US2913504A - Vapor phase cracking of cyclopentadiene dimer - Google Patents

Description

Nov. 17, 1959 G. o. HILLARD, JR., Erm. 2,913,504

VAPOR PHASE CRCKING 0F' CYCLOPENTDIENE DIMER Filed July 15, 1956 Ov? mv tOhScOU-Elll l t. l

George Oliver Hillard, AJr.

Inventors Leon Clifford Kenyon, Jr.

By Attorney United Aoser-e Patente,

VAPOR PHASE CRACKING F CYCLO- PENTADIENE DllVIER George Oliver Hillard, Jr., and Leon Clifford Kenyon, Jr., Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application `luly 13, 1956, Serial No. 597,662 Claims. (Cl. 26o-666) This invention relates to a process for vapor phase cracking of dimers of C5-C6 cyclodienes under carefully controlled conditions for obtaining a good production of the desired high quality monomers with low coke formation.

In accordance with the present invention it has been demonstrated that successful operation without excessive coking is obtained through control of several factors. One important factor is the cracking temperature throughout the vapor cracking zone and in relation to the quality of the dimer concentrate subjected to cracking. To obtain a desired even temperature, a uniform heat distribution is needed in the cracking furnace. Another factor is the pressure throughout the cracking zone. Other related factors are methods of obtaining a constant ow and prevention of pressure buildup, for which purpose multiple passes are used and preferably a feed relatively free of water is used for the cracking or dedimerization.

It has been known that -vapor phase cracking of the cyclodiene dimers has in the past involved difficulties due to coke formation. The formation of coke in a vapor phase cracking apparatus prevents the use of the apparatus for more than a few hours. Removal of the coke is a dicult and time consuming operation.

The vapor phase cracking processes which have been proposed in the past have generally used relatively high temperatures in the range of 550 to 800 F. without proper control of the temperatures in relation to feed compositions, ow rates, heat distribution or pressure control.

The vapor phase cracking process of the present invention has been operated successfully with single-tower and 2tower recovery systems, such as illustrated, in the flow diagram of the drawing.

Referring to the schematic flow diagram which has been made to illustrate both a single and a 2-tower system, the process starts with preheating of the cyclodiene dimer concentrate passed from feed line 1 by pump 2 into the preheating vessel 3. The cyclodiene dimer concentrate which can be used as a feed should contain at least 70-100% dimer of C5 and C6 cyclodiene and no more than about 30% of higher boiling hydrocarbons, such as C7 cyclodiene dimers and C8-C9 aromatics.

The cyclodiene dimer concentrate feed into the preheater 3 is heated by heat exchange with a heating iluid passed through coil 4 to a temperature in the range of 150 to 300 F. to vaporize the feed partially. The dimer concentrate vapors passed by line 5 from the preheater are divided into separate streams or passes which are to ow through two or more cracking furnace tubes, e.g. tubes 7 and 8, located within the furnace 9. A complete length of each tube pass may be made up of 'interconnected sections mounted in the furnace to obtain uniform heat. The furnace is provided with a sucient number of burners to maintain uniform heat distribution of the tubes. An improved operation was obtained by using 4 premix natural gas burners 10 for each tube pass.

From the parallel passes, such as from the two parallel passes 7 and 8 through the furnace as shown, the cracked vapor products are made to How through lines 11 and 12, then are recombined in line 1 3. The combined vapors are passed through a heat exchange cooler 14 to be cooled to a temperature of 300 F. or in the range of 200 F. to 350 F. before they are introduced into the fractionating tower when utilizing a single tower distillation such as to tower 24 and omittingtower 17.

In the operation of a 2-tower system, the cracked vapors are passed through lines 15 and 16 into the prefractionator tower 17 entering the bottom of the tower without cooling. l v

The prefractionator tower 17 may be equipped with relatively few plates, eg. 8 to 12 plates. The prefractionator v17.serves to separate theC5 and C6 cyclodiene monomers from heavier materials. The C5 and C6 monomer vapors are taken overhead from the tower 17 through line 18, thence through cooling condenser 19 to receiver 20. A portion of the distillate or condensate. in receiver 20 is reuXed by pump 21 and line 22 to the upper part of the tower 17. The remaining portion of the C5-C6 distillate is sent through line 23 to the second tower'l or main fractionator 24. The bottoms fraction of the prefractionator 17 withdrawn through line 2 6. This material may be combined with bottoms from tower 24. and recracked to improve yields. y i

'When the prefractionator is not used and the operation is conducted as a one-tower system, the cooled cracked vapors are passed from the cooler 14 throughline -15 and line 27 to the feed `line 23 of the main fractionator 24.` The feed to tower 24 goes to knockout drum 49 to remove many polymers formed in cracking. The feedto the tower leavesy the drum 49 via line 51. Heavy ends are withdrawn from drum 49 by line 50. Drum 49 is not used vin 2tower operation. Y Fractionator 24 is equipped with about 30 plates and receives the feed at one or more intermediate plates, such as about the 15th plate. For flexibility of control the feed may be passed into the fractionating tower 24 through alternative feed lines 27, 28, or 29. The cyclopentadiene or C5 monomer vapors are fractionated in the tower 24 and taken overhead through line 30, then through cooling condenser 31 into the distillate receiver 32. A portion of the overhead distillate is returned as reux by pump 33 and line 34. The remaining portion of the distillate is passed from receiver 32 ythrough line 35 to the dimerizer tank 36. A pressure controlled gas Vent 37 is connected at the upper part of tank 36; Dimer` is withdrawn from tank 36 through line 38. C6 monomer, i.e. methyl cyclopentadiene, is removed from about the 5th to the 7th plate from the bottom ofthe tower 24 through line 39 to the dimerizer tank 40 which has a pressure controlled gas vent 41 and an outlet for. the dimer through line 42. Bottoms of the' fractionator 24 are withdrawn through liner4 3 and a portion thereof may be removed for purging through, line 440. A remaining portion of the bottoms from tower 24 is passedV through line 44 through tubes 45 and 46 in a heat 'furnace' which serves as a reboilerand which may also serve to recrack a portion of the dimers in the bottoms. The reheated lbottoms is passed through a heatexchanger 47 for further temperature control, thence through line 48 ;back in to abottom, partgofthetower- 24. Drum 49 is of extreme importance to remove heavy polymers formed during cracking. This is a small amount but in early operations, this heavy material terminated operations when reuxed in the vapor inlet line.

As an example of satisfactory monomer product recovery operation, the fractionating tower 24 was operated with the cracked vapors entering at a temperature of 300 F. at the 11th and at the 15th plates. The C5 monomers were taken overhead at a vapor temperature of 100 F.108 F. using a reiiux ratio of 3.5/1, i.e. 3.5 volumes of the distillate being returned as reflux to 1 part per volume which was not returned. The reboiler tubes were heated to give the reboiled bottoms a temperature of 290 F. The C5 monomers were dimerized in the dimerizer by being held at 165 F.180 F. for 12 hours to give about 90% dimerization. The C5 content of the final dimer product averaged about 97% purity and the recovery of monomer was of the order of 50 to 60%.

It was found through test operations that when the quality of the dimer concentrate feed to the cracking furnace tubes was too low, i.e. with a content of more than 30% of C7+ hydrocarbons, coking took place very rapidly and the run limits had to be shortened, making the operation impractical. For practical operation of the furnace the feed to the cracking furnace should contain no less than 70% dimers of C5 and C5 cyclodienes and no more than 30% of heavier components. With this lowest permissible quality the cracking temperatures essentially have to be well below 550 F. for keeping the run over a practical period without coking. With the feeds containing lower amounts of the heavier and contaminated materials, e.g. C7 dimers, C5+ aromatics, the cracking temperatures in the cracking tubes can be lowered to as low as 500 F. for satisfactory cracking over an extended period of time without coking.

For the most successful operations with the feed containing about 80 and 90% dimers of C5-C cyclodienes, the temperatures in each of the tubes were maintained throughout the tubes uniformly in the range of 520 F. to 530 F. with inlet pressures up to 60 p.s.i.g. and outlet pressures of l to 20 p.s.i.g.

Using two separate vapor streams, the feed rate to the preheater was 4.4 gallons per minute continuously and the outlet vapor temperatures of the tubes was maintained at a temperature of 530 F. in a run which lasted over 500 hours. A 95 %l cyclopentadiene purity dimer was produced throughout this run. In test runs where the feed rate was not constant, fluctuations were found to favor coke formation.

Carefully controlled firing rates in the cracking furnace for obtaining even temperature distribution was found to be consequential. For example, in having fewer ame burners there were greater temperature variations in the cracking tubes and these Variations led to more coke formation.

The lower pressure was found to favor less coke formation and longer runs. Thus, it was demonstrated that inlet pressures reduced below 40 p.s.i.g. gave better results of reduced coking.

As already pointed out, improved results were obtained as the quality of the feed was raised by having more than 70% C5 and C5 dimers present with less than 30% of higher boiling components.

The presence of water in the dimer concentrate feed tended to promote coking by increasing pressures. A substantially dry dimer feed gave satisfactory operation. However, from about V10 to 1.0% by weight of water may be present without creating excessive pressures in the cracking tubes.

Example Conditions and results of dimer concentrate vapor phase cracking for large scale production of high purity 4 cyclopentadiene and methyl cyclopentadiene are given as follows:

Feed composition 40 to 88% C5 cyclopentadiene. Feed rate, gallons per minutes 2.4 to 4.4.

Furnace tube outlet temperatures 500 F. to 550 F. Cracking Zone temperature diier- The invention described is claimed as follows:

l. Process for producing high purity cyclopentadiene by vapor phase cracking of crude cyclopentadiene dimer concentrate, which comprises continuously passing a feed of the crude cyclopentadiene dimer concentrate containing essentially at least 70 to 90% cf cyclopentadiene dimer and methyl cyclopentadiene dimer to a preheating and vaporizing zone, vaporizing the feed at a temperature of 150 to 300 F., dividing the vapors into at least two separate streams which ow through separate tubular conduits in a heating and cracking zone, uniform- 1y heating the vapors passed through said heating and cracking zones to maintain a substantially constanttemperature therein within the range of 500 to 550 F.,

maintaining pressures in said heating and cracking zones in a range of 5 to 120 p.s.i.g. and with a pressure drop no greater than p.s.i., passing the cracked vapors lfrom outlets of said heating and outlet tubes to a cooling zone where the vapors are cooled to a temperature of about 300 F., then passing the cooled cracked vapors into a fractionating zone where the C5 and C5 cyclodiene monomers are fractionally distilled from heavier materials.

2. In a process for producing high purity cyclopentadiene by vapor phase cracking a crude concentrate of cyclopentadiene dimer, the improvement which comprises dividing vapors of said concentrate into separate streams and passing said streams through at least 2 separate tubular conduits, heating said conduits uniformly to substantially the same temperatures throughout the lengths in a heating furnace to maintain the vapors of the concentrate passed through sad conduit at similar temperatures in the range of 500 to 550 F., and subsequently fractionating the resulting cracked vapor products to recover cyclopentadiene monomer.

3. ln a process for producing high purity cyclopentadiene by vapor phase cracking of a crude cyclopentadiene dimer concentrate, the improvement which comprises vaporizing said concentrate at a temperature in the range of to 300 F., dividing the vapors of the concentrate into separate continuous vapor streams, passing the separate vapor streams continuously through parallel heating tubes which are uniformly and equally spaced from burner llames which supply heat to said tubes to maintain even similar temperatures of 500-550 F. in each of the separate vapor streams, maintaining pressures in thetubes in the range of 5 to 120 p.s.i.g., and subsequently fractionating the resulting cracked vapors removed from each of the heated tubes.

4. ln a process for producing high purity cyclopentadiene and methyl cyclopentadieneby vapor phase cracking of a crude concentrate containing their dimers, the improvement which comprises vaporizing said concentrate, dividing vapors of said concentrate containing less than 30 wt. percent of C7 and higher hydrocarbon components into at least two continuous streams, passing said streams through separate parallel tubular conduits with less than 1.0% by weight of water vapor in the hydrocarbon vapor streams, controlling the rate of flow and the heating ofthe vapors in each of said conduits to maintain even similar temperatures of about 500 to 550 F. in each of the vapor streams, maintaining pressures on the vapors being cracked in said conduit at less than 120 p.s.i.g., subsequently cooling the cracked vapor streams from said conduit and fractionating the cracked vapors to separate fractional distillates of cyclopentadiene monomer and methyl cyclopentadiene monomer.

5. In a process yfor producing high purity cyclopentadiene by vapor phase cracking of a crude concentrate of cyclopentadiene dimer, the improvement which comprises adjusting the temperature in a heating and cracking zone according to the concentration of cyclopentadiene and methyl cyclopentadiene in the incoming feed, said temperature varying in the range of 500-550 F. with the highest temperature in said range for feeds of about 70% C5-C6 cyclodiene concentration, and the lowest temperature in said range for feeds of 90% or greater C5-C5 cyclodiene concentration and keeping this temperature within narrow limits by dividing the feed stream which has been previously vaporized at a temperature of 150 to 300 F. into separate streams and passing the separate streams through said heating and cracking zone wherein evenly distributed heating is provided for each and all of the separate streams.

References Cited in the le of this patent UNITED STATES PATENTS 1,756,407 Vobach et al. Apr. 29, 1930 2,511,936AK Morrell etal June 20, 1950 2,636,056 lJones Apr. 21, 1953 2,733,280 Hamner Jan. 31, 1956 2,735,875 Hubbard et al Feb. 21, 1956 2,801,270 Nelson et al July 30, 1957

Claims (1)

1. PROCESS FOR PRODUCING HIGH PURITY CYCLOPENTADIENE BY VAPOR PHASE CRACKING OF CRUDE CYCLOPENTADIENE DINNER CONCENTRATE, WHICH COMPRISES CONTINUOUSLY PASSING A FEED OF THE CRUDE CYCLOPENTADIENE DIMER CONCENTRATE CONTAINING ESSENTIALLY AT LEAST 70 TO 90% OIF CYCLOPENTADIENE DIMER AND METHYL CYCLOPENTADIENE DIMER TO A PREHEATING AND VAPORIZING ZONE, VAPORIZING THE FEED AT A TEMPERATURE OF 150* TO 300*F., DIVIDING THE VAPORS INTO AT LEAST TWO SEPARATE STREAMS WHICH FLOW THROUGH SEPARATE TUBULAR CONDUITS IN A HEATING AND CRACKING ZONE, UNIFORMLY HEATING THE VAPORS PASSED THROUGH SAID HEATING AND CRACKING ZONES TO MAINTAIN A SUBSTANTIALLY CONSTANT TEMPERATURE THEREIN WITHIN THE RANGE OF 500* TO 550*F., MAINTAINING PRESSURES IN SAID HEATING AND CRACKING ZONES IN A RANGE OF 5 TO 120 P.S.I.G. AND WITH A PRESSURE DROP NO GREATER THAN 105 P.S.I., PASSING THE CRACKED VAPORS FROM OUTLETS OF SAID HEATING AND OUTLET TUBES TO A COOLING

Images