US3175970A - Process for preparing a jet fuel - Google Patents

Description

March 30, 1965 P. G. BERCIK ETAL PROCESS FOR PREPARING A JET FUEL Filed March 20. 1962 SMS Qh.

mthan the aromatic content of the cycle oil.

ho-nditions, extracts composed of 90 to 97 percent aro- United States Patent Otitice 3,175,970 PRGCESS FOR PREPARING A JET FUEL Paul G. Bereik, Glensllaw, Harold Beuther, Gibsonia, and Alfred M. Henke, Springdale, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Filed Mar. 20, 1962, Ser. No. 180,963

3 Claims. (Cl. 208-212) This invention relates to a process for making fuels for jet engines and more specifically jet fuels which have been termed JP-X Fuels.

The JP-X Fuels must have the following properties: A net heat of combustion of over 18,350 B.t.u.s per pound of the fuel and over 135,000 B.t.u.s per gallon of the fuel. Further, fuels of this class must have good low temperature lluidity properties, below 40 F. freeze point and excellent thermal stability. It is apparent `that the prioduction of fuels meeting these specifications presents a difficult problem, particularly when it is recognized that the fuels must be made at a reasonable cost.

We have discovered in accordance with the invention that fuels meeting these specications can be prepared efliciently by the process described more fully hereinafter. The charge stock for the process is acatalytic cycle gas oil formed when heavier oils are cracked in conventional catalytic cracking units. In the present process the cycle gasoil is fractionated to obtain a fraction having an initial boiling point of at least about 475 F., a 50 percent point above about 550 F., a 75 percent point above about 675 F. and anend point lower than about 715 F. Cycle gas oils of this type contain a high percentage of aromatic hydrocarbons. We have found that an excellent jet fuel can Abe obtained using a cycle gas oil of the boiling ranges referred to `above and employing a process involving additionally a solvent extraction of the cycle gas oil and subjecting the extract to a hydrogenation pretreatment to reduce substantially the sulfur and nitrogen content of the extract. The extract, after removal of sulfur and nitrogen, is subjected to a saturative hydrogenation treatment to convert the aromatic hydrocarbons to saturated condensed ring hydrocarbons.

The invention will be understood more clearly by reference to the accompanying drawing which is a flow diagram illustrating a preferred manner of carrying out the process of the invention. Referring to the drawing, a fractionof cycle oil as described above is flowed through line 1 to a solvent extraction column 2. Solvent is introduced into the .column through line 3. The rathnate is withdrawn from the bottom of column 2 through line d and may be `processed for recovery of solvent. The extraction is carried out so `as to obtain an extract yield equal to or less than the aromatic content of the cycle oil and for best results `the extraction is carried out so as to obtain an extract yeld of about 5 to about 20 percent by volume'less Under these matics c an=be obtained.

The solvent extract stream is withdrawn through lineS and `fed to a distillation column 6 where the solvent is evaporated and withdrawn through line 7. The extract is Withdrawn as bottoms from distillation column y6 through line 8. The extract is .then mixed with hydrogen introduced through `line 9 and the mixture is Vflowed through line 10 to heater 1l. The resulting mixture is flowed through line 12 to a tirst catalytic hydrogenation unit 13, wherein the extract is subjected to a relatively mild catalytic hydrogenation effective however to reduce the `nitrogen and sulfur content `ot the extract to a low level. `We `have found that if the sulfur and/or nitrogen content of the treated extract is too high, the catalyst employed for the saturative hydrogenation will be rapidly deactivated and the fuel produced Will have poor stability, owing to relatively high aromatic, sulfur and nitrogen contents. In accordance with the invention the first hydrogenation is preferably carried out so as to reduce the sulfur in the extract to less than 150 ppm. and the nitrogen content to less than 30 ppm. The treated product, together with excess hydrogen, is removed from the bottom of catalytic hydrogenation unit 13 through line 14 to a conventional separator 15 in which excess gas is separated frorn the hydrogenated extract. Excess gas is removed through line 16 to a gas scrubber, not shown. After the separation, the treated extract is flowed through line i7 in admixture with hydrogen introduced through line 18 and the mixture is introduced through line 19 into a heater 20. The heated product is then ilowed through line 21 into a second catalytic hydrogenation unit 22. This hydrogenation unit is operated so as to saturate the aromatic hydrocarbons in the extract. The hydrogenated extract is Withdrawn from the hydrogenation unit through line 23 to a separator 2d from which excess hydrogen is removed through line 25 and may beused as recycle to the hydrogenation units. The substantially `completely hydrogenated product is yremoved from -the separator through line 26 to a fractionator 27 and the JP-X Fuel is removed from the fractionator through line 28 and thence to storage. Lighter and heavier fractions are withdrawn through lines 29 and 30, respectively.

ln order to describe the invention more clearly, it is pointed out that there are five rnain elements making .up the process. The first is the selection of the charge stock. While any cycle oils having the .properties within the ranges heretofore described are satisfactory charge stocks for the process, we prefer in accordance with the invention to employ cycle oils or fractions of such oils having initial boiling points higher than about 500 F.,l a 50 percent point higher than about 600 F., a 75 percent point less than about 650 F. and an end point less than about 690 F. Use of cycle stocks having these inspections results in jet fuels having good volumetric heats of combustion and low freezing points, and, in addition, the yields of the fuels are excellent.

The invention will be understood more fully by reference to the following example.

Example The catalytic cycle oil treated in this example had `approximately the following composition, percent by weight:

S15-600 F. 50.0 60G-650 F. 37.5 G50-685 F. 12.5

This cycle oil was subjected to solvent extraction with acetonitrile as the solvent. The volume ratio of the solvent and cycle oil was 1:1 and the extraction Was carried out ata temperature of F. The extract was then sub.- jected to catalytic hydrogenation which reduced substantially the nitrogen and `sulfur in the extract. The catalyst employed in this rhydrogenation was a nickel tungsten catalyston an alumina non-cracking base. 32 percent of the catalyst was composed of `equal partis of nickel and tungsten, the rest being the alumina base.. The hydrogenation was carried out at a temperature of about 723 F., a pressure of about 1000 pounds per square inch gauge, and a. hydrogen circulation rate of 4000 s.c.f./ bbl. The liquid space velocity, volume per volume per hour, was 0.5.

VThe treated extract substantially free of nitrogen and sulfur was then subjected to a less severe hydrogenation which was effective to saturate the aromatic hydrocarbons. The catalyst .employed in this phase of the process was a catalyst comprising nickel deposited on keiselguhr in which 48 percent by `weightof the catalyst was Patented Mar. 30, 1955 nickel. This hydrogenation was carried out at a temperature of 5715 F., a pressure of 1000 p.s.i.g. and a hydrogen circulation rate (standard cubic feet per barrel) of 8000. The liquid space velocity, volume per volume For the first hydrogenation of the extract any of the familiar hydrogenation catalysts can be used, provided the catalyst does not have strong catalytic cracking properties at the hydrogenation conditions employed. For

per hour, was 0.5. The product yield, percent by volume 5 example, catalysts comprising one or more metals such of the cycle oil, was as follows: as cobalt, nickel, molybdenum, or tungsten deposited on .a non-cracking base can be used. Further, it will heV xgact 5'02 understood that the temperatures for this operation can SJCQ g-lure-I be varied, depending upon the charge stock. For exam- 350425, F' t fuel 10'0 10 ple, temperatures w1th1n the range of about 600 to 800 600., F 'Je F. can be used. Also, the pressure employed in this .-I- fuel 2.2 180 350 F. gasoline 2.6 operation can be var-ied'withrn the range of 500 to 5000 p.s.1.g. and space velocities within the range of 0.2 to 3.0 In 4the following table the product inspections are set can be used, depending upon the other variables. Fur-l out. ther, the hydrogen circulation rate can be varied over the Cycle First Final 425-600" 35o-254 Product Inspections, Description Oil Eytract Hydro- Hydro- F., F., Jet

genation genation .TP-X Fuel Aromatics, percent by Vol 55. 0 92. 3 62. 5 1. 5 2. 8 1. 9 Heat o Combustion, Net:

Btn/1b. 18,404 18,542 aan/gal-. 135,269 131,371 Freeze Point; F. -7 Sulfur, percent 1. 28 2.12 .003 Nitrogen, percent 0.035 0.055 .008

A fuel prepared in accordance with the example Was range 2500 to 10,000 standard cubic feet of hydrogen per tested to determine its thermal stability. The test em- 30 barrel. ployed was the CFR Fuel Coker Test Procedure. This As stated heretofore, the second hydrogenation is detest procedure is described in detail in the Manual of signed to convert the aromatic extract to a product corn- ASTM Standards on Petroleum Products, ASTM D posed substantially of saturated condensed ring hydro- 1660-59T. In accordance with this test method, aviation carbons. While the catalyst employed in the specific turbine fuels are subjected to flow conditions and temexample is a highly efficient catalyst for this purpose, perature stresses similar to those in combustion gas turit should be recognized that other hydrogenation catabine or jet aircraft engines by circulation through a simulysts can be employed to achieve good results. Some lated aircraft fuel system at a temperature above 300 examples of such catalysts are 0.5 to 5 percent palladium F., at a rate of 6 pounds of fuel per hour, for a period or platinum supported on alumina and 15 percent to 50 of 300 minutes. The test apparatus comprises a fuel syspercent nickel supported on alumina. tem containing two heated sections, one of which is a Further, the process conditions for the second hydropreheater section that simulates the hot fuel line sections genation can be varied. For example, depending upon of an aviation turbine engine as typified by the engine the other variables, -the temperature may be between fuel lubricating oil cooler. The extent of fouling of heat about 400 to 700 F., the pressure may range from about transfer surfaces in the preheater section by fuel degrada- 500 to about 5000 p.s.i.g., and the hydrogen circulation tion deposits is determined by inspection and the extent rate may vary between about 2500 to 10,000 standard of such foul-ing is used as one index of the temperature, cubic feet of hydrogen per barrel. The space velocity stability of the aviation turbine engine. Preheater deemployed may, for example, be in the range of about 0.2 posits are rated according to the following scale: 0=no to 3. visible deposits; 1=visible haze or dulling, but no visible 50 Obviously many modifications and Variations 0f the color; 2=barely visible coloration; 3=light tan to peainvention as hereinbefore set forth may be made without cock stain; 4=heavier than 3. departing from the spirit and scope thereof, and therefore 'Ihe second heated section comprises a filter section only such limitations should be imposed as are indicated that simulates the nozzle area or fuel inlet area of the in the appended claims. combustion zone of a jet engine where fuel degradation We claim: particles may be trapped. A precision, sintered stainless 1. A process of making a hydrocarbon composition steel filter is employed in the lilter to trap fuel degrada; Iadapted to be employed as a jet fuel which comprises tion particles formed during the test. The extent of the fractionating a catalytic cracking cycle oil to obtain a build-UP 0f fuel degradation particles in the lter section fraction containing nitrogen and sulfur and having an is indicated by the pressure dilferential across the filter initial boiling point more than 475 F., a 50 percent and this pressure differential is used as another index of point more than 550 F., a 75 percent point less than the hightemperature stability of the aviation turbine fuel. 675 F. and an end point less than 715 F., solvent ex- In carrymg out the test described, the temperature of the tracting said fraction, recovering the extract, reducing fuel at the outlet of the preheater section was maintained the sulfur and nitrogen content of said extract by catalytic at 450 F. and the filter temperature wals maintained at 65 hydrogen-ation, catalytically hydrogenating the resulting 500 F- composition to saturate said composition, fractionating The results of this test were the following: The flter the resulting hydrogenated composition, -and recovering pressure drop in inches of mercury was 0.1 and the prefrom said hydrogenated composition a fuel having a net heater dePosits were zero. heat of combustion of more than 18,350 B.t.-u.s per It will be understood that changes' can be made in the 70 pound and more than 135,000 B.t.u.s per gallon of the process described in the example Without departing from fuel. the scope of the invention. In the solvent extraction step 2. A process of making a hydrocarbon composition of the process, other solvents can be employed in place adapted to be employed as a jet fuel which comprises of acetonitrile; for example, furfural, sulfur dioxide, amfractionating a catalytic cracking cycle oil to obtain a monia and ethylene glycol can be employed` fraction having an initial boiling point of at least about 500 F., a 50 percent point more than about 600 F., a 75 percent point less than 650 F. and an end point less than 690 F., solvent extracting said fraction, recovering the extract, reducing the sulfur and nitrogen content of said extract by catalytic hydrogenation, catalytically hydrogenating the resulting composition to saturate said composition, fractionating the resulting hydrogenated composition, Aand recovering from said hydrogenated con1- position a fuel having a net heat of combustion of more than 18,350 B.t.u.s per pound and more than 135,000 B.t.u.s per gallon of the fuel.

3. A process of making a hydrocarbon composition adapted to be employed as a jet fuel which comprises fractionating `a cycle oil from catalytic cracking to obtain a fraction containing nitrogen and sulfur and having an initial boiling point more than 475 F., a 50 percent boiling point more than 550 F., ya 75 percent boiling point less than 675 F. and an end point less than 715 F., solvent extracting said fraction, recovering the extract, reducing the sulfur and nitrogen content of said extract by catalytic hydrogenation, catalytically hydrogenating the resulting composition to saturate said composition, fractiona-tng .the resulting hydrogenated composition, and recovering 'from said hydrogenated composition a fuel adapted for use Ias a jet fuel.

References Cited by the Examiner UNITED STATES PATENTS 3,001,932. 9/61 Pietsch 208-216 3,077,733 2/63 AXe et al. 208--143 ALPHONSO D. SULLIVAN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,175,970 March 30, 1965 Paul G. Bereik et a1.

rs in the above numbered pat- It is hereby certified that error appea etters Patenil should read as ent requiring correction and that the said L corrected below.

Column 1, line 55, for "yel 3 and 4, in the table, heading to for "S50-Z540" read S50-4259 d" read yield columns the seventh column thereof,

Signed and sealed this 17th dayolf-August 1965.

(SEAL) Attest:

EDWARD J. BRENNER ERNEST W. SWIDER Avttesting Officer Commissioner of Patents

Claims (1)

1. A PROCESS OF MAKING A HYDROCARBON COMPOSITION ADAPTED TO BE EMPLOYED AS A JET FUEL WHICH COMPRISES FRACTIONATING A CATALYTIC CRACKING CYCLE OIL TO OBTAIN A FRACTION CONTAINING NITROGEN AND SULFUR AND HAVING AN INITIAL BOILING POINT MORE THAN 475*F., A 50 PERCENT POINT MORE THAN 550*F., A 75 PERCENT POINT LESS THAN 675*F. AND AN END POINT LESS THAN 715*F., SOLVENT EXTRACTING SAID FRACTION, RECOVERING THE EXTRACT, REDUCING THE SULFUR AND NITROGEN CONTENT OF SAID EXTRACT BY CATALYTIC HYDROGENATION, CATALYTICALLY HYDROGENATING THE RESULTING COMPOSITION TO SATURATE SAID COMPOSITION, FRACTIONATING THE RESULTING HYDROGENATED COMPOSITION, AND RECOVERING FROM SAID HYDROGENAT*ED COMPOSITION A FUEL HAVING A NET HEAT OF COMBUSTION OF MORE THAN 18350 B.T.U''S PER POUND AND MORE THAN 135000 B.T.U.''S PER GALLON OF THE FUEL.

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