US3080223A - Stabilized distillate fuels - Google Patents

Description

3,080,223 Patented Mar. 5, 1963 3,080,223 STABILIZED DISTILLATE FUELS Philip Monuikeudam, Nanuet, N.Y., John V. Clarke, Jr.,

Cranford, NJ., and James P. Black, Brooklyn, N.Y., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed June 29, 1960, Ser. No. 39,451 16 Claims. (Cl. 44-73) The present invention relates to petroleum distillate fuels and more particularly relates to kerosines and aviation turbo fuels meeting the distillation specification of ASTM specifications for Aviation Turbine Fuels, D-165559T, having incorporated therein minor amounts of a combination of additive agents which are effective for improving the stability and allied properties of such fuels. In a preferred embodiment, the invention relates to fuels for turbo-jet aircraft, which fuels have been inhibited against the formation of sludge, sediment and heat exchanger tube deposits by a novel method and combination of additives free of the water tolerance difficulties and other undesirable properties which have characterized additives suggested for this use in the past.

Gas turbine engines used in jet aircraft are provided with heat exchangers through which the engine lubricating oil is circulated in order to cool the oil and prevent its thermal degradation. The fuel burned in the engine is used as the cooling medium or a heat sink in these heat exchangers. As the fuel passes through the heat ex" changer, it undergoes a temperature increase of several hundred degrees in a matter of seconds. Any unstable constituents in the fuel quickly react under these severe conditions to form deposits which adhere to the heat exchanger tube surfaces and the nozzles through which the fuel is subsequently sprayed into the engine combustion chamber. The heat transfer characteristics of the heat exchangers are impaired by the presence of these deposits. Deposits formed on the insides of the nozzles cause distortions in the fuel spray pattern which may result in uneven heating and eventual warpage of the combustion chamber liners of the engine. It is expected that turbine powered aircraft will be operating at ever increasing speeds and temperatures, thus the temperature to which the fuel can be brought without undergoing thermal degradation is becoming of extreme importance. Presently used turbo fuels are thermally stable at the 300 F. temperature level, but begin to degrade before the temperature reaches 400 F. Future fuels will be required to maintain their thermal stability at tempera tures of from 450 to 600 F.

Certain dispersant ashless additives have been proposed in the past to prevent the accumulation of deposits, but the use of such additives has not been successful. The problems caused by the tendency of dispersant-type additives to suspend water with which aviation turbo fuels come into contact are equally serious. At the temperatures prevailing at the altitudes at which jet aircraft must operate to obtain maximum fuel utilization, any water dispersed in the fuel quickly freezes to form ice crystals which may block screens, lines, and orifices in the distribution system through which the fuel is transferred from one fuel tank to another, and from the fuel tanks into the engine itself. Since jet fuels are frequently stored and transported in tanks containing an aqueous phase, the use of dispersant additives which promote the suspension of water increases the likelihood that water will be present in the fuel as it is introduced into the aircraft, and hence increases the danger that ice formation and accompanying difficulties will occur.

These and other difticulties encountered with additives employed in the past for improving the stability of aviation turbo fuels are avoided in accordance with the present invention through the use in such fuels of a combination additive agent which is considerably more effective for preventing the formation of sludge, sediment and deposits than are dispersants in general. This additive combination at the same time exhibits little or none of the tendency toward the suspension of water which has characterized dispersant-type additives used heretofore. It has now been found that the use of certain phosphosulfurized hydrocarbons having molecular weights between about and about 50,000 in combination with certain metal chelating agents as additives for distillate fuels results in fuel products which are surprisingly stable under extremely severe conditions and which have excellent water tolerance properties. Moreover, the additive combinntion of the invention is effective at very low concentrations, is substantially ashless, is compatible with a wide variety of other additives, and has other characteristics which render it particularly attractive for use as an additive agent in distillate fuels. In addition, it has been discovered that certain processing of the turbo fuel with the subsequent incorporation of the additive combination of the invention results in a fuel product of exceptionally high thermal stability.

The phosphosulfurized hydrocarbons which are utilized as one constituent of the additive combination of the invention are prepared by reacting a C to C olefin polymer with a sulfide of phosphorus. Olefinic polymers prepared by the polymerization or copolymerization of low molecular weight olefins and diolefins such as ethylene, propylene, butylene, isobutylene, butadiene, isoprene, and cyclopentadiene, are suitable materials for the phosphosulfurization. Polymers of mono-olefins wherein the molecular weight ranges from about 100 to about 50,000 and preferably ranges from about 250 to about 10,000 are particularly effective in preparing the phosphosulfurized hydrocarbons of the invention.

One method of carrying out such a polymerization reaction is to employ a Friedel-Crafts catalyst such as boron fluoride or aluminum trichloride at low temperatures in the range of from about 0 F. to about 40 F. Other methods familiar to those skilled in the art, carried out at higher temperatures and with other polymerization catalysts may also be used. Polypropylenes and polyisobutylencs having average molecular weights between about 300 and about 8000 are particularly effective. v

The sulfide of phosphorus employed in preparing the phosphosulfurized hydrocarbons may be P 8 P 8 P 5 P 8 or a similar phosphorus sulfide. as a phosphosulfurizing agent.

The phosphosulfurization reaction may be effected by reacting 2 to about 5 moles of the olefin polymer with each mole of the phosphorus sulfide at temperatures of from 200 to 600" F. It is usually preferred to add the phosphorus sulfide to the oil in powdered form at a temperature in the range of from about 200 F. to about 250 F. and then to heat the mixture to a reaction temperature between about 300 F. and about 400 F. Agitation should be provided during the addition of the phosphorus sulfide in order to ensure complete mixing. The mixture is held at the reaction temperature for a period of from about 2 to about hours and at the end of that time is filtered to obtain the phosphosulfurized hydrocarbon product. It is ordinarily desirable to employ an amount of the phosphorus sulfide that will react completely with the olefin polymer. The reaction is continued until substantially all of the phosphorus sulfide has been reacted. In some cases it may be found desirable to blow the product with steam, alcohol, ammonia, or an amine at an elevated tem perature in the range of from about 200 F. to about 300" F. in order to improve the odor of the product.

The second constituent of the additive combination of the invention may be a variety of metal chelating or metal deactivating agents. Preferred chelating agents are those prepared by the condensation of a hydroxy aromatic aldehyde such as salicylaldehyde with an alkylene polyarnine. The preferred class of metal chelating agents are those N,N-disalicylidene-di-amino-alkanes, wherein the alkane group has from 1 to 6 carbon atoms, i.e. can be ethane, propane, butane, pentane, and hexane, and the amino groups are on the carbon atoms separated by no more than one carbon atom. A particularly desirable member of this class is N,N-disalicylidene 1,2-propanediamine. This material is preferably added dissolved in a vehicle such as xylene. Other chelating agents similarly effective include the condensation products of sallcylaldehyde with amino phenols, the tetraammonium salt of ethylene diamine tetraacetic acid and N,N'-bis(acetylacetone) ethylene diamine.

The phosphosulfurized polymers are employed in the distillate fuels of the invention in concentrations ranging from about 1 to about 30 parts per million, based on the weight of the fuel. Concentrations between about 2 and about 10 parts per million have been found to be effective under extremely severe conditions and will be preferred in most cases. The metal chelating agents employed as the second constituent of the additive combination are used in concentrations ranging between about 5 and about 60 parts per million, again based on the weight of the fuel. Metal chclating agent concentrations ranging between about 10 and about 30 parts per million are preferred. The total amount of the combined additive agent employed may thus range from about 6 parts per million to about 90 parts per million and will preferably fall between about 12 parts per million and about 40 parts per million. It is generally desirable to utilize the metal chelating agents in concentrations of from 1 to 25 times the concentrations in which the phosphosulfurized polymers are used, with from 3 to 12 times the preferred concentration range.

The fuels in which the additive combination of the invention is used are petroleum distillate fuels meeting the P 8 is preferred ASTM distillation specifications for Aviation Turbine Fuels, Dl655-59T, and which preferably boil in the range between 300 F. and about 550 F. These distillate fuel products frequently exhibit unstable characteristics which can be overcome or greatly reduced by means of the additive combination. As pointed out heretofore, the combined additive agents are particularly beneficial when used in aviation turbo fuels, and permit the marketing of such fuels with significantly higher stability levels than can be obtained with equivalent amounts of additives employed heretofore. Specifications for aviation turbo fuels are set forth in U.S. military specifications MIL-F- 4 MIL-F-5624D, MIL-F-25558B(1), and MlL-F-25656(l) and in ASTM specifications for Aviation Turbine Fuels, D-l655-59T. The properties of such petroleum distillate fuels are well known to those skilled in the art and need not be set forth in detail to permit an understanding of the present invention.

The additive agents which make up the combination additive employed for improving distillate fuel stability in accordance with the invention may be added directly to such fuels or may instead be blended in a diluent to form a concentrate which is subsequently added to the fuels. An organic solvent such as benzene, xylene, toluene, diethylene glycol, pyridine, kerosene, or the like may be used as the vehicle for such a concentrate.

The nature and objects of the invention may be more fully understood by referring to a series of tests carried out to determine the effect of the additive combination when used in petroleum distillate fuels.

In a first series of experiments, various amounts of phosphosulfurized polyisobutylene and disalicylal diami nopropane were added individually and in combination to a number of aviation turbo fuels and kerosenes which were then tested to determine their thermal stability by means of CFR fuel coker tests. The base fuels employed in this first series of experiments had the following prop erties:

Property Base Base Base Base Base fuel 1 fuel 2 fuel 3 fuel 4 fuel 5 Gravity. API 41. 0 44. 6 43. 3 42. 5 40. 2 Free-tine point, l -00 -43 60 -59 -70 AS 1 M distillation:

Initial boilin': point." F 359 324 323 334 371 10% point. F 407 354 374 361 298 50% Point. F" 4H 419 410 399 436 point, F- 406 495 489 469 489 Final tnilinz point, F 530 544 535 494 52-1 Smore point, mm 23. 0 25. 0 24. 0 20.0 24. 0 Sulfur. wel ht. percent 0. 02 0.077 0.076 0.017 0. 027 Heat content. B.t.u/# 18,685 18, 720 18, 705 18, 501 18, 694

The CFR fuel coker test used to measure the thermal stability of samples of the above fuels with and without the additive combination is carried out in apparatus which closely resembles an actual fueling system. The fuel is pumped from a supply tank through a screen and rotam eter to an annular aluminum heat exchanger where it is heated to the test temperature. The heated fuel is then passed from the heat exchanger through a sintered metal filter held at a temperature F. above the fuel temperature. Fuel performance is determined by measuring the time required for the pressure drop across the metal filter to increase by 25 inches of mercury or by the pressure increase which occurs during 300 minutes, whichever takes place first. This test has been found to give an extremely reliable indication of the stability properties of a turbo fuel under actual service conditions. The test is more fully described in CRC Manual No. 3, dated March 1957, of the Coordinating Research Council of the American Petroleum Institute and the Society of Automotive Engineers.

Due to recent increases in the stability level required of aviation turbo fuels, CRC fuel coker tests of such fuels carried out at preheater temperatures of 400 F. and filter temperatures of 500 F. are generally considered a better indication of the acceptability of a fuel from the stability standpoint than are tests carried out at the 300 F./400 F. level. In order to demonstrate the surprising eifectiveness of the addition of the invention, samples of the fuels described above containing a number of commercial additive agents which have resulted in fuels of acceptable stability at the lower test conditions were tested at the 400/500 F. level along with the additive of the invention. The results of these tests are set forth in Table I below.

Additive CFR fuel coker Base I concentratest results 1 fuel Additive 1 tion. by No. weight.

parts per Merit Tube dcznillion rating posits 3 None None 110 4 Additive A.. 6. 7 900 4 Additive A.. 3. 3 830 2 Additive B. 13.3 None None 270 Additive A 3.3 900 1 Additive 13.. 13. 3 None None 310 2 Additive A 3.3 000 1 Additive B 13.3

one None 180 4 Additive B 50 115 Additive 0.. 6. 7 630 4 Additive C 13.3 825 4 Additive B 9.3 900 1 Additive C 6. 7 Commercial a 150 200 3 Commercial additive E. 70 820 4 Commercial additive F 56 850 4 Commercial additive G. 70 410 4 Commercial additive II 70 298 4 Commercial additive I 7 375 4 The additives tested were the following: Additive A- Polyisobutylene having about 1,100 average molecular weight, treated with 15 weight percent Pass. Additive B-Disalicylal diaminopropaue. Additive CPolyisobutylene having about 1,100 average molecular weight. treated with 10 weight percent P285. Commercial additive D-4,4'-bis(2-methyl-6-tertiaryoutylphenol). Commercial additive E-An alkylcoco amine phosphate. Commercial additive F-A dimer of linoleic acid with a minor amount of an alkyl phosphate. Commercial additive G-Etl1vlene diamiue salt of dinonyl naphthalene sulfonic acid. Commercial additive II-NH4 salt of dinonyl naphthalene sulfonic acid. Commercial additive I- Amine salt of dilinoleic acid.

-Tests with base fuels 1, 2, and 3 were carried out with 300 F. preheater temperature and 400 F. filter temperature. Tests with base fuel 4 were carried out with 400 F preheater temperature and 500 F. filter temperature.

".lube deposits were rated as follows: No visible deposits. lvisible haze or dullmg but no visible color. 2- Barely visible dlscloroation. 3Light tan to peacock stain. 4-1-Ieavier than 3.

Norm-A rating of 2 is considered the maximum acceptable rating.

The data in the above table demonstrate that a combination of as little as 3.3 parts per million of phospho snlfurized polyisobutylene and 13.3 parts per million of disalicylal diaminopropanc resulted in a fuel having excellent stability characteristics from the standpoint of both merit rating and tube deposits. The merit rating is primarily an indication of the tendency of the fuel to clog screens, orifices and filters in a fuel system; while the tube deposit rating measures the extent to which deposits will be built up in the heat exchanger tubes and nozzles of a turbine engine operated on the fuel. The data in the table show that neither the individual constituents of the additive combination of the invention nor a large number of commercial additives were as effective as was the combination. The commercial additives tested were all additives which have been proposed to give acceptable stability when tested at the 300/400 F. level. The data show that none of these commercial additives raised the stability of any of the fuels sufiiciently to meet the requirements of the more severe 400/500 F. test, despite the fact that they were used in concentrations considerably higher than the concentrations at which the additive combination of the invention was found effective.

Further tests carried out to determine the effect of the additive combination upon the Water tolerance of fuels to which it is added demonstrated that the additive combination is free of the adverse effect upon water tolerance which has characterized additives employed heretofore. The tests employed were carried out in accordance with the method described in Federal T est Standard No. 791, Method 3251.6, Interaction of Water and Aircraft Fuel." In brief, this test involves the agitation of 80 cc. of the fuel to be tested with 20 cc. of water for a two-minute period, after which the mixture is allowed to I settle for five minutes. At the end of the settling period, the condition of the fuel-water interface is noted. The interface is assigned a rating as follows.

INTERACTION OF WATER AND AIRCRAFT FUELS [Method 3251.6, Fed. Test Std. N0. 791] Appearance of interface: Interface rating Clear and clean 1 A few small clear bubbles covering not more than 50% of the interface 1B Shred of lace and/0r film at interface 2 Loose lace and/or slight scum 3 Tight lace and/or heavy scum 4 TABLE 'II Effect of Additives Upon Fuel-Water T olerance Additive concentration Water Base fuel No. Additive by wcivht, tolerance parts per interface million rating 1 None None 1 Additive A" 6. 7 2 Additive 13.- 3.3 1B Additive B" 13. 3

None 1 8. 3 1B 13.3 None 1 3. 3 1B Additive 13.. 13.3

The data set forth in Table II above demonstrate that the use of the additive combination of the invention in aviation turbo-jet fuels and similar distillate fuel products does not increase the interface dcmcrit rating above the acceptable level of 1B. The additives, unlike dispersant-type additives employed to improve the stability of turbo-jet fuels and similar products in the past, meet the critical water tolerance requirements for such fuels and do not materially increase the danger that appreciable amounts of water will be suspended upon contact of the fuels with the aqueous phase present in storage tanks, pipe lines and tank trucks. This improved water tolerance constitutes an extremely important advantage of the additive combination of the invention over stabilizing additives used in the past.

While water tolerance tests of the type described above have been widely used, they have not always been satisfactory in predicting field performance. More recently, the effect of fuel additives on the water tolerance of fuels has been investigated by a method that gives greatly improved correlation with field performance. This new method uses a small filter-separator similar to the larger filter-separator units used on aircraft rcfuelcrs. In the particular test here described, 1% of water was added to the fuel ahead of a gear pump, which provides the mixed fuel-water input to the filter-separator. The effluent from the filter-separator was examined for Water content both analytically and visually. In the following table, the additive combination of the invention is compared with the base fuel and with two corrosion inhibitors approved under military specification MIL-F-5624D.

7 TABLE III Eflect of Jet Fuel Additives n Water-Carryover Through Laborat ry Filter-Separator 1 1% water added to fuel ahead of rear pump.

2 ASTM Turbine Fuel Type C (ASTM Standards on Petroleum Products, 1958).

3 As in Table I.

This table shows that the additive combination of the invention has essentially no effect on water carryover even when used in concentrations well above those required for good fuel stability. In this respect, the additive combination of the invention is far superior to commercial additives previously approved for use in jet fuel.

An exceptionally thermally stable turbo fuel composition which will successfully pass the critical fuel coker test at 450/500 F. can be obtained by the process of alkali or caustic washing, followed by water washing the petroleum fuel prior to the incorporation of the additive combination of the invention. The caustic washing is accomplished in the conventional refinery manner by scrubbing the fuel mixture with an aqueous solution of a strong base such as sodium hydroxide, caustic soda and the like. A strong caustic solution concentration of at least 5 Baum with a caustic solution to fuel ratio of from 1/20 gallons to l is preferred. The caustic wash is followed by an aqueous wash in the conventional refinery manner to remove any entrained caustic or other impurities, such as amines and the like, utilized in the various caustic regenerative processes. Water washing can be carried out in a mixer-settler or in a tower if more intimate contact is desired.

The results achieved by this process and the inventive additive combination in producing a highly stable turbo 4 fuel is more fully shown by Table IV.

TABLE IV Eflect of Caustic and Water Washing and Additives on Stability of Jet Fuel CFR fuel eokcr test results, 450/500 F. Base Causticiuel water Additive 5 5 No. treatppm. Code Filter Pressure ment 1 rating test drop across tube time in filtcr,in. deposits minutes of lig 5 (1).... None None 4 133 25 s (2)-- ---do---.- Additive 1L3..- 4 300 0 Additive B. 50-- 5 (3)-.. Yes".-- None 4 225 25 5 (4)... Yes... Additive A. 3... 2 300 0 Additive B. 50..

'lreatment of fuel consisted of caustic washing with agitation in a stainless steel vessel with a 30 Be. sodium hydroxide solution and a eaus tic solution incl ratio of gallons for one hour followed by two fiveminute water washes.

2 See footnote 1 of Table I for additive identification.

3 Tests conducted in standard CFR fuel coker with 450/500 F. preheater/filter temperature at fuel flow rate of 6 lbs./hr.. and 5 hours operatice time. All data was result of duplicate tests except for item 1.

1 Tube deposits were rated as in Table I. footnote 3.

drop of 12 inches of mercury in 300 minutes, and a maximum preheater tube deposite code rating of less than 3. As shown, the caustic-water wash alone did not change the tube deposit rating of the base fuel and gave only slight improvement in the time to reach a filter drop pressure of 25" of mercury. The separate incorporation of the additive combination of the invention to the base fuel did improve both the tube deposit rating and the filter drop pressure and time, but not sufficiently to allow it to pass the more severe specifications at a 450/500 F. preheater/ filter test level. The combination of the causticwater wash with the subsequent addition of the additive combination gave the unexpected result of increasing the thermal stability of the fuel beyond the expected levels when either component was used independently. The surprising improvement in thermal stability which allows the fuel to meet the high specifications recited allows the use of these fuels at a much higher temperature range without danger of excessive deposit formation and filter plugging.

As demonstrated, a caustic treatment with water washing followed by the addition of the inventive combination imparts exceptional thermal stability to a previously unstable turbo fuel. The data of Table V as follows establishes that caustic concentrations of 5 Baum and above are effective for this purpose, with a Baum concentration of 5 to 50 especially preferred. Suitable caustic solutions are those of sodium, magnesium, potassium hydroxide, and the like. The methods of caustic treating and water washing hydrocarbons, particularly petroleum fuels, are well known, and are set forth, for example, in Petroleum Refinery Engineering by W. L. Nelson; Mc- Graw-Hill Book Company, Inc., 1941; Chemical Refining of Petroleum by V. A. Kalichevsky and B. A. Stagner, Reinhold Publishing Corp., 1942; and other publications.

TABLE V Eflect of Caustic Concentration on Stability of Jet Fuel CFR fuel coker test results, I Caustic 450/500 F. Base concentra- Additive,

fuel tion in p.p.m. N 0. Baum Code Filter test Pressure Rating time in drop across tube deminutes filter. in. of

posits 4 Hg 1 Treatment of fuel as in footnote 1 of Table IV, except for using caustic concentration.

2 Additive concentration 3 p.p.m. additive A with 50 p.p.m. additive 5 As in Table IV, footnote 3. As in Table IV, footnote 4.

What is claimed is:

1. A petroleum distillate fuel meeting the ASTM distillation specifications for Aviation Turbine Fuels, D- 1655-59T, and having improved water tolerance and thermal stability characteristics to which has been added from 6 to about parts per million of a thermal stability additive consisting essentially of: (l) a phosphosulfurizedhydrocarbon obtained by reacting about 2 to about 5 moles of a C to C olefin polymer of from to about 50,000 average molecular weight with about 1 mole of a sulfide of phosphorus at a temperature of from 200 to 600 F. and (2) a N,N-disa1icylidene-diaminoalkane chelating agent wherein the alkane group has from 1 to 6 carbon atoms, said chelating agent being present in a concentration ratio of from 1 to 25 times the concentration of said phosphosulfurized hydrocarbon.

2. A fuel as defined by claim I wherein said concentration ratio is from 3 to 12.

3. A fuel as defined by claim 1 wherein the said olefin polymer has an average molecular weight of from 250 to about 10,000.

4. A fuel as defined by claim 1 wherein said chelating agent is 1,2propaue diamine-N,N-disalicylidene.

5. A fuel as defined by claim l wherein the said additive has been added from 1?. to 40 parts per million.

6. A fuel as defined in claim 1 wherein said fuel is a caustic-aqueous washed turbo-jet fuel.

7. A petroleum turbo-jet fuel boiling in the range between 300 and about 550 F. and having improved water tolerance and thermal stability characteristics, to which has been added from 12 to 40 parts per million of a thermal stability additive consisting essentially of: (l) a phosphosulfurizcd hydrocarbon obtained by reacting about 2 to about 5 moles of a C to C olefin polymer of from lit to about 10.000 average molecular Weight with about 1 mole of a sulfide of phosphorus at a temperature of from 200 to 600 F. and (2) a chelating agent of SEN-disalicylidene-diamiuo-alkane, wherein the alkane groups have from 1 to 6 carbon atoms, said chelating agent being present in a concentration ratio of from 3 to 12 times the concentration of the said phosphosulfurized hydrocarbon.

s. A fuel as defined in claim 7 wherein said olefin polymer is poiyisobutylenepf about 1100 average molecular weight.

9. A fuel as defined in claim 7 wherein said N,N'- salicylidenediai'nino-all;ane is 1,2 propane diatnine N,N'- disalicylidene.

10. A process for cooling the lubricating oil in a jet engine comprising using as a coolant for heat transfer with the lubricating oil a thermally stabilized petroleum distillate fuel boiling in the range between 300 to 550 F., to which has been added from 6 to about 90 parts per million of a thermal stability additive consisting essentially of: (1) a phosphosulfurized hydrocarbon obtained by reacting about 2 to about 5 moles of a C to C olefin polymer of from 100 to about 50,000 average molecular weight with about 1 mole of a sulfide of phosphorus at a temperature of from 200 to 600 F. and (2) a chelating agent of a N,N-disalicylidene-diamino-alkane wherein the alkane group has from 1 to 6 carbon atoms, said chelating agent being present in a concentration ratio of from 1 to times the concentration of said phosphosulturized hydrocarbon.

11. A process as defined in claim 10 wherein said concentration ratio is from 3 to 12.

12. A process as defined by claim 10 wherein the said olefin polymer has an average molecular weight of from 250 to about 10,000.

13. A process as defined by claim 10 wherein said chelating agent is-a 1,2-propane diamine-N,N'-disalicylidene.

14. A process as defined by claim 10 wherein the said additive has been added from 12 to 40 parts per million.

15. A process as defined in claim 10 wherein said fuel is a caustic-aqueous washed turbo-jet fuel.

16. A process as defined in claim 10 wherein said fuel has been caustic washed with a 5 to Baum solution of sodium hydroxide at a caustic to fuel ratio of from 1/20 to l/l.

References Cited in the file of this patent UNITED STATES PATENTS 2,316,078 Loane et al. Apr. 6, 1943 2,316,080 Loane et al. Apr, 6, 1943 2,382,905 Pedersen et al. Aug. 14, 1945 2,626,208 Brown Jan. 20, 1953 2,768,999 Hill Oct. 30, 1956 2,932,942 Ecke et a1 Apr. 19, 1960 3,0l4,793 Weisgerber et al Dec. 26, 1961

Claims (1)

1. A PETROLEUM DISTILLATE FUEL MEETING THE ASTM DISTILLATION SPECIFICAIONS FOR AVIATION TRUBINE FUELS, D1655-59T, AND HAVING IMPROVED WATER TOLERANCE AND THERMAL STABILITY CHARACTERISTICS TO WHICH HAS BEEN ADDED FROM 6 TO ABOUT 90 PARTS PER MILLION OF A THERMAL STABILITY ADDITIVE CONSISTING ESSENTIALLY OF: (1) A PHOSPHOSULFURIZED HYDROCARBON OBTAINED BY REATING ABOUT 2 TO ABOUT 5 MOLES OF A C2 TO C4 OLEFIN POLYMER OF FROM 100 TO ABOUT 50, 000 AVERAGE MOLECULAR WEIGHT WITH ABOUT 1 MOLE OF A SULFIDE OF PHOSPHORUS AT A TEMPERATURE OF FROM 200 TO 600* F. A AND (2) A N, N-DISALICYLIDENE-DIAMINOALKANE CHEALTING AGENT WHEREIN THE ALKLANE GROUP HAS FROM 1 TO 6 CARBON ATOMS, SAID CHEALTING AGENT BEING PRESENT IN A CONCENTRATION RATIO OF FROM 1 TO 25 TIMES THE CONCENTRATION OF SAID PHOSPHOSULFURIZED HYDROCARBON.