US3216929A

US3216929A - Method of making inherently stable jet fuels

Info

Publication number: US3216929A
Application number: US148155A
Authority: US
Inventors: John A Favre
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1961-10-27
Filing date: 1961-10-27
Publication date: 1965-11-09
Anticipated expiration: 1982-11-09

Description

METHOD oF MAKING INHERENTLY STABLE JET FUELS Filed oct. 27. 1961 J. A. FAVRE Nov. 9, 1965 2 Sheets-Sheet 1 METHOD oF MAKING INHERENTLY STABLE JET FUELS Filed 0013. 27. 1961 J. A. FAVRE Nov. 9, 1965 2 Sheets-Sheet 2 TO CONDUIT 36 FEEDj l7 74 TO MOTOR F U E L 5 3 E Tw WZ G VN N8 Lw .m5 OT SC NK A ...LEN OR BA TT T X O E T 5 l 6 7 J 5 G F FEEDJ INVENTOR. J. A. FAVRE United States Patent 3,216,929 METHOD F MAKING INHERENTLY STABLE JET FUELS John A. Favre, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Filed Oct. 27, 1961, Ser. No. 148,155 Claims. (Cl. 208-312) This invention relates to a hydrocarbon fuel and to a process and apparatus for preparing the same. In one of its aspects, the invention relates to a process and apparatus for removing high-boiling aromatic compounds from a hydrocarbon fuel, and to the fuel thus produced. In another aspect, the invention relates to process and apparatus for separating a hydrocarbon fuel into various boiling-range cuts, removing detrimental compounds from certain of these cuts, and combining the cuts to produce a hydrocarbon fuel. In still another aspect, the invention relates to method and apparatus for removing detrimental compounds such as indene and indane and/or compounds containing hydroxyl radicals and/or sulfur from a hydrocarbon fuel, and to the fuel thus produced.

The modern jet aircraft are fueled by relatively inexpensive middle fractions, that is, from straight run or cracked and reformed stock from which the gasoline has been recovered; further distillation yields a fraction which has been suitable for jet fuel. It is customary to limit the end point by ASTM distillation to 600 F., to remove sulfur compounds and to reduce aromatics to 25 percent by volume. This practice of leniency in specification has been helpful to the refiners in that they have been able to supply the large volume of jet fuels demand with only slight infringement and consequent unbalance of motor fuel blending stocks.

Recent indications based on field observations are that it will be necessary to tighten Ithe `specifications on jet fuels. The reason for failure is not on the combustion characteristics of the fuel, but rather because icing prior to the filtering step caused filter plugging and resulted in flame-out. Preheaters installed ahead of the filters corrected the icing tendency, but caused heavy deposits to be laid down in the preheater and filter plugging by carbonaceous deposits.

It is an object of this invention to prepare a jet fuel having stability at the preheater temperature range. It

is another object of this invention to provide a jet fuel which does not lay down deposits in the preheater or plug the fuel filter in the jet engine system when utilized. It is another object of fthe invention to provide a method and apparatus whereby stabilized jet fuels can be prepared Without undue unbalance of refinery inventories.

Other aspects, objects, and the several advantages of the invention will become apparent to one skilled in the art upon a study of this disclosure, drawing, and the appended claims.

In accordance with this invention the above objects are attained by separating a mixture boiling in the range about to 600 F. (by ASTM distillation) into three fractions; initial to 320 F., S20-400 F. and 400 F.-i;

'removing aromatics from the 400 F.l fraction and from the initial to 320 F. fraction; and blending the nonaromatic constituents from all fractions with aromatics from the middle fraction with or without prior separation so that the resulting jet fuel contains from 1 to 25 percent by volume of the middle boiling aromatics. In one embodiment, the mixture treated comprises a naphtha re- 3,216,929 Patented Nov. 9, 1965 e. CC

sulting from reforming of a catalytically cracked cycle oil. In another embodiment, a high-boiling portion of aromatics separated from the low-boiling (i.e., initial to 320 F.) fraction of the feed mixture, as well as aromatics from the middle (i.e., 320-400 F.) fraction, are blended into the jet fuel product. In another embodiment, a cut from about 350 F. to about 360 F. containing the detrimental compounds indene and indane is removed from the fuel. This latter removal can be accomplished either by a further fractionation of the above-referred-to middle or 320-400 F. cut with removal of the indaneindene containing cut as a sidedraw therefrom, or by separating the feed mixture into three fractions; initial to 350 F., S50-400 F., and 400 R+; topping the middle or 350-400 F. cut to remove indene and indane; and then treating the three remaining cuts as stated above.

It has been suggested in the prior art that condensed ring aromatic compounds are detrimental to hydrocarbon fuels, and to jet fuels in particular, while alkylated single ring aromatics are not detrimental. This suggestion in the prior art is directed toward the problem of ice formation in the fuel, which causes plugging of the fuel filter as stated previously. Icing has, as stated, been prevented by preheating the fuel prior to its filtration. I have noW discovered that the resulting problem of filter plugging caused by carbonaceous deposits resulting from preheating the fuel can be eliminated by use of a fuel from which essentially all aromatic compounds boiling above about 400 F. have been removed. I have further discovered that the presence of not only higher-boiling aromatic compounds, but also compounds of the same boiling range containing hydroxyl radicals and/or sulfur and the bicyclics indene and indane, are detrimental to the thermal stability of a jet fuel and can be substantially completely removed by the process of my invention.

FIGURE l is a flow diagram of a presently preferred embodiment of the invention.

FIGURE '2 illustrates a method for removing a narrow boiling range intermediate cut.

FIGURE 3 illustrates alternative apparatus for removing a narrow boiling range middle cut.

In order to provide a more complete understanding of my invention, reference is now made to the accompanying drawing, which is a flow diagram of a presently-preferred embodiment of my invention. In FIGURE l, a suitable hydrocarbon feed is passed by way of conduit 1 to a fractionation column 2. The feed is fractionated in the column to produce an overhead stream 3 preferably boiling in the range 50-320 F., an intermediate stream 4 preferably boiling in the range 320-400 F., and a kettle product 5 preferably boiling in the range 400-600 F. The overhead stream is passed by way of conduit 3 to a solvent extraction zone 6, wherein it is contacted with an aromatic-preferential solvent introduced into the zone by way of conduit 7. A raffinate stream is removed from zone 6 (IAF 10-24-61) and passed by Way of conduit 8 to a stripping zone 9, wherein residual solvent is removed. An aromatic-free rafiinate is recovered overhead by Way of conduit 12; recovered solvent is returned by way of conduits 13 and 7 to the extraction zone 6. Solvent rich in aromatics is recovered from extraction zone 6 and passed by Way of conduit 14 to a heated ash zone 15. Aromatics flashed from the solvent are taken overhead by way of conduit 16 to a fractionator 17, and solvent containing heavier aromatics is passed by way of conduit 18 to a secondary ash zone 19. Aromatics removed in this zone can be passed by way of conduit 21 and its associated valve to a refrigerated separator 22, or can alternately be passed by Way of conduit 23 and its associated valve through conduit 16 to fractionator 17. Solvent containing still heavier aromatics is passed by way of conduit 24 to a vacuum flash zone 25; aromatics recovered here are passed by way of

conduits

26 and 21 to separator 22. Recovered solvent is returned by way of conduits 27 and 7 to extraction zone 6. It is to be understood that

ash zones

15, 19, and 25 are operated at progressively lower pressures as known in the art. Solvent passed by way of conduit 21 to separator 22 is cooled to cause separation of a solvent phase returned by way of conduit 34 to secondary flash zone 19 and an extract phase removed by way of conduit 32. This latter phase can be passed by way of conduit 33 to extraction zone 6, can be added via conduit 32 to fuel blending tank 58, or can be removed as an aromatic product by Way of conduit 30.

The intermediate stream from column 2 can be passed by way of conduit 4 and its associated valve to a second solvent extraction zone 35, which preferably uses the same type solvent as does zone 6. Alternately, this intermediate cut can be passed directly to blending tank 58 by way of conduit 36 and its associated valve. A portion of. the cut can be withdrawn by way of conduit 37 for use in motor fuel if desired. The intermediate fraction passed to extraction zone 35 is contacted therein with solvent introduced by way of conduit 38; this solvent can, if desired, be obtained from the previously-described solvent extraction system by way of conduit 40. A solvent extract rich in` aromatics is removed from zone 35 and passed by way of conduit 39 to a stripper 41 :wherein aromatics are stripped from the solvent and passed by way of conduit 42 to blending tank 58. Solvent is returned to extraction zone 35 by Way of conduit 38, and excess solvent can be withdrawn from the system by way of conduit 43. A raflinate free from aromatics is withdrawn from extraction zone and passed by way of conduit 44 to a stripper 45, wherein entrained solvent is removed. The resulting aromatic-free stream is passed by way of conduit 46 to blending tank 58. Recovered solvent is passed by way of conduit 47 to conduit 38.

The high-boiling stream from fractionator 2 is passed by way of conduit 5 to one of a pair of cyclically-operating adsorbers 48 wherein aromatics and other detrimental components of the stream are retained on an adsorbent such as silica gel or a molecular sieve. The resulting aromatic-free stream is passed by way of conduit 49 to blending tank 58. Adsorbent in vessels 48 can be regenerated by flushing rst with a stream of methanol and then hot butane, both introduced by way of

conduits

56 and 51. Desorbent is removed by way of conduit 52 to a desorbent recovery zone 53 wherein methanol and butane are recovered for re-use by way of conduit 54, and a heavy aromatics stream is removed by way of conduit 55.

The light aromatics-free raffinate stream in conduit 12 can be partially withdrawn by way of conduit 11 for use as a motor fuel blending stock, but is preferably passed to blending tank 58. If it is desired to adjust the volatility of the fuel product, this light stream in conduit 12 can alternately be by-passed by way of conduit 65 and its associated valve to a topping column 64, wherein light ends are removed for motor fuel blending by way of conduit 63. The remainder of the cut is passed by way of

conduits

62 and 12 to blending tank 58. In addition to

streams

12, 32, 36, 42, 46, and 49, previously described as being added to blending tank 58, there can be added other components such as additives by way of conduit 59 (eg. antioxidants) and butane by way of conduit 61 for nal volatility adjustment. The desired jet fuel is withdrawn by way of conduit 66.

It will be evident to one skilled in the art that various necessary or desirable pieces of equipment, such as heat exchangers, boilers, valves, control means, pumps, storage vessels, mixers, and the like, have been omitted from the drawing for the sake of clarity.

Typical conditions useful in operation of the equipment of the figure are as follows.

Extraction zone 6:

Pressure 25400 p.s.i.g. Temperature 230-240 F. Solvent (diethylene glycol) 240-250 F. Extraction zone 35:

Pressure 25-100 p.s.i.g. Temperature Z-300 F. Solvent (diethylene glycol) 3D0-350 F. Flash zone l5 Z50-300 F., 15-20 p.s.i.g. Flash zone 19 300 F., atmospheric pressure..

Feedstocks useful in the practice of my invention will` typically contain 25 to 80 volume percent or more of aro-- matics and thus would not meet the jet fuel requirement; of 25.0 percent maximum aromatic content. These feedstocks will vary somewhat in composition but will have a boiling range of about 50 to about 600 F. with both initial and end point variable. A typical reformed catalytically cracked naphtha suitable for use in my invention has the following properties:

Gravity API 43.9 ASTM Distillation, F.:

I. B.P 80 5 109 10 130 20 178 30 230 40 250 50 263 Rec 94.0

Rs. L2

Loss 4.8 Reid Vapor Press, p.s.i 16.7 Naphthenes and parains, vol. percent 25.3 Olens, vol. percent 0.3 Aromatics, vol. percent 74.4

Using the method of this invention, the following products can be obtained from this feedstock based on 1,000 bbls. of reformed naphtha charged.

Stream Product Volume,

N o. bbls.

3 OHP (Initial, 320 F.) 830 4 (36) MP (32o-400 F.) 120 5 BP (40G-H.v 50 Total Charge 1000 Init., 320 F. Paralimic Naphtha. 105 Init., 250 F. Paralnic Naphtha. 122 (3g-Cm ParafIin-naphtheues 43 Benzene 92 Toluene C3 Aromatics 326 Naphthene-parallins (S20-400 F.) 47 Aromatics (S20-400 F.) 73 Cgi-Cw Aromatics 6l 400+ Paraln-naphthene 44 Diand poly-cyclic aromatics 6 .IP-6 fuel @5G-485 F.) 178 Blend Composition: Bbls. Stream 62 43 Stream 46 47 Stream 49 44 Stream 42 44 Total Stream 66 178 Percent Aromatics 24. 7 Specific Gravity 0. 788

9 a, F Final End Point, F-- Residue, percent.. Loss, percent- Freezing Pt., F Corrosion (212 F., 3 hr Sulfur, Wt. percent Aromatics, Vol. percent Bromine Number (cg./g.) Viscosity at 40 F. centistokes Residue (400 F. Air jet), mg./100 ml. Net Heat of Combustion, B.t.u./lb 16 hr. Accelerated Gum, rug/100 ml.. Thermal Stability The following specific examples will serve to illustrate the advantages of my invention.

EXAMPLE I In order to show the effect of the process on the perormance of a jet fuel made thereby, the following tests were performed. The base fuel was a 400+ fraction from a JP-6 type jet fuel. This fraction was selected because it is believed to be the portion causing deposits in preheater and lilter plugging during operation. The material was non-aromatic. 'Ihermal stability tests were run using a CFR Fuel Coker at a fuel-out temperature of 450 F.

The base oil resulted in a pressure drop across the lter of only 0.13 mercury pressure after 300 minutes operation yand the preheater tube Walls had a C-FR color rating of 1 (slight haze, no color).

The base oil with 1.0 weight percent alpha-methylnaphthalene required only 223 minutes operation to result in a 25 mercury pressure drop across the filter, and to form a bronze lacquer on the preheater tubes resulting in a CFR color rating of 4 whereas a 2 rating is considered bad and lb (light tan) coloration is permitted.

To test the purity of the alpha-methylnaphthalene, it was redistilled and a second run was made with the base oil containing 1.0 weight percent of the redistilled alphamethylnaphthalene. A pressure drop of 25 mercury pressure developed across the lter in 215 minutes and again the CFR color rating was 4.

In a test of the 'base oil with 1.0 weight percent triethyl benzene, after 300 minutes operation only 0.02" mercury pressure drop had developed across the iilter and a CFR color rating of 0 was given because no visible color or deposit appeared on the preheater tubing.

Thus by removing the fused ring aromatics and adding alkyl aromatics a highly thermostable jet fuel is produced whose stability is superior to non-aromatic or highly volatile jet fuels which have been suggested for this service.

EXAMPLE II Table l Filter Pressure Heater Deposit Test Drop, Rating Inches Mercury Base oil #l 0.00 0 (no visible deposits). Base oil #l plus:

0.25 vol. percent redistilled AMN-- 0. 37 "3 (light tan deposits). 0.45 vol. percent redistilled AMN-- 0. 35 5 (tan deposits and heavier). 0.45 vol. percent percent pur- 0.78 1 (slight haze,

ity AMN. no color).

When heterocyclics, i.e. ring sulfur compounds, are present in the fuel, the total of heterocyclics and bicyclic aromatics must be below 0.45 volume percent and preferably should be absent in JP-6 type fuels. Distillation and solvent extraction are ineffective in making the separation between bicyclic aromatics and heterocyclics boiling in the same temperature range, that is, above about 400 F. It has been found that adsorption is effective to remove these high-boiling heterocyclics. A further important feature of my invention resides in the discovery that there exists near the cut point (ie. about 392 F. to about 400 F.) between the intermediate and the high-boiling fractions a wide gap between the boiling point of the desired mononuclear aromatics and the detrimental bicyclic aromatics.

The preceding examples and FIGURE l are particularly useful when there is no indene or indane present in the feedstock. Presence of either or both of these compounds makes desirable a modification of the method set forth in FIGURE l. Referring now to FIGURE 2, it is seen that the middle or 320-400 F. cut in conduit 4 is passed to a fractionator 67 wherein the indene and/ or indane is removed as a sidedraw comprising material boiling from about 350 F. to about 360 F. by Way of conduit 68. Overhead from this column is passed by way of

conduits

69, 70, and 36 to blending tank 58. Alternatively, this cut can be passed by way of conduit 71 to conduit 72 wherein it is admixed with kettle product therein for treatment in solvent extraction zone 35 to remove aromatics as described in conjunction with FIGURE l.

Another method for removal of indene and/ or indane is shown in FIGURE 3. In accordance with this method, fractionation column 2 is operated to produce the follow ing streams: overhead in conduit 3', initial, 350 F.; sidedraw in conduit 4', S50-400 F.; and kettle product in conduit 5, 400 F.-|-. The material in conduits 3', and 5 is treated as in FIGURE 1. The center cut in conduit 4 is passed to a topping fractionator 73, wherein the overhead containing indene and/or indane is removed by way of conduit 74 for use as motor fuel; this cut boils preferably from about 350 F. to about 360 F. The remainder of this center cut is preferably taken as kettle product by way of conduit 75 to fuel blending tank 58, but can be treated to remove aromatics by passing via conduit 76 to solvent extraction zone 35.

In order to show the detrimental effects of indene and indane, the following tests were made.

EXAMPLE III The same base oil used in Example 1I was used to show the effect of small additions of indene and indane on the thermal stability of the oil in a CFR Fuel Coker test. The same conditions were used as in Example II.

Table II is a compilation of the data.

When indene or indane are present in the fuel to the extent of 1 percent or more, the fuel lays down deposits in the preheater which exceed the permitted deposits in accordance with the CFR Fuel Coker test.

As will be obvious from this disclosure and these examples, there are provided process and apparatus for producing a hydrocarbon fuel which comprises fractionating an `aromatics-containing hydrocarbon feed boiling in the range from about 50 F. to about 600 F. to form three fractions, a first low boiling fraction, a second intermediate boiling fraction, and a third high boiling fraction which contains detrimental aromatics usually boiling above about 400 F.; removing aromatics from the rst and the third fractions; and blending the non-aromatic portions of the first and the third fractions with the second fraction to produce a hydrocarbon fuel containing from about 1 to about 25 volume percent aromatics.

Reasonable variation and modification are possible within the scope of this disclosure, the appended claims, and the drawing of the invention, the essence of which is that there is provided a hydrocarbon fuel free of aromatic compounds boiling above about 400 F. and indene and indane and containing from about 1 to about 25 volume percent of intermediate aromatics boiling in the range of about 300 F. to about 400 F., and a method and apparatus for preparing the same.

I claim:

1. A process for producing a hydrocarbon fuel from a reformed catalytically-cracked highly aromatic naphtha feed having a boiling range of about 50 F. to about 600 F. which comprises fractionating said feed into three fractions, a first fraction having a boiling range of about 50 F. to about 320 F., a second fraction having a boiling range of about 320 F. to about 400 F., and a third fraction having a boiling range of about 400 F. to about 600 F.; treating said first fraction by solvent extraction to remove aromatics therefrom; treating said third fraction by adsorption to remove aromatics therefrom; and blending the thus-treated first and third fractions with said second fraction to produce a fuel containing from about 1 to about 25 volume percent of aromatics boiling in the range of about 300 F. to about 400 F.

2. The process of claim 1 wherein there is further added to said resulting blend a high-boiling portion of the aromatics removed from said first fraction.

3. The process of claim 1 wherein said second fraction is treated to remove aromatics therefrom prior to said blending step, and wherein aromatics thus removed are admixed in said blending step to produce the desired hydrocarbon fuel.

I4. The process of claim 1 wherein the aromatics in said fuel have a boiling range from about 300 F. to about 392 F.

5. The process of claim 4 wherein said feed comprises a reformed catalytically-cracked naphtha.

6. The process of claim 1 wherein there is removed from said second fraction prior to said blending a portion boiling from about 350 F. to about 360 F.

7. The process of claim 1 wherein said first fraction boils from about50 F. to about 350 F. and said second fraction boils from about 350 F. to about 400 F. and wherein said second fraction is topped to about 360 F. prior to said blending.

8. A process for producing a hydrocarbon fuel containing not more than 25 volume percent aromatics comprising the steps of:

(a) passing a feed comprising a reformed naphtha containing from about 25 volume percent to about 80 volume percent aromatics to a separation zone;

(b) separating the feed of step a into a first fraction having a boiling range of about 50 F. to about 320I F., a second fraction having a boiling range of about 320 F. to about 400 F. and a third fraction having a boiling range of about 400 F. to about 600 F.;

(c) treating said first fraction by solvent extraction to remove aromatics therefrom whereby to obtain a first product stream substantially free of aromatics;

(d) treating said third fraction by adsorption to remove aromatics therefrom whereby to obtain a second product stream substantially free of aromatics; and

(e) blending together said rst product stream, said second product stream and said second fraction whereby to obtain a resulting hydrocarbon fuel comprising only components present in the said feed to step a and whereby the aromatics content is in the range of about 1 volume percent to about 25 volume percent.

9. A process according to claim 8 wherein the said second fraction is further separated prior to blending to remove components boiling in the range from about 350 F. to about 360 F. therefrom.

10. A process according to claim 8 wherein at least a Vportion of the aromatics removed in step c are also added to the blending of step e.

References Cited by the Examiner UNITED STATES PATENTS 2,345,934 4/44 Gregory 196-155 2,388,732 11/45 Finsterbusch 196-155 2,749,225 6/56 Barnum et al. 208--15 2,892,769 6/59 Frazier et al 208-15 2,910,426 10/59 Gluesenkamp et al 208-66 3,015,549 1/62 Ciapetta et al 208-15 FOREIGN PATENTS 870,474 6/ 61 Great Britain.

ALPHONSO D. SULLIVAN, Primary Examiner.

JOSEPH R. LIBERMAN, Examiner.

Claims

1. A PROCESS FOR PRODUCING A HYDROCARBON FUEL FROM A REFORMED CATALYTICALLY-CRACKED HIGHLY AROMATIC NAPHTHA FEED HAVING A BOILING RANGE OF ABOUT 50*F. TO ABOUT 600* F. WHICH COMPRISES FRACTIONATING SAID FEED INTO THREE FRACTIONS, A FIRST FRACTION HAVING A BOILING RANGE OF ABOUT 50* F. TO ABOUT 320*F., A SECOND FRACTION HAVING A BOILING RANGE OF ABOUT 320*F. TO ABOUT 400*F., AND A THIRD FRACTION HAVING A BOILING RANGE OF ABOUT 400*F. TO ABOUT 600*F.; TREATING SAID FIRST FRACTION BY SOLVENT EXTRACTION TO REMOVE AROMATICS THEREFROM; TREATING SAID THIRD FRACTION BY ADSORPTION TO REMOVE AROMATICS THEREFROM; AND BLENDING THE THUS-TREATED FIRST AND THIRD FRACTIONS WITH SAID SECOND FRACTION TO PRODUCE A FUEL CONTAINING FROM ABOUT 1