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

Abstract

A method for producing a catalytically active multi-element oxide containing the elements Mo, W, V, Cu, and Sb, by producing an aqueous solution or suspension using a source of at least one of the elemental components W, Mo, and V of the catalytically active multi-element oxide, mixing the resulting aqueous solution or suspension with sources of the elemental components Cu and Sb of the catalytically active multi-element oxide, producing a powder P by drying the resulting aqueous solution or suspension, optionally using the resulting powder P to obtain a geometrically shaped precursor, and subjecting the powder P or the geometrically shaped precursor to a heat treatment to form the catalytically active multi-element oxide, wherein copper acetate is used as the source of the elemental component Cu and antimony oxide is used as the source of the elemental component Sb.

Description

[Technical Field]

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

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

[0003] Multi-element oxides containing Mo, W, V, Cu, and Sb are known, for example, from WO 2021 / 213823, U.S. Pat. No. 5,959,143, U.S. Pat. No. 6,762,148, EP 0 711 745, and EP 3 488 926.

[0004] WO 2021 / 213823 discloses the production of multi-element oxides using copper acetate and antimony acetate as sources of the elemental components Cu and Sb.

[0005] US Pat. No. 5,959,143 and EP-A-3488926 disclose the production of multi-element oxides using copper sulfate and antimony acetate as sources of the elemental components Cu and Sb.

[0006] US Pat. No. 6,762,148 discloses the production of multi-element oxides using copper sulfate and antimony acetate as sources of the elemental components Cu and Sb.

[0007] EP 0 711 745 A1 discloses the preparation of multi-element oxides using copper nitrate or copper oxide and antimony acetate as sources of the elemental components Cu and Sb.

[0008] A drawback of the production of multi-element oxides in WO 2021 / 213823, U.S. Pat. No. 5,959,143, U.S. Pat. No. 6,762,148, EP 0 711 745, and EP 3 488 926 is the low catalytic activity of the multi-element oxides and the associated high temperatures required for the conversion. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2021 / 213823 [Patent Document 2] U.S. Patent No. 5,959,143 [Patent Document 3] U.S. Patent No. 6,762,148 [Patent Document 4] European Patent Application Publication No. 0711745 [Patent Document 5] European Patent Application Publication No. 3488926 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, Cu, and Sb, which were expected to have particularly high activity. [Means for solving the problem]

[0011] Accordingly, there is provided a method for producing a catalytically active multi-element oxide comprising the elements Mo, W, V, Cu and Sb, the ratio of which elements is expressed by the following general formula (I): Mo 12 W a V b Cu c Sb d (I) where: a=0.4~3.0, b=1.0~6.0, c=0.1~3.0, and d=0.1 to 3.0, The molar ratio of element Mo in the total amount of all non-oxygen elements is 5-95 mol %, and the production of catalytically active multi-element oxides is a) preparing an aqueous solution or suspension using a source of at least one of the elemental components W, Mo, and V of the catalytically active multi-element oxide; b) mixing the aqueous solution or suspension obtained in a) with sources of the elemental components Cu and Sb of the catalytically active multi-element oxide; c) producing a powder P by drying and optionally grinding the aqueous solution or suspension obtained in b); d) optionally using the powder P obtained in c) and optionally adding one or more shaping aids and mixing them homogeneously, and then obtaining a geometrically shaped precursor from the mixture obtained; e) subjecting the powder P obtained in c) or the geometrically shaped precursor obtained in d) to a heat treatment to form a catalytically active multi-element oxide, A method is provided in which copper acetate is used as the source of the elemental component Cu and antimony oxide is used as the source of the elemental component Sb.

[0012] In the general formula (I), the stoichiometric coefficient a of the element W is preferably 0.6 to 2.5, more preferably 0.8 to 2.0, and most preferably 1.0 to 1.6.

[0013] In the general formula (I), the stoichiometric coefficient b of the element V 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 for acrylic acid (CO x (decrease in selectivity, i.e., decrease in total combustion), activity passes through a maximum.

[0015] The stoichiometric coefficient c of the element Cu in the general formula (I) is preferably 0.4 to 2.5, more preferably 0.6 to 2.0, and most preferably 0.8 to 1.5.

[0016] Sb enhances 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 0.2 to 1.5, more preferably 0.25 to 1.2, and most preferably 0.3 to 0.8.

[0018] The molar ratio of the element Mo in the total amount of all non-oxygen elements is preferably 20 to 90 mol %, more preferably 35 to 85 mol %, and most preferably 50 to 80 mol %.

[0019] For producing catalytically active multi-element oxides, the process of the present invention involves preparing aqueous solutions or suspensions using suitable sources of the elemental components Mo, W, V, Cu, and Sb.

[0020] When preparing catalytically active multi-element oxides, it is preferred to use copper(II) acetate monohydrate (Cu(CH3COO)2H2O) as the source of elemental component Cu and antimony(III) oxide (Sb2O3) as the source of elemental component Sb. [Effects of the Invention]

[0021] Surprisingly, it has been found that the use of copper acetate, in particular copper(II) acetate monohydrate, as the source of the elemental component Cu and antimony oxide, in particular antimony(III) oxide, as the source of the elemental component Sb, clearly increases the activity of the catalytically active multi-element oxide compared to other sources. DETAILED DESCRIPTION OF THE INVENTION

[0022] First, in a), at least one source of each of the elemental components W, Mo, and V is used to prepare an aqueous solution or suspension.

[0023] The temperature of the aqueous solution or suspension in a) is preferably 60 to 130°C, more preferably 70 to 120°C, and most preferably 75 to 110°C. The aqueous solution or suspension may be preheated or may be heated only after the addition of the source of elemental component W. The duration of addition is not subject to any limitation. The order in which the sources of elemental components W, Mo, and V are added is also not subject to any limitation. Advantageously, in a), the source of elemental component W is weighed first, followed by the source of elemental component Mo, and finally the source of elemental component V. In a), it is preferred to prepare an aqueous solution. The pH is preferably 3 to 8, more preferably 4 to 7, and most preferably 5 to 7.

[0024] The addition can be carried out under normal pressure, reduced pressure, or increased 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 pumped, in each case with circulation. Preferably, the solution or suspension is stirred for 1 to 180 minutes, even more preferably 2 to 120 minutes, particularly preferably 3 to 60 minutes, and especially preferably 5 to 30 minutes after each addition of the sources of the elemental components W, Mo, and V, and before the addition of the next source.

[0025] Subsequently, in b), the aqueous solution or suspension obtained in a) is mixed with sources of the elemental components Cu and Sb. The order of addition is not subject to any restrictions. Advantageously, in b), the source of the elemental component Sb is weighed out first. In b), it is preferred to prepare an aqueous suspension.

[0026] The sources of the elemental components Sb and / or Cu may be added preferably in solid form or as an aqueous solution or suspension.

[0027] The temperature of the aqueous solution or suspension in step b) is preferably 60 to 130°C, more preferably 70 to 120°C, and most preferably 75 to 110°C. When adding the sources of elemental components Cu and Sb in step b), the temperature of the aqueous solution or suspension should preferably be kept constant. The aqueous solution or suspension obtained in step a) may be cooled or heated before the addition. The addition can be carried out under normal pressure, reduced pressure, or increased 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 pumped while circulating. Preferably, the solution or suspension is stirred for 1 to 300 minutes, even more preferably 5 to 180 minutes, particularly preferably 10 to 120 minutes, and particularly preferably 20 to 90 minutes after adding the source of elemental component Sb and before adding the source of elemental component Cu. Preferably, the solution or suspension is stirred for another 1 to 180 minutes, more preferably 3 to 120 minutes, particularly preferably 5 to 90 minutes, and particularly preferably 10 to 60 minutes after adding the source of elemental component Cu. The pH is preferably 3 to 8, more preferably 4 to 7, and most preferably 5 to 7.

[0028] A preferred source of elemental component W is ammonium paratungstate heptahydrate. A preferred source of elemental component Mo is ammonium heptamolybdate tetrahydrate. A preferred source of elemental component V is ammonium metavanadate.

[0029] Besides oxides, other useful sources of elemental components are quite generally metalates, polymetalates, halides, nitrates, formates, oxalates, acetates, carbonates, and hydroxides, among others.

[0030] If the solubility of the elemental component source in the aqueous medium is essentially inadequate for the purpose of the method of the present invention, for example, the pH of the aqueous medium can be suitably modified by adding an appropriate modifier to improve the solubility of the elemental component source in the aqueous medium. Suitable modifiers include Brønsted acids and Brønsted bases that decompose into gaseous components under the action of high temperatures, which are used in the heat treatment of the geometrically shaped precursor to form the desired catalytically active multi-element oxide. Examples of such pH modifiers include ammonia, nitric acid, hydrochloric acid, acetic acid, formic 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.

[0031] Alternatively and / or additionally, complexing agents soluble in aqueous media can be added to the aqueous solution or suspension, which, under the action of elevated temperature and in the presence of at least molecular oxygen, decompose into gaseous compounds and / or escape as gaseous compounds and are able to complex the elemental components of the source in ionic form, thus generally also improving the solubility in aqueous media. Examples of such complexing agents include ammonia and ethylenediaminetetraacetic acid and its salts, preferably those with good water solubility.

[0032] The use of elevated temperatures is a further means for improving solubility in aqueous media. Of course, in the context of the procedure of the present invention, it is also possible to simultaneously employ more than one of the various options addressed to improve solubility in aqueous media.

[0033] As well as sources of the elemental components Mo, W, V, Cu, and Sb, it is possible to add further sources of elemental components in the process of the invention, 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.

[0034] In c), the aqueous solution or suspension obtained in b) is dried and optionally milled to produce a powder P.

[0035] The aqueous solution or suspension obtained in b) is preferably spray-dried in c). By spray-drying the aqueous solution or suspension obtained in b), it is possible to directly produce powder P.

[0036] In the spray-drying operation, an aqueous solution or suspension is introduced through a nozzle, which can be operated by hydraulic pressure, compressed air, or inert gas, or through a rotating atomizer disk, where it is broken down into fine droplets and dried within a fraction of a second to obtain powder P. The hot gas stream can, in principle, flow in the opposite direction to the atomizing jet, i.e., countercurrent, or, preferably, alongside the atomizing jet, i.e., cocurrent. The spray tower can be operated using a directly or indirectly preheated gas stream. For example, a directly heated gas stream is preferably used, in which hot fuel gas, e.g., produced by the combustion of a fuel such as methane, is mixed with an additional air stream and flows 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 loss on ignition of the resulting powder P is preferably 5% to 35%, more preferably 15% to 25%, by weight, based on its total mass. Ignition loss is determined by the mass loss when heat treated in air at 400°C for 3 hours.

[0037] Generally, the powder P obtainable as described has a relatively uniform particle size.

[0038] The aqueous solution or suspension to be spray-dried is advantageously passed through at least one filter on its way from its production site to the spray-drying apparatus before entering the spray-drying apparatus, for example to remove any coarse particles that may clog the spray nozzle. The temperature of the conveying conduit is expediently maintained at the final production temperature of the aqueous solution or suspension. The temperature is preferably 60 to 130°C, more preferably 70 to 120°C, and most preferably 75 to 110°C. At this time, the remaining solution or suspension, respectively, that has not been spray-dried is constantly mixed by stirring. The residence time in the vessel (= the average residence time of the aqueous solution / suspension in the vessel divided by the average rate at which the solution / suspension is added to the spray-drying apparatus) is preferably 0.1 to 30 hours, more preferably 0.5 to 15 hours, and even more preferably 1 to 5 hours.

[0039] Industrially, the aqueous solutions or suspensions to be spray-dried are usually produced in stirred vessels made of stainless steel of type 1.4541 (DIN 10020). The spray-drying apparatus and the stirring apparatus are suitably made of the same material.

[0040] The powder P obtained in c) can be directly subjected to a heat treatment (also called calcination) in e) to form the catalytically active multi-element oxide. Alternatively, it is possible to first prepare a geometrically shaped precursor in d).

[0041] The geometrically shaped precursors subjected to heat treatment in the method of the invention may in each case be produced from powder P by using various alternative methods.

[0042] In a simple embodiment of the method of the invention, the powder P is used to directly form a geometrically shaped precursor of any desired geometry by compaction, e.g., press-congealing or tableting (e.g., as shown for comparable powder mixtures in documents DE 102008054586 A1, DE 102008040093 A1, and DE 102008040094 A1). Examples of typical geometric shapes of shaped precursors according to the invention are spheres (the diameter of which may be, for example, 2 to 10 mm), as well as solid or hollow cylinders (rings) with an outer diameter and length typically between 2 and 10 mm. In the case of hollow cylinders, a wall thickness of 1 to 3 mm is appropriate.

[0043] Of course, it is also possible to mix further auxiliaries for subsequent shaping (shaping auxiliaries) into the powder P. Useful auxiliaries include glidants or lubricants, such as graphite, carbon black, polyethylene glycol, stearic acid, salts of stearic acid, starch, polyacrylic acid, mineral oil, vegetable oil, water, boron nitride, boron trifluoride, glycerol, fine Teflon powder, and / or cellulose ethers.

[0044] The aforementioned lubricants may partially or completely decompose during the heat treatment of the geometrically shaped precursor and / or may be chemically transformed to form substances that escape in gaseous form.

[0045] The mixture to be compressed may contain additional reinforcing agents, such as glass, asbestos, silicon carbide, and / or potassium titanate microfibers, to further shape the precursor and promote coherence of the resulting geometric shape.

[0046] In contrast to lubricants, reinforcing aids are typically essentially completely preserved during the inventive heat treatment of the geometrically shaped precursor.

[0047] Of course, it is also possible to further mix the lubricant and the reinforcing agent together.

[0048] Based on the total amount of powder mixture to be compressed into a shaped precursor in accordance with the present invention, the total amount of shaping aids present is generally no more than 30% by weight, usually no more than 20% by weight, and often no more than 10% by weight (but often 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).

[0049] The shaping in the production of the geometrically shaped precursor can preferably be carried out by extruding a plastically formable mass (obtained kneaded material / mass) by kneading powder and liquid.

[0050] An advantageous method of kneading, extruding and drying is employed, for example, in EP-A-3805194.

[0051] When the shaping in the production of the geometrically shaped precursor is carried out by extrusion or strand pressing, it is advantageous to further mix in at least one liquid (liquid binder). This liquid 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 (e.g., formic acid, acetic acid (preferably), propionic acid, fumaric acid, and / or maleic acid or their corresponding aqueous solutions, and / or a component of such an aqueous solution).

[0052] Calculated as pure lower organic carboxylic acids, these (preferably acetic acid) are advantageously incorporated in a total amount of 5 to 15% by weight, based on the content of powder P in the entire mixture. The total water content of the resulting mixture can be 5% to 45% by weight, preferably 10% to 30% by weight. To ensure favorable shaping by extrusion, it is preferable to adjust the water content so that the resulting plastically formable mass has good formability. Too low a liquid content can result in a hard plastic mass with a very high viscosity. In contrast, too high a liquid content can result in a mass with a low viscosity and insufficient plastic formability.

[0053] The incorporation of one or more lower organic carboxylic acids (preferably acetic acid) and / or their aqueous solutions is suitably carried out by kneading with maximum uniformity. The temperature during kneading is generally below 50°C. Typically, said temperature is in the range of 20 to 50°C, suitably in the range of 30 to 40°C. Kneading preferably takes less than 12 hours, more preferably 10 to 360 minutes, most preferably 20 to 120 minutes.

[0054] The resulting plastically formable mass (resulting kneaded material, resulting kneaded composition) is then shaped by extrusion into bodies (shaping precursors) of the desired geometric shape. In the simplest case, these may be strands (solid cylinders). Naturally, rings are also possible extrudates according to the invention.

[0055] In the case of a geometrically shaped precursor obtained by extrusion, the heat treatment of the precursor includes drying the precursor. Generally, this drying is 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. Drying can be carried out under an atmosphere of air, dry air, or nitrogen.

[0056] The ignition loss of the molding precursor is suitably 5% by mass to 35% by mass, particularly suitably 15% by mass to 25% by mass, based on the total mass of the molding precursor. The ignition loss is determined by the mass loss when heat-treated in air at 400°C for 3 hours.

[0057] The powder P obtained in c) or the shaped precursor obtained in d) is then subjected to a heat treatment to form the catalytically active multi-element oxide (also called calcination).

[0058] The calcination is carried out at a temperature of 200 to 600° C., preferably 300 to 500° C., more preferably 350 to 450° C., particularly preferably 360 to 430° C. (in each case material temperature). In particular during the calcination, the material advantageously has a very substantially uniform temperature according to the invention.

[0059] Calcination can be carried out in a batch or continuous manner.

[0060] In the case of batch firing, a temperature program with one or more temperature plateaus can be employed, as described in EP 1 633 467. The heating rate is preferably 0.1 to 20 K / min, more preferably 0.5 to 10 K / min, most preferably 1 to 5 K / min.

[0061] In continuous firing, the material passes through an oven. The firing may be carried out isothermally or using various temperature zones as described in EP 1 322 585. The temperature of the first temperature zone is preferably at least 30° C. lower than the highest temperature of the other temperature zones.

[0062] Calcination may be carried out in a stationary or moving bed of powder P or shaped precursor. Calcination of the shaped precursor is preferably carried out in a moving bed. Suitable apparatuses are rotary kilns, as described in EP-A-1 633 467, or belt kilns, as described in EP-A-1 322 585. Rotary kilns are preferred.

[0063] The heat treatment (especially the calcination) of the powder P or the geometrically shaped precursor can be carried out either in an inert gas atmosphere, or in an oxidizing (gas) atmosphere, for example, in air (or another mixture of an inert gas and oxygen), or in 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 will be understood that the overall reducing atmosphere may be limited in its molecular oxygen content). The oxidizing (gas) atmosphere preferably contains 0.1% to 15% by volume, more preferably 0.5% to 10% by volume, and most preferably 1% to 8% by volume of molecular oxygen. A preferred oxidizing (gas) atmosphere contains, in addition to molecular oxygen, an inert gas, for example, nitrogen, and water vapor. The water vapor content is preferably less than 20% by volume, more preferably less than 10% by volume. Oxygen contents above and below the aforementioned limits usually reduce the resulting catalytic activity. In principle, the heat treatment can alternatively be carried out under reduced pressure.

[0064] During calcination, heat generation in the powder P or shaped precursor may become uncontrollable, resulting in damage to the catalytically active multi-element oxide produced. If ammonium salts are used at temperatures between 150 and 350°C, for example, ammonia may be released during calcination and may burn. Uncontrolled heat generation can be limited by adequate heat and gas exchange. Alternatively, the amount of material being calcined, the amount and composition of the atmosphere, and the temperature program can be adjusted.

[0065] If the heat treatment of the powder P or the geometrically shaped precursor is carried out in a gas atmosphere, the powder or precursor may be stationary or flowing.

[0066] In general, the heat treatment (especially the calcination) of the powder P or the geometrically shaped precursor may take 24 hours or more. Often, the heat treatment (especially the calcination) lasts from a few minutes to several hours, e.g., 0.5 to 10 hours, or 1 to 5 hours. Elevated temperatures are usually associated with shorter heat treatment (especially the calcination) durations, while lower temperatures generally involve longer heat treatment (especially the calcination) times. Higher temperatures (especially the calcination) and longer treatment times generally reduce the specific surface area of ​​the catalytically active multi-element oxide produced during the heat treatment of the geometrically shaped precursor (of the precursor composition).

[0067] The BET specific surface area of ​​the catalytically active multi-element oxide obtainable according to the present invention is typically between 10 and 32 m 2 / g, preferably 12 to 28 m 2 / g, more preferably 14 to 26 m 2 / g, most preferably 16-24m 2 / g (determined by gas adsorption (N2) according to Brunauer-Emmett-Teller (BET)). The description of the BET determination method is found in DIN ISO 9277 and J. Am. Chem. Soc. Vol. 60 , No. 2, pp. 309-319 (1938).

[0068] The thermal treatment (especially the calcination) of the geometrically shaped precursor is preferably carried out in a gas atmosphere containing oxygen and ammonia, which may be generated from the shaped precursor itself by incorporating an appropriate amount of ammonium ions into the shaped precursor.

[0069] The catalytic activity of the catalytically active multi-element oxide obtained by heat treatment exhibits optimum properties depending on the oxygen content of the calcination atmosphere as a whole.

[0070] Suitable calcination methods according to the present invention are disclosed, for example, in WO 2004 / 108284, EP 0 724 481, WO 2008 / 104577, WO 2004 / 108267 and WO 95 / 11081.

[0071] The resulting geometrically shaped catalyst bodies obtained during the thermal treatment of the geometrically shaped precursors can be used as such in fixed catalyst beds (so-called unsupported catalysts) in the catalysis of the heterogeneously catalyzed partial gas-phase oxidation of acrolein to acrylic acid.

[0072] The preferred geometric shape of the unsupported catalyst according to the present invention is, for example, a solid or hollow cylinder with an outer diameter and length of 2 to 10 mm. In the case of a hollow cylinder, a wall thickness of 1 to 3 mm is suitable. Of course, the unsupported catalyst may also have a spherical geometric shape, in which case the diameter of the sphere may be 2 to 10 mm.

[0073] 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 with a non-uniform geometric shape, can also be converted into a finely divided form (for example, ground into powder or chips) for catalyzing the heterogeneously catalyzed partial oxidation of acrolein to acrylic acid (including in a fluidized or moving bed).

[0074] However, particularly advantageously, in accordance with the invention, the catalytically active multi-element oxide is converted into a finely divided form (e.g., comminuted to a powder or chips, for example by grinding), and this finely divided form is applied to the outer surface of the geometrically shaped support as a catalytically active multi-element oxide shell (to obtain a so-called eggshell catalyst).

[0075] Typically, the application is carried out with the aid of a liquid binder, which functions as a bonding fluid and with its help bonds the finely divided catalytically active multi-element oxide to the outer surface of the geometrically shaped support. The bonding fluid is then at least partially removed again from the coated geometrically shaped support (e.g., by passing hot gas through it, 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.

[0076] A low residual water content is advantageous. In general, the aforementioned residual water content is typically at least 0.5% by weight, often at least 2% by weight. The analysis of the residual water content herein is generally based on determination using an HB43 moisture analyzer from 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 this temperature. The measurement is terminated if the mass loss within 20 seconds is less than 1 mg.

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

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

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

[0080] Surface roughness R of the outer surface of the geometrically shaped support Z is preferably in the range of 30 to 100 μm, more preferably in the range of 50 to 70 μm (determined with the Hommel Tester for DIN-ISO surface measurement parameters from Hommelwerke to DIN 4768 Sheet 1). Particularly preferred are carriers with rough surface geometry made of CeramTec (DE) made from C220 steatite.

[0081] The support material may be porous or non-porous, preferably non-porous (the total volume of pores in a geometrically shaped support is advantageously less than or equal to 1% by volume, based on the volume of the corresponding geometrically shaped support).

[0082] The BET specific surface area (per unit mass) of the support material is preferably low, preferably less than 5, even more preferably less than 3, even more preferably less than 1, and especially preferably less than 0.5 m 2 / g.

[0083] The geometrically shaped carrier may be of regular or irregular shape, although geometrically shaped carriers that are of regular shape are preferred.

[0084] The longest dimension of the geometrically shaped carrier is typically in the range of 1 to 10 mm (the longest dimension is the longest straight line connecting two points on the outer surface of the shaped carrier).

[0085] Preferably, spheres or (solid) cylinders, especially hollow cylinders (rings) or Berl saddles, are used as the geometrically shaped carriers. The preferred diameter of the carrier spheres is 1 to 6 mm. When a cylinder is used as the geometrically shaped carrier, 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 more typically 1 to 4 mm. A very particularly preferred geometrically shaped carrier is a hollow cylindrical carrier having a length of 3 to 8 mm, an outer diameter of 4 to 8 mm, and a wall thickness of 1 to 2 mm. Examples of preferred ring shapes for shaped carriers include hollow cylinders with a geometric shape of 7 mm x 3 mm x 4 mm (external diameter x length x inner diameter), as well as hollow cylinders with geometric shapes of 6 mm x 6 mm x 4 mm, 7 mm x 7 mm x 5 mm, 8 mm x 8 mm x 6 mm, 7 mm x 7 mm x 4 mm, 6 mm x 6 mm x 3 mm, and 6.5 mm x 6.5 mm x 5 mm. Preferred geometric shapes of the support are also all shaped supports (especially all those disclosed as examples) disclosed in Research Disclosure Database Number 532036 in August 2008. The production of the eggshell catalysts CE and IE disclosed herein can also be carried out using any of the annular supports (especially those with a geometric shape of 7 mm x 4 mm x 3 mm or 6 mm x 6 mm x 4 mm) disclosed herein as examples.

[0086] The thickness of the catalytically active multi-element oxide shell applied to the outer surface of a geometrically shaped support (in particular the annular supports detailed above, the outer surface of which further comprises a surface defining the ring cavity) is suitably and generally between 10 and 1000 μm. In the case of eggshell catalysts, the thickness of this shell is preferably between 10 and 500 μm, more preferably between 100 and 500 μm, and most preferably between 200 and 450 μm.

[0087] Advantageously, the shell thickness is substantially uniform across the individual eggshell catalysts. When producing relatively large production batches of eggshell catalysts, the shell thickness is also substantially uniform across several individual eggshell catalyst rings. The above-mentioned uniformity of the shell thickness is suitably often within the range of the figures shown in the examples of DE 10360058 A1.

[0088] The finely divided catalytically active multi-element oxide can be applied to the outer surface of the geometrically shaped support, for example, by first wetting the outer surface with a liquid binder in a controlled manner (e.g., by spraying). The thus-wetted geometrically shaped support is then brought into contact with the finely divided catalytically active multi-element oxide, which subsequently fixes a layer of the active composition on the wetted surface (e.g., by sprinkling the finely divided catalytically active multi-element oxide (active composition powder) onto the wetted geometrically shaped support described in EP 0 714 700 A1).

[0089] In this context, "wetted in a controlled manner" means that the support surface is adequately wetted to adsorb the liquid binder, but the liquid phase itself is not visually visible on the support surface. If the support surface is too wet, the finely divided catalytically active multi-element oxide will aggregate into separate aggregates, but will not adhere to the surface. Details can be found in DE-A-2909671 and DE-A-10051419, EP-A-0714700, and WO 2022 / 090019. It will be understood that this operation can be repeated periodically to achieve an increase in layer thickness. In this case, the coated base body becomes a new "support", etc.

[0090] Alternatively, it is possible to adopt all other application methods recognized as prior art in EP-A-0 714 700 for the preparation of the eggshell catalysts detailed above.

[0091] Examples of useful liquid binders include water, organic solvents, or solutions of organic substances (e.g., organic solvents) in water, 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; aminoalcohols, such as ethanolamine or diethanolamine; and monofunctional or polyfunctional organic amides, such as formamide. Suitable organic binder components (binder promoters) that are 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 aforementioned 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 binder is its ability to thoroughly wet both the finely divided catalytically active multi-element oxide (i.e., 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, of course, adapted to the desired shell thickness. For shell thicknesses in the range of 100 μm to 500 μm, suitable active composition powders are preferably those in which at least 50% of the total number of granular powder particles pass through a sieve with a mesh size (circular mesh) of 1 to 20 μm, or alternatively 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, the remarks on page 18 of WO 2005 / 120702 are equally applicable.

[0094] The eggshell catalyst obtainable as described is preferably obtained by the preparation method described and detailed by way of example in EP-A-0714700 (see also WO 2011 / 134932 and the examples in DE-A-10360057). An aqueous solution of 75% by weight of water and 25% by weight of glycerol is a preferred liquid binder. The method for heat-treating the geometrically shaped precursor is advantageously carried out according to the present invention by the procedure described and detailed by way of example in DE-A-10360057.

[0095] Alternatively, the procedure of the present invention encompasses a method for producing a catalytically active multi-element oxide, in which a geometrically shaped precursor is formed using a (fine-grained) mixture of powder P and, optionally, one or more shaping aids, in such a way that a shell of this (fine-grained) mixture (fine-grained precursor composition mixture) 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 heat treatment of the geometrically shaped precursor thus obtained (including at least partial removal of the liquid binder further used for 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 (catalytically essentially inactive) geometrically shaped support.

[0096] As already mentioned, the catalytically active multi-element oxides obtainable according to the invention are particularly suitable for catalyzing the heterogeneously catalytic 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. These catalytically active multi-element oxides are particularly notable for the long service life of the catalyst beds packed together during the partial oxidation process, during which the target product is formed with high activity. A preferred use form of the catalytically active multi-element oxides obtainable according to the invention is that of eggshell catalysts, preferably having a cyclic geometric shape. Here, it is particularly preferred to use the eggshell catalysts detailed in the examples of this specification in all examples and comparative examples in, for example, 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, and it is possible to replace the catalysts used in each of these international publications (the statements made about the eggshell catalysts of the examples of this specification are also applicable to the eggshell catalysts of the comparative examples of this specification).

[0097] In principle, the catalytically active multi-element oxides obtainable according to the invention are also likewise suitable in a correspondingly advantageous manner for catalysis of the heterogeneously catalyzed partial gas-phase oxidation of methacrolein to methacrylic acid.

[0098] The above is particularly true when the heterogeneously catalytic 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 10307983 A1, DE 19948523 A1, DE 19910508 A1, WO 2008 / 104577 A1, WO 2011 / 134932 A1, DE 19927624 A1, and DE 10360057 A1.

[0099] Heterogeneous 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 passed through a catalyst bed at an elevated temperature, the catalyst of which contains, as an active component, at least one catalytically active multi-element oxide obtainable according to the present invention, and the conversion of (meth)acrolein to (meth)acrylic acid occurs 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, steam as a component of the reaction gas mixture improves selectivity and activity. Furthermore, inert diluent gases with high molar specific heats, such as n-propane or carbon dioxide, are advantageous. These gases are preferably chemically converted to a degree of 5 mol% or less, more preferably 3 mol% or less, and most preferably 1 mol% or less, or are not chemically converted at all when the reaction gas mixture passes through the catalyst bed.

[0100] A heat exchange reactor is particularly suitable for carrying out the gas-phase partial oxidation of (meth)acrolein. The heat exchange reactor has at least one primary space and at least one secondary space separated from each other by a partition wall. In at least one primary 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 transfer medium flows through the secondary space, and heat exchange occurs between the two spaces via the partition wall, with the purpose of monitoring and controlling the temperature of the reaction gas mixture during its passage 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 with one or more temperature zones, as described in EP-A-0700174, EP-A-0700893, DE-A-19910508, DE-A-19948523, DE-A-19910506, DE-A-19948241, DE-A-2830765, DE-A-2513405, U.S. Pat. No. 3,147,084, DE-A-2201428, EP-A-0383224, JP-A-2007-260588, and JP-A-58-096041.

[0102] A fixed catalyst bed in this context takes the form of a corresponding bed of shaped catalyst bodies (optionally in admixture with inert geometric bodies for dilution) in the metal tubes (catalyst tubes) of a shell-and-tube reactor, and a temperature medium or multiple temperature mediums are conducted around the metal tubes (if there is more than one temperature zone, a corresponding number of spatially and essentially distinct temperature mediums are conducted around the metal tubes). The temperature medium is generally a salt melt. The reaction gas mixture is conducted through the catalyst tubes.

[0103] Alternatively, the fixed catalyst bed may also be in a hot plate reactor in the space between the hot plates through which the heat transfer medium flows, as recommended in DE 102004017150 A1, DE 19952964 A1 and DE 10361456 A1.

[0104] As already mentioned, the fixed catalyst bed may very generally consist not only of the catalyst obtainable according to the present invention, but also of such catalyst diluted with an inert geometric body. As used herein, an inert geometric body may also be a carrier (support) of the geometric shape used in the preparation of the eggshell catalyst of the present invention. Upstream and / or beyond the fixed catalyst bed may be a bed of inert shaped bodies only (such a bed of inert shaped bodies only is not usually included in the calculation of the space velocity of the reactant gas or reactant gas components over the fixed catalyst bed).

[0105] The catalyst tubes used in shell-and-tube reactors are conventionally made from ferritic steel and typically have a wall thickness of 1-3 mm. The internal diameter of the catalyst tube is generally 20-30 mm, often 21-29 mm or 23-28 mm. The length of the catalyst tube 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. Often, 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), with the distribution appropriately selected so that the distance between the central internal axes of adjacent catalyst tubes (referred to as the catalyst tube pitch) is between 35 and 45 mm (see EP 0 468 290 A1).

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

[0108] Packing the catalyst tubes in a shell-and-tube reactor with a catalyst obtainable according to the present invention (especially those detailed in the examples (and other comparative examples) of this specification) is advantageous, especially when the shell-and-tube reactor is operated at a (meth)acrolein space velocity relative to the packed catalyst of at least 90 L(STP) / l·h, or at least 110 L(STP) / l·h, or 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. Of course, such a packed catalyst is also advantageous for smaller (meth)acrolein space velocities (e.g., 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] The space velocity of the reaction gas input mixture over a fixed catalyst bed is herein understood to mean the amount of reaction gas input mixture in standard litres (=l(STP)) fed to the fixed catalyst bed per hour based on the volume of that bed (the bed volume does not include any part of the bed consisting only of inert material, which is the volume of the vacant space occupied by the bed (or a relevant part thereof)), i.e. based on the bed volume of the fixed catalyst bed, and the corresponding volume of gas in litres (unit = l(STP) / l·h) which it occupies under standard conditions, i.e. at 0° C. and 101.3 kPa.

[0110] The space velocity may also be based on only one component of the reactant gas input mixture (e.g., only the organic starting compound to be partially oxidized), in which case the space velocity is similarly expressed as the volume of component (e.g., the organic starting compound to be partially oxidized) in standard liters (units = l(STP) / l h) fed to the fixed catalyst bed based on bed volume per hour (bed volume does not include bed portions consisting solely of inert material, which is the volume of void space occupied by the bed (or its relevant bed portion)).

[0111] The fixed catalyst bed is generally configured so that its volume-specific activity increases in the direction of flow of the reactant gas.

[0112] This can be easily achieved by reducing the level of dilution of the fixed catalyst bed with inert shaped bodies in the direction of reaction gas flow. Alternatively, the specific activity per unit volume can be adjusted by using catalysts with different BET specific surface areas. Furthermore, it is possible to use eggshell catalysts with different pore volumes or eggshell thicknesses. Here, activity increases with increasing BET specific surface area, pore volume, or eggshell thickness.

[0113] Otherwise, the heterogeneous catalytic partial oxidation using the eggshell catalysts obtainable according to the invention can be carried out in all respects in a very general manner, as detailed in DE 103 50 822. The (meth)acrolein content in the reaction gas input mixture can have a value of 3% to 15% by volume, often 3.5% to 10% by volume, or even 4% to 8% by volume (in each case based on the total volume of the reaction gas input mixture).

[0114] The molar ratio of oxygen to (meth)acrolein in the reaction gas input mixture is usually at least 1. Typically, this ratio has a value of not more than 3. In many cases, the heterogeneous catalytic (meth)acrolein partial oxidation to (meth)acrylic acid is carried out at a volume ratio (l(STP)) of (meth)acrolein to oxygen to steam to inert gas present in the reaction gas input mixture of 1:(1-3):(0-20):(3-30), preferably 1:(1-3):(0.5-10):(7-10).

[0115] Useful inert diluent gases (these are gases or mixtures of gases that remain chemically unchanged to the extent of at least 95 mol%, preferably at least 97 mol%, or at least 99 mol%, and best up to 100 mol% in a single pass of the reaction gas mixture through the catalyst bed (e.g., 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 among these). The reaction temperature in such heterogeneous catalytic (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 often 245 to 320°C. The operating pressure (absolute pressure) is usually 101.3 to 350 kPa, or 101.3 to 250 kPa, or 101.3 to 205 kPa (especially as the input pressure to the fixed catalyst bed). 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.

[0116] The (meth)acrolein conversion is typically at least 90 mol %, often at least 98 mol %, often at least 98.5 mol %, or even at least 99 mol %, based on a single pass of the reaction gas mixture through the fixed catalyst bed.

[0117] Otherwise, the method of partial oxidation according to the invention can be carried out in full accordance with the recommendations of the teachings of DE 102007019597 A1 or WO 2008 / 104577 or WO 2011 / 134932.

[0118] More specifically, the source used for the (meth)acrolein necessary for the partial oxidation of the present invention may be directly a (meth)acrolein-containing product gas mixture of the heterogeneous catalytic partial oxidation of C3 / C4 precursor compounds of (meth)acrolein (e.g., propene or isobutene) to (meth)acrolein, and there is no need to previously remove (meth)acrolein from such a product gas mixture.

[0119] (Meth)acrylic acid can be removed from the product gas mixture of the partial oxidation in known manner, for example, by first converting the (meth)acrylic acid into a condensed phase by adsorption and / or condensation means. Subsequent thermal separation processes, such as rectification and / or crystallization, can then isolate the (meth)acrylic acid from the condensed phase at any desired purity (see DE 602004924 and WO 2006 / 114428, as well as the prior art documents cited therein).

[0120] The present invention further provides a catalytically active multi-element oxide comprising the elements Mo, W, V, Cu, and Sb, in which the ratio of said elements is represented by the following general formula (I): Mo 12 W a V b Cu c Sb d (I) where: a=0.4~3.0, b=1.0~6.0, c=0.1~3.0, and d=0.1 to 3.0, The molar ratio of the element Mo in the total amount of all non-oxygen elements is between 5 and 95 mol %, and the catalytically active multi-element oxide can be obtained by one of the methods mentioned above.

[0121] The BET surface area of ​​the catalytically active multi-element oxide is preferably 10 to 32 m 2 / g, preferably 12 to 28 m 2 / g, more preferably 14 to 26 m 2 / g, most preferably 16-24m 2 / g.

[0122] The stoichiometric coefficient a of the element W in the general formula (I) is preferably 0.6 to 2.5, more preferably 0.8 to 2.0, and most preferably 1.0 to 1.6.

[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 2.5, more preferably 0.6 to 2.0, and most preferably 0.8 to 1.5.

[0125] The stoichiometric coefficient d of the element Sb in the general formula (I) is preferably 0.2 to 1.5, more preferably 0.25 to 1.2, and most preferably 0.3 to 0.8.

[0126] The molar ratio of the element Mo in the total amount of all non-oxygen elements is preferably 20 to 90 mol %, more preferably 35 to 85 mol %, and most preferably 50 to 80 mol %.

[0127] The catalytically active multi-element oxides used for the oxidation of acrolein to acrylic acid are typically not in a form in which all metal elements are present in their maximum oxidation state. By maximum oxidation state of a metal element, we mean the oxidation state in which each element typically exists at its maximum in the oxide of the metal element. The maximum oxidation states of the relevant elements are V(V), Mo(VI), W(VI), Cu(II), and Sb(V).

[0128] For example, vanadium may not be in the V(V) oxidation state, or not entirely in that state, but may be in, for example, the V(IV) or V(III) oxidation state, or may be in a mixed oxidation state: it is possible for some of the vanadium to be in the V(V) oxidation state and another portion to be in the V(IV) oxidation state, or for some of the vanadium to be in the V(IV) oxidation state and another portion to be in the V(III) oxidation state.

[0129] The other metal elements in the mixed metal oxides can be in different oxidation states, for example, Cu(I), Mo(V), Mo(IV), and Sb(III).

[0130] In principle, a delocalized state can be envisaged where a relatively high electron mobility would allow one to distinguish between non-discrete metal atoms in different oxidation states.

[0131] Without wishing to engage in any further theoretical interpretations, catalytically active multi-element oxides can be analyzed by redox titration after decomposition in aqueous solution. The oxidizable electron content is quantitatively determined by titration with KMnO4 as the oxidizing agent. For this purpose, the catalytically active multi-element oxides are used directly in powder form before application to the shaped support.

[0132] Catalytically active multi-element oxides having a defined ratio R of oxidizable electrons to vanadium have particularly advantageous properties in the oxidation of acrolein to acrylic acid. 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].

[0133] This ratio R is preferably 1.1 to 2.2, more preferably 1.2 to 2.1, and most preferably 1.3 to 2.0.

[0134] Titration using KMnO4 as the oxidizing agent is carried out as follows: Place 15 ml of 96% sulfuric acid, 15 ml of water, and 10 ml of 85% phosphoric acid in a long-necked flask on a stirring hotplate and purge with argon to remove air. Weigh 100–200 mg of sample into a weigh boat and rinse with water into the long-necked flask. Heat the flask to a boil under argon until the solution volume is concentrated to 40 ml and the sample is completely dissolved (approximately 30–45 minutes, depending on the amount of water required).

[0135] The solution is then transferred to a titration vessel equipped with a Pt electrode and potentiograph combination, e.g., Titrando 808 (Metrohm AG, Herisau, Switzerland). The titration is carried out under argon atmosphere at 80 °C. The sample is titrated with an aqueous KMnO solution (0.02 mol / l) until the color changes to reddish-purple (KMnO is in excess). During the titration, the electrochemical potential is measured and recorded using the combined Pt electrode.

[0136] The titration curve should show an inflection point. The absence of an inflection point indicates the absence of oxidizable electrons. The volume of the KMnO4 solution at the endpoint is read from the titration curve.

[0137] The specific content of oxidizable electrons e is e=(V*C*5) / EW where V is the volume of the KMnO4 aqueous solution [l], C is the concentration of the KMnO4 aqueous solution [mol / l], and z is the mass of the sample [g].

[0138] In some cases, the titration curve may show multiple turning points, indicating the presence of electrons with different oxidation potentials. Two turning points likely indicate the presence of V(III) and V(IV).

[0139] The present invention provides a method for producing an eggshell catalyst in which a catalytically active multi-element oxide of the present invention and optionally a binder are applied to the exterior surface of a geometrically shaped support.

[0140] The present invention further provides an eggshell catalyst comprising a geometrically shaped support and, applied to the exterior surface of the geometrically shaped support, a catalytically active multi-element oxide of the present invention and, optionally, a binder.

[0141] The present invention provides a process for preparing acrylic acid by vapor-phase catalytic oxidation of acrolein over a fixed catalyst bed, in which the fixed catalyst bed comprises the catalytically active multi-element oxide of the present invention or the eggshell catalyst of the present invention. [Example]

[0142] Example 1 Cyclic eggshell catalyst C1 with catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.1 Sb 0.4 O n

[0143] Preparation of eggshell catalyst: To 3000 g of water in a 10 L flask at 95° C., 171 g of ammonium paratungstate heptahydrate (W content=70.65% by weight) was added with stirring (using a paddle stirrer at 250 rpm), and the mixture was stirred for an additional 5 minutes, resulting in a clear solution with a temperature of approximately 95° C. and a pH of 6.3.

[0144] Subsequently, 1.161 g of ammonium heptamolybdate tetrahydrate (Mo content=54.3% by weight) was added and the mixture was stirred for a further 5 minutes, resulting in a clear solution with a temperature of about 95° C. and a pH of 6.1.

[0145] Subsequently, 192 g of ammonium metavanadate (V content=43.56% by mass) was added and the mixture was stirred for a further 5 minutes, resulting in an orange solution with a temperature of about 95° C. and a pH of 6.5.

[0146] Subsequently, 32 g of antimony trioxide (Sb2O3, Sb content=83.54% by weight) was added and the mixture was stirred for another 30 minutes, resulting in a black suspension with a temperature of about 95° C. and a pH of 6.6.

[0147] Subsequently, 120.4 g of copper(II) acetate monohydrate (Cu(CHCOO)HO, Cu content = 31.8 wt%) was added and the mixture was stirred for another 10 min, resulting in a black suspension with a temperature of about 95 °C and a pH of 6.2.

[0148] The resulting suspension was finally continuously introduced into a Mobile Minor 2000 spray tower equipped with a FO A1 atomizing head (GEA Niro, Soeborg, Denmark) by a rotary atomizer at 30,000 rpm for approximately 2 hours. Drying was performed using a hot air stream (9 m 3 (STP) / h) at an inlet temperature of 310° C. and an outlet temperature of 120° C. A powder was obtained.

[0149] 1000 g of the powder was placed in a ZS1-80 kneader (Coperion Werner & Pfleiderer GmbH & Co. KG; Stuttgart, Germany). This powder was kneaded with 370 g of aqueous acetic acid (acetic acid content 35% by mass) at room temperature at 15 rpm for 30 minutes. The material was then extruded (length 1-10 cm, diameter 6 mm). The extrudates were dried in a circulating air drying cabinet under a thin air flow (5% by volume O in N, 300 L (STP) / h) at 120 °C for 16 hours.

[0150] 400 g of the precursor composition removed from the air-circulating drying cabinet was subjected to batch calcination in a rotary kiln (similar to U.S. Pat. No. 9,149,799). Calcination was carried out under a gas flow consisting of air and nitrogen (total flow rate 186 L (STP) / h) with an oxygen content of 2.3% by volume. The rotary kiln was heated to 400°C within 2 hours and maintained at that temperature for an additional 1 hour. Subsequently, heating was stopped and the material was allowed to cool to ambient temperature while continuing to rotate.

[0151] The material removed from the rotary kiln was subsequently ground to a fine powder in a ZM200 mill (Retsch GmbH, Haan, Germany).

[0152] This fine powder was used to prepare 1500 g of a C220 steatite type (Ceram Tec GmbH, Plochingen, Germany) cyclic carrier (outer diameter 7 mm, length 3 mm, inner diameter 4 mm, surface roughness Rz 45 μm, BET surface area 0.035 m). 2 / g). Coating was performed in a Hi-Coater LHC 25 / 36 mixer (Gebruder Lodige Maschinenbau GmbH, Paderborn, Germany). This mixer was modified for continuous powder feeding. For this purpose, a funnel-shaped container was connected to the mixer drum (diameter 36 cm) via a hose (outer diameter 11.1 mm, inner diameter 8 mm). For coating, 300 g of fine powder was introduced into the funnel-shaped container. Feeding was achieved by a 50 ms pressure pulse and a positive pressure of 0.7 bar. During feeding, the contents of the funnel-shaped container were set in motion by a V-shaped modified anchor stirrer (manufactured in-house). A 1-second pause was provided between each 2-second stirring period.

[0153] The binder used was a 25% by weight aqueous glycerol solution. In parallel with the powder feed, the solution was metered into the mixer at 3 g / min using a two-phase nozzle, type 570 S75 (Dusen-Schlick GmbH, Coburg, Germany). The powder feed was 6 cm below the two-phase nozzle and tilted downwards by 40°. The powder was fed into the outside of the spray cone of the two-phase nozzle. The mixer drum rotated clockwise at 15 rpm. Coating was carried out within 40 minutes at 25°C. The rotation speed was then reduced to 2 rpm, and drying was carried out in an air flow (220 l (STP) / h) at 130°C for 30 minutes. This was followed by cooling to 25°C. The powder was incorporated into the surface of the support. Neither the formation of paired supports nor agglomeration was observed.

[0154] The coated carriers were then degreased in a UM400 circulating air drying cabinet (Memmert GmbH & Co. KG, Schwabach, Germany). The coated carriers were uniformly distributed on a 2 cm thick perforated sheet. The perforated sheet had a thickness of 0.5 cm, an aperture 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.

[0155] The cyclic eggshell catalyst C1 had an oxidation-active composition content of 14.9 wt %. The BET surface area of ​​the catalytically active multi-element oxide was 18.2 m 2 / g. The ratio R was 1.8.

[0156] Analysis of eggshell catalyst: A reaction tube (stainless steel (material 1.4541), 30 mm outer diameter, 2 mm wall thickness, 26 mm inner diameter, 464 cm length) was filled from top to bottom as follows: Section 1: Length 80cm Empty tube; Section 2: Length 60cm a preliminary bed of steatite rings with a geometrical shape of 7 mm × 3 mm × 4 mm (external diameter × length × internal diameter, C220 steatite from Ceram Tec GmbH); Section 3: 100cm long a fixed catalyst bed consisting of a homogeneous mixture of 20% by mass of steatite rings with a geometrical shape of 7 mm × 3 mm × 4 mm (external diameter × length × internal diameter, C220 steatite from Ceram Tec GmbH) and 80% by mass of eggshell-type catalyst; Section 4: 200cm long Section 3, a fixed catalyst bed consisting of only eggshell catalyst; Section 5: 10cm long downstream bed of the same steatite ring as in section 2; Section 6: Length 14cm Catalyst substrate made of stainless steel (material 1.4541) to accommodate the fixed catalyst bed.

[0157] The reaction gas mixture flowing from top to bottom through each reaction tube packed as described above 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 oxides, 7% by volume of water, and 82.3% by volume nitrogen.

[0158] The feed temperature of the reaction gas mixture (at the inlet to the reaction tube) was 210° C., and the space velocity of acrolein (as defined in DE 19927624 A1) over the fixed catalyst bed was 80 l (STP) / lh.

[0159] Along the length of the reaction tube (except for the last 10 cm of the empty tube in section 1 and the last 3 cm of the tube in section 6), a stirred, externally electrically heated salt bath (50 kg of a mixture of 53% by weight of potassium nitrate, 40% by weight of sodium nitrite, and 7% by weight of sodium nitrate, salt melt) was flowed around the reaction tube (flow rate in the tube was 3 m / s). The salt bath temperature TB (temperature at which the salt bath was fed) was set in all cases to obtain an acrolein conversion of 99.3 mol % based on a single pass of the reaction gas mixture through the fixed catalyst bed. No change in the salt bath temperature due to additional heating was observed along the reaction tube (the salt bath released more heat than the reaction tube released into the salt bath).

[0160] The selectivity for acrylic acid production (S AS (mol %)) is understood to mean:

number

[0161] CO x The selectivity of production (total combustion) is calculated similarly.

[0162] An active composition (catalyst) that produces the same conversion at a lower temperature under otherwise unchanged reaction conditions has a higher activity.

[0163] The conversion rate of acrolein (C AC (mol %)) is understood to mean:

number

[0164] Table 1 below shows the results obtained after 100 hours of operation as a function of the eggshell catalyst used.

[0165] Example 2 (Comparative Example) Cyclic eggshell catalyst C2 having catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.1 Sb 0.4 O n

[0166] The procedure was the same as in Example 1. The source used for copper was 48.4 g of copper(II) oxide (CuO, Cu content = 79.1 wt%) instead of copper(II) acetate monohydrate. The cyclic eggshell catalyst C2 had an oxidation-active composition content of 14.9 wt%. The BET surface area of ​​the catalytically active multi-element oxide was 5.5 m 2 / g. The ratio R was 1.7.

[0167] Example 3 (Comparative Example) Cyclic eggshell catalyst C3 with catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.1 Sb 0.4 O n

[0168] The procedure was the same as in Example 1. The source used for copper was 143 g of copper(II) nitrate hydrate (Cu(NO3)22.5H2O, Cu content = 26.8 wt%) instead of copper(II) acetate monohydrate. The cyclic eggshell catalyst C3 had an oxidation-active composition content of 14.7 wt%. The BET surface area of ​​the catalytically active multi-element oxide was 16.2 m 2 / g. The ratio R was 1.5.

[0169] Example 4 (Comparative Example) Cyclic eggshell catalyst C4 with catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.1 Sb 0.4 O n

[0170] The procedure was the same as in Example 1. The source used for copper was 150.7 g of copper(II) sulfate hydrate (Cu(SO4)5H2O, Cu content = 25.4 wt%) instead of copper(II) acetate monohydrate. The cyclic eggshell catalyst C4 had an oxidation-active composition content of 14.9 wt%. The BET surface area of ​​the catalytically active multi-element oxide was 16.5 m 2 / g. The ratio R was 1.7.

[0171] <Example 5 (Comparative Example)> Cyclic eggshell catalyst C5 with catalytically active oxide composition Mo 12 W 1.2 V3Cu 1.1 Sb 0.4 O n

[0172] The procedure was the same as in Example 1. The source used for antimony was 63.5 g of antimony(III) acetate (Sb content = 42 wt%) instead of antimony(III) oxide. The cyclic eggshell catalyst C5 had an oxidation-active composition content of 14.7 wt%. The BET surface area of ​​the catalytically active multi-element oxide was 12.8 m 2 / g. The ratio R was 1.7.

[0173] [Table 1]

[0174] From the test results shown in Table 1, it is clear that the salt bath temperature TB required for an acrolein conversion of 99.3 mol% in Example 1 of the present invention is much lower than that in the comparative example, and therefore the catalyst of the present invention has higher activity, which is even more surprising in that the catalyst compositions are the same.

Claims

1. A method for producing a catalytically active multi-element oxide comprising the elements Mo, W, V, Cu, and Sb, wherein the ratio of said elements is represented by the following general formula (I): Mo １２ W ａ V ｂ Cu ｃ Sb ｄ (I) where: a=0.4~3.0, b=1.0~6.0, c=0.1 to 3.0, and d=0.1 to 3.0, The molar ratio of the element Mo in the total amount of all non-oxygen elements is 5 to 95 mol %, and the production of the catalytically active multi-element oxide is a) preparing an aqueous solution or suspension using a source of at least one of the elemental components W, Mo, and V of said catalytically active multi-element oxide; b) mixing the aqueous solution or suspension obtained in a) with sources of Cu and Sb, the elemental components of the catalytically active multi-element oxide; c) producing a powder P by drying and optionally grinding the aqueous solution or suspension obtained in b); d) optionally using the powder P obtained in c) and optionally adding one or more shaping aids to homogeneously mix the mixture, and then obtaining a geometrically shaped precursor from the mixture obtained; e) subjecting the powder P obtained in c) or the geometrically shaped precursor obtained in d) to a heat treatment to form the catalytically active multi-element oxide, A method wherein copper acetate is used as a source of said elemental component Cu and antimony oxide is used as a source of said elemental component Sb.

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

3. 3. The method according to claim 1, wherein the stoichiometric coefficient a of the element W in the general formula (I) is 1.0 to 1.6, and / or the stoichiometric coefficient b of the element V in the general formula (I) is 2.5 to 4.

5.

4. 4. The method according to any one of claims 1 to 3, wherein copper (II) acetate monohydrate is used as the source of the elemental component Cu and antimony (III) oxide is used as the source of the elemental component Sb.

5. 5. The method according to any one of claims 1 to 4, wherein water-soluble salts are used as sources of the elemental components Mo, V, and / or W.

6. 6. 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.

5.

7. 7. The method according to claim 1, wherein the stoichiometric coefficient d of the element Sb in the general formula (I) is 0.3 to 0.

8.

8. A catalytically active multi-element oxide comprising the elements Mo, W, V, Cu, and Sb, wherein the ratio of said elements satisfies the following general formula (I): Mo １２ W ａ V ｂ Cu ｃ Sb ｄ (I) where: a=0.4~3.0, b=1.0~6.0, c=0.1 to 3.0, and d=0.1 to 3.0, A catalytically active multi-element oxide, wherein the molar ratio of the element Mo in the total amount of all non-oxygen elements is between 5 and 95 mol %, and wherein the catalytically active multi-element oxide is obtainable by the method according to any one of claims 1 to 7.

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

5.

10. The BET surface area of ​​the catalytically active multi-element oxide is 16 to 24 m ２ 10. The catalytically active multi-element oxide according to claim 8 or 9, wherein the metal ion content is 1000 ppm / g.

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

5.

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

8.

13. 13. A method for producing an eggshell catalyst, comprising the step of applying the catalytically active multi-element oxide of any one of claims 8 to 12 and optionally a binder to the exterior surface of a geometrically shaped support.

14. 13. An eggshell catalyst comprising a geometrically shaped support, a catalytically active multi-element oxide according to any one of claims 8 to 12 applied to the outer surface of said geometrically shaped support, and optionally a binder.

15. 15. A process for producing acrylic acid by the vapor-phase catalytic oxidation of acrolein over a fixed catalyst bed, wherein the fixed catalyst bed comprises the catalytically active multi-element oxide of any one of claims 8 to 12 or the eggshell catalyst of claim 14.

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