WO2002022257A1

WO2002022257A1 - Catalyst precursor for producing maleic acid anhydride

Info

Publication number: WO2002022257A1
Application number: PCT/EP2001/010339
Authority: WO
Inventors: Sebastian Storck; Jens Weiguny; Andreas Tenten
Original assignee: Basf Aktiengesellschaft
Priority date: 2000-09-15
Filing date: 2001-09-07
Publication date: 2002-03-21
Also published as: DE10046072A1

Abstract

The invention relates to a method for producing a catalyst precursor containing vanadium, phosphorus and oxygen, for producing maleic acid anhydride by heterogeneously catalytic gas phase oxidation of a hydrocarbon with at least four carbon atoms, by reacting a pentavalent vanadium compound with a pentavalent phosphorus compound in the presence of an alcohol with a reducing action. According to the inventive method, (i) the alcohol with the reducing action is an alcohol of general formula (I), wherein the radicals R1 and R2, independently of each other, mean hydrogen, C1-to C9-alkyl or C1- to C9-hydroxyalkyl and the radical R3 means C1-to C9-alkyl or C1- to C9-hydroxyalkyl; (ii) the reaction is carried out without adding modifiers and co-reduction agents selected from the following series: hydrogen halide, sulphur dioxide, fuming sulphuric acid and tensides; and (iii) bringing together the pentavalent vanadium compound, the pentavalent phosphorus compound and the alcohol with the reducing action, forming the catalyst precursor by heating and isolating the same. The invention also relates to a catalyst precursor that can be obtained using this method, to a method for producing a catalyst from the catalyst precursor, to a catalyst that can be obtained using this method and to a method for producing maleic acid anhydride on this catalyst.

Description

Catalyst precursor for the production of maleic anhydride

Description 5

The present invention relates to a catalyst precursor containing vanadium, phosphorus and oxygen, and to a process for its preparation for the production of maleic anhydride by heterogeneous catalytic gas-phase oxidation of a hydrocarbon with at least four carbon atoms, by reacting a pentavalent vanadium compound with a pentavalent phosphorus. Compound in the presence of a reducing alcohol.

Furthermore, the present invention relates to a vanadium, phosphorus and oxygen-containing catalyst and 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.

25

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, for example, to give polymers such as polytetrahydrofuran or polyvinyl

30 pyrrolidone to be processed.

The catalyst precursor containing vanadium, phosphorus and oxygen is generally prepared by simultaneous or successive reaction of the three components pentavalent vanadium compound, pentavalent phosphorus compound and reducing agent and subsequent isolation.

US Pat. No. 4,333,853 describes the preparation of the catalyst precursor by slurrying vanadium pentoxide in 40% 100% phosphoric acid and isobutanol, heating under reflux and subsequent isolation of the precursor by filtration.

US Pat. No. 4,315,864 discloses the use of olefinic alcohols such as allyl alcohol, methallyl alcohol 45 and crotyl alcohol as reducing agents. The reduction of the five-valent vanadium by Heating under reflux can take place either before or after the addition of the five-valent phosphorus compound.

U.S. Patent 4,016,105 describes the reduction of the five-valent vanadium by refluxing in aqueous solution in the presence of a five-valent phosphorus compound, a secondary alcohol and a coreductant. The aldehydes formaldehyde and acetaldehyde and reducing carboxylic acids are mentioned as suitable co-reducing agents.

US Pat. No. 4,632,915 describes the preparation of an iron- and lithium-promoted catalyst precursor in the presence of methanol, ethanol, 1-propanol or a secondary alcohol while introducing offgas as the coreductant.

US Pat. No. 5,158,923 discloses the preparation of a promoted catalyst precursor by reducing and dissolving vanadium pentoxide with hydrogen chloride or hydrogen bromide gas in an alcoholic reducing agent in the presence of the promoter compounds. The catalyst precursor was then precipitated by adding phosphoric acid and heating under reflux, some of the alcohol being distilled off. Primary and secondary alcohols are mentioned as alcoholic reducing agents. The coreduction agents mentioned are very corrosive and therefore require a considerable amount of equipment.

US Pat. Nos. 4,560,674, 4,562,268 and 4,657,158 describe the preparation of the catalyst precursor in the presence of a primary or secondary alcohol and a modifier selected from the series consisting of hydrogen iodide, sulfur dioxide, fuming sulfuric acid and surfactants. The addition of the modifiers mentioned has the decisive disadvantage that the first three substances are very corrosive compounds, which require considerable outlay in terms of equipment, and if the surfactants are used there is a risk of foam formation and the associated safety risks.

US Pat. No. 4,668,652 teaches a special variant for the preparation of the catalyst precursor, in which the phosphorus compound is first placed in an alcoholic solvent and heated under reflux and then the vanadium compound which is likewise suspended in an alcoholic solvent is continuously added within 0 , 5 to 4 hours is added, the water of reaction being continuously drawn off. C 1 -C 6 -alkanols are mentioned as alcoholic solvents. The continuous The addition of the vanadium compound is complicated because an additional template and metering device are required.

I. J. Ellison et al. , J. Chem. Soc. Chem. Commun. , 1994, pages 1093 to 1094 and G.J. Hutchings et al. , Catalysis Today 33,

1997, pages 161 to 171 describe a two-stage preparation of the catalyst precursor in which, in a first stage, VOP0 .2 H ₂ 0 is synthesized by reaction of vanadiurapentoxide with 85% phosphoric acid in an aqueous medium by heating under reflux and by filtration and washing with water and acetone was isolated and in a second stage suspended in an alcohol by heating under reflux to the precursor VOHPO -0.5 H ₂ 0 and isolated by renewed filtration and drying. Primary and secondary C4 to C10-A1 canoles were used as alcohols. It was found that the use of the primary 1-alkanols after preforming by calcination of the VOHPO -0.5 H ₂ 0 precursor leads to a (VO) P0 catalyst with a high BET surface area and high selectivity in the synthesis of maleic anhydride. A two-stage synthesis of the catalyst precursor with intermediate insulation is extremely complex and expensive on an industrial scale.

The object of the present invention was to find 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 with at least four carbon atoms, which no longer has the disadvantages mentioned above only one, non-corrosive reducing agent without the addition of modifiers and coreductants leads to success, is technically simple to carry out in a one-step synthesis and which, after a preforming which is also technically easy to carry out, leads to a catalyst of 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 reacting a five-valent vanadium compound with a five-valent phosphorus compound in the presence of a reducing alcohol found, which is characterized in that one (i) as a reducing alcohol, an alcohol of the general formula (I)

I

R ₂ C CH ₂ CH ₂ OH (I),

R ₃

in which the radicals R 1 and R _2, independently of one another, are hydrogen, C 1 -C ₉ -alkyl or C 1 -C ₉ -hydroxyalkyl and the radical R is C 1 -C ₆ -alkyl or C 1 -C ₆ -hydroxyalkyl,

(ii) the reaction is carried out without the addition of modifiers and coreductants selected from the series consisting of hydrogen halide, sulfur dioxide, fuming sulfuric acid and surfactants, and

(iii) the pentavalent vanadium compound, the pentavalent phosphorus compound and the reducing alcohol combine, form the catalyst precursor by heating and isolate it.

The reducing alcohol to be used in the process according to the invention is characterized by the general formula (I)

Ri

R ₂ C CH ₂ CH ₂ OH (I), I

R ₃

in which the radicals R_ and R independently of one another hydrogen, Cι ~ to Cg-alkyl or Cι ~ to Cg-hydroxyalkyl and the radical R ₃ C_- to Cg-alkyl or Cι ~ to Cg-hydroxyalkyl mean, said Ci to Cg-alkyl radicals and C ~ ~ to Cg-hydroxyalkyl radicals can be unbranched or branched. Examples of the C 1 -C 6 -alkyl radicals are methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methyl-propyl, 2-methylpropyl, 1, 1-dimethylethyl, pentyl, 1-methylbutyl, 2-methylbutyl , 3-methylbutyl, 2, 2-dimethylpropyl, 1-ethylpropyl, hexyl, 1, 1-dimethylpropyl, 1,2-dimethylpropyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl , 1,2-dimethylbutyl, 1, 3-dimethylbutyl, 2,2-dimethylbutyl, 2, 3-dimethylbutyl, 3, 3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1, 1, 2-trimethylpropyl, 1st , 2, 2-trimethylpropyl, 1-ethyl-l-methylpropyl, l-ethyl-2-methylpropyl, heptyl, octyl and Called nonyl. Examples of the C_ to C ₉ hydroxyalkyl radicals are hydroxymethyl, 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl, 5-hydroxypentyl, 6-hydroxyhexyl, 7-hydroxyheptyl, 8-hydroxyoxyctyl and 9-hydroxynonyl ,

Alcohols of the formula (I) are preferably used in which the radicals R 1 and R independently of one another are hydrogen or C 1 -C 4 -alkyl and the radical R _{3 is} unbranched C 1 -C 4 -alkyl. Examples of the alcohols used with preference are 1-butanol, 1-pentanol (amyl alcohol), 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, 3-methyl-1-butanol (isoamyl alcohol) , 3-methyl-1-pentanol, 3-methyl-1-hexanol, 3-methyl-1-heptanol, 3-methyl-1-octanol, 3-methyl-1-nonanol, 3-methyl-1 -decanol, 3,3-dimethyl-1-butanol, 3, 3-dimethyl-1-pentanol, 3, 3-dimethyl-1-hexanol, 3, 3-dimethyl-1-heptanol, 3, 3-dimethyl -l-octanol, 3,3-dimethyl-1-nonanol and 3, 3-dimethyl-l-decanol called.

The alcohols 1-butanol, 1-pentanol (amyl alcohol), 1-hexanol, 1-heptanol, 1-octanol, 1-noanol, 1-decanol and 3-methyl-1-butanol (isoamyl alcohol) are particularly preferably used. The alcohols 1-butanol, 1-pentanol (amyl alcohol), 1-hexanol and 3-methyl-1-butanol (isoamyl alcohol), in particular 1-butanol and 1-pentanol, are very particularly preferred.

It is also essential in the process according to the invention that the reaction of the five-valent vanadium compound with the five-valent phosphorus compound in the presence of the alcohol mentioned is chosen from the series of hydrogen halide, specifically hydrogen chloride, hydrogen bromide and hydrogen iodide, sulfur dioxide, without the addition of modifiers and coreductants. smoking

Performs sulfuric acid and surfactants. Technically customary contaminations of the starting materials and the apparatus used with the modifiers and coreductants listed are possible in the process according to the invention and are therefore included. A total content of halogen, sulfite, sulfate and surfactants of 0.01% by weight, based on the total mass of the suspended reaction mixture, is regarded as technically customary.

In the process according to the invention, the pentavalent vanadium compound, the pentavalent phosphorus compound and the reducing alcohol are combined, as a rule subsequently formed by heating the catalyst precursor and isolating it.

In the process according to the invention, the oxides, the acids and the inorganic and organic salts which contain pentavalent vanadium, or ren mixtures. The use of vanadium pentoxide (VOs), ammonium metavanadate (NH ₄ V0 ₃ ) and ammonium polyvanadate ((NH) _{2 6} 0i ₆ ), in particular vanadium pentoxide (V ₂ O ₅ ), is preferred. The five-valent vanadium compounds present as a solid are used in the form of a powder, preferably in a grain 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.

As pentavalent phosphorus compounds in the process according to the invention, phosphorus pentoxide (P ₂ O ₅ ), orthophosphoric acid (H ₃ P0), pyrophosphoric acid (HP ₂ 0), polyphosphoric acids of the general formula H _{n + 2} P _n 0 _{3n +} ι with n≥3 or their Mixtures used. The content of the compounds and mixtures mentioned is usually given in% by weight, based on H3P04. The use of 80 to 110% HP0 is preferred, particularly preferably 95 to 110% H ₃ P0 ₄ and very particularly preferably 100 to 105% H ₃ P0.

The joining of the three components of pentavalent vanadium compound, pentavalent phosphorus compound and reducing alcohol can be done in different ways in the method according to the invention. In general, the assembly is carried out in the reaction apparatus suitable for the subsequent reaction, for example a stirred kettle, in a temperature range from 0 to 50 ° C., preferably ambient temperature. Temperature increases are possible through the release of heat from the mixture.

In a preferred variant, the reducing alcohol is placed in the reactor and the pentavalent vanadium compound is added, preferably with stirring. Then the pentavalent phosphorus compound, which can optionally be diluted with a further subset of the reducing alcohol, is added. If the entire amount of the reducing alcohol has not yet been added, the part still missing can also be added to the reaction apparatus.

In another variant, the reducing alcohol and the pentavalent phosphorus compound are placed in the reactor and the pentavalent vanadium compound is added, preferably with stirring.

It should be noted that in addition to the above, another liquid diluent can also be added. Examples are alcohols and in small amounts Called water. The process according to the invention is preferably carried out without the addition of a diluent.

The relative molar ratio of the pentavalent phosphorus compound to be added to the pentavalent vanadium compound to be added 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 1.1 to 1.5 and particularly preferably 1.15 to 1.3.

The amount of the reducing alcohol to be added must 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. If, as in the preferred variant, no so-called liquid diluent is added, the amount of the reducing alcohol to be added is to be dimensioned at least in such a way that a slurry can be formed with the five-valent vanadium compound which is mixed intimately of the five-valued phosphorus compound to be added. In general, the molar alcohol / vanadium ratio is 5 to 15 and preferably 6 to 9.

When the pentavalent vanadium compound, the pentavalent phosphorus compound and the reducing alcohol are combined, the slurry is heated to react the compounds mentioned and form the catalyst precursor. The temperature range to be selected depends on various factors, in particular the boiling point of the alcohol added. In general, a temperature of 50 to 200 ° C., preferably 100 to 200 ° C., is set. The volatile compounds, such as water, the reducing alcohol 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, 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. After the aforementioned temperature treatment has ended, the catalyst precursor formed is isolated, it being possible, if appropriate, to interpose a cooling phase and a storage or aging phase of the cooled reaction mixture before the isolation. During the isolation, the solid catalyst precursor is separated from the liquid phase. Suitable methods are, for example, filtering, decanting or centrifuging. The catalyst precursor is preferably isolated by filtration.

The isolated catalyst precursor can be processed unwashed or washed. The isolated catalyst precursor is preferably washed with a suitable solvent in order, for example, to remove alcohol still adhering to it or its degradation products. Suitable solvents are, for example, alcohols (e.g. methanol, ethanol, 1-propanol, 2-propanol), aliphatic and / or aromatic hydrocarbons (e.g. pentane, hexane, benzine, benzene, toluene, xylenes), ketones (e.g. 2-propanone ( Acetone), 2-butanone, 3-pentanone, ethers (for example 1, 2-dimethoxyethane, tetrahydrofuran, 1,4-dioxane) or mixtures thereof If the catalyst precursor is washed, 2-propanone and / or methanol and methanol is particularly preferably used.

After isolation of the catalyst precursor or after washing, the solid is generally dried. The drying can be carried out under different conditions. They are generally carried out in the range from vacuum to atmospheric pressure. The drying temperature is generally 30 to 250 ° C, whereby drying under vacuum compared to drying under atmospheric pressure can often use lower temperatures. 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.

In addition to vanadium, phosphorus and oxygen, the catalyst precursor which can be prepared by the process according to the invention can also contain so-called promoters. 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 the published documents WO 97/12674 and WO 95/26817 and in the patents US Pat. No. 5,137,860, US Pat. No. 5,296,436, US Pat. No. 5,158,923 and US Pat. No. 4,795,818. Preferred promoters are compounds of the elements cobalt, molybdenum, iron, zinc, hafnium, Zirconium, lithium, titanium, chromium, manganese, nickel, copper, boron, silicon, antimony, tin, niobium and bismuth, particularly preferably molybdenum, iron, zinc, antimony, bismuth, lithium. The promoted catalyst precursor according to the invention can contain one or more promoters. The total content of promoters is generally not more than about 5% by weight, in each case as oxide and calculated in the annealed state of the catalyst precursor.

If promoted catalyst precursors are produced by the process according to the invention, the promoter is generally added in the form of an inorganic or organic salt when the five-valent vanadium compound, the five-valent phosphorus compound and the reducing alcohol are combined. Suitable promoter compounds are, for example, the acetates, acetylacetonates, oxalates, oxides or alkoxides of the aforementioned promoter metals, such as cobalt (II) acetate, cobalt (II) acetylacetonate, cobalt (II) chloride, molybdenum (VI) oxide, molybdenum (III) chloride, iron (III) acetylacetonate, iron (III) chloride, zinc (II) oxide, zinc (II) acetylacetonate, lithium chloride, lithium oxide, bismuth (III) chloride , Bismuth (III) ethyl hexanoate, nickel (II) ethyl hexanoate, nickel (II) oxalate, zirconyl chloride, zirconium (IV) butoxide, silicon (IV) ethoxide, niobium (V) chloride and niobium (V) oxide. For further details, reference is made to the aforementioned WO patent applications and US patents.

In a particularly preferred embodiment, the desired amounts of vanadium pentoxide powder and 1-butanol are placed in a stirred tank and the reactor contents are slurried by stirring. Now the desired amount of phosphoric acid, which is preferably mixed with further 1-butanol, is added to the stirred slurry. The resulting vanadium, phosphorus, and alcohol-containing slurry is refluxed and held at the desired temperature for several hours. The reaction mixture is then cooled with further stirring and placed on a suction filter. The filtered catalyst precursor is then washed with methanol and dried at a negative pressure of 1 to 30 kPa abs, preferably 1 to 2 kPa abs at 50 to 200 ° C., preferably 50 to 100 ° C.

The catalyst precursor obtainable by the process according to the invention is distinguished by a high proportion of the outer [001] surface of the VOHPO .0.5 H ₂ 0 phase. According to the explanations in E. Bordes et al., Catalysis Today 16, 1993, pages 27 to 38, this changes into the so-called preforming of the catalyst precursor by a temperature treatment

[100] surface of the (VO) ₂ P0 ₇ phase of the finished catalyst. The [100] surface of the (VO) ₂ P ₂ 0 ₇ phase applies according to E. Bordes et al., Catalysis Today 16, 1993, pages 27 to 38 and K. Inumaru et al., Chemistry Letters 1992, pages 1955 to 1958 as a highly selective surface for the oxidation of n-butane to maleic anhydride. Due to the high proportion of the [100] surface of the (VO) ₂ P ₂ θ ₇ ~ Pϊ ^ι ase, the catalyst according to the studies by IJ Ellison et al. , J. Chem. Soc. Chem. Commun., 1994, pages 1093 to 1094 and GJ Hutchings et al. , Catalysis Today 33, 1997, pages 161 to 171 also have a high BET surface area, which requires high activity.

The catalyst precursor obtainable according to the invention thus represents a selectivity and activity-determining precursor of a catalyst which has a high selectivity and a high activity in the oxidation of hydrocarbons to maleic anhydride.

The process for producing the catalyst precursor can be carried out in a technically simple manner by assembling all the components and then heating and isolating them in one step and does completely without any modifiers, coreductants or other auxiliaries.

Since the reducing alcohols (I) are used in the process according to the invention without the addition of modifiers, such as hydrogen halide, sulfur dioxide or fuming sulfuric acid, the reaction mixture is not corrosive. This has advantages in the safety-related and material design of the apparatus as well as in handling the starting materials and the reaction mixture.

Furthermore, a catalyst precursor 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 precursor according to the invention has the properties and advantages listed above.

The invention furthermore relates to a process for the preparation of a vanadium, phosphorus and oxygen-containing catalyst for the production of maleic anhydride by heterogeneously catalyzed 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 an 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 is used as the catalyst precursor as described above.

In the process according to the invention for producing the catalyst, the catalyst precursor according to the invention is preformed 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. The preforming can be carried out either directly with the powdered catalyst precursor or with the catalyst precursor obtained after shaping. Preforming the catalyst precursor after shaping is preferred.

The preforming 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 processes are described, for example, in the patents US 5,137,860 and US 4,933,312 and the published patent application EP-A 0 756 518, to which reference is expressly made, however, without limitation.

The shaping, which is preferably carried out before the preforming and thus with the catalyst precursor powder, can be carried out in various ways, such as, for example, the extrusion of the pasted catalyst precursor powder or the tableting. Tableting is preferred.

In the case of shaping via tableting, the catalyst precursor powder is generally mixed with a tabletting aid and, if appropriate, with a pore former, and mixed thoroughly. The catalyst is preferably prepared without the addition of a pore former.

Tableting aids are generally catalytically inert and improve the tabletting properties of the catalyst precursor 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 generally remain in the activated catalyst, typically the The content of tableting aid in the finished catalyst is about 2 to 6% by weight.

Pore formers are substances that are used for the targeted adjustment of the pore structure in the macroporous area. In principle, they can be used regardless of the molding process. As a rule, these are compounds containing carbon, hydrogen, oxygen and / or nitrogen, which are added before shaping and are largely removed again in the subsequent preforming of the catalyst with sublimation, decomposition and / or evaporation. Suitable pore formers are stearic acid, ammonium carbonate, ammonium oxalate, ammonium carbonate, ammonium hydrogen carbonate, ammonium acetate, ammonium formate, melamine and polyoxymethylene. The finished catalyst can nevertheless contain residues or decomposition products of the pore former.

In the method according to the invention, the catalyst precursor powder mixed with a tabletting aid and optionally a pore former is preferably pre-compressed in a tablet press. The pre-compressed particles are then ground into granules in a mill and shaped into shaped bodies in a tablet press. Ring tablets (hollow cylinders) are preferably produced, since they have a larger outer surface than corresponding tablets and thus have clear advantages with regard to activity and pressure loss in the reactor.

In a preferred embodiment for shaping, the catalyst precursor powder is intensively mixed with about 2 to 4% by weight of graphite as a lubricant and pre-compressed in a tablet press. The pre-compressed particles are ground in a mill to form granules with a particle diameter of approximately 0.2 to 1.0 mm and formed into rings in a ring tablet press.

In a further embodiment for shaping, the catalyst precursor powder is mixed intensively with about 2 to 4% by weight of graphite as a lubricant and additionally with 5 to 20% by weight of a pore former and further treated as described above and shaped into rings ,

In a preferred embodiment for the discontinuous preforming of the shaped, pore former-free catalyst precursor, it is heated in a tubular or rotary tube oven under an air atmosphere to about 350 to 400 ° C. and left at this temperature for about 1 hour. It is then switched to a nitrogen-water vapor atmosphere, at about 400 to 450 ° C heated up and left under these conditions for a further 2 to 6 hours. Finally, the finished catalyst is cooled to room temperature.

In a preferred embodiment for the continuous preforming of the shaped, pore-forming catalyst precursor, the latter is heated in a belt calcining oven to about 350 to 400 ° C. in an air atmosphere and left at this temperature for about 1 hour. It is then switched to a nitrogen-water vapor atmosphere, heated to about 400 to 450 ° C. and left under these conditions for a further 2 to 6 hours. Finally, the finished catalyst is cooled to room temperature.

As stated above, the catalyst obtainable according to the invention has a high selectivity and a high activity in the oxidation of hydrocarbons open to maleic anhydride and is technically simple to produce from the catalyst precursor according to the invention by preforming at elevated temperature.

Furthermore, a catalyst for the production of maleic anhydride by heterogeneously catalytic 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 catalysts according to the invention preferably have 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 1.2. The average oxidation state of the vanadium is preferably +3.9 to +4.4 and particularly preferably 4.0 to 4.3. The catalysts of the invention preferably have a BET surface area of 10 to 50 m ² / g and particularly preferably 15 to 30 m ² / g. They preferably have a pore volume of 0.1 to 0.5 ml / g and particularly preferably 0.1 to 0.3 ml / g. The bulk density of the catalysts according to the invention is preferably 0.5 to 1.5 kg / 1 and particularly preferably 0.5 to 1.0 kg / 1.

The catalyst according to the invention has the properties and advantages listed above.

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

Tube-bundle reactors are generally used in the process according to the invention for the production of maleic anhydride. A tube bundle reactor in turn consists of at least one reactor tube which is surrounded by a heat transfer medium for heating and / or cooling. In general, the tube bundle reactors used industrially contain a few hundred to several tens of thousands of reactor tubes connected in parallel.

The hydrocarbons in the process according to the invention are aliphatic and aromatic, saturated and unsaturated hydrocarbons with at least four carbon atoms, such as, for example, 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, C5 mixture , Hexenes, hexanes, cyclohexane and benzene. 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 entry into 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 inert gas. The proportion of inert gas is usually 50 to 95% by volume at the start. Inert gases are all gases that do not directly contribute to the formation of maleic anhydride, such as nitrogen, noble gases, carbon monoxide, carbon dioxide, water vapor, oxygenated and non-oxygenated hydrocarbons with less than four carbon atoms (e.g. methane, ethane, propane, methanol, Formaldehyde, formic acid, ethanol, acetyaldehyde, acetic acid, propanol, propionaldehyde, propionic acid, acrolein, Crotonaldehyde) and their mixtures. Generally, the inert gas is introduced into the system via the oxygen-containing gas. However, it is also possible to add further inert gases separately. Enrichment with further inert gases, which can originate, for example, from the partial oxidation of the hydrocarbons, is possible via a partial recycling of the reaction effluent that may have been prepared.

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. Their concentration at the beginning, ie at the reactor inlet, 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 ppm by volume is preferred, particularly preferably 0.5 to 10 ppm by volume. Volatile phosphorus compounds are understood to be all those phosphorus-containing compounds which are present in the desired concentration in gaseous form under the conditions of use. For example, compounds of the general formulas (II) and (III) may be mentioned

Xi PX ₃ Xi P X3

I (II), and | ⁽ HD,

X ₂ ^x 2

where X ¹ , X ² and X ³ independently of one another hydrogen, halogen, Ci to Cg alkyl, C _{3 to} Cg cycloalkyl, Cg to Cio aryl, C ~ to Cg alkoxy, C ₃ to Cg Cycloalkoxy and Cg to Cio Aroxy mean. Compounds of the formula (IV) are preferred

0 _R] _p_ ₀ R _{3 (lv) ι}

OR ₂

where R ¹ , R ² and R ³ independently of one another are hydrogen, C ₁ -C ₆ -alkyl, C ₃ -C ₆ -cycloalkyl and Cg- to C ₀ -aryl. Particularly preferred are the compounds of formula (III) in which R ¹ , R ² and R ³ independently of one another are C 1 -C ₄ -alkyl, for example methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl and 1, 1-dimethylethyl. Trimethyl phosphate, triethyl phosphate and tri-propyl phosphate, in particular triethyl phosphate, are very particularly preferred.

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 tube bundle 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 (e.g. up to 0.05 MPa abs) as well as above normal pressure (e.g. 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. During 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 catalytic gas phase oxidation is carried out “straight through” on the catalyst according to the invention. Air as gas containing oxygen and inert gas is fed into the feed unit in a quantity-controlled manner. The quantity of n-butane is also regulated, but is preferably supplied in liquid form via a pump and evaporated in the gas stream. The ratio between the amounts of n-butane and oxygen supplied is generally adjusted according to the exothermic nature of the reaction and the desired space / time yield and is therefore dependent, for example, on the type and amount of the catalyst. As a further component, trialkyl phosphate is preferably added to the gas stream as a volatile phosphorus compound in a quantity-controlled manner. The volatile phosphorus compound can be added, for example, undiluted or diluted in a suitable solvent, for example water. The required amount of the phosphorus compound depends on various parameters, for example the type and amount of the catalyst or the temperatures and pressures in the system, and must be adapted for each system.

The gas flow is passed through a static mixer for thorough mixing and through a heat exchanger for heating. The mixed and preheated gas stream is now passed to the tube bundle reactor in which the catalyst according to the invention is located. The tube bundle reactor is advantageously heated by a molten salt circuit. The temperature is set such that a conversion of 75 to 90% per reactor pass is preferably achieved.

The product gas stream originating from the tube bundle reactor is cooled down in a heat exchanger and fed to the unit for separating the maleic anhydride. In the preferred embodiment, the unit contains at least one apparatus for the absorptive removal of the maleic anhydride and optionally the oxygenated hydrocarbon by-products. Suitable apparatuses are, for example, containers filled with an absorption liquid through which the cooled discharge gas is passed or apparatuses in which the absorption liquid is sprayed into the gas stream. The maleic anhydride-containing solution is discharged from the plant for further processing or for isolation of the valuable product. The remaining gas stream is also discharged from the plant and, if necessary, fed to a unit for recovering the unreacted n-butane.

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 method according to the invention also enables high selectivity, a high yield and therefore also a high space / time yield of maleic anhydride.

Examples

Example 1 (Preparation of the catalyst precursors)

The seven catalyst precursors A to G were prepared according to the following procedure.

Vanadium pentoxide powder with an average grain size of 120 μ (manufacturer GfE, Nuremberg, Germany) was suspended in 1700 mL of the alcohol mentioned with stirring in a cylindrical 5 L flat-ground agitator. The amount of vanadium pentoxide powder added was calculated so that the molar alcohol / V205 ratio was 27.5. To this slurry, a solution consisting added 100% phosphoric acid ^'in 300 ml of said alcohol. The amount of phosphoric acid added was calculated so that the molar H ₃ P0 ₄ / V ₂ θ ₅ ratio was 2.4. The slurry was refluxed for 21 hours and then cooled to room temperature. The resulting precipitate was filtered off, washed with methanol and dried in vacuo at 50 ° C. for 48 hours.

An X-ray diffraction pattern was recorded in each case from the VOHPO ₄ -0.5 H ₂ O samples obtained (catalyst precursor) using an X-ray powder diffractometer of the "D5000 from Siemens Theta / Theta" type. The measurement parameters were as follows:

Circle diameter 435 mm

X-ray radiation CuKα

Tube voltage 40 kV

Tube current 30 mA

Variable aperture aperture V20 V20 variable aperture

Secondary graphite monochromator

Monochromator aperture 0.1 mm

scintillation

Detector aperture 0.6 mm increment 0.02 ° 2Θ

Continuous step mode

Measuring time 2.4 s / step

Measuring speed 0.5 ° 2Θ / min

The two crystallographic surfaces of interest could be assigned from the X-ray diffraction diagram as follows: the signal of the [001] surface corresponds to a 2Θ value of approximately 15.5 °, the signal of the [220] surface has a 2 © value of approximately 30.5 °. The results obtained are shown in Table 1.

Table 1:

10

15

* Comparative Example

20

The examples show that the catalyst precursors according to the invention have a significantly lower I [ooi] / I [ ₂ 20] ratio of the corresponding X-ray diffraction lines than the non-inventive catalyst precursors and those according to the prior art

25 nik Since the diffraction intensity represents a certain measure for the layers lying one above the other in the crystal structure, one can directly compare two X-ray diffraction diagrams with a low intensity to a smaller number of layers one above the other and with a high intensity to a higher one

Close the number of layers on top of each other. A smaller I [ooi] / I [ ₂₂₀ ] ratio thus corresponds to a larger I [ooi] / I [ ₂₂₀ ] ratio, fewer superimposed [001] layers and more superimposed [220] layers. It follows that the crystallites, which in the X-ray diffraction

35 grams show a smaller I [ooι] / l [ ₂₂₀ ] ratio, on average have a higher [001] / [220] ratio on the outer surface.

.Because the [001] surface of the VOHPO ₄ -0.5 H ₂ 0 phase is exactly as described in E. Bordes et al. , Catalysis Today 16,

40 1993, pages 27 to 38 during the preforming of the catalyst precursor by a heat treatment into the [100] surface of the (VO) ₂ P0 phase of the finished catalyst, and this according to E. Bordes et al., Catalysis Today 16 , 1993, pages 27 to 38 and K. Inumaru et al., Chemistry Letters 1992, pages 1955 to

45 1958 has been detected as a highly selective surface for the oxidation of n-butane to maleic anhydride, thus has the finished catalyst, which consists of a catalyst precursor small I [ooi] / I [ ₂ o] ratio was produced, a high selectivity in the oxidation of hydrocarbons to maleic anhydride. In conjunction with a high activity, this results in a high yield of valuable product.

Example 2 (preparation of the catalysts)

The catalyst precursors A, C, F * and G * were further processed into the catalysts as follows. The corresponding catalyst precursor powder was mixed with 3% by weight of graphite, mixed thoroughly and formed into 5x3x2 rings in a tablet press (outer diameter x height x diameter of the inner hole; in each case in mm). The rings were then heated in a tube furnace under air with a heating rate of 7.5 ° C / min first to 250 ° C, then with a heating rate of 2 ° C / min to 285 ° C and at this temperature for 10 minutes leave. The gas atmosphere was then switched from air to nitrogen / water (molar ratio 1: 1), heated to 425 ° C. and left under these conditions for 3 hours. Finally, the mixture was cooled to room temperature under nitrogen.

The BET surface area of the finished catalysts was then determined. The results obtained are shown in Table 2.

Table 2;

The results show that the catalysts produced according to the invention have a larger BET surface area than those produced according to the prior art.

Example 3 (catalytic test)

A catalytic test was carried out in a test facility with catalysts A, C, F * and G *. The test facility was equipped with a feed metering unit and an electrically heated reactor tube. The length of the reaction tube was 30 cm and the inside diameter of the reactor tube was 11 mm. In each case, 12 g of catalyst in the form of a grit of grain size 0.7 to 1.0 mm were mixed with the same volume of inert material (steatite balls) and filled into the reaction tube. The remaining empty volume was filled with further inert material (steatite balls). The reactor was operated in a "straight pass". The reactor pressure was 0.1 MPa abs. n-Butane was evaporated and metered in gaseous quantities. The test facility was operated with a GHSV of 2400 h ^_1 , an n-butane concentration of 1.4% by volume and a water content of 1.0% by volume. The resulting product gas was analyzed by gas chromatography.

Table 3 shows the data obtained after a running time of 600 hours.

Table 3

Legend: T: average reaction temperature u. Sales based on n-butane

S: selectivity of the converted n-butane to maleic anhydride A: yield of maleic anhydride (A = U x S)

The experiments show that the catalysts A and C produced by the process according to the invention with 68.5 and 68.8% have a significantly higher selectivity of maleic anhydride than the catalysts F * and G * according to the prior art with 59.8 and 66.8%. Since the experiments were carried out with approximately the same n-butane conversion, the yield of the catalysts is also significantly higher than that of the catalysts according to the prior art. The reaction temperature when using the catalysts prepared according to the invention can be kept relatively low at 388 and 383 ° C. despite the high yield achieved. The relationship between the

I [ooi] / I [ ₂₂₀ ] ratio and the selectivity or the

Yield could thus be confirmed experimentally.

Claims

claims

1. 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 reacting a five-valent vanadium compound with a five-valent phosphorus compound in the presence of a reducing agent Alcohol, characterized in that one

(i) as a reducing alcohol, an alcohol of the general formula (I)

R _l

R ₂ - CH CH ₂ OH (I),

R3

in which the radicals R and R _2, independently of one another, are hydrogen, Ci to Cg-alkyl or C _{1 to} C 6 -hydroxyalkyl and the radical R _{3 is} C ₁ to Cg-alkyl or C 1 to Cg-hydroxyalkyl,

(ii) the reaction is carried out without the addition of modifiers and coreductants selected from the series consisting of hydrogen halide, sulfur dioxide, fuming sulfuric acid and surfactants, and (iii) the pentavalent vanadium compound, the pentavalent compound

Combines phosphorus compound and the reducing alcohol, forms the catalyst precursor by heating and isolates it.

2. The method according to claim 1, characterized in that 1-butanol and / or 1-pentanol is used as the reducing alcohol.

3. Process according to claims 1 to 2, characterized in that vanadium pentoxide is used as the pentavalent vanadium compound.

4. Process according to claims 1 to 3, characterized in that orthophosphoric acid, py ^' rophosphoric acid, polyphosphoric acids or mixtures thereof are used as the pentavalent phosphorus compound.

5. Process according to claims 1 to 4, characterized in that one carries out the reaction between the pentavalent vanadium compound with the pentavalent phosphorus compound in the presence of a reducing alcohol at a temperature between 50 and 200 ° C.

6. Catalyst precursor for the production of maleic anhydride by heterogeneous catalytic gas phase oxidation of a hydrocarbon with at least four carbon atoms, obtained according to claims 1 to 5.

7. 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 ₂ ), hydrogen oxide (H ₂ 0) and / or inert gas in a temperature range from 250 to 600 ° C, characterized in that a catalyst precursor according to claim 6 is used.

8. Catalyst for the production of maleic anhydride by heterogeneous gas phase oxidation of a hydrocarbon having at least four carbon atoms, obtainable according to claim 7.

9. 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 8 is used.

10. The method according to claim 9, characterized in that one carries out the heterogeneous catalytic gas phase oxidation in a tube bundle reactor at a temperature of 350 to 480 ° C and a pressure of 0.1 to 1.0 MPa abs.

11. The method according to claims 9 to 10, characterized in that n-butane is used as the hydrocarbon.

12. The method according to claims 9 to 11, characterized in that one carries out the heterogeneous catalytic gas phase oxidation in the presence of a volatile phosphorus compound. Catalyst precursor for the production of maleic anhydride

Summary

Process for the preparation of a vanadium, phosphorus and oxygen-containing catalyst precursor for the production of maleic anhydride by heterogeneous catalytic gas phase oxidation of a hydrocarbon having at least four carbon atoms, by reacting a five-valent vanadium compound with a five-valent phosphorus compound in the presence of a reducing alcohol, in which you

(i) as a reducing alcohol, an alcohol of the general formula (I)

Ri R ₂ C CH ₂ CH ₂ OH (I),

! E3

in which the radicals Ri and R ₂ independently of one another are hydrogen, C Wasserstoff ~ to Cg-alkyl or Cχ ~ to Cg-hydroxyalkyl and the radical R _{3 is} Cχ ~ to C ₉ -alkyl or Cχ ~ to Cg-hydroxyalkyl,

(ii) carries out the reaction without the addition of modifiers and coreductants selected from the series consisting of hydrogen halide, sulfur dioxide, fuming sulfuric acid and surfactants, and (iii) combines the pentavalent vanadium compound, the pentavalent phosphorus compound and the reducing alcohol Heating the catalyst precursor and isolating it, catalyst precursor obtainable from this process, process for producing a catalyst from the catalyst pre-cursor, catalyst obtainable from this process and process for producing maleic anhydride on this catalyst.