DE1468824B2 - Process for the production of aromatic acid anhydrants by gas phase oxidation - Google Patents

Description

rR ²

R ³

in which R ¹ , R ² , R ³ and R ^{4 can be} hydrogen atoms, methyl, ethyl or propyl radicals with the proviso that either R ¹ and R ² or R ³ and R ^{4 are} methyl, ethyl or propyl radicals, and of octahydroanthracene, octahydrophenanthrene, anthracene or phenanthrene, with oxygen-containing gases at elevated temperatures in the presence of a catalyst containing vanadium, niobium and oxygen, characterized in that the process is carried out in the presence of a catalyst based on vanadium and niobium which niobium in one Contains an amount of 0.05 to 1, in particular 0.1 to 0.3 g atom of niobium per g atom of vanadium, and that the contact time of the reaction mixture is 0.01 to 2 seconds at temperatures between 400 and 600 ^° C. and at pressures is between 0.5 and 30 at.

2. The method according to claim 1, characterized in that there is a 75 to 99 percent by weight Applying catalyst containing carrier material.

3. The method according to claim 1 or 2, characterized in that a catalyst is used, by dissolving vanadium pentoxide and niobium oxalate in aqueous oxalic acid solution, Evaporation and subsequent calcination of the residue has been prepared.

4. The method according to claim 3, characterized in that one pyromellitic dianhydride based on Durol.

It is known that alkyl aromatic hydrocarbons by reaction with oxygen-containing Gases, e.g. B. air, at elevated temperature in the presence of an oxidation catalyst, e.g. B. one Vanadium oxide supported catalyst, can be oxidized in a targeted manner. When the alkyl aromatic hydrocarbon contains two adjacent alkyl substituents on the ring, which are preferably lower alkyl radicals the oxidation reaction leads to the anhydride. The alkyl aromatic hydrocarbon contains two Groups of two adjacent alkyl substituents, the oxidation leads to the dianhydride.

It is already known to catalytically oxidize Durol in this way to pyromellitic dianhydride. However, this process proved to be neither techin where R ¹ , R ² , R ³ and R ⁴ hydrogen atoms, methyl, ethyl or propyl radicals, with the proviso that either R ¹ and R ² or R ³ and R ^{4 are} methyl -, Ethyl or propyl radicals, as well as octahydroanthracene, octahydrophenanthrene, anthracene and phenanthrene, with oxygen-containing gases at elevated temperatures in the presence of a vanadium, niobium and oxygen-containing catalyst, which is characterized in that the process in the presence of a catalyst on the Based on vanadium and niobium, which niobium contains 0.05 to 1, in particular 0.1 to 0.3 g-atoms of niobium per g-atom of vanadium, and that the contact time of the reaction mixture is 0.01 to 2 seconds at temperatures between 400 and 600 ⁰ C and at pressures between 0.5 and 30 atmospheres.

The catalyst can be in any conditioning, e.g. B. in the form of granules, grain or "Pellets", preferably on a solid support such as aluminum oxide, silicon carbide, magnesium oxide or other known or customary carriers are present. When using a carrier material, this is preferably in amounts of 75 to 99 percent by weight, in particular 85 to 95 percent by weight of the Total catalyst available.

The catalyst is preferably used in the form of a fixed bed and has one for this purpose Particle size in the range from 1 to 13, preferably 3.2 to 6.4 mm. The catalyst can also be finely divided Form to be manufactured for use in the fluidized bed. The particle size distribution in this case is, for example, in the range from 10 to 100 μ.

The preferred catalysts used for the purposes of the invention are prepared by drying a solution containing the vanadium and niobium components or by drying the solution in the presence of the support. For example, the required amounts of vanadium in the form of vanadium pentoxide and niobium in the form of niobium oxalate can be dissolved in an oxalic acid solution. Solid granules of the carrier, e.g. B. pure "aluminum oxide or silicon carbide is then added to the oxalic acid solution. The resulting mixture is heated and rolled to dryness, the vanadium-niobium compounds coating the carrier particles. The catalyst can then be calcined in air at a temperature of between 300 and 550 ^{° C., for example.} It is also possible,

3 4

the oxalic acid solution in the absence of the carrier for, in particular, at a temperature significantly below 500 ° C in Evaporate to dryness and the solids obtained is kept within this range. the to grind, to granulate and to use as such- reaction is carried out at pressures between 0.5 to 30 at, before or before the granulation with the carrier - preferably between 1 and 5 at, carried out, to mix material. Preferably, in each case 5 The contact time of the gas stream with the catalyst a carrier material with a small inner surface is between 0.01, depending on the temperature and pressure used. and 2 seconds.

Activators, e.g. B. Alkali metals and alkaline earths The preferred oxygen-containing gas is air

oxides, sulfates or phosphates, boron, silver, manganese can also be used, but mixtures of or phosphorus, antimony or arsenic can also be used in the form of oxygen and any other diluent compounds soluble in the vanadium-niobium oxalate, such as water vapor, nitrogen or Carbon dioxide, mixture can be added. The amount of activator to be used. The hydrocarbon used is between 0.1 and 5% of the amount of niobium plus z. B. Durol, must be in an amount of about 0.01 vanadium in the catalyst. The quantitative ratio of up to 1.5 mole percent be present in the gas stream.
Niobium to vanadium is chosen so that the g-atom 15 The reaction can be carried out in any conventional pre-ratio of Nb / V in the catalyst between 0.05 directions, in which gases are above and 1, preferably between 0.1 and 0, 3 vaiiert. a catalyst are performed and the temperature

The exact nature and structure of the temperature control are accessible on this. For example, they are not known in a reaction tube, a chamber or a way formed catalyst, however, it is assumed that an inorganic poly-tube reactor, in which the catalyst is arranged meres, which contains the vanadium and niobium. is to be carried out, with a heat transfer without a commitment to a certain shaping medium circulating for temperature control,
or structure is intended, the reaction product can be used in any known

Way formed catalyst in this description ter way, e.g. B. by condensation, referred to as niobium vanadate. 25 means or isolated by washing and in the usual way

Any alkylbenzenes of the general formula can be purified. For example, pyro-

dianhydride be deposited by condensation in a condenser, which is kept at a temperature between 20 and 35O ⁰ C,. The 30 pyromellitic dianhydride can then in an or-

^s l — R ² ganic solvents such as p-dioxane, diacetonal

alcohol, cellulose solve acetate, diphenyl ether, 1,2-dimethoxyethane or ketones can be dissolved and decolorized with activated charcoal. That crystallized out on cooling 35 Pyromellitic dianhydride is separated off, for example, by centrifugation or filtration; the solvent can be recovered and recycled

where R ¹ , R ² , R ³ and R ^{4 are} hydrogen, methyl, ethyl or else can be used to dissolve the condensed or propyl radicals, with the proviso that pyromellitic dianhydride from the cooler uses either R ¹ and R ² or R ³ and R * Methyl-, ethyl- 40 det. For continuous operation it or propyl residues can be useful as starting materials if two or more are used alternately. The preferred group of drifted coolers are present
alkyl aromatic hydrocarbons form the crude pyromellitic dianhydride can also

Tetraalkylbenzenes which contain lower alkyl radicals. by washing with water at one temperature The catalytic oxidation of these tetraalkylbenzenes 45 between about 32 and 150 ° C can be obtained. the Filtration leads to the formation of the corresponding acid anhy- water-insoluble products dride. The alkyl aromatic hydrocarbons ha- or centrifuged separated, and the aqueous praise preferably pairs of alkyl substituents on solution is decolorized with activated charcoal. The neighboring ones when they cool down Carbon atoms of the ring. Preferably pyromellitic acid obtained from the clarified solution wise, these are lower alkyl groups, e.g. B. Methyl 50 becomes dehydrated. The crude pyromellitic dian residue. hydride can be obtained by recrystallization as above

Described as examples of alkylaromatic hydrocarbons, further purified,
Substances that are oxidized according to the invention According to another, preferred method of

can be mentioned: o-xylene, durol, octahydro- recovery of the reaction products, eg. B. of pyroanthracene, Tetraethyl or tetrapropylbenzene, 55 mellitic dianhydrides, from the reaction gases wer-ethyltrimethylbenzene, Diethyldimethylbenzene, prod these to a temperature below that of solidification trimethylbenzene. Octahydrophenanthrene, anthration point of the pyromellitic dianhydride cooled cene and phenanthrene can also be prepared according to and the solid particles thus formed of the Dianhy invention are oxidized. drids caught on a filter cloth.

Durol is particularly preferred as alkyl-60

aromat started to pyromellitic dianhydride example 1

to manufacture. Octahydroanthracene can also be used for
be used for this purpose. A catalyst that contains niobium vanadate with a

A mixture of alkylaromatic Nb / V atomic ratio employed of 0, 18, and aluminum-hydrocarbon, for example, of durene, and oxygen-65 oxide contained as a carrier was prepared as follows:-containing gas is passed over the catalyst gelei- 60 g V ₂ O ₅ were dissolved in 149 g of oxalic acid in water at tet, while the temperature between 400 and about 50 ° C carefully. A solution of 63.4 g of 600 ° C, preferably between 400 and 500 ° C and niobium oxalate in water was slowly converted to vanadium

oxalate solution given. Then 150 g of an acid leached and dried aluminum oxide (alundum) was added. The mixture was evaporated to dryness with rolling. The supported catalyst was ^{calcined at 500 °} C. for 1 hour. This catalyst was used to oxidize durene to pyromellitic dianhydride. 50 ml of the catalyst were placed in a reactor tube with an internal diameter of 19 mm and which had an axial thermocouple pocket. 70 ml of uncoated alundum were arranged over the catalyst as a preheating zone.

6.0 ml of Durol and 5421 air were passed over the catalyst every hour. The following yields were received:

temperature
⁰ C Pyromellitic dianhydride
(PMDA)
Weight percent (mole percent) 450
500 89 (54.9)
101 (62)

0.5 to 30 at, preferably 1 to 5 at. The molar concentration of o-xylene in air or in a mixture of oxygen and inert gas, such as nitrogen, steam or CO ₂ , is 0.1 to 1.5 mol percent. The phthalic anhydride is obtained by direct condensation from air on cooled surfaces or by washing in water with subsequent evaporation and dehydration.

Example 6

The catalyst described in Example 2 was used for the oxidation of o-xylene to phthalic anhydride used. The reaction was carried out in a steel reactor with an internal diameter of 19 mm, which was enclosed by a brass block and contained an axial thermocouple pocket. The product was obtained by direct condensation from the residual gas as well as by washing with water. The analysis of the product was carried out by gas chromatography and by pH titration. The following yields were obtained:

Example2

A catalyst having the same Nb / V ratio as that of Example 1 was used in the same Wise made except that SiC was used as the carrier. When testing the Catalyst in the same way, the same yields were obtained.

Amount of gas used

V / cat.-vol. / Hour 3,000
12,000

Yield of phthalic anhydride

Weight percent (mole percent)
400 ⁰ CI 450 ⁰ CI 500 ⁰ C

66 (47)
14 (10)

98 (70)
74 (52.8)

91 (65) 94 (67)

Example 7 Example 3

A catalyst having the same Nb / V ratio as that of Example 1 was used in the same Wise made except that no carrier was used. The catalyst solids were ground and granulated and tested in the same way. The same yields of PMDA were made obtain.

Example 4

The experiment described in Example 1 was repeated with catalysts whose Nb / V ratios varied between 0.1 and 1.0. The results obtained are summarized in the following table:

In the manner described in Example 6 were supported catalysts with Nb / V atomic ratios up to to 1 manufactured and tested. The highest yields are given below:

Nb / V atomic ratio

40

45 0.1

0.25
0.50
1.0

Phthalic anhydride
Weight percent (mole percent)

94 (67)
98 (70)
75 (53.5)
66 (47)

Example 8

Nb / V ratio temperature
⁰ C PMDA
Weight percent
(Mole percent) 0.1
0.18
0.36
1.0 500
500
500
525 101 (62)
101 (62)
89 (54.9)
50 (30.9)

Example 5

50 ml of a niobium vanadate catalyst prepared according to Example 2 with an Nb / V atomic ratio of 0.25 were mixed with 70 ml of silicon carbide granules. The mixture was placed in a reactor tube filled with an inner diameter of 23 mm, which was provided with a jacket. The reaction temperature was controlled by a thermocouple and maintained with a heat transfer medium. At a room air velocity of 9500 V / cat.-vol. / Hour, a durol concentration of 0.28 mole percent and an average catalyst bed temperature of 418 ° C a yield of 56 mole percent was achieved.

Example 9

O-xyol is converted into phthalic anhydride 65 via the catalysts prepared according to Example 1
oxidized. The reaction temperatures are 400 600 ml of a catalyst containing SiC as a carrier

up to 600 ° C, preferably 425 to 525 ° C. The cones with an Nb / V ratio of 0.25 were cycle times are 0.01 to 20 seconds, the pressures in a reactor with an internal diameter of 25.4 mm

7 8

and 1.5 m length filled. The reactor was made with a lat as a support and is manufactured as follows: 30 g of jacket provided. The reaction _{temperature was maintained at approximately V 2} O ₅ in 74.6 g of oxalic acid in water by carefully dissolving a eutectic salt mixture 50 ° C. Was passed through the jacket to the vanadium oxalate solution. Durol in a solution of 27.8 g of niobium oxalate in a concentration of 0.24 to 0.35 mol percent in air 5 is slowly added to water. After adding 300 g of silicon car, it was oxidized to PMDA. The product was through double granules, the mixture is cooled to dryness from the residual gas of the reactor and then evaporated while it is rolled. The carrier catalyst, which collects the solid PMDA particles on a sator, is calcined at 500 ° C. for 1 hour.
won a filter cloth. With an average 50 ml of the catalyst, a reactor tube with a temperature of 393 ° C. and an internal diameter of 19 mm is placed in the catalyst bed, which is provided with an axial thermocouple and a room flow velocity of the air. Above the Kavon 4000 V / cat.-vol. / Hour If 34 mol percent of the catalyst were used, 70 ml of uncoated silicon car PMDA were obtained. Arranged as a preheating zone for an average temperature granulate. Above the temperature of the catalyst bed of 41 ° C (measuring point catalyst is octahydroanthracene at a Kon-433 ° C) and a room flow rate 15 concentration of 0.1 mol percent in air at 450 ⁰ C the air of 6000 V / Kat.-Vol. / Hours. an exit was made. The contact time is 0.5 seconds. By direct condensation of solids of 72 percent by weight (44.4 mole percent), pyromel is obtained. At an average catalyst bed litsäuredianhydrid in a yield of 60 GeTemperatur of 416 ⁰ C (the measuring point 451 ° C) and weight percent (51.7 mole percent) was obtained,
a room air velocity of 20

20,000 V / cat.-vol. / Hour the yield was 69 Ge B eis ρ ie 1 11
weight percent (42.5 mole percent).

Example 10 Under the conditions mentioned in Example 10

25 becomes octahydrophenanthrene to the anhydride of

A catalyst that oxidizes niobium vanadate with a 1,2,3,4-benzene-tetacarboxylic acid. From-

Nb / V ratio of 0.25 and silicon carbide granulate is 54 percent by weight (46 mol percent).

Claims (1)

Patent claims: 1. Process for the preparation of aromatic acid anhydrides by catalytic gas phase oxidation of alkylbenzenes of the general formula R ¹ still economically interesting, and pyromellitic dianhydride is currently still using the technically complex and dangerous nitric acid oxidation process manufactured. The invention is a process for the preparation of aromatic acid anhydrides by catalytic gas phase oxidation of alkylbenzenes of the general formula