DE2032339A1 - Catalyst for the preparation of pyromeihic acid and process for its preparation - Google Patents

Description

¹¹ catalyst for the production of pyromellitic acid and process for its production "

Priority: July 16, 1969, Switzerland. Registration no. : .10 900/69

Processes for the production of aromatic acids or their anhydrides by catalytic oxidation of alkylbenzenes in the liquid and in the vapor phase by means of oxygen or air are known. The chemical elements, the compounds of which have a catalytic effect on the kinetics of the oxidation of alkylbenzenes in the vapor phase, are also known. These elements, which mainly belong to groups 4, 5 and 6 of the periodic system, are vanadium, titanium, tin, phosphorus, niobium, chromium, molybdenum, tungsten, bismuth and silver. The most common element is vanadium because it is the most active in the vapor phase oxidation of alkylbenzenes. The other elements are used together with vanadium to increase the effectiveness, selectivity and service life of the catalysts.

* "■ '■ ■■« ■■■' ■ set and act primarily as reaction promoters and -be-

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faster.

The invention relates to a catalyst for the production of Pyromellitic acid from 1,2,4 »5-tetraalkylbenzene in the presence of Oxygen, consisting of a porous carrier with a content vanadium and tungsten compounds, which the. Achievement higher yields in the oxidation than the known catalysts allowed.

The catalyst according to the invention is characterized by a content, expressed stoichiometrically as parts by weight of the oxides, of 0.1 to 51 ° tungstic acid (WO,), 0.5 to 10 $ vanadium pentoxide, 0.1 to 2 % phosphoric anhydride and 0, 1 to 2 $ sodium oxide, each based on the weight of the marker.

The invention also relates to a method of production of the new catalyst, which is characterized in that a porous catalyst support with a reduction of Vanadium perite oxide obtained aqueous solution of vanadium tetroxide, a colloidal solution of tungstic acid, more aqueous Impregnated phosphoric acid and sodium hydroxide solution, the loaded carrier dried and containing oxygen while passing through Gases, especially air, is calcined.

For the production of the vanadium component, for example, on known: Vanadium pentoxide obtained by calcining ammonium metavanadate in acidic solution (hydrochloric acid) with sulfur dioxide or in aqueous solution with oxalic acid ,, formaldehyde ^ Alcohol, hydrogen sulfide or hydroxylamine in solution

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can be reduced by VanactLntetroxid.

The colloidal solution of tungstic acid can e.g. by dissolving of ammonium tungstate in water or by hydrolysis of tungsten chloride can be obtained. Hydrolysis is particularly suitable of tungsten tetrachloride in the presence of ethyl alcohol and ethyl ether.

The catalyst carrier is mostly silicon carbide or Carborundum with a particle size of 2000 to 6000yu is used. It is convenient to use in a rotating mixer mixed the various solutions and then heated to dryness with evaporation of the solvents, the carrier is coated with the active catalyst components.

The ratios of V: W: P; Na, expressed in Atomic weights, preferably 1: (0.01 to 0.5): (0.01 to 0.2): (0.01 to 0.2). The heating takes e.g. 5 to 7 hours; at the end a temperature of 170 to 180 ° C is reached.

The calcination is expediently carried out by introducing the dried, still warm catalyst into an electric furnace and increasing the temperature, preferably at a rate of at most 50 ^° C. per hour to 350 to 500 ^° C. At the same time, preheated air is passed over the catalyst, preferably in one Amount of more than 10 Nl per hour.

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The active part of the catalyst consists of the oxides of the Elements it contains «The great effect and selectivity, however, can be attributed to the presence of well-defined complexes such as liatric salts of heteropoly acids of phosphorus, vanadium and tungsten. With the catalyst there are "higher yields in the oxidation of 1,2,4,5-tetraalkylbenzene of pyromellitic acid than previously achieved. Also the quality of the product received is good, so it is without further Cleaning can be used in the manufacture of plastics. If necessary, however, it can also be done with the usual Methods such as crystallization or treatment with activated charcoal can be further purified.

To carry out the oxidation reaction, the catalyst is introduced into reactors for plague or fluidized bed processes. The first pail is a reactor with a heating jacket and tubes. The reaction takes place at temperatures between 300 and 600 C and is always exothermic. The heat of reaction is by diathermic fluids (molten salt, mercury, etc.) or directly by water in the fluidized bed process.

In the reactors, the alkylbenzoi, which is mixed with air or oxygen-containing gas, at atmospheric or fed in at a higher pressure. The alkylbenzoi is fed in with the aid of a metering pump and preferably with preheated air mixed. The mixture preferably contains 0.1 to 0.5 volume of alkylbenzoi. The contact time with the catalyst is about

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'- ■ - ■ 5 -

0.02 "to 2.0 seconds. The acid recovered is from the the gases leaving the reactor are separated by conventional methods, e.g. by sublimation on cooled condensers With the help of filters or by separation from the washing water the reactor gases. -

Example 1 . ·

Bin rotary mixing a grain size of ^ 2000yu, an aqueous 10 percent solution of Vanadintetroxid and a solution of 5 i ° of ammonium tungstate in warm water is charged in such proportions with corundum that the 'active catalyst constituents (VPOC and WO · *) 5 percent of the Make up the weight of the wearer and the ratio V: W is equal to 20 ι 1. This ratio has been found to be most effective in terms of aromatic acid yield with the two component catalyst.

This mixture is evaporated to dryness by heating, Λ which takes about 5 to 7 hours; a temperature of 170 to 180 ^° C. is reached in the process. Then wild calcined in an electric furnace for 4 to 5 hours at 450 ° C,

3 '■■■■ "■■' .- ■■■

70 cm of the catalyst obtained in this way are introduced into a tubular reactor 50 cm long and 2.1 cm inside diameter, which is in an "electrically" heated salt bath. The salt bath is ^{heated to 410 0} O and then a preheated mixture of air and 1,2,4,5-Tetraethylbenzene (Durol.) By weight -.- *; ■ - · · · · "■ '■■

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Ratio 120: 1 with a throughput speed of about 17h initiated. . . *

The yield of pyromellitic acid deposited by sublimation from the gas leaving the reactor is about 40 to 45 mol. . ₍

Example 2

Aqueous phosphoric acid and sodium hydroxide solution are also added to the catalyst mixture specified in Example 1 and located in the mixer, while maintaining certain ratios of the catalyst components. After drying at 170 to 180 ⁰ C, the calcination is carried out while raising the temperature to 10 ° C / h up to 450 ⁰ C while passing 50 l / h air.

When carrying out the oxidation in the same way as in Example 1

the following yields are obtained:. ,,

°. Yield,

M0I.56

a) Atomic ratio V: ¥; P: Na = 20: 1: 0.2: 1 54

b) atomic ratio V: W: P: Na = 10: 1: 0.2: 0.5 58

Example 3

To prepare the tungsten component, tungsten tetrachloride is first produced by thermal decomposition of tungsten hexachloride. 10 g of the tetrachloride are dissolved in a mixture of 50 cm * ethyl alcohol and ethyl ether. The solution is diluted with ethyl alcohol to 500 cm and then for the preparation of the colloidal tungsten solution with the same amount of fc

Water added. 10 9812/1472

The catalyst is otherwise prepared as in Example 2 ■ described with the atomic ratio of the experiment do The yield of pyromellitic acid in this case is 64 tf

Example 4 '■.

The catalyst is prepared as in Example 5 »In the The oxidation reaction described in Example 1 is a mixture of air and 1,2,4-trimethyl-5-isQpropylbenzene used The yield of pyromellitic anhydride is 63 #

These examples show that it is particularly due to the presence of sodium and phosphorus in addition to the known catalyst components Vanadium and tungsten arrives. The addition of sodium and phosphorus increases the yield of pyromellitic acid elevated.

Claims

1 09 8 1 ^; 2 J-Xi * 72

Claims (6)

- 8 claims 1. Catalyst for the production of pyromellitic acid from 1, 2,4,5-tetraalkylbenzene in the presence of oxygen, "consisting of a porous support with a content of vanadium and tungsten compounds, characterized by a stoichiometric content of 0.1 to 5 i °, expressed stoichiometrically as parts by weight of the oxides Wolf ramsäure (WO _5), 0.5 "to 10 io vanadium pentoxide, 0.1 to 2 <fo phosphoric anhydride and 0.1 to 2 fo sodium oxide, in each case based on the weight of the carrier. 2. Catalyst according to claim 1, characterized in that the atomic weight ratio of V: W: P: Na as i: (0.01 - 0.5): (0.01 - 2): (0.01 - 0.2) behaves. 3. Catalyst according to claim 1, characterized in that the atomic ratio of the constituents V, W, P, Na itself like 10: 1: 0.2: 0.5 behaves. 4. A method for producing a catalyst according to the claims 1 to 3, characterized in that a porous catalyst support with a by reduction of vanadium pentoxide obtained aqueous solution of vanadium tetroxide, impregnated with a colloidal solution of tungstic acid, aqueous phosphoric acid and sodium hydroxide solution ¹ , the loaded carrier is dried and calcined while passing through oxygen-containing gases. 1 0 9 8 1 2 / U 7 2 5. The method according to claim. 4 »characterized in that the impregnation by means of a hydrolysis of tungsten tetrachloride in the presence of ethyl alcohol and Tungstic acid solution obtained from ethyl ether takes place. 6. The method according to claim 4 »characterized in that for calcination the temperature by at most 50 ⁰ C per ■ hour increased to 350 to 500 ⁰ C and preheated air in an amount of more than 10 Nl per hour is passed through the catalytic converter, · 109812 / U72