US2946831A - Pentane dehydrogenation - Google Patents

Description

July 26, 1960 J. B. MAERKER PENTANE DEHYDROGENATION led July 16, 1958 Vmf--J 1 a/azfm/ #54mm/@Prawn i am cac/@141203 INVENTOR.

@94618131 PENTaNE DEHYDRoGENAfrIoN y John B. Maerker, Secane, Pa., assigner to Hondrylrocess Corporation, Wilmington, Del., a corporation of Delaware Filed July r6, 195s, ser. 'N o.749,1114 n v s claims. (c1. 26o-'630) This invention relates to 4the dehydrogenation 4of pentane.

YThe usefulness of a combustion motor in cold weather is dependent in part gasoline in starting VanA internal upon the more volatile components. A full'range gasoline Normal pentane has Ian F-l octane number of 61.7 and 'i a blending value which may be as low as 57. The mis-Y cellaneous markets for normal pentane as a solvent, as a raw material -for chemical manufacture and the like havev v been extremely small relative to the quantities of technical pentane produced in the normal operation of petroleum refineries and natural gasoline plants. Accordingly, normal pentane has been much used in gasoline, notwithstanding its low octane number. `inasmuch as normal pentane tends to depress the octane number of the gasoline pool signiiicantly more than othervolatile components would, the use of normal pentane in gasoline has to acertain extent increased lthe need for capacity to produce high octane number components, -such as ethylbenzene, xylene -and the like for achieving any particular octaneV number in the gasolinelpool. I Y Y As the market demand for higher octane gasoline has required raising of the octane number `of the gasoline pool, the disadvantages of Vusingnormal pentane in the gasoline have increased significantly. Although normal pentane is not particularly disadvantageous and/or costly to use (Le. necessitating increased Afacilities to prepare suicient high octane components to counteract the elect vof low octane number pentane) in a gasoline having an octane numberof 80, even minoramounts of normal pentane are undesirable in premium gasoline having an F-l octane number above 100. Normal pentane has previously generally been disposed of as a component of gasoline thus operating more protably than by disposing of the normal pentane as an inexpensive fuel, but the reverse might prevail if there were a sufficient demand for gasoline having :an octane number above 100.

Heretofore, it has been recognized that Vthe 972.3V octane Some volatile commuch as theoperating cost Vand lrequired investmentofv such a plant would be so high. Certain of the necessary separation steps in such a hypothetical plant are both diflicult and costly. The 8 C. difference between the' boiling points olf normal pcutane and isopentene is so small that the preparation of a grade of isopentene containing less than about %V normal pentane is relatively costly. The separation of saturated from unsaturated hydrocarbons is more dinicult and costly when dealing with C5 hydrocarbons than when dealing with C3 or C4 hydrocarbons. The existence of numerous makes the olen-diolen separation very much more dtlicult :for C5 hydrocarbons than yfor C4 hydrocarbons. In

v'the manufacture of C4 d-ioleiins, the concentration of isomers other than the desired 1,3 butadiene is so small that it can. be ignored. However, in the manufacture of isov piene, signilicant amounts of piperylene and/ or other C5 dioleiins tend to be produced, and must be separated in orderto market a commercially attractive grade of isoprene. Although small quantities of isoprene have been manufactured as lay-products of certain thermal processing of hydrocarbons, no commercial plant for the manufracture of isoprene from C5 hydrocarbons has been conjstructed, notwithstanding the available market for isoprene `at a price significantly higher than the price at which buta- 4,diene is sold.

Prior workers concerned with isomerization reactions vhave noted that the reactiou'rate at which skeletal isomnumber of pure isopentane and especially the 89 blending value of isopentaneV were more attractive than the 61.7v and 57 values -for Ynormalpentane. It, has also been known that?. -methyl Zrbutene hasl anoctane Anumber of 99.1 and 'that the octanenumbers ,ofV the several other fisopentenes andreven the sveral. normal pentenes were s-ignicantlyghigher than 61.7. ,Y p

It has long been recognized that a plant could be de- Vsign'edto convert normal pentane into isopentene. However, petroleum technologists have recognizedrthat there were more profitable refineryv improvements, even iffone were to assume that the Visopentenecould be. marketed at a `price. equal tovv thatr of other high Yoctane gasoline, and even `i-f one were to assume that the normal pentane feed `had. avalue pas, low` as the value of residual fuel oil, inaserization occurs in C5I hydrocarbons is significantly higher tor unsaturated hydrocarbons thanto'r saturated hydrocarbons. The prior art connoted that the best procedute for converting normal pentane to isopentene required first dehydrogenating to "form normal'pentenes and then catalytically isomerizingA to form isopentenes. Various. thermodynamic 'and reaction rate studies have enhanced the' attractiveness of this chronology of the process steps (dehydrogenationand then isomerization) for converting normal pentane to isopentenes.l

Y Various procedures have .been proposed for converting normal pentane to isopentane, and for separating the isopentane from the product. Such methods have generally involved-the use of a recycle ratio which' was so high and/ or such excessive cost for the'separation of the isoperitane from the eiiiuent from the isomerization zone that such proposals have not been widely adopted. In recent-years, it has been established that by the use of superatmospheric pressure, several mols of hydrogen per Amol of hydrocarbon, and a catalyst consisting predominantly of alumina and containing minor amounts of halide and minor amounts of platinum, the hydroisomerization of normal pentane to isopentane could be conducted for long periods of operation without regeneration. There has not been 'a widespread adoption of such a method because refinery managers have deemed other possible improvements to be more proiitable.

In accordance with the present invention, a gasoline component having a high. octane number because of its isopentene co'ntent is prepared from a pentane charge stock containing a major proportion 'of the normalisemer by a multi-step method in which the investment costs and operating costs are kept remarkably low by thecorrect relationship among the process steps.y This method involves the s tepsof: mixing a feedstock stream com sistingV predominantly vof normal'pentane with a recycle stream consisting predominantly of C5 acyclic hydrocarbons; passing said mixture', together with several mols of hydrogen per mol of hydrocarbons, over a platinum on halided alumina catalyst at isomerization conditions 'including a space rate from 1 to 6 volumes of liquid hydrocarbon per volume of catalyst per hour, aY pressure of from V15Uto 5i) atmospheres, and4 a temperature of Patented July 26,

isomers'- prising copper chromite at a temperature from 60 F; to

320 F. at a liquid space rate `from 0.5 to 6 per hour, at a hydrogen to hydrocarbon ratio of from 0.01 to 1 to prepare an olefin stream substantially free from diole-Y fins; and withdrawing a stream of pentenes Vcontaining d pressure of 230 pounds per square inch at a temperature of 825 F. and a space rate of 4 volumes of liquid pentane per volume of catalyst per hour to form an isomerizate consisting of about 61% isopentane and 39% normal pentane.

. EXAMPLE IIY Liquid C hydrocarbons were separated from the hydrogenative isomerization step of Example I and found` to consist essentially of 61% isopentane and. 39% normal pentane. Such a mixture was subjected to dehydrogenation at atmospheric pressure over a catalyst consisting of chro'mia on alumina, varying process conditions as indicated in Table I.

Table I DEHYDROGENATIONl 0F PENTANE ooNTArNING ABOUT 51% ISOPENTANES s2 F-i e V1 2 3 4 5V 5 V7 s V9 2 2 2v 2 2 2.2 2.2 2.2 2.2 942 999 904 955 909 1,001 94s 951 1,001 0 0 0 0 0 1 1 0 0 50 50 50 50 50- 5o 50 50 150 pentane 32.5 27.1 33.3 33.5 35.1 33.0 53.4 34.4 32.1 iso-pentane.. 45.7 45.8 55.5 40.7 39.8 55.5 57.0 57.4 53.8 13.7 19.9 as 13.2 17.1 7.7 7.1 5.9 7.2 1.5 3.5 0.9y 1.7 3-0 0.1` 0.2 0.5 0.9 0.4 1.3 0.1 0.4 1.0 0.5 0.3 0.7 0.7 15.5 25.4 9.3 15.0 23.3 11.9 8.7 7.3 15.2 84.5 7&5 57.1 79.4 72.1 .58.8 73.0 55.5 49.2 Dehydro S51. 04.0 89.0 97.8 90.5 85.5 59.7 75.9 75.5 55.5 F-1 clear 85.7 91.0 92.5 90.0 02.5 58.4 87.1 207i 59.2

a high proportion of isopentenes as a fraction for im- EXAMPLE III parting both a high octane number and'controlled'volatility to a fuel for high compression internal combustion motors.

fIn various modilications and/or subcombinations of modifications of the invention: the hydrocarbons subjected to the chromia on alumina catalyst are admired with from 0.1-to 6 mols of hydrogen; the hydrogen to hydrocarbon ratio in the dehydrogenation step is substantially the `same as 'the ratio in the isomerization step; the unsaturatcdhydrocarbons remaining after the separation o'f theparainic recycle stream are separated to forma monooleln rich stream and a' diolen-rich stream, thedioleiin Vrich streamV is separated to recover an isoprene stream, withdrawing' said isoprene stream as a product ofthe process, subjecting only'thernon-isoprene fraction of the diolen rich stream to the'selective hydro genation step,A and mixing the effluent from said selective hydrogenation stepV with the monoolen-rich stream to form said stream of pentenes; the dehydrogenation is conducted "at a total pressure offrom'0.l to 0.5 Vatmosphere and in the presence of Vfrom 0.1 to 1 mol of hydrogen per mol of hydrocarbon at a temperature between 1000`F. and 1200" F. to produce a substantial yieldof isoprene with minimized coke formation: or the dehydrogenation isconducted at a total press-ure of from 1 to 2 atmospheres and in the presence of from 0.5 to 3 mols of hy-v drogen per mol of Vhydrocarbon at a temperature between 1000u F. and 1200" F. to produce a substantial yield of pentenes with minimized diolen formation and with minimized coke formation.

The accompanying flow sheet indicates the relationship of several processing steps and the'flexibility of the invention by reason orthe'optional character of certain steps. Thus, the present invention. provides for a plant which can be operated with flexibility and which can adapt to the changing market prices and demands for variousstarting materials and/or products.y

EXAMPLE I Technical grade n-pentane, mixed with 2 molsof hydrogen per mol of pentane is subjected to an isomerization" zone containing a catalyst consisting of 96.5% gamma alumina, 3% chloride, and 0.5% platinum'at a Y Normal pentane is mixed with a recycle stream comprising normal pentane and minor amounts of isopentane, pentene, and isopentene, and mixed with hydrogen to provide one mol of hydrogen per mol of hydrocarbon, and passed through an. isomerization zone containing a catalyst consisting of 96.5% gamma alumina, 2% chloride, 1% iluoride and 0.5% platinum atV a pressure of 250 p.s.i.g., a temperature of 900 F. and` a space rate of 3 v./v./hour. The effluent therefrom is reduced in pressure, and passed at 0.1 atmosphere through a catalyst consisting of 80% gamma alumina and 20% chromia at a temperature'of 1025 F. at a space rate of l v./v./hour to dehydrogenate C5 hydrocarbons. After quenching and removal of hydrogen (some of which is recycled), methane, ethane, propane, butane, isobutane and the like, the C5 hydrocarbons are extractively distilled using aqueous cyclohexanone as the extractant. Normal pentane vapors contaminatedwith vapors of so'me isopentane, pentenes, and isopentenes are withdrawn from the top of the extractive distillation column. The thus witbdrawn vapors are recycled to the hydroisomerization unit. An aqueous solution of cyclohexanone, containing dissolved unsaturates, is withdrawn from the bottom of the extractive distillation column and sent to a stripper column. The unsaturated C5 hydrocarbons recovered from the stripper column are Water Washed to remove traces of cyclohexanone, and are then solvent extracted With aqueous cupric ammonium acetate to remove most of the diolens from the pentenes. The pentene raflinate stream is the principal product of the process, and is suitable as a high octane number volatile component for gasoline. The diolen stream separated by solvent extraction is distilled to provide a major stream of a technical grade of isoprene and a minor stream ofY technical grade of piperylene, containing minor amounts of the miscellaneous C5 diolens. The iso'prene stream is Withdrawn as a product and may be further purified if desired prior to polymerization into an elastomer. The piperylene stream is mixed with slightly more than an equimolar amount of hydrogen and with the pentene ranate stream from the diolen extraction step and passed over a copper chromite on alumina catalyst in the liquid phase atroom temperature and atmospheres pressure to prepare a puried pentene stream. To the extent that the pentene raffinate contains trace amounts vof diolens, these gum-formers are removed by the selective hydrogenation. The thus puried pentene stream iswithdrawn as a product useful for imparting both a high octane number and controlled volatility to gasoline.` i l The ability of the method .to prepare not merely at! unsaturated fraction would be subjected tothe selectiveV hydrogenation to eliminate troublesome quantities of dioleiins, and to make feasible the preparation of large quantities vof pentenes having good anti-knock character-- istics. Surprisingly, the separation of a parainic recycle stock from the dehydrogenation zone is more advantageous in upgrading octane number per unit investment cost than the separation of a normal pentane recycle stock for the isomerization step and the separation of a moderately pure isopentane recycle stream for they de' hydrogenation step. The normal pentenes have octane numbers significantly less than those of the isopentenes. However, because the isomen'zate contains so much isopentane, and because the dehydrogenation is measurably selective Yfor the isopentane, the concentration of the normal pentenes in the predominantly isopentene product from the dehydrogenation zone is not so excessive as to lower the octane number below the limits tolerable in high octane gasoline.

EXAMPLE IV Pentane is subjected to hydrogenative isomerization using the catalyst, pressure and temperature of Example L but using approximately double the space rate, .whereby Y the product contains about 38% isopentane andV 62% normal pentane. Certain natural-gasoline fractions rhave about this same isomer distribution.' Such pentane mixture is dehydrogenated at latmospheric pressure and in the presence of 1 mol of H2fper'mol of pentane over a chroma on alumina catalyst, starting `at 975 F. and raising thetemperature to lO25 F. during a 12 hour run. The C5 fraction is separated from the eiiiuent, and extractively distilled to provide a paranic recycle stream and an unsaturated product. Selective hydrogenation of the diolen content of the pentene fraction in the liquid phase over a copper chromite catalyst provides a fraction useful-for imparting both a high octane number and volatility to gasoline.

l EXAMPLEV A mixture of 62% normal pentane and 38% isopentane was dehydrogenated over a chromia-alumina catalyst at 1000 F. andl atmosphere pressure. The space rate and hydrogen to hydrocarbon ratio were adjusted in ve runs as shown in Table II.

Table Il These data establish that at'the conditions tested, any hydrogen rto hydrocarbon ratio within the range from about 0.3 to about 5 possessed advantages meriting engineering evaluation, and that surprisingly superior results are attainable within the range fromabout 0.3 to about 1.5 Hg/HC ratio. 1

VEXAMPLE v1V `'Ihe 'eect of long on-stream dehydrogenation. was

tested at atmosphericpressure, 1025 F. and allowing-- the total reaction mixture to be in contact with the'catalyst for a constant time period, as shown in Table III.

Table III Y LONG CYCLE DEHYDROGENETION RunNo 1s y 17 2 i 1 i 0.5 1,025 1,025 1,025 Y 4 8 2 4 8 4 8 15 7 40 38 25 41.5 s1 05H10 6.5 3.8' 27.8 22:5 17 V81.5]V 23 Dehydrosel 69 77 82 .81-V 82 82 8e Endet-1r-, 89 86.5 83.6 94.1 90.8 87.5 8.7 86.2

This andsir'nilarv data helped to establish that the presence of hydrogen the reaction mixture enhanced the stability of the performance of the process suiciently to make a long cycle dehydrogenation method feasible.

' VExfnt/IPLE V11 In determining whether a dehydrogenation unit should be operated at an increasing temperature or at a constant temperature, comparative runs were made. In one, the temperature Was constant at 1025 F., and in the other, the temperature was 975 for the first two hours, 1000 for the next six hours and 1025 for the last four hours of twelve hour tests, as shown in Table I V.

` Table 1V Yo'oNsftANr VERSUS INCREASING TEMPERATURE Constant Increasing T v./v./Hr 1 1 50 E12/no 1 1 4 8 4 8 '12 32.5 24.8 30.5 25 27.5 21 17 28.8 22. 22 81 8a se 9a 92 F-i clear 92 94.2 87.5 .8 89 86.8

By suchand similar data, it was established that the temperature is advantageously increased during each dehydrogenation cycle, thereby at least partially overcoming the temporary decrease in catalyst activity prior to each regeneration.

EXAMPLE VIII When mixtures of normal pentane and isopentane are dehydrogenated, the selectivity for isopentane dehydrogenation is siguicant, but some normal pentene is also Dehydrogenation tests were con-I Obviously many modifications and variations of the invention as hereinbefore settorth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

The invention claimed is:

l. The method of preparing both isoprene and a C fraction of high octane number from a feedstock stream consisting predominantly of normal pentane which includes the steps of: mixing a feedstock stream consisting predominantly of normal pentane with a recyclestream consisting predominantly of C5 acyclic saturated hydrocarbons; passing said mixture, together with several mols of hydrogen per mol of hydrocarbon, over a platinum on halided alumina catalyst at isomerization conditions inciuding a space rate from 1 to 16 volumes of liquid hydrocarbon per volume of catalyst per hour, a pressure of from to 50 atmospheres and a temperature of 600 to 950 F.; subjecting all of the C5 hydrocarbon effluent from the isomerization catalyst to dehydrogenation over a chromia on alumina catalyst at a liquid space rate of from 0.5 to 3 volumes of liquid C5 hydrocarbon per volume of catalyst per hour, a pressure from 0.1 to 2 atmospheres, and a temperature from 900 F. to 1200v F.; separating from the etliuent from the chromia on alumina dehydrogenation catalyst unconverted C5 acyclic saturated hydrocarbons for inclusion in said recycle stream; separating from the effluent from the dehydrogenation catalyst Va stream consisting essentially of pentenes, isoprene and, miscellaneous pentadienes; separating and withdrawing isoprene from the effluent from the dehydrogenation catalyst; subjecting the ranate remaining after isoprenewithdrawal to selective hydrogenation.

over a catalyst containing copper chromite at a temperature from 60 F. to 320 F. at a liquids'pace rate from 0.5 to 6 volumes of liquid ratlnate per volume of catalyst per hour at a hydrogen to hydrocarbon ratio of vfrom 0.01 to 1 to selectively hydrogenate themiscellaneous pentadienes to pentenes and to prepare aV pentene stream substantially free from diolens; and withdrawing said stream of pentenes containing a high proportion of. isopentenes as a fraction for imparting both a high octane number and controlled volatility to a fuel for high compression linternal combustion motors.

2. The method according to claim 1 in which the hydrocarbons subjected to the chromia on alumina catalyst are admixed with from 0.1 to 6 mols of hydrogen.

'3.' The method according to claim 1 in which thehydrogen Vto hydrocarbonratio in the Ydehydrogenatitm step is substantially the same as the ratio in the isomerization step. Y

4. The method according to claim 1 in whichcthe dehydrogenation is conducted at a `total pressure of lfrom 0.1 to 0.5 atmosphere and in the presence of from 0.1

to 1 mol of hydrogen per mol of hydrocarbon at a temperature between 1000J F. and 1075 F. to produce a substantial yield of isoprene with minimized coke formation. i

5.' A method of preparing a fraction rich Ain isopentenes Vfrom a. feed stock stream consisting predominantly ofacyclic C5 hydrocarbons which includes the steps of:

mixing a feed stock stream consisting'predominantly ofV acyclic C5 hydrocarbons with a Vrecycle stream consisting predominantly'of' C5 acyclic hydrocarbons; passing said mixture together with severalrnols of hydrogen per mol of hydrocarbon over a platinum on halided alumina cata.- lyst at isomerization conditions including a space rate of from 1 to 6 volumes of liquid hydrocarbon per volume of catalyst per hour, a pressure of from 15 to 50 atmospheres and a temperature of from 600 F. to 950 F.; subjecting all of the hydrocarbon eluent from the isomerization catalyst directly to dehydrogenation Yover a chromia on alumina catalyst at a liquid space rate of from 0.5 to 3, a pressure of from 0.1 to 2 atmospheres, and a temperature of from 900 F. to 1200 F., whereby some of the normal pentane is dehydrogenated to normal pentenes and more of the iso-pentane is dehydrogenated to Yiso-pentenes; separating from the eluent from the dehydrogenation catalyst unconverted parafns for inclusionv in said Yrecycle stream; separation from the eifluent from the dehydrogenation catalyst a stream consisting predominantly of pentenes and pentadienes; subjecting a fraction comprising a major amount of pentenes and a minor amount of pentadienes to selective hydrogenation over a catalyst containing copper chromite at a temperature of from F. to 320 F. at a liquid space rate of from 0.5 to 6 per hour at a hydrogen to hydrocarbon ratio of from .0.01 to 1 to selectively hydrogenate the pentadienes to pentenes and to prepare a pentene stream containing not more than trace amounts of diolefins; and withdrawing a stream of pentenes containing a high propcntion of iso-pentenes as a fraction for imparting both ahigh octane-number and controlledvolatility to a :fuel for highl compression internal combustion motors.

Reerences Cited in the file of this patent Y UNITED 'STATES PATENTS 2,181,640 v Deanesly et al. Nov. 28, 1939 2,199,132 Hull Apr. 30, A1940 2,377,113 Thomas May 29, 1945 2,781,324 Haensel Feb. 12, -1957

Claims (1)

1. THE METHOD OF PREPARING BOTH ISOPRENE AND A C5 FRACTION OF HIGH OCTANE NUMBER FROM A FEEDSTOCK STREAM CONSISTING PREDOMINANTLY OF NORMAL PENTANE WHICH INCLUDES THE STEPS OF: MIXING A FEEDSTOCK STREAM CONSISTING PREDOMINANTLY OF NORMAL PENTANE WITH A RECYCLE STREAM CONSISTING PREDOMINANTLY OF C5 ACYCLIC SATURATED HYDROCARBON, PASSING SAID MIXTURE, TOGETHER WITH SEVERAL MOLS OF HYDROGEN PER MOL OF HYDROCARBON, OVER A PLATINUM ON HALIDED ALUMINA CATALYST AT ISOMERIZATION CONDITIONS INCLUDING A SPACE RATE FROM 1 TO 6 VOLUMES OF LIQUID HYDROCARBON PER VOLUME OF CATALYST PER HOUR, A PRESSURE OF FROM 15 TO 50 ATMOSPHERES AND A TEMPERATURE OF 600* TO 950*F., SUBJECTING ALL OF THE C5 HYDROCARBON EFFLUENT FROM THE ISOMERIZATION CATALYST TO DEHYDROGENATION OVER A CHROMIA ON ALUMINA CATALYST AT A LIQUID SPACE RATE OF FROM 0.5 TO 3 VOLUMES OF LIQUID C5 HUDROCARBON OVER VOLUME OF CATALYST PER HOUR, A PRESSURE FROM 0.1 TO 2 ATMOSPHERES, AND A TEMPERATURE FROM 900*F. TO 1200* F., SEPARATING FROM THE EFFLUENT FROM THE CHROMIA ON ALUMINA DEHYDROGENATION CATALYST UNCONVERTED C5 ACYCLIC SATURATED HYDROCARBONS FOR INCLUSION IN SAID RECYCLE STREAM, SEPARATING FROM THE EFFLUENT FROM THE DEHYDROGENATION CATALYST A STREAM CONSISTING ESSENTIALLY OF PENTONES, ISOPRENE AND, MISCELLANEOUS PENTADIENES, SEPARATING AND WITHDRAWING ISOPRENE FROM THE EFFLUENT FROM THE DEHYDROGGENATION CATALYST, SUBJECTING THE RAFFINATE REMAINING AFTER ISOPRENE WITHDRAWAL TO SELECTIVELY HYDROGENATION OVER A CATALYST CONTAINING COPPER CHROMITE AT A TEMPERATURE FGROM 60*F. TO 320*F. AT A LIQUID SPACE RATE FROM 0.5 TO VOLUMES OF LIQUID RAFFINATE PER VOLUME OF CATALYST PER HOUR AT A HYDROGEN TO HYDROCARBON RATIO OF FROM 0.01 TO 1 TO SELECTIVELY HYDROGENATE THE MISCELLANEOUS PENTADIENES TO PENTENES AND TO PREPARE A PENTENE STREAM SUBSTANTIALLY FREE FROM DIOLEFINS, AND WITHDRAWING SAID STREAM OF PENTENES CONTAINING A HIGH PROPORTION OF ISOPENTENES AS A FRACTION FOR IMPARING BOTH A HIGH OCTANE NUMBER AND CONTROLLED VOLATILITY TO A FUEL FOR HIGH COMPRESSION INTERNAL COMBUSTION MOTORS.

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