Process for the manufacture of catalytically active multi-element oxides containing the elements molybdenum, tungsten, vanadium, copper and antimony

Abstract

A method for producing a catalytically active multi-element oxide containing the elements molybdenum, tungsten, vanadium, copper and antimony, wherein from at least one source each of the elements tungsten, molybdenum, vanadium, copper and antimony of the multi-element oxide an aqueous solution or an aqueous suspension is generated, a powder P is generated by drying the aqueous solution or the aqueous suspension obtained, optionally a geometric precursor shaped body is produced using the powder P obtained, and the powder P or the geometric precursor shaped body is subjected to a heat treatment to form the catalytically active multi-element oxide, characterized in that antimony pentoxide (V) Sb2O5 is used as a source of the element antimony.

Description

[0001] describe

[0002] This invention relates to a method for manufacturing catalytically active multi-element oxides containing molybdenum, tungsten, vanadium, copper, and antimony.

[0003] The present invention also relates to catalytically active multi-element oxides obtainable according to the invention, the use of these catalytically active multi-element oxides for catalyzing heterogeneous partial gas-phase oxides of acrolein to acrylic acid, the use of these catalytically active multi-element oxides for manufacturing shell catalysts particularly suitable for such catalysis, and shell catalysts obtainable according to the invention.

[0004] For example, multi-element oxides containing molybdenum, tungsten, vanadium, copper and antimony are known from WO 2021 / 213823, US 5,959,143, US 6,762,148, EP 0 711 745 A1 and EP 3488 926 A1.

[0005] It is known from WO 2021 / 213823 that copper acetate and antimony acetate are used as sources of copper and antimony for the manufacture of multi-element oxides.

[0006] It is known from EP 3 488 926 A1 that copper sulfate and antimony oxide are used as sources of elemental copper and antimony to manufacture multi-element oxides.

[0007] It is known from US 6,762,148 that copper sulfate and antimony acetate are used as sources of copper and antimony for the manufacture of multi-element oxides.

[0008] It is known from EP 0 711 745 A1 that copper nitrate or copper oxide and antimony oxide are used as sources of elemental copper and antimony to manufacture multi-element oxides.

[0009] The disadvantage of using multi-element oxides of WO 2021 / 213823, US 5,959,143, US 6,762,148, EP 0 711 745 A1 and EP 3488 926 A1 is low catalytic activity, which requires high temperatures during the reaction.

[0010] Therefore, the object of this invention is to provide an improved method for manufacturing catalytically active multi-element oxides containing molybdenum, tungsten, vanadium, copper, and antimony. The catalytically active multi-element oxides should, in particular, possess higher activity.

[0011] Therefore, a method is provided for manufacturing a catalytically active multi-element oxide containing molybdenum, tungsten, vanadium, copper, and antimony, wherein the proportions of these elements conform to the requirements of general formula (I).

[0012] Mo12 W a V b Cu c Sb d (I),

[0013] in

[0014] a = 0.4 to 3.0,

[0015] b = 1.0 to 6.0,

[0016] c = 0.1 to 3.0 and

[0017] d = 0.1 to 3.0

[0018] This means that the molar percentage of molybdenum in the total amount of all elements except oxygen is between 5 molar percentage and 95 molar percentage, of which

[0019] a) An aqueous solution or aqueous suspension is prepared from at least one of the elemental components of the multi-element oxide: tungsten, molybdenum, vanadium, copper, and antimony.

[0020] b) Powder P is produced by drying the aqueous solution or aqueous suspension obtained in a) and optionally pulverizing it.

[0021] c) Optionally, using the powder P obtained in b), and optionally with the addition of one or more molding aids, after uniform mixing, a geometric precursor molded body is produced from the resulting mixture, and

[0022] d) Heat-treat the powder P obtained in b) or the geometric precursor obtained in c) to form a catalytically active multi-element oxide.

[0023] Its characteristic is that antimony oxide (V)Sb2O5 is used as the source of the elemental composition antimony.

[0024] In general formula (I), the stoichiometric coefficient α of tungsten is preferably 0.6 to 2.5, particularly preferably 0.8 to 2.0, and even more particularly preferably 1.0 to 1.6.

[0025] In general formula (I), the stoichiometric coefficient b of vanadium is preferably 1.5 to 5.5, particularly preferably 2.0 to 5.0, and even more particularly preferably 2.5 to 4.5.

[0026] Copper increases the selectivity for acrylic acid (reduces the selectivity for carbon oxides, i.e., reduces the total amount of combustion), and the activity reaches its maximum.

[0027] In general formula (I), the stoichiometric coefficient c of copper is preferably 0.4 to 2.5, particularly preferably 0.6 to 2.0, and even more particularly preferably 0.8 to 1.5.

[0028] Antimony enhances the long-term stability of catalytically active multi-element oxides.

[0029] In general formula (I), the stoichiometric coefficient d of antimony is preferably 0.2 to 1.5, particularly preferably 0.25 to 1.2, and even more particularly preferably 0.3 to 0.8.

[0030] The aqueous suspension is preferably used as a source of antimony. The aqueous suspension preferably contains Sb₂O₅ particles, particularly nanoparticles. The average particle size of the Sb₂O₅ particles in the suspension is preferably 1 nm to 100 nm, more preferably 2 nm to 85 nm, more preferably 3 nm to 70 nm, particularly preferably 4 nm to 55 nm, and especially preferably 5 nm to 40 nm. The average particle size is the volume average particle size, which can be determined by light scattering. Preferably, the aqueous suspension also contains at least one base, particularly for stabilizing the Sb₂O₅ particles. The base is preferably an amine, particularly a tertiary amine. The pH of the Sb₂O₅ aqueous suspension is preferably 2 to 10, more preferably 3 to 9, particularly preferably 4 to 8, and especially preferably 5 to 7. The Sb₂O₅ aqueous suspension preferably contains 5 to 70% by weight of Sb₂O₅, preferably 10 to 65% by weight, more preferably 15 to 60% by weight, and especially preferably 20 to 55% by weight, in each case based on the total mass of the suspension.

[0031] Preferably, the aqueous suspension containing antimony is substantially free of alkali metal ions, especially sodium. The molar ratio of antimony to alkali metal in the aqueous suspension is preferably 1:1, more preferably 1:5, and even more preferably 1:10.

[0032] Of the total amount of all elements except oxygen, the molar percentage of molybdenum is preferably 20 to 90 moles, particularly preferably 35 to 85 moles, and even more particularly preferably 50 to 80 moles.

[0033] In the method according to the invention, a catalytically active multi-element oxide is manufactured by generating an aqueous solution or aqueous suspension from suitable sources of the elemental components molybdenum, tungsten, vanadium, copper and antimony.

[0034] Suitable sources of copper for preparing the elemental oxides according to the invention are, in particular, copper(II) sulfate pentahydrate, copper(II) nitrate hydrate (copper content = 26.1% by weight) and copper(II) acetate monohydrate (Cu(CH3COO)2H2O), wherein the latter is preferred.

[0035] Surprisingly, it was found that the activity of the catalytically active multi-component oxide was significantly increased when antimony oxide (V)Sb2O5 was used as the source of elemental antimony compared to other sources.

[0036] First, in a), an aqueous solution or aqueous suspension is prepared from at least one of the elemental components tungsten, molybdenum, vanadium, copper, and antimony.

[0037] Step a) is preferably divided into two sub-steps a1) and a2), wherein, in a1), the aqueous solution or aqueous suspension is first generated from at least one source of the elemental components of the multi-element oxide, namely tungsten, molybdenum, and vanadium, and then in a2), the aqueous solution or aqueous suspension obtained in a1) is mixed with a source of the elemental components of the multi-element oxide, namely copper and antimony. This preferred embodiment of the method is described in detail below.

[0038] The temperature of the aqueous solution or suspension in a1) is preferably 60°C to 130°C, particularly preferably 70°C to 120°C, and even more preferably 75°C to 110°C. The solution or suspension may be preheated or heated after the source of the elemental component tungsten is added. The addition time is not limited. The order in which the sources of the elements tungsten, molybdenum, and vanadium are added is not limited. Advantageously, in a1), the source of the elemental component tungsten is metered first, then the source of the elemental component molybdenum, and finally the source of the elemental component vanadium. Preferably, the aqueous solution is prepared in a1). The pH value is preferably 3 to 8, particularly preferably 4 to 7, and even more particularly preferably 5 to 7.

[0039] The addition can be carried out under standard pressure, vacuum, or overpressure. The pressure is preferably 0.5 bar to 2 bar, particularly preferably 0.8 bar to 1.2 bar, and even more particularly preferably 0.9 bar to 1.1 bar. During dissolution or suspension, the solution or suspension is advantageously stirred or circulated. Preferably, after the addition of the sources of the elemental components tungsten, molybdenum, and vanadium and before the addition of the next source, the solution or suspension is stirred for 1 minute to 180 minutes, more preferably 2 minutes to 120 minutes, particularly preferably 3 minutes to 60 minutes, and even more particularly preferably 5 minutes to 30 minutes.

[0040] Next, in a2), the source of the elemental components copper and antimony is added to the aqueous solution or aqueous suspension obtained in a1). The order of addition is not limited. Advantageously, the source of the elemental component antimony is first measured in a2). Preferably, the aqueous suspension is prepared in a2).

[0041] The source of the elemental components antimony and / or copper is preferably added as a solid, an aqueous solution or an aqueous suspension.

[0042] The temperature of the aqueous solution or suspension in a2) is preferably 60°C to 130°C, particularly preferably 70°C to 120°C, and even more preferably 75°C to 110°C. When adding the sources of elemental components copper and antimony in a2), the temperature of the aqueous solution or suspension should preferably be kept constant. The aqueous solution or suspension obtained in a) can be cooled or heated before addition. Addition can be carried out under standard pressure, vacuum, or overpressure. The pressure is preferably 0.5 bar to 2 bar, particularly preferably 0.8 bar to 1.2 bar, and even more preferably 0.9 bar to 1.1 bar. During dissolution or suspension, the solution or suspension is advantageously stirred or circulated. Preferably, after adding the source of elemental component antimony and before adding the source of elemental component copper, the solution or suspension is stirred for 1 minute to 300 minutes, more preferably 5 minutes to 180 minutes, particularly preferably 10 minutes to 120 minutes, and even more preferably 20 minutes to 90 minutes. Preferably, after adding the source of elemental copper, the solution or suspension is stirred for 1 minute to 180 minutes, more preferably 3 minutes to 120 minutes, particularly preferably 5 minutes to 90 minutes, and even more particularly preferably 10 minutes to 60 minutes. The pH value is preferably 3 to 8, particularly preferably 4 to 7, and even more particularly preferably 5 to 7.

[0043] Ammonium paratungstate heptahydrate is a preferred source of tungsten, ammonium heptamolybdate tetrahydrate is a preferred source of molybdenum, and ammonium metavanadate is a preferred source of vanadium.

[0044] Besides oxides, metal salts, polymetallic salts, halides, nitrates, formates, oxalates, acetates, carbonates, and hydroxides are also commonly considered sources of elemental composition.

[0045] If the solubility of the elemental component in the aqueous medium is insufficient to achieve the purpose of the method according to the invention, the pH of the aqueous medium can be appropriately altered, for example, by adding a corresponding regulator to improve the solubility of the elemental component in the aqueous medium. Suitable regulators are primarily considered to be Burgh's acids and bases that decompose into gaseous components under increased temperature, such as those used in heat-treated geometric precursor moldings to form the desired catalytically active multi-element oxides. Examples of such pH regulators include ammonium salts of ammonia, nitric acid, hydrochloric acid, acetic acid, formic acid, and strong and weak Burgh's acids, such as ammonium nitrate, ammonium chloride, ammonium carbonate, ammonium bicarbonate, ammonium acetate, ammonium formate, and ammonium oxalate.

[0046] Alternatively or additionally, water-soluble complexing agents may be added to the aqueous medium. These complexing agents, under increased temperature conditions, at least in the presence of molecular oxygen, decompose into gaseous compounds and / or escape as gaseous compounds, and can complex with elemental components present in ionic form at the source. This typically also leads to improved solubility in the aqueous medium. Examples of such complexing agents include ammonia and ethylenediaminetetraacetic acid and their salts, preferably water-soluble salts.

[0047] Using high temperature is another measure to improve solubility in aqueous media. Of course, within the framework of the method according to the present invention, more than one of the above methods can be used simultaneously to improve solubility in aqueous media.

[0048] In addition to the sources of molybdenum, tungsten, vanadium, copper and antimony, sources of other elements may be added to the method according to the invention, such as tantalum, chromium, cerium, nickel, cobalt, iron, manganese, zinc, niobium, bismuth, lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, silicon, aluminum, titanium and zirconium.

[0049] In b), powder P is produced by drying the aqueous solution or aqueous suspension obtained in a) and optionally pulverizing it.

[0050] In b), the aqueous solution or aqueous suspension obtained in a) is preferably spray-dried. Powder P can be directly generated by spray-drying the aqueous solution or aqueous suspension obtained in a).

[0051] In spray drying, an aqueous solution or suspension is selectively introduced into a hot gas stream, preferably a hot air stream, through a nozzle operated by liquid pressure, compressed air, or inert gas, or by a rotating atomizing disc, where it is broken into fine droplets. The hot gas stream dries the powder P into powder P within a fraction of a second. The hot gas stream can be substantially opposite to the jet direction (countercurrent) or preferably in the same direction (co-current). The spray tower can be operated with a directly or indirectly preheated gas stream. Directly heated gas streams are preferred, in which hot fuel gases generated by burning fuels such as methane are mixed with an additional air stream and propelled into the spray tower. Typical inlet temperatures of the hot gas stream are 250°C to 390°C, preferably 270°C to 380°C, and typical outlet temperatures are 90°C to 150°C. The heating loss of the produced powder P, calculated by its total weight, is preferably 5% to 35% by weight, particularly preferably 15% to 25% by weight. The heating loss is determined by the weight loss when heat-treated in air at 400°C for 3 hours.

[0052] The powder P typically has a relatively uniform particle diameter.

[0053] During the journey from the production site to the spray drying apparatus, the aqueous solution or suspension to be spray-dried is advantageously guided through at least one filter to separate any coarse particles that may be present, such as those that could clog the nozzles, before entering the spray drying apparatus. The temperature of the delivery line is specifically maintained at the final value of the production temperature of the aqueous solution or suspension. The temperature is preferably 60°C to 130°C, particularly preferably 70°C to 120°C, and even more preferably 75°C to 110°C. The respective residual solutions or suspensions that have not yet been spray-dried are advantageously and continuously mixed by stirring. The residence time in the container (= average residence time of the aqueous solution / suspension in the container divided by the average addition rate of the solution / suspension in the spray dryer) is preferably 0.1 h to 30 h, particularly preferably 0.5 h to 15 h, and even more particularly preferably 1 h to 5 h.

[0054] In large-scale production, aqueous solutions or suspensions requiring spray drying are typically generated in stirred vessels made of type 1.4541 stainless steel (DIN EN 10020). The spray drying equipment and agitator are specifically made of the same material.

[0055] The powder P obtained in b) can be directly heat-treated (also known as calcination) in d) to form a catalytically active multi-element oxide. Alternatively, a geometric precursor can be fabricated in c) first.

[0056] In the method according to the invention, different variations of the method can be used to produce heat-treated geometric precursor molded bodies from powder P.

[0057] In a simplified embodiment of the method according to the invention, a geometric precursor molded body of any desired geometry is formed directly from powder P by compression, such as compression polymerization or tableting (e.g., as exemplarily described for comparable powdered mixtures in documents DE 10 2008 054586A, DE 10 2008 040093 A, and DE 10 2008 040094 A). Typical precursor molded body geometries according to the invention include spheres (whose diameter can be, for example, 2 mm to 10 mm) and solid cylinders or hollow cylinders (rings) with an outer diameter and length typically 2 mm to 10 mm. If it is a hollow cylinder, the wall thickness is specifically 1 mm to 3 mm.

[0058] Of course, additives (molding aids) for subsequent molding can also be incorporated into powder P. Lubricants or slurries, such as graphite, carbon black, polyethylene glycol, stearic acid, stearates, starch, polyacrylic acid, mineral oil, vegetable oil, water, boron nitride, boron trifluoride, glycerin, fine polytetrafluoroethylene powder, and / or cellulose ethers, can be considered as such additives.

[0059] The aforementioned lubricant can be partially or completely decomposed and / or chemically transformed within the heat treatment framework of the geometric precursor molding body, as necessary, to form gaseous escaping substances.

[0060] As a further molding aid, the mixture to be compressed may contain added so-called reinforcing agents that promote cohesion in the resulting geometric precursor molded body. Such reinforcing agents may, for example, be microfibers made of glass, asbestos, silicon carbide, and / or potassium titanate.

[0061] Unlike lubricants, in the framework of heat treatment of geometric precursor molded bodies according to the present invention, reinforcing agents generally remain essentially intact.

[0062] Of course, lubricants and reinforcing agents can also be mixed together.

[0063] For the total amount of the powdered mixture to be compressed into a precursor molded body according to the present invention, the total amount of molding aids contained is generally no more than 30% by weight, mostly no more than 20% by weight, and in many cases no more than 10% by weight (but generally at least 0.1% by weight, or at least 0.2% by weight, or at least 0.5% by weight, or at least 1% by weight).

[0064] When generating a geometric precursor, it is preferable to shape it by kneading powder and liquid and extruding a plastically formable blank (the resulting kneaded mixture, the resulting kneaded blank).

[0065] For example, EP 3 805 194 A1 uses an advantageous method of kneading, squeezing and drying.

[0066] If molding is carried out during the process of producing a geometric precursor molded body by extrusion or extrusion molding, it is advantageous to incorporate at least one liquid (liquid binder). This liquid is preferably water, an aqueous solution, and / or a component of an aqueous solution. Advantageously, lower (C2 to C5) organic carboxylic acids (e.g., formic acid, acetic acid (preferably), propionic acid, fumaric acid, and / or maleic acid, or their respective aqueous solutions and / or components of such aqueous solutions) are incorporated as at least one of the above-mentioned liquid molding aids.

[0067] Calculated as pure lower organic carboxylic acids, these organic carboxylic acids (preferably acetic acid) are advantageously incorporated in a total amount of 5 to 15 wt%, depending on the content of powder P in the total mixture. The total water content of the resulting mixture can be from 5 to 45 wt%, preferably from 10 to 30 wt%. The water content is preferably adjusted so that the resulting plastically moldable preform has good formability to ensure advantageous molding by extrusion. Too low a liquid content may result in a hard plastic preform with very high viscosity. Conversely, too high a liquid content may result in an insufficiently moldable preform with low viscosity.

[0068] One or more lower organic carboxylic acids (preferably acetic acid) and / or their aqueous solutions are selectively incorporated by kneading and made as uniformly as possible. The temperature during kneading typically does not exceed 50°C. Typically, the above temperature is between 20°C and 50°C, and specifically between 30°C and 40°C. The kneading time is preferably less than 12 hours, particularly preferably between 10 minutes and 360 minutes, and even more preferably between 20 minutes and 120 minutes.

[0069] The resulting malleable preform (the resulting kneaded material, the resulting kneaded preform) is then extruded into a shape of the desired geometry (precursor shape). In the simplest case, these shapes can be twisted shapes (solid cylinders). Of course, according to the invention, rings are also considered possible extrusions.

[0070] In the case of geometric precursor molded articles produced by extrusion, their heat treatment includes drying. Drying is typically carried out at temperatures below 200°C, preferably up to 150°C, but usually at temperatures of at least 60°C, at least 80°C, or at least 100°C. Drying can be carried out in air, dry air, or a nitrogen atmosphere.

[0071] Based on its total weight, the resulting heat loss of the precursor molding is specifically between 5% and 35% by weight, and particularly between 15% and 25% by weight. The heat loss is determined by the weight loss after heat treatment in air at 400°C for 3 hours.

[0072] Next, the powder P generated in b) or the precursor formed in c) is heat-treated to form a catalytically active multi-element oxide (also known as calcination).

[0073] Calcination is carried out at a final temperature of 200°C to 600°C, preferably 300°C to 500°C, particularly preferably 350°C to 450°C, and even more particularly preferably 360°C to 430°C (the material temperature in each case). In particular, during the calcination process, according to the invention, the material advantageously has the most uniform temperature possible.

[0074] Calcination can be carried out discontinuously or continuously.

[0075] In discontinuous calcination, a temperature program with one or more temperature plateaus can be used, as described in EP 1 633467 A. The heating rate is preferably from 0.1 K / min to 20 K / min, particularly preferably from 0.5 K / min to 10 K / min, and even more particularly preferably from 1 K / min to 5 K / min.

[0076] During continuous calcination, the material passes through the furnace. Calcination can be carried out isothermally, or it can be carried out using different temperature zones, as described in EP 1 322 585 A. The temperature of the first temperature zone is preferably at least 30°C lower than the highest temperature of the other temperature zones.

[0077] Calcination can be performed while the powder P or precursor molded body is stationary or in motion. Precursor molded body calcination is preferably performed during motion filling. Suitable apparatus includes the rotary kiln described in EP 1 633 467 A or the belt calcination furnace described in EP 1 322 585 A. The rotary kiln is preferred.

[0078] Heat treatment (especially calcination) of powder P or geometric precursor molded bodies can be carried out either in an inert gas and an oxidizing (gaseous) atmosphere such as air (or another mixture of inert gas and oxygen) or in a reducing atmosphere (e.g., a mixture of inert gas and reducing gases such as hydrogen, ammonia, carbon monoxide, methane and / or acrolein, or the aforementioned reducing gases themselves) (of course, the overall reducing atmosphere can also have a limited amount of molecular oxygen). The oxidizing (gaseous) atmosphere preferably contains 0.1 volume percent to 15 volume percent of molecular oxygen, particularly preferably 0.5 volume percent to 10 volume percent, and even more particularly preferably 1 volume percent to 8 volume percent. In addition to molecular oxygen, the preferred oxidizing (gaseous) atmosphere also contains inert gases such as nitrogen and water vapor. The water vapor content is preferably less than 20 volume percent, particularly preferably less than 10 volume percent. Oxygen contents above and below the above limits generally reduce the catalytic activity produced. However, heat treatment can also be carried out essentially under vacuum.

[0079] During calcination, uncontrolled heat generation may occur in the powder P or precursor mold, damaging the catalytically active multi-element oxide to be manufactured. When ammonium salts are used, ammonia may be released and combusted during calcination, for example, at temperatures between 150°C and 350°C. Uncontrolled heat generation can be limited through sufficient heat and gas exchange. However, the amount of material to be calcined, the quantity and composition of the atmosphere, and the temperature program can also be adjusted.

[0080] If the powder P or the geometric precursor is heat-treated in a gaseous atmosphere, the gaseous atmosphere can be either static or flowing.

[0081] Heat treatment (especially calcination) of powdered P or geometric precursor preforms can take up to 24 hours or longer in total. Heat treatment (especially calcination) typically takes from minutes to hours, for example, 0.5 to 10 hours, or 1 to 5 hours. Higher temperatures generally result in shorter heat treatment (especially calcination) times, and lower temperatures generally result in longer heat treatment (especially calcination) times. Within the framework of heat treatment of geometric precursor preforms (precursor blanks), high temperatures and long treatment times (especially calcination) generally reduce the specific surface area of ​​the resulting catalytically active multi-element oxides.

[0082] The BET specific surface area of ​​the catalytically active multi-element oxides obtained according to the present invention is typically 10 m². 2 / g to 32 m 2 / g, preferably 12 m 2 / g to 28 m 2 / g, preferably 14 m 2 / g to 26 m 2 / g, further preferably 16 m 2 / g to 24m 2 / g (determined by gas adsorption (N2) according to the Brunauer-Emmet-Teller (BET) method). For instructions on the BET determination method, please refer to DIN ISO 9277 and J. Am. Chem. Bulletin of the American Chemical Society. 60 Volume 2, Issue 2, pp. 309-319 (1938).

[0083] The heat treatment (especially calcination) of the geometric precursor is preferably carried out in a gaseous atmosphere containing oxygen and ammonia. Ammonia can be generated from the precursor by adding a suitable amount of ammonium ions to it.

[0084] The catalytic activity of multi-element oxides produced during heat treatment is usually optimal depending on the oxygen content in the calcination atmosphere.

[0085] For example, WO 2004 / 108284, EP 0 724 481 A, WO 2008 / 104577, WO 2004 / 108267 and WO95 / 11081 disclose suitable calcination methods according to the present invention.

[0086] The geometric catalyst molded body that appears (generated) within the framework of heat treatment of the geometric precursor molded body can serve as such a geometric catalyst molded body in a catalyst fixed bed (as a so-called fully active catalyst) for the heterogeneous partial gas phase oxide of acrolein to acrylic acid.

[0087] According to the present invention, a suitable geometry for the fully active catalyst is, for example, a solid or hollow cylinder with an outer diameter and length of 2 mm to 10 mm. If it is a hollow cylinder, the wall thickness is specifically 1 mm to 3 mm. Of course, the fully active catalyst can also have a spherical geometry, wherein the diameter of the sphere can be 2 mm to 10 mm.

[0088] The geometrically shaped catalysts obtained according to the method of the invention (catalytically active multi-element oxides obtained according to the invention; catalysts obtained according to the invention), especially if their geometry is not particularly uniform during their formation, can also be converted into fine-grained shapes (e.g., crushed into powder or fragments) for the heterogeneous catalytic partial oxides of acrolein to acrylic acid (also in a fluidized bed or moving bed).

[0089] However, according to the invention, it is particularly advantageous to convert the catalytically active multi-element oxide into a fine-particle shape (e.g., crushed into powder or fragments, for example by grinding), and to apply this fine-particle shape (to obtain a so-called shell catalyst) as a shell from the catalytically active multi-element oxide onto the outer surface of the geometrically shaped body.

[0090] Application is typically carried out with the aid of a liquid binder. The liquid binder, acting as an adhesive, binds the fine, catalytically active multi-element oxides to the outer surface of the geometrically shaped support. The adhesive is then at least partially removed from the applied geometrically shaped support (e.g., by conduction of hot gas, as described in WO 2006 / 094766). The residual water content of the resulting catalyst is preferably no more than 1.0% by weight, particularly preferably no more than 0.5% by weight, and even more particularly preferably no more than 0.2% by weight, depending on the total mass of the catalyst.

[0091] Low residual moisture content is advantageous. Typically, the aforementioned residual moisture content is at least 0.5% by weight, and often at least 2% by weight. Information regarding residual moisture content in this literature generally refers to measurements performed using an HB43 moisture analyzer from Mettler Toledo AG Laboratory & Weighing Technologies, located at Lake Griffin (CH-8606). For this purpose, approximately 5 g of catalyst was heated to 120°C over approximately 50 seconds using infrared radiation and maintained at this temperature. The measurement was terminated when the weight loss was less than 1 mg within 20 seconds.

[0092] Specifically, alumina, silica, silicates such as clay, kaolin, talc (preferably C-220 talc from Ceram Tec (Germany), or preferably with a small amount of water-soluble alkali), pumice, aluminum silicate, magnesium silicate, silicon carbide, and zirconium dioxide are considered as materials for geometrically shaped carriers. Specifically, the geometrically shaped carriers are largely inert in the relevant partial oxidation processes (i.e., when used only as "catalysts" for, for example, the corresponding heterogeneous partial gas-phase oxidation of acrolein to acrylic acid, they are largely inert, meaning they essentially do not cause any conversion of acrolein).

[0093] The outer surface of the geometric carrier molded body can be either smooth or rough. Advantageously, the outer surface of the geometric carrier molded body is rough, because increased surface roughness generally improves the adhesion of the applied catalytically active multi-element oxide.

[0094] In particular, a carrier molded body with a fragmented coating on its outer surface (the preferred geometric carrier molded body according to the present invention is a hollow cylinder with a fragmented coating on its outer surface) can be regarded as a geometric carrier molded body with obvious surface roughness.

[0095] Surface roughness R of the outer surface of the geometric carrier molding body Z Preferably, the surface roughness is between 30µm and 100µm, and particularly preferably between 50µm and 70µm (measured according to Table 1 of DIN 4768 using a Hommel tester for DIN-ISO surface measurement parameters from Hommelwerke). Particularly preferred are geometrically shaped carrier bodies with rough surfaces made of C220 talc from Ceram Tec (Germany).

[0096] The carrier material can be porous or non-porous. Preferably, the carrier material is non-porous (the total volume of the pores in the geometric carrier molded body advantageously does not exceed 1 volume percentage of the volume of each geometric carrier molded body).

[0097] The BET specific surface area (based on its unit mass) of the carrier material is preferably low, preferably less than 5, more preferably 3, particularly preferably 1, and even more particularly preferably 0.5 m². 2 / g.

[0098] The geometric carrier can be formed in a regular or irregular manner, with the regularly formed geometric carrier being the preferred option.

[0099] The longitudinal elongation of a geometric carrier molded body is typically between 1 mm and 10 mm (the longitudinal elongation is the longest direct line connecting two points on the outer surface of the carrier molded body).

[0100] Spheres or (solid) cylinders, particularly hollow cylinders (rings) or bell saddle rings, are preferred as the geometric carrier molding body. The beneficial diameter range for the carrier sphere is 1 mm to 6 mm. If a cylinder is used as the geometric carrier molding body, its length is preferably 2 mm to 10 mm, and its outer diameter is preferably 4 mm to 10 mm. If it is a ring, the wall thickness is typically also 1 mm to 4 mm. Hollow geometric carrier molding bodies with a length of 3 mm to 8 mm, an outer diameter of 4 mm to 8 mm, and a wall thickness of 1 mm to 2 mm are particularly preferred. Hollow cylinders with a geometry of 7 mm x 3 mm x 4 mm (outer diameter x length x inner diameter) and hollow cylinders with geometries of 6 mm x 6 mm x 4 mm, 7 mm x 7 mm x 5 mm, 8 mm x 8 mm x 6 mm, 7 mm x 7 mm x 4 mm, 6 mm x 6 mm x 3 mm, and 6.5 mm x 6.5 mm x 5 mm are examples of advantageous annular geometries for carrier molding bodies. Advantageous geometries for carrier molding bodies also include all (particularly all) carrier molding bodies disclosed in Research Publication Database No. 532036 in August 2008. Any annular carrier molding body disclosed therein (particularly annular carrier molding bodies with geometries of 7 mm x 4 mm x 3 mm or 6 mm x 6 mm x 4 mm) can also be used for the fabrication of the shell catalysts VS and ES disclosed in this document.

[0101] The thickness of the catalytically active multi-element oxide shell applied to the outer surface of a geometrically shaped support (particularly the aforementioned annular support, wherein its outer surface also includes the envelope of an annular cavity) is typically between 10 µm and 1000 µm. This shell thickness of the shell catalyst is preferably between 10 µm and 500 µm, particularly preferably between 100 µm and 500 µm, and even more particularly preferably between 200 µm and 450 µm.

[0102] Advantageously, the shell thickness of a single shell catalyst is made as uniform as possible. When manufacturing large batches of shell catalysts, the shell thickness on multiple individual shell catalyst rings is also made as uniform as possible. Specifically, the aforementioned shell thickness uniformity is generally within the specifications described in the examples of DE 103 60 058 A.

[0103] Fine catalytically active multi-element oxides can be applied to the outer surface of a geometrically shaped body, for example, by first wetting the outer surface with a liquid binder in a controlled manner (e.g., spraying). By contacting the geometrically shaped body, which has been wetted in this manner, with the fine catalytically active multi-element oxides, an active preform layer is subsequently adhered to the wetted surface (e.g., by sprinkling the wetted geometrically shaped body with fine catalytically active multi-element oxides (with active preform powder) as described in EP 0 714 700 A).

[0104] The term "controlled wetting" here refers to properly wetting the carrier surface so that it absorbs the liquid binder, but without the appearance of a visible liquid phase on the carrier surface. If the carrier surface is too wet, the fine catalytically active multi-element oxides will aggregate into individual aggregates instead of being arranged on the surface. For more information, please refer to DE29 09 671 A, DE 100 51 419 A, EP 0 714 700 A, and WO 2022 / 090019 A1. This process can also be repeated periodically to achieve greater layer thickness. In this case, the coated substrate becomes a new "carrier body," etc.

[0105] However, all other application methods of the prior art recognized in EP 0 714 700 A can also be used to manufacture the aforementioned shell catalyst.

[0106] For example, solutions of water, organic solvents, or organic substances (e.g., organic solvents) in water, in organic solvents, or in aqueous solutions of organic solvents are all considered liquid adhesives. Examples of organic adhesives include mono- or poly-organic alcohols, such as ethylene glycol, 1,4-butanediol, 1,6-hexanediol, or glycerol; mono- or poly-organic carboxylic acids, such as propionic acid, oxalic acid, malonic acid, glutaric acid, or maleic acid; amino alcohols, such as ethanolamine or diethanolamine; and mono- or poly-organic amides, such as formamide. Monosaccharides and oligosaccharides, such as glucose, fructose, sucrose, and / or lactose, are suitable as suitable organic adhesive components (adhesive accelerators) soluble in water, organic liquids, or mixtures of water and organic liquids.

[0107] Particularly advantageously, solutions consisting of 20 to 90 wt% water and 10 to 80 wt% organic compounds are used as liquid binders. The organic content of the aforementioned liquid binder is preferably 10 to 50 wt%, particularly preferably 20 to 30 wt%. Solutions consisting of 20 to 90 wt% water and 10 to 80 wt% glycerol are further particularly preferred liquid binders. Advantageously, the glycerol content in these aqueous solutions is 10 to 50 wt%, particularly preferably 20 to 30 wt%. The main advantage of these preferred binders is that they are able to wet fine catalytically active multi-element oxides (or fine precursor preforms (see below)) and the outer surface of the geometrically shaped carrier in a completely satisfactory manner.

[0108] The fineness of the fine catalytically active multi-element oxide (or its precursor preform (see below)) applied to the outer surface of the geometrically shaped carrier must, of course, be matched to the desired shell thickness. This active preform powder is suitable for shell thicknesses ranging from 100 µm to 500 µm, wherein preferably at least 50% of the total number of granular powder particles pass through a sieve with an aperture size (circular sieve) of 1 µm to 20 µm or alternatively 1 µm to 10 µm, and the proportion of particles with a longitudinal elongation exceeding 50 µm (particles that no longer pass through a sieve with an aperture size (circular sieve) of 50 µm) is less than 10% by weight. Furthermore, the content described on page 18 of WO 2005 / 120702 also applies accordingly.

[0109] Preferably, the shell catalyst obtainable in the manner described is produced according to the manufacturing method described and exemplified in EP 0 714 700 A (see also examples in WO 2011 / 134932 and DE 103 60 057 A). An aqueous solution consisting of 75% by weight water and 25% by weight glycerol is preferred as a liquid binder. According to the invention, the heat treatment method for the geometric precursor molding is advantageously performed according to the method described and exemplified in DE 103 60 057 A.

[0110] However, the method according to the invention also includes methods for producing catalytically active multi-element oxides, in which a geometric precursor molded body is formed using a (fine) mixture of powder P and optionally one or more molding aids, such that the shell is applied directly from the (fine) mixture (of the fine precursor preform) to the outer surface of the geometrically supported molded body in the manner described in the application of the active preform shell. Within the framework of the geometrically supported molded body produced in this way by heat treatment (which also includes at least partial removal of the liquid binder also used for application), the shell catalyst according to the invention is obtained directly, wherein the shell of the catalytically active multi-element oxide is applied to the outer surface of the (catalytically substantially inert) geometrically supported molded body.

[0111] As previously stated, the catalytically active multi-element oxides obtained according to the present invention are particularly suitable for catalyzing the heterogeneous partial gas-phase oxides of acrolein to acrylic acid, as described in WO 2007 / 082827, WO 2004 / 085365, WO 2004 / 085367, WO 2004 / 085368, WO 2004 / 085369, WO 2004 / 085370, WO 2005 / 016861, WO 2005 / 047226 and WO 2005 / 042459. Here, they are characterized in particular by the long service life of the catalyst bed packed with them during partial oxidation, during which a highly active target product is formed. A preferred application form of the catalytically active multi-element oxides obtained according to the present invention is a shell catalyst, which preferably has a toroidal geometry. Particularly preferred is the exemplified shell catalyst used in the examples of this document, such as in all embodiments and comparative examples of WO documents WO 2007 / 082827, WO 2004 / 085365, WO 2004 / 085367, WO 2004 / 085368, WO 2004 / 085369, WO 2004 / 085370, WO 2005 / 016861, WO 2005 / 047226 and WO 2005 / 042459, which can replace the individual catalysts used therein (the content of the shell catalysts exemplified in this document described above also applies to the shell catalysts in the comparative examples of this document).

[0112] However, the catalytically active multi-element oxides obtained according to the present invention are also applicable to the catalytic conversion of heterogeneous partial gas-phase oxides of methacrolein to methacrylic acid in a correspondingly advantageous manner.

[0113] The above is particularly applicable when acrolein or methacrolein (hereinafter referred to as "(meth)acrylaldehyde") is heterogeneously catalyzed in a partial gas-phase oxidation to acrylic acid or methacrylic acid (hereinafter referred to as "(meth)acrylaldehyde") under high (meth)acrylaldehyde loadings, as described in DE 103 07 983 A, DE 199 48 523 A, DE 199 10 508 A, WO 2008 / 104577, WO2011 / 134932, DE 199 27 624 A and DE 103 60 057 A.

[0114] Heterogeneous catalytic partial gas-phase oxidation can be carried out in a manner known per se. That is, a reaction gas mixture containing (meth)acrylaldehyde, molecular oxygen, and at least one inert diluent gas is guided through a catalyst bed at an increased temperature. The catalyst bed, serving as the active preform, has at least one catalytically active multi-element oxide obtained according to the invention. During the residence of (meth)acrylaldehyde in the catalyst bed, (meth)acrylaldehyde reacts with (meth)acrylic acid. Preferably, a fixed catalyst bed is used. However, fluidized beds or moving beds are also generally used in the method according to the invention. Typically, using water vapor as a component of the reaction gas mixture improves selectivity and activity. Furthermore, inert diluent gases with increased molar specific heat, such as n-propane or carbon dioxide, are also advantageous. The gases involved here are those whose chemical change when the reaction gas mixture passes through the catalyst bed is preferably no more than 5 molar percentage, particularly preferably no more than 3 molar percentage, further particularly preferably no more than 1 molar percentage, or no chemical change at all.

[0115] The heat exchange reactor is particularly suitable for the gas-phase partial oxidation of (meth)acrolein. The heat exchange reactor has at least one main chamber and at least one auxiliary chamber, separated by a partition. A catalyst pack comprising at least one catalytically active multi-element oxide obtained according to the invention is placed in at least one main chamber, and a reaction gas mixture containing (meth)acrolein flows through this catalyst pack. Simultaneously, a fluid heat transfer medium flows through the auxiliary chamber, and heat exchange occurs between the two chambers through the partition. This heat exchange is designed to monitor and control the temperature of the reaction gas mixture as it passes through the catalyst bed.

[0116] Typically, the gas-phase partial oxidation of (meth)acrylaldehyde is carried out in a tube bundle (heat exchanger) reactor with one or more temperature zones, as described in EP 0 700 174 A, EP 0 700 893 A, DE 199 10 508 A, DE 199 48 523 A, DE 199 10 506 A, DE 199 48 241 A, DE 28 30 765 A, DE 25 13 405 A, US 3,147,084, DE22 01 428 A, EP 0 383 224 A, JP 2007-260588 and JP S58-096041.

[0117] The catalyst fixed bed is located in the metal tubes (contact tubes) of the tube bundle reactor in the form of a corresponding catalyst molded packing (optionally mixed with diluted inert geometric shapes). A temperature medium is directed around the metal tubes (in the case of more than one temperature zone, a corresponding number of spatially spaced, substantially separated temperature media are directed around the metal tubes). The temperature medium is typically a salt melt. The reactant gas mixture is directed through the contact tubes.

[0118] Alternatively, the catalyst fixed bed can also be located in the gaps between the heat-transfer medium flowing in the heat-shelf reactor, as suggested in DE 10 2004 017 150 A, DE 199 52 964 A and DE 103 61 456 A.

[0119] As previously stated, a catalyst fixed bed can generally only consist of a catalyst obtained according to the present invention, but it can also consist of a catalyst diluted with an inert geometric shape. The geometric support shape (support body) used to manufacture the shell catalyst according to the present invention can be used herein as an inert geometric shape. Pure inert shape filler can be located in front of and / or behind the catalyst fixed bed (such pure inert shape filler is typically not included in the calculation of the reaction gas or reaction gas component loading of the catalyst fixed bed).

[0120] The contact tubes used in tube bundle reactors are typically made of ferritic steel and have a wall thickness of 1 mm to 3 mm. Their inner diameter is typically 20 mm to 30 mm, often 21 mm to 29 mm or 23 to 28 mm. Their length is typically 2 m to 4 m.

[0121] Specifically, the number of contact tubes installed in the tube bundle vessel is at least 5,000, preferably at least 10,000. The number of contact tubes installed in the reaction vessel is typically between 15,000 and 40,000. Tube bundle reactors with more than 50,000 contact tubes are an exception. Under normal circumstances, the contact tubes are arranged in a uniformly distributed manner within the vessel (preferably 6 equidistant adjacent tubes per contact tube), wherein this distribution is specifically selected such that the distance between the central inner axes of the nearest contact tubes (the so-called contact tube spacing) is 35 mm to 45 mm (see, for example, EP 0 468 290 A) .

[0122] Using melts of salts such as potassium nitrate, potassium nitrite, sodium nitrite, and / or sodium nitrate, or alloys of low-melting-point metals such as sodium and mercury, and various metals, as heat exchange media in tube bundle reactors is particularly beneficial.

[0123] If the tube bundle reactor is operated with a (meth)acrylaldehyde loading on the catalyst pack at a loading of at least 90 NI / l•h, or at least 110 NI / l•h, or at least 130 NI / l•h, or at least 150 NI / l•h, or at least 160 NI / l•h, or at least 170 NI / l•h, or at least 180 NI / l•h, or at least 200 NI / l•h, or at least 220 NI / l•h, or at least 240 NI / l•h, or at least 260 NI / l•h, then it is particularly advantageous to load the catalyst obtained according to the invention, especially the catalyst exemplarily implemented in the examples and comparative examples of this document, into the contact tubes of the tube bundle reactor. Of course, such catalyst loading is also advantageous for smaller (e.g., not exceeding 130 NI / l•h, or not exceeding 100 NI / l•h, or not exceeding 80 NI / l•h, or not exceeding 60 NI / l•h) (meth)acrylonitrile loadings.

[0124] In this literature, the reaction gas inlet mixture load of the catalyst fixed bed is understood as the quantity of the reaction gas inlet mixture in standard liters (= Nl; under normal conditions, i.e., at 0°C and 101.3 kPa, the corresponding volume of gas), based on the packing volume of the catalyst fixed bed (the packing portion made of purely inert material is not included in the packing volume here; furthermore, the packing volume is the volume of voids occupied by the packing (or its related packing portion), i.e., based on its packing volume, the quantity supplied to the catalyst fixed bed per hour (-> unit = Nl / l·h).

[0125] The loading can also be based on only one component of the reactant gas inlet mixture (e.g., only on the organic starting compound to be partially oxidized). It is then supplied to the catalyst fixed bed per hour in the volume of that component (e.g., the organic starting compound of the partially oxidized compound) in standard liters, based on the packing volume of the catalyst fixed bed (the packing portion made of purely inert material is not included in the packing volume here; moreover, the packing volume is the volume of voids occupied by the packing (or its associated packing portion)). (-> Unit = Nl / l·h)

[0126] The volumetric activity of a fixed catalyst bed is typically designed to increase in the direction of the reactant gas flow.

[0127] This can be easily achieved by designing to reduce the dilution of the catalyst bed by the inert molded body in the direction of the reactant gas flow. Alternatively, the volumetric activity can be adjusted by using catalysts with different BET specific surface areas. Shell catalysts with different pore volumes or shell thicknesses can also be used. The activity here increases with increasing BET specific surface area, pore volume, or shell thickness.

[0128] Furthermore, heterogeneous catalytic partial oxidation using the shell catalyst obtained according to the invention can generally be carried out in all respects as implemented in DE103 50 822 A. The (meth)acrylaldehyde content in the reactant gas inlet mixture can be from 3 volume percent to 15 volume percent, typically from 3.5 volume percent to 10 volume percent, or from 4 volume percent to 8 volume percent (each depending on the total volume of the reactant gas inlet mixture).

[0129] The molar ratio of oxygen to (meth)acrylaldehyde in the reactant gas inlet mixture is typically at least 1. This ratio usually does not exceed 3. In many cases, the heterogeneous catalytic partial oxidation of (meth)acrylaldehyde to (meth)acrylic acid is carried out in a volume ratio (NI) of (meth)acrylaldehyde present in the reactant gas inlet mixture to oxygen, water vapor, and inert gas of 1:(1 to 3):(0 to 20):(3 to 30), preferably 1:(1 to 3):(0.5 to 10):(7 to 10).

[0130] Here, nitrogen, carbon dioxide, carbon monoxide, inert gases, propane, ethane, methane, butane, and / or pentane (i.e., each gas as the sole diluent gas or mixed with another or more of these inert diluent gases) are considered inert diluent gases (these are gases or mixtures of such gases whose chemical properties remain unchanged at least 95 mol%, preferably at least 97 mol%, or at least 99 mol%, and most preferably 100 mol%, when the reaction gas mixture passes through the catalyst bed (e.g., a fixed catalyst bed) once). The temperature for this heterogeneous catalytic partial oxidation of (meth)acrylaldehyde is typically in the range of 200°C to 400°C, commonly 220°C to 380°C, in many cases 230°C to 350°C, and frequently 245°C to 320°C. The operating pressure (absolute pressure) is typically 101.3 kPa to 350 kPa, or 101.3 kPa to 250 kPa, or 101.3 kPa to 205 kPa (particularly as the inlet pressure into the fixed catalyst bed). However, (meth)acrylonitrile can also be partially oxidized using the catalyst obtained according to the present invention at working pressures below atmospheric pressure.

[0131] Depending on the reaction gas mixture passing through the catalyst fixed bed once, the conversion of (meth)acrylaldehyde is typically at least 90 mol%, often at least 98 mol%, in many cases at least 98.5 mol%, and even at least 99 mol%.

[0132] Furthermore, the partial oxidation method according to the present invention can be implemented entirely in accordance with the recommendations of DE 10 2007 019 597 A or WO2008 / 104577 or WO 2011 / 134932.

[0133] In particular, heterogeneous catalytic partial oxidation of (meth)acrylaldehyde C3 / C4 precursor compounds (e.g., propylene or isobutylene) to (meth)acrylic acid, and the resulting (meth)acrylaldehyde-containing product gas mixture, can be used directly as a source of (meth)acrylaldehyde required for partial oxidation according to the present invention, without prior separation of (meth)acrylaldehyde from such product gas mixtures.

[0134] The separation of (meth)acrylic acid from a mixture of partially oxidized product gases can be carried out in a manner known per se, for example, by first converting (meth)acrylic acid into a condensate phase by absorption and / or condensation. (Meth)acrylic acid of any purity can then be separated from the condensate phase by subsequent thermal separation methods, such as rectification and / or crystallization (see DE602004924 T and WO 2006 / 114428 and the prior art cited in these documents).

[0135] Another object of the present invention is a catalytically active multi-element oxide containing molybdenum, tungsten, vanadium, copper and antimony, wherein the proportions of these elements conform to the requirements of general formula (I).

[0136] Mo 12 W a V b Cu c Sb d (I),

[0137] in

[0138] a = 0.4 to 3.0,

[0139] b = 1.0 to 6.0,

[0140] c = 0.1 to 3.0 and

[0141] d = 0.1 to 3.0

[0142] This means that the molar percentage of molybdenum in the total amount of all elements except oxygen is between 5 and 95 molar percentages, which can be obtained by one of the methods mentioned above.

[0143] The typical BET surface area of ​​catalytically active multi-element oxides is 10 m². 2 / g to 32 m 2 / g, preferably 12 m 2 / g to 28 m 2 / g, preferably 14 m 2 / g to 26 m 2 / g, further preferably 16 m 2 / g to 24 m 2 / g.

[0144] In general formula (I), the stoichiometric coefficient α of tungsten is preferably 0.6 to 2.5, particularly preferably 0.8 to 2.0, and even more particularly preferably 1.0 to 1.6.

[0145] In general formula (I), the stoichiometric coefficient b of vanadium is preferably 1.5 to 5.5, particularly preferably 2.0 to 5.0, and even more particularly preferably 2.5 to 4.5.

[0146] In general formula (I), the stoichiometric coefficient c of copper is preferably 0.4 to 2.5, particularly preferably 0.6 to 2.0, and even more particularly preferably 0.8 to 1.5.

[0147] In general formula (I), the stoichiometric coefficient d of antimony is preferably 0.2 to 1.5, particularly preferably 0.25 to 1.2, and even more particularly preferably 0.3 to 0.8.

[0148] Of the total amount of all elements except oxygen, the molar percentage of molybdenum is preferably 20 to 90 moles, particularly preferably 35 to 85 moles, and even more particularly preferably 50 to 80 moles.

[0149] Catalytically active multi-element oxides, such as those used to oxidize acrolein to acrylic acid, typically do not exist with all of their constituent metals in their maximum oxidation state. The maximum oxidation state of a metal refers to the oxidation state in which the element typically exists to the greatest extent in its oxide. The maximum oxidation states of relevant elements are V (V), Mo (VI), W (VI), Cu (II), and Sb (V).

[0150] For example, vanadium may not be in or completely in oxidation state V (V), but may be in oxidation state V (IV) or V (III) or a mixture of oxidation states. It is possible that some vanadium is in oxidation state V (V) and some is in oxidation state V (IV), or some is in oxidation state V (IV) and some is in oxidation state V (III).

[0151] Other metallic elements in mixed metal oxides can also exist in different oxidation states. Other relevant elements have oxidation states such as Cu(I), Mo(V), Mo(IV), and Sb(III).

[0152] Basically, discrete states are conceivable if relatively high electron mobility leads to non-discrete metal atoms that can be distinguished by different oxidation states.

[0153] This section does not intend to provide further theoretical explanations. Catalytically active multi-element oxides, after digestion in an aqueous solution, can be subjected to redox-titration analysis. KMnO4 is used as the oxidant for titration to quantitatively determine the content of oxidizable electrons. Therefore, powdered catalytically active multi-element oxides are used directly before being applied to the molded support.

[0154] During the oxidation of acrolein to acrylic acid, catalytically active multi-element oxides with a defined ratio R of oxidizable electrons to vanadium exhibit unique partitioning characteristics. The ratio R is...

[0155] R = e / CV,

[0156] Where e is the ratio of oxidizable electrons per gram [mol / g], and CV is the ratio of vanadium per gram [mol / g].

[0157] The ratio R is preferably 1.1 to 2.2, particularly preferably 1.2 to 2.1, and even more particularly preferably 1.3 to 2.0.

[0158] The steps for titration using KMnO4 as an oxidant are as follows:

[0159] Place 15 ml of 96% sulfuric acid, 15 ml of water, and 10 ml of 85% phosphoric acid into a long-necked flask on a heated stirring plate, and purge with air-free argon. Weigh 100 mg to 200 mg of the sample into the long-necked flask, rinse with water, and pour into the flask. Heat the flask to boiling point under an argon atmosphere until the solution volume is reduced to 40 ml and the sample is completely dissolved (approximately 30 to 45 minutes, depending on the required amount of water).

[0160] The solution was then transferred to a titration vessel equipped with a combined platinum electrode and potentiometer (e.g., 808 Titrando, Herisau Metrohm AG, Switzerland). Titration was performed under an argon atmosphere at 80°C. The sample was titrated with an aqueous solution of KMnO4 (0.02 mol / L) until a purple-red color was obtained (KMnO4 in excess). During the titration, the electrochemical potential was measured and recorded using the combined platinum electrode.

[0161] The titration curve should show a transition point. The absence of a transition point indicates the absence of oxidizable electrons. Read the volume of the KMnO4 aqueous solution at the endpoint from the titration curve.

[0162] The specific content e of oxidizable electrons is

[0163] e = (V * C * 5) / EW

[0164] Where V is the volume of the KMnO4 aqueous solution [l], C is the concentration of the KMnO4 aqueous solution [mol / l], and z is the weight of the sample [g].

[0165] In some cases, the titration curve may show multiple transition points. This means that electrons with different oxidation potentials are present. Two transition points may indicate the presence of V(III) and V(IV).

[0166] Another object of the present invention is a method for manufacturing a shell catalyst, wherein a catalytically active multi-element oxide according to the invention and an optional binder are applied to the outer surface of a geometrically shaped carrier.

[0167] Another object of the present invention is a shell catalyst, which consists of a geometrically shaped support body and a catalytically active multi-element oxide according to the present invention, and optionally a binder, applied to the outer surface of the geometrically shaped support body.

[0168] Another object of the present invention is a method for producing acrylic acid by gas-phase catalytic oxidation of acrolein in a catalyst fixed bed, wherein the catalyst fixed bed comprises a catalytically active multi-element oxide according to the present invention or a shell catalyst according to the present invention. Example

[0169] Example 1

[0170] Annular shell catalyst C1 with catalytically active oxidation preform

[0171] Mo 12 W 1。2 V3Cu 1.2 Sb 0。5 O n

[0172] Manufacturing shell catalysts:

[0173] While stirring (using a paddle stirrer at 250 rpm) at 95°C, add 3000 g of water to a 10 L flask containing 171 g of ammonium paratungstate heptahydrate (tungsten content = 70.65% by weight) and continue stirring for 5 minutes. A clear solution with a temperature of approximately 95°C and a pH of 6.3 is obtained.

[0174] Then, 1161 g of ammonium heptamolybdate tetrahydrate (molybdenum content = 54.3% by weight) was added, and stirring was continued for 5 minutes. A clear solution with a temperature of approximately 95°C and a pH of 6.1 was obtained.

[0175] Then, 192 g of ammonium metavanadate (vanadium content = 43.56% by weight) was added, and stirring was continued for 5 minutes. An orange solution with a temperature of approximately 95°C and a pH of 6.5 was obtained.

[0176] Then, 115 g of antimony pentoxide suspension (Sb₂O₅; Sb content = 29.1% by weight); NYACOL ® (A1538 of Nyacol Nano Technologies, Inc., Ashland, USA) and stirred for another 30 minutes. A black suspension with a temperature of approximately 95°C and a pH of 6.6 was obtained.

[0177] Subsequently, 131.4 g of copper(II) acetate monohydrate (Cu(CH3COO)2 H2O; copper content = 31.8% by weight) was added, and stirring was continued for 10 minutes. A black suspension with a temperature of approximately 95°C and a pH of 6.2 was obtained.

[0178] Finally, the obtained suspension was fed into a Mobile Minor 2000 spray tower (GEA Niro, Solborg, Denmark) equipped with an F0 A1 nozzle through a rotary atomizer at a speed of 30,000 revolutions per minute for approximately 2 hours. The hot airflow (9 Nm³) 3 The drying process is carried out at an inlet temperature of 310℃ and an outlet temperature of 120℃ ( / h). Powder is obtained.

[0179] 1468 g of powder was injected into a ZS1-80 kneader (Coperion Werner & Pfleiderer GmbH, Stuttgart, Germany). The powder was kneaded with 530 g of an aqueous acetic acid solution (acetic acid content 32% by weight) at 15 rpm for 40 minutes at ambient temperature. The material was then extruded (1 cm to 10 cm in length, 6 mm in diameter). The beam was dried in a circulating air drying oven at 120°C for 16 hours in a lean gas flow (5% oxygen by volume in nitrogen, 300 NL / h).

[0180] 400 g of precursor billet, removed from the circulating air drying oven, was subjected to discontinuous calcination in a rotary kiln (see US9,149,799 B2). Calcination was carried out in an air and nitrogen gas flow with an oxygen content of 2.3% by volume (total 186 NL / h). The rotary kiln was heated to 400°C over two hours and maintained at this temperature for one hour. The heating was then turned off, and the billet was cooled to ambient temperature while continuing to rotate.

[0181] The material taken from the rotary kiln is pulverized into a fine powder in a ZM 200 mill (Retsch GmbH, Germany).

[0182] Fine powder was used to coat 1600g of Steatit C 220 type (Ceram Tec GmbH, Prozingen, Germany) annular carrier body (outer diameter 7mm, length 3mm, inner diameter 4mm, surface roughness Rz 45µm, BET surface 0.035 μm). 2 / g). Coating was carried out in a Hi-Coater LHC 25 / 36 mixer (Gebrüder Lödige GmbH, Paderborn, Germany). This mixer was modified for continuous powder metering. For this purpose, a funnel-shaped container was connected to the mixer drum (36cm diameter) via a flexible hose (11.1mm outer diameter, 8mm inner diameter). During coating, 230g of fine powder was injected into the funnel-shaped container. Metering was performed using a pressure shock of 50ms and an overpressure of 0.7 bar. During metering, the contents of the funnel-shaped container were stirred using a modified V-type anchor stirrer (homemade). Stirring times were 2s each, followed by a 1s pause.

[0183] A 25% by weight aqueous solution of glycerol was used as the binder. The solution was metered into the mixer at a rate of 3 g / min using a 570 S75 dual-material nozzle (Düsen-Schlick GmbH, Coburg, Germany), while powder metering was performed simultaneously. The powder metering device was located 6 cm below the dual-material nozzle, tilted downwards at a 40° angle. Metering was performed outside the spray cone of the dual-material nozzle. The mixer drum rotated clockwise at 15 rpm. Coating was carried out at 25°C for 40 minutes. The rotation speed was then reduced to 2 rpm, and drying was performed at 130°C in an airflow (220 Nl / h) for 30 minutes. Cooling was then performed to 25°C. The powder was absorbed by the carrier surface. No twinning or aggregation was observed.

[0184] Subsequently, glycerin adhering to the coated carrier substrate was removed in a UM 400 circulating air drying oven (Memmert GmbH & Co. KG, Schwabach, Germany). The coated carrier substrate was uniformly distributed on a perforated plate with a layer thickness of 2 cm. The perforated plate thickness was 0.5 cm, the pore size ratio was 60%, and the area was 35 cm x 26 cm. The circulating air drying oven was heated to 300 °C at a rate of 3 K / min and maintained at this temperature for 2 hours. It was then cooled to 40 °C to 50 °C over 2 to 3 hours.

[0185] The oxidation-active preform ratio of the annular shell catalyst C1 is 10.7% by weight. The BET surface area of ​​the catalytically active multi-element oxide is 22.8 m² / g.

[0186] Research on shell catalysts :

[0187] The reaction tube (stainless steel (material 1.4541); outer diameter 30mm; wall thickness 2mm; inner diameter 26mm; length 464cm) is filled from top to bottom as follows:

[0188] Part 1: Length 80cm

[0189] Empty pipe:

[0190] Part 2: Length 60cm

[0191] Prefilled with talc rings (outer diameter × length × inner diameter; C220 talc from Ceram Tec) with a geometry of 7mm × 3mm × 4mm;

[0192] Part 3: Length 100cm

[0193] A catalyst fixed bed is filled with a homogeneous mixture consisting of 20% by weight talc rings (outer diameter × length × inner diameter; C220 talc from Ceram Tec) with a geometry of 7 mm × 3 mm × 4 mm and 80% by weight shell catalyst.

[0194] Part 4: Length 200cm

[0195] The catalyst fixed bed is filled with only the same shell catalyst as in part 3;

[0196] Part 5: Length 10cm

[0197] Refilling consisting of talc rings identical to those in part 2;

[0198] Part 6: Length 14cm

[0199] Stainless steel catalyst chair (material 1.4541) for accommodating a fixed catalyst bed.

[0200] A mixture of reactant gases having the following contents flows from top to bottom through the corresponding reaction tube loaded as described above:

[0201] 4.3% acrolein by volume

[0202] 0.3% by volume propylene

[0203] 0.2% by volume propane,

[0204] 0.3% by volume acrylic acid

[0205] 5.1 volume percentage of oxygen

[0206] 0.4% by volume carbon dioxide

[0207] 7% by volume water and

[0208] 82.3% nitrogen by volume

[0209] The feed temperature of the reaction gas mixture (at the inlet of the reaction tube) is 210 °C, and the acrolein loading of the catalyst solid bed (defined in DE199 27 624 A) is 80 Nl / lh.

[0210] The reaction tube, excluding the last 10 cm of empty tube in section 1 and the last 3 cm of empty tube in section 6, is surrounded by an externally heated, stirred salt bath (a mixture of 53% potassium nitrate, 40% sodium nitrite, 7% sodium nitrate, and 50 kg of molten salt) at a flow velocity of 3 m / s at the tube. The salt bath temperature TB supplied is adjusted in all cases to achieve a 99.3 mol% acrolein conversion based on a single pass of the reaction gas mixture through the catalyst fixed bed. The salt bath temperature does not change along the reaction tube due to additional heating (the heat radiated from the salt bath is greater than the heat transferred from the reaction tube to the salt bath).

[0211] In this literature, the selectivity of acrylic acid formation (S) AS (Mole percentage) is understood as:

[0212]

[0213] The selectivity of nitrogen oxide formation (total combustion) is calculated using a similar method.

[0214] At lower temperatures and with unchanged reaction conditions, the main active preform (main catalyst) that yields the same conversion rate has higher activity.

[0215] In this literature, the conversion rate of acrolein (U AC (Mole percentage) is understood as:

[0216]

[0217] Table 1 below shows the results obtained after 100 hours of operation, depending on the shell catalyst used:

[0218] Example 2 (Comparative Example)

[0219] Annular shell catalyst C2 with catalytically active oxidation preform

[0220] Mo 12 W 1.2 V3Cu 1.2 Sb 0.5 O n

[0221] The procedure was performed as in Example 1. 39.9 g of antimony(III) oxide (Sb₂O₃; Sb content = 83.5%) was used instead of antimony(V) as the antimony source. The oxidation-active preform ratio of the annular shell catalyst C₂ was 10.22 wt%. The BET surface area of ​​the catalytically active multi-element oxide was 15.9 m² / g.

[0222] Example 3 (Comparative Example)

[0223] Annular shell catalyst C3 with catalytically active oxidation preform

[0224] Mo 12 W 1.2 V3Cu 1.2 Sb 0.5 O n

[0225] The procedure was performed as in Example 1. 77.5 g of antimony acetate (III) (Sb(CH3COO)3; antimony content = 43 wt%) was used instead of antimony oxide (V) as the source of antimony. The oxidation-active preform ratio of the annular shell catalyst C3 was 10.1 wt%. The BET surface area of ​​the catalytically active multi-element oxide was 15.9 m² / g.

[0226] Table 1. Experimental Results

[0227]

[0228] *) Not based on the present invention

[0229] TB [°C] Salt bath temperature

[0230] U AC [%] Acrolein Conversion Rate

[0231] S AS [mol%] Selectivity for acrylic acid

[0232] Y AS [mol%] Acrylic acid yield

[0233] The experimental results shown in Table 1 indicate that the salt bath temperature TB required for the acrolein conversion to reach 99.3 mol% according to Example 1 of the present invention is significantly lower than that of the comparative example, thus the catalyst according to the present invention exhibits higher activity. This is even more surprising given that these catalysts have the same composition.

Claims

1. A method for manufacturing a catalytically active multi-element oxide containing molybdenum, tungsten, vanadium, copper, and antimony, wherein the proportions of these elements conform to the requirements of general formula (I). Mo 12 W a V b Cu c Sb d (I), in a = 0.4 to 3.0, b = 1.0 to 6.0, c = 0.1 to 3.0 and d = 0.1 to 3.0 This means that the molar percentage of molybdenum in the total amount of all elements except oxygen is between 5 molar percentage and 95 molar percentage, of which a) An aqueous solution or aqueous suspension is prepared from at least one of the elemental components of the multi-element oxide: tungsten, molybdenum, vanadium, copper, and antimony. b) Powder P is produced by drying the aqueous solution or aqueous suspension obtained in a) and optionally pulverizing it. c) Optionally, using the powder P obtained in b), and optionally with the addition of one or more molding aids, after uniform mixing, a geometric precursor molded body is produced from the resulting mixture, and d) Heat-treat the powder P obtained in b) or the geometric precursor obtained in c) to form a catalytically active multi-element oxide. Its features Antimony oxide (V)Sb₂O₅ was used as the source of the elemental component antimony.

2. The method according to claim 1, characterized in that, In b), the aqueous solution or aqueous suspension obtained in a) is spray-dried.

3. The method according to claim 1 or 2, characterized in that... An aqueous suspension was used as the source of the elemental component antimony.

4. The method according to claim 3, characterized in that... The pH of the aqueous suspension containing the element antimony is between 5 and 7.

5. The method according to any one of claims 1 to 4, characterized in that, Copper acetate was used as a source of the elemental component copper.

6. The method according to any one of claims 1 to 5, characterized in that, Water-soluble salts are used as a source of the elemental components molybdenum, vanadium, and / or tungsten.

7. The method according to any one of claims 1 to 6, characterized in that, The stoichiometric coefficient d of the antimony element in general formula (I) is 0.3 to 0.

8.

8. A catalytically active multi-element oxide containing molybdenum, tungsten, vanadium, copper, and antimony, wherein the proportions of these elements conform to the requirements of general formula (I). Mo 12 W a V b Cu c Sb d (I), in a = 0.4 to 3.0, b = 1.0 to 6.0, c = 0.1 to 3.0 and d = 0.1 to 3.0 This means that the molar percentage of molybdenum in the total amount of all elements except oxygen is between 5 and 95 molar percentages, which can be obtained by any one of the methods according to claims 1 to 7.

9. The catalytically active multi-element oxide according to claim 8, wherein the stoichiometric coefficient a of the tungsten element in general formula (I) is 1.0 to 1.6 and / or the stoichiometric coefficient b of the vanadium element in general formula (I) is 2.5 to 4.

5.

10. The catalytically active multi-element oxide according to claim 8 or 9, wherein the BET surface area of ​​the catalytically active multi-element oxide is from 16 m² / g to 24 m² / g.

11. The catalytically active multi-element oxide according to any one of claims 8 to 10, wherein the stoichiometric coefficient c of the copper element in general formula (I) is 0.8 to 1.

5.

12. The catalytically active multi-element oxide according to any one of claims 8 to 11, wherein the stoichiometric coefficient d of the antimony element in general formula (I) is 0.3 to 0.

8.

13. A method for manufacturing a shell catalyst, characterized in that, The catalytically active multi-element oxide according to any one of claims 8 to 12, and optionally a binder, are applied to the outer surface of the geometrically shaped body.

14. A shell catalyst comprising a geometrically shaped support body and a catalytically active multi-element oxide according to claims 8 to 12, and optionally a binder, applied to the outer surface of the geometrically shaped support body.

15. A method for producing acrylic acid by gas-phase catalytic oxidation of acrolein in a catalyst fixed bed, wherein the catalyst fixed bed comprises a catalytically active multi-element oxide according to claims 8 to 12 or a shell catalyst according to claim 14.

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