EP2061596A1 - Catalysts from vpo precursors having a defined particle size distribution, production and use thereof - Google Patents

Abstract

Disclosed are a catalyst precursor or catalyst and a method for the production thereof. According to said method, a) a suspension is produced which contains a vanadium, phosphorus, and oxygen-containing precursor (VPO precursor), the ultrasonically dispersed particles of which have an average diameter d<SUB>50, primary particles</SUB> of less than 1.3 µm in an aqueous solution and which are provided in the form of agglomerates having an average diameter d<SUB>50, agglomerates</SUB> of 2 to 20 µm in water, the average diameters of the primary particles and the agglomerates of the VPO precursor being determined by means of laser diffraction according to ISO 13320, b) the suspension is spray dried, and c) if necessary, the catalyst precursor obtained in step b) is transformed into the catalyst by means of a thermal treatment. Also disclosed is the use of said catalyst for gas phase oxidation of hydrocarbons.

Description

 Catalysts from VPO precursors with defined particle size distribution, their preparation and use.

description

The present invention relates to catalyst precursors or catalysts obtainable by spray-drying a suspension containing a vanadium-, phosphorus- and oxygen-containing precursor (VPO precursor). The thus obtained catalyst precursor can optionally be converted into the catalyst by subsequent thermal treatment. The ultrasonically dispersed primary particles of the VPO precursor have an average diameter dso, pnmarpamkei less than 1.3 μm in aqueous solution and are present in water in the form of agglomerates with a mean diameter d 50, agglomerates of from 2 μm to 20 μm. Moreover, the present invention relates to processes for preparing these catalyst precursors or catalysts and to the use of the catalysts for the gas phase oxidation of hydrocarbons. The present invention further relates to a process for the preparation of maleic anhydride by gas phase oxidation of hydrocarbons having at least four carbon atoms in the presence of the catalysts of the invention. Another object of this invention is a VPO precursor whose ultrasonically dispersed primary particles in aqueous solution have a mean diameter dso, pnmarpamkei smaller than 1, 3 microns and in water in the form of agglomerates with a mean diameter dso, agglomerates of 2 microns to 20 microns, wherein the average diameter of the primary particles and the agglomerates of the VPO precursor by laser diffraction according to ISO 13320 are determined.

It is understood that the above-mentioned and below to be explained features of the subject invention can be used not only in the combination given but also in other combinations, without departing from the scope of the invention.

Vanadium-, phosphorus- and oxygen-containing catalysts (VPO catalysts) are used for the catalytic oxidation of suitable hydrocarbons in the gas phase (see Ullmann's Encyclopedia of Industrial Chemistry, 6 ^th Edition, 2000 electronic release, Chapter "Maleic and Fumaric Acids, Maleic Anhydride An important process using such catalysts is the production of maleic anhydride by oxidation of C4 hydrocarbons, which can be carried out, for example, in fixed-bed or fluidized-bed reactors.The fluidized bed process enables better heat removal and thus the use of higher hydrocarbon concentrations However, fluidized bed processes, the catalysts used are exposed to strong mechanical stress, resulting in increased abrasion of the catalysts. The technical literature describes various methods for the preparation of VPO catalysts with the aim of improving the abrasion resistance of VPO catalysts, so that they can be used for gas-phase oxidation in the fluidized bed process.

Impregnation allows preformed carrier materials, which already have a high abrasion resistance, to be impregnated with a catalytically active material. No. 4,455,434 describes, for example, a process for the preparation of VPO catalysts by impregnation of a support material with a vanadium alkoxide solution and a solution containing phosphoric acid. Such catalysts have an unsatisfactory activity, since the proportion of active material is relatively low compared to the support material.

As a rule, the preparation of VPO catalysts is carried out by spray-drying a suspension of a vanadium, phosphorus and oxygen-containing precursor. To increase the abrasion resistance of the VPO catalysts, admixtures of particles having sufficient mechanical strength, such as, for example, silicon dioxide, may be added before the spray drying. By suitable choice of the size of the particles in this case both embedded and encapsulated catalysts can be produced.

In the case of embedded catalysts, the species required to provide strength is distributed evenly throughout the particle cross-section of the spray-dried catalyst. Methods for preparing such catalysts are disclosed in DE-A-1 951 536 and DE-A-1 966 418. The achievement of a high mechanical strength is favored by a high proportion of inert material, while the activity of the catalyst is increased by a high proportion of active material. As a rule, a suitable balance between these properties must therefore be found for the respective application.

In the case of encapsulated catalysts, the inert particles are located substantially in an outer shell of the spray-dried catalyst particle which is formed by the inert particles flowing with the spray-drying liquid flowing to the surface of the catalyst particle and polymerizing there. Encapsulated catalysts can be prepared, for example, by the methods described in EP-A-0 225 062, US Pat.

US 5,302,566 or US 6,362,128. Encapsulation by the formation of an outer shell of inert material provides protection against abrasion, but may interfere with the diffusion of the substrates through the outer shell. In addition, the addition of the shell-forming inert particles can complicate the processing during the production, since these reduce the stability of the suspension of the VPO catalyst stage, since shell-forming inert particles already in the Suspension tend to polymerize and thus to an undesirable increase in viscosity.

Other methods of increasing the abrasion resistance of VPO catalysts rely on modification of the VPO precursor. Thus, in US Pat. No. 4,525,471, a catalyst with improved mechanical properties obtained by a) compacting the VPO precursor by tableting or pelleting; b) comminuting the compacted VPO precursor by grinding to a particle size of less than 1 micron and c) then spray-drying a suspension containing the comminuted particles of the VPO precursor. A similar method is disclosed in US 5,498,731. In this publication, catalysts having good mechanical properties are obtained by spray-drying a solution obtained by comminuting a VPO precursor in a jet mill. The particles of the mechanically comminuted VPO precursor are not more than 3 μm in size and have a narrow particle size distribution (d2s / d75 ≦ 6).

In EP-A-0608837, the particle size of the VPO precursor is adjusted not by mechanical processes but already during the manufacturing process of the VPO precursor. By reduction of a vanadium alkoxide as a pentavalent vanadium compound and subsequent selective hydrolysis of the vanadium alkoxide in the presence of a phosphorus compound, particles having a size of about 5 μm are obtained according to the examples, which are then further processed by spray-drying to give the corresponding catalysts.

Another method for producing VPO precursors having primary particles of about 100 nm is described in Chinese Patent CN-A-131 1058. The primary particles of the VPO precursor obtained in accordance with the disclosure are further processed into catalysts by tableting, mechanical comminution and sieving. The catalysts thus obtained have a particle size of from 25 to 40 mesh (420 to 707 μm) and are used for the gas-phase oxidation of butane to maleic anhydride.

JP-02055211 describes crystalline VPO precursors having a characteristic crystallite particle size distribution, with 30% by volume of the crystallites having a size of less than 1 μm. The preparation of such VPO precursors is carried out by reduction of a pentavalent vanadium compound in a mixture of isobutanol and toluene. The catalysts prepared by spray-drying from the VPO precursors described allow for a yield of maleic anhydride in the oxidation of butane of 54.6%.

In US Pat. Nos. 4, 510, 258 and US Pat. No. 4,511,670, the resistance of a finely divided solid VPO precursor to abrasion by acid treatment is increased. The fine Division is achieved by grinding, whereby particles of less than 10 microns (example, 0.5 microns) arise. The acid treatment during drying (spray drying) favors an agglomeration of the particles of the VPO precursor and thus leads to larger catalyst particles which are to have an increased abrasion resistance.

By means of the present invention, improved catalysts for the gas phase oxidation of hydrocarbons, in particular for the production of maleic anhydride, are provided. According to the invention, it has been found that catalysts can be obtained by the following process steps

a) Preparation of a suspension containing a vanadium, phosphorus and oxygen-containing precursor (VPO precursor) whose ultrasonically dispersed primary particles in aqueous solution have an average diameter dso, pnmarpamkei smaller than 1, 3 microns and in water in the form of agglomerates with a mean diameter dso, agglomerates of 2 .mu.m to 20 .mu.m are present, wherein the average diameter of the primary particles and the agglomerates of the VPO precursor are determined by laser diffraction according to ISO 13320 and b) spray-drying the suspension, wherein the catalyst precursor thus obtained if necessary is transferred by c) thermal treatment in the catalyst,

have a particularly good property profile.

Since suitable VPO precursors can be prepared and processed by various synthesis variants, it is possible to use existing infrastructure in the preparation of the precursors themselves, as well as in the further processing of the VPO precursors to catalysts. This allows the user a high degree of flexibility and cost-effectiveness. In particular, the catalysts which are prepared from the VPO precursors are characterized by a balanced property profile. Thus, they have a balanced ratio of mechanical resistance, in particular abrasion resistance, activity and selectivity. In particular, the abrasion resistance is improved over conventional catalysts, which is advantageous in a fluidized bed process for the production of maleic anhydride. The overall improved property profile of the catalysts allows optimized economy of the process, for example, by a favorable ratio of active material content to inert material and by long service life with a high load of the catalyst. The catalysts of the invention are also characterized in the process by a good handling and a good ability to heat transfer.

The object of this invention was also a process for the preparation of maleic anhydride by oxidation of hydrocarbons having at least four carbon atoms. atoms, in particular n-butane, using the catalysts of the invention are available.

Furthermore, the above-described vanadium, phosphorus and oxygen-containing VPO precursors were found, which are characterized in that the ultrasonically dispersed primary particles of the VPO precursor in aqueous solution have a mean diameter dso, pnmarpamkei smaller than 1, 3 microns and that the VPO precursor is present in water in the form of agglomerates with a mean diameter d 50, agglomerates of 2 μm to 20 μm, the mean diameters of the primary particles and the agglomerates of the VPO precursor being determined by laser diffraction according to ISO 13320 ,

Preparation of the VPO precursor:

The VPO precursors according to the invention are composed of primary particles. As primary particles, those particles or particles are usually referred to, which are still recognizable as individuals by suitable physical methods. Agglomerates are loose aggregations of primary particles whose cohesion is so low that they can be broken up by dispersing. By dispersion is meant according to the division of agglomerates in a liquid medium into smaller particles or particles. Dispersing can be done by introducing energy into the liquid medium. The energy can be introduced, for example, by vigorous stirring, in particular by means of a dissolver (stirring disk device) or ultrasound. In the case of ultrasound, the mechanical energy is introduced via sound waves which are capable of dividing the agglomerates. In the following description, the term primary particles is understood as meaning those particles which are present under the conditions of the method described below for determining the particle size distribution (PGV) of the primary particles and whose PGV is determined by means of this method.

The term agglomerates is understood below to mean those particles which are present under the conditions of the method described below for determining the PGV of the agglomerates and whose PGV is determined by means of this method.

To determine the particle size distribution (PGV) of the primary particles, a mixture of water and the VPO precursor is first prepared. The concentration of VPO precursor is 2 g in 100 ml of water.

The mixture of VPO precursor and water is dispersed by means of ultrasound at a power of 240 watts. The mixture is pumped directly from the vessel, in which the dispersion is carried out by means of ultrasound, continuously into the measuring cell of the analyzer. The determination of the PGV is carried out by means of laser diffraction ISO 13320. The average particle diameter dso, Pnmarpamkei (median value) obtained as the measurement result is defined here such that 50% of the total particle volume consists of primary particles with this or a smaller diameter. The determination of the PGV of the primary particles and thus of the mean diameter of the primary particles dso, pnmarpamkei takes place according to the embodiment described in the examples.

The determination of the PGV of the agglomerates is also carried out by means of laser diffraction. In contrast to the measurement procedure above, however, only so much energy is entered that the agglomerates are not dispersed, but merely agitated. The agglomerates of the VPO precursor can form a loose sediment of low density after sedimentation of the measurement solution. The undoing of this process, for example by gentle stirring, is hereinafter referred to as stirring. The measurement of the PGV of the agglomerates thus takes place in the stirred state. Since the formation of the agglomerates and thus also the PGV of the agglomerates is dependent both on the concentration and on the energy input during stirring, the determination of the PGV should preferably be carried out under the conditions mentioned below in order to ensure reproducibility of the results.

The determination of the PGV of the agglomerates is carried out in a mixture of 2 g VPO precursor and 100 ml of water. The VPO precursor should be used dry, i. the carbon content characteristic of residual organic solvent should be less than 5% by weight.

The preparation of the mixture is carried out in a beaker with a volume of 150 ml. Immediately before the measurement, the mixture is stirred. This is done by means of a magnetic stirrer at a speed n of 600 revolutions per minute. The stirring time is at least 30 seconds, but not longer than 60 seconds. The thus dispersed mixture is pumped continuously into the measuring cell of the laser diffraction apparatus, where the determination of the volume-related particle size distribution according to ISO 13320 is carried out. The mean particle diameter dso, agglomerates (median value) obtained as the measurement result is here defined such that 50% of the total particle volume consists of primary particles with this or a smaller diameter. The mood of the PGV of the agglomerates and thus dso, agglomerates takes place according to the embodiment given in the examples.

According to the invention, the primary particles of the VPO precursor dispersed in ultrasound in aqueous solution should have an average diameter dso, particle size less than 1.3 μm. Preferably, the mean diameter dso, Pπmarpartikei is in a range of 0.5 to 1, 0 .mu.m and more preferably, the average diameter dso, Pπmarpartikei is in a range of 0.6 to 0.85 microns. Furthermore, the average diameter of the agglomerates dso, agglomerates in a range of 2 to 20 microns, preferably in a range of 2.5 to 15 microns and more preferably in a range of 3 to 10 microns.

Other parameters that can characterize an advantageous VPO precursor are the diameter dio, pnmarpamkei and the diameter dgo, pnmarpamkei. The diameter dio pπmarpartikei is defined so that 10% of the total particle volume consists of primary particles with this or a smaller diameter. The diameter dgo, pπmarpar- tikei is analogously defined so that 90% of the total particle volume consist of particles with this or a smaller diameter, the membrane should normally be less than 1.3 μm, preferably in the range of 0.15 to 0.8 microns and more preferably in the range of 0.2 to 0.6 microns, dgo, pnmarpamkei is usually less than 5 microns. Preferably dgo, pπmarpamkei is in a range of 0.5 to 4 microns and more preferably in a range of 0.8 to 3 microns.

An advantageous VPO precursor may further be characterized by the parameters dio, A _gg iomerate and dgo, agglomerates. The diameters d-io, agglomerates and dgo, agglomerates are defined so that 10% and 90% of the total particle volume consist of agglomerates with this or a smaller diameter. The diameter dio, agglomerates should be less than 10 microns in the rule. Preference is given to dio, agglomerates in the range of 0.2 to 6 microns and more preferably in the range of 0.4 to 4.5 microns. dgo, agglomerates is usually less than 40 microns. Preferably dgo, agglomerates in the range of 1 to 30 microns and more preferably in the range of 3 to 20 microns.

The following interpretation, which is not intended to be limiting for the invention, can describe the relationship between the particle size distribution of the primary particles and the agglomerates of the VPO intermediates and the properties of the catalysts: The primary particle size is decisive for the catalytic activity of the catalysts prepared from the primary particles, as the catalytic surface increases with decreasing primary particle size. At the same time, the adhesion forces between the primary particles increase with increasing surface area, which increases the abrasion resistance of the catalyst particles. However, the primary particles must also have a certain tendency to agglomerate (which, apart from the primary particle size, also depends on their surface condition), since this is accompanied by the mechanical cohesion of the primary particles in the catalyst particle and thus by the abrasion resistance of the catalysts prepared from the VPO precursors.

Such catalysts, which are obtainable from the precursors according to the invention, have according to the invention a comparatively better abrasion resistance than catalysts obtained from non-inventive VPO precursors. Inventive VPO precursors are present when the primary particles of the VPO precursor in the ultrasonically dispersed state have a mean diameter d 50 of less than 1.3 μm and in the stirred state the VPO precursor in the form of agglomerates has a mean diameter d 50 of 2 μm to 20 microns is present.

VPO precursors having such a particle size distribution can be prepared both by mechanical comminution of the VPO precursors and directly by appropriate synthesis of the VPO precursors.

In one possible embodiment, the PGV of the primary particles and the agglomerates can be adjusted by mechanical comminution of a VPO precursor.

Suitable processes for the mechanical comminution of VPO precursors can be found for example in the patents DE 3429164, US 4525471, US 5302566 or US 5498731. Particularly suitable methods for mechanical comminution are the milling of the dried VPO precursor in a ball mill or jet mill. Other suitable methods can be found for example from Ullmann's Encyclopedia, 6 ^th Edition, Electronic Release, Chapter "Size Reduction". Whether the VPO precursor after mechanical crushing a inventions dung proper distribution of PGV regarding dso pnmarpamkei and dso, agglomerates, can easily be detected by a person skilled in the art by means of the analytical methods disclosed for the determination of dso, primary particles and dsO.

In a further embodiment, the particle distribution of the VPO precursor according to the invention can be adjusted directly by a suitable synthesis by carrying out the following steps:

I) reacting a pentavalent vanadium compound in an organic, reducing solvent or a mixture of organic, reducing solvents,

II) addition of a polyol,

III) addition of a phosphorus compound,

IV) isolation of the VPO precursor formed in the previous reaction step,

V) drying of the VPO precursor.

In the first process step I), the reaction of a pentavalent vanadium compound in an organic, reducing solvent or a mixture of organic, reducing solvents.

Vanadium pentoxide (V2O5) is preferably used as the pentavalent vanadium compound. However, it is also possible to use vanadic acid or salts of vanadic acid, such as vanadyl oxalate, vanadyl chloride or ammonium tetavanadate as starting materials to take. Vanadium pentoxide is preferably used in a particle size range of 50 to 500 μm. If significantly larger particles are present, the solid is usually comminuted before being used and optionally sieved. Suitable apparatus are, for example, ball mills or planetary mills.

The pentavalent vanadium compound is at least partially reduced by reaction with an organic reducing solvent or a mixture of organic reducing solvents.

Suitable organic, reducing solvents generally contain an oxidizable functional group. In particular, organic solvents are suitable which contain one or more hydroxyl groups, such as primary or secondary or branched, saturated alcohols having 3 to 6 carbon atoms, cycloaliphatic alcohols or aromatic alcohols. Examples of such primary or secondary, unbranched or branched C 3 to C 6 alcohols are n-propanol (1-propanol), isopropanol (2-propanol), n-butanol (1-butanol), sec-butanol (2-butanol), isobutanol (2-methyl-1-propanol), 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-2 -butanol, 2,2-dimethyl-1-propanol, 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-hexanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, 3 Methyl 2-pentanol, 4-methyl-2-pentanol, 2,2-dimethyl-1-butanol, 2,3-dimethyl-1-butanol or 3,3-dimethyl-1-butanol, 3,3-dimethyl -2-butanol. Suitable cycloaliphatic alcohols are, in particular, cyclopentanol or cyclohexanol. Benzyl alcohol is suitable as the aromatic alcohol.

Preference is given to n-propanol (1-propanol), n-butanol (1-butanol), isobutanol

(2-methyl-1-propanol), 1-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, cyclohexanol and benzyl alcohol used as an organic, reducing solvent.

Furthermore, suitable mixtures of the abovementioned organic, reducing solvents can be used. Particularly suitable are mixtures of the abovementioned alcohols, in particular mixtures of isobutanol and benzyl alcohol. Hereinafter, the term "organic, reducing solvent" is also understood as meaning mixtures of organic, reducing solvents described above.

Optionally, the reaction with the organic, reducing solvent in the presence of further suitable as a reducing agent compounds. Examples of such compounds are oxalic acid, hydrazine, hydroxylamine or formic acid.

The amount of organic, reducing solvent and optionally further reducing agent used should be greater than that for the reduction of the vanadium amount required stoichiometrically from oxidation state +5 to an oxidation state in the range +4.0 to +4.9. In general, the molar ratio of the functional groups of the reducing organic reducing agent to the pentavalent vanadium compound is 10 to 25 to 1, and preferably 12 to 20 to 1.

If vanadium pentoxide is used as the pentavalent vanadium compound, the solids content of the vanadium pentoxide in the reducing organic solvent is generally from 0.1 to 15% by weight, preferably from 0.5 to 8% by weight and more preferably from 1 to 4% by weight. -%. In other pentavalent vanadium compounds, the solids content is usually also in the above ranges.

The reaction of the pentavalent vanadium compound with the reducing organic solvent may be carried out in suitable reactors, for example a stirred tank, with mixing. Stirrers with different stirring geometries, such as, for example, disk stirrers, impeller stirrers, inclined blade stirrers or propeller stirring, are suitable as mixing units.

The reaction of the pentavalent vanadium compound in the organic reducing solvent is usually carried out with heating and mixing.

The reaction generally takes place with thorough mixing, as a rule by means of suitable stirring devices such as stirrers and the like. The energy input by stirring is usually 0.1 to 1 W / kg, preferably 0.15 to 0.8 W / kg and more preferably 0.28 to 0.35 W / kg.

The temperature range selected depends on various factors, for example the boiling point of the added organic reducing solvent. In general, the temperature of 80 to 160 ⁰ C, preferably 100 to 120 ⁰ C.

The volatile compounds, such as water, the organic reducing solvent and its degradation products, such as aldehyde or carboxylic acid, evaporate from the reaction mixture and can be either removed or partially or completely condensed and recycled. Preference is given to partial or complete recycling by heating under reflux. Particularly preferred is the complete recirculation under reflux.

The reaction at elevated temperature generally takes several hours. The duration of the reaction of the pentavalent vanadium compound with the reducing organic solvent is usually from 1 to 30 hours, preferably from 2 to 10 hours, in particular from 3 to 5 hours. Before the addition of the polyol (process step II)), a cooling is generally carried out from the temperature set in process step I to a temperature which is significantly below the reflux temperature of the organic, reducing solvent. This temperature is for example in the range of 20 to 120 ⁰ C, preferably in the range of 50 to 110 ⁰ C and particularly preferably from 80 to 100 ⁰ C. The cooling is usually linear. Cooling ramps are for example 5 to 120 ° C / h, preferably 10 to 100 ° C / h and particularly preferably 25 to 85 ° C / h.

In process step (II), the addition of a polyol takes place.

The polyols used are especially dihydric aliphatic alcohols, such as ethylene glycols, propylene glycols or higher-chain glycols, diglycols and / or polymeric polyols, in particular polyether polyols. Suitable polyetherols are generally polyethylene glycols of ethylene oxide and / or propylene oxide having a molecular weight of 500 g / mol to about 20,000 g / mol. These can be used individually or as any mixtures of several alcohols with one another or else with tri- and / or higher-functional alcohols and / or polyols, such as, for example, Trimethylolpropane or glycerol, are used.

The polyols used are generally readily miscible with the organic, reducing solvent. Preferably used polyols are dihydric aliphatic alcohols, such as ethylene glycol. Propylene glycol. Diethylene glycol, 1, 3-propanediol, 1, 4-butanediol, 1, 5-pentanediol or 1, 6-hexanediol and polyether diols having a molecular weight of 500 to 20,000 g / mol.

Particularly preferred are dihydric aliphatic alcohols, such as ethylene glycol. Propylene glycol, diethylene glycol, 1, 4-butanediol or 1,6-hexanediol and polyether diols having a molecular weight of 1000 to 10000 g / mol used.

The amounts of polyol component used should be selected so that the mass ratio of polyol to pentavalent vanadium compound in the range of 0.05 to 2 kg of polyol per kg of vanadium compound, preferably in the range of 0.3 to 1, 5 kg of polyol per kg of vanadium compound and especially preferably in the range of 0.5 to 1.2 kg of polyol per kg of vanadium component.

After the addition of the polyol component, the reaction mixture can optionally be heated. Preferably, after addition of the polyol component, the reaction mixture is heated to the reflux temperature of the reducing organic solvent used. The heating is preferably carried out linearly. Heating ramps are, for example, 5 to 80.degree. C./h, preferably 20 to 60.degree. C./h, and particularly preferably 35 to 65.degree. C./h. After reaching the elevated temperature, the reaction mixture for some time, for example 0.5 to 10 hours, preferably 0.75 to 5 hours and more preferably 1 to 2 hours are kept at this temperature.

In process step III), the addition of a phosphorus compound takes place.

Before the phosphorus compound is added, the reaction mixture is generally cooled to a temperature which is significantly below the reflux temperature, as described above. The cooling is usually linear. Cooling ramps are for example 5 to 120 ° C / h, preferably 20 to 80 ° C / h and particularly preferably 30 to 50 ° C / h.

The addition of the phosphorus compound is generally carried out at a temperature of 20 to 90 ⁰ C, preferably at a temperature of 30 to 80 ⁰ C and particularly preferably at a temperature of 40 to 70 ⁰ C.

Examples of suitable five- or trivalent phosphorus compounds include ortho, pyrophosphate, polyphosphoric acid, phosphoric acid esters and phosphorous acid. A pentavalent phosphorus compound is preferred, especially orthophosphoric acid (H3PO4), pyrophosphoric acid (H4P2O7), polyphosphoric acid (H _n + 2Pnθ3n + i with n> 3) inserted or mixtures thereof. Furthermore, a mixture of ortho-, pyro- and polyphosphoric acid can be used, which is prepared by incorporation of phosphorus pentoxide in water or aqueous phosphoric acid (85 to 100%).

The molar ratio of the phosphorus compound to the vanadium compound may be e.g. 1, 0 to 1, 3 to 1 and particularly preferably 1, 2 to 1, 3 to 1.

After the addition of the phosphorus compound, the reaction mixture can optionally be heated. Preferably, after addition of the phosphorus compound, the reaction mixture is heated to the reflux temperature of the reducing organic solvent used. The heating is preferably carried out linearly. Aufheizrampen be, for example, 5 to 70 ° C / h, preferably 10 to 60 ° C / h and particularly preferably 30 to 50 ° C / h. After reaching the elevated temperature, the reaction mixture may remain for some time, e.g. for a further 0.1 to 24 hours, preferably 1 to 15 hours and preferably for 3 to 8 hours at this temperature.

Furthermore, in the preparation of the VPO precursor so-called promoter components can be added. Suitable promoters are the elements of groups 1 to 15 of the periodic table and their compounds. Suitable promoters are described, for example, in WO 97/12674 and WO 95/26817 and in US Pat

US 5,137,860, US 5,296,436, US 5,158,923 and US 4,795,818. Preferred promoters are compounds of the elements cobalt, molybdenum, iron, zinc, Hafnium, zirconium, lithium, titanium, chromium, manganese, nickel, copper, boron, silicon, antimony, tin, niobium and bismuth, more preferably molybdenum, iron, cobalt, niobium, zinc, antimony, bismuth, lithium. The promoted VPO precursors and the catalysts prepared therefrom may contain one or more promoters. In general, the promoter components are added before, during or after the reaction of the vanadium pentoxide in the presence of the reducing organic solvent or with the phosphorus compound. Alternatively, it is possible to add it after completion of the precipitation (preferably at reduced temperature) and, if appropriate, a renewed heating. The content of promoters is generally in total in the finished catalyst generally not more than about 5 wt .-%, each calculated as oxide.

Suitable promoter components are, for example, the acetates, acetylacetonates, oxalates, oxides or alkoxides of the abovementioned promoter metals, such as cobalt (II) acetate, cobalt (II) acetylacetonate, cobalt (II) chloride, molybdenum (VI) oxide, molybdenum (III) chloride, iron (III) acetylacetonate, iron (III) chloride, zinc (II) oxide, zinc (II) acetylacetonate, lithium chloride, lithium oxide, bismuth (III) chloride , Bismuth (III) ethyl hexanoate, nickel (II) ethyl hexanoate, nickel (II) oxalate, zirconyl chloride, zirconium (IV) butoxide, silicon (IV) ethoxide, niobium (V) chloride and niobium (V). oxide. For further details, reference is made to the aforementioned WO publications and US patents.

In process step IV), the isolation of the VPO precursor formed in the previous reaction step takes place.

Before the isolation of the solid formed in the course of the reaction, a cooling phase may optionally be carried out, as well as a storage or aging phase of the cooled reaction mixture. A storage or aging phase, for example, by leaving the precipitate formed in a temperature range of 20 to 50 ⁰ C without stirring. The duration of the storage or aging phase is usually 1 to 24 hours, preferably 3 to 20 and more preferably 8 to 15 hours.

Suitable methods for isolating the precipitate formed from the reducing organic solvent are evaporation of the solvent, filtration, centrifugation or decantation. Preferably, the precipitate is separated by filtration from the reducing organic solvent.

The filtration can be carried out in the inventive method in principle in the known, suitable for filtration devices. Examples of suitable devices are suction filters, plate filters and centrifuges (eg inverting filter centrigug). The use of a suction filter is preferred. Suitable filter media are filter papers, porous filter sheets, tight meshes and fabrics, with dense nets and fabrics generally being preferred. Preferably, the Carrying out a pressure filtration. Particularly preferred is the use of a heated Druckfilternutsche, which is equipped in a very particularly preferred embodiment with a heated stirrer. The heatable stirrer can be used for stirring up the suspension, for smoothing out the filter cake, for heat input during the subsequent drying process, and for loosening up the product discharge.

In general, the pressure filtration at an absolute pressure of 0.1 to 2 MPa, preferably 0.2 to 1, 0 MPa and more preferably 0.3 to 0.5 MPa above the filter suction and at a temperature of 10 to 50 ⁰ C, more preferably carried out from 20 to 30 ⁰ C.

The isolated precipitate can be processed unwashed or washed. The washing of the isolated precipitate has the advantage that still adhering residues of the alcohol (II) and its degradation products can be further reduced. Examples of suitable solvents for the washing process are alcohols, aliphatic and / or aromatic hydrocarbons (eg pentane, hexane, benzines, benzene, toluene, xylene), ketones (eg 2-propanone (acetone), 2-butanone, 3-pentanone), Ethers (eg, 1, 2-dimethoxyethane, tetrahydrofuran, 1, 4-dioxane) or mixtures thereof called. If the isolated precipitate is washed, it is preferred to use one of the organic, reducing solvents and / or acetone selected in the preceding reaction. The washing of the isolated precipitate in the pressure filtration filter is preferably carried out by at least one, preferably 1 to 20 and particularly preferably 3 to 10, resuspension procedures. During a resuspension process, the filter cake is brought into suspension after being blown dry by addition of a solvent in the filter chute with stirring and then the solvent is separated from the filter cake again. After resuspension is usually a re-blowing the Nutschkuchens dry under introduction of an inert gas. Preferably, the resuspension is carried out in acetone.

In process step V), the precipitate is dried after isolation.

Drying is generally considered to be a temperature treatment in the range of 30 to 250 ° C, which is usually at a pressure of 0.0 ("vacuum") to

0.1 MPa abs ("atmospheric pressure") is performed. Drying under vacuum usually allows a lower temperature to be used than drying under atmospheric pressure. The gaseous atmosphere optionally present during drying may contain oxygen, water vapor and / or inert gases, such as nitrogen, carbon dioxide or noble gases. Preferably, the drying is carried out at a pressure of 1 to 30 kPa abs, more preferably 10 to 20 kPa abs and a temperature of 50 to 200 ⁰ C, more preferably between 100 and 150 ⁰ C, under oxygen-containing or oxygen-free residual gas atmosphere, such as air or nitrogen, by. The drying is preferably carried out under an oxygen-free residual gas atmosphere. The drying can be carried out, for example, in the device used for filtration or in a separate apparatus, for example a drying cabinet or a continuous belt dryer. Preferably, the drying is carried out in the apparatus used for filtration. The duration of the drying can be several hours. The duration of the drying depends on the residual carbon content, which should amount to 5% by weight or less and preferably between 1, 0 and 2.5% by weight in the dried VPO precursor. As a rule, this results in a drying time of between 1 and 50 hours, preferably between 5 and 30 hours and more preferably between 10 and 25 hours.

The VPO precursors according to the invention can be used for the preparation of catalyst precursors or catalysts for the gas phase oxidation of hydrocarbons, in particular butane.

The present invention accordingly also relates to catalyst precursors or catalysts obtainable by the following process steps:

a) Preparation of a suspension containing a vanadium, phosphorus and oxygen-containing precursor (VPO precursor) whose ultrasonically dispersed primary particles in aqueous solution have an average diameter dso, pnmarpamkei smaller than 1, 3 microns and in water in the form of agglomerates with an average diameter dso, agglomerates of 2 microns to 20 microns is present, the middle

Diameter of the primary particles and of the agglomerates of the VPO precursor are determined by laser diffraction according to ISO 13320, b) spray-drying the suspension and c) optionally converting the catalyst precursor obtained in step b) into the catalyst by thermal treatment.

a) Preparation of the suspension

The catalyst precursors or catalysts according to the invention are prepared by spray-drying a suspension which contains the VPO precursor according to the invention. As a suitable suspension medium usually water is used.

The carbon content in the VPO precursor is usually 5 wt .-% or less, preferably between 1, 0 and 2.5 wt .-%. The mass fraction of the dry VPO precursor according to the invention in the suspension should be selected so that the viscosity of the suspension is in a range which can be processed for spray drying. Among other things, the viscosity of the suspension is dependent on the average particle size of the VPO precursor. It has proved to be advantageous if, depending on the average diameter of the agglomerates dso, Aggbmerate, the mass fraction of the VPO precursor to the suspension is set as follows:

2 μm <dso, agglomerates <5 μm: preferably 10 to 35 wt.% VPO precursor, particularly preferably 15 to 25 wt.% VPO precursor, based on the total mass of the suspension used.

5 μm <dso, agglomerates <10 μm: preferably 15 to 40% by weight VPO precursor, more preferably 20 to 35% by weight VPO precursor, based on the total mass of the suspension used.

10 μm <dso, agglomerates <20 μm: preferably 20 to 50 wt.% VPO precursor, particularly preferably 25 to 40 wt.% VPO precursor, based on the total mass of the suspension used.

The suspension may contain suitable additives. Additives are substances that are not actually the active component, but that can act as fillers or binders, for example. Suitable additives may, for example, be selected from the group consisting of silica, zirconium dioxide, zinc oxide, aluminum oxide, boron oxide, titanium dioxide, germanium oxide, iron oxide. Preferably, silicon dioxide is used as additive.

The additives can be used at least partially in colloidal form. Colloidal form in this context means that the average diameter of the additive particles (dso, additive) is in the range of 4 to 100 nm.

The mean diameter dso, additive is defined to be 50% of the total particle volume of the silica particles having this or a smaller diameter. A suitable method for determining the particle size distribution of the silicon dioxide particles, for example, the laser diffraction according to ISO 13320. In general, the value for dso, sihαumdioxid also by the respective manufacturer of silica particles and / or silica dispersions can be learned. The additives in colloidal form are usually present as sol, in which the additive particles are dispersed in a liquid medium.

Preference is given to using a silica sol in which the additive silicon dioxide in colloidal form is dispersed in water. The mean diameter d 50, additive of the added additives in colloidal form, is generally in the range from 4 to 15 nm, preferably in the range from 4 to 10 nm and particularly preferably in the range from 4 to 8 nm. In particular, the mean diameter of the dispersed silicon dioxide is in the sol usually in the range of 4 to 15 nm, preferably in the range of 5 to 10 nm and particularly preferably in the range of 5 to 8 nm. Examples of suitable commercially available silica sols are Nalco® 2326 (Nalco Co., Naperville, IL, USA; d ₅ o, additive: 5 nm, 15% by weight SiO ₂ , pH = 9, NH ₄ ⁺ as counterion), Ludox® SM30 (Grace Davison, Worms, D; dso, additive: 7 nm , 30% by weight SiO ₂ , pH = 10, Na ⁺ as counter ion) or Ludox® HS40 (Grace Davison, Worms, D; dso, additive: 12 nm, 40% by weight SiO ₂ , pH = 10, Na ⁺ as counterion).

The additive may also be present as silica in the form of polysilicic acid.

In the context of the invention, the polysilicic acid is the condensation product of monosilicic acid or orthosilicic acid (Si (OH) ₄ ) which has been polymerized in a pH range between 1 and 4 and consists of silicon dioxide particles which as a rule have an average diameter of less than 3 to 4 nm. After just a few hours, polysilicic acid tends to gel at room temperature. The degree and rate of further polymerisation (gelling) depends on various factors, such as the set pH, the silicon

Concentration and temperature. Under alkaline conditions, polysilicic acid rapidly transforms to silica, which is in colloidal form. By definition, silica in colloidal form generally has a mean particle diameter of 5 nm or more. Silica in colloidal form can be stabilized in a pH range between 8 and 10. Since polysilicic acid usually tends to gel at room temperature after only a few hours, in this embodiment it is necessary to freshly prepare the polysilicic acid before spray-drying. The preparation is typically carried out from a commercially available sodium silicate solution (eg soda waterglass from Merck KGaA ,: about 27 wt .-% SiO ₂ and about 8 wt .-% Na ₂ O, pH = 11) by acidic ion exchange. In ion exchange, Na ⁺ ions are replaced by HsO ⁺ ions. Due to the tendency to condensation of the polysilicic acid, it is advantageous to prepare the suspension in coolable containers. The temperature of the suspension should generally be in a range of 0 to 20 ⁰ C and preferably from 5 to 10 ⁰ C.

The mean diameter dso, additive of polysilicic acid may be temporally changeable for the reasons described above. In the calculations for determining the ratio (dso, pnmarpamkei / dso, additive), therefore, a value of 1 nm was assumed for the mean diameter dso, additive of polysilicic acid prepared fresh as described above. Based on the dry mass of the catalyst are usually 3 to 25% by weight, preferably 6 to 15 wt .-% and particularly preferably 7 to 10 wt .-% additives used, calculated as the corresponding oxide of the additive used, for example as SiÜ2 or ÜO2. As a rule, from 3 to 25% by weight, preferably from 6 to 15% by weight and more preferably from 7 to 10% by weight, of silicon are used, calculated as SiO 2, based on the dry mass of the catalyst.

The additives used may be partially or completely present as silica in the form of polysilicic acid.

In a preferred embodiment, the proportion of silicon dioxide in the form of polysilicic acid in the additives is 50% by weight or less, more preferably 25% by weight or less, and particularly preferably 6% by weight or less, based on the sum of the dry matter the total added additives. In this preferred embodiment, additive particles in colloidal form are used in the suspension, which are sufficiently large in relation to the primary particle size of the VPO precursor according to the invention. The ratio of the diameters of the primary particles of the VPO precursor to the diameter of the particles of the additive used (d 50, additive) should be in the range from 90 to 170 in this particular embodiment. As a result, after the spray drying of the suspension, so-called "embedded catalysts" are generally obtained, Such catalysts have a morphology in which the additive particles are distributed over the entire cross section of the spray-dried powder.

In a further preferred embodiment, additives are added whose particle size is sufficiently small in comparison to the primary particle size of the VPO precursor according to the invention to produce so-called "encapsulated catalysts." The morphology of "encapsulated catalysts" differs from the morphology of "embedded catalysts". in that the additives are usually in the outer shell of the spray-formed catalysts after spray drying. "Encapsulated catalysts" are preferably formed when the ratio of the average diameters of the primary particles of the vanadium-, phosphorus- and oxygen-containing VPO precursor to the diameter of the additive particles of (dso, Pnmarpamkei / dso, additive) is more than 500.

It is therefore advantageous for this preferred embodiment to use the additive as a silica in the form of polysilicic acid in order to achieve a size ratio (dso, pnmarpamkei / dso, innards) of 500 or more required for the formation of encapsulated catalysts. However, the additives may also be present in colloidal form or as a mixture of the two forms if the corresponding size ratio (dso, pnmarpamkei / dso, inner substances) is in the range of 500 or more. Preferably, the additives are in the form of silica in colloidal form, as silicon dioxide in the form of polysilicic acid or as a mixture containing both silica in colloidal form and silica in the form of polysilicic acid. Silica in the form of polysilicic acid is preferably used as additive.

In order for the corresponding size ratio (dso, Pnmarpamkei / dso, additive) is in the range of 500 or more, it is advantageous if the average diameter of the primary particles of the VPO precursor used at least 0.65 .mu.m, preferably at least 0.7 .mu.m and more preferably at least 0.8 microns.

It is also possible to obtain catalysts having a morphology comprising both "embedded catalyst" and "encapsulated catalyst" elements. Such a morphology may look like that most of the additive particles are near the outer surface, but some of the additive particles are distributed over the entire particle cross-section. Furthermore, a mixed morphology can be such that the shell of additive particles has more or less large gaps. Catalysts having such a mixed morphology can be obtained, for example, if the ratio of the average diameter of the primary particles to the mean diameter of the additive particles (dδO, primary particles / d 50, additive) in the range Vθn 170 bJS 500 Nβgt.

The morphology of the catalysts can be determined, for example, by electron microscopy in conjunction with energy-dispersive X-ray analysis (EDX).

Furthermore, the suspension may contain spray aids. Examples of suitable spraying aids are cellulose derivatives, polyvinylpyrrolidones, copolymers of vinylpyrrolidone and vinyl acetate, starch derivatives, polyvinyl alcohols or water-soluble dispersants of the Sokalan® type (BASF AG). The spray aids are generally added in amounts of 0 to 20 wt .-%, in particular 1 to 10 wt .-%, based on the composition of the suspension.

The suspension should generally be homogenized before spray-drying and the additives should be sufficiently dispersed. Homogenization and dispersion can be carried out by intensive stirring. In an advantageous embodiment, the simultaneous use of a propeller stirrer and an Ultra Turrax stirrer takes place. The combination of the two stirrers allows optimum mixing or homogenization and dispersion of the particles in the suspension of solid particles. In general, the homogenization and dispersion is carried out in a cooled jacketed vessel.

b) spray-drying the suspension The preparation of the spray powder (catalyst precursor) is carried out by spray-drying the suspension by spraying the suspension into an inert gas. Either the sputtering temperature can be chosen so that the suspension has the viscosity suitable for sputtering, or the solids content of the suspension can be chosen so that the suspension has the appropriate viscosity at a particular sputtering temperature, the latter being preferred. In general, the suspension is atomized at room temperature.

The viscosity of the suspension present in the spray tower original can be adjusted as described above by the proportion of added VPO precursor.

Fluxing or dispersing agents can be used to further reduce the viscosity. Suitable flow or dispersants are, for example, flow or dispersants of the type Sokalan® (manufacturer: BASF Aktiengesellschaft).

For atomization, atomizers such as pressure nozzles, pneumatic atomizers, rotary atomizers or ultrasonic atomizers can be used. Preferably, a laminar operated rotary atomizer (LAMROT) is used. Such a rotary atomizer is described, for example, in WO 94/213843.

After atomization, the liquid droplets may be dried in a drying chamber, for example, in a spray tower of known type (see, for example, K. Masters: Spray Drying Handbook, Leonhard Hill Books, London, 1972).

As a rule, drying should take place in a sufficiently large spray tower so that a slow and uniform drying of the spray powder is ensured.

If a LAMROT rotary atomizer is used to atomize the suspension, for example, the diameter of the spray tower is typically greater than 1.5 m. Preferably, the diameter of the spray tower in this case should be between 2 and 4 m and the total height of the spray tower should preferably be between 2 and 10 m.

The heat required for the evaporation of the suspension medium is preferably supplied at the top of the tower by an inert drying gas. The drying gas is above all air. However, other gases such as nitrogen or carbon dioxide can be used. The gas temperature at the top of the drying tower is preferably greater than the evaporation temperature of the suspension medium. When using water as the suspension medium, it is 100 ^° C. or more. It is preferably in the range from 120 to 150 ^° C. Too high temperatures on Head of the spray tower can cause too fast drying and thus a reduced abrasion resistance of the catalyst particles.

Preferably, the drying gas flows together with the liquid droplets through the drying tower and is sucked off at the outlet of the tower together with the dry matter. The gas temperature at the outlet of the tower (outlet temperature) depends on the desired residual content of the suspension medium in the powder. The outlet temperature is usually in the range of 80 to 130 ⁰ C, preferably in the range of 90 to 110 ⁰ C.

The powder can generally be separated from the gas stream by filters or cyclones, as usual. Cyclones for solids separation are preferably used for the preparation of the powders according to the invention.

The powders of the invention obtainable by the process according to the invention generally have an average particle size (number average) of from 40 to 120 μm, preferably from 50 to 100. In particular, the average particle size is from 60 to 90 μm.

The spray powder thus obtained is the catalyst precursor of the invention, which is optionally converted by thermal treatment in the catalyst of the invention. It goes without saying that the preparation of the catalyst precursor and the catalyst can be carried out at different locations. Before the catalyst precursor is converted into the catalyst according to the invention, the catalyst precursor can be stored or transported in a suitable manner.

c) Preparation of the catalyst

The catalyst is prepared by thermal treatment of the catalyst precursor.

If the catalyst is to be used later in fixed bed reactors, the catalyst precursor will usually be subjected to shaping before the thermal treatment. Common methods of shaping are described, for example, in Ullmann [Ullmann's Encyclopedia Electronic Release 2000, Chapter: 'Catalysis and Catalysts', S28-32] and by Ertl et al. [Ertl, Knözinger, Weitkamp: Ηandbook of Heterogeneous Catalysis ", VCH Weinheim, 1997, pages 98 ff].

As described in the abovementioned references, moldings in any spatial form, for example round, angular, oblong or the like, for example in the form of strands, tablets, granules, spheres, cylinders or granules, can be obtained by the shaping process. Common methods of shaping are, for example, extrusion, Tableting, ie mechanical pressing or pelleting, ie compacting by circular and / or rotating movements.

If the catalyst is to be used in a fluidized bed process, the catalyst precursor obtained from step b) is generally treated thermally

By suitable combination of temperatures, treatment times and gas atmospheres during the thermal treatment adapted to the respective catalyst system, the mechanical and catalytic property of the catalyst can be influenced and thus adjusted in a targeted manner.

In a preferred embodiment, the thermal treatment of the catalyst precursor is carried out as a two-stage calcination. The calcination stages can each be carried out batchwise, for example in a shaft furnace, tray furnace, muffle furnace, heating cabinet or in a fluidized bed reactor or continuously, for example in a rotary kiln, belt kiln or rotary kiln. It may successively contain various portions in terms of temperature such as heating, keeping the temperature constant or cooling and successively various portions with respect to the atmospheres such as oxygen-containing, water vapor-containing, oxygen-free gas atmospheres.

The thermal treatment of the catalyst precursor is usually carried out as a two-stage calcination, wherein the two-stage calcination of the spray powder is preferably carried out in a fluidized bed reactor.

The first stage of calcination is usually carried out in an oxidizing atmosphere with an oxygen content of 2 to 21 vol .-% and usually takes place in a temperature range of 300 to 400 ⁰ C. In general, the oxidizing atmosphere consists of air; alternatively, mixtures of oxygen, inert gases (eg nitrogen or argon), hydrogen oxide (water vapor) and / or air can also be used.

The duration of the first calcination stage in the process according to the invention is preferably to be selected such that a mean oxidation state of the vanadium is set to a value of +3.9 to +4.4, preferably +4.0 to +4.3.

The duration of the first calcination stage is generally dependent on the nature of the VPO precursor, the set temperature and the selected gas atmosphere, in particular the oxygen content. In general, the period of the first calcination stage extends to a duration of over 20 minutes, and preferably over 60 minutes. Generally, a period of up to 120 minutes is sufficient to set the desired average oxidation level. Under appropriately set conditions (eg lower range of the temperature interval and / or low content at molecular oxygen), but also a period of over 6 hours may be required.

The average oxidation state is usually determined by potentiometric titration according to the method described in the examples.

Since the determination of the average oxidation state of vanadium during calcination is extremely difficult to determine for reasons of apparatus and time, it is advantageous to experimentally determine the time required in preliminary experiments. As a rule, this is a series of measurements in which it is annealed under defined conditions, the samples after different times removed from the system, cooled and analyzed with respect to the mean oxidation state of the vanadium.

During the second calcining step in the thermal treatment of the catalyst precursor, the catalyst intermediate obtained is in a non-oxidizing atmosphere, for example containing less than 0.5% by volume of molecular oxygen and 5 to 85% by volume of hydrogen oxide (water vapor). -%, preferably from 40 to 60 vol .-% treated. Here, the temperature is generally in the range of 300 to 500 is ⁰ C and preferably in the range of 350 to 450 ⁰ C. The non-oxidizing atmosphere may predominantly nitrogen and / or noble gases adjacent said hydrogen oxide, such as argon included. Gases, such as carbon dioxide are suitable in principle. The non-oxidizing atmosphere preferably contains more than 40% by volume of nitrogen.

By the duration of the second calcination stage, the proportion of crystalline vanadyl pyrophosphate can be adjusted.

The proportion of crystalline vanadyl pyrophosphate present in the catalyst is determined by X-ray diffractometric analysis (XRD), for example by the method described in the Examples. The ratio of the peak heights of the reflections measured at XRD at 2Θ = 23.0 ° and 2Θ = 28.5 ° is usually between 0.6 and 0.9.

In general, the calcination comprises a further step to be carried out after the second stage of the two-stage calcination, wherein the calcined catalyst precursor in an inert gas atmosphere to a temperature of less than 300 ⁰ C, preferably less than 200 ° C and more preferably of less than 150 ⁰ C cools.

Since the catalyst precursor usually has a temperature of less than 100 ^° C. before the beginning of the calcination, this is usually before the first calcining stage. to heat up. The heating can be carried out using various gas atmospheres. Preferably, the heating is carried out in an oxidizing atmosphere, as used, for example, in the first calcining stage or in an inert gas atmosphere as described in the second calcination stage. A change of the gas atmosphere during the heating phase is possible. Particularly preferred is the heating in the oxidizing atmosphere, which is also used in the first stage of the two-stage calcination.

Before, between and / or after the stages of the two-stage calcination further steps are possible. Without being limiting, further steps include, for example, changes in temperature (heating, cooling), changes in the gas atmosphere (conversion of the gas atmosphere), further holding times, transfers of the catalyst intermediate into other apparatus or interruptions of the entire quenching process.

In a particular embodiment, the thermal treatment of the catalyst precursor obtained after step b) can be carried out in situ, i. the thermal treatment of the catalyst precursor is carried out in the reactor in which the reaction carried out with the catalyst takes place, for example the gas-phase oxidation of hydrocarbons. As described below, gas phase oxidation of hydrocarbons usually occurs in a fluidized bed reactor, i. that in this embodiment, the thermal treatment is preferably carried out in situ in a fluidized bed reactor.

The catalyst preferably prepared by the process according to the invention usually has a phosphorus / vanadium atomic ratio of from 0.9 to 1.5, more preferably from 0.9 to 1.2, and most preferably from 1.0 to 1.1. The average oxidation state of the vanadium is preferably from +3.9 to +4.4, in particular from 4.05 to 4.20, and particularly preferably from 4.12 to 4.16.

The catalysts of the invention can be used for the gas phase oxidation of hydrocarbons, in particular for the production of maleic anhydride by gas phase oxidation of hydrocarbons having at least four carbon atoms.

In the process according to the invention for the preparation of maleic anhydride, fluidized bed reactors are generally used.

As hydrocarbons are usually aliphatic or aromatic, saturated or unsaturated hydrocarbons having at least four carbon atoms, such as 1, 3-butadiene, 1-butene, 2-cis-butene, 2-trans-butene, n-butane, C ₄ - Mixture, 1, 3-pentadiene, 1, 4-pentadiene, 1-pentene, 2-cis-pentene, 2-trans-pentene, n-pentane, cyclopentadiene, dicyclopentadiene, cyclopentene, cyclopentane, Cs-mixture, hexenes, hexanes, Cyclohexane and / or benzene used. Preference is given to 1-butene, 2-cis-butene, 2-trans-butene, n-butane, benzene or mixtures thereof. Particularly preferred is the use of n-butane and n-butane-containing gases and liquids. The n-butane used can be derived, for example, from natural gas, from steam crackers or FCC crackers (FCC = fluidic catalytic cracking).

The addition of the hydrocarbon is generally quantified, i. under constant specification of a defined amount per time unit. The hydrocarbon can be metered in liquid or gaseous form. Preferably, the dosage in liquid form with subsequent evaporation before entering the fluidized bed reactor.

As the oxidizing agent are oxygen-containing gases, such as air, synthetic air, an oxygen-enriched gas or so-called "pure", i. e.g. used oxygen derived from the air separation. The oxygen-containing gas is also added with volume control.

The oxidizing agent usually contains a hydrocarbon concentration of 0.5 to 15% by volume and an oxygen concentration of 8 to 25% by volume. The one hundred vol .-% missing share is composed of other gases such as nitrogen, noble gases, carbon monoxide, carbon dioxide, water vapor, oxygenated hydrocarbons (eg methanol, formaldehyde, formic acid, ethanol, acetaldehyde, acetic acid, propanol, propionaldehyde, propionic acid, acrolein, Crotonaldehyde) and their mixtures together. Preferably, the n-butane content of the total amount of hydrocarbon is more than 90% and more preferably more than 95%.

The inventive method is generally carried out at a temperature of 350 to 480 ⁰ C. Method of the invention at a temperature of 380-460 ⁰ C is preferred, more preferably from 380 to 440 ° C.

The process according to the invention can be carried out at a pressure below normal pressure (for example up to 0.05 MPa abs) or above normal pressure (for example up to 10 MPa abs). Preference is given to a pressure of 0.1 to 1.0 MPa abs, more preferably 0.15 to 0.7 MPa abs.

The process according to the invention can be carried out in two preferred process variants, the "straight through" variant and the "recirculation" variant. In the "straight pass", maleic anhydride and, if appropriate, oxygenated hydrocarbon by-products are removed from the reactor effluent and the remaining gas mixture is discharged and optionally thermally recycled. In the "recycling" is also removed from the reactor effluent maleic anhydride and optionally oxygenated hydrocarbon by-products, the remaining gas mixture containing unreacted hydrocarbon, completely or partially recycled to the reactor. Another variant of the "recycling" is the removal of the unreacted hydrocarbon and its return to the reactor.

In a particularly preferred embodiment for the preparation of maleic anhydride, n-butane is used as the starting hydrocarbon and the heterogeneously catalyzed gas-phase oxidation is carried out in the "straight pass" on the catalyst according to the invention.

In the method according to the invention using the catalysts according to the invention a high loading of the catalyst is made possible due to the high activity and selectivity. As a result of the long service lives, which are due to the good mechanical properties of the catalyst, the efficiency of the process can be further improved.

An advantage of the present invention is that using the VPO precursor of the present invention, improved catalysts for the gas phase oxidation of hydrocarbons having at least four carbon atoms to produce maleic anhydride can be obtained. The catalysts of the invention have a balanced property profile and can thus be used in an economical, large-scale process. In particular, the catalysts are distinguished by improved abrasion resistance. An improved abrasion resistance is a prerequisite for achieving long service lives in a fluidized bed process, since the catalysts are subjected to particularly high mechanical stresses in this process. Catalyst life is an important factor that determines the economics of a large scale process. Further properties which positively influence the property profile can be set by using the catalysts according to the invention. Thus, the use of the most expensive VPO precursor compared to the addition of inexpensive, inactive additives can be reduced while maintaining a high activity of the catalyst in the production of maleic anhydride. Reducing catalyst costs while maintaining or even increasing throughput results in a reduction in product-specific costs. It is also possible for new investments with the help of an active and abrasion-resistant catalyst to reduce the specific investment costs or to increase the capacity of existing plants without investment costs. Due to the great variability that exists in the selection of the preparation processes and further processing methods of the VPO precursor, with the respectively existing infrastructure for the production and further processing of the VPO precursor an improvement of the property profile of the catalysts in the production of maleic acid can be achieved. hydride can be achieved. The characterization method used to select and determine the VPO precursors of the present invention is simple and flexible to use in a wide range of applications.

The invention will be illustrated in the following examples.

Definitions and abbreviations used:

The quantities used in this document are defined as follows, unless otherwise stated: mass-related space velocity (WHSV) = n-butane m catalyst ^' *

n KW, reactor, one ⁿ KW, reactor, off

Sales X

¹ KW, reactor, a

¹ MSA, reactor, from selectivity S n KW, reactor, one ⁿ KW, reactor, off

Yield Y X S x conversion of hydrocarbons per reactor passage Xn-butane conversion to n-butane per reactor passage

S selectivity with respect to maleic anhydride per reactor passage

YMSA yield of maleic anhydride per reactor passage rTln-butane mass of n-butane m catalyst catalyst mass t time unit [h] nKW, reactor, a mass flow of hydrocarbons at the reactor inlet [mol / h] nKW, reactor, from mass flow of hydrocarbons at the reactor outlet [mol / h] nMSA, reactor, from mass flow of maleic anhydride at the reactor outlet [mol / h]

VPO precursor vanadium-, phosphorus- and oxygen-containing catalyst precursor

US dispersed ultrasonic dispersed PGV particle size distribution RPM revolutions per minute

Vox Mean oxidation state of vanadium U50, particle size Mean diameter, defined so that 50% of the total particle volume consists of particles with this or a smaller diameter. Q50, agglomerates Mean diameter defined as 50% of the total particle volume consisting of agglomerates of this or smaller diameter. Q50, catalyst precursor Mean diameter, defined so that 50% of the total particulate volume of the catalyst precursor particles consists of particles of this or smaller diameter.

U 50, mean diameter additive, defined as having 50% of the total particle volume of the particles of the additives consisting of particles of this or a smaller diameter,

P / V molar ratio of phosphorus to vanadium

I reaction reaction temperature

AR abrasion rate

K Kelvin h hour (s) bar bar above atmospheric pressure bar absolute bar

Used measuring methods:

Determination of residual carbon content:

To determine the residual carbon content, about 50 to 200 mg of the precisely weighed powdery sample in the presence of a pure oxygen stream in a quartz tube heated to about 1000 ⁰ C were added and annealed. The combustion gas obtained was passed through an IR zone and the content of carbon dioxide was determined quantitatively. From the amount of detected carbon dioxide, the residual carbon content of the sample could be recalculated.

Determination of the particle size distribution of the VPO precursors in the US dispersed state:

To determine the particle size distribution (PGV) of the primary particles of the VPO precursor was a mixture of 2 g of the dried VPO precursor in 100 ml of deionized water for 10 minutes by ultrasonic sonotrode (Schoeller Schall with generator TG400) at a power P of 240 watts externally and then continuously stirred in module MS17 and pumped into the measuring cell of the laser diffraction spectrometer "Malvern Mastersizer S." The volume-related particle size distribution was determined according to ISO 13320 at a wavelength of 632.8 nm ) is here defined so that 50% of the total particle volume consists of particles with this or a smaller diameter. A plot of the particle size distribution usually shows the volume fraction of the suspension with particles less than or equal to the particle size indicated on the abscissa.

Determination of the particle size distribution of the VPO precursors in the stirred state:

To determine the particle size distribution (PGV) of the VPO precursor in the stirred state, about 2 g of solid were suspended in 100 ml of VE-H2O in a 150 ml beaker; with a magnetic stirrer (Teflon-coated magnetic stirrer with a length of 20 mm, a diameter of 6 mm and a center ring), the suspension was in the presence of a baffle (height: 120 mm, width: 20 mm) at a speed n = about 600 rpm. Stirred uniformly for at least 30 seconds but not more than 60 seconds and then continuously stirred in module MS17 and pumped into the measuring cell of the laser diffraction spectrometer "Malvern Mastersizer S." The volume-related particle size distribution was determined according to ISO 13320. The mean particle diameter in the stirred state dso.Aggiomerate (median value) is defined here such that 50% of the total particle volume consists of agglomerates with this or a smaller diameter A plot of the particle size distribution usually shows the volume fraction of the suspension with particles smaller than or equal to the one indicated on the abscissa particle size.

Determination of the particle size distribution of the catalyst precursor (spray powder):

To determine the particle size distribution (PGV) of the catalyst precursor this was passed through a dispersing in the dry disperser Sympatec RODOS and dry-dispersed there with compressed air at a pressure of 0.1 bar (this existing agglomerates are transferred to the original spray powder) and in the free jet in the Blown measuring cell. From them, the volume-related particle size distribution was then determined according to ISO 13320 with the laser diffraction spectrometer Malvern Mastersizer S. The mean particle diameter d 50, catalyst precursor, given as the measurement result, is defined here such that 50% of the total particle volume consists of particles with this or a smaller diameter. Determination of the molar P / V ratio

The determination of the molar P / V ratio is carried out by atomic spectroscopy.

For the determination, in each case about 200 mg of the sample were mixed with 25 ml of hydrochloric acid (about 5 mol / l), heated and kept boiling for one hour. After cooling, transfer to a 250 ml volumetric flask and make up to 250 ml with demineralised water. The measurement is then carried out in the atomic emission spectrometer with inductively coupled plasma (ICP-AES) using ARL 3580 according to the measuring program IS 41 with a Meinhard atomizer, a dilution of 1:10, a simultaneous measurement with Se as an internal standard and at wavelengths of 178 nm ( P), 327 nm (V) and 363 nm (Sc).

Determination of the mean vanadium oxidation stage

The determination of the mean oxidation state of the vanadium was carried out by potentiometric titration.

For determination, 200 to 300 mg each of the sample was placed under argon atmosphere in a mixture of 15 ml of 50% sulfuric acid and 5 ml of 85% phosphoric acid, and dissolved by heating. The solution is then transferred to a titration vessel equipped with two Pt electrodes. The titrations were each carried out at 80 ^° C. First, a titration with 0.1 molar potassium permanganate solution was carried out. When two steps were obtained in the potentiometric curve, the vanadium was present in a mean oxidation state V _0x of +3 to less +4. If only one stage was obtained, the vanadium was present in an oxidation state of +4 to +5.

In the former case (two stages / + 3 <V _0x <+ 4), the solution did not contain V ⁵⁺ , that is, all vanadium was detected by titration. On the consumption of the 0.1 molar potassium permanganate solution and the position of the two stages, the amount of V ³⁺ and V ^{4+ was} calculated. The weighted average then gave the mean oxidation state.

In the latter case (one step / + 4 <V _0x <+5), the amount of V ^{4+ could} be calculated from the consumption of the 0.1 molar potassium permanganate solution.

By subsequent reduction of the entire V ^{5+ of} the resulting solution with a 0.1 molar ammonium iron (II) sulfate solution and re-oxidation with 0.1 molar potassium permanganate solution, the total amount of vanadium was calculated. The difference between the total amount of vanadium and the amount of V ⁴⁺ gave the amount of V ⁵⁺ originally present. The weighted average then gave the mean oxidation state.

X-ray diffractometric analysis of the catalysts:

For X-ray diffractometric analysis, the catalysts were pulverized and measured in a "D5000" X-ray powder diffractometer from Siemens The measurement parameters are given in Table 1. Table 1: Measurement parameters in the X-ray diffractometric analysis of the catalysts

The respective peak height results from the difference between the maximum intensity of the respective signal and the determined background.

abrasion test

In order to evaluate the mechanical stability of the prepared catalysts against the stresses they would be exposed to in a gas / solid fluidized bed, all the catalysts were subjected to the abrasion test described below. As a result, it provides an abrasion rate which describes the strength of the particles.

To determine the abrasion, about 20 g of a precisely weighed sample of the catalyst (mo, catalyst), which was prescreened with a 45 μm sieve, were placed on a 32 μm sieve of 192 mm diameter. Distance below the screen was rotated 10 mm in a slit die (0.5 mm slit width) with 32 U-min- ^1, leaked out of the 100 m ³ -lτ ¹ nitrogen at sonic velocity. The catalyst, accelerated by the jet, bounced against a plexiglass lid 8 mm above the screen. The sample material was subjected to intensive mechanical stress. The trial time was 3 hours. The resulting abrasion (particles with diameters <32 microns) came out with the gas through the mesh. The mass of the remaining particles was determined quantitatively by weighing at a distance of about 15 minutes. The abrasion rate AR, expressed in g-kg- ^1- lτ ¹ , is calculated as the quotient of the mass loss within the last hour of the test rriAbneb and the mass of the catalyst remaining after the experiment mκatai _yS ator after end of the experiment and the measurement time of 1 hour: AR = (rTlAbrieb / ΓTIO, catalyst "fTlAbπeb) ■

The lower the abrasion rate, the higher the mechanical stability of the catalyst.

The attrition rates of the catalysts according to the invention are generally less than 60 g-kg- ^1- h " ¹ and preferably less than 30 g-kg- ¹ -hr ¹ and are very suitable for fluidized bed processes.

Catalytic tests

The catalytic tests were carried out in a screening apparatus with parallel electrically heated fixed bed reactors (Dmnen = 5 mm) over copper blocks. For this, 1, 1 g of fluidized bed catalyst was mixed with steatite split (0.10 mm <d <0.35 mm) so that a fill height of 120 mm resulted in the reactor (about 60 vol .-% active mass). This catalytically active bed was between a feed of 250 mm Steatitkugeln (0.5 mm <d <1, 0 mm) and 10 mm Steatitsplit (0.10 mm <d <0.35 mm) on the one hand and a desquam of 10 mm steatite split (0.10 mm <d <0.35 mm) and 120 mm Steatitkugeln (0.5 mm <d <1, 0 mm) on the other hand fixed. The input gas used was a n-butane-air mixture homogeneously mixed via a static mixer. The mean reactor pressure, the catalyst loading with n-butane and the n-butane concentration was here, as indicated in Table 2, gradually increased over 50 h to 1, 0 barü, 0.1 15 hr ¹ and 2.05 vol .-% , The Reaktionstempe- temperature (Treaction) was chosen so that the value specified in Table 2 n-butane conversion (X _n-butane) was established. The analysis of the product gas stream was carried out by gas chromatography using a flame ionization detector. The total duration of the catalytic test was 75 hours. The lower the reaction temperature required and the higher the yield of MSA (YMSA), the higher the catalytic activity of the catalyst.

Table 2 Reaction conditions in catalytic testing

I) Preparation of VPO Precursors A to E:

Example A:

Preparation of the VPO Precursor A According to the Invention

In a nitrogen-inertized, externally heated via pressurized water 0.2 m ³ -

Steel / enamel stirred tanks with baffles were charged with 96 kg of isobutanol and 84 kg of benzyl alcohol. After starting up the three-stage impeller stirrer (137 rpm) 5.33 kg vanadium pentoxide were added within 20 minutes and then the energy input by Rüherdrehzahl (setpoint 87 rpm) reduced. The suspension was heated to reflux (about 16 ° C.) in the course of 50-60 minutes and left at this temperature for 6 hours. The mixture was then cooled linearly to 90 ^° C. within 50 minutes (30K / h). At 90 ^° C., 5.33 kg of polyethylene glycol were added via sluice gate within 20 minutes, heated to reflux again within 20 minutes and refluxed for 1 hour. Subsequently, it was cooled linearly to 60 ° C. within 80 minutes (40K / h). At 60 ⁰ C was then within 10 minutes with 8.17 kg of aqueous o-phosphoric acid (85%) precipitated (P / V = 1, 21), the kettle contents linearly refluxed within 30 minutes (5 K / h ) and leave under these conditions for 5 hours. Subsequently, the suspension was cooled linearly to 40 ° C. within 2 hours with stirring (40K / h). After reaching 40 ° C internal temperature, the stirrer was turned off and the suspension allowed to stand for 12 hours for aging. After stirring for 5 minutes (87 rpm), it was drained off into a heatable pressure filter chute previously rendered inert with nitrogen and filtered off at room temperature at a pressure above the filter chute of up to 0.3 MPa abs. The filter cake was made by continuous introduction of nitrogen and stirring with a centrally arranged, adjustable in height Stirrer is blown dry within about 10 minutes. After dry-blowing, the mixture was resuspended with 40 kg of acetone for 30 minutes and then the washing medium was squeezed off. The process was carried out a total of 3 times. After the last dry-blowing, the filter cake was placed under vacuum (about 15 kPa abs (150 mbar abs)), slowly rising jacket temperature (up to 120 ⁰ C) and use of the stirrer (clockwise, 10 rpm, 5-minute stirring, 25 minutes Pause) heated. After reaching the 120 ⁰ C jacket temperature was dried for 24 hours. The drying was carried out to a residual carbon content of less than 2.5% by weight in the dried VPO precursor. The VPO precursor A thus prepared had the particle size distribution shown in FIG. 1 with the mean particle diameters listed in Table 4. The measurement results for the residual carbon content, the ratio of phosphorus to vanadium and the oxidation state of the vanadium are given below: PN = 1, 040 residual carbon content: 2.2 wt .-%

Oxidation level of vanadium (Vo _x ): 3.99.

Example B:

Preparation of the VPO Precursor B According to the Invention

In a nitrogen-inertized, externally heated via pressurized water 0.2 m ³ -

Steel / enamel stirred tanks with baffles were charged with 67kg isobutanol and 59kg benzyl alcohol. After the three-stage impeller stirrer (137 rpm) had been put into operation, 3.73 kg of vanadium pentoxide were added within 20 minutes and then the energy input was reduced by means of a stirrer speed (nominal value 87 rpm). The suspension was heated to reflux (about 16 ° C.) in the course of 50-60 minutes and left at this temperature for 6 hours. The mixture was then cooled linearly to 90 ^° C. within 50 minutes (30K / h). At 90 ° C 3.73 kg of polyethylene glycol were added via sluice gate within 20 minutes, heated again within 20 minutes at reflux and boiled under reflux for 1 hour. Subsequently, it was cooled linearly to 60 ° C. within 80 minutes (40K / h). At 60 ⁰ C was then within 5 minutes with 5.20 kg of aqueous o-phosphoric acid (85%) precipitated (PA / = 1, 10), the kettle contents linearly refluxed within 30 minutes (45 K / h) and leave under these conditions for 5 hours. Subsequently, the suspension was cooled linearly to 40 ° C. within 2 hours with stirring (40K / h).

After reaching 40 ° C internal temperature, the stirrer was turned off and the suspension allowed to stand for 12 hours for aging. After stirring for 5 minutes (87 rpm), it was drained off into a heatable pressure filter chute previously rendered inert with nitrogen and filtered off at room temperature at a pressure above the filter chute of up to 0.3 MPa abs. The filter cake was dry blown by continuous introduction of nitrogen and stirring with a centrally located, height-adjustable stirrer within about 10 minutes. After the blow-dry was resuspended with 60 kg of acetone for 30 minutes and then the washing medium was squeezed. The process was carried out a total of 3 times. After the last dry-blowing, the filter cake was placed under vacuum (about 15 kPa abs (150 mbar abs)), slowly rising jacket temperature (up to 120 ⁰ C) and use of the stirrer (clockwise, 10 rpm, 5-minute stirring, 25 minutes Pause) heated. After reaching the 120 ⁰ C jacket temperature was dried for 24 hours. The drying was carried out to a residual carbon content of <2.5 wt .-% in the dried catalyst precursor.

The VPO precursor B thus prepared had the particle size distribution shown in FIG. 2 with the average particle diameters listed in Table 4. The measurement results for the residual carbon content, the ratio of phosphorus to vanadium and the oxidation state of the vanadium are given below. In addition, the specific surface area was determined by the BET method according to DIN 66.131. PN = 1, 040

Residual carbon content: 2.1% by weight. Oxidation state of vanadium (Vo _x ): 4.0. BET = 47 m ² / g

Example C:

Preparation of the VPO Precursor C According to the Invention

383 kg of isobutanol and 337 kg of benzyl alcohol were initially introduced into a 2 m ³ steel / enamel stirred tank with baffles, which had been rendered inert by means of nitrogen and were externally heated by pressurized water. After the three-stage impeller stirrer (123 rpm) had been put into operation, 21.3 kg of vanadium pentoxide were added within 20 minutes and the energy input was then reduced by means of an rpm (nominal value 81 rpm). The suspension was heated to reflux (about 16 ° C.) within 70 minutes and left at this temperature for 5 hours. The mixture was then cooled linearly to 90 ^° C. within 50 minutes (30K / h). At 90 ° C., 21.3 kg of polyethylene glycol were added via a sluice gate within 10 minutes, heated to reflux again within 20 minutes and refluxed for 1 hour. It was then cooled linearly to 60 ° C within 40 minutes (40K / h). At 60 ^° C., 33.8 kg of aqueous o-phosphoric acid (85% strength) were then precipitated within 10 minutes (PA / =

1, 25), the contents of the vessel are refluxed linearly (45 K / h) for 1.5 hours and left under these conditions for 4 hours. Subsequently, the suspension was cooled linearly to 40 ° C. within 2 hours with stirring (40K / h).

After reaching internal temperature 40 ^° C., the stirrer was switched off and the suspension allowed to stand for 12 hours for aging. After stirring for 5 minutes (81 rpm) was in a previously inertized with nitrogen, heated Druckfilternutsche drained and filtered off at room temperature at a pressure above the filter chute of up to 0.3 MPa abs. The filter cake was dry-blown by continuous introduction of nitrogen and stirring with a centrally located, height-adjustable stirrer within about 20 minutes. After dry-blowing, the mixture was resuspended with 100 kg of acetone for 30 minutes and then the washing medium was squeezed off. The process was carried out a total of 3 times. After the last dry-blowing, the filter cake was placed under vacuum (about 15 kPa abs (150 mbar abs)), slowly rising jacket temperature (up to 120 ⁰ C) and use of the stirrer (clockwise, 10 rpm, 5-minute stirring, 25 minutes Pause) heated. After reaching the 120 ⁰ C jacket temperature was dried for 24 hours. The drying was carried out to a residual carbon content of <2.5 wt .-% in the dried catalyst precursor.

The mean diameters of the primary particles of the VPO precursor and the agglomerates are listed in Table 3. The measurement results for the residual carbon content, the ratio of phosphorus to vanadium and the oxidation state of the vanadium are given below.

PΛ / = 1, 037 residual carbon content: 1.4% by weight

Oxidation level of vanadium (Vo _x ): 3.98.

Example D:

Preparation of the non-inventive VPO precursor D

383 kg of isobutanol and 337 kg of benzyl alcohol were initially introduced into a 2 m ³ steel / enamel stirred tank with baffles, which had been rendered inert by means of nitrogen and were externally heated by pressurized water. After starting up the three-stage impeller stirrer (123 rpm), 21.3 kg of vanadium pentoxide were added within 20 minutes, and then the energy input was reduced by means of an rpm (nominal value 81 rpm). The suspension was heated to reflux (about 1 16 ° C) within 70 minutes and left at this temperature for 5 hours. The mixture was then cooled linearly to 90 ^° C. within 50 minutes (30K / h). At 90 ° C., 21.3 kg of polyethylene glycol were added via a sluice gate within 10 minutes, heated to reflux again within 20 minutes and refluxed for 1 hour. It was then cooled linearly to 60 ° C within 40 minutes (40K / h). At 60 ⁰ C was then within 10 minutes with 35.6 kg of aqueous o-phosphoric acid (85%) precipitated (PA / = 1, 32), the vessel contents linearly refluxed within 1, 5 hours (45 K / h) and left under these conditions for 4 hours. Subsequently, the suspensions were sion over 2 hours with stirring linearly cooled to 40 ⁰ C (40K / h). After reaching internal temperature 40 ^° C., the stirrer was switched off and the suspension allowed to stand for 12 hours for aging. After stirring for 5 minutes (81 rpm), it was drained off into a heatable pressure filter chute previously rendered inert with nitrogen and filtered off at room temperature at a pressure above the filter chute of up to 0.3 MPa abs. The filter cake was dry-blown by continuous introduction of nitrogen and stirring with a centrally located, height-adjustable stirrer within about 20 minutes. After dry-blowing, the mixture was resuspended with 100 kg of acetone for 30 minutes and then the washing medium was squeezed off. The process was carried out a total of 3 times. After the last dry-blowing, the filter cake was placed under vacuum (about 15 kPa abs (150 mbar abs)), slowly rising jacket temperature (up to 120 ⁰ C) and use of the stirrer (clockwise, 10 rpm, 5-minute stirring, 25 minutes Pause) heated. After reaching the 120 ⁰ C jacket temperature was dried for 24 hours. The drying was carried out to a residual carbon content of <2.5% by weight in the dried catalyst precursor.

The mean diameters of the primary particles of the VPO precursor and the agglomerates are listed in Table 3. The measurement results for the residual carbon content, the ratio of phosphorus to vanadium and the oxidation state of the vanadium are given below.

PΛ / = 1, 042

Residual Carbon Content: 1, 1 wt% Oxidation Level of Vanadium (Vo _x ): 4.00.

Example E:

Preparation of the non-inventive VPO precursor E

In a 0.2 m ³ - steel / enamel stirred tank with baffles, which had been rendered inert by nitrogen and were externally heated by pressurized water, 67 kg of isobutanol and 59 kg of benzyl alcohol were initially charged. After the three-stage impeller stirrer (137 rpm) had been put into operation, 13.05 kg of vanadium pentoxide were added over the course of 20 minutes, and the energy input was then reduced by means of an rpm (nominal value 87 rpm). The suspension was heated to reflux (about 1 16 ° C) within 50-60 minutes and left at this temperature for 5 hours. Subsequently, within

50 minutes linearly cooled to 90 ° C (30K / h). At 90 ° C 0.71 kg of polyethylene glycol were added via sluice gate within 20 minutes, heated again within 20 minutes at reflux and boiled under reflux for 1 hour. It was then cooled linearly to 60 ⁰ C within 80 minutes (40K / h). At 60 ° C was then within 5 minutes with 20.0 kg of aqueous o-phosphoric acid (85%) precipitated (PA / = 1, 21), the contents of the kettle linearly heated to reflux within 30 minutes (45 K / h) and leave under these conditions for 5 hours. The suspension was then cooled over 2 hours with stirring linearly to 40 ⁰ C (40K / h).

After reaching 40 ⁰ C internal temperature of the stirrer was switched off and the suspensions pension for 12 hours aging allowed to stand. After 5 minutes of stirring

(87 rpm) was discharged into a previously heated with nitrogen, heated pressure filter and filtered off at room temperature at a pressure above the filter chute of up to 0.3 MPa abs. The filter cake was dry blown by continuous introduction of nitrogen and stirring with a centrally located, height-adjustable stirrer within about 10 minutes. After dry-blowing, the mixture was resuspended with 100 kg of acetone for 30 minutes and then the washing medium was squeezed off. The process was carried out a total of 3 times. After the last dry-blowing, the filter cake was placed under vacuum (about 15 kPa abs (150 mbar abs)), slowly rising jacket temperature (up to 120 ⁰ C) and use of the stirrer (clockwise, 10 rpm, 5-minute stirring, 25 minutes Pause) heated. After reaching the 120 ⁰ C jacket temperature was dried for 24 hours. The drying was carried out to a residual carbon content of <2.5 wt .-% in the dried catalyst precursor.

The mean diameters of the primary particles of the VPO precursor and the agglomerates are listed in Table 3. The measurement results for the residual carbon content, the ratio of phosphorus to vanadium and the oxidation state of the vanadium are given below.

PΛ / = 1, 042

Residual carbon content: 1.3 wt.% Oxidation level of vanadium (Vo _x ): 3.98

Table 3: Diameters of primary particles dso, Pnmarpartikei and agglomerates dso, agglomerates of VPO precursors A to E.

II) Preparation of the catalyst precursor (spray powder):

Example A-1: Preparation of a Catalyst Precursor from VPO Precursor A

6 kg of demineralized (VE) were dissolved in a cooled to 5-10 ⁰ C double jacket vessel 11 for preparing the Sprühturmvorlage submitted water and stirred with a propeller stirrer. 43.0 g of sodium silicate solution (soda waterglass from Merck KGaA, Darmstadt, D, article number: 1.05621.9040: about 27% by weight SiO ₂ and about 8% by weight Na ₂ O) were then added over about 10 minutes , pH = 11) and 1470.9 g of colloidal SiO ₂ sol (Nalco® 2326 from Nalco Co., Naperville, IL, USA; d ₅ o, additive: 5 nm, 15% by weight SiO ₂ , pH = 9, NH ₄ ⁺ as counterion). The solution was stirred with the propeller 5 min further and then acidic ion exchanger in a likewise temperature-controlled at 5-10 ⁰ C double jacketed vessel with 6.5 kg (DOWEX ^® HCR W2, Sigma-Aldrich, Saint Louis, Missouri, USA) converted. There, the suspension was stirred with continued cooling with a helical stirrer until the pH had dropped within about 5 minutes from initially about 14 to 3-4. The thus freshly prepared mixture of polysilicic acid and colloidal SiO ₂ -SoI was then pumped into another cooled to 5-10 ⁰ C jacketed tank. It was passed through a cartridge filter, which was permanently installed after the container.

Subsequently, the acidic ion exchanger was rinsed with demineralized water and regenerated with 10% H ₂ SO ₄ . To this end, as much H ₂ SO _{4 was} added to the ion exchanger with continued cooling that about 1 cm of liquid stood over the ion exchange resin. The resin and the acid were mixed with a helical stirrer. After 5 minutes, the stirrer was stopped and the acid was pumped off. At the outlet of the container was a sieve which retained the ion exchange resin. Subsequently, the resin was washed with deionized water. So much water was added that again stood about 1 cm of liquid over the resin. The resin-water mixture was also stirred with the helical stirrer for 5 minutes. The demineralized water was pumped off and a second cycle of regeneration with H ₂ SO ₄ and washing with deionized water was carried out. After this second cycle, the ion exchanger was rinsed with demineralised water until a pH of 3.5 was reached. At this pH, the proportion of SO ₄ ² "ions in the solution was no longer detectable, so that contamination of the catalyst with SO ₄ ² " ions could be prevented. Until the next use, the acidic ion exchanger was stored under demineralised water.

Parallel to the regeneration of the ion exchanger, the dispersion of the VPO precursor A in the freshly prepared mixture of polysilicic acid and colloidal SiO ₂ -SoI: In a cooled to 5-10 ° C double-walled container was this simultaneously with a propeller stirrer and an Ultra-Turrax stirrer intensely stirred. 2.5 kg of VPO precursor A were added in portions within about 1 hour and homogeneously dispersed. The suspension was then transferred to the spray tower receiver. From this was during the heating phase of the spray tower (diameter in the cylindrical part: 2.7 m, height of the cylindrical part: 1, 5 m, after Conical part with a height of 2.2 m below) then demineralised water and then during the spray-drying, the suspension with an eccentric screw pump in the LAMROT rotary atomizer (see T. Schröder, P. Walzel, Chem. Ing. Techn (68) 5/1996, pp. 562-566 and WO 94/21383) in the spray tower. As a volume flow of the suspension about 1 1 were l / h, the rotational speed of the rotary atomizer was 80 S ^'1. About an air manifold to the spray tower in cocurrent process were about 800 m ³ / h preheated (about 60 kW heater, heated to 170 ⁰ C) drying air is supplied. the air distributor in this case had the object of the drying air sharing in the ratio 50:50 in an axial and bear any costs a radial component in order to optimize the flow guide in the spray tower. the temperatures in the spray tower were 139 ° C at the atomiser, 107 ⁰ C in the cylindrical part and 106 ^° C. at the spray tower exit The dried powder was collected in a product receiver flanged to the conical part of the spray tower. The fines of the solid were discharged with the exhaust stream through a centrally located dip tube and placed in a cyclone separator (temperature 92 ° C), followed by cleaning the exhaust air with a bag filter The filter was automatically cleaned by spraying with compressed air every 2 minutes during the spray drying.

Example A-2:

Preparation of a Catalyst Precursor from VPO Precursor A

The catalyst precursor A-2 was prepared as described in Example A-1 with the VPO precursor A, with the difference that instead of a mixture of sodium silicate solution and the colloidal SiO 2 Nalco® 2326 (d = 5 nm) exclusively colloidal Si02 Ludox® SM30 (Grace Davison, Worms, D; dso, additive: 7 nm, 30% by weight SiO 2, pH = 10, Na ⁺ as counter ion) was used as the SiO 2 source.

Example A-3: Preparation of a catalyst precursor from the VPO precursor A.

The preparation of catalyst precursor A-3 was carried out as described in Example A-1 with VPO precursor A, with the difference that instead of a mixture of sodium silicate solution and colloidal SiO 2, pure sodium silicate solution was used as the SiO 2 source.

Example B-1:

Preparation of a catalyst precursor from VPO precursor B

The preparation of the catalyst precursor B-1 was carried out as described in Example A-1, with the difference that in place of the VPO precursor A, the VPO precursor B was used. Example B-2:

Preparation of a catalyst precursor from VPO precursor B

The preparation of catalyst precursor B-2 was carried out as in Example A-3, with the difference that VPO precursor B was used instead of VPO precursor A.

Example C-1:

Preparation of a Catalyst Precursor from VPO Precursor C

The preparation of the catalyst precursor C-1 was carried out as in Example A-3, with the difference that instead of the VPO precursor A, the VPO precursor C was used.

Comparative Example D-1:

Preparation of a Catalyst Precursor from VPO Precursor D Catalyst precursor D-1 was prepared as in Example A-1, with the difference that instead of VPO precursor A, the significantly coarser VPO precursor D was used.

Comparative Example E-1: Preparation of a Catalyst Precursor from VPO Precursor E

The catalyst precursor E-1 was prepared as in Example A-3, with the difference that instead of the VPO precursor A, the hardly agglomerated VPO precursor E was used.

Comparative Example E-2:

Preparation of a Catalyst Precursor from VPO Precursor E

The catalyst precursor E-2 was prepared as in Example A-2, with the difference that instead of the VPO precursor A, the hardly agglomerated VPO precursor E was used.

The properties of the catalyst precursors (spray particles) prepared in Experiments A-1, A-2, A-3, B-1, B-2, C-1, D-1, E-1 and E-2 in Table 4. A distinction between encapsulated and embedded catalysts was made by electron microscopy in conjunction with energy dispersive X-ray analysis (EDX). Table 4: Characterization of the spray particles

1) additive in the form of polysilicic acid. The average diameter of the polysilicic acid is about 1 nm (manufacturer's specification: <4 nm).

III) Preparation of the catalysts from the catalyst precursors:

Example 1 :

Preparation of a catalyst according to the invention from the catalyst precursor A-1

2 kg of catalyst precursor A-1 were introduced via a hose into a fluidized-bed reactor made of glass (internal diameter = 10 cm, height = 50 cm) kept at room temperature. The reactor was closed and there were 170 Nl-Ir ¹ to about 150 ⁰ C temperature-controlled air is introduced, with a bubbling fluidized bed trained. The air was removed at the tempered at 250 ⁰ C reactor head via a filter cartridge. Now the reactor was heated up to a bed temperature of 345 ° C according to the specified heating ramps:

1. heat with 4 K-min- ¹ to 120 ⁰ C and hold for 30 min,

2. Heat with 4 K-min- ¹ to 250 ⁰ C and hold for 30 min, 3. Heat with 2 K-min- ¹ to 335 ° C and hold for 45 min.

Then, the atmosphere of air to a mixture of 57 Nl-Ir ¹ ISb and 57 Nl h ^"1 H2O was converted, further heated at a heating rate of 1, 5 ^K-min-1 to 425 ° C and this temperature for 180 min The water supply was then switched off and cooled to room temperature under 100 μl Ir ¹ N ^2, after which the catalyst was suctioned off via a tube by means of a vacuum.

The catalyst prepared in this way was examined for its abrasion resistance (compare abrasion test) and its catalytic performance (see catalytic tests). The corresponding values are summarized in Table 5.

Example 2:

Preparation of a catalyst according to the invention from the catalyst precursor B-1

The preparation of the catalyst 2 was carried out as described in Example 1, with the difference that instead of the catalyst precursor A-1, the catalyst precursor B-1 was used. The catalyst prepared in this way was examined for its abrasion resistance (compare abrasion test) and its catalytic performance (see catalytic tests). The corresponding values are summarized in Table 5.

Example 3:

Preparation of a catalyst according to the invention from the catalyst precursor A-2

The preparation of the catalyst 3 was carried out as described in Example 1, with the difference that instead of the catalyst precursor A-1, the catalyst precursor A-2 was used. The catalyst prepared in this way was examined for its abrasion resistance (compare abrasion test) and its catalytic performance (see catalytic tests). The corresponding values are summarized in Table 5. Due to the coarser SiO 2 species used, the catalyst shows a still acceptable, but not optimal abrasion resistance.

Example 4:

Preparation of a catalyst according to the invention from the catalyst precursor A-3

The preparation of the catalyst 4 was carried out as described in Example 1, with the difference that instead of the catalyst precursor A-1, the catalyst precursor A-3 was used. The catalyst prepared in this way was tested for its abrasion resistance (cf. Abrasion test) and its catalytic performance (see Catalytic Tests). The corresponding values are summarized in Table 5. With good abrasion resistance, the yield of MSA achievable with this catalyst is below the target value due to the encapsulation with SiO 2.

Example 5:

Preparation of a catalyst according to the invention from the catalyst precursor C-1

The preparation of the catalyst 5 was carried out as described in Example 1, with the difference that instead of the catalyst precursor A-1, the catalyst precursor C-1 was used. The catalyst prepared in this way was examined for its abrasion resistance (compare abrasion test) and its catalytic performance (see catalytic tests). The corresponding values are summarized in Table 5. With good abrasion resistance, the yield of MSA achievable with this catalyst is clearly below the target value due to the encapsulation with SiC "2.

Example 6:

Preparation of a catalyst according to the invention from the catalyst precursor B-2

The preparation of the catalyst 6 was carried out as described in Example 1, with the difference that instead of the catalyst precursor A-1, the catalyst precursor B-2 was used. The catalyst prepared in this way was examined for its abrasion resistance (compare abrasion test) and its catalytic performance (see catalytic tests). The corresponding values are summarized in Table 5. With good abrasion resistance, an MSA yield below the target value can also be expected for this catalyst due to the encapsulation with SiC "2.

Comparative Example 1

Preparation of a non-inventive catalyst from the catalyst precursor D-1

The preparation of the catalyst V1 was carried out as described in Example 1, with the difference that instead of the catalyst precursor A-1, the catalyst precursor D-1 was used. The catalyst prepared in this way was examined for its abrasion resistance (compare abrasion test) and its catalytic performance (see catalytic tests). The corresponding values are summarized in Table 5. The catalyst shows very poor abrasion resistance due to the very coarse particles of the VPO precursor Comparative Example 2

Preparation of a non-inventive catalyst from the catalyst precursor

E-1

The preparation of the catalyst V2 was carried out as described in Example 1, with the difference that instead of the catalyst precursor A-1, the catalyst precursor E-1 was used. The catalyst prepared in this way was examined for its abrasion resistance (compare abrasion test) and its catalytic performance (see catalytic tests). The corresponding values are summarized in Table 5. Abrasion resistance is not sufficient for an encapsulated catalyst.

Comparative Example 3

Preparation of a non-inventive catalyst from the catalyst template

E-2

The preparation of the catalyst V2 was carried out as described in Example 1, with the difference that instead of the catalyst precursor A-1, the catalyst precursor E-2 was used. The catalyst prepared in this way was tested for its abrasion resistance (compare abrasion test) and its catalytic performance (see Catalytic Tests). The corresponding values are summarized in Table 5. The abrasion resistance does not meet the requirements of a fluidized bed process.

In Examples 1 to 3 and Comparative Example 3, embedded catalysts are obtained. The catalysts from experiments 1 to 3 were obtained from VPO precursors according to the invention, while the catalyst from comparative experiment V3 was prepared from a VPO precursor having an agglomerate size d50 and agglomerates of less than 2 μm. The catalysts according to the invention have an abrasion rate of 6, 25 or 58 g-kg- ^1- lτ ¹ , while the catalyst not according to the invention has an at least 4-fold higher abrasion rate of 253 g-kg- ^1- lτ ¹ .

In Examples 4 to 6, encapsulated catalysts were obtained from VPO precursors according to the invention. The abrasion rates were between 14 and 21 g-kg- ^1- lτ ¹ . In comparative experiment V2, encapsulated catalysts were obtained from a non-inventive VPO precursor which had an agglomerate size d50 and agglomerates of less than 2 μm. The abrasion rate of 59 g-kg- ^1- lτ ^{1 was} significantly higher than the attrition rates of the catalysts according to the invention.

In Comparative Example C1, using a non-inventive coarse VPO precursor having an agglomerate size dso, agglomerates of more than 20 μm, a catalyst was obtained in which the additive particles were largely present in the vicinity of the surface and formed a capsule. Despite the encapsulation, the abrasion rate was with 277 g-kg- ¹ -h " ¹ significantly worse than in the encapsulated catalysts of Examples 4 to 6 according to the invention.

Examples 1 to 3, as well as Comparative Example C1 show that with embedded catalysts higher yields of MSA in the production of maleic anhydride from butane (see section "catalytic tests") were obtained, but that encapsulated catalysts had on average better abrasion rates.

Irrespective of the further processing of the VPO precursors to form embedded or encapsulated catalysts or, if appropriate, mixed forms of these morphologies, comparatively better attrition rates were achieved by using a VPO precursor according to the invention than with non-inventive VPO precursors.

Table 5: Comparison of the properties of the various VPO fluidized bed catalysts. The specific surface area by means of the BET method was determined according to DIN 66.131.

Claims

claims

1. A process for the preparation of a catalyst precursor or a catalyst by a) preparation of a suspension containing a vanadium, phosphorus and

Oxygen-containing precursor (VPO precursor) whose ultrasonically dispersed primary particles in aqueous solution have a mean diameter dδo, Primarpartikei smaller than 1, 3 microns and those in water in the form of agglomerates with a mean diameter dso, agglomerates of 2 microns to 20 μm, the mean diameters of the primary particles and the agglomerates of the VPO precursor being determined by laser diffraction according to ISO 13320, b) spray-drying the suspension and c) optionally converting the catalyst precursor obtained in step b) into the catalyst by thermal treatment ,

2. A process for preparing a catalyst precursor or a catalyst according to claim 1, characterized in that at least one additive from the group of silica, zirconium dioxide, zinc oxide, alumina, boron oxide, titanium dioxide, germanium oxide and iron oxide is added to the suspension.

3. A process for preparing a catalyst precursor or a catalyst according to claim 2, characterized in that one uses as an additive silica.

4. A process for preparing a catalyst precursor or a catalyst according to any one of claims 2 to 3, characterized in that the proportion of additive, calculated as oxide, in the thermally treated catalyst in the range of 6 to 15 wt .-%, based on the dry mass of the thermally treated catalyst.

5. A process for preparing a catalyst precursor or a catalyst according to any one of claims 2 to 4, characterized in that the additive is present at least partially in colloidal form.

6. A process for preparing a catalyst precursor or a catalyst according to any one of claims 2 to 5, characterized in that the additive is at least partially in colloidal form, wherein the average diameter of the particles in colloidal form is 15 nm or less.

7. A process for preparing a catalyst precursor or a catalyst according to any one of claims 2 to 6, characterized in that the additive is present partially or completely as silica in the form of polysilicic acid.

8. A process for preparing a catalyst precursor or a catalyst according to claim 7, characterized in that the proportion of silicon dioxide in the form of polysilicic acid is less than 50 wt .-%, based on the sum of the dry matter of the added additives.

9. A process for preparing a catalyst precursor or a catalyst according to any one of claims 2 to 8, characterized in that the ratio of the average diameter of the primary particles of the VPO precursor (dso, Pπmarpartikei) to the mean diameter of the particles of the additive

(d so, additive) is in the range of 90 to 170.

10. A process for preparing a catalyst precursor or a catalyst according to any one of claims 2 to 8, characterized in that the ratio of the average diameter of the primary particles of the VPO precursor

(dso, Pπmarpartikei) to the mean diameter of the particles of the additive (dso, additive) is more than 500.

1 1. catalyst precursors or catalysts obtainable by a process according to claims 1 to 10.

12. Catalysts according to claim 1 1 with an abrasion rate (AR) of less than 30 g kg- ¹ -h- ¹ .

13. Vanadium-, phosphorus- and oxygen-containing precursor (VPO precursor), characterized in that the ultrasonically dispersed primary particles of the VPO precursor in aqueous solution have an average diameter dso, primarpam- kei smaller than 1, 3 microns, and that the catalyst precursor in water in the form of agglomerates having a mean diameter dso, agglomerates of 2 .mu.m to 20 .mu.m, wherein the average diameter of the primary particles and the

Aggiomerates of VPO precursor can be determined by laser diffraction according to ISO 13320.

14. Use of a catalyst according to claim 11 or 12 for Gasphasenoxi- dation of hydrocarbons.

15. Use of a catalyst according to claim 1 1 or 12 for the preparation of maleic anhydride by gas phase oxidation of hydrocarbons having at least four carbon atoms, in particular n-butane.

16. A process for the preparation of maleic anhydride by gas phase oxidation of hydrocarbons having at least four carbon atoms, in particular n-butane, characterized in that one carries out the oxidation in the presence of a catalyst according to claim 1 1 or 12.