US2768224A

US2768224A - Isoprene concentrates

Info

Publication number: US2768224A
Authority: US
Publication date: 1956-10-23
Anticipated expiration: 1973-10-23

Description

L. B. PAGE ET AL 2,768,224

PROCESS FORSEPARATING PIPERYLENE AND ISOPRENE CONCENTRATES Oct. 23, 1956 Filed Jan. 2, 1955 mh Ezmozoo uzmimmmi 555028 mzmmmofi ll' 1" moh zotoqfi $13 on G L I 2 0 a a m L vw i l' km L T Q mobiotoqmm L 4 LL I 55cm \LEMI m Al. V A N 60.52335 mutwmm BE N5 LVO 1 15.? 55 2 2 mi 13221: nven'tors B3 5% att g United States Patent PROCESS FOR SEPARATING PIPERYLENE ISOPRENE CONCENTRATES Leon B. Page and James W. Rector, Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application January 2, 1953, Serial No. 329,346 3 Claims. (Cl. 260-6815) This invention relates to the treatment of highly cracked hydrocarbon mixtures containing mainly alkenes and dienes in the C4 to C12 range to effect a separation of an isoprene concentrate and of a piperylene concentrate freed of other dienes.

The recovery of the isoprene and piperylene concentrates separately is beneficial for any subsequent purification, such as extractive distillation. By the recovery method of the present invention, wherein a certain sequence of fractionation under selected conditions is used, higher isoprene recovery and improved operability of equipment are obtained. Less opportunity is given for undesired polymerization which fouls equipment; and with lowered fouling better yields are obtained-of the separated dienes as monomers. The method allows an increase in handling capacity of equipment.

The preferred sequence of operation involves the following iour steps:

(1) Heat soaking to dimerize cyclic diolefins (particularly cyclopentadiene).

(2) Fractionation to distill C4C5 from Cs+ components of the heat soaked mixture.

(3) Superfractionation of C4-C5 distillate to remove heavy C5 components (piperylene concentrate) from isoprene and lighter components in the distillate from step (2).

(4) Final fractionation to remove C4 and lighter C5 components from the isoprene concentrate, which is the distillate product from step (3).

The flow plan in the attached drawing illustrates a preferred method of operation.

In the drawing, a high temperature cracked naphtha fraction boiling in the range of 30 F. to 420 F., but which contains a preponderance of C5 and Cs unsaturated and aromatic hydrocarbons, serves as a starting material from an initial zone 1. This feed material is passed by line 2 into the heat soaking vessel 3.

In the heat soaking vessel 3, the naptha fraction is held at temperatures inthe range of 180 F. to 260 F. under a pressure of 120 p. s. i. g. for a number of hours until the cyclic diolefin components are dimerized. The cyclopentadiene, at its usual concentration in the mixture, i. e. about .5 to 2 weight percent, will be 40 to 80% dimerized at temperatures of 220 240 F. in about 8 to 12 hours.

The heat soaked naphtha fraction containing the formed dimers is passed from the soaker 3 by line 4 into an intermediate part of a fractionating column 5 to effect the separation between C5 and lighter components from Cs+ components with the use of moderate temperatures to minimize dimerization or polymerization of other dienes present and to minimize cracking of the dimers formed from the cyclic dienes.

Fractionating column 5 is equipped with a suitable number of fractionating plates, e. g. about 20 to 30. Bottoms of Ce+ components are withdrawn by line 6. A portion of the bottoms is recycled through reboiler 7. Distilled C5 and lighter components are withdrawn overhead through line 8. The overhead is condensed in condenser 9 and a portion is refluxed to the upper part of column 5 by line 10. The remaining portion of the distillate is passed on through line 11 by pump 12 into the next fractionating column 13.

It has been found desirable to operate the first fractionating column 5 at the lowest practical pressures, preferably about 0 to 30 p. s. i. g. This allows the use of low bottoms temperature, 190260 F., minimizing the dimerization of cyclic dienes and also minimizing the cracking of the cyclic dienes formed in the heat soaking step. The overhead vapor temperatures that are suitable are in the range of F. to 170 F.

The intermediate fractionating column 13 is used as a superfractionator to make a split between very closeboiling hydrocarbon components of the distillate from column 5, i. e. to divide between isoprene and heavier components which includes the piperylene. Column 13 is equipped with the necessary fractionating plates, about 50 in number.

The residual liquid or bottom that is to include the piperylene is withdrawn from the bottom part of column 13 by line 14, a portion of this bottom is recycled through the reboiler 15.

The distilled isoprene and lighter components are withdrawn overhead by line 16, and the vapors are condensed in condenser 17. A portion of the distillate is refluxed by line 18 to the upper part of column 13.

By using proper conditions in the superfractionating column 13 a satisfactory separation may be made of iso prene from piperylene. It is advantageous to use a somewhat higher pressure in column 13 than in the first fractionating column 5. In column 13, pressures of the order of 1040 p. s. i. g. are suitable. Under this pressure the bottoms temperature is maintained at about 140 F.-190 F. and the overhead vapor temperature is kept at about F-170 F.

The overhead distillate from column 13 which is not refluxed is passed on by line 19 and pump 20 to an intermediate part of the third fractionating column 21 in which isoprene concentrate is to be collected as a bottoms prodllCt.

Fractionating column 21 is equipped with from 20 to 30 plates. The isoprene concentrate is removed as a bottoms product by line 22 and a portion of this bottoms is recycled through reboiler 23. C4 and light C5 components are distilled overhead through line 24 and condensed in condenser 25. A portion of the distillate is refluxed by line 26 to the upper part of column 21. The remaining C4 and light C5 components are withdrawn through line 27.

In column 21 a pressure in the range of 30-60 p. s. i. g. is used. Under these pressures, the bottoms temperature of column 21 is maintained in the range of 170 to 210 F. and the overhead vapor temperature is maintained in the range of -160 F.

The normal procedure for a series of fractionating steps of this type is to remove progressively heavier overhead cuts. In this case fractionating columns 5, 13, and 21 are operated in such a manner as to remove progressively lighter bottoms cuts. This method of operation has many advantages in the preparation of isoprene and piperylene concentrates. By removing the Ce-lmaterial first at substantially low pressures and temperatures, the fouling of equipment due to the polymerization of dienes is minimized. As the pressure is increased in the subsequent fractionating steps in columns 13 and 21, temperatures below the level at which serious fouling occurs are possible since there are no heavy ends present to raise the bottoms temperature. A further advantage of this method of operation is that the circulation of isoprene and piperylene through the tower reboilers is minimized. This tends to reduce fouling, and it also increases the recovery of these materials by minimizing the formation of isoprene and piperylene dimers and codimers.

The bottoms from the superfiractionator column 13 is a piperylene concentrate having valuable uses as such or may be more easily purified by extractive distillation. In the 3rd column 21 the isoprene concentrate obtained as a bottoms product may contain of the order of 20 to 40 weight percent of isoprene well suited for extractive distillation; for example, using aqueous acetone or other polar solvents like those that are known.

Procedures for purifying the isoprene and piperylene in their respective concentrates by extractive distillation with aqueous acetone or other polar organic solvents are in the U. S. Patents 2,426,705, 2,426,706 of Patterson et al. and John A. Patterson. These patents indicate that there are problems in making a separation between the various C5 hydrocarbons and show that it has been diflicult to keep the isoprene free of higher C5 components when the isoprene concentrate is distilled from a mixture which includes substantial amounts of cyclopentadiene and piperylene.

With the method of the present invention the dimerization of the cyclic diene and elimination of the cyclic diene as a drner should aid in bringing about a more clear cut separaton of isoprene from the higher C5 component in which piperylene is retained.

Based on analyses of a representative feed composition, the following fractionating column conditions and compositions of the product streams obtainable are summarized:

TABLE Typical fractionating tower conditions for stream compositions Splitter Super- Fraction- Tower Conditions Fraction- Fraetionator ator ator Overhead Pressure, p. s. i. g -30 10-40 30-60 Overhead Temp, F 100-170 110-170 130-160 Bottoms Temp., F 190-260 140-190 170-210 Splitter Super- Fraction- Stream Compositions Fraction- Fractionator ator ator Component Feed OH Bot- OH Bot- OH Bottoms toms toms C4 2.0 4 7 25 Isoprene 7. 3 16 22 1 27 Piperylenm. 7. 3 15 1 1 41 1 Other C5S 29. 5 02 1 70 45 74 72 06+ 5 .9 3 98 9 The procedure of the present invention allows recovery of an isoprene concentrate which contains substantially above 20 weight percent isoprene with very little piperylene as compared to the method wherein the isoprene concentrate is distilled from a mixture containing the C5 components including cyclopentadiene and C5+ components. For instance, as shown in U. S. Patent 2,426,705 the isoprene concentrate separated by the latter method did not very easily contain as much as 20 weight percent or more of isoprene and would tend to be contaminated by more than 0.5 weight percent cyclopentadiene.

Although the present method does not require the presence of substantial amounts of C4 components in the initial feed, it can advantageously treat a feed which contains a substantial amount of C4 components.

The described invention is claimed as follows:

1. A process for separating isoprene and piperylene concentrates from a naphtha fraction containing mainly C4 to C12 alkenes, aromatic hydrocarbons, and dienes, which comprises heat soaking under pressure at temperatures of about 180 to 260 F. for a number of hours to form di-rners selectively from cyclic dienes therein, fractionally distilling C4 and C5 components from the heat soaked fraction at about 190 to 260 F. under a pressure of 0 to 30 p. s. i. g. while keeping Cs+ components in the residual part of the heat soaked fraction, increasing pressure of the distilled C4 and C5 components, distilling isoprene and lighter C5 components with C4 components from heavier C5 components containing piperylene under increased pressure in the range of 10 to 20 p. s. i. g. at about to 190 F. further increasing pressure for the distilled isoprene and lighter components, and distilling C4 and C5 components lighter than isoprene from a remaining portion of C components containing the isoprene under an increased pressure of 30 to 60 p. s. i. g. at about to 210 F.

2. A process for separating isoprene and piperylene concentrates from a naphtha fraction containing mainly alkenes, aromatic hydrocarbons, and dienes in the C4 and C12 range, which comprises heat soaking said fraction to selectively dimerize cyclic diene components in said fraction at 180 to 260 F., fractionally distilling C4 and C5 components from the heat soaked fraction heated to a temperature of to 260 F. in a first fractionation zone under a pressure of 0 to 30 p. s. i. g. while keeping Ce+ components with dimers of the cyclic dienes in a residual part of said fraction, passing the C4 and C5 components distilled into a higher pressure second fractionation zone under a pressure of 10 to 40 p. s. i. g., and distitling from said second zone, isoprene with lighter C5 and C4 components while keeping piperylene in a part of the C5 components heated to a temperature of 140 to 190 F.

3. A process for separating isoprene and piperylene concentrates from a naphtha fraction containing a preponderance of C5 and Cs unsaturated and aromatic hydrocarbons boiling in the range of 30 F. to 420 F., said naphtha fraction containing about 0.5 to 2 weight percent cyclopentadiene with isoprene and piperylene, which comprises heat soaking said fraction to a selectively dimerized cyclic diene component therein at 180 to 260 F., fractionally distilling C4 and C5 components from the heat soaked fraction in a first fractionation zone under a pressure of 0 to 30 p. s. i. g. with a bottoms temperature of 190 to 260 F. while keeping aromatic Ce+ components with dimers of the cyclodienes in a bottoms part of said first fractionation zone, passing the C4 and C5 component into a higher pressure second fractionation zone, distilling isoprene with lighter C5 and C4 components under a pressure of 10 to 40 p. s. i. g. with a bottoms temperature of 140 to 190 F. in said second Zone, passing the isoprene with the lighter C5 and C4 components into a higher pressure third fractionation zone, and distilling the C4 and C5 components lighter than isoprene overhead from said third fractionation Zone under a pressure of 30 to 60 p. s. i. g. with a bottoms temperature of 170 to 210 F. to concentrate the isoprene in bottoms of the third fractionation Zone.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. A PROCESS FOR SEPARATING ISOPRENE AND PIPERYLENE CONCENTRATES FROM A NAPHTHA FRACTION CONTAINING MAINLY C4 TO C12 ALKENES, AROMATIC HYDROCARBONS, AND DIENES, WHICH COMPRISES HEAT SOAKING UNDER PRESSURE AT TEMPERATURES OF ABOUT 180* TO 260* F. FOR A NUMBER OF HOURS TO FORM DIMERS SELECTIVELY FROM CYCLIC DIENES THEREIN, FRACTIONALLY DISTILLING C4 AND C5 COMPONENTS FROM THE HEAT SOAKED FRACTION AT ABOUT 190* TO 260* F. UNDER A PRESSURE OF 0 TO 30 P.S.I.G WHILE KEEPING C6+ COMPONENTS IN THE RESIDUAL PART OF THE HEAT SOAKED FRACTION, INCREASING PRESSURE OF THE DISTILLED C4 AND C5 CONPONENTS, DISTILLING ISOPRENE AND LIGHTER C5 COMPONENTS WITH C4 COMPONENTS FROM HEAVIER C5 COMPONENTS CONTAINING PIPERYLENE UNDER INCREASED PRESSURE IN THE RANGE OF 10 TO 20 P.S.I.G. AT ABOUT 140* TO 190* F. FURTHER INCREASING PRESSURE FOR THE DISTILLED ISOPRENE AND LIGHTER COMPONENTS, AND DISTILLING C4 AND C5 COMPONENTS LIGHTER THAN ISOPRENE FROM A REMAINING PORTION OF C5 COMPONENTS CONTAINING THE ISOPRENE UNDER AN INCREASED PRESSURE OF 30 TO 60 P. S. I. G AT ABOUT 170* TO 210* F.