DE10344265A1 - (Meth)acrylic acid production in high yield, for use as monomer, by gas-phase oxidation of saturated hydrocarbon precursor(s) over two beds of mixed metal oxide catalysts with specific selectivity properties - Google Patents

Abstract

In the production of (meth)acrylic acid ((M)AA) by passing a gaseous mixture of saturated hydrocarbon precursor(s) (SHP's), oxygen and inert gas through a reactor charged with a mixed metal oxide catalyst (M) containing molybdenum and vanadium, (M) is contained in two beds (I) and (II) of different composition, spaced in the flow direction, having specific selectivity properties on increasing the temperature. Production of (meth)acrylic acid ((M)AA) by heterogeneous gas-phase oxidation at elevated temperature involves passing a gaseous mixture of saturated hydrocarbon precursor(s) (SHP's), oxygen and inert gas(es) at initial pressure P through a reactor charged with a catalyst comprising (as active mass) a mixed metal oxide (M) containing molybdenum and vanadium, at least one of tellurium, antimony and bismuth and at least one of niobium, tantalum, tungsten, cerium and titanium and having an X-ray diffractogram peaks at 2tau values of 22.2 +- 0.5[deg] (h) (strongest peak; half-value breadth at most 0.5[deg]), 27.3 +- 0.5[deg] (i) (half-value breadth 1.0[deg] or less) and 28.2 +- 0.5[deg] (k) (half-value breadth 1.0[deg] or less). The novel feature is that the whole of (M) is contained in two beds (I) and (II) of different composition, spaced in the flow direction. Beds (I) and (II) are such that if the particular bed was the only catalyst present in the same reactor the respective selectivities S1> and S2> for (M)AA would have maximum values (on increasing the conversion of SHP's by increasing the temperature under otherwise identical conditions on a single pass of gas through the reactor) of S1>max and S2>max respectively, where S1>max occurs at lower SHP conversion than S2>max and at an increasing SHP conversion S1> is less than S2>, whereas S1>max is more than S2>max.

Description

This The invention relates to a process for the preparation of (meth) acrylic acid by heterogeneously catalyzed gas phase partial oxidation of at least one saturated Hydrocarbon precursor compound with increased Temperature at which one of the at least one saturated hydrocarbon precursor compound, molecular Oxygen and at least one reaction gas starting mixture containing inert gas with an inlet pressure P by a pressure in a reactor unit Catalyst feed leads, whose catalysts are designed so that their active mass at least is a multimetal oxide M, the elements Mo and V, at least one of the elements Te, Sb and Bi and at least one of the elements from the group comprising Nb, Ta, W, Ce and Ti and its X-ray diffraction an X-ray diffraction program which has diffraction reflexes h, i and k, the apexes of which diffraction reflexes (2⊝) 22.2 ± 0.5 ° (h), 27.3 ± 0.5 ° (i) and 28.2 ± 0.5 ° (k), the diffraction reflex h being the most intense within the X-ray diffractogram as well as a full width at half maximum 0.5 ° and the half-width of the diffraction reflex i and the diffraction reflex k is ≤ 1 ° in each case.

The Spelling (meth) acrylic acid is foreshortened in this writing for methacrylic acid or Acrylic acid.

Forms (meth) acrylic acid reactive monomers, e.g. for the production of polymers which et al can be used as adhesives are suitable.

Industrially can (meth) acrylic acid et al by heterogeneously catalyzed gas phase partial oxidation of Propane or isobutane can be produced.

By heterogeneously catalyzed partial gas phase partial oxidation of a Mixtures of propane and isobutane can be mixed with acrylic acid and methacrylic acid be generated.

propane and isobutane are therefore described in this document as saturated hydrocarbon precursor compounds of (meth) acrylic acid designated.

Processes for the preparation of (meth) acrylic acid by heterogeneously catalyzed gas phase partial oxidation of at least one saturated hydrocarbon compound according to the preamble of this document are known (cf. for example EP-A 1192987 . DE-A 10122027 , JP-A 2000-256257, EP-A 608838 . EP-A 1193240 . EP-A 1238960 . JP-A 10-36311 . EP-A 1254706 . DE-A 10051419 . EP-A 962253 , WO-A 99/003825, JP-A 11-57479 and DE-A 10338529 ).

adversely What is important about these processes is that the process conditions are otherwise specified dependent on from the reaction temperature in one pass of the reaction gas mixture maximum achievable by the catalyst feed (reactor unit) Yield of (meth) acrylic acid cannot fully satisfy.

The The object of the present invention was therefore an improved Processes for the production of (meth) acrylic acid are available too ask, the heightened Yields of (meth) acrylic acid allows.

Accordingly, a process for the production of (meth) acrylic acid by heterogeneously catalyzed gas phase partial oxidation of at least one saturated hydrocarbon precursor compound at elevated temperature, in which a reaction gas starting mixture containing the at least one saturated hydrocarbon precursor compound, molecular oxygen and at least one inert gas has an inlet pressure P through a in a reactor unit located catalyst feed, the catalysts are connected so that their active composition is at least one multimetal oxide M, which contains the elements Mo and V, at least one of the elements Te and Sb and at least one of the elements from the group comprising Nb, Ta, W, Ce and Contains Ti and whose X-ray diffractogram is an X-ray diffraction program that has diffraction reflections h, i and k, the apexes of the diffraction reflections (2⊝) 22.2 ± 0.5 ° (h), 27.3 ± 0.5 ° (i) and 28.2 ± 0.5 ° (k), with the diffraction reflection reflex h is the most intense within the X-ray diffraction program and has a half-value width of at most 0.5 ° and the half-value width of the diffraction reflex i and the diffraction reflex k is ≤ 1 °,
which is characterized by
that the catalyst feed in its entirety consists of two catalyst beds I, II which are spatially consecutive in the flow direction of the reaction gas mixture and contain different catalysts, the catalyst bed I being such that when the total catalyst coat The same reactor unit would only consist of type I catalyst bed, the selectivity S ^{I of} the (meth) acrylic acid formation under otherwise identical conditions of the gas phase partial oxidation depending on the conversion of the saturated hydrocarbon precursor compound increased by increasing the reaction temperature, based on a single passage of the reaction gas mixture through the reactor unit, passes through a maximum value S ^I _max ,
and the catalytic bed II is such that if the total catalyst feed of the same reactor unit would only consist of type II catalytic bed, the selectivity S ^{II of} the (meth) acrylic acid formation under otherwise identical conditions of the gas phase partial oxidation depending on the increased conversion of the saturated hydrocarbon precursor compound by increasing the reaction temperature , based on a single passage of the reaction gas mixture through the reactor unit, a maximum value S ^II _max passes through,
with the proviso that the value S ^I _max with a lower conversion of the saturated hydrocarbon precursor compound than the value S ^II _max and with increasing conversion of the saturated hydrocarbon precursor compound S ^I <S ^II applies, whereas S ^I _max > S ^II _max .

The Thought the production of (meth) acrylic acid by heterogeneously catalyzed Gas phase partial oxidation of at least one saturated hydrocarbon compound to be carried out in a structured catalyst feed from Catalysis Letters Vol. 87, Nos. 3-4, April 2003, p. 195 bis 199 known in abstract form. A disadvantage of this publication however is that they are over the way of structuring remains silent.

In the EP-A 1193240 If such a structured feed is used, for example, one containing only one catalyst, the volume concentration of this catalyst increasing within the feed in the flow direction of the reaction gas mixture.

background the present invention is the observation that the selectivity of (meth) acrylic acid formation in a procedure according to the preamble to this Font usually goes through a maximum if you, under otherwise constant process conditions, sales of at least one saturated hydrocarbon precursor with one pass of the reaction gas mixture through the catalyst feed increased by increasing the reaction temperature.

Further it was observed that, with essentially the same method of manufacture of catalysts with multimetal oxides M as active material, element compositions of the multi-metal oxide M, which are characterized in that the aforementioned selectivity maximum in the case of catalyst feeds with active materials from such Multimetal oxide M catalysts with comparative low sales the at least one saturated Hydrocarbon precursor compound lies and very pronounced is, but decreases sharply with increasing sales (such element compositions of the multimetal oxide M are hereinafter referred to as element compositions A)) while in another group of element compositions of the multi-metal oxide M (hereinafter referred to as element compositions B) the corresponding maximum selectivity with comparatively high sales lies, less pronounced and decreases less with increasing sales.

Multi metal oxides M of type A are preferably suitable in the process according to the invention to feed the catalyst bed I while multimetal oxides M of type B, preferably for feeding the catalyst bed II suitable.

As a rule, the multi-metal oxides M of type A include the multi-metal oxides of stoichiometry A, Mo ₁ V _a Te _b Nb _c X ¹ _d O _n (A) ,With
X ¹ = Ag, Ga, Pd and / or Sm,
a = 0.01 to 1,
b => 0 to 1,
c => 0 to 1,
d => 0 to 0.5 and
n = a number determined by the valency and frequency of the elements in A other than oxygen.

The multimetal oxides M of type B generally include multimetal oxides of stoichiometry B, MO ₁ V _a Te _b Nb _c X ² _e O _x (B) ,With
X ² = Ni, Co, Bi, Cu, Fe, Mn, Nd, Pb, Re and / or Pt,
a = 0.01 to 1,
b => 0 to 1,
c => 0 to 1,
e = ≥ 0 to 0.5 and
x = a number determined by the valency and frequency of the elements in B other than oxygen.

Prefers is the stoichiometric Coefficient a both in the case of stoichiometry A and in the case of stoichiometry B, independently from the preferred areas for the other stoichiometric Coefficients of the two stoichiometries A, B 0.05 to 0.6, particularly preferably 0.1 to 0.6 or 0.5.

Independent of the preferred areas for the other stoichiometric Coefficients of the two stoichiometries A, B is the stoichiometric Coefficient b preferably 0.01 to 1, and particularly preferably 0.01 or 0.05 or 0.1 to 0.5 or 0.4.

The stoichiometric Coefficient c which is advantageous according to the invention to be used multimetal oxides M of stoichiometry A, B is independent of the preferred areas for the other stoichiometric coefficients of stoichiometries A, B 0.01 to 1 and particularly preferably 0.01 or 0.05 or 0.1 to 0.5 or 0.4. A very particularly preferred according to the invention Area for the stoichiometric Coefficient c that is independent from the preferred areas for the other stoichiometric Coefficient of stoichiometry A, B can be combined, the range is 0.05 to 0.2.

Preferred according to the invention is the stoichiometric Coefficient d or e of the stoichiometries A, B, independently from the preferred areas for the other stoichiometric Coefficients, 0.00005 or 0.0005 to 0.5, particularly preferred 0.001 to 0.5, common 0.002 to 0.3 and often 0.005 or 0.01 to 0.1.

Particularly favorable multi-metal oxides M of stoichiometry A or B to be used according to the invention are those whose stoichiometric coefficients a, b, c and d or e are simultaneously in the following grid:
a = 0.05 to 0.6;
b = 0.01 to 1 (or 0.01 to 0.5);
c = 0.01 to 1 (or 0.01 to 0.5); and
d, e = 0.0005 to 0.5 (or 0.001 to 0.3).

Very particularly favorable multimetal oxides M of type A, B to be used according to the invention are those whose stoichiometric coefficients a, b, c and d or e are simultaneously in the following grid:
a = 0.1 to 0.6;
b = 0.1 to 0.5;
c = 0.05 or 0.1 to 0.5; and
d, e = 0.001 to 0.5 or 0.002 to 0.3 or 0.005 to 0.1.

The aforementioned relationships remain essentially even if you look at the stoichiometries A, B the element Te through the element Sb or through the element Bi or replaced by at least two of the elements Sb, Te and Bi.

Further all of the above-mentioned relationships remain essentially the same get if you look at the stoichiometries A, B the element Nb by one of the elements Ce, Ti, W or Ta or by a mixture of elements from the group comprising Nb, Ti, W, Ta and Ce replaced.

It is now generally known that catalytically active multimetal oxides M can occur in different crystalline phases (cf. e.g. DE-A 10246119 and DE-A 10254279 ).

A the possible crystalline phases, the so-called k-phase (with a hexagonal structure, often too Called M2 phase), is characterized by an X-ray diffractogram, that at the 2⊝ vertex positions Special 22.1 ± 0.5 °, 28.2 ± 0.5 °, 36.2, ± 0.5 °, 45.2 ± 0.5 ° and 50.0 ± 0.3 ° high intensity Has diffraction reflexes.

A second specific crystal structure (orthorhombic structure) in which the relevant multimetal oxides M can occur is generally referred to as the i-phase (often also as the M1-phase). Your X-ray diffraction pattern is characterized, among other things, by the fact that it has 22.2 ± 0.5 °, 27.3 ± 0.5 °, 28.2, ± 0.5 ° particularly intense diffraction reflections in the 2⊝ vertex positions The difference to the k phase at the 2⊝ vertex position 50.0 ± 0.3 ° shows no diffraction reflex (cf. DE-A 10119933 and DE-A 10118814 ).

In the usual manufacturing processes of the relevant multimetal oxides M (for example the manufacturing processes according to WO 0206199, EP-A 1192987 . EP-A 529853 such as EP-A 603836 ) Neither pure k-phase nor pure i-phase are now obtained, but rather mixed crystal structures, which are an overgrown mixture of k and i phases, in which the k phase portion normally dominates.

The intensity ratio is a measure of the i-phase fraction in these mixed crystal structures R = P i / (P i + P k ) where P _{i is} the intensity of the diffraction reflex i at 2⊝ = 27.3 ± 0.5 ° and P _{k is} the intensity of the diffraction reflex k at 2⊝ = 28.2 ± 0.5 ° in the associated X-ray diffractogram.

Especially High i-phase components are present when 0.55 or 0.65 ≤ R ≤ 0.85. High i-phase proportions in the multimetal oxides to be used according to the invention M are preferred according to the invention both for that of stoichiometry A as well as that of stoichiometry B. According to the invention advantageous is for both stoichiometries A, B pure i-phase.

Preferred according to the invention applies to both stoichiometries A, B therefore 0.65 ≤ R ≤ 0.85 or 0.67 ≤ R ≤ 0.75 and R = 0.69 to 0.75 or R = 0.71 to applies with very particular preference 0.74 or 0.73 or R = 0.72.

In addition to the diffraction reflections h, i and k, the X-ray diffractogram of the catalytically active multimetal oxides M to be used according to the invention (regardless of their stoichiometry) generally also contains further diffraction reflections, the apex of which lies at the following diffraction angles (2⊝):
9.0 ± 0.4 ° (l),
6.7 ± 0.4 ° (o) and
7.9 ± 0.4 ° (p).

Is cheap according to the invention it further if the x-ray diffractogram additionally contains a diffraction reflex, whose apex is at the diffraction angle (2⊝) = 45.2 ± 0.4 ° (q).

Often contains the X-ray diffractogram of to be used according to the invention Multimetal oxides M (independent from their stoichiometry) also the reflections 29.2 ± 0.4 ° (m) and 35.4 ± 0.4 ° (n) (vertex positions).

If the intensity 100 is assigned to the diffraction reflex h, it is advantageous according to the invention if the diffraction reflexes i, l, m, n, o, p, q have the following intensities in the same intensity scale:
i: 5 to 95, often 5 to 80, sometimes 10 to 60;
l: 1 to 30;
m: 1 to 40;
n: 1 to 40
o: 1 to 30;
p: 1 to 30 and
q: 5 to 60.

Contains the X-ray diffractogram those to be used according to the invention Multimetal oxides M (independent from their stoichiometry) of the aforementioned additional Diffraction reflections, the full width at half maximum is usually ≤ 1 °.

The specific surface area of multimetal oxides M to be used according to the invention is (regardless of their stoichiometry) frequently 1 to 40 m ² / g, advantageously 10 or 11 or 12 to 40 m ² / g and frequently 15 or 20 to 40 or 30 m ² / g (determined by the BET method, nitrogen).

According to the invention, the use is preferred (regardless of the stoichiometry), as already mentioned of such multimetal oxides M, whose X-ray diffractogram has no diffraction reflex with the vertex position 2⊝ = 50.0 ± 0.3 °.

All information in this document relating to an X-ray diffractogram relates to an X-ray diffractogram generated using Cu-Kα radiation as X-ray radiation (Siemens diffractometer Theta-Theta D-5000, tube voltage: 40 kV, tube current: 40 mA, aperture diaphragm V20 (variable ), Anti-scatter aperture V20 (variable), secondary monochromator aperture (0.1 mm), detector aperture (0.6 mm), measuring interval (2⊝): 0.02 °, measuring time per step: 2.4 s, detector: scintillation counter tube; the definition The intensity of a diffraction reflex in the X-ray diffractogram in this document relates to that in the DE-A 19835247 , the DE-A 10122027 , as well as in the DE-A 10051419 and DE-A 10046672 laid down definition; the same applies to the definition of the full width at half maximum).

According to the manufacturing processes described in the prior art (cf. e.g. DE-A 19835247 . EP-A 529853 . EP-A 603836 . EP-A 608838 . EP-A 895809 . EP-A 962253 . EP-A 1080784 . EP-A 1090684 . EP-A 1123738 . EP-A 1192987 . EP-A 1192986 . EP-A 1192982 . EP-A 1192983 and EP-A 1192988 ) for multimetal oxides M mixed-crystal systems from i- and k-phase are usually obtained. According to these processes, an intimate, preferably finely divided, dry mixture is generated from suitable sources of the elemental constituents of the multimetal oxide M and this is thermally treated at temperatures of 350 to 700 ° C. or 400 to 650 ° C. or 400 to 600 ° C. In principle, the thermal treatment can take place both under oxidizing, reducing and also under an inert atmosphere. For example, air, air enriched with molecular oxygen or air depleted in oxygen can be considered as the oxidizing atmosphere. However, the thermal treatment is preferably carried out under an inert atmosphere, ie, for example under molecular nitrogen and / or noble gas. The thermal treatment is usually carried out at normal pressure (1 atm). The thermal treatment can of course also be carried out under vacuum or under positive pressure.

He follows thermal treatment in a gaseous atmosphere these both stand and flow. It preferably flows. Overall, the thermal treatment can last up to 24 hours or more Claim.

Prefers the thermal treatment is first carried out under oxidizing (oxygen containing) atmosphere (e.g. in air) at a temperature of 150 to 400 ° C or 250 up to 350 ° C (= Pre-decomposition step). Subsequently, the thermal Appropriate treatment under Inert gas at temperatures from 350 to 700 ° C or 400 to 650 ° C or 450 up to 600 ° C continued. Of course, the thermal treatment can also do so take place that the catalyst precursor mass before its thermal Treatment first (optionally after pulverization) tableted (if necessary with the addition of 0.5 to 2 wt .-% of finely divided graphite), then is treated thermally and then split again.

The intimate mixing of the starting compounds can be done in dry or done in wet form.

He follows it in dry form, the starting compounds are convenient used as a fine powder and after mixing and optionally Compacting subjected to calcination (thermal treatment).

However, the intimate mixing is preferably carried out in wet form. Usually, the starting compounds are in the form of an aqueous solution (optionally with the use of complexing agents; cf. for example DE-A 10145958 ) and / or suspension mixed together. The aqueous mass is then dried and, after drying, calcined. The aqueous mass is expediently an aqueous solution or an aqueous suspension. The drying process preferably takes place immediately after the preparation of the aqueous mixture (in particular in the case of an aqueous solution; cf. for example JP-A 7-315842 ) and by spray drying (the outlet temperatures are usually 100 to 150 ° C; the spray drying can be carried out in cocurrent or in countercurrent), which requires a particularly intimate dry mixture, especially if the aqueous mass to be sprayed is a aqueous solution or suspension. However, it can also be dried by evaporation in a vacuum, by freeze-drying or by conventional evaporation.

Suitable sources for the elementary constituents in carrying out the above-described preparation of i- / k-phase crystal multi-metal oxide materials are all those which are capable of forming oxides and / or hydroxides when heated (optionally in air). It goes without saying that oxides and / or hydroxides of the elemental constituents can already be used as such starting compounds used or used exclusively. Ie, in particular, all come in the scriptures EP-A 1254707 . EP-A 1254709 and EP-A 1192987 mentioned starting compounds into consideration.

suitable Sources for the element Mo are e.g. molybdenum oxides like molybdenum trioxide, Molybdates such as ammonium heptamolybdate tetrahydrate and molybdenum halides like molybdenum chloride.

Suitable starting compounds for element V are, for example, vanadium oxysulfate hydrate, vanadylacetylacetonate, vanadates such as ammonium metavanadate, vanadium oxides such as vanadium pentoxide (V ₂ O ₅ ), vanadium halides such as vanadium tetrachloride (VCl ₄ ) and vanadium oxyhalides such as VOCl ₃ . It is also possible to use those starting vanadium compounds which contain the vanadium in oxidation state +4.

Suitable sources for the element tellurium are tellurium oxides such as tellurium dioxide, metallic tellurium, tellurium halides such as TeCl ₂ , but also telluric acids such as orthothelluric acid H ₆ TeO ₆ .

Advantageous antimony starting compounds are antimony halides such as SbCl ₃ , antimony oxides such as antimony trioxide (Sb ₂ O ₃ ), antimony trioxide pretreated with H ₂ O ₂ , antimonic acids such as HSb (OH) ₆ , but also antimony oxide salts such as antimony oxide sulfate (SbO) ₂ SO ₄ and antimony.

Suitable niobium sources are e.g. B. niobium oxides such as niobium pentoxide (Nb ₂ O ₅ ), niobium oxide halides such as NbOCl ₃ , niobium halides such as NbCl ₅ , but also complex compounds of niobium and alcohols (e.g. ethanol, n-propanol), organic carboxylic acids and / or dicarboxylic acids such as. B. oxalates and alcoholates. Of course, those in the EP-A 895 809 used solutions containing Nb.

Regarding everything other possible Elements (especially Pb, Ni, Cu, Co, Bi and Pd) come as suitable starting compounds, especially their halides, nitrates, Formates, oxalates, acetates, carbonates and / or hydroxides into consideration. Suitable starting compounds are often also their oxo compounds such as B. tungstates or the acids derived from these. Become frequent ammonium salts are also used as starting compounds.

Further polyanions of the Anderson type also come as starting compounds considered as z. B. in Polyhedron Vol. 6, No. 2, pp. 213-218, 1987 are described. Another suitable literature source for polyanions of the Anderson type forms Kinetics and Catalysis, Vol. 40, No. 3, 1999, pp 401 to 404.

Other suitable polyanions as starting compounds are e.g. B. such of the Dawson or Keggin type. Such starting compounds are preferred used, which increased at Temperatures either in the presence or in the absence of oxygen, optionally with the release of gaseous compounds, in their Convert oxides.

In the i / k-phase mixed-crystal multimetal oxides M obtainable as described (pure i-phase multimetal oxides M are obtained at random by the procedure described above), the proportion of i-phase can now be increased or isolated by Wash out phase with suitable liquids to the desired extent. It is preferred to calcine again after washing, as is the case EP-A 1254709 describes. The calcination conditions are generally the same as those recommended for the production of the multimetal oxide M to be washed. However, the pre-decomposition can be omitted.

Such washing liquids include, for example, organic acids and aqueous solutions of organic acids (e.g. oxalic acid, formic acid, acetic acid, citric acid and tartaric acid), inorganic acids (e.g. nitric acid), aqueous solutions of inorganic acids (e.g. aqueous telluric acid or aqueous nitric acid), alcohols and aqueous hydrogen peroxide solutions consideration. Furthermore, the JP-A 7-232071 a process for the preparation of multimetal oxides M rich in i-phase. The washing process of EP-A 1254707 as well as the EP-A 1254706 ,

An increased proportion of i-phase (and, in favorable cases, essentially pure i-phase) generally arises in the production of multimetal oxides M if they are produced by the hydrothermal route, as is the case, for example, with DE-A 10029338 , the DE-A 10254278 and describe JP-A 2000-143244. In this case too, it can be washed and washed EP-A 1254709 be recalcined below.

Active multimetal oxides M of stoichiometry A, B with d or e> 0, which can advantageously be used according to the invention, can also be produced by first preparing a multimetal oxide M 'that differs from a multimetal oxide M only in that d = 0.

Such a, preferably finely divided, multimetal oxide M 'can then be impregnated with solutions (for example aqueous) of elements X ¹ , X ² (for example by spraying), subsequently dried (preferably at temperatures 100 100 ° C.) and then, as for the multimetal oxide M 'have already been described, calcined (preferably in an inert gas stream) (pre-decomposition in air is preferably avoided here). The use of aqueous nitrate and / or halide solutions of elements X ¹ , X ² and / or the use of aqueous solutions in which the elements X ¹ , X ^{2 are} complexed with organic compounds (for example acetates or acetylacetonates) is for this manufacturing variant particularly advantageous.

The available as described to be used according to the invention active multimetal oxides M, especially those of stoichiometry A, B, can in the method according to the invention as such [e.g. as powder or after tabletting the powder (often under Addition of 0.5 to 2% by weight of finely divided graphite) and the following Split into chippings] or formed into shaped bodies as catalysts for the inventive method be used. The individual catalyst bed can be used Fixed bed, a walking bed (a fluid bed) or a fluidized bed his.

The shaping into shaped bodies can take place, for example, by application to a carrier body, as is shown in FIG DE-A 10118814 , or PCT / EP / 02/04073, or DE-A 10051419 is described. It can also be in correspondence to DE-A 4442346 be followed.

The for the in the method according to the invention active multimetal oxides M to be used are carrier bodies preferably chemically inert. That is, they intervene in the process of heterogeneous according to the invention catalyzed gas phase partial oxidation by the to be used according to the invention Multimetal oxides M, in particular those of stoichiometries A, B, catalyzed will, essentially not.

As Material for the carrier bodies come according to the invention in particular Aluminum oxide, silicon dioxide, silicates such as clay, kaolin, steatite (preferably with a low water-soluble alkali content and preferably from Ceramtec in DE, e.g. Steatite C220), 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 rough, because an increased surface roughness usually an increased Adhesion of the applied active material shell conditionally.

The surface roughness R _{z of} the support 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).

Further can the carrier material porous or nonporous his. Conveniently, the carrier material is non-porous (total volume of the pores based on the volume of the carrier body ≤ 1% by volume).

The Thickness of the coated catalysts according to the invention active oxide mass shell is usually 10 to 1000 microns. she can but also 50 to 700 μm, 100 to 600 μm or 150 to 400 μm be. Possible Shell thicknesses are also 10 to 500 μm, 100 to 500 μm or 150 up to 300 μm.

in principle come for the inventive method any geometries of the carrier body in Consideration. Your longest dimension is usually 1 to 10 mm. Preferably, however, balls or cylinders, especially hollow cylinder, used as a carrier body. Favorable diameter for carrier balls 1.5 to 5 mm. If cylinders are used as carrier bodies, their Length preferred 2 to 10 mm and their outer diameter preferably 4 to 10 mm. In the case of rings, the wall thickness is also usually more at 1 to 4 mm. Suitable according to the invention annular Carrier bodies can also a length from 3 to 6 mm, an outer diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm. Is possible but also a carrier ring geometry of 7 mm × 3 mm × 4 mm or 5 mm × 3 mm × 2 mm (Outer diameter × length × inner diameter).

Shell catalysts to be used according to the invention can be produced in a very simple manner, for example by forming multimetal oxides M to be used according to the invention, in particular those of the general stoichiometry A, B, converting them into a finely divided form and finally using a liquid binder on the surface of the Carrier body applies. The surface of the Trä body moistened in the simplest way with the liquid binder and attached to the moistened surface by contacting finely divided active oxide mass, for example those of the general stoichiometry A, B, a layer of the active mass. Finally, the coated carrier body is dried. Of course, the process can be repeated periodically to achieve an increased layer thickness. In this case, the coated base body becomes the new “support body” etc. After coating, it can be calcined again under the conditions already mentioned (preferably again under inert gas).

The fineness of the catalytically active multimetal oxide to be applied to the surface of the carrier body, for example that of the general stoichiometry A, B, is of course adapted to the desired shell thickness. For the shell thickness range from 100 to 500 μm, z. B. those active mass powders, of which at least 50% of the total number of powder particles pass through a sieve with a mesh size of 1 to 20 μm and whose numerical proportion of particles with a longest dimension above 50 mm 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 grain size distribution is often as follows:

Here are:
D = diameter of the grain,
x = the percentage of grains whose diameter is ≥ D; and
y = the percentage of grains whose diameter is <D.

For carrying out the coating process described on an industrial scale, it is recommended, for. B. the application of the in DE-A 2909671 , as well as that in the DE-A 10051419 disclosed process principle. That is, the carrier bodies to be coated are rotated in a preferably inclined (the angle of inclination is usually ≥ 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) 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 supplied active mass powder, which is caused by the rolling movement on the outer surface of the z. B. compacted cylindrical or spherical support body into a coherent shell.

at Passes through demand the base body so coated in Course of the subsequent rotation the spray nozzles, in turn while being humidified in order to keep moving take up another layer of finely divided oxidic active material to be able to etc. (intermediate drying is usually not necessary). Finely divided oxidic active material and liquid binder are used usually fed 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 be layered surface of the carrier body is made in a controlled manner. In short, this means that the carrier surface is expediently moistened in such a way that, although it has adsorbed liquid binder, 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 agglomerates instead of being drawn onto the surface. Detailed information can be found in the DE-A 2909671 and in the DE-A 10051419 ,

The aforementioned final Removal of the liquid used Binder can in a controlled manner, for. B. by evaporation and / or sublimation. In the simplest case, this can be done hotter by exposure Gases of the appropriate temperature (often 50 to 300, often 150 ° C) occur. By Exposure hotter However, gases can only be pre-dried. The final drying can then, for example, in a drying oven of any kind (e.g. B. belt dryer) or in the reactor. The acting temperature should not be above that for the production of the oxidic active material applied calcination temperature. Of course you can drying also exclusively performed in a drying oven become.

As Binder for the coating process can independently of the type and geometry of the support body are used: 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, glutaric or maleic acid, Amino alcohols such as ethanolamine or diethanolamine as well as one or polyvalent organic amides such as formamide. Cheap binders are also Solutions, consisting of 20 to 90 wt .-% water and 10 to 80 wt .-% one dissolved in water organic compound, its boiling point or sublimation temperature at normal pressure (1 atm)> 100 ° C, preferably> 150 ° C. With The organic compound from the above listing is advantageous potential organic binder selected. Preferably is the organic portion of the aforementioned aqueous binder solutions 10 up to 50 and particularly preferably 20 to 30% by weight. As organic Components also come in monosaccharides and oligosaccharides such as glucose, fructose, sucrose or lactose as well as polyethylene oxides and polyacrylates.

Of It is important that the production is more suitable according to the invention Shell catalysts not only by applying the finished, finely ground active oxide masses M, e.g. general stoichiometry A, B, on the moistened surface of the carrier body can.

Much more can also be a finely divided instead of the active multimetal oxides M. precursor material the same on the moistened carrier surface (under Application of the same coating method and binder) applied and the calcination is carried out after the coated carrier body has dried (es can also carrier body with impregnated with a precursor solution, below dried and then calcined become). Finally the k phase different from the i phase can be washed out. following can be calcined again in the manner described.

As such a finely divided precursor mass comes z. B. the mass that can be obtained, that one can get from the sources of the elementary constituents of the desired to be used according to the invention active multimetal oxide M, e.g. that of general stoichiometry A, B, first one if possible intimate, preferably finely divided, dry mixture (e.g. by spray drying an aqueous suspension or solution the sources) and this finely divided dry mixture (if necessary after tableting with the addition of 0.5 to 2% by weight of fine particles Graphite) at a temperature of 150 to 350 ° C, preferably 250 to 350 ° C under oxidizing (Oxygen-containing) atmosphere (e.g. under air) thermally treated (a few hours) and finally subject to grinding if necessary.

To the coating of the carrier body with the precursor mass will then come, preferably under an inert gas atmosphere (all other atmospheres also possible) at temperatures from 360 to 700 ° C or 400 up to 650 ° C or 450 to 600 ° C calcined.

Needless to say, can the shaping of active multimetal oxides which can be used according to the invention M, e.g. those of general stoichiometry A, B, also by Extrusion and / or tableting of both fine-particle multimetal oxide M, as well as of finely divided precursor mass of an active multimetal oxide M (if necessary, washing out of the i phase different phases in conclusion take place, possibly including recalcination).

Balls, solid cylinders and hollow cylinders (rings) come into consideration as geometries. The longest The dimensions of the aforementioned geometries are 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 thickness is also usually 1 to 4 mm. Annular unsupported catalysts 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. However, a fully catalytic converter ring geometry of 7 mm × 3 mm × 4 mm or 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter) is also possible.

Of course, for the method according to the invention for the geometry of the multimetal oxide M catalysts to be used, in particular those of the general stoichiometry A, B, all of those DE-A 10101695 into consideration.

The definition of the intensity of a diffraction reflex in the X-ray diffractogram in this document, as already said, refers to that in the DE-A 19835247 , as well as in the DE-A 10051419 and DE-A 10046672 laid down definition.

That is, A ¹ denotes the vertex of a reflex 1 and B ¹ in the line of the X-ray diffractogram, when viewed along the intensity axis perpendicular to the 2⊝ axis, is the closest pronounced minimum (minima showing reflex shoulders are not taken into account) to the left of the vertex A ¹ and B. ² in a corresponding manner, the closest pronounced minimum to the right of the vertex A ¹ and C ¹ denotes the point at which a straight line drawn from the vertex A ¹ perpendicular to the 2⊝ axis intersects a straight line connecting the points B ¹ and B ² , then the Intensity of the reflex 1 is the length of the straight line section A ¹ C ¹ , which extends from the apex A ¹ to the point C ¹ . The expression minimum means a point at which the gradient gradient of a tangent applied to the curve in a base region of the reflex 1 changes from a negative value to a positive value, or a point at which the gradient gradient goes towards zero, whereby for the definition of the gradient gradient, the coordinates of the 20 axis and the intensity axis are used.

In this document, the half-width is in a corresponding manner the length of the straight line section that results between the two intersection points H ¹ and H ² if a parallel to the 2⊝ axis is drawn in the middle of the straight line section A ¹ C ¹ , where H ¹ , H ² mean the first intersection of these parallels with the line of the X-ray diffractogram as defined above on the left and right of A ¹ .

FIG. 6 also shows an exemplary implementation of the determination of half-width and intensity DE-A 10046672 ,

Needless to say, can those to be used according to the invention active multimetal oxides M, especially those of general stoichiometry A, B, also in with finely divided, e.g. colloidal, materials, such as Silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, niobium oxide, diluted Form can be used as catalytic active materials.

The Dilution mass ratio can up to 9 (thinner): 1 (active mass). That is, possible Dilution mass ratio e.g. 6 (thinner): 1 (active composition) and 3 (thinner): 1 (active mass). The diluents can be incorporated before and / or after the calcination, usually even before drying. It is usually done before shaping. The induction takes place before drying or before calcination, the thinner must do so chosen be that in the fluid medium or in the calcination essentially preserved. This is e.g. in the case of correspondingly high Temperatures burned dilution oxides usually given.

A Differentiation in rather for a catalyst bed I or rather for a fixed catalyst bed II Suitable catalysts is not only about the stoichiometry of their active mass forming multimetal oxide M possible. Rather, such a differentiation can be made with the same stoichiometry e.g. also about the manufacturing process can be effected.

Emotional the maximum calcination temperature used e.g. in the area from 470 to 570 ° C, the result is a catalyst that is more suitable for a catalyst bed I. is. The maximum applied calcination temperature is moving however, in the range from> 570 ° C to 670 ° C results a catalyst that is more for a Catalyst bed II is suitable.

Washing the multimetal oxide M as described using suitable washing liquids (for example organic acids, inorganic acids, hydrogen peroxide solutions, etc.) can also be used a shift in the multimetal oxide M from "more suitable for a catalyst bed II" to "more suitable for a catalyst bed I".

In addition can the working pressure or the GHSV in the two catalyst beds I, II selected differently become. Preferred according to the invention is placed in the catalyst beds II (e.g. opposite the catalyst beds I) increased Working pressure selected.

In general, therefore, catalysts are suitable for the process according to the invention whose multimetal oxide M has the following general stoichiometry C Mo ₁ V _a M ¹ _b M ² _c M ³ _d O _m (C) is enough with
M ¹ = at least one of the elements from the group comprising Te and Sb;
M ² = at least one of the elements from the group comprising Nb, Ti, W, Ta and Ce;
M ³ = at least one of the elements from the group comprising Pb, Ni, Co, Bi, Pd, Ca, Mg, Fe, Mn, Ag, Pt, Cu, Au, Ga, Zn, Sn, In, Re, Ir, Sm , Sc, Y, Pr, Nd and Tb;
a = 0.01 to 1,
b => 0 to 1,
c => 0 to 1,
d = ≥ 0 to 0.5 (preferably> 0 to 0.5) and
m = a number determined by the valency and frequency of the elements other than oxygen in (C).

Regarding the stoichiometric Coefficients a, b, c and d of the multimetal oxides C apply to the Multimetal oxide A said. The same applies to the X-ray diffractogram of the multimetal oxides C.

Either the catalyst bed I as well as the catalyst bed II can at method according to the invention Fluid bed, fluid bed or be a fixed bed. You can the catalyst bed I and the catalyst bed II both in one reactor as well as in different series Reactors. That is, the reactor unit of the process according to the invention can only consist of one reactor or of several, e.g. cascaded Reactors exist. You can the various bed types mentioned above can also be used in combination become.

in the The simplest case is both the catalyst bed I and the catalyst bed II each have a fixed bed all in a single reactor, preferably in a tube bundle reactor, are located.

Are located the catalyst beds in different reactors can do that Reaction gas mixture at the transition from one to the other reactor, optionally by inert gas and / or Oxygen can be supplemented.

In particular if the catalyst beds are in a single reactor, the reaction gas mixture remains at the transition from the catalyst bed I usually get into the catalyst bed II.

Of course, in the process according to the invention, it is possible to separate from the target product contained in the product gas mixture leaving the catalyst feed and to recycle remaining residual product gas mixture as circulating gas and to recycle it as part of the reaction gas starting mixture, as is the case, for example, in DE-A 10316465 as well as in the EP-A 1193240 is recommended.

Farther can in the method according to the invention the catalyst beds I, II on substantially uniform or are kept at different temperatures (below temperature the temperature of a catalyst bed is in this document the catalyst bed when exercising of the method according to the invention however in the fictitious absence of a chemical reaction (i.e., without the influence of the heat of reaction) Roger that).

The temperature of the catalyst bed I is preferably set to the value at which, in the event that the total catalyst feed of the same reactor unit would only consist of type I catalyst bed, the selectivity S ^{I of} the (meth) acrylic acid formation under otherwise identical conditions of the gas phase partial oxidation, their maximum value S ^I _max reached.

In the process according to the invention, the temperature of the catalyst bed II is preferably set to the value at which, in the event that the total catalyst feed of the same reactor unit would only consist of type II catalyst bed, the selectivity S ^{II of} the (meth) acrylic acid formation under otherwise identical conditions of the gas phase partial oxidation , reaches its maximum value S ^II _max .

The scope of the catalyst bed I (for example the length of the corresponding catalyst bed) is advantageously chosen according to the invention such that under the process conditions selected, the conversion of the saturated hydrocarbon precursor compound existing at the end of the catalyst bed I does not exceed 20 or 10 mol%, preferably not more than 5 mol% deviates from the sales value to which S ^I _max belongs, this sales value simultaneously forming the basis for the aforementioned percentage deviation.

If the catalyst bed I and the catalyst bed II are in different reactors, setting different bed temperatures is trivial. But even if they are in one and the same reactor, there is a different catalyst bed temperature, for example by using a multi-zone reactor like this DE-A 19910506 , the DE-A 10313213 , the DE-A 10313208 and the EP-A 1106598 described in a simple manner for the case of tube bundle reactors. A uniform temperature for the catalyst bed I and the catalyst bed II can be achieved, for example, in a simple manner in a single-zone, multi-contact tube, fixed-bed reactor, as is the case with DE-A 4431957 , the EP-A 700714 and the EP-A 700893 describe.

Essential according to the invention the active mass of the catalysts of the catalyst bed I or II each from only one or from more than one multimetal oxide M exist. Can too along one Catalyst bed I (or II) change the catalysts contained. Further can the catalysts of the catalyst bed I or II in the respective catalyst bed are also diluted with inert shaped diluent bodies. As materials for such inert shaped diluents come all those are considered, from which also the support bodies for the coated catalysts can exist. The geometry of the respective shaped dilution body preferably corresponds that of the ones to be diluted Catalysts. But it can also differ from their geometry his.

Further can the proportion within the individual catalyst beds I, II the inert shaped diluent in flow direction decrease the reaction gas mixture continuously, abruptly or stepwise or increase. Between catalyst bed I and catalyst bed II if necessary in the method according to the invention pure inert dilution tablets.

The The temperature of the catalyst beds I, II is advantageous according to the invention 200 to 550 ° C, often 230 up to 480 ° C or 300 to 440 ° C.

As Source for the needed molecular oxygen can be used e.g. Air, with Air enriched or de-oxygenated or pure oxygen can be used.

In addition to the saturated hydrocarbon precursor compound and molecular oxygen and, if appropriate, water vapor, the reaction gas starting mixture can be considered as inert diluent gases (which are generally understood to be gases which are more than 95 mol%, preferably more than, in the process according to the invention (based on a single pass) 98 mol% remain unchanged chemically) include, for example, N ₂ and CO ₂ . The reaction gas starting mixture often also contains CO, for example in the cycle gas mode.

This means that the reaction gas starting mixture with which the entire catalyst feed is to be loaded at pressures of generally 1 to 10 bar or 2 to 5 bar (in principle, negative pressure can also be used) can have the following contents, for example:
1 to 15 or 20, preferably 1 to 10 or 7% by volume of precursor compound (for example propane),
0 or 5 to 25 or 50 vol.% Water vapor and
10 to 80 vol .-% air.

However, it can also have the following contents:
2 to 10% by volume of precursor compound (eg propane),
5 to 20 vol.% Water vapor,
60 to 85 vol .-% nitrogen, and
5 to 15 vol .-% oxygen.

Otherwise, a reaction gas starting mixture can also be used according to the invention as a reaction gas starting mixture, as described in the documents EP-A 608838 , WO 0029106, the JP-A 10-36311 , the DE-A 10316465 , the EP-A 1192987 , the EP-A 1193240 and the DE-A 10338529 is described.

In the method according to the invention deactivated multimetal oxide active materials can be used as in the DE-A 10338529 described can be reactivated.

If crude propane is used as the saturated hydrocarbon in the process according to the invention, this is preferred as in FIG DE-A 10246119 , respectively.

DE-A 10118814 , or PCT / EP / 02/04073.

The commissioning of a fresh catalyst feed can be carried out as in the DE-A 10122027 described.

Based to the propane and / or contained in the reaction gas starting mixture Sales of isobutane of propane and / or isobutane in the process according to the invention, based on one pass of the reaction gas mixture through the whole Catalyst feed (= the sum of all consecutively arranged individual catalyst beds) usually 10 or 20 to 90 or 70 mol%, often 30 to 60 mol% and frequently 40 to 60 mol% or 45 to 55 mol% be.

The selectivity the target product formation ((meth) acrylic acid) is usually 40 to 98 or 95 to 90 mol%, often 50 to 80 mol%, often 60 to 80 mol% be.

The target product separation and any recycle gas can be carried out as in the DE-A 10316465 described.

The Load on the entire catalyst feed (pure inert zones not included) with propane and / or iso-butane can be 10 to 1000 Nl / l (catalyst feed) / h or 20 to 800 Nl / l / h, or 50 up to 600 Nl / l / h, or 100 to 500 Nl / l / h, or 150 to 300 Nl / l / h be.

The Load on the entire catalyst feed (pure inert zones not included) with reaction gas starting mixture 10 up to 10000 Nl / l / h, or 300 to 6000 Nl / l / h or 600 to 3000 Nl / l / h be. The average residence time in the catalyst feed can be 0.01s to 10s, or 0.1 to 10s, or 2 to 6s.

advantage of the method according to the invention is an elevated maximum yield of (meth) acrylic acid based on one time Passage of the reaction gas mixture through the catalyst feed the reactor unit.

Examples and comparative examples

A) Production of a coated catalytic converter A with a multimetal oxide active composition A which is a stoichiometry A has the following composition:

Mo ₁ V _0.28 Te _0.13 Nb _0.10 Ga _0.019 O _n .

79.65 g of ammonium metavanadate (78.55% by weight of V ₂ O ₅ , GfE Nürnberg) were dissolved at 80 ° C. in 3000 ml of water (three-necked flask with stirrer, thermometer and reflux condenser, heating). A yellowish, clear solution resulted. This solution was cooled to 60 ° C. and then, while maintaining the 60 ° C. in the order mentioned, 122.34 g telluric acid (99% by weight H ₆ TeO ₆ , Aldrich) and 400.00 g ammonium heptamolybdate (82, 52% by weight of MoO _{3 from} Starck / Goslar) were stirred into the solution. The resulting deep red solution was cooled to 30 ° C. and then, while maintaining the 30 ° C. with a solution of 33.40 g of gallium (III) nitrate hydrate (19.17% by weight Ga, from Aldrich), in 40 g of water (solution was carried out at 25 ° C) was added. A solution A was thus obtained which had 30 ° C.

In 81.94 g of ammonium nioboxalate were separated from this in a beaker at 60 ° C (20.8% by weight of Nb, from Starck / Goslar) in 500 ml of water with retention a solution B solved. solution B was at 30 ° C cooled and at this temperature combined with solution A having the same temperature, being the solution B to the solution A was given. The addition took place continuously over a period of 5 min. An orange suspension was formed.

This suspension was then spray-dried in a spray dryer from Niro (spray dryer Niro A / S Atomizer, portable minor system, centrifugal atomizer from Niro, DK) within 1.5 hours. The initial temperature was 30 ° C. The gas inlet temperature ^T was 320 ° C, the gas exit temperature ^from T was 110 ° C. The resulting spray powder was also orange.

1% by weight of finely divided graphite (sieve analysis: min. 50% by weight ≤ 24 μm, max. 10% by weight> 24 μm and ≤ 48 μm, max. 5% by weight> 48 μm) was added to the spray material , BET surface area: 6 to 13 m ² / g) mixed.

The resulting mixture became hollow cylinders (rings) of geometry 16 mm × 25 mm × 8 mm (outer diameter × height × inner diameter) so compacted (pressed) that the resulting lateral compressive strength the rings were approximately 10 N.

Two portions of 100 g of the rings were each in a rotary kiln according to Figure 1 DE-A 10122027 under an air flow of 100 Nl / h within 27.5 min. first heated linearly from 25 ° C to 275 ° C and then maintain this temperature and the air flow for 1 h. Immediately afterwards, the air flow was replaced by a nitrogen flow of 100 Nl / h and heated linearly from 275 ° C to 600 ° C within 32.5 min. This temperature and the nitrogen flow were then maintained for 2 hours. The entire rotary kiln was then cooled to 25 ° C. while maintaining the nitrogen flow.

Black rings of the composition Mo _1.0 V _0.30 Te _0.21 Nb _0.08 Ga _0.04 O _n (weighing stoichiometry: Mo _1.0 V _0.30 Te _0.23 Nb _0.08 Ga _{0, 04} O _n ) received.

The Rings were then in a Retsch mill (Centrifugal, Type ZM 100, Retsch, DE) ground (grain size ≤ 0.12 mm).

100 g of this powder were stirred in 1000 ml of a 10% strength by weight aqueous HNO ₃ solution at 70 ° C. under reflux for 7 h, the solid was filtered off from the resulting slurry and washed with water until free of nitrates. The filter cake was dried in air at 110 ° C. in a muffle furnace overnight.

The resulting active composition A had the composition Mo ₁ V _0.28 Te _0.13 Nb _0.1 Ga _0.019 O _n .

The associated Röntgendiffraktrogramm shows pure i-phase.

38 g of the active mass powder obtained were based on 150 g of spherical support bodies with a diameter of 2.2 to 3.2 mm (R _z = 45 mm, support material = steatite from Ceramtec, DE, total pore volume of the support ≤ 1% by volume) applied to the total carrier volume). For this purpose, the carrier was placed in a coating drum with 2 l internal volume (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.

To At the end of the coating, the coated carrier body was under Air while 16 h at 150 ° C dried in a muffle furnace. The result was a coated catalyst A with 20 wt .-% active mass fraction.

B) Manufacture of a coated catalytic converter B with a multimetal oxide active composition B, which has a stoichiometry B has the following composition:

Mo ₁ V _0.29 Te _0.14 Nb _0.13 Ni _0.007 O _x .

87.61 g of ammonium metavanadate (78.55% by weight of V ₂ O ₅ , from GfE Nuremberg, DE) were dissolved at 80 ° C. in 3040 ml of water (three-necked flask with stirring, thermometer, reflux condenser and heating) with stirring. A clear, yellowish solution resulted. This solution was cooled to 60 ° C. and then, while maintaining the 60 ° C. in the order mentioned, 117.03 g of telluric acid (99% by weight H ₆ TeO ₆ , from Aldrich) and 400.00 g of ammonium heptamolybdate (82, 52% by weight of MoO _{3 from} Starck / Goslar) were stirred into the solution. The resulting deep red solution was cooled to 30 ° C. and then, while maintaining the 30 ° C., with 25.60 g of an aqueous solution of 5.60 g of nickel (II) nitrate hexahydrate (98% by weight, from Fluka) in 20 g of water (solution was carried out at 25 ° C.). A solution A was thus obtained which had 30 ° C.

In 112.67 g of ammonium nioboxolate were separated from this in a beaker at 60 ° C (20.8% by weight of Nb, from Starck / Goslar) in 500 ml of water with retention a solution B solved. solution B was at 30 ° C chilled and at this temperature with the same temperature solution A united, being the solution B to the solution A was given. The addition took place continuously over a period of 5 minutes. An orange suspension was formed.

This suspension was then spray-dried in a spray dryer from Niro (spray dryer Niro A / S Atomizer, portable minor system, centrifugal atomizer from Niro, DK) within 1.5 hours. The initial temperature was 30 ° C. The gas inlet temperature ^T was 320 ° C, the gas exit temperature ^from T was 110 ° C. The resulting spray powder was also orange.

1% by weight of finely divided graphite (sieve analysis: min. 50% by weight ≤ 24 μm, max. 10% by weight> 24 μm and ≤ 48 μm, max. 5% by weight> 48 μm) was added to the spray material , BET surface area: 6 to 13 m ² / g) mixed.

The resulting mixture became hollow cylinders (rings) of geometry 16mm x 2.5 mm × 8 mm (outer diameter × height × inner diameter) so compacted (pressed) that the resulting lateral compressive strength the rings were approximately 10 N.

Two portions of 100 g of the rings were each in a rotary kiln according to Figure 1 DE-A 10122027 under an air flow of 50 Nl / h within 27.5 min. first heated linearly from 25 ° C to 275 ° C and then maintain this temperature and the air flow for 1 h. Immediately afterwards, the air flow was replaced by a nitrogen flow of 50 Nl / h and within 32.5 min. heated linearly from 275 ° C to 600 ° C. This temperature and nitrogen flow were then maintained for 2 hours. Finally, the entire rotary kiln was cooled to 25 ° C. while maintaining the nitrogen flow.

Black rings of the composition Mo _1.0 V _0.33 Te _0.19 Nb _0.11 Ni _0.01 O _x (weighing stoichiometry: Mo _1.0 V _0.33 Te _0.22 Nb _0.11 Ni _{0, 01} O _x ) received.

The Rings were then in a Retsch mill (Centrifugal, Type ZM 100, Retsch, DE) ground (grain size ≤ 0.12 mm).

100 g of this powder were stirred in 1000 ml of a 10% strength by weight aqueous NHO ₃ solution for 7 hours at 70 ° C. under reflux, the solid was filtered off from the resulting slurry and washed with water until free of nitrates. The filter cake was dried in air at 110 ° C. in a muffle furnace overnight. The resulting active composition B had the composition Mo _1.0 V _0.29 Te _0.14 Nb _0.13 Ni _0.007 O _x .

The associated X-ray diffraction showed pure i-phase.

38 g of the active mass powder obtained were based on 150 g of spherical support bodies with a diameter of 2.2 to 3.2 mm (R _z = 45 μm, support material = steatite from Ceramtec, DE, total pore volume of the support ≤ 1% by volume) applied to the total carrier volume). To do this became the carrier placed in a coating drum with 2 l internal volume (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.

To At the end of the coating, the coated carrier body was under Air while 16 h at 150 ° C dried in a muffle furnace. The result was a coated catalyst B with 20% by weight of active mass.

C) Manufacturing process of acrylic acid by heterogeneously catalyzed gas phase partial oxidation of propane

1. Comparative examples

35.0 g of the respective shell catalyst A, B are each in one Single tube reactor installed (tube length: 140 cm, inner diameter: 8.5 mm, outer diameter: 60 mm, V2A steel, catalyst bed length: 53.0 cm, in addition to warm up the reaction gas starting mixture from a 30 cm long pre-fill Steatite balls from Ceramtec (C 220, 2.2 to 3.2 mm diameter), Furthermore, the reaction tube with the same steatite balls the catalyst zone finally ) Filled, which is heated by electric heating mats. The installation of each Shell catalyst takes place at a mat temperature of 350 ° C in air.

The respective reaction tube is then run in while maintaining the mat temperature of 350 ° C. for 24 h with a reaction gas starting mixture (feed gas mixture) which has the following composition:
3.3 vol .-% propane,
10 vol.% O ₂ ,
40 vol% N ₂ and
46.7 vol.% H ₂ O.

The residence time (based on the bulk catalyst volume) is chosen to be 2.4 s, the reaction tube inlet pressure is 2 bar absolute, the GHSV is 1500 h ⁻¹ (based on the feed gas mixture).

Then the (propane) conversion U-selectivity S (the acrylic acid formation) dependence determined by maintaining the other boundary conditions Heating mat temperature is increased accordingly (up to 410 ° C).

The The following table shows the results depending on the shell catalyst used. Also shows the yield of acrylic acid (Molar amount of acrylic acid formed in 1 h).

Table 1

2. Examples

The Comparative examples are repeated as described. The catalyst bed length (feed) is structured as follows:

Example 1: in the direction of flow of the reaction gas mixture initially to 10% of the bulk length of the coated catalyst A (bed I), then to 90% of the packed bed catalyst B (bed II).

Example 2: in the direction of flow of the reaction gas mixture initially on 20% of the bulk length shell catalyst A (bed I), then to 80% of the packed bed catalyst B (bed II).

The Table 2 below shows the results.

Table 2

If the reaction tube inlet pressure is increased to 3 bar absolute, the results are as follows: Table 3

Claims (21)

A process for the preparation of (meth) acrylic acid by heterogeneously catalyzed gas phase partial oxidation of at least one saturated hydrocarbon precursor compound at elevated temperature, in which a starting gas mixture containing the at least one saturated hydrocarbon precursor compound, molecular oxygen and at least one inert gas is introduced with an inlet pressure P through a catalyst feed located in a reactor unit leads, the catalysts of which are such that their active composition is at least one multimetal oxide M which comprises the elements Mo and V, at least one of the elements Te, Sb and Bi and at least one of the elements from the group comprising Nb, Ta, W, Ce and Contains Ti and whose X-ray diffractogram is an X-ray diffraction program that has diffraction reflections h, i and k, the apexes of the diffraction reflections (2⊝) 22.2 ± 0.5 ° (h), 27.3 ± 0.5 ° (i) and 28.2 ± 0.5 ° (k), the diffraction reflex h is the most intense within the X-ray diffractogram and has a half-value width of at most 0.5 ° and the half-value width of the diffraction reflex i and the diffraction reflex k is each ≤ 1 °, characterized in that the catalyst feed in its entirety consists of two in the flow direction of the reaction gas there are mixed spatially successive catalyst beds I, II containing different catalysts, the catalyst bed I being such that if the total catalyst feed of the same reactor unit would only consist of catalyst bed of type I, the selectivity S ^{I of} the (meth) acrylic acid formation would otherwise be identical Conditions of the gas phase partial oxidation, depending on the conversion of the saturated hydrocarbon precursor compound increased by increasing the reaction temperature, based on a single passage of the reaction gas mixture through the reactor unit, passes through a maximum value S ^I _max , and the catalyst bed II is such that if the total catalyst feed of the same reactor unit is only from Type II catalyst bed would exist, the selectivity S ^{II of} the (meth) acrylic acid formation under otherwise identical conditions of the gas phase partial oxidation depending on by increasing the rea tion temperature increased conversion of the saturated hydrocarbon precursor compound, based on a single passage of the reaction gas mixture through the reactor unit, passes through a maximum value S ^II _max , with the proviso that the value S ^I _{max is} at a lower conversion of the saturated hydrocarbon precursor compound than the value S ^II _max and with increasing conversion of the saturated hydrocarbon precursor compound S ^I <S ^II applies, whereas S ^I _max > S ^II _max . A method according to claim 1, characterized in that the active mass of the catalysts of the catalyst bed I at least one multimetal oxide M of stoichiometry A, Mo ₁ V _a Te _b Nb _c X ¹ _d O _n (A), with X ¹ = Ag, Ga, Pd and / or Sm, a = 0.01 to 1, b => 0 to 1, c => 0 to 1, d => 0 to 0.5 and n = a number, which is determined by the valency and frequency of the elements in A other than oxygen. A method according to claim 2, characterized in that the stoichiometric Coefficient a of stoichiometry A is 0.05 to 0.6. A method according to claim 2 or 3, characterized in that the stoichiometric Coefficient b of stoichiometry A is 0.01 to 1. Method according to one of claims 2 to 4, characterized in that that the stoichiometric Coefficient c of the stoichiometry A is 0.01 to 1. Method according to one of claims 2 to 5, characterized in that that the stoichiometric Coefficient d of the stoichiometry A is 0.00005 to 0.5. Method according to one of claims 2 to 6, characterized in that that the stoichiometric Coefficient of stoichiometry A are in the following grid: a = 0.05 to 0.6; b = 0.01 to 1; c = 0.01 to 1; and d = 0.00005 to 0.5. Method according to one of claims 2 to 7, characterized in that that in stoichiometry A the element Te through the element Sb or through the element Bi is replaced. Method according to one of claims 2 to 7, characterized in that that in stoichiometry A the element Te by at least two of the elements Sb, Te and Bi is replaced. Method according to one of claims 1 to 9, characterized in that the active mass of the catalysts of the catalyst bed II at least one multimetal oxide M of stoichiometry B, MO ₁ V _a Te _b Nb _c X ² _e O _x (B), with X ² = Ni, Co, Bi, Cu, Fe, Mn, Nd, Pb, Re and / or Pt, a = 0.01 to 1, b => 0 to 1, c => 0 to 1, e = ≥ 0 to 0.5 and x = a number which is determined by the valency and frequency of the elements in B other than oxygen. A method according to claim 10, characterized in that the stoichiometric Coefficient a of stoichiometry B is 0.05 to 0.6. A method according to claim 10 or 11, characterized in that the stoichiometric Coefficient b of the stoichiometry B is 0.01 to 1. Method according to claims 10 to 12, characterized in that that the stoichiometric Coefficient c of the stoichiometry B is 0.01 to 1. Method according to claims 10 to 13, characterized in that that the stoichiometric Coefficient e of the stoichiometry B is 0.00005 to 0.5. Method according to one of claims 10 to 14, characterized in that that the stoichiometric coefficient of stoichiometry B are in the following grid: a = 0.05 to 0.6; b = 0.01 to 1; c = 0.01 to 1; and d = 0.00005 to 0.5. Method according to one of claims 10 to 15, characterized in that that in stoichiometry B the element Te by the element Sb or by the element Bi is replaced. Method according to one of claims 10 to 16, characterized in that that in stoichiometry B the element Te by at least two of the elements Te, Sb and Bi is replaced. Method according to one of claims 1 to 17, characterized in that for the intensity ratio R = P i / (P i + P k ) where P _{i is} the intensity of the diffraction reflex i at 2⊝ = 27.3 ± 0.5 ° and P _k the intensity of the diffraction reflex k at 2⊝ = 28.2 ± 0.5 ° in the X-ray diffractogram of the at least one multi-metal oxide M, 0 , 55 ≤ R ≤ 0.85 applies. Method according to one of claims 1 to 18, characterized in that that the X-ray diffractogram of the at least one multi-metal oxide M with no diffraction reflex the vertex position 2⊝ = 50.0 ± 0.3 °. Method according to one of claims 1 to 19, characterized in that that the catalysts of the catalyst beds I, II shell catalysts are. Method according to one of claims 1 to 20, characterized in that that it is both the catalyst bed I and the catalyst bed II is a fixed bed.