US3529032A

US3529032A - Cracking of olefins

Info

Publication number: US3529032A
Application number: US592999A
Authority: US
Inventors: Kenneth J Frech
Original assignee: Goodyear Tire and Rubber Co
Current assignee: Goodyear Tire and Rubber Co
Priority date: 1959-03-30
Filing date: 1966-11-09
Publication date: 1970-09-15
Anticipated expiration: 1987-09-15

Description

States Unite 14 Claims ABSTRACT OF THE DISCLOSURE A promoted pyrolysis process is disclosed which comprises providing a mixture of an olefin having in its mole cule a carbon-to-carbon single bond which is in a position beta to the double bond and at least 0.5 and not more than 50 mole percent of bromine or a bromine containing compound, subjecting the mixture to temperatures ranging from about 500 C. to 900 C. for very short periods of time to cleave the carbon-carbon single bond in a position beta to the double bond of said olefin.

This application is a continuation-in-part of application Ser. No. 476,186, filed July 30, 1965, which in turn was a continuation-in-part of application Ser. No. 253,289, filed Jan. 23, 1963, which is a continuation-in-part of application Ser. No. 802,633, filed Mar. 30, 1959, all of which are now abandoned.

This invention relates to the cracking of olefins. More specifically, it relates to method of improving the cracking of olefins. Most specifically, it relates to methods of improving the efiiciency of cracking of olefins to form specific diolefins and parafiinic hydrocarbons or to form certain other specific olefins.

It is known that olefins may be thermally decomposed or cracked by subjecting them to relatively high temperatures. By the term cracking or cracked as employed throughout this application is meant that the olefin molecule splits into two fragments. These two fragments themselves form molecules of other material as explained later. This thermal decomposition or cracking of olefins is usually conducted within a closed zone or reactor in the absence of oxygen. Temperatures employed in cracking of olefins usually range from about 300 C. to about 1000 C. Usually olefins are cracked while in a gaseous state and may be fed to the cracking zone either relatively pure, as mixtures of olefins, in mixture with other hydrocarbons or in mixture with diluents such as nitrogen, steam and the like. The thermal decomposition of olefins usually results in the formation of a predominance of a diolefin and a parafiinic hydrocarbon and/ or in the formation of a predominance of two other olefins. The particular materials which predominate when olefins are cracked depend largely upon the configuration of the olefin which is cracked. By configuration is meant the position of the double bond and the position of the side chains, if any. For instance, an olefin containing six carbons with a side chain, i.e. a methyl group attached to the second carbon atom of the main or straight chain portion of the compound and the double bond in the 2 position such as 2-methylpentene-2 when subjected to cracking will upon decomposition produce as the predominant products 2-methylbutadiene-1,3 a diolefin, and methane, a paraffin. On the other hand another 6 carbon olefin having a methyl group attached to the second carbon of the straight chain and the double bond in the 1 position such as Z-methylatent M 3,529,032 Patented Sept. 15, 1970 pentene-l when cracked will produce two other olefins, isobutylene and ethylene. When still another isomer such as 4-methylpentene-1 is cracked two mols of propylene are produced. These differences in products obtained when different isomeric forms of methylpentene are cracked are due to the fact that olefins crack at the position beta to the double bond. That is, the scission occurs at the bond that is in the position beta to the double bond or that the split occurs between the two carbon atoms that are second and third removed from the carbon atom which is attached to the double bond. Further the sum of the carbon atoms of the main or predominate products of the cracking is equal to the number of carbon atoms contained in the olefin which was subjected to the cracking. In 2-methylpentene-2 the cracking removes only one carbon atom from the 6-carbon olefin, in Z-methylpentene-l two carbon atoms are removed, in 4-methylpentene-l three carbon atoms are removed because of the location of the beta position, resulting in the products mentioned above. Thus, the particular olefin employed usually designates the main or predominant products which result from the cracking of olefins.

Employing the most favorable conditions conducive to cracking olefins to form these desired products, it has been found that olefins decompose at a very low rate per pass through the cracking zone. These conditions being temperature, residence time in the zone, and the ratio of the olefin to the gaseous diluent, if any, employed. It is usually the practice to increase the yield of decomposition of olefins and of the desired end products by separating the unreacted or undecomposed olefin from the products resulting from the cracking and returning or recycling the unreacted olefin to the cracking zone. Usually, however, regardless of how many recycles are carried out the ultimate yield or ultimate decomposition of the olefin is not greater than about 60 mol percent of the olefin being converted or decomposed to the desired products, the remaining 40% being converted to undesirable products as the result of side reactions caused by high temperature or long residence times in the cracking zone.

It is, therefore, the main object of this invention to provide a method whereby the yield of the desired products produced by cracking olefins is increased. Another object is to provide a method whereby the cracking of olefins to desired products per pass is increased. Another object is to increase the ultimate yield of desired products from the cracking olefins. Another object is to provide a method whereby the residence time of cracking of olefins may be decreased. Another object is to provide a method whereby the promotion of undesirable side reactions during the cracking of olefins is decreased. Another object is to provide a method whereby olefins may be cracked at lower temperatures. Another object is to provide a promoter for the cracking of olefins to the desired products. Still another object is to provide a method whereby the size of equipment needed to crack a certain volume of olefins is reduced.

The objects of this invention are accomplished by cracking olefins in the presence of bromine.

In general, the cracking of olefins in accordance with the practice of this invention may be carried out in any conventional manner usually employed in the art of cracking olefins.

Generally, the conditions of cracking may be widely varied, depending upon the particular olefin to be cracked and the products desired. For instance, the temperature of cracking may be varied from about 300 C. to about 1000 C. However, it is usually preferred to crack olefins at temperatures ranging between 500 and 900 C. and it is generally most preferred to employ temperatures ranging between 600 and 700 C.

The time that the olefins are in the cracking zone during the practice of this invention may range broadly from about 0.001 to about 3 seconds. However, it is preferable that times varying from 0.05 to 0.5 second be employed. These times are referred to usually as residence times and are usually defined as the time required for one mol of incoming gas, be it pure olefin or mixtures with other ole fins or diluents, to pass through the cracking zone. The rate of feed of olefins to the cracking zone ma also be expressed in another term called space velocity. Space velocity is reported in units of volume of gas/volume of reactor space/hour and is usually called gaseous hourly space velocity (GHSV). Space velocity employed in cracking of olefins in the practice of this invention may range broadly from 3,600,000 to 1200 GHSV. However, it is generally preferred to employ space velocity ranging from about 72,000 to 7200 GHSV. Thus, the space velocity is inversely proportional to the residence time.

Generally, the olefins are fed to the cracking reactor either as pure olefins or in mixture with other olefins or in mixture with some inert diluent. By the term inert diluent is meant that the diluent does not in any way affect the cracking of the olefin and has no effect upon the products formed in the cracking operation. it is usually desirable to employ a diluent such as steam, carbon dioxide, hydrogen or parafiins such as methane, ethane, propane, butanes, pentanes, and olefins such as ethylene. These hydrocarbons do not crack at the temperatures employed to crack the olefins in the practice of this invention. Of these, steam is preferred because of economy and because it suppresses the formation of coking and aids in the removal of coke via the reaction H Q+C=H +CO if coke is formed. Propane and pentane are also preferred.

The ratio of diluent to olefin employed in the practice of this invention may be widely varied from about 0.5/ l to about 15/ 1 or more mols of diluent per mol of olefin. However, if more than about a 15/1 ratio is employed the process is no longer economical. It is preferred to use a diluent to olefin ratio ranging from about 2.0/1 to 4.0/ 1.

The pressures employed in the cracking zone while cracking olefins may be varied from about 10 millimeters of mercury to 500 pounds per square inch gauge. However, it is preferred that the pressure range from about "atmospheric to about 35 pounds per square inch gauge.

The bromine (Br) employed in the practice of this invention may be used in amounts varying from about 0.5 to about 50 mol percent of bromine based on the total mols of the olefin to be cracked. A more preferred range of bromine is from about 1.5 to about 40 mol percent. Still a more preferred range varies from about 2.5 to about 25 mol percent. It has been found, however, that excellent results have been obtained by employing from about 5 to about mol percent of bromine.

The bromine employed to increase the efficiency of the cracking of olefins in accordance with the practice of this invention may be supplied either in the gaseous form or as a liquid under pressure. In addition to bromine itself, any organic or inorganic bromine-liberating compound, i.e. an organic or inorganic bromine-containing compound which decomposes under the conditions of cracking employed to produce bromine, may also be employed to accomplish the purposes of this invention. If organic bromine-liberating compounds are to be employed, it has been found convenient to use them in the form of a solution by dissolving them in the olefin to be cracked. If an inorganic bromine-liberating compound is to be employed, it has been found convenient to dissolve the inorganic bromine in water which is later converted to steam and as such forms the inert cracking diluent. Representative examples of the organic bromides which have been successfully employed in the practice of this invention are ethyl bromide, 2-bromopropane, l-bro-mobutane,

1 bromopropane, a bromo toluene, bromobenzene, bromochloro methane, 1,2-dibromoethane and the like. Representative examples of the inorganic bromides which have been successfully employed in the practice of this invention are hydrogen bromide and a water-soluble bromine salt such as NH Br. Of these it is preferred to employ NI-LLB].- and hydrogen bromide.

If the promoter is a compound which produces hydrogen bromide under the cracking conditions employed or is the preferred embodiment, hydrogen bromide or NH Br, the amounts may vary broadly from about 0.5 to about 50 mol percent based on the total mols of olefin to be cracked. A more preferred range of hydrogen bromide is from about 0.5 to about 25 mol percent. Still a more preferred range varies from about 0.5 to about 10 mol percent. Best results are usually obtained by employing from about 1.5 to about 5 mol percent of hydrogen bromide based on the mols of olefin to be cracked.

All the compounds useful in the practice of this invention must either decompose or dissociate to form bromine in the form of Br. Even bromine (Brgas at the temperatures employed dissociates to the form Br. However, when the bromine passes from the cracking zone to Where it is recovered it is in the form HBr regardless of form in which it was introduced. Since HBr is a preferred form of introducing bromine in the practice of this invention and is soluble in water, a very good and economical embodiment of this invention is to employ HBr as the bromine producing agent and steam as the cracking diluent thereby providing a solution of HBr in water which can be recovered and recycled over and over again.

The practice of this invention is illustrated by the following experiments which are to be interpreted as representative rather than restrictive of the scope of this invention. The results and conditions of the cracking experiments are reported in table form.

All of the cracking experiments were performed in a reactor assembly consisting of a hairpin coil prepared from A-inch OD 316 stainless steel tubing. This coil reactor was immersed in a bed of fluidized heat transfer powder which was microspheroidal silica-alumina cracking catalyst. The heat transfer powder was heated both by electrical resistance heaters and by combustinig a natural gas flame in the fluidized powder bed. The temperature gradient from top to bottom of the bed was never more than 5 to 6 C. and the gradient from the fluidized bed to the tube walls Was about 56 C. The temperatures within the fluidized bed were measured by conventional thermocouple techniques as Were the temperatures Within the cracking zone. The procedure employed was to bring the heat transfer powder up to about 500 C. employing the electrical resistance heaters While fluidizing the heat transfer powder with air. Then the natural gas burner was employed to bring the heat transfer powder up to the desired cracking or operating temperature. The bromine vvas supplied in the form of a bromine-liberating compound which at the cracking temperatures dissociated to produce bromine as Br; a calculated amount of the compound was dissolved in either the olefins or the Water, depending on the particular compound employed, to give the desired amount of bromine (Br) required in each experiment. The Water and the olefin were pumped at the proper rates necessary to produce the H O/hydrocarbon ratio desired and to give the desired residence time of the materials in the cracking zone or cracking reactor. When all variables had been adjustated to give the desired operating conditions the product of the cracking were col lected if liquid by means of cooled receivers and if gas were metered at atmospheric and room temperature conditions. The products were analyzed for content and yields by conventional analytical methods. Conventional recycle techniques were employed to obtain the ultimate yield.

The results of each experiment as Well as operating conditions are reported in the tables below wherein column one is the experiment number, column two is the actual cracking temperature, column three is the residence time in seconds, column four is the ratio of diluent/hydrocarbon, column five is the mol percent of bromine as Br The pressure employed in these experiments was 0.97 pound per square inch gauge. Steam was employed as the diluent.

Resi- M01 percent Percent Experl- Temp, dence Ratio M01 percent isoprene efficiency to ment 0. time HzO/HC HBr yield isoprene 674. 6 0. 4410 4. 12 5. 50 54. 76 61. 90 672. 5 O. 2070 4. 22 4. 29 41. 95 66. 65 663. 4 0. 5410 5. 01 None 23. 68 52. 96 660. 5 0. 5550 4. 98 None 25. 03 57. 20

regardless of the compound from whence it came based on the mols of olefin charged, unless otherwise noted, column six is the yield of desired product reported in mol percent per mol of olefin charged, and column seven is the ultimate yield also called efliciency of the desired product obtained by employing recycle techniques.

EXPERIMENTS 1-6 Decomposition of 2-methylpentene-2 to isoprene In these experiments hydrogen bromide was employed as the bromine-producing compound. Experiments 2, 4 and 6 were considered controls and do not contain any EXPERIMENTS 15-23 Decomposition of 2-methylpentene-2 to isoprene M01 Percent percent efliciency Temp, Resldence Ratio Bromine isoprene to Experiment 0. time H/HC compound yield isoprene 15 642. 0 0. 1904 3. 16 Ethyl bromide 27. 27 36. 75 16 653. 3 0. 2803 2. 96 2-bromo- 35. 38 54. 76

propane. 17 656. 0 0. 2117 2. l-bromo- 36. 96 51. 02

butane. 18 654. 7 0. 2187 2. 86 l-bromo- 34. 67 46. 60

propane. 19 649. 0 0. 2406 2. 92 ot-BYODIIO- 25. O6 32. 12

toluene. 20 647. 9 0. 2437 2. 60 Bromo- 17. 24 45. 60

benzene. 21 649. 2 0. 2287 2. 76 Bromo-chloro- 27. 36 41. 15

methane. 655. 1 0. 2206 2. 66 1,2-di-bromo- 33. 05 44. 02

ethane. 656. 0 O. 2109 2. 80 None 13. 49 39. 80

bromine. The pressure employed in the cracking of these experiments was about 0.98 pounds per square inch absolute. Steam was used as the diluent.

Thus it can be observed from the foregoing experiments that the use of bromine in the cracking of these particular olefins results in a striking increase in the Resl- M01 percent Percent Temp., dence Ratio M01 percent isoprene efficiency to 0. time HgO/HO HBr yield isoprene 576. 0 0. 46 3. 18 3. 16 8. 00 55. 00 575. 0 0. 50 3. 25 None 6. 00 40. 50 600.0 0.53 2. 53 2. 52 17. 72 58. 68 602. 3 0. 57 4. 00 None 8. 38 39. 09 626. 0 0. 50 2. 90 2. 89 30. 46 57. 75 626. 7 0. 54 4. 00 None 12. 98 49. 40

EXPERIMENTS 7-10 Decomposition of 2-methylpentene-2 to isoprene In these experiments hydrogen bromide was employed 55 as the bromine-producing compound and is reported as mol percent hydrogen bromide per mol of olefin charged. Experiments 7 and 10 are considered controls and do not contain any bromine. The pressure employed in the cracking in these experiments was about 0.97 pound per square inch gauge. Steam was used as the diluent:

Resi- Mo1 percent Percent Experi- Temp., dence Ratio M01 percent isoprene efificiency to ment 0. time HzO/HC HBr yield isoprene 651. 0 0. 2028 5. 59 None 10. 97 51. 11

677. 4 0. 2070 6. 15 None 21. 15 41. 50

EXPERIMENTS 11-14 Decomposition of 3-methylpentene-2 to isoprene in bromine is employed in the remaining experiments there is illustrated that a very definite advantage is obtained either in the increase of the desired product per pass or in increase in the ultimate yield when olefins are cracked.

Similar results may be obtained employing the general techniques employed in examples above wherein the fol- In these experiments hydrogen bromide was used as the bromine-producing compounds and is reported as mol percent HBr per mol of olefin. Experiments 13 and 14 are considered controls and do not contain any bromine.

lowing representative olefins may be cracked in accordance with the practice of this invention. These olefins are listed in groups which will crack to produce predominatly one desired diolefin or one desired olefin.

Representative of the olefins that will decompose to form as a major product 2-methylpentadiene-1,3 and 4- ployed to produce iodine and chlorine. The conditions employed were similar and the results and conditions are listed below. Experiment 24 is considered as the control and does not contain any iodine, chlorine or bromine. Experiments 25 and 26 contain chlorine and 27-30 contain iodine.

methylpentadiene-1,3 are: 2-methylhexene-3; Z-ethylpentene-l; 2,4-dimethylpentene-2; 2-methylheptene-3; 4,4- dimethylhexene-Z; 2-propylpentene-2 and 2,6-dimethylheptene-3. Of these 2-methylheXene-3, and 2,4-dimethylpentene-2 are preferred.

Representative of the olefins which will decompose to form as a major product 3-methylpentadiene-l,3 are 3- methylhexene-3; 3-methylheptene-3; 3,4-dimethylhexene- 2; 3,6-dimethylheptene-3. Of these 3-methylhexene-3; 3-methylheptene-3 and 3,4-dimethylhexene-2 are preferred.

Representative of the olefins which decompose to form as a major product 2,3-dimethyl butadiene-l,3 are: 2,3- dimethylpentene-Z; 2,3,3-trimethylbutene-l; Z-isopropylpentene-l; 2,3,3-trimethylpentene-1; 2,3-dimethylheptene- 2; and 2,3-dimethylhexene-2. Of these 2,3-dimethylpentene-2; 2,3,3-trimethylbutene-l; 2,3,3-trimethylpentene-l; 2,3-dimethylhexene-2 and 2,3-dimethylpentene-1 are preferred.

Representative of the olefins which decompose to form as a major product 2-ethy1 butadiene-1,3 are: 3-ethylpentene-2; and 3-ethylhexene-2. Of these 3-ethylpentene-2 and 3-ethylheXene-2 are preferred.

Representative of the olfins which will decompose to form as a major product butadiene-l,3 are: pentene-Z; hexene-2; 3-methylpentene-l; cyclohexene; 3-methylbutene-l; Z-heptene; 3-methylhexene-1; S-methylhexene-Z; 2-octene; -methylheptene-2; 3,5-dimethylhexene-l; 3,4,4- trimethylpentene-l; 6-methylheptene-2; nonene-2; and 3- methyloctene-l. Of these pentene-2; hexene-Z; heptene-2 and cyclohexene are preferred.

Representative of the olefins which will decompose to form as a major product isoprene are: 2-methylpentene-2; 3-methylpentene-2; Z-ethylbutene-l; 3,3-dimethylbutene-l; 2,3-dimethylbutene-l; 2-methylhexene-2; 3-methylhexene- 2; 2,3-dimethylpentene-1; 3,3-dimethylpentene-1; 2- methylheptene-2; 3-methylheptene-2; 2-ethylhexene-l; 3,3- dimethylhexene-l; 2,5-dimethylhexene-2; 3,5-dimethylheXene-2; 2,3-dimethylpentene-1 and 3,3-dimethylpentene- 1. Of these, Z-methylpentene-Z; 3-methyl-pentene-2; 2- ethylbutene-l; 2,3-dimethylbutene-1; 3,3-dimethylbutene- 1; 2-methylhexene-2; 3-methylhexene-2; 2,3-dimethylpentene-l and 3,3-dimethylpentene-1 are preferred.

Representative of the olefins that will decompose to form as a major product piperylenes are: hexene-3; 4- methylpentene-Z; heptene-3; 4-methylheXene-2; octene-3; 4-methylheptene-2; 3-ethylhexene-1; 4,5-dimethylheptene 2; and 4,5,5-trimethylhexene-2. Of these hexene-3; 4- methylpentene-2 and heptene-3 are preferred.

The following experiments were performed to illustrate that the improvements gained by the practice of this invention are peculiar to bromine alone and not to halogens in general.

EXPERIMENTS 24-30 Decomposition of 2-methylpentene-2 In these experiments the olefin 2-methylpentene-2 Were cracked in a manner similar to the prior experiments except hydrogen iodide and hydrogen chloride were em- Thus it is noted that by employing iodine and chlorine while cracking olefins instead of any improvement being obtained, there is a detrimental effect obtained. In all cases poorer yields are obtained than was obtained in the control experiments.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

What is claimed is:

1. A promoted pyrolysis process which comprises providing a mixture of at least one olefin having in its molecule a carbon-to-carbon single bond which is in a position beta to the double bond and selected from the group consisting of 2-methylhexane-3, Z-ethyIpentene-l, 2,4- dimethylpentene 2, 2 methylheptene-3, 4,4-dimethy1- hexene 2, 2 propylpentene-2, 2,6-dimethylheptene-3, 3 methylhexene 3, 3 methylheptene-3, 3,4-dimcthylhexene 2, 3,6 dimethylheptene-3, 2,3-dimethylpentene- 2, 2,3,3 trimethylbutene 1, 2-isopropy1pentene-1, 2,3,3- trimethylpentene 1, 2,3 dimethylheptene 2, 2,3-dimethylhexene 2, 3 ethylpentene 2, 3-ethylhexene 2, pentene 2, hexene 2, 3 methylpentene 1, cyclohexene, 3 methylbutene 1, 2 heptene, 3 methylhexene 1, 5- methylhexene 2, 2 octene, 5 methylheptene 2, 3,5- dimethylhexene 1, 3,4,4 trimethylpentene 1, 6-methy1- heptene 2, nonene 2, 3 methyloctene 1, 2 methylpentene 2, 3 methylpentene 2, 2 ethylbutene 1, 3,3- dimethylbutene 1, 2,3 dimethylbutene 1, Z-methylhexene 2, 3 methylhexene 2, 2-methy1heptene-2, 3- methylheptene 2, 2 ethylhexene 1, 3,3 dimethylhexene 1, 2,5 dimethylhexene 2, 3,5 dimethylhexene 2, 2,3 dimethylpentene 1, 3,3 dimethylpentene 1, hexene 3, 4 methylpentene 2, heptene 3, 4methylhexene 2, octene 3, 4 methylheptene-2, 3-ethylhexene-1, 4,5 dimethylheptene 2 and 4,5,5-trimethylheXene-2 and a cracking promoter comprising at least 0.5 mole percent and not more than 50 mole percent, based on the moles of said olefin in said mixture of bromine, cleaving the carbon-to-carbon single bond which is in a position beta to the double bond of said olefins, by subjecting said mix ture to temperatures ranging from about 500 C. to about 900 C. for periods of time varying from about 0.05 to about 0.5 second.

2. A process according to claim 1 in which the olefin pyrolyzed is at least one selected from the group consisting of Z-methyl pentene-2; 3-methyl pentene-2; 2-ethyl butene-l; 3,3-dimethylbutene-1; 2,3-dimethyl butene-l; 2- methyl hexene-2; 3-methyl hexene-2; 3,3-dimethyl pentene-l; and 2,3-dimethyl pentene-l and in which isoprene is prepared as the major product.

3. A process according to claim 1 in which the olefin to be pyrolyzed is at least one selected from the group consisting of 3-ethyl pentene-2 and 3-ethyl hexene-2 and in which 2-ethyl butadiene-l,3 is prepared as the major product.

4. A process according to claim 1 in whch the olefin to be pyrolyzed is at least one selected from the group consisting of pentene-2; hexene-Z; 3-methyl butene-l; heptene-Z; and cyclohexene and in which butadiene-1,3 is prepared as the major product.

5. A process according to claim 1 in which the olefin to be pyrolyzed is at least one selected from the group consisting of 2,3-dimethy1 pentene-Z; 2,3,3-trimethyl butene-l; 2,3,3-trimethyl pentene-l; and 2,3-dimethyl hexene-2 and in which 2,3-dimethyl butadiene-l,3 is prepared as the major product.

6. A process according to claim 1 in which the olefin pyrolyzed is at least one selected from the group consisting of hexene-3; 4-methy1 pentene-2; heptene-3; and 4-methy1 hexene-Z and in which piperylene is prepared as the major product.

7. A process according to claim 1 in which the olefin pyrolyzed is at least one selected from the group consisting of 3-methy1 hexene-3; 3-methy1 heptene-S; and 3,4-dimethyl hexene-Z and in which 3-methyl pentadiene-l,3 is prepared as the major product.

8. A process according to c aim 1 in which the olefin pyrolyzed is at least one selected from the group consisting of 2,4-dimethyl pentene-2; Z-methyl heptene-3; 4,4-dimethyl hexene-Z; and 2-propyl pentene-Z and in which 2- methyl pentadiene-1,3 and 4-methy1 pentadiene-l,3 are prepared as the major products.

9. A method according to claim 1 in which the bromine is provided by means of hydrogen bromide.

10. A method according to claim 2 in which the bromine is provided by means of hydrogen bromide.

11. A method according to claim 1 in which the bromine is provided by means of ammonium bromide.

12. A process according to claim 2 in which bromine is provided by means of ammonium bromide.

13. A process according to claim 2 in which the olefin to be pyrolyzed is Z-methyl pentene-Z and the bromine is provided by means of ammonium bromide.

14. A process according to claim 2 in which the olefin to be pyrolyzed is 3-methyl pentene-2 and the bromine is provided by means of ammonium bromide.

References Cited UNITED STATES PATENTS 1,880,310 10/1932 Wullf 260679 2,370,513 2/1945 Amos et a1. 260680 2,397,638 4/1946 Bell et a1. 260683 2,402,034 6/1946 Folkins et a1. 260683 2,404,056 7/1946 Gorin et a1. 260680 2,423,494 7/1947 Folkins et a1. 260683 3,104,269 9/1963 Schaffel 260680 3,250,821 5/ 1966 Bullard 260680 FOREIGN PATENTS 807,149 1/1959 Great Britain. 831,249 3/ 1960 Great Britain. 1,275,949 10/ 1961 France.

247,253 9/1963 Australia.

PAUL M. COUGHLAN, 111., Primary Examiner US. Cl. X.R. 260--683