EP1755779A1 - Method for the production of multi-metal oxide masses - Google Patents

Abstract

The invention relates to a method for the hydrothermal production of multi-metal masses, comprising Mo and V, using essentially exclusively sources from the group of oxides, oxide hydrates, oxy-acids and hydroxides as source of the elemental constituents of the multi-metal oxide masses and a part amount of the source of the included elemental constituents has an oxidation number below the maximum oxidation number thereof.

Description

Process for producing a multimetal oxide mass

description

The present invention relates to a method for producing a multimetal oxide mass M of general stoichiometry I,

With

M ¹ = at least one of the elements from the group comprising Al, Ga, In, Ge, Sn, Pb, As, Bi Se, Te and Sb;

M ² = at least one of the elements from the group comprising Sc, Y, La, Ti, Zr, Hf, Nb, Ta, Cr, W, Mn, Fe, Co, Ni, Zn, Cd and the lanthanides;

M ³ = at least one of the elements from the group comprising Re, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag and Au;

M ⁴ = at least one of the elements from the group comprising Li, Na, K, Rb, Cr, Be, Mg, Ca, Sr, Ba, NH ₄ and TI;

a = 0.01 to 1; b => 0 to 1; c => 0 to 1; d => 0 to 0; 57 e => 0 to 0.5 and n = a number which is determined by the valency and frequency of the elements other than oxygen in (I),

in which a mixture G from sources of the elemental constituents of the multimetal oxide mass M is subjected to a hydrothermal treatment and the newly formed solid is separated off.

Multimetal oxide compositions M of general stoichiometry I and processes for their preparation are known (cf. for example EP-A 318 295, EP-A 512 846, EP-A 767 164, EP-A 865 809, EP-A 529 853, EP-A 608 838, EP-A 962 253, DE-A 102 48 584, DE-A 101 19 933, DE-A 101 18 814, DE-A 100 29 338, DE-A 103 59 027, DE-A 103 21 398 , EP-A 1 407 819, Applied Catalysis A: General 194-195 (2000), pp. 479-485; Applied Catalysis A: General 200 (2000), pp. 135-143; Chem. Commun. 1999, p. 517-518; Res. Chem. Intermed. 26 (2) (2000), S 137-144; Topics Catal. 15 (2001) pp. 153-160; Catalysis Sur- veys from Japan 6 (1/2) (2992) 33-44 and Appl. Catal. A: General 251 (2003), pp. 411-424.

It is also known from the aforementioned prior art that such multimetal oxide compositions M as active compositions for catalysts for heterogeneously catalyzed partial gas phase oxidation and for heterogeneously catalyzed partial gas phase ammoxidation (differs from pure partial gas phase oxidation essentially by the additional presence of ammonia) of (for example 3 to 8, in particular 2 or 3 and / or 4 carbon atoms) saturated and unsaturated hydrocarbons, alcohols and aldehydes are suitable. Partial oxidation products include α.ß-monoethylenically unsaturated aldehydes (e.g. acrolein and methacroiein) and, ß-monoethylenically unsaturated carboxylic acids (e.g. acrylic acid and methacrylic acid) and their nitriles (e.g. acrylonitrile and methacrylonitrile). The target compounds acrolein, acrylic acid and / or acrylonitrile are e.g. as described available from the hydrocarbons propane and / or propene. Acrolein itself can also be the starting compound for the preparation of the latter two compounds. These target compounds form important intermediates which e.g. used for the production of polymers, e.g. can be used as adhesives.

In a corresponding manner, methacroiein and methacrylic acid can be obtained from isobutane and isobutene. Methacroiein can also be the starting compound for the production of methacrylic acid.

Furthermore, it is known from the acknowledged prior art that multimetal oxide compositions M predominantly occur in two different crystal phases, which are referred to in the literature as “i-phase” and as “k-phase”.

The associated X-ray diffractogram is used as a fingerprint of the respective crystal phase to identify it and to identify its crystalline structure.

The X-ray diffractogram of the crystalline i-phase is characterized in that the subsequent X-ray diffraction pattern RMi, reproduced in the form of of the wavelength of the X-rays used ^'independent interplanar spacings d [A], d [A] 3.06 + 0.2 3.17 + 0.2 3.28 + 0.2 3.99 + 0.2 9.82 + 0.4 11.24 + 0.4 13.28 + 0.5

contains.

The X-ray diffractogram of the crystalline k-phase is characterized in that it has the following X-ray diffraction pattern RMk, reproduced in the form of network plane distances d [A], [Ä] 4.02 + 0.2 3.16, which are independent of the wavelength of the X-ray radiation used + 0.2 2.48 + 0.2 2.01 + 0.2 1.82 + 0.1,

contains.

The i-phase and k-phase are similar to one another, but differ primarily in that the X-ray diffractogram of the k-phase normally has no diffraction reflections for d> 4.2 A. The k phase usually also contains no diffraction reflections in the range 3.8 A> d> 3.35 A. Furthermore, the k phase generally does not contain any diffraction reflections in the range 2.95 A> d> 2.68 Å.

Furthermore, it is known from the aforementioned prior art that the catalytic activity (activity, selectivity of target product formation) of the multimetal oxide compositions with i-phase structure is generally superior to those in other (e.g. k-phase) structures.

However, it is also known from the aforementioned prior art that it is very difficult to produce multimetal oxide compositions M in an i-phase structure.

So usually mixed crystal systems are obtained, which have only (for example, in addition to k-phase) a certain i-phase component and from which phase component I is isolated thereby from the aspect of optimum catalyst performance, that the ^' other phases (eg the k phase) washed out with suitable liquids (eg WO 02/06199, JP-A 7-232071, DE-A 102 54 279 and EP-A 1 407 819).

The production of multimetal oxide compositions M of general stoichiometry I is generally carried out in such a way that an intimate dry mixture is produced from their starting compounds (sources) containing elemental constituents and this is thermally treated at elevated temperature.

Increased i-phase proportions up to exclusive i-phase are generally obtained if a mixture of sources of the elemental constituents of the multimetal oxide mass M is subjected to hydrothermal treatment and the newly formed solid is separated off (cf. A 2003 / 0187299A1, DE-A 100 29 338, EP-A 1 270 068, EP-A 1 346 766 and EP-A 1 407 819).

According to the teaching of the prior art, more or less all possible compounds which contain elementary constituents chemically bound are considered as sources of the elementary constituents.

However, a disadvantage of such a hydrothermal production method is that its reproducibility, especially when it is produced in large-scale quantities, is not fully satisfactory. In other words, the i-phase portion resulting from such a production fluctuates around a mean value in a comparatively large range during repeated production. In addition, this mean value is often a comparatively low i-phase component. In addition, the catalytic performance of the product which is immediately available hydrothermally is often unsatisfactory and generally requires subsequent thermal treatment to improve it.

The object of the present invention was therefore to provide a hydrothermal process for the production of multimetal oxide compositions M of general stoichiometry I which is improved with respect to the disadvantages mentioned.

Accordingly, a method for producing a multimetal oxide mass M of general stoichiometry I,

MO VaMWoMVβOn (I),

With M ¹ = at least one of the elements from the group comprising AI (+3), Ga (+3), In (+3), Ge (+4), Sn (+4), Pb (+4), As (+ 5), Bi (+5), Se (+6), Te (+6) and Sb (+5);

M ² = at least one of the elements from the group comprising Sc (+3), Y (+3), La (+3), Ti (+4), Zr (+4), Hf (+4), Nb (+ 5), Ta (+5+), Cr (+5), W (+6), Mn (+7), Fe (+3), Co (+3), Ni (+3), Zn (+2 ), Cd (+2) and the lanthanides (Ce (+4), Pr (+3), Nd (+3), Pm (+3), Sm (+3), Eu (+3), Gd (+ 3), Tb (+4), Dy (+3), Ho (+3), Er (+3), Tm (+3), Yb (+3) and Lu (+3));

M ³ = at least one of the elements from the group comprising Re (+7), Ru (+8), Rh (+8), Pd (+8), Os (+8) lr (+8+), Pt (+8 ), Cu (+2), Ag (+1) and Au (+1);

M ⁴ = at least one of the elements from the group comprising Li (+1), Na (+1), K (+1), Rb (+1), Cs (+1), Be (+2), Mg (+ 2), Ca (+2), lr (+2), Ba (+2), NH ₄ (+1) and Tl (+1);

a = 0.01 to 1 (preferably 0.01 to 0.5); b => 0 to 1 (preferably> 0 to 0.5); c => 0 to 1 (preferably> 0 to 0.5); d => 0 to 0.5 (preferably> 0 to 0.1); e => 0 to 0.5 (preferably> 0 to 0.1 or 0) and n = a number which is determined by the valency and frequency of the elements other than oxygen in (I),

in which a mixture G of sources of the elementary constituents of the multimetal oxide mass M is subjected to a hydrothermal treatment and the newly formed solid is separated off, which is characterized in that the sources of the elementary constituents of the multimetal oxide mass M are exclusively sources from the group comprising compounds , which consist only of the elementary constituents of the multimetal oxide mass M and elementary constituents of water (O, H, OH), the elementary constituents of the multimetal oxide mass M itself in their elemental form and elemental constituents of the multimetal oxide mass M containing ammonium salts (ie, sources from of the group comprising oxides, oxide hydrates, oxygen acids, hydroxides, oxide hydroxides of the elemental constituents, the metal elements of the elemental constituents and compounds such as ammonium metavanadate or ammonium heptamolybodate) are used with the proviso that the molar ratio MV N H ^ Mo from NH contained in mixture G and Mo contained in mixture G is <0.5 and at least a partial amount of. Sources of elementary constituents that have elementary constituents contained in these sources with an oxidation number that is below the maximum oxidation number of the respective elemental constituent (this is the one behind the individually listed elements M ¹ , M ² , M ³ and M ⁴ in brackets with a positive sign).

According to the invention, at least a subset of the (of mixture G) sources of the elemental constituent V preferably contains the vanadium with an oxidation number <+5 (e.g. +4, or +3, or + 2, or 0).

The hydrothermal production of multimetal oxide active materials is familiar to the person skilled in the art (cf. also, for example, Applied Catalysis A: 194 to 195 (2000) 479-485; Kinetics and Catalysis; Vol. 40, No. 3, 1999, pp 401 to 404; Chem . Commun., 1999, 517 to 518; JP-A 6/227 819 and JP-A 2000/26123).

In particular, in this document, with regard to the procedure according to the invention, the thermal treatment of a, preferably intimate, mixture G of sources of the elemental constituents of the desired multimetal oxide mass M in a pressure vessel (autoclave) in the presence of superatmospheric water vapor, usually at temperatures of> 100 ° C to 600 ° C, understood. The pressure range typically extends to (> 1 bar) up to 500 bar, preferably up to 250 bar. Of course, according to the invention, temperatures above 600 ° C. and water vapor pressures above 500 bar can also be used, but this is less expedient in terms of application technology.

The hydrothermal treatment according to the invention is particularly advantageously carried out under conditions under which water vapor and liquid aqueous phase coexist. This is possible in the temperature range from> 100 to 374.15 ° C (critical temperature of the water) using the appropriate pressures. The amounts of water are expediently dimensioned such that the liquid aqueous phase is able to absorb the total amount of the starting compounds of the elemental constituents in suspension and / or solution.

According to the invention, however, such a hydrothermal procedure is also possible in which the, preferably intimate, mixture G of the starting compounds of the elemental constituents completely absorbs the amount of liquid water in equilibrium with the water vapor.

According to the invention, the hydrothermal treatment according to the invention advantageously takes place at temperatures> 100 ° C. to 300 ° C., preferably at temperatures from 120 ° C. or from 150 ° C. to 250 ° C. (e.g. 160 ° C. to 180 ° C.).

Based on the sum formed from water and the mixture G (or the elements contained therein of the elementary constituents of the multimetal oxide mass M), According to the invention, the weight fraction of the latter in the autoclave generally bears at least 1% by weight. The aforementioned proportion by weight is usually not above 90% by weight. Weight proportions of 5 to 60 or 10 to 50% by weight are preferred, more preferably 20 or 30 to 50% by weight.

In addition to the sources according to the invention of the elemental constituents of the multimetal oxide mass M and water, no further substances are preferably involved in the hydrothermal procedure according to the invention. Based on the mixture G, the proportion by weight of such further substances should normally be <10% by weight, advantageously <5% by weight and even better <3% by weight. As such possible

Foreign substances are, for example, all the substances listed in DE-A 100 29 338 and EP-A 1 407 819 but also H ₂ O ₂ (taking into account the preferred redox conditions).

During the hydrothermal treatment according to the invention, it is possible to either stir (preferably) or not to stir.

In the process according to the invention, the molar ratio MV is advantageously <0.3, particularly preferably <0.1 and very particularly preferably 0.

Based on the total amount of the sources of the elemental constituent V contained in the mixture G and the total molar amount of V contained in these sources, in the process according to the invention preferably at least 5 mol%, or at least 10 mol%, preferably at least 20 mol% or at least 30 mol%, very particularly preferably at least 40 mol% or at least 50 mol% and most preferably at least 60 mol% or at least 70 mol% or at least 80 mol% or at least 90 mol% or more (with particular advantage the total amount) of the V contained in these sources as vanadium, the oxidation number of which is <+5.

The arithmetic mean oxidation number of the V averaged over the molar total amount of V of the vanadium sources contained in the mixture G is preferably +3.5 to +4.5, particularly preferably +3.8 to +4.2 and very particularly preferably +4 ,

In general (especially if the V is contained in at least a subset of its sources in its maximum oxidation number), the composition of the mixture G in the process according to the invention is preferably chosen with regard to the oxidation numbers of the elemental constituents contained in the sources for the mixture G in such a way that with a change of all elementary constituents different from V (+5), which are not contained in the sources of the mixture G in their maximum oxidation number (including V (<+ 5)), in their respective maximum (with V in its second highest Oxidation number +4) Oxidation number the resulting reduct potential is just sufficient to set the mean oxidation number of the total V contained in the sources of the mixture G to a value from 3.5 to 4.5, particularly preferably from 3.8 to 4.2 and very particularly preferably from 4.

If the hydrothermal treatment according to the invention is carried out under an oxidative, molecular oxygen-containing atmosphere (e.g. under standing, closed air), the aforementioned reduction potential can be correspondingly higher.

Overall, the conditions of the hydrothermal treatment according to the invention are preferably chosen such that the above reduction potential is actually implemented in the manner described during the hydrothermal treatment.

To determine the oxidation number of V or another elemental constituent within a source, the rules known per se apply, according to which the oxidation number of a certain element in a chemical compound can be obtained as follows:

1. The oxidation number of an atom in a free element is zero. 2. The oxidation number of a monatomic ion is equal to its charge.

3. In a covalent compound of known structure, the oxidation number corresponds to the charge that each atom contains when the binding electron pairs are completely assigned to the more electron-negative atom. With electron pairs between two identical atoms, each atom receives one electron.

(cf. Fundamentals of general and organic chemistry, Verlag Sauerländer, Aarau, Diesterweg Salle, Frankfurt am Main, 4th edition, 1973).

Accordingly, sources of element V for the process according to the invention are primarily: vanadium oxides such as VO ₂ , V ₂ O ₃ , V ₆ O ₁₃ , V ₃ O ₇ , V ₄ O ₉ and VO, elemental vanadium, and, under Consideration of the quantity limits according to the invention, also compounds such as V ₂ O ₅ and ammonium metavanadate.

Suitable sources for the element Mo according to the invention are, for example, molybdenum oxides such as MoO ₃ and MoO ₂ , but elemental Mo, taking into account those according to the invention

Quantity limits, including compounds such as ammonium heptamolybdate and its hydrates.

According to the invention, sources of the element tellurium are, for example, tellurium oxides such as TeO ₂ , metallic tellurium, but also telluric acids such as orthotelluric acid H ₆ TeO ₆ . Antimony starting compounds which are advantageous according to the invention are, for example, antimony oxides such as Sb ₂ O ₃ , elemental Sb, but also antimonic acids such as HSb (OH) ₆ .

Niobium sources suitable according to the invention are, for example, niobium oxides such as Nb ₂ O ₅ or elemental Nb.

An advantageous bismuth source according to the invention is Bi ₂ O ₃ . An advantageous source of gold is gold hydroxide. Further advantageous starting compounds for the process according to the invention are, for example, silver oxide, copper hydroxide, copper oxide, alkali and alkaline earth oxide or hydroxide, scandium oxide, iridium oxide, zinc oxide, Ga ₂ O, Ga ₂ O ₃ etc. Of course, mixed oxides also come as sources of the elemental constituents into consideration, which contain more than one elementary constituent and, if appropriate, have been obtained by a hydrothermal route, for example by the hydrothermal route according to the invention. Further sources of the elementary constituents which are suitable according to the invention can be found in the documents of the cited prior art.

The hydrothermal treatment according to the invention itself generally takes from a few minutes or hours to a few days. A period of 48 hours is typical. In terms of application technology, the inside of the autoclave to be used for the hydrothermal treatment is coated with Teflon. Before the hydrothermal treatment, the autoclave, optionally including the aqueous mixture it contains, can advantageously be evacuated. Then, before the temperature increase, it can preferably be filled with inert gas (N ₂ , noble gas such as He, Ne and / or argon). Both measures can also be omitted in a less advantageous manner. Of course, the aqueous mixture can additionally or alternatively be flushed with inert gas for advantageous inerting prior to the hydrothermal treatment according to the invention. In terms of application technology, the aforementioned inert gases can also be used expediently to set above atmospheric pressure before the hydrothermal treatment in the autoclave.

Upon completion of the hydrothermal treatment, the autoclave can either be quenched to room temperature or slowly, i.e. be brought to room temperature over a longer period of time (e.g. left by yourself).

It is essential according to the invention that the solid newly formed in the course of the hydrothermal treatment according to the invention and separated off after the end of the hydrothermal treatment is normally a multimetal oxide M with an increased or exclusive i-phase content and that this is obtained according to the invention in improved reproducibility , It is also essential according to the invention that the multimetal oxides M obtainable by the process according to the invention develop the desired catalytic activity even without a thermal treatment following the hydrothermal treatment.

It goes without saying that the multimetal oxides M obtainable according to the invention can additionally advantageously be thermally aftertreated before they are used as active compositions for the heterogeneously catalyzed processes mentioned at the outset. This thermal aftertreatment can be carried out at temperatures of 200 to 1200 ° C, preferably 350 to 700 ° C, often 400 to 650 ° C and often 400 to 600 ° C.

In principle, it can take place both under an oxidizing, reducing and under an inert (preferred according to the invention) atmosphere. The oxidizing atmosphere is e.g. Air, air enriched with molecular oxygen or air de-oxygenated.

Preferably the thermal treatment is carried out under an inert atmosphere, i.e. e.g. carried out under molecular nitrogen and / or noble gas (He, Ar and / or Ne) (inert atmosphere in this document always means that the content of molecular oxygen then normally <5% by volume, preferably <3% by volume, particularly preferably <1% by volume or <0.1% by volume and most preferably 0% by volume). Of course, the thermal aftertreatment can also be carried out under vacuum.

Overall, the thermal aftertreatment can take up to 24 hours or more. A thermal aftertreatment is preferably carried out first under an oxidizing (oxygen-containing) atmosphere (e.g. under air) at a temperature of 150 ° C to 400 ° C or 250 ° C to 350 ° C. Thereafter, the thermal aftertreatment is expediently continued under inert gas at temperatures of 350 ° C. to 700 ° C. or 400 ° C. to 650 ° C. or 400 ° C. to 600 ° C. Of course, the thermal aftertreatment of the hydrothermally generated multimetal oxide M can also be carried out in such a way that the hydrothermally generated multimetal oxide M is first tableted, then thermally aftertreated and then split.

Appropriately from an application point of view, the multimetal oxide M obtainable in the context of the hydrothermal process according to the invention is split up for the purpose of its thermal aftertreatment.

Furthermore, both the multimetal oxide compositions M obtainable according to the invention by hydrothermal means and their secondary or successor multimetal oxide compositions which have been thermally post-treated as described can be further treated in an advantageous manner by, for example, in DE-A 102 54 279 and EP-A 1 ^: 4Q7 819 beBciTilben, "with suitable liquids. As such liquid For example, organic acids or their aqueous solutions (e.g. oxalic acid, formic acid, acetic acid, citric acid and tartaric acid) as well as inorganic acids and their aqueous solutions (e.g. sulfuric acid, perchloric acid, hydrochloric acid, nitric acid, boric acid and / or telluric acid) but also alcohols, alcoholic solutions the aforementioned acids or hydrogen peroxide and their aqueous solutions. Of course, mixtures of the aforementioned washing liquids can also be used for washing. Furthermore, JP-A 7-232 071 and DE-A 103 21 398 also disclose a suitable washing process. Such a wash generally leaves pure i-phase (or an increased i-phase portion), which in the washed state normally also has an additionally improved catalyst performance.

The intimate mixing of the starting compounds of the elementary constituents to obtain the mixture G to be treated hydrothermally can take place in dry or in wet form. If it is in dry form, the starting compounds are expediently used as finely divided powders. However, the intimate mixing is preferably carried out in wet, aqueous form. The starting compounds are preferably mixed with one another in the form of an aqueous solution (optionally with the use of small amounts of complexing agents) and / or finely divided suspension.

In addition to the diffraction reflex layers already mentioned at the outset, the X-ray diffraction pattern RMi of the multimetal oxide masses M which can be obtained hydrothermally according to the invention or their secondary masses (or also subsequent masses) which can be obtained by thermal aftertreatment and / or by washing as described (or depending on those contained) Elements and the crystal geometry (eg needle shape or platelet shape)) additional characteristic diffraction reflex intensities.

Based on the intensity of the diffraction reflex representing the network plane distance d [A] = 3.99 + 0.2, these (relative) diffraction reflex intensities I (%) are as follows: d [A] I (%) 3.06 + 0.2 ( preferably + 0.1) 5 to 65 3.17 + 0.2 (preferably + 0.1) 5 to 65 3.28 + 0.2 (preferably + 0.1) 15 to 130, often 15 to 95 3.99 + 0.2 (preferably + 0.1) 100 9.82 + 0.4 (preferably + 0.2) 1 to 50, often 1 to 30 11, 24 + 0.4 (preferably + 0.2) 1 to 45, often 1 to 30 13.28 + 0.5 (preferably + 0.3) 1 to 35, often 1 to 15. In addition to the particularly characteristic diffraction reflections already mentioned, the following x-ray diffraction pattern RMi also frequently shows the following diffraction reflections, also reproduced in the form of network plane spacings d [A] which are independent of the wavelength of the x-ray radiation used: d [A] 8.19 + 0, 3 (preferably + 0.15) 3.51 + 0.2 (preferably + 0.1) 3.42 + 0.2 (preferably + 0.1) 3.34 + 0.2 (preferably + 0.1) 2.94 + 0.2 (preferably + 0.1) 2.86 + 0.2 (preferably + 0.1).

Relative to the intensity of the diffraction reflex representing the network plane distance d [A] = 3.99 + 0.2, the (relative) intensities I (%) of the above diffraction reflexes are often as follows: d [A] I (%) 8.19 + 0.3 (or + 0.15) 0 to 25 3.51 + _0.2 (or + 0.1) 2 to 50 3.42 + 0.2 (or + 0.1) 5 to 75 3.34 + 0.2 (or + 0.1) 5 to 80 2.94 + 0.2 (or + 0.1) 5 to 55 2.86 + 0.2 (or + 0.1 ) 5 to 60.

In many cases, the following diffraction reflections supplement the aforementioned X-ray diffraction pattern RMi: d [A] 2.54 + 0.2 (preferably + 0.1) 2.01 + 0.2 (preferably + 0.1).

The (relative) diffraction reflex intensities obtained in the same way as above are often as follows for these diffraction reflections: d [A] I (%) 2.54 + 0.2 (or + 0.1) 0.5 to 40 2, 01 + 0.2 (or + 0.1) 5 to 60.

According to the invention, preferred among the aforementioned X-ray diffraction patterns RMi (or the multimetal oxide masses belonging to them or their subsequent masses), those in the rruei the network plane spacing d- [A] = 3.99 + 0.2 (or + 0.1) or the diffraction reflex representing the network plane distance d [A] = 3.28 + 0.2 (or + 0.1) is the most intense (most intense) diffraction reflex.

Furthermore, those X-ray diffraction patterns RMi (or the multimetal oxide masses belonging to them or their successor masses) are preferred in which the 2Θ-half width of the diffraction reflex d [A] = 3.99 + 0.2 (or + 0.1) <1 °, preferably <0.5 °. The 2Θ half-value width of the other diffraction reflections mentioned is normally <3 °, preferably <1, 5 °, particularly preferably <1 °.

All information in this document relating to an X-ray diffractogram is based on an X-ray diffractogram generated using Cu-Kα radiation (λ = 1.54178 A) (Siemens diffractometer Theta-Theta D-5000, tube voltage: 40kV, tube current: 40mA, aperture diaphragm V20 (variable), anti-scatter diaphragm V20 (variable), secondary monochromator diaphragm (0.1 mm), detector diaphragm (0.6 mm), measuring interval (2Θ): 0.02 °, measuring time per step: 2.4 s, detector: Scintillation counter tube; the definition of the intensity of a diffraction reflex in the X-ray diffractogram in this document refers to those in DE-A 198 35 247, DE-A 101 22 027, and in DE-A 100 51 419 and DE-A 100 46 672 laid down definition, which are hereby an integral part of this application; the same applies to the definition of the 2Θ half-value width).

The wavelength λ of the X-ray radiation used for diffraction and the diffraction angle Θ (the apex of a reflection in the 2Θ order is used as the diffraction reflex layer in this document) are linked as follows via the Bragg relationship:

2 sin Θ = λ / d,

where d is the network plane distance of the atomic spatial arrangement belonging to the respective diffraction reflex.

Preferred multimetal oxide compositions M of general stoichiometry I (and the subsequent compositions belonging to them) obtainable according to the invention are those for which:

M ¹ = at least one of the elements from the group comprising Sb, Bi, Se and Te;

M ² = at least one of the elements from the group comprising Ti, Zr, Nb, Cr, W, Fe, Co, Ni and Zn;

M ³ = at least one of the elements from the group comprising Re, Pd and Pt; M ⁴ = at least one of the elements from the group comprising Rb, Cs, Sr, and Ba;

a = 0.01 to 1 (preferably 0.01 to 0.5); b => 0 to 1 (preferably> 0 to 0.5); c => 0 to 1 (preferably> 0 to 0.5); d => 0 to 0.5 (preferably> 0 to 0.1); e => 0 to 0.5 (preferably ≥ 0 to 0.1 or 0) and n = a number which is determined by the valency and frequency of the elements other than oxygen in (I).

According to the invention, the stoichiometric coefficient a of the multimetal oxide compositions M obtainable according to the invention (and the subsequent compositions belonging to them), particularly independently of the preferred ranges for the other stoichiometric coefficients of the multimetal oxide compositions M and the selected element composition, is 0.05 to 0.5 0.1 to 0.5.

Regardless of the preferred ranges for the other stoichiometric coefficients of the multimetal oxide materials M and the element composition selected, the stoichiometric coefficient b is preferably> 0 or 0.01 to 0.5, and particularly preferably 0.1 to 0.5 or to 0.4.

The stoichiometric coefficient c of the multimetal oxide compositions M obtainable according to the invention, regardless of the preferred ranges for the other stoichiometric coefficients of the multimetal oxide compositions M and the selected element composition, is advantageously from 0.01 to 0.5 and particularly preferably from 0.1 to 0.5 or to 0.4. A very particularly preferred range for the stoichiometric coefficient c, which, regardless of the preferred ranges for the other stoichiometric coefficients of the multimetal oxide materials M obtainable according to the invention, can be combined with all other preferred ranges in this document and all selected element compositions, is the range 0.05 to 0 ; 2.

The stoichiometric coefficient d of the multimetal oxide compositions M obtainable according to the invention, regardless of the preferred ranges for the other stoichiometric coefficients of the multimetal oxide compositions M and the selected element composition, is preferably> 0 or 0.00005 or 0.0005 to 0.5, particularly preferably 0.001 to 0.5, often 0.002 to 0.3 and often 0.005 or 0.01 to 0.1.

Regardless of the preferred ranges for the other stoichiometric coefficients of the multimetal oxide masses M and the selected element composition, the coefficient e can also be> 0 to 0.1 and advantageously also 0. Multimetal oxide compositions M which are obtainable according to the invention and whose stoichiometric coefficients a, b, c and d are simultaneously in the following grid are particularly favorable:

a = 0.05 to 0.5; b = 0.01 to 1 (or 0.01 to 0.5); c = 0.01 to 1 (or 0.01 to 0.5); d = 0.0005 to 0.5; and e => 0 to 0.5.

Multimetal oxide compositions M obtainable according to the invention are particularly favorable, their stoichiometric coefficients a, b, c and d simultaneously lying in the following grid:

a = 0.1 to 0.5 b = 0.1 to 0.5; c = 0.1 to 0.5; d = 0.001 to 0.5, or 0.001 to 0.3, or 0.001 to 0.1; and e => 0 to 0.2 or to 0.1. fl1 is preferably Bi, Se, Te and / or Sb and very particularly preferably Te.

All of the above applies in particular when M ^{2 is} at least 50 mol% of its total amount of Nb, Ti, Zr, Cr, W, Fe.Co, Ni, Zn and / or Ta and very particularly when M ² at least 50 mol% or at least 75 mol% of its total amount, or 100 mol% of its total amount Nb and at least one of the elements Ti, Zr, Cr, Ta, W, Fe, Co, Ni and Zn or Nb and / or Ta is.

Above all, however, regardless of the meaning of M ² , it applies if M ^{3 is} at least one element from the group comprising Re, Pd and Pt.

However, all of the above applies above all when M ^{2 contains} at least 50 mol% of its total amount, or at least 75 mol%, or 100 mol% Nb and M ^{3 contains} at least one element from the group comprising Re, Pd and Pt is.

However, all of the above applies above all when M ^{2 contains} at least 50 mol%, or at least 75 mol%, or 100 mol% of its total amount of Nb and at least one of the elements Co, Ni, Ta, W, Fe and M ^{3 is} at least one element from the group comprising Re, Pd and Pt. All statements regarding the stoichiometric coefficients are particularly preferred when M ¹ = Te, M ² = Nb and at least one of the elements Ni, Co, Fe and M ³ = at least one element from the group comprising Pd, Re and Pt.

Inexpensive multimetal oxide compositions M obtainable according to the invention are those (in particular all of the above) with e = 0. If e> 0, M ^{4 is} preferably Cs.

Further stoichiometries I which are suitable according to the invention are those in this document which are disclosed in the cited prior art for the multimetal oxide materials of stoichiometry (I).

The multimetal oxide compositions M of the general stoichiometry I which are obtainable according to the invention by hydrothermal means as described or the secondary compositions of these multimetal oxide compositions (they generally also have the stoichiometry I) can be used as such (ie as a powder or as chippings) or as shaped articles Shaped as catalytic active materials for all partial gas phase oxidations and / or amoxidations of eg saturated and unsaturated hydrocarbons or lower aldehydes and / or alcohols are used. The catalyst bed can be a fixed bed, a moving bed or a fluidized bed. The shape can e.g. by extrusion or tableting in the case of unsupported catalysts or by application to a support body (production of coated catalysts) as described in DE-A 10118814 or PCT / EP / 02/04073 or DE-A 10051419.

The support bodies to be used in the case of coated catalysts for the multimetal oxide compositions M obtainable according to the invention and their subsequent compositions are preferably chemically inert. This means that they essentially do not intervene in the course of the partial catalytic gas phase oxidation or amoxidation of the hydrocarbon (eg propane and / or propene to give acrylic acid), alcohol or aldehyde, which is catalyzed by the multimetal oxide compositions M obtainable according to the invention and their subsequent compositions on.

According to the invention, aluminum oxide, silicon dioxide, silicates such as clay, kaolin, steatite (preferably steatite from CeramTec (DE) of type C-220, or preferably with a low water-soluble alkali content), pumice, Aluminum silicate and magnesium silicate, silicon carbide, zirconium dioxide and thorium dioxide.

The surface of the carrier body can be both smooth and rough. The surface of the carrier body is advantageously rough, since an increased surface roughness generally results in an increased adhesive strength of the applied active material shell. The surface roughness R _{z of} the carrier body is often in the range from 5 to 200 μm, often in the range from 20 to 100 μm (determined in accordance with DIN 4768 Sheet 1 using a "Hommel Tester for DIN-ISO surface measurement parameters" from Hommelwerke, DE).

Furthermore, the carrier material can be porous or non-porous. The carrier material is expediently non-porous (total volume of the pores based on the volume of the carrier body <_1% by volume).

The thickness of the active oxide mass shell located in the shell catalysts according to the invention is usually from 10 to 1000 μm. However, it can also be 50 to 700 μm, 100 to 600 μm or 150 to 400 μm. Possible shell thicknesses are also 10 to 500 μm, 100 to 500 μm or 150 to 300 μm.

In principle, any geometries of the carrier bodies can be considered for the method according to the invention. Their longest dimension is usually 1 to 10 mm. However, balls or cylinders, in particular hollow cylinders, are preferably used as carrier bodies. Favorable diameters for carrier balls are 1.5 to 4 mm. If cylinders are used as carrier bodies, their length is preferably 2 to 10 mm and their outside diameter is preferably 4 to 10 mm. In the case of rings, the wall thickness is also usually 1 to 4 mm. Annular carrier bodies suitable according to the invention can also have a length of 3 to 6 mm, an outer diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm. A carrier ring geometry of 7 mm x 3 mm x 4 mm or 5 mm x 3 mm x 2 mm (outer diameter x length x inner diameter) is also possible.

The shell catalysts can be produced in a very simple manner by forming multimetal oxide compositions M or their back-up composition in the manner according to the invention, converting them into a finely divided form and finally applying them to the surface of the support body with the aid of a liquid binder. For this purpose, the surface of the carrier body is moistened in the simplest manner with the liquid binder, and a layer of the active composition is attached to the moistened surface by contacting it with finely divided active multimetal oxide composition M obtained according to the invention M or finely divided follower composition. Finally, the coated carrier body is dried. Of course, one can achieve an increased

Repeat the process periodically. In this case the coated base body becomes the new "support body" etc.

The fineness of the catalytically active multimetal oxide composition M of the general formula (I) to be applied to the surface of the carrier body or its subsequent composition is of course adapted to the desired shell thickness. For the shell thickness range from 100 to 500 ^" μm, £ B are suitable ^. Such active bulk powders, from which pass at least 50% of the total number of powder particles through a sieve with a mesh size of 1 to 20 μm and whose numerical proportion of particles with a longest dimension above 50 μm is less than 10%. As a rule, the distribution of the longest dimensions of the powder particles corresponds to a Gaussian distribution due to the manufacturing process. The particle size distribution is often as follows:

Here are:

D = diameter of the particle, x = the percentage of particles whose diameter is> D; and y = the percentage of particles whose diameter is <D.

For carrying out the coating process described on an industrial scale, it is recommended, for. B. the application of the process principle disclosed in DE-A 2909671 and in DE-A 10051419. That is, the carrier bodies to be coated are rotated in a preferably inclined (the angle of inclination is generally> 0 ° and <90 °, usually> 30 ° and <90 °; the angle of inclination is the angle of the center axis of the rotating container against the horizontal) (e.g. B. turntable or coating drum). The rotating rotary container leads the z. B. spherical or cylindrical carrier body under two consecutively arranged metering devices at a certain distance. The first of the two metering devices suitably corresponds to a nozzle (for example an atomizing nozzle operated with compressed air) through which the carrier bodies rolling in the rotating turntable are sprayed with the liquid binder and moistened in a controlled manner. The second metering device is located outside the atomizing cone of the sprayed-in liquid binder and serves to supply the finely divided oxidic active material (for example via a shaking channel or a powder screw). The controlled, moistened carrier balls take up the active mass powder that is fed through the rolled lumbar movement on the outer surface of the z. B. compacted cylindrical or spherical support body into a coherent shell.

If necessary, the base body coated in this way again passes through the spray nozzles in the course of the subsequent rotation, is moistened in a controlled manner in order to be able to take up a further layer of finely divided oxidic active material, etc. (intermediate drying is generally not necessary). Fine-particle oxidic active material and liquid binder are usually fed in continuously and simultaneously.

The removal of the liquid binder can be done after the coating z. B. by the action of hot gases such as N ₂ or air. Remarkably, the coating method described brings about both a fully satisfactory adhesion of the successive layers to one another and also the base layer on the surface of the carrier body.

It is essential for the coating method described above that the moistening of the surface of the carrier body to be coated is carried out in a controlled manner. In short, this means that the carrier surface is appropriately moistened so that it has adsorbed liquid binder, but no liquid phase as such appears visually on the carrier surface. If the surface of the carrier body is too moist, the finely divided catalytically active oxide mass agglomerates into separate aggiomerates instead of being drawn onto the surface. Detailed information on this can be found in DE-A 2909671 and in DE-A 10051419.

The aforementioned final removal of the liquid binder used can be carried out in a controlled manner, for. B. by evaporation and / or sublimation. In the simplest case, this can be done by exposure to hot gases of the appropriate temperature (often 50 to 300, often 150 ° C). The effects of hot gases can also only be used for predrying. The final drying can then take place, for example, in a drying oven of any type (for example a belt dryer) or in the reactor. The temperature acting should not be above the calcination temperature used to produce the oxidic active composition. Of course, drying can also be carried out exclusively in a drying oven.

Regardless of the type and geometry of the support body, the following can be used as binders for the coating process: water, monohydric alcohols such as ethanol, methanol, propanol and butanol, polyhydric alcohols such as ethylene glycol, 1, 4-butanediol, 1, 6-hexanediol or glycerol, mono- or polyvalent organic carboxylic acids such as propionic acid, oxalic acid, malonic acid, glutaric acid or maleic acid, amino alcohols such as ethanolamine or difethane αirrirrs as well as mono- or polyvalent organic ganic amides such as formamide. Favorable binders are also solutions consisting of 20 to 90% by weight of water and 10 to 80% by weight of an organic compound dissolved in water, whose boiling point or sublimation temperature at normal pressure (1 atm)> 100 ° C., preferably> 150 ° C, is. The organic compound is advantageously selected from the above list of possible organic binders. The organic proportion of the aforementioned aqueous binder solutions is preferably 10 to 50 and particularly preferably 20 to 30% by weight. Monosaccharides and oligosaccharides such as glucose, fructose, sucrose or lactose as well as polyethylene oxides and polyacrylates are also suitable as organic components.

Balls, solid cylinders and hollow cylinders (rings) come into consideration as geometries (both for solid catalysts and for shell catalysts). The longest dimension of the aforementioned geometries is usually 1 to 10 mm. In the case of cylinders, their length is preferably 2 to 10 mm and their outside diameter is preferably 4 to 10 mm. In the case of rings, the wall density is also usually 1 to 4 mm. Suitable annular unsupported catalysts can also have a length of 3 to 6 mm, an outer diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm. A full catalyst ring geometry of 7 mm x 3 mm x 4 mm or 5 mm x 3 mm x 2 mm (outer diameter x length x inner diameter) is also possible. Of course, all those of DE-A 101 01 695 are also suitable for the geometry of the multimetal oxide active compositions M obtainable according to the invention and their successor compositions.

The specific surface area of multimetal oxide compositions M (and their subsequent compositions) obtainable according to the invention is in many cases 1 to 80 m ² / g between 40 m ² / g, often 11 or 12 to 40 m ² / g and frequently 15 or 20 to 40 or 30 m ² / g (determined according to the BET method, nitrogen).

Otherwise, the statements made in DE-A 103 03 526 apply to the multimetal oxide compositions M and their subsequent compositions obtainable according to the invention.

That is, of course, the multimetal oxide compositions M and their subsequent compositions obtainable according to the invention can also be used with finely divided, e.g. colloidal, essentially only thinning materials, such as silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide and niobium oxide diluted form can be used as catalytic active materials.

The dilution mass ratio can be up to 9 (thinner): 1 (active mass). This means that possible dilution mass ratios are, for example, 6 (thinner): 1 (active mass) and 3 (thinner): 1 (active mass). The thinners can be incorporated before and / or after a thermal aftertreatment. The multimetal oxide compositions M obtainable according to the invention and their successor compositions are suitable as such or in the form just described (as already mentioned) as active compositions for heterogeneously catalyzed partial gas phase oxidations (including oxide hydrogenations) and / or ammoxidations of saturated and / or unsaturated hydrocarbons and of alcohols and aldehydes (for example in a process according to DE-A 103 16465).

Such saturated and / or unsaturated hydrocarbons are in particular ethanol, ethylene, propane, propylene, n-butane, isobutane and isobutene. The main target products are acrolein, acrylic acid, methacroiein, methacrylic acid, acrylonitrile and methacrylonitrile. However, they are also suitable for the heterogeneously catalyzed partial gas phase oxidation and / or amoxidation of compounds such as acrolein and methacroiein.

But ethylene, propylene and acetic acid can also be the target product.

A complete oxidation of a hydrocarbon, alcohol and / or aldehyde is understood in this document to mean that the total carbon contained in the hydrocarbon, alcohol and / or aldehyde is converted into oxides of carbon (CO, CO ₂ ).

All of the different reactions of the hydrocarbon under the reactive action of molecular oxygen are subsumed in this document with the term partial oxidation. The additional reactive action of ammonia characterizes the partial ammoxidation.

The multimetal oxide compositions M and their subsequent compositions obtainable according to this document are preferably suitable as catalytic active compositions for the conversion of propane to acrolein and / or acrylic acid, from propane to acrylic acid and / or acrylonitrile, from propylene to acrolein and / or acrylic acid, from propylene to Acrylonitrile, from isobutane to methacroiein and / or methacrylic acid, from isobutane to methacrylic acid and / or methacrylonitrile, from ethane to ethylene, from ethane to acetic acid and from ethylene to acetic acid.

The implementation of such partial oxidations and / or ammoxidations (by the choice of the ammonia content in the reaction gas mixture, which can be controlled in a manner known per se, the reaction can essentially be designed exclusively as partial oxidation, or exclusively as partial ammoxidation, or as a superimposition of both reactions; cf. For example, WO 98/22421) is known per se from the multimetal oxide compositions of general stoichiometry I of the prior art and can be carried out in a completely corresponding manner. If crude propane or crude propylene is used as the hydrocarbon, this is preferably composed as described in DE-A 102 46 119 or DE-A 101 18 814 or PCT / EP / 02/04073. The same procedure as described there is preferred.

A partial oxidation of propane to acrylic acid to be carried out with multimetal oxide M active composition (or successor active composition) catalysts can e.g. as described in EP-A 608 838, EP-A 1 407 819, WO 00/29106, JP-A 10-36311 and EP-A 1 192 987. ,

For example, air, oxygen-enriched or de-oxygenated air or pure oxygen can be used as the source of the required molecular oxygen. Such a process is also advantageous if the reaction gas starting mixture contains no noble gas, in particular no helium, as the inert diluent gas. In addition to propane and molecular oxygen, the reaction gas starting mixture can of course also comprise inert diluent gases such as N ₂ , CO and CO ₂ . Water vapor as a component of the reaction gas mixture is advantageous according to the invention.

That is, the reaction gas starting mixture with which the multimetal oxide active composition M obtainable according to the invention or its subsequent composition at reaction temperatures of e.g. 200 to 550 ° C or from 230 to 480 ° C or 300 to 440 ° C and pressures from 1 to 10 bar or 2 to 5 bar, for example, have the following composition:

1 to 15, preferably 1 to 7% by volume of propane, 44 to 99% by volume of air and 0 to 55% by volume of water vapor.

Reaction gas starting mixtures containing water vapor are preferred.

Other possible compositions of the reaction gas starting mixture are:

70 to 95 vol% propane, 5 to 30 vol% molecular oxygen and 0 to 25 vol% water vapor. It goes without saying that a product gas mixture which does not consist exclusively of acrylic acid is obtained in such a process. Rather containing product gas mixture ^■ addition to unconverted propane Nebenkompöneπter such as prop-ervAcroiein, C0 _2, CO, H ₂ O, acetic acid, propionic acid, etc., from which the acrylic acid must be separated.

This can be done as is known from the heterogeneously catalyzed gas phase oxidation of propene to acrylic acid.

Ie, the acrylic acid contained can be taken up from the product gas mixture by absorption with water or by absorption with a high-boiling inert hydrophobic organic solvent (for example a mixture of diphenyl ether and diphyl which may also contain additives such as dimethyl phthalate). The resulting mixture of absorbent and acrylic acid can then _be, rectification, extraction and / or crystallization worked up in a manner known per se to give pure acrylic acid. Alternatively, the basic separation of the acrylic acid from the product gas mixture can also be carried out by fractional condensation, as described, for example, in DE-A 19 924 532.

The resulting aqueous acrylic acid condensate can then e.g. can be further purified by fractional crystallization (e.g. suspension crystallization and / or layer crystallization).

The residual gas mixture remaining in the basic separation of acrylic acid contains, in particular, unreacted propane, which is preferably recycled into the gas phase oxidation. For this purpose, e.g. partially or fully separated by fractional pressure rectification and then returned to the gas phase oxidation. However, it is more favorable to bring the residual gas into contact with a hydrophobic organic solvent in an extraction device (e.g. by passing it through), which the propane is able to absorb preferentially.

The absorbed propane can be released again by subsequent desorption and / or stripping with air and returned to the process according to the invention. In this way, economic total propane sales can be achieved. As with other separation processes, propene formed as a secondary component is generally not or not completely separated from the propane and circulated with it. This also applies to other homologous saturated and olefinic hydrocarbons. Above all, it applies very generally to heterogeneously catalyzed partial oxidations and / or amoxidations of saturated hydrocarbons according to the invention.

It makes it noticeably noticeable that the multallall oxide masses M obtainable according to the invention and their successor masses can also heterogeneously catalyze the partial oxidation and / or amoxidation of the homologous olefinic hydrocarbon to the same target product. Thus, with the multimetal oxide compositions M obtainable according to the invention and their successor compositions as active compositions, acrylic acid by heterogeneously catalyzed partial gas phase oxidation of propene with molecular oxygen as in DE-A 101 18 814 or PCT / EP / 02/04073 or JP-A 7-53448 described.

That is, a single reaction zone A is sufficient to carry out the process. In this reaction zone there are exclusively multimetal oxide mass M or successor mass catalysts available as catalytically active masses.

This is unusual since the heterogeneously catalyzed gas phase oxidation of propene to acrylic acid generally takes place in two successive steps. In the first step, propene is usually essentially oxidized to acrolein, and in the second step, acrolein formed in the first step is usually oxidized to acrylic acid.

Conventional processes of heterogeneously catalyzed gas phase oxidation of propene to acrylic acid therefore usually use a special type of catalyst tailored to the oxidation step for each of the two aforementioned oxidation steps.

In other words, the conventional processes of heterogeneously catalyzed gas-phase oxidation of propene to acrylic acid work with two reaction zones, in contrast to the process according to the invention.

Of course, in the propene partial oxidation process, there can be only one or more than one multimetal oxide mass M or follow-up mass catalyst obtainable according to the invention in one reaction zone A. Of course, the catalysts to be used can be diluted with inert material, as was recommended in this document, for example, as a support material.

Along the one reaction zone A, in the process of the propene partial oxidation, there can be only one temperature or a temperature of a heat transfer medium which changes along the reaction zone A for temperature control of the reaction zone A. This change in temperature can be increasing or decreasing.

If the propene partial oxidation process according to the invention is carried out as a fixed bed oxidation, it is expediently carried out in a tube bundle reactor, the contact tubes of which are charged with the catalyst. A liquid, usually a salt bath, is usually passed around the contact tubes as a heat transfer medium. A plurality of temperature zones along the reaction zone A can then be realized in a simple manner by passing more than one salt bath around the contact tubes in sections along the contact tubes.

The reaction gas mixture is viewed in the catalyst tubes via the reactor either in cocurrent or in countercurrent to the salt bath. The salt bath itself can perform a pure parallel flow relative to the contact tubes. Of course, this can also be superimposed on a cross flow. Overall, the salt bath around the catalyst tubes can also carry out a meandering flow, which, viewed only via the reactor, is conducted in cocurrent or countercurrent to the reaction gas mixture.

The reaction temperature in the propene partial oxidation process can be 200 ° to 500 ° C. along the entire reaction zone A. Usually it will be 250 to 450 ° C. The reaction temperature is preferably 330 to 420 ° C., particularly preferably 350 to 400 ° C.

The working pressure in the propene partial oxidation process can be either 1 bar, less than 1 bar or more than 1 bar. Typical working pressures according to the invention are 1.5 to 10 bar, frequently 1.5 to 5 bar.

The propene to be used for the propene partial oxidation process is not subject to particularly high purity requirements.

As already mentioned and as for all one- or two-stage processes of heterogeneously catalyzed gas-phase oxidation of propene to acrolein and / or acrylic acid, propene can be used for such a process in general, e.g. Propene (also called raw propene) of the following two specifications can be used without any problems:

a) Polymer grade propylene:

Of course, all the above-mentioned possible companions of propene can also be contained in the crude propene in two to ten times the individual amount mentioned, without the usability of the crude propene for the process or for the known processes of one or two stages to affect heterogeneously catalyzed gas phase oxidation of propene to acrolein and / or acrylic acid in general.

This applies in particular when, as with saturated hydrocarbons, water vapor, carbon oxides or molecular oxygen, it is anyway a question of compounds which are used either as inert diluent gases or as reaction partners in increased amounts η..a £ in the abovementioned processes 3r & al i €> rS $ fe events take part. Usually the raw propene as such is mixed with circulating gas, Air and / or molecular oxygen and / or diluted air and / or inert gas mixed for the process of heterogeneously catalyzed gas phase oxidation of propene to acrolein and / or acrylic acid.

However, propene is also suitable as a source of propene for the process according to the invention, which is formed as a by-product in a process which differs from the process according to the invention and e.g. contains up to 40% of its weight propane. This propene can additionally be accompanied by other accompanying components which do not substantially disrupt the process according to the invention.

Pure oxygen as well as air or air enriched or depleted with oxygen can be used as the oxygen source for the propene partial oxidation process.

In addition to molecular oxygen and propene, a reaction gas starting mixture to be used for the propene partial oxidation process usually also contains at least one diluent gas. As such, nitrogen, carbon oxides, noble gases and lower hydrocarbons such as methane, ethane and propane come into consideration (higher ones, eg C ₄ hydrocarbons should be avoided). Water vapor is also often used as a diluent. Mixtures of the aforementioned gases frequently form the diluent gas for the partial propene oxidation process.

The heterogeneously catalyzed partial oxidation of propene is advantageously carried out in the presence of propane.

The reaction gas starting mixture for the propene oxidation process is typically composed as follows (molar ratios):

Propene: Oxygen: H ₂ O: other dilution gases = 1: (0.1 - 10): (0 - 70): (0: 20).

The aforementioned ratio is preferably 1: (1-5): (1-40): (0-10).

If propane is used as the diluent gas, this can, as described, advantageously also be partially oxidized to acrylic acid.

According to the invention, the reaction gas starting mixture advantageously contains molecular nitrogen, CO, CO ₂ , water vapor and propane as the diluent gas. The molar ratio of propane: propene can assume the following values in the propene oxidation process: 0 to 15, often 0 to 10, often 0 to 5, advantageously 0.01 to 3.

In the partial propene oxidation process, the loading of the catalyst with propene can be, for example, 40 to 250 Nl / l ^» h or more. The loading of starting reaction gas mixture is often in the range from 500 to 15,000 Nl / I ^»h, often in the range 600 to 10,000 Nl / lh, often 700 to 5,000 Nl / l * h.

Of course, in the process of propene partial oxidation to acrylic acid, a product gas mixture is obtained which does not consist exclusively of acrylic acid. Rather, the product gas mixture contains, in addition to unconverted propene, secondary components such as propane, acrolein, CO ₂ , CO, H ₂ O, acetic acid, propionic acid, etc., from which the acrylic acid must be separated.

This can be done as is generally known from the heterogeneously catalyzed two-stage (in two reaction zones) gas phase oxidation of propene to acrylic acid.

This means that the acrylic acid contained in the product gas mixture can be absorbed by absorption with water or by absorption with a high-boiling inert hydrophobic organic solvent (e.g. a mixture of diphenyl ether and diphyl which may also contain additives such as dimethyl phthalate). The resulting mixture of absorbent and acrylic acid can then be worked up in a manner known per se by rectification, extraction and / or crystallization to give pure acrylic acid. Alternatively, the basic separation of the acrylic acid from the product gas mixture can also be carried out by fractional condensation, as it is e.g. is described in DE-A 199 24 532.

The resulting aqueous acrylic acid condensate can then e.g. can be further purified by fractional crystallization (e.g. suspension crystallization and / or layer crystallization).

The residual gas mixture remaining in the basic separation of acrylic acid contains, in particular, unreacted propene (and possibly propane). This can be separated from the residual gas mixture, for example by fractional pressure rectification, and then recycled into the gas phase oxidation according to the invention. However, it is more favorable to bring the residual gas into contact with a hydrophobic organic solvent in an extraction device (for example by passing it through), which the propene (and optionally propane) is able to absorb preferentially. The absorbed propene (and optionally propane) can be released again by subsequent desorption and / or stripping with air and returned to the process according to the invention. In this way, economic total propene sales can be achieved. If propene is partially oxidized in the presence of propane, propene and propane are preferably separated off and recycled together.

In a completely corresponding manner, the multimetal oxides M and their subsequent compositions obtainable according to the invention can be used as catalysts for the partial oxidation of isobutane and / or isobutene to methacrylic acid.

Their use for the ammoxidation of propane and / or propene can e.g. as described in EP-A 529 853, DE-A 23 51 151, JP-A 6-166668 and JP-A 7-232071.

They can be used for the ammoxidation of n-butane and / or n-butene as described in JP-A 6-211767.

Their use for the oxydehydrogenation of ethane to ethylene or the further reaction to acetic acid can be carried out as described in US Pat. No. 4,250,346 or as described in EP-B 261 264.

They can be used for the partial oxidation of acrolein to acrylic acid as described in DE-A 102 61 186.

However, the multimetal oxide compositions M and their subsequent compositions obtainable according to the invention can also be integrated into other multimetal oxide compositions (for example, mixing their finely divided compositions, optionally pressing and calcining, or mixing, preferably aqueous) as slurries, drying and calcining (for example as described in EP-A 529 853 describes)). It is preferably calcined again under inert gas.

The resulting multimetal oxide compositions (hereinafter referred to as total compositions) preferably contain> 50% by weight, particularly preferably> 75% by weight, and very particularly preferably> 90% by weight or> 95% by weight of multimetal oxide compositions M obtainable according to the invention or their successive dimensions and are also suitable for the partial oxidations and / or amoxidations discussed in this document.

The geometric shape of the total masses is expediently as described for the multimetal oxide masses M according to the invention and their successor masses. For the purpose of heterogeneously catalyzed partial gas phase oxidation of propane to acrylic acid, the multimetal oxide compositions M obtainable according to the invention, their successor compositions and multimetal oxide compositions or catalysts containing such compositions are preferably put into operation as described in DE-A 101 22 027.

In conclusion, it should be noted that the excellent reproducibility when using the procedure according to the invention is attributed to the fact that the desired multimetal oxide M occurs in an environment which essentially contains only water and its constituents H, O, OH. In this way, the multimetal oxide M is quasi below its natural intrinsic pH, which obviously gives the procedure a particularly robust character.

Examples and comparative examples

A) Production of multimetal oxide materials

Example 1: Production of a multimetal oxide mass of the weighing stoichiometry

The following were introduced into an autoclave with a built-in stirrer and an internal volume of 2.5 l in finely divided form:

123.27 g of MoO ₃ (from Riedel-de-Haen Brand, 30926 Seelze; MoO ₃ content>99.9%; 0.86 mol of Mo);

23.06 g VO ₂ (Alfa Aesar, 76057 Karlsruhe; VO ₂ content = 99.5%; 0.28 mol VO ₂ , V oxidation state = 4.03);

3.69 g TeO ₂ (Sigma Aldrich, 82018 Taufkirchen;> 99% TeO ₂ ; 0.023 mol TeO ₂ );

and 1500 ml of water.

The lid of the autoclave was closed and the portion of air in the autoclave above the aqueous phase was exchanged for nitrogen by flushing with nitrogen. The autoclave was then heated continuously (linearly) to 175 ° C. in the course of 10 hours under autogenous pressure with continuous stirring (700 rpm) and held at this temperature with further stirring for 48 hours. The mixture was then cooled to room temperature (25 ° C.). The autoclave -was opened and the black powder formed was filtered, washed three times ^'mitje' 2ü0 ml Washed water at 25 ° C and then dried at 80 ° C for 12 h in a vacuum drying cabinet.

The experiment carried out as described was repeated ten times. In all cases, the same result described below was obtained.

As the powder X-ray diffractogram (XRD) shown in FIG. 1 shows, only the i-phase is obtained. The associated scanning electron micrograph (SEM) (FIG. 2, three different magnifications) shows needle-shaped crystals with a high length-to-thickness ratio of approximately 50 to 100.

An advantage of the "needle" or "fiber shape" is likely to be that other (additional) crystallographic surfaces are more accessible to catalysis compared to an isotropic material.

Titrimetric analysis shows that the V in the i-phase formed has the oxidation state 4.02 to 4.05. The specific surface was 45 m ² / g. Chemical analysis showed a satisfactory agreement with the weighing stoichiometry.

Comparative Example 1: Production of a multimetal oxide mass of the weighing stoichiometry

The following were introduced into the autoclave from Example 1 in finely divided form:

151.87 g (NH ₄ ) ₆ Mo ₇ O ₂₄ 4 H ₂ O (HC Starck, 38642 Goslar; MoO ₃ content 81.5%; 0.86 mol Mo);

66.64 g of vanadyl sulfate hydrate VOSO ₄ (H ₂ O) _x (from Alfa Aesar, 76057 Karlsruhe; V content = 21.4% by weight; 0.28 mol V);

3.69 g TeO ₂ (as in Example 1);

and 1500 ml of water.

The procedure was then as in Example 1 (hydrothermal). The experiment carried out as described was repeated ten times. In two cases there was an increased proportion of i-phase in the multimetal oxide powder formed. In the eight other experiments, on the other hand, a phase mixture was obtained which contained only a small i-phase portion.

Among the other phases were identified: phase 81-2414 (c) of the JPDS arterK o. ^ Moo.ββJO ^ -hexagonalj.'phase 05-0508 of the JPDS file [MoO ₃ , "^" öτ- thorhombic], phase 47-0872 of the JPDS file [HMo _5l 35θi5 _l 75 (OH) ₁ , _β -1.7 H ₂ O] and phase 77-0649 (c) of the JPDS file triklin].

Example 2: Production of a multimetal _{oxide mass of} the weighing _{stoichiometry} Mo V _G , ₃₂ Bio _ι027 O _x

The following were introduced into the autoclave from Example 1 in finely divided form:

123.27 g MoO ₃ (as in Example 1);

23.06 g VO ₂ (as in Example 1);

5.36 g Bi ₂ O ₃ (Riedel-de Haen Brand, 30926 Seelze;> 99.5% Bi ₂ O ₃ ; 0.023 mol Bi);

and 1500 ml of water.

The procedure was then as in Example 1 (hydrothermal).

The experiment carried out as described was repeated ten times. In all cases, the same result described below was achieved.

The powder X-ray diffractogram (cf. FIG. 3) showed in all cases only i-phase for the black powder obtained. The associated scanning electron micrograph (FIG. 4, three different magnifications) shows needle-shaped crystals with a high length-to-thickness ratio of approximately 30 to 150.

The chemical analysis showed a satisfactory agreement with the weighing stoichiometry. According to titrimetric analysis, the V in the i-phase formed had an oxidation state of 4.02 to 4.07. The specific surface was 38 m ² / g.

Comparative _Example 2: Production of a multimetal _{oxide mass of weighing stoichiometry} Mo ₁ V _0ι32 Bio, o ₂ 7θχ

The procedure was as in Example 2. Instead of MoO ₃ , however, 151.87 g (NH) ₆ Mo ₇ O ₂ -4H ₂ O (as in Comparative Example 1) and instead of VO ₂ became 66.64 g of vanadyl sulfate hydrate (VOSO ₄ (H ₂ O) _x ) (as in Comparative Example 1). The experiment was repeated ten times. In two cases, an increased proportion of i-phase was obtained in the black powder produced.

In the eight other reproductions, on the other hand, a phase mixture with only a digestive part was obtained. The remaining phases could be identified ai≤ ' Phase 05-0508 of the JPDS file [MoO ₃ , orthorhombic], as phase 47-0872 of the JPDS file [HMo ^ O ^ OH eI JH ₂ O], as phase 48-0744 of the JPDS file (Bi-VO ₄ , tetragonal), as phase 85-0630 of the JPDS file (Bi _0.88 Mθo _{, 37} Vo _{, 63} O), as crystal structure of phase 70-2321 (c) of the JPDS file [Sb ₂ Mo ₁₀ O ₃₁ , orthorhombic ], as the crystal structure of phase 33-0104 of the JPDS file (Sb ₄ Mθι ₀ O ₃₁ , hexagonal) and / or phase 77-0649 (c) of the JPDS file [(V ₀ , ₉₅ Mθo, ₉₇ θ ₅ , triclinic In addition, there were other phases that could not be identified using the XRD diffraction reflexes.

Example 3: Production of a multimetal oxide mass of the weighing stoichiometry

The procedure was as in Example 2. However, a mixture of 2.85 g of V powder (from Chempur, 76204 Karlsruhe; V content>99.5%; 0.056 mol V) and 20.36 g of V ₂ O ₅ (from the Gesellschaft für Elektrometallurgie (GfE), 90431 Nürnberg; V ₂ O ₅ content = 99.97%; 0.224 mol V).

The autoclave was closed and the proportion of air in the autoclave above the aqueous solution was replaced by nitrogen flushing with nitrogen.

The autoclave was then heated continuously (linearly) to 90 ° C. over a period of 3 hours with continuous stirring (700 rpm) and under autogenous pressure and stirred at this temperature for 10 hours.

The mixture was then heated continuously (linearly) to 175 ° C. in the course of 8 hours with continuous stirring (700 rpm) and under autogenous pressure and held at this temperature with stirring for 24 hours. The mixture was then cooled to room temperature (25 ° C.) and, as in Example 1, the black powder formed was filtered off, washed with water and dried.

The experiment carried out as described was repeated ten times. The same result as in Example 2 was obtained in six of the 10 embodiments.

In four of the ten versions, solids crystallized that corresponded to those from comparative example 2.

Example 4: Production of a multimetal oxide mass of the weighing stoichiometry

The procedure was as in Example 1. Instead of the 23.06 g VO ₂ , however, only 18.0 g VO _{2 were} used and the Te compound was omitted. Example 5: Preparation of a multimetal oxide material of the Stoichiometry Mo ₁ V _{0, 25} NbO, o Bio _98, o _{42 x} θ

The procedure was as in Example 1. That is, 123.27 g of MoO _{3 were} weighed out again, as well as the quantities of VO ₂ , Nb ₂ O ₅ and Bi ₂ O ₃ required according to the stoichiometry required.

Example 6: Production of a multimetal oxide mass of weighing stoichiometry M01Vo.3Sbo.25Nbo.12Ox

The procedure was as in Example 1. That is, 123.27 g of M0O _{3 were} weighed out again, as well as the quantities of VO ₂ , Sb ₂ O ₃ and Nb ₂ O ₅ required in this regard according to the stoichiometry required.

Example 7: Production of a multimetal oxide _{mass of} the weighing stoichiometry MθιV _0ι3 Nbo, i ₃ Sbo _, i ₃ θ _{4, 25}

The procedure was as in Example 1. That is, 123.27 g of M0O3 were weighed out again, as well as the quantities of VO ₂ , Nb ₂ O ₅ and Sb ₂ O ₃ required according to the stoichiometry required.

Example 8: Production of a multimetal oxide mass of weighing stoichiometry M0 Vo.3Nbo.13Nio.13Ox

The procedure was as in Example 1. That is, 123.27 g of M0O _{3 were} weighed out again, as well as the quantities of VO ₂ , Nb ₂ O ₅ and NiO required in this regard according to the stoichiometry required.

EXAMPLE 9 Production of a Multimetal Oxide Mass of Weighing Stoichiometry MθιVo, ₃ Nb _0, i ₃ Cθo _, ι ₃ Oχ

The procedure was as in Example 1. That is, 123.27 g of MoO _{3 were} weighed out again, as well as the quantities of VO ₂ , Nb ₂ O ₅ and CoO required in this regard according to the stoichiometry required.

Example 10: Preparation of a multimetal oxide material of the Stoichiometry Mθ V _{0, 3} Nb _0ι i Cro _3, O ₃ iOχ

The procedure was as in Example 1. That is, 123.27 g of M0O3 were weighed out again, as well as the quantities of VO ₂ , Nb ₂ O ₅ and Cr ₂ O ₃ required in this regard according to the stoichiometry required. Example 11: Production of a multimetal oxide mass of the weighing stoichiometry

The procedure was as in Example 2. 100 g of the obtained and dried multimetal oxide mass were placed in 500 g of a 10% strength by weight aqueous nitric acid. The resulting aqueous suspension was stirred under reflux at 80 ° C for 5 h. Then it was cooled to 25 ° C. The solid in the black suspension was separated from the aqueous phase by filtration, washed free of nitrate with water and then dried in a forced-air drying cabinet at 120 ° C. overnight.

Example 12

The procedure was as in Example 2. 100 g of the obtained and dried multimetal oxide mass were in a rotary ball oven (internal volume: 1 liter) according to FIG. 1 of DE-A 100 29 338 under a stream of molecular nitrogen (10 Nl / h) at a heating rate of 2 ° C./min from room temperature Heated 500 ° C and kept at this temperature while maintaining the nitrogen flow for 6 h. The mixture was then left to cool to 25 ° C. while maintaining the nitrogen flow.

Example 13

As in Example 5, but was thermally aftertreated as in Example 12.

Example 14

As in Example 6, but as in Example 12, thermal treatment was carried out.

Example 15

As in Example 7, but was thermally aftertreated as in Example 12.

Example 16

As in Example 10, but as in Example 12, thermal treatment was carried out.

B) Production of coated catalysts from the multimetal oxide materials produced in A) The respective active material powder was ground in a Retsch mill (centrifugal mill, type ZM 100, from Retsch, DE) (grain size <0.12 mm). 38 g each of the powder present after grinding was placed on 150 g spherical support bodies with a diameter of 2.2 to 3.2 mm (Rz = 45 μm, support material = steatite C 220 from Ceramtec, DE, total pore volume of the support <1% by volume .-% based on the total carrier volume) applied. For this purpose, the carrier was placed in a coating drum with an internal volume of 2 l (angle of inclination of the drum center axis against the horizontal = 30 °). The drum was rotated at 25 revolutions per minute. An atomizer nozzle operated with 300 Nl / h of compressed air was used for 60 min. about 25 ml of a mixture of glycerol and water (weight ratio glycerol: water = 1: 3) was sprayed onto the carrier. The nozzle was installed in such a way that the spray cone moistened the carrier bodies in the drum, which were transported by driving plates to the uppermost point of the inclined drum, in the upper half of the rolling path. The finely divided active material powder was introduced into the drum via a powder screw, the point at which the powder was added being within the rolling zone or below the spray cone. Due to the periodic repetition of wetting and powder metering, the base-coated carrier body itself became the carrier body in the subsequent period.

After completion of the coating, the coated carrier body was dried in air in a muffle furnace at 150 ° C. for 16 h.

The result was coated catalysts SB1 to SB16 and SVB1 and SVB2, each with 20% by weight of active mass (B1 means that the multimetal oxide from Example 1 from A) was used; SVB1 means accordingly that the multimetal oxide according to Comparative Example 1 from A) was used).

C) Testing the coated catalysts produced in B)

A tubular reactor made of steel (inside diameter: 8.5 mm, length: 140 cm, wall thickness: 2.5 cm) was charged with 35.0 g each of the respective coated catalyst from B (catalyst bed length in all cases approx. 53 cm). Before the catalyst bed, a pre-fill of 30 cm steatite balls (diameter: 2.2 to 3.2 mm, manufacturer: Ceramtec, steatite C 220) and after the catalyst bed, a bed of the same steatite balls was added to the remaining length of the tubular reactor.

The outside temperature T of the charged reaction tube was raised along the entire length from the outside by means of electrically heated heating mats. set the desired value.

Then the reaction tube was charged with a reaction gas starting mixture of the molar composition propane: air: H ₂ O = 1:15:14 (the inlet side was on the side of the next;}). The residence time (based on the catalyst bed) volume) was set to 2.4 sec. The inlet pressure was 2 bar absolute.

The reaction tube feed was first run in at the outside temperature T = 350 ° C. of the charged reaction tube over a period of 24 h before this outside temperature was set to its respective value.

The following table shows the resulting propane conversion (U ^PAN (mol%)), the resulting selectivity of acrylic acid formation (S _A cs (mol%)) and the selectivity depending on the coated catalyst used and the set outside temperature T (° C) by-product formation on propene (S _PE N (mol%)).

table

US Provisional Patent Application No. 60 / 577,929, filed on June 9, 2004, is incorporated into the present application by reference. In view of the above teachings, numerous changes and deviations from the present invention are possible. It is therefore believed that the invention, within the scope of the appended claims, may be practiced otherwise than as specifically described herein.

Claims

claims 1. Process for the preparation of a multimetal oxide mass M of general stoichiometry I, MθιV _a M ¹ _b M ² _c M ³ _d M ⁴ _e O _n (I) with M ¹ = at least one of the elements from the group comprising AI, Ga, In, Ge, Sn, Pb, As, Bi, Se, Te and Sb; M ² = at least one of the elements from the group comprising Sc, Y, La, Ti, Zr, Hf, Nb, Ta, Cr, W, Mn, Fe, Co, Ni, Zn, Cd and the lanthanides; M ³ = at least one of the elements from the group and comprising Re, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, Au; M ⁴ = at least one of the elements from the group comprising Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, NH ₄ and TI; a = 0.01 to 1; b => 0 to 1; c => 0 to 1; d => 0 to 0.5; e => 0 to 0.5 and n = a number which is determined by the valency and frequency of the elements other than oxygen in (I), in which a mixture G from sources of the elementary constituents of the multimetal oxide mass M is subjected to a hydrothermal treatment and the newly formed solid separates, characterized in that as sources of the elementary constituents of the multimetal oxide mass M, only sources from the group comprising compounds which consist only of the elementary constituents of the multimetal oxide mass M and of elemental constituents of water are the elemental constituents of the Multimetal oxide mass M itself, in its elemental form and elementary constituents of the ammonium salts containing multimetal oxide mass M, are used with the proviso that the molar ratio MV NH ₄ / M0 of NH ₄ contained in mixture G and Mo contained in mixture G is <0.5 and at least a subset of the sources included in these Sources contain 4 drawings. has elementary constituents with an oxidation number that is below the maximum oxidation number of the respective elemental constituent. 2. The method according to claim 1, characterized in that it is carried out at a temperature of 120 to 300 ° C. 3. The method according to claim 1 or 2, characterized in that it is carried out at a pressure> 1 bar to 500 bar. 4. The method according to any one of claims 1 to 3, characterized in that at least a subset of the sources of the elemental constituent V contains vanadium, the oxidation number of which is +4, or +3, or +2, or 0. 5. The method according to any one of claims 1 to 4, characterized in that at least one of the compounds from the group comprising VO ₂ , V ₂ O ₃ , VO, V ₆ O ₃ , V ₃ O ₇ , V as the source of the elemental constituent V ₄ O ₉ and elemental vanadium is also used. 6. The method according to any one of claims 1 to 5, characterized in that the molar ratio MV is <0.3. 7. The method according to any one of claims 1 to 6, characterized in that the molar ratio MV is <0.1. 8. The method according to any one of claims 1 to 7, characterized in that at least 40 mol% of the V contained in the mixture G is contained as V, the oxidation number of which is <+5. 9. The method according to any one of claims 1 to 7, characterized in that at least 70 mol% of the V contained in the mixture G is contained as V, the oxidation number of which is <+5. 10. The method according to any one of claims 1 to 9, characterized in that the stoichiometric coefficients a, b, c and d are simultaneously in the following grid: a = 0.05 to 0.5; b = 0.01 to 0.5; c = 0.01 to 0.5; d = 0.0005 to 0.5 and e => 0 to 0.5. 11. The method according to any one of claims 1 to 9, characterized in that the stoichiometric coefficients a, b, c and d are simultaneously in the following grid: a = 0.1 to 0.5; b = 0.1 to 0.5; c = 0.1 to 0.5; d = 0.001 to 0.1 and e => 0 to 0.1. 12. The method according to any one of claims 1 to 11, characterized in that M ^{1 is} at least one element from the group comprising Sb, Bi, Se and Te. 13. The method according to any one of claims 1 to 12, characterized in that M ² at least 50 mol% of its total amount of Nb and at least one of the elements from the group comprising Ti, Zr, Cr, Ta, W, Fe, Co , Ni and Zn is. 14. The method according to any one of claims 1 to 13, characterized in that M ^{3 is} at least one element from the group comprising Re, Pd and Pt. 15. The method according to any one of claims 1 to 14, characterized in that the stoichiometric coefficient e = 0. 16. A process for the preparation of a multimetal oxide composition M of general stoichiometry I from claim 1, characterized in that a process according to one of claims 1 to 15 is first carried out, the newly formed solid is separated off and thermally aftertreated and then optionally with a washes organic acid or its aqueous solution, or with an inorganic acid or its aqueous solution, or with an alcohol or with hydrogen peroxide or its aqueous solution. 17. A method for producing a multimetal oxide mass M of general stoichiometry I from claim 1, characterized in that one first carries out a process according to one of claims 1 to 15, the newly formed solid is separated off and then with an organic acid or its aqueous Washes, or with an inorganic acid or its aqueous solution, or with an alcohol or with hydrogen peroxide or its aqueous solution. 18. The method according to any one of claims 1 to 15, characterized in that it is carried out under an inert gas atmosphere. 19. The method according to any one of claims 1 to 17, characterized in that the thermal aftertreatment and the washing is carried out under an inert gas atmosphere. 20. The method according to any one of claims 1 to 15, characterized in that, based on the sum of water and the sources of the elementary constituents of the multimetal oxide mass M, the weight fraction of the latter in the hydrothermal treatment is 5 to 50% by weight.