DE1945727C - Process for the preparation of a catalyst and its use for the oxidation of o-xylene - Google Patents

Description

1. Antimony oxide or Nb ₂ O ₅ , UO ₂ , SnO ₂ , PbO ₂ , MnO ₂ , GeO ₂ , TaO ₂ and TeO ₂ in an amount of 0.1 to 9.0 mol per mol of vanadium oxide

as well as simultaneously with the application of component I or subsequently in any order or at the same time

II. I to 20 percent by weight, based on the finished catalyst, vanadium oxide (calculated as V ₂ O ₅ ),

III. 0.4 to 4.0 moles of potassium oxide per mole of antimony oxide (or equivalent oxide of the component I) as well as

IV. 0.5 to 3 moles of sulfur trioxide per mole of potassium oxide, where components III and IV are predominantly in the form of potassium sulfate or Potassium pyrosulphate is added, whereupon the product is calcined at 300 to 700.degree.

2. The method according to claim 1, characterized in that the components are in a molar ratio from

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applies to the titanium dioxide.

3. Use of the catalysts prepared by the process of claims 1 and 2 for the catalytic vapor phase oxidation of o-xylene to phthalic anhydride.

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The oxidation of naphthalene to produce phthalic anhydride is known. For this purpose have already been many suitable catalysts are described in which the active component is mostly vanadium is. Attempts to use the same catalysts to oxidize o-xylene to phthalic anhydride weren't particularly successful. It became very low and economically unacceptable Yields obtained and large amounts of carbon oxides formed.

The previously known catalysts, which were specially developed for the oxidation of o-xylene, have significant disadvantages. Such a known catalyst is made by melting Vanadium pentoxide and optionally a mixture containing alkali pyrosulphate or hydrogen sulphate made on a porous support.

However, this catalyst only works satisfactorily when the gaseous reaction mixture from oxygen and o-xylene furthermore contains chlorine or a chlorine compound. There is also a catalyst known for the oxidation of o-xylene to phthalic anhydride, which is a main component Group 5A or 6A metal oxide, e.g. B. Vanadium. Contains molybdenum, chromium or tungsten, but in this case bromine or a volatile bromine compound must be added to the gaseous oxidation mixture can be added.

In contrast, the invention is primarily based on the object of producing a catalyst which door is suitable for the oxidation of o-xylene to phthalic anhydride and which one with high selectivity provides approximately quantitative conversion values without the use of halogens or halogen compounds must be added to the oxidation mixture.

To solve this problem, we propose a method for producing a catalyst, which Vanadium oxide applied to a titanium dioxide inert »·. Potassium oxide and also other metal oxides contains, and which is characterized by it. that you can either use the following corp components as dry compounds or as salts from water Solution to 40 to 95 percent by weight, based on the total catalyst. finely divided titanium dioxide applies :

I. Antimony oxide or Nb ₂ O 1, UO ₂ , SnO ₂ , PbO.

MnO ,. GeO ₂ , TaO ₂ and ToO ₂ in an amount of 0 to 9.0 mol per mol of vanadium oxide

as well as simultaneously with the application of component I or subsequently in any order or simultaneously

II.! up to 20 percent by weight, based on the finished catalyst, of vanadium oxide (calculated as V ₂ Oj).

III. 0.4 to 4.0 moles of potassium oxide per mole of antimony oxide (or equivalent oxide of component 1) such as

IV. 0.5 to 3 moles of sulfur trioxide per mole of potassium oxide, components III and IV being predominantly in the form of potassium sulfate or potassium pyrosulfate inflicts

after which the product calcined at 300 to 700 ⁰ C. The individual components are preferably applied to the titanium dioxide in the following molar ratios:

Components I
Components III
Components IV

II = 0.2: 1 to 2.0: 1,

I = 0.6: 1 to 1: 1 and

III = 0.5: 1 to 3.0: 1.

It has been found that o-xylene can be used in a fixed bed process with the aid of the catalysts thus prepared can be converted into phthalic anhydride with good yield and that the formation is undesirable Connections is largely suppressed.

To carry out the reaction by passing o-xylene with air in the vapor phase over the maintained at a temperature of 250 to 450 ⁰ C catalyst. The time for the reaction is about 0.1 to 5, preferably 0.5 to 3 seconds.

The titanium dioxide support is essential for the catalyst system produced according to the invention because it affects the catalyst activity in the oxidation to such an extent that it is not influenced by any other Carrier can be replaced. If you use titanium dioxide together with vanadium pentoxide and the potassium sulfate-antimony oxide mixture on an inert carrier, such as silicon dioxide or aluminum

oxide, precipitates, the oxidation of o-xylene does not proceed satisfactorily and the yields are low obtained on phthalic anhydride. The titanium dioxide must therefore be present as a carrier phase. If on the other hand the titanium dioxide as a carrier door the mixture of vanadium pentoxide, antimony oxide and omits potassium sulfate, the oxidation of the o-xylene likewise produces only low yields Obtained phthalic anhydride. Finally, when using titanium dioxide alone, the o-xylene will flow unchanged by the catalyst.

As the titanium dioxide, a product having a large surface area is preferably used, which is obtained by precipitating titanium dioxide from an acidic sulfate solution, washing, then drying, calcining and crushing. It is best with a grain size> ^r on 20 to 600 μm. preferably from 20 to 300 μπι used. The inner surface should be about 5 to 200 nr / g.

Since the catalyst produced according to the invention is used in a solid bed system, it can advantageously be shaped into spheres or other bodies of suitable size after production, with good results being achieved with a size of approximately 4 × 4 mm. However, in the preparation of the catalyst, preference is given to reducing the particle size of the titanium dioxide to the range given above. ^{in order to ensure sufficient contact A of the} other components of the system with the titanium dioxide in the individual stages of catalyst production.

Other important components are potassium oxide and sulfur trioxide. These components can thereby be introduced that you can either potassium sulfate or potassium pyrosulfate as a component Dry mixture or in solution are added to the catalyst.

Under certain. In some circumstances it may also be useful _{to replace the antimony oxide (usually Sb 2} O ₃ ) with other oxides. Thus, instead of the antimony oxide, the oxides UO ₂ . Nb ₂ O ₅ , SnO ₂ , PbO ₂ , MnO ₂ , GeO ₂ , TaO ₂ and TeO ₂ can be used. For the sake of simplicity, however, the preparation of the catalyst is described below using antimony oxide.

The antimony oxide is preferably added to the catalyst in dry form as trioxide. However In certain cases it can also be advantageous to use the antimony in one for impregnating the titanium dioxide carrier add the solution used.

The catalyst can be prepared by the following process. One possibility is that the titanium dioxide is mixed dry with antimony oxide and the dry mixture is impregnated with a solution which is prepared by dissolving vanadium pentoxide in a dilute sulfuric acid solution containing potassium sulfate and continuously saturating it with sulfur dioxide. The mixture thus impregnated is then dried, pelletized and 24 hours at 110 ⁰ C calcined at 400 ⁰ C. In the impregnation process, the aqueous solution can have any concentration; it is only necessary that the composition of the finished catalyst be in the above-mentioned ranges according to the invention.

According to the other embodiment, titanium dioxide, potassium pyrosulphate, antimony trioxide and vanadium pentoxide can be used Mix thoroughly with each other in the correct proportions, tableting in the known manner and calcine at 400 ° C for 24 hours. Satisfactory results are achieved with tableting, if ms'i the components with a suitable Lubricants mixed and processed in a conventional tablet machine. The last stage of the Catalyst manufacture is calcining. The calcination can take about 4 to 24 hours at temperatures from about 300 to 700.degree. C., preferably at about 400.degree.

Maintaining a precise reaction temperature is important for the oxidation of the o-xylene. The oxidation is expediently carried out at 300 to 4 10 ° C. and preferably at 350 to 390 ° C. When the system is in operation, the catalyst is introduced into a suitable reactor and heated to the desired temperature, and the o-xylene is introduced into the system as a mixture with a gas containing molecular oxygen, such as, for example, air. The preferred molar ratio of air to o-xylene is 80 to 150 zr 1. The flow rate of the gases and vapors is regulated so that the desired apparent contact time of the reactants with the catalysts is achieved. The chein contact time is the time that the starting mixture is in contact with the catalyst, whereby the entire reaction zone is considered to be catalyst-free:

Dummy contact time =

Reactor space occupied by the catalyst

Flow velocity of the gases at normal temperature and pressure

The oxidation can be carried out at atmospheric pressure, but it is expedient at weak elevated pressure, for example up to 3 atmospheres, to work.

The invention is illustrated in more detail by the following examples:

example 1

Manufacture of the catalyst

Titanium dioxide produced by precipitation and calcination was sieved to separate the particles having a size in the range of 0.25.0.044 mm (inner mesh size). The titanium dioxide had a surface area of about 20 m ² / g and a water pore volume of about 0.3 cm ³ / g. The titanium dioxide was dry blended with an amount giving an antimony trioxide content of 6 percent by weight.

An amount of potassium pyrosulfate giving a K ₂ O content of 2.0 percent by weight and an SO ₃ content of 2.0 percent by weight in the finished catalyst was dissolved in water together with an amount of vanadyl sulfate giving a vanadium pentoxide content of 6 percent by weight in the finished catalyst. This solution was then sprayed into a rotating bed of the dry mixture of antimony trioxide and titanium dioxide. Mixing was continued until the liquid phase was well distributed. Then the mixture was ^{dried at 110 0} C and using an organic binder in a normal tablet machine to contact

bodies of 4x4 mm size processed. These contact bodies were ^{calcined at 400 °} C. for 24 hours. The finished catalyst had the following composition, expressed in oxides:

V ₂ O ₅

Sb, Ü ₃

K ₂ 0

SO ₃

TiO ₂

Weight percent

6.0
6.0
2.0
2.0
84.0

Example 2

The catalyst prepared by the above procedure was subjected to a test in a reactor, which consists of a steel tube with an inner diameter of 2.54 cm and a length of 305 cm and equipped with thermocouples and the necessary devices for temperature regulation was. The catalyst bed was 244 cm deep. The first 91.5 cm of the catalyst bed was closed 50% mixed with inert sand. The rest of the reactor contained pure catalyst. The reactor was on brought a temperature of 346 ° C, and o-xylene was at a rate of 0.066 kg / h. passed through. Sulfur dioxide was in an amount corresponding to 0.7 percent by weight of the o-X ^ lols initiated the reactor. The air was blown at a rate of 2.345 kg / hour. fed. The at The values determined in this experiment are summarized in the following table:

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Table I.

Reactor pressure in atü 0.518

Γ thalic anhydride yield

in kg / hour 0.080

Total conversion

in mole percent 100

Selectivity in mole percent 87.2

From these values it can be seen that when using the one prepared as described above Phthalic anhydride catalyst system can win in excellent yield.

Example 3

This example aims to highlight the importance of attendance of antimony in the catalyst can be shown, including - "the yield when using a 6% antimony containing Catalyst can be compared with the yield using a catalyst without antimony. In these tests, the mock contact time based on normal temperature and pressure was 2.5 seconds. The mole ratio of air to o-xylene was 123. Sulfur dioxide was in a 0.7 weight percent of the o-xylene corresponding amount passed into the reactor. The temperature was on the door the highest selectivity and conversion kept optimal value. The catalysts were as follows Composition in percent by weight:

Catalyst A

V ₂ O ₅ 6.0 6.0

Sb ₂ O ₃ 6.0 0

K ₂ 0 2.0 2.0

SO ₃ 2.0 2.0

TiO ₂ 84.0 90.0

The values determined in these tests are compiled in the following table:

Table II

Catalyst B

Catalyst A Catalyst B Temperature, ^G C 393 401 o-xylene conversion in mole percent 99.2 96.2 Selectivity in mole percent. 76.3 65.5 Phthalic anhydride yield in percent by weight 105.6 88.6

The improvement in selectivity and phthalic anhydride yield through use can be seen from these values of antimony oxide as a catalyst component.

Example 4

This example aims to highlight the importance of the relationship from antimony oxide to potassium oxide in the catalyst systems of the invention. The reaction conditions were the same as in Example 3. The catalysts had the following composition in percent by weight:

catalyst V ₂ O ₅ A. C. D. 40 Sb, O, 6.0
6.0
2.0
2.0
84.0 6.0
6.0
3.4
5.6
79.0 6.0
9.6
0
0
84.4 K, O so, TiO ₂

The values determined in these tests are compiled in the following table:

catalyst

Temperature in ^c C

o-xylene conversion

in mole percent

selectivity

in mole percent

Phthalic anhydride yield in percent by weight

393
99.2 76.3

105.6

95.8 72.8

97.3

404 99.6 27.6

38.4

These values clearly show the importance of the ratio of K ₂ O to Sb ₂ O ₃ , ie selectivity and yield are improved if this ratio is kept in the range according to the invention.

Claims (1)

Components I Components IH Components IV II = 0.2: 1 to 2.0: 1, I - 0.6: 1 to 1: 1 and III = 0.5: 1 to 3.0: 1 '5 Claims: 1. Process for the production of a catalyst, which vanadium oxide applied to a titanium dioxide carrier, Contains potassium oxide and also other metal oxides, thereby marked The following components can be used either as dry compounds or as Salts from aqueous solution to 40 to 95 percent by weight, based on the total catalyst, finely divided titanium dioxide applies: