AU592372B2 - Processing aromatic vacuum gas oil for jet fuel production - Google Patents

Abstract

Premium jet fuel is produced by dewaxing aromatic vacuum gas oil boiling above the specification for jet fuel over zeolite beta and fractionating the dewaxed material to produce a kerosene fraction boiling in the jet fuel range. Conventional hydrotreating of the kerosene fraction produces a premium jet fuel product.

Description

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I r li-- i- ;-Yu~P~ AUSTRALIA 592372 Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: 630,q/l 6 Complete Specification Lodged: Accepted: Published: Priority Related Art: I tiJz ium-unt IOfliiZS 0h W1ame1fnts made un4 Sact= 49.

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Name(s) of Applicant(s): ''Si ,Address(es) of Applicant(s): at t 4 a: APPLICANT'S REF.: F-3664 MOBIL OIL CORPORATION 150 East 42nd Street New York, New York 10017 United States of America Kenneth Michael Mitchell Stuart Shan-san Shih Actual Inventor(s): t Address for Service is: PHILLIPS, ORMONDE AND FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne, Australia, 3000 Complete Specification for the invention entitled: "PROCESSING AROMATIC VACUUM GAS OIL FOR JET FUEL PRODUCTION" The following statement is a full description of this invention, including the best method of performing it known to applicant(s): P19/3/84 1 r F-3664

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PROCESSING AROMATIC VACUUM GAS OIL FOR JET FUEL PRODUCTION This invention relates to the production of premium jet fuel from aromatic vacuum gas oil.

Refining petroleum crude oils to obtain jet fuel is well known.

The jet fuel must meet certain specifications for freeze point, pour point, smoke point and weight percent sulfur. It may be necessary to subject these fuels to additional processing to meet required specifications.

In U. S. Patent No. 4,501,926 to LaPierre et al, gas oil and

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2 contact zeolite beta catalyst to selectively isomerize the paraffinic waxy components in a gas oil feed. U. S. Patent No.

i c; 4,501,926 discloses other useful feedstocks, including crude oils, 4 kerosenes, jet fuels, lubricating oil stocks, heating oils and other distillate fractions, whose pour point and viscosity need to be maintained within certain specification limits.

However, although a pour point specification may be met by the above, the sulfur in the product may exceed specifications, thus requiring additional processing, typically in a hydrotreater.

U. S. Patent No. 3,573,198 to Parker et al teaches smoke point improvement of jet fuel kerosene fractions by treating a sulfurous kerosene fraction by a two-stage process. The first stage principally desulfurizes and the second stage principally saturates aromatics by contact with a catalystic of alumina, a halogen component, a Group VIII noble metal component and a Group VII-B .metallic component. U. S. 3,573,198 does not suggest upstream S processing most appropriate for combination with its process.

Highly olefinic/aromatic kerosene is the least desirable feed for this process.

r-'tsst~~~--ll F-3664 -2- U. S. Patent No. 4,427,534 to Brunn et al discloses production of jet and diesel fuels from highly aromatic oils using a sulfided, halogen-promoted Group VIB-Group VIII metal on an alumina-containing support. The process has the disadvantage that it employs hydrocracking, which opens aromatic molecules to form paraffinic material. By opening aromatic rings, the hydrocracked products can have a higher pour point than the feed to hydrocracking.

To produce high quality jet fuel from vacuum gas oil, containing to 50 wt. aromatics requires severe operating conditions, such as high pressure, to treat aromatic chargestocks by hydrocracking.

Hydrocracking can increase pour point. It would be desirable to produce jet fuel at moderate pressure from aromatic chargestocks.

SThis is particularly significant since it is projected that refineries will process a higher proportion of heavy crudes, which are typically aromatic.

S Accordingly, the present invention provides a process for I? producing jet fuel from a vacuum gas oil feed havig at least 20 to wt aromatics and boiling above ~1 (65£by contacting the 'Iso rvEex *c, 1 ce-vc feed with a *e aa catalyst comprising a hydrogenation component S 20,* and zeolite beta having a silica:alumina ratio of at least 30:1 at 199-538 0 C (3900 to 10000F), a pressure of atmospheric to 10,400 kPa -l (1500 psig), a liquid hourly space velocity of 0.2 to 5.0 hr in the presence of hydrogen to produce a dewaxed effluent stream, wherein most aromatics in the feed are unchanged; separating the dewaxed effluent stream into a kerosene fraction containing hydrocarbons boiling below 343 0 C (650 0 F) and a heavier fraction; hydrotreating the kerosene fraction with a conventional hydrotreating catalyst under conventional hydrotreating conditions teo produco a hydrotrcatcd koroacno s tream; and ticoafring-drgf 3 hydrotreated kerosene stream a jet fuel product.

The process of the present inven roduces jet fuel having a low freeze point and lo point from a vacuum gas oil boiling above 288C )preferably above 343°C (650°F). Vacuum gas oils Ily boil in th6 range from 288 to 566 0 C (550 to 1050°F), mor-e| i 2a to produce a hydrotreated kerosene stream; and stripping the hydrotreated kerosene stream to produce a jet fuel product.

The hydrogenation component comprises 0.1 to 5.0 wt.% of a noble metal of group VIII of the Periodic Table, preferably 0.1 to 1.2 wt.% platinum.

The process of the present invention produces jet fuel having a low freeze point and low pour point from a vacuum gas oil boiling above 288 0 C (550°F) preferably above 343 0 C (650 0 The vacuum gas oil contains more wt.% O aromatics than paraffins and at least 2 wt.% sulfur. Vacuum gas oils typically boil in the range from 288 to 566°C (5500 to 1050°F), more a *0 0 o e o o 0 0 ae, ''at a t a tC acr

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tC C CC r Ire i F-3664 -3usually 343 to 454 0 C (6500 to 8500F). Furthermore, the process of the present invention produces jet fuel from highly aromatic (at least 20-50 wt aromatics) feeds with minimal conversion of aromatics during isomerization of paraffins into jet fuel hydrocarbons, thus improving jet fuel quality by not converting the aromatics into higher pour point paraffins. The process also improves jet fuel quality by mild hydrotreating of the kerosene cut separated from other hydrocarbons in the effluent from isomerization, thus allowing easy processing to produce a jet fuel which meets jet fuel specifications for aromatics content, pour point, freeze point, sulfur content and smoke point.

The figure illustrates isom.erization dewaxing followed by hydrotreating of a kerosene fraction.

The vacuum gas oil feed comprises aromatics, paraffinic, waxy components and sulfur compounds. The vacuum gas oil stream 12 is nr t combined with a hydrogen stream 14 to form a combined stream 16.

Typically the vacuum gas oil comes from a vacuum distillation tower (not Flown). The combined stream 16 passes into reactor preferably a co-current downflow trickle bed reactor. Feed contacts catalyst comprising a hydrogenation component and zeolite beta to produce a dewaxed effluent stream 22. The aromatics are substantially unchanged in the dewaxing unit 20. The preferred isomerization conditions are a temperature of 199 to 5380C (3900 to 1000°F), a pressure of atmospheric to 10,400 kPa (1500 psig), a liquid hourly space velocity (LHSV) from 0.2 to 5.0 hr 1 and a hydrogen feed rate of 90 to 900, n 1/1, normal liters per liter of liquid feed (500 to 5000 SCF/bbl of vacuum gas oil). Most preferably, the temperature is 371 to 454 (7000 to 8500F), the pressure is 2200 to 3500 kpa (300 to 500 psig) the liquid hourly C 3G space velocity is 0.5 to 2.0 hr and the hydrogen feed rate is 180 to 540 n 1/1 (1000 to 3000 SCF/bbl).

The dewaxed effluent is separated by separator 30 into a vapor stream 34 and a liquid stream 36. The vapor (H 2 and C1-C hydrocarbons) may be recycled, used as fuel gas or separately processed. The liquid, comprising C5+ hydrocarbons, enters i r F-3664 -4-

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It A t t I It tO li 9 C distillation tower 40 which produces a naphtha stream 42, typically

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5 to 143 0 C (2900F) a kerosene stream 46 and a bottoms stream 44.

The aromatics impair the subsequent hydrotreating of the kerosene.

Tower 40 facilitates downstream hydrotreating of the kerosene because the aromatics (which are not changed much in reactor 20) are still high boiling and concentrate in the bottoms stream 44. The kerosene stream 46 is combined with hydrogen from stream 48 to form a hydrotreater feed stream 49, which enters hydrotreater The kerosene 46 has some olefins and sulfur compounds. The hydrotreater 50 removes some of the sulfur and saturates some of the olefins. Hydrotreater 50 contains conventional hydrotreating catalysts, and operates at conventional conditions.

Typically the hydrotreater operates at 1800 to 5600 kPa (250 to 800 psig), a temperature of 240 to 427 0 C (4000 to 800 0 a liquid hourly space velocity from 0.5 to 10.0 hr 1 and a hydrogen feed rate of 90 to 900 n 1/1 (500 to 5000 SCF/bbl). The hydrotreated effluent stream 52 passes from hydrotreater 50 into separator which separates stream 52 into a C 4 vapor stream 64 and a liquid stream 66.

The liquid stream 66 passes to a stripper 70. The hydrotreated liquid is preferably steam-stripped by steam, from line 72 into a naphtha stream 74 and a jet fuel. stream-76. The jet fuel stream 76 typically comprises 143 to 288 0 C (2900 to 5500F) hydrocarbons.

Preferably, the jet fuel stream 76 has a smoke point within 1 mm of the smoke point of the kerosene stream 46. The jet fuel, stream 76, preferably meets jet fuel smoke point specifications, and may be blended into the refinery jet fuel pool.

Boiling point of the jet fuel is related to freeze point. The higher boiling point components have higher freeze points than the lower boiling point components. Distillation cut points can be adjusted by conventional means, by changing fractionator reflux rates, temperatures, etc. For jet fuel, the freeze point may range from -400 to -50 0 C (-400 to -58 0

F).

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F-3664 The isomerization dewaxing catalyst comprises zeolite beta with a hydrogenation component. Zeolite beta is described in U.S. Patent Nos. 3,308,069 and Re. 28,341. Isomerization dewaxing is described in U.S. 4,412,220.

The hydrotreating catalyst and process are conventional.

Typically the hydrotreating catalyst is Ni, Mo, Co, W, NiMo, CoMo, etc., on an amorphous support such as alumina.

This invention will be illustrated by the examples. Dewaxing and hydrotreating were run in a 100 cc downflow fixed bed test reactor. The test reactor had a 2.5 cm (1-inch nominal) inside diameter and a 91 cm (36-inch) length, including a 30 cm (12-inch) preheater, a 30 cm (12-inch) catalyst space and a 30 cm (12-inch) bottoms space. 75 cc of catalyst was used. H 2 was added at a rate of 360 nl/1 (2000 SCF/bbl).

Examples 1-5 illustrate prior art processes (Examples 1-4) or processes which do not form part of the state of the art but which are not claimed as the invention (Example Str.

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1 F-3664 6 Example 1 (Prior Art) I The feed properties are shown below.

TABLE 1 Boiling range 0 C 204-371 343-454 Boiling range OF 400-700 650-850 Gravity, OAPI 34.5 25.1 Density g/cc 0.852 0.904 Hydrogen, Wt 13.50 12.53 Sulfur, Wt 1.43 2.16 INitrogen, ppm 110 540 -tit fiCompositions, Wt Paraffins, Wt 43.9 29.0 Naphthenes 24.3 25.5 31.8 45.5 Distillation, OC/OF 214/418 349/660 233/452 358/676 303/577 403/758 364/687 448/838 374/706 457/854 The 204-371 0 C (400-7000F) fraction is a typical light gas oil.

3 ~01 The 343-454 0 C (650-8500F) fraction is a typical aromatic vacuum gas oil, and is preferred feedstock for use in the present invention.

F-3664 -7- EXAMPLE 2 (Prior Art) This example reports catalyst properties of two hydrotreating catalysts and one isomerization dewaxing catalyst.

TABLE 2 Catalyst Properties Pt/Zeolite Beta Catalyst Al,2 0 3/NiMo Al 20 3/CoMo

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4*a# 9 0# 0 4 #4 a 4

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54 44 at a I i:

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a I a *4 t t 1 a 5 Chemical Compositions Pt, Wit Ni, Wt Co, Wt MoO 3 Wt Physical Properties Surface Area, m 2 /g Pore Volume, cc/g 0 Avg. Pore Diameter, A Pore Size Distribution, 30 Angstroms 30 100 Angstroms 100 200 Angstroms 200 300 Angstroms 300+ Angstroms 20.0 0.56 16.2 135 0.389 113 230 0.52 90 371 0.70 76 The isomerization dewaxing catalyst, platinum zeolite beta, comprised about 35 wt alumina 65 wt zeolite beta to which was added 0.56 wt platinum. The catalyst was prepared by blending wt zeolite beta and 35 wt alumina with water. This was then extruded to 1.6m outside diameter pellets and dried at 121°C (250°F) in nitrogen., F-3664 -8- Then, the catalyst was heated at 2.8 0 C/min (50F/min) in nitrogen and calcined in nitrogen for 3 hours at 5380C (10000F) then calcined in air for 3 hours at 538 0 C (10000F). The air-calcined catalyst was steamed 10 hours at 538 0 C (10000F) and 1 atm steam pressure. The i catalyst was ammonium-exchanged twice at room temperature with 1 normal NH 4

NO

3 washed with water and dried at 121 0 C (250 0

F)

I overnight. Then, the catalyst was exchanged for 12 hours at room temperature with Pt(NH 3 4 C1 2 at a concentration of 4 milliliters water per gram of platinum salt, with stirring. The catalyst was then washed 4 times until free of chlorine. The washed catalyst was then dried at 121 0 C (2500F) overnight and calcined for 3 hours at 3490C (6600F) in a 60% air, 40% N mixture which has a dew point of -6°C (220F).

The resulting zeolite beta catalyst had an alpha value of based on zeolite. The significance of the alpha value and a method for determining it are described in U. S. Patent No. 4,016,218 and J. Catalysis, 61, 390-366 (1980). Catalysts having an alpha value based on zeolite of 10 to 150, preferably 10 to 100, or most preferably 30 to 70, are preferred for isomerization dewaxing.

2C Alpha can be changed by steaming, by alkali-exchange or by varying the silica:alumina ratio of the zeolite.

*1 F-3664 Example 3 (Prior Art) This example shows what can be achieved by hydrotreating alone, hydrotreating follows by isomerization dewaxing, and isomerization dewaxing alone of Arabian Light Gas Oil TABLE 3

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fttt 9 09*t ft 't 0 4 9* ft., 9 r 9 .9 o t ft., 8t 9 0 tOt.

0 0 to 9 9

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t #9 Process operating Conditions Catalyst (1) Catalyst (2) Pressure, psig kPa Temperature ,OC/OF Temperature ,OC/OF Overall LHSV, Hr 1 l Kerosene Properties Cut Points, OC Cut Points, OF Freeze Point, OC Freeze Point, OF Smoke Point, mm Diesel Index Composition Saturates, Vol Olefins, Vol Aromatics, Vol CoMo/A 2 0 3 500 3500 399/750 0.5 149/260 300-500 -39 -38 16 37.5 45 55 NiMo/A 2 0 3 Pt/Zeolite Beta 350 2500 399/750 399/750 0.5 143/288 290-550 -40 -40 13.5 43.4 58 3 39 Hydrotreating! Hydrotreating Dewaxing Dewaxing Pt/zeolite beta 350 2500 399/750 143/288 290-550 -39 -39 19.5 58.5 69 4 27 -r i. 1 F-3664 The results show that contacting light gas oil with the platinum zeolite beta catalyst produced in high quality jet fuel.

Example 4 (Prior Art) This example demonstrates the production of jet fuels from a heavier feed, the vacuum gas oil shown in Table 1. This heavy feed was processed over the platinum zeolite beta catalyst of Example 2.

The feed (vacuum gas oil) is within the scope of the invention but the processing (isomerization dewaxing alone) is not.

The reactor pressure was 2500 kPa (350 psig), the liquid hourly space velocity was 1.0 hr 1 the temperature was 416 to 421 0

C

(7800 to 7900F), with 356 nl/1 (2000 SCF/bbl) of H 2 The reactor effluent was distilled to produce a 143 to 288 0 C (2900 to 5500F) fraction, equivalent to stream 46 of the figure. Table 4 lists the properties of the 1430C+ (2900F effluent and its 143 to 288 0

C

(2900 to 5500F) fraction. The 143 to 288 0 C (2900 to 550 0 F) fraction meets smoke point requirements, but has too much sulfur (0.67 wt and olefins (7.7 vol

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cr0 t P tr I C i' 1, F-3664 -1 -11- TABLE 4 Isomerization-Dewaxing of Vacuum Gas Oil 4 Product Fraction Gravity, OA~PI Density, g/cc H, Wt S, Wt Pour Point, OC/OF Freeze Point,OC/OF Diesel Index Smoke Point, mm KV at 400C, CS Ky at 10O00C, CS Liquid Volume Saturates Olefins A~romatics Distillation, OC/OF 70%.

90% 1430C+ 290OF 30.0 0.876 13.04 1.39 -32/-25 44. 1 3.692 1.389 149/301 173/343 242/468 296/565 372/702 419/786 434/814 143-288 0

C

290-550OF 43.3 0.809 13.76 0.67 -54/-65 -42/-43 58.2 19.0 1.363 0.711 65.4 7.7 26.9 124/256 142/288 186/367 223/434 252/486 281/538 290/554 It

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44 4 C (t 3 0 Example 5 (Comparison Test) This example demonstrates isomerization-dewaxing followed by hydrotreating of the entire effluent. The entire 1430C+ (2900F+) effluent from the test reactor is hydrotreated using the F-3664 -12conventional NiMo/A1 2 0 3 hydrotreating catalyst listed in Table 2. The effluent from hydrotreater was distilled to form a jet fuel fraction 143 to 288 0 C (2900 to 5500F) whose properties are summarized in Table 5. Hydrotreating the entire 143 0 C (290 0

F

dewaxing reactor effluent degraded the jet fuel as shown by its lower smoke point and higher aromatics content compared to the unhydrotreated 143-2880C (2900 to 5500F) fraction produced in Example 4 and listed in Table 4.

Example 6-8 (Invention) This example demonstrates isomerization-dewaxing of a vacuum gas oil followed by hydrotreating the kerosene fraction of the dewaxed effluent. The dewaxed effluent of Example 4 is fractionated to produce a kerosene fraction of 143 to 288 0 C (2900 to 550 0

F)

representing stream 46 of the figure. This fraction was hydrotreated at varying temperatures using the conventional (NiMo/Al 2 0 3 hydrotreating catalyst of Table 2. The hydrotreated material was stripped to recover a jet fuel product of 143 to 2880C (2900 to 5500F). Hydrotreating conditions and jet fuel product properties are listed in Table -i F-3664 -13- TAB8LE Isomerization-Dewaxing Then Hydrotreating 5 6 7 8 Example Hydrotreater Feed Isomerization------ Jet Fuel Effluent Fraction Boiling Range Pressure, psig kPa Temperature, OF

OC

LHSV, Hr 1 l 2900F+ 143 0

C+

2900 5500 F Fraction 1430 288 0 C 500 3500 500 3500 500 3500 500 3500 601 316 1.0 651 344

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2 Feed Rate, SCF/B Jet Fuel Product Gravity, OAPI Gravity, g/cc H, Wt Wt Pour Point, OC/OF Freeze Point, OF Diesel Index Smoke Point, mm Naphthalenes, Vol Composition, Vol Saturates olef ins Aromatics 2000 356 39.6 0.827 13.21 0.006 -48/-55 -41/-42 49.7 16.0 2.32 62.5 2.6 34.9 2000 356 43 0.811 13.95 0.076 -48/-55 -41/-42 60.8 19.0 2.03 71.2 1.8 27.0 2000 356 42.4 0.814 14.47 0.026 -48/-55 -41/-42 60.0 20.0 1.49 72.6 2.2 25.3 2000 356 42.0 0.815 13.84 0.02 -48/-55 -41/-42 59.4 18.5 2.3 71.3 2.3 26.4 Jet A Spec.

31-51 0.-87-0-78 0.3 -40/-40 18 3

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rr 1 '4 '4J qr araun~ara~nrr~- i -r F-3664 -14- In Example 5, the entire 1430C+ (2900F isomerization dewaxing reactor effluent is hydrotreated. Even though the boiling range of the jet fuel product is the same (because of fractionation to obtain a 143 to 288 0 C product) in Examples 5-8, the jet fuel made in Example 5 is not as good as the jet fuel made in Examples 6-8.

Increasing the hydrotreating temperature from 3160C (6010F), in Example 6 to 344 0 C (to 651 0 F) in Example 7 gave a jet fuel product having less sulfur and a higher smoke point.

Hydrotreating at 371 0 C (7000F), in Example 8, gives a jet fuel 10 product with an 18.5 mm smoke point, as opposed to the 20.0 mm smoke point of the product from Example 7.

The results in Table 5 indicate that hydrotreating the jet fuel fraction, the 143-288 0 C (2900 to 550 0 F) fraction, separately from 288 0 C (5500F components, improves the jet fuel quality, as shown by a higher diesel index, higher smoke point and lower volume percent olefins. The 143-288 0 C (2900 to 550 0 F) fractions after hydrotreating, as shown in Examples 6-8, can be blended directly into refinery jet fuel pools.

Thus, the present invention provides jet fuel which meets typical freeze point, pour point and smoke point specifications.

The process of the present invention can produce jet fuel from 3430C (6500°F) feedstocks which are highly aromatic. The process selectively cracks heavy paraffins to jet fuel boiling range materials while it converts little of the heavy aromatics in the feed into the jet fuel fraction. Jet fuel quality is improved by mildly hydrotreating the kerosene cut separately from heavier hydrocarbons. The present invention also removes aromatics from the hydrotreater feedstock by fractionating heavier hydrocarbons away from the kerosene fraction prior to hydrotreating, because aromatics tend to concentrate in the heavier hydrocarbons.

Isomerization-dewaxing, followed by fractionating and hydrotreating, produces high quality jet fuel at low pressures even from chargestocks containing 20 to 50 wt. aromatics. This is significant since refineries will process more heavy crudes which e contain more aromatics.

Claims (9)

1. A process for producing jet fuel from a vacuum gas oil feed having at least 20 to 50 wt aromatics and boiling above s5 oan tsarnerilso Lof by contacting the feed with-adewaxing catalyst comprising a hydrogenation component and zeolite beta having a silica:alumina ratio of at least 30:1 at 199-538 0 C (3900 to 10000F), a pressure of atmospheric to 10,400 kPa (1500 psig), a liquid hourly space velocity of 0.2 to 5.0 hr 1 in the presence of hydrogen to produce a dewaxed effluent stream, wherein most aromatics in the feed are unchanged; separating the dewaxed effluent stream into a kerosene fraction containing hydrocarbons boiling below 343 0 C (6500F) and a heavier fraction; hydrotreating the kerosene fraction with a conventional hydrotreating catalyst under conventional hydrotreating conditions to produce a hydrotreated kerosene stream; and +o prc>LLk.ce Unr ngram the hydrotreated kerosene stream a jet fuel product.

2. The process of Claim 1, further characterized in that the kerosene fraction boils within the range of 143-288 0 C (2900 to 550 0 F).

3. The process of Claim 1 or 2 further characterized in that the dewaxing occurs at a pressure from 2200 to 3500 kPa (300 to 500 psig).

4. The process of any preceeding Claim further characterized in that the hydrogenation component of the dewaxing catalyst comprises 0.1 to 5.0 wt of a noble metal of Group VIII of the I IPeriodic Table. 30

5. The process of Claim 4 further characterized in that the hydrogenation component is 0.1 to 1.2 wt platinum.

6. The process of any preceeding Claim further characterized in that the vacuum gas oil feed boils above 343 0 C (6500F) and contains more weight aromatics than paraffins. F-3664 -16-

7. The process of any preceeding Claim further characterized in that the vacuum gas oil contains at least 2.0 wt. sulfur, the =Ct le-ast fo-VV dewaxing step converts p i of the feed to olefins, the kerosene fraction comprises olefins and sulfur, and the conventional hydrotreating removes a portion of the sulfur, and saturates a 6 majority of thP n -fins in the kerosene fraction. DATED.-22 September 19-9-6 PHILLIPS ORMOD FITZPATRICK Attore for: i r I S i: 17

8. The process substantially as hereinbefore particularly described with reference to any one of examples 6 to 8. DATED: 24 October, 1989 MOBIL OIL CORPORATION By their Patent Attorneys: PHILLIPS ORMONDE FITZPATRICK q dr, onvi j r U I

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