EP1485203A1

EP1485203A1 - Catalyst-precursor for the production of maleic acid anhydride and method for the production thereof

Info

Publication number: EP1485203A1
Application number: EP03744350A
Authority: EP
Inventors: Jens Weiguny; Sebastian Storck; Mark Duda; Cornelia Dobner
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2002-03-15
Filing date: 2003-03-12
Publication date: 2004-12-15
Also published as: AU2003209726A1; DE10211449A1; CN1642640A; JP2005527346A; KR20040091741A; US7157403B2; US20050222435A1; WO2003078059A1

Abstract

The invention relates to a method for producing a catalyst-precursor containing vanadium, phosphorous and oxygen for the production of maleic acid anhydride by means of heterogeneous catalytic gas phase oxidation of a hydrocarbon having at least four hydrocarbon atoms by reacting vanadium pentoxide (I) in the presence of a primary or secondary, non-cyclic or cyclic, non-branched or branched, saturated alcohol having 3 - 6 carbon atoms (II) with one five or 3-valent phosphorous compound (III) by agitating in a temperature range of between 80 - 160 DEG C and subsequently filtration of the obtained suspension, wherein a filtration resistance of < alpha >H<. eta >of </=50.10<13> mPa<.>s/m2 is adjusted by (a) the manner in which the phosphorous compound (III) and the vanadium pentoxide (I) are brought together in the presence of the alcohol (II), (b) by the influence of an agitator power of between 0.01 0.6 W/kg suspension and/or (c) by the filtration in a temperature range of between 65 DEG C - 160 DEG C. The invention also relates to a catalyst-precursor obtained according to said method for producing a catalyst from the catalyst-precursor, a catalyst which can be obtained according to said method, in addition to a method for producing maleic acid anhydride on said catalyst.

Description

Catalyst precursor for the production of maleic anhydride and process for its production

description

The present invention relates to a process for the preparation of a vanadium, phosphorus and oxygen-containing catalyst precursor for the production of maleic anhydride by heterogeneous gas-phase oxidation of a hydrocarbon having at least four carbon atoms, by reaction of vanadium pentoxide (I) in the presence of a primary or secondary, non-cyclic or cyclic , unbranched or branched, saturated alcohol with 3 to 6 carbon atoms (II) with a pentavalent or trivalent phosphorus compound (III) with stirring in a temperature range from 80 to 160 ° C and subsequent filtration of the suspension obtained, and a catalyst precursor which according to this process was made.

Furthermore, the present invention relates to a catalyst containing vanadium, phosphorus and oxygen and to a process for its production using the catalyst precursor according to the invention.

The present invention further relates to a process for the preparation of maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms using the catalyst according to the invention.

Maleic anhydride is an important intermediate in the synthesis of γ-butyrolactone, tetrahydrofuran and 1,4-butanediol, which in turn are used as solvents or are further processed, for example, into polymers such as polytetrahydrofuran or polyvinylpyrrolidone.

The production of maleic anhydride by oxidation of hydrocarbons such as n-butane, n-butenes or benzene on suitable catalysts has long been known. In general, vanadium, phosphorus and oxygen are used for this purpose

Catalysts (known as VPO catalysts) are used (see üllmann's Encyclopedia of Industrial Chemistry, ^th edition 6, 2000 eleσtronic release, Chapter "MALEIC AM) Fumaric ACIDS, Maleic Anhydride - Production"). The generally used catalysts containing vanadium, phosphorus and oxygen are usually produced as follows:

(1) Synthesis of a vanadyl phosphate hemihydrate precursor

(V0HP0 • iH ₂ θ) from a pentavalent vanadium compound (e.g. V ₂ O ₅ ), a pentavalent or trivalent phosphorus compound (e.g. ortho- and / or pyrophosphoric acid, phosphoric acid ester or phosphorous acid) and a reducing alcohol (e.g. Isobutanol), isolation of the precipitate and drying, optionally shaping (eg tableting); and (2) preforming to vanadyl pyrophosphate ((VO) ₂ P ₂ 0 ₇ ) by calcination.

Various methods are known for producing the VPO catalyst precursor. They differ mainly (i) in the nature of the reducing alcohol, (ii) by the presence or absence of additional components such as promoters, modifiers or pore formers, (iii) by the order and the times of addition of the individual components in connection with the selected temperatures and (iv) in the isolation of the catalyst precursor formed.

EP-A 0 151 912 teaches the preparation of a VPO catalyst precursor in which vanadium pentoxide is reacted with phosphoric acid in the presence of isobutanol and a modifier selected from the series consisting of hydrogen iodide, sulfur dioxide, fuming sulfuric acid and surfactant. The mixture is heated under reflux and the catalyst precursor is then isolated by distilling off the solvent or by filtration.

EP-A 0 221 876, WO 94/04269 and US 4,147,661 describe the preparation of a VPO catalyst precursor in which phosphoric acid, isobutanol, vanadium pentoxide and a promoter component are reacted in the presence of supplied hydrogen chloride gas. The catalyst precursor is isolated by distilling off the solvent or by filtration.

The addition of the above-mentioned modifiers has the decisive disadvantage that hydrogen halides, sulfur dioxide and fuming sulfuric acid are very corrosive compounds, which require a considerable outlay in terms of apparatus, and if the surfactants are used, there is a risk of foam formation with the associated safety risks. Furthermore, the addition of the modifiers can lead to impurities in the precipitated catalyst precursor, which Performance (activity, selectivity, space / time yield, lifespan) can have a negative impact.

Isolating the catalyst precursor by distilling off the solvent also has the disadvantage that all non-volatile impurities, such as non-volatile degradation products of the alcohol, and impurities introduced via the reactant components remain in the precursor. During the subsequent calcination, there is, for example, the risk of uncontrolled decomposition or oxidation of the thermally unstable and oxidation-sensitive components and of an uncontrolled reduction of the vanadium by these components. In all the cases mentioned, there is a risk of irreversible damage to the catalyst. Furthermore, the catalyst precursor obtained by distilling off the solvent contains volatile phosphorus components due to the usually used excess of phosphorus, which are released during the calcination or when starting the oxidation reaction and can lead to undesired deposits.

No. 5,274,996 teaches the production of a VPO catalyst precursor by combining isobutanol, oxalic acid, vanadium pentoxide and phosphoric acid at room temperature, heating under reflux, if appropriate distilling off part of the solvent and isolating the catalyst precursor by decanting or filtering the cold mixture.

US 4,333,853 and EP-A 0 056 183 disclose the preparation of a VPO catalyst precursor by combining vanadimpentoxide, isobutanol and orthophosphoric acid or a mixture of ortho- and pyrophosphoric acid, heating under reflux, cooling the suspension obtained and isolating the pre - cursors by filtration.

EP-A 0 031 696 teaches the preparation of a VPO catalyst precursor by reducing vanadium pentoxide with isobutanol under reflux, removing the undissolved vanadium components, adding phosphoric acid, heating under reflux, cooling the suspension obtained and isolating the precursor by filtration ,

No. 5,922,637 discloses the production of a Mo-promoted VPO catalyst precursor by reducing vanadium pentoxide in the presence of a molybdenum-containing promoter component with isobutanol / benzyl alcohol at 77 ° C., cooling to 30 ° C., addition of Phosphoric acid, heating under reflux, cooling of the suspension obtained and isolation of the precursor by filtration.

EP-A 0 804 963 and US 4,668,652 disclose the preparation of a VPO catalyst precursor by heating a solution of isobutanol and phosphoric acid under reflux to boiling temperature, adding a suspension of vanadium pentoxide in isobutanol to the hot solution, further heating under reflux, cooling the resulting Suspension and isolation of the precursor by filtration.

EP-A 0 799 795, US 4,064,070 and US 4,132,670 describe the preparation of a VPO catalyst precursor in which a suspension of vanadium pentoxide and isobutanol or isobutanol / benzyl alcohol is heated under reflux to boiling temperature for several hours and then to the hot mixture Phosphoric acid is supplied. The mixture is refluxed for several hours, cooled and the precursor isolated.

WO 95/26817 teaches the production of an Fe- and Sb-promoted VPO catalyst precursor by combining vanadium pentoxide, isobutanol, benzyl alcohol and an iron and antimony-containing promoter component, heating under reflux, dropwise addition of phosphoric acid to the heated suspension, and more Reflux and isolate the precursor by filtration.

Isolating the precursor by decanting has the disadvantage that only a part of the liquid phase can be removed as a result and the remaining part is removed by evaporation during the subsequent drying. Associated with this are the disadvantages mentioned above when distilling off the solvent.

According to the invention, it was recognized that when carrying out the described processes, in which the precursor is isolated by filtration after precipitation, on an industrial scale, ie on a 100 kg or ton scale, the serious disadvantage of very long filtration times of many days to a few Weeks. As a result, the required apparatus is blocked over a long period of time and the production time of large amounts of catalyst precursor is enormously extended.

The object of the present invention was to provide a process for the preparation of a vanadium, phosphorus and oxygen-containing catalyst precursor for the production of maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon with at least four carbon atoms, which does not have the disadvantages mentioned above, is technically simple to carry out and the catalyst precursor can also be isolated quickly and efficiently on an industrial scale and, after a preforming to a catalyst which is also technically simple to carry out high activity and high selectivity.

Accordingly, a process for the preparation of a vanadium, phosphorus and oxygen-containing catalyst precursor for the production of maleic anhydride by heterogeneous gas-phase oxidation of a hydrocarbon having at least four carbon atoms, by reaction of vanadium pentoxide (I) in the presence of a primary or secondary, non-cyclic or cyclic , unbranched or branched, saturated alcohol having 3 to 6 carbon atoms (II) with a five- or trivalent phosphorus compound (III) with stirring in a temperature range from 80 to 160 ° C and subsequent filtration of the suspension found, which is characterized in that one by at least two measures in a row

(a) (i) adding the phosphorus compound (III) to that in the alcohol

(II) slurried and heated to 50 to 160 ° C vanadium pentoxide (I), the previous contact time between the vanadium pentoxide (I) and the

Alcohol (II) before beginning the addition of the phosphorus compound

(III) at a temperature> 50 ° C <1 hour; or

(ii) contacting the vanadium pentoxide (I) with the

Phosphorus compound (III) in the presence of the alcohol (II) at a temperature of> 0 ° C and <50 ° C and then heating at a heating rate of> 1.5 ° C / min to a temperature of 50 to 160 ° C;

(b) Effect of a stirring power in the reaction of the vanadium pentoxide (I) in the presence of the alcohol (II) with the phosphorus compound (III) from 0.01 to 0.6 W / kg of suspension, the physical being used in the calculation of the stirring power -chemical properties of the mixed feedstocks before implementation and at 20 ° C are taken as a basis; and

(c) filtration at a temperature of 65 ° C to 160 ° C; sets a filtration resistance ^a H ^'r l of <50 • 10 ¹³ mPa-s / m ² . The essence of the invention is the setting of a filtration resistance ^a H ^'r l of <50 • 10 ¹³ mPa-s / m ² in the filtration of the by reaction of vanadium pentoxide (I) in the presence of the alcohol (II) _ with the phosphorus compound (III) suspension obtained by at least two of the measures from the series (a), (b) and (c).

The filtration resistance ^a H ^'' is a well known parameter for filterability of suspensions at the given ¹⁰ temperature and for example in the VDI guideline 2762 "filterability of suspensions / determination of Filterkuchenwider- state", in February 1997 described by the Association of German Engineers. He is come together from the product of the specific and

3_g filter resistance x ^H related to the filter cake height and the dynamic viscosity ^. The smaller the filtration resistance

H ^T l, the better the suspension can usually be filtered.

20

The filtration resistance ^H ^ is determined in accordance with the above-mentioned VDI guideline 2762. For this purpose, a representative sample of the suspension is placed in a pressure filter with at least 20 cm ² filter area and at least 300 mL filling volume and

"by providing a constant differential pressure at the desired filtration temperature. The end of the filtration can be seen by equalizing the differential pressure due to the formation of cracks in the filter cake. The relationship that is decisive for the evaluation is given by the formula (IV)

30

in which the constants and variables are defined as follows: 5 t time since the start of filtration

A filter area

H _erι a height of the filter cake at the end of the filtration ₀ H ^'r l filtration resistance

V _end total filtrate volume

Δp pressure difference

V (t) filtrate volume at time t

R _τ filter resistance 5 dynamic viscosity. In the method according to the invention, one is preferably provided

Filtration resistance H ^" " of <25 10 ¹³ mPa-s / m ² , particularly preferably <20 10 ¹³ mPa-s / m ² and very particularly preferably _ <10 -10 ¹³ mPa-s / m ² .

Measure (a)

One of the measures according to the invention for adjusting a ⁰ filtration resistance ^a H ^'r l <50 • 10 ¹³ mPa-s / m ² relates to the manner of contacting the vanadium pentoxide (I) containing component and the phosphorus compound (III) component containing , Surprisingly, the following two alternative measures were found:

Measure (a) (i)

In measure (a) (i), the phosphorus compound (III) is added to that which is slurried in alcohol (II) and heated to 50 to 160 ° C., preferably to 60 to 160 ° C. and particularly preferably to 80 to 160 ° C. Vanadium pentoxide (I), the previous contact time between the vanadium pentoxide (I) and the alcohol (II) before the start of the addition of the phosphorus compound (III) at a temperature> 50 ° C. <1 hour. The additions are generally carried out with mixing, preferably with stirring.

Preferably, the previous contact time between the vanadium pentoxide (I) and the alcohol (II) before the addition of the phosphorus compound (III) is started at a temperature

> 50 ° C <45 minutes and particularly preferably <30 minutes. In a particularly preferred variant, the vanadium pentoxide (I) heated to> 50 ° C. is prepared by bringing together vanadium pentoxide (I) heated to> 0 ° C. and <50 ° C. with the alcohol (II) heated to 50 to 160 ° C. ,

In general, the combination is carried out in the reaction apparatus suitable for the subsequent reaction, for example a stirred kettle, with mixing.

The phosphorus compound (III) to be added can be added in undiluted or diluted form. If the phosphorus compound (III) is added in dilute form, a mixture with the alcohol (II) is preferred. To reduce the viscosity, it may be advantageous to add the viscosity To temper phosphorus compound (III) to a temperature in the range from 40 to 100 ° C., preferably from 40 to 60 ° C.

In one possible variant, a slurry of vanadium pentoxide (I) in alcohol (II) is placed in the reactor and then brought to a temperature of 50 to 160 ° C. The phosphorus compound (III), which may optionally be diluted with the alcohol (II), is then introduced into this slurry with stirring. To reduce the viscosity of the phosphorus compound (III) to be fed, it may be advantageous to temper it to a temperature in the range from 40 to 100.degree.

In another possible variant, the alcohol (II) is initially introduced and then preferably brought to a temperature of 50 to 160 ° C. Vanadium pentoxide is then added as a solid or, if appropriate, in the form of a slurry in alcohol (II) and the phosphorus compound (III), which may optionally be diluted with the alcohol (II), with stirring. The vanadium pentoxide or its slurry can optionally also be heated to an elevated temperature, for example 50 to 160 ° C. To reduce the viscosity of the phosphorus compound (III) to be fed, it may be advantageous to temper it to a temperature in the range from 40 to 100.degree. With the addition of the phosphorus compound (III), the supply of the vanadium pentoxide (I) can already be started. The addition of the phosphorus compound (III) is preferably started after about 10 to 100% and particularly preferably about 50 to 100% of the total amount of the vanadium pentoxide (I) has been added.

Measure (a) (ii)

In measure (a) (ii), the vanadium pentoxide (I) is combined with the phosphorus compound (III) in the presence of the alcohol (II) at a temperature of ≥ 0 ° C and <50 ° C and then heated at a heating rate of 1.5 ° C / min to a temperature of 50 to 160 ° C. The bringing together and the subsequent heating are generally carried out with mixing, preferably with stirring.

The temperature range specified for the bringing together of the vanadium pentoxide (I) and the phosphorus compound (III) in the presence of the alcohol (II) relates to the mixing temperature reached in each case. The individual components can be at different temperatures. Preferably he follows the bringing together at a temperature of 10 to 45 ° C and particularly preferably at a temperature of 20 to 40 ° C.

The order in which the individual components are added is generally immaterial. For example, it is possible to submit the alcohol (II) and to supply the vanadium pentoxide (I) and the phosphorus compound (III) in parallel or successively. Furthermore, it is also possible to provide the phosphorus compound (III), if appropriate mixed with the alcohol (II), and to add the vanadium pentoxide (I) and, if appropriate, further alcohol (II) together or successively. Furthermore, it is also possible to submit the vanadium pentoxide (I) suspended in alcohol (II) and to supply the phosphorus compound (III). The bringing together and the subsequent heating are generally carried out with mixing, preferably with stirring.

The phosphorus compound (III) to be added can be added in undiluted or diluted form. If the phosphorus compound (III) is added in dilute form, one is

Mixture with the alcohol (II) is preferred. To reduce the viscosity, it may be advantageous to temper the phosphorus compound (III) to be added to a temperature in the range from 40 to 100 ° C., preferably from 40 to 60 ° C.

The mixture obtained is then at a heating rate of> 1.5 ° C / min and preferably of> 2 ° C / min to a temperature of 50 to 160 ° C, preferably 60 to 160 ° C and particularly preferably 80 to 160 ° C. heated up.

It should be pointed out that within the scope of the present invention measure (a) is optional provided that measures (b) and (c) are fulfilled. A few further possible variants of the bringing together are therefore described below, which do not fall under measure (a) according to the invention, but can nevertheless be carried out under the above-mentioned condition.

In one of the variants of the combination which does not fall under measure (a) according to the invention, the vanadium pentoxide (I) is brought with the phosphorus compound (III) in the presence of the alcohol (II) at a temperature of> 0 ° C. and <50 ° C together and then heats to a temperature of 50 to 160 ° C at a heating rate of <1.5 ° C / min. The bringing together and the subsequent heating are generally carried out with mixing, preferably with stirring.

In a further variant of the bringing together, which does not fall under measure (a) according to the invention, the phosphorus compound (III), which can optionally be diluted with the alcohol (II), is initially taken and then preferably brought to a temperature of 50 to 160 ° C. Vanadium pentoxide (I) is then added as a solid or optionally in the form of a slurry in the alcohol (II). The vanadium pentoxide (I) or its slurry can optionally also be heated to an elevated temperature, for example 50 to 160 ° C. The combination is generally carried out with mixing, preferably with stirring.

Furthermore, so-called promoter components can be added in the manufacture of the catalyst precursor. The elements of the 1st to 15th group of the periodic table and their compounds are mentioned as suitable promoters. Suitable promoters are described, for example, in WO 97/12674 and WO 95/26817 as well as in US 5,137,860, US 5,296,436, US 5,158,923 and US 4,795,818. Compounds of the elements cobalt, molybdenum, iron, zinc, hafnium, zircon, lithium, titanium, chromium, manganese, nickel, copper, boron, silicon, antimony, tin, niobium and bismuth are preferred as promoters, particularly preferably molybdenum, iron, zinc , Antimony, bismuth, lithium. The promoted catalysts can contain one or more promoters. In general, the promoter components are added during, before, during or after the reaction of the vanadium pentoxide (I) in the presence of the alcohol (II) with the phosphorus compound (III). The total amount of promoters in the finished catalyst is generally not more than about 5% by weight, calculated as oxide.

Suitable promoter components are, for example, the acetates, acetylacetonates, oxalates, oxides or alkoxides of the aforementioned promoter metals, such as cobalt (II) acetate, cobalt (II) acetyl acetonate, 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, zircon (IV) butoxide, silicon (IV) ethoxide, niobium (V) chloride and niobium (V) - oxide. For further details, reference is made to the aforementioned W0 laid-open documents and US patents. The relative molar ratio of the phosphorus compound (III) to the vandium pentoxide (I) is generally adjusted according to the desired ratio in the catalyst precursor. The molar phosphorus / vanadium ratio in the reaction mixture for the preparation of the catalyst precursor is preferably 1.0 to 1.5 and particularly preferably 1.1 to 1.3.

The amount of alcohol (II) should advantageously be above the stoichiometrically required amount for the reduction of the vanadium from the oxidation level +5 to an oxidation level in the range +3.5 to +4.5. The amount should also be such that a slurry can be formed with the vanadium pentoxide (I), which enables intensive mixing with the phosphorus compound (III). In general, the molar ratio of the alcohol (II) to the vanadium pentoxide (I) is 10 to 25 and preferably 12 to 20.

If the components vanadium pentoxide (I), the alcohol (II) and the phosphorus compound (III) are combined, the mixture is reacted over a period of usually several hours with mixing, preferably with stirring, to a temperature of 80 to for a period of usually several hours Heated 160 ° C. The temperature range to be selected depends on various factors, for example the boiling point of the alcohol (II) added, and can be optimized by simple experiments. The volatile compounds, such as water, the alcohol (II) and its degradation products, such as aldehyde or carboxylic acid, evaporate from the reaction mixture and can either be removed or partially or completely condensed and recycled. Partial or complete recycling by heating under reflux is preferred. Complete recycling is particularly preferred. The reaction at elevated temperature generally takes several hours and is dependent on many factors, such as the type of components added or the temperature. In addition, the properties of the catalyst precursor can also be set and influenced in a certain range by means of the temperature and the selected heating duration. The parameters of temperature and time can easily be optimized for an existing system with just a few tests. The time required for the implementation mentioned is usually 1 to 25 hours. Measure (b)

Another one of the measures according to the invention for adjusting a filtration resistance ^{H '^} <50 ^■ 10 ¹³ mPa-s / m ^2, the action of a stirring power in the reaction of the vanadium pentoxide (I) in the presence of the alcohol (II) with the phosphorus compound (III) from 0.01 to 0.6 W / kg of suspension, the physicochemical properties of the mixed feedstocks before the reaction and at 20 ° C being used as the basis for calculating the stirring power.

The stirring power is to be understood as the power per unit mass of the suspension due to the stirring. The stirring performance is a well-known parameter for stirring solutions and suspensions from the field of stirring technology. It is described, for example, in Werner Hemming, "Process engineering" from the "Kamprath series Technology, short and sweet", Vogel Verlag, Würzburg, 1975, ISBN 3-8023-0084-X, Chapter 6.1.1 and in Marko Zlokarnik, " Mixing Technology - Theory and Practice ", Springer-Verlag Berlin 1999, chapter 2.1, pages 73 to 79. -

The stirring power P is calculated with knowledge of the dimensionless performance index N _e according to formula (V)

P = N _e - p - d ⁵ - n ³ (V), where p stands for the average density of the suspension, d for the diameter of the stirrer and n for the speed of the stirrer. The dimensionless performance index N _e depends on the system and can be determined with knowledge of the stirrer shape and the modified dimensionless Reynold index Re _M

Re _M = ^ ~ (VI), v where v stands for the kinematic viscosity and n and d have the meaning given above, are determined from the diagram for determining the performance characteristics. A corresponding diagram is contained, for example, in Marko Zlokarnik, "Mixing Technology - Theory and Practice", Springer-Verlag Berlin 1999, page 77, Figure 2.2. When calculating the stirring power, the physicochemical properties of the mixed feedstocks, namely the kinematic viscosity V and the density p, are used before the reaction and at 20 ° C.

In the method according to the invention, measure (b) is preferably allowed to stir from 0.01 to 0.5 W / kg of suspension, particularly preferably from 0.02 to 0.5 W / kg of suspension and very particularly preferably from 0.05 to 0 , 4 W / kg suspension.

The method according to the invention can in principle be carried out using different stirrer geometries. Depending on the viscosity range of the suspension to be stirred, disk stirrers, impeller stirrers, inclined blade stirrers, propeller stirrers and their modifications are preferred. Depending on the size of the approach and the volume and the geometry of the stirring container, it may be advantageous to use a stirrer with several, for example two or three, stirring elements attached to the stirring shaft. In this case one speaks of a "multi-stage" stirrer. The stirring is generally carried out in the presence of one or more baffles.

It should be pointed out that within the scope of the present invention measure (b) is optional provided that measures (a) and (c) are fulfilled. In this case it is also possible, for example, to allow the reaction of the vanadium pentoxide (I) in the presence of the alcohol (II) with the phosphorus compound (III) to have a significantly higher stirring power.

After the reaction of the vanadium pentoxide (I) in the presence of the alcohol (II) with the phosphorus compound (III) has ended, the precipitate formed is filtered off, a cooling phase and a storage or aging phase of the cooled reaction mixture possibly being interposed before the filtration ,

Measure (c)

The third of the measures to set a

Filtration resistance ^a H ^'r l of <50 • 10 ¹³ mPa-s / m ² is the filtration of the precipitate formed at a temperature of 65 ° C to 160 ° C. The filtration is preferably carried out at a temperature of 70 to 160 ° C. and particularly preferably at a temperature of

80 to 160 ° C. In principle, the filtration in the process according to the invention can be carried out in the known devices suitable for filtration. Examples of suitable devices are filters, plate filters and centrifuges (eg inverting filter centrifuges). The use of a nutsche is preferred. Suitable filter media are filter papers, porous filter foils, close-meshed nets and fabrics, with narrow-meshed nets and fabrics being generally preferred. Pressure filtration is preferred.

The use of a heatable pressure filter chute, which in a very particularly preferred embodiment is equipped with a heatable stirrer, is particularly preferred. The heated agitator can, for stirring up the suspension for leveling of the filter cake, cknüngsvorgang to heat input during subsequent Tro ^'and to loosen up the contract Produktaus- serve.

The isolated precipitate can be processed unwashed or washed. Washing the isolated precipitate has the advantage that residues of the alcohol (II) which are still adhering and their breakdown products can be reduced further. Examples of suitable solvents for the washing process are alcohols, aliphatic and / or aromatic hydrocarbons (e.g. pentane, hexane, benzine, benzene, toluene, xylenes), ketones (e.g. 2-propanone (acetone), 2-butanone, 3-pentanone, ether (for example 1,2-dirthethoxyethane, tetrahydrofuran, 1,4-dioxane) or mixtures thereof, if the isolated precipitate is washed, the alcohol (II) chosen in the previous reaction is preferably used.

It should be pointed out that measure (c) is optional in the context of the present invention, provided that measures (a) and (b) are fulfilled. In this case, it is also possible, for example, to carry out the filtration of the precipitate formed at a significantly lower temperature.

The filtration resistance ^{H '} ^ depends, among other things, on the temperature at which the filtration is carried out and the particle size distribution of the particles formed in the reaction of the vanadium pentoxide (I) in the presence of the alcohol (II) with the phosphorus compound (III). The latter is significantly influenced in the context of the measures according to the invention by carrying out measure (a), measure (b) or both measures (a) and (b). The suspension obtainable when carrying out the process according to the invention preferably has a volume Proportion of the suspension with particles <10 μ of <30%, particularly preferably of <20% and very particularly preferably of <10%. The particle size distribution mentioned is usually determined by means of laser diffraction spectrometry.

The isolated precipitate can be further processed in various ways. For example, the isolated precipitate can be further processed in a moist, dried or pre-annealed state, with a smooth transition generally occurring between drying and pre-tempering.

Drying is generally considered to be a temperature treatment in the range from 30 to 250 ° C., which is generally carried out at a pressure of 0.0 (“vacuum”) to 0.1 MPa abs (“atmospheric pressure”). When drying under vacuum, a lower temperature can generally be used than when drying under atmospheric pressure. The gas atmosphere which may protrude during drying can contain oxygen, water vapor and / or inert gases such as nitrogen, carbon dioxide or noble gases. Drying is preferably carried out at a pressure of 1 to 30 kPa abs and a temperature of 50 to 200 ° C. under an oxygen-containing or oxygen-free residual gas atmosphere, such as, for example, air or nitrogen. Drying can be carried out, for example, in the device used for the filtration or in a separate apparatus, for example a drying cabinet or a continuously operating belt dryer. Drying is preferably carried out in the device used for the filtration.

Preheating is generally considered to be a temperature treatment in the range from 200 to 350 ° C., preferably from 250 to 350 ° C. In principle, the annealing can be carried out in a wide pressure range, the use of low pressures generally promoting the removal of organic components. In general, the heat treatment is carried out at a pressure of 0.0 ("vacuum") to 0.15 MPa abs, preferably at about 0.1 MPa abs ("atmospheric pressure"). The annealing generally takes several minutes to several hours and is dependent on many factors, such as, for example, the concentration of the phosphorus compound (III) used, the type of alcohol used (II), the further treatment of the deposited precipitate (eg aging of the precipitate) as well as the selected tempering temperature. For example, it is possible that a long-term tempering at a low temperature leads to a similar result to a shorter-term tempering at a medium or higher temperature. The parameters of temperature and time for an existing system can be can be optimized. As a rule, the required annealing time is 0.5 to 10 hours. The gas atmosphere present during the tempering can contain oxygen, water vapor and / or inert gases such as nitrogen, carbon dioxide or noble gases. The tempering is preferably carried out in air.

The heat treatment can be carried out batchwise or continuously, for example. Drying ovens, muffle furnaces, belt calciners, vortex dryers or rotary tubes may be mentioned as suitable apparatus. In order to obtain a uniformly tempered product, it is generally advantageous to use a continuously operating tempering process with mixing of the powder to be tempered. Tempering in a continuously operated rotary tube is therefore particularly preferred.

In the process according to the invention, the isolated precipitate is preferably dried and then tempered in a temperature range from 250 to 350 ° C. in an air atmosphere.

In general, the product produced by the process described above is shaped into particles with an average diameter of at least 2 mm and preferably of at least 3 mm. The mean diameter of a particle is the mean of the smallest and the largest dimension between two plane-parallel plates.

Particles are understood to mean both randomly shaped particles and geometrically shaped particles, so-called shaped bodies. The tempered product obtained from step (c) is preferably shaped into shaped bodies. Examples of suitable moldings are tablets, cylinders, hollow cylinders, balls, strands, wagon wheels or extrudates. Special shapes, such as "Trilobes" and "Tristars" (see WO 93/01155) or moldings with at least one notch on the outside (see US Pat. No. 5,168,090) are also possible.

The shaping is preferably carried out by tableting, with the dried and preferably the preheated catalyst precursor powder usually being used for this purpose. Tablets, cylinders and hollow cylinders may be mentioned as preferred molded articles. For tableting, a tabletting aid is generally added to the powder and mixed intimately. Tableting aids are generally catalytically inert and improve the tabletting properties of the so-called powder, for example by increasing the sliding and free-flowing properties. Graphite may be mentioned as a suitable and preferred tabletting aid. The tabletting aids added remain in the Usually in the activated catalyst. The content of tabletting aid in the finished catalyst is typically about 2 to 6% by weight.

Moldings with an essentially hollow cylindrical structure are particularly preferably formed. An essentially hollow-cylindrical structure is to be understood as a structure which essentially comprises a cylinder with an opening passing between the two cover surfaces. The cylinder is characterized by two essentially parallel cover surfaces and a lateral surface, the cross section of the cylinder, i.e. parallel to the lid surfaces, is essentially circular in structure. The cross section of the through opening, i.e. parallel to the cover surfaces of the cylinder is essentially also of a circular structure. The through opening is preferably located in the center of the cover surfaces, other spatial arrangements not being ruled out.

The term "essentially" indicates that deviations from the ideal geometry, such as, for example, slight deformations of the circular structure, non-plane-parallel top surfaces, chipped corners and edges, surface roughness or notches in the outer surface, the top surfaces or the inner surface of the through Bore are included in the catalyst of the invention. In the context of the accuracy of the art of tableting, circular cover surfaces, a circular cross section of the bore passing through, parallel cover surfaces and macroscopically smooth surfaces are preferred.

The essentially hollow cylindrical structure can be described by an outer diameter di, a height h as the distance between the two cover surfaces and a diameter of the inner hole (through opening) d ₂ . The outer diameter di is preferably 3 to 10 mm, particularly preferably 4 to 8 mm, very particularly preferably 4.5 to 6 mm. The height h is preferably 1 to 10 mm, particularly preferably 2 to 6 mm, very particularly preferably 2 to 3.5 mm. The diameter of the opening d ₂ passing through is preferably 1 to 8 mm, particularly preferably 2 to 6 mm, very particularly preferably 2 to 3 mm. A hollow-cylindrical structure is particularly preferred which (a) has a ratio of the height h to the diameter of the through opening d of at most 1.5 and (b) a ratio of the geometric surface A _geo to the geometric volume V _geo of at least 2 mm ^-1 , as described for example in WO 01/68245. In the method according to the invention, by carrying out at least two measures from the series (a), (b) and (c) of the measures according to the invention, a filtration resistance becomes

^H ^ set from <50 ■ 10 ¹³ -mPa-s / m ² . It is immaterial within the scope of the invention which two of the measures according to the invention are carried out. At this point it should be pointed out again that in measure (a) there are two alternative possibilities according to the invention for bringing together the starting materials vanadium pentoxide (I), alcohol (II) and phosphorus compound (III), namely measure (i), below abbreviated as (ai) and measure (ii), hereinafter abbreviated as (a-ii).

The following may be explicitly mentioned as possible combinations of the measures according to the invention: (a-i) and (b), (a-i) and (c), (b) and (c),

(a-i) and (b) and (c), (a-ii) and (b), (a-ii) and (c) as well

(a-ii) and (b) and (c).

Of the above seven combinations, those combinations which contain measure (a-i) or (a-ii) are preferred. These preferred combinations are: (ai) and (b), (ai) and (c), (ai) and (b) and (c), (a-ii) and (b), (a-ii) and ( c) and (a-ii) and (b) and (c).

The combinations which contain measure (a-i) and the combinations which contain all three measures (a), (b) and (c) according to the invention are particularly preferred. These particularly preferred combinations are: (a-i) and (b), (a-i) and (c), (a-i) and (b) and (c) as well as (a-ii) and (b) and (c).

The combinations which contain all three measures (a), (b) and (c) according to the invention are very particularly preferred. These very particularly preferred combinations are: (a-i) and (b) and (c) and (a-ii) and (b) and (c), in particular (a-i) and (b) and (c).

The vanadium pentoxide (I) is preferably used in the form of a powder, particularly preferably in a particle size range from 50 to 500 μm. If significantly larger particles are present, the solid is crushed and, if necessary, sieved. Suitable devices are, for example, ball mills or planetary mills.

The primary or secondary, noncyclic or cyclic, unbranched or branched, saturated alcohol having 3 to 6 carbon atoms (II) is generally a primary or secondary, unbranched or branched branched C ₃ - to C _ß- alkanol, cyclopentanol, cyclohexanol or mixtures thereof. Suitable 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-l-hexanol, 3-methyl-l-pentanol, 4-methyl-l-pentanol, 3-methyl-2-pentanol, 4-methyl-2-pentanol, 2, 2-dimethyl-1-butanol, 2, 3-dimethyl-1-butanol, 3, 3-dimethyl-1-butanol,

3, 3-dimethyl-2-butanol, cyclopentanol, cyclohexanol and mixtures thereof. Primary, unbranched or branched C ₃ - to Cs-alkanols and cyclohexanol are particularly preferably used. N-Propanol (1-propanol), n-butanol (1-butanol), isobutanol (2-methyl-l-propanol),

1-pentanol, 2-methyl-l-butanol, 3-methyl-l-butanol and cyclohexanol, especially of isobutanol.

Examples of suitable pentavalent or trivalent phosphorus compounds (III) include ortho-, pyro-, polyphosphoric acid, phosphoric acid esters and phosphorous acid. A pentavalent phosphorus compound, particularly preferably orthophosphoric acid (HP0 ₄ ), pyrophosphoric acid (H ₄ P ₂ 0), polyphosphoric acid (H _{n + 2} P _n 0 _{3n +} ι with n> 3) or mixtures thereof are preferably used.

In a very particularly preferred embodiment, a mixture of ortho-, pyro- and polyphosphoric acid with a calculated H ₃ PO content of 102 to 110% by weight, in particular 104 to 106% by weight, is used. The phosphoric acid to be used is generally prepared by introducing phosphorus pentoxide into water or aqueous, for example 85 to 100%, phosphoric acid.

In a particularly preferred embodiment for the preparation of the catalyst precursor, a slurry of vanadium pentoxide in isobutanol is placed in a suitable stirrer at a temperature of> 0 ° C. and <50 ° C. and 102 to 110% phosphoric acid are added with stirring. The mixture is then heated to a temperature of 80 to 120 ° C. with stirring at a rate of from 0.01 to 0.6 W / kg of suspension at a heating rate of> 1.5 ° C./min and is stirred for several hours with the Leave the above stirring power under reflux conditions. Subsequently, the hot suspension, preferably in the said temperature range of ⁸⁰ to 120 ° C filtered, washed with a small amount of isobutanol and at a temperature in the range of 100 to 200 ° C under vacuum. The isolated and dried precipitate is now continuous, preferably in a rotary tube, in air at about atmospheric pressure in a temperature range from 250 to 350 ° C and an average residence time in the range from 0.5 to 5 hours, preferably from 1 to 3 hours. The tempered product obtained is then intimately mixed with 2 to 6% by weight of graphite and tabletted into tablet-shaped or hollow cylindrical shaped bodies. The catalyst precursor is preferably tableted into hollow cylinders with an outer diameter di of 5 to 6 mm, a height h of 3 to 4 mm and a diameter of the opening d of 2 to 3 mm.

In a very particularly preferred embodiment for producing the catalyst precursor, a slurry of vanadium pentoxide in isobutanol heated to 50 to 120 ° C. is provided in a suitable stirring apparatus. The slurry mentioned can be provided in various ways, for example by bringing together vanadium pentoxide and isobutanol and then heating to the desired temperature or introducing vanadium pentoxide into previously heated isobutanol. 102 to 110% phosphoric acid is then added to this slurry of vanadium pentoxide in isobutanol, heated to 50 to 120 ° C., with stirring with a stirring power of 0.01 to 0.6 W / kg of suspension. The mixture is then left for several hours with further stirring with the above-mentioned stirring power at a temperature of 80 to 120 ° C. under reflux conditions, it possibly being necessary to heat up to reach 80 to 120 ° C. beforehand. The hot suspension is then filtered, preferably in the temperature range mentioned from 80 to 120 ° C., washed with a little isobutanol and dried under vacuum at a temperature in the range from 100 to 200 ° C. The isolated and dried precipitate is then annealed continuously, preferably in a rotary tube, in air at about atmospheric pressure in a temperature range from 250 to 350 ° C. and an average residence time in the range from 0.5 to 5 hours, preferably from 1 to 3 hours , The tempered product obtained is then intimately mixed with 2 to 6% by weight of graphite and tabletted into tablets or hollow cylindrical shaped bodies. The catalyst precursor is preferably tableted into hollow cylinders with an outer diameter di of 5 to 6 mm, a height h of 3 to 4 mm and a diameter of the opening d ₂ of 2 to 3 mm.

Furthermore, a catalyst precursor for the production of maleic anhydride by heterogeneous gas phase oxidation of a hydrocarbon with at least four carbons was Found atoms of matter, which is obtainable according to the inventive method described above.

The process according to the invention enables the production of a catalyst precursor containing vanadium, phosphorus and oxygen for the production of maleic anhydride by heterogeneous gas-phase oxidation of a hydrocarbon having at least four carbon atoms, the preparation of the catalyst precursor being simple to carry out technically, and the catalyst precursor also being technical The scale, above all, can be isolated quickly and efficiently and, as a selectivity and activity-determining precursor, enables the production of a catalyst with a high activity and a high selectivity. The fast and efficient filtration contributes significantly to the fast and efficient production of the entire catalyst precursor. A significantly higher throughput can be achieved with the same filtration capacity.

The invention furthermore relates to a process for the preparation of a catalyst containing vanadium, phosphorus and oxygen for the production of maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms, by treating a catalyst precursor containing vanadium, phosphorus and oxygen in at least one atmosphere, comprising oxygen (0 ₂ ), hydrogen oxide (H ₂ 0) and / or inert gas in a temperature range from 250 to 600 ° C, which is characterized in that a catalyst precursor according to the invention according to the above is used as the catalyst precursor Description begins.

Examples of suitable inert gases are nitrogen, carbon dioxide and noble gases.

The calcination can be carried out batchwise, for example in a shaft furnace, tray furnace, muffle furnace or heating cabinet, or continuously, for example in a rotary tube, belt calcining furnace or rotary ball furnace. It can contain successively different sections with regard to the temperature, such as heating, keeping the temperature constant or cooling, and successively different sections with regard to the atmospheres, such as, for example, oxygen-containing, water vapor-containing, oxygen-free gas atmospheres. Suitable preforming methods are described, for example, in the patents US 5,137,860 and US 4,933,312 and the published patent application WO 95/29006, to which reference is expressly made, however, without limitation. Continuous calcination in a belt calcining furnace with at least two, for example two to ten, quays is particularly preferred. Zination zones, which may have a different gas atmosphere and a different temperature. The mechanical and catalytic properties of the catalyst can be influenced and thus specifically adjusted by a suitable combination of temperatures, treatment times and gas atmospheres adapted to the respective catalyst system.

In the process according to the invention, preference is given to calcination, in which the catalyst precursor 10

(i) heated in at least one calcination zone in an oxidizing atmosphere with an oxygen content of 2 to 21% by volume to a temperature of 200 to 350 ° C. and left under these conditions until the desired mean oxidation level of the vanadium has been reached; and

(ii) in at least one further calcination zone in a non-oxidizing atmosphere with an oxygen content of <0.5% by volume and a hydrogen oxide content of 20 to 75% by volume to a temperature of 300 to 500 ° C heated and left 20> 0.5 hours under these conditions.

In step (i), the catalyst precursor is in an oxidizing atmosphere with a molecular oxygen content of generally 2 to 21 vol .-% and preferably from 5 to

25 21 vol .-% at a temperature of 200 to 350 ° C and preferably from 250 to 350 ° C for a period that is effective to set the desired average oxidation state of the vanadium. In general, step (i) uses mixtures of oxygen, inert gases (e.g. nitrogen or argon), hydrogen oxide (water

30 steam) and / or air and air. From the point of view of the catalyst precursor passed through the calcining zone (s), the temperature can be kept constant during the calcining step (i), on average rising or falling. Since step (i) is generally preceded by a heating phase, the

As a rule, the temperature initially rises before then leveling off at the desired final value. In general, therefore, the calcination zone of step (i) is preceded by at least one further calcination zone for heating the catalyst precursor.

40

The period of time over which the heat treatment in step (i) is maintained should preferably be selected in the process according to the invention such that an average oxidation state of the vanadium is from +3.9 to +4.4, preferably from +4 , 0 to 5 +4.3. Since it is extremely difficult to determine the average oxidation state of the vanadium during the calcination for apparatus and time reasons, the required time period can advantageously be determined experimentally in preliminary tests. As a rule, a series of measurements is used for this, in which heat treatment is carried out under defined conditions, the samples being removed from the system after different times, cooled and analyzed for the average oxidation state of the vanadium.

The time period required in step (i) is generally dependent on the nature of the catalyst precursor, the temperature set and the gas atmosphere selected, in particular the oxygen content. In general, the period in step (i) is over 0.5 hours, and preferably over 1 hour. In general, a period of up to 4 hours, preferably up to 2 hours, is sufficient to set the desired average oxidation state. Under appropriately set conditions (e.g. lower range of the temperature interval and / or low molecular oxygen content), a period of over 6 hours may also be required.

In step (ii), the catalyst intermediate obtained is in a non-oxidizing atmosphere with a molecular oxygen content of ≤0.5% by volume and hydrogen oxide (water vapor) from 20 to 75% by volume, preferably from 30 to 60 Vol .-% at a temperature of 300 to 500 ° C and preferably from 350 to 450 ° C for a period of> 0.5 hours, preferably 2 to 10 hours and particularly preferably 2 to 4 hours. In addition to the hydrogen oxide mentioned, the non-oxidizing atmosphere generally contains predominantly nitrogen and / or noble gases, such as argon, for example, which is not to be understood as a restriction. Gases such as carbon dioxide are also suitable in principle. The non-oxidizing atmosphere preferably contains> 40% by volume of nitrogen. From the point of view of the catalyst precursor guided through the calcination zone (s), the temperature can be kept constant during the calcination step (ii), and can rise or fall on average. If step (ii) is carried out at a higher or lower temperature than step (i), there is usually a heating or cooling phase between steps (i) and (ii), which is optionally implemented in a further calcination zone. In order to enable an improved separation from the oxygen-containing atmosphere of step (i), this further calcining zone between (i) and (ii) can be purged, for example, for purging with an inert gas, such as nitrogen. Step (ii) is preferred in a temperature 50 to 150 ° C higher than step (i).

In general, the calcination comprises a further step (iii) to be carried out after step (ii), in which the calcined catalyst precursor is heated to a temperature of <300 ° C., preferably <200 ° C. and especially in an inert gas atmosphere cools preferably from <150 ° C.

Before, between and / or after steps (i) and (ii), or (i), (ii) and (iii), further steps are possible in the calcination according to the inventive method. Without being limiting, further steps include changes in the temperature (heating, cooling), changes in the gas atmosphere (change in the gas atmosphere), further holding times, transfers of the catalyst intermediate stage to other apparatuses or interruptions in the entire calcining process.

Since the catalyst precursor generally has a temperature of <100 ° C before the start of the calcination, this is the case

Step (i) is usually heated. The heating can be carried out using different gas atmospheres. The heating is preferably carried out in an oxidizing atmosphere, as defined in step (i), or in an inert gas atmosphere, as defined in step (iii). It is also possible to change the gas atmosphere during the heating phase. Heating in the oxidizing atmosphere, which is also used in step (i), is particularly preferred.

Furthermore, a catalyst for the production of maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon with at least four carbon atoms was found, which can be obtained by the process according to the invention described above.

The catalyst preferably produced by the process according to the invention has a phosphorus / vanadium atom ratio of 0.9 to 1.5, particularly preferably 0.9 to 1.2 and very particularly preferably 1.0 to 1.1, an average oxidation state of the vanadium from +3.9 to +4.4 and particularly preferably from 4.0 to 4.3, a BET surface area from 10 to 50 m / g and particularly preferably from 20 to 40 m ² / g Pore volume from 0.1 to 0.5 ml / g and particularly preferably from 0.2 to 0.4 ml / g and a bulk density from 0.5 to 1.5 kg / 1 and particularly preferably 0.5 to 1.0 kg / 1. The catalyst according to the invention is technically simple, quick and efficient to produce and, in the heterogeneous catalytic gas phase oxidation of a hydrocarbon having at least four carbon atoms to maleic anhydride, enables a high hydrocarbon load with high conversion, high activity, high selectivity and a high space / time yield.

The invention furthermore relates to a process for producing maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms with gases containing oxygen, which is characterized in that a catalyst according to the invention is used as described above.

In the process according to the invention for the production of maleic anhydride, tube-bundle reactors are generally used. As hydrocarbons are generally aliphatic and aromatic, saturated and unsaturated hydrocarbons with at least four carbon atoms, such as

1,3-butadiene, 1-butene, 2-cis-butene, 2-trans-butene, n-butane, C 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 benzene are suitable. 1-Butene, 2-cis-butene, 2-trans-butene, n-butane, benzene or mixtures thereof are preferably used. The use of n-butane and n-butane-containing gases and liquids is particularly preferred. The n-butane used can originate, for example, from natural gas, steam crackers or FCC crackers.

The addition of the hydrocarbon is generally quantity-controlled, i.e. with constant specification of a defined quantity per unit of time. The hydrocarbon can be metered in liquid or gaseous form. Dosing in liquid form with subsequent evaporation before entering the tube bundle reactor is preferred.

Oxygen-containing gases, such as air, synthetic air, an oxygen-enriched gas or so-called "pure", i.e. e.g. Oxygen from air separation is used. The oxygen-containing gas is also added in a quantity-controlled manner.

The gas to be passed through the tube bundle reactor generally contains a hydrocarbon concentration of 0.5 to 15 vol. -% and an oxygen concentration of 8 to 25 vol .-%. The too one hundred percent by volume missing portion consists of other gases such as nitrogen, noble gases, carbon monoxide, carbon dioxide, water vapor, oxygenated hydrocarbons (e.g. methanol, formaldehyde, formic acid, ethanol, acetyaldehyde, acetic acid, propanol, propionaldehyde, propionic acid, acrolein, Crotonaldehyde) and their mixtures together. The n-butane portion of the total amount of hydrocarbon is preferably> 90% and particularly preferably ≥95%.

In order to ensure a long catalyst life and further increase in conversion, selectivity, yield, catalyst load and space / time yield, a volatile phosphorus compound is preferably added to the gas in the process according to the invention. At the beginning, ie at the reactor inlet, their concentration is at least 0.2 ppm by volume, ie 0.2-10 " ⁶ parts by volume of the volatile phosphorus compounds based on the total volume of the gas at the reactor inlet. A content of 0.2 to 20 volumes is preferred ppm, particularly preferably from 0.5 to 10 ppm by volume. Volatile phosphorus compounds are to be understood as meaning all those phosphorus-containing compounds which are present in the desired one

Concentration is gaseous under the conditions of use. Examples of suitable volatile phosphorus compounds are phosphines and phosphoric acid esters. The C 1 -C ₄ -alkyl phosphoric acid esters are particularly preferred, very particularly preferably trimethyl phosphate, triethyl phosphate and tripropyl phosphate, in particular triethyl phosphate.

The process according to the invention is generally carried out at a temperature of 350 to 480 ° C. The temperature mentioned is understood to mean the temperature of the catalyst bed located in the Rorbund reactor which would be present in the absence of a chemical reaction if the process were carried out. If this temperature is not exactly the same at all points, the term means the number average of the temperatures along the reaction zone. In particular, this means that the true temperature present on the catalyst can also lie outside the stated range due to the exothermic nature of the oxidation reaction. The process according to the invention is preferably carried out at a temperature of 380 to 460 ° C., particularly preferably 380 to 430 ° 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) as well as above normal pressure (for example up to 10 MPa abs). This means the pressure in the tube bundle reactor unit. A pressure of 0.1 to 1.0 MPa abs is preferred, particularly preferably 0.1 to 0.5 MPa abs.

The process according to the invention can be carried out in two preferred process variants, the variant with "straight passage" and the variant with "return". In the "straight pass", maleic anhydride and possibly oxygenated hydrocarbon by-products are removed from the reactor discharge and the remaining gas mixture is discharged and, if necessary, thermally utilized. In the "recycle", maleic anhydride and possibly oxygenated hydrocarbon by-products are also removed from the reactor discharge, and the remaining gas mixture, which contains unreacted hydrocarbon, is returned in whole or in part to the reactor. Another variant of the "recycling" is the removal of the unreacted hydrocarbon and its recycling to the reactor.

In a particularly preferred embodiment for the production of maleic anhydride, n-butane is used as the starting hydrocarbon and the heterogeneous gas phase oxidation is carried out “straight through” on the catalyst according to the invention.

The process according to the invention using the catalysts according to the invention enables a high hydrocarbon load on the catalyst with a high conversion as a result of high activity. The process according to the invention also enables high selectivity, a high yield and therefore also a high space / time yield of maleic anhydride.

definitions

Unless otherwise stated, the sizes used in this document are defined as follows:

^m maleic acid hydride 'catalytic converter ^' *

Space / time yield

V 'Kohlwassrstojf load = catalytic converter

ⁿ KW, reactor, on ⁿ KW, Vealctoη from sales U = ⁿ KW, reactor, on ⁿ MSAReahor, off

Selectivity S ⁿ KW, reactor, an ⁿ KW, ~ R & actuator, off

Yield A u-s

^ Maleic anhydride Mass of maleic anhydride produced

[G]

Vi catalyst bulk volume catalyst, totaled over all reaction zones [1] time unit [h]

«Hydrocarbon volume of the hydrocarbon in the gas phase [Nl] standardized to 0 ° C and 0.1013 MPa (mathematical size. If a hydrocarbon is in the liquid phase under these conditions, the hypothetical gas volume is calculated using the ideal gas law.)

U Sales of hydrocarbons per reactor run

Selectivity regarding Maleic anhydride per reactor run

Yield of maleic anhydride per reactor pass ⁿ KW, reactor, a mass flow of hydrocarbons at the reactor inlet [mol / h] ⁿ KW, reactor, from mass flow of hydrocarbons at the reactor outlet [mol / h] ⁿ KW, plant, a mass flow of hydrocarbons at the inlet of the plant [mol / h] ⁿ K, plant, from mass flow of hydrocarbons at the outlet of the plant [mol / h] ⁿ MSA, reactor, from mass flow of maleic anhydride at the reactor outlet [mol / h] ⁿ MSA, plant, from mass flow of maleic anhydride at the outlet the system [mol / h]

Examples

Determination of the filtration time (for examples 1 to 4)

To determine the filtration time, the suspension obtained in Examples 1 to 4 was placed at a temperature T in a glass filter, left without further mechanical action, such as stirring, and the course of the filtration was followed. The filtration time is defined as the time between the application of the suspension to the glass filter see until the time the filter cake was present without excess mother liquor.

Determining the stirring power 5

The stirring power was determined analogously to the explanations in the description, calculating the modified dimensionless Reynold index Re _M according to formula (VI), determining the resulting one and taking into account the shape of the stirrer

10 dimensionless key performance indicator N _e and calculation according to formula (V). The speed of the stirrer n, the diameter of the stirrer d, the kinematic viscosity V of the mixed feedstocks before the reaction at 20 ° C., the density p of the mixed feedstocks before the reaction were used to determine the stirring power

15 20 ° C and the diagram for determining the performance characteristics according to Marko Zlokarnik, "Mixing technology - theory and practice", Springer-Verlag Berlin 1999, page 77, Figure 2.2.

Determination of the filtration resistance by pressure filtration

20

The determination of the filtration resistance by pressure filtration is a known method and, for example, in the VDI guideline 2762 "Filterability of suspensions / determination of the filter cake resistance" by the Association of German Engineers, February

25 1997 described. For the experimental determination of the filtration resistance, the amounts of suspension specified in the individual examples were placed in a heatable pressure filter at the desired filtration temperature. This was equipped with a filter area A of 20 cm ^{2 of} a polypropylene fabric

30 with a maximum pore diameter of 45 μm and an average pore diameter of 10 μm (fabric "PP 2703" from Verseidag. The pressure filter was now closed ^' and the desired differential pressure Δp of 0.4 MPa was set by applying nitrogen and over the entire Pressure filtration constant

35 held. Time measurement started when the lower drain tap was opened. The course of the filtrate mass over time was recorded by a computer. Cracks formed at the end of the filtration, which led to a rapid compensation of the pressure difference. This point in time was used as the end point for the

40 solution of the filtration time _& recorded. After the pressure filtration had ended, the total volume of the filtrate Vp, _end and the height of the filter cake H _en a were determined. The filtration resistance

* stand ^α # ^ was then in accordance with simplified formula 5 H l ff .V

- -end ^v F, end, neglecting the much lower filter resistance R _{τ of} the polypropylene fabric, calculated from the determined data.

Determination of the particle size distribution

To determine the particle size distribution, a representative sample containing a solids content of about 1 g was placed in a beaker from the suspension obtained in Examples 5.1 to 5.3 and made up to 100 mL with isobuatnol. The suspension homogenized by intensive stirring was then continuously passed through the measuring cell of a laser diffraction spectrometer (type Malvern Mastersizer S) and measured with a gas laser with a wavelength of 632.8 nm. The light beam emerging from the sample was imaged onto a detector by a lens system, the undiffracted light being masked out. The local intensities at the detector elements were read into a computer and converted into a particle size distribution. The graph shows the volume fraction of the suspension with particles smaller than or equal to the particle size indicated on the abscissa.

Determination of the residual isobutanol content in the dried catalyst precursor

To determine the residual isobutanol content, approximately 4 g of the dried catalyst precursor and approximately 10 g of N, N-dimethylformamide were precisely weighed into a heatable stirrer with reflux condenser. The mixture was then heated to boiling temperature with stirring and left under these conditions for 30 minutes. After cooling, the suspension was filtered and the isobutanol content in the filtrate was quantified by gas chromatography. The residual isobutanol content was then calculated from the determined concentration of isobutanol in N, N-dimethylformamide and the weighed-in amounts of N, N-dimethylformamide and catalyst precursor.

test facility

The test facility was equipped with a feed unit and a reactor tube. The replacement of a tube bundle reactor by a reactor tube is very possible on a laboratory or pilot plant scale, provided the dimensions of the reactor tube are in the range of one technical reactor tube. The system was operated in a "straight pass".

^' The hydrocarbon was added in a quantity-controlled manner in liquid form via a pump. Air was added in a quantity-controlled manner as the oxygen-containing gas. Triethyl phosphate (TEP) was also added in liquid form in a quantity-controlled manner.

The tube bundle reactor unit consisted of a tube bundle reactor with a reactor tube. The length of the reactor tube was 6.5 m, the inner diameter 22.3 mm. A multi-thermocouple with 20 temperature measuring points was located in a protective tube with an outer diameter of 6 mm inside the reactor tube. The reactor tube was surrounded by a temperature-controlled heat transfer circuit and the reaction gas mixture flowed through it from top to bottom. The upper 0.3 m of the reactor tube were filled with inert material and formed the preheating zone. The reaction zone contained 2.2 L catalyst each. A molten salt was used as the heat transfer medium.

Immediately after the tube bundle reactor unit, gaseous product was removed and fed to the gas chromatographic on-line analysis. The main stream of the gaseous reactor discharge was discharged from the plant.

The plant was operated as follows:

Concentration of n-butane at the reactor inlet = 2.0 vol. -% GHSV = 2000 Nl / l _Ka talysator h ^■ pressure at the reactor outlet = 0.2 MPa abs

Concentration of triethyl phosphate (TEP) = 2 ppm by volume Concentration of water vapor = 1.5% by volume

Example 1: Influence of the average heating rate after the addition of phosphoric acid to the template containing vanadium pentoxide and isobutanol at 25 ° C. on the filtration time

The stirring apparatus used was equipped with a double-jacket vessel thermostatted via ethylene glycol, a reflux condenser, a temperature sensor, a stirrer and four evenly arranged baffles. The baffles had a height corresponding to the inner height of the double jacket vessel and protruded 10% of the inside diameter of the double jacket vessel into the vessel. 242.6 g of vanadium pentoxide and 286.3 g of 105% phosphoric acid in 2 L of isobutanol were placed in the above-mentioned stirring apparatus at 25 ° C. and at the desired average heating rate heated with constant stirring and under reflux to the boiling point of the reaction mixture (about 108 ° C). After the boiling temperature was reached, the temperature was maintained for 16 hours. Over the entire period, the suspension was stirred at a constant stirring power, that is to say at a constant speed. The mixture was then cooled to 85 ° C. with further stirring and filtered through a glass suction filter (porosity 4, diameter 19 cm with a filter area of 284 cm ² ) at 85 ° C. and the filtration time was determined. The results obtained are shown in Table 1.

As a comparison between Examples 1.1 and 1.2 shows, the heating rate after the addition of phosphoric acid to the template containing vanadium pentoxide and isobutanol has a decisive influence on the filtration time. If a heating rate of 2 ° C / min is set, the filtration time will be shorter by a factor of 4.7 under otherwise identical conditions than if a heating rate of 1 ° C / min is set.

Example 2:

Influence of the stirring power in the reaction of the vanadium pentoxide in the presence of isobutanol with phosphoric acid on the filtration time

242.6 g of vanadium pentoxide and 286.3 g of 105% phosphoric acid in 2 L of isobutanol were placed in a stirring apparatus as described in Example 1 at 25 ° C. and at an average heating rate of 2 ° C./min with constant stirring and heated under reflux to the boiling temperature of the reaction mixture (about 108 ° C). After the boiling temperature was reached, the temperature was maintained for 16 hours. Over the entire period, the suspension was stirred at a constant stirring power, that is to say at a constant speed. The mixture was then cooled to 85 ° C. with further stirring and filtered through a glass filter (porosity 4, diameter 19 cm with a filter area of 284 cm ² ) at 85 ° C. and the filtration time was determined. The results obtained are shown in Table 2.

Examples 2.1 to 2.3 show that with decreasing stirring power, which was set for the same stirrer geometry by reducing the stirrer speed, the filtration time was significantly reduced. With a reduction in the stirring power from 0.61 W / kg (example 2.1) to 0.09 W / kg (example 2.3), the filtration time could be reduced by a factor of 3.1. Examples 2.3 and 2.4 show that the effect described is essentially independent of the stirrer geometry. If a very similar stirring power of 0.09 or 0.07 W / kg is set, the mainly radially mixing impeller stirrer and the mainly axially mixing propeller stirrer lead to the same filtration time under otherwise identical conditions.

Example 3: Influence of the Filtration Temperature on the Filtration Time

242.6 g of vanadium pentoxide and 286.3 g of 105% phosphoric acid in 2 L of isobutanol were placed in a stirring apparatus as described in Example 1 at 25 ° C. and at an average heating rate of 2 ° C./min with constant stirring and heated under reflux to the boiling temperature of the reaction mixture (about 108 ° C). After the boiling temperature was reached, the temperature was maintained for 16 hours. Over the entire period, the suspension was stirred at a constant stirring power, that is to say at a constant speed. The mixture was then cooled to the desired filtration temperature with continued stirring and filtered through a glass suction filter (porosity 4, diameter 13 cm with a filter area of 133 cm ² ) at the desired filtration temperature and the filtration time was determined. The results obtained are shown in Table 3.

A comparison between Examples 3.1 with 3.2 and 3.3 with 3.4 shows that at a filtration temperature of 85 ° C compared to a filtration temperature of 25 ° C, a filtration time shorter by a factor of 2.3 is achieved. The effect occurs regardless of the type of stirrer used and the stirring performance.

Example 4:

Influence of the addition temperature of phosphoric acid and vanadium pentoxide on the filtration time

In Example 4.1, 242.6 g of vanadium pentoxide and 286.3 g of 105% phosphoric acid in 2 L of isobutanol were placed in a stirring apparatus as described in Example 1 at 25 ° C. and at an average heating rate of 1 ° C./min heated with constant stirring and under reflux to the boiling point of the reaction mixture (about 108 ° C). After the boiling temperature was reached, the temperature was maintained for 16 hours. Over the entire period, the suspension was stirred at a constant stirring power, that is to say at a constant speed. Then was cooled to 85 ° C. with further stirring and filtered through a glass filter (porosity 4, diameter 19 cm with a filter area of 284 cm ² ) at 85 ° C. and the filtration time was determined.

In Example 4.2, 242.6 g of vanadium pentoxide in 2 L of isobutanol were placed in a stirring apparatus as described in Example 1 at 25 ° C. and at an average heating rate of 1 ° C./min with constant stirring and under reflux to 92 ° C. heated. At this temperature, 286.3 g of 105% phosphoric acid heated to 25 ° C. were then added. The mixture was then heated to the boiling point of the reaction mixture (about 108 ° C.) and kept at this temperature for 16 hours. Over the entire period, the suspension was stirred at a constant stirring power, that is to say at a constant speed. The mixture was then cooled to 85 ° C. with further stirring and filtered through a glass filter (porosity 4, diameter 19 cm with a filter area of 284 cm ² ) at 85 ° C. and the. Filtration time determined.

In Example 4.3, 1.8 L of isobutanol were heated to 92 ° C. with constant stirring and under reflux in a stirring apparatus as described in Example 1, and at this temperature 242.6 g of vanadium pentoxide powder tempered at 25 ° C. and one 25 ° C temperature solution from 286.3 g of 105% phosphoric acid in 0.2 L isobutanol fed over a period of 30 minutes. The mixture was then heated to the boiling point of the reaction mixture (about 108 ° C.). After the boiling temperature was reached, the temperature was maintained for 16 hours. Over the entire period, the suspension was stirred at a constant stirring rate, that is to say at a constant speed. The mixture was then cooled to 85 ° C. with further stirring and filtered through a glass suction filter (porosity 4, diameter 19 cm with a filter area of 284 cm ² ) at 85 ° C. and the filtration time was determined.

The results obtained are shown in Table 4.

A comparison between Examples 4.1 and 4.2 shows that when the phosphoric acid is added to the initial charge containing vanadium pentoxide and isobutanol at a temperature of 92 ° C., the filtration time is shorter by a factor of 2 than when it is added at 25 ° C. Furthermore, if both vanadium pentoxide and phosphoric acid are added to isobutanol at 92 ° C, the filtration time is a factor of 3 shorter than when adding at 25 ° C. Example 5:

Influence of the mean heating rate after the addition of the phosphoric acid to the template containing vanadium pentoxide and isobutanol at 25 ° C. and the stirring power during the reaction on the filtration time and on the particle size distribution

242.6 g of vanadium pentoxide and 286.3 g of 105% phosphoric acid in 2 L of isobutanol were placed in a stirring apparatus as described in Example 1 at 25 ° C. and at an average heating rate of 1 ° C./min (Example 5.1 ) or 2 ° C / min (Examples 5.2 and 5.3) with constant stirring and under reflux to the boiling point of the reaction mixture (about 108 ° C). After the boiling temperature was reached, the temperature was maintained for 16 hours. Over the entire period, the suspension was stirred at a constant stirring power, that is to say at a constant speed, of 0.19 W / kg suspension in Examples 5.1 and 5.2 or 0.07 W / kg suspension in Example 5.3. The mixture was then cooled to the desired filtration temperature of 25 ° C. with further stirring and pressure filtration was carried out to determine the filtration resistance.

The particle size distribution was determined by taking 100 ml of a representative sample of the suspension from the stirrer after cooling and measuring as described under "Determining the particle size distribution".

The results obtained are shown in Table 5. A graphical representation of the volume fraction of the suspension with particles smaller than or equal to the particle size indicated on the abscissa can be found in Figure 1.

A comparison between Examples 5.1 and 5.2 shows the significant influence of the heating rate after adding the phosphoric acid to the template containing vanadium pentoxide and isobutanol at 25 ° C. At a low heating rate of 1 ° C / min, a relatively high filtration resistance of 99 · 10 ¹³ mPa-s / m ² , a filtration time of 115 minutes and a volume fraction of the suspension with particles <10 μm of 25% are obtained. At twice the heating rate of 2 ° C / min (Example 5.2), a relatively low filtration resistance of 13 • 10 ¹³ mPa-s / m ² , a filtration time of 14 minutes and a volume fraction of the suspension with particles ≤IO μm received by 17%. Since example 5.1 only makes use of one of the three measures according to the invention, namely the setting of a stirring power of 0.19 W / kg suspension, this example is a comparative example. If the stirring power is reduced to that of Example 5.2 to 0.07 W / kg suspension (Example 5.3), the filtration resistance is only 5.7 • 10 ¹³ mPa-s / m ² , the filtration time is 7 minutes and the volume fraction the suspension with parti- no <10 μm 5%.

Example 6:

Production of the catalyst precursor on a ton scale

A system as described below was used to produce the catalyst precursor on a ton scale. A steel / enamel kettle with a three-stage impeller stirrer and a capacity of 8 m ^{3 was} used as the precipitation container with pressurized water. The precipitation tank was equipped with a dip tube (diameter 70 mm) and a paddle baffle (diameter 180 mm) as a baffle. In order to ensure operation under reflux, a water-cooled condenser was attached above the stirred tank, connected via an inlet and outlet. Isobutanol and phosphoric acid were metered in via a pump and vanadium pentoxide via a screw conveyor. There was a valve at the bottom of the stirred tank in order to feed the suspension via a line to a heatable pressure filter after the reaction had ended. This was fitted with a Hasteloy fabric with a mesh size of approx. 20 μ and had a diameter of 2.7 m, which corresponds to a filter area of almost 6 m ² . The pressure filter chute was heated via the outer wall and an internal stirrer. The stirrer is attached in the middle, adjustable in height and was suitable in many ways for whirling up the suspension, smoothing the filter cake, for introducing heat during the drying process and for loosening up the product discharge. The mother liquor which had passed through the filter fabric was collected in a collecting container. In order to enable pressure filtration, it was possible to inject nitrogen in the part above the filter fabric. To enable drying under vacuum, the pressure filter chute was also equipped with a vacuum connection.

In the production of the catalyst precursor on a ton scale according to Example 6, the stirred kettle was made inert with nitrogen and 6.1 m ^{3 of} isobutanol were introduced. After commissioning the three-stage impeller stirrer, which was regulated over the entire precipitation process with a stirring power of 0.68 W / kg, 736 kg vanadium pentoxide were fed in at room temperature (20-30 ° C) via the screw conveyor and 900 kg 105% Phosphoric acid pumped in. A further 0.2 m ^{3 of} isobutanol were pumped in to clean the pump. Then the reaction mixture with a Heating rate of 1 ° C / min heated to about 100 to 108 ° C under reflux and left under these conditions for 14 hours. 5 L of a representative sample of the suspension were then taken to determine the filtration resistance and the remaining hot suspension was drained into the pressure filter which had previously been inertized with nitrogen and heated to about 144 ° C. with 0.4 MPa (4 bar) steam. The agitator of the pressure filter was operated at 3 rpm in order to ensure a uniform formation of the filtration base layer when the suspension was admitted. After the stirred tank has been completely emptied, it is rinsed with 0.2 m ^{3 of} isobutanol in order to remove any adhering product residues from the stirred tank. After the entire product suspension was on the pressure filter, the steam-heated stirrer was moved out of the suspension and the steam heating was set to a temperature of about 100 ° C. This measure prevented boiling of the isobutanol. The part above the filter fabric was now pressurized to a pressure of 0.35 MPa abs, starting at 0.1 MPa abs, while at the same time the drain tap below the filter was opened at the beginning of the pressure task. The measurement of the filtration time started at the beginning of the printing task. Towards the end of the pressure filtration, the mother liquor had run out over the filter cake and the first cracks appeared, which led to a rapid drop in pressure. The rapid drop in pressure was recorded as the end point for measuring the filtration time. When the pressure drop was reached, the stirrer was brought down to smooth the filter cake until pressure could build up again. The filter cake was blown dry within a period of about one hour by continuously introducing nitrogen and stirring with a stirrer heated to 100 ° C. No further increase in the fill level was observed in the collecting container. After blowing dry, the steam heating of the stirrer was set to 0.55 MPa (5.5 bar), which corresponds to a temperature of approx. 155 ° C, and at the same time vacuum with a pressure in the range of 0.1 MPa abs (1st bar abs) up to 15 kPa abs (150 mbar abs). A constant heat input was ensured by further stirring in the area of the filter cake to be dried. Drying was carried out to a residual isobutanol content of <2% by weight in the dried catalyst precursor. The filtration time was 120 hours.

The results obtained are shown in Table 6. Example 7:

Production of the catalyst precursor on a ton scale

The catalyst precursor was produced in the system described in Example 6. 6.1 m ^{3 of} isobutanol were placed in the stirred tank which had been rendered inert with nitrogen. After commissioning the three-stage impeller stirrer, which was regulated over the entire precipitation process with a stirring power of 0.25 W / kg, 736 kg vanadium pentoxide were fed in at room temperature (20-30 ° C) via the screw conveyor. The mixture was then heated to 90 ° C. under reflux at a heating rate of 1 ° C./min. At this temperature, 900 kg of 105% phosphoric acid were now pumped in. A further 0.2 m ^{3 of} isobutanol were pumped in to clean the pump. The reaction mixture was then heated under reflux to about 100 to 108 ° C and proceeded analogously to the description in Example 6. The drying was carried out up to a residual isobutanol content of <2% by weight in the dried catalyst precursor. The results obtained are shown in Table 6. The filtration time was 2.7 hours.

Example 8:

Production of the catalyst precursor on a ton scale

The catalyst precursor was produced in the system described in Example 6. 6.1 m ^{3 of} isobutanol were placed in the stirred tank which had been rendered inert with nitrogen. After starting up the three-stage impeller stirrer, which was regulated over the entire precipitation process with a stirring power of 0.25 W / kg, the isobutanol was heated to 90 ° C. under reflux. At this temperature, the addition of 736 kg of vanadium pentoxide was started via the screw conveyor. After about 2/3 of the desired amount of vanadium pentoxide had been added after about 20 minutes, the pumping in of 900 kg of 105% phosphoric acid was started with further addition of vanadium pentoxide. A further 0.2 m ^{3 of} isobutanol were pumped in to clean the pump. The reaction mixture was then heated under reflux to about 100 to 108 ° C and proceeded analogously to the description in Example 6. The drying was carried out up to a residual isobutanol content of <2% by weight in the dried catalyst precursor. The filtration time was 1.7 hours.

The results obtained are shown in Table 6.

Examples 6 to 8 for the production of the catalyst precursor on a ton scale show the effect of the various measures on the filtration time or the filtration resistance. In example 6, in which the stirring power is 0.68 W / kg Suspension, the addition temperature of the vanadium pentoxide and the phosphoric acid 20 to 30 ° C, the heating rate after addition of the phosphoric acid 1 ° C / min and the filtration temperature was 80 to 100 ° C, a filtration resistance of 70 • 10 ¹³ mPa-s / m ² and a filtration time of 120 hours can be achieved. Since example 6 only uses one of the three measures according to the invention, namely filtration at a temperature of 80 to 100 ° C., this example is a comparative example.

If, as happened in Example 7, the stirring power is reduced to 0.25 W / kg of suspension and the phosphoric acid is added to the vanadium pentoxide / isobutanol slurry heated to 90 ° C., the filtration time drops significantly to 2.7 hours. If the vanadium pentoxide is also added to the isobutanol, which is heated to 90 ° C., the filtration time drops to 1.7 hours and the filtration resistance to 1.3 • 10 ¹³ mPa> s / m ² .

Example 9:

Catalytic test of the catalyst from Example 8

Precursor powder, which was prepared according to Example 8, was annealed for 2 hours in air in a rotary tube with a length of 6.5 m, an inner diameter of 0.9 m and internal spiral spirals. The speed of the rotary tube was 0.4 rpm. The powder was fed into the rotary tube in an amount of 60 kg / h. The air supply was 100 m ³ / h. The temperatures of the five heating zones of the same length measured directly on the outside of the rotary tube were 250 ° C, 300 ° C, 340 ° C, 340 ° C and 340 ° C. After cooling to room temperature, the VPO precursor was intimately mixed with 1% by weight of graphite and compacted in a roller compactor. The fine material in the compact with a particle size <400 μm was sieved off and returned to the compacting. The coarse material with a particle size> 400 μ was mixed with a further 2% by weight of graphite and tableted in a tabletting machine to form 5x3x2.5 mm hollow cylinders (outer diameter x height x diameter of the inner hole). In order to obtain the desired amount of catalyst precursor of about 3 t, several runs were carried out in Example 8.

About 2.7 t of the 5x3x2.5 mm hollow cylinders obtained (see "Manufacture of the catalyst precursor") were continuously poured onto the gas-permeable conveyor belt of a belt calcining device from two series-connected, identical belt carcassing machines with a total of eight carcassing zones at a bed height of 9 to 10 cm given. The first 1.4 t were used to set the operating parameters of the belt calciner once used. Since they were not a uniform material, they were not considered further below.

The belt calciner was operated at atmospheric pressure. An encapsulated transition zone was located between calcining zones 4 and 5. Each of the eight caining zones each included a fan to generate gas circulation. Each of the eight caining zones was supplied with the desired amount of fresh gas. A corresponding amount of gas was removed to maintain the desired atmospheric pressure. The volume of gas circulating per unit of time in each calcination zone was greater than the volume of gas supplied or removed per unit of time. To reduce the gas exchange, there was a partition between two successive calcining zones, which was open in the area of the flow of the catalyst precursor. The length of each calcining zone l _n was 1.45 m. The speed of the conveyor belt was set according to the desired dwell time of about 2 hours per calcining zone. The individual zones were operated as shown in Table 7:

Table 7:

Parameters for operating the belt calciner

A catalytic performance test was carried out in the test plant described above with a representative sample of 2.2 L of the continuously calcined catalyst. At a salt bath temperature of 395 ° C, an n-butane conversion of 84.8% was achieved. The yield of maleic anhydride was 57.5%. Table 1:

Influence of the mean heating rate after the addition of phosphoric acid to the template containing vanadium pentoxide and isobutanol at 25 ° C. on the filtration time

kinematic viscosity v of the mixed feed at 20 ° C: 10.4 -10- ⁶ m / s density p of the mixed feed at 20 ° C: 962 kg / m ³

Table 2:

Influence of the stirring power in the implementation of the vanadium pentoxide in the presence of isobutanol

Phosphoric acid on the filtration time

Kinematic viscosity V of the mixed feed at 20 ° C: 10.4 -10- ⁶ m ² / s Density p of the mixed feed at 20 ° C: 962 kg / m ³

Table 3:

Influence of the filtration temperature on the filtration time

Table 4:

* after adding the phosphoric acid.

Kinematic viscosity v of the mixed feedstocks at 20 ° C: 10.4 -10-6 m ² / s Density p of the mixed feedstocks at, 20 ° C: 962 kg / m ³

Table 5:

* Comparative example

Table 6:

Production of the catalyst precursor on a ton scale

* Comparative example n.a. : not determined.

Claims

claims

1. Procedure for the preparation of a vanadium, phosphorus and oxygen-containing catalyst precursor for the production of maleic anhydride by heterogeneous gas-phase oxidation of a hydrocarbon with at least four carbon atoms, by reaction of vanadium pentoxide (I) in the presence of a primary or secondary, non-cyclic or cyclic , unbranched or branched, saturated alcohol with 3 to 6 carbon atoms (II) with a pentavalent or trivalent phosphorus compound (III) with stirring in a temperature range from 80 to 160 ° C and subsequent filtration of the suspension obtained, characterized in that by at least two measures from the series

(a) (i) adding the phosphorus compound (III) to the im

Alcohol (II) slurried and heated to 50 to 160 ° C vanadium pentoxide (I), the previous contact time between the vanadium pentoxide

(I) and the alcohol (II) before the start of the addition of the phosphorus compound (III) at a temperature> 50 ° C ≤ 1 hour; or

(ii) contacting the vanadium pentoxide (I) with the

(b) Effect of a stirring power in the reaction of the vanadium pentoxide (I) in the presence of the alcohol (II) with the phosphorus compound (III) from 0.01 to 0.6 W / kg suspension, the physico-chemical Properties of the mixed

Feedstocks before implementation and at 20 ° C; and

(c) filtration at a temperature of 65 ° C to 160 ° C;

sets a filtration resistance ^a H ^'r l of ≤50 • 10 ¹³ mPa-s / m ² .

Sign.

2. The method according to claim 1, characterized in that in measure (a) measure (i) is selected and the phosphorus compound (III) is suspended in the alcohol (II) and heated to 80 to 160 ° C vanadium pentoxide (I) admits.

3. Process according to claims 1 to 2, characterized in that measure (a) is selected in measure (a) and the vanadium pentoxide (I) heated to> 50 ° C by bringing together to> 0 ° C and <50 ° C temperature-controlled vanadium pentoxide (I) with the alcohol (II) temperature-controlled at 50 to 160 ° C.

4. Process according to claims 1 to 3, characterized in that a stirring power of 0.01 to 0.5 W / kg of suspension is allowed to act in measure (b).

5. The method according to claims 1 to 4, characterized in that one sets a filtration temperature of 80 to 160 ° C in measure (c).

6. The method according to claims 1 to 5, characterized in that a filtration resistance ^H ^ of <25 • 10 ¹³ mPa-s / m ^{2 is} set.

7. Process according to claims 1 to 6, characterized in that orthophosphoric acid, pyrophosphoric acid, polyphosphoric acid or mixtures thereof are used as the phosphorus compound (III).

8. Process according to claims 1 to 7, characterized in that isobutanol is used as the alcohol (II).

9. Catalyst precursor for the production of maleic anhydride by heterogeneous gas-phase oxidation of a hydrocarbon with at least four carbon atoms, obtainable by the process according to claims 1 to 8.

10. A process for the preparation of a vanadium, phosphorus and oxygen-containing catalyst for the production of maleic anhydride by heterogeneous catalytic gas-phase oxidation of a hydrocarbon having at least four carbon atoms, by treatment of a vanadium, phosphorus and oxygen-containing catalyst precursor in at least one atmosphere comprising oxygen ( 0), hydrogen oxide (H0) and / or inert gas in a temperature range from 200 to 600 ° C, characterized in that a catalyst precursor according to claim 9 is used.

11. Catalyst for the production of maleic anhydride by heterogeneous catalytic gas phase oxidation of a hydrocarbon with at least four carbon atoms, obtainable by the process according to claim 10.

12. A process for the preparation of maleic anhydride by heterogeneous catalytic gas phase oxidation of a hydrocarbon having at least four carbon atoms with gases containing oxygen, characterized in that a catalyst according to claim 11 is used.