DE1251305B - Process for the production of unsaturated hydrocarbons by thermal cleavage of isobutylene - Google Patents

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German class: 12 ο - 19/01

N19267IVb / 12o
2nd December 1960
5th October 1967

It is already known to produce methylacetylene (propyne) and allene (propadiene) by thermal cleavage of isobutylene, working in the presence of steam at a temperature of 800 to 900 ^° C. and residence times of 0.1 to 10 seconds.

According to another known process, the cleavage of isobutylene is carried out at a temperature of 773 ^° C., a residence time of 0.46 seconds, but a reduced pressure of 0.143 atmospheres.

The process according to the present invention, in which the cleavage likewise takes place at a temperature of over 700 ^° C. and with a residence time of less than one second, is characterized in that undiluted isobutylene is used at normal pressure, a residence time of 0.2 to 0.01 seconds and at a corresponding temperature range from 750 to 1050 ^° C. to the cleavage and thereby separating allene and / or methylacetylene formed from the cleavage mixture obtained. It is advantageous to use azomethane as a catalyst.

The starting compound need not be chemically pure isobutylene, but can be essentially one be a mixture consisting of isobutylene, like commercial fractions, as they are in extraction or distillation initially incurred in petroleum processing. The expression used below Isobutylene therefore also affects such starting materials.

The cleavage can be carried out in any conventional manner, e.g. B. by using pyrolysis tubes or from snakes made of quartz or stainless steel with fillers, such as pumice stone, or in masonry Chambers or ovens, as are customary for carrying out pyrolysis reactions.

The gas obtained after the cleavage is expediently cooled quickly, for example by it passes through a cooling chamber or quenched with cold water.

In addition to all or a mixture of all and methyl acetylene, methane is always formed; the amount Additional products that may arise under certain conditions can be made by selection corresponding cracking conditions reduced to a low level and even negligible amounts will. Unreacted isobutylene can be returned to the cracking zone.

The separation of the alien and methylacetylene from methane and unreacted isobutylene and any other by-products present and the separation of the alien from methylacetylene can be carried out in a conventional manner, e.g. B. by cooling, process for the production of unsaturated
Hydrocarbons through thermal fission
of isobutylene

Applicant:

Nederlandse Organizatie voor
Toegepast-Natuurwetenschappelijk Onderzoek
ten behoeve van Nijverheid, Handel en Verkeer,
The hague

Representative:

Dipl.-Ing. R. Amthor, patent attorney,

Frankfurt / M., Mittelweg 12

Named as inventor:

Hendricus Gerardus Peer, Rijswijk;

Otto Ernst van Lohuizen, Arnhem (Netherlands)

Claimed priority:

Great Britain 4 December 1959 (41 316)

fractional distillation or by absorption processes.

The process according to the invention results in significantly higher throughputs of isobutylene under simplified operating conditions compared to the known cleavage which works with steam and compared with the cleavage which works with negative pressure. The simplified working conditions are compared to the working with water vapor due to the fact that one does not as in a Cleavage in the presence of steam (greater than 50% ^for "i even up to 90 ° / _0), the apparatus with substantial amounts of dilution gas, such. B. Nitrogen, and this must be dimensioned, but also the heat must be recovered from the diluent gas after the end of the cracking process. When working under normal atmospheric pressure, a perfect seal, which must also be kept closed during the entire process, is a difficult problem.

Provide the throughputs achieved by the use according to the invention of undiluted isobutylene at least double and up to ten times the amount per oven pass compared to the cleavage of one

709 650/419

diluted isobutylene. Surprisingly, if the proportion is below atmospheric pressure, and no tar or coke formation with undiluted isobutylene, and it does not even need to as hitherto regarded as indispensable because of this possibility, permanent monitoring or apparatus Tricks.

The following tables show the influence of the contact time and after experimental investigations Temperature on the cleavage of the isobutylene at a pressure prevailing in the cracking zone that is practically Normal pressure is. "Practically normal pressure" is to be understood as meaning that the partial pressure of isobutylene in the initial charge is practically one atmosphere and that the entire process is at practically atmospheric pressure is carried out.

For the investigations, isobutylene was passed through a quartz tube and the tube by means of a Tube furnace heated to the desired temperature. The contact time was determined by the flow rate of isobutylene controlled. The resulting mixture was analyzed by infrared spectrography and confirmed the results obtained by gas chromatography. The investigations are still at temperatures of -180 ° C volatile substances, such as methane, largely from the mixture obtained separated by cooling it to -180 ° C before analysis. The applies to every attempt Numerical value for the specified compounds in percent by volume of the total volume of the mixture. The sign "-" means that no set is found, the sign "t" that the set was less than 1 percent by volume, and "s" that the amount was between 1 and 3 percent by volume, and "M" that there was a substantial amount.

Table 1
Contact time 0.2 seconds

750 Temperatu
800 r (° second C)
850 Isobutylene
All 94
1 89
2.2 75
4th Methyl ... t
S. S. Ethylene
acetylene
Methane ... t 13.4 (m) Benzene ... Table 2
Contact time 0.1 S.

Table 3
Contact time 0.05 seconds

Isobutylene ....

All

Methyl acetylene

Ethylene

acetylene

benzene

Temperature ( ⁰ C) 825 * 850 *

90 3 0.3

0.5

81 4.2 2 0.8

1.1

* In these experimental studies, infrared spectrography shows that not all of the methane is removed has been. A very small amount of propene is also found.

Table 4
Contact time 0.02 seconds

Isobutylene

All

Methyl acetylene ....

Propylene

Ethane

Ethylene

acetylene

Butadiene

Butylene

benzene

Temperature (° C) 950 900 925 88.5 98.4 94 5.2 1.0 3.3 1.8 t 0.5 32, 0.4 1.6 0.4 - t 0.4 t t - - t t - - 0.8 - t

81 ± 4 6.8 3.9 6.3 1.8 0.4 0.4 0.8

If a gaseous catalyst is added to the initial charge of isobutylene, the results can be improved somewhat. In Tables 5 and 6 the results are more experimental Investigations shown in which azomethane is added to isobutylene. Of the The percentage of azomethane in the table is 53 percent by volume of the volume of the initial isobutylene present, and in Table 6, it is 8 volume percent with respect to the initial present isobutylene.

Table 5

Contact time 0.02 seconds 3 percent by volume of azomethane

Isobutylene

All

Methyl acetylene

Ethylene

acetylene

methane

benzene

Temperature ( ⁰ C) 800

1.5

t
t

825 850 88 82 2.7 4.2 - 1.5 1.5 4.2 t t t t

Isobutylene

875 6o Allen

Methyl acetylene

Propylene

Ethane

Ethylene

acetylene

Butadiene

Butylene

benzene

65

4.5

7.7

Temperature ( ⁰ C) 925 875 900 90 96 94.5 4.1 2.0 3.0 1.5 t 0.5 2.7 1.0 1.9 0.6 t 0.4 t t t t - t 0.5 - 0.4 - t

80 6.5 3.2 5.8 2.1 0.6 0.4 0.6

- 1.5

Table 6

Contact time 0.02 seconds 8 percent by volume of azomethane

Table 9

Isobutylene

All

Methyl acetylene ....

Propylene

Ethane

Ethylene

acetylene

Butadiene

Butylene

benzene

Temperature ( ⁰ C) 900 850 875 81 92 89 5.1 3 4.2 1.8 0.6 1.2 4.2 2.1 3.1 1.5 0.7 1.0 1.4 1.3 1.3 0.1 0.5 0.1 0.6 0.3 0.4 4.0 1.0 t t

925

78 5.9 2.9 5.4 2.4 2.1 0.3

3.2 1.0

Tables 7 and 8 show the results obtained with a contact time of 0.01 second are obtained, with the results in Table 7 without the use of azomethane and in Table 8 when using 2 percent by volume of azomethane based on the original volume are indicated on isobutylene.

Table 7
Contact time 0.01 second

Isobutylene

All

Methyl acetylene

Propylene

Ethane

Ethylene

acetylene

Butadiene

benzene

Temperature ( ⁰ C) 1025 950 975 87.5 98.2 96.5 5.4 0.5 1.9 2.1 0.3 3.3 0.2 0.7 0.7 - 0.7 t - t - - -. 1.2 - 0.5 -

1050

81 7

3.5 5.6 1.2 0.2 0.5

1.5

Table 8

Contact time 0.01 second 2 percent by volume of azomethane

Isobutylene

acetylene

Methyl acetylene

Propylene

Ethane

Ethylene

acetylene

Butadiene

benzene

950

Temperature ( ⁰ C) I 975 I 1000

97
1.7
0.3
0.6
t
t

0.4

94 2.8 1.2 1.2 t t t 0.8

90 4.5 1.2 2.4 0.6 t t 0.5

Shown begin the education try Training the of drops From the table Cloud at ° C at ⁰ C 4th 950 975 5 925 950 6th 875 900 7th 1025 1050 8th 1000

35

40

45

55

At a given temperature, the incipient formation of a slight cloud is observed, and at a higher temperature this cloud condenses into visible drops, which are probably oily and this probably indicates the formation of aromatics (see in this context Table 9).

The tables show that with very short contact times, e.g. B. with less than 0.05 seconds, a mediocre yield of allene and / or methylacetylene can be achieved without a significant formation of decomposition products occurs; this is particularly true when ^{temperatures above 900 °} C. are used.

When using z. B. a temperature of 1025 ⁰ C and a contact time of 0.01 second, the amount of unsaturated C ₃ hydrocarbons is about 10.8 percent by volume, calculated on the initial volume of isobutylene, and of these unsaturated Cg hydrocarbons is in the final The mixture obtained contained the allene in an amount of about 50 percent by volume, the methylacetylene in an amount of 20 percent by volume and the propene in an amount of 30 percent by volume. At a temperature of 950 ° C. and a contact time of 0.02 seconds, the conversion of isobutylene into unsaturated Ca hydrocarbons is somewhat lower, namely 10.2 percent by volume, of these unsaturated C ₃ hydrocarbons in the mixture finally obtained All is present in an amount of about 50 percent by volume, methyl acetylene in an amount of about 18 percent by volume, and propylene in an amount of about 32 percent by volume.

Adding azomethane does not change the general picture significantly, but it was found that you can work with a slightly lower temperature to achieve optimal yields than without azomethane.

Claims (2)

Patent claims: 1. Process for the production of unsaturated hydrocarbons by thermal cleavage of isobutylene at a temperature above 700 ^° C. and with a residence time of less than one second, characterized in that undiluted isobutylene is obtained at normal pressure, with a residence time of 0.2 to 0, 01 seconds and at a corresponding temperature range from 750 to 1050 ⁰ C subjected to the cleavage and thereby separating allene and / or methylacetylene formed from the cleavage mixture obtained. 2. The method according to claim 1, characterized by the use of azomethane as Catalyst. Considered publications:
U.S. Patent Nos. 2,763,703, 2,429,566.