DE10261186A1 - Heterogeneously catalyzed gas-phase partial oxidation of acrolein to acrylic acid, used to produce polymers for adhesives, involves using active multimetal oxide material containing e.g. molybdenum and vanadium - Google Patents

Abstract

A heterogeneously catalyzed gas-phase partial oxidation of acrolein to acrylic acid over a catalytically active multimetal oxide material which contains the elements molybdenum and vanadium, tellurium or antimony, and elements consisting of niobium, tantalum, tungsten or titanium, whose X-ray diffraction pattern has no reflections with the peak position 2 theta = 50 +/- 0.30 but has reflections whose peaks are at specified diffraction angles. Heterogeneously catalyzed gas-phase partial oxidation of acrolein to acrylic acid over a catalytically active multimetal oxide material which contains the elements molybdenum and vanadium, tellurium or antimony, and elements consisting of niobium, tantalum, tungsten or titanium, whose X-ray diffraction pattern has no reflections with the peak position 2 theta = 50 +/- 0.30 but has reflections h, i and k whose peaks are at the diffraction angles (2 theta) 22.2 +/- 0.5 degrees (h), 27.3 +/- 0.50 (i) and 28.2 +/- 0.50 (k). The reflection (h ) is the one with the strongest intensity within the X-ray diffraction pattern and having a full width at half height of not more than 0.50; the intensity (Pi) of the reflection (i) and the intensity (Pk) of the reflection (k) fulfill the relationship that R is 0.65-0.85, where R is the intensity ratio defined by the formula R = Pi/(Pi + Pk); and the full width at half height of the reflection (i) and of the reflection (k) is in each case at most 10. The catalytically active multimetal oxide material is of formula (I). Mo1VaM1bM2cM3dOn (I). M1 = element(s) from the group consisting of Te and Sb; M2 = element(s) from the group consisting of Nb, Ti, W, Ta and Ce; M3 = element(s) consisting of Pb, Ni, Co, Bi, Pd, Ag, Pt, Cu, Au, Ga, Zn, Sn, In, Re, Ir, Sm, Sc, Y, Pr, Nd or Tb; a = 0.01-1; b = 0-1; c = 0-1; d = 0-0.5; n = number that is determined by the valency and frequency of the elements other than oxygen in formula (I).

Description

The present invention relates to a process of heterogeneously catalyzed gas phase partial oxidation of acrolein to acrylic acid on a catalytically active multimetal oxide composition 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 Nb, Ta, W and Ti and whose X-ray diffractogram has no diffraction reflex with the apex position 2⊝ = 50.0 ± 0.3 ° but diffraction reflections h, i and k, whose apex at the diffraction angles (2⊝) 22.2 ± 0.5 ° (h), 27, 3 ± 0.5 ° (i) and 28.2 ± 0.5 ° (k), where
The diffraction reflex h is the most intense within the X-ray diffractogram and has a half-value width of at most 0.5 °,
- The intensity P _{i of} the diffraction reflex i and the intensity P _{k of} the diffraction reflex k satisfy the relationship 0.65 <R <0.85, in which R is given by the formula R = P i / (P i + P k ) is defined intensity ratio, and
- The half-width of the diffraction reflex i and the diffraction reflex k is each ≤ 1 °.

Acrylic acid is an important monomer that as such or in the form of an alkyl ester to produce e.g. polymers suitable as adhesives are used.

Its production by heterogeneously catalyzed gas phase partial oxidation of acrolein to acrylic acid is generally known (cf. e.g. EP-A 714700 O. EP-A 700893 , as well as the literature cited in these documents) and in particular as a second oxidation stage in the production of acrylic acid by two-stage heterogeneously catalyzed gas phase partial oxidation based on propene.

The procedure recognized in the preamble is from the DE-A 10119933 and from the DE-A 10118814 known. In these two documents, the X-ray diffractogram is assigned to a phase in accordance with the preamble of this document, which phase is referred to as i-phase both in the two documents and in this document. Similar procedures are out of the EP-A 1090684 , from the JP-A 11/343261 , from the JP-A 11/343262 and from the EP-A 938463 known.

A disadvantage of the prior art processes the technology is that the selectivity the formation of acrylic acid can fully satisfy.

The object of the present invention was therefore to provide an improved process for the production of acrylic acid starting from acrolein, which, inter alia, has an increased selectivity of acrylic acid formation. It was from the EP-A 1192987 It is known that when using multimetal oxide compositions according to the preamble of this document as active compositions for the single-stage production of acrylic acid by heterogeneously catalyzed gas phase partial oxidation of propane or of propane and propene, a process improvement can be achieved by comprising the multimetal oxide compositions with at least one element from the group Ni, Pd, Cu, Ag and Au doped.

Similarly, as a solution to the problem according to the invention, a process of heterogeneously catalyzed gas phase partial oxidation of acrolein to acrylic acid on a catalytically active multimetal oxide composition comprising the elements Mo and V, at least one of the elements Te and Sb and at least one of the elements from the group Nb, Ta , W and Ti and whose X-ray diffractogram does not have a diffraction reflex with the vertex position 2⊝ = 50.0 ± 0.3 ° but has diffraction reflections h, i and k, whose vertexes at the diffraction angles (2⊝) 22.2 ± 0.5 ° (h), 27.3 ± 0.5 ° (i) and 28.2 ± 0.5 ° (k), where
The diffraction reflex h is the most intense within the X-ray diffractogram and has a half-value width of at most 0.5 ° C,
The intensity P _{i of} the diffraction reflex i and the intensity P _{k of} the diffraction reflex k the relationship 0.65 ≤ R? 0.85, in the R this by the formula R = P i / (P i + P k ) is defined intensity ratio, and
The half-width of the diffraction reflex i and the diffraction reflex k is each ≤ 1 °, found,
which is characterized in that the catalytically active multimetal oxide mass of the general stoichiometry I Mo ₁ V _a M ¹ _b M ² _c M ³ _d O _n (I), 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, 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 and
n = a number which is determined by the valency and frequency of the elements other than oxygen in (I),
is.

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 invention, preferably 0.67 R R 0,7 0.75 and R = 0.69 to 0.75 or R = 0.71 to applies with very particular preference 0.74, or R = 0.72.

In addition to the diffraction reflections h, i and k, the X-ray diffractogram of multimetal oxide materials (I) to be used according to the invention 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).

According to the invention it is also favorable if that X-ray diffraction additionally contains a diffraction reflex, whose apex is at the diffraction angle (2⊝) = 45.2 ± 0.4 ° (q).

Frequently contains the X-ray diffractogram of to be used according to the invention Multimetal oxide masses (I) 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;
o: 1 to 30;
p: 1 to 30 and
q: 5 to 60.

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

The specific surface area of multimetal oxide compositions (I) to be used according to the invention is frequently 1 to 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).

According to the invention, the stoichiometric is preferred Coefficient a of those to be used according to the invention Multimetal oxide materials (2), independently from the preferred areas for the other stoichiometric Coefficients of the multimetal oxide masses (I), 0.05 to 0.6, particularly preferably 0.1 to 0.6 or 0.5.

Regardless of the preferred areas for the other stoichiometric Coefficients of those to be used according to the invention Multimetal oxide masses (I) the stoichiometric Coefficient b preferably 0.01 to 1, and particularly preferably 0.01 or 0.1 to 0.5 or 0.4.

The stoichiometric coefficient c those to be used according to the invention Multimetal oxide masses (I), independently from the preferred areas for the other stoichiometric Coefficients of the multimetal oxide masses (I) 0.01 to 1 and especially preferably 0.01 or 0.1 to 0.5 or 0.4. A very special one according to the invention preferred area for the stoichiometric Coefficient c, the, independent from the preferred areas for the other stoichiometric Coefficients of those to be used according to the invention Multimetal oxide materials (I), with all other preferred areas in This font can be combined, the range is 0.05 to 0.2.

According to the invention, the stoichiometric is preferred Coefficient d of those to be used according to the invention Multimetal oxide materials (I), independent from the preferred areas for the other stoichiometric Coefficients of the multimetal oxide masses (I), 0.00005 and 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.

Multimetal oxide materials (I) whose stoichio metric coefficients a, b, c and d 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 = 0.0005 to 0.5 (or 0.001 to 0.3).

Multimetal oxide materials (I) to be used according to the invention, whose stoichiometric coefficients a, b, c and d are simultaneously in the following grid, are particularly favorable:
a = 0.1 to 0.6;
b = 0.1 to 0.5;
c = 0.1 to 0.5; and
d = 0.001 to 0.5, or 0.002 to 0.3, or 0.005 to 0.1.
M ¹ is preferably Te.

All of the above applies above all when M ^{2 is} at least 50 mol% of its total amount of Nb and very particularly preferably when M ^{2 is} at least 75 mol% of its total amount or 100 mol% of its total amount of Nb.

But above all, regardless of the meaning of M ² , it also applies if M ³ comprises at least one element from the group comprising Ni, Co, Bi, Pd, Ag, Au, Pb and Ga or at least one element from the group Ni, Co, Pd and Bi is.

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 Ni, Co, Bi, Pd, Ag, Au, Pb and Ga.

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 M ^{3 has} at least one element from the group comprising Ni, Co, Pd and Bi is.

All statements with regard to the stoichiometric coefficients are particularly preferred if M ¹ = Te, M ² = Nb and M ³ = at least one element from the group comprising Ni, Co and Pd.

The principle of a targeted process for producing multimetal oxide compositions (I) to be used according to the invention is disclosed, for example, in WO 0206199 and the literature citations cited in this document. Then, in a manner known per se, a multimetal oxide mass is first produced which has the stoichiometry (I), but which is generally a mixed crystal system composed of i-phase and other phases (eg k-phase). The k phase is according to the scriptures DE-A 10119933 and DE-A 10118814 , characterized, for example, by the fact that their X-ray diffractogram at the 2⊝ vertex positions is 22.1 ± 0.3 °, 28.2 ± 0.3 °, 36.2 ± 0.3 °, 45.2 ± 0.3 ° and 50.0 ± 0.3 ° with the highest intensity diffraction reflections. The proportion of i-phase can now be isolated from this mixture by washing the other phases, for example the k-phase, with suitable liquids. Such liquids include, for example, organic acids and aqueous solutions of organic acids (for example oxalic acid, formic acid, acetic acid, citric acid and tartaric acid), inorganic acids (for example nitric acid), aqueous solutions for inorganic acids (for example 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 i-phase multimetal oxide materials. The washing process is also suitable EP-A 1254707 ,

Mixed crystal systems from the i- and k-phase are generally obtained using the manufacturing processes described in the prior art (cf., for example DE-A 19835247 . EP-A 529853 . EP-A 603836 . EP-A 608838 . EP-A 895809 . DE-A 19835247 . 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 ). According to these processes, an intimate, preferably finely divided, dry mixture is generated from suitable sources of the elementary constituents of the multimetal oxide composition 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.

The thermal treatment takes place under gaseous The atmosphere, it can both stand and flow. It preferably flows. In total, the thermal treatment can last up to 24 h or more. take advantage of.

The thermal treatment is preferably carried out first under an oxidizing (oxygen-containing) atmosphere (for example under air) at a temperature of 150 to 400 ° C. or 250 to 350 ° C. (= pre-decomposition step). Thereafter, the thermal treatment is expediently continued under inert gas at temperatures of 350 to 700 ° C or 400 to 650 ° C or 450 to 600 ° C. It goes without saying that the thermal treatment can also be carried out in such a way that the catalyst precursor mass is initially (counter to if necessary after pulverization) tabletted (optionally with the addition of 0.5 to 2% by weight of finely divided graphite), then thermally treated and subsequently split again.

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

If it is done in a dry form, be the starting compounds expediently 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 is preferably carried out 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 generally 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 also be used as such starting compounds or used exclusively. Ie, in particular, all come in the scriptures EP-A 1254707 . EP-A 1254709 and EP-A 1192987 starting compounds mentioned:
Suitable sources for the element Mo are, for example, molybdenum oxides such as molybdenum trioxide, molybdates such as ammonium heptamolybdate tetrahydrate and molybdenum halides such as 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 ), antimonic acids such as HSb (OH) ₆ , but also antimony oxide salts such as antimony oxide sulfate (SbO) ₂ SO ₄ and antimony acetate.

Suitable sources of niobium are, for example, 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 composed of niobium and organic carboxylic acids and / or dicarboxylic acids such as oxalates and alcoholates. Of course, those in the EP-A 895 809 used solutions containing Nb.

Regarding all 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.

Furthermore come as starting compounds also consider Anderson type polyanions, e.g. in polyhedron Vol. 6, No. 2, pp. 213-218, 1987. Another suitable literature source for Anderson type polyanions form Kinetics and Catalysis, Vol. 40, No. 3, 1999, pp 401 to 404.

Other suitable as starting compounds Polyanions are e.g. those of the Dawson or Keggin type. Preferably such starting compounds are used, which are at elevated temperatures either in the presence or in the absence of oxygen, if necessary releasing gaseous Compounds to convert into their oxides.

The i- / k-phase mixed crystal multimetal oxide materials obtainable as described (pure i-phase multimetal oxides are obtained at random by the procedure described above) can then be washed as described by suitable washing (in which the stoichiometry generally changes only insignificantly) Multimetal oxides (I) to be used according to the invention are transferred. 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 mass to be washed.

An increased proportion of i-phase (and, in favorable cases, essentially pure i-phase) occurs in the production of precursor multimetal oxides (which can be converted into multimetal oxides (I) according to the invention by washing as described) when they are produced by the hydrothermal route he follows, such as it DE-A 10029338 , the DE-A 10254278 and the JP-A 2000-143244 describe. In this case too EP-A 1254709 be recalcined below.

The production of to be used according to the invention However, multimetal oxide materials (I) can also be made in that one first generates a multimetal oxide mass I ', which differs from a multimetal oxide mass (I) only in that that d = 0.

Such a, preferably finely divided, multimetal oxide mass I 'can then be impregnated with solutions (for example aqueous) of elements M ³ (for example by spraying), subsequently dried (preferably at temperatures 100 100 ° C.) and then calcined as described for the precursor multimetal oxides ( 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 M ³ and / or the use of aqueous solutions in which the elements M ^{3 are} complexed with organic compounds (for example acetates or acetylacetonates) is particularly advantageous for this production variant.

The available as described to be used according to the invention Multimetal oxides (I) can 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 for the inventive method be used. The catalyst bed can be a fixed bed, a moving bed or a fluidized bed.

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 100.51419 is described. It can also be carried out in accordance with DE-A 4442346.

Those for those in the process according to the invention Multimetal oxide materials (I) to be used are carrier bodies preferably chemically inert. That is, they intervene in the process of partial inventions catalytic gas phase oxidation by those to be used according to the invention Multimetal oxide materials (I) is catalyzed, essentially not on.

According to the invention, in particular, come as the material for the carrier body Aluminum oxide, silicon dioxide, silicates such as clay, kaolin, steatite (preferably with a low water-soluble alkali content and preferably from Ceramtec in DE), pumice, aluminum silicate and Magnesium silicate, silicon carbide, zirconium dioxide and thorium dioxide into consideration.

The surface of the carrier body can be both smooth and be rough too. The surface of the carrier body is advantageously rough, since there is 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 "Rommel Tester for DIN-ISO surface measurement parameters" from Hommelwerke, DE).

Furthermore, the carrier material porous or nonporous his. Conveniently, the carrier material is non-porous (total volume of the pores related to the volume of the support 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 method according to the invention 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).

The preparation to be used according to the invention Shell catalysts can easily be e.g. done so that one to be used according to the invention Multimetal oxide compositions of the general formula (I) forms them converted into a finely divided form and finally with the help of a liquid Binder on the surface of the carrier body. This is the surface of the carrier body in easiest way with the liquid Binder moistened and brought into contact with fine particles active oxide mass of the general formula (I) a layer of the active mass on the moistened surface attached to. In conclusion the coated carrier body is dried. Of course, the process can be used to achieve an increased layer thickness repeat periodically. In this case the coated body becomes new "carrier body" etc. After the successful Coating can again under the conditions already mentioned be calcined (preferably again under inert gas, e.g. washed Multimetal oxide (I)).

The fineness of the catalytically active multimetal oxide composition of the general formula (I) to be applied to the surface of the support body is of course adapted to the desired shell thickness. For the shell thickness range from 100 to 500 μm are suitable, for example, such 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 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 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 passes the, for example, spherical or cylindrical carrier bodies under two metering devices arranged in succession 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 which is compacted by the rolling movement on the outer surface of the eg cylindrical or spherical carrier body to form a coherent shell.

If necessary, it runs through the base coat Carrier body 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 liquid binder can be removed after the coating has ended, for example 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 support surface is appropriately moistened so that it has adsorbed liquid binder, but no liquid phase as such appears visually on the support 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 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 example 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). Exposure to hot gases can also only result in 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 only be done in a dryer oven.

As binders for the coating process, regardless of the type and geometry of the carrier body 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.

It is important that the manufacture more suitable according to the invention Shell catalysts not only by applying the finished, finely ground active oxide compositions of the general formula (I) the moistened surface of the carrier body take place can.

Rather, instead of being active Oxide mass also a finely divided precursor mass of the same on the moistened Carrier surface (under Application of the same coating method and binder) applied and the calcination can be carried out after drying the coated carrier body (it can also carrier body with impregnated with a precursor solution, below dried and then be calcined). Finally can, if necessary, the phases other than the i phase are washed out. Calcination can then be carried out again in the manner described become.

As such a finely divided precursor mass comes e.g. the mass that can be obtained by that you can get from the sources of the elementary constituents of the desired to be used according to the invention active oxide mass of the general formula (I) first as intimate as possible, preferably finely divided, dry mixture generated (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) thermal treated (a few hours) and finally if necessary a grinding subjects.

After coating 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 400 to 600 ° C calcined.

Of course, the shape usable according to the invention Multimetal oxide materials (I) also by extrusion and / or tableting both of finely divided multimetal oxide mass (I) and of finely divided precursor material a multimetal oxide mass (I) (if necessary the washing out of the phases other than the i-phase is then carried out, if necessary including a recalcination).

Both come as geometries Balls, solid cylinders and hollow cylinders (rings) into consideration. The longest dimension of the aforementioned geometries usually 1 to 10 mm. In the case of cylinders, it is 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. Ring-shaped unsupported catalysts suitable according to the invention 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 full catalyst ring geometry of 7 mm × 3 mm × 4 mm or of 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter).

Of course, for the method according to the invention, all those of the geometry of the multimetal oxide active materials (I) to be used also come DE-A 10101695 into consideration.

It is essential according to the invention, as already said, that the multimetal oxide materials (I) to be used according to the invention have an X-ray diffractogram (in this document always based on Cu-K _α radiation) which has diffraction reflections h, i and k, the apex of which is at the diffraction angles ( 2⊝) 22.2 ± 0.4 ° (h), 27.3 ± 0.4 ° (i) and 28.2 ± 0.4 ° (k), where
The diffraction reflex h is the most intense within the X-ray diffractogram and has a half-value width of at most 0.5 °,
- The intensity P _{i of} the diffraction reflex i and the intensity P _{k of} the diffraction reflex k meet the designation 0.65 ≤ R ≤ 0.85, in which R is given by the formula R = P i / (P i + P k ) is defined intensity ratio, and
- The half-width of the diffraction reflex i and the diffraction reflex k is each ≤ 1 °.

At the same time, the X-ray diffractogram have no diffraction reflex with the apex position 2⊝ = 50.0 ± 0.3 °.

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, denotes 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 apex A ¹ and C ¹ denotes the point at which a straight line drawn from the apex 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, the length of the straight 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 2⊝ 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 .

An example of how the half-width and intensity are determined is also shown in FIG 6 in DE-A 10046672.

It goes without saying that those to be used according to the invention Multimetal oxide materials (I) also with fine-particle. e.g. colloidal Materials such as silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, Niobium oxide, more dilute 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.

If the training takes place before the Drying or before calcination, the thinner must be selected so that it is in the fluid Medium or in the calcination is essentially preserved. This is e.g. in the case of burned at correspondingly high temperatures Oxides usually given.

Otherwise, the process according to the invention of the heterogeneously catalyzed gas phase partial oxidation of acrolein to acrylic acid can be carried out in the manner described in EP-A 714700 or in the EP-A 700893 , as well as the literature cited in these writings. That is, normally you will get a reaction gas starting mixture containing the molecular oxygen and the acrolein in a molar ratio of O ₂ : C ₃ H ₄ O, an acrolein, molecular oxygen and at least one inert gas consisting of at least 20% of its volume of molecular nitrogen ≥ 1 contains, at elevated temperature above or through a catalyst bed (usually a fixed bed), the active composition of which is a multimetal oxide composition (I), that the acrolein conversion in a single pass ≥ 90 mol% and the associated selectivity of acrylic acid formation ≥ 90 mol%.

The method according to the invention is expedient as a second oxidation stage in the production of acrylic acid two-stage catalytic gas phase oxidation based on propene applied. It is usually used as the reaction gas starting mixture the product gas mixture of the first oxidation stage, if appropriate supplemented by a source of molecular oxygen.

Both air and air depleted in molecular nitrogen (for example 90 90% by volume of O ₂ , 10% by volume of N ₂ ) can be considered as the source of the molecular oxygen required in the process according to the invention.

The molar ratio of 02: acrolein in the reaction gas starting mixture in the method according to the invention, As already mentioned, preferably ≥ 1 be. Usually will this ratio with values ≤ 3 lie. Frequently is the molar ratio from 02: acrolein in the reaction gas starting mixture according to the invention 1 to 2 or 1 to 1.5.

The working pressure in the method according to the invention both below normal pressure (e.g. up to 0.5 bar) and are above normal pressure. Typically the working pressure at values from 1 to 5 bar, often 1 to 3 bar. Usually the reaction pressure is 100 bar do not exceed.

The acrolein content in the reaction gas starting mixture can in the inventive method e.g. at values of 3 to 15 vol.%, often at 4 to 10 vol.% or 5 to 8 vol .-% (each based on the total volume).

The process according to the invention is often used with an acrolein: oxygen: water vapor: inert gas volume ratio (N1) of 1: (1 to 3): (0 to 20): (3 to 30), preferably 1: (1 to 3) : (0.5 until 10). Execute (7 to 8).

The reaction temperature is for the process according to the invention typically 220 to 300 ° C, often 230 up to 280 ° C be.

The load on a fixed catalyst bed can in the method according to the invention ≥ 100 Nl acrolein / l cat. · h, mostly however 300 Nl acrolein / l cat. · h be.

Inert diluent gases are used in the process according to the invention prefer to use those that become closed during a single pass implement less than 5 mol%, preferably less than 2 mol%.

Inert diluent gases which are suitable according to the invention are in particular CO ₂ , CO, N ₂ , noble gases and water vapor.

Cheap is the method according to the invention in the presence of propane and / or propene. This is due to the fact that the catalysts of the invention can also catalyze their partial oxidation to acrylic acid.

Of course, the process according to the invention can also be carried out as a high-load process in more than one reaction zone, such as, for example, the DE-A 19910508 , the DE-A 19948248 and the DE-A 19927624 describe.

The process according to the invention will be carried out in the presence of propane and / or propene, among other things, if it is the third reaction stage of a three-stage production of acrylic acid from propane, such as that EP-A 938463 , the DE-A 19837518 , the DE-A 19837518 , the DE-A 19837517 , the DE-A 19837520 , the DE-A 10246119 and the DE-A 10245585 and describe the literature cited in these writings.

In addition, in the process according to the invention it is advantageous to compare the composition of the reaction gas starting mixture analogously to the teaching of DE-A 10122027 to change at least once during the implementation of the process so that the proportion of the diluent gas water vapor contained in the reaction gas starting mixture, based on the molar amount of acrolein contained in the reaction gas starting mixture, is less after the change.

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

This can be done as in the DE-A 10122027 be performed. The residual gas remaining in the course of this separation can be further used as circulating gas (recycling, as a rule, into a propene and / or propane oxidation) or fed to its combustion and used, for example, for the production of water vapor and / or for energy generation.

In the method according to the invention Deactivated multimetal oxidation masses (I) can by passing molecular oxygen and / or gases containing water vapor under the temperature and pressure conditions the reaction causing the deactivation are reactivated. Such a gas can e.g. Air, a mixture of air and water vapor, but also lean air (air depleted in molecular oxygen) or a mixture of water vapor and lean air. Also one can Mixture of nitrogen and water vapor can be used. The oxygen content of the regeneration gas can therefore be ≥ 0 amount to 20 mol%. Frequently it will be 2 to 10 mol%, sometimes 2 to 15 mol%.

For the rest, the conditions of the process according to the invention can also EP-A 1090684 , the JP-A 11/343262 and the JP-A 11/343261 be applied.

The multimetal oxide compositions (I) to be used according to the invention can, however, also be integrated into other multimetal oxide compositions for the process according to the invention (for example those described in the DE-A 19910508 recommended as multimetal oxide active materials for the heterogeneously catalyzed gas phase partial oxidation of acrolein to acrylic acid; For example, mix their finely divided masses, if necessary press and calcine them, or mix them as slurries (preferably aqueous), dry and calcine them. It is preferably calcined again under inert gas. The calcination temperature is normally one of those used to produce the multimetal oxide materials to be integrated into one another. The lowest calcination temperature is usually used. In favorable cases, calcination after blending can also be dispensed with.

The resulting multimetal oxide masses (hereinafter referred to as total masses) preferably contain> 50% by weight, particularly preferably ≥ 75 % By weight, and very particularly preferably ≥ 90% by weight or ≥ 95% by weight those to be used according to the invention Multimetal oxide materials (I).

The total masses at 2⊝ = 50.0 ± 0.3 ° preferably also contain no diffraction reflex peak position. If the total amount at 2⊝ = 50.0 ± 0.3 ° contains a diffraction reflex peak position, it is advantageous if the proportion by weight of the multimetal oxide compositions (I) according to the invention is ≥ 80% by weight, or ≥ 90% by weight, or 95 % By weight. Such total masses can also contain multimetal oxides of stoichiometry (I) in k-phase structure and are obtainable, for example, by the fact that in the preparation of the invention multimetal oxide materials (I) to be used are not washed out quantitatively. R for the total masses is preferably 0,6 0.65 and 0 0.90.

The geometrical shape takes place for the total masses in an appropriate manner as for the multimetal oxide materials (I) described.

The advantage of the multimetal oxide compositions (I) to be used according to the invention is based on their excellent target product selectivity. It is surprising that the M ³ promoters are effective in the pure i-phase for the process according to the invention.

According to the invention, the process of heterogeneously catalyzed gas phase partial oxidation of acrolein to acrylic acid in a tube bundle reactor is advantageously carried out in such a way that the volume-specific activity of the catalyst feed increases continuously and / or suddenly in the direction of the flow of the reaction gas mixture, as is the case, for example, in DE-A 10246119 is practiced in the exemplary embodiment using a comparable active composition.

In conclusion, it should be noted that the method according to the invention also done so can be that one a reaction gas starting mixture essentially free of molecular oxygen with increased Temperature above the multimetal oxide mass conducts, then the spent multimetal oxide mass reoxidized with a gas containing molecular oxygen (e.g. air), then again transferred to molecular oxygen essentially free reaction gas starting mixture etc. The above-mentioned procedure in a fluidized bed is preferred carried out. As a rule, it requires a further improvement in selectivity.

Examples

A) Manufacture of multimetal oxide shell catalysts

Comparative Example 1 (preparation of a multimetal oxide catalyst with the active composition Mo ₁ V _{0 0 0 33} Te ₁₉ Nb _0.11 Ni _0.01 O _X containing i and k phase) 87.61 g of ammonium metavanadate (78.55 wt .-% V ₂ O ₅ , GfE Nürnbern, 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 6.80 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.

They were in a beaker separately at 60 ° C 112.67 g of ammonium nioboxolate (20.8% by weight of Nb, from Starck / Goslar) dissolved in 500 ml of water to obtain a solution B. Solution B was cooled to 30 ° C 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 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). 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.

100 g of the spray powder was made in a rotary kiln 1 (Quartz glass ball with 1 liter internal volume; 1 = furnace housing, 2 = rotary lobe, 3 = heated room, 4 = nitrogen / air flow) 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.

There was a black powder of the composition Mo _1.0 V _{0, 33} Te _0.19 Nb _0.11 Ni _0.01 O _x (Stoichiometry: Mo _1.0 V _{0, 33} Te _0.22 Nb _0.11 Ni _{0 , 01} O _x The associated X-ray diffractogram shows the 2 (R = 0.26). BET = 8.0 m ² / g.

The active material powder was then in a Retsch mill (Centrifugal, Type ZM 100, Retsch, DE) ground (grain size ≤ 0.12 mm).

38 g of the powder present after grinding was placed on 150 g of spherical carrier bodies with a diameter of 2.2 to 3.2 mm (R ₂ = 45 μm, carrier material = steatite from Ceramtec, DE, total pore volume of the carrier ≤ 1 vol. % based on the total carrier volume). For this purpose, the carrier was placed in a coating drum with 2 1 internal volume (angle of inclination of the drum center axis against the horizontal = 30 °). The drum was rotated at 25 revolutions per minute. About one with 300 Nl / h compressed air operated atomizer nozzle were over 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 wetted 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 finishing the coating, the coated carrier body under Air while 16 h at 150 ° C dried in a muffle furnace. The result was a coated catalyst VB1 with 20% by weight of active mass.

example 1

Like Comparative Example 1. The powder resulting after grinding in the Retsch mill was, however, stirred in 1000 ml of a 10% strength by weight aqueous HNO ₃ solution for 7 hours at 70 ° C. under reflux. The remaining solid was filtered off from the resulting slurry and washed free of nitrate with water. The filter cake was then dried in air at 110 ° C. in a muffle furnace overnight.

The resulting active material had a composition Mo _1.0 V _{0, 29} Te _0.14 Nb _0.13 Ni _0.007 O _x. The associated X-ray diffractogram shows 3 (R = 0.71). BET = 20.2 m ² / g.

It became in the same way on the same carrier applied as in Comparative Example 1, so that a coated catalyst B1 with 20% by weight of active mass resulted.

Comparative Example 2

Like comparative example 1, instead 6.80 g of nickel (II) nitrate hexahydrate, however, became 6.17 g of palladium (II) nitrate Dihydrate (98%, Fluka) used.

The resulting active material had a composition Mo _1.0 V _{0, 33} Te _0.19 Nb _0.11 Pd _0.01 O _x on. The associated X-ray diffractogram shows 4 (R = 0.25). BET = 9.3 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst VB2 with 20% by weight active mass fraction resulted.

Example 2

As in Example 1, but the active composition from Comparative Example 2 was washed with aqueous nitric acid. The resulting active material had a composition Mo _1.0 V _{0, 33} Te _0.19 Nb _0.11 Pd _0.01 O _x.

The associated X-ray diffractogram shows 5 (R = 0.73). BET = 22.5 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst B2 with 20% by weight of active composition resulted.

Comparative Example 3

Like comparative example 1, the approach was however halved in quantity and instead of then 3.40 g Nickel (II) nitrate hexahydrate became 12.34 g palladium (II) nitrate Dihydrate (98%, Fluka) used.

The resulting active material had a composition Mo _1.0 V _{0, 33} Te _0.22 Nb _0.11 Pd _0.04 O _x on. The associated X-ray diffractogram shows 6 (R = 0.35). BET = 9.3 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst VB3 with 20% by weight of active composition resulted.

Example 3

As in Example 1, but the active composition from Comparative Example 3 was washed with aqueous nitric acid. The resulting active material had a composition Mo _1.0 V _{0, 29} Te _0.13 Nb _0.001 Pd _0.13 O _x. The associated X-ray diffractogram shows 7 (R = 0.74). BET = 17.4 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst B2 with 20% by weight of active composition resulted.

Comparative Example 4

Like comparative example 1, instead of 6.80 g of nickel (II) nitrate hexahydrate, however, 3.41 g of cobalt (II) nitrate Hexahydrate (98%, Riedel-de-Haen) used.

The resulting active material had a composition Mo _1.0 V _{0, 33} Te _0.19 Nb _0.11 Pd _0.005 O _x on. The associated X-ray diffractogram shows 8th (R = 0.24). BET = 8.9 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst VB4 with 20% by weight of active composition resulted.

Example 4

Like example 1, but it was Active composition from comparative example 4 washed with aqueous nitric acid.

The resulting active material had a composition Mo _1.0 V _{0, 29} Te _0.13 Nb _0.004 O _{x 0.11} Co. The associated X-ray diffractogram shows 9 (R = 0.73). BET = 24.6 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst B4 with 20% by weight of active composition resulted.

Comparative Example 5

Like Comparative Example 1, but instead of 6.80 g of nickel (II) nitrate hexahydrate, 5.65 g of copper (II) nitrate trihydrate ( 99 %, Acros Organics) used.

The resulting active material had a composition Mo _1.0 V _{0, 33} Te _0.19 Nb _0.11 Cu _0.01 O _x on. The associated X-ray diffractogram shows 10 (R = 0.27). BET = 6.7 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst VB5 with 20% by weight active mass fraction resulted.

Example 5

Like example 1, but it was Active composition from comparative example 5 washed with aqueous nitric acid.

The resulting active material had a composition Mo _1.0 V _{0, 28} Te _0.13 Nb _0.13 Cu _0.003 O _x. The associated X-ray diffractogram shows 11 (R = 0.74). BET = 23.1 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst B5 with 20% by weight of active composition resulted.

Comparative Example 6

Like comparative example 1, instead of 6.80 g of nickel (II) nitrate hexahydrate, however, 5.68 g of bismuth (III) nitrate became Pentahydrate (98.5%, from Merck) was used.

The resulting active material had a composition Mo _1.0 V _{0, 33} Te _0.19 Nb _0.11 Bi _0.004 O _x on. The associated X-ray diffractogram shows 12 (R = 0.18). BET = 9.0 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst VB6 with 20 wt .-% active mass fraction resulted.

Example 6

As in Example 1, but the active composition from Comparative Example 6 was washed with aqueous nitric acid. The resulting active material had a composition Mo _1.0 V _{0, 15} Te _0.15 Nb _0.005 O _{x 0.14} Bi. The associated X-ray diffractogram shows 13 (R = 0.70). BET = 22.0 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst B6 with 20% by weight of active composition resulted.

Comparative Example 7

Like comparative example 1, instead of 6.80 g of nickel (II) nitrate hexahydrate, however, became 3.84 g of lead (II) nitrate (Riedel-de-Haen, 99%) used.

The resulting active material had a composition Mo _1.0 V _{0, 34} Te _0.18 Nb _0.11 Pb _0.004. The associated X-ray diffractogram shows 14 (R = 0.30). BET = 2.2 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst VB7 with 20% by weight Ak active mass share resulted.

Example 7

As Example 1, but it has been washed, the active composition of Comparative Example 7 with aqueous nitric acid: The resulting active material had a composition Mo _1.0 V _{0, 28} Te _0.13 Nb _0.13 O _x Pb _0.001.

The associated X-ray diffractogram shows 15 (R = 0.67). BET = 27.1 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst B7 with 20% by weight of active composition resulted.

Comparative Example 8

Like comparative example 1, but with the difference that the 5.60 g of nickel (II) nitrate hexahydrate was not added. The resulting active material had a composition Mo _1.0 V _{0, 33} Te _0.16 Nb _0.13 O _x Pb _0.001 in. The associated X-ray diffractogram shows 16 (R = 0.26). BET = 6.7 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst VB7 with 20% by weight of active composition resulted.

Comparative Example 9

As in Example 1, but the active composition from Comparative Example 7 was washed with aqueous nitric acid. The resulting active material had a composition Mo _1.0 V _{0, 33} Te _0.16 Nb _0.13 O _x.

The associated X-ray diffractogram shows 17 (R = 0.68). BET = 26.0 m ² / g. It was applied in the same way to the same support as in Comparative Example 1, so that a coated catalyst VB8 with 20 wt .-% active mass fraction resulted.

B) testing of those produced in A) Multimetal shell catalysts

With 35.0 g each Shell catalyst from A) became a tubular reactor made of steel (Inner diameter: 8.5 mm, length: 140 cm, wall thickness: 2.5 cm) (catalyst bed length in all make approx. 53 cm). Before the catalyst bed, a pre-bed of 30 cm steatite balls (diameter: 2.2 to 3.2 mm, manufacturer: Fa. Ceramtec) and after the catalyst bed on the remaining length of the Pipe reactor a refill same steatite balls attached.

Using electrically heated heating mats was from the outside the outside temperature of the charged reaction tube over the entire length 350 ° C set.

Then the reaction tube with a reaction gas starting mixture of the molar composition
5.5% by volume of acrolein,
0.3% by volume of propene,
6.0 vol% molecular oxygen,
0.4 vol.% CO,
0.8 vol% CO ₂ ,
9.0 vol .-% water and
78.0 vol% molecular nitrogen
loaded (the entry side was on the side of the refill). The residence time (based on the catalyst bed volume) was set to 2.4 seconds. The inlet pressure was 2 bar absolute.

The reaction tube _feed was first run in at the aforementioned outside temperature of the charged reaction tube over a period of 24 h before this outside temperature was increased so that, based on a single passage through the reaction tube, conversion of acrolein (U _ACR ) of about 98 mol% in all cases % resulted.

The table below shows the outside temperature T (° C) required for this conversion, as well as the resulting selectivity of acrylic acid formation (S _ACS (mol%)) depending on the shell catalyst used. In addition, the table shows the intensity ratio R of the active composition located on the coated catalyst and the composition of this active composition.

Claims (27)

Process of heterogeneously catalyzed gas phase partial oxidation of acrolein to acrylic acid on one Catalytically active multimetal oxide mass, 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 Nb, Ta, W and Ti and whose X-ray diffractogram has no diffraction reflection with the peak position 2⊝ = 50.0 ± 0 , 3 ° but has diffraction reflexes h, i and k, whose apexes at the diffraction angles (2⊝) 22.2 ± 0.5 ° (h), 27.3 i 0.5 ° (i) and 28.2 ± 0 , 5 ° (k), where - the diffraction reflex h is the most intense within the X-ray diffractogram and has a half-value width of at most 0.5 ° C, - the intensity P _{i of} the diffraction reflex i and the intensity P _{k of} the diffraction reflex k the relationship 0.65 ≤ R ≤ 0.85, in R this by the formula R = P i / (P i + P k ) defined intensity ratio, and - the half-width of the diffraction reflex i and the diffraction reflex k is each ≤ 1 °, characterized in that the catalytically active multimetal oxide mass has a general stoichiometry (I) MO ₁ V _a M ¹ _b M ² _c M ³ _d O _n (I), 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, 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 and n = a number determined by the valency and frequency of the. elements other than oxygen is determined in (I). A method according to claim 1, characterized in that 0.67 ≤ R ≤ 0.75. A method according to claim 1, characterized in that 0.69 ≤ R ≤ 0.75. A method according to claim 1, characterized in that 0.71 ≤ R ≤ 0.74. A method according to claim 1, characterized in that R = 0.72. Method according to one of claims 1 to 5, characterized in that the specific surface area of the catalytically active multimetal oxide composition (I) is 11 to 40 m ² / g. Method according to one of claims 1 to 6, characterized in that that the X-ray diffractogram the catalytically active multimetal oxide mass (I) still further diffraction reflections with its apex position at the following diffraction angles-2⊝: 9.0 ± 0.4 ° (l), 6 7 ± 0, 4 ° (o), and 7.9 ± 0.4 ° (p) A method according to claim 7, characterized in that this X-ray diffraction the catalytically active multimetal oxide mass (I) still further diffraction reflections with its apex position at the following diffraction angles-2⊝: 29.2 ± 0.4 ° (m), and 35.4 ± 0.4 ° (n). Method according to Claim 8, characterized in that the intensity of the diffraction reflections h, i, l, m, n, o, p, q have the following intensities in the same intensity scale: h = 100, i = 5 to 95, l = 1 up to 30, m = 1 to 40, o = 1 to 30, p = 1 to 30, and q = 5 to 60. Method according to one of claims 1 to 9, characterized in that that a = 0.05 to 0.6. Method according to one of claims 1 to 10, characterized in that that b = 0.01 to 1. Method according to one of claims 1 to 11, characterized in that that c = 0.01 to 1. Method according to one of claims 1 to 12, characterized in that that d = 0.0005 to 0.5. Method according to one of claims 1 to 13, characterized in that that a = 0.1 to 0.6; b = 0.1 to 0.5; c = 0.1 to 0.5 and d = 0.001 to 0.5. Method according to one of claims 1 to 14, characterized in that M ^{2 is} at least 50 mol% of its total amount of Nb. Method according to one of claims 1 to 14, characterized in that M ^{2 is} at least 75 mol% of its total amount of Nb. Method according to one of claims 1 to 14, characterized in that M ^{2 is} exclusively Nb. Method according to one of claims 1 to 17, characterized in that M ^{3 is} at least one element from the group comprising Ni, Co, Bi, Pd, Ag, Au, Pb and Ga. Method according to one of claims 1 to 17, characterized in that M ^{3 is} at least one element from the group comprising Ni, Co, Pd and Bi. Method according to one of claims 1 to 17, characterized in that M ¹ = Te, M ² = Nb and M ³ = at least one element from the group comprising Ni, Co and Pd. A method according to claim 1, characterized in that the multimetal oxide mass (I) in a total multimetal oxide mass is included, their X-ray diffractogram has no diffraction reflex with the apex position 2⊝ = 50.0 ± 0.3 °. A method according to claim 21, characterized in that the multimetal oxide mass (I) in the total multimetal oxide mass in comprising at least one finely divided material from the group Silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide and niobium oxide diluted Form is present. A method according to claim 22, characterized in that the total multimetal oxide mass is ≥ 80% by weight multimetal oxide mass (I) contains and the X-ray diffractogram the total multimetal oxide mass has a diffraction reflex with the apex position 2⊝ = 50.0 ± 0.3 °. A method according to claim 22, characterized in that for the X-ray diffractogram of the total multimetal oxide mass R ≥ 0.65 and ≤ 0.90 Fulfills is. Method according to one of claims 1 to 24, characterized in that that the heterogeneously catalyzed gas phase partial oxidation of acrolein in the presence of propane and / or propene. Method according to one of claims 1 to 25, characterized in that that it was in a tube bundle reactor carried out becomes. Method according to one of claims 1 to 26, characterized in that that the catalytically active multimetal oxide mass (I) component a shell catalyst.