DE1468824C3 - - Google Patents

Description

R ¹

R ²

R ³

in which R ¹ , R ² , R ^{: i} 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 are, as well as 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 an amount of 0.05 to 1, in particular 0.1 to 0.3 gram atom per gram atom of vanadium, niobium, and that the contact time of the Umsetzgemisches 0.01 to 2 seconds at temperatures between 400 and 600 ⁰ C. and at pressures between 0.5 and 30 atm.

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 carrier catalyst, can be oxidized in a targeted manner. When the alkyl aromatic hydrocarbon contains two adjacent alkyl substituents on the ring, the "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 procedure turned out to be neither techR ³

in which R ¹ , R ² , R ³ and R ^{1 can be} hydrogen atoms, methyl, ethyl or propyl radicals, with the proviso that either R ¹ and R ² or R ^;) 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 catalyst containing vanadium, niobium and oxygen, which is characterized in that the process is carried out in the presence of a catalyst 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 α-alumina 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 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, depending on temperature and pressure, lies between 0.01 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. They can, for example, be formed in a reaction tube, a chamber or a catalyst manner, but it is assumed that an inorganic poly-tube reactor, in which the catalyst is arranged, is present, 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-

mellitic dianhydride by condensation in one

οι cooler that operates at a temperature between 20 and

350 ⁰ C is held, are deposited. The 30 pyromellitic dianhydride can then in an or-

- R ² ganic solvents such as p-dioxane, diacetonal

1 alcohol, cellulose solve acetate, diphenyl ether, 1,2-dimeth-

\ ./ oxyethane or ketones dissolved and with activated charcoal

j can be decolorized. That crystallized out on cooling

R3 35 pyromellitic dianhydride is z. B. by centrifuge

yaw or filtration separated; 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 These are wise lower alkyl radicals, e.g. methyl 50 is 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 the alkyl aromatic Nb / V atomic ratio used of 0.18 and aluminum hydrocarbon, e.g. B. Durol, and the acid 65 contained as a carrier, was prepared as follows: Substance-containing gas is passed over the catalyst 60 g of V ₂ O ₅ were in 149 g of oxalic acid in water at tet, while the temperature was between 400 and about 50 ° C carefully dissolved. 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:

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

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

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:

Example 2

Deployed

Amount of gas

V / cat.-vol. / Hour

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

3,000
12,000

Yield of phthalic anhydride

Weight percent (mol 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 with the exception 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 receive.

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

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 and having an Nb / V atomic ratio of 0.25 were mixed with 70 ml of silicon carbide granules. The mixture was filled into a reactor tube of 23 mm inside diameter, which was provided with a jacket. The reaction temperature was controlled by a thermocouple and maintained with a heat transfer medium. At a space velocity of the air flow of 9,500 V /, Cat Vol. / Hr. Of a Durolkonzentration of 0.28 mole percent and an average catalyst bed temperature of 418 ⁰ C was achieved, a yield of 56 mole percent.

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

to 600 ⁰ C, preferably 425-525 ° C. The con- saiors having a Nb / V-ratio of 0.25 were cycle times are 0.01 to 20 seconds, the pressures in a reactor of 25.4 mm internal diameter

and 1.5 m length filled. The reactor was jacketed. The reaction temperature was maintained by passing a eutectic salt mixture through the jacket. Durol in one Concentration of 0.24 to 0.35 mole percent in air was oxidized to PMDA. The product was through Cooling from the residual gas of the reactor and subsequent collection of the solid PMDA particles won a filter cloth. At an average catalyst bed temperature of 393 ° C and a room air velocity of 4000 V / cat-vol. / hour. became 34 mole percent PMDA received. At an average temperature of the catalyst bed of 41 ° C (measuring point 433 ° C) and a room air velocity of 6000 V / cat.-vol. / Hour. became a yield of 72 weight percent (44.4 mole percent). At an average catalyst bed temperature of 416 ° C (measuring point 451 ° C) and a room air velocity of 20,000 V / cat.-vol. / Hour the yield was 69 weight percent (42.5 mole percent).

Example 10

lat as a carrier is prepared as follows: 30 g of V ₂ O ₅ are carefully dissolved in 74.6 g of oxalic acid in water at about 50 ^{° C.} A solution of 27.8 g of niobium oxalate in water is slowly added to the vanadium oxalate solution. After adding 300 g of silicon carbide granules, the mixture is evaporated to dryness while being rolled. The supported catalyst is calcined at 500 ° C. for 1 hour.

50 ml of the catalyst are placed in a reactor tube

ίο filled with an inner diameter of 19 mm, which is provided with an axial thermocouple. 70 ml of uncoated silicon carbide granulate are placed over the catalyst as a preheating zone. Over the catalyst Octahydroanthracen is passed, at a concentration of 0.1 mole percent in air at 45O ⁰ C. The contact time is 0.5 seconds. Direct condensation of solids gives pyromellitic dianhydride in a yield of 60 percent by weight (51.7 mole percent).

Example 11

Under the conditions mentioned in Example 10, 25 octahydrophenanthrene becomes the anhydride of A catalyst that oxidizes niobium vanadate with a 1,2,3,4-benzene-tetacarboxylic acid. The Off-Nb / V ratio of 0.25 and silicon carbide granulate is 54 percent by weight (46 mole percent).

309 537/537

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 ⁴ - R ² 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