US3236764A

US3236764A - Jet fuel manufacture

Info

Publication number: US3236764A
Application number: US414355A
Authority: US
Inventors: Herder Marvin J Den; Wilford J Zimmerschied
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1964-11-27
Filing date: 1964-11-27
Publication date: 1966-02-22
Anticipated expiration: 1983-02-22

Description

Feb. 22, 1966 Original Filed June 29. 1961 M. J. DEN HERDER ET AL 3,

JET FUEL MANUFACTURE 2 Sheets-Sheet 1 CATALYTICALLY CRACKED GAS OIL F lg. 1

Hydrogen Hydr ogen DISTILLATION V v Hydrogen FlRST FIRST FIRST HYDROGENATION HYDROGENATION HYDROGENATION S 8 N S 8 N S 8 N Compounds Compounds %T5'lil and H and H 2 SEPARATION SEPARATION SEPARATION Hydrogen ---0Hydrogen ---O Hydrogen l SECOND SECOND SECOND HYDROGENATION HYDROGENATION HYDROGENATION DISTILLATION DISTILLATION DISTILLATION Bolloms Bottoms Bofloms Thermally Stable Thermally Stable Thermally Sloble Je'r Fuel Jel fuel Jet l'-'uel I L. 4.. l l Thermally Stable Jet Fuel INVENTORS:

Marv/n J. Denherder BY Wilford J. Zimmersc/zied WM/QM A TTOR/VE Y 1966 M. J. DEN HERDER ET AL 3,236,764

JET FUEL MANUFACTURE 2 Sheets-Sheet 2 Original Filed June 29, 1961 HEddlHlS HHddlHiS ATTORNEY United States Patent 3,236,764 JET FUEL MANUFACTURE Marvin I. Den Herder, Olympia Fields, 101., and Wilford J. Zimmerschied, Crown Point, Ind., assignors to Standard Uil Company, Chicago, 11]., a corporation of lndiana Continuation of application Ser. No. 120,542, June 29, 1961. This application Nov. 27, 1964, Ser. No. 414,355

4 Claims. (Cl. 208210) This is a continuation of co-pending application Serial No. 120,542, filed June 29, 1961, now abandoned, which application is in turn a continuation-in-part of application Serial No. 804,437, filed April 6, 1959, now US. Patent 3,126,330.

This invention relates to the production of a high performance jet fuel of the type required by supersonic aircraft or ballistic missiles, which fuel is characterized by high temperature stability, maximum energy content, and good handling characteristics at both high and low temperatures. The invention particularly relates to the manufacture of such a jet fuel from cycle gas oil, i.e., the refractory gas oil separated from product gasoline produced by catalytically cracking gas oil, by a coordinated sequence of distillations and hydrogenations of selective fractions from such oil.

Fuels for supersonic jet engines should have net heats of combustion upwards from about 18,400 B.t.u. per pound and 130,000 B.t.u. per gallon, an aromatics content of as low as possible, a freezing point below 40 F., good stability at high temperatures, and low viscosity at -30 F. Stability at high temperatures, in the region of about 800 F., is necessary in order to permit use of the fuel prior to combustion thereof as a coolant for the engine and air frame. The object of this invention is to provide a high performance jet fuel which will meet these requirements, and to do so by a technique which will not require excessive capital investment and operating expense. Additionally, this invention enables the manufacture of such a jet fuel from raw material (cycle gas oil, hereinafter referred to as cat gas oil) which is available in large supply in most refineries. This invention contributes to the defense of the nation by enabling the production of greater quantities of high performance jet fuel as a result of utilizing a raw material which is plentifully available, than has been heretofore possible.

The thermally stable jet fuel of this invention comprises condensed bicyclic naphthenes (generally called decalins) substantially free of aromatics and parafiins. Decalins are present in crude petroleum, but comprise usually only a small fraction of crude petroleum and are not readily separated from other hydrocarbons of comparable boiling range which occur in crude oil. A similar situation exists in respect of the corresponding condensed bicyclic aromatics (usually called naphthalenes). However, condensed bicyclic aromatics having less than 15 carbon atoms per molecule are present in cat gas oil in a significantly greater concentration than in that portion of crude oil corresponding in boiling range to the cat gas oil. However, even with the increased concentration of the condensed bicyclic aromatics, the cat gas oil contains large amounts of paraffins and monocyclic naphthenes and aromatics which boil in the same range as the above referred to condensed bicyclic aromatics.

This invention is directed to the manufacture of a thermally stable jet fuel comprising decalins substantially free of aromatics and paraffius from selected narrow boiling fractions of cat gas oil. As illustrated in FIGURE 1, catalytically cracked gas oil-is fractionated into narrow fractions each boiling within a 60 F. boiling range, preferably into fractions of 30-40 boiling range, and which also boil within the range of about 450 to 570 F. The

narrow boiling fractions of cat gas oil are then subjected individually to a first hydrogenation in the presence of hydrogen and a sulfur resistant hydrogenation catalyst under hydrogenation conditions effective to convert sulfur-containing and nitrogen-containing compounds in such fractions to compounds boiling below the boiling range of such fractions, and further effective to convert a substantial proportion of the condensed bicyclic aromatics in such fractions to tetralins. The lower boiling sulfurand nitrogen-containing compounds and excess hydrogen are separated from the effluent from the first hydrogenation. The remainder of the first hydrogenation effluent is then subjected to a second hydrogenation in the presence of hydrogen and a second hydrogenation catalyst which is more active for hydrogenation of hydrocarbons than the above-mentioned sulfur resistant catalyst under hydrogenation conditions effective to convert condensed bicyclic hydrocarbons to decalins. The product, a thermally stable jet fuel, is then separated from the effluent from the second hydrogenation by distillation. The product jet fuel comprises decalins substantially free of aromatics and paratfins and having heats of combustion of at least 18,400 B.t.u. per pound and 131,000 B.t.u. per gallon, and a freezing point of not greater than about -70 F.

The cat gas oil used as raw material for this process may be obtained from any of the conventional catalytic cracking processes, either fixed bed, moving bed, or fluidized bed. The source of the feed to the catalytic cracking unit is unimportant. The severity of the catalytic cracking operation does influence the desirability of the resulting cat gas oil for use in this process, in that a high severity catalytic cracking operation yields cat gas oil having a higher percentage of condensed bicyclic aromatics than does low severity operations. However, this is merely a question of desirability; a cat gas oil from a low severity catalytic cracking operation is suitable for use in this process, although it will yield a smaller percentage of product jet fuel.

The cat gas oil is distilled into one or more fractions boiling within a 60 F. boiling range, preferably a boiling range of 3040 F., and which fractions also boil individually within the range of about 450 to 570 F. A large number of the alkyl naphthalenes having 11 to 14 .carbon atoms per molecule boil within such range. Conventional distillation equipment may be used, but should be designed to give sufficiently sharp fractionation to minimize the boiling range over-lap between successive narrow boiling fractions of cat gas oil taken from the distillation tower for processing in this invention.

The first hydrogenation of a narrow boiling cat gas oil fraction is conducted in the presence of hydrogen and a sulfur resistant hydrogenation catalyst. This first hydrogenation is conducted at conditions effective to desulfurize and denitrogenize the narrow boiling fraction, and also effective to convert a substantial proportion of the condensed bicyclic aromatics to tetralin. Illustrative sulfur resistant catalysts are those comprising cobaltmolybdenum, generally supported on alumina, nickel sulfide and nickel-tungsten sulfide. The catalyst may be used in any of several different physical forms, such as granules, or shaped into pellets or pills, and the like, when a fixed catalyst bed hydrogenation unit is used, or even as a fiuidizable powder if a fluid bed system is to be used. Because of the high pressure involved, the hydrogenations of this invention are preferably conducted in fixed bed units.

The primary criteria of the hydrogenation conditions to be used are that the narrow boiling cat gas oil fraction be substantially desulfurized and denitrogenized, and that a substantial proportion, advantageously more than half, of the condensed bicyclic aromatics be converted to tetralin. It is desirable to minimize cracking of the hydrogenation feed, and to this end the hydrogenation temperature should not substantially exceed 800 F., and is preferably in the range of 675800 F., advantageously 720-750 F. The hydrogenation pressure may vary from about 400 p.s.i.g., to several thousand pounds p.s.i.g., preferably from about 1000 to 2500 p.s.i.g., and advantageously about 1500 p.s.i.g. The temperature and pressure of hydrogenation should be correlated, using increasing pressure as the temperature is increased. Liquid hourly space velocities in the range of 0.1 to may be used, preferably space velocities in the range of about 0.5 to 2.

The amount of hydrogen chemically consumed in the first hydrogenation depends upon the extent to which condensed aromatics are hydrogenated, the fraction of the feed which comprises readily hydrogenatable compounds, and, to a lesser extent, the amount of nitrogen and sulfur in the feed. However, as an approximation it may be expected that about 30 to 50 percent of the total hydrogen chemically consumed within the process will be consumed in the first hydrogenation. The theoretical hydrogen consumption for converting methyl naphthalene to methyl tetralin is about 1900 s.c.f. per barrel of methyl naphthalene; the conversion of the methyl tetralin to methyl decalin requires about an additional 2800 s.c.f. per barrel of methyl naphthalene feed. Slightly lesser amounts of hydrogen are required for the hydrogenation of C and C naphthalenes to their corresponding decalins. In respect of any particular narrow boiling cat gas oil the hydrogen which will be chemically consumed may be already calculated from the knowledge of the composition of such fractions, including data on the sulfur and nitrogen content thereof.

It is desirable to conduct the hydrogenation in the presence of excess hydrogen. Therefore, the amount of hydrogen charged to the first hydrogenation unit may range from about 1500 s.c.f per barrel of liquid charge to 10,000 s.c.f. per barrel, preferably 2500 to 6000 s.c.f. per barrel. The hydrogen used does not need to be of any exceptional purity, and may be the hydrogen make-gas from a catalytic reforming operation which comprises about 75 mol percent hydrogen and the remainder primarily light hydrocarbons.

The presence of H 8 in the hydrogen feed gas is not objectionable.

After the first hydrogenation, the etfiuent therefrom is cooled and the gaseous phase separated from the liquid phase. The gaseous phase comprises predominantly hydrogen and includes light hydrocarbons, hydrogen sulfide, and in many instances ammonia. The gaseous phase of the efiluent may be rejected from the system and used for some other purpose, or it may be recycled to the first hydrogenation unit, or used, after removal of hydrogen sulfide and ammonia, in the hereinafter described second hydrogenation step. If it is recycled to the first hydrogenation unit, it is preferable to process the stream through a hydrogen sulfide removal unit, such as an ethanol amine desulfurizer, in order to prevent the build-up of hydrogen sulfide. It may be desirable, depending upon the cat gas oil fraction which has been hydrogenated and the conditions of hydrogenation, to strip dissolved contaminants from the liquid phase of the first hydrogenation effluent prior to again hydrogenating the liquid phase.

The hydrogenation of the above-mentioned liquid phase is conducted in the presence of hydrogen and a catalyst which is more active for hydrogenation of hydrocarbons than the above-described sulfur resistant catalyst under conditions which are effective to convert condensed bicyclic hydrocarbons to decalins. The greater hydrogenation activity of the catalyst used in the second hydrogenation is required because of the greater difficulty in hydrogenating tetralins to decalins compared to the hydrogenation of naphthalenes to tetralins. Suitable catalysts for use in the second hydrogenation include supported 7 nickel, e.g., nick-el onralumina or kieselguhr, or a noble metal such as platinum or palladium, on alumina. It is preferred that the catalyst have a minimum of cracking activity, and for that reason it is desirable that the catalyst be substantially free of halides. Relatively lower temperatures are used in the second hydrogenation unit than in the first hydrogenation unit, also in order to minimize cracking. Temperatures in the range of 575 to 700, preferably 600 to 650 F. are used. The pressures described above in respect to the first hydrogenation unit are suitable for use in the second unit, and it is frequently desirable to use comparable pressures in each unit, Liquid hourly space velocities in the range of 0.1 to about 5, preferably from A to about A may be used. Generally, a lower space velocity will be used in the second hydrogenation unit than in the first hydrogenation unit. The amount of hydrogen charged to the unit will be in the general range as disclosed above in respect of the first hydrogenation unit, but will generally be somewhat higher, in any given plant practicing this invention, in the second hydrogenation unit. Inasmuch as the catalyst suitable for use in the second hydrogenation unit are not only more active but are also less sulfur resistant than the catalysts which may be used in the first hydrogenation unit, the hydrogen charged to the second unit should be substantially free of hydrogen sulfide.

The efiluent from the second hydrogenation unit is separated into a gaseous phase and a liquid phase. The gaseous phase comprises predominantly hydrogen having a low sulfur content and is advantageously recycled within the system. The liquid phase is distilled to obtain the product fuel. It is frequently advantageous, although not mandatory, to remove the lowest boiling 1-10 percent of the liquid phase as a forecut, and withdrawing the product jet fuel as a side stream heart cut from the distillation tower. Depending upon the cat gas oil and various particulars of the processing sequence, the product jet fuel will amount to A to about /2 or more of the liquid phase charged to the final distillation. The above-mentioned forecut, if taken, comprises a substantially saturated hydrocarbon stream suitable for use in kerosene. The bottom stream from the distillation is also substantially saturated, will generally have a high cetane number, and is advantageously blended into diesel fuel.

The following information will delineate this invention with greater specificity. Light cat gas oil obtained from a fluid catalytic cracking unit was distilled into three narrow boiling cat gas oil fractions. Inspection test data on the distillation charge and on the narrow boiling fractions distilled therefrom are given in Table I:

Cat gas oil fraction No. 1 was first hydrogenated over a cobalt-molybdenum catalyst supported on alumina at 730740 F., a pressure of 1500 p.s.i.g., and a volume hourly space velocity of 1.0. Bottled hydrogen, in a nonrecycle system, was used in the amount of 3100 s.c.f. of. hydrogen per barrel of cat oil fraction No. l. The effluent from the hydrogenation was cooled and separated into gaseous and liquid products. The liquid product was then rehydrogenated over a catalyst comprising 1 weight percent platinum-on-alumina which was substantially free of halide. This hydrogenation was conducted at 630 F., a pressure of 1500 p.s.i.g., and a volume hourly space velocity of 0.5. As before, once-through hydrogen was used in the amount of 4000 s.c.f. per barrel of liquid feed to the hydrogenation. Both hydrogenation steps were conducted in bench scale isothermal reactors. Inspection tests on the effluent from each hydrogenation step referred to above are given in Table II. It is noted that the first hydrogenation reduced the sulfur content from 0.64 weight percent to 0.001 percent.

Table II.Processing of cat gas oil fraction N0. 1

The liquid product from the second hydrogenation was distilled into a plurality of small cuts, and each cut analyzed for heat content, specific gravity, and freezing point. For the cuts which represented the 2 volume percent through 46 volume percent of the liquid efliuent from the second hydrogenation, the heats of combustion varied from 18,490 to 18,562 B.t.u. per pound, and from 131,029 to 132,045 B.t.u. per gallon. The weighted average heat contents were 18,520 B.t.u. per pound and 131,667 B.t.u. per gallon. The freezing points of the various cuts were all below 80 F., and the aromatic contents were less than 2.5 volume percent.

Cat gas oil fractions 2 and 3, as referred to in Table I above, were processed in a similar manner using the same process conditions and type of catalyst. Data on the liquid phase of the effluent from each hydrogenation step is set forth in Tables III and IV.

Table III.Prcessing of cat gas oil fraction N0. 2

First Second Hydrogena- Hydrogenation Efiiluent tion Efiiuent Gravity, API 34.5 37. 6 ASTM Distillation:

iti 421 430 10% 458 457 30%. 485 476 50%. 496 490 70% 507 504 90% 519 519 Max 531 520 Sulfur, wt. percent 0.002 0. 001 Yield, vol. percent of Fraction 104. 106. 5

Table IV.-Pr0cessing of cat gas oil fraction N0. 3

In respect of cat gas oil fraction No. 2, the heats of combustion determined on fractions representing 12 through 52 volume percent of the final liquid hydrogenation product varied between the limits of 18,263 to 18,560 B.t.u. per pound, and from 131,667 through 133,831 B.t.u. per

gallon. The weighted average heat contents were 18,450 B.t.u. per pound and 132,590 B.t.u. per gallon. The average aromatics content was between 2.0 and 2.5 volume percent.

In respect of cat gas oil fraction No. 3, the fractions representing from 8.8 through 31.8 volume percent of the final liquid hydrogenation product had weighted average heats of combustion of 18,457 B.t.u. per pound and 135,644 B.t.u. per gallon. The composite freezing point was about F.; the aromatics content was between 1.5 and 2 percent.

The product jet fuel comprises predominantly decalins substantially free of paraffins and aromatics. In addition to its use as a jet fuel, the product of this process may also be used as a raw material for additional chemical processes. In this connection it is to be understood that as used herein the word decalins includes not only the fully saturated molecule (Ciel I18) resulting from the hydrogenation of naphthalene, but also alkyl substituted homologues thereof. Furthermore, the product fuel may and often will contain minor proportions, amounting to a few percentage points, of fully saturated derivatives of decalin wherein an alkyl substituent has formed a bridge between the two saturated 6-carbon atom rings, e.g., the fully saturated compound resulting from the hydrogenation of acenaphthylene.

The invention will be more clearly understood from the following detailed description of a specific example read in conjunction with accompanying FIGURE 2 which forms a part of the specification, and which is a schematic flow diagram illustrating the process of the invention.

A catalytic gas oil from a catalytic cracking unit is introduced through line 11 to distillation column 12. The charge to the distillation column may be heated by a heater, not shown. From the distillation column 12 are withdrawn one or more cat gas oil fractions designatcd fractions 1, 2 and 3 through

lines

13a, 13b and 130, which are collected in

storage tanks

14a, 14b and 140. The distillation is conducted so that these fractions have a narrow boiling range of not more than about 60 F., preferably 30-40 F., and in addition each boils within the range of about 450-570 F. Collecting these fractions in tankage is not essential, but is a convenient expedient where only one set of hydrogenation reactors is available for subsequent processing on a blocked-out basis. Depending upon the boiling range of the cat gas oil charge, an over-head cut may be optionally taken through line 15 and disposed of outside of the system, for instance, by blending into a No. 2 furnace oil. In similar fashion, it is generally advantageous to take a bottoms cut through line 16 for blending into No. 2 furnace oil.

The description of FIGURE 2 continues with respect to fraction No. 2 stored tank 14b. However, it is to be understood that the processing sequence described with respect thereto is applicable on a blocked-out basis to fractions 1 and 3. It is also to be understood that the figure omits graphic representation of heaters, heat exchangers, pumps, compressors and valves, which are believed to be unnecessary to an acceptable understanding of the process.

The cat gas oil fraction is withdrawn from tank 1412 through line 17, and heated to an elevated temperature which, because of the exothermic character of the hydrogenation reaction, will generally be somewhat below the intended operating temperature of 675800 F. Hydrogen from

lines

18 and 19 is mixed with the cat gas oil fraction prior to the charging thereof to the first hydrogenation unit 20. The hydrogenation unit 20 is operated at pressures, space velocities, and hydrogen charge rates as hereinabove described. The hydrogenation unit uses a sulfur resistant catalyst, such a cobalt-molybdate on alumina, preferably in the form of a fixed bed. Hydrogenation unit 20 may comprise one or more reactors in parallel which are, because of the high exothermic nature of the hydrogenation reaction, provided with suitable heat removal means, such as a molten salt or a eutectic mixture comprising biphenyl (generally referred to as Dowtherm) circulated through internal tubes.

The effluent from hydrogenation unit is withdrawn through line 21, cooled and run to separator 22, wherein a hydrogen-rich gas phase is separated from liquid hydrocarbons. The hydrogen-rich gas phase will have a lower hydrogen concentration than the hydrogen introduced through line 19, because of both hydrogen consumed and also because of dilution with a minor amount of light hydrocarbons cracked during the hydrogenation process. It will also contain increased amounts of hydrogen sulfide and ammonia as a result of the removal of sulfur and nitrogen from the cat gas oil fraction charged to the hydrogenation unit. The hydrogen-rich gas phase is withdrawn from the separator 22 through line 23 and may be either rejected from the system through line 24 or recycled via line 25 to the hydrogenation unit. If the latter procedure is followed, it is advantageous to process the hydrogen-rich recycle gas through a hydrogen sulfide removal unit 26, which may be of a conventional type, e.g., an ethanol amine type of desulfurizer. Provision may also be made to reject from the system light hydrocarbons which may otherwise build up to undesirable concentrations. Hydrogen-rich recycle gas from hydrogen sulfide removal unit 26 is recycled through

lines

27, 28 and 19 to first hydrogenation unit 20. Provision may also be made for recycling hydrogen through line 29 to a second hydrogenation unit described hereinafter.

From separator 22 the liquid phase effluent is withdrawn through line 30 for further processing. This may optionally include, as shown in the figure, stripping of the liquid phase in stripper 31 to complete the removal of low boiling constitiuents, including ammonia and hydrogen sulfide and light hydrocarbon gases, which are rejected through line 32 as off-gas.

From stripper 31, liquid hydrocarbons are withdrawn through line 33, heated and mixed with hydrogen from line 34 prior to being charged through line 35 to second hydrogenation unit 36. The hydrogen from line 34 may be derived from an independent source through line 37, or it may include hydrogen recycled through line 29 after having been purified in hydrogen sulfide removal unit 26, and may include recycle hydrogen separated from the effluent from second hydrogenation unit 36.

Second hydrogenation unit 36 is operated at process conditions as hereinabove described, for instance, 650 F., 1500 p.s.i.g. pressure, /2 volume hourly space velocity, and 4000 s.c.f. hydrogen per barrel of liquid feed. The catalyst used is more active than the catalyst used in first hydrogenation unit 20, and is suitable halide-free platinum on alumina. The catalyst and the process conditions used in conjunction therewith employed in second hydrogenation unit 36 are selected to complete the partial hydrogenation which was accomplished in first hydrogenation unit 20. As was described in respect of first hydrogenation unit 20, second hydrogenation unit 36 should be provided with means to remove the exothermic heat of reaction resulting from the hydrogenation.

The efiiuent from second hydrogenation unit 36 is removed through line 36a, cooled, and separated into gaseous and liquid phases in separator 38. The hydrogenrich gaseous phase is removed through line 38a and either rejected from the system through line 39 or, more preferably, and with provision for avoiding the build-up in concentration of light hydrocarbons therein, recycled through line 40 to hydrogenation unit 36. The liquid phase is withdrawn from separator 38 through line 41 and charged to distillation tower 42. From tower 42 a light ends forecut may be optionally taken over-head through line 43 for blending into a suitable product, such as kerosene. The jet fuel which is the product of this process is withdrawn through line 44, and a bottom cut suitable for use, for instance, in diesel fuel, is withdrawn through line 45. The product jet fuel withdrawn through line 44 comprises predominantly decalins substantially free of aromatics and paraffins and having heat of combustion of at least about 18,400 B.t.u. per pound and about 131,000 B.t.u. per gallon, and a freezing point of not greater than about 70 F. The viscosities at 30 F. of the jet fuels produced by this process are in the range of about 15-50 centistokes.

The heats of combustion referred to above were calculated from hydrogen content (Industrial and Engineering Chemistry, volume 43, page 94 1) which in turn was obtained in the manner described in Analytical Chemistry, volume 23, page 324. The freezing point data were determined by ASTM designation Dl477-57T. The quantities of naphthalene and tetralins were determined by the fluorescent indicator analyses prescribed by ASTM designation method D-1319.

Having thus described the invention, what is claimed 1. A process for manufacturing thermally stable jet fuel, which process comprises separating by distillation from catalytically cracked gas oil containing condensed bicyclic hydrocarbons a plurality of fractions each boiling within a 60 F. boiling range and also each boiling within the range of about 450 to 570 F., subjecting each of said farctions to a first hydrogenation in the presence of hydrogen and a sulfur-resistant hydrogenation catalyst under hydrogenation conditions including a temperature in the range of about 675 to 800 F., a pressure in the range of about 400 to 2500 p.s.i.g. and a liquid-hourly space velocity in the range of about 0.1 to 10, effective to convert sulfur-containing and nitrogen-containing compounds in each of said fractions to sulfurand nitrogencontaining compounds boiling below said fractions and effective to convert a substantial proportion of the condensed bicyclic aromatics in each of said fractions to tetralins, separating from the efiluent from each of said first hydrogenations sulfurand nitrogen-containing compounds boiling below said fractions and hydrogen, thereafter subjecting the remainder of said hydrogenation efiluents to a second hydrogenation in the presence of hydrogen and a second hydrogenation catalyst which is more active for hydrogenation of hydrocarbons than said sulfurresistant catalyst under conditions including a temperature in the range of about 575 to 700 -F., a pressure in the range of about 400 to 2500 p.s.i.g. and a liquid hourly space velocity in the range of about 0.1 to 5, effective to convert condensed bicyclic hydrocarbons to decalins and separating by distillation from the efiluent of each of said second hydrogenations a thermally stable jet fuel comprising decalins substantially free of aromatics and paraffins, said jet fuel having a heat of combustion of at least about 18,400 B.t.u. per pound, and about 131,000 B.t.u. per gallon, and a freezing point of not greater than about 70 F.

2. The process of claim 1 wherein said sulfur-resistant catalyst comprises supported cobalt molybdenum, and where said second hydrogenation catalyst comprises platinum-on-alumina.

3. The process of claim 1 wherein said second hydrogenation catalyst comprises metallic nickel.

4. The method of making thermally stable, highly naphthenic condensed bicyclic hydrocarbon jet fuel of high heat content and low freezing point and substantially free of aromatics and paraffins, which method comprises separately hydrofining each of a plurality of cycle gas oil fractions each containing condensed bicyclic hydrocarbons under conditions including a temperature in the range of about 675 to 800 F., a pressure in the range of about 400 to 2500 p.s.i.g. and a liquid-hourly space velocity in the range of about 0.1 to 10 for effecting desulfurization thereof and converting a substantial proportion of condensed bicyclic aromatics in each of said gas oil fractions to tetralins, said fractions each boiling within a 60 F. boiling range and also within the 9 limits of about 450 to 570 F., saturating each of said hydrofined gas oil fractions by hydrogenation in the presence of an active hydrogenation catalyst under conditions including a temperature in the range of about 575 to 700 F., a pressure in the range of about 400 to 5 2500 p.s.i.g. and a liquid hourly space velocity in the range of about 0.1 to 5, and distilling each of the resulting hydrogenation products to obtain as said jet fuel highly naphthenic fractions each boiling below the boiling range of the respective fraction fed to said hydrofining and comprising predominantly condensed bicyclic hydrocarbons substantially free from parafiins and aromatics.

References Cited by the Examiner UNITED STATES PATENTS 2,671,754 3/1954 De Rosset et a1. 208-89 2,878,179 3/1959 Hennig 20857 2,956,002 10/1960 Folkins 208-15 DELBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner.

Claims

1. A PROCESS FOR MANUFACTURING THERMALLY STABLE JET FUEL, WHICH PROCESS COMPRISES SEPARATING BY DISTILLATION FROM CATALYTICALLY CRACKED GAS OIL CONTAINING CONDENSED BICYCLIC HYDROCARBONS A PLURALITY OF FRACTIONS EACH BOILING WITHIN A 60*F. BOILING RANGE AND ALSO EACH BOILING WITHIN THE RANGE OF ABOUT 450 TO 570*F., SUBJECTING EACH OF SAID FRACTIONS TO A FIRST HYDROGENATION IN THE PRESENCE OF HYDROGEN AND A SULFUR-RESISTANT HYDROGENATION CATALYST UNDER HYDROGENATION CONDITIONS INCLUDING A TEMPERATURE IN THE RANGE OF ABOUT 675 TO 800*F., A PRESSURE IN THE RANGE OF ABOUT 400 TO 2500 P.S.I.G. AND A LIQUID-HOURLY SPACE VELOCITY IN THE RANGE OF ABOUT 0.1 TO 10, EFFECTIVE TO CONVERT SULFUR-CONTAINING AND NITROGEN-CONTAINING COMPOUNDS IN EACH OF SAID FRACTIONS TO SULFUR- AND NITROGENCONTAINING COMPOUNDS BOILING BELOW SAID FRACTIONS AND EFFECTIVE TO CONVERT A SUBSTANTIAL PROPORTION OF THE CONDENSED BICYCLIC AROMATICS IN EACH OF SAID FRACTIONS TO TETRALINS, SEPARATING FROM THE EFFLUENT FROM EACH OF SAID FIRST HYDROGENATIONS SULFUR- AND INTROGEN-CONTAINING COMPOUNDS BOILING BELOW SAID FRACTIONS AND HYDROGEN, THEREAFTER SUBJECTING THE REMAINDER OF SAID HYDROGENATION EFFLUENTS TO A SECOND HYDROGENATION IN THE PRESENCE OF HYDROGEN AND A SECOND HYDROGENATION CATALYST WHICH IS MORE ACTIVE FOR HYDROGENATION OF HYDROCARBONS THAN SAID SULFURRESISTANT CATALYST UNDER CONDITIONS INCLUDING A TEMPERATURE IN THE RANGE OF ABOUT 575 TO 700*F., A PRESSURE IN THE RANGE OF ABOUT 400 TO 2500 P.S.I.G. AND A LIQUID HOURLY SPACE VELOCITY IN THE RANGE OF ABOUT 0.1 TO 5, EFFECTIVE TO CONVERT CONDENSED BICYCLIC HYDROCARBONS TO DECALINS AND SEPARATING BY DISTILLATION FROM THE EFFLUENT OF EACH OF SAID SECOND HYDROGENATIONS A THERMALLY STABLE JET FUEL COMPRISING DECALINS SUBSTANTIALLY FREE OF AROMATICS AND PARAFFINS, SAID JET FUEL HAVING A HEAT OF COMBUSTION OF AT LEAST ABOUT 18,400 B.T.U. PER POUND, AND ABOUT 131,000 B.T.U. PER GALLON, AND A FREEZING POINT OF NOT GREATER THAN ABOUT -70*F.