US2831904A

US2831904A - Depolymerization of dicyclopentadiene

Info

Publication number: US2831904A
Application number: US530758A
Authority: US
Inventors: Robert W F Kreps
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1954-08-31
Filing date: 1955-08-26
Publication date: 1958-04-22
Anticipated expiration: 1975-04-22

Description

April 22, 1958 v R. w. F. KREPS 2,831,904

DEPOLYMERIZATION OF DICYCLOPENTADIENE Filed Aug. 26, 1955 f 14 1 1| PARTIAL DEPOLYMERIZATION RECTIFICATION W 1 CONDENSATION Is SEPARATION l8 km FIG. I

CYGLOPENTADIENE TO IMMEDIATE use 226 DICYCLOPENTADIENE AUXILIARY E F uoum 229 ,23I 2 CYCLOPENTADIENE TO STORAGE 215 ,zu

FIG. II

INVENTOR ROBERT W.F. KREPS BY my MJY HIS ATTORNEY United States Patent DEPOLYMERIZATION OF DICYCLOPENTADIENE Robert W. F. Kreps, Amsterdam, Netherlands, assignor to Shell Development Company, New York, N. Y., a corporation of Delaware Application August 26, 1955, Serial No. 530,758

Claims priority, application Netherlands August 31, 1954 6 Claims. (Cl. 260-666) This invention relates to a process for depolymerizing dicyclopentadiene.

Commercial processes are known for preparing cyclopentadiene from dicyclopentadiene by thermal depolyrnerization. in general, these processes operate by vaporizing the dicyclopentadiene and passing the vapors through a cracking zone at a high temperature. Such processes are plagued by difficulties due to rapid coking in the cracking zone by carbonization of by-products formed in the process. it has also been proposed to depolymerize dicyclopentadiene in the liquid phase by applying heat to a liquid body of dicyclopentadiene and withdrawing the vapors of monomer. Only relatively low monomer yields are obtainable in such processes due to the formation of higher poiymers such as tri-, tetraand penta-cyclopentadiene and the like during the relatively long residence times prevailing.

It is a principal object of the present invention to provide a commercially useful process for producing cyclopentadiene at high yield and in high purity from dicyclopentadiene. Other objects of the present invention will appear from the following description thereof, which will be made with reference to the accompanying drawings wherein:

Fig. I is a simplified schematic presentation of the invention; and

Fig. II is a simplified schematic flow sheet of a preferred mode of practicing the present invention.

It has now been found that cyclopentadiene in high yield and high purity can be obtained from dicyclopentadiene in a continuous process. This is accomplished by adding liquid dicyclopentadiene to a body of liquid comprising essentially an auxiliary liquid having an initial boiling point higher than 250 C. and a narrow boiling range while the temperature of the body of liquid is maintained above 200 C. but below the initial boiling point of the auxiliary liquid and removing vapors of cyclopentadiene from the liquid as rapidly as formed. A bleed stream is preferably withdrawn from the body of liquid and replaced by fresh auxiliary liquid. The additions and removals of these several streams, and the addition of heat are carried out in such a manner that the concentration of mono-plus dicyclopentadiene in the liquid is maintained at less than 10% by weight and preferably less than 5% by weight. The auxiliary liquid employed is preferably a parafiinic hydrocarbon fraction.

In the process of the present invention, the formation of undesirable side products, such as trimer or still higher polymers, is entirely or substantially entirely avoided, and

substantially quantitative yields of monocyclopentadiene may be obtained in substantially pure form. Such small amounts of higher polymers as may form remain dissolved in the auxiliary liquid under the process conditions and can be readily separated from a bleed stream thereof, e. g. by cooling to atmospheric temperature or by distillation.

The auxiliary liquid used may be any liquid which is inert, i. e. non-reactive, with respect to the dimer and monomer of cyclopentadiene and which boils or begins to boil above 250 C. without decomposing. The auxiliary liquid is of such a nature that the concentration of cyclopentadiene dimer plus monomer therein at the reaction conditions may be maintained at less than 10% and preferably lessthan 5% by weight. It has been found that highly paraflinic liquids are very suitable for this purpose. High boiling parattinic hydrocarbons such as pentadecane, hexadecane, octadecane and the like and mixtures of such hydrocarbons are, for example, suitable. It has also been found that some petroleum fractions boiling above 250 C., such as gas oil fractions or spindle oil fractions may be very suitable for this purpose, it being advisable to use fractions which contain low concentrations of aromatics and consist mainly of paraffin hydrocarbons. Such oils are referred to herein as parafiinic hydrocarbon fractions. A high concentration of aromatics in the liquid may make it less suitable. The temperature range within which the boiling point or boiling range of the auxiliary liquid lies is preferably from 250 C. to 350 C. If the auxiliary liquid employed is a petroleum fraction or the like, it is necessary for best results that it have a narrow boiling range. The spread between the initial and final boiling point is preferably within 50 C., and if it is more, at least the spread between the 10% and 90% point should be no more than 50 C.

Auxiliary liquids of the type mentioned will be able to keep any polymer formed in the depolymerization step in solution up to concentration of about 20% by weight at reaction temperature. At atmospheric temperature, solid resins will be precipitated from highly parafiinic oils containing such high concentrations of polymer.

The dicyclopentadiene employed as feed in the present process is preferably of a high degree of purity, e. g. having a dimer content of 95% by weight or more. Technical mixtures of dicyclopentadiene having considerably lower dimer contents, e. g. down to 70% or less, may also be employed. When technical dicyclopentadiene of low dimer content is employed as starting material, the cyclopentadiene produced is less pure and may have to be further purified by rectification. As a result of the high dimerization rate of the monomer this generally entails losses due to polymerization. It is therefore generally desirable to purify the crude dicyclopentadiene before depolymerization, if it is not sufficiently pure. This may be effected, for example, by means of distillation. Depending on the nature of the initial material, this may be effected by removing the low boiling impurities such as benzene and toluene by continuous fractional distillation at atmospheric pressure using a short residence time. A high reflux ratio, e. g. 5-10, is preferably used. Depolymerization during distillation is substantially avoided in this manner. Removal of high boiling components, which frequently may be co-polymers of cyclopentadiene with components which are low boiling in themselves such as C -dienes and methyl cyclopentadiene, may be effected by vacuum fractionation of the starting material or by vacuum flashing thereof. This prevents contamination of the monocyclopentadiene product of the process by low boiling components which would be formed from the co-polymers during the depolymerization step.

In order to obtain the best yield of cyclopentadiene it is important to prevent, as far as possible, therepolymerization of the monomer product to the dimer or higher polymers. This is preferably done by reducing the temperature of the monomer vapors as rapidly as possible to approximately 45 C. and then further chilling the pure monomer obtained at that temperature to a temperature below -10 C., e. g. a temperature in the range between -30 and C. At approximately 40 C. the dimerization of the liquid monomer is at a tolerably low level and at -80 C. it is practically nil. The dimer content of the monomer may thus be limited to a Patented Apr. 22, 1958.

low value even after prolonged storage; for example, the dimer content of cyclopentadiene after 200 hours storage at 20 C. is approximately 9% and after 30 days at -30 is less than 1%. t

The formation of dimer in the monomer product of the present invention can also be avoided by immediately using the vaporous monomer stream for conversion into valuable derivatives of cyclopentadiene. Thus, the gaseous monomer substantially entirely free of dimer may be immediately passed to a reaction zone to be reacted with acetylene, for example, according to the process of British Patent No. 701,211 to form bicyclo-(2,2,l)-2,5- heptadiene, also known as l,4-methano-2,S-cyclohexadiene. The cyclopentadiene may also be converted into hexaehlorocyclopentadiene by reaction with chlorine according to the process of British Patent No. 703,202 or by the prior art methods discussed therein. The above mentioned derivatives of cyclopentadiene are intermediary products in the preparation of the insecticides known as aldn'n and dieldrin. In carrying out the process according to the present invention, the space velocity (i. e. the weight of dimer charged per hour divided by the weight of the body of liquid in the depolymerization zone) may vary within wide limits, e. g. from 0.15 to l or more. Variation between 0.15 and 1 causes no significant change in the process, the tendency being to obtain a slight increase in monomer yield, 6. g. from 1 to 2% at the higher space velocities.

Inorder to prevent an undesirable accumulation in the auxiliary liquid of cyclopentadiene trimer and/or higher polymers and of any other high boiling impurities derived from the dicyclopcntadiene feed it is preferable to Withdraw continually, i. e. continuously or intermittently, a part of the body of liquid from the depolymerization zone and supply a quantity of clean auxiliary liquid equivalent to the amount withdrawn. The amount of bleed stream withdrawn per hour may suitably be in the range between 1% and 30%, by volume, of the body of liquid, depending in part on the rate of polymer formation and on the amount of impurities introduced with the feed. The polymers and other high boiling components in the bleed stream withdrawn may then be separated therefrom and the purified auxiliary liquid recycled to the depolymer zation zone. According to the nature of the auxiliary liquid the separation may be effected, for example, by cooling the bleed stream to atmospheric temperature at which the polymers wholly or mainly precipitate, or by distillation in which the auxiliary liquid may be separated both from low boiling and high boiling impurities.

The depolymerization step of the present invention is carrled out at a temperature above 200 C. Although temperatures as high as SOD-600 C. may be employed in the depolymerization zone, it is not necessary to go to such high temperatures and certain practical inconveniences are associated with them. It is preferred, therefore, to operate at temperatures between 200 and 350 C. and more especially between 250 and 300 C. If the boiling point or boiling range of the auxiliary liquid lies between 250 and 350 C. the temperature in the depolymerization zone must be within 50 C. of the boiling point or initial boiling pointof the auxiliary liquid but must be below the boiling point itself, preferably by'at least 3 to 10 degrees centigrade. By employing temperatures in this critical range, particularly when employing a paraffinic hydrocarbon fraction as auxiliary liquid, and by controlling the rates of addition of dimer and withdrawal of monomer, it is found that the concentration of cyclopentadiene dimer plus monomer in the body of liquid and depolymerization zone can be maintained below 10% by weight and preferably below 5% by weight. By maintaining this condition, the formation of the higher polymers in the depolymerization zone and the consequent loss of cyclopentadiene to waste products is maintained at extremely low values. Temperatures in the depolymerization zone at which the auxiliary liquid begins to boil must be avoided since at such temperatures the dicyclopentadiene introduced is immediately entrained in part with the vapors of the boiling auxiliary liquid and the contact in the liquid phase may become so short that the depolymerization remains incomplete. Operating at the boiling point or initial boiling point of the auxiliary liquid is also very disadvantageous from the point of view of heat economy, since a great deal of heat must then be continuously supplied to maintain the evaporation and additional cooling capacity must be supplied to condense the evaporated auxiliary liquid and dimer for return to the depolymerization zone. Decomposition of the auxiliary liquid may also be an undesirable effect of operating at the boiling point thereof.

A simplified schematic representation of the present invention is shown in Figure I, which illustrates the es sential operating steps of the invention. Dicyclopentadiene feed is charged to the depolymerization zone through line 11. Other streams entering the depolymerization zone, from sources described below, are auxiliary liquid through line 12, liquid reflux through line 14 and rectifier bottoms, essentially dicyclopentadiene, through line 15. Leaving the depolymerization zone are a liquid bleed stream through line 19 and a vapor stream through line 20. The liquid bleed stream enters a separation zone where purified auxiliary liquid is recovered and may be returned to the depolymerization zone through

lines

18 and 12. Provision is made for adding makeup auxiliary liquid through line 16. The material discarded from the separation zone through line 21 will include trimer and heavier polymer and may also include impurities boiling below the initial boiling point of the auxiliary liquid. The vapor stream withdrawn through line 20 is subjected to partial condensation. The preponderant portion of the auxiliary liquid and dicyclopentadiene which was carried along in the vapor stream as vapor or as entrained liquid is condensed and returned to the depolymerization zone through line 14. The resultant vapor stream, which is essentially monocyclopentadiene, passes through line 22 to a rectification step where it is subjected to further concentration by fractional distillation to produce a mono cyclopentadiene of very high purity, generally 98% or better, and preferably 99.5% or better which is withdrawn by line 24. According to the present invention, the product from line 24 is either chilled immediately to a temperature of l0 C. or lower prior to being placed in storage, or it is employed directly as charge stock to processes for the production of derivatives of cyclopentadiene. The stream in line 24 represents the overhead of the fractional distillation. The bottoms of the distillation contain dicyclopentadiene and may include small r amounts of auxiliary liquid and of cyclopentadiene trimer and higher polymers and also methylcyclopentadiene and its polymers. This bottoms stream is withdrawn through line 15 and is preferably returned, at least in part, to the depolymerization zone.

A preferred mode of practicing the present invention will now be described in more detail by means of Figure 11 which is a schematic flow sheet thereof. Essential equipment shown consists of heater A, evaporator B and fractionating column C. Other important equipment shown includes heat exchangers D, E and F, reboiler G, liquid accumulator H, and the appropriate connecting piping.

Heater A may represent a gas fired furnace or other suitable equipment. Evaporator B is essentially a drum with provisions for separate withdrawal of liquid and vapor streams. Fractionator C represents a conventional rectification column such as a bubble-plate or packed column, known to the art. The other equipment shown is also conventional. To simplify the drawing and description, numerous necessary valves, pumps and other associated equipment are not shown. Their placement asap-e04;

will be apparent to anyone skilled in the design or operation of chemical processes.

To place the present process in operation, auxiliary liquid, which may be a highly paraifinic gas oil boiling between 300 and 350 C., is charged through

lines

211 and 212 into evaporator B to establish a liquid level therein. Liquid from evaporator B is then withdrawn through line 213 by a pum not shown, and is circulated through coil 214 of heater A and from there into line 212 and back to the evaporator. This operation is continued until the temperature of the body of liquid in evaporator B is within the range suitable for operation according to the present invention, e. g. approximately 280 C. Evaporator B, together With the circuit of

lines

213, 214, and 212, corresponds to the depolymerization zone of Figure I. Charging of dicyclopentadiene is then begun by adding liquid dicyclopentadiene through line 215 into the circulating stream of hot auxiliary liquid in line 212. The dicyclopentadiene in line 215 may be at any temperature suitable for maintaining it in liquid phase, e. g. at a temperature above about 30.4 C., which is the melting point of pure dicyclopentadiene or even lower, since impurities tend to depress the melting point significantly. The dicyclopentadiene feed stock enters line 215 from a storage tank, not shown, where it is preferably maintained under a dry inert gas blanket to keep out oxygen and moisture, and at a relatively low temperature, e. g. below 40 C. The stability of the dicyclopentadiene feed may be preserved by an addition of a small amount of an oxidation inhibitor such as 0.05% by weight alpha naphthol. The mixture of dicyclopentadiene and auxiliary liquid passes to evaporator B, wherein a substantial body of liquid is maintained. A portion. of the body of liquid continues to circulate through heater A, where sufiicient heat is added to maintain the temperature of the whole body of liquid at the desired temperature. The temperature at the outlet of coil 214 will be higher than that in drum B, e. g. it may be about 295 C. when drum B is at 280 C.

Vapors of monocyclopentadiene are liberated from the body of liquid in drum B and are withdrawn as a vapor stream through line 216. This stream is cooled in heat exchanger D to a temperature, for example, of about 150 C. at which the preponderant part of the auxiliary liquid and dicyclopentadiene, carried along in the vapor stream, are condensed. The cooled stream from heat exchanger D passes through line 218 to accumulator H which may be a simple drum in which liquid is accumulated and withdrawn through line 219 for return to evaporator B while vapor is withdrawn through line 220 and charged to rectification column C. Column C may operate at essentially atmospheric pressure with a top temperature, for example, of approximately 45 C. and bottoms temperature of approximately 110 C. Auxiliary liquid and any dicyclopentadiene entering the column through line 220 pass to the bottom of the column. Any dior poly-cyclopentadiene formed during the fractionation also accumulates in the bottoms. Methylcyclopentadiene, produced when the dimer charged to the process contains methylcyclopentadiene dimer, or codimer with cyclopentadiene, also is accumulated in the fractionator bottoms. If methylcyclopentadiene is present, it will generally be necessary to permit a small amount of cyclopentadiene to be withdrawn with the bottoms.

In the fractionation of cyclopentadiene produced by depolymerization of dicyclopentadiene according to prior art processes, difiiculty is sometimes experienced due to formation of resins in the fractionating column with consequent deposit of the solids and plugging of the column. In the process of the present invention the small amount of vapor of auxiliary liquid which enters the fractionating column along with the cyclopentadiene acts as solvent for any resins which may be found in the lower portion of the fractionating column. By control of the temperature in the evaporator B and condenser D, the amount of cent Carbon in Paraflln Chain, percent..

6 auxiliary liquid entering column C may be controlled to obtain this desirable washing action. Excessive amounts of auxiliary liquid must be avoided since their presence in the bottoms of fractionator C tends to raise the temperature required to be maintained therein for the desired reboiling action.

Liquid bottoms are withdrawn from column C through line .221, part being returned to the fractionator through line 222 containing reboiler G and part being recycled, if desired, to evaporator B through line 224. All or part of the bottoms also may be withdrawn from the system through line 225 instead of being recycled to the evaporator.

Purified monocyclopentadiene, which may be 98% to 99.9% pure, is withdrawn as vapor overhead from column C through line 226. If desired, a part of this stream may be withdrawn through line 228 and charged directly to a process for converting it to cyclopentadiene derivatives, e. g. by reaction with acetylene or with chlorine. At least a portion of the cyclopentadiene vapor from line 226 is passed to line 229 containing reflux condenser E in which it is condensed and cooled to approximately 5 C. The liquid leaving condenser B may be split, part being returned as reflux to column C via line 230 and the remainder being withdrawn, if desired, via line 231 containing chiller F. In chiller F the liquid cyclopentadiene product is further cooled to a temperature below -l0 C. e. g. 40 C. and is then passed to refrigerated storage.

The invention will be further illustrated by means of the following examples. Example I presents the results of a number of runs using various auxiliary liquids at several temperatures of operation and illustrates the significance of maintaining the temperature and concentration of dimer in the depolymerization zone in the specified ranges. Examples II and Ill present typical operations carried out according to the present invention.

EXAMPLE I Table II shows the results of a number of experiments for depolymerizing dicyclopentadiene using various auxiliary liquids boiling above 250 C. at different reaction temperatures. Some inspection data for the several auxiliary liquids are given in Table I. In these experiments technical dicyclopentadiene (98%) was passed into a reaction vessel containing the high-boiling auxiliary liquid which was heated to the required reaction temperature; the monocyclopentadiene formed passed in vapor form through a fractionating column provided on the reaction vessel, and which was provided at the top with a reflux cooler kept at a temperature of 45 C., after which the monomer escaping from the cooler in vapor form was condensed in a cooling vessel kept at C. The liquid hourly space velocities employed in these runs ranging from 0.3 to 0.5, did not significantly aifect the results. The numbers in the column headed .AT represent the diiterence, in degrees Centigrade, between the reaction temperature and the boiling point or initial boiling point of the auxiliary liquid.

Table I Auxiliary Liquid Used Inspections n-hexan-octaheavy spindle decane deeane gas oil oil traction Boiling Point, C./760 mm. Hg 287 317 Boiling Range, ASTM, 0.:

IBP 302 328 403 Sulfur content, percent wt nil nil 1. 79 Carbon in Aromatic Structure,

percent 0 0 -15 -20 Carbon in Naphthene Structure,

per 0 0 -20 -25 The results of the runs with hexadecane and octadecanc as auxiliary liquids clearly show that an increase in the reaction temperature, bringing it closer to the boiling point of the auxiliary liquid, accompanied by a reduction of dimer concentration in the liquid phase, results in an increase in the yield. of cyclopentadiene. it is also illustrated by the operation at 225 C. (AT of 92) and also to considerable extent by the operation at 25 C. (AT of 67) that at such high values of AT the cyclopentadiene recovery is unsatisfactorily low and the dimer concentration in the bottoms liquid is high. A substantial formation of polymer in the bottoms liquid was observed at these conditions. Thus, although the rate of formation of polymer increases with increasing temperature, it is found that by maintaining a relatively high temperature in the depolymerization zone (thus reducing the concentration of the reactants involved) the formation of polymer is reduced and the recovery of monomer is greatly increased.

The relatively low yield of cyclopentadiene in the run employing spindle oil as auxiliary liquid may be attrib uted, at least in part, to the fact that the spindle oil had a relatively wide boiling range and contained a relatively high concentration of non-paraffinic constituents. The amount of polymer (tricyclopentadiene and higher) formed in the liquid phase was as high or higher in this run than in the runs in which the depolymerization was carried out at lower temperatures and the AT exceeded 50C.

EXAMPLE II The starting material was technical dicyclopentadiene (98%) and the auxiliary liquid used was a parafiinic heavy gas oil fraction boiling between 315 C. and 355 C. The apparatus consisted of a heatable 7-liter reaction vessel communicating at the top, via a reflux cooler for condensing dicyclopentadiene and gas oil, with a cooling vessel which was cooled by a mixture of solid CO and acetone and in which the inonocyclopentadiene formed was condensed. Dicyclopentadiene was continuously supplied at a rate of about 0.5 kg. per kg. of liquid phase per hour to the body of liquid in the reaction vessel, the volume of which was kept at 4 liters and the temperature at 275 C. At the same time, also continuously, a small part of the liquid phase was withdrawn from the reaction vessel at a rate of 0.2 liter per hour (5 volume percent of the body of liquid) and replaced by a quantity of fresh auxiliary liquid corresponding to the quantity withdrawn. The experiment was continued for 164 hours, no separation of solid material in the liquid phase or deposits on the heating elements of the reaction vessel occurring at all, and the cyclopentadiene yield (with a purity of 99%), based on dimer supplied, being 96%.

EXAMPLE lll Starting from a technical dicyclopentadiene with a dicyclopentadiene content of approximately 75%, a main fraction with a dicyclopentadicne content of 94.5%, boiling between 88 and 95 C. at 62 to 63 mm. Hg, was separated by vacuum fractionation (at 62 to 63 mm. Hg). This fraction was depolymerized in a manner similar to 8 that indicated in Example II. The bleed rate was 20% by weight in this run. No polymer was found in the auxiliary liquid.

The monocyclopentadiene yield was 99.5%, the composition of this monomer being as follows:

Percent Monocyclopentadiene 96.0 Dicyclopentadiene 1.0 Methylcyclopentadiene 0.4 c C -arornatics 2.6

Depolymerization of the dicyclopentadiene not previously distilled (containing approximately 20% of highboiling components, including cyclopentadiene copolymers) under the same conditions also gave a substantially quantitive yield of monocyclopentadiene. In this case, however, the monomer obtained was more highly contaminated, its composition being as follows:

Percent Monocyclopentadiene 93.2 Dicyclopentadiene 1.4 Methylcyclopentadiene 1.6 C -dienes 0.4 Pentenes 0.5 Benzene 0.6 Toluene 0.5 C C -ar0matics 1.8

I claim as my invention:

1. Process for converting dicyclopentadiene into monocyclopentadiene which comprises maintaining in a depolymerization zone a body of liquid comprising essentially an auxiliary liquid which is a paraffinic hydrocarbon fraction which has an initial boiling point above 250 C. and of which at least boils within a range no greater than about 50 C., lying within the range between 250 C. and about 350 C., adding heat to said body of liquid to maintain it at a temperature in the range between 200 and 350 C. and within 50 C. but below said initial boiling point, continually adding relatively cool liquid dicyclopentadiene to said body of liquid, continuously withdrawing from said zone, as a vapor stream, monocyclopentadiene substantially at the rate at which it is formed, continually withdrawing a small bleed stream from said body of liquid and adding to said body of liquid an amount of fresh auxiliary liquid approximately equivalent to said bleed stream, and by means of said additions and withdrawals maintaining within said body of liquid in said depolymerization zone a concentration of cyclopentadiene dimer plus monomer no greater than 5% by weight, and a concentration of cyclopentadiene polymer no greater than 10% by weight.

2. Process according to claim 1 in which auxiliary liquid is recovered from said bleed stream and returned as at least a portion of said fresh auxiliary liquid.

3. Process according to claim 1 in which said withdrawn vapor stream is rapidly cooled to approximately 40 C. and the monocyclopentadiene then purified by fractional distillation.

4.. Process according to claim 3 in which the purified monocyclopentadiene is condensed and further cooled to a temperature below 10.

5. Process according to claim 1 in which said withdrawn vapor stream of monocyclopentadiene is promptly charged to a reaction zone for conversion to a chemical derivative thereof.

6. Process for converting dicyclopentadiene into monocyclopentadiene which comprises maintaining in an evaporation zone a body of liquid comprising essentially an auxiliary liquid which is a paraffinic hydrocarbon frac tion which has an initial boiling point above 250 C. and of which at least 80% boils within a range no greater than about 50 C. lying within the range between 250 C. and about 350 C., continuously withdrawing a portion of said body of liquid, adding sufiicient heat thereto to maintain said body of liquid at a temperature in the 9 range between 200 C. and 350 C. and within 50 C. but below said initial boiling point, adding liquid dicyclopentadiene to said portion and returning the resulting admixture to siad evaporation zone, continuously Withdrawing from said evaporation zone a vapor stream consisting essentially of monocyclopentadiene, continually withdrawing a portion of said body of liquid as a bleed stream and adding to said body an amount of fresh auxiliary liquid approximately equivalent to said bleed stream, maintaining within said body of liquid a total concentration of cyclopentadiene dimer and monomer no greater than about 5% by weight, submitting said with drawn vapor stream to partial condensation to condense the preponderant part of material heavier than monocyclopentadiene contained therein, returning said condensed portion to said body of liquid, passing the resulting vapor stream to a fractionation zone, withdrawing from 10 said fractionation zone a liquid bottoms stream comprising dicyclopentadiene and auxiliary liquid and with drawing as overhead from said fractionation zone a stream of monocyclopentadiene vapor of high purity.

References Cited in the file of this patent UNITED STATES PATENTS 2,453,044 Stafi Nov. 2, 1948 2,490,866 Gerhart Dec. 13, 1949 2,582,920 Businger et a1. Jan. 15, 1952 2,636,054 Johnson Apr. 21, 1953 2,733,280 Hamner Jan. 31, 1956 FOREIGN PATENTS 612,893 Great Britain Nov. 18, 1948 1,125,666 France July 16, 1956

Claims

1. PROCESS FOR CONVERTING DICYCLOPENTADIENE INTO MONOCYCLOPENTADIENE WHICH COMPRISES MAINTAIN IN A DEPOLYMERIZATION ZONE A BODY OF LIQUID COMPRISING ESSENTIALLY AN AUXILIARY LIQUID WHICH IS A PARAFFINIC HYDROCARBON FRACTION WHICH HAS AN INITIAL BOILING POINT ABOVE 250* C. AND OF WHICH AT LEAST 80% BOILS WITHIN THE RANGE NO GREATER THAN ABOVE 50*C., LYING WITHIN THE RANGE BETWEEN 250*C. AND ABOUT 350*C., ADDING HEAT TO SAID BODY OF LIQUID TO MAINTAIN IT AT TEMPERATURE IN THE RANGE BETWEEN 200*C AND 350*C. AND WITHIN 50*C. BUT BELOW SAID INITIAL COOLING POINT, CONTINUALLY ADDING RELATIVELY COOL LIQUID DICYCLOPENTADIENE TO SAID BODY OF LIQUID, CONTINUOUSLY WITHDRAWING FROM SAID ZONE, AS A VAPOR STREAM MONOCYCLOPENTADIENE SUBSTANTIALLY AT THE RATE AT WHICH IT IS FORMED CONTINUALLY WITHDRAWING A SMALL BLEED STREAM FROM SAID BODY OF LIQUID AND ADDING TO SAID BODY OF LIQUID AN AMOUNT OF FLESH AUXILIARY LIQUID APPROXIMATELY EQUVALENT TO SAID BLEED STREAM, AND BY MEANS OF SAID ADDITIONS AND WITHDRAWALS MAINTAINING WITHIN SAID BODY OF LIQUID IN SAID DEPOLYMERIZATION ZONE A CONCENTRATION OF CYCLOPENTADIENE DIMER PLUS MONOMER NO GREATER THAN 5% BY WEIGHT, AND A CONCENTRATION OF CYCLOPENTADIENE POLYMER NO GREATER THAN 10% BY WEIGHT.