US2801270A - Recovery of cyclodienes with vapor phase cracking - Google Patents

Description

y 1957 J. F. NELSON ET AL 2,801,270

RECOVERY OF CYLODIENES WITH VAPOR PHASE CRACKING Filed Nov. 16. 1953 a: to

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"@251 M fv vLi P H JOSE H FJIELSQ mason w. HUBBARD 0r ATM/HIE) United States Patent C) RECOVERY OF CYCLODIENES WITH VAPOR PHASE CRACKKNG Joseph F. Nelson and Fred W. Banes, Westfield, and Addison W. Hubbard, Cranford, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware Application November 16,1953, Serial No. 392,322

4 Claims. (Cl. 260-666) This invention relates to a process for recovering high purity cyclopentadiene and methyl cyclopentadiene from crude concentrates of their dimers, codimers, trimers, and cotrimers, subjected to a vapor phase cracking. The vapor phase cracking is made more eflicient by including a continuous undercutting step for removing certain high-boiling ends between a tubular preheater of the feed and the cracking tube. Preheating of the crude dimers, codimers and higher polymers in a continuous stream partly maintained in liquid phase followed by continuous removal of the heavier liquid ends of the preheat feed brings about a significant reduction in coking of the cracking tube.

Vapor phase cracking of the cyclodiene dimers and higher polymers can give higher conversions to the monomers as compared to liquid phase cracking, but a serious problem associated with vapor phase cracking is the coking of the cracking tube. It is known that in the past some proposed processes have dealt with vapor phase cracking of a very narrow boiling range cyclopentadiene dimer fraction substantially free of other cyclopentadiene polymers. It has been indicated that for such vapor phase cracking large amounts of gaseous diluents or other measures should be employed to prevent undesired forrnation of coke and/or high polymer resins. Such measures described in the past have not been found suitable for a process of recovering both cyclopentadiene monomer and methylcyclopentadiene monomer from a crude mixed dimer and polymer stream. For one thing, the use of a large amount of gaseous diluent can be upsetting to the recovery of the separate monomers. Also difliculties arise in making a suitable separation of heavy ends between a feed preheater and a cracking tube if gaseous diluents are used improperly.

The technique of the present invention is designed to minimize coking of the cracking tube while obtaining improved recovery of both high purity cyclopentadiene and methyl cyclopentadiene. It has been demonstrated to be efiicient without the use of any gaseous diluent.

The invention will be described by reference to the flow diagram in the drawing. Here the crude feed of cyclodiene dimer and polymers is supplied by line 1 to the preheater 2 surrounded by suitable heating medium as in furnace 3. A high boiling recycle fraction is admixed through line 4 with the feed entering the preheating tube 2.

The preheating tube 2 operates with an outlet temperature of about 250 to 300 F. and with pressures of about 1 to 30 p. s. i. a. maintained therein. Using a liquid feed rate of 15 to 50 volumes per unit vaporizer volume per hour the feed may be almost completely "ice vaporized on leaving the outlet of the preheating tube 2. Since there is always some liquid flow in this preheating or vaporizing tube and since temperatures are below 300 C., no coking occurs while an appreciable 5 amount of cracking of dimer takes place therein.

The preheated liquid and vapor mixture is discharged from the outlet of the preheater tube 2 to line 5 into the flash drum 6. The drum 6 acts as a bottoms knockout to continuously remove heavy ends boiling mainly above about 275 C. to 280 C. while vaporized and partially cracked products are separated, e. g., withdrawn overhead by line 7. The bottoms are continuously withdrawn through line 8 from drum 6. Bailles, 9, provided in the upper part of drum 6 help to knock out entrained heavy ends which are to be prevented from entering the cracking tube or coils, 10, with the vapors sent therethrough through line 7.

The cracking tube 10 is heated by surrounding heating gases or heating means as in furnace 11.

In the cracking tube 10, the cracking of the dimers, codimers, trimers and cotrimers of the C5Ce cyclodienes is completed at temperatures of 350 to 450 C. in contact times of 0.5 to 3.5 seconds. To obtain short contact time a vapor velocity in the range of 200 to 300 feet per second is used. With the refractory type high boiling polymers absent, coking difliculties are substantially reduced in the cracking tube.

If any gaseous diluent is to be added, e. g., steam or inert hydrocarbon gas, it would be introduced into the flash drum 6 through inlet 12. The introduction of the diluent means a decrease in capacity with a unit designed to operate without the use of a diluent.

The cracking tube effluent in passed from an outlet of the cracking tube 10 through a heat exchange cooler 13 by line 14 into an intermediate part of a splitter tower 15. The splitter tower 15 is a fractionating means for removing cyclopentadiene and methyl cyclopentadiene monomers continuously as an overhead vapor stream and continuously removing dimers and higher polymers as a bottoms. The overhead vapor stream is taken off from tower 15 through line 16. The bottoms are withdrawn from tower 15 through line 17. A portion of the bottoms may be recycled through line 18 and reboiler 19 to a bottom part of the tower 15. Another portion of the bottoms may be purged from the system through line 20. Any desired portion of the bottoms may be passed through line 21 into the recycle line 22 for return to the preheater feed line 1.

The splitter tower 15, equipped with about 10 to 15 plates for fractionation is operated at an overhead temperature of about 50-60 C. using reflux ratio of from 1:1 to 5:1. The overhead monomer vapors may be cooled in condenser 23 in being passed to the receiver 24. Reflux is returned to the upper part of tower 15 through line 25. Distillate of the monomer is passed from receiver 24 through line 26 into the next fractionating column 27.

If steam distillate has been used in the cracking tube water condensate would have to be withdrawn through line 28. Any gaseous diluent would be removed from receiver 24 by vent line 29. A suitable bottoms temperature in the splitter tower 15 is of the order of to C. An intermediate fraction of C7-C9 hydrocarbons, such as would include C7 cyclodienes, is advantageously purged as a side stream 30 below the feed splitter tower 15 supplied to the next tower 27 should be principally C5 and Cs cyclodienes. Some dimerization and further polymerization takes place in the splitter tower 15 to yield the bottoms which may be recycled to the preheater coil 2.

Column 27 which is used for separating the C5 and Ca cyclodiene monomers may be fed at a midpoint with the mixture of the monomers and may be provided with about 30 plates. In column 27 the overhead product is taken oif at a vapor temperature of about 40 to 43 C. at a reflux ratio of 2:1 to 5:1. Generallyit is preferable for this overhead product to be a high purity cyclopentadiene monomer.

The methyl cyclopentadiene product is advantageously taken 011 as a side stream from a lower part of the column 27, below the feed inlet, e. g., at about the 5th plate from the bottom and at a temperature of about 73 -80 C. In column 27, additional dimerization and polymerization occurs to yield a bottoms product.

The bottoms is withdrawn from column 27 through line 36. A portion of the bottoms may be recycled through reboiler 37 and line 38. Any portion of the bottoms from column 27 which will not be recracked may be purged through purge line 39. The portion of the bottoms from column 27 to be recracked may be recycled by way of line 22 and line 4 to the inlet of the preheater coil 2. A mixed purged stream may be removed from the system through line 41. Some purging is desirable to prevent the buildup of high boiling polymers and other fill in the recycle streams. Ordinarily, it is desirable to hold the recycle rate in the range of from /2 to 5 halves of the fresh feed.

The general kind of crude feed for which the present process is adapted is one which will contain about 35 to 45% cyclopentadiene (CPD) in the form of dimer and codimers, 30 to 35% methyl cyclopentadiene (MCPD) in the form of dimer and codimers and contain in the remaining 35 to 20%, C7 cyclodienes and acylic dienes as dimers and codimers, and some aromatics and higher polymers. It will have an initial boiling point of about 135 C. and contain 9 4-98 volume percent boiling up to about 280 C. and from 2 to 6 volume percent boiling higher than about 280 C. A more detailed analysis of a representative fresh feed is shown in the following Table I.

TABLE I Analysis of fresh feed [Vacuum Dlst.]

Boiling Wt. Wt. Percent of Total in Fraction Out No. Range, Percent C. at 1 on Atmos. Feed CPD MCPD 134-157 12. 51 4. 5 3. 9 157-170 4. 27 5. 3 1. 170-171 11. 12 20. 9 3. 5 CPD Dimer. 171-175 11. 22 21. 7 5. 7 175-184 10. 56 15.1 11.5 CPD-MCPD 184-187 11. 24 12. 16. 7 Oodimer. 187-193 10. 50 10. 17. 2 193-199 10.33 4.3 20. 9 MCPD Dimer 199-209 9. 49 3. 4 13. 2 209-280 3. 26 2. 1 5.0

Residue 5. 50 0. 2 0. 7

The total feed in this case contained 36.1 wt. percent CPD and.36.8 wt. percent MCPD. These data, as well as those from which the figures in Table I were derived, were obtained by cracking the feed or fractions thereof at 400 F. The monomer products thus formed were then subjected to mass spectrometer analyses.

Another sample of feed was cracked at 400 Fraud analyzed for total CPD and MCPD in the manner described above. A sample of this same feed was'then analyzed directly in the mass spectrometer to determine the quantities of dimers and codimers. These data are given in Table II.

4 TABLE II Analysis of fresh feed Mass Wt. percent on No. Total Feed Cyclopentadiene (as monomer) 66 37. 5 CPD Combined in Feed as OPD D1mer 132 21.0 OPD Combined in Feed as CPD-MCPD Codimers 146 14. 4 lllethylcyclopentadicne (as Monomer) 80 33.9 MCPD Combined in Feed as MCPD Dimer 160 12. 7 MCPD Combined in Feed as MCPD-CPD Codimer 146 17. 4

Wt. percent of CPD as:

CPD Dlmer CPD-MCPD Ood Wt. percent of MCPD as:

MCPD Dimer MCPD-CPD Codimers ing feed boiling as high as 195 C. or higher. If methylcyclopentadiene is also to be recovered the feed endpoint is 210 C. or preferably 275 280 C.

EXAMPLE 1 When using the feed described in Table I and operating the preheating or vaporizing tube with an outlet temperature of 225 C. then undercutting the preheater effluent in a knockout or flash drum, a purge stream of heavy material representing 2 volume percent of the feed was continuously removed as bottoms. When this heavy purge material was subjectedto cracking at 425 C. there was recovered only 12% of cyclopentadiene and methyl cyclopentadiene monomers based on the amount of purge stream and' at the same time there was considerable coke formation in the cracking tube. In comparison thereto the material which is vaporized at up to 280 C. and thus removed from the knockout drum is easily cracked completely at 400 C. leaving no coke residue.

EXAMPLE 2 A fraction of the feed described in Table II, containing 37.5 wt. percent CPD and 33.9 wt. percent MCPD as dimers and codimers, was cut to have a boiling range of about 270 to 276 C. so as to contain cyclopentadiene trimer. This material was easily cracked at 400C. at 1.5 seconds contact time with relatively little coke formation. The recovered cyclopentadiene monomers represented 97% of the theoretical yield. In contrast, cracking materials including tetramers of the cyclodienes boiling above 280 C. gave very low yields of the C5-C5 cyclodiene monomers and caused excessive coke formation. This indicates the refractory nature of the components boiling above the range of the C5 to Ca cyclodiene trimers, i. e., boiling above 280 C.

' EXAMPLE 3 A concentrate of cyclodiene dimers, codimers and higher boiling components, yielding 42.2% cyclopentadiene, 34.4% methyl cyclopentadiene with 5% of C7 cyclopentadienes, C5 acyclic dienes, and 14% of other hydrocarbons including aromatic, olefins and high boiling polymers, was used in a series of vapor phase cracking experiments. The overall feed boiled in the range of 135 to above 280 C., volume percent distilling oif at about 280 C. The feed was cracked at 400 C. in 1.5 seconds contact time at a vapor velocity of 2.5 per second. The total run length was 15-20 hours.

After each run the cracking tube was washed thoroughly with a light hydrocarbon to remove any soluble residue and the remaining insoluble residue deposited on the tubes was burned out at 1100 F. by passing air through the tube. The combustion gases were caught in a conventional Drierite-Ascarite type train to determine the amount of Water the carbon dioxide evolved. These gas evolutions were used to estimate the quantities of coke deposit in the cracking tube. Data illustrating the advantages of continuously undercutting the cracking feed to prevent material boiling above 280 C. from entering the cracking tube is shown in the following table:

Table III Relation of coke deposits to feeds Wt. Per- Wt. Percent uncent Coke deroutting Deposition on Total based on It is evident from data such as shown in Table II that continuous removal of high boiling refractory bottoms from fresh and recycle feed is necessary. It is also necessary to remove a certain amount of the fresh feed or mixed feeds by undercutting to prevent high boiling materials boiling about 280 C. from entering the cracking tube. Thus it can be seen that it is desirable to have any recycle which is to be admixed with the fresh feed pass through the preheater or vaporizer to be subjected to the similar undercutting.

Examination of the cracking tube before burn out showed that coke tended to be deposited at the entrance of the high temperature cracking tube when heavy ends boiling above 280 C. were permitted to enter the cracking tube and these deposited residues were the chief source of coke.

Having described the invention it is claimed as follows:

1. A process of recovering Cs and Cs cyclodiene monomers which comprises preheating in a continuous stream a crude condensate containing cyclodiene dimers, codimers, trimers and cotrimers, boiling in the range of about 135 to 280 C. and a minor amount of higher boiling components boiling above about 280 C., said higher boiling components containing cyclodiene tetramers which when subjected to vapor phase cracking form coke, preheating said condensate to vaporize the dimer, codimer and trimer components, boiling up to about 280 C., maintaining said higher boiling components including the cyclodiene tetramers in liquid phase, separating the vaporized arated from the remaining vapors of said stream, and subjecting said remaining vapors in continuous stream of restricted cross section to the vapor phase cracking.

3. In the recovery of C5 and Cs cyclodienes as monomers from a crude mixture of their dimers, codimers, trimers, cotrimers and higher polymers, preheating said mixture to vaporize components boiling up to 280 C., separating components thereof boiling above 280 C. including said higher polymers as liquids, vapor phase cracking the separated vapor components kept free of said components boiling above 280 C. in a continuous stream, cooling the vapor phase cracked vapor components and introducing them into a first fractionation zone, separating an overhead distillate of cyclopentadiene and methyl cyclopentadiene from said first fractionation zone, removing a side stream of C7 to C9 components in a lower part of said first fractionation zone below its feed point, and withdrawing a liquid dimer containing fraction from a bottom part of first fractionation zone, passing the overhead distillate from said first fractionation zone into an intermediate part of a second fractionation zone, distilling overhead from said fractionation zone cyclopentadiene monomer, withdrawing a side stream of methyl cyclopentadiene monomer between the bottom and the feed inlet of said second fractionation zone and withdrawing dimer containing liquid bottoms from a bottom part of said second fractionation zone, and recycling dimer-containing bottoms fractions from said fractionation zone to the preheating zone.

4. In the process of claim 3, supplying an inert lower boiling diluent to the vapors passed through said vapor phase cracking zone, and separating said diluent from the overhead distillate of the first fractionation zone before the hydrocarbon distillate containing cyclopentadiene and methyl cyclopentadiene is supplied to said second fractionation zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,240,160 Kaplan Apr. 29, 1941 2,535,418 Holland Dec. 26, 1950 2,582,920 Businger et al Jan. 15, 1952

Claims (1)

1. A PROCESS OF RECOVERING C5 AND C6 CYCLODIENE MONOMERS WHICH COMPRISES PREHEATING IN A CONTINUOUS STREAM A CRUDE CONDENSATE CONTAINING CYCLODIENE DIMERS, CODIMERS, TRIMERS AND COTRIMERS, BOILING IN THE RANGE OF ABOUT 135* TO 280*C. AND A MINOR AMOUNT OF HIGHER BOILING COMPONENTS BOILING ABOVE ABOUT 280*C., SAID HIGHER BOILING COMPONENTS CONTAINING CYCLODIENE TETRAMERS WHICH WHEN SUBJECTED TO VAPOR PHASE CRACKING FORM COKE, PREHEATING SAID CONDENSATE TO VAPORIZE THE DIMER CODIMER AND TRIMER COMPONENTS, BOILING UP TO ABOUT 280*C., MAINTAINING SAID HIGHER BOILING COMPONENTS INCLUDING THE CYCLODIENE TETRAMERS IN LIQUID PHASE, SEPARATING THE VAPORIZED COMPONENTS WHICH BOIL IN THE RANGE OF 135* TO 280*C. FROM THE LIQUID PHASE AND SUBJECTING TO VAPOR PHASE CRACKING SAID VAPORIZED COMPONENTS FREE OF COMPONENTS HIGHER BOILING THAN 280*C. INCLUDING CYCLODIENE TETRAMERS AT TEMPERATURES IN THE RANGE OF ABOUT 350* TO 450*C.

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