DE1235895B - Process for the production of methyl methacrylate by dehydrating methyl isobutyrate - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY Int. CL:

GERMAN

PATENT OFFICE

EDITORIAL

* Vf 0 & fpi 235 895 German class: 12 ο-21

Number: 1235 895

File number: E19045IV b / 12 ο

Filing date: March 17, 1960

Opened on: March 9, 1967

411

It is known to produce methyl methacrylate by dehydrating methyl isobutyrate in vapor form State at high temperatures in the presence of a dehydrogenation catalyst. US Pat. No. 2101820, for example, serves as suitable dehydrogenation catalysts Nickel, copper, platinum, copper chromite and copper-zinc-cadmium. With these catalysts leaves However, a direct dehydrogenation of methyl isobutyrate to methyl methacrylate in do not achieve good yields. Rather, in this process, isobutyraldehyde is preferred converted into a-methylacrolein, which is then converted to methacyrlic acid is oxidized, whereupon the acid is esterified: It is therefore a multi-stage process.

From USA. Patent 2,719,171 it is further known to produce methyl methacrylate by oxidative dehydrogenation of methyl isobutyrate with oxygen in the presence of iodine at temperatures from 450 to 800 ⁰ C. However, this process has the disadvantage that iodine is not a very useful catalyst because it has to be removed from the reaction product by extraction or distillation. Furthermore, iodine causes severe corrosion at the high temperatures used, so that special requirements must be placed on the building materials of the reaction vessel. A further disadvantage of this process is that it can only be carried out if the greatest safety measures are observed, since combustible, vaporous organic compounds are mixed with oxygen.

On the other hand, it is also known to produce methyl methacrylate by heating ^ -methoxyisobutyric acid in the presence of an acidic catalyst such as sulfuric acid. According to this procedure However, mixtures of methyl methacrylate and methacrylic acid are always formed.

According to another known process, methyl methacrylate can also be obtained from acetone cyanohydride produce; this is first converted into methacrylic acid amide, from which the Methacrylic acid methyl ester is obtained. However, this process is also multi-stage.

Finally, it is known from French patent 790262 to use unsaturated nitriles To produce dehydrogenation of the saturated nitriles in the presence of aluminum oxide as catalysts. Aluminum oxide is also used as a catalyst for isomerizing and dehydrocycling gasoline fractions according to U.S. Pat. No. 2,726,195.

Process for the production of
Methyl methacrylate by dehydration
of methyl isobutyrate

Applicant:

Eastman Kodak Company,
Rochester, NY (V. St. A.)

Representative:

Dr.-Ing. W. Wolff and H. Bartels, patent attorneys, Stuttgart, Lange Str. 51

Named as inventor:

Edgar Lamar McDaniel,

Howard Seth Young, Kingsport, Term. (V. St. A.)

Claimed priority:

V. St. v. America April 1, 1959 (803 345)

It has now been found, surprisingly, that methyl isobutyrate can be dehydrogenated in the vaporous state directly, in excellent yields to methyl methacrylate at high temperatures and in the presence of a catalyst, if the dehydrogenation is carried out at temperatures of 400 to 800 ^° C., preferably about 500 to 650 ° C, in the presence of aluminum oxide with a surface area of about 50 to 250 m ² per gram as a catalyst, the accelerator still 0.1 to 30%, preferably 1 to 15%, based on the total catalyst weight, vanadium, molybdenum , Titanium, zirconium, niobium, chromium, copper, zinc, cadmium, lead, manganese, antimony, bismuth, lithium, cerium, tungsten, palladium, silver, barium, calcium, strontium or magnesium as an element or as an oxide Partial pressure of about 500 to 1 torr, advantageously 250 to 25 torr, and one

709 51S / 561

3 4

Residence time of the methyl isobutyrate can be easily separated from about the reaction mixture From 0.05 to 10 seconds, preferably about 0.5 to 10 seconds, its use is technically particularly preferred Seconds. partaking. The finding that water vapor when

The processes of the invention used in the process of the invention as a diluent gas on catalysts are extraordinarily long-lived, 5 is reversible, was surprising because it is over Water vapor is insensitive and · supply · it is known that water is poisonous in terms of effectiveness Methacrylic acid methyl ester in pure form. acts of aluminum oxide catalysts (cf.In-

The aluminum oxide used as a catalyst in the process of the invention, Industrial and Engineering Chemistry, Vol. 43, 1951, can be selected from γ-, χ-, η-, κ- p. 501; Vol. 44, 1952, p. 107, and the USA.-Patent or 0 -Aluminiumoxide or α-Aluminiuraoxyd- io script 2790 015). It was also to be expected that monohydrate or mixtures thereof would exist. They are methyl isobutyrate and / or are in the calcined state, are porous and methyl methacrylate is adsorptive under the reaction effects. conditions of the method of the invention in contradiction

Process for the production of such aluminum 'wart hydrolyzed by steam or decomposed oxides are known. · I'sj would be.

A particularly suitable aluminum oxide is / Before carrying out the process of Erfinaktivicrte so-called "BAYER" -Aluminiumoxyd. The liquid isobutyric acid methyl ester is converted into the vapor state in this consists of a mixture of α-aluminum. After the oxide monohydrate, χ-jaluminium oxide and y-aluminum oxide, this vapor is passed over the in a reacnium oxide. The catalyst, which is arranged in large quantities as a processing vessel, is used to cool the intermediate product in: the production of the gases leaving the reaction vessel. As a result, aluminum from bauxite produced aluminum results in a liquid which generally contains about nium oxide of the composition Al ₂ O ₃ -3 H ₂ O, which is 95 to 99% methyl methacrylate and also referred to as α-aluminum oxide trihydrate, without converted methyl isobutyrate . Controlled calcination of this α-aluminum-worthy impurities and by-products of beminium oxide trihydrate gives the so-called standing. The methacrylic acid methyl ester can be derived from the »activated BAYER aluminum oxide«. unreacted methyl isobutyrate easily

Another aluminum oxide suitable for carrying out the process by distillation or by extraction with Löder's invention can be separated off by solvents.
Calcining of gel-like α-aluminum oxide mono- 30 The aluminum oxide catalysts have a hydrate can be achieved. Such an aluminum oxide has a long life. Gradually deposited on them has smaller pores and an even larger surface area but various substances, including carbon than the activated ¹ '"BAYER" aluminum oxide and substance. The catalysts in this case consists mainly of α-aluminum oxide but can easily be revived by making them monohydrate. This form of aluminum oxide can also be converted into γ-aluminum oxygen and 97% nitrogen or another ineroxide which also treats a suitable gas-containing gas mixture ^{at 500 to 625 ° C. with a flow of about 3% by further calcination,} where catalyst is. ■ by the carbon and other precipitates dated

In order to carry out the process of the invention the catalyst has to be removed. A treatment suitable for this type of treatment _: aluminum oxide is formed as a highly exothermic course.

Mixture with y-aluminum oxide during calcining When carrying out the process of the invention

of / 5-alumina trihydrate. / 5-aluminum oxide with a freshly prepared aluminum oxide trihydrate can be achieved by the action of water on the catalyst a so-called light-off time beamalgamicrtcs Manufacture aluminum. in which the catalyst is not or only very much

Another type of aluminum oxide that is not very effective. This starting time is guided of the method of the invention is suitable, usually at least about 4, mostly about 5 to 6 hours made of activated bauxite, which is known to be the. By adding an accelerator to the hydrated aluminum oxide is called. freshly made or revived activated By calcining bauxite, an aluminum oxide is then obtained, which can significantly reduce the light-off time activated aluminum oxide, which can be shortened from y-aluminum 50. In many cases such increase oxide and other types of activated aluminum accelerators also reduce the effectiveness of the aluminum oxide consists. oxyds, so that even better degrees of conversion and

It has been found that the dehydrogenation gives yields. As particularly vorteildes Tsobiittersäuremethylesters in the vapor state with exemplary accelerator, the oxides of Vanavcrmindertem pressure have the methyl methacrylate 55 ^din s, molybdenum and calcium proved. Suitable in great purity arises. The isobutyric acid vanadium oxides are the dioxide, trioxide, tetroxide methyl ester part pressure is through in the reaction vessel and pentoxide. Suitable molybdenum oxides are MoO ₂ , reduced by a vacuum pump. But it can also MoO ₃ , Mo ₂ O ₃ and Mo ₂ O ₅ . An inert diluent gas such as nitrogen, helium or MoO ₃ is particularly suitable. The accelerator can be added to the aluminum argon, carbon dioxide or water vapor, for the oxidation of the catalyst in the form of reducing the methyl isobutyrate partial pressure, acetate, nitrate or another salt. If a diluent gas is used to reduce the partial pressure by calcining the partial pressure, the mixture or, in the course of the dehydrogenation, predominantly corresponds to the sum of the partial pressures in gaseous gas and, if necessary, partially in methyl isobutyrate and the diluent carbonate or the same Salt underlying gas is atmospheric pressure. Metal is transferred. If necessary, can also

A cheap diluent gas is water vapor. Mixtures of several accelerators used Since the water vapor from the resulting orgarii- will be. Contains such a catalyst mixture

up to 20% copper oxide, 0.2 to 3% chromium oxide or 1 to 14% calcium, strontium or barium oxide, based on the total catalyst weight.

The addition of the accelerator, the light-off time of freshly prepared or revived activated Aluminiumoxydkatalysatoren about 30 minutes or less to about 2 hours ver ^J can shorten.

The following examples illustrate the process of the invention.

The degree of conversion in% given in the examples is calculated as follows:

Yield in%

Moles of methyl methacrylate formed
Moles of methyl isobutyrate fed in

Moles of methyl methacrylate formed
Moles of methyl isobutyrate consumed

100,

100.

The hourly gas throughput rate is 3600 divided by the average residence time in seconds. The hourly liquid flow rate is the volume of the per Volume of the catalyst liquid isobutyric acid methyl · - so introduced into the reaction vessel every hour esters.

example 1

Activated γ-aluminum oxide in pellet form with a pellet diameter of about 3.2 mm and a surface area of 80 m ² / g was heated ^{to 600 °} C. in a reaction vessel made of heat-resistant glass in a stream of nitrogen. Methyl isobutyrate was passed over this catalyst at 600 ^° C. and a partial pressure of 50 torr in a mixture with nitrogen at a total pressure of 1 atm. The average residence time was 1 second at an hourly gas flow rate of 3600. The duration of the experiment was 12 hours. The reaction mixture leaving the vessel was in the form of five. Fractions examined. The first fraction consisted of the reaction mixture that was collected after an experiment of 2 hours, the second fraction consisted of the reaction mixture that was collected after an experiment of 2 to 4 hours, the third fraction of the reaction mixture that was collected after an experiment of 4 to 6 hours, the fourth fraction from the reaction mixture that was collected after an experiment of 6 to 9 hours and the fifth fraction from the reaction mixture that was collected after an experiment of 9 to 12 hours.

The individual fractions were in four cascaded Cold traps are caught, one with cold water and the other three with a mixture of dry ice and isopropyl alcohol were cooled. Each fraction examined consisted of the combined amounts in the four Cold traps. The risen reaction products were weighed and determined by gas chromatography. From the amounts of methyl isobutyrate introduced into the reaction vessel and the amounts obtained Amounts of methyl methacrylate and recovered methyl isobutyrate were the degree of conversion and the yield are calculated. It was found that the fractions collected only consisted of methyl methacrylate and methyl isobutyrate. Gaseous by-products, such as carbon monoxide, carbon dioxide, methane and hydrogen, were not retained in the cold traps. There were summarized in Table I. obtained results.

Table I.

fraction Removal time Degree of implementation
of isobutter
acid methyl ester
in methacrylic
acid methyl ester
in O Yield to
Methacryl
acid methyl
ester in ° / o <■ 1
2
3
4th
5 Obis 2 hours
2 to 4 hours
4 to 6 hours
6 to 9 hours
9 to 12 hours 0
2.3
10.1
12.7
11.7 0
3.0
38.5
57.0
58.0

As can be seen from Table I, no methyl methacrylate is produced in the first two hours of the experiment educated. The light-off time was over after about 4 hours of testing. Thereupon the effect of the aluminum oxide was almost constant.

Example 2

A portion of the catalyst described in Example 1 was in an extraction device after Soxhlet extracted with water until no more alkali could be detected in the water. The sodium oxide content of the catalyst was reduced from 0.48 to 0.24% by the extraction. The washed Aluminum oxide was then calcined at 600 ° C. with a supply of air and then placed in a reaction vessel brought from heat-resistant glass. This was followed by at 600 ° C. and at a partial pressure of 50 torr of methyl isobutyrate in nitrogen at a total pressure of 1 atm at an average Dwell time of one second passed over this catalyst.

The removal of the water-soluble alkali does not result in any significant change in the degree of conversion achieved. However, the yield is higher than when the one not extracted in Example 1 was used Catalyst.

In a further experiment, the methyl isobutyrate was used at 600 ° C. over the same catalyst passed, but at a partial pressure of 380 torr in nitrogen at a total pressure of 1 at and with an average dwell time of 8 seconds.

In another experiment, water vapor was used as a diluent instead of nitrogen used, also with an isobutyric acid methyl ester partial pressure of 380 Torr and one)

Total pressure of 1 at and an average Verwcilzeit of 8 seconds was worked. Finally, in an experiment, pure, undiluted methyl isobutyrate at 600 ° C. and

passed a residence time of 8 seconds over the catalyst.

The test results are compiled in the tables.

Table Π

Partial pressure * Dwell time
in seconds Diluents fraction Removal time Degree of implementation
in o / o yield
in o / o 50
50
50
50
50
50
380
380
760 1
1
1
1
1
1
8th
8th
8th N ₂
N ₂
N ₂
N ₂
N ₂
N ₂
N ₂
Steam
none 1
2
3
4th
5
6th
1
1
1 Obis 2 hours
2 to 4 hours
4 to 6 hours
6 to 9 hours
9 to 12 hours
12 to 15 hours
Obis 1.5 hours
0 to 1.5 hours
Obis Ί, 5 hours 0
4.6
10.8
12.6
11.9
11.1
17.8
16.4
15.7 0
8.0
44.3
58.1
61.0
63.5
47.5
45.6
34.7

= Partial pressure of methyl isobutyrate at a total pressure of 1 at.

Example 3

The catalyst used was γ-aluminum oxide in the form of pellets with a diameter of 3.2 mm and a surface area of 180 m ² / g. The catalyst was made from an alumina gel. It contained 2% graphite, which was added as a lubricant when the aluminum oxide was pressed into lozenges. The catalyst was used as in Example 1. This time, however, the duration of the experiment was 18 hours. The test results are shown in table ΠΙ.

Tabel m yield
in O fraction Removal time Degree of implementation
in ° / o 0
0
2.5
41.4
64.1
58.4
62.4 1
2
3
4th
5
6th
7th Obis 2 hours
2 to 4 hours
4 to 6 hours
6 to 9 hours
9 to 12 hours
12 to 15 hours
15 to 18 hours 0
0
2.1
11.4
12.5
12.5
11.5

Example 4

The process described in Example 1 was repeated using lozenges with a diameter of 3.2 mm made of α-aluminum oxide monohydrate with a surface area of 180 to 210 m ² / g. Tabele TV shows the results.

Table IV

35

40

fraction Removal time Degree of implementation
in 0/0 yield
in 0/0 1 Obis 2 hours 0 0 2 2 to 4 hours 2.0 2.3 3 4 to 6 hours 9.7 46.7 4th 6 to 9 hours 9.2 55.6 5 9 to 12 hours 8.3 48.8

Example 5

The process described in Example 1 was repeated using a catalyst composed of γ-aluminum oxide containing 10 percent by weight of vanadium pentoxide in the form of particles about 1.4 to 2 mm in size with a surface area of about 170 to 180 m ² / g. For comparison purposes, a catalyst made from the same γ-alumina without accelerator was used under the same conditions. The results are shown in Table V.

Table V

fraction

/ -Aluminum oxide as a catalyst

Removal time

Degree of implementation in ° / o

the end fraction prey in O 1 0 2 0 3 5.6 4th 37.0 5 59.3 6th 60.1 7th 58.6

y-aluminum oxide + V ₂ O ₆ as a catalyst

Degree of implementation in 0/0

Removal time

Yield in "/ o

0 to 2 hours
2.00 to 4 hours
4 to 6.07 hours
6.07 to 9.07 hours
9.07 to 12.07 hours
12.07 to 15.07 hours
15.07 to 18.07 hours

3.6

9.9
11.6
12.3
11.5 0 to

2.07 to

4.07 to

6.07 to

9.07 to

11.90 to

14.90 to

2.07 hours

4.07 hours

6.0 hours

9.07 hours

11.90 hours

14.90 hours

17.90 hours

6.2 15.7 14.5 13.7 14.1 13.5

8.4 52.0 62.3 57.4 58.0 68.0

As can be seen from Table V, the vanadium pentoxide sets the light-off time of the γ-aluminum oxide decreases and increases the degree of conversion and the yield.

"I 235 895

ίο

Example 6

The process described in Example 1 was repeated using a catalyst composed of γ-aluminum oxide containing 10 percent by weight of vanadium pentoxide in the form of lozenges about 3.2 mm in size with a surface area of 70 m ² / g. However, this time the dehydrogenation temperature was 590 ° e. In addition, the dwell times have been changed. The results are shown in Table VI.

Table VI

Dwell time Hourly liquid T7r st Ir t ί η τι XJ «ι f η η Ι» η- · aqra ■ ♦ Degree of implementation yield in seconds throughput speed * ■ ΓΙ d & LlUIl .CfULUcIIlJ 11 CZiCl t in «/ ο in ° / o 0.5 0.77 1 0 - to 1.00 hours 3.1 3.8 0.5 0.77 2 , 1.00 to 1.92 hours 14.5 55.5 0.5 0.77 3 • 1.92 to 2.92 hours 18.0 66.7 1 0.38 4th 2.92 to 3.04 hours 12.2 42.9 1 0.38 5 3.04 to 4.10 hours 16.9 38.5 1 0.38 6th 4.10 to 5.08 hours 10.3 50.4

* In milliliters per milliliter of catalyst and per hour.

Example 7

The catalyst used was γ-aluminum oxide with a surface area of 80 m ² / g and containing 10 percent by weight of vanadium trioxide. The catalyst was placed in the reaction vessel as in Example 1. The methyl isobutyrate was passed over the catalyst at 600 ° C. and an hourly liquid throughput rate of 0.26 ml per millimeter of catalyst and per hour at 600 ° C. and at a partial pressure of 500 torr in nitrogen at a total pressure of 1 atm. The average residence time was 1.5 seconds. The results are shown in Table VII.

Table VII

Mixture with nitrogen at 1 at total pressure at 600 ° C and an hourly liquid throughput rate of 0.26 ml per millimeter of catalyst and per hour as well as an average Dwell time of 1.5 seconds used. The results are shown in Table VIII.

Table VIII

fraction Removal time Implementation
degree in ° / o the end
prey
in ο /. 1
2 0 to 3.62 hours
3.62 to 6.07 hours 6.0
13.8 8.2
39.1

fraction Removal time Implementation
degree in% the end
prey
in % T-I CS 0 to 2.52 hours
2.52 to 6.02 hours 1.9
13.6 2.1
36.6

Example 8

3.2 mm large pastilles made of activated "BAYER" aluminum oxide with a surface area of ^{80 m 2} / g were mixed with enough peroxyvanadmic acid and then calcined that the catalyst contained 20% vanadium pentoxide. The catalyst was according to the method described in Example 1 at an isobutyric acid methyl ester partial pressure of 50 Torr im

Example 9

For the dehydrogenation of methyl isobutyrate to methyl methacrylate, a γ-aluminum oxide catalyst containing 10 percent by weight vanadium pentoxide was used in the form of 1.4 to 2 mm particles with a surface area of about 170 to 180 m ² / g. The dehydration was carried out at 600 ° C., a methyl isobutyrate partial pressure of 50 torr and an average residence time of one second. During the first six hours of the test, nitrogen was used as the diluent at a total pressure of 1 atm. Various mixtures of nitrogen and water vapor were then used at a total pressure of 1 atm. The results are shown in Table IX.

Table DC

Diluents fraction Removal time Degree of implementation
in o / o yield
in o / o N ₂ 1 0 to 2.03 hours 0 0 N ₂ 2 2.03 to 4.03 hours 8.3 13.2 N ₂ 3 4.03 to 6.03 hours 16.0 57.7 190 Torr water vapor + 4th 6.03 to 9.03 hours 15.6 58.0 520 Torr N ₂ 380 Torr water vapor + 5 9.03 to 12.03 hours 13.6 59.9 330 Torr N ₂ 570 Torr water vapor + 6th 12.03 to 15.03 hours 12.0 43.2 140 Torr N ₂ 670 Torr water vapor + 7th 15.03 to 18.03 hours 11.3 64.3 40 Torr N ₂ 670 Torr water vapor + 8th 18.03 to 21.03 hours 10.1 48.0 40 Torr N ₂ 670 Torr water vapor + 9 21.03 to 24.03 hours 10.1 55.1 40 Torr N ₂

709 518/561

Example 10

For the dehydrogenation of methyl isobutyrate, a catalyst composed of γ-aluminum oxide, which contained 10 percent by weight of molybdenum trioxide, was used in the form of lozenges about 3.2 mm in size with a surface area of 170 to 180 m ² / g. The dehydrogenation was carried out in a reaction vessel as in Example 1 at different temperatures and residence times. The diluent used for the methyl isobutyrate was nitrogen at a total pressure of ί at. The results are shown in Table X.

Table X

temperature
in ⁰ C Partial pressure of the isobutter
acid methyl ester
in torr Dwell time
in seconds fraction Removal time Degree of implementation
in »/ ο yield
in Vo 587 86 0.95 1 0 to 4.00 hours 1.8 2.8 587 86 0.95 2 4.00 to 5.57 hours 6.9 37.8 619 72 1.03 3 5.57 to 7.67 hours 13.2 37.5 603 47 0.69 4th 7.67 to 9.77 hours 9.6 61.4 585 81 1.40 5 9.77 to 12.22 hours 10.0 50.9 608 98 1.23 6th 12.22 to 14.05 hours 11.9 41.1 607 83 0.97 7th 14.05 to 15.75 hours 9.9 50.4 593 37 1.01 8th 15.75 to 19.65 hours 10.0 58.2 595 107 0.53 9 19.65 to 20.47 hours 5.0 72.9

Example 11

As in Example 1, the process was repeated using a catalyst composed of γ-aluminum oxide containing 9 percent by weight of molybdenum dioxide in the form of lozenges about 3.2 mm in size with a surface area of about 80 m ² / g. However, the average residence time was only Va second. The hourly liquid flow rate was 0.74 ml per millimeter of catalyst. The results are shown in Table XI.

Table XI

fraction Removal time Implementation
degree in ° / o the end
prey
in O 1
2
3
4th
5 0 to 1.00 hours
1.00 to 2.33 hours
2.33 to 4.08 hours
4.08 to 6.08 hours
6.08 to 9.08 hours 0
1.9
6.7
6.9
7.2 0
2.9
42.9
39.7
62.8

Example 12

As in Example 1, the process was carried out using a catalyst made of activated "BAYER" aluminum oxide, which consisted of γ-aluminum oxide, α-aluminum oxide monohydrate and χ-aluminum oxide and contained 10 percent by weight of molybdenum trioxide. The catalyst had a surface area of 80 m ² / g and was in the form of lozenges about 3.2 mm in size. The average residence time was 1/2 second and the hourly liquid flow rate was 0.74 ml per millimeter of catalyst. The results are shown in Table XTT.

Table ΧΠ

fraction Removal time Implementation
degree in% the end
prey
in % 1
2
3
4th
5 0 to 1.00 hours
1.00 to 2.83 hours
2.83 to 4.95 hours
4.95 to 7.18 hours
7.18 to 14.36 hours 0
4.7
5.5
5.4
5.4 0
17.8
38.2
36.3
43.6

Example 13

a) As in Example 1 was dehydrated methyl isobutyrate in the presence of a catalyst comprising a gel-like y-alumina containing 10 weight percent of molybdenum trioxide in the form of about 1, 4 to 2 mm large particles having a surface area of about 170 to 180m ² / g. The dehydration was carried out at 600 ° C., at a partial pressure of methyl isobutyrate of 500 torr and an average residence time of 1 second. The diluent used was initially nitrogen and then steam, each at a total pressure of 1 atm.

The results are shown in Table XTTTa.

Table XIIIa

Diluents fraction Removal time Degree of implementation in ° / o Yield in% N ₂
N ₈
N ₂
N ₂ · ■
N ₂
N ₂
Steam 1
2
3
4th
5
6th
7th Obis 2 hours
2 to 4 hours
4 to 6 hours
6 to 9 hours
9 to 12 hours
12 to 15 hours
15 to 17 hours 0
3.1
13.2
15.1
15.5
14.6
13.8 0
4.3
41.2
57.5
67.2
59.1
55.7

b) Comparative experiment

For comparison, a catalyst made of a-aluminum oxide, that is not activated is used with 10 percent by weight molybdenum trioxide. The catalyst was obtained by calcining natural O-aluminum monohydrate (= diaspore) in the air for 1 hour obtained at 560 ° C with conversion to α-aluminum oxide. The alumina was washed with water Ammonium heptamolybdate solution soaked, dried and used to convert the ammonium salt into Calcined molybdenum trioxide.

39 ml of this catalyst are introduced in the form of about 2 to 5 mm large particles in a reaction vessel as in Example 1 and in a A stream of nitrogen heated to 600 ° C. Then S methyl isobutyrate was introduced. The dehydration was carried out at a methyl isobutyrate partial pressure of 50 torr and an average Dwell time of Va second. The diluent was nitrogen at a total pressure of 1 atm used. The results are shown in Table XIHb.

Table XIHb

fraction Removal time Implementation
degree in ° / o yield
in Vo 1
2
3 0 to 2 hours
2 to 4 hours
4 to 6 hours 0.2
0.6
0.9 0.2
1.4
4.1

Example 14

It was first made from y-aluminum oxide and Manganese dioxide made existing catalyst.

282 g of a solution of manganese nitrate with a manganese nitrate content of 143 g were diluted to 500 ml with distilled water. At the same time, 225 g of approximately 3.2 mm pellets of activated "BAYER" aluminum oxide with a surface area of 80 m ² / g were placed in a stainless steel wire basket. The basket was then immersed in the manganese nitrate solution for 10 minutes. The pastilles were then allowed to drain off and dried in a porcelain evaporation dish on a hot plate. The dried pastilles were then immersed in the manganese nitrate solution for another 10 minutes and dried as before. The lozenges were then heated to 200 ° C. for 1 hour and 20 minutes and then to 400 ° C. for 1 hour and 45 minutes in a muffle furnace in the open air. The lozenges were allowed to cool in a desiccator. They were dark blue and had a metallic appearance.

50 g of the lozenges were then placed in the reaction vessel described in Example 1 and used as a catalyst according to the method described in Example 1. As a diluent for the methyl isobutyrate was again used nitrogen. The total pressure was 1 at Table XIV shows the results.

Table XTV

temperature
in ⁰ C Partial pressure of the
Isobutyric acid methyl ester
in torr Length of stay
in seconds fraction Removal time Degree of implementation
in % yield
in O 590
590
590
600
600 100
100
50
100
50 0.5
1.0
0.5
0.5
1.0 1
2
3
4th
5 0 to 2.00 hours
2.00 to 3.03 hours
3.03 to 4.06 hours
4.06 to 4.58 hours
4.58 to 5.61 hours 0
3.3
3.4
2.4
5.7 0
6.3
36.7
41.1
61.6

Example 15

152 g of activated "BAYER" aluminum oxide in the form of 3.2 mm pellets with a surface area of 80 m ² / g were soaked in a solution of 65.3 g of manganese acetate tetrahydrate in 200 ml of water. The water was then evaporated from the lozenges and these were then dried at 550 ° C. in a stream of air. 27 ml of the catalyst were then placed in a reaction vessel as in Example 1 and heated to 600 ° C. in a stream of nitrogen. A mixture of nitrogen and methyl isobutyrate in a molar ratio of 14.2: 1 was then passed over the catalyst at 600 ° C. at an hourly liquid throughput rate of 0.25 ml per milliliter of catalyst and an average residence time of 1.5 seconds. The results are shown in Table XV.

Tabel XV yield
in o / o fraction Removal time 7.6 55 1 Obis 3 hours 42.3 2 3 to 6 hours 37.6 3 6 to 8 hours 24.9 4th 8 to 11 hours 45.5 5 11 to 14 hours 66.3 6o 6 14 to 16 hours Implementation
degree in% 5.7 10.5 11.3 7.4 8.6 12.0

Example 16

Pastilles made of activated »BAYERe aluminum oxide with a particle size of about 3.2 mm and a surface area of 80 m ² / g were immersed in a solution of magnesium acetate in dilute acetic acid and then dried at 100 ° C. The dip-dry process was repeated twice.

repeated. The lozenges were then placed in a muffle furnace calcined in air at 600 ° C. The magnesium hook of the catalyst corresponded to about 10 percent by weight of magnesium oxide, MgO. The catalyst was then tested as in Example 1 for its effectiveness. The residence time of the mixture of nitrogen and methyl isobutyrate was 0.5 seconds. The results are shown in Table XVI.

Table XVI

fraction Removal time Implementation
degree in Vo yield
in O 1
2
3 0 to 2 hours
2 to 4 hours
4 to 6 hours 0.6
3.6
4.1 0.7
8.4
46.2

Example 17

A catalyst was made from γ-aluminum oxide and 10% calcium oxide by dipping pastilles made of activated "BAYER" aluminum oxide with a diameter of 3.2 mm and a surface area of 80 m ² / g in an aqueous calcium nitrate solution and then at 100 ° C were dried. The dipping and drying were repeated three times in total. The pastilles obtained were then calcined at 600 ° C. in a stream of air, the nitrate being converted into the oxide. The catalyst was then tested as in Example 1. The residence time of the mixture of nitrogen and methyl isobutyrate was 0.5 seconds. The results are shown in Table XVII.

Table XVII

fraction Removal time Implementation
degree in% yield
in% 1
2 0 to 3 hours
3 to 6 hours 5.9
5.5 15.0
36.1

Example 18

a) An aluminum oxide catalyst with 10 percent by weight calcium oxide was prepared by dipping pastilles of activated "BAYER" aluminum oxide with a size of 3.2 mm and a surface area of 80 m ² / g in an aqueous calcium acetate solution and drying. This procedure was repeated two more times. The pastilles were then calcined at 600 ° C. in a muffle furnace in a stream of air with decomposition of the acetate. The calcium was mainly in the form of calcium oxide and calcium carbonate. The calcium carbonate is converted into calcium oxide in the course of the dehydration. The catalyst was then tested as in Example 1. The residence time of the mixture of methyl isobutyrate and nitrogen was 0.5 seconds. The results are shown in Table XVIIIa.

20th fraction Table XVIIIa Implementation
degree in% yield
in «/ ο »5 1
2 Removal time 5.0
8.1 9.7
53.5 0 to 3 hours
3 to 6 hours

b) Comparative example

Catalysts of the type described in Example 18, a) were produced which contained the following oxides instead of calcium oxide: 10 percent by weight each of boron oxide, sodium oxide, potassium oxide, cobalt oxide and thallium oxide or 20 percent by weight iron oxide, Fe ₂ O ₃ . The catalysts were tested as in Example 1. The degrees of conversion and yields achieved were unsatisfactory in all cases, as can be seen from the following table XVITTb:

Table XVIIIb

Added oxide Removal time

Degree of implementation in O

yield in »/ ο

Boron oxide

Sodium oxide
Sodium oxide
Potassium oxide.
Potassium oxide.
Cobalt oxide ..

Thallium oxide
Thallium oxide
Iron oxide ...
Iron oxide ...

up to 6 hours
up to 4 hours
up to 6.5 hours
up to 2.5 hours
2.5 to 5.1 hours

0.3

0.6

0.1

0.5

0.4

1.5

0.1

1.0

The catalyst was already after 8 minutes
covered with a carbon precipitate and ineffective

0 to 2 hours 0.1 0.1 2 to 4.22 hours 0.9 1.4 0 to 3 hours 1.4 3.1

After another hour the catalyst was off
covered with a carbon precipitate and ineffective

Example 19

A catalyst with a calcium content corresponding to 2 percent by weight calcium oxide was produced by soaking pastilles made of activated "BAYER" aluminum oxide with a particle size of 3.2 mm and a surface area of 80 m ² / g with a solution of calcium acetate in dilute aqueous acetic acid became. The pastilles were dried and calcined at 600 ° C. in a stream of air. The calcium was in the form of calcium oxide and calcium carbonate. The catalyst was then tested as in Example 1. The residence time of the mixture of methyl isobutyrate and nitrogen was 1 second. The results are shown in Table XIX.

1 235 895 18th 17th Example 21 Table XIX

fraction 'Marriage time Implementation
degree in Vo yield
in »/ ο 1
2
3
4th
5 Obis 2 hours
2 to 4 hours
4 to 6 hours
6 to 9 hours
9 to 12 hours 0
12.8
15.2
14.2
15.8 0
35.3
54.0
56.4
60; 0

Table XX

fraction Removal time Implementation
degree in ° / o yield
in ° / o 1
2
3
4th
5 Obis 2 hours
2 to 4 hours
4 to 6 hours
6 to 9 hours
9 to 12 hours 0
4.8
11.7
13.4
11.7 0
12.5
62.6
64.6
71.1

According to the method described in Example 1, a catalyst with a strontium content, corresponding to 10 percent by weight of strontium oxide. The catalyst was then as in the example 1 checked. The residence time of the mixture of methyl isobutyrate and nitrogen was 0.5 seconds. The results are shown in Table XXI.

Table XXI Example 20

The procedure described in Example 19 was repeated using a catalyst which instead of 2 percent by weight calcium oxide contained 1 percent by weight calcium oxide. It became the results shown in Table XX were obtained.

fraction Removal time Implementation
degree in ° / o yield
in ° / o 1
2
3 0 to 2 hours
2 to 4 hours
4 to 6 hours 4.7
7.9
7.6 8.4
38.4
52.4

Example 22

Following the procedure described in Example 18, a catalyst with a barium content was produced accordingly 10 weight percent barium oxide, produced. The catalyst was then as in Example 1 as checked. The residence time of the mixture of methyl isobutyrate and nitrogen was 0.5 second initially and 1 second at the end. The results Table XXII shows.

Table XXII

temperature
in ⁰ C Dwell time
in seconds fraction Removal time Degree of implementation
in "Io yield
in ° / o 600
600
590 0.5
0.5
1.0 1
2
3 0 to 2.0 hours
2.0 to 4.2 hours
4.4 to 6.4 hours 3.6
7.0
7.3 6.6
36.5
51.8

Example 23

A catalyst with 10 percent by weight of titanium dioxide on γ-aluminum oxide was prepared by soaking pastilles of activated "BAYER" aluminum oxide with a size of 3.2 mm and a surface area of 80 m ² / g with a solution of titanium lactate in dilute aqueous lactic acid became. After drying, the lozenges were calcined in air at 600 ° C., as a result of which the lactate decomposed to form the oxide. The catalyst was then tested as in Example 1. The residence time of the mixture of methyl isobutyrate and nitrogen averaged 0.5 seconds. The results are shown in Table XXIII.

Table XXIII

fraction Removal time Implementation
grad in "Io yield
in »/ 0 1
2 0 to 3.0 hours
3.0 to 6.3 hours 2.9
5.0 5.5
29.6

Example 24

A catalyst with 10 percent by weight of zirconium dioxide on γ-aluminum oxide was produced by soaking pastilles made of activated "BAYER" aluminum oxide with a size of 3.2 mm and a surface area of 80 m ² / g with a zirconyl acetate solution. These pastilles were then dried, calcined and tested as in Example 23. The results are shown in Table XXIV.

Table XXIV

fraction Removal time Implementation
degree in ° / o yield
in ° / o 1
2 0 to 3 hours
3 to 6 hours 4.0
6.0 8.2
38.8

SS

Example 25

A catalyst with 10.5 percent by weight of niobium pentoxide, Nb ₂ O ₅ , on γ-aluminum oxide was produced by using pastilles of activated "BAYER" aluminum oxide with a size of

about 3.2 mm and a surface area of 80m ² / g were soaked with a solution of acidic niobium (V) oxalate in dilute oxalic acid. These pastilles were then dried and calcined in air at 600 ° C., producing the acidic niobium oxalate The catalyst was then tested as in Example 1. The residence time of the mixture of methyl isobutyrate and nitrogen was 0.5 seconds, and the results are shown in Table XXV.

709 518/561

Table XXV

fraction Removal time Implementation
degree in ° / o yield
in Vo ¹ Ü
2
3 0 to 2 hours
2 to 4 hours
4 to 6 hours 0.4
3.9
4.3 0.5
20.6
75.3

Example 26

As in Example 1, a catalyst made of 3.2 mm pellets of activated "BAYER" aluminum oxide with a surface area of ^{80 m 2} / g and containing 20 percent by weight of chromium dioxide, Cr ₂ O ₃ , was tested. The results shown in Table XXVI were obtained.

Table XXVI

fraction Removal time Implementation
degree in% yield
in·/" 1
2
3
4th
5 Obis 2 hours
2 to 4 hours
4 to 6 hours
6 to 9 hours
9 to 12 hours 4.2
11.9
11.7
11.1
10.3 5.6
58.6
60.1
59.2
64.9

Example 27

As in Example 1, 3.2 mm pastilles made of γ-aluminum oxide with a surface area of 80 m ² / g and 0.45% palladium were tested for their effectiveness. The residence time of the mixture of methyl isobutyrate and nitrogen was 0.5 seconds. The results are shown in Table XXVII.

Table XXVII

fraction Removal time Implementation
degree in ° / o yield
in o / o 1
2
3 0 to 2 hours
2 to 4 hours
4 to 6 hours 1.4
4.5
5.1 1.7
21.3
46.4

fraction Removal time Implementation
degree in ° / o yield
in"/" 1
2
3 0 to 2 hours
2 to 4 hours
4 to 6 hours 2.8
4.7
4.4 5.5
28.8
41.2

Example 28

A catalyst with 12 percent by weight cupric oxide, CuO, on γ-aluminum oxide was prepared by adding pastilles of activated "BAYER" aluminum oxide with a size of about 3.2 mm and a surface area of 80 m ² / g with an aqueous solution of cupric nitrate were soaked. These pastilles were dried and calcined at 500 ° C. in order to decompose the nitrate to the oxide. The catalyst was then tested as in Example 1. The residence time of the mixture of methyl isobutyrate and nitrogen was 0.5 seconds. The results are shown in Table XXVIII.

Table XXVIII

Example 29

As in Example 18, a 10 weight percent silver catalyst was prepared using a aqueous silver nitrate solution prepared and tested. The results are shown in Table XXIX.

Table XXIX

ίο group

2
3
4th

Removal time

0 to 2 hours
2 to 4 hours
4 to 6 hours
6 to 9.7 hours

Degree of implementation in "/ ο

1.4

9.9

11.6

11.3

Yield in »/ ο

1.8
36.1
60.2
55.4

Example 30

As in Example 18, a catalyst with ao a zinc oxide content of 10 percent by weight was prepared and checked. The results are shown in Table XXX.

Table XXX

fraction Removal time Implementation
degree in% yield
in o / o 1
2
3 0 to 2 hours
2 to 4 hours
4 to 6 hours 3.2
6.6
6.9 5.7
35.1
56.4

Example 31

As in Example 1, a catalyst made of γ-aluminum oxide with a surface area of 80 m ² / g and 10 percent by weight cadmium oxide was tested in the form of pellets about 3.2 mm in size. During the dehydration, the cadmium oxide was largely reduced to metallic cadmium. The results are shown in Table XXXI.

Table XXXI

fraction Removal time Implementation
degree in% yield
in O 1
2
3
4th
5 Obis 2 hours
2 to 4 hours
4 to 6 hours
6 to 9 hours
9 to yl hours 0.3
7.4
8.1
10.8
9.3 0.3
24.0
56.7
67.8
66.6

Example 32

As in Example 18, a catalyst was prepared, instead of 10 percent by weight calcium oxide 10 percent by weight lead oxide, PbO, contained and tested. The results are shown in Table XXXIT.

Table XXXII

fraction Removal time Implementation
degree in o / o yield
in 0/0 1
65 2
3
4th
5 0 to 2 hours
2 to 4 hours
4 to 7 hours
7 to 10 hours
10 to 12 hours 1.5
12.1
11.5
10.7
10.5 1.7
45.0
55.7
61.8
60.3

Example .33

A catalyst was made from γ-aluminum oxide with 5 percent by weight of antimony oxide, Sb ₂ O ^, by soaking 240 g of approximately 3.2 mm pellets of activated "BAYER" aluminum oxide with a surface area of 80 m ² / g with a solution were obtained by dissolving 20 g of sulfur in 200 ml of aqueous ammonium sulfide solution and then

the following addition of 10; ₂ g of antimony oxide, Sb 2 O ₃ , was produced. The solution was dried onto the lozenges and these were calcined at a temperature slowly increasing to 500.degree. This burned off the sulfur and converted the antimony sulfide into antimony tetroxide. The catalyst was then tested as in Example 1. The results are shown in Table XXXIII.

Table XXXIII

temperature
Ui ⁰ C fraction Removal time Dwell time
in seconds Degree of implementation
in Vo yield
in Vo 600 1 0 to 2.00 hours 1 0 0 600 2 2.00 to 4.00 hours 1 4.3 7.7 600 3 4.00 to 5.88 hours 1 9.8 43.9 600 4th 5.88 to 8.88 hours 1 11.3 63.6 600 5 8.88 to 11.88 hours 1 10.7 67.9 550 6th 11.88 to 13.88 hours 2 7.2 53.0 600 7th 13.88 to 15.88 hours 2 19.2 62.2 630 8th 15.88 to 17.88 hours 1 17.1 55.2

Example 34

A catalyst consisting of γ-aluminum oxide pellets about 3.2 mm in size with a surface area of about 80 m ² / g and a bismuth trioxide content of 11.5 percent by weight, calculated as bismuth, was tested by the method described in Example 1. The results are shown in Table XXXIV.

Table XXXIV

oxide 5% lithium oxide, Li ₂ O, contained. The catalyst was tested as in Example 1. The results are shown in Table XXXV.

fraction Removal time Implementation
degree in o / o yield
in% 1
2
3
4th
5 Obis 2 hours
2 to 4 hours
4 to 6 hours
6 to 9 hours
9 to 12 hours 0
3.8
7.8
9.9
8.8 0
6.6
46.2
68.2
67.1

30th fraction Table XXXV Implementation
degree in Vo yield
in Vo 35 1
³⁵ 2
3
4th
5 Removal time 2.1
10.4
10.7
10.4
9.4 2.7
37.4
40.1
47.4
53.3 Obis 2 hours
2 to 4 hours
4 to 6 hours
6 to 9 hours
9 to 12 hours

Example 35

As in Example 18, a catalyst was prepared which, instead of 10 percent by weight calcium

Example 36

As in Example 18, a catalyst with 10 percent by weight of cerium oxide, CeO ₂ , was prepared, a cerium nitrate solution being used instead of the calcium acetate solution. 100 ml of the catalyst were tested as in Example 1. The results are shown in Table XXXVI.

Table XXXVI

temperature
in ° C Dwell time
in seconds fraction Removal time Degree of implementation
in Vo yield
in Vo 600 1 1 0 to 2 hours 0.1 0.1 600 1 2 2 to 4 hours 5.1 10.9 600 1 3 4 to 6 hours 8.8 50.8 600 1 4th 6 to 9 hours 10.1 62.0 600 1 5 9 to 12 hours 8.8 63.0 550 2 6th 12 to 14 hours 6.1 48.9 600 2 7th 14 to 16 hours 16.5 48.4 630 1 8th 16 to 18 hours 14.5 51.7

Example 37 6 ₅ WO ₃ , in the form of about 1.4 to 2 mm large partial

A commercially available catalytic converter was used for the dehydrogenation of methyl isobutyrate

y-aluminum oxide with a surface area of about as in Example 1 was used. The results shows the

180m ² / g and 10 weight percent tungsten trioxide, Table XXXVII.

Table XXXVII

fraction Removal time Implementation
degree in%> yield
in «/ ο 1
2
3
4th
5 ^a Obis 2 hours
2 to 4 hours
4 to 6 hours
6 to 9 hours
9 to 12 hours 0
4.4
8.0
8.8
8.7 0
7.7
54.0
59.8
76.1.

Example 38

The longevity of the according to the method of the invention results from the following experiments a to c catalysts used.

Attempt a

A catalyst consisting of 2200 ml of activated aluminum oxide with a surface area of 80 m ² / g and 10 percent by weight V ₂ O ₅ in the form of balls with a diameter of about 3.2 mm was placed in a reaction tube with a diameter of 7.62 cm and 61 cm in length. Methyl isobutyrate vapors were passed through the reaction tube at a temperature of 585 to 618 ° C. for 505 hours. It was worked under negative pressure. The partial pressure of the ester was 20 mm of mercury. The usage was 2.0 to 2.8 seconds. The degree of conversion of methyl isobutyrate to methyl methacrylate was 16.6%. The yield of methyl methacrylate was 72.5%.

Attempt b

A catalyst consisting of 281 activated aluminum oxide with a surface area of 80 m ² Zg and 10 percent by weight MoO ₃ in the form of spheres with a diameter of 4.762 mm was introduced into a tube that had a diameter of 10.16 cm. and had a length of 3.65 m. The temperature of the reaction tube was 570 to 606 ° C. and the test time was 292 hours. It was worked under negative pressure. The partial pressure of the methyl isobutyrate was 55 to 80 mm of mercury. A usage time of 3.5 to 4.5 seconds was observed. The degree of conversion of methyl isobutyrate to methyl methacrylate was 15.1%. The yield of methyl methacrylate was 72.3%.

Attempt c

A catalyst consisting of particles of pure activated aluminum oxide with a surface area of 80 m ^s / g and a particle size of 3.2 mm was placed in a tube with a length of 61 cm and a diameter of about 5 cm. Methyl isobutyrate vapors were passed through the tube at a temperature of 591 to 613 ° C. for 347 hours. It was worked under negative pressure; the temperature of the ester was 25 to 40 mm of mercury. The residence time was 1.4 to 2.2 seconds, the degree of conversion of methyl isobutyrate to methyl methacrylate was 14.1% and the yield of methyl methacrylate was 58.1%.

When experiments a, b and c were terminated, the catalytic effect had not yet decreased.

The following experiments show that the dehydrogenation catalysts used in the process of the invention are superior to the other known dehydrogenation catalysts in their effect.

Attempt 1
5

A chromium oxide gel catalyst such as that disclosed in U.S. Patents 2,385,552 and 2,671,107 was used is described. For this purpose, according to the in Inorganic Syntheses, Vol. 2, 1946, p. 190,

ίο the process described amorphous chromium oxide gel is produced. _{CrO 3 was} reduced in aqueous solution with hot aqueous ethanol. 50 ml of the obtained black chromium oxide gel was then placed in a reaction vessel at room temperature. In this, the catalyst was slowly heated to 600 ° C. over the course of 4 hours and 15 minutes.

28 ml of methyl isobutyrate were then passed over this catalyst over the course of two hours

passed in a stream of nitrogen at 600 ° C. and with a residence time of ⁸ A seconds. The partial pressure of methyl isobutyrate in nitrogen at a total pressure of 1 atm was 50 mm of mercury. The degree of conversion was 4.3% and the yield of methyl methacrylate was only 21.0%.

Attempt 2

50 ml of a catalyst made from sintered silica with 10 percent by weight vanadium pentoxide were placed in a reaction vessel and heated to 600.degree. After passing 40 ml methyl isobutyrate at 600 ° C within ³ U hours at a residence time of 1 ¹ U seconds, and a partial pressure of 50 mm of mercury in the stream of nitrogen at 1 atm total pressure were obtained less than 1% methyl methacrylate.

Attempt 3

There were two attempts with copper chromite as catalysts, which are described in US Pat. No. 2101820 are described. One catalyst was made of copper chromite and the other was made of Barium copper chromite. The catalysts were as in Example 1 at temperatures of 475.degree checked. In both cases, no or only very insignificant amounts of methyl methacrylate could be used can be obtained.

Claims (4)

Patent claims: 1. A process for the preparation of methyl methacrylate by dehydrogenating methyl isobutyrate in the vaporous state at high temperatures in the presence of a dehydrogenation catalyst, characterized in that the dehydrogenation is carried out at temperatures of 400 to 800 ° C, preferably about 500 to 650 ° C, in the presence of aluminum oxide with a surface area of about 50 to 250 m ² / g as a catalyst, the accelerator 0.1 to 30%, preferably 1 to 15%, based on the total catalyst weight, vanadium, molybdenum, titanium, zirconium, niobium, chromium, copper , Zinc, cadmium, lead, manganese, antimony, bismuth, lithium, cerium, tungsten, palladium, silver, barium, calcium, strontium or magnesium as an element or as an oxide, at a partial pressure of about 500 to 1 Torr, before partly 250 to 25 Torr, and a residence time of the methyl isobutyrate of about 0.05 to 10 seconds, preferably about 0.5 to 5 seconds. 2. The method according to claim 1, characterized in that to reduce the Pressure of the methyl isobutyrate this with an inert gas, preferably nitrogen and / or water vapor, diluted. 3. The method according to claim 1 or 2, characterized in that the dehydration in Presence of γ-aluminum oxide and / or α-aluminum oxide monohydrate as a catalyst performs. 4. The method according to any one of claims 1 to 3, characterized in that the Carries out dehydration in the presence of γ-aluminum oxide with a surface area of about 50 to 250 m ² / g, which contains at least vanadium trioxide, vanadium pentoxide, molyb-S däntrioxyd, molybdenum dioxide or calcium oxide as an accelerator. Considered publications:
German Patent Nos. 729 342, 822243; ίο German interpretative document No. 1046 030;
French Patent No. 790,262;
U.S. Patents Nos. 2101820, 2,385,552,
671107, 2719171, 2726195. Legacy Patents Considered: German Patent No. 1127 890.