EP0931048A1

EP0931048A1 - Process for producing a catalytically active multimetal oxide material

Info

Publication number: EP0931048A1
Application number: EP97942001A
Authority: EP
Inventors: Heiko Arnold; Friedrich-Georg Martin; Hermann Petersen
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1996-09-19
Filing date: 1997-09-09
Publication date: 1999-07-28
Also published as: DE19638249A1; AU4383597A; ID18317A; JP2001500427A; WO1998012167A1

Abstract

In a process for producing multimetal oxide materials which contain tungsten and/or molybdenum, sulphur, phosphorus, arsenic, boron, silicium and/or germanium, vanadium and/or niobium as well as antimony and which are suitable as catalysts for the gas-phase catalytic oxidative conversion of methacrolein into methacrylic acid, sources which at least partially contain ammonium ions are used, and calcination is carried out in a calcination atmosphere largely devoid of NH3.

Description

Process for the production of a catalytically active multimetal oxide mass

description

The present invention relates to a process for producing a catalytically active multimetal oxide composition of the general formula I xa ¹ xb ² x ³ cxd ⁴ xe ⁵ sbf on (i;

in which the variables have the following meaning:

X ¹ tungsten and / or molybdenum,

X ² S, P, As, B, Si and / or Ge,

X ³ V and / or Nb,

X ⁴ Cu, Ag, Zn, Cd, Fe, Ni, Co, Ru, Rh, Pd, Bi and / or alkaline earth, X ⁵ alkali, NH ⁺ ₄ , Tl and / or Te a 12 b 0.01 to 10, c 0.2 to 6, d 0 to 10, e 0 to 10, f 0.1 to 10 and n a number which is determined by the valency and frequency of the elements in I other than oxygen,

in which an intimate, preferably finely divided, dry mixture is produced from sources of their elemental constituents containing at least partial ammonium ions and this is calcined at temperatures of 150 ° C. to 450 ° C. in a calcining atmosphere containing molecular oxygen.

In addition, the present invention relates to the multimetal oxide compositions obtainable using the process according to the invention and to their use as catalysts for the gas-phase catalytic oxidative production of methacrylic acid from methacrolein.

Catalytically active multimetal oxide compositions of the general formula I and their use as catalysts for the gas-phase catalytic oxidative production of methacrylic acid from methacrolein are known (cf., for example, DE-A 43 29 907). They are usually produced by producing an intimate, preferably finely divided, dry mixture from sources of their elemental constituents and calcining them at temperatures of 150 ° C. to 450 ° C.

A large number of sources which are particularly suitable for the preparation of catalytically active multimetal oxide compositions I are those starting compounds which contain ammonium ions. Preferred sources of molybdenum are, for example, the ammonium salt of molybdic acid and the ammonium salt of

Phosphormolybdic acid. A favorable source of vanadium is ammonium vanadate and advantageous sources of phosphorus or sulfur form the di-ammonium phosphate or ammonium sulfate. According to EP-B 442 517, it is also very generally advantageous to use compounds such as ammonium carbonate, ammonium hydrogen carbonate, ammonium sulfate and ammonium hydrogen sulfate in the production of multimetal oxide compositions of the general formula I.

As a direct consequence of the use of sources containing ammonium ions for the production of multimetal oxide compositions of the general formula I, NH _{3 is} released during the calcination of the corresponding catalyst precursor stage. This means that the calcination takes place in a calcination atmosphere containing ammonia. This applies in particular to the large-scale production of multimetal oxide compositions of the general formula I if no special measures are taken in the course of the calcination, since an increased absolute amount of H _{3 is of course} released in the course of the calcination of a large amount of catalyst precursors.

According to the teaching of DE-26 10 249 C2 (for example page 3, lines 35 to 38) and EP-B 113 156 (for example page 3, lines 23 to 28), a content of NH ₃ in the calcination atmosphere has an effect within the scope of Production of at least one element X ¹ and at least one element X ² and antimony-containing catalytically active multimetal oxide compositions on the resulting catalyst activity (with respect to the catalytic gas phase oxidation of methacrolein to methacrylic acid) advantageously. According to our own investigations, the above does not apply to multimetal oxide compositions of the general formula I which additionally contain the element V and / or niobium.

It was therefore an object of the present invention to provide an improved process for the preparation of multi-, suitable for the catalytic gas phase oxidation of methacrolein to methacrylic acid. to provide metal oxide compositions of the general formula I.

Accordingly, a process for the preparation of a catalytically active multimetal oxide composition of the general formula I, in which one produces the most intimate, preferably finely divided, dry mixture of at least partially sources of elemental constituents containing ammonium ions, and this at temperatures of 150 ° C. to 450 ° C. in one calcined molecular oxygen-containing calcination atmosphere, which is characterized in that the calcination takes place in such a calcination atmosphere, the NH content of which during the entire calcination period <. 0.75 vol .-% and their molecular 0 ₂ content during the entire calcination period> _. 5 vol .-% is.

The calcination is preferably carried out in such a calcination atmosphere, the NH ₃ content of which during the entire calcination period is <0.5, advantageously <.0.25, with particular advantage £ 0.1 and with very particular advantage <.0.05 vol. -%. According to the invention, the content of molecular 0 _{2 in} the calcination atmosphere is preferably> 5 to <25 vol. The residual amount of the calcination atmosphere preferably consists of inert gases such as N ₂ or noble gases. The duration of the calculation usually extends to a few hours.

The process according to the invention proves to be particularly advantageous for the production of those multimetal oxide compositions of the general formula I for which the variables have the following meaning:

X ¹ tungsten and / or molybdenum,

X ² S, P, As and / or Si,

X ³ V and / or Nb,,

X ⁴ Cu, Ag, Zn, Fe, Ni, Co, Rh and / or Bi, X ⁵ alkali, l, Te and / or NH ⁺ ₄ , a 12 b 0.2 to 3, c 0.2 to 3, d 0 to 2, e 0 to 3, f 0.2 to 3 and n a number which is determined by the valency and frequency of the elements in I other than oxygen.

Even in the case of these multimetal oxide compositions I, the process according to the invention requires increased catalytic activity with regard to the gas-phase catalytically active conversion of methane acrolein to methacrylic acid. In accordance with the teaching of DE-A 43 29 907, it is advantageous according to the invention if senarmontite is used as the source for at least part of the Sb contained in the multimetal oxide materials I.

Senarmontite is preferably used as the source of antimony for at least 25% and particularly preferably for at least 50% of the Sb contained in the multimetal oxide compositions I. Of course, the process according to the invention also includes the production of such multimetal oxide compositions, for the production of which at least 80% of the Sb contained is added as senarmontite. However, it is preferred that 1 to 10% of the total Sb contained in the multimetal oxide compositions I according to the invention is in an amorphous environment. The senarmontite to be used for producing the multimetal oxide compositions I according to the invention is advantageously used in finely divided form. The large diameters are expediently> 0 to <50 μm. However, they can also be 0.1 to 25 or 0.5 to 5 μm.

Other sources of the constituents of the multimetal oxide compositions of the general formula I are oxides or compounds which can be converted into oxides by heating in the presence of oxygen. In addition to the oxides, halides, nitrates, formates, oxalates, acetates, carbonates or hydroxides are therefore particularly suitable as starting compounds. Possible starting compounds of Mo and V are also their tungstates and vanadates or the acids derived from them. Regarding the element Sb, in addition to senarmontite as an element source, valentinite and / or simple salts of Sb such as antimony nitrate are also considered.

The intimate mixing of the starting compounds can take place in dry or in wet form. If it is carried out in dry form, the starting compounds are expediently used as finely divided powders and, for example, after mixing, are shaped (for example tableted) to form catalyst bodies which are then subjected to the calcination according to the invention. However, the calcination according to the invention can also take place before the shaping. However, the intimate mixing is preferably carried out in wet form. The starting compounds are usually mixed together in the form of a solution and / or suspension. It is advantageous if the senarmontite used as the starting compound does not dissolve if possible. This can be influenced, for example, by first mixing the sources of the other elemental constituents and stirring in the senarmontite only a short time before the liquid mixed mass dries. After the mixing process is complete, the fluid mass is dried and calcined according to the invention after drying (before or after shaping). Drying is preferably carried out by spray drying. The resulting powder is often too fine for direct shaping, which is why it is often either by means of solid compaction and subsequent grinding to a defined one

Particle size coarsened or with the addition of a liquid, usually water, processed into a plasticine and shaped as such and then calcined according to the invention. If the intimate mixing takes place in wet form, an elevated temperature can also be used. Furthermore, the dissolving and / or suspending can be accompanied by an addition of acids or bases.

_Z weckmäßigerweise the multi according to the invention obtainable are metal oxides of the general formula I einge- as unsupported catalysts sets, that is, which consist as such catalyst body exclusively from the inventive composition. Hollow cylinders with an outer diameter and a length of 4 to 10 mm and a wall thickness of 1 to 3 mm form the preferred catalyst geometry.

An aqueous mixture of the starting components can additionally be used as auxiliary in amounts of 1 to 20% by weight, based on the calcined catalyst mass, of organic compounds such as cyclic compounds containing nitrogen, e.g. Pyridine, but also contain carboxylic acids or alcohols. Drying from wet, usually aqueous, mixture is usually carried out at 60 to 180 ° C. Methods known per se, such as tableting, extrusion or extrusion molding, can be used to form the catalyst mass or its non-calcined precursor mass, whereby lubricants such as graphite 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. However, the compositions according to the invention can also be used in the form of supported or coated catalysts, i.e. applied to a preformed, essentially inert, material for the production of methacrylic acid by gas phase oxidation of methacrolein, the application to the essentially inert material e.g. in the form of the aqueous starting solution or suspension, combined with subsequent drying and calcination according to the invention or as pulverized mass which has already been calcined according to the invention in combination with a binder.

The multimetal oxide compositions I obtainable according to the invention can of course also be used in powder form as catalysts. The multimetal oxide compositions I obtainable according to the invention are particularly suitable as catalysts for the catalytic gas phase oxidation of methacrolein to methacrylic acid, the methacrylic acid formation taking place with increased activity.

The catalytic gas phase oxidation of methacrolein to methacrylic acid using the catalysts obtainable according to the invention is carried out in a manner known per se, i.a. shown in DE-A 40 22 212, way. The same applies to the separation of methacrylic acid from the product gas stream. The

Oxidizing agent Oxygen can be used in the form of air, for example, but also in pure form. Because of the high heat of reaction, the reactants are preferably diluted with inert gas such as N, CO ₂ saturated hydrocarbons and / or with water vapor. With a methacrolein: oxygen: water vapor: inert gas ratio of 1: (1 to 3): (2 to 20): (3 to 30), particularly preferably 1: (1 to 3): (3 to 10): (7 to 18) worked. The methacrolein used can have been obtained in various ways, for example by gas phase oxidation of isobutylene, tert. -Butanol or methyl ether of tert. Butanol. It is advantageous to use methacrolein, which can be obtained by condensing propanal with formaldehyde in the presence of secondary amines and acids in the liquid phase in accordance with the processes described in DE-PS 875 114 or in DE-AS 28 55 514. The gas phase oxidation can be carried out both in fluidized bed reactors and in fixed bed reactors. It is preferably carried out in tube bundle reactors in the tubes of which the catalyst mass, preferably in the form of cylindrically shaped particles, is fixedly arranged. The reaction temperature is generally 250 to 350 ° C, the reaction pressure is usually in the range of 1 to 3 bar and the total space load is preferably 800 to 1800 Nl / l / h. Under these conditions, the methacrolein conversion in a single reactor pass is usually 50 to 80 mol%. The boundary conditions mentioned are preferably coordinated with one another within the framework of the grid mentioned in such a way that a single passage through the reactor results in a methacrolein conversion of 60 to 70 mol%. The increased activity of methacrylic acid formation when using the masses I obtainable according to the invention as catalysts also exists at methacrolein room loads of more than 60 Nl / l / h. Interestingly, the masses I obtainable according to the invention retain their advantageous properties essentially unchanged over an increased operating time.

In the gas phase oxidation described, however, it is usually not pure methacrylic acid that is obtained, but rather a product mixture from which the methacrylic acid is subsequently separated must become. This can be carried out in a manner known per se, for example by washing the reaction gases with water after indirect and / or direct cooling at from 40 to 80 ° C., an aqueous methacrylic acid solution being obtained from which the methacrylic acid is usually extracted by an organic Solvent removed and separated from the same by distillation.

In addition to the gas-phase catalytic oxidation of methacrolein to methacrylic acid, the compositions according to the invention are also capable of gas-phase catalytic oxidation of other organic compounds such as, in particular, other alkanes, alkanols, alkanals, alkenes and alkanols (for example propylene, acrolein, tert. Preferably having 3 to 6 carbon atoms). -Butanol, methyl ether of tert-butanol, isobutene, isobutane or isobutyraldehyde) to olefinically unsaturated aldehydes and / or carboxylic acids, as well as the corresponding nitriles (ammoxidation, especially of propene to acrylonitrile and of isobutene or . ter. -Butanol to methacrylic - nitrile). The production of acrylic acid, acrolein and methacrolein may be mentioned by way of example. However, they are also suitable for the oxidative dehydrogenation of organic compounds.

It is essential according to the invention that the low ammonia content of the calcination atmosphere required according to the invention can hardly be achieved in the predominantly used calcination in the tray furnace through which air flows, especially not when larger amounts of catalyst precursors have to be calcined.

The calcination according to the invention is therefore preferably carried out on a belt calciner. The calcination material rests in thin layers on endless conveyor belts that run horizontally in the calcination channel. The belts generally consist of sieve belts (close-meshed wire nets), which allow large amounts of hot calcination gases (e.g. hot fresh air) to be passed through the calcination material (suction and / or pressure). Released ammonia is thus led away directly from the calcination material, which results in a calcination atmosphere essentially free of NH ₃ . The hot calcination gases can be blown vertically from below as well as obliquely onto the material being passed.

In addition to the amount of molecular oxygen required according to the invention, the hot calcination gas normally contains inert gases such as N ₂ and / or noble gases as a residual amount. Hot air is used as the hot calcination gas in a particularly simple manner. The calcination according to the invention is advantageously designed in several stages.

For example, a two-step method of calcination is favorable. The first calcination stage is carried out at a temperature of 150 to 300 ° C, preferably 190 to 280 ° C. The calcination temperature in the second calcination stage is then 350 to 450 ° C, preferably 370 to 400 ° C. In both calcination stages, the calcination atmosphere comprises at least 5% by volume of 0. The 0 ₂ content is usually 25% by volume in both calcination stages. As a rule, the volatile NH ₃ has already escaped after the first calculation stage. The developing ammonia must be removed according to the invention in such a way that the calcination atmosphere is particularly preferred in both stages <0.75% by volume, better <0.5% by volume, preferably <0.25% by volume

Is <0.1% by volume and very particularly preferably <0.005% by volume. The calcination time in both stages normally extends to a few hours.

The calcination time in the first calcination step advantageously extends from 0.5 to 1.5 h and the calcination time in the second calcination step advantageously extends from 1 h to 10 h, usually 1 h to 5 h H. With very particular advantage, the first calcination step is, according to the invention, first of all calcining at about 190 ° C. for about 20 minutes. The mixture is then calcined at 220 ° C. for about 50 minutes and finally again at 270 ° C. for about 50 minutes. The second calcination stage is carried out with particular advantage at about 370 to 400 ° C. for about 3 hours. The above applies in particular to the multimetal oxide according to Example M6 from DE-A 43 29 907.

In conclusion, it should be noted that an increased content of NH _{3 in} the calcination atmosphere during the calcination to produce catalytically active multimetal oxides I leads to an irreversible reduction in the activity thereof.

Examples

a) Preparation of a catalyst precursor

530 g of ammonium heptamolybdate tetrahydrate, 17.5 g of ammonium metavanadate, 48.9 g of cesium nitrate and 81.6 g of 45% by weight were added to 600 g of water at 50 ° C. -% ortho-phosphoric acid, 3.9 g 35 wt. -% aqueous ammonium sulfate solution and 36.5 g of antimony trioxide

(99% by weight senarmontite and 1% by weight valentinite, average grain size diameter: 0.5 μm). Then was this aqueous mixture was heated to 95 ° C., a solution of 51.5 g of aqueous nitric copper solution (15% by weight of Cu) was added and the mixture was evaporated to dryness at the temperature mentioned. Hollow cylinders with an outer diameter of 7 mm, a length of 6 mm and a hollow circle diameter of 3 mm were then formed from the mass obtained in this way and calcined as described below. The resulting multimetal oxide stoichiometry was:

Mθ ₁₂ Pι, ₅ Vo, 6CSι, oCUo, 5SbιS ₀ , θ -

b) Calcination of the catalyst precursor

A steel tube with an inside diameter of 16 cm, which was heated electrically from outside to 290 ° C., was used as the calcination apparatus. A support grid extending over the cross section of the pipe was installed in the pipe, to which the catalyst precursor from a) was applied at a bed height of only 5 cm. During the calcination, the catalyst precursor bed was flowed through with 10 Nm ³ / h (Nm ³ = standard cubic meter, ie based on 25 ° C. and 1 atm.) Of hot calcination gas (T = 290 ° C.). As a result of the low bed height and the high exposure to calcination gas, the calcination atmosphere essentially corresponded to the composition of the calcination gas. The calcination time was 3 hours.

The following calcination gas compositions were used:

100 vol% air,

99.43 vol% air, 0.57 vol% NH ₃ 98.9 vol% air, 1.1 vol% NH ₃ 98.43 vol% air, 1.57 vol% NH ₃ 98, 37 vol% air, 1.63 vol% NH ₃ 98 vol% air, 2 vol% NH ₃

Catalysts A, B, C, D, E and F were obtained in a corresponding manner.

C) Testing the catalyst activity

The calcined hollow cylinders from c) were pulverized (arithmetically average grain diameter: 1 to 2 mm) and in a tubular reactor (10 mm inner diameter, 100 g catalyst bed, salt bath temperature: 290 ° C.) with a gas mixture of the composition

5 vol.% Methacolein, 9 vol. Oxygen, 25 vol.% Water vapor and 61 vol.% Nitrogen

charged with an average residence time of 3 seconds and a methacrolein loading of 0.11 g / g / h (the figures in volume refer to Nl). The reaction gases obtained were cooled to 40 ° C and successively with water and 50 wt. - Washed aqueous acetic acid. The washing liquids were then analyzed by gas chromatography and polarography and the methacrolein conversion was calculated from the analysis results.

The following table shows the methacrolein conversions achieved in a single pass, depending on the catalysts A, B, C, D, E and F used. A high methacrolein conversion ([number of moles of converted methacrolein / number of moles of methacrolein used] × 100%) shows a high catalyst activity. The selectivity of methacrylic acid formation ([number of moles of methacrolein converted to methacrylic acid / number of moles of methacrolein total converted 100%) was 88% in all cases.

table

Used catalyst sales

A 79

B 72

C 62

D 62

E 62

F 63

The results obtained show the harmful effect of an NH ₃ legume during the calcination. When using catalysts of appropriate composition and manufacture which have been calcined in a conventional manner in an air-flow tray oven, the conversion achieved as described is below 70%.

Claims

claims

1. Process for the preparation of a catalytically active multimetal oxide composition of the general formula I

X ¹ X ² X ³ X ⁴ X ⁵ Sb 0 (i), from cdefn

in which the variables have the following meaning:

X ¹ tungsten and / or molybdenum, X ² S, P, As, B, Si and / or Ge, χ3 V and / or Nb, χ ⁴ Cu, Ag, Zn, Cd, Fe, Ni, Co, Ru, Rh , Pd, Bi and / or alkaline earth, X ⁵ alkali, NH ⁺ ₄ , Tl and / or Te a 12 b 0.01 to 10, c 0.2 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 in I other than oxygen,

in which an intimate dry mixture is prepared from sources of elemental constituents containing at least partial ammonium ions and this is calcined at temperatures of 150 ° C to 450 ° C in a molecular atmosphere containing molecular oxygen, characterized in that the content of NH in the calcining atmosphere during the entire calcining period ₃ <0.75 vol .-% and molecular oxygen> 5 vol .-%.

2. The method according to claim 1, characterized in that the

Variables of the general formula I have the following meaning:

X ¹ tungsten and / or molybdenum,

X ² S, P, As and / or Si, X ³ V and / or Nb,,

X ⁴ Cu, Ag, Zn, Fe, Ni, Co, Rh and / or Bi,

X ⁵ alkali, l, Te and / or NH + ₄ , a 12 b 0.2 to 3, c 0.2 to 3, d 0 to 2, e 0 to 3, f 0, 2 to 3 and n is a number which is determined by the valency and frequency of the elements in I other than oxygen.

3. The method according to claim 1 or 2, characterized in that the NH content of the calcination atmosphere is <0.25% by volume.

4. The method according to claim 1 or 2, characterized in that the calcination is carried out in two successive stages, the temperature of the first calcination stage being 150 to 300 ° C and the temperature of the second calcination stage being 350 to 450 ° C .

5. The method according to any one of claims 1 to 4, characterized in that the calcination is carried out on a belt calciner.

6. multimetal oxide compositions obtainable by a process according to any one of claims 1 to 5.

7. The process of catalytic gas phase oxidation of methacrolein to methacrylic acid, characterized in that a multimetal oxide composition according to claim 6 is used as the catalyst.

8. Use of multimetal oxide compositions according to claim 6 as catalysts in the catalytic gas phase oxidation of methacrolein to methacrylic acid.