US3855326A

US3855326A - Production of olefinic hydrocarbons

Info

Publication number: US3855326A
Application number: US00420092A
Authority: US
Inventors: D Joy; P Jhawar
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1970-05-08
Filing date: 1973-11-29
Publication date: 1974-12-17
Anticipated expiration: 1991-12-17

Abstract

A mixture of olefinic hydrocarbons useful as a termonomer in EPDM rubbers contains 2-propen-1-yl-norbornene-5 and is produced by distilling a pyrolysis gasoline fraction to produce a distillate boiling in the range 10* to 80*C and separating this distillate fraction by redistillation into an isoprene-containing fraction and a piperylene-containing fraction. The piperylene fraction is heat-soaked at a temperature in excess of 150*C to produce the desired olefinic mixture. As an alternative feature of the process a part or all of the cyclopentadiene in the pyrolysis gasoline may be removed by heat-soaking at 100*-120*C, cyclopentadiene being re-introduced at a later stage in the process to produce a preferred mole ratio of 0.5 to 3 : 1 in the piperylene fraction before the latter in turn is heat-soaked.

Description

ited States Patent 1 ,loy et al. I l

[451 Dec. '17, 1974 1 PRODUCTION OF OLEFINIC HYDROCARBONS [75] ,lnventors: David Richard Joy; Pannalal Sohanlal Jhawar, both of Stockton-on-Tees, England [73] Assignee: Imperial Chemical Industries Limited, London, England [22] Filed: Nov. 29, 1973 [21] Appl. N0.: 420,092

Related US. Application Data [63] Continuation-in-part of Ser. No. 136,547, April 22,

1971, abandoned.

[30] Foreign Application Priority Data 3,766,283 10/1973 Lorette 260/666 PY Primary Examiner-Delbert E. Gantz Assistant ExaminerVeronica OKeefe Attorney, Agent, or Firm-Cushman, Darby & Cushman [57 ABSTRACT A mixture of olefinic hydrocarbons useful as a termonomer in EPDM rubbers contains 2-propen-l-ylnorbornene-S and is produced by distilling a pyrolysis gasoline fraction to produce a distillate boiling in the range 10 to 80C and separating this distillate fraction by redistillation into an isoprene-containing fraction and a piperylene-containing fraction. The piperylene fraction is heat-soaked at a temperature in excess of 150C to produce the desired olefinic mixture. As an alternative feature of the process apart or all ofthe cyclopentadiene in the pyrolysis gasoline may be removed by heat-soaking at 100-l2()C, cyclopentadiene being re-introduced at a later stage in the pro-.

cess to produce a preferred mole ratio of 0.5 to 3 1 in the piperylene fraction before the latter in turn is heat-soaked.

' 15 Claims, No Drawings PRODUCTION OF OLEFINIC' HYDROCARBONS This is a Continuation-in-Part ofour copending US. applicationSer. No. 136,547 filed Apr. 22, 1971 and now abandoned.

The present invention relates to the production of mixtures of olefinic hydrocarbons, particularly mixtures of olefinic hydrocarbons suitable for copolymerisation with ethylene and propylene.

Co-polymers of ethylene and propylene with a third co-monomer are known to be products possessing valuable elastomeric properties and are frequently referred to as EPDM rubbers. The third monomer is generally a molecule containing at least two olefin'ic bonds, one of which takes part in the polymerisation process with the ethylene and propylene while the other remains unreacted and is, therefore, available for a subsequent vulcanisation process in which cross-linking takes place between polymer chains.

A wide variety of compounds have been suggested as the third co-monomer among which may be instanced S-ethylidene norb ornene-2, 1,4-hexadiene and dicyclopentadiene. The majority of these third co-monomers are derived from olefines which are themselves of petroleum origin and ether the olefines or co-monomer or both are the subject of complicated and expensive ex-. traction processes to obtain them in suitably pure form.

The cost of the third co-monomer is an appreciable factor in the cost of the finished co-polymer, not necessarily becauseof a high level of incorporation, but be cause of its cost of production. We have now devised a process in which a relatively crude unrefined hydrocarbon mixture may be used to produce a mixture of di-olefines which on polymerisation with ethylene and propylene produce a co-polymer with properties as goodas those of a co-polymer produced from ethylene and propylene and one of the more conventional sub-, stantially pure co-monorners.

According to the invention a process for the production of a mixture of olefinic hydrocarbons suitable for co-polymerisation with ethylene and propylene comprises:

a. distilling a pyrolysis gasoline fraction derived from a cracked hydrocarbon feedstock to'produce a distillate boiling in the range 10 to 80C and comprisingpiperylene and isoprene, b. re-distilling said distillate to produce an isoprene concentrate" and a piperylene concentrate," and fraction. The pyrolysis gasoline usually boils in the ap-' proximate range 0 to 200C and consists of a number of saturated and unsaturated aliphatic hydrocarbons,

naphthenes and aromatic hydrocarbons containing 4 to 10 carbon atoms. Notable constituents of the pyrolysis gasoline fraction are isoprene, piperylene, cyclopentadiene, pentanes, pentenes, hexanes, hexenes, cyclopentane, cyclopentene, styrene, cyclohexane, methylcyclohexane, benzene, toluene and xylenes. The hydrocarbon feedstock which is employed in the cracking process is generally of petroleum origin and may be one of the crude oil distillation fractions, such as naphtha (boiling range 32 to 205C), kerosine (boiling range 205C to 260C) or light or heavy gas oil (boiling ranges 205 to 315C and 315 to 430C respectively). Steam is generally added during the cracking process and a steam cracked naphtha is a preferredsource of the pyrolysis gasoline for use in the present process.

Before it is-used as feedstock in the process of the present invention, the pyrolysis gasoline is generally first subjected to a distillation in which C hydrocarbons such as butadiene and butenes are removed as an overhead fraction.- The residue from this distillation is then suitable for use in stage (a) of the process of the present invention to produce a distillate boiling in the range 10 to C. The residue from this stage (a) distillation which comprises aromatic hydrocarbons, naphthenes and higher boiling ole-fines and paraffins may be submitted to separation'processes, e.g. distillation and/or solvent extraction processes to produce aromatics, such as benzene and toluene and naphthenes such as cyclohexane.

The distillate fraction boiling in the range 10 to 80C, preferably boils in the range 20 to 60C and comprises piperylene and isoprene. It may also contain cyclopentadiene, n-pentane, isopentane, pentene-l, trans-pentene-2, Z-methylbutene-Z, cyclopentene and cyclopentane.

The cyclopentadiene may be present as its dimer, dicyclopentadiene and the piperylene may be present in one or both of its cis and trans' forms.

If desired the cyclopentadiene and its dimer-may be removed'wholly or in part in an additional step immediately before or immediately after the distillate fraction is split into isoprene and piperylene concentrates. This may be achieved by'heating the distillate fraction or the piperylene concentrate in a sealed system to a tempe rature of to C, preferably for V2 5 hrs.,

particularly 1' 2 hrs. for partial conversion, or 3 4 hrs. for total conversion of cyclopentadiene to dicyclopentadiene. The latter is separated from the distillate trans-pentene-Z, 2-methylbutene-2, cyclopentene, cy-- clopentane and a trace of benzene. lf desired thisconcentrate may be subjected to a distillation to remove one or more of the components boiling higher and/or lower than piperlyene before undergoing the reaction stage (c) (for example, the removal of cyclopentadiene as described above). All of the foregoing distillations are preferably carried out continuously in a series of distillation columns in which the residue or distillate I from one column forms the feed to the next.

The piperylene concentrate is heated at a temperature of at least 150C, preferably 150 to 350C, more preferably 150 to 250C, for periods of up to 24 hours, e.g. 0.01 hrs. or more such as 1 to 24 hrs. Typically, heating periods will vary between 8 hours at 170C to 15 minutes at 220C. The intention of this heating step is to cause the cyclopentadiene and the piperylene in the piperylene concentrate to co-dimerise so if necessary cyclopentadiene and/or piperylene may be added before stage (c) to produce the ratio of cyclopentadiene to piperylene required. Addition of cyclopentadiene is especially necessary if the cyclopentadiene originally present in the fraction boiling in the range 10 to 80C has been removed before or after division of the latter into the isoprene concentrate and piperylene concentrate. The cyclopentadiene may be present or may be added in the form of its dimer which dissociates to cyclopentadiene during the reaction. It is preferred that the mole ratio of cyclopentadiene to piperylene in the piperylene concentrate be in the range 0.5 to 3 1, more preferably 0.5 to 1.2 1, especially 0.5 to 0.7 l. The piperylene concentrate with or without added cyclopentadiene is preferably heated in a sealed system under its autogenous pressure at the relevant temperature. The cyclopentadiene and piperylene co-dimerise to produce one or more of 4-methyl- 4,7,8,9-tetrahydroindene, 7-methyl-4,7,8,9- tetrahydroindene, 2-vinyl-3-methyl norborneneor Z-propen-l-yl-norbornene-S, desirably the latter. in addition both the piperylene and the cyclopentadiene may dimerise to give a number of isomeric decadienes and dicyclopentadiene respectively. The product of the process, therefore, may contain one or more of the dimers described as well as unreacted components originally present in the piperylene concentrate. It is usually preferable to remove these unreacted components, e.g. by distillation, to leave the mixture of dimers which are suitable for incorporation in a polymer without further treatment. If desired, however, one or more of the dimers may be separated from the product mixture and used individually or together in a polymer preparation. For example, it is preferred that a fraction be distilled from the product of the process boiling in the range 80 to 87C at 50 mm. Hg and comprising at least 50 per-,

cent, preferably at least 90 percent, by weight 2-propen-l-yl-norbornene-S. This fraction provides a very effective third monomer.

The invention will now be further described with reference to the following Examples.

EXAMPLE I A debutanised pyrolysis gasoline fraction boiling in the range 0 to 200C and derived from a stream cracked naphtha was distilled to produce a fraction of boiling range 10 to 80C. This fraction was redistilled in a 30 tray Oldersaw batch distillation column under atmospheric pressure and a distillate taken boiling in the range to 37C comprising isoprene, n-pentane, iso-pentane and pentene-l (isoprene concentrate). The residue from this distillation (piperylene concentrate) comprised 34 wt. percent cyclopentadiene and dicyclopentadiene, 20 wt. percent trans-piperylene and 13 wt. percent cis-piperylene. Also present were n-pentane (11.15 wt. percent) trans-pentene-2 (1.72 wt. percent), 2-methyl-butene-2 (4.8 wt. percent), cyclopentene (7.04 wt. percent) cyclopentane (10.46 wt. percent) and benzene (5.13 wt. percent).

EXAMPLE 2 Example 1 was repeated to produce a piperylene concentrate containing 30 wt. percent cyclopentadiene and dicyclopentadiene, 19 wt. percent transpiperylene and 13 wt. percent cis-piperylene. The balance of the concentration was made up of the compounds described for the similar concentrate in Exam- 'ple 1. 3 Kilograms of the concentrate were heated in a stainless steel autoclave at 190C for 3 hours. The

product was then distilled and a fraction comprising wt. percent 2-propen-l-yl-norbornene-S, 20 wt. percent dicyclopentadiene and 5 wt. percent piperylene dimers obtained.

The fraction was incorporated into a polymer as follows:

The polymerisation apparatus consisted of a flanged flask provided with tubes for feeding and discharging gases, a stirrer, a thermometer and a serum cap through which the diene and catalyst could be introduced. The tube for introducing the gases reached the bottom of the vessel and the apparatus was kept at a constant temperature of 20C.

The flask was filled half full with 684 parts of anhydrous heptane which was then saturated at --20C by passing through it for 15 minutes a mixture of propylene and ethylene in a molar ratio of4 l. The flow rate of the gas mixture was equivalent to 8.5 times the total volume of the solvent in the flask per minute. 1.9 parts of the mixture of dienes prepared as above was then introduced into apparatus followed by 0.302 part of diethyl aluminum chloride as a solution in about 0.52 part of heptane and 0.097 part of vanadium tetrachloride as a solution in about 1.0 part of heptane and polymerisation commenced immediately. After a polymerisation period of 15 minutes, 7.93 parts of methanol were added to deactivate the catalyst and the polymer solution was washed with dilute HCI to remove catalyst residues. The polymer was precipitated by addition of the solution to an excess of methanol. It was then spread out on a tray and dried overnight in a vacuum oven.

Parts by weight of the polymer were then compounded on a laboratory roll-mill with 1.5 parts of sulphur, 5 parts of zinc oxide, 1 part of stearic acid, 1.5 parts of tetramethylthiuram monosulphide, 0.5 part of mercaptobenzothiazole and 50'parts of HAF carbon black and a small sample ofthe thus compounded polymer was vulcanised in a Wallace-Shawburn Curometer.

The Curometer indicated that a time of 9 minutes at C was required to achieve 95 percent of the maximum cure.

Three separating samples of the remaining com pounded polymer were cureclin a hydraulic press at a temperature of C'for, respectively, 15, 20 and 30 minutes, to form A; inch thick sheets.

Standard dumbell-shaped specimens having between the shoulders a nick 1 inch long and 1/16 inch wide were cut from the cured sheets. The tensile strength at break, the modulus, and the elongation to break of each specimen were measured on a Type E tensometer using a rate of elongation of 20 i 2 inches/minute at room temperature. The tensile strength was 178 kgm/sq.cm., the percent elongation to break 440 and the 300 percent modulus 135 kgm/sq.cm.

Under comparable conditions polymer prepared from ethylene, propylene and 1,4-endomethylene-6- methyl-l,4,5,8,9,IO-hexahydronaphthalene (known to produce an excellent co-polymer with ethylene and propylene) gave the following results:

95% cure time Tensile strength 300% modulus /6 elongation to break minutes at 150C 173 kg/square cm.

I 12 kg/squarc cm. 435

EXAMPLE 3 ture.

This fraction was incorporated into a polymer in a 3. The process of claim 1 in which the distillate produced in stage (a) boils in the range to 60C.-

4. The process of claim 1 in which cyclopentadiene and its dimer in the distillate obtained in step (a) are removed at least in part in an additional step before the distillate fraction from step (a) is split into isoprene and piperylene concentrates in stage (b).

5. The process of claim 1 in which the distillate fraction from stage (a) or the piperylene concentrate from stage (b) is heated in a sealed system at 100 to 120C for /2 to 5 hours to convert any cyclopentadiene which is present to dicyclopentadiene which is then removed as the residue in a further distillation.

6. The process of claim 1 in which the piperylene concentrate is heated at a temperature in the range 150 to 250C for a period up to 24 hours to produce 2-propen-l-yl-norbornene-S.

similar manner to Example 2 using 2.8 parts of the mixture.

The polymer produced had the following properties:

9 minutes at 160C 185 kg/squarc cm. kg/square cm.

We claim:

1. In a process for the production ofa mixture of olefinic hydrocarbons suitable for copolymerisation with ethylene and propylene the following steps in combination,

a. distilling a pyrolysis gasoline fraction derived from a cracked hydrocarbon feedstock to produce a distillate boiling in the range 10 to 80C comprising piperylene, isoprene and at least one member of the group consisting of cyclopentadiene, dicyclopentadiene', n-pentane, isopentane, pentene-l, trans-pentene-Z, 2-methylbutene-2, cyclopentene, cyclopentane and benzene,

b. redistilling said distillate to produce an isoprene concentrate and a piperylene concentrate, the latter including piperylene and at least one hydrocarbon selected from the group consisting of cyclopentadiene, dicyclopentadiene, n-pentane', transpentene-Z, Z-methylbutene-Z, cyclopentene, cyclopentane and benzene, v

c. heating said piperylene concentrate at a temperature of at least 150C for a period of time up'to 24 hours with added cyclopentadiene or dicyclopentadiene if one or other of these latter is not present in sufficient amount so as to codlmerise said piperylene and cyclopentadiene and produce a mixture of olefinic hydrocarbons including 2-propen-l-ylnorbornene-S, said. mixture being suitable for polymerisation with ethylene and propylene.

2. The process of claim 1 in which the pyrolysis gasoline boils in the range 0 to 200C and is derived from a steam cracked naphtha.

7. The process of claim 1 in which at'le'ast one member of the group consisting of cyclopentadiene and piperylene is added to the piperylene concentrate before stage (0) to provide the required ratio of cyclopentadiene and piperylene for said co-dimerisation.

8. Theprocess of claim 1 in which the mole ratio of cyclopentadiene to piperylene in the piperylene concentrate is in the range 0.5 to 3 l.

9. The process of claim 1 in which the product of stage (c) is distilled to give a fraction boiling in the range 80 to 97C at 5 mm. Hg and comprising at' least 50 percent by'weight 2-propen-l-yl-norbornene 5.

10. The process of claim 1 in which a steam cracked naphtha boiling in the range 0 to 200C is a. distilled to produce a distillate boiling in the range I 10 to C comprisingpiperylene and isoprene.

b. said distillate is redistilled to produce an isoprene concentrate boiling in the range 10 to 40C and a piperylene-concentrate boiling in the range 40 to 80C,

(c) said piperylene concentrate is heated at a temperature in the range to 250C for a period of up to 24 hours, and

d. said heated piperylene concentrate is distilled to produce a fraction boiling in the range 80 to 87C at 5 0 mm. Hg comprising at least SO-percent by.

weight 2'-propenl -yl-norbornene-5, said fraction being suitable for co-polymerisation with ethylene and propylene. v I

11. The process of claim 10 inwhich cyclopentadiene and its. dimer area also present in the distillate of step (a) and. these are removed wholly or in part in an additional'ste'p before the distillate fraction is split into isoprene and piperylene concentrates by heating said l step (c) to produce a mole ratio of cyclopentadiene to piperylene in the range 0.5 to 1.2 l.

13. In a process for'the production of a mixture of olefinic hydrocarbons suitable for copolymerisation with ethylene and propylene, the step which comprises heating a piperylene concentrate including piperylene and cyclopentadiene at a temperature in the range of at least 150C for a period of time up to 24 hours to codimerise said cyclopentadiene and piperylene and produce a mixture of olefinic hydrocarbons including at least onemember of the group consisting of 4-methyl- 4,7,8,9-tetrahydroindene; 7-methyl-4,7,8,9- tetrahydroindene; 2-vinyl-3-methyl norborneneand 2-propen-l-yl-norbornene-S, said mixture being suitable for polymerisation with ethylene and propylene, said piperylene concentrate being obtained by (a) distilling a pyrolysis gasoline fraction derived from a cracked hydrocarbon feedstock to produce a distillate boiling in the range 10 to 80C comprising piperylene, isoprene and at least one member of the group consisting of cyclopentadiene, dicyclopentadiene, n-pentane, isopentane, pentene-l, trans-pentene-Z, 2- methylbutene-2, cyclopentene, cyclopentane and benzene, and (b) redistilling said distillate to produce an isoprene concentrate and said piperylene concentrate, cyclopentadiene or dicyclopentadiene being added to said piperylene concentrate if not present in sufficient amount to codimerise with the piperylene.

14. In a process for the production of a mixture of 'olefinic hydrocarbons suitable for copolymerisati'on with ethylene and propylene, the following steps in combination,

a. distilling a pyrolysis gasoline fraction derived from a cracked hydrocarbon feedstock to produce a distillate boiling in the range 10 to 80C comprising piperylene,- at least one member of the group consisting of cyclopentadiene and its dimer, and isoprene, b. redistilling said distillate to produce an isoprene concentrate and a piperylene concentrate, the latter including piperylene and cyclopentadiene, c. heating said piperylene concentrate at a temperature of at least 150C for up to 24 hours to codimerise said cyclopentadiene and piperylene and produce'a mixture of olefinic hydrocarbons including at least one member of the group consisting of 4- methyl-4,7,8,9-tetrahydroindene; 7-methyl-4,7,8,- 9-tetrahydroindene; 2-vinyl-3-methyl norbornene- 5 and 2-propen-l-yl-norbornene-S, said mixture being suitable for polymerisation with ethylene and propylene.

15. In a process for the production of a mixture of olefinic hydrocarbons suitable for copolymerisation with ethylene and propylene, the following steps in combination.

a. distilling a pyrolysis gasoline fraction derived from a cracked hydrocarbon feedstock to produce a distillate boiling in the range 10 to C comprising piperylene, at least one member of the group consisting of cyclopentadiene and its dimer, and isoprene,

b. redistilling said distillate to produce an isoprene concentrate and a piperylene concentrate, the latter including piperylene and cyclopentadiene,

c. heating said piperylene concentrate at a temperature in the range to 250C for up to 24 hours to codimerise said cyclopentadiene and piperylene and produce a mixture of olefinic hydrocarbons including at least one memberof the group consisting of 4-methyl-4,7,8,9-tetrahydroindene; '7-methyl- 4,7,8,9-tetrahydroindene; 2-vinyl-3-methyl norbornene-5 and 2-propen-l-yl-norbornene-S, said mixture being suitable for polymerisation with ethylene and propylene.

Claims

1. IN A PROCESS FOR THE PRODUCTION OF A MIXTURE OF OLEFINIC HYDROCARBONS SUITABLE FOR COPOLYMERISATION WITH ETHYLENE AND PROPYLENE THE FOLLOWING STEPS IN COMBINATION, A. DISTILLING A PYROLYSIS GASOLINE FRACTION DERIVED FROM A CRACKED HYDROCARBON FEEDSTOCK TO PRODUCE A DISTILLATE BOILING IN THE RANGE 10* TO 80*C COMPRISING PIPERYLENE, ISOPRENE AND AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF CYCLOPENTADIENE, DICYCLOPENTADIENE, N-PENTANE, ISOPENTANE, PENTENE-1, TRANS-PENTENE-2, 2-METHYLBUTENE-2, CYCLOPENTENE, CYCLOPENTANE AND BENZENE, B. REDISTILLING SAID DISTILLATE TO PRODUCE AN ISOPRENE CONCENTRATE AND A PIPERYLENE CONCENTRATE, THE LATTER INCLUDING PIPERYLENE AND AT LEAST ONE HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF CYCLOPENTADIENE, DICYCLOPENTADIENE, N-PENTANE, TRANSPENTENE-2, 2-METHYLBUTENE-2, CYCLOPENTENE, CYCLOPENTANE AND BENZENE, C. HEATING SAID PIPERYLENE CONCENTRATE AT A TEMPERATURE OF AT LEAST 150*C FOR A PERIOD OF TIME UP TO 24 HOURS WITH ADDED CYCLOPENTADIENE OR DICYCLOPENTADIENE IF ONE OR OTHER OF THESE LATTER IS NOT PRESENT IN SUFFICIENT AMOUNT SO AS TO CODIMERISE SAID PIPERYLENE AND CYCLOPENTADIENE AND PRODUCE A MIXTURE OF OLEFINIC HYDROCARBONS INCLUDING 2PROPEN-1-YL-NORBORNENE-5, SAID MIXTURE BEING SUITABLE FOR POLYMERISATION WITH ETHYLENE AND PROPYLENE.

2. The process of claim 1 in which the pyrolysis gasoline boils in the range 0* to 200*C and is derived from a steam cracked naphtha.

3. The process of claim 1 in which the distillate produced in stage (a) boils in the range 20* to 60*C.

5. The process of claim 1 in which the distillate fraction from stage (a) or the piperylene concentrate from stage (b) is heated in a sealed system at 100* to 120*C for 1/2 to 5 hours to convert any cyclopentadiene which is present to dicyclopentadiene which is then removed as the residue in a further distillation.

6. The process of claim 1 in which the piperylene concentrate is heated at a temperature in thE range 150* to 250*C for a period up to 24 hours to produce 2-propen-1-yl-norbornene-5.

7. The process of claim 1 in which at least one member of the group consisting of cyclopentadiene and piperylene is added to the piperylene concentrate before stage (c) to provide the required ratio of cyclopentadiene and piperylene for said co-dimerisation.

8. The process of claim 1 in which the mole ratio of cyclopentadiene to piperylene in the piperylene concentrate is in the range 0.5 to 3 : 1.

9. The process of claim 1 in which the product of stage (c) is distilled to give a fraction boiling in the range 80* to 97*C at 5 mm. Hg and comprising at least 50 percent by weight 2-propen-1-yl-norbornene-5.

10. The process of claim 1 in which a steam cracked naphtha boiling in the range 0* to 200*C is a. distilled to produce a distillate boiling in the range 10* to 80*C comprising piperylene and isoprene. b. said distillate is redistilled to produce an isoprene concentrate boiling in the range 10* to 40*C and a piperylene concentrate boiling in the range 40* to 80*C, (c) said piperylene concentrate is heated at a temperature in the range 150* to 250*C for a period of up to 24 hours, and d. said heated piperylene concentrate is distilled to produce a fraction boiling in the range 80* to 87*C at 50 mm. Hg comprising at least 50 percent by weight 2-propen-1-yl-norbornene-5, said fraction being suitable for co-polymerisation with ethylene and propylene.

11. The process of claim 10 in which cyclopentadiene and its dimer area also present in the distillate of step (a) and these are removed wholly or in part in an additional step before the distillate fraction is split into isoprene and piperylene concentrates by heating said distillate fraction in a sealed system at 100* to 120*C for 1/2 to 5 hours to convert cyclopentadiene wholly or in part to dicyclopentadiene and removing said dicyclopentadiene as a residue in a distillation.

12. The process of claim 11 in which cyclopentadiene and/or piperylene are added to the piperylene concentrate after the redistilling in step (b) but prior to step (c) to produce a mole ratio of cyclopentadiene to piperylene in the range 0.5 to 1.2 : 1.

13. In a process for the production of a mixture of olefinic hydrocarbons suitable for copolymerisation with ethylene and propylene, the step which comprises heating a piperylene concentrate including piperylene and cyclopentadiene at a temperature in the range of at least 150*C for a period of time up to 24 hours to co-dimerise said cyclopentadiene and piperylene and produce a mixture of olefinic hydrocarbons including at least one member of the group consisting of 4-methyl-4,7,8,9-tetrahydroindene; 7-methyl-4,7,8,9-tetrahydroindene; 2-vinyl-3-methyl norbornene-5 and 2-propen-1-yl-norbornene-5, said mixture being suitable for polymerisation with ethylene and propylene, said piperylene concentrate being obtained by (a) distilling a pyrolysis gasoline fraction derived from a cracked hydrocarbon feedstock to produce a distillate boiling in the range 10* to 80*C comprising piperylene, isoprene and at least one member of the group consisting of cyclopentadiene, dicyclopentadiene, n-pentane, isopentane, pentene-1, trans-pentene-2, 2-methylbutene-2, cyclopentene, cyclopentane and benzene, and (b) redistilling said distillate to produce an isoprene concentrate and said piperylene concentrate, cyclopentadiene or dicyclopentadiene being added to said piperylene concentrate if not present in sufficient amount to codimerise with the piperylene.

14. In a process for the production of a mixture of olefinic hydrocarbons suitable for copolymerisation with ethylene and propylene, the following steps in combination, a. distilling a pyrolysis gasoline fraction derived from a cracked hydrocarbon feedstock to produce a distillate boiling in the range 10* to 80*C comprising piperylene, at least one member of the group consisting of cyclopentadiene and its dimer, and isoprene, b. redistilling said distillate to produce an isoprene concentrate and a piperylene concentrate, the latter including piperylene and cyclopentadiene, c. heating said piperylene concentrate at a temperature of at least 150*C for up to 24 hours to codimerise said cyclopentadiene and piperylene and produce a mixture of olefinic hydrocarbons including at least one member of the group consisting of 4-methyl-4,7,8,9-tetrahydroindene; 7-methyl-4,7,8,-9-tetrahydroindene; 2-vinyl-3-methyl norbornene-5 and 2-propen-1-yl-norbornene-5, said mixture being suitable for polymerisation with ethylene and propylene.

15. In a process for the production of a mixture of olefinic hydrocarbons suitable for copolymerisation with ethylene and propylene, the following steps in combination. a. distilling a pyrolysis gasoline fraction derived from a cracked hydrocarbon feedstock to produce a distillate boiling in the range 10* to 80*C comprising piperylene, at least one member of the group consisting of cyclopentadiene and its dimer, and isoprene, b. redistilling said distillate to produce an isoprene concentrate and a piperylene concentrate, the latter including piperylene and cyclopentadiene, c. heating said piperylene concentrate at a temperature in the range 150* to 250*C for up to 24 hours to codimerise said cyclopentadiene and piperylene and produce a mixture of olefinic hydrocarbons including at least one member of the group consisting of 4-methyl-4,7,8,9-tetrahydroindene; 7-methyl-4,7,8,9-tetrahydroindene; 2-vinyl-3-methyl norbornene-5 and 2-propen-1-yl-norbornene-5, said mixture being suitable for polymerisation with ethylene and propylene.