DE19922156A1 - Multimetal oxide composition, useful as oxidation catalyst, especially for gas phase production of (meth)acrylic acid, is based on crystallites of constant composition - Google Patents

Abstract

Multimetal oxide composition (I) comprises: (i) a multimetal oxide (II) of molybdenum with vanadium, niobium, tantalum, tungsten and/or rhenium and boron, silicon, phosphorus, germanium, arsenic and/or antimony and optionally other metal(s) or (ii) a mixture of (II) and another multimetal oxide (III), in which (I) consists of crystallites of constant composition. Multimetal oxide composition is of formula (I); (A)p(B)q (I) Mo12X<1>aX<2>bX<3>cX<4>dX<5>eOx (II) MofX<6>gX<7>hOy (III) A = a multimetal oxide of formula (II); B = a multimetal oxide of formula (III); X<1> = hydrogen, up to 97 mole-% of which may be replaced by ammonium, potassium, rubidium and/or cesium; X<2> = vanadium, niobium (Nb), tantalum (Ta), tungsten and/or rhenium; X<3> = boron, silicon, phosphorus, germanium, arsenic and/or antimony (Sb); X<4> = chromium, manganese, iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), magnesium (Mg), calcium (Ca), strontium (Sr) and/or barium (Ba); X<5> = sulfur; X<6> = Cu, Fe, Co, Ni, Zn, cadmium, Mn, Mg, Ca, Sr and/or Ba; X<7> = Nb, Ta and/or Sb; a = 1-3; b = 0.1-2; c = 0-5; d, e = 0-1; f = 0-2; g = 0.5-1.5; h = 2-4; x, y = values depending on the valency and frequency ox elements other than oxygen; p = 1; and q = 0; or p, q not = 0 and p/q = (160-1):1. The standard deviation of the stoichiometric coefficient a of the variable X<1> of individual crystallites of component A is less than 0.15, especially less than 0.10. Independent claims are also included for: (a) methods of preparing the multimetal oxide (I); (b) the apparatus used in preparation.

Description

The invention relates to multimetal oxide compositions, processes for their preparation, and Devices for performing the method. The invention further relates to Use of the multimetal oxide materials as oxidation catalysts, in particular for Gas-phase catalytic oxidative production of (meth) acrylic acid.

The term multimetal oxide mass used here denotes salt-like built heteropoly compounds that are derived from phosphoromolybdic acid. Next They usually contain metallic and transition metallic molybdenum and phosphorus Elements, especially copper, vanadium, arsenic, antimony, cesium and potassium (see DE-A-43 29 907, DE-A-26 10 249, JP-A-7/185354). Multimetal oxide materials have been of industrial importance as catalysts in the past 20 years in purely acid-catalyzed reactions as well as in oxidation reactions, especially in the oxidative production of methacrylic acid. A serious disadvantage However, compared to catalyst types of other classes of compounds reduced service life.

DE-A 44 05 060 proposes multimetal oxide compositions with a two-phase structure, the gross element composition of which essentially corresponds to that of the multimetal oxide compositions according to the invention, with improved catalytic activity and selectivity and with an improved service life. The multimetal oxide compositions according to DE-A 44 05 060 correspond to formula I.

[A] _p [B] _q (I),

in which the variables have the following meaning:

A Mo ₁₂ X _a ¹ X _b ² X _c ³ X ⁴ S _e X _f ⁵ O _x
BX ⁶ _g X ⁷ _h O _y
X ¹ phosphorus, arsenic, boron, germanium and / or silicon,
X ² vanadium, niobium and / or tungsten,
X ^{3 is} hydrogen, of which up to 97 mol% can be replaced by potassium, rubidium, cesium and / or ammonium (NH ₄ ),
X ⁴ antimony and / or bismuth,
X ⁵ rhenium and / or rhodium,
X ⁶ copper, iron, cobalt, nickel, zinc, cadmium, manganese, magnesium, calcium, strontium and / or barium,
X ⁷ niobium, tantalum and / or antimony,
a 1 to 6, preferably 1 to 3 and particularly preferably 1.5 to 2.5
b 0 to 6, preferably 0.2 to 4 and particularly preferably 0.5 to 2,
c 3 to 5,
d 0 to 6, preferably 0 to 3 and particularly preferably 0.5 to 1.5,
e 0 to 3, preferably 0.01 to 1 and particularly preferably 0.01 to 0.2,
f 0 to 3, preferably 0.01 to 1 and particularly preferably 0.1 to 0.5,
g 0.5 to 1.5, preferably 0.9 to 1.1,
h 2 to 4, preferably 2 to 3 and particularly preferably 2 to 2.5,
x, y numbers determined by the valency and frequency of the elements in I other than oxygen, and
p, q numbers other than zero, whose ratio p / q is 12: 0.1 to 12: 48, preferably 12: 0.25 to 12: 12 and particularly preferably 12: 0.5 to 12: 4,

that the portion [A] _p in the form of three-dimensionally extended areas A of the chemical composition, which are differentiated from their local environment due to their different chemical composition
A Mo ₁₂ X _a ¹ X _b ² X _c ³ X _d ⁴ S _e X _f ⁵ O _x

and the proportion [B] _q in the form of three-dimensionally extended regions B of the chemical composition which are delimited from their local environment on account of their chemical composition which is different from their local environment

BX ⁶ _g X ⁷ _h O _y

included, the areas A, B relative to each other as in a fine-particle mixture are distributed from A and B.

In contrast, it is an object of the invention, the catalyst life of multime to further improve tall oxide masses. A method for producing the Multimetal oxide materials with improved tool life and for carrying out the Appropriate devices are provided.

The object is achieved by multimetal oxide compositions of the formula

[A] _p [B] _q (I),

solved, in which the variables have the following meaning:

A Mo ₁₂ X _a ¹ X _b ² X _c ³ X _d ⁴ X _e ⁵ O _x
B Mo _f X ⁶ _g X ⁷ _h O _y
X ¹ H, of which up to 97 mol% can be replaced by ammonium, K, Rb and / or Cs,
X ² V, Nb, Ta, W and / or Re,
X ³ B, Si, P, Ge, As and / or Sb,
X ⁴ Cr, Mn, Fe, Co, Ni, Cu, Zn, Mg, Ca, Sr and / or Ba,
X ⁵ S,
X ⁶ Cu, Fe, Co, Ni, Zn, Cd, Mn, Mg, Ca, Sr and / or Ba,
X ⁷ Nb, Ta and / or Sb,
a 1 to 3,
b 0.1 to 2,
c 0 to 5,
d 0 to 1,
e 0 to 1,
f 0 to 2,
g 0.5 to 1.5,
h 2 to 4,
x, y numbers which are determined by the valency and frequency of the elements other than oxygen in (I),
p = 1 and q = 0 or
p, q integers other than zero, whose ratio p / q is from 160: 1 to 1: 1,
where the standard deviation of the stoichiometric coefficient a of the variable X ^{1 of} individual crystallites within component A of the multimetal oxide mass is less than 0.15, in particular less than 0.10.

It was found that the service life of multimetal oxide catalysts depends to a large extent on the spread with respect to the composition of the individual crystallites of component A within the multimetal oxide mass [A] _p [B] _q .

Multimetal oxide materials have a largely crystalline structure: Primary structure is the structure of the anion of the salt-like heteropolyver bonds referred to. The anion is a molecular ion, built up over a complex Linking oxometalate polyhedra or a heteroatom with Oxometalate polyhedra.  

Some of these primary structures were named after their discoverers, for example the Keggin structure, PMo ₁₂ O ₄₀ , or the Dawson structure, P ₂ Mo ₁₈ O ₆₄ . The primary structure is the same in the solid as in the solution. The anions of the primary structure and the cations on the lattice sites are defined in the secondary structure. With the same primary structure, the secondary structure is determined, for example, by the degree of hydration, by the ion radius of the counterions (cations) and by the charge of the anions of the primary structure. Component A of the multimetal oxide mass is composed of individual crystallites that have this secondary structure. Crystalline particles with grain sizes in the range from 0.1 to 10 μm are defined as crystallite, the grain size denoting the diameter of the particles in a known manner. The constancy of the composition of these individual crystallites is essential for uniform catalyst properties.

The constancy of the cesium content of different individual crystallites is of particular importance, since otherwise the crystallites with a relatively low cesium content are predominantly involved in the catalytic process, which leads to an in-depth reduction of the molybdenum to molybdenum oxides, and the primary structure of the Keggin unit, for example disintegrates. The alkali metal cations released in the process migrate into neighboring crystallites in which the heteropoly structure is still present, displacing the protons still present there, which are decisive for the catalytic activity, and thus lead to an exponential drop in the catalyst activity. The standard deviation s is defined in a known manner by the formula (II)

in which
s = standard deviation
n = number of measurements
j = measurement number
x = measured value
x = arithmetic mean of all measured values. (see E. Kreyszig: Advanced Engineering Mathematics, J. Wiley, New York, 5 ^th Edition, 1983, p 895th).

The multimetal oxide compositions according to the invention can be produced by different methods:

A first procedure involves the following steps:

• a) Preparation of one or more, preferably 2 or 3, in particular aqueous solutions and / or dispersions of element sources of the Multi metal oxide masses,
• b) optionally entering pH-lowering agents or producing Solutions that are predominantly or exclusively pH-lowering agents contain,
• c) mixing the solutions and / or dispersions,
• d) optionally heating, especially in the presence of inert or Reactive gases,
• e) drying, in particular evaporation or spray drying,
• f) shaping, in particular into tablets or hollow cylinders and
• g) calcining.

In process stage a), aqueous solutions and / or dispersions of the Element sources of the multimetal oxide mass produced. The element sources are are either already oxides or such compounds that are caused by heating, optionally in the presence of oxygen, can be converted into oxides. In addition to the oxides Halides, hydrates, formates, Oxalates, acetates, carbonates, hydroxides, ammonium compounds and / or inorganic Acids into consideration. Sources which are particularly suitable for the individual elements are in DE-A 44 05 060. In doing so, individual elements become a solution and / or dispersion which can be mixed as homogeneously as possible and which are not  or cause almost no precipitation of heteropoly compounds. In at least one the solutions and / or dispersions may preferably have a pH-lowering agent Nitric acid, are entered (process stage b).

In process stages a) and b), warm, d. H. a temperature of about 40 to 60 ° C, containing solutions and / or dispersions.

Process stage c), ie the mixing of the previously prepared solutions and / or dispersions of the element sources, is of crucial importance for the properties of the multimetal oxide materials obtained. JP-A-7/185354 specifies mixing times of 8 minutes, preferably 25 seconds, (claim 2 or claim 3). In contrast, the mixing times according to the invention are considerably shorter: less than one second, preferably less than 10 ^-3 seconds, particularly preferably less than 10 ^-5 seconds. This quasi-instantaneous mixture separates the precipitation product, which already has the secondary structure or a precursor of the secondary structure of the heteropoly compound, so quickly that the diffusion processes and thus segregations due to different solubility products no longer play a role. This process control of the extremely fast mixture ensures the low standard deviation of the composition of different individual crystallites within the multimetal oxide mass, in particular with regard to the content of components 1.

The precipitation product is worked up in a known manner. With some It may be advantageous for recipes to first heat the dispersion produced especially in the presence of inert or active gases, whereas other recipes have one immediate separation of the precipitate from the liquid phase with subsequent Require drying, especially by evaporation or spray drying. The The masses obtained are then shaped, for example as tablets or Hollow cylinder and finally calcined, usually at temperatures from 350 to 500 ° C, preferably 350 to 400 ° C.  

In a further process, a, preferably aqueous, solution or Dispersion of the element sources and optionally a pH-lowering agent, especially nitric acid.

The precipitation with formation of the secondary structure or a precursor of the secondary Structure is temperature-induced in the subsequent process steps c1), d. H. by Heating causes, the heating time until the precipitation of 50% of the precipitation product is less than a second. Heating can be done by indirect heating in a flow tube, by heat conduction or radiation, or preferably by direct heating by injecting steam, for example, into the solution or dispersion. Conversely, the solution or dispersion can also be converted into a very hot fluid, for example oil, in the form of fine droplets.

According to a further preferred process, process steps c) and c1) be combined, d. H. the precipitation can be brought about by rapid mixing and heating become.

The following devices are proposed according to the invention for the decisive process stages c) and / or c1):
A first embodiment is designed as a cylindrical, in particular circular cylindrical, double-jacket tube, with a plurality of preferably circular bores through the inner jacket, with a diameter of the bores preferably in the region of the wall thickness of the inner jacket. The solution or dispersion of the element sources is added through the inner tube, optionally with the addition of a pH-lowering agent, in particular nitric acid; passed and through the space between the inner shell and outer shell water vapor, which passes through the preferably circular holes in the inner shell into the fluid flowing through the inner tube, heats it, thereby causing the formation of the precipitate.

An embodiment of a device for carrying out process step c) includes a flow tube onto which at least one, preferably two or three, inlet pipes openings with formation of at least one mixing point, preferably symmetrical, where the ratio of the diameter of the flow pipe and inlet pipes in the Mixing points causes a degree of turbulence of Re ≧ 3000.

A first mixing point is preferably located at the upstream end of the Flow tube by opening preferably 2 or 3, in particular symmetrically arranged supply lines, trained. In the event of the confluence of 2 Zu Run lines in the upstream end of the flow tube become these preferably in a vertical projection to one another and to the flow tube in each case in one Angle of 120 ° arranged. However, a mixing point can also be opened by a single supply line to a suitable location of the flow tube are formed.

The ratio of the inner diameter of the flow pipe and the feed lines must be chosen so that a high degree of turbulence is achieved in the mixing points, which is characterized by a value of the Reynolds dimension figure of ≧ 3000. The Reynolds measure is known by the equation

Re = Duρ.η ^-1 ,

with D = diameter, u = flow velocity of the fluid, ρ = density and η = Viscosity, defined.

In the area of the mixing point (s), the flow tube can preferably be used static mixer, a dynamic mixer or a shear force mixer.

According to a further preferred embodiment, in the flow tube, Connection to at least one mixing point, at least one heating zone must be installed a heating of the fluid in the flow tube with a heating rate of  guaranteed at least 20 ° C per second. Can be used as a heating medium for example, microwaves can also be used.

Preferably, in the flow direction downstream of the mixing point (s), if appropriate Heating zone (s) a pressure control valve must be installed. About the pressure control valve Suspension relaxed after the mixture is complete.

Another preferred embodiment provides that the mixing point (s) into one Circuit is (are), with the downstream end of the Flow pipe opens into a stirred tank and a Umpumpleitung the bottom of the Stirring container with the mixing point (s) connects. The multimetal oxide masses according to the invention are used as oxidation catalysts with improved service life, in particular used for the gas-phase catalytic oxidative production of (meth) acrylic acid.

The multimetal oxide materials are preferably used as full catalysts used, with the geometry of a hollow cylinder with an outer diameter and one Length of 2 to 10 mm and a wall thickness of 1 to 3 mm.

The invention is explained in more detail below with the aid of exemplary embodiments and a drawing. Figs. 1 to 4 show the preferred embodiments of the apparatus for performing the method steps c) and optionally c1).

Fig. 1 shows a flow tube, preferably made of stainless steel, with an inside diameter of preferably 6 mm, at the upstream end of which feed lines 2 open to form a mixing point 3 . The feed lines 2 are preferably also stainless steel tubes and have an inside diameter of preferably 4 mm. Dosing scales for checking the mass flows FIC or for controlling ratio-controlled mass flows FFIC and valves are built into the feed lines. Fig. 1 shows three inlet lines 2, the symmetrical flow to the mixing point 3, and a further feed line 2, which opens at an appropriate, further downstream location of the flow tube 1. A heating section 4 is installed from the mixing point 3 , for example as a heating jacket through which a heat transfer medium flows.

FIG. 2 shows a further preferred embodiment of a device according to the invention, the reference numbers from FIG. 1 being used accordingly for identical elements. The device shown in FIG. 2 contains, in addition to the device from FIG. 1, a static mixer 5 in the area of the mixing point 3 .

Fig. 2a shows an enlarged detail with the mixing point 3 in the static mixer 5.

Fig. 3 shows a further preferred embodiment of a device according to the invention, with two heating sections 4 with temperature regulators TIC and a pressure control valve and a pressure regulator PIC at the downstream end of the flow tube.

Fig. 4 shows the integration of the flow tube 1 with feed lines 2 and 3 in a mixing point circuit via a stirred tank 6 and a recirculating line. 7 The inside diameter of flow tube 1 and pumping line 7 is preferably 24 mm, the inside diameter of the inlet lines 2 is preferably 4 mm. The flow tube 1 opens into the stirred tank 6 , preferably in the upper part thereof. The pumping line 7 starts at the bottom of the tube container 6 . The pumped mass flow is controlled in a suitable manner, for example via a magnetic inductive flow meter, not shown. If the pH value rises above a predetermined limit, usually in the range between 1 and 2, the metering of the mass flow via the feed line 2 is interrupted; a pH indicator with switch contact QIS ^{+ is} used for this. A static mixer is preferably installed in the flow tube 1 in the area of the mixing point 3 , for example a wire mesh packing made of stainless steel 1.4401, laboratory packing EX® from Sulzer.

Examples

The examples relate to the production of multimetal oxide compositions M according to the invention and of multimetal oxide masses MV for comparison (the content of hydrogen, Ammonium and oxygen of the resulting masses determine the respective Manufacturing process firm; the values were not determined regularly and are therefore in the stoichiometries specified are not regularly included).

The solvent or dispersant is in all examples and comparative examples Water.

The terms conversion, selectivity, deactivation rate, standard deviation and mixing time are defined here as follows, unless stated otherwise:

The deactivation rate is defined as the temperature increase of the heating medium in degrees Kelvin between the time after 120 hours of operation and 720 hours of operation is necessary in order to maintain the given conversion of (meth) acrolein.

In the present case, the standard deviation with regard to the concentration of components X ^{1 was carried out} by evaluating 10 measurements in each case. The concentration measurements were carried out using analytical transmission electron microscopy. For this purpose, the multimetal oxide materials were embedded in polymethyl methacrylate and cut into slices approximately 100 nanometers thick using an ultramicrotome from Reichert. These disks were installed as samples in a Model 400 KVFX transmission electron microscope from JEOL. The element concentration was determined with the aid of an energy-dispersive X-ray detector and the associated evaluation unit (model Noran TN5500) with a resolution of 0.05 µm (compare Goldstein et al .: Principles of Analytical Electronmicroscopy, Plenum Press 1989, page 155).

The mixing time was according to the equation

calculated, with relative speed = [1/2. (v ² _{material flow 1} + v ² _{material flow 2} )] ^1/2 where v denotes the speed, for the special case of a mixing point with two inlet pipes leading in at an angle of 120 ° C.

M1: 27.60 g / sec of a first, 40 ° C. hot mixed solution of 31.03% by weight of molybdate phosphoric acid, 0.41% by weight of vanadium and 0.41% by weight were introduced into the mixing point 3 of a device according to FIG .-% arsenic acid and a second, 60 ° C hot mixed solution with a mass flow of 10.53 g / sec with 42.62 wt .-% cesium nitrate and 10.57 wt .-% copper (II) nitrate trihydrate. The resulting precipitation suspension was evaporated to dryness at 85 ° C. in the course of 3 hours. Hollow cylinders with an outer diameter of 7 mm, a length of 6 mm and an inner diameter of 3 mm were then formed and calcined in an air stream at 380 ° C. for 5 hours.

MV2: Example 1 of EP-A-0 467 144 was reworked. In 5000.00 g of water were at 40 ° C 4260.00 ammonium heptamolybdate tetrahydrate, 141.13 g ammonium metavanadate, 391.92 g cesium nitrate, 388.90 g 40% orthophosphoric acid, 30.36 g 35% aqueous ammonium sulfate solution and 193.07 g antimony trioxide (100% Senarmontite, average particle size 2.5 µm) stirred. The suspension was inside heated from 20 minutes to 95 ° C and then with 19.48 g of rhenium heptoxide and 242.90 g of copper (II) nitrate trihydrate are added and at 85 ° C. within 3 hours Evaporated dry. Hollow cylinders with a  Outside diameter of 7 mm, a length of 6 mm and a hollow circle diameter of 3 mm and calcined for 5 hours at 380 ° C in an air stream.

M2: In the mixing point 3 of a device according to FIG. 1, a first mixed solution with 50.71% by weight ammonium heptamolybdate tetrahydrate and 1.68% by weight ammonium metavanadate, a second solution, was fed via feed line 2 , 46.67 g / sec a mass flow of 9.63 g / sec with 22.60% by weight of cesium nitrate and 17.04% by weight of orthophosphoric acid and a third dispersion with a mass flow of 3.27 g / sec with 1.80% by weight % Ammonium sulfate and 49.67% by weight antimony trioxide (100% senarmontite, average particle size 2.5 µm). The solutions or dispersions 1 to 3 were each metered into the mixing point at an initial temperature of 40.degree. The mixture was heated to 95 ° C. in a 1.75 m long heating section and then a fourth 90 ° was heated via a further feed line 2 , which is welded to the flow tube at an angle of 60 ° and has an inner diameter of 4 mm Solution with a mass flow of 2.40 g / sec with 56.18 wt .-% copper (II) nitrate trihydrate and 4.51 wt .-% rhenium heptoxide added. The resulting precipitating solution was evaporated to dryness at 85 ° C. within 3 hours. Hollow cylinders with an outer diameter of 7 mm, a length of 6 mm and an inner diameter of 3 mm were formed from the mass obtained in this way and calcined in an air stream at 380 ° C. for 5 hours.

MV3: Example 1 of EP-A-0 424 900 was reworked: 300.00 g of water were added at 40 ° C 100.00 g ammonium heptamolybdate tetrahydrate, 1.66 g ammonium metavanadate, 4.77 potassium nitrate, 8.16 g 85% orthophosphoric acid in 10 g water and 4.13 g of antimony trioxide (75% senarmontite, 25% valentinite, with a number-average Particle diameter of 3.6 µm) stirred. The suspension was removed within 20 Minutes heated to 95 ° C and then with 1.14 g copper (II) nitrate trihydrate in 30 Parts of water and 4.46 g of 20% nitric acid are added. Then was at 85 ° C. evaporated to dryness within 3 hours. The resulting mass turned 16 Dried at 130 ° C for hours. Then hollow cylinders with a  Outside diameter of 7 mm, a length of 6 mm and an inside diameter of 3 mm shaped and calcined for 5 hours at 380 ° C in an air stream.

M3: 235.34 g / sec of a first, 40 ° C. hot mixed solution of 47.16% by weight ammonium heptamolybdate tetrahydrate, 0.78% by weight were fed into the mixing point 3 of the device shown in FIG. Ammonium metavanadate and 2.45% by weight potassium nitrate and 2.82 g / sec 41 ° C hot mixed suspension of 41.05% by weight ortho-phosphoric acid and 2.29% by weight antimony trioxide (75% senarmontite, 25% Valenti nit, metered with a number-average particle diameter of 3.6 µm). The mixture was heated in a heating section to 95 ° C. and then a third, 40 ° C. hot mixed solution with a mass flow of 28.75 g / sec with 0.66% by weight copper (II) nitrate trihydrate and 0. 52 wt .-% nitric acid added. The resulting precipitation solution was evaporated to dryness at 85 ° C. in the course of 3 hours. Hollow cylinders with an outer diameter of 7 mm, a length of 6 mm and an inner diameter of 3 mm were formed from the mass obtained in this way and calcined in an air stream at 380 ° C. for 5 hours.

MV4: Example 1 of JP-A-7/185354 was reworked: 519 g of 85% by weight phosphoric acid, 130 g of copper (2) phosphate trihydrate, 819 g of cesium nitrate and 284 g of 60% strength aqueous arsenic acid were added in 4800 g ion-exchanged water dissolved with stirring, the solution being kept at 40 ° C. 6356.00 g of ammonium heptamolybdate tetrahydrate were dissolved in 6990 g of ion-exchanged water in a stirred tank with a two-stage paddle stirrer, which was thermostated to 40 ° C. While the stirring speed of the two-stage paddle stirrer was set to 150 rpm (mixing time 15.7 seconds, power consumption 0.12 kW / m ³ ), the entire first solution was conveyed into the second solution within 2 minutes. There was a precipitation. 137 g of vanadium pentoxide were added to the resulting suspension. The measurement of the mean particle diameter by means of centrifugal sedimentation gave a value of 15 µm. Steam was then passed through the outer jacket of the stirred tank and the stirrer speed was increased to 200 rpm (mixing time 11.8 seconds, power consumption 0.28 kW / m ³ ). The mixture was then thermostated at 125 ° C. for 42 hours, a suspension having a viscosity of 4740 cP and an average particle size of 2.6 μm being obtained. The suspension was dried at 120 ° C. The dry solid showed the fingerprint of the Dawson structure of the heteropoly compound. The dry material was ground, mixed with the addition of 30 parts of water and 4 parts of glass fibers, kneaded and extruded to give moldings with a diameter of 3 mm and a length of 7 mm. The moldings were dried at 120 ° C. and calcined at 35 ° C. in a nitrogen atmosphere. The X-ray diffraction diagram of the mass obtained in this process step showed the Keggin structure of the heteropoly compound.

M4: 22.69 g / sec of a first mixed suspension with 51.16% by weight ammonium heptamolybdate tetrahydrate and 1.10% by weight were fed into the mixing point 3 of the device according to FIG. Vanadium pentoxide and 21.62 g / sec of a second, 40 ° C hot mixed solution with 6.80 wt .-% phosphoric acid, 2.01 wt .-% copper (II) phosphate trihydrate, 12.62 wt .-% cesium nitrate and 2.63% by weight of arsenic acid metered. The mixture was heated in a heating section from 125 ° C. and then expanded into a spray dryer via a pressure-maintaining valve to normal pressure. The dry material was ground, kneaded with the addition of 30 parts of water and 4 parts of glass fibers and extruded to give moldings 5 mm in diameter and 7 mm in length. The moldings were dried at 120 ° C. and calcined at 435 ° C. under a nitrogen atmosphere. The X-ray diffraction pattern of the product obtained at this stage of the process showed the Keggin structure of the heteropoly compound.

M5. In the mixing point 3 of Figure 2 were 22.26 g / sec of a first, 40 ° C hot mixed solution of 39.87 wt .-% of ammonium heptamolybdate tetrahydrate, 1.32 wt .-% of ammonium metavanadate, 3.67 wt % Cesium nitrate, 2.77% by weight orthophosphoric acid, 0.10% by weight ammonium sulfate, 2.74% by weight antimony trioxide (100% senarmontite, number average particle diameter 3.6 µm) and 2.27% by weight % Copper (II) nitrate trihydrate and 2.44 g / sec of a second solution of 65.00% by weight nitric acid. The resulting precipitation solution was evaporated to dryness at 85 ° C. in the course of 3 hours. The solid was ground and heat treated in a nitrogen flow at 190 ° C in a fluidized bed for 20 minutes. Hollow cylinders with an outer diameter of 7 mm, a length of 6 mm and an inner diameter of 3 mm were then formed and calcined in an air stream at 380 ° C. for 5 hours.

M6: 28.27 g / sec of a first, 40 ° C. hot mixed solution with 41.86% by weight ammonium heptamolybdate tetrahydrate, 2.52% by weight ammonium metavanadate, 4.20 were placed in the mixing point 3 of a device according to FIG % By weight of cesium nitrate, 2.22% by weight of orthophosphoric acid, and 2.60% by weight of copper (II) nitrate trihydrate and 3.54 g / sec of a second solution of 65.00% by weight - dosed nitric acid. The resulting fall solution was evaporated to dryness at 85 ° C. in the course of 3 hours. Hollow cylinders with an outer diameter of 7 mm, a length of 6 mm and an inner diameter of 3 mm were then formed and calcined in an air stream at 380 ° C. for 5 hours.

M7: 89.03 g / sec of a 40 ° C. mixed solution of 39.87% by weight ammonium hepta molybdate tetrahydrate, 1.32% by weight ammonium metavanadate, 3.67% by weight cesium nitrate, 2.77% by weight orthophosphoric acid, 0.10% by weight ammonium sulfate, 2.74% by weight Antimony trioxide (100% senarmontite, number average particle diameter 3.6 µm) and 2.27 wt .-% copper (II) nitrate trihydrate were in the inner tube of a cylindrical Double jacket tube dosed. The double jacket tube consisted of two concentric, each 2 mm thick tubes with an inner diameter of 15 or 28 mm and a length of 6 m. From the mixing point, the delivery pipe continued to have one Diameter of 15 mm. The outer diameter was 19 mm. The whole The outer surface of the inner tube showed a total of about 500, evenly over length and circumference distributed through holes with a diameter of 2 mm. In the Steam was introduced between the inner and outer tube, whereby Steam temperature and amount were set so that the suspension at the end of the Rohrs had a temperature of 150 ° C. At the end of the heating section was a  Pressure maintaining valve arranged. This was followed by a heated pipe section Unheated pipe section 0.5 m long, in a buffer tank with 20 l volume ended.

M8: 145.69 g / sec of a 40 ° C. mixed suspension of 48.73% by weight ammonium heptamolybdate tetrahydrate, 2.15% by weight ammonium metavanadate and 3.35% were added to the mixing point 3 of a device according to FIG .-% antimony trioxide (100% senarmontite, number-average particle diameter 3.2 µm) and 30.39 g / sec in a mixed solution at 60 ° C with 25.79% by weight cesium nitrate, 16.21% by weight ortho-phosphoric acid , 1.46% by weight ammonium sulfate and 13.32% by weight copper (II) nitrate trihydrate. From the mixing point, the flow pipe was designed as a double-walled pipe, corresponding to the device described for M7, but with a length of the double-walled pipe of 4 m. The vapor pressure was controlled so that the suspension reached a temperature of 95 ° C at the end of the heating section. The resulting precipitation solution was collected in a 1 m ³ storage container and stirred there at 85 ° C. for 2 hours. Mixed suspension was continuously drawn off from the storage container and spray-dried. The resulting spray powder (component A) was dry-mixed with Lindgrenit, Cu ₃ (MoO ₄ ) ₂ (OH) ₂ , average particle size 7.2 μm (component B) for 25 minutes. The molar mixing ratio of component A to component B was 1: 0.1. The dry matter was formed with the addition of 3% by weight of graphite into hollow cylinders (outer diameter × length × inner diameter equal to 7 × 6 × 3 mm), slowly heated to 380 ° C. in an air stream and calcined at 380 ° C. for 5 hours.

MV9: 1000 g of ammonium heptamolybdate were added in succession to 1200 g of water tetrahydrate, 55.21 g of ammonium metavanadate and 128.80 g of cesium nitrate. The The temperature of the aqueous solution was raised to 40 to 45 ° C. Then 76 % By weight of ortho-phosphoric acid and 2.49 g of ammonium sulfate and the Temperature set to 45 to 48 ° C. Then 51.60 g of antimony trioxide (100 ° Senarmontite, number average particle diameter of 2.4 µm) added, to 95 ° C warmed, held at this temperature for one hour and at one  Outlet temperature of 110 ° C spray dried. The resulting component A was with copper antimonate of average particle size 5.1 µm (component B) 25 minutes long dry mixed. The molar mixing ratio of component A to com component B was 1: 0.2.

M9: Two solutions were metered into mixing point 3 in the manner described for M8. In contrast to M8, solution 1 had a mass flow of 290.50 g / sec and a proportion of 48.88% by weight of ammonium heptamolybdate tetrahydrate, 2.70% by weight of ammonium metavanadate and 2.52% by weight of antimony trioxide (Senarmontit 100 %, number-average particle diameter 2.4 µm) and solution 2 a mass flow of 62.37 g / sec, a proportion of 29.32% by weight of cesium nitrate, 15.80% by weight of orthophosphoric acid, 0.57% by weight. -% ammonium sulfate and 12.98 wt .-% copper (II) nitrate trihydrate. Component A was obtained analogously to M8, as component B, in contrast to M8, copper antimonate with an average particle size of 5.1 μm and a molar mixing ratio of component A to component B of 1: 0.2 was selected. The further procedure corresponds to the description of M8, the dimensions of the hollow cylinders differing from M8 being 5 × 3 × 2 mm.

M10: 52.55 g / sec of a mixed solution at 40 ° C. with 45.04% by weight ammonium heptamolybdate tetrahydrate, 2.71% by weight ammonium metavanadate and 2.19% by weight were added to the mixing point 3 of a device according to FIG % ortho-phosphoric acid and 6.50 g / sec of a 65.00% by weight nitric acid. The precipitation solution was evaporated to dryness at 85 ° C. in the course of 3 hours, and then thermostated in a nitrogen stream at 190 ° C. in a fluidized bed for 20 minutes. Hollow cylinders measuring 7 × 6 × 3 mm were then formed and calcined in an air stream at 380 ° C. for 5 hours.

M11: Analog M10, but solution 1 with mass flow of 40.23 g / sec, 44.12% by weight Ammonium heptamolybdate tetrahydrate, 2.66% by weight ammonium metavanadate, 2.03 % By weight of cesium nitrate and 2.14% by weight of orthophosphoric acid and solution 2 with 4.87 g / sec from 65% by weight nitric acid.  

M12: Analogous to M10 but solution 1 with a mass flow of 41.04 g / sec with 43.25 g % By weight ammonium heptamolybdate tetrahydrate, 2.60% by weight ammonium metavanadate, 3.98% by weight of cesium nitrate and 2.10% by weight of orthophosphoric acid and solution 2 with a mass flow of 4.87 g / sec, 65.00% by weight nitric acid.

M13: Analogous to M10 but with a mass flow of 41.86 g / sec of solution 1 42.40% by weight ammonium heptamolybdate tetrahydrate, 2.55% by weight ammonium metavanadate, 5.85% by weight cesium nitrate and 2.06% by weight ortho-phosphoric acid as well Solution 2 with a mass flow of 4.87 g / sec 65.00% by weight nitric acid.

M14: Analog M10 but with a mass flow of 42.68 g / sec with 41.59% by weight Ammonium heptamolybdate tetrahydrate, 2.50% by weight ammonium metavanadate, 7.65 % By weight of cesium nitrate and 2.02% by weight of orthophosphoric acid and solution 2 with a Mass flow of 4.87 g / sec 65.00% by weight nitric acid.

M15: Mixing point 3 was integrated into a circuit according to FIG. 4. First, a first solution of 65.00% by weight nitric acid was placed in the stirred tank 6 and pumped through the pump line 7 at a dosage of 100.00 g / sec. The pumping line with a preferred inner diameter of 24 mm and the feed line 2 with a preferred inner diameter of 4 mm open into a mixing point 3 at the upstream end of a flow tube 1 with a preferred inner diameter of 24 mm. The flow tube 1 opens into the stirred tank 6 , preferably in the upper part thereof. A static mixer consisting of a wire mesh packing made of stainless steel 1.4401, laboratory packing EX® from Sulzer is preferably installed in the flow tube 1 from the mixing point 3 . Via the feed line 2 was introduced into the mixing station 3, a solution with a mass flow of 1.00 g / sec a 40 ° C hot mixed solution of 44.40 wt .-% of ammonium heptamolybdate tetrahydrate, 4.08% by weight cesium nitrate and 2, 6 wt .-% ortho-phosphoric acid metered. The dosing was stopped as soon as a pH of 2 was reached. The precipitation solution obtained was withdrawn from the stirred kettle and spray-dried at an inlet temperature of 380 ° C. and an outlet temperature of 120 ° C. The solid present in the case solution showed the X-ray diffraction pattern of the Keggin structure. The spray powder was then heat-treated in a nitrogen bed at 190 ° C. in a heat bed for 20 minutes, shaped into hollow cylinders measuring 7 × 6 × 3 mm and calcined in a stream of air at 380 ° C. for 5 hours.

M16: Analogous to M15 but with a mixed solution with 43.86% by weight of ammo niumheptamolybdate tetrahydrate, 1.21% by weight ammonium metavanadate, 4.04% by weight Cesium nitrate and 2.13% by weight orthophosphoric acid.

M17: Analogous to M15 but with a mixed solution of 43.34% by weight ammo niumheptamolybdate tetrahydrate, 2.39% by weight ammonium metavanadate, 3.99% by weight Cesium nitrate and 2.10% by weight ortho-phosphoric acid.

M18: Analogous to M15 but with a mixed solution with 42.33% by weight ammo niumheptamolybdate tetrahydrate, 4.67% by weight ammonium metavanadate, 3.89% by weight Cesium nitrate and 2.06% by weight ortho-phosphoric acid.

M19: Analogous to M15 but with a mixed solution of 41.36 wt.% Ammo niumheptamolybdate tetrahydrate, 6.85% by weight ammonium metavanadate, 3.81% by weight Cesium nitrate and 2.01% by weight ortho-phosphoric acid.

M20: 47.20 g / sec of a mixed solution at 40 ° C. with 50.15% by weight ammonium heptamolybdate tetrahydrate as well as 2.77% by weight ammonium metavanadate and 8.13 g were placed in the mixing point 3 of a precipitation apparatus according to FIG. 3 / sec of a 60 ° C mixed solution with 14.13 wt .-% ortho-phosphoric acid and 26.77 wt .-% cesium nitrate. The mixture was heated to 90 ° C. in heating section 4 , then a 80 ° C. solution of 16.83% by weight copper (II) nitrate trihydrate was added via a further feed line at 2.00 g / sec another heating section 4 heated and then relaxed into a spray dryer via a pressure maintaining valve to normal pressure. The spray drying was carried out at a gas inlet temperature of 380 ° C and a gas outlet temperature of 120 ° C. Hollow cylinders measuring 7 × 6 × 3 mm were then formed and calcined in an air stream at 380 ° C. for 5 hours.

M21: Analogous to M20, but the last added solution with a mass flow of 2.00 g / sec and a proportion of 16.83 wt .-% copper (II) nitrate trihydrate.

M22: Analogous to M20, but the last added solution with a mass flow of 1.72 g / sec and 58.83% by weight copper (II) nitrate trihydrate.

M23: Analog M20, but solution 1 with a mass flow of 53.08 g / sec with 44.59 % By weight ammonium heptamolybdate tetrahydrate, 2.46% by weight ammonium metavanadate and 0.61 wt% antimony trioxide (100% senarmontite, number average particle diameter 3.6 µm), and solution 2 with a mass flow of 7.73 g / sec with 15.86 % By weight of germanium dioxide and 21.66% by weight of cesium hydroxide and solution 3 with a mass flow of 4.12 g / sec with 8.20% by weight of copper (II) nitrate trihydrate and 10; 20th % By weight nitric acid. Contrary to the manufacturing process her the M20 mass accounted for the second heating stage.

M24: 26.38 g / s of a mixed solution at 40 ° C. with 44.86% by weight ammonium heptamolybdate tetrahydrate and 2.48% by weight ammonium metavanadate as well as 6.29 g were added to the mixing point 3 of a precipitation apparatus according to FIG. 3 / s of a mixed solution at 60 ° C. with 9.14% by weight of o-phosphoric acid and 17.31% by weight of cesium nitrate. The mixture was heated to 150 ° C. in heating section 4 and then expanded to normal pressure in a spray dryer via a pressure maintaining valve. The spray drying was carried out at a gas inlet temperature of 520 ° C and a gas outlet temperature of 110 ° C. The processing into hollow cylinders and calcination was carried out analogously to M20.

The use of the multimetal oxide compositions according to the examples given is described below as catalysts for the gas phase oxidation of methacrolein to methacrylic acid. To test the catalytic activity, the shaped catalyst bodies were pulverized (average grain diameter 2 to 3 mm) and in tubular reactors with an inner diameter of 8 mm and 50 g of catalyst bed and salt bath cooling with a gas mixture of the composition 6% by volume methacrolein, 9% by volume oxygen 16% by volume % Water vapor and 69 vol.% Nitrogen with a residence time of 3 seconds and a methacrolein loading of 0.2 g per g of catalyst per hour. The results with regard to conversion, selectivity, deactivation rate and standard deviation with regard to the concentration of element X ¹ are summarized in the table below. Compared to the comparison masses MV, the catalyst masses M show a significantly lower standard deviation of the concentration of component X ¹ and correspondingly lower deactivation rates, ie improved service life.

Claims (15)

1. Multimetal oxide compositions of the formula
[A] _p [A] _q (I)
in which the variables have the following meaning:
A Mo ₁₂ X _a ¹ X _b ² X _c ³ X _d ⁴ X _e ⁵ O _x
B Mo _f X ⁶ _g X ⁷ _h O _y
X ¹ H, of which up to 97 mol% can be replaced by ammonium, K, Rb and / or Cs,
X ² V, Nb, Ta, W and / or Re,
X ³ B, Si, P, Ge, As and / or Sb,
X ⁴ Cr, Mn, Fe, Co, Ni, Cu, Zn, Mg, Ca, Sr and / or Ba,
X ⁵ S,
X ⁶ Cu, Fe, Co, Ni, Zn, Cd, Mn, Mg, Ca, Sr and / or Ba,
X ⁷ Nb, Ta and / or Sb,
a 1 to 3,
b 0.1 to 2,
c 0 to 5,
d 0 to 1,
e 0 to 1,
g 0.5 to 1.5,
f 0 to 2,
h 2 to 4,
x, y numbers which are determined by the valency and frequency of the elements other than oxygen in (I),
p = 1 and q = 0 or
p, q integers other than zero, whose ratio p / q is from 160: 1 to 1: 1,
where the standard deviation of the stoichiometric coefficient a of the variable X ^{1 of} individual crystallites within component A of the multimetal oxide mass is less than 0.15, in particular less than 0.10. 2. A process for the preparation of multimetal oxide compositions according to claim 1, which comprises the following process steps:

• a) preparation of one or more, preferably 2 or 3, in particular aqueous solutions and / or dispersions of element sources of the metal oxide masses,
• b) if appropriate, adding pH-lowering agents or preparing solutions which predominantly or exclusively contain pH-lowering agents,
• c) mixing the solutions and / or dispersions,
• d) optionally tempering, in particular in the presence of inert or reactive gases,
• e) drying, in particular evaporation or spray drying,
• f) shaping, in particular into tablets or hollow cylinders and
• g) calcining,

characterized in that the mixing time in process step c) is less than 1 second, preferably less than 10 ^-3 seconds, particularly preferably less than 10 ^-5 seconds. 3. A process for the preparation of multimetal oxide compositions according to claim 1, which comprises the following process steps:

• a) preparation of an aqueous solution or dispersion of element sources of the multimetal oxide materials,
• b) optionally adding pH-lowering agents,
• c) heating the solution or dispersion,
• d) optionally tempering, in particular in the presence of inert or reactive gases,
• e) drying, in particular evaporation or spray drying,
• f) shaping, in particular into tablets or hollow cylinders, characterized in that the heating time in step c) is less than 1 second.

4. The method according to claim 3, characterized in that the heating by Direct contact with steam, especially at a temperature of 90 to 120 ° C he follows. 5. A process for the preparation of multimetal oxide compositions according to claim 1, which comprises the following process steps:

• a) preparation of one or more, preferably 2 or 3, in particular aqueous solutions and / or dispersions of element sources of the metal oxide masses,
• b) if appropriate, adding pH-lowering agents or preparing solutions which predominantly or exclusively contain pH-lowering agents,
• c) mixing the solutions and / or dispersions,
• d) heating the mixture of solutions and / or dispersions,
• e) optionally tempering, in particular in the presence of inert or reactive gases,
• f) drying, in particular evaporation or spray drying,
• g) shaping, in particular into tablets or hollow cylinders and
• h) calcining,

characterized in that the mixing time in step c) is less than 1 second, preferably less than 10 ^-3 seconds, particularly preferably less than 10 ^-5 seconds and / or that the heating time in step c1) is less than 1 second. 6. The method according to any one of claims 2 to 5, characterized in that in Stage a) and / or b) warm solutions and / or dispersions, especially with a temperature of 20 to 95 ° C can be produced. 7. Device for carrying out process step c1) according to claim 3 or 4, from a cylindrical, in particular circular cylindrical double jacket tube with a multiplicity of preferably circular bores through the inner jacket, preferably with a diameter of the bores in the area of the wall thickness of the inner jacket. 8. Device for carrying out process step c) according to one of claims 2 or 5 from a flow tube onto which at least one, preferably two or three feed lines with formation of at least one mixing point, preferred symmetrical, mouth, the ratio of the diameter of the flow tube and feed lines in the mixing points a degree of turbulence of Re ≧ 3000 causes. 9. The device according to claim 8, characterized in that in the region of Mixing point (s) in the flow tube is a static mixer, a dynamic one Mixer or a shear force mixer is installed. 10. The device according to claim 8 or 9, characterized in that in the stream mungsrohr following at least one mixing point at least one Auf  heating zone is installed, which is a heating of the fluid in the flow tube with a Guaranteed speed of at least 20 ° C per second. 11. The device according to one of claims 8 to 10, characterized in that in Flow pipe downstream of the mixing point (s) and optionally up heating zone (s) a pressure control valve is installed. 12. The device according to one of claims 8 to 11, characterized in that the Mixing point (s) is (are) involved in a cycle, which is downstream located end of the flow tube opens into a stirred tank, and one Pumping the bottom of the stirred tank with the mixing point (s) connects. 13. Multimetal oxide materials, obtainable by a process according to one of the An sayings 1 to 6. 14. Use of the multimetal oxide materials according to claim 13 as oxides tion catalyst, in particular for gas-phase catalytic oxidative production of (meth) acrylic acid. 15. Use according to claim 14, characterized in that it is in the used catalyst is a full catalyst, the geometry that of a hollow cylinder with an outer diameter and a length of 2 to 10 mm and a wall thickness of 1 to 3 mm.