US3000987A - Hydrocarbon conversion process - Google Patents

Description

3 000 987 HYDROCARBON Cl IVERSION PROCESS Milton M. Wald, Walnut Creek, Califi, assignor to Shell Oil Company, New'York Nya a corporation of Delaware N0 Drawing. Filed Dec. 21, 1959, Ser. No. 860,722 6 Claims. Cl. 260- 6735) This invention relates to the catalytic conversion of certain olefins to aromatic compounds. More particularly, it relates to a catalytic dehydroisomerization designed to convert specific olefins to particular aromatic species with much greater selectivity than other processes.

The production and recovery of aromatic hydrocarbons from non-aromatic hydrocarbons has been and is a continuing object or" much research anddevelopment and various methods, including catalytic reforming, have been utilized for the purpose. Iodine has been utilized in stoichiometric amounts for the dehydrocyclization of aliphatic compounds into aromatic compounds. This reaction, however, requires large inventories o-f iodine, which is both expensive and hazardous, particularly when required to be handled in large amounts, and also necessitates the regeneration of the stoichiometric amounts of iodine.-

It is an object of the present invention to provide an improved process for the conversion of certain non-aromatic hydrocarbons, particularly certain olefins to aromatic hydrocarbons. It is a further object of the invention to provide an improved process for the conversion of certain olefins to aromatic hydrocarbons utilizing only catalytic amounts of iodine for this purpose. Other objects and advantages of this invention will be apparent to one skilled in the art from the description of the invention.

Now, in accordance with the present invention, an iodine-catalyzed process is provided for converting certain aliphatic olefinic (alkene) hydrocarbons, including aryl substituted alkenes having from 7 to 18 carbon atoms per molecule into aromatic hydrocarbons. The olefins are further defined as being olefinic aliphatic hydrocarbons which contain a chain of at least 4 carbon atoms and in which (1) the total number of carbon atomsin the chain plus (2) the number of quaternary carbon atoms in the chain is at least 6 and the longest chain contains no more than contiguous non-quaternary carbon atoms.

The process comprises contacting the olefinic hydrocarbons in vapor phase with a catalytic amount, 0.5-2.5 mole percent, of vaporous iodine, based on the total olefinic hydrocarbon present, at a temperature in the range of about 400 to about 550 C., at a pressure in the range of from about less than atmospheric to about 250 p.s.i.g. fora time in the range of from 15 seconds to about 10 minutes. The reaction zone may be provided by a conventional furnace containing coils of tubing or nited States Patent 0 Patented Sept. 19, 1961 ice An important condition of the present process is therelatively low pressure at which the reaction must be conducted as compared with the pressures which may be utilized when stoichiometric amounts of iodine are employed. As data hereinafter show, it is necessary to maintain the pressure no higher than about 250 p.s.i.a.-

in order to prevent excessive coke and heavy liquid productformation. Preferably, the pressure is maintained I below about 100 p.s.i.a., optimum results being obtained between about 0 and 75 pounds.

The time of reaction is normally longer than that re-' stantial extent the range of hydrocarbons which will ocour in the product. It is advisable to maintain the temperature at from about 450 to about 550 C. in order to achieve maximum selectivity of production of aromatic hydrocarbons from the corresponding olefins. Intermediate temperatures promote the formation of branched paraffin hydrocarbons besides the aromatic hydrocarbons, both of which will have essentially the same carbon atom content per molecule as the feed olefins employed.

The feed hydrocarbons may comprise olefins preferably having from 7 to 18 carbon atoms per molecule of which all but 2 of the hydrogen substituents may be replaced, if desired, with alkyl or aryl radicals. Moreover, the olefin should contain a chain of at least 4 carbon atoms and the total number of carbon atoms in the chain plus the number of quaternary carbon atoms in the chain should be at least 6, the longest chain containing no more than 5 contiguous non-quaternary carbon atoms. It is possible by this means to synthesize aromatics starting with the corresponding appropriate olefin. Diisobutylene may be employed to synthesize para-xylene while diphenyl hexenes may be employed to produce terphenyls. Monophenyl hexenes may be utilized for the production of biphenyl. Other suitable hydrocarbons include 3,3-

I dimethyl pentene and 2,2,5-trimethyl hexene.

any other suitable heat exchange apparatus, designed for .At the lower temperatures recited above, namely, be

tween about 400 and 450 0, highly desirable branched;

paratlins also are formed as major components of the reaction product. Thus, firom the reaction of diisobutylene at temperatures in the order of 400 C. in the pres-, ence of 12% by weight of iodine catalyst, at major reaction product is isooctane, 2,2,4-trimethyl pentane, a highly desirable gasoline component utilized for improving the octane rating of gasolines.

The precise course of the catlytic reaction is not clearly defined at present. However, for the purpose of understanding, it may be tentatively postulated that the overall reactions are as follows, utilizing diisobutylene as an example:

CH3 CH: /CH: 4 /GCH=CCH3 +3 C-C'-H:CH

CH; CH: CHa CH5 CH3 CH3 By the above reaction it will be seen that diisobutylene is converted at temperatures in the order of 400-450 C. into a theoretical yield of 25% para-xylene and a 75% yield of isooctane. When the higher temperatures are employed, namely, between about 450 and 550 C., diisobutylene is converted into a 40% theoretical yield of para-Xylene and a 60% theoretical yield of the less desirable isobutane according to the following equation:

om (B) The isobutane may be dehydrogenated to isobutylene which may be dimerized and recycled to the aromatization step, so that essentially 100% conversion to aromatic is finally obtained on a recycle basis. Of course, these theoretical yields are not completely attained in .praotice but are approached to an economic extent, as will be seen by the data given in the tables hereinafter. Still greater yields of the desired products may be obtained by the use of hydrogen acceptors which may be cracking products obtained in the cracking of the olefins present as the feed material or may be added low molecular weight olefins ranging from 2 to carbon atoms per molecule, such as ethylene, propylene, butylenes and amylenes. Under these conditions the theoretical production of the aromatic compound is 100% according to the following equation:

As mentioned before, diphenyl hexene may be used to produce terphenyls. Thus, Z-phenyl propene dimer gives rise to terphenyl and its iodine catalyzed conversion in the presence of excess ethylene may be represented by the equation:

CHa

/C-CH=CCH3+3 C2H4 CH3 Phenyl Phenyl The 2,4-diphenyl-4-methyl pentene-l is believed to isomerize to the pentene-Z isomer in its conversion to terphenyl.

The iodine utilized as catalyst in this process may comprise iodine itself or hydrogen iodide as well as the alkyl iodides normally produced in the process. It is preferable to utilize the by-product alkyl iodides as the iodine source. Mixtures of these sources of reactant iodine may be employed if desired.

The chief object of the invention is the production of aromatic hydrocarbons and/ or branched paraflins having essentially the same number of carbon atoms as the feed hydrocarbon while at the same time minimizing cracking and also prevention of the formation of undue amounts of high boiling liquid products.

The present process has several important economic advantages over the stoichiometric reaction of iodine with hydrocarbons. Primarily it eliminates the need for handling large quantities of iodine, thus reducing the loss of expensive iodine and eliminating the necessity for an external regeneration unit to convert hydrogen iodide back to iodine. Also in the catalytic process the small amount of hydrogen iodide formed can be allowed to add to the excess olefin present and the alkyl iodide thus formed recycled for its iodine equivalent. Furthermore, the simultaneous conversion of a portion of the diisobutylene to isooctane (in a preferred embodiment of the process) represents an upgrading in those locations where diisobutylene is being used as a gasoline component.

The process of the invention is illustrated by the data contained in the following table utilizing diisobutylene as the feed hydrocarbon and isopropyl iodide as the source of iodine. It will be seen according to Table I that the temperature varied from 400 to 525 C., the pressure was held constant at a maximum of 75 pounds per square inch gauge and reaction times from /2 minute to 5.3 minutes were utilized.

TABLE I Dehydroisomerizatz'on of diisobutylene-efiect of temperature FLOW EXPERIMENTS .400 500 525 Pressure, p.s'.i.g. 75 75 75 Residence Time, min 5. 3 1.0 O. 5 Feed, moles:

Diisobutylene I v V 1. 068 1.097 Isopropyl Iodide 0. 014 0.022 0.022 Products, Cs equivalents/ moles diisobutylene consumed:

Methane 0. 1 0. 8 1. Cgs 1. 6 2. 'Osobu'tane 10. 7 32.2 25. Isobutylene 7. 5 16. 6 20. Misc. C5 and Cu. sm. 5. 3 5. Toluene. 0.9 2. 2 1. 20. 2 3. 5 2. 3.0 3. 8 6. 15.1 26.0 23. 2 a 3. 8 3. High Boiling Material 11 20.0 7. 0 7. Conversion, percent 37. 9 83. 6 78. Material Balance, percent 92. 2 96. 5 100.

e Corrected for Cas from the isopropyl iodide fed.

b Probably 2,5-dimcthylhexenes and hexadienesl a Moles/100 moles diisobutylene consumed.

6 Estimated from lack of closure of GLC analysis. Corrected for the amount of iodine which should be'present.

It will be seen according to Table I that the use of relatively low reaction temperatures resulted in the formation of a substantial isooctane yield which was in fact even higher than para-xylene yield. The formation of higher boiling material was, however, higher than desired. When the reaction temperature was raised as in Runs 2 and 3 in Table I to 500 and 525 C., respectively,

' the production of paraxylene was materially improved and isooctane yield was reduced to a low level. The formation of cracking products became evident at the expense of isooctane production.

The limiting factor of pressure is illustrated by the data contained in Table II, the same feed stock and catalyst being employed and temperatures of 450-500 C. being utilized.

TABLE II Dehydroisomerization of diisobutylene-reflect of pressure 'FLOW EXPERIMENTS Run N o 4 5 6 7 Temp, C 450 450 500 500 Pressure, p.s.i.g. 1,000 250 75 0 Residence Time, min 1 l 1.0 0.5 Feed. moles:

Diisobutylerie 1. 411 1. 077 1. 068 0. 806 Isopropyl Iodide 0.030 0.022 0.022 O. 049 Products, Ca equivalents/100 moles diisobutylene consumed:

Methane 0.2 0.8 0. 7 0 's e sm. 1.6 0.4 Isobutane 18. 4 24. 9 32. 2 12. 7 Isobutylene 7. 4 15. 4 16. 6 22. 1 ise. O5 and 1. 7 1. 5 5.3 1.8 Toluene sm. 0. 7 2. 2 1. 2 Isooctanc- 30.6 18. 7 3. 5 2. 3 Unknown Crs' sm. sm. 3.8 17.9 p-Xylene 10.1 17.0 26.0 14. 0 High Boiling Material e 17.0 9.1 7.0 9. 4 Hz d sm. 3. s a. 1 Coke 9.3 9. 9 sm. sm. Conversion, percent, 72. 0 73. 5 83. 6 52.0

According to Table 11, the use of excessive pressures in the order of 1000 pounds results in the formation of large amounts of high boiling materials and coke. Reducing this pressure to 250 pounds as in Run 5 of the above table correspondingly reduced the formation of high boiling materials but the coke content is still undesirably high. Still further reduction in the maximum pressure to 75 pounds as in Runs 6 and 7 resulted in the formation of only small amounts of coke and about the same amount of high boiling materials. The production of paraxylene is improved by using pressures no higher than about 250 p.s.i.g.

While the present process comprises a distinct advantage over the prior processes even with respect to limited relatively low pressures or with respect to the use of nearly catalytic amounts of iodine, it was of interest to determine whether or not changing the iodine concentration within relatively narrow limits while maintaining only catalytic amounts present altered the course of the desired reaction. It will be seen by reference to Table III that the use of iodine concentrations from about 1 to about 2 mole percent based on the olefin feed resulted in the formation of products having approximately the same para-xylene content.

TABLE III Dehydroisomerization of diz'sobutylene-efiect of iodide concentration FLOW EXPERIMENTS Run No 8 9 10 Temp, O 500 Pressure, p.s.i.g 75 Residence Time, min 2.0 1. 0 Feed, moles:

Diisobutylene 1. 068 gsolpropyl Iodide 0. 0. 022

er Products, equivalents/100 moles diisobutylene consumed:

Conversion, percent Material Balance, percen I Corrected for 05's from the isopropyl iodide fed.

b Probably 2,5-din1ethylhexenes and hexadienes.

B Estimated from lack of closure of GLO analysis. Corrected for the amount of iodine which should be present.

6 Moles/100 moles diisobutylene consumed.

B Oyclohexanc. Of the cyclohexane fed, 4% was dehydrogenated to benzene during the reaction. Most of the rest was recovered unchanged.

The use of lower molecular weight olefins such as ethylene, propylene, butenes and amylenes as hydrogen acceptors in the iodine catalyzed dehydrogenation reaction results in a materially improved yield in the desired products of the reaction product. This is in accordance with one of the equations given earlier in this specification and the data contained in Table IV illustrate this advantage still further.

TABLE IV Dehydroisomerization of diisobutylene-use of lower olefins as hydrogen acceptors FLOW EXPERIMENTS Run No- 11 12 13 14 Temp, C 500 500 500 500 Pressure. p.s.i.g 75 75 75 Residence Time, min 1. 0 0. 5 1.0 1.0 Feed, moles:

Diisobutylene 1. 068 0. 557 0. 608 0. 400 Isopropyl Iodide 0. 022 0. 012 0.012 O. 016 Olefin C2114 CsHt C4Hs Amount. 1. 685 1. 520 1. 161 Products, Ca equivalents/ moles diisobutylene consumed:

Methane 0. 8 0. 7 1. 1 1. 5 Isobutane 32. 2 12. 1 17. 8 Isobutylene 16. 6 17. 26 20. 7 Sat. Olefin 31. 6 70. 7 149.0 Isooctane 3. 5 0. 8 0. 8 1. 1 Misc. 05's--. 3. 8 9.0 4. 4 2. 8 Xylene 26.0 19. 5 31. 7 45. 1 Hydrogen B 3. 8 sm. 2. 2 4.0 High Boiling Material B 7. 0 9. 3 5. 5 9. 8 Diisobutylene Conversion, percent-.. 83. 6 68. 6 85.1 82.0 Material Balance, percent 96. 5 94. 6 95. 2 102. 6

added i-O4Ha; and 35.5 is n-butane from the saturation of the 1 and 2- butenes added. Of the O olefins fed, 21.7% of the l-C-iHB and 25.6% of the 11-C4Hs'8 were consumed.

I Estimated from lack of closure of GLO analysis. Corrected for the amount 01 iodine which should be present.

It will be seen by the data contained in the above table that the production of para-xylene is virtually double by the addition of lower olefins to the feed mixture. This is in accordance with the higher theoretical yield postulated by Equation C given hereinbefore.

I claim as my invention:

1. A process for converting alkene hydrocarbons having 7 to 18 carbon atoms per molecule and containing a chain of at least 4 carbon atoms, the total number of carbon atoms in the chain plus the number of quaternary carbon atoms in the chain being at least 6, the longest chain containing no more than 5 contiguous non-quaternary carbon atoms into corresponding aromatic hydrocarbons, which comprises contacting said alkene hydro carbon with a catalytic amount comprising about 0.5- 2.5 mole percent of a reaction iodine species at a temperature in the range of from about 400 to about 550 C. and a pressure in the range of from about 0 to about 250 p.s.i.a. for atime in the range of from 0.25 to about 10 minutes.

2. A process according to claim 1 wherein the alkene hydrocarbon is an acyclic monoolefin.

3. A process according to claim 1 wherein the alkene hyrocarbon is diisobutylene.

' 4. A process according to claim 1 wherein the alkene hydrocarbon is 2-phenylpropene dimer.

5. A process according to claim 1 wherein the alkene hydrocarbon is diisobutylene, the major aromatic hydrocarbon product is paraxylene and isooctane is produced in substantial proportion in the process.

6. A process for converting diisobutylene into paraxylene which comprises contacting a mixture of diisobutylene and butylenes with a catalytic amount comprising about 2 mole percent, based on the diisobutylene, of a lower alkyl iodide at a temperature of about 500 C., a pressure of about 75 p.s.i.g. for about one minute.

References Cited in the file of this patent UNITED STATES PATENTS 2,666,798 Condon Jan. 19, 1954 2,785,209 Schmetterling et al. Mar. 12, 1957 2,880,252 Raley et al. Mar. 31, 1959

Claims (1)

1. A PROCESS FOR CONVERTING ALKENE HYDROCARBONS HAVING 7 TO 18 CARBON ATOMS PER MOLECULE AND CONTAINING A CHAIN OF AT LEAST 4 CARBON ATOMS, THE TOTAL NUMBER OF CARBON ATOMS IN THE CHAIN PLUS THE NUMBER OF QUATERNARY CARBON ATOMS IN THE CHAIN BEING AT LEAST 6, THE LONGEST CHAIN CONTAINING NO MORE THAN 5 CONTIGUOUS NON-QUATERNARY CARBON ATOMS INTO CORRESPONDING AROMATIC HYDROCARBONS, WHICH COMPRISES CONTACTING SAID ALKENE HYDROCARBON WITH A CATALYTIC AMOUNT COMPRISING ABOUT 0.52.5 MOLE PERCENT OF A REACTION IODINE SPECIES AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 400* TO ABOUT 550* C. AND A PRESSURE IN THE RANGE OF FROM ABOUT 0 TO ABOUT 250 P.S.I.A FOR A TIME IN THE RANGE OF FROM 0.25 TO ABOUT 10 MINUTES.