DE4329907A1 - Multimetal oxide compositions containing at least the elements antimony and phosphorus and additionally at least one of the two elements Mo, W - Google Patents

Abstract

Multimetal oxide compositions containing at least the elements antimony and phosphorus and additionally at least one of the two elements Mo, W, where part of the antimony is present as senarmontite. These compositions are suitable as catalysts for preparing methacrylic acid by catalytic gas-phase oxidation of methacrolein.

Description

The present invention relates to multimetal oxide compositions, the we at least the elements antimony and phosphorus and additionally we at least one of the two elements Mo, W contained.

Moreover, the present invention relates to methods for Her Position of these masses, as well as their use for gas phase gas lytic oxidative production of methacrylic acid from meth acrolein.

Multimetal oxide materials containing at least the elements antimony and Phosphorus and additionally at least one of the two elements Mo, W contain, are often described above. It is also all common previously known that such Multimetalloxidmassen Ver use as catalysts for the gas-phase catalytic oxidative Preparation of 3 to 6 C-atoms having α, β-monoethylenic unsaturated carboxylic acids and their reduced appearance form, the corresponding aldehydes are suitable.

Usually, these multimetal oxide materials are herge provides that one of suitable sources in a conventional manner their constituents as intimate as possible, preferably fine part, dry mixture and this produces a calcination subjects. It is essential, as is well known, only that it the sources are either already oxides or around such compounds obtained by heating, optionally in Presence of oxygen, are convertible into oxides. In addition to the Oxides are therefore mainly used as starting compounds Halides, nitrates, formates, oxalates, acetates, carbonates or Hydroxides recommended (see, for example, DE-A 40 22 212), wherein the intimate Mixing can be done dry or wet. A disadvantage of this However, prior art multimetal oxide catalysts are that in their use for gas-phase catalytically oxidative Her position of methacrylic acid from methacrolein at given Me thacrolein conversion does not affect the selectivity of methacrylic acid formation to satisfy.

EP-B 180 997 recommends the preparation of multimetal oxide at least the elements antimony, phosphorus and molyb As a Sb source of finely divided antimony trioxide with an average particle size of not more than 0.2 microns too  use. Such prepared Multimetalloxidmassen are suitable itself according to the teaching of EP-B 180 997 as catalysts for gas phase catalytically oxidative production of methacrylic acid Methacrolein, with increased selectivity of Methacrylsäurebil dung. A disadvantage of the multimetal thus produced oxide masses, however, is that even when used for gas phase from the point of view of oxidative production of methacrylic acid Methacrolein at a given Methacroleinumsatz the selectivity can not fully satisfy the methacrylic acid formation.

The object of the present invention was therefore multimetal oxide To provide mass that at least the elements An timon and phosphorus and additionally at least one of them Elements Mo, W included, which when used for gas phase catalytic oxidative production of methacrylic acid from methacrolein at a given Methacroleinumsatz increased selectivity of Methacrylsäurebildung condition.

Accordingly, multimetal oxide compositions containing at least the ele Antimony and phosphorus and additionally at least one of contained two elements Mo, W, found characterized that they are at least part of the total in ih NEN existing amount of Sb in the form of three-dimensional expand contain crystalline areas, the crystal structure of the Have Senarmontit. Senarmontite is one of the various possible crystalline forms of antimony trioxide. The presence of this crystal modification, its structure well known (Swanson, Fuyat, Natl. Bur. Stand. (U.S.), Circ. 539, 3 31 (1954)), z. B. prove that the X-ray diffraction of the multimetal oxide composition the diffraction pattern of senarmontite (fingerprint, eg the above literature quote). From the intensity of the diffraction lines can be to detect the quantity of available Senarmontite and the Width of the diffraction lines gives the average dimensions the contained Senarmontitkristallite again. Access to The latter information is easier to do if you use X-ray apply diffraction and transmission electron microscopy together det.

Played in the form of the wavelength used X-ray independent lattice plane distances d [Å] are the eight most intense diffraction lines of Senarmontite:

there] Intensity [%] 6.44 12 3.22 100 2.79 40 2.56 11 1.97 42 1.68 35 1.61 11 1.28 12

The intensity data are relative reference values and on the highest intensity diffraction line. The associated Diffraction angles R result from the Bragg relationship:

sinR = λ / 2d,

where λ is the wavelength of Röntgenstrahlung used for X-ray diffraction radiation. In general, this will be the Cu-K _α radiation, with λ = 1.5406 Å.

Preferably, at least in the compositions of the invention 25%, more preferably at least 50% of the contained Sb as Senarmontite ago. Of course, the present invention includes also those multimetal oxide materials in which at least 80% or the total amount of Sb present as Senarmontit is present. However, it is preferred that 1 to 10% of the total existing Sb present in an amorphous environment.

Furthermore, it is advantageous if the multi Metal oxide of subsequent stoichiometry I suffice

X¹ _a X² _b X³ _c X⁴ _d X⁵ _e Sb _f O _n (I),

in which the variables have the following meaning:

X¹ tungsten and / or molybdenum,
X²S, P, As, B, Si and / or Ge,
X³ V, Nb, Ta and or Re,
X⁴ Cu, Ag, Zn, Cd, Fe, Ni, Co, Ru, Rh, Pd, Bi and / or alkaline earth,
X⁵ Alkali, NH₄⁺, Tl and / or Te,
a 12,
b 0.01 to 10,
c 0.01 to 6,
d 0 to 10,
e 0 to 10,
f 0.1 to 10 and
n is a number which is determined by the valency and frequency of the elements other than oxygen in I.

Among these masses, those are preferred for which the variables have the following meaning:

X¹ tungsten and / or molybdenum,
X² S, P, As, and / or Si,
X³ V, Nb, and or Re,
X⁴ Cu, Ag, Zn, Fe, Ni, Co, Rh, and / or Bi,
X⁵ alkali and / or NH₄⁺, Tl Te,
a 12,
b 0.2 to 3,
c 0.2 to 3,
d 0 to 2,
e 0 to 3 and
f 0.2 to 3.

However, masses of the general are very particularly advantageous Formula II

M₁₂P₀V _p X⁶ _g X⁷ _h X⁸ _i Sb _j Re _k S _l O _m (II),

in which the variables have the following meaning:

X⁶ potassium, rubidium and / or cesium, preferably cesium,
X⁷ copper and / or silver,
X⁸ cerium, boron, zirconium, manganese and / or bismuth,
o 0.5 to 3.0
p is 0.01 to 3.0, preferably 0.65 to 1.0, especially before 0, 8,
g is 0.2 to 3.0, preferably 1.1 to 1.5, particularly preferably 1.2,
h 0.01 to 2.0,
i 0 to 2.0,
j 0.01 to 2.0,
k is 0 to 1.0, preferably <0 and particularly preferably 0.04 to 1,
from 0.001 to 0.5, preferably from 0.03 to 0.5 and
m is a number determined by the valence and frequency of the elements other than oxygen in II.

An essential influence of the expansion of the fiction in the according to multimetal oxide compositions contained Senarmontitbereiche the quality of the multimetal oxide compositions according to the invention could can not be determined. With a decrease of the stretch goes a slight increase in the selectivity of methacrylic acid formation associated. Conveniently, the largest diameter <0 to  50 μm. However, you can also be 0.1 to 25 or 0.5 to 5 microns be carry.

The compositions of the invention are in a conventional manner he hältlich. In general, they are made by that one of well-known sources of their elementa ren constituents as intimate as possible, preferably fine dry mixture and this produces a calcination wherein the calcination before or after shaping to Catalyst bodies of certain geometry can be done. Essential is, as is well known, only that it ent is not already dealing with oxides or such compounds that by heating, optionally in the presence of oxygen, in Oxides are convertible. Besides the oxides come therefore as Starting compounds especially halides, nitrates, formates, Oxalates, acetates, carbonates or hydroxides into consideration. suitable Starting compounds of Mo and V are also their tungstates and Vanadates or the acids derived from these. According to the invention one is already ent of Senarmontit ent. with respect to the element Sb speaking fineness as an element source, given if combined with Valentinit (another crystal modification of Sb₂O₃) and / or simple salts of Sb, such as antimony nitrate.

The intimate mixing of the starting compounds can be carried out in dry or in wet form. If it takes place in dry form, who the starting compounds expediently as finely divided Powder used and z. B. after mixing into catalyst bodies desired geometry shaped (for example, tableted), then the Be subjected to calcination. But the calcination can also done before shaping. Preferably, the intimate Vermi but in wet form. Usually the output compounds in the form of a solution and / or suspension with mixed together. According to the invention, it should be noted that the amount of Senarmontite used during wet mixing gangs is not completely resolved. This can be z. B. thereby be influenced that first the sources of the remaining ele mentary constituents mix and the Senarmontit only a short time stirred in before drying the liquid mixture. After Ab  conclusion of the mixing process, the fluid mass is dried and calcined after drying (before or after shaping). Preferably drying takes place by spray drying. The resulting Powder is often too fine for direct forming, which is why it often with the addition of a liquid, usually water, too processed a plasticine and molded as such and then is calcined.

For example, the compositions according to the invention can be characterized be provided that as suitable called starting compounds the constituent elemental constituents, if appropriate at elevated temperature and with the addition of acids or bases, in aqueous medium by dissolving and / or suspending finely ver divides, mixes and produces said dry matter. The calci Drying is usually carried out at temperatures from 180 to 480, preferably 350 to 450 ° C in the air stream or in inert atmosphere, z. B. N₂ or CO₂.

It is noteworthy that the proportion of Sb, that before calcination the dry matter in it is present as Senarmontit, while the calcination as such is substantially preserved, while, for example, other common sources of the Sb like Valentinit or usual Sb salts like antimony nitrate etc. late during the course of calcination, which is usually a few hours who claim to lose their crystalline identity Dissolve, so to speak, in the multimetal oxide and after completion of the Calcination of the Sb introduced into the multimetal oxide masses in an amorphous environment.

Conveniently, the compositions of the invention as a full used catalysts, d. H. as such catalyst bodies, the consist exclusively of the composition of the invention. there form hollow cylinder with an outer diameter and a length from 4 to 10 mm and a wall thickness of 1 to 3 mm before called catalyst geometry. The calcination can in several Temperature levels and / or in different atmospheres Runaway be led. So z. B. in a first stage at 200 to 260 ° C. in air, in a second stage at 420 to 460 ° C in nitrogen and in a third stage at 350 to 410 ° C again in air be calcined. Contain the compositions of the invention Rhe It is preferable to use rhenium (VII) oxide as a source thereof used. Molybdenum is preferably used as the ammonium salt of Mo lybdenum or phosphomolybdic acid, boron z. B. as boric acid, Vana usually as ammonium vanadate or vanadium oxalate, Phosphorus with advantage as ortho-phosphoric acid or di-ammonium Phosphate, sulfur as ammonium sulfate and the rest of Sb ver different metals normally as nitrates, oxides, hydroxides,  Carbonates, chlorides, formates, oxalates, acetates or hydroxides used.

An aqueous mixture of the starting components can be used as an aid additionally in amounts of 1 to 20 wt .-%, based on the calci nierte catalyst mass, organic compounds such as nitrogen containing cyclic compounds, e.g. As pyridine, but also Contain carboxylic acids or alcohols. Dry from wet Mixture is usually carried out at 60 to 180 ° C. To form the Catalyst mass or its uncalcined precursor composition can be known methods such as tabletting, extrusion or extruding, lubricants such as Gra phit or stearic acid, as well as molding aids and reinforcing agents Such as microfibers made of glass, asbestos, silicon carbide or potassium titanate can be added. The compositions of the invention but can also in the form of carrier or shell catalyst ren, d. H. to a preformed, substantially inert, material applied, for the production of methacrylic acid by Gasphaseno xidation be applied by methacrolein, wherein the application on the substantially inert material z. B. in the form of aqueous Starting solution or suspension, connected with subsequent Drying and calcination or as already calcined pulveri Mass in combination with a binder can be done. Of course, the compositions of the invention can also in Powder form can be used as catalysts.

The multimetal oxide compositions according to the invention are suitable in particular dere as catalysts for the catalytic gas phase oxidation from methacrolein to methacrylic acid, the methacrylic acid bil tion with increased selectivity.

Catalytic gas phase oxidation of methacrolein to meth acrylic acid using the catalysts of the invention takes place in known per se, u. a. in DE-A 40 22 212 Darge put, way. Likewise applies to the separation of meth acrylic acid from the product gas stream. The oxidizing agent acid fabric can z. B. in the form of air, but also in a pure form be set. Due to the high heat of reaction, the Reak tion partner preferably with inert gas such as N₂, CO₂, saturated Hydrocarbons and / or diluted with water vapor. virtue In the case of a methacrolein, for example, oxygen becomes: water vapor: inert gas Ratio of 1: (1 to 3): (2 to 20): (3 to 30), especially be preferably from 1: (1 to 3): (3 to 10): (7 to 18) worked. The used methacrolein can be obtained in various ways been, z. By gas phase oxidation of isobutylene, tert. Butanol or methyl ether of tert-butanol. With advantage Methacrolein used by condensation of propanol with  Formaldehyde in the presence of secondary amines and acids in liquid phase according to the in DE-PS 8 75 114 or DE-AS 28 55 514 described method is available. The gas phase xidation can be used in fluidized bed reactors as well as in solid Be performed bed reactors. Preferably, it is in tube bundle reactors carried out in their tubes the catalyst mass, preferably in the form of cylindrically shaped particles, is fixed. The reaction temperature is usually 250 to 350 ° C, the reaction pressure is usually in the range from 1 to 3 bar and the total space load is preferably 800 to 1800 Nl / l / h. Under these conditions lies the Methacro turnover in one reactor usually at 50 to 80 mol%. Preferably, the mentioned boundary conditions within the framework of said grid coordinated so that with simple passage through the reactor a Methacroleinumsatz from 60 to 70 mol% results. The increased selectivity of Me thacrylic acid formation when using the compositions of the invention as Catalysts also exist in methacrolein space burdens of more than 60 Nl / l / h. Interestingly, keep the invention appropriate masses their properties over an increased service life essentially unchanged at.

However, in the described method, it usually does not pure methacrylic acid, but obtained a product mixture of in which the methacrylic acid must be subsequently separated. This can be done in a conventional manner, for. B. by the Reaction gases after indirect and / or direct cooling at Tem from 40 to 80 ° C with water, wherein an aqueous Methacrylic acid solution is obtained from the methacrylic acid usually by extraction with an organic solution removed medium and separated from selbigem by distillation becomes.

In addition to the gas-phase catalytic oxidation of methacrolein to Methacrylic acid but the compositions of the invention also the gas phase catalytic oxidation of other organic Compounds such as in particular other, preferably 3 to 6 C Atoms, alkanes, alkanols, alkanals, alkenes and alkenes nols (for example propylene, acrolein, tert-butanol, methyl ethers of tert-butanol, isobutene, isobutane or isobutyraldehyde) olefinically unsaturated aldehydes and / or carboxylic acids, as well as the corresponding nitriles (ammoxidation, especially of propene to acrylonitrile and from isobutene or tert-butanol to methacrylic to catalyze nitrile). An example is the production of acrylic acid, acrolein and methacrolein. They are suitable also for the oxidative dehydrogenation of organic compounds.  

Conversion, selectivity and residence time are in this document, unless otherwise stated, defined as follows:

Examples a) Preparation of compositions of the invention M and compositions MV for comparison General manufacturing instructions

• i) In 600 g of water at 50 ° C 530 g Ammoniumheptamolyb tetrahydrate, A g ammonium metavanadate, B g cesiumni C, 45% by weight ortho-phosphoric acid, D g 35 wt .-% aqueous ammonium sulfate solution and E g Stirred in antimony trioxide or antimony nitrate.
• ii) Subsequently, this aqueous mixture was heated to 95 ° C he, a solution of F g of copper (II) nitrate trihydrate to set and evaporated to dryness at the temperature mentioned. From the mass thus obtained were subsequently ßend hollow cylinder with an outer diameter of 7 mm, a length of 6 mm and a hollow circle diameter of 3 mm formed and calcined at 380 ° C for 5 h in an air stream. X-ray diffraction powder images of the resulting moldings using the Cu-K _α radiation exhibited the Cesium salt at 2R = 10.5 °, 21.3 °, 26.2 ° (major maximum) and 30.3 ° diffraction maxima the Phosphormolybdatovana datoheteropolysäure could be assigned.

The numerical sets A, B, C, D, E and F are chosen that in the table waiving the oxygen specification reproduced stoichiometries resulted. The numbers average diameter d (μm) of the finely divided used  Sb₂O₃ and its percentage composition of Senarmontit (St) and Valentinit (V) also show the table.

b) The selectivity S of methacrylic acid formation when applied the masses of a) as gas phase oxidation catalysts

For this comparative overview, the hollow cylinders were made a) pulverized (arithmetic mean grain diameter: 1 to 2 mm) and in tube reactors (10 mm internal diameter, 100 g Catalyst bed, salt bath cooling) at Reaktionsstemperatu in the range 270 to 310 ° C with a gas mixture of Zusam mensetzung

5% by volume methacrolein
9 vol.% Oxygen
25 vol .-% water vapor and
61% by volume of nitrogen

with an average residence time of 3 sec and a Methacroleinbelastung of 0.11 g / g / h fed (the information in% by volume refer to Nl). The salt bath temperature was in all cases adjusted so that a single metha Crude sales of approximately 62% resulted. The obtained Reak gases were cooled to 40 ° C and successively with What washed and 50 wt .-% aqueous acetic acid.

Subsequently, the washing liquids were gas chromatographed analyzed graphically and polarographically and from the Analy results of the selectivity of methacrylic acid formation he expects.

The results also show the table.  

table

The masses M₁ to M₃ in the X-ray diffraction recording all had the fingerprint of the Senarmontitkristallstruktur on (Cu-K _α radiation). In the masses MV1 and MV2, however, no fingerprint of Valentinit was detectable. It is assumed that in both MV1 and MV2 and MV3 the total amount of Sb used is in an amorphous environment.

Claims (7)

1. Multimetal oxide compositions which comprise at least the elements antimony and phosphorus and additionally at least one of the two elements Mo, W, characterized in that they contain at least a portion of the total amount of Sb present in them in the form of three-dimensionally extended crystalline regions which form the Have crystal structure of Senarmontit. 2. Multimetal oxide compositions according to claim 1, which are at least 25% their antimony total content as Senarmontit contained. 3. Multimetal oxide compositions according to claim 1 or 2, which are 1 to 10% their antimony content in amorphous environment present and the Have residual amount of Sb as Senarmontit present. 4. Multimetal oxide compositions according to claim 1 to 3, which follow the stoichiometry I satisfy X¹ _a X² _b X³ _c X⁴ _d X⁵ _e Sb _f O _n (I), in which the variables have the following meaning: X¹ tungsten and / or molybdenum,
X²S, P, As, B, Si and / or Ge,
X³ V, Nb, Ta and or Re,
X⁴ Cu, Ag, Zn, Cd, Fe, Ni, Co, Ru, Rh, Pd, Bi and / or alkaline earth,
X⁵ Alkali, NH₄⁺, Tl and / or Te,
a 12,
b 0.01 to 10,
c 0.01 to 6,
d 0 to 10,
e 0 to 10,
f 0.1 to 10 and
n is a number which is determined by the valency and frequency of the elements other than oxygen in I. 5. Multimetal oxide compositions according to claim 1 to 5, in which the Maximum diameter of the contained Senarmontitphasen in the range 0.5 to 5 microns are. 6. Process for the preparation of methacrylic acid by katalyti gas phase oxidation of methacrolein, characterized thereby characterized in that compositions according to claims 1 to 5 than Catalysts are used. 7. A process for the preparation of compositions according to claims 1 to 3, characterized in that suitable starting connections of the elementary Be constituting the masses parts intimately mixed together, as a Sb-off co-ordinated with Senarmontit, and from that he dry dry mix formed or formed at 180 to Calcined at 480 ° C.