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2,409,15 Patented Oct. 8, 1946 STATES PATENT'OFFICE 2,409,156 FUEL COMPOSITION Walter A. Schulze and Richard 0. Alden, Bartle's ville, Okla., assignors to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application March 28, 1942, Serial No. 436,714 4 Claims. (Cl. 44-80) 1 2 This invention relates to an improved motor fuel composition for use in high output aircraft as a source of volatility to adjust the vapor pres sure of the blend and to produce desirable dis engines. More speci?cally, this invention relates to an aviation fuel conforming to rigid speci? portion of the distillation curve. tillation characteristics, especially in the initial are ordinarily available in somewhat smaller vol ume than base stocks prepared from naturally occurring distillates, blending formulas which re tion, combustion characteristics which provide superior power output over a broad range of fuel air ratios, and particularly over the range classi ?ed as rich mixtures. High octane number aviation fuels are manu ' Since the synthetic isoparai?n blending stocks cations of antiknock rating, vapor pressure, and distillation characteristics, and having, in addi quire minimum volumes of such synthetic stocks 10 are preferred. Assuming that isopentane is plen tiful and used to the maximum extent possible within vapor pressure and front-end volatility limits, it then remains to select and prepare other components commonly termed base stocks of both high number and low vapor pressure. blending stocks and naturally occurring base 15 These octane characteristics are most conveniently ob stocks which are segregated with such precision as tained by segregation of isopara?ins, such as the to approximate the purity of the synthetic hy factured and blended according to speci?cations s0 strict that the selection of suitable components is limited in many cases to high purity synthetic drocarbons. Such fuels must have high octane number ratings and this in turn means that the isohexanes, etc., as being more valuable ‘than a full boiling range naphtha, unless the naphtha is de?cient in normal (low octane number) paraf components must have high octane number rat ?ns' or has unusually high octane number as a ings and/or excellent response to the addition result of its content of naphthene hydrocarbons. of antidetonants. Further, the unsaturation of The net result of the above described blending the components must be exceedingly low in or procedure is the production of fuels of suitable der that the fuels be substantially free of gum distillation characteristics, vapor pressure, gum and of susceptibility to gum formation. rl‘hese 25 stability, and octane number rating, comprising quali?cations together with rigid requirements largely isoparaf?ns of 5 to about 8 or 9 carbon for vapor pressure, end point, and distillation atoms, substantially free of C4 hydrocarbons, and characteristics, sharply limit the choice of fuel preferably containing only minor amounts of C5 components to the relatively low-boiling predom inantly paraf?nic hydrocarbons, say of 5 to 9 30 to C9 normal para?ins. The content of naph thenes is often small, since these compounds are carbon atoms, and preferably to the higher oc usually present in only small quantities or in tane number branched-chain or isopara?ins. many cases are removed more or less completely In the manufacture of aviation fuels of 90 to by the precise fractionation which separates the 100 octane number or those fuels having anti knock ratings beyond the conventional octane 35 normal C5, C6, and C7 parai?ns from the isoparaf ?ns in naphtha base stocks. scale, the procedure usually includes the manu The complex and strenuous requirements of facture of synthetic isoparai?ns as one blending military aviation under present war conditions component. For example, processes, such as se have emphasized some de?ciencies of aviation lective polymerization, thermal or catalytic alky fuels under certain conditions. Such conditions, lation, or the like, may be utilized to prepare 40 for example, are those which require increased concentrates of iso-octanes together with usually or emergency power for improved and rapid take much smaller amounts of higher and lower homo off, particularly with heavy loads, rapid accelera logues. Thermal alkylaticn may produce such stocks as neohexane, which are highly desirable tion and climb during combat. The production As a second component, base 45 of maximum power output under these conditions blending stocks. stocks comprising isohexanes, isoheptanes, iso octanes, etc., may in many instances be prepared by precise fractionation schemes from crude oil and/ or natural gasolines. A third component, which is ordinarily consid ered separately, is isopentane which can be pre- ' is of primary importance and the development of fuels which will meet these severe requirements under all conditions is an essential military re quirement. It is also obvious that fuels which meet rigid military requirements will be of great value in the development of commercial aviation. The term “rich mixture performance” as now used by the art, and as referred to herein, de scribes the power output of aviation engines un pared in substantially pure form by fractionation of hydrocarbon mixtures containing it. This last named material is ordinarily the lowest boiling stock'included in aviation fuels, and it functions 55 derv rich mixture conditions, such, for example, 3 25,469,156 4 as would be obtained by substantially increasing aromatic homologues which might be present in the fuel concentration in an air-fuel mixture at the intake of an aviation engine. This perform ance is usually de?ned in terms related to a standard 100 octane number reference fuel, the relative improvement being stated in ml. of tetra crude or impure alkylated benzene mixtures. A further purpose served by the used of the sub stantially pure compound is the elimination of associated impurities which may have deteriora ethyl lead. While laboratory tests and octane ratings by tive effects on the fuel and/or on aircraft fuel systems in which it is used. In the investigation and testing of isoparaf the conventional methods employed for aviation fin aviation fuel blends containing aromatic hy fuels indicate satisfactory performance, more re— 10 drocarbon additives for the purposes outlined cent test procedures involving fuel performance above, it has been found necessary to disregard in supercharged test engines (for example Method the conventional concepts of the use and prop AN-VV-F-748) have indicated a de?ciency in erties of aromatics as a class. For example, the power output of said predominantly isoparaf whereas aromatics have been previously regard ?nic fuels. This de?ciency has been shown to ed as enhancing the octane rating of ordinary occur most markedly in rich mixture ratings of fuels, it is necessary in the present instance to the fuel corresponding to take-off or emergency limit the quantity of aromatic to avoid degrada power requirements in aircraft at fuel-air ratios tion of the octane number and response to tetra very much higher than the lean mixture ratios ethyl lead antidetonant. Further, while aro ordinarily employed for ef?cient cruising opera“ 20 matic hydrocarbons have heretofore been re tion. This discrepancy in the incremental power garded as equivalents within the limits of their output with greatly increased fuel-air ratio and physical properties, such equivalency is entirely fuel consumption has introduced a new consid lacking in the present application as will be illus eration into the previous blending formulas to trated hereinafter. deal with the rich mixture rating of the ?nished 25 While speci?c embodiments of the present in fuels. vention may be invoked in a great variety of Since the predominantly isopara?inic fuel blending operations involving isoparaf?nic blend compositions are very satisfactory from the ing and base stocks, one satisfactory procedure standpoint of most speci?cations not involving may be outlined in the following operations. A rich mixture requirements and permit the pro 30 fuel is to be prepared, according to a blending duction of larger volumes of ?nished fuel per vol formula, from iso-octane, isopentane and a naph ume of synthetic blending stocks than are possi tha comprising C6 and C1 isoparaf?ns in pro ble with other blending formulas, it is ordinarily portions which produce 100 octane number with most advantageous to retain the isopara?in 4 ml. of tetraethyl lead per gallon. This blend blending formulas insofar as possible. This pro 35 ing formula is altered according to the present cedure requires that such special performance invention to include isopropylbenzene by use of a characteristics as lean and rich mixture ratings predetermined volume per cent of an isopropyl be obtained through the inclusion of minor pro ben'zene-isopentane mixture having a vapor pres portions of substantially pure hydrocarbon addi sure substantially equal to that of the ?nished tives. These additive compounds must be care 40 fuel (usually '7 pound Reid vapor pressure). fully selected so that the desired improvements The volume of the mixture used replaces a cor are obtained with such ‘small quantities that responding volume of isopara?in base stock and other fuel characteristics are not impaired and synthetic blending stock with the blending pro blend speci?cations are not infringed. portions of the latter usually being readjusted to It is an object of the present invention to pro produce the same octane number rating as vide an improved fuel composition for use in before. aircraft engines whereby the effective operation The isopropylbenzene may be added alone to and power output of the engines are improved. fuel blends, but it is often more convenient to t is a further object of this invention to provide employ the isopentanized mixture. The advan an improvement in the blending formulas for 50 tages lie in the maximum utilization of isopen~ preparing predominantly isopara?inic aviation tane and less dif?culty in blending to meet vapor fuels whereby the rich mixture de?ciencies ‘of pressure speci?cations. The amount of isopro said isopara?in blends are effectively eliminated. pylbenzene thus included in the ?nished fuel is Another object is to provide a method for im further limited by its relatively high boiling point proving the power output of aviation fuels under 55 (306.5° F.) which restricts the volume permissi rich mixture conditions. A further object is to ble in a fuel having a maximum 90 per cent evap provide an isopara?inic aviation fuel of 100 oc orated temperature of 275° F. tane number rating or better containing a rela The isopropylbenzene employed in the fuel tively minor proportion of an added compound providing greatly improved rich mixture char 60 compositions may be derived from any suitable source, provided a relatively pure product is ob acteristics without undesirably affecting the tained. In many cases, it is di?cult to separate other characteristics of the fuel. A still further isopropylbenzene from complex mixtures of aro~ object is to provide a hydrocarbon fuel compo matic and other types of hydrocarbons such as sition which will meet all desired specifications for volatility, vapor pressure, distillation charac 65 may result from the non-selective alkylation of teristics, and octane number together with a mixed stocks such as gasoline fractions. For this method for its preparation. reason, the preferred source of isopropylbenzene We have now found that aviation fuels of the for the present invention is the selective alkyla type described and comprising essentially iso tion of benzene with propylene or its equivalent para?in hydrocarbons have greatly improved oc 70 alkylating agents in the presence of suitable al tane number ratings at high fuel-air ratios when kylation catalysts such as boron ?uoride or hy minor proportions of isopropylbenzene are added. drogen ?uoride which produce the branched The isopropylbenzene is employed as the sub chain derivative exclusively. The isopropyl ben stantially pure compound since its e?icacy is zone which may be thus produced in high yields highly speci?c and de?nitely superior to other is substantially free of undesirable impurities 2,409,156 5 and/or polyalkylated benzenes. ' _‘ ' 6 tane number ratings of 100 octane number avia-w and is readily separated from unreacted benzene ' The amounts of isopropylbenzene'added will‘ tlon fuels. .Test method AN-VV-F-.748, as re ferred to herein is identi?ed as Army-Navy Aero nautical Speci?cation Fuel; Aircraft Engine, Gen obviously be dependent on the other fuel com eral Speci?cation (Method for Supercharged ponents and on the rich mixture octane rating Knock Test) AN-VV-F-748 dated September 22, which is desired in the ?nal blend. In most 1941. The test method described therein is. used cases, the isopropylbenzene will vary between for determining lean and rich mixture ratings about one and about 20 volume per cent of the blend, with a somewhat narrower range'of about 10 of 100 octane aviation fuels. In this latter speci ?cation (AN-VV-F-748) a lean mixture is shown two to about 10 volume per cent usually pre to be about .06 pound of fuel per pound of air and ferred. The compound in substantially pure a rich mixture at least about .09 pound of fuel form is relatively expensive, and hence, is not per pound of air. ordinarily used to replace the conventional blending ingredients- Also, excessive amounts As illustrations of the improvedperformance' blend and/or to impart sufficient aromaticity to propylbenzene to isoparafilnic aviation fuels, the may tend to decrease the lead response of the 15 characteristics obtained by the addition of iso the fuel to increase the solvent and swelling action on rubber-lined fuel tanks. ~ - . ‘a 1 following examples are cited: Example I In this connection, it has been found that iso propylbenzene, perhaps because of the branched 20 A 100 octane number aviation fuel was pre pared according to blending formula A, given side-chain, exhibits quite different properties from below, plus 4 ml. tetraethyl lead per gallon. This those of benzene, toluene, xylenes and even ethyl formula was then modi?ed to permit" the inclu and n-propylbenzenes. One way in which the sion of ?ve volume per cent of each of the follow diiferent and more desirable properties of isopro pylbenzene are evidenced is in reduced swelling 25 ing additives: (1) benzene, (2) ethylbenzene, and (3) isopropylbenzene. These three modi?ed of and diffusion through rubber or rubber-like blends, noted below as B, C, and D conformed to materials with which the compounds or fuel com fuel speci?cations and rated approximately .100 positions containing them are in contact. Com octane number with 4 ml. tetraethyl lead'per parative data are given below for an isoparaf?nic aviation fuel (blend A) and for said fuel after 30 gallon. Isoparai?n components, volume per cent ‘ Formula " ' Aromggiggilitlve Isooctane Isoheptane Isohexane Isopentane 33. 0 30.9 18.0 V 30. 9 30. 9 per cent) 36. 0 l3. 0 16.9 33.8 13.5 Benzene. l6. 8 l6. 8 33. 7 33. 7 l3. 6 l3. 6 None. Ethylbenzene. Isopropylbenzenc. _ _ These blends were rated according to the Army addition thereto of 5 per cent and 15 per cent of Navy test method AN-VV-F-746 and also accord ing to the supercharged engine method AN-VV-v 45 contact with a moderately oil-resistant synthetic benzene, ethylbenzene, and isopropylbenzene, in F-748. rubber, as represented by I-Iycar Q. R. Octane numbers above 100 are recorded Aromatic additive Blend A . Benzene Aromatic concentration (volume percent)__ Percent swelling (24 hours) ______________ _. Di?usion (grams/hour) Ethylbenzenc 1x233‘? None ______ __ 5 l5 2. 2 3. 48 0. 014 ...... .. 0. 035 0.112 5 0. 5 0. 025 l5 2. 4 0. 059 5 0. 5 0.022 15 .9 0. 034 2. 7 4. 0 1. 2 1. 6 Increased solvency due to aromatic (mg/gm. rubber per 24 hours) ___________________________________________________ __ (Reference) These results indicate that the swelling, diffu sion, and solvency effects with the alkylated ben 10.7 18. 7 as ml. of tetraethyl lead in 100 octane number 60 iso-octane in the following table. zenes are appreciably less than with benzene it self. This eifect is apparently due to decreased aromaticity resulting from the alkyl group, and varies particularly with the length of the side 65 chain. This means that better service character istics result from the use of isopropylbenzene and/or that larger concentrations of isopropyl benzene may be employed without encountering difficulties in service. Test method AN-VV-F-746 as referred to here in is the method identi?ed as Army-Navy Aero nautical Speci?cation Fuel; Aircraft-Engine Gen Antiknock rating Blend formula ’ AN-VY&F—74B AN-VV-F-745 - I —— Lean mixture Rich mixture lvn. TEL Ml. TEL’ Ml. TEL __ 0 . 0'5~ 0. 20 0. 65 __ 100 0. 30 0. 80 0.- 100 0. 20 0. 80 0. 03 0. 30 1. 25 D ________________ _ _ These results indicate the substantially improved eral Speci?cation (Method for Knock-Test rich mixture rating provided by isopropylbenzene AN-VV-F-746), dated October 5, 1940. This method is utilized for determining ordinary oo 75 as compared to the fuel A alone and to formulas 2,409,156 13 and C with benzene and ethylbenzene. The ~ effect of the aromatic additives is very slight in the conventional (F746) rating, and also in the lean mixture supercharged ratings. and contains isopentane in an amount not more than is suf?cient to result in a Reid vapor pressure While a, certain small improvement is indicated for benzene and ethylbenzene, the ‘magnitude ofv the improvement is in most instances not su?icient to justify the use of these additives. ml. of tetraethyl lead ?uid per gallon, said hydro carbons being so proportioned that said mixture has gasoline characteristics of distillation range not greater than seven pounds, and maintaining during said operating period for said aviation en The use of gine rich-mixture operating conditions such that the fuel-air ratio is at least about .09. benzene in particular is questionable in view of other and undesirable effects on the qualities and 10 2. An improved method of operating an avia properties of the fuels. On the other hand, the tion gasoline engine requiring a fuel having an superior qualities of isopropylbenzene are clearly ' octane number of at least about 100, which con indicated since the rich mixture rating of fuel D sists of supplying to said engine as the fuel dur is approximately twice that of fuel A when con ing an operating period a gasoline comprising sidered in terms of mi. TEL in iso-octane. essentially ‘a mixture of isoparaf?n hydrocarbom having not less than 5 and not more than 9 car Example II bon atoms per molecule and about 10 per cent A special aviation fuel was prepared by blend by volume of isopropyl benzene and at least about ing commercial iso-octane, neohexane, and iso 3 ml. of tetraethyl lead ?uid per gallon, said hy pentane in proper proportions to meet vapor pres 20 drocarbons being so proportioned that said mix sure and distillation speci?cations, and to meet turev has gasoline characteristics of distillation octane number requirements with 3 ml. TEL per range and contains isopentane in an amount not gallon. This composition was then modi?ed more than is su?icient to result in a Reid vapor pressure not greater than seven pounds, and by the inclusion of a mixture of 78 per cent iso propylbenzene (Boiling Range 305 to 308° F.) and 22 per cent isopentane to produce a fuel con taining 10 per cent isopropylbenzene. The com parative octane ratings of these fuels with 3 ml. TEL per gallon were as given below in terms of m1. TEL in 100 octane iso-octane. Octane numbers by the AN-VV-F-746 method were approximately 100. maintaining during said operating period for said aviation engine rich-mixture operating condi tions such that the fuel-air ratio is at least about .09. 3. An improved method of operating an'avia tion gasoline engine requiring a fuel having an octane number of at least about 100, which com prises supplying to said engine as the fuel during an operating period a gasoline which consists Octane rating (AN-VV-F-748 method) Lean mixture 25 Rich mixture essentially of a mixture of isoparaf?n hydrocar 35 bons having not less than ?ve nor more than nine carbon atoms per molecule and isopropyl benzene in an amount between about 1 and about 20 per cent by volume of the total and at least about 3 ml. of tetraethyl lead ?uid per gallon, said hydro Ref. blend+l0% isopropylbenzenanh 0. 80 2.6 40 carbons being so proportioned that said mixture has gasoline characteristics of distillation range In this case, without appreciably affecting the and contains isopentane in an amount not more conventionally determined octane number, the than is sufficient to result in a Reid vapor pres rich mixture rating of the fuel was raised 0.6 ml. sure not greater than about seven pounds, and TEL in iso-octane. maintaining during said operating period for said Reference blend _____________________ _. 0.80 2. 0 While the foregoing speci?c examples provide illustrations of the improvement obtained through the practice of the present invention, it will be apparent that the variations which can be pro duced through changing the volume ratio, quality, and hydrocarbon type of the blending compo nents are numerous. Therefore, no limitation of the scope of the invention is intended. Also, while the invention has been described and exempli?ed in application to predominantly isopara?inic fuel blends, it is broadly applicable to fuel composi tions suitable for the purposes outlined and within aviation engine rich-mixture operating conditions such that the fuel-air ratio is at least about .09. 4. An improved method of operating an avia tion gasoline engine requiring a fuel having an 50 octane number of at least about 100, which com prises supplying to said engine as the fuel during an operating period a gasoline comprising essen tially a mixture of isoparai?n hydrocarbons hav ing not less than ?ve nor more than nine car 55 bon atoms per molecule and isopropyl benzene in an amount between about 2 and about 10 per cent by volume of the total and at least about 3 the limits prescribed. ml. of tetraethyl lead ?uid per gallon, said hydro What is claimed-is: v carbons being so proportioned that said mixture 1. An improved method of operating an avia has gasoline characteristics of distillation range 60 tion gasoline engine requiring a fuel having an and contains isopentane in an amount not more octane number of at least about 100, which con than is su?icient to result in a Reid vapor pres sists of supplying to said engine as the fuel dur sure not greater than about seven pounds, and ing an operating period a gasoline comprising maintaining during said operating period for said essentially a mixture of isopara?in hydrocarbons 65 aviation engine rich-mixture operating conditions having ?ve, six, seven, eight and nine carbon such that the fuel-air ratio is at least about .09. atoms per molecule and about 10 per cent by vol WALTER A. SCHULZE. ume of isopropyl benzene and at least about 3 , RICHARD C. ALDEN.