DE10338529A1 - Preparation of (meth)acrylic acid comprises heterogeneously catalyzed gas phase partial oxidizing of saturated hydrocarbon precursor compound(s) through charging catalyst bed that is disposed in reactor - Google Patents

Abstract

(Meth)acrylic acid is prepared by heterogeneously catalyzed gas phase partial oxidizing of saturated hydrocarbon precursor compound(s) through charging a catalyst bed that is disposed in reactor and whose catalytically active composition is a multimetal oxide containing molybdenum and vanadium, tellurium or antimony, and element(s) from niobium, tantalum, tungsten, cerium, or titanium. Preparation of (meth)acrylic acid comprises heterogeneously catalyzed gas phase partial oxidizing of saturated hydrocarbon precursor compound(s) through charging a catalyst bed that is disposed in reactor and whose catalytically active composition is a multimetal oxide containing molybdenum and vanadium, tellurium or antimony, and element(s) from niobium, tantalum, tungsten, cerium, or titanium; adding molecular oxygen as an oxidant and steam as a promoter at elevated temperature with a charging gas mixture; and adding diluent gas(es) that is inert under the conditions of the heterogeneously catalyzed gas phase partial oxidation. The x-ray diffraction of saturated hydrocarbon precursor compound(s) has reflections h, i, and k whose peak locations are at the reflection angles 22.2+-0.5[deg], 27.3+-0.5[deg], and 28.2+-0.5[deg]. The reflection h is the most intense in the x-ray diffractogram and has a half-height width of =0.5[deg]. The intensity Pi of the reflection I, and intensity Pk of the reflection k satisfy the relationship R=0.55-0.85 where R is the intensity ratio defined through R=Pi/(Pi + Pk). The half-height width of the reflection i and reflection k are =1[deg]. The steam content of the charging gas mixture is 5-25 vol.%, and the molar ratio V of molecular oxygen present in the charging gas mixture to the saturated hydrocarbon precursor compound(s) present in the charging gas mixture is 1.5:1-2.5:1.

Description

• – der Beugungsreflex h innerhalb des Röntgendiffraktogramms der intensitätsstärkste ist, sowie eine Halbwertsbreite von höchstens 0,5° aufweist,
• – die intensität P_i des Beugungsreflexes i und die Intensität P_k des Beugungsreflexes k die Beziehung 0,55 ≤ R ≤ 0,85 erfüllen, in der R das durch die Formel R = Pi/(Pi + Pk)definierte Intensitätsverhältnis ist, und
• – die Halbwertsbreite des Beugungsreflexes i und des Beugungsreflexes k jeweils ≤ 1° beträgt,

bei erhöhter Temperatur mit einem Beschickungsgasgemisch belastet, das neben der wenigstens einen gesättigten Kohlenwasserstoffvorläuferverbindung, molekularem Sauerstoff als Oxidationsmittel und Wasserdampf als Förderer noch wenigstens ein sich unter den Bedingungen der heterogen katalysierten Gasphasen-Partialoxidation im wesentlichen inert verhaltendes Verdünnungsgas umfasst.The present invention relates to a process for the preparation of (meth) acrylic acid by heterogeneously catalyzed gas phase partial oxidation of at least one saturated Kohlenwasserstoffvorläufenrerbindung, wherein one is in a reactor catalyst bed whose catalytically active material is a multimetal oxide, 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 Ti and whose X-ray diffractogram has diffraction peaks h, i and k whose vertices at the diffraction angles (2Θ) are 22.2 ± 0.5 ° (h), 27.3 ± 0.5 ° (i) and 28.2 ± 0.5 ° (k), where

• The diffraction reflex h within the X-ray diffractogram is the highest intensity, and has a half 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 0.55 ≦ R ≦ 0.85, in which R is represented by the formula R = P i / (P i + P k ) defined intensity ratio is, and
• The half-width of the diffraction reflex i and of the diffraction reflex k is respectively ≦ 1 °,

loaded at elevated temperature with a feed gas mixture, which in addition to the at least one saturated hydrocarbon precursor compound, molecular oxygen as the oxidant and water vapor as a conveyor still at least one under the conditions of heterogeneously catalyzed gas phase partial oxidation substantially inert behaviors diluent gas.

The Notation (meth) acrylic acid is shortened in this document for methacrylic acid or Acrylic acid.

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

Industrially may be (meth) acrylic acid et al by heterogeneously catalyzed gas-phase partial oxidation of propane or isobutane getting produced.

By heterogeneously catalyzed partial gas phase oxidation of a mixture from propane and iso-butane can acrylic acid and methacrylic acid be generated in the mixture.

propane and iso-butane are therefore referred to herein as saturated hydrocarbon precursor compounds of (meth) acrylic acid designated.

method for the production of (meth) acrylic acid by heterogeneously catalyzed gas phase partial oxidation at least a saturated one Hydrocarbon precursor compound in which one is located in a reactor catalyst bed, the Catalytically active material is a multimetal oxide that contains the elements Mo and V, at least one of the elements Te and Sb and at least one of the elements of the group comprising Nb, Ta, W and Ti and contains X-ray diffraction Diffraction reflections h, i and k whose vertices in the Diffraction angles (2Θ) 22.2 ± 0.5 ° (h), 27.3 ± 0.5 (i) and 28.2 ± 0.5 ° (k), at elevated temperature loaded with a feed gas mixture, in addition to the at least a saturated hydrocarbon precursor compound, molecular oxygen as the oxidant and water vapor as the promoter still at least one under the conditions of heterogeneously catalyzed Gas phase partial oxidation Substantially inert diluent gas are known (see, e.g., EP-A 1192987, DE-A 10122027, JP-A 2000-256257, EP-A 608838, EP-A 1193240, EP-A 1238960, EP-A 962253, JP-A 10-36311 and EP-A 1254706).

According to the teaching These prior art documents are in the presence of water vapor particularly advantageous in the feed gas mixture, since it is u.a. the selectivity the (meth) acrylic acid formation promotes (cf. e.g. EP-B 608838 page 4), wherein according to the teaching of the prior Technique an increasing amount of water vapor in the feed gas mixture increasingly beneficial. Also, the activity of the catalytically active multimetal oxide is favorably influenced by the presence of water vapor.

From is the catalytically active multimetal oxide to be used also known that the catalyzed partial oxidation by the oxygen is produced in the multimetal oxide active masses, on the way of a redox reaction by means of the feed gas mixture contained molecular oxygen steadily into the multimetal oxide active material must be replenished.

Increased molar conditions from molecular oxygen to saturated hydrocarbon precursor compound in the feed gas mixture are therefore generally advantageous considered.

adversely in the aforementioned, recommended as particularly advantageous procedures is, however, that the (meth) acrylic acid in the product gas of the heterogeneous did not catalyze partial gas phase oxidation as a pure substance but is obtained as part of a mixture from which separated the (meth) acrylic acid must be (see, for example, DE-A 10316465). Due to the high affinity of (meth) acrylic acid for water is a separation of (meth) acrylic acid in the product gas mixture However, water vapor contained particularly energy consuming. Advantageous from this point of view would be therefore one possible low water vapor content in the feed gas mixture.

One Another aspect is that the reaction gas mixture in the passage through the catalyst bed overcome the resistance of the same got to. The required energy must be the feed gas mixture fed in advance (in the form of compaction work, in principle, the Reaction gas mixture but also sucked through the catalyst bed become).

The this total work to be done is of course the greater (especially also with cycle gas guidance), the bigger the Amount of feed gas mixture is. Under this aspect would not be only a low water vapor content of advantage, but also a preferably low ratio of molecular oxygen contained in the feed gas mixture to saturated hydrocarbon precursor compound contained in the feed gas mixture. The latter even more so when not pure oxygen as an oxygen source or nitrogen-depleted air but used air itself In this case, every oxygen molecule will additionally be replaced by four nitrogen molecules accompanied.

Advantageous would be therefore a method of heterogeneously catalyzed gas phase partial oxidation at least one saturated Hydrocarbon precursor compound to (meth) acrylic acid, even at comparatively low water vapor contents the feed gas mixture and comparatively small molar conditions of molecular oxygen contained in the feed gas mixture to at least one saturated in the feed gas mixture Hydrocarbon precursor compound unfolds its full performance.

It It is now generally known that catalytically active multimetal oxides, 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 Ti, in different crystalline phases may occur (See, for example, DE-A 10246119 and DE-A 10254279).

A the possible crystalline phases, the so-called k-phase (with hexagonal structure), is by an X-ray diffractogram characterized in the 2Θ-vertex layers 22.1 ± 0.5 °, 28.2 ± 0.5 °, 36.2 ± 0.5 °, 45.2 ± 0.5 ° and 50.0 ± 0.3 ° intensity Has diffraction reflections.

A second specific crystal structure (orthorhombic structure) in the relevant multimetal oxide active masses may occur usually referred to as i-phase. Your X-ray diffractogram is u.a. thereby characterized in that it is at the 2Θ-vertex positions 22.2 ± 0.5 °, 27.3 ± 0.5 ° and 28.2 ± 0.5 ° intensity Diffraction reflections, in contrast to the k-phase at the 2Θ-vertex position 50.0 ± 0.3 ° but none Diffraction reflection shows (see DE-A10119933 and DE-A 10118814).

at the usual Method of preparation of the relevant multimetal oxide compositions (e.g. Production method according to EP-A 1192987, EP-A 529853 and EP-A 603836) are now normally neither pure k-phase still pure i-phase but obtained mixed crystal structures, which are a fused mixture of k and i phases, where normally the k-phase fraction dominates.

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

Especially high i-phase fractions are present when 0.55 or 0.65 ≤ R ≤ 0.85. Pure i-phase is present, if additionally the 2Θ-vertex-position 50.0 ± 0.3 ° no diffraction reflex shows (see, e.g., DE-A 10246119).

Increased i-phase Shares are u.a. producible by the k- and i-phase containing mixed crystal structures with suitable liquids such as. aqueous nitric acid washes.

According to the invention was now surprising found that the elements Mo and V, at least one of the elements Comprising Te and Sb as well as at least one of the elements from the group Nb, Ta, W and Ti-containing multimetal oxide active compositions containing a increased i-phase share in their performance (activity and selectivity with respect to the Target compound) with respect to the heterogeneously catalyzed gas phase partial oxidation of at least one saturated Hydrocarbon precursor compound to (meth) acrylic acid in many areas largely independent of the feed gas mixture contained water vapor content or molar ratio of molecular oxygen too saturated Hydrocarbon precursor compound are.

• – der Beugungsreflex h innerhalb des Röntgendiffraktogramms der intensitätsstärkste ist, sowie eine Halbwertsbreite von höchstens 0,5° aufweist,
• – die Intensität P_i des Beugungsreflexes i und die Intensität P_k des Beugungsreflexes k die Beziehung 0,55 ≤ R ≤ 0,85 erfüllen, in der R das durch die Formel R = Pi/(Pi + Pk)definierte Intensitätsverhältnis ist, und
• – die Halbwertsbreite des Beugungsreflexes i und des Beugungsreflexes k jeweils ≤ 1° beträgt,

bei erhöhter Temperatur mit einem Beschickungsgasgemisch belastet, das neben der wenigstens einen gesättigten Kohlenwasserstoffvorläuferverbindung, molekularem Sauerstoff als Oxidationsmittel und Wasserdampf als Förderer noch wenigstens ein sich unter den Bedingungen der heterogen katalysierten Gasphasen-Partialoxidation im wesentlichen inert verhaltendes Verdünnungsgas umfasst, gefunden, das dadurch gekennzeichnet ist, dass der Wasserdampfgehalt des Beschickungsgasgemischs 5 bis 25 Vol.-% beträgt, und das molare Verhältnis V von im Beschickungsgasgemisch enthaltenem molekularem Sauerstoff zur im Beschickungsgasgemisch enthaltenen wenigstens einen gesättigten Kohlenwasserstoffvorläuferverbindung 1,5 : 1 bis 2,5 : 1 beträgt.Accordingly, as a solution to the problems of the prior art processes, a process for producing (meth) acrylic acid by heterogeneously catalyzed gas phase partial oxidation of at least one saturated hydrocarbon precursor compound comprising: 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 and Ti and whose X-ray diffractogram has diffraction reflections h, i and k whose vertices at the diffraction angles (2Θ) 22.2 ± 0.5 ° (h), 27.3 ± 0.5 ° (i) and 28.2 ± 0.5 ° (k),
in which

• The diffraction reflex h within the X-ray diffractogram is the highest intensity, and has a half 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 0.55 ≤ R ≤ 0.85, in which R is represented by the formula R = P i / (P i + P k ) defined intensity ratio is, and
• The half-width of the diffraction reflex i and of the diffraction reflex k is respectively ≦ 1 °,

at elevated temperature loaded with a feed gas mixture, which in addition to the at least one saturated hydrocarbon precursor compound, molecular oxygen as the oxidant and water vapor as a conveyor still at least one under the conditions of heterogeneously catalyzed gas phase partial oxidation substantially inert behaviors diluent gas found found characterized in that the water vapor content of the feed gas mixture is 5 to 25% by volume, and the molar ratio V of molecular oxygen contained in the feed gas mixture to the at least one saturated hydrocarbon precursor compound contained in the feed gas mixture is 1.5: 1 to 2.5: 1.

When inert diluent gases be in the process of the invention Gases understood by molecular oxygen, water vapor and the at least one saturated one Hydrocarbon precursor compound are different, and in the single passage of the feed gas mixture through the catalyst bed to at least 95 mol% and most especially preferably remain unchanged to 100 mol .-% chemically unchanged.

The inert diluent gases capital together with the water vapor with their heat capacity to absorb released heat of reaction and at the same time the explosion behavior of the feed gas mixture (Reaction gas starting mixture) favorable to influence. Besides, it usually practices an advantageous influence on the reaction rate. Typically, non-combustible inert diluent gases Gases used.

One the most common co-used inert diluent gases is molecular nitrogen, which is always used automatically comes when as an oxygen source for the heterogeneous invention catalyzed gas phase partial oxidation air is used.

frequently Circulating gas is also used as an inert diluent gas (cf. e.g. DE-A 10316039 or EP-A 1180508). As circulating gas, the residual gas is called, the in the heterogeneously catalyzed gas phase partial oxidation of at least an organic precursor compound then remains when the target product from the product gas mixture (Meth) acrylic acid more or less selective (e.g., by absorption into a suitable Solvent) has separated. As a rule, it consists predominantly of those for the heterogeneous catalyzed gas phase partial oxidation used inert diluent gases, Water vapor and unwanted full In addition to oxidation formed carbon oxides. As a rule, it also contains unreacted Reactants, i. Propane and molecular oxygen, and optionally Intermediates such as propene and / or acrolein.

According to the invention preferred is used as an oxygen source (apart from contained in recycle gas molecular oxygen) exclusively air as an oxygen source uses.

Farther is the proportion of water vapor in the feed gas mixture according to the invention is preferably 10 up to 20% by volume. It can also be 6 to 20 vol.% Or 7 to 15 vol.% be. Further is the molar ratio V of molecular oxygen contained in the feed gas mixture to at least one saturated in the feed gas mixture Hydrocarbon precursor compound preferred according to the invention 1.75: 1 to 2.25: 1, but it can also be 1.8 to 2.3.

Particularly according to the invention Advantageously, the aforementioned preferred embodiment variants of Feeding gas mixture in the process according to the invention simultaneously Fulfills.

According to the invention preferred also applies 0.65 ≤ R ≤ 0.85 or 0.67 ≤ R ≤ 0.75 and very particularly preferably R = 0.69 to 0.75 or R = 0.71 to 0.74 or 0.73, or R = 0.72. This also in particularly advantageous Way in the particularly advantageous embodiments of the feed gas mixture.

In addition to the diffraction reflections h, i and k, the X-ray diffractogram of the catalytically active multimetal oxide compositions to be used according to the invention generally also contains further diffraction reflections whose vertices lie at the following diffraction angles (2θ):
9.0 ± 0.4 ° (l),
6.7 ± 0.4 ° (o) and
7.9 ± 0.4 ° (p).

According to the invention is low it further, if the X-ray diffractogram additionally contains a diffraction reflex, whose vertex is at the diffraction angle (2Θ) = 45.2 ± 0.4 ° (q).

Often contains the X-ray diffractogram to be used according to the invention Multimetal oxide active masses also have the reflexes 29.2 ± 0.4 ° (m) and 35.4 ± 0.4 ° (n) (vertex positions).

Assigning the intensity 100 to the diffraction reflex h, it is favorable 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, partially 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 the invention to be used Multimetal oxide Aktivmassen of the aforementioned additional Diffraction reflections, the half width of the same is usually ≤ 1 °.

The specific surface area of multimetal oxide active compositions to be used according to the invention is often 1 to 40 m ² / g, advantageously 10, 11 or 12 to 40 m ² / g and often 15 or 20 to 40 or 30 m ² / g ( determined by the BET method, nitrogen).

According to the invention preferred is the use of such Multimetalloxidaktivmassen whose X-ray diffractogram has no diffraction reflex with the vertex position 2Θ = 50.0 ± 0.3 °.

All in this document on an X-ray diffractogram The data refer to a using Cu-Ka radiation as X-radiation generated X-ray diffractogram (Siemens Theta-Theta D-5000 diffractometer, tube voltage: 40 kV, tube current: 40 mA, aperture diaphragm V20 (variable), diffuser diaphragm V20 (variable), Sekundärmonochromatorblende (0.1 mm), detector aperture (0.6 mm), measuring interval (2Θ): 0.02 °, measuring time each Step: 2.4 s, detector: scintillation counter tube; the definition of intensity a diffraction reflex in the X-ray diffractogram refers in this document to those in DE-A 19835247, DE-A 10122027, as well as those laid down in DE-A 10051419 and DE-A 10046672 Definition; The same applies the definition of the half width).

Particularly advantageous according to the invention is the use of catalytically active multimetal oxide active compositions to be used according to the invention which are of 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 group consisting of Nb, Ti, W, Ta and Ce;
M ³ = at least one of the elements from the group comprising Pb, Ni, Co, Bi, Pd, 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
n = a number which is determined by the valency and frequency of the elements other than oxygen in (I),
suffice.

Prefers is the stoichiometric Coefficient a of the multimetal oxide active materials (I), independent of the preferred areas for the other stoichiometric Coefficients of the active multimetal oxide materials (I), 0.05 to 0.6, more preferably 0.1 to 0.6 or 0.5.

Independent of the preferred areas for the other stoichiometric Coefficients of the invention preferred to be used multimetal oxide (I) 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.

Of the stoichiometric Coefficient c of the invention advantageous is to be used Multimetalloxidaktivmassen (I), regardless of the preferred areas for the other stoichiometric Coefficients of multimetal oxide active materials (I) 0.01 to 1 and particularly preferably 0.01 or 0.1 to 0.5 or 0.4. A very particular invention preferred range for the stoichiometric Coefficients c, the, independent from the preferred areas for the other stoichiometric Coefficients of the invention advantageous to be used Multimetalloxidaktivmassen (I), with all others Preferred ranges can be combined in this document, is the area 0.05 to 0.2.

According to the invention preferred is the stoichiometric Coefficient d of the invention to be used Multimetal oxide active (I), regardless of the preferred ranges for the other stoichiometric Coefficients of the multimetal oxide active materials (I), 0.00005 and 0.0005, respectively to 0.5, more preferably 0.001 to 0.5, often 0.002 to 0.3 and often 0.005 and 0.01 to 0.1, respectively.

Particularly advantageous according to the invention to be used Multimetalloxidaktivmassen (I) whose stoichiometric 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).

Very particularly favorable according to the invention to be used Multimetalloxidaktivmassen (I) whose stoichiometric coefficients a, b, c and d are simultaneously in the following grid:
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, and 0.005 to 0.1, respectively.

M1 is preferably Te.

All of the above applies especially when M ^{2 is} at least 50 mol% of its total amount of Nb and most 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, irrespective of the meaning of M ² , then, when M ^{3 is} at least one element selected from the group comprising Pt, Fe, Re, Mn, Cu, Ni, Co, Bi, Pd, Ag, Au, Pb and Ga or at least one member selected from the group consisting of Ni, Co, Pd, Pt, Fe and Bi.

Above all, however, all the above applies even if M ^{2 contains} at least 50 mol% of its total amount, or at least 75 mol%, or 100 mol% of Nb and M ³ at least one element from the group comprising Pt, Fe, Re, Mn, Cu, Ni, Co, Bi, Pd, Ag, Au, Pb and Ga.

Above all, however, all the above applies even if M ^{2 is} at least 50 mol%, or at least 75 mol%, or 100 mol% of its total amount of Nb and M ^{3 is} at least one element selected from the group consisting of Ni, Co, Pd, Pt, Fe and Bi is.

With very particular preference all statements regarding the stoichiometric coefficients are valid when M ¹ = Te, M ² = Nb and M ³ = at least one element from the group comprising Ni, Co, Pt and Pd.

The Principle of a specific method for the production of inventively used Multimetal oxide active compounds, especially those of the general Formula (I) discloses, e.g. WO 0206199 and in this document cited references. Thereafter, in a conventional manner first produces a multimetal oxide composition which has the desired stoichiometry, but a usually intimately fused mixed crystal system of i-phase and k-phase is. In this mixture, the proportion of i-phase can now thereby increased or be isolated by allowing the k-phase with suitable liquids in the desired Scoured out circumference. As such liquids come for example organic acids and watery solutions organic acids (e.g., oxalic acid, formic acid, Acetic acid, citric acid and tartaric acid), inorganic acids (e.g., nitric acid), aqueous solutions inorganic acids (e.g., aqueous telluric or watery Nitric acid), Alcohols and watery hydrogen peroxide solutions into consideration. Furthermore, JP-A 7-232071 also discloses a method for the preparation of multimetal oxide active materials rich in i-phase. As well the washing process of EP-A 1254707 and EP-A 1254706 is suitable.

Mischkristallysteme i-and k-phase are usually after those in the prior art obtained (see, for example, 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). After these procedures is derived from suitable sources of the elemental constituents of the multimetal oxide material one possible produces intimate, preferably finely divided, dry mixture and this at temperatures of 350 to 700 ° C or 400 to 650 ° C or 400 to 600 ° C thermally treated. The thermal treatment can in principle under oxidizing, reducing as well as under inert the atmosphere respectively. As an oxidizing atmosphere, e.g. Air, with molecular Oxygen enriched air or deoxygenated air into consideration. Preferably, however, the thermal treatment in an inert atmosphere, i.e., e.g. under molecular nitrogen and / or noble gas. Usually the thermal treatment is carried out at normal pressure (1 atm). Of course, the thermal treatment even under vacuum or under pressure respectively.

He follows the thermal treatment under a gaseous atmosphere, can these both stand and flow. Preferably, it flows. Overall, the thermal treatment can take up to 24 h or more in Claim.

The thermal treatment is preferably carried out initially 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 conveniently carried out under inert gas at temperatures of 350 to 700 ° C or 400 to 650 ° C or 450 to 600 ° C continued. Of course, the thermal treatment can also be carried out so that the catalyst precursor initially before its thermal treatment (optionally after pulverization) tabletted (optionally with the addition of 0.5 to 2 wt .-% of finely divided graphite), then thermally treated and subsequently split again ,

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

He follows in dry form, the starting compounds are conveniently used as finely divided powder and after mixing and optionally Compressing the calcination (thermal treatment) subjected.

Preferably However, the intimate mixing is done in wet form. Usually the starting compounds are in the form of an aqueous solution (optionally with the concomitant use of complexing agents; see. e.g. DE-A 10145958) and / or suspension mixed together. Subsequently, will the watery Mass dried and calcined after drying. Conveniently, it is the aqueous Mass around a watery solution or an aqueous one Suspension. The drying process preferably takes place immediately following the preparation of the aqueous mixture (in particular in the case of an aqueous Solution; see. e.g. JP-A 7-315842) and by spray-drying (the outlet temperatures are usually 100 to 150 ° C; the spray drying can be done in cocurrent or countercurrent), which is a special intimate dry mix conditionally, especially if it is the spray-drying aqueous Mass around a watery solution or suspension. But it can also be by evaporation in vacuo, dried by freeze-drying, or by conventional evaporation.

When Sources for the elementary constituents come in the context of carrying out the above-described preparation of i- / k-phase-Mekristall-Multimetalloxidmassen all those considered when heating (if necessary Air) oxides and / or hydroxides to form assets. Of course, as such starting compounds also already oxides and / or hydroxides co-used with the elementary constituent or used exclusively become. That is, in particular, all of the documents EP-A 1254707, EP-A 1254709 and EP-A 1192987 said starting compounds in Consideration.

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

Suitable starting compounds for the element V are, for example, vanadium oxysulfate hydrate, vanadyl acetylacetonate, 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 can also be used as Vanadinausgangsverbindungen those which contain the vanadium in the oxidation state +4.

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 are suitable as sources for the tellurium element.

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

Suitable niobium sources are z. As niobium oxides such as niobium pentoxide (Nb ₂ O ₅ ), niobium oxyhalides such as NbOCl ₃ , niobium halides such as NbCl ₅ , but also complex compounds of niobium and organic carboxylic acids and / or dicarboxylic acids such. As oxalates and alcoholates. Of course, the niobium sources which can be used are also the Nb-containing solutions used in EP-A 895 809.

Regarding all other possible Elements (especially of 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 As tungstates or derived from these acids. Become frequent as starting compounds and ammonium salts used.

Further come as starting compounds and polyanions of the Anderson type into consideration, as they z. In Polyhedron Vol. 6, no. 2, pp. 213-218, 1987 are described. Another suitable source of literature for polyanions Anderson type Kinetics and Catalysis, Vol. 3, 1999, pp 401-404.

Other as starting compounds suitable polyanions z. B. such from the Dawson or Keggin type. Preferably, such starting compounds used, which increased at Temperatures either in the presence or absence of oxygen, optionally with the release of gaseous compounds into their Convert oxides.

The available as described i / k phase mixed crystal multimetal oxide materials (pure i-phase multimetal oxides are at best obtained randomly according to the procedure described) can then as described by suitable washing (in which the stoichiometry usually only insignificantly changes) in to be used according to the invention active multimetal oxides, in particular those of stoichiometry (I). Preference is given to calcining again after the washing, as it is EP-A 1254709 describes. The calcination conditions are included usually the same, which is also used for the production of the to be washed Multimetal oxide compositions were recommended.

One increased Share of i-phase (and in favorable make essentially pure i-phase) arises in the production of Precursor multimetal oxides (Which by washing described in accordance with invention to be used active multimetal oxides, in particular those of the general formula (I) can) then, if their production takes place hydrothermally, as it is e.g. DE-A 10029338, DE-A 10254278 and JP-A 2000-143244 describe. Also in this case, EP-A 1254709 can recalcined following become.

The Preparation of the invention advantageous but can also be characterized by using active multimetal oxide materials (I) with d> 0 done that first produces a multimetal oxide material I ', which differs from a multimetal oxide composition (I) only in that that d = 0.

Such, preferably finely divided, multimetal oxide composition I 'can then be impregnated with solutions (eg aqueous) of elements M ³ (eg by spraying), subsequently dried (preferably at temperatures ≦ 100 ° C.) and then calcined as described for the precursor-multimetal oxides ( preferably in an inert gas stream) (preference is given here to a pre-decomposition in air). 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 preparation variant.

The available as described to be used according to the invention active multimetal oxides, in particular those of the formula (I), in the inventive method as such [e.g. as a powder or after tableting the powder (often under Addition of 0.5 to 2 wt .-% of finely divided graphite) and subsequent splitting crushed into chippings] or shaped into moldings as catalysts for the inventive method be used. In this case, the catalyst bed can be a fixed bed, a moving bed (a fluid bed) or be a fluidized bed.

The Forming into moldings can e.g. by applying to a carrier body, as in the DE-A 10118814 or PCT / EP / 02/04073 or DE-A 10051419 becomes. It can also proceed in accordance with DE-A 4442346 become.

The for the in the process according to the invention to be used active multimetal oxide, in particular those of the general formula (I) to be used carrier body are preferably chemical inert. That is, they intervene in the course of the heterogeneous invention catalyzed gas phase partial oxidation, which can be used by the invention Multimetal oxide compositions, in particular those of the general formula (I), is essentially not catalyzed.

When Material for the carrier bodies come particularly according to the invention Alumina, silica, silicates such as clay, kaolin, steatite (preferably with low water-soluble alkali content as well 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. Advantageously, the surface of the Carrier body rough, because an increased surface roughness usually an elevated one Adhesive strength of the applied active mass shell conditioned.

Frequently, the surface roughness R _{Z of} the carrier body in the range of 5 to 200 microns, often in the range of 20 to 100 microns (determined according to DIN 4768 Part 1 with a "Hommel Tester for DIN-ISO Oberflä Chenmeßgrößen "the Fa. Hommelwerke, DE).

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

The Thickness of the shell catalysts of the invention located active oxide mass shell is usually from 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 stretch is usually 1 to 10 mm. Preferably, however, spheres or cylinders, in particular hollow cylinder, used as a carrier body. Cheap diameter for carrier balls amount 1.5 to 5 mm. If cylinders are used as carrier bodies, then theirs is Length preferably 2 to 10 mm and its outer diameter preferably 4 to 10 mm. In addition, in the case of rings, the wall thickness is usually at 1 to 4 mm. According to the invention suitable annular Carrier body can also a length from 3 to 6 mm, an outside diameter from 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 be prepared in the simplest manner, e.g. done so that to be used according to the invention Multimetal oxide active compounds, in particular those of the general Formula (I), transforms them into a finely divided form and finally with the help of a liquid Binder on the surface of the carrier body applies. This is the surface of the carrier body in easiest way with the liquid Binder moistened and by contacting with finely divided active oxide material, e.g. those of the general formula (I), a Layer of the active composition attached to the moistened surface. Finally the coated carrier body is dried. Of course you can to achieve an increased layer thickness the process repeat periodically. In this case, the coated body is for new "carrier" etc .. After successful Coating can again under the conditions already mentioned calcined (preferably again under inert gas).

The fineness of the catalytically active multimetal oxide composition to be applied to the surface of the carrier body, for example that of the general formula (I), is, of course, adapted to the desired shell thickness. For the shell thickness range of 100 to 500 microns z. B. such active mass powder, of which at least 50 of the total number of powder particles pass through a sieve of mesh size 1 to 20 microns and their numerical proportion of particles with a longitudinal expansion above 50 mm is less than 10%. As a rule, the distribution of the longitudinal extents of the powder particles corresponds to the production of a Gaussian distribution. Frequently, the particle size distribution is 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 described coating method on an industrial scale is recommended z. B. the application of the in DE-A 2909671, as well as the disclosed in DE-A 10051419 process principle. That is, the support bodies to be coated are 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 Rotating container central axis against the horizontal) rotating rotary container (eg turntable or coating drum) submitted. The rotating rotary container leads the z. B. spherical or cylindrical carrier body under two at a certain distance successively arranged metering devices. The first of the two metering devices expediently corresponds to a nozzle (for example a spray 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 of the atomizing cone of the sprayed liquid binder and serves to supply the finely divided oxidic active material (eg via a vibrating trough or a powder screw). The controlled moistened carrier balls absorb the supplied active mass powder, which is due to the rolling movement on the outer surface of the z. B. cylindrical or spherical carrier body compacted into a coherent shell.

at Needs go through the so-primed carrier body in Course of the next turn turn the spray nozzles, will In doing so, moisturizes controlled to continue in the process of moving on take up a further layer of finely divided oxidic active material to be able to etc. (intermediate drying is usually not required). Finely divided oxidic active material and liquid binder are thereby usually fed continuously and simultaneously.

The removal of the liquid binder may, after completion of the coating z. B. by the action of hot gases, such as N ₂ or air done. It is noteworthy that the coating process described produces both a fully satisfactory adhesion of the successive layers to one another and the base layer on the surface of the support body.

Essential for the coating method described above is that moistening the surface to be coated of the carrier body in controlled manner. In short, this means that the carrier surface is moistened appropriately, that this is liquid Having adsorbed binder, but no liquid phase on the support surface as such visually appears. Is the carrier body surface too moist, the finely divided catalytically active oxide mass agglomerates to separate Agglomerates instead of growing on the surface. detailed Information on this can be found in DE-A 2909671 and in DE-A 10051419.

The aforementioned final Removal of the used liquid Binder can in a controlled manner z. B. by evaporation and / or sublimation. In the simplest case, this can be hotter by exposure Gases of appropriate temperature (often 50 to 300, often 150 ° C) take place. By Exposure hotter Gases can also be effected only a pre-drying. The final drying can then, for example, in a drying oven of any kind (eg. B. belt dryer) or in the reactor. The acting temperature should not be above that for the preparation of the oxide active composition applied Calcinationstemperatur lie. Of course you can the drying also exclusively carried out in a drying oven become.

When Binder for the coating process can independently be used on the type and geometry of the carrier body: water, monohydric alcohols such as ethanol, methanol, propanol and butanol, polyvalent ones 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 and on or polyfunctional organic amides such as formamide. Cheap binders are also Solutions, consisting of 20 to 90 wt .-% water and 10 to 80 wt .-% of a dissolved in water organic compound, its boiling point or sublimation temperature at atmospheric pressure (1 atm)> 100 ° C, preferably> 150 ° C, is. With Advantage is the organic compound from the above listing potential selected organic binder. Preferably the organic fraction of the aforementioned aqueous binder solutions 10 to 50 and more preferably 20 to 30 wt .-%. As organic Components are also monosaccharides and oligosaccharides such as glucose, fructose, sucrose or lactose and polyethylene oxides and polyacrylates.

From Significance is that the preparation according to the invention suitable Coated catalysts not only by applying the finished, finely ground active oxide materials, e.g. of general formula (I), on the moistened carrier body surface take place can.

Rather, instead of the active oxide composition, a finely divided precursor composition thereof may also be applied to the moistened carrier surface (using the same coating methods and binders) and the calcination carried out after drying the coated carrier body (support bodies may also be impregnated with a precursor solution, subsequently dried and subsequently calcined become). Finally, the k-phase different from the i-phase can be washed out. Subsequently, it can be calcined again in the manner described.

When such a finely divided precursor mass comes z. For example, the mass which is obtainable thereby that from the sources of elementary constituents of the desired to be used according to the invention active oxide material, e.g. those of the general formula (I), first a preferably intimate, preferably finely divided, dry mixture produced (eg. by spray drying an aqueous Suspension or solution the sources) and this finely divided dry mixture (optionally after tabletting with the addition of 0.5 to 2 wt .-% of finely divided Graphite) at a temperature of 150 to 350 ° C, preferably 250 to 350 ° C under oxidizing (Oxygen-containing) atmosphere (eg, under air) thermally treated (a few hours) and finally when needed a grind subjects.

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

Needless to say, For example, the shaping of active multimetal oxide materials useful in the invention, e.g. those of the general formula (I), also by extrusion and / or Tableting of both finely divided multimetal oxide active material, as well as of finely divided precursor mass a multimetal oxide active mass (if necessary the leaching of the phases different from the i-phase take place finally, if necessary including a Recalcination).

When Geometries come in this case both balls, solid cylinder and hollow cylinder (Rings) into consideration. The longest extent the aforementioned geometries usually 1 to 10 mm. In the case of cylinders is their Length preferably 2 to 10 mm and its outer diameter preferably 4 to 10 mm. In addition, in the case of rings, the wall thickness is usually at 1 to 4 mm. According to the invention suitable annular unsupported catalysts can also a length from 3 to 6 mm, an outside diameter from 4 to 8 mm and a wall thickness of 1 to 2 mm. Is possible but also a Vollkatalysatorringgeometrie of 7 mm × 3 mm × 4 mm or of 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter).

Needless to say, come for the inventive method for the Geometry of the multimetal oxide active compositions to be used, in particular those of general formula (I), including all those of DE-A 10101695 in Consideration.

• – der Beugungsreflex h innerhalb des Röntgendiffraktogramms der intensitätsstärkste ist, sowie eine Halbwertsbreite von höchstens 0,5° aufweist,
• – die Intensität P_i des Beugungsreflexes i und die Intensität P_k des Beugungsreflexes k die Beziehung 0,55 ≤ R ≤ 0,85 erfüllen, in der R das durch die Formel R = Pi/(Pi + Pk)definierte Intensitätsverhältnis ist, und
• – die Halbwertsbreite des Beugungsreflexes i und des Beugungsreflexes k jeweils ≤ 1° beträgt.

According to the invention, it is essential, as already stated, that the multimetal oxide active compositions to be used according to the invention, especially those of the general formula I, have an X-ray diffractogram (in this document always based on Cu-Ka radiation) which has diffraction peaks h, i and k whose Vertices at the diffraction angles (2Θ) are 22.2 ± 0.5 ° (h), 27.3 ± 0.5 ° (i) and 28.2 ± 0.5 ° (k), where

• The diffraction reflex h within the X-ray diffractogram is the highest intensity, and has a half 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 0.55 ≤ R ≤ 0.85, in which R is represented by the formula R = Pi / (Pi + Pk) defined intensity ratio is, and
• - The half-width of the diffraction reflection i and the diffraction reflection k is ≤ 1 °.

simultaneously should the X-ray diffractogram particularly preferably no diffraction reflex with the vertex position 2Θ = 50 ± 0.3 °.

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

That is, A ¹ denotes the vertex of a reflection 1, and B ¹ in the line of the X-ray diffractogram, when viewed along the intensity axis perpendicular to the 2Θ axis, indicates the nearest distinct minimum (reflective shoulders indicating minima are left unconsidered) to the left of vertex A ¹ and B ² in FIG Similarly, the nearest distinct minimum to the right of the vertex A ¹ and C ¹ denotes the point at which one of the vertex A ¹ perpendicular to the 2Θ-axis drawn straight line intersects the points B ¹ and B ² connecting straight line, then the intensity of the reflex 1 is the length of the straight line section A ¹ C ¹ , which extends from the vertex A ¹ to the point C ¹ . The term minimum means a point at which the slope 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 approaches zero, wherein for the determination the slope gradient, the coordinates of the 2Θ axis and the intensity axis are used.

The half-width in this document is correspondingly the length of the straight line section which arises between the two intersections H ¹ and H ² , if one draws a parallel to the 2Θ-axis in the middle of the straight section A ¹ C ¹ , where H ¹ , H ² mean the respective first intersection of these parallels with the line of the X-ray diffractogram as defined above to the left and right of A ¹ .

An exemplary implementation of the determination of half-width and intensity also shows the 6 in DE-A 10046672.

Needless to say, can the invention to be used Multimetal oxide active materials, in particular those of the general formula (I), also in finely divided, e.g. colloidal, materials, like Silica, titania, alumina, zirconia, niobium oxide, diluted Form can be used as catalytic active compounds.

The Dilution mass ratio can while up to 9 (thinner): 1 (active mass). That is, possible Dilution mass ratio amount e.g. 6 (thinner): 1 (active mass) and 3 (thinner): 1 (active mass). The incorporation of the diluents can be before and / or after Calcination, usually even before drying done. Usually it takes place before shaping.

He follows the incorporation before drying or before the calcination, the thinner must be so to get voted, that in the fluid medium or in the calcination substantially preserved. This is e.g. in the case of at correspondingly high Temperatures of calcined oxides are usually given.

For the rest, can the method according to the invention, especially in the case of a heterogeneously catalyzed gas phase partial oxidation from propane to acrylic acid, as in EP-A 608838, WO 0029106, JP-A 10-36311, DE-A 10316465 and described in EP-A 1192987.

When Source for the needed molecular oxygen can e.g. Air, oxygenated or oxygen depleted air or pure oxygen become.

Incidentally, the starting reaction gas mixture in addition to propane and molecular oxygen and water vapor as inert diluent gases include, for example, N ₂ , CO and CO ₂ .

That is, the reaction gas starting mixture, with which the catalyst bed at reaction temperatures of, for example, 200 to 550 ° C or 230 to 480 ° C or 300 to 440 ° C and pressures of 1 to 10 bar, or 2 to 5 bar to load (it can be used in principle also negative pressure), may have, for example, the following contents:
From 1 to 15, preferably from 1 to 7,% by volume of propane,
5 to 25% by volume of steam and
10 to 80 vol.% Air.

It can also have the following contents:
2 to 10% by volume of propane,
5 to 20% by volume of steam,
60 to 85% by volume of nitrogen, and
5 to 15% by volume of oxygen.

At the inventive method Deactivated multimetal oxidative materials can be prepared by passing molecular oxygen and / or water vapor-containing gases under the temperature and Reactivates pressure conditions of the deactivation causing reaction become. Such a gas may 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, a mixture made of nitrogen and water vapor. The oxygen content of the regeneration gas can therefore ≥ 0 to 20 mol%. Often it will be 2 to 10 mol%, sometimes 2 to 15 mol%.

Becomes as a saturated one Hydrocarbon used in the process according to the invention crude propane is this is preferred as in DE-A 10246119 or DE-A 10118814 or PCT / EP / 02/04073 described composed.

The Commissioning a fresh catalyst feed can be done as in DE-A 10122027 described.

Becomes the inventive method carried out on a fixed catalyst bed, this may be e.g. in a tube bundle reactor whose contact tubes of one or more of each other independent Tempering media (for example salt baths) flows around (in the latter case one speaks of a multi-zone reactor).

The Temperature of the individual zones usually takes in the direction of flow of the reaction gas mixture too.

suitable One-zone tube bundle reactors are e.g. in EP-A 700714 and in EP-A 700893.

According to the invention suitable Multi-zone tube bundle reactors are e.g. in DE-A 19927624, DE-A 19948242, DE-A 19948241, DE-A 19910508 and DE-A 19910506. An implementation of the inventive method in the fluidized bed can e.g. as described in WO 02/0811421.

Based to the propane contained in the starting reaction gas mixture and / or Iso-butane will be the sales on propane and / or iso-butane in the inventive method, based on a single pass of the reaction gas mixture through the catalyst bed usually 10 or 20 to 70 mol%, often 30 to 60 mol% and in many cases 40 to 60 mol% and 45 to 55 mol%, respectively. The selectivity of target product formation becomes common 40 to 98 or 95 to 90 mol%, often 50 to 80 mol%, often 60 to 80 mol%.

The Target product separation and possible circulation of gas can be as described in DE-A 10316465 respectively.

The Loading the catalyst bed (inert beds not included) with Propane and / or iso-butane can be 10 to 1000 Nl / l (catalyst bed) / (h) or 20 to 800 Nl / l / h, or 50 to 600 Nl / l / h, or 100 to 500 Nl / l / h, or 150 to 300 Nl / l / h.

The Loading the catalyst bed (inert beds not included) with Starting reaction gas mixture can be 10 to 10000 Nl / l / h, or 300 to 6000 Nl / h / l, or 300 to 2000 Nl / l / h. The mean residence time the catalyst charge can be 0.01 s to 10 s, or 0.1 to 10 s, or 2 to 6 s.

Examples and Comparative Examples

A) Preparation of an inventively used Multimetal oxide catalyst

In 44.6 l of water were dissolved at 80 ° C in a stainless steel container with stirring 1287.25 g ammonium metavanadate (77.5 wt .-% V ₂ O ₅ , Fa. GfE, DE-Nuremberg). There was a clear yellowish solution. This solution was cooled to 60 ° C and then successively in the order mentioned while maintaining the 60 ° C first 1683.75 g of telluric acid (99 wt .-% H ₆ TeO ₆ , Fa. Fluka) and then 5868.0 g of ammonium heptamolybdate ( 81.5 wt .-% MoO ₃ , Fa. Starck) stirred. The result was a deep red solution A. In a second stainless steel container 1599.0 g of ammonium niobium oxalate (21.1 wt .-% Nb, Fa. Starck, DE-Goslar) were dissolved at 60 ° C in 8.3 l of water to a solution B. , The two solutions A and B were cooled to 30 ° C and combined at this temperature, wherein the solution B was stirred into the solution A. Stirring was continuous over a period of 10 minutes. An orange-colored aqueous suspension resulted.

This suspension was then spray-dried (T = 30 ° C _{storage tank,} T ^a = 240 ° C, T ^out = 110 ° C, drying time: 1.5 h, the spray tower Fa Nipolosa.). The resulting spray was also orange colored. 1% by weight of finely divided graphite (sieve finish: at least 50% by weight ≦ 24 μm, at most 10% by weight 24 24 μm and ≦ 48 μm, at most 5% by weight 48 48 μm) was sprayed into the sprayed material , BET surface area: 6 to 13 m ² / g).

The resulting mixture became hollow cylinders (rings) of geometry 16 mm × 2.5 mm × 8 mm (outer diameter × height × inner diameter) so compacted (compressed), that the resulting side crushing strength of the rings was about 10 N.

200 g of these rings were in two portions of 100 g in succession in a rotary ball furnace according to 1 calcined DE-A 10122027. For this purpose, the rotary kiln was under an air flow of 50 Nl / h with a linear heating ramp within 27.5 min. heated from 25 ° C to 275 ° C and held at this temperature while maintaining the air flow for 1 h. Subsequently, within 32.5 min. heated with a linear heating ramp from 275 ° C to 600 ° C, the air flow was replaced by a nitrogen flow of 50 Nl / l. The 600 ° C and nitrogen flow were maintained for 2 hours and the entire furnace then allowed to cool by itself while maintaining the nitrogen flow to 25 ° C. This resulted in black tablets of composition Mo _1.0 V _0.33 Te _0.15 Nb _0.11 O _x .

In a Retsch mill, the tablets were ground dry to a particle size ≤ 100 microns. 150 g of the milled material was stirred in 1500 ml of a 10 wt .-% aqueous HNO ₃ solution for 7 h at 70 ° C under reflux, the solid filtered from the resulting slurry and washed with water nitrate-free. The filter cake was dried overnight in air at 110 ° C in a muffle furnace. The resulting active composition had the composition Mo _1.0 V _0.27 Te _0.12 Nb _0.13 O _x . Its X-ray diffractogram (cf. 1 ) showed pure i-phase with R = 0.74. It contained no diffraction reflex with the vertex position 2Θ = 50.0 ± 0.3 °.

75 g of the active material powder was 300 g spherical support body with a diameter of 2.2-3.2 mm (= carrier material of the steatite Ceramtec, DE, total pore volume of the support ≤ 1 vol .-% based on the total volume of carrier;. R _Z = 45 microns) applied. For this purpose, the carrier body in a coating drum with 2 l internal volume (inclination angle of the drum center axis against the horizontal = 30 °) were submitted. The drum was rotated at 25 revolutions per minute. About a with 300 Nl / h compressed air operated atomizer nozzle were over 60 min. about 30 ml of a mixture and glycerol and water (weight ratio glycerol: water = 1: 3) sprayed onto the carrier body. The nozzle was installed in such a way that the spray cone wetted in the drum by entrainment plates to the top point of the inclined drum carried carrier in the upper half of the roll-off. The finely divided active mass powder was introduced into the drum via a powder screw, but the point at which the powder was added within the rolling distance was below the spray cone. As a result of the periodic repetition of wetting and powder addition, the base-coated carrier body itself became the carrier body in the subsequent period.

To Completion of the coating were the coated carrier body during 16 Hours at 120 ° C in a convection oven (company Binder, DE, interior volume 53 l) dried. Glycerol was characterized by a subsequent two-hour heat treatment at 150 ° C removed under air. It became a coated catalyst to be used according to the invention S20 obtained with 20 wt .-% active composition.

B) Procedure

35.0 g of the shell catalyst S20 were in a single tube reactor installed (pipe length: 140 cm, inner diameter: 8.5 mm, outer diameter: 60 mm, V2A Steel, catalyst bulk length: 54.5 cm, in addition to warm up of the reaction gas starting mixture from a 30 cm long feed Steatite balls from the company Ceramtec (C220, 2.2-3.2 mm diameter), continue was the reaction tube with the same steatite spheres after the catalyst zone finally ) Filled, which was heated by electric heating mats. At a mat temperature of 350 ° C the shell catalyst was installed in air in the tubular reactor.

Thereafter, while maintaining the mat temperature of 350 ° C for 24 hours, the reaction tube was charged with a reaction gas starting mixture (feed gas mixture) having the following composition: 3.3% by volume Propane, 10 vol.% O ₂ , 40 vol.% N ₂ and 46.7% by volume H ₂ O.

The residence time (based on the catalyst bed volume) was chosen to 2.4 s, the reaction tube inlet pressure was 2 bar absolute, the GHSV was 1500 h ^-1 (based on feed gas mixture).

After that was for in each case 24 h, the composition of the feed gas mixture changed and thereby the mat temperature in each case adjusted so that the propane conversion, based on a single reaction tube passage, always about 40 mol% amounted to. The remaining Boundary conditions were maintained as described.

Between the individual feed gas mixture composition variants each for one Hour the break-in composition applied to as a reference point ensure that the catalyst bed is not damaged would have. The mat temperature was 390 ° C.

In dependence from the feed gas mixture composition, the following results were obtained achieved:

1st comparative example

Feed gas: 3.3 vol.% Propane; 10% by volume O ₂ ; 40% by volume of N ₂ ; 46.7 vol .-% H ₂ O. At a matte temperature of 390 ° C, the propane conversion (based on single pass) was 40 mol%. The selectivity of acrylic acid formation was 71 mol%.

2nd Comparative Example

Feed gas: 3.3 vol.% Propane; 10% by volume O ₂ ; 86.7% by volume of N ₂ ; 0 vol .-% H ₂ O. At a matte temperature of 410 ° C, a propane conversion of 41 mol% and a selectivity of acrylic acid formation of 45 mol% was achieved.

3. Comparative Example

Feed gas: 3.3 vol.% Propane; 10% by volume O ₂ ; 70% by volume of N ₂ ; 16.7 vol .-% H ₂ O. At a mat temperature of 390 ° C, a propane conversion of 40 mol% and a selectivity of acrylic acid formation of 70 mol% was achieved.

4. Comparative Example

Feed gas: 3.3 vol.% Propane; 3.3% by volume O ₂ ; 76.7% by volume of N ₂ ; 16.7 vol .-% H ₂ O. At a mat temperature of 415 ° C, a propane conversion of 41 mol% and a selectivity of acrylic acid formation of 68 mol% was achieved.

1st example:

Feed gas: 3.3 vol.% Propane; 8.0 vol.% O ₂ ; 72.0% by volume of N ₂ ; 16.7 vol .-% H ₂ O. At a mat temperature of 390 ° C, a propane conversion of 40 mol% and a selectivity of acrylic acid formation of 70 mol% was achieved.

2nd example:

Feed gas: 3.3 vol.% Propane; 6.0% by volume O ₂ ; 74% by volume of N ₂ ; 16.7 vol .-% H ₂ O. At a mat temperature of 395 ° C, a propane conversion of 40 mol% and a selectivity of acrylic acid formation of 72 mol% was achieved.

3rd example:

Feed gas: 3.3 vol.% Propane; 8.0 vol.% O ₂ ; 82.7% by volume of N ₂ ; 6.0% by volume of H ₂ O. At a mat temperature of 400 ° C., a propane conversion of 39 mol% and a selectivity of acrylic acid formation of 70 mol% were achieved.

4th example:

Feed gas: 5.0% by volume of propane; 10.0 vol.% O ₂ ; 68.3% by volume of N ₂ ; 16.7 vol .-% H ₂ O. At a mat temperature of 395 ° C, a propane conversion of 40 mol% and a selectivity of acrylic acid formation of 71 mol% was achieved.

Claims (22)

Process for the preparation of (meth) acrylic acid by heterogeneously catalyzed gas-phase partial oxidation of at least one saturated hydrocarbon precursor compound comprising reacting a catalyst bed in a reactor whose catalytically active material is a multimetal oxide comprising Mo and V, at least one of Te and Sb and at least one of the elements from the group comprising Nb, Ta, W, Ce and Ti and whose X-ray diffractogram has diffraction reflectances h, i and k whose vertices at the diffraction angles (2Θ) are 22.2 ± 0.5 ° (h) , 27.3 ± 0.5 ° (i) and 28.2 ± 0.5 ° (k), where - the diffraction reflex h is the highest intensity within the X-ray diffractogram, and has a maximum half-width of 0.5 °, - the intensity P _{i of} the diffraction reflection i and the intensity P _{k of} the diffraction reflection k satisfy the relationship 0.55 ≤ R ≤ 0.85, in which R is represented by the formula R = P i / (P i + P k ) is defined intensity ratio, and - the half-width of the diffraction reflection i and the diffraction reflection k each ≤ 1 °, loaded at elevated temperature with a feed gas mixture, in addition to the at least one saturated hydrocarbon precursor compound, molecular oxygen as the oxidant and steam as a conveyor at least one under characterized in that the water vapor content of the feed gas mixture is 5 to 25% by volume and the molar ratio V of molecular oxygen contained in the feed gas mixture to the at least one saturated gas present in the feed gas mixture Hydrocarbon precursor compound is 1.5: 1 to 2.5: 1. Method according to claim 1, characterized in that that the water vapor content of the feed gas mixture 10 to 20 Vol .-% is. Method according to claim 1 or 2, characterized V is 1.75: 1 to 2.25: 1. Method according to one of claims 1 to 3, characterized that air is used as the oxygen source. Method according to one of claims 1 to 4, characterized that 0.65 ≤ R ≤ 0.85 is satisfied. Method according to one of claims 1 to 4, characterized that 0.69 ≤ R ≤ 0.74 is satisfied. Method according to one of claims 1 to 4, characterized that 0.71 ≤ R ≤ 0.73 is satisfied. Method according to one of claims 1 to 4, characterized that R = 0.72. Method according to one of claims 1 to 8, characterized that the X-ray diffractogram contains even more diffraction reflections whose vertices at the following diffraction angles are: 9.0 ± 0.4 ° (l), 6.7 ± 0.4 ° (o) and 7.9 ± 0.4 ° (p). Method according to one of claims 1 to 9, characterized that the X-ray diffractogram still contains a diffraction reflex q, whose vertex at the diffraction angle is 45.2 ± 0.4 °. Method according to one of claims 1 to 10, characterized in that the X-ray diffraction pattern contains even more diffraction reflections whose vertices at the following diffraction angles lie: 29.2 ± 0.4 ° (m), 35.4 ± 0.4 ° (n). Method according to one of Claims 1 to 11, characterized in that the X-ray diffractogram contains diffraction reflections h, i, k, l, m, n, o, p and q which have the following relative intensities in the same intensity scale: H: 100 i: 5 to 95, 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. Method according to one of claims 1 to 12, characterized in that the specific surface area of the active multimetal oxide composition is 10 to 40 m ² / g. Method according to one of claims 1 to 14, characterized that the X-ray diffractogram has no diffraction reflex with the vertex position 2Θ = 50.0 ± 0.3 °. Method according to one of claims 1 to 14, characterized in that the active Multimetalloxidmasse such a stoichiometry 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 group consisting of Nb, Ti, W, Ta and Ce; M ³ = at least one of the elements of the group include Pb, Ni, Co, Bi, Fe, Mn, 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 represented by the valency and frequency of elements other than oxygen in (I ) is determined. Method according to claim 15, characterized in that that d> 0. Method according to claim 15, characterized in that that d is 0.00005 to 0.5. Method according to one of claims 1 to 17, characterized the catalyst bed contains coated catalysts. Method according to one of claims 1 to 18, characterized that it is carried out at reaction temperatures of 200 to 550 ° C. Method according to one of claims 1 to 19, characterized that it is carried out at a reaction pressure of 1 to 10 bar. Method according to one of claims 1 to 20, characterized that the conversion of the hydrocarbon precursor compound at a single Passage through the catalyst bed is 30 to 60 mol%. Method according to one of claims 1 to 21, characterized that the loading of the catalyst bed with propane 10 to 1000 Nl / l / h is.