WO2005118545A1

WO2005118545A1 - Gas-phase oxidation of alkyl-substituted heterocyclic compounds

Info

Publication number: WO2005118545A1
Application number: PCT/EP2005/005926
Authority: WO
Inventors: Jochen Petzoldt; Hagen Wilmer; Frank Rosowski
Original assignee: Basf Aktiengesellschaft
Priority date: 2004-06-04
Filing date: 2005-06-02
Publication date: 2005-12-15
Also published as: DE102004027414A1

Abstract

The invention relates to a method for producing heterocyclic carboxylic acids and heterocyclic carboxylic acid anhydrides, comprising the partial gas-phase oxidation of alkyl-substituted heterocyclic compounds in the presence of coated catalysts. Said method is characterised by high yields of the valuable product from a catalyst provided with a high charge of the starting product.

Description

Gas phase oxidation of alkyl substituted heterocyclic compounds

The present invention relates to a process for the preparation of heterocyclic carboxylic acids and heterocyclic carboxylic acid anhydrides comprising the partial gas phase oxidation of alkyl-substituted heterocyclic compounds in the presence of coated catalysts, which is distinguished by high yields of valuable product at high catalyst loads with the starting product.

An economically important heterocyclic carboxylic acid is nicotinic acid (pyridine-3-carboxylic acid). Nicotinic acid is widely used in the fields of medicine and agriculture as a B vitamin and as an intermediate for pharmaceutical products and for growth regulators of plants.

Nicotinic acid can be produced industrially by catalytic gas phase oxidation of 3-picoline in tube bundle reactors. The starting material is a mixture of a gas containing molecular oxygen, for example air, water vapor and the 3-picoline to be oxidized. The mixture is usually passed through a plurality of tubes arranged in a reactor (tube bundle reactor), in which there is a bed of at least one catalyst.

Various processes for the production of nicotinic acid are known.

DE 198 22 788 describes the oxidation of 3-methylpyridine to nicotinic acid in the gas phase using oxidation catalysts based on vanadium oxide. The active mass of the catalysts comprises 5 to 30% by weight of one or more compounds of the formula M _x V ₆ 0 ₁₅ , where M is selected from Li, Na, K, Rb, Cs, Mg, Ca and mixtures of these elements and 0 <x <1. The carrier material consists of 90 to 100% by weight of SiO ₂ and 0 to 10% by weight of Al ₂ O ₃ and / or ZrO ₂ , the BET specific surface area being 1 to 50 m ² / g. The active mass is applied to grains of the carrier material with a diameter of 1 to 3 millimeters. The use of coated catalysts based on support bodies is not described.

CH 543 510 discloses a process for the preparation of pyridine carboxylic acids in the gas phase by contacting the methyl-substituted pyridine compound with an oxygen-containing gas. The catalyst consists of a vanadium oxide-containing active material that is applied to grains of the carrier material silicon carbide with a diameter of approx. 2 millimeters. The use of coated catalysts based on support bodies is not described.

DE 2647 712 describes a process for the production of nicotinic acid from alkylpyridines with β-methyl or ethyl groups by gas phase oxidation on one solid catalyst phase with air and water vapor. A V ₂ O ₅ catalyst which contains TiO ₂ as a promoter and is heated to 1250 ° C. serves as the catalyst. Pumice and zeolites are described as substrates.

EP-A 747 359 describes a process for the production of nicotinic acid by a single-stage gas-phase oxidation of β-picoline with oxygen in the presence of water vapor. The process is carried out at temperatures from 250 to 290 ° C. in the presence of a catalyst based on oxides of vanadium and titanium. The yield is at least 82%. V ₂ O ₅ is supported on TiO ₂ . The use of coated catalysts based on support bodies is not described.

DE 198 39 559 describes the direct oxidation of β-picoline by feeding β-picoline and water separately to the reactor and only combining them at the beginning of the catalyst bed. The catalyst used is a vanadium oxide-containing catalyst, the support of which consists of a titanium dioxide with a high surface area (> 100 m ² / g) produced by the sulfate method, the vanadium oxide content being between 5 and 50% by weight. The TiO ₂ supported with vanadium oxide is pressed into tablets, these are then ground and sieved and one of the sieve fractions is used as a catalyst. The use of coated catalysts is not described.

CN 1 296 004 also describes a process for the production of nicotinic acid. The active composition of the catalyst contains 58% by weight of NH ₄ VO as the main constituent, as well as Sb ₂ O ₃ , Sm ₂ O ₃ , TiO ₂ and (NH ₄ ) ₂ Cr ₂ O ₇ . The active mass is carried by spraying onto Al ₂ O ₃ or silicon carbide balls. Before the oxidation reaction, the supported catalyst is activated at 400 to 450 ° C for 6 to 8 hours.

Japanese published patent application JP 2002-331239 describes a gas phase process for the production of nicotinic acid from 3-picoline in the presence of catalysts containing vanadium and chromium. The active mass is applied to silica sol and the catalyst grains suitable for the reaction are obtained by sieving. The use of coated catalysts is not described.

J. Appl. Chem. Biotechnol. 27 (1977) 499-509 describes the oxidation of 3-methylpyridine to nicotinic acid using supported catalysts with a coating of vanadium pentoxide and titanium dioxide in a weight ratio V ₂ O ₅ to TiO ₂ greater than 1: 4 on pumice stone, which according to 5 hour annealing at 400 ° C has a BET surface area of 15-100 m ² / g, preferably 25-50 m ² / g.

Large-scale processes are particularly advantageous when the so-called space-time yield (RZA) is as high as possible, ie with the smallest possible reactors and the highest possible yield of valuable products is achieved in a short time. The RZA is directly linked to the catalyst load. The catalyst load gives the mass of the starting product, which is brought into contact with the total mass of the catalyst per unit of time. The catalyst load is usually characterized by the specification of the WHSV (weight hourly space velocity):

WHSV = ^mEdukt l ^h "'' catalyst

The above-described processes for the direct oxidation of 3-picoline to nicotinic acid have the disadvantage that the STA on nicotinic acid are insufficient at high catalyst loads with starting material.

The object of this invention was therefore to find a process for the preparation of heterocyclic carboxylic acids in which the space-time yield is increased compared to the known processes.

Surprisingly, it was found that this object is achieved by a process for the preparation of heterocyclic carboxylic acids and heterocyclic carboxylic acid anhydrides comprising the partial gas phase oxidation of alkyl-substituted heterocyclic compounds by reacting the alkyl-substituted heterocyclic compounds with gas containing molecular oxygen in the presence of a supported catalyst, the vanadium and at least contains a support material in the active composition, characterized in that the supported catalyst is a coated catalyst, in which the active composition is applied in a shell shape to a support body and the vanadium content of the active composition, calculated as V ₂ O ₅ , is at most 20% by weight ,

The process according to the invention enables a high RZA in that the β-picoline partial pressure can be increased (higher WHSV at constant GHSV; GHSV = gas hourly space velocity [I (gas) / l (cat) / h]). As a result, the volume flow of the other components, such as water and air, which represent the majority of the volume flow, decreases with a constant total educt quantity. The resulting smaller volume flows of the process according to the invention in turn lead to a reduction in the size of the apparatus and pipes in the system, as a result of which the energy input into the system, e.g. for preheating the educt mixture, is lower. Due to the higher partial pressure of the product in the product gas mixture, separation is also easier or more complete.

A high RZA can also be achieved by increasing the GHSV while maintaining the starting gas composition. In this case, GHSV and WHSV correlate linearly. The higher RZA reduces the reaction volume with a constant volume flow. In order to achieve a high RZA, it is necessary to carry out the process with the highest possible catalyst loads. The WHSV is a measure of the catalyst load, ie the higher the WHSV, the greater the catalyst load. The process according to the invention is preferred for a WHSV of at least 0.04 h ^"1 , particularly preferably at least 0.06 h ^{" 1} , very particularly preferably at least 0.075 h ^"1 and in particular at least 0.09 h ^{" 1} . It is most preferred to carry out the process at a WHSV of at least 0.1h ^'1 .

The heterocyclic compounds which are oxidized to carboxylic acids or carboxylic anhydrides in the process according to the invention have an at least 5-membered ring, at least one ring atom being a heteroatom selected from nitrogen, oxygen or sulfur.

Examples which do not represent an enumeration limiting the invention are alkyl-substituted pyrroles, furans, thiophenes, imidazoles, oxazoles, thiazoles, pyrazoles, 3-pyrroline pyrrolidines, pyridines, pyrimidines, purines, quinolines, isoquinolines, carbazoles, indoles and benzofurans.

Preferred alkyl substituents are branched and unbranded Ci to C ₆ alkyl radicals such as methyl, ethyl, n-propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, pentyl, 1-methylbutyl, 2nd -Methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, -ethylpropyl, hexyl, 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,

1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, 1-ethyl-2-methylpropyl. Preferred alkyl radicals are methyl, ethyl and n-propyl.

The aforementioned heterocyclic compounds can be substituted at different ring positions with respect to the hetero atom (s) one or more times with the same or different alkyl radicals. Preferred alkyl substituents are C 1 to C ₄ alkyl, particularly preferably methyl, ethyl, n-propyl, particularly preferred is methyl.

Examples of special alkyl-substituted heterocyclic compounds which can be oxidized to carboxylic acids by the process according to the invention are methylpyrrole, ethylpyrroles, propylpyrroles, methylfurans, ethylfurans, propylfuran, methylthiophenes, ethylthiophenes, propylthiophenes, methylimidazoles, ethylimidazoles, propylimidazoles, propylimidazoles, propylimidazoles, Ethyloxazole, propyloxazole, methylthiazole, ethylthiazole, propylthiazole, methylpyrazole, ethylpyrazole, propylpyrazole, methyl-3-pyrroline-pyrolidine, ethyl-3-pyrrolinepyrolidine, propyl-3-pyrrolinepyrolidine, picoline, ethylpyrimidine, ethylpyrimidine, Methylpuri- ne, ethylpurine, propylpurine, methylquinoline, ethylquinoline, propylquinoline, methylisoquinoline, ethylisoquinoline, propylisoquinoline, methylcarbazole, ethylcarbazole, propylcarbazole, methylylindole, ethylylindole, propylindole, methylbenzofuran, ethylbenzofuran and propylbenzofuran and propylbenzofuran.

Particularly preferred heterocyclic compounds which are oxidized to carboxylic acids by the process according to the invention are alkyl pyridines, 2-picoline, 3-picoline, 4-picoline, 2-ethyl pyridine, 3-ethyl pyridine, 4-ethyl pyridine and 2-methyl-5-ethyl pyridine are particularly preferred. 3-Picolin is very particularly preferred.

Accordingly, the process according to the invention for producing nicotinic acid (3-pyridinecarboxylic acid) from 3-picoline (3-methylpyridine) is particularly preferred.

In the context of the present invention, the carrier material is a component of the active composition (active composition). In the case of a coated catalyst, this active composition is applied to the carrier body. The carrier body preferably consists of a material which is essentially inert and essentially non-porous under the reaction conditions of the process according to the invention. Shell catalysts are understood to mean catalysts which consist of support bodies, the outer surface of which are partially or completely covered with a catalytically active composition. The outer surface of a carrier body is the surface that can be wetted by liquid water under normal conditions by completely immersing the body in the water.

Oxidized supported catalysts are suitable as catalysts. In addition to vanadium, which is preferably present as vanadium pentoxide, the active composition contains at least one carrier material. The carrier materials can be titanium dioxide, zirconium dioxide, silicon oxide, aluminum oxide, magnesium oxide, silicon carbide, titanium dioxide and zirconium dioxide are preferred, in particular titanium dioxide is used.

The titanium dioxide used is preferably in anatase form and advantageously has a BET surface area of 5 to 50 m / g, preferably 10 to 35 m ² / g, in particular 13 to 28 m ² / g. Mixtures of titanium dioxide in anatase form with different BET surface areas can also be used, with the proviso that the resulting BET surface area has a value of 5 to 50 m ² / g, preferably 10 to 35 m / g, in particular 13 to 28 m ² / g. For example, commercially available TiO ₂ with a BET surface area of approximately 20 m ² / g can be used.

Vanadium oxides or vanadium compounds which convert to vanadium oxide when heated in air, preferably individually or in the form of mixtures thereof, are preferably used as the component of the active composition containing vanadium. V ₂ O ₅ or NH V0 ₃ are preferably used. The amount of vanadium, calculated as V ₂ O ₅ and related The total weight of the active components is preferably in the range from 0.5 to 15, particularly preferably in the range from 1 to 12,% by weight. A proportion of 1 to 10% by weight of vanadium component, calculated as V ₂ O ₅ and based on the total weight of the active components, is particularly preferably used.

A preferred embodiment of the invention is accordingly a process for the preparation of heterocyclic carboxylic acids and heterocyclic carboxylic acid anhydrides comprising the partial gas phase oxidation of alkyl-substituted heterocyclic compounds by reacting the alkyl-substituted heterocyclic compounds with molecular oxygen-containing gas in the presence of a supported catalyst which contains vanadium in the active composition characterized in that the supported catalyst is a coated catalyst in which the active mass is applied in a shell shape on a support body and 90 to 99% by weight of titanium, calculated as TiO ₂ , 1 to 10% by weight of vanadium, calculated as V ₂ O ₅ , and optionally contains further constituents in an amount of up to 1% by weight.

In addition, the catalytically active composition can contain a large number of other oxidic compounds in small amounts which, as promoters, influence the activity and selectivity of the catalyst, for example by reducing or increasing its activity. Such promoters are, for example, the alkali metal oxides, thallium (l) oxide, aluminum oxide, zirconium oxide, iron oxide, nickel oxide, cobalt oxide, manganese oxide, tin oxide, silver oxide, copper oxide, chromium oxide, molybdenum oxide, tungsten oxide, iridium oxide, tantalum oxide, niobium oxide, arsenic oxide, antimony oxide, cerium oxide, gold -, platinum and palladium compounds and phosphorus compounds such as phosphorus pentoxide. The alkali metal oxides act, for example, as promoters which reduce activity and increase selectivity. Based on the total mass of the catalyst, the proportion of active mass is 5 to 50, preferably 5 to 40, particularly preferably 10 to 35% by weight.

In a further preferred embodiment of the invention, the active composition of the catalyst accordingly contains further constituents selected from alkali metal oxides, thallium (l) oxide, aluminum oxide, zirconium oxide, iron oxide, nickel oxide, cobalt oxide, manganese oxide, tin oxide, silver oxide, copper oxide, chromium oxide, molybdenum oxide, tungsten oxide, Iridium oxide, tantalum oxide, niobium oxide, arsenic oxide, antimony oxide, cerium oxide and phosphorus oxide.

To produce the coated catalysts, an aqueous and / or organic solvent-containing solution or suspension of the active composition constituents and / or their precursor compounds, which are hereinafter referred to as "mash", is used in the processes of DE-A 1642938 and DE-A 17 69 998 is, on a generally inert under the reaction conditions in a heated coating drum at elevated Sprayed on temperature until the desired proportion of active mass in total catalyst weight is reached. According to DE 21 06 796, the coating can also be carried out in fluidized coaters, as are given, for example, in DE 12 80 756. However, high losses occur when spraying in the coating drum and when coating in a fluidized bed, since considerable quantities of the mash are atomized or parts of the active composition already coated are abraded and abraded and carried off by the exhaust gas. Since the active mass fraction of the overall catalyst should generally only have a slight deviation from the target value, since the activity and selectivity of the catalyst are strongly influenced by the amount of active mass applied and the layer thickness of the shell, the catalyst frequently has to be determined in the described production methods in order to determine the the amount of active material applied is cooled, removed from the coating drum or the fluidized bed and weighed. If too much active material is deposited on the catalyst carrier, it is generally not possible to subsequently and gently remove the amount of active material applied without affecting the strength of the shell, in particular without cracking in the catalyst shell.

In order to alleviate these problems, the technology has been adopted to add organic binders, preferably copolymers, advantageously in the form of an aqueous dispersion, of vinyl acetate / vinyl laurate, vinyl acetate / acrylate, styrene / acrylate, vinyl acetate maleate and vinyl acetate / ethylene to the mash, binder quantities of 10-20% by weight, based on the solids content of the mash, were used (EP-A 744214). If the mash is applied to the carrier without organic binders, coating temperatures above 150 ° C are advantageous. When the above-mentioned binder is added, the usable coating temperatures are between 50 and 450 ° C., depending on the binder used (DE 21 06 796). The applied binders burn out within a short time after the catalyst has been introduced into the reactor and the reactor has been started up. The addition of the binder also has the advantage that the active composition adheres well to the support, so that transport and filling of the catalyst are made easier.

Regularly shaped, mechanically stable carriers are suitable as carrier bodies, such as preferably spherical, ring-shaped, semi-ring-shaped, saddle-shaped, bowl-shaped, cube-shaped, cuboid, truncated cone or truncated cone, pyramid or truncated pyramid, prism-shaped or cylindrical carrier bodies. Ring-shaped carrier bodies are particularly preferred.

Numerous embodiments for ring-shaped carrier bodies are described in the prior art. DE-A 3445289 (US-A 4,656, 157) describes, for example, a ring carrier which differs from "normal rings" in that its end faces are rounded. EP-A 220933 describes a catalyst which has a "four-winged" shape, as a result of which the catalyst has better physical properties with regard to breaking strength and pressure build-up.

GB-A 21 93907 describes a catalyst in cylindrical shape, the outer shell of which is provided in the longitudinal direction with ribs which are dimensioned and arranged in such a way that the individual catalyst bodies cannot get caught.

US-A 4,328,130 also describes a catalytic converter form in which a cylinder is traversed in the longitudinal direction with a plurality of channels and ribs, the recesses being narrower than the ribs in order to avoid snagging.

Catalyst forms are known from EP-A 004 079 (USA 4,370,492 and US-A 4,370,261), which are strand sections with a star-shaped cross section or ribbed strands.

EP-A 1 108470 discloses inert carrier bodies in the form of rings, characterized in that the rings have one or more notches on the upper and / or lower flat side of the ring. On pages 8 to 12 of EP-A 1 108470 numerous possible embodiments of this type of support body are shown.

According to the drawings on pages 20 to 35, EP-A 552 287 discloses geometric structures provided with cavities which are suitable as support bodies for the coated catalysts of the process according to the invention. Specifically, the cylinders, cubes, cones, truncated cones, pyramids, truncated pyramids, spheres and prisms. The cavities can be evenly spaced on the outer surface in which such cavities are located and can be of the type of grooves, holes and troughs.

With regard to the possible spatial configurations of the carrier bodies, reference is made in full to the disclosures of the abovementioned documents.

The size of the support bodies is mainly determined by the dimension, especially by the inner diameter of the reaction tubes, when the catalyst is used in tube or tube bundle reactors. The carrier diameter should then be between 1/2 and 1/10 of the inside diameter.

Steatite in the form of spheres with a diameter of 3 to 6 mm or rings with an outer diameter of 5 to 9 mm and a length of 4 to 7 mm is preferably used, the size being selected in accordance with the inner diameter of the reactor tube. Examples of suitable materials for the carrier body are silicate, silicon carbide, porcelain, aluminum oxide, magnesium oxide, tin dioxide, rutile, aluminum silicate, magnesium silicate (steatite), duranite, earthenware, silicon dioxide, aluminates, metals, metal alloys, zirconium silicate or cerium silicate or mixtures thereof , with steatite being preferred.

Gas phase oxidations on shell catalysts do not only take place on the outer surface of the shell. In order to achieve the catalyst activity and selectivity required for the complete implementation of the high loading of the reaction gas with starting material used in industrial processes, efficient use of the entire active material shell of the catalyst and thus good accessibility of the reaction gas to the reaction centers located in this shell is advantageous. Since the gas phase oxidation of heterocyclic compounds to carboxylic acids and / or carboxylic acid anhydrides takes place via a large number of intermediate stages and the product of value on the catalyst can be further oxidized to carbon dioxide and water, an optimal conversion is achieved in order to achieve a high conversion of starting material while at the same time suppressing the oxidative degradation of the product of value Adaptation of the dwell time of the reaction gas in the active composition is advantageous by producing a suitable active composition structure (for example its porosity and pore radius distribution) in the catalyst shell.

The catalysts coated with active composition are filled into reaction tubes which are thermostatted from the outside to the reaction temperature, for example by means of salt melting, and the reaction gas at temperatures of generally above 290 ° C. to 400 ° C., preferably from 300 to 380 ° C., via the catalyst bed prepared in this way C and particularly preferably from 310 to 350 ° C and at an overpressure of generally 0.1 to 2.5 bar, preferably from 0.3 to 1.5 bar with a space velocity of generally 750 to 5000 h-1.

The reaction gas fed to the catalyst is generally generated by mixing a gas containing molecular oxygen, which in addition to oxygen may also contain suitable reaction moderators and / or diluents, such as water vapor, carbon dioxide and / or nitrogen, with the heterocyclic compound to be oxidized, where the gas containing the molecular oxygen, for example 1 to 99 mol%, preferably 2 to 50 mol% and particularly preferably 6 to 20 mol% oxygen, 0 to 50 mol%, preferably 0 to 35 mol% water vapor and 0 to 50 mol%, preferably 0 to 1 mol% carbon dioxide, balance nitrogen. To generate the reaction gas, the molecular oxygen-containing gas is generally charged with 10 g to 150 g per Nm ^{3 of} gas, preferably 15 to 120 g per Nm ^{3 of} the heterocyclic compound to be oxidized (Nm ³ = standard cubic meter = 1 m ³ at 0 ° C and 1013 mbar). It is also possible to carry out the gas phase oxidation in such a way that two or more zones of the catalyst bed in the reaction tube are thermostatted to different reaction temperatures, for example reactors with separate salt baths, as described in DE-A 22 01 528 or DE-A 28 30765 , can be used. If the reaction is carried out in two reaction zones, as described in DE-A 40 13051, the reaction zone located towards the gas inlet of the reaction gas, which generally comprises 30 to 80 mol% of the total catalyst volume, is reduced to 1 to 20 ° C, preferably by 1 to 10 ° C and in particular by 2 to 8 ° C higher reaction temperature than the reaction zone located towards the gas outlet thermostatted. Alternatively, the gas phase oxidation can also be carried out without division into temperature zones at a single reaction temperature.

Regardless of the temperature structuring, catalysts can be used in the above-mentioned reaction zones of the catalyst bed which differ in their catalytic activity and / or chemical composition of their active composition. When using two reaction zones in the first reaction zone, that is to say in the reaction zone located toward the gas inlet of the reaction gas, a catalyst is preferably used which is somewhat less catalytic than the catalyst located in the second reaction zone, ie toward the gas outlet Has activity. In general, the reaction is controlled by the temperature setting in such a way that in the first zone most of the heterocyclic compound contained in the reaction gas is converted with maximum yield. It is also possible to carry out the process with three, four or more reaction zones, the catalysts in the individual zones differing in their catalytic activity and / or chemical composition of their active composition.

For example, the catalyst system can consist of three to five layers. In the case of a three-layer catalyst system with zones i, ii and iii, the following applies to the BET surface area of the titanium dioxides used in anatase modification: BET _Zθ ne (i) <BET _{2on8 (l} i) <

BET zone (iii).

If the process according to the invention is carried out using a plurality of reaction zones in which different catalysts are located, shell catalysts can be used in all reaction zones.

Salt bath-cooled tube bundle reactors as are customary in other partial oxidation reactions are preferred as reactors for carrying out the process according to the invention. Such reactors have reaction tubes with diameters in the range of typically 20 to 30 mm and lengths in the range of typically 2 to 7 m. Several thousand pipes can be installed in a reactor. reactors This type is used, for example, in the prior art in the synthesis of phthalic anhydride, acrylic acid and maleic anhydride.

In principle, distillation, crystallization, absorption, desublimation, extraction and combinations of these methods are suitable for the subsequent processing of the heterocyclic carboxylic acids which are liquid or solid under normal conditions (23 ° C., 1013 mbar).

Examples 1) Preparation of catalyst

51) Spherical coated catalyst with 20% by weight of active composition (weight ratio of vanadium compounds: titanium compounds = 4:96, calculated as V ₂ O ₅ : TIO ₂ )

A suspension containing 422.4 g of anatase (BET surface area 20 m ² / g), 17.6 g of V ₂ O ₅ , 47.5 g of oxalic acid, 135.4 g of formamide and 1577.3 g of water was in a spray dryer transferred a powder.

218.8 g of the spray powder obtained in this way, together with 34.4 ml of a binding liquid composed of 40% by weight glycerol and 60% by weight water, were placed in a coating drum over 38 g on 700 g steatite balls with a diameter of 3.5 to 4.5 mm applied.

After calcination at 450 ° C. for 2 hours, the weight of the catalytically active composition was 20.4%, based on the total weight of the catalyst.

52) Ring-shaped coated catalyst with 20% by weight of active composition (weight ratio of vanadium compounds: titanium compounds = 4:96, calculated as V ₂ O ₅ : TiO ₂ )

A suspension containing 470.5 g of anatase (BET surface area 20 m ² / g), 19.7 g of V ₂ O ₅ , 53.0 g of oxalic acid, 150.6 g of formamide and 706.5 g of water was added together with 53 , 2 g of Acronal ^® DS 2348 as binder within 52 min in a coating drum on 1300 g of steatite rings of dimensions 8 * 6 * 1, 5 (outer diameter ^* height * inner diameter).

After calcination at 450 ° C. for 2 hours, the weight of the catalytically active composition thus applied was 19.8%, based on the total weight of the catalyst.

S3) Spherical shell catalyst with 27 wt .-% active mass

(Weight ratio of vanadium compounds: titanium compounds = 4:96, calculated as V ₂ O ₅ : TiO ₂ )

The preparation was carried out analogously to Example S1, but 142.9 g of the spray powder together with 52.0 g of the binding liquid were applied to 300 g of steatite balls with a diameter of 3.5 to 4.5 mm.

S4) Ring-shaped coated catalyst with 10% active mass (Weight ratio vandium compounds: titanium compounds = 4:96, calculated as V ₂ O ₅ : TiO ₂ ) 486 g of a suspension containing 504.0 g of anatase (BET surface area 20 m ² / g), 21.0 g of V ₂ O ₅ , 56.7 g of oxalic acid, 161.3 g of formamide and 757.0 g of water, together with 22.8 g of Acronal ^® DS 2348 as a binder, were placed on 1300 g of steatite rings of size 8 * 6 * 4 in a coating drum within 30 min. 8 mm applied. After calcination at 450 ° C. for 2 hours, the weight of the catalytically active composition thus applied was 10.9%, based on the total weight of the catalyst. 2) Gas phase oxidation of 3-picoline 01) 148.2 g of the catalyst prepared according to Example S1 were introduced into a stainless steel reactor with an inner diameter of 15 mm and a centered thermowell with an outer diameter of 3.17 mm (1/8 inch). Water and 3-picoline were metered in liquid via pumps and evaporated together in air which was metered in via a mass flow controller. At a temperature of 312 ° C (Ex. O1 a) or 343 ° C (O1 b), the gas mixture was passed over the catalyst bed. The temperature of the reactor was achieved using a salt bath. The compositions of the educt and product gas mixtures were analyzed by means of gas chromatography. 02) 1220 g of the catalyst prepared according to Example S2 were introduced into a reactor with an inner diameter of 26 mm and a centered thermal sleeve with a 4 mm outer diameter. The starting materials were metered in and the gas mixtures were analyzed analogously to Example O1. The temperature for the production of nicotinic acid using the process according to the invention using the catalyst according to S2 was 321 ° C. (02a), 328 ° C. (02b) and 347 ° C. (O2c). 04) 1160 g of the catalyst prepared according to Example S4 were introduced into a reactor with an inner diameter of 26 mm and a centered thermal sleeve with a 4 mm outer diameter. The starting materials were metered in and the gas mixtures were analyzed analogously to Example 01. The temperature for producing nicotinic acid using the process according to the invention using the catalyst according to S4 was 351 ° C. (04a), 325 ° C. (04b), 353 ° C. ( 04c), 331 ° C (O4d).

* The conversion of 3-picoline was determined from the ratios of the corresponding areas of the 3-methylpyridine signals of the gas chromatograms of the educt and product stream. ** The selectivity of nicotinic acid results from the selectivities of the other reaction products according to the relationship

100% -ΣSelektivitäten _wei tere products) - wherein the selectivities of further products resulting from the determined relative proportions of these products by GC on the amount of unreacted 3-picoline, taking into account the stoichiometry of the particular reaction. The sum of the selectivities is 100%. *** The yield of nicotinic acid is derived from _Nico tinsäure yield = SelektivitätNicotinsäure * turnover3-p _IC0] _in

Claims

claims

1. A process for the preparation of heterocyclic carboxylic acids and heterocyclic carboxylic acid anhydrides comprising the partial gas phase oxidation of 5 alkyl-substituted heterocyclic compounds by reacting the alkyl-substituted heterocyclic compounds with gas containing molecular oxygen in the presence of a supported catalyst which contains vanadium and at least one support material in the active composition , 10 that the supported catalyst is a coated catalyst in which the active mass is applied in a shell-like manner to a support body and the vanadium content of the active mass, calculated as V ₂ O ₅ , is at most 20% by weight.

2. The method according to claim 1, characterized in that the active mass contains as at least one carrier material TiO ₂ .

3. The method according to claims 1 or 2, characterized in that the active mass is 5 to 50 wt .-%, based on the total mass of the catalyst. 20

4. The method according to claims 1 to 3, characterized in that the active mass is 10 to 35 wt .-%, based on the total mass of the catalyst.

25 5. The method according to claims 1 to 4, characterized in that the active mass 90 to 99 wt .-% titanium, calculated as TiO ₂ , 1 to 10 wt .-% vanadium, calculated as V ₂ O ₅ , and optionally contains further constituents in an amount of up to 1% by weight of the active composition.

6. The method according to claims 1 to 5, characterized in that the active composition further components selected from alkali metal oxides, thallium (l) oxide, aluminum oxide, zirconium oxide, iron oxide, nickel oxide, cobalt oxide, manganese oxide, tin oxide, silver oxide, copper oxide, Contains chromium oxide, molybdenum oxide, tungsten oxide, iridium oxide, tantalum oxide, niobium oxide, arsenic oxide, antimony oxide, cerium oxide and 35 phosphorus pentoxide.

7. The method according to claims 1 to 6, characterized in that the carrier body is cylindrical or annular.

40 8. The method according to any one of claims 1 to 7, characterized in that the method is carried out at a temperature greater than 290 ° C.

t I Method according to one of claims 1 to 8 for the production of nicotinic acid, characterized in that 3-methylpyridine is used as the heterocyclic compound.