Method for producing catalytically active multi-element oxides containing the elements Mo, W, V and Cu

Abstract

The present invention relates to a method for producing a catalytically active multi-element oxide comprising Mo, W, V and Cu, comprising preparing an aqueous solution using a source of at least one elemental component W of the multi-element oxide, mixing the resulting aqueous solution with sources of elemental components Mo and V of the multi-element oxide, producing a powder P by drying the resulting aqueous solution, optionally producing a geometric precursor body using the resulting powder P, and heat-treating the powder P or the geometric precursor body to form a catalytically active mass and drying the aqueous solution comprises 1.6 to 5.0% by weight of W and 7.2 to 26.0% by weight of Mo relative to the total amount of the aqueous solution.

Description

[Technical Field]

[0001] The present invention relates to a method for producing catalytically active multi-element oxides containing the elements Mo, W, V and Cu.

[0002] The present invention also relates to the catalytically active multi-element oxide obtainable according to the invention, to its use for catalysis of the heterogeneously catalyzed partial gas-phase oxidation of acrolein to acrylic acid, and to its use for producing an eggshell catalyst particularly suitable for this catalysis, as well as to the eggshell catalyst obtainable according to the invention. [Background technology]

[0003] Multi-element oxides containing Mo, W, V and Cu are known, for example, from US 2011 / 0275856, JP 2018-43197, US 6,994,833, EP 1 138 385 A and WO 2004 / 108267.

[0004] US 2011 / 0275856 and JP 2018-43197 disclose the production of multi-element oxides. First, an aqueous solution is produced using a source of elemental component W. Then, sources of elemental components Mo and V of the multi-element oxide are added.

[0005] US 6,994,833 discloses the preparation of multi-element oxides using sources of the elemental components Mo, W and V to form aqueous solutions.

[0006] EP 1 138 385 A discloses the preparation of multi-element oxides using sources of the elemental components W, V and Mo to form aqueous solutions.

[0007] WO 2004 / 108267 discloses the preparation of a multi-element oxide. First, an aqueous solution is prepared using a source of the elemental component Mo. Then, sources of the elemental components V and W of the multi-element oxide are added.

[0008] A disadvantage of the production of multi-element oxides according to US 2011 / 0275856, JP 2018-43197, US 6,994,833, EP 1 138 385 A and WO 2004 / 108267 is the low concentrations of Mo, W, V and Cu in the aqueous solution and the associated low space-time yield in the production of the multi-element oxide itself. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] US Patent Application Publication No. 2011 / 0275856 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-43197 [Patent Document 3] U.S. Patent No. 6,994,833 [Patent Document 4] European Patent Application Publication No. 1 138 385 [Patent Document 5] International Publication No. 2004 / 108267 Summary of the Invention [Problem to be solved by the invention]

[0010] It was therefore an object of the present invention to provide an improved method for producing catalytically active multi-element oxides containing the elements Mo, W, V and Cu. The method should in particular improve the space-time yield in the production of the catalytically active multi-element oxide itself, increase the activity of the catalytically active multi-element oxide and increase the specific surface area. [Means for solving the problem]

[0011] Therefore, there is provided a method for producing a catalytically active multi-element oxide comprising the elements Mo, W, V, Cu and optionally Sb, the ratio of the elements being such that: Mo 12 W a V b Cu c Sb d (I) [In the formula, a=0.4 to 5.0, preferably 0.6 to 3.5, more preferably 0.8 to 2.5, and most preferably 1.0 to 2.0, b=1.0 to 6.0, preferably 1.5 to 5.5, more preferably 2.0 to 5.0, most preferably 2.5 to 4.5, c=0.2 to 1.8, preferably 0.4 to 1.6, more preferably 0.6 to 1.4, and most preferably 0.8 to 1.2; d=0.0 to 2.0, preferably 0.1 to 1.6, more preferably 0.2 to 1.2, most preferably 0.3 to 0.8] Accordingly, the molar ratio of the element Mo to the total amount of all non-oxygen elements is 5 to 95 mol%, preferably 10 to 90 mol%, more preferably 15 to 85 mol%, and most preferably 20 to 80 mol%, The method is a) forming an aqueous solution or suspension using at least one source of elemental component W of the multi-element oxide; b) mixing the aqueous solution or suspension obtained in a) with a source of the elemental components Mo, V and optionally Sb of the multi-element oxide; c) mixing the aqueous solution or suspension obtained in b) with a source of the elemental components Cu and optionally Sb of the multi-element oxide; d) drying and optionally milling the aqueous solution or suspension obtained in c) to produce a powder P; e) optionally using the powder P obtained in d) and optionally adding one or more shaping aids, obtaining, after homogeneous mixing, a geometric shape precursor from the mixture obtained; f) subjecting the powder P obtained in d) or the geometrically shaped precursor obtained in e) to a heat treatment to form a catalytically active multi-element oxide; Including, the aqueous solution or suspension used in d) contains, in each case relative to the total amount of the aqueous solution or suspension, 1.6% by mass to 5.0% by mass, preferably 1.9% by mass to 5.2% by mass, more preferably 2.1% by mass to 4.5% by mass, and most preferably 2.3% by mass to 3.8% by mass of W and 7.2% by mass to 26.0% by mass, preferably 8.7% by mass to 22.0% by mass, more preferably 10.1% by mass to 18.0% by mass, and most preferably 11.5% by mass to 15.0% by mass of Mo, A method is provided.

[0012] The stoichiometric coefficient a of the element W in the general formula (I) is preferably 0.6 to 3.5, more preferably 0.8 to 2.5, and most preferably 1.0 to 2.0.

[0013] The stoichiometric coefficient b of the element V in the general formula (I) is preferably 1.5 to 5.5, more preferably 2.0 to 5.0, and most preferably 2.5 to 4.5.

[0014] Cu increases the selectivity to acrylic acid (CO x Selectivity decreases (i.e., total combustion decreases) and activity exceeds a maximum value.

[0015] The stoichiometric coefficient c of the element Cu in the general formula (I) is preferably 0.4 to 1.6, more preferably 0.6 to 1.4, and most preferably 0.8 to 1.2.

[0016] Sb increases the long-term stability of the catalytically active multi-element oxide.

[0017] The stoichiometric coefficient d of the element Sb in the general formula (I) is preferably 0.1 to 1.6, more preferably 0.2 to 1.2, and most preferably 0.3 to 0.8.

[0018] The molar ratio of the element Mo to the total amount of all non-oxygen elements is preferably 10 to 90 mol %, more preferably 15 to 85 mol %, and most preferably 20 to 80 mol %.

[0019] To produce the catalytically active multi-element oxide, the process of the present invention uses suitable sources of the elemental components Mo, W, V, Cu and optionally Sb to form an aqueous solution or suspension.

[0020] First, in a), at least one source of elemental component W is used to form an aqueous solution or suspension.

[0021] The temperature of the aqueous solution or suspension in a) is preferably 60 to 120°C, more preferably 80 to 110°C, and most preferably 85 to 100°C. The solution or suspension can be preheated or heated only after the addition of the source of elemental component W. The duration of the addition is not subject to any restrictions. The source of elemental component W is preferably metered in within a range of less than 5 hours, more preferably within 0.1 to 120 minutes, and most preferably within 0.2 to 30 minutes. The addition can be carried out under normal pressure, reduced pressure, or elevated pressure. The pressure is preferably 0.5 to 2 bar, more preferably 0.8 to 1.2 bar, and most preferably 0.9 to 1.1 bar. During dissolution or suspension, the solution is advantageously stirred or circulated by a pump. The dissolution or suspension time depends on the temperature, energy input, and concentration, and is preferably 5 hours or less, more preferably 1 to 120 minutes, and most preferably 2 to 60 minutes or 2 to 30 minutes. It is preferred to prepare an aqueous solution in a).

[0022] The aqueous solution or suspension obtained in a) is then mixed in b) with sources of the elemental components Mo, V and optionally Sb. The order of addition is not subject to any restrictions. Advantageously, in b), the source of the elemental component Mo is metered in first. It is preferred to prepare an aqueous solution in b).

[0023] The temperature of the aqueous solution or suspension should be kept constant during the addition of the sources of elemental components Mo, V, and optionally Sb in step b). The aqueous solution or suspension obtained in step a) can be cooled or heated before the addition. The source of elemental component Mo is preferably metered in within a time period of less than 5 hours, more preferably within 0.1 to 120 minutes, and most preferably within 0.2 to 45 minutes. The source of elemental component V is preferably metered in within a time period of less than 5 hours, more preferably within 0.1 to 120 minutes, and most preferably within 0.2 to 30 minutes. The optional source of elemental component Sb is preferably metered in within a time period of less than 5 hours, more preferably within 0.1 to 120 minutes, and most preferably within 0.2 to 20 minutes. The addition can be carried out under standard pressure, reduced pressure, or elevated pressure. The pressure is preferably 0.5 to 2 bar, more preferably 0.8 to 1.2 bar, and most preferably 0.9 to 1.1 bar. During dissolution or suspension, the solution or suspension is advantageously stirred or circulated by a pump. The dissolution or suspension time depends on the temperature, energy input and concentration, and is preferably 5 hours or less, more preferably 1 to 120 minutes, and most preferably 2 to 60 minutes or 2 to 30 minutes.

[0024] The pH is preferably 3-8, more preferably 4-7, and most preferably 5-7.

[0025] Ammonium paratungstate heptahydrate is a preferred source of elemental component W. Ammonium heptamolybdate tetrahydrate is a preferred source of elemental component Mo. Ammonium metavanadate is a preferred source of elemental component V. Antimony acetate or antimony oxide is a preferred source of elemental component Sb.

[0026] Other useful sources of elemental components are, quite generally, metalates, polymetalates, halides, nitrates, formates, oxalates, acetates, carbonates, and hydroxides, in addition to oxides.

[0027] If the solubility of the available elemental component source in the aqueous medium is essentially inadequate for the purpose of the method of the present invention, the pH of the aqueous medium can be suitably adjusted, for example, by adding a suitable adjuster, to improve the solubility of the elemental component source in the aqueous medium. Suitable adjusters include Brønsted acids and Brønsted bases, which are used particularly in the heat treatment of the geometrically shaped precursor and decompose under high temperatures to form gaseous components and the desired catalytically active multi-element oxide. Examples of such pH adjusters include ammonia, nitric acid, hydrochloric acid, acetic acid, formic acid, oxalic acid, and ammonium salts of strong and weak Brønsted acids, such as ammonium nitrate, ammonium chloride, ammonium carbonate, ammonium bicarbonate, ammonium acetate, ammonium formate, and ammonium oxalate.

[0028] Alternatively and / or additionally, aqueous-soluble complexing agents can be added to the aqueous medium, which decompose under the action of high temperature and in the presence of at least molecular oxygen to form gaseous compounds and / or escape as gaseous compounds and can complex elemental components that are in ionic form in the source, and the addition of the complexing agent generally also improves the solubility in the aqueous medium. Examples of such complexing agents include ammonia and ethylenediaminetetraacetic acid, and salts thereof, preferably those with good water solubility.

[0029] Another measure to improve solubility in aqueous media is the use of elevated temperatures. Of course, more than one of the various options discussed for improving solubility in aqueous media can be used simultaneously within the context of the procedure of the present invention.

[0030] Surprisingly, the solubility of at least one source of elemental component W depends on the order of metering. The source of elemental component W must be metered in before the sources of elemental components Mo, V and optionally Sb. If the order of metering is incorrect, the source of elemental component W will only be incompletely dissolved.

[0031] In c), the aqueous solution or suspension obtained in b) is then mixed with a source of the elemental component Cu and optionally Sb, the source of the elemental component Cu being advantageously added in solid form in this case.

[0032] During the addition of at least one source of elemental component Cu in step c), the temperature of the aqueous solution or suspension should be maintained constant. The aqueous solution or suspension obtained in step b) can be cooled or heated before the addition. The source of elemental component Cu is preferably metered in within a period of less than 5 hours, more preferably within 0.1 to 120 minutes, and most preferably within 0.2 to 20 minutes. The addition can be carried out under normal pressure, reduced pressure, or elevated pressure. The pressure is preferably 0.5 to 2 bar, more preferably 0.8 to 1.2 bar, and most preferably 0.9 to 1.1 bar. During dissolution or suspension, the solution or suspension is advantageously stirred or circulated by a pump. The dissolution or suspension time depends on the temperature, energy input, and concentration, and is preferably 5 hours or less, more preferably 1 to 120 minutes, and most preferably 2 to 60 minutes or 2 to 30 minutes.

[0033] The pH is preferably 3-8, more preferably 4-7, and most preferably 5-7.

[0034] Useful sources of elemental component Cu for the production of multi-element oxides according to the invention include, inter alia, copper(II) sulfate pentahydrate, copper(II) nitrate hydrate (Cu content=26.1% by weight) and copper(II) acetate monohydrate, of which the latter is preferred. Antimony acetate or antimony oxide are preferred sources of elemental component Sb.

[0035] As well as sources of the elemental components Mo, W, V, Cu and optionally Sb, other sources of elemental components such as Ta, Cr, Ce, Ni, Co, Fe, Mn, Zn, Nb, Bi, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Si, Al, Ti and Zr can be added in the process of the present invention.

[0036] The aqueous solution or suspension obtained in c) is dried and optionally milled in d) to produce a powder P.

[0037] The aqueous solution or suspension used for drying in d) preferably contains 1.9 to 5.2% by mass, more preferably 2.1 to 4.5% by mass, and most preferably 2.3 to 3.8% by mass of W relative to the total amount of the aqueous solution or suspension.

[0038] The aqueous solution or suspension used for drying in d) preferably contains 8.7 mass % to 22.0 mass %, more preferably 10.1 mass % to 18.0 mass %, and most preferably 11.5 mass % to 15.0 mass % of Mo relative to the total amount of the aqueous solution or suspension.

[0039] The powder P can be produced directly by spray drying the aqueous solution or suspension obtained in c).

[0040] In the spray-drying operation, an aqueous solution or suspension is introduced through a nozzle, which may be operated by liquid pressure, compressed air, or inert gas, or through a rotating atomizer disk, where it is split into fine droplets, a hot gas stream, preferably a hot air stream, and dried within a fraction of a second to produce powder P. The hot gas stream can, in principle, flow in the opposite direction to the spray jet, i.e., countercurrent, or, preferably, flow together with the spray jet, i.e., cocurrent. The spray tower can be operated with a directly or indirectly preheated gas stream. It is preferred to use a directly heated gas stream, e.g., hot fuel gas generated by the combustion of a fuel, e.g., methane, mixed with an additional air stream and flowing into the spray tower. Typical inlet temperatures of the hot gas stream are in the range of 250-390°C, preferably 270-380°C, and typical outlet temperatures are in the range of 90-150°C. The residual moisture content of the resulting powder P is suitably 10% by weight or less, particularly suitably 6% by weight or less, based on its total mass. A low residual moisture content is advantageous. In general, the residual moisture content is typically at least 0.5% by weight, and frequently at least 2% by weight. The residual moisture content analysis in this document is generally based on its determination using an HB43 Moisture Analyzer manufactured by Mettler Toledo AG Laboratory & Weighing Technologies, CH-8606 Greifensee. For this purpose, approximately 5 g of catalyst is heated to 120°C by infrared radiation within approximately 50 seconds and maintained at that temperature. The measurement is terminated when the mass loss within 20 seconds is less than 1 mg.

[0041] Generally, the powder P obtainable as described has a relatively uniform particle diameter.

[0042] On its way from the site of its production to the spray-drying apparatus, the aqueous solution or suspension to be spray-dried is advantageously passed through at least one filter before entering the spray-drying apparatus in order to remove any coarse particles present therein that could, for example, block the spray nozzle. The temperature of the conveying conduit is then suitably maintained at the final production temperature of the aqueous solution or suspension. In any case, the remaining solution or suspension that has not yet been spray-dried is advantageously constantly mixed by stirring and maintained at the starting temperature appropriate for its spray drying.

[0043] In industry, aqueous solutions or suspensions to be spray-dried are usually produced in stirred tanks made of stainless steel type 1.4541 (DIN EN 10020). The spray-drying apparatus and the stirrer are suitably made from the same material.

[0044] The powder P obtained in d) can be directly subjected to a heat treatment (sometimes called calcination) in f) to form the catalytically active multi-element oxide. Alternatively, a geometric precursor can be first produced in e).

[0045] The geometrical precursors of interest that are subjected to heat treatment in the method of the invention can be produced in each individual case from the powder P by using various method variants.

[0046] In a simple embodiment of the method of the invention, powder P is used to directly form geometrically shaped precursors of any desired geometry by compression, such as press agglomeration or tableting (examples for comparable powder mixtures are given, for example, in documents DE 10 2008 054586 A, DE 10 2008 040093 A and DE 10 2008 040094 A). Examples of typical shaped precursor geometries according to the invention are spheres (the diameter of which can be, for example, 2 to 10 mm), more typically solid or hollow cylinders (rings) with an outer diameter and length of 2 to 10 mm. In the case of hollow cylinders, a wall thickness of 1 to 3 mm is appropriate.

[0047] Of course, shaping aids (shaping aids) can then be additionally mixed into the powder P. Useful shaping aids include flow agents or lubricants, such as graphite, carbon black, polyethylene glycol, stearic acid, stearates, starch, polyacrylic acid, mineral oil, vegetable oil, water, boron nitride, boron trifluoride, glycerol, fine Teflon powder and / or cellulose ethers.

[0048] The lubricants mentioned above may partially or completely decompose and / or be chemically transformed during the heat treatment of the geometric shape precursor to form substances that possibly escape in gaseous form.

[0049] As another shaping aid, the mixture to be compressed can contain added reinforcing agents that promote consistency in the resulting geometric shape precursor. Such reinforcing agents can be, for example, glass, asbestos, silicon carbide, and / or potassium titanate microfibers.

[0050] In contrast to lubricants, reinforcing aids are generally essentially preserved during the inventive heat treatment of the geometrically shaped precursor.

[0051] Of course, lubricants and reinforcing agents can also be additionally mixed in together.

[0052] Relative to the total amount of powdered mixture to be compressed into a shaped precursor in accordance with the present invention, the total amount of shaping aids present is generally not more than 30% by weight, usually not more than 20% by weight, and often not more than 10% by weight (but frequently 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).

[0053] If shaping in the production of the geometrically shaped precursor is carried out by extrusion or strand pressing, it is advantageous to additionally incorporate at least one liquid (liquid binder), which is preferably water, an aqueous solution and / or a component of an aqueous solution. Advantageously, the at least one liquid shaping aid incorporated is a lower (C2-C5) organic carboxylic acid, such as 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.

[0054] Calculated as pure lower organic carboxylic acids, these (preferably acetic acid) are advantageously incorporated in total in an amount of 5 to 15% by weight relative to the content of powder P in the total mixture. The total water content of the resulting total mixture can be 5% to 45% by weight, preferably 10% to 30% by weight.

[0055] The incorporation of one or more lower organic carboxylic acids (preferably acetic acid) and / or their aqueous solutions is suitably carried out by kneading under conditions of maximum homogeneity. The temperature during the kneading process is generally below 50°C. Typically, said temperature is in the range of 20-50°C, suitably in the range of 30-40°C. The kneading preferably takes less than 12 hours, more preferably 10-360 minutes, most preferably 20-120 minutes.

[0056] The resulting plastically formable mass (resulting kneaded material, resulting kneaded composition) is then shaped by extrusion into shaped bodies (shaped precursors) of the desired geometric shape. In the simplest case, these can be strands (solid cylinders). Naturally, rings are also conceivable extrudates according to the invention.

[0057] In the case of extruded geometric-shaped precursors, the heat treatment includes drying them, which is generally carried out at a temperature of less than 200°C, preferably less than or equal to 150°C, but typically at least 60°C, or at least 80°C, or at least 100°C.

[0058] Subsequently, the powder P obtained in d) or the shaped precursor obtained in e) is subjected to a heat treatment (sometimes called calcination) to form a catalytically active multi-element oxide.

[0059] Calcination is carried out at an end temperature (in each case material temperature) of 200 to 600° C., preferably 300 to 500° C., more preferably 370 to 430° C. Advantageously, especially during calcination, the material according to the invention has a very substantially uniform temperature.

[0060] Calcination can be carried out batchwise or continuously.

[0061] In the case of batch calcination, a temperature program with one or more temperature plateaus can be used, as described in EP 1 633 467 A. The heating rate is preferably between 0.1 and 20 K / min, more preferably between 0.5 and 10 K / min, most preferably between 1 and 5 K / min.

[0062] In the case of continuous calcination, the material moves through an oven. In this case, the calcination can be carried out isothermally or 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.

[0063] The calcination of the powder P or the shaped precursor can be carried out in a stationary or moving bed. The calcination of the shaped precursor is preferably carried out in a moving bed. Suitable apparatuses are rotary kilns as described in EP 1 633 467 A or belt calciners as described in EP 1 322 585 A. Rotary kilns are preferred.

[0064] The heat treatment (especially the calcination) of the powder P or the geometric-shaped precursor can be carried out under an inert gas or an oxidizing (gaseous) atmosphere, such as air (or another mixture of an inert gas and oxygen), or even under a reducing atmosphere (e.g., a mixture of an inert gas and a reducing gas such as hydrogen, ammonia, carbon monoxide, methane, and / or acrolein, or the reducing gas alone). (It is recognized that the overall reducing atmosphere can also have a limited molecular oxygen content.) The oxidizing (gaseous) atmosphere preferably contains 1% to 15% by volume, more preferably 1.5% to 10% by volume, and most preferably 2% to 8% by volume of molecular oxygen. Preferred oxidizing (gaseous) atmospheres contain not only molecular oxygen but also an inert gas such as nitrogen and water vapor. The water vapor content is preferably less than 5% by volume, more preferably less than 2% by volume. Oxygen contents above or below the above limits usually result in a decrease in the activity of the resulting catalyst. In principle, the heat treatment can alternatively be carried out under reduced pressure.

[0065] Calcination can lead to uncontrolled heat generation in the powder P or shaped precursor, resulting in damage to the catalytically active multi-element oxides produced. If ammonium salts are used at temperatures of, for example, 150-350°C, ammonia may be released and burn during calcination. Uncontrolled heat generation can be limited by sufficient heat and gas exchange. Alternatively, the amount of material to be calcined, the amount and composition of the atmosphere, and the temperature program can be adjusted.

[0066] If the heat treatment of the powder P or the geometrically shaped precursor is carried out in a gaseous atmosphere, this may be stationary or flowing.

[0067] Overall, the heat treatment (especially calcination) of the powder P or geometric-shaped precursor can take up to 24 hours or more. Frequently, the heat treatment (especially calcination) lasts from a few minutes to several hours, e.g., 0.5 to 10 hours, or 1 to 5 hours. Higher temperatures typically result in shorter heat treatment (especially calcination) times, while lower temperatures generally result in longer heat treatment (especially calcination) times. Higher temperatures (especially calcination) and longer treatment times generally reduce the specific surface area of ​​the catalytically active multi-element oxide, resulting in the process of heat treatment of the geometric-shaped precursor (precursor composition).

[0068] The specific BET surface area of ​​the catalytically active multi-element oxides obtained according to the present invention (as determined by gas adsorption (N) by Brunauer-Emmett-Teller (BET)) is typically 16-35 m 2 / g, preferably 17 to 32 m 2 / g, more preferably 18 to 29 m 2 / g, most preferably 19-26m 2 / g. A description of the BET determination method can be found in DIN ISO 9277 and J. Am. Chem. Soc., Vol. 60, No. 2, pp. 309-319 (1938).

[0069] The heat treatment (especially the calcination) of the geometrically shaped precursor is preferably carried out in a gas atmosphere containing oxygen and ammonia, the latter being generated from the shaped precursor itself by incorporating a suitable amount of ammonium ions.

[0070] The catalytic activity of the catalytically active multi-element oxide obtained upon heat treatment generally exhibits an optimum depending on the oxygen content of the calcination atmosphere.

[0071] Calcination methods suitable according to the invention are disclosed, for example, in documents WO 2004 / 108284, EP 0 724 481 A, WO 2008 / 104577, WO 2004 / 108267 and WO 95 / 11081. Of these, the calcination methods disclosed in the latter WO documents are particularly preferred.

[0072] The geometrically shaped catalyst bodies obtained (resulting) within the scope of the thermal treatment of the geometrically shaped precursors can be used as such (called unsupported catalysts) in fixed catalyst beds for the catalysis of the heterogeneously catalyzed partial gas phase oxidation of acrolein to acrylic acid.

[0073] Suitable unsupported catalyst geometries according to the present invention are, for example, solid or hollow cylinders with an outer diameter and length of 2 to 10 mm. In the case of hollow cylinders, wall thicknesses of 1 to 3 mm are suitable. Unsupported catalysts can, of course, also have spherical geometries, in which case the sphere diameter can be 2 to 10 mm.

[0074] The geometrically shaped catalyst bodies obtainable by the process according to the invention (catalytically active multi-element oxides obtainable according to the invention; catalysts obtainable according to the invention), especially when obtained in a non-uniform geometric shape, can also be converted into a finely divided form (for example, ground into powder or small pieces) and used for catalysis of the heterogeneously catalyzed partial oxidation of acrolein to acrylic acid (including in a fluidized or moving bed).

[0075] However, particularly advantageously in accordance with the present invention, the catalytically active multi-element oxide is converted into a finely divided form (e.g., by grinding, e.g., comminuted into powder or small pieces), and this finely divided form is applied to the outer surface of the geometrically shaped support as a shell of catalytically active multi-element oxide (to obtain what is called an eggshell catalyst).

[0076] Typically, application is carried out using a liquid binder, which acts as a binding fluid and is used to bind the finely divided catalytically active multi-element oxide to the outer surface of the geometric support. The binding fluid is then at least partially removed again from the coated geometric support (e.g., by avoiding hot gases, as described in WO 2006 / 094766). The residual water content of the resulting catalyst is preferably 1.0% by weight or less, more preferably 0.5% by weight or less, and most preferably 0.2% by weight or less, in each case based on the total weight of the catalyst.

[0077] Useful materials for the geometrically shaped supports include, inter alia, alumina, silica, silicates such as clay, kaolin, steatite (preferably C-220 steatite from Ceram Tec (DE), or preferably a steatite with a low water-soluble alkali content), pumice, aluminum silicate, magnesium silicate, silicon carbide, and zirconia. The geometrically shaped supports are suitably substantially inert to the relevant partial oxidation (i.e., they are largely inert when used alone, for example, as a "catalyst" for the corresponding heterogeneously catalyzed partial gas-phase oxidation of acrolein to acrylic acid, meaning that they essentially do not cause conversion of acrolein).

[0078] The outer surface of the geometrically shaped support may be smooth or rough, and advantageously is rough, since increased surface roughness generally increases the bonding strength of the applied catalytically active multi-element oxide.

[0079] Useful geometrically shaped supports having a distinct surface roughness include, in particular, shaped supports having a grit layer on their outer surface (a preferred geometrically shaped support according to the present invention is a hollow cylinder having a grit layer on its outer surface).

[0080] Surface roughness R of the outer surface of the geometric shape support Z is preferably in the range of 30 to 100 μm, more preferably in the range of 50 to 70 μm (determined using a "Hommel Tester for DIN-ISO Surface Measurement Parameters" from Hommelwerke in accordance with DIN 4768 Sheet 1). Rough-surface geometry supports made of C220 steatite from Ceram Tec (DE) are particularly preferred.

[0081] The support material may be porous or non-porous. The support material is preferably non-porous (the total volume of pores in the geometric support is advantageously 1% by volume or less, relative to the volume of the respective geometric support). Therefore, the specific BET surface area (relative to its mass unit) of the support material is preferably low.

[0082] The geometrically shaped supports may be regular or irregular, with regular geometrically shaped supports being preferred.

[0083] The longest extent of the geometrically shaped support is typically in the range of 1-10 mm (the longest extent is the longest straight line connecting two points on the outer surface of the shaped support).

[0084] Spheres or (solid) cylinders, in particular hollow cylinders (rings) or Berl saddles, are preferably used as geometric support shapes. A convenient diameter for a sphere is 1 to 6 mm. If a cylinder is used as the geometric support shape, its length is preferably 2 to 10 mm, and its outer diameter is preferably 4 to 10 mm. In the case of a ring, the wall thickness is additionally typically 1 to 4 mm. Hollow cylindrical geometric support shapes with a length of 3 to 8 mm, an outer diameter of 4 to 8 mm, and a wall thickness of 1 to 2 mm are very particularly preferred geometric support shapes. Examples of convenient ring geometries for shaped supports include hollow cylinders with a geometry of 7 mm x 3 mm x 4 mm (external diameter x length x internal diameter) and with geometries of 6 mm x 6 mm x 4 mm, 7 mm x 7 mm x 5 mm, and 5 mm x 3 mm x 2 mm. Advantageous geometric supports are all shaped supports disclosed in Research Disclosure Database Number 532036, August 2008, in particular all those disclosed as examples therein. The production of eggshell catalysts CE and IE disclosed therein can also be carried out using any of the ring-shaped supports disclosed as examples therein, in particular those with a geometry of 7 mm x 4 mm x 3 mm or 6 mm x 6 mm x 4 mm.

[0085] The thickness of the catalytically active multi-element oxide shell applied to the outer surface of the geometrically shaped support (particularly the ring-shaped support detailed above, including the outer surface of which defines the ring cavity) is suitably and generally 10 to 1000 μm. In the case of eggshell catalysts, this shell thickness is preferably 10 to 500 μm, more preferably 100 to 500 μm, and most preferably 200 to 450 μm.

[0086] Figure 3 shows X-ray microtomography (X-ray μCT) of the ring-shaped eggshell catalyst. Figures 4 and 5 show X-ray diffraction of the ring-shaped eggshell catalyst. The eggshell catalyst was a coated ring-shaped support (outer diameter 7 mm, length 3 mm, inner diameter 4 mm, surface roughness Rz 45 μm) of steatite C 220 type (Ceram Tec GmbH, Plochingen, Germany), with an oxidation-active composition content of approximately 20% by mass.

[0087] Advantageously, the shell thickness is substantially uniform over each individual eggshell catalyst. In the case of relatively large-scale production batches of eggshell catalyst, the shell thickness is also substantially uniform over several individual eggshell catalyst rings. The uniformity of the shell thickness is often within the range of values ​​described in the examples of DE 103 60 058 A.

[0088] The finely divided catalytically active multi-element oxide can be applied to the outer surface of the geometric support, for example, by first wetting (e.g., spraying) the outer surface with a liquid binder in a controlled manner, and then contacting the thus-wetted geometric support with the finely divided catalytically active multi-element oxide to fix a layer of the active composition to the wetted surface (e.g., by sprinkling the finely divided catalytically active multi-element oxide (active composition powder) onto the wetted geometric support as described in EP 0 714 700 A).

[0089] In this context, "controlled wetting" means that the support surface is properly wetted so that the liquid binder is absorbed, but the liquid phase itself is not visually apparent on the support surface. If the support surface is too wet, the finely divided catalytically active multi-element oxide will aggregate and form separate aggregates rather than adhering to the surface. More details on this can be found in DE 29 09 671 A and DE 100 51 419 A, as well as EP 0 714 700 A. It is recognized that the operation can be repeated periodically to increase the layer thickness. In this case, the coated substrate becomes a new "support", etc.

[0090] Alternatively, all other application methods recognized as prior art in EP 0 714 700 A for the production of the eggshell catalysts detailed above can be used.

[0091] Examples of useful liquid binders include water, organic solvents, or aqueous solutions of organic substances (e.g., organic solvents), or organic solvents or aqueous solutions of organic solvents. Examples of organic binders include monohydric or polyhydric organic alcohols such as ethylene glycol, 1,4-butanediol, 1,6-hexanediol, or glycerol; monobasic or polybasic organic carboxylic acids such as propionic acid, oxalic acid, malonic acid, glutaric acid, or maleic acid; amino alcohols such as ethanolamine or diethanolamine; and monofunctional or polyfunctional organic amides such as formamide. Suitable organic binder components (binder promoters) soluble in water, organic liquids, or mixtures of water and organic liquids are monosaccharides and oligosaccharides such as glucose, fructose, sucrose, and / or lactose.

[0092] Particularly advantageously, the liquid binder used is a solution consisting of 20% to 90% by weight of water and 10% to 80% by weight of an organic compound. The organic component in the liquid binder is preferably 10% to 50% by weight, more preferably 20% to 30% by weight. A very particularly preferred liquid binder is a solution consisting of 20% to 90% by weight of water and 10% to 80% by weight of glycerol. Advantageously, the glycerol content in these aqueous solutions is 10% to 50% by weight, more preferably 20% to 30% by weight. One advantage of the preferred binders is that they are able to completely and satisfactorily wet both the finely divided catalytically active multi-element oxide (or the finely divided precursor composition (see below)) and the outer surface of the geometrically shaped support.

[0093] The fineness of the micronized catalytically active multi-element oxide (or its precursor composition (see below)) applied to the outer surface of the geometrically shaped support is naturally adapted to the desired shell thickness. For a shell thickness range of 100 to 500 μm, suitable active composition powders are those in which at least 50% of the total number of preferably granular powder particles pass through a sieve with a mesh size (circular mesh) of 1 to 20 μm or 1 to 10 μm, and the numerical proportion of particles with a longest dimension exceeding 50 μm (particles that do not pass through a sieve with a mesh size (circular mesh) of 50 μm) is less than 10% by weight. For the rest, what is described on page 18 of WO 2005 / 120702 is equally applicable.

[0094] The eggshell catalyst obtainable as described is preferably obtained by the preparation method described and detailed in the example in EP 0 714 700 A (see also WO 2011 / 134932 and DE 103 60 057 A Examples). An aqueous solution of 75% by weight of water and 25% by weight of glycerol is a preferred liquid binder. Advantageously, in the present invention, the heat treatment method of the geometric-shaped precursor is carried out according to the procedure described and detailed in the example in DE 103 60 057 A.

[0095] The procedure of the present invention also encompasses a method for producing a catalytically active multi-element oxide, in which a geometrically shaped precursor is shaped together with a (fine-grained) mixture of powder P and, optionally, one or more shaping aids, in such a way that the shell of this (fine-grained) mixture (of the fine-grained precursor composition) is applied directly to the outer surface of the geometrically shaped support (in a manner corresponding to that described for the application of the active composition shell). During the heat treatment of the geometrically shaped precursor thus obtained (which also includes at least partial removal of the liquid binder additionally used for the application), the eggshell catalyst of the present invention is directly obtained, in which a shell of catalytically active multi-element oxide is applied to the outer surface of the (essentially catalytically inactive) geometrically shaped support.

[0096] As mentioned above, the catalytically active multi-element oxides obtainable according to the present invention are particularly suitable for catalysis of the heterogeneously catalyzed partial gas-phase oxidation 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. They are particularly notable in that the catalyst beds in which they are packed have a long service life during the partial oxidation process, during which the target product is formed with high activity. A preferred form of use of the catalytically active multi-element oxides obtainable according to the present invention is the use of eggshell catalysts, preferably having a ring-shaped geometry. In this case, it is particularly preferable to use the eggshell catalysts detailed by way of example in the examples of this document, for example in all the examples and all the comparative examples of the above-mentioned 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, in each of which the catalysts used therein can be replaced (what is said therein about the eggshell catalysts according to the examples of this document is also applicable to the eggshell catalysts according to the comparative examples of this document).

[0097] In principle, the catalytically active multi-element oxides obtainable according to the invention are likewise advantageously suitable for catalyzing the heterogeneously catalyzed partial gas-phase oxidation of methacrolein to methacrylic acid.

[0098] This is particularly true when the heterogeneously catalyzed partial gas-phase oxidation of acrolein or methacrolein (i.e., "(meth)acrolein" for short) to acrylic acid or methacrylic acid (i.e., "(meth)acrylic acid" for short) is carried out at high (meth)acrolein loadings, as described in DE 103 07 983 A, DE 199 48 523 A, DE 199 10 508 A, WO 2008 / 104577, WO 2011 / 134932, DE 199 27 624 A and DE 103 60 057 A.

[0099] Heterogeneously catalytic partial gas-phase oxidation can be carried out in a manner known per se. In other words, a reaction gas mixture containing (meth)acrolein, molecular oxygen, and at least one inert diluent gas is conducted at high temperature through a catalyst bed, the catalyst comprising at least one catalytically active multi-element oxide obtainable according to the present invention as an active composition, and its conversion to (meth)acrylic acid takes place during the residence time of (meth)acrolein in the catalyst bed. The catalyst bed is preferably a fixed catalyst bed. However, in principle, fluidized or moving beds are also useful for the process according to the present invention. In general, flow as a component of the reaction gas mixture leads to improved selectivity and activity. Furthermore, inert diluent gases with high molar heat capacities, such as n-propane or carbon dioxide, are advantageous. These are gases that undergo chemical changes, preferably to an extent of 5 mol% or less, more preferably to an extent of 3 mol% or less, and most preferably to an extent of 1 mol% or less, or not at all, when the reaction gas mixture passes through the catalyst bed.

[0100] A heat exchanger reactor is particularly suitable for carrying out the gas-phase partial oxidation of (meth)acrolein. The heat exchanger reactor has at least one main space and at least one sub-space, which are separated from each other by a dividing wall. In at least one main space, a catalyst packing containing at least one catalytically active multi-element oxide obtainable according to the present invention is arranged, through which a reaction gas mixture containing (meth)acrolein flows. At the same time, a fluid heat carrier flows through the sub-space, and heat exchange takes place between the two spaces through the dividing wall. The purpose is to monitor and control the temperature of the reaction gas mixture as it passes through the catalyst bed.

[0101] Generally, the gas-phase partial oxidation of (meth)acrolein is carried out in a shell-and-tube (heat exchanger) reactor having 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, DE 22 01 428 A, EP 0 383 224 A, JP 2007-260588 and JP S58-096041.

[0102] In this case, the fixed catalyst bed takes the form of a corresponding bed of shaped catalyst bodies (possibly in admixture with diluting inert geometric bodies) in the metal tubes (catalyst tubes) of the shell-and-tube reactor, and one or more temperature carriers are conducted around the metal tubes (in the case of more than one temperature zone, a corresponding number of spatially essentially distinct temperature carriers are conducted around the metal tubes). The temperature carrier is generally a salt melt. The reaction gas mixture is conducted through the catalyst tubes.

[0103] Alternatively, the fixed catalyst bed can also be present in the space between the thermoplates in a thermoplate reactor, through which the heat carrier flows, as recommended in DE 10 2004 017 150 A, DE 199 52 964 A and DE 103 61 456 A.

[0104] The fixed catalyst bed, as already mentioned, can quite generally consist solely of the catalyst obtainable according to the present invention, but can also consist of such catalyst diluted with an inert geometric body. In this case, the inert geometric body can be the geometric support (support) used for the production of the eggshell catalyst of the present invention. Upstream and / or outside the fixed catalyst bed, a bed of purely inert shaped bodies can be installed (such a bed of purely inert shaped bodies is usually not included in the calculation of the space velocity of the reactant gas or reactant gas components relative to the fixed catalyst bed).

[0105] The catalyst tubes used in shell-and-tube reactors are conventionally made of ferritic steel and typically have a wall thickness of 1-3 mm. Their internal diameter is generally 20-30 mm, frequently 21-29 mm or 21-26 mm. Their length is suitably 2-4 m.

[0106] The number of catalyst tubes contained in a shell-and-tube vessel is suitably at least 5,000, preferably at least 10,000. Frequently, the number of catalyst tubes contained in a reactor vessel is between 15,000 and 40,000. Shell-and-tube reactors having more than 50,000 catalyst tubes are usually the exception. Within the vessel, the catalyst tubes are usually arranged in a uniform distribution (preferably six equidistant adjacent tubes per catalyst tube), the distribution being suitably selected so that the separation distance between the central axes of adjacent catalyst tubes (called the catalyst tube pitch) is between 35 and 45 mm (see, for example, EP 0 468 290 A).

[0107] Particularly advantageous heat exchange media for shell-and-tube reactors are melts of salts such as potassium nitrate, potassium nitrite, sodium nitrite and / or sodium nitrate, or low-melting metals such as sodium, mercury, and alloys of various metals.

[0108] Filling the catalyst tubes in a shell-and-tube reactor with the catalyst obtainable according to the invention, in particular those detailed in the examples (but also in the comparative examples) of this document, is advantageous, especially when the shell-and-tube reactor is operated at a (meth)acrolein space velocity relative to the catalyst charge of at least 130 l(STP) / l·h, or at least 150 l(STP) / l·h, or at least 160 l(STP) / l·h, or at least 170 l(STP) / l·h, or at least 180 l(STP) / l·h, or at least 200 l(STP) / l·h, or at least 220 l(STP) / l·h, or at least 240 l(STP) / l·h, or at least 260 l(STP) / l·h. Naturally, such catalyst packings are also advantageous when the (meth)acrolein space velocity is lower (for example, 130 l(STP) / l·h or less, or 100 l(STP) / l·h or less, or 80 l(STP) / l·h or less, or 60 l(STP) / l·h or less).

[0109] Typically, the (meth)acrolein space velocity relative to the catalyst charge is at least 400 l(STP) / l·h, or at least 350 l(STP) / l·h, or at least 300 l(STP) / l·h, or at least 280 l(STP) / l·h (corresponding space velocities can also be achieved in a thermoplate reactor).

[0110] The space velocity of the reaction gas injection mixture relative to the fixed catalyst bed is understood in the present document to mean the amount of reaction gas injection mixture in standard litres per hour fed to the fixed catalyst bed relative to its volume (bed sections consisting purely of inert material are not included in the bed volume; in fact, the bed volume is the volume of the empty space occupied by the bed (or its relevant section)), i.e. relative to the bed volume (=l(STP); the volume in litres that the corresponding gas volume would occupy under standard conditions, i.e. at 0°C and 101.3 kPa) (→ unit = l(STP) / l·h).

[0111] The space velocity may also be based on only one component of the reaction gas injection mixture (e.g., only the organic starting compound to be partially oxidized). In that case, it is the amount (→ unit = l(STP) / l·hr) of the volume (unit: standard liters) of this component (e.g., the organic starting compound to be partially oxidized) fed to the fixed catalyst bed per hour relative to the bed volume (sections of the bed consisting purely of inert material are not included in the bed volume; incidentally, the bed volume is the volume of the empty space occupied by the bed (or its relevant section)).

[0112] The volumetric specific activity of the fixed catalyst bed is generally configured to increase in the flow direction of the reaction gas.

[0113] This can be achieved in a simple way by reducing the level of dilution of the fixed catalyst bed with inert shaped bodies in the flow direction of the reaction gas. Alternatively, the volumetric specific activity can be adjusted by using catalysts with different specific BET surface areas. Furthermore, eggshell catalysts with different pore volumes or different eggshell thicknesses can be used. In this case, the activity increases as the specific BET surface area, pore volume, or eggshell thickness increases.

[0114] In other circumstances, the heterogeneously catalytic partial oxidation using the eggshell catalyst obtainable according to the invention can be carried out quite generally in all the embodiments detailed by DE 103 50 822 A. The (meth)acrolein content in the reaction gas injection mixture can have a value of 3% to 15% by volume, frequently 4% to 10% by volume, or 5% to 8% by volume (in each case relative to the total volume of the reaction gas injection mixture).

[0115] The molar ratio of oxygen to (meth)acrolein in the reaction gas injection mixture is usually at least 1. Typically, this ratio has a value of not more than 3. In many cases, the heterogeneously catalyzed (meth)acrolein partial oxidation to (meth)acrylic acid is carried out at a volume ratio (l(STP)) of (meth)acrolein to oxygen to inert gas present in the reaction gas injection mixture of 1:(1-3):(0-20):(3-30), preferably 1:(1-3):(0.5-10):(7-10).

[0116] Useful inert diluent gases (these are gases or mixtures of gases that are preserved chemically unchanged to the extent of at least 95 mol%, preferably to the extent of at least 97 mol%, or to the extent of at least 99 mol%, and up to the extent of 100 mol%, during a single pass of the reaction gas mixture through a catalyst bed (e.g., a fixed catalyst bed)) include nitrogen, carbon dioxide, carbon monoxide, noble gases, propane, ethane, methane, butane, and / or pentane (i.e., each as the sole diluent gas or as a mixture with one or more other inert diluent gases). The reaction temperature in such heterogeneously catalyzed (meth)acrolein partial oxidation is typically in the range of 200 to 400°C, generally 220 to 380°C, often 230 to 350°C, and frequently 245 to 285°C or 245 to 265°C. The operating pressure (absolute pressure) (especially as the injection pressure into the fixed catalyst bed) is usually 101.3 to 350 kPa, or 101.3 to 250 kPa, or 101.3 to 205 kPa. The partial oxidation of (meth)acrolein using the catalyst obtainable according to the present invention can, of course, also be carried out at an operating pressure below atmospheric pressure.

[0117] The (meth)acrolein conversion based on a single pass of the reaction gas mixture through a fixed catalyst bed is typically at least 90 mol%, frequently at least 98 mol%, often at least 99 mol%, or even at least 99.9 mol%.

[0118] In other circumstances, the partial oxidation process of the invention can be carried out in a manner that corresponds generally to the teaching of DE 10 2007 019 597 A or WO 2008 / 104577 or WO 2011 / 134932.

[0119] More specifically, the source used for the (meth)acrolein required for the partial oxidation of the present invention can be directly a (meth)acrolein-containing product gas mixture of the heterogeneously catalyzed partial oxidation of C3 / C4 precursor compounds of (meth)acrolein (e.g., propene or isobutene) to (meth)acrolein, without any prior removal of (meth)acrolein from such a product gas mixture.

[0120] (Meth)acrylic acid can be removed from the product gas mixture of the partial oxidation in a known manner, for example, by first converting the (meth)acrylic acid into a condensed phase by absorption and / or condensation measures. Subsequent thermal separation methods, such as rectification and / or crystallization, can then isolate the (meth)acrylic acid from the condensed phase at any desired purity (see DE 602004924 T and WO 2006 / 114428, and the prior art cited therein).

[0121] The present invention relates to a catalytically active multi-element oxide comprising the elements Mo, W, V, Cu and optionally Sb, in which the ratio of the elements is represented by the general formula (I) Mo 12 W a V b Cu c Sb d (I) [In the formula, a=0.4 to 5.0, preferably 0.6 to 3.5, more preferably 0.8 to 2.5, and most preferably 1.0 to 2.0, b=1.0 to 6.0, preferably 1.5 to 5.5, more preferably 2.0 to 5.0, most preferably 2.5 to 4.5, c=0.2 to 1.8, preferably 0.4 to 1.6, more preferably 0.6 to 1.4, and most preferably 0.8 to 1.2; d=0.0 to 2.0, preferably 0.1 to 1.6, more preferably 0.2 to 1.2, most preferably 0.3 to 0.8] and the molar ratio of the element Mo to the total amount of all non-oxygen elements is 5 to 95 mol %, preferably 10 to 90 mol %, more preferably 15 to 85 mol %, most preferably 20 to 80 mol %, and the catalytically active multi-element oxide is obtainable by one of the above methods, and the BET surface area of ​​the catalytically active multi-element oxide is 16 to 35 m 2 / g, preferably 17 to 32 m 2 / g, more preferably 18 to 29 m 2 / g, most preferably 19-26m 2 / g of catalytically active multi-element oxide.

[0122] The stoichiometric coefficient a of the element W in the general formula (I) is preferably 0.6 to 3.5, more preferably 0.8 to 2.5, and most preferably 1.0 to 2.0.

[0123] The stoichiometric coefficient b of the element V in the general formula (I) is preferably 1.5 to 5.5, more preferably 2.0 to 5.0, and most preferably 2.5 to 4.5.

[0124] The stoichiometric coefficient c of the element Cu in the general formula (I) is preferably 0.4 to 1.6, more preferably 0.6 to 1.4, and most preferably 0.8 to 1.2.

[0125] The stoichiometric coefficient d of the element Sb in the general formula (I) is preferably 0.1 to 1.6, more preferably 0.2 to 1.2, and most preferably 0.3 to 0.8.

[0126] The molar ratio of the element Mo to the total amount of all non-oxygen elements is preferably 10 to 90 mol %, more preferably 15 to 85 mol %, and most preferably 20 to 80 mol %.

[0127] The BET surface area of ​​the catalytically active multi-element oxide is preferably 17 to 32 m 2 / g, more preferably 18 to 29 m 2 / g, most preferably 19-26m 2 / g.

[0128] Catalytically active multi-element oxides used in the oxidation of acrolein to acrylic acid typically do not have all of the metal elements present in their maximum oxidation states. What is meant by maximum oxidation state of the metal elements is the maximum oxidation state in which each element typically exists as its oxide. Maximum oxidation states of relevant / related elements are V(V), Mo(VI), W(VI), Cu(II), and Sb(V).

[0129] For example, vanadium may not be in the V(V) oxidation state, or may not be entirely in the V(V) oxidation state, but may be in, for example, the V(IV) or V(III) oxidation state, or mixed oxidation states. A portion of the vanadium may be in the V(V) oxidation state and another portion in the V(IV) oxidation state, or a portion of the vanadium may be in the V(IV) oxidation state and another portion in the V(III) oxidation state.

[0130] Other metal elements in the mixed metal oxides may also be in different oxidation states, for example, Cu(I), Mo(V), Mo(IV) and Sb(III).

[0131] In principle, delocalized states can be considered when the relatively high electron mobility has the effect of being able to distinguish between non-discrete metal atoms with different oxidation states.

[0132] In this case, without entering into any other theoretical interpretation, the catalytically active multi-element oxide can be analyzed by redox titration after digestion with an aqueous solution. The content of oxidizable electrons is quantitatively determined by titration using KMnO4 as the oxidizing agent. For this purpose, the catalytically active multi-element oxide is used directly in powder form before being applied to a shaped support.

[0133] Catalytically active multi-element oxides with a defined ratio R of oxidizable electrons to vanadium have particularly advantageous properties in the oxidation of acrolein to acrylic acid. The ratio R is: R=e / CV where e is the specific content of oxidizable electrons per gram [mol / g] and CV is the specific content of vanadium per gram [mol / g]. is.

[0134] The ratio R is preferably 1.0 to 2.0, more preferably 1.1 to 1.9, and most preferably 1.2 to 1.8.

[0135] Titration using KMnO4 as the oxidizing agent is carried out as follows:

[0136] 15 ml of 96% sulfuric acid, 15 ml of water, and 10 ml of 85% phosphoric acid are introduced into a long-necked flask on a stirring hotplate and purged with argon to remove air from them. 100–200 mg of sample is weighed into a weigh boat and rinsed into the long-necked flask with water. The flask is heated under argon to boiling, reducing the volume of the solution to 40 ml and completely dissolving the sample (approximately 30–45 min, depending on the amount of water required).

[0137] The solution is then transferred to a titration vessel equipped with a composite Pt electrode and a potentiograph, e.g., Titrando 808 (Metrohm AG, Herisau, Switzerland). The titration is carried out at 80 °C under an argon atmosphere. The sample is titrated with an aqueous KMnO4 solution (0.02 mol / l) until the color changes to red-purple (excess KMnO4). During the titration, the electrochemical potential is measured and recorded using the composite Pt electrode.

[0138] The titration curve should show an inflection point. The absence of an inflection point indicates that there are no electrons available for oxidation. Read the volume of the KMnO4 solution at the endpoint from the titration curve.

[0139] The specific content of oxidizable electrons e is e=(V*C*5) / EW [In the formula, 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 mass of the sample [g]] is.

[0140] In some cases, a titration curve may show multiple turning points. This means that electrons with different oxidation potentials are present. Two turning points likely indicate the presence of V(III) and V(IV). Figure 6 shows a titration curve with two turning points. Figure 7 shows a titration curve with one turning point.

[0141] The present invention further provides a method for producing an eggshell catalyst, in which the catalytically active multi-element oxide of the present invention and optionally a binder are applied to the exterior surface of a geometrically shaped support.

[0142] The present invention further provides an eggshell catalyst comprising a geometrically shaped support and, coated on the exterior surface of the geometrically shaped support, a catalytically active multi-element oxide of the present invention and, optionally, a binder.

[0143] The present invention further provides a process for preparing acrylic acid by the vapor-phase catalytic oxidation of acrolein in a fixed catalyst bed, wherein the fixed catalyst bed comprises the catalytically active multi-element oxide of the present invention or the eggshell catalyst of the present invention. [Brief explanation of the drawings]

[0144] [Figure 1] FIG. 10 is a diagram showing the particle size distribution of powder P in Example 22. [Figure 2] FIG. 10 is a diagram showing the particle size distribution of powder P in Example 23. [Figure 3] FIG. 1 shows x-ray microtomography (X-ray μCT) of the ring-shaped eggshell catalyst in Example 1. [Figure 4] FIG. 1 shows the x-ray diffraction of the ring-shaped eggshell catalyst in Example 23. [Figure 5] FIG. 1 shows the x-ray diffraction of the ring-shaped eggshell catalyst in Example 9. [Figure 6] FIG. 1 shows the titration curve of the catalyst in Example 9. [Figure 7] FIG. 1 shows the titration curve of the catalyst in Example 22. DETAILED DESCRIPTION OF THE INVENTION

[0145] Accordingly, the present invention specifically encompasses the following embodiments of the invention:

[0146] 1. A method for producing a catalytically active multi-element oxide containing the elements Mo, W, V, Cu and optionally Sb, in which the ratio of the elements is represented by the general formula (I): Mo 12 W a V b Cu c Sb d (I) [In the formula, a=0.4~5.0, b=1.0~6.0, c=0.2~1.8, d=0.0~2.0] the molar ratio of the element Mo to the total amount of all non-oxygen elements is 5 to 95 mol %; The method is a) forming an aqueous solution or suspension using at least one source of elemental component W of the multi-element oxide; b) mixing the aqueous solution or suspension obtained in a) with a source of the elemental components Mo, V and optionally Sb of the multi-element oxide; c) mixing the aqueous solution or suspension obtained in b) with a source of the elemental components Cu and optionally Sb of the multi-element oxide; d) drying and optionally milling the aqueous solution or suspension obtained in c) to produce a powder P; e) optionally using the powder P obtained in d) and optionally adding one or more shaping aids, obtaining, after homogeneous mixing, a geometric shape precursor from the mixture obtained; f) subjecting the powder P obtained in d) or the geometrically shaped precursor obtained in e) to a heat treatment to form a catalytically active multi-element oxide; Including, d) the aqueous solution or suspension used contains in each case 1.6% to 5.0% by mass of W and 7.2% to 26.0% by mass of Mo, relative to the total amount of the aqueous solution or suspension; method.

[0147] 2. The method according to embodiment 1, wherein the stoichiometric coefficient a of element W in general formula (I) is 0.6 to 3.5.

[0148] 3. The method according to embodiment 1 or 2, wherein the stoichiometric coefficient a of the element W in the general formula (I) is 0.8 to 2.5.

[0149] 4. The method according to any one of embodiments 1 to 3, wherein the stoichiometric coefficient a of the element W in the general formula (I) is 1.0 to 2.0.

[0150] 5. The method according to any one of embodiments 1 to 4, wherein the stoichiometric coefficient b of element V in general formula (I) is 1.5 to 5.5.

[0151] 6. The method according to any one of embodiments 1 to 5, wherein the stoichiometric coefficient b of element V in general formula (I) is 2.0 to 5.0.

[0152] 7. The method according to any one of embodiments 1 to 6, wherein the stoichiometric coefficient b of element V in general formula (I) is 2.5 to 4.5.

[0153] 8. The method according to any one of the preceding embodiments, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is 0.4 to 1.6.

[0154] 9. The method according to any one of the preceding embodiments, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is 0.6 to 1.4.

[0155] 10. The method according to any one of the preceding embodiments, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is 0.8 to 1.2.

[0156] 11. The method according to any one of the preceding embodiments, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is 0.1 to 1.6.

[0157] 12. The method according to any one of the preceding embodiments, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is 0.2 to 1.2.

[0158] 13. The method according to any one of the preceding embodiments, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is 0.3 to 0.8.

[0159] 14. The method according to any one of the preceding embodiments, wherein the molar ratio of the element Mo to the total amount of all non-oxygen elements is 10 to 90 mol %.

[0160] 15. The method according to any one of the preceding embodiments, wherein the molar ratio of the element Mo to the total amount of all non-oxygen elements is 15 to 85 mol %.

[0161] 16. The method according to any one of the preceding embodiments, wherein the molar ratio of the element Mo to the total amount of all non-oxygen elements is 20 to 80 mol %.

[0162] 17. The method according to any of the preceding embodiments, wherein the aqueous solution or suspension obtained in c) is dried and pulverized in d).

[0163] 18. The method according to any of the preceding embodiments, wherein the aqueous solution or suspension obtained in c) is spray-dried in d).

[0164] 19. The method according to any of the preceding embodiments, wherein the powder P obtained in d) is used in e) to produce a geometrically shaped precursor.

[0165] 20. The method according to any one of the preceding embodiments, wherein the powder P obtained in d) is used in e), one or more shaping aids are added, and after uniform mixing, a geometric shape precursor is obtained from the resulting mixture.

[0166] 21. The method according to any one of the preceding claims, wherein the aqueous solution or suspension used in d) contains 1.9% to 5.2% by weight of W.

[0167] 22. The method of any one of the preceding claims, wherein the aqueous solution or suspension used in d) contains 2.1% to 4.5% by weight of W.

[0168] 23. The method according to any one of the preceding claims, wherein the aqueous solution or suspension used in d) contains 2.3% to 3.8% by weight of W.

[0169] 24. The method of any one of the preceding claims, wherein the aqueous solution or suspension used in d) contains 8.7% to 22.0% by weight of Mo.

[0170] 25. The method of any one of the preceding embodiments, wherein the aqueous solution or suspension used in d) contains 10.1% to 18.0% by weight of Mo.

[0171] 26. The method of any one of the preceding embodiments, wherein the aqueous solution or suspension used in d) contains 11.5% to 15.0% by weight of Mo.

[0172] 27. The method of any one of embodiments 1 to 26, wherein water-soluble salts are used as sources of the elemental components Mo, W, and V.

[0173] 28. The method of any of the preceding embodiments, wherein in b) mixing is performed with at least one source of the elemental component Sb of the multi-element oxide.

[0174] 29. The method of any of the preceding embodiments, wherein in c) mixing of the multi-element oxide with at least one source of elemental component Sb is performed.

[0175] 30. The method of any one of the preceding claims, wherein in b) the multi-element oxide is admixed with a source of at least one of the elemental components Ta, Cr, Ce, Ni, Co, Fe, Mn, Zn, Nb, Bi, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Si, Al, Ti, or Zr.

[0176] 31. The method of any one of the preceding claims, wherein in c) the multi-element oxide is admixed with a source of at least one of the elemental components Ta, Cr, Ce, Ni, Co, Fe, Mn, Zn, Nb, Bi, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Si, Al, Ti, or Zr.

[0177] 32. The method of any one of embodiments 1 to 31, wherein a water-soluble salt is used as the source of the elemental component Sb.

[0178] 33. The method according to any of the preceding embodiments, wherein the source of the elemental component Cu of the aqueous solution or suspension obtained in b) is added in solid form.

[0179] 34. The method of any one of embodiments 1 to 33, wherein an aqueous solution is prepared in b).

[0180] 35. Catalytically active multi-element oxides containing the elements Mo, W, V, Cu and optionally Sb, in which the ratio of the elements is represented by the general formula (I): Mo 12 W a V b Cu c Sb d (I) [In the formula, a=0.4~5.0, b=1.0~6.0, c=0.2~1.8, d=0.0~2.0] 35. The catalytically active multi-element oxide can be obtained by the method according to any one of claims 1 to 34, wherein the molar ratio of the element Mo to the total amount of all non-oxygen elements is 5 to 95 mol %, and the BET surface area of ​​the catalytically active multi-element oxide is 16 to 35 m 2 / g of catalytically active multi-element oxide.

[0181] 36. The catalytically active multi-element oxide according to embodiment 35, wherein the stoichiometric coefficient a of element W in general formula (I) is 0.6 to 3.5.

[0182] 37. The catalytically active multi-element oxide according to embodiment 35 or 36, wherein the stoichiometric coefficient a of element W in general formula (I) is 0.8 to 2.5.

[0183] 38. The catalytically active multi-element oxide according to any one of embodiments 35 to 37, wherein the stoichiometric coefficient a of element W in general formula (I) is 1.0 to 2.0.

[0184] 39. The catalytically active multi-element oxide of any one of embodiments 35 to 38, wherein the stoichiometric coefficient b of element V in general formula (I) is 1.5 to 5.5.

[0185] 40. The catalytically active multi-element oxide of any one of embodiments 35 to 39, wherein the stoichiometric coefficient b of element V in general formula (I) is 2.0 to 5.0.

[0186] 41. The catalytically active multi-element oxide of any one of embodiments 35 to 40, wherein the stoichiometric coefficient b of element V in general formula (I) is 2.5 to 4.5.

[0187] 42. The catalytically active multi-element oxide of any one of embodiments 35 to 41, wherein the stoichiometric coefficient c of element Cu in general formula (I) is 0.4 to 1.6.

[0188] 43. The catalytically active multi-element oxide of any of embodiments 35 to 42, wherein the stoichiometric coefficient c of element Cu in general formula (I) is 0.6 to 1.4.

[0189] 44. The catalytically active multi-element oxide of any one of embodiments 35 to 43, wherein the stoichiometric coefficient c of element Cu in general formula (I) is 0.8 to 1.2.

[0190] 45. The catalytically active multi-element oxide of any one of embodiments 35 to 44, wherein the stoichiometric coefficient d of element Sb in general formula (I) is 0.1 to 1.6.

[0191] 46. ​​The catalytically active multi-element oxide of any one of embodiments 35 to 45, wherein the stoichiometric coefficient d of element Sb in general formula (I) is 0.2 to 1.2.

[0192] 47. The catalytically active multi-element oxide according to any one of embodiments 35 to 46, wherein the stoichiometric coefficient d of element Sb in general formula (I) is 0.3 to 0.8.

[0193] 48. The catalytically active multi-element oxide of any of embodiments 35 to 47, wherein the catalytically active multi-element oxide comprises at least one of the elements Ta, Cr, Ce, Ni, Co, Fe, Mn, Zn, Nb, Bi, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Si, Al, Ti, or Zr.

[0194] 49. The catalytically active multi-element oxide according to any one of embodiments 35 to 48, wherein the molar ratio of the element Mo to the total amount of all non-oxygen elements is 10 to 90 mol %.

[0195] 50. The catalytically active multi-element oxide according to any one of embodiments 35 to 49, wherein the molar ratio of the element Mo to the total amount of all non-oxygen elements is 15 to 85 mol %.

[0196] 51. The catalytically active multi-element oxide according to any one of embodiments 35 to 50, wherein the molar ratio of the element Mo to the total amount of all non-oxygen elements is 20 to 80 mol %.

[0197] 52. The BET surface area of ​​catalytically active multi-element oxides is 17-32 m 252. The catalytically active multi-element oxide of any of embodiments 35 to 51, wherein the .gtoreq.100 kJ / g.

[0198] 53. The BET surface area of ​​catalytically active multi-element oxides is 18-29 m 2 53. The catalytically active multi-element oxide of any of embodiments 35 to 52, wherein the .gtoreq.100 kJ / g.

[0199] 54. The BET surface area of ​​catalytically active multi-element oxides is 19-26 m 2 54. The catalytically active multi-element oxide of any of embodiments 35 to 53, wherein the .gtoreq.100 kJ / g.

[0200] 55. The catalytically active multi-element oxide of any one of embodiments 35 to 54, wherein the ratio R of the catalytically active multi-element oxide is 1.0 to 2.0.

[0201] 56. The catalytically active multi-element oxide of any one of embodiments 35 to 55, wherein the ratio R of the catalytically active multi-element oxide is 1.1 to 1.9.

[0202] 57. The catalytically active multi-element oxide of any one of embodiments 35 to 56, wherein the ratio R of the catalytically active multi-element oxide is 1.2 to 1.8.

[0203] 58. A method for preparing acrylic acid by the gas-phase catalytic oxidation of acrolein over a fixed catalyst bed, wherein the fixed catalyst bed comprises the catalytically active multi-element oxide of any of embodiments 35 to 57.

[0204] 59. Use of the catalytically active multi-element oxide of any of embodiments 35 to 57 as a catalyst for the heterogeneously catalyzed partial gas-phase oxidation of acrolein to acrylic acid.

[0205] 60. A method for producing an eggshell catalyst, comprising applying the catalytically active multi-element oxide of any one of embodiments 35 to 57 to the exterior surface of a geometrically shaped support.

[0206] 61. A method for producing an eggshell catalyst, comprising applying the catalytically active multi-element oxide and binder of any of embodiments 35 to 57 to the exterior surface of a geometrically shaped support.

[0207] 62. Use of a multi-element oxide according to any of embodiments 35 to 57 for producing an eggshell catalyst.

[0208] 63. An eggshell catalyst comprising a geometrically shaped support and the catalytically active multi-element oxide of any one of embodiments 35 to 57 applied to the outer surface of the geometrically shaped support.

[0209] 64. An eggshell catalyst comprising a geometrically shaped support and the catalytically active multi-element oxide of any one of embodiments 35 to 57 and a binder applied to the outer surface of the geometrically shaped support.

[0210] 65. A process for preparing acrylic acid by the gas-phase catalytic oxidation of acrolein in a fixed catalyst bed, wherein the fixed catalyst bed comprises the eggshell catalyst of embodiment 63 or 64.

[0211] 66. Use of the eggshell catalyst according to embodiment 63 or 64 as a catalyst for the heterogeneously catalyzed partial gas-phase oxidation of acrolein to acrylic acid. [Example]

[0212] (Example 1) (Comparative Example) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.2 O n Ring-shaped eggshell catalyst C1 Eggshell catalyst generation: A first solution was prepared by stirring 102.5 g of copper (II) acetate monohydrate (Cu content=32% by mass) and 3180 g of water at 70° C. for 30 minutes.

[0213] For the second solution, 900 g of ammonium heptamolybdate tetrahydrate (Mo content = 55% by weight) was added to 7066 g of water at 90°C while stirring. While maintaining the temperature, the mixture was stirred for 5 minutes, 156 g of ammonium metavanadate (V content = 42% by weight) was added, and the mixture was stirred for an additional 40 minutes. Subsequently, 132 g of ammonium paratungstate heptahydrate (W content = 72% by weight) was added, and the mixture was stirred for an additional 30 minutes. An orange solution was obtained.

[0214] Next, the first solution was added to the second solution, and the mixture was stirred for 15 minutes. To the resulting solution, 1530 g of 25% by weight NH3 aqueous solution was added, and the temperature was 25° C. A clear solution with a temperature of about 70° C. and a pH of 8.5 was obtained.

[0215] Finally, the resulting solution was introduced into a Mobile Minor 2000 spray tower (GEA Niro, Soeborg, Denmark) equipped with an F0 A1 spray head via a rotary atomizer at 30,000 rpm. Drying was carried out in a hot air stream at an inlet temperature of 350 °C and an outlet temperature of 120 °C. The powder was introduced into a ZS1-18 kneader (Coperion Werner & Pfleiderer GmbH & Co. KG; Stuttgart, Germany). The powder was kneaded at 15 rpm for 30 min with 100 ml of glacial acetic acid and 200 ml of water at room temperature. Subsequently, the material was extruded (length 1-10 cm, diameter 6 mm). The extrudates were dried at 110 °C for 16 h in an air-circulating drying cabinet.

[0216] 1000 g of the precursor composition removed from the air-circulating drying cabinet was calcined batchwise in a rotary kiln (similar to US 9,149,799 B2). Calcination was carried out in a gas flow composed of air and nitrogen with an oxygen content of 2.3% by volume. The rotary kiln was heated to 400°C within 1 hour and maintained at that temperature for a further 2 hours. Subsequently, the heating was switched off and the material was allowed to cool to room temperature while continuing to rotate.

[0217] The material removed from the rotary kiln was subsequently ground to a fine powder in a ZM 200 mill (Retsch GmbH, Haan, Germany).

[0218] The fine powder was used to coat 1600 g of a C 220 steatite-type (Ceram Tec GmbH, Plochingen, Germany) ring-shaped support (outer diameter 7 mm, length 3 mm, inner diameter 4 mm, surface roughness Rz 45 μm). Coating was performed in a Hi-Coater LHC 25 / 36 mixer (Gebruder Lodige Maschinenbau GmbH, Paderborn, Germany). The mixer was retrofitted for continuous powder dosing. For this, a funnel-shaped container was connected to the mixer body via a hose (outer diameter 11.1 mm, inner diameter 8 mm). For coating, 500 g of fine powder was introduced into the funnel-shaped container. Dosing was performed using a 50 ms pressure pulse and a positive pressure of 0.7 bar. During dosing, the contents of the funnel-shaped container were moved by a V-shaped modified anchor stirrer (manufactured in-house). There was a one-second pause between the two-second stirring periods.

[0219] The binder used was a 25% by weight aqueous glycerol solution. In parallel with the powder dosing, the solution was metered into the mixer at 3 g / min via a 570 S75 two-phase nozzle (Dusen-Schlick GmbH, Coburg, Germany). The powder dosing was 6 cm lower than the two-phase nozzle and tilted downwards by 40°. The powder was dosed outside the spray cone of the two-phase nozzle. The mixer body rotated clockwise at 15 rpm. Coating was carried out at 25°C within 40 minutes. The rotation speed was then reduced to 2 rpm, and drying was carried out in an air flow (220 l / h) at 130°C for 30 minutes. After this, the mixture was cooled to 25°C. The powder was incorporated into the substrate surface. No formation of twin substrates or agglomeration was observed.

[0220] The coated substrates were subsequently degreased in a UM 400 circulating air drying cabinet (Memmert GmbH & Co. KG, Schwabach, Germany). The coated substrates were uniformly distributed over a 2 cm thick perforated sheet. The perforated sheet had a thickness of 0.5 cm, an aperture ratio of 60%, and an area of ​​35 cm x 26 cm. The circulating air drying cabinet was heated to 300 °C at 3 K / min and maintained at that temperature for a further 2 h. This was followed by cooling to 40-50 °C within 2-3 h.

[0221] The ring-shaped eggshell catalyst C1 had an oxidation-active composition content of 20.7 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 14 m 2 / g.

[0222] Eggshell catalyst analysis: A reactor tube (stainless steel (material 1.4541); outer diameter 30 mm; wall thickness 2 mm; inner diameter 26 mm; length 464 cm) was filled from the top downwards as follows: Section 1: Length 80cm empty tubes; Section 2: Length 60cm a preliminary bed of steatite rings (C 220 steatite from Ceram Tec GmbH) with a geometrical dimension of 7 mm × 3 mm × 4 mm (external diameter × length × internal diameter); Section 3: Length 100cm a fixed catalyst bed consisting of a homogeneous mixture of 20% by mass of steatite rings (C 220 steatite from Ceram Tec GmbH) with a geometry of 7 mm x 3 mm x 4 mm (external diameter x length x internal diameter) and 80% by mass of eggshell catalyst; Section 4: Length 200cm a fixed catalyst bed consisting exclusively of eggshell catalyst as in section 3; Section 5: Length 10cm downstream bed of the same steatite ring as in section 2; Section 6: Length 14cm A catalyst substrate made of stainless steel (material 1.4541) to accommodate the fixed catalyst bed.

[0223] The reaction gas mixture introduced through each of the reaction tubes filled as described above and flowing downwards through the reaction tubes from the top had the following contents: 4.3% by volume acrolein, 0.3% by volume of propene, 0.2% by volume of propane, 0.3% by volume of acrylic acid, 5.1% by volume of oxygen, 0.4% by volume of carbon dioxide, 7% by volume of water, 82.3% by volume nitrogen.

[0224] The feed temperature of the reaction gas mixture (at the inlet to the reactor tube) was 210°C, and the space velocity of acrolein relative to the fixed catalyst bed was 80 l(STP) / l·h (as defined in DE 199 27 624 A).

[0225] A stirred, externally electrically heated salt bath (a mixture of 53% by weight of potassium nitrate, 40% by weight of sodium nitrite, and 7% by weight of sodium nitrate; 50 kg of salt melt) flowed around the reactor tube (flow velocity in the tube was 3 m / s) over the length of the reactor tube (except for the last 10 cm of empty tube in section 1 and the last 3 cm of tube in section 6). The salt bath temperature TB (to which the salt bath was supplied) was set so that in each case the acrolein conversion was 99.3 mol% for a single pass of the reaction gas mixture through the fixed catalyst bed. There was no change in the salt bath temperature along the reactor tube due to additional heat (the salt bath gave off more heat than was released into it by the reactor tube).

[0226] The selectivity of acrylic acid formation in this paper (S AA (mol%)) is

[0227]

number

[0228] is understood to mean

[0229] CO x The selectivity of formation (total combustion) is calculated similarly.

[0230] An active composition (catalyst) that leads to the same conversion at a lower temperature under otherwise unchanged reaction conditions has a higher activity.

[0231] In this paper, the conversion rate of acrolein (C AC (mol%)) is

[0232]

number

[0233] is understood to mean

[0234] Table 1 below shows the results obtained as a function of the eggshell catalyst used after 100 hours of operation.

[0235] (Example 2) (Comparative Example) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.2 O n Ring-shaped eggshell catalyst C2 The procedure was the same as in Example 1. The ring-shaped eggshell catalyst C2 had an oxidation-active composition content of 15.8 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 14.8 m 2 / g.

[0236] (Example 3) (Comparative Example) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 2.4 O n Ring-shaped eggshell catalyst C3 The procedure was the same as in Example 1. 205.0 g of copper(II) acetate monohydrate was used instead of 102.5 g of copper(II) acetate monohydrate, and the ring-shaped eggshell catalyst C3 had an oxidation-active composition content of 20.0 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 13.5 m. 2 / g.

[0237] (Example 4) (Comparative Example) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.2 Sb 0.5 O n Ring-shaped eggshell catalyst C4 The procedure was the same as in Example 1. To the second solution, 56.5 g of antimony acetate (Sb content = 46.3 wt%) was additionally added, while the ring-shaped eggshell catalyst C4 had an oxidation-active composition content of 20.7 wt%. The BET surface area of ​​the catalytically active multi-element oxide was 14.0 m 2 / g. The ratio R was 1.60.

[0238] (Example 5) (Comparative Example) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.2 O n Ring-shaped eggshell catalyst C5 The procedure was the same as in Example 1. Without adding NH3 aqueous solution, the ring-shaped eggshell catalyst C5 had an oxidation-active composition content of 20.7 wt %. The BET surface area of ​​the catalytically active multi-element oxide was 19.3 m 2 / g. The ratio R was 1.75.

[0239] (Example 6) (Comparative Example) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.2 O n Ring-shaped eggshell catalyst C6 The procedure was the same as in Example 1. In preparing the second solution, ammonium paratungstate heptahydrate was added first, followed by ammonium heptamolybdate tetrahydrate, and then ammonium metavanadate. Without adding aqueous NH3, the ring-shaped eggshell catalyst C6 had an oxidation-active composition content of 21.0 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 19.6 m. 2 / g. The ratio R was 1.49.

[0240] (Example 7) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.2 O n WE1 ring-shaped eggshell catalyst The procedure was the same as in Example 1. To prepare the second solution, ammonium paratungstate heptahydrate was first added and the mixture was stirred for 5 minutes. Then, ammonium heptamolybdate tetrahydrate was added and the mixture was stirred for another 10 minutes. Subsequently, ammonium metavanadate was added and the mixture was stirred for another 5 minutes. Furthermore, 1017 g of water was used instead of 3180 g to prepare the first solution, and 2261 g of water was used instead of 7066 g to prepare the second solution. This increased the concentration of the solutions by 3.2 times. Without the addition of aqueous NH3 solution, the ring-shaped eggshell catalyst WE1 had an oxidation-active composition content of 20.2 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 20.5 m. 2 / g. The ratio R was 1.38.

[0241] (Example 8) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.2 O n WE2 ring-shaped eggshell catalyst The procedure was the same as in Example 7. No first solution was prepared. Copper (II) acetate monohydrate was added in solid form to the second solution, and the ring-shaped eggshell catalyst WE2 had an oxidation-active composition content of 20.7% by mass. The BET surface area of ​​the catalytically active multi-element oxide was 19.6 m. 2 / g.

[0242] (Example 9) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.2 Sb 0.5 O n WE3 ring-shaped eggshell catalyst The procedure was the same as in Example 7. 56.5 g of antimony acetate (Sb content = 46.3 wt%) was additionally added to the second solution. The first solution was not prepared. Copper (II) acetate monohydrate was added in solid form to the second solution, and the ring-shaped eggshell catalyst WE3 had an oxidation-active composition content of 20.6 wt%. The BET surface area of ​​the catalytically active multi-element oxide was 17 m 2 / g. The ratio R was 1.65.

[0243] (Example 10) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.2 O n WE4 ring-shaped eggshell catalyst The procedure was the same as in Example 7. No first solution was prepared. Copper (II) acetate monohydrate was added in solid form to the second solution, and the ring-shaped eggshell catalyst WE4 had an oxidation-active composition content of 15.0 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 21.6 m. 2 / g. The ratio R was 1.43.

[0244] (Example 11) (Comparative Example) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 0.0 O n Ring-shaped eggshell catalyst C7 The procedure was the same as in Example 10. Without copper(II) acetate monohydrate, the ring-shaped eggshell catalyst C7 had an oxidation-active composition content of 15.3 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 23 m. 2 / g. The ratio R was 1.01.

[0245] (Example 12) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 0.2 O n WE5 ring-shaped eggshell catalyst The procedure was the same as in Example 10. However, 17.1 g of copper(II) acetate monohydrate was used instead of 102.5 g of copper(II) acetate monohydrate, and the ring-shaped eggshell catalyst WE5 had an oxidation-active composition content of 15.8 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 26 m. 2 / g.

[0246] (Example 13) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 0.4 O n WE6 ring-shaped eggshell catalyst The procedure was the same as in Example 10. However, 34.2 g of copper(II) acetate monohydrate was used instead of 102.5 g of copper(II) acetate monohydrate, and the ring-shaped eggshell catalyst WE6 had an oxidation-active composition content of 15.5 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 23.8 m. 2 / g.

[0247] (Example 14) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 0.8 O n WE7 ring-shaped eggshell catalyst The procedure was the same as in Example 10. However, 68.3 g of copper(II) acetate monohydrate was used instead of 102.5 g of copper(II) acetate monohydrate, and the ring-shaped eggshell catalyst WE7 had an oxidation-active composition content of 15.1 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 20.1 m. 2 / g. The ratio R was 1.26.

[0248] (Example 15) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.0 O n WE8 ring-shaped eggshell catalyst The procedure was the same as in Example 10. However, 85.4 g of copper(II) acetate monohydrate was used instead of 102.5 g of copper(II) acetate monohydrate, and the ring-shaped eggshell catalyst WE8 had an oxidation-active composition content of 15.1 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 25.9 m. 2 / g. The ratio R was 1.35.

[0249] (Example 16) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.1 O n WE9 ring-shaped eggshell catalyst The procedure was the same as in Example 10. However, 94.0 g of copper(II) acetate monohydrate was used instead of 102.5 g of copper(II) acetate monohydrate, and the ring-shaped eggshell catalyst WE9 had an oxidation-active composition content of 15.3 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 21.4 m. 2 / g. The ratio R was 1.37.

[0250] (Example 17) (Comparative Example) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 2.4 O n Ring-shaped eggshell catalyst C8 The procedure was the same as in Example 8. However, 205.0 g of copper(II) acetate monohydrate was used instead of 102.5 g of copper(II) acetate monohydrate, and the ring-shaped eggshell catalyst C8 had an oxidation-active composition content of 20.0 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 12.5 m. 2 / g. The ratio R was 1.85.

[0251] (Example 18) (Comparative Example) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.2 O n Ring-shaped eggshell catalyst C9 The procedure was the same as in Example 1. 2261 g of water was used to generate the second solution instead of 7066 g, i.e., the concentration of the solution was increased by 3.2 times. None of the salts went into complete solution. Ring-shaped eggshell catalyst C9 had an oxidation-active composition content of 21.0 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 14.8 m. 2 / g.

[0252] (Example 19) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.4 O n WE10 ring-shaped eggshell catalyst The procedure was the same as in Example 8. However, 119.6 g of copper(II) acetate monohydrate was used instead of 102.5 g of copper(II) acetate monohydrate, and the ring-shaped eggshell catalyst WE10 had an oxidatively active composition content of 20.8 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 22.8 m. 2 / g.

[0253] (Example 20) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.8 O n WE11 ring-shaped eggshell catalyst The procedure was the same as in Example 8. However, 153.7 g of copper(II) acetate monohydrate was used instead of 102.5 g of copper(II) acetate monohydrate, and the ring-shaped eggshell catalyst WE11 had an oxidation-active composition content of 21.5 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 17.7 m. 2 / g.

[0254] (Example 21) (Comparative Example) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 2.0 O n Ring-shaped eggshell catalyst C10 The procedure was the same as in Example 8. However, 171.0 g of copper(II) acetate monohydrate was used instead of 102.5 g of copper(II) acetate monohydrate, and the ring-shaped eggshell catalyst C10 had an oxidation-active composition content of 21.2 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 12.0 m. 2 / g.

[0255] (Example 22) (Comparative Example) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.2 O n Ring-shaped eggshell catalyst BV1 A first solution was prepared in a stainless steel vessel with a volume of 920 L and a paddle stirrer. 12.1 kg of copper(II) acetate monohydrate (Cu content = 32% by weight) was dissolved in 398 kg of water with stirring at about 25°C. The mixture was stirred for an additional hour.

[0256] A second solution was prepared in a stainless steel vessel with a volume of 3200 L and a propeller stirrer. To the initial charge of 921 kg of water at 40°C, 108.8 kg of ammonium heptamolybdate tetrahydrate (Mo content = 55% by weight) was added with stirring. The mixture was heated to 90°C and stirred for 30 minutes. While maintaining the temperature, 18.2 kg of ammonium metavanadate (V content = 42% by weight) was added to the mixture, which was stirred for another 40 minutes. Subsequently, 16.1 kg of ammonium paratungstate heptahydrate (W content = 72% by weight) was added, and the mixture was stirred for another 30 minutes. An orange solution was obtained. The resulting solution was cooled to 80°C. The ratio R was 0.59.

[0257] The first solution was then added to the second solution, and the mixture was stirred for 15 minutes while maintaining a temperature of 80° C. To the resulting solution, 176 kg of 25% by weight aqueous NH3 solution was added, the temperature of which was 25° C. A clear solution was obtained with a temperature of about 70° C. and a pH of 8.5.

[0258] The resulting solution was transferred to a stainless steel vessel with a capacity of 8000 l and a cross-beam agitator. The solution was heated to 80°C and finally introduced into an F 15 spray tower (GEA Niro, Soeborg, Denmark) via a rotary atomizer at 16000 rpm. Drying was carried out in a hot air stream at an inlet temperature of 375°C and an outlet temperature of 92°C. The resulting spray powder had the particle size distribution shown in Figure 1.

[0259] The subsequent procedure was the same as in Example 1.

[0260] The ring-shaped eggshell catalyst BV1 had an oxidation-active composition content of 20.1 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 15.9 m. 2 / g.

[0261] (Example 23) Catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.2 O n Ring-shaped eggshell catalyst BV2 To 1319 kg of water initially charged into a 3200 L stainless steel vessel equipped with a propeller stirrer, 76 kg of ammonium paratungstate heptahydrate (W content = 72% by mass) was added at 90-95°C while stirring. After 20 minutes, while maintaining the temperature, 513.4 kg of ammonium heptamolybdate tetrahydrate (Mo content = 55% by mass) was added to the mixture, which was then stirred for an additional 10 minutes. Then, 85.9 kg of ammonium metavanadate (V content = 42% by mass) was added, and the mixture was stirred for an additional 10 minutes. An orange solution was obtained. Subsequently, 57.1 kg of copper(II) acetate monohydrate (Cu content = 32% by mass) was added, and the mixture was stirred for an additional 15 minutes. The resulting spray powder had the particle size distribution shown in Figure 2.

[0262] The subsequent procedure was the same as in Example 22.

[0263] The ring-shaped eggshell catalyst BV2 had an oxidation-active composition content of 20.7 wt. %. The BET surface area of ​​the catalytically active multi-element oxide was 23.2 m2 / g.

[0264] [Table 1]

Claims

1. 1. A method for producing a catalytically active multi-element oxide comprising the elements Mo, W, V, Cu and optionally Sb, the ratio of the elements being represented by the general formula (I): Mo １２ W ａ V ｂ Cu ｃ Sb ｄ (I) During the ceremony, a=1.0~2.0, b=2.5~4.5, c=0.2~1.8, d=0.0 to 2.0 the molar ratio of the element Mo to the total amount of all non-oxygen elements is 5 to 95 mol %; The method is a) forming an aqueous solution or suspension using at least one source of elemental component W of the multi-element oxide; b) combining the aqueous solution or suspension obtained in a) with a source of the elemental components Mo, V and optionally Sb of the multi-element oxide; c) mixing the aqueous solution or suspension obtained in b) with a source of the elemental components Cu and optionally Sb of the multi-element oxide; d) drying and optionally milling the aqueous solution or suspension obtained in c) to produce a powder P; e) optionally using the powder P obtained in d) and optionally adding one or more shaping aids, after homogeneous mixing, to obtain a geometric shape precursor from the mixture obtained; f) subjecting the powder P obtained in d) or the geometrically shaped precursor obtained in e) to a heat treatment to form a catalytically active multi-element oxide; and the aqueous solution or suspension used in d) contains in each case 1.9 to 3.8% by weight of W and 10.1 to 18.0% by weight of Mo, relative to the total amount of the aqueous solution or suspension.

2. 2. The method according to claim 1, wherein the aqueous solution or suspension obtained in c) is spray-dried in d).

3. 3. The method according to claim 1 or 2, wherein the aqueous solution or suspension used in d) contains 2.3 to 3.8% by weight of W and / or 11.5 to 15.0% by weight of Mo, in each case relative to the total amount of the aqueous solution or suspension.

4. 4. The method according to claim 1, wherein water-soluble salts are used as the source of the elemental components Mo, V and / or W.

5. 5. The method according to claim 1, wherein the stoichiometric coefficient c of the element Cu in the general formula (I) is 0.8 to 1.

2.

6. 6. The method according to any one of claims 1 to 5, wherein in b) or c) mixing is carried out with at least one source of the elemental component Sb of the multi-element oxide.

7. 7. A method for producing an eggshell catalyst, comprising the step of applying a catalytically active multi-element oxide obtained by the method of any one of claims 1 to 6 and optionally a binder to the outer surface of a geometrically shaped support.

8. 10. A process for preparing acrylic acid by the gas-phase catalytic oxidation of acrolein in a fixed catalyst bed, wherein the fixed catalyst bed comprises a catalytically active multi-element oxide obtained by the process of any one of claims 1 to 6 or an eggshell catalyst obtained by the process of claim 7.

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