US2733279A

US2733279A - Process for recovery and purification of

Info

Publication number: US2733279A
Authority: US
Publication date: 1956-01-31
Anticipated expiration: 1973-01-31

Description

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La., asslgnors to Esso Research and Engineering Company, a corporation of Delaware J 'Application January 11, 1952, serial No. 266,914

4 claims. (ci. 26o-666) mers in effecting their purification and to recover these monomers from fractions of cracked petroleum naphtha containing the cyclodienes as monomers, dimers, and

codimers mixed with other unsaturated hydrocarbons and (2) Stripping of additional Cs-CQ hydrocarbons from the residual Cs-Ciz fraction is accomplished at relatively higher temperatures (e. g., at 240 F. to 410 F.) than.

the initial fractionation to insure removal of Cs-C components from this residual fraction in which dimers and codimers are concentrated.

(3) Processing of the lightest fractions for eliminating C4 and lower hydrocarbons is carried out at lower temperatures (e. g., at below 160 F.) for protection against interpolymerization.

(4) Processing of the streams of Cs-Cs hydrocarbons to selectively dimerize the cyclodiene components and recover the resulting dimers asv a residual fraction diluted with a restricted amount of Cfr-Cs hydrocarbons is carried out at moderate temperatures (e. g., at below 260 F.), preferably with the aid of steam, to minimize ldecomposition of the dimers.

(5)l Depolymerization of C10-C12 dimers and codimers diluted with restricted amounts of Ci-Cp hydrocarbons in the residual streams is carried out at appropriate high temperatures mainly above 350 F and preferably in consecutive stages at 380 to 410 F. and 390 to 420 F.

lt is known that some processes have dealt only with recovery of cyclopentadiene from coal tar light ends, and others have dealt with recovery of cyclopentadiene from certainA lowl boiling fractionsgof cracked petroleum dis' tillat'es. y

The cyclodienes present in highly cracked petroleum distillates have now been analyzed as being present in a number of homologs and polymeric forms, for example, the monomers of C5 and Ce cyclodienes, their higher homologs, also, the dimers, codimers, higher polymers of these homologous cyclodienes, and interpolymers with other diolens. The dimer and codirner forms are stable at ordinary atmospheric temperatures but on being heated to elevated temperatures of the order of 280 and higher they start to undergo cracking or depolymerization. The monomeric forms are unstable even at ordinary temperatures and4 undergo polymerization as they are heated to temperatures above 140 F. On account I Patented Jan. 3l, 1956 pice of the various forms in which ythe cyclodienes tend to be present in highly crackednnaphtha distillates, there have been problems of determining the best manner of segregating a maximum amount of the cyclodienes desired and recovering them as monomers of highest purity.

In the past, the processes for the recovery of cyclopentadiene from cracked petroleum naphthas have been represented by operations which went to two somewhat opposite extremes.

In-one type of prior art process, attempts were made to "depolymerize all of the cyclopentadiene dimer, first in a wide-boiling range naphtha including hydrocarbons lower and higher than C5 hydrocarbons, after which the cyclopentadiene monomer together with other C5 and lower unsaturated hydrocarbons were separated from higher hydrocarbons (Cs and up); then the cyclopentadiene monomer was dimerized in the presence of Cs and lighter hydrocarbons. That type of process was found unsuitable for the present objects. It omitted recovery of cyclopentadiene with methyl cyclopentadiene from their codimers, and resulted in the formation of a highly contaminated product, contamination being apparently due to the dimerization in the presence of highly reactive C4 unsaturated hydrocarbons. The other type of process which went toward an opposite extreme for obtaining greater purity, eliminated the cyclopentadiene monomer with other C5' and lighter hydrocarbons from the cracked naphtha distillate, so as to leave cyclopentadiene dimers highly diluted in an aromatic naphtha portion of the initial cracked naphtha and thereafter the dimer was decomposed' to monomer in this aromatic fraction so that the final monomer could be fractionally distilled away from the vhigher boiling hydrocarbons.

The type of operation which is particularly suitable for obtaining a concentrate of the cyclodienes in accordance with the present invention is distinguished from each of the above described opposite extremes, because the present invention particularly requires obtaining a concentrate in which Ce as well as Cs cyclodienes are recovered to the greatest extent possible, as dimers and codimers substantially free of other hydrocarbons except for a restricted amount in the C1 to C9 range.

In order to obtain'the cyclodiene dimer and codimer concentrates, the following division of fractions is ern-y ployed:

(a) A light naphtha distillate cut I rich in Cs-Cs components is readily separated from the cracked naphtha distillate `if this stream is allowed to contain some C4 come ponents and components in the Ci to C9 range. This light naphtha stream is subjected to fractionation mainly at low temperatures, e. g., by compressing, cooling, and

stripping to eliminate substantially all the C4 and lighter hydrocarbons. With C4 and lighter hydrocarbons eliminated, the remaining Cs-Cs portion of this cut I can be soaked to dimerize said monomers, then can be fractionated at moderate temperatures to obtain a concentrate of a very good recovery is obtained from the decomposition of the dimers and codimers. This Cs-Cs rich distillate cut is very close in its composition to the above described Cs-Cs rich fraction from cut I with C.; and lower elimimesmo nated. Accordingly, either of the Cs-Cs rich fractions or a combination thereof serves as a suitable feed stock for the remaining operational steps which include first a thermal soaking or dimerizing of the cyclodiene monomers present into dimers and codimers, followed by a fractionation step to remove Cs to Cghydrocarbon components from the Cio-C12 cyclodiene polymers concentrate containing a minor amount of C7 to C9 hydroY carbons.

Next, the cyclodiene residual dimer concentrates are subjected to liquid phase depolymerization preferably in' at least two stages at appropriate temperatures with rapid removal of monomers formed by decomposition of the polymers in order to minimize the reverse polymerizing reaction and assure depolymerization of the codimer.

(c) In a dual or multiple stage liquid-phase cracking or depolymerization, the cyclodiene dimer concentrate with controlled dilution by Cr-Cg hydrocarbons is kept as free as possible of other types of reactive unsaturated hydrocarbon compounds and the cyclodiene polymers, mainly Cm--Crz dimers and' codimers, subjected to the liquid phase cracking are prevented from being diluted excessively by hydrocarbons which would prevent the temperature from being raised to a suitable high degree. The C5 and Ce cyclodiene monomers that are stripped out as fast as they are formed in each of the cracking stages are immediately and quickly passed to a fractionation zone to recover distillates of the C5 and Cs cyclodienes having a high purity. It is essential that a limited amount of inert hydrocarbons, especially in the C7 to C9 range, be present to aid in stripping the monomers and for keeping the monomers diluted during their fractionation. The distillate bottoms from the fractionating zone will contain some C5 and Ca cyclodiene dimers and codimers with heavier polymers, but since it is desirable to prevent excessive accumulation of low boiling hydrocarbons which would prevent the desired high depolymerization temperatures from being maintained there has to be a purge of such materials. Also, a purge of higher cyclodiene polymers which resist dissociation, as the distillate bottoms are recycled to the cracking zones` The general principles of the operations employed in the present invention have been described, and more details will be given with reference to the accompanying drawings together with specific examples.

In the drawing the general iiow plan is shown for obtaining the feed stock to be used in the depolymerizing operation and final purification.

In the simplified flow plan shown in the drawing, a

late stream; therefore, it is suflicient to state that petroleum hydrocarbons boiling in the range of 250-700 F. are cracked in the vapor phase at l000 F. to 1600 F; for a short period of 1 to 5 seconds, preferably in the presence of 50 to 90 mole per cent steam based on the hydrocarbon feed and under a pressure of 1 to l0 atm. The naphtha distillate distilled from the cracked petroleum will be of approximately C1-Ci2 range and will contain C5 and Cs cyclodienes in various forms, mono mers, dimers, and codimers, together largely with unsaturated aliphatic hydrocarbons and aromatic hydrocarbons within this range. The naphtha distillate may be a condensed distillate which is free of the normally gaseous C1C3 hydrocarbons or may be maintained in the vapor phase, including some normally gaseous hydro carbons.

The naphtha distillate essentially containing come ponents within the Cs-Ciz range is passed by line 1 into what will be termed a splitting unit, such as a conventional fractionating column 2, for making a split between an overhead C4-C9 stream (cut I) and a residual Cs to C12 stream (cut II). It is to be noted that this split is not made with exacting limits, and thus the overhead (cut I) stream tends to contain hydrocarbons lower than C5 up to C9 hydrocarbons while the residual cut II stream also contains some C5 to C9 components. This rough splitting between the two cuts is desirable not only for the sake of economy, but also for a number of other reasons'. The rough splitting between the two cuts mentioned reduces opportunities for interpolymerization of the cyclodienes with the aliphatic diolefins and satisfactorily segregates the two types of material which are to be further processed.

Suitable operation conditions in the cut splitting operation, 'such as carried out in fractionating column 2, are as follows:

No. of plates 6.

Overhead vapor temperature to 100 F. Pressures 20 to 55 p. s. i. g. Maximum bottoms temperatures 175 F.

Holdup time of' liquids below 1 to 5 minutes Feed plate 3.

The overhead (cut I) stream removed through line 3 from the splitter unit 2 is subjected to relatively low temperature operations for eliminating C4 and lighter hydrocarbons. These relatively low temperature operations may include compression and cooling by means of compressor 4 and heat exchanger 5 in line 3, but finally in the fractionating column 6, the higher boiling residual portion of the cut I stream is separated as a bottoms product substantially free of C4 and lower boiling hydrocarbons. The eliminated C4 and lighter hydrocarbons are removed in the overhead stream line 7 from the column 6.

Column 6 is used purposely to remove the C4 and lighter hydrocarbons under conditions which give very little opportunity for interpolymerization between the reactive C4 unsaturates and the cyclodienes that are to be concentrated in the liquid residue. In general, the conditions of operation in column 6 are as follows:

Vapor overhead temperature 35 F. to 62 Pressures 5 to 20 p. s. i. g.

, Bottoms temperatures F. to 160 F. Holdup time below feed plate 5 to l5 minutes.

The residual bottoms are withdrawn from column 6 through line 8. This residual bottoms portion of the cut I stream should in general have an ASTM distillation range of about 96 F. to 344 F., the high end point being due to the presence of some dimerized cyclodienes. It is interesting to note also that this residual portion of the cut I stream contains relatively small amounts of Cs and higher hydrocarbons other than methyl cyclopentadiene' and the cyclodiene dimers; for example, only about 10 weight percent of such other Cs to C9 hydrocarbons, including about 3 weight percent benzene. Therefore, in this residual portion of cut I, the C5 and C6 cyclodiene monomers are present in suitably higher concentration to undergo dimerization quite readily on being heated to a moderate soaking temperature of about F. to 240 F.'in a period of 12 to 6 hours.

From the splitting unit 2, the residual cut II stream is withdrawn as bottoms through line 9 to be sent into V a relatively higher temperature stripping zone 10. The

present in the cut II stream of C5 to C12 hydrocarbons.v Heat is indicated to be supplied to bottoms of the frac# tionating zone 10 by the heater 11. In this high temperature fractionating zone an incipient depolymerization temperature is desirable. be prolonged and there is nevertheless slight opportunity for interpolymerization between the cyclodienes and ali- Therefore, the holdup time can4 essere phatic unsaturates since the unsaturates in the cut II stream are relatively high molecular weight and less reactive than the aliphatic unsaturates in the aforementioned cut I stream. The desired cyclodiene monomer stream is taken overhead from fractionating zone by line 12. For simplification, the cyclodiene monomer overhead stream from fractionating zone 10 is shown to be joined with the residual portion of the cut'I stream withdrawn by line 8 from fractionating column 6, thence to be subjected to a dimerization in a soaking unitv13, although each of these streams could be separately subjected to dimerizing and later fractionation.

Typical operating conditions for obtaining the Csand Cs cyclodiene monomer bearing distillate from the cut 1I stream of C5 to C12 range, as in the high temperature stripping zone 10 are as follows:

Holdup time of liquid below feed plate--minutes 30-60 The residual liquid bottoms of the fractionating zone will contain hydrocarbons higher than C7, including cyclodiene polymers which did not undergo decomposition.

The soaked liquid products containing substantially all the cyclodienes in the form of dimers and codimers are passed from the soaking unit 13 into a fractionating column by line 16.

The purpose of the fractionating column 15 is to separate the polymers of the cyclodienes, dimers, and codimers, as a residual bottoms concentrate that can be removed through line 17. To obtain this concentrate, the other hydrocarbons are distilled overhead from column 15 and withdrawn through line 18 to the fullest extent possible without incurring loss of the cyclodienes by depolymerization. Therefore, column 15 is operated under such conditions that minimize depolymerization of the cyclodiene polymers while distilling therefrom the other types of C5 through C9 hydrocarbons that are present. In doing this, however, it has been found desirable from a practical viewpoint to leave a restricted amount of such other hydrocarbons with the polymers of the cyclopentadiene. A suitable restricted amount of such other types of hydrocarbons is of the order of l0 to 30 weight percent and mainly such hydrocarbons in the C1 to C9 range. Accordingly, column 15 is operated under the following represented conditions:

The distillation in column 15 is advantageously carried out with introduction of steam by line 19.

v'Ille next phase of the overall operation which will be described pertains to the liquid phase depolymerization treatments and associated fractionation of the cyclopentadiene and methyl cyclopentadiene monomers that are to be recovered as a pure distillate.

The cyclodiene polymer concentrate which is withdrawn as bottoms from column 15 through line 17 is sent to a first stage of the first cracking'or depolymerizing vessel 20. Residual liquid from the high temperature stripper is suiiciently free of cyclodiene dimers and may be removed by line 45.

Vapors evolved from the liquid polymer concentrate in vessel are to be rapidly withdrawn therefrom. The liquid polymer concentrate in vessel 20 has to be maintained at a sufficiently elevated temperature, above 350 F... for accomplishing the depolymerization while the liquid is boiling under a pressure that maintains the cyclodiene polymers in liquid phase, e. g., a moderate pressure of 2 to 20 p. s. i. g. Increased pressures favor the repolymerization of cyclodiene monomers and are, therefore, to be avoided. Accordingly, the vapors taken overhead from vessel 20 should principally comprise the-'Cs and Cs cyclodiene monomers with a minor volume proportion of CvCs hydrocarbons that benecially act as diluents and stripping agents.

The vapors taken overhead from vessel 20 may be passed up through a superimposed retluxing zone but they should be passed quickly by line 26 to the fractionating column 27. Practically all the Cs and Cs cyclodiene monomer vapors are to be carried rapidly with C1 to C9 hydrocarbon vapors to the fractionating column 27.

In fractionating column 27, the vapors from line 26 undergo fractionation on passing upwardly through 5 to 10 plates at temperatures of the order of 175 F. to 160 F. In this fractionation, C7 to C9 hydrocarbons with a small aniount of cyclodiene dimers formed through repolymerization are condensed to liquid which flows to the bottom of column 27. The Cs and Cs cyclodiene monomers in purified form reach the upper plates of fractionating column 27 at temperatures of 150 to 160'I F. and then may be distilled overhead for further fractionation,I or a mixed monomer distillate may be condensed and collected.

Overhead distillate from fractionator 27 may be passed by line 28 into a subsequent fractionator 29, wherein the Ce cyclodiene is condensed and recovered as a bottoms fraction withdrawn by line 30. The cyclopentadiene or C5 cyclodiene monomer vapor is recovered as a distillate as it is passed through overhead line 31, then through cooling condenser 32 and collected in receiver 33. Some reuxing of cyclopentadiene distillate from receiver 33 through line 34 to the upper part of fractionator 29 is helpful inmaking a sharper separation between the individual monomer products. The cyclodiene product is removed by line 35.

The fractionator 29 is operated at temperatures between a bottoms temperature of about 160 F. and a top temperature of about *l F.

The second stage depolymerizing vessel 36 receives residual cyclodiene polymer liquid from vessel 20 through line 37 and is advantageously operated at a higher vdepolymerization temperature. Heat may be supplied to vessel 36"by suitable heating means, e. g. heating coil 38 and a heat exchanger 39 for supplying heat to recycled bottoms condensate from fractionator 27 as this concentrate is returned through line 40 and line 41 to vessel 36.

Control of the liquid recycle from the bottom of fractionator 27 to either

vessel

20 or 36, or to both, is neces,-

sary to prevent accumulation of relatively low-boiling CP1y to C9 hydrocarbons in thes'e vessels. Therefore, to avoid excessive buildup of these relatively lower-boiling hydrocarbons, some of the reux being recycled through line 40 is purged through a withdrawal line 42 or withdrawal line 43 from vessel 36. The cyclodiene monomer vapors 'v are withdrawn overhead as rapidly as possible from vessel 36 and may be passed directly by line 44 to join the stream of vapors in line 26 entering the fractionator 27. The vapors leave the vessel 36 at a temperature of about 350' F. to 380 F. v

The following factors guide the selection of operating conditions during the depolymerizing treatment ofthe cyclodiene polymer'concentrates: i I

(a) The depolymerization of the polymer concentrates is negligible until the temperature of the liquid concentrate is maintained at above 350 F.

(b) The cyclodiene monomers have to be stripped from the liquid concentrate as fast as they are formed with the aid of a limited amount of C7 to Cs hydrocarbons since excessive amounts ofy these intermediate boiling hydrotion zone.

carbons would lower the temperature in the depolymeriza-'- (c) After a substantiah amount of the cyclo-diene--l dimers undergo vdepolymerization in the concentrate, it,

is necessary to increase the depolymerization temperature,

e. g. to above 380 F., to accomplish further depolymerization at a suitable rate.

(d) The monomer bearing vapors being transferred from the depolymerization zones to a fractionation zone have to be substantially free of other close-boiling hydrocarbons, especially other C-C7 hydrocarbons boiling up to about 175 F., so that the separation of these monomers by fractionation can be carried out most expeditiously with quick cooling in order to avoid recombination of the monomers into dimers and higher polymers that havegreater thermal stability than the dimers and make this recovery of the available cyclodienes.

summarized results of continuous two-stage liquid phase depolyrnerization runs on cyclodiene polymer concentrates are given in the following tabulation:

TABLE Continuous two-stage operation FEED: Concentrate of 67.7 weight per cent ilrneriz/.ed cyclo-v dienes with Cq-CU hydrocarbons.

CONDITIONS: Feed charged continuously to two-k for 8-10 hours total residence time. Vapore wor: from each depolymerizing vessel continuously to o of a plate Oldcrshaw column held at 100 I?. c

The data of the table showed quite emphatically that the i temperature required for satisfactory recovery and high purity are substantially above 350 F., preferably in the range of 380 to 410. F. and 390 to 420 F. for the second stage.

The feed used in making the runs shown in the table was a concentrate obtained by first combining a Cs-Cn light cracked naphtha fraction with a Cia-C9 cracked naphtha fraction, dimerizing the combined fractions at 240 F. for 61/2 hours, then fractionating to remove mostly light Cf.' and lower boiling hydrocarbons from the residual concentrate. The operation rate tolerated recycling up to 18 weight of the cracker product fractionator bottoms from column 27 based on the fresh feed.

`Reviewing features of the process described in comparison to other types of processes, the advantages of the presently developed process were determined to be considerable with regard to higher recovery of the monomers with high purity at lower investment cost.

The added amount of cyclodiene polymer in the concentrate from the separately treated low-boiling distillatcs (of C15-C9 range) gave a 50% increase in yield of recovered cyclodiene monomers. accounted for particularly by recovery of cyclopentadiene with methyl cyclopentadi'ene from a large part of their monomers and polymers and partly by repression of interpermitted maintenance of the elevated temperatures in` the depolymerization and reduced the purging, thus making a saving in depolyrnerizing and fractionating equipment and thus lowering the loss of polymers in the purge. i In the stage-wise cracking, the temperature maintained in any stage may be between 350 F. and 450 F., but the temperature should be at least above 380 F. in one stage to obtain eicient depolymerization.

This increase in yield' is- Having described the invention it is claimed aS follows:

from the naphtha a C4 to C9 hydrocarbon cut at temperatures below 175 F., removing C4 hydrocarbons from the C4 to C9 cut at temperatures below 160 F to obtain a remaining C5 to C9 hydrocarbon fraction, soaking said C5 to C9 hydrocarbon fraction at temperatures of about F. to 240 F. until the cylodienes in said fraction are dimerized, fractionally distilling C5 to C9 components from the resulting soaked fraction to obtain the cyclodiene dimers as a concentrate substantially free of C5 and lower-boiling hydrocarbons, passing a high boiling residual portion of said initial cracked naphtha containing C5 to C12 hydrocarbons into a high temperature stripping zone, stripping said residual naphtha fraction of additional C5 to C9 hydrocarbons at temperatures between 240 F. and 410 F., soaking said additional C5 to C9 hydrocarbons at about 150 F. to 240 F. to obtain more of the cyclodiene dimers, passing the cyclodiene dimers into a depolymerization zone in which the cyclodiene dimers undergo depolymerization at temperatures ranging from above 350 F. to about 450' F.,

rapidly removing the resulting cyclodiene monomerv `vapors with higher boiling C'1-C9 hydrocarbons present .and C5 cyclodienes with some higher components in the Cr to C9 range but free of hydrocarbons lower boilingv than the cyclodienes, dimerizing the C5 and C5 cyclodiene monomers present in said C5 to C9 fraction, concentrating resulting C10 to C12 cyclodiene dimers and codimers formed in the C5 to C9 fraction and stripping therefrom C5 to C9 hydrocarbons until the resulting residual concentrate contains 60 to 90% of said dimers and codimers with less than 40% of hydrocarbons in the C7 to C9 range.

3. In recovering C5 and C5 cylodienes from cracked petroleum naphtha, the steps which comprise fractionally distilling at below F. C4 to C9 distillation fraction from the naphtha to form a residual C5 to C12 fraction, stripping additional C5 to C9 hydrocarbons from said residual C5 to C12 fraction at 240 to 410 F., stripping Akin said combined C5 to C9 fractions, concentrating resulting C19 to C12 cyclodiene dimers and codimers formed in said combined C5 to C9 fractions by stripping therefrom C5 to C9 hydrocarbons until a residue of said combined fractions contains 60 to 90% of the C10 to C12 cyclodiene dimers and codimers with less than 40% of hydrocarbons in the C7 to C9 range.

4. In the process defined by claim 3, depolymerizing the C19 to C12 dimers and codimers in said resulting residual concentrate at temperatures in the range ofY '380 F. to 420 F.

References Cited in the lile of this patent UNITED STATES PATENTS 2,508,922 Luten, Jr., et al May 23, 1950 2,511,936 Morrell et al. .Tune 20, 1950 2,636,054 Johnson, Jr Apr. 21, 1953 2,636,055 Jones Apr. 21, 1953 2,636,056 Jones Apr. 21,' 1953 l FOREIGN PATENTS 636,308 Great Britain Apr. 26, 1950

Claims

1. IN RECOVERING C5 AND C4 CYCLODIENES FROM CARCKED PERTOLEUM NAPHTHA, THE STEPS WHICH COMPRISE DISTILLING FROM THE NAPHTHA A X4 TO C5 HYDROCARBONS CUT AT TEMPERATURES BELOW 175* F., REMOVING C4 HYDROCARBONS FROM THE C4 TO C9 CUT AT TEMPERATURE BELOW 160* F. TO OBTAIN A REMAINING C5 TO C9 HYDROCARBON FRACTION, SOAKING SAID C5 TO C9 HYDROCARBON FRACTION AT TEMPERATURES OF ABOUT 150* F. TO 240* F. UNTIL THE CYLODIENES IN SAID FRACTION ARE DIMERIZED, FRACTIONALLY DISTILLING C5 TO C9 COMPONENTS FROM THE RESULTING SOAKED FRACTION TO OBTAIN THE CYCLODIENE DIMERS AS A CONCENTRATE SUBSTANTIALLY FREE OF C6 AND LOWER-BOILING HYDROCARBONS , PASSING A HIGH BOILING RESIDUAL PORTION OF SAID INITIAL CRACKED NAPHTHA CONTAINING C5 TO C12 HYDROCARBONS INTO A HIGH TEMPERATURE STRIPPING ZONE, STRIPPING SAID RESIDUAL NAPHTHA FRACTION OF ADDITIONAL C5 TO C9 HYDROCARBONS AT TEMPERATURES BETWEEN 240* F. AND 410* F., SOAKING SAID ADDITIONAL C5 TO C9 HYDROCARBONS AT ABOUT 150* F. TO 240* F. TO OBTAIN MOSE OF THE CYCLODIENE DIMERS, PASSING THE CYCLODIENE DIMERS INTO A DEPOLYMERIZATION ZONE IN WHICH THE CYCLODIENE DIMERS INTO A DEPOLYMERIZATION AT TEMPERATURES RANGING FROM ABOVE 350* FF. TO ABOUT 450* F., RAPIDLY REMOVING THE RESULTING CYCLODIENE MONOMER CAPORS WITH HIGHER BOILING C7-C9 HYDROCARBONS PRESENT IN SAID CONCENTRATES TO A FRACTIONATION ZONE, AND FRACTIONALLY SEPARATING THE CYCLODIENE MONOMERS.