metal element, and a compound containing any Group VA non-metallic element.

[0049] According to the catalyst preparation method of the present invention, the Group VA non-metallic element is preferably phosphorus (P). Preferably, the compound containing the Group VA non-metallic element is at least one selected from the group consisting of ammonium dihydrogen phosphate, triammonium phosphate, and phosphorus pentoxide. The content of the compound containing the Group VA non-metallic element introduced into the first coating, calculated as an element, may be 0.1 to 0.5 mass%, preferably 0.3 to 0.4 mass%. According to the catalyst preparation method of the present invention, the second coating may contain a compound containing a Group VA non-metallic element, or may not contain a compound containing a Group VA non-metallic element. The second slurry may contain a Group VA non-metallic element, or may not contain a Group VA non-metallic element. Preferably, the second slurry does not contain a Group VA non-metallic element.

[0050] According to the catalyst preparation method of the present invention, the alkali metal element is preferably cesium (Cs). Preferably, the compound containing an alkali metal element is at least one selected from the group consisting of MNO3, M2SO4, MCl, and M2CO3, where M is an alkali metal element. The content of the compound containing an alkali metal element in elemental equivalent introduced into the first coating may be 0.1 to 0.3 mass%, more preferably 0.15 to 0.2 mass%. The content of the compound containing an alkali metal element in elemental equivalent introduced into the second coating may be 0.1 to 0.7 mass%, more preferably 0.3 to 0.5 mass%.

[0051] According to the catalyst preparation method of the present invention, specific examples of the auxiliary metal element may include, but are not limited to, at least one selected from the group consisting of rubidium (Rb), cerium (Ce), niobium (Nb), chromium (Cr), tungsten (W), silver (Ag), cobalt (Co), gallium (Ga), indium (In), antimony (Sb), bismuth (Bi), zirconium (Zr), and erbium (Er). In one preferred embodiment, the auxiliary metal element is at least one selected from the group consisting of niobium, zirconium, and antimony. Preferably, the compound containing the auxiliary metal element is at least one selected from the group consisting of an oxide of the auxiliary metal and a water-soluble salt containing the auxiliary metal. The water-soluble metal salt refers to a substance having a solubility in water of 1 g / 100 g water or more, and may be at least one selected from the group consisting of nitrates, carbonates, sulfates, oxalates, and chlorides.

[0052] According to the catalyst preparation method of the present invention, the content of the compound containing the auxiliary metal element, calculated as an oxide, introduced into the first coating may be 1 to 6 mass%, preferably 1.5 to 5 mass%, more preferably 2 to 4.5 mass%, and even more preferably 3 to 4 mass%. The content of the compound containing the auxiliary metal element, calculated as an oxide, introduced into the second coating may be 1 to 6 mass%, preferably 1.2 to 5 mass%, and more preferably 1.5 to 3 mass%.

[0053] According to the catalyst preparation method of the present invention, in one preferred embodiment, the auxiliary metal elements in the first slurry are niobium, zirconium, and antimony. In this preferred embodiment, the content of the niobium element-containing compound introduced into the first coating in terms of Nb2O5 may be 0.15 to 0.2 mass%, the content of the zirconium element-containing compound introduced into the first coating in terms of ZrO2 may be 0.4 to 0.45 mass%, and the content of the antimony element-containing compound introduced into the first coating in terms of Sb2O3 may be 2.8 to 3.2 mass%.

[0054] According to the catalyst preparation method of the present invention, in one preferred embodiment, the auxiliary metal elements in the second coating are niobium and antimony. In this preferred embodiment, the content of the niobium element-containing compound introduced into the second coating, calculated as Nb2O5, may be 0.12 to 0.18 mass%, and the content of the antimony element-containing compound introduced into the second coating, calculated as Sb2O3, may be 1.5 to 2 mass%.

[0055] In the catalyst preparation method of the present invention, the content of each element introduced into the first coating and the second coating is calculated based on the input amount and is calculated based on the total amount (oxide equivalent) of the raw materials forming the coating, and the raw materials do not contain a dispersion medium.

[0056] According to the catalyst preparation method of the present invention, the first slurry and the second slurry may each independently contain oxalic acid, and the mass ratio of the oxalic acid to the vanadium source in the first slurry and the second slurry may each be 2 to 2.5:1.

[0057] According to the catalyst preparation method of the present invention, the first slurry and the second slurry may each independently contain a binder. The binder is at least one selected from the group consisting of a vinyl acetate-acrylate copolymer emulsion, a vinyl acetate-ethylene copolymer emulsion, a vinyl acetate-maleic acid ester copolymer emulsion, and an acrylic acid-maleic acid copolymer emulsion. The binder content may be 4 to 4.3 mass% based on the total amount of the first slurry. The binder content in the second slurry may be 4.3 to 4.6 mass%.

[0058] According to the catalyst preparation method of the present invention, the second slurry contains a pore expander. The pore expander may be at least one selected from the group consisting of stearic acid and sodium stearate. The content of the pore expander may be 3.9 to 4.2 mass% based on the total amount of the second slurry. According to the catalyst preparation method of the present invention, the first slurry preferably does not contain a pore expander.

[0059] According to the catalyst preparation method of the present invention, the first dispersion medium and the second dispersion medium each independently contain water and an aqueous organic solvent. Preferably, the aqueous organic solvent is at least one selected from the group consisting of methanol, ethanol, formamide, and N,N-dimethylamide. According to the catalyst preparation method of the present invention, the mass ratio of water to aqueous organic solvent in the first dispersion medium and the second dispersion medium each independently may be 1:0.1 to 1, preferably 1:0.3 to 0.8, and more preferably 1:0.4 to 0.7.

[0060] According to the catalyst preparation method of the present invention, the first slurry and the second slurry can be obtained by uniformly mixing the components.

[0061] In one embodiment, the first slurry may be prepared by a method comprising the following steps.

[0062] (1-1) A mixed solution A is obtained by mixing oxalic acid, a vanadium source, a compound containing a Group VA non-metallic element, a compound containing an alkali metal element, and a first dispersion medium.

[0063] (1-2) The mixed solution A is mixed with a titanium source, a compound containing an auxiliary metal element, and a binder to obtain a first slurry.

[0064] The mixing in step (1-1) and step (1-2) may each be carried out at a temperature of 20 to 90° C. The mixing in step (1-2) may be carried out in a ball mill, and the ball milling time may be 1 to 5 hours, preferably 2 to 4 hours.

[0065] In one embodiment, the second slurry may be prepared by a method comprising the following steps.

[0066] (2-1) Mixture B is obtained by mixing oxalic acid, a vanadium source, a compound containing any Group VA non-metallic element, a compound containing an alkali metal element, and a first dispersion medium.

[0067] (2-2) The mixed solution B is mixed with a titanium source, a compound containing an auxiliary metal element, and a binder to obtain a second slurry.

[0068] The mixing in step (2-1) and step (2-2) may each be carried out at a temperature of 20 to 90° C. The mixing in step (2-2) may be carried out in a ball mill, and the ball milling time may be 1 to 5 hours, preferably 2 to 4 hours.

[0069] According to the catalyst preparation method of the present invention, the support is an inert inorganic support and may be at least one selected from the group consisting of alumina, talc, silicon carbide, aluminum silicate, quartz, and ceramics. According to the catalyst preparation method of the present invention, the shape of the support may be cylindrical, spherical, ring-shaped, or granular. Preferably, the shape of the support is ring-shaped. In one preferred embodiment, the support is a ring-shaped support, and the outer diameter of the support (i.e., the diameter of the outer ring) may be 3 to 13 mm, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13 mm. Preferably, the outer diameter of the support is 5 to 9 mm. In this preferred embodiment, the wall thickness of the support (i.e., the difference between the diameter of the outer ring and the diameter of the inner ring / 2) is 0.1 to 10 mm, preferably 0.1 to 5 mm, and more preferably 1 to 3 mm. In this preferred embodiment, the height of the carrier may be 2 to 12 mm, for example 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 mm, but is preferably 3 to 8 mm.

[0070] According to the catalyst preparation method of the present invention, the weight ratio of the first coating, the second coating, and the support may be 5.5-6.8:1.9-3.5:100, but is preferably 5.8-6.7:1.9-2.9:100.

[0071] According to the catalyst preparation method of the present invention, the coating temperature of the first slurry is higher than the coating temperature of the second slurry. In the present invention, the coating temperature refers to the temperature of the support at the time of spraying. Preferably, when the coating temperature of the first slurry is T1 and the coating temperature of the second slurry is T2, T1-T2 (the difference between T1 and T2) is within a range of 70 to 150°C, preferably within a range of 80 to 120°C, and more preferably within a range of 85 to 105°C. In one preferred embodiment, the coating temperature of the first slurry may be 200 to 250°C, for example, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, or 250°C. In another preferred embodiment, the coating temperature of the second slurry may be 100 to 130°C, for example, 100, 105, 110, 115, 120, 125, or 130°C.

[0072] According to the catalyst preparation method of the present invention, a first coating may be formed by curing a first slurry layer formed on the surface of a support by a conventional method. In the present invention, the term "curing" refers to the slurry layer losing its fluidity and changing from a liquid to a solid. In one embodiment, the first coating may be formed by drying the first slurry layer with a first airflow. The temperature of the first airflow is such that the first slurry layer loses its fluidity and a coating is formed. The temperature of the first airflow may be 200 to 250°C, for example, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, or 250°C.

[0073] According to the catalyst preparation method of the present invention, a second slurry is applied to the surface on which the first coating has been formed to form a second slurry layer. After the application is completed, the second coating may be formed by directly purging with a purge gas, or the second coating may be formed by first drying with a second airflow and then purging with a purge airflow. The temperature of the purge airflow is preferably 380-450°C, for example, 380, 385, 400, 405, 410, 415, 420, 425, 430, 435, 440, 445, or 450°C. The temperature of the second airflow is preferably 100-150°C, for example, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, or 150°C.

[0074] According to the catalyst preparation method of the present invention, the first slurry and the second slurry may be applied to a support by a conventional method. In one embodiment, the first slurry and the second slurry are each applied to a support by spraying. In this embodiment, the spraying rates of the first slurry and the second slurry per 2000 g of support may be independently 30 to 60 mL / min, for example, 30 mL / min, 35 mL / min, 40 mL / min, 45 mL / min, 50 mL / min, 55 mL / min, or 60 mL / min, but are preferably 35 to 50 mL / min.

[0075] Spraying can be performed using a conventional spraying device. For example, the spraying device may include a hot air blower, a coating body, an exhaust fan, a slurry spraying system, a control system, and a high-voltage power cabinet. The coating body may include a coating drum and its power mechanism. The coating drum is housed within the coating body and has an adjustable rotation speed. The coating drum has a horizontal, hollow, columnar structure, which increases the probability of contact between the active ingredient and the inert carrier material. The horizontal, hollow, columnar structure is perforated with a round mesh with a pore size of 1 to 8 mm, preferably 3 to 4 mm, allowing hot air to enter the coating drum. After evaporating the solvent in the slurry on the carrier, the evaporated solvent is removed from the coating drum. The rotation speed of the coating drum is preferably 5 to 10 rpm. The slurry spraying system includes a nozzle and a supply system, which includes a tank, an agitator, a supply pump, and a transport pipeline. The supply pump can adjust the spraying speed, and the nozzle is used to spray the slurry supplied by the supply pump evenly onto the surface of the carrier.

[0076] According to a third aspect of the present invention, there is provided a catalyst prepared by the method according to the second aspect of the present invention.

[0077] The catalyst prepared by the method according to the second aspect of the present invention comprises a support and a catalytically active component coating carried on the support, the catalytically active component coating comprising a first coating and a second coating, the first coating being close to a surface of the support and the second coating being distant from the surface of the support, wherein the mass ratio of titanium element calculated as Ti to vanadium element calculated as V in the first coating is Ti / V 1 the mass ratio of titanium element (calculated as Ti) to vanadium element (calculated as V) in the second coating is Ti / V 2 Then, Ti / V 2 =Ti / V 1 +ΔTi / V, and ΔTi / V is within the range of 3 to 9. Preferably, ΔTi / V is within the range of 3.5 to 8.5.

[0078] According to a fourth aspect of the present invention, there is provided the use of a catalyst according to the first aspect of the present invention, or a catalyst according to the third aspect of the present invention, as a catalyst for the reaction of preparing 1,2,4,5-benzenetetracarboxylic acid anhydride by oxidation of 1,2,4,5-tetraalkylbenzene.

[0079] The 1,2,4,5-tetraalkylbenzene is preferably 1,2,4,5-tetramethylbenzene (ie, durene).

[0080] According to a fifth aspect of the present invention, there is provided a process for preparing 1,2,4,5-benzenetetracarboxylic acid anhydride, comprising the step of contacting a gas comprising 1,2,4,5-tetraalkylbenzene and oxygen gas with a catalyst according to the first or third aspect of the present invention to obtain a product stream comprising 1,2,4,5-benzenetetracarboxylic acid anhydride.

[0081] According to the method for preparing 1,2,4,5-benzenetetracarboxylic anhydride of the present invention, the 1,2,4,5-tetraalkylbenzene is preferably 1,2,4,5-tetramethylbenzene (ie, durene).

[0082] According to the method for preparing 1,2,4,5-benzenetetracarboxylic anhydride of the present invention, the concentration of 1,2,4,5-tetraalkylbenzene is 1 to 50 g / m 3 However, it is preferably 10 to 30 g / m 3 The concentration of 1,2,4,5-tetraalkylbenzene refers to the grams of 1,2,4,5-tetraalkylbenzene contained in a unit volume of gas containing oxygen gas, and the higher the value, the higher the content of durene in the gas containing oxygen gas.

[0083] According to the method for preparing 1,2,4,5-benzenetetracarboxylic anhydride of the present invention, the temperature at which the raw material mixed gas comes into contact with the catalyst may be 300 to 400°C, preferably 320 to 360°C, and more preferably 330 to 350°C.

[0084] According to the method for preparing 1,2,4,5-benzenetetracarboxylic anhydride of the present invention, the mixed gas of raw materials containing 1,2,4,5-tetraalkylbenzene and oxygen gas may be mixed in a conventional reactor. In one embodiment, the reactor is a fluidized bed reactor. In one preferred embodiment, the reactor is a fixed-bed reactor. In a more preferred embodiment, the reactor is a fixed-bed single-tube reactor. In this more preferred embodiment, the fixed-bed single-tube reactor may have a tube length of 3000 to 4800 mm and an inner diameter of 20 to 30 mm. The reaction heat may be forcibly exchanged outside the reaction tube of the fixed-bed single-tube reactor by circulating a molten salt. In this preferred embodiment, the catalyst may be a single-stage catalyst (i.e., one stage of catalyst is packed in the reaction tube of the fixed-bed single-tube reactor) or two or more stages (i.e., two or more stages of catalyst are packed in the reaction tube of the fixed-bed single-tube reactor).

[0085] According to the method for preparing 1,2,4,5-benzenetetracarboxylic anhydride of the present invention, the volumetric space velocity of the gas containing oxygen gas is 1500 to 5000 h -1 However, it is preferable that the time is 2000 to 4000 hours. -1 is.

[0086] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited thereto.

[0087] In the following examples and comparative examples, the mass ratio of titanium element to vanadium element (Ti / V) in the first coating and the second coating of the catalyst is 1 and Ti / V 2The Ti / V mass ratio was measured using a scanning electron microscope (HITACHI-4800) equipped with an energy spectrometer (EDAX GENESIS XM2 SYSTEM 60x). The test method is as follows: Using an EDAX energy spectrometer (TEAM Octane Super), the test was performed under the same test conditions as the scanning electron microscope. After cooling the catalyst particles with liquid nitrogen, they were cut longitudinally from the uncoated side to obtain semi-particles with exposed cross sections. The semi-particles were then fixed to conductive tape and coated with gold, platinum, or carbon to improve their electrical conductivity. The test sample was then placed on the sample stage of the scanning electron microscope. The cross-sections of the semi-particles were observed under the scanning electron microscope, and the Ti / V mass ratio was measured at various coating thicknesses (also referred to as the "longitudinal direction") using the energy spectrometer. The Ti / V mass ratio at the same coating thickness was measured as follows: Three adjacent points along the horizontal direction of the coating (i.e., perpendicular or nearly perpendicular to the coating thickness direction) were randomly selected and magnified by the same factor (typically 500-1000x). The Ti / V mass ratio, vanadium content, and titanium content at each point were measured using an energy spectrometer. The values ​​measured at the three points were averaged to determine the horizontal Ti / V mass ratio. The first and second coatings were distinguished based on the difference in the Ti / V mass ratio between two adjacent points along the coating thickness direction. If the difference in the Ti / V mass ratio between two adjacent points is within the ΔTi / V range defined in this invention, the two points belong to the first and second coatings, respectively. If the difference in the Ti / V mass ratio between two adjacent points is below the ΔTi / V range defined in this invention (including both endpoints), the two points belong to the same coating. For the energy spectrometer test conditions, the excitation source was a high-energy electron beam with an energy of 15 kV.

[0088] In the following examples and comparative examples, the total pore volume of the catalyst was measured by the BET specific surface method using a fully automatic chemisorption analyzer manufactured by Micromeritics, Inc., USA. The test method is specifically as follows: A predetermined amount of sample was placed in a sample tube, heated to 350°C at a rate of 10°C / min, and vacuum-suctioned for 4 hours to degas the sample tube. The sample tube was then placed in an analytical instrument for pore isothermal analysis, and the specific surface area of ​​the catalyst was calculated by the BET method.

[0089] In the following examples and comparative examples, the preparation of the slurry is carried out at room temperature (25° C.).

[0090] In the following examples and comparative examples, the titanium dioxide is anatase type titanium dioxide having a specific surface area of ​​20 to 30 m 2 / g.

[0091] Examples 1 to 4 prepare catalysts according to the present invention. Example 1

[0092] 1. Preparation of the first slurry (1-i) 123.23 g of ammonium metavanadate, 275.36 g of oxalic acid, 2.11 g of cesium sulfate, 10.23 g of ammonium dihydrogen phosphate, formamide, and 350 g of water were mixed to prepare a solution A-1 having a formamide to water weight ratio of 0.7:1. (1-ii) Solution A-1 was placed in a ball mill together with 630 g of titanium dioxide, 6.12 g of niobium oxalate, 7.24 g of zirconium sulfate, and 23.1 g of antimony trioxide, and then 70 g of vinyl acetate / ethylene copolymer emulsion was added thereto, followed by ball milling for 4 hours to obtain a first slurry. 2. Preparation of the second slurry (2-i) 69.82 g of ammonium metavanadate, 161.3 g of oxalic acid, 4.57 g of cesium sulfate, formamide, and 350 g of water were mixed to prepare a solution B-1 having a formamide to water weight ratio of 0.7:1. (2-ii) Solution B-1 was placed in a ball mill together with 630 g of titanium dioxide, 4.86 g of niobium oxalate, 13.96 g of antimony trioxide, and 63 g of stearic acid, and then 70 g of vinyl acetate / ethylene copolymer emulsion was added and ball milled for 4 hours to obtain a second slurry. 3. Preparation of catalyst (1-iii) 2000 g of support ceramic rings (outer diameter 8 mm, height 6 mm, wall thickness 1.5 mm, made of talc rings) were placed in a drum, and the drum speed was controlled at 10 rpm. The first slurry was placed in the stirring can of the liquid material spraying system and stirred. The hot air blower was started, and hot air at 100°C was passed through the drum to preheat the support ceramic rings. When the temperature of the support ceramic rings reached 210°C, the supply nozzle was opened, and the spraying rate of the first slurry was controlled at 30 mL / min. The first slurry was sprayed from the nozzle onto the surface of the support and quickly dried with hot air at 220°C. When the inner coating content reached 6.2 wt% of the support weight, spraying was completed, and a catalyst intermediate was obtained. (2-iii) The second slurry was placed in the stirring vessel of the liquid spraying system and stirred. The hot air blower was started, and hot air at 100 °C was passed through the drum. When the temperature of the support reached 120 °C, the supply nozzle was opened, and the spraying rate of the second slurry was controlled at 30 mL / min. The second slurry was sprayed from the nozzle onto the surface of the catalyst intermediate and quickly dried with hot air at 120 °C. When the outer coating content reached 2.3 wt% of the support weight, the spraying was completed and the support was purged with hot air at 400 °C for 2 h to obtain catalyst S1. The composition and total pore volume of this catalyst are shown in Table 1. Catalyst S1 included a support and a first coating (i.e., inner coating) and a second coating (i.e., outer coating) sequentially supported on the support. In catalyst S1, the weight ratio of the first coating, second coating, and support was 6.2:2.3:100. Example 2

[0093] 1. Preparation of the first slurry (1-i) 123.23 g of ammonium metavanadate, 275.36 g of oxalic acid, 2.11 g of cesium sulfate, 10.23 g of ammonium dihydrogen phosphate, formamide, and 350 g of water were mixed to prepare a solution A-1 having a formamide to water weight ratio of 0.7:1. (1-ii) Solution A-1 was placed in a ball mill together with 630 g of titanium dioxide, 6.12 g of niobium oxalate, 7.24 g of zirconium sulfate, and 23.1 g of antimony trioxide, and then 70 g of vinyl acetate / ethylene copolymer emulsion was added and ball milled for 4 hours to obtain a first slurry. 2. Preparation of the second slurry (2-i) 57.31 g of ammonium metavanadate, 123.89 g of oxalic acid, 3.77 g of cesium sulfate, formamide, and 350 g of water were mixed to prepare a solution B-2 having a formamide to water weight ratio of 0.7:1. (2-ii) Solution B-2 was placed in a ball mill together with 630 g of titanium dioxide, 3.92 g of niobium oxalate, 11.29 g of antimony trioxide, and 63 g of stearic acid, and then 70 g of vinyl acetate / ethylene copolymer emulsion was added and ball milled for 4 hours to obtain a second slurry. 3. Preparation of catalyst (1-iii) 2000 g of support ceramic rings (outer diameter 8 mm, height 6 mm, wall thickness 1.5 mm, made of talc rings) were placed in a drum, and the drum speed was controlled at 10 rpm. The first slurry was placed in the stirring can of the liquid material spraying system and stirred. The hot air blower was started, and hot air at 100°C was passed through the drum to preheat the support ceramic rings. When the temperature of the support ceramic rings reached 210°C, the supply nozzle was opened, and the spraying rate of the first slurry was controlled at 30 mL / min. The first slurry was sprayed from the nozzle onto the surface of the support and quickly dried with hot air at 220°C. When the inner coating content reached 5.8 wt% of the support weight, spraying was completed, and a catalyst intermediate was obtained. (2-iii) The second slurry was placed in the stirring vessel of the liquid spraying system and stirred. The hot air blower was started, and hot air at 100°C was passed through the drum. When the temperature of the support reached 120°C, the supply nozzle was opened, and the spraying rate of the second slurry was controlled at 30 mL / min. The second slurry was sprayed from the nozzle onto the surface of the catalyst intermediate and quickly dried with hot air at 120°C. When the outer coating content reached 1.9 wt% of the support weight, the spraying was completed and the support was purged with hot air at 400°C for 2 h to obtain catalyst S2. The composition and total pore volume of this catalyst are shown in Table 1. Catalyst S2 included a support and a first coating (i.e., inner coating) and a second coating (i.e., outer coating) sequentially supported on the support. In catalyst S2, the weight ratio of the first coating, second coating, and support was 5.8:1.9:100. Example 3

[0094] 1. Preparation of the first slurry (1-i) 102.55 g of ammonium metavanadate, 230.27 g of oxalic acid, 1.72 g of cesium sulfate, 8.76 g of ammonium dihydrogen phosphate, formamide, and 350 g of water were mixed to prepare a solution A-3 having a formamide to water weight ratio of 0.7:1. (1-ii) Solution A-3 was placed in a ball mill together with 630 g of titanium dioxide, 5.83 g of niobium oxalate, 7.15 g of zirconium sulfate, and 21.8 g of antimony trioxide, and then 70 g of vinyl acetate / ethylene copolymer emulsion was added and ball milled for 4 hours to obtain a first slurry. 2. Preparation of the second slurry (2-i) 69.82 g of ammonium metavanadate, 161.3 g of oxalic acid, 4.57 g of cesium sulfate, formamide, and 350 g of water were mixed to prepare a solution B-1 having a formamide to water weight ratio of 0.7:1. (2-ii) Solution B-1 was placed in a ball mill together with 630 g of titanium dioxide, 4.86 g of niobium oxalate, 13.96 g of antimony trioxide, and 63 g of stearic acid, and then 70 g of vinyl acetate / ethylene copolymer emulsion was added and ball milled for 4 hours to obtain a second slurry. 3. Preparation of catalyst (1-iii) 2000 g of support ceramic rings (outer diameter 8 mm, height 6 mm, wall thickness 1.5 mm, made of talc rings) were placed in a drum, and the drum speed was controlled at 10 rpm. The first slurry was placed in the stirring can of the liquid material spraying system and stirred. The hot air blower was started, and hot air at 100°C was passed through the drum to preheat the support ceramic rings. When the temperature of the support ceramic rings reached 210°C, the supply nozzle was opened, and the spraying rate of the first slurry was controlled at 30 mL / min. The first slurry was sprayed from the nozzle onto the surface of the support and quickly dried with hot air at 220°C. When the inner coating content reached 6.5 wt% of the support weight, spraying was completed, and a catalyst intermediate was obtained. (2-iii) The second slurry was placed in the stirring tank of the liquid spraying system and stirred. The hot air blower was started, and hot air at 100 °C was passed through the drum. When the support temperature reached 120 °C, the supply nozzle was opened, and the spraying rate of the second slurry was controlled at 30 mL / min. The second slurry was sprayed from the nozzle onto the surface of the catalyst intermediate and quickly dried with hot air at 120 °C. When the outer coating content reached 2.7 wt% of the support weight, the spraying was completed and the support was purged with hot air at 400 °C for 2 h to obtain catalyst S3. The composition and total pore volume of this catalyst are shown in Table 1. Catalyst S3 included a support and a first coating (i.e., inner coating) and a second coating (i.e., outer coating) sequentially supported on the support. In catalyst S3, the weight ratio of the first coating, second coating, and support was 6.5:2.7:100. Example 4

[0095] 1. Preparation of the first slurry (1-i) 102.55 g of ammonium metavanadate, 230.27 g of oxalic acid, 1.72 g of cesium sulfate, 8.76 g of ammonium dihydrogen phosphate, formamide, and 350 g of water were mixed to prepare a solution A-3 having a formamide to water weight ratio of 0.7:1. (1-ii) Solution A-3 was placed in a ball mill together with 630 g of titanium dioxide, 5.83 g of niobium oxalate, 7.15 g of zirconium sulfate, and 21.8 g of antimony trioxide, and then 70 g of vinyl acetate / ethylene copolymer emulsion was added and ball milled for 4 hours to obtain a first slurry. 2. Preparation of the second slurry (2-i) 57.31 g of ammonium metavanadate, 123.89 g of oxalic acid, 3.77 g of cesium sulfate, formamide, and 350 g of water were mixed to prepare a solution B-2 having a formamide to water weight ratio of 0.7:1. (2-ii) Solution B-2 was placed in a ball mill together with 630 g of titanium dioxide, 3.92 g of niobium oxalate, 11.29 g of antimony trioxide, and 63 g of stearic acid, and then 70 g of vinyl acetate / ethylene copolymer emulsion was added and ball milled for 4 hours to obtain a second slurry. 3. Preparation of catalyst (1-iii) 2000 g of support ceramic rings (outer diameter 8 mm, height 6 mm, wall thickness 1.5 mm, made of talc rings) were placed in a drum, and the drum speed was controlled at 10 rpm. The first slurry was placed in the stirring can of the liquid material spraying system and stirred. The hot air blower was started, and hot air at 100°C was passed through the drum to preheat the support ceramic rings. When the temperature of the support ceramic rings reached 210°C, the supply nozzle was opened, and the spraying rate of the first slurry was controlled at 30 mL / min. The first slurry was sprayed from the nozzle onto the surface of the support and quickly dried with hot air at 220°C. When the inner coating content reached 6.7 wt% of the support weight, spraying was completed, and a catalyst intermediate was obtained. (2-iii) The second slurry was placed in the stirring vessel of the liquid spraying system and stirred. The hot air blower was started, and hot air at 100°C was passed through the drum. When the support temperature reached 120°C, the supply nozzle was opened, and the spraying rate of the second slurry was controlled at 30 mL / min. The second slurry was sprayed from the nozzle onto the surface of the catalyst intermediate and quickly dried with hot air at 120°C. When the outer coating content reached 1.9 wt% of the support weight, the spraying was completed and the support was purged with hot air at 450°C for 2 h to obtain Catalyst S4. The composition and total pore volume of this catalyst are shown in Table 1. Catalyst S4 included a support and a first coating (i.e., inner coating) and a second coating (i.e., outer coating) sequentially supported on the support. In Catalyst S4, the weight ratio of the first coating, second coating, and support was 6.7:1.9:100. Comparative Example 1

[0096] In Comparative Example 1, a catalyst was prepared using the same method as in Example 1, except that the second slurry was not prepared and the prepared catalyst did not contain a second coating. The specific procedures were as follows: A first slurry was prepared using the same method as in Example 1. 2000 g of a support ceramic ring (same as in Example 1) was placed in a drum, and the drum speed was controlled at 10 rpm. The first slurry was then placed in the stirring can of the liquid material spraying system and stirred. A hot air blower was started, and hot air at 100°C was blown through the drum to preheat the support ceramic ring. When the temperature of the support ceramic ring reached 210°C, the supply nozzle was opened, and the spraying rate of the first slurry was controlled at 30 mL / min. The first slurry was sprayed onto the surface of the support through the nozzle and quickly dried with hot air at 220°C. When the inner coating content reached 8.3 wt% of the support weight, spraying was completed to obtain catalyst DS1. Catalyst DS1 included a support and a coating carried on the support, and in catalyst DS1, the weight ratio of the coating to the support was 8.3:100. Comparative Example 2

[0097] In Comparative Example 2, the first slurry was not prepared, and the catalyst prepared did not contain a first coating. Instead, the second slurry, prepared in the same manner as in Example 1, was directly sprayed onto the surface of the support to form a coating. The specific procedure was as follows: The second slurry was prepared in the same manner as in Example 1. 2000 g of a support ceramic ring (same as in Example 1) was placed in a drum, and the drum speed was controlled at 10 rpm. The first slurry was then placed in the stirring can of the liquid material spraying system and stirred. The hot air blower was started, and hot air at 100°C was blown through the drum to preheat the support ceramic ring. When the temperature of the support ceramic ring reached 210°C, the supply nozzle was opened, and the spraying rate of the first slurry was controlled at 30 mL / min. The first slurry was sprayed onto the surface of the support through the nozzle and quickly dried with hot air at 220°C. When the inner coating content reached 8.8 wt% of the support weight, the spraying was completed to obtain catalyst DS2. Catalyst DS2 included a support and a coating carried on the support, and in catalyst DS2, the weight ratio of the coating to the support was 8.8:100. Comparative Example 3

[0098] In Comparative Example 3, the first slurry was not prepared, and the catalyst prepared did not contain a first coating. Instead, the second slurry, prepared in the same manner as in Example 2, was directly sprayed onto the surface of the support to form a coating. The specific procedure was as follows: The second slurry was prepared in the same manner as in Example 2. 2000 g of a support ceramic ring (same as in Example 2) was placed in a drum, and the drum speed was controlled at 10 rpm. The second slurry was then placed in the stirring can of the liquid material spraying system and stirred. The hot air blower was started, and hot air at 100°C was blown through the drum to preheat the support ceramic ring. When the temperature of the support ceramic ring reached 210°C, the supply nozzle was opened, and the spraying rate of the second slurry was controlled at 30 mL / min. The second slurry was sprayed onto the surface of the support through the nozzle and quickly dried with hot air at 220°C. When the inner coating content reached 8.7 wt% of the support weight, the spraying was completed to obtain catalyst DS3. Catalyst DS3 included a support and a coating carried on the support, and in catalyst DS3, the weight ratio of the coating to the support was 8.7:100. Comparative Example 4

[0099] 1. Preparation of the first slurry (1-i) 102.55 g of ammonium metavanadate, 230.27 g of oxalic acid, 1.72 g of cesium sulfate, 8.76 g of ammonium dihydrogen phosphate, formamide, and 350 g of water were mixed to prepare a solution A-3 having a formamide to water weight ratio of 0.7:1. (1-ii) Solution A-3 was placed in a ball mill together with 630 g of titanium dioxide, 5.83 g of niobium oxalate, 7.15 g of zirconium sulfate, and 21.8 g of antimony trioxide, and then 70 g of vinyl acetate / ethylene copolymer emulsion was added and ball milled for 4 hours to obtain a first slurry. 2. Preparation of the second slurry (2-i) 90.28 g of ammonium metavanadate, 218.12 g of oxalic acid, 5.97 g of cesium sulfate, formamide, and 350 g of water were mixed to prepare a solution B-4 having a formamide to water weight ratio of 0.7:1. (2-ii) Solution B-4 was placed in a ball mill together with 630 g of titanium dioxide, 6.51 g of niobium oxalate, 17.85 g of antimony trioxide, and 63 g of stearic acid, and then 70 g of vinyl acetate / ethylene copolymer emulsion was added and ball milled for 4 hours to obtain a second slurry. 3. Preparation of catalyst (1-iii) 2000 g of a support ceramic ring (same as in Example 3) was placed in a drum, and the drum speed was controlled at 10 rpm. The first slurry was placed in the stirring can of the liquid material spraying system and stirred. The hot air blower was started, and hot air at 100°C was passed through the drum to preheat the support ceramic ring. When the temperature of the support ceramic ring reached 210°C, the supply nozzle was opened, and the spraying rate of the first slurry was controlled at 30 mL / min. The first slurry was sprayed from the nozzle onto the surface of the support and quickly dried with hot air at 220°C. When the inner coating content reached 6.8 wt% of the support weight, spraying was completed, and a catalyst intermediate was obtained. (2-iii) The second slurry was placed in the stirring vessel of the liquid spraying system and stirred. The hot air blower was started, and hot air at 100°C was passed through the drum. When the support temperature reached 120°C, the supply nozzle was opened, and the spraying rate of the second slurry was controlled at 30 mL / min. The second slurry was sprayed from the nozzle onto the surface of the catalyst intermediate and quickly dried with hot air at 120°C. When the outer coating content reached 1.9 wt% of the support weight, the spraying was completed, and the catalyst was purged with hot air at 400°C for 2 hours to obtain Catalyst DS4. The composition and total pore volume of this catalyst are shown in Table 1. Catalyst DS4 included a support and a first and second coatings sequentially supported on the support. In Catalyst DS4, the weight ratio of the first coating, the second coating, and the support was 6.8:1.9:100. Comparative Example 5

[0100] 1. Preparation of the first slurry (1-i) 102.55 g of ammonium metavanadate, 230.27 g of oxalic acid, 1.72 g of cesium sulfate, 8.76 g of ammonium dihydrogen phosphate, formamide, and 350 g of water were mixed to prepare a solution A-3 having a formamide to water weight ratio of 0.7:1. (1-ii) Solution A-3 was placed in a ball mill together with 630 g of titanium dioxide, 5.83 g of niobium oxalate, 7.15 g of zirconium sulfate, and 21.8 g of antimony trioxide, and then 70 g of vinyl acetate / ethylene copolymer emulsion was added and ball milled for 4 hours to obtain a first slurry. 2. Preparation of the second slurry (2-i) 40.19 g of ammonium metavanadate, 84.32 g of oxalic acid, 2.33 g of cesium sulfate, formamide, and 350 g of water were mixed to prepare a solution B-5 having a formamide to water weight ratio of 0.7:1. (2-ii) Solution B-5 was placed in a ball mill together with 630 g of titanium dioxide, 2.48 g of niobium oxalate, 7.32 g of antimony trioxide, and 63 g of stearic acid, and then 70 g of vinyl acetate / ethylene copolymer emulsion was added and ball milled for 4 hours to obtain a second slurry. 3. Preparation of catalyst (1-iii) 2000 g of a support ceramic ring (same as in Example 3) was placed in a drum, and the drum speed was controlled at 10 rpm. The first slurry was placed in the stirring can of the liquid material spraying system and stirred. The hot air blower was started, and hot air at 100°C was passed through the drum to preheat the support ceramic ring. When the temperature of the support ceramic ring reached 210°C, the supply nozzle was opened, and the spraying rate of the first slurry was controlled at 30 mL / min. The first slurry was sprayed from the nozzle onto the surface of the support and quickly dried with hot air at 220°C. When the content of the inner coating reached 6.9 wt% of the support weight, spraying was completed, and a catalyst intermediate was obtained. (2-iii) The second slurry was placed in the stirring vessel of the liquid spraying system and stirred. The hot air blower was started, and hot air at 100°C was passed through the drum. When the support temperature reached 120°C, the supply nozzle was opened, and the spraying rate of the second slurry was controlled at 30 mL / min. The second slurry was sprayed from the nozzle onto the surface of the catalyst intermediate and quickly dried with hot air at 120°C. When the outer coating content reached 2.1 wt% of the support weight, the spraying was completed, and the support was purged with hot air at 400°C for 2 hours to obtain Catalyst DS5. The composition and total pore volume of this catalyst are shown in Table 1. Catalyst DS5 included a support and a first and second coatings sequentially supported on the support. In Catalyst DS5, the weight ratio of the first coating, the second coating, and the support was 6.9:2.1:100. Comparative Example 6

[0101] A catalyst was prepared in the same manner as in Example 1, except that the second slurry was used in step 3 (1-iii) and the first slurry was used in step (2-iii), i.e., the second slurry was used to form the first coating (i.e., the inner coating) and the first slurry was used to form the second coating (i.e., the outer coating), to obtain catalyst DS6. The composition and total pore volume of this catalyst are shown in Table 1. Catalyst DS6 included a support and a first coating (i.e., the inner coating) and a second coating (i.e., the outer coating) sequentially supported on the support, and the weight ratio of the first coating, the second coating, and the support in catalyst DS6 was 6.2:2.3:100.

[0102] [Table 1]

[0103] 1: mass ratio of titanium / vanadium in the first coating (Ti / V 1 ) and the mass ratio of titanium to vanadium (Ti / V) in the second coating 2 ) was measured by scanning electron microscopy-energy spectroscopy, and Ti / V 1is the mass ratio of titanium element (converted to Ti) to vanadium element (converted to V) in the first coating, and Ti / V 2 is the mass ratio of titanium element (converted to Ti) to vanadium element (converted to V) in the second coating, and Ti / V 2 =Ti / V 1 +ΔTi / V.

[0104] 2: The contents of titanium (Ti), phosphorus (P), cesium (Cs), and auxiliary agents are calculated based on the input amounts and are calculated based on the total amount (oxide equivalent) of raw materials forming the coating, which does not include the dispersing medium. The titanium (Ti) content is expressed in elemental titanium equivalent, the phosphorus (P) content is expressed in P equivalent, the cesium (Cs) content is expressed in Cs equivalent, and the auxiliary agent content is expressed in oxide equivalent. Test Examples and Comparative Test Examples

[0105] The catalyst performance was evaluated using a fixed-bed single-tube reactor simulating industrial production conditions. The fixed-bed single-tube reactor had an inner diameter of 29 mm and a tube length of 4,400 mm. Heat transfer was performed by circulating molten salt outside the reaction tube. The outlet of the reactor was connected to an analytical system and a reactant collection system. The catalyst is packed in a single-stage (i.e., one stage of a single tube) or two-stage (i.e., two stages of a single tube) manner, with the total catalyst packing height being 2000 mm. In the case of two-stage packing, the first stage is packed at the inlet end of the reaction tube, and the second stage is packed at the outlet end of the reaction tube, with the packing height of the first stage being 1200 mm and the packing height of the second stage being 800 mm. In the test examples and comparative test examples, the catalysts were activated in an oxidizing atmosphere at a temperature of 410° C. for 4 hours before the reaction.

[0106] In the test examples and the comparative test examples, the gas phase oxidation reaction method was the same, the reaction pressure was atmospheric pressure (i.e., 1 standard atmospheric pressure), air was used as the oxygen-containing gas, and the space velocity of air was 2000 h -1During the reaction, the durene feed concentration was gradually increased, and sampling analysis was performed at the outlet of the reactor under each condition to evaluate the durene conversion and pyromellitic dianhydride yield at the maximum catalyst load (i.e., the maximum durene feed concentration, i.e., the durene concentration listed in Table 2), as well as the molten salt temperature and maximum load listed in Table 2. The test results are shown in Table 2.

[0107] [Table 2]

[0108] Comparing Test Example 1, Comparative Test Example 1, and Comparative Test Example 2, it was found that using a catalyst having the first and second coatings according to the present invention can more effectively improve the yield of pyromellitic dianhydride than forming a single layer of catalytically active coating on the surface of the carrier in Test Example 1. Comparing Test Example 1 and Comparative Test Example 6, it was found that forming the first and second coatings on the surface of the carrier using the method of the present invention is effective in improving the yield of pyromellitic dianhydride.

[0109] Comparing Test Example 3, Test Example 4, and Test Example 5, it was found that controlling the mass ratio of the titanium content (calculated as Ti) to the vanadium content (calculated as V) in the first coating and the second coating within the range defined in the present invention can effectively improve catalytic activity and obtain significantly improved selectivity to pyromellitic dianhydride.

[0110] Comparing Test Example 5 with Test Comparative Example 3, it was found that when two stages of catalysts were packed into one reaction tube, the catalyst of the present invention could not only function at a higher durene concentration, but also improve the durene conversion rate and the selectivity to pyromellitic dianhydride.

Claims

1. A catalyst for the vapor phase oxidation of 1,2,4,5-tetraalkylbenzene, comprising: The present invention comprises a support and a catalytically active component coating carried on the support, the catalytically active component coating comprising a first coating and a second coating, the first coating being close to a surface of the support and the second coating being distant from the surface of the support, the first coating and the second coating each independently containing vanadium element and titanium element, and a mass ratio of titanium element calculated as Ti to vanadium element calculated as V in the first coating being Ti / V. １ the mass ratio of titanium element (calculated as Ti) to vanadium element (calculated as V) in the second coating is Ti / V ２ Then, Ti / V ２ = Ti / V １ +ΔTi / V, where ΔTi / V is in the range of 3 to 9; a mass ratio Ti / V 1 of titanium element in the first coating calculated as Ti to vanadium element in the first coating calculated as V is 7 to 8.5:1; a mass ratio Ti / V 2 of titanium element calculated as Ti in the second coating to vanadium element calculated as V in the second coating is 12 to 15.5:1; the content C Ti 1 of titanium element in the first coating calculated as Ti is within a range of 40 to 60 mass %, A catalyst in which the content C Ti 2 of titanium element in terms of Ti in the second coating is in the range of 45 to 65 mass %.

2. 2. The catalyst of claim 1, wherein the catalytically active component coating further contains at least one selected from the group consisting of a Group VA non-metal element, an alkali metal element, and an auxiliary metal element, and the auxiliary metal element is at least one selected from the group consisting of a rare earth element, a Group VIB element, a Group VIII element, a Group IIIA metal element, a Group VA metal element, and a Group IVB element other than titanium.

3. The catalytically active component coating further contains at least one selected from the group consisting of a Group VA non-metallic element, an alkali metal element, and an auxiliary metal element; the Group VA non-metal element is phosphorus; the alkali metal element is cesium, 2. The catalyst according to claim 1, wherein the auxiliary metal element is at least one selected from the group consisting of niobium, zirconium, and antimony.

4. The catalyst of claim 1 , wherein the second coating is deposited on a surface of the first coating.

5. The catalyst described in claim 4, wherein the first coating is adhered to the surface of the support.

6. 2. The catalyst of claim 1, wherein the total pore volume of the catalyst is 0.03 to 0.08 mL / g.

7. 2. The catalyst according to claim 1, wherein the support is at least one selected from the group consisting of alumina, talc, silicon carbide, aluminum silicate, quartz, and ceramics.

8. A method for preparing a catalyst for the vapor phase oxidation of 1,2,4,5-tetraalkylbenzene, comprising the steps of: (1) applying a first slurry containing a first dispersing medium, a first vanadium source, and a first titanium source to a surface of a support to form a first coating; (2) applying a second slurry containing a second dispersing medium, a second vanadium source, a second titanium source, and a pore expander onto the surface of the carrier on which the first coating has been formed to form a second coating; The mass of the vanadium source introduced into the first coating in terms of V is C Ｖ １２ , the mass of the titanium source introduced into the first coating in terms of Ti is C Ｔｉ １２ , the mass of the vanadium source introduced into the second coating in terms of V is C Ｖ ２２ , the mass of the titanium source introduced into the second coating in terms of Ti is C Ｔｉ ２２ Then, Ti / V １２ =C Ｔｉ １２ / C Ｖ １２ , Ti / V ２２ =C Ｔｉ ２２ / C Ｖ ２２ , Ti / V ２２ = Ti / V １２ +ΔTi / V ２ and ΔTi / V ２ is in the range of 3 to 9, the content C Ti 12 of the titanium source introduced into the first coating in terms of Ti is in the range of 40 to 60 mass %; the content C Ti 22 of the titanium source introduced into the second coating in terms of Ti is in the range of 45 to 65 mass %, The preparation method, wherein the pore expander is at least one selected from the group consisting of stearic acid and sodium stearate.

9. 9. The method of claim 8, wherein the first vanadium source and the second vanadium source are each independently at least one selected from the group consisting of ammonium metavanadate, vanadium pentoxide, and sodium vanadate.

10. The method described in claim 8, wherein the first titanium source and the second titanium source are each independently at least one selected from the group consisting of titanium dioxide and metatitanic acid.

11. The method described in claim 8, wherein the carrier is at least one selected from the group consisting of alumina, talc, silicon carbide, aluminum silicate, quartz, and ceramics.

12. The method according to any one of claims 8 to 11, wherein the weight ratio of the first coating, the second coating, and the carrier is 5.5-6.8:1.9-3.5:

100.

13. the first slurry further contains at least one compound selected from the group consisting of a compound containing a Group VA non-metallic element, a compound containing an alkali metal element, and a compound containing an auxiliary metal element, and the auxiliary metal element is at least one element selected from the group consisting of a rare earth element, a Group VIB element, a Group VIII element, a Group IIIA metal element, a Group VA metal element, and a Group IVB element other than titanium; the content of the compound containing a Group VA non-metallic element introduced into the first coating is 0.1 to 0.5 mass% in terms of element; the content of the compound containing an alkali metal element introduced into the first coating is 0.1 to 0.3 mass% in terms of the element; The method according to any one of claims 8 to 11, wherein the content of the compound containing the auxiliary metal element introduced into the first coating is 1 to 6 mass % in terms of oxide.

14. The first slurry further contains at least one compound selected from the group consisting of a compound containing a Group VA non-metallic element, a compound containing an alkali metal element, and a compound containing an auxiliary metal element; The method according to any one of claims 8 to 11, wherein the Group VA non-metallic element is phosphorus, the alkali metal element is cesium, and the auxiliary metal element is at least one element selected from the group consisting of niobium, zirconium, and antimony.

15. The compound containing a Group VA non-metallic element is at least one selected from the group consisting of ammonium dihydrogen phosphate, triammonium phosphate, and phosphorus pentoxide; The compound containing an alkali metal element is at least one selected from the group consisting of MNO 3 , M 2 SO 4 , MCl, and M 2 CO 3 , where M is an alkali metal element; The method according to claim 13, wherein the compound containing the auxiliary metal element is at least one selected from the group consisting of an oxide of the auxiliary metal and a water-soluble salt containing the auxiliary metal.

16. the second slurry further contains a compound containing an alkali metal element, a compound containing an auxiliary metal element, and a compound containing any Group VA non-metal element, the auxiliary metal element being at least one selected from the group consisting of rare earth elements, Group VIB elements, Group VIII elements, Group IIIA metal elements, Group VA metal elements, and Group IVB elements other than titanium; the content of the compound containing an alkali metal element introduced into the second coating is 0.1 to 0.7 mass% in terms of the element; The method according to any one of claims 8 to 11, wherein the content of the compound containing the auxiliary metal element introduced into the second coating is 1 to 6 mass % in terms of oxide.

17. The second slurry further contains a compound containing an alkali metal element, a compound containing an auxiliary metal element, and a compound containing any Group VA non-metal element; The method according to any one of claims 8 to 11, wherein the Group VA non-metallic element is phosphorus, the alkali metal element is cesium, and the auxiliary metal element is at least one selected from the group consisting of niobium, zirconium, and antimony.

18. The compound containing a Group VA non-metallic element is at least one selected from the group consisting of ammonium dihydrogen phosphate, triammonium phosphate, and phosphorus pentoxide; The compound containing an alkali metal element is at least one selected from the group consisting of MNO 3 , M 2 SO 4 , MCl, and M 2 CO 3 , where M is an alkali metal element; The method according to claim 16, wherein the compound containing the auxiliary metal element is at least one selected from the group consisting of an oxide of the auxiliary metal and a water-soluble salt containing the auxiliary metal.

19. The method according to any one of claims 8 to 11, wherein the content of the pore expander is 3.9 to 4.2 mass % based on the total amount of the second slurry.

20. The application temperature of the first slurry is higher than the application temperature of the second slurry; The application temperature of the first slurry is T １ , the application temperature of the second slurry is T ２ Then, T １ -T ２ is in the range of 70 to 150°C, The application temperature of the first slurry is 200 to 250°C, The application temperature of the second slurry is 100 to 130°C. The method according to any one of claims 8 to 11, wherein the method for forming the second coating comprises purging the second slurry applied to the surface of the carrier on which the first coating has been formed with a purge airflow, and the temperature of the purge airflow is 380 to 450°C.

21. Use of the catalyst according to any one of claims 1 to 7 as a catalyst for the reaction for preparing 1,2,4,5-benzenetetracarboxylic anhydride by oxidation of 1,2,4,5-tetraalkylbenzene.

22. 1. A process for preparing 1,2,4,5-benzenetetracarboxylic anhydride, comprising: A method for preparing 1,2,4,5-tetraalkylbenzene, comprising contacting a gas containing 1,2,4,5-tetraalkylbenzene and oxygen gas with the catalyst of any one of claims 1 to 7 to obtain a product stream containing 1,2,4,5-benzenetetracarboxylic acid anhydride.

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