US 2407718 A
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RNS ,Nwww MSS w 2 Sheets-Sheet 1 AVIATION SUPER FUEL Filed Aug. 31', 1942 R. F. MARSCHNER TAL.
Sept. 17, 1946:
Patented Sept. 17, 1946 AVIATION SUPERFUEL Robert F. Marsclmer, Homewood, Ill., and Don R.
Carmody, Hammond, Ind., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application August 31, 1942, Serial No. 456,786
This invention relates to new and improved superfuels adapted for aviation purposes. It pertains more particularly to blends of which the major component is a high octane number base stock such as isooctane and the minor component is a blending agent exemplified by hydrocarbon-ketone azeotropes. The preferred lowboiling azeotropes are mixtures of acetone with `diisopropyl, neohexane or cyclopentane but we may also employ other azectropes such as mixtures of methylethyl ketone with benzene, cyclohexane or triptane and we may employ a ketone such as methylisobutyl ketone for forming an azeotrope with isooctane itself.
Ketones have been employed in ordinary gasolines and even in gasolines to which a minor amount of isooctane has been added but heretofore no such blend has met the strict present-day requirements for aviation superfuel. Furthermore, no prior blends have utilized the azeotropeforming properties of ketones for solving the problem of making high octane number base stocks meet aviation volatility requirements.
For modern aviation engines the fuel must not only have a high antiknock value under all conditions of use, a high lead tetraethyl response, etc. but it must also meet certain initial, intermediate and overall volatility requirements. Volatility speciications for 100 octane number aviation fuels are summarized in the drawings. The dotted lines represent the literal maxima set on boiling point, but for practical purposes the dashed line defines the upper limit. If any point on the A. S. T. M. distillation curve of a fuel falls below the lowest dashed line, it probably will eX- ceed '7.0 pounds R. V. P. If the fuel is to have a Reid vapor pressure approaching 7.0 pounds, however, the point will be in the vicinity of 135 F. and the 10%-l-50% (307 F.) specification auto-matically sets the minimum 50% point at 172 F. For practical purposes the intermediate dashed line represents the lower distillation limit. This leaves a rather narrow band into which the complete distillation curve of aviation superfuel falls in meeting specifications.
Commercial isooctane can have an initial boiling point of about 165 F. but between the 10% and 90% points the boiling temperature is within the range of about 210 and about 240 F., and it has a Reid Vapor pressure of only about 2 p. s. i.
The isooctane described herein is the commercial product which can, for instance, be prepared by polymerizing a mixture of isobutylenes and other butenes, diluted with butanes, to isooctenes. Subsequently, the isooctenes are hydrogenated to produce a hydrocodimer isooctane fraction. Alkylate isooctane can be prepared by the alkylation of isobutane with butenes or by the dehydroalkylation of isobutane or by the destructive alkylation of higher branched parains, for eX- ample by the sulfuric acid process. The term iseoctane as used in this specication and in the appended claims (unless more. expressly defined in the speciiic instances) is hereby dened as including not only ZA-trimeth'ylpentane but also commercial isooctanes comprising primarily trimethylpentanes such as hydrocodimer isooctaney alkyla-te isooctane, etc., as such products are commercially produced and marketed. The manner in which a commercial isooctane alone fails to meet distillation specifications is illustrated by its distillation curve on Figure l.
It is therefore an object of our invention to adjust the distillation characteristics of commercial isooctane. More specifically it; is :an object of our invention to adjust the vapor pressure and the volatility of an aviation gasoline comprising commercial isooctane. A further object is to lower the mid point of the aviation superfuel without adversely aecting the antiknock properties. Another object is to provide a blended isoo-ctane aviation fuel having th'e desired initial and overall boiling-characteristics. An additional object is to provide a tailor-made fuel of high lead response and lean and rich octane numbers.
An important object of our invention is to utilize maximum amounts of high octane number base stocks such as isooctane with available high octane number hydrocarbons such as cyclopentane, neohexane and diisopropyl so that a maximum amount of a superfuel passing all specifications can be produced with a minimum amount of these particular hydrocarbons. In other words, our object is to decrease the amount of cyclopentane, neohexane or diisopropyl which must be added to a base stock in order to meet the most rigorous specifications Without decreasing overall performance while at the same time obtaining the desired volatility of the blend.
To attain these objects we propose a unique 3 aviation superfuel comprising between about 60 and about 90 volume percent of a base stock having a clear octane number of at least 85, for example commercial isooctane. The azeotropic mixture as the low boiling ingredient can be used in quantities ranging between about and about 40 Volume percent of the blend. This azeotrope comprises between about 30 and 50 volume percent of a hydrocarbon selected from the group consisting of cyclopentane, neohexane, and diisopropyl and between about 50 and about 70 volume percent of a ketone or mixture of ketones. The amount of th'e low-boiling azeotrope'can be further lowered by employing a higher boiling azeotrope as exemplied by mixtures of benzene, cy-
clohexane or triptane with methylethyl ketone or by including a small amount of a higher ketone such as methylisobutyl ketone in the blend. Y
One outstanding feature of our invention is the use of azeotropes which boil below the boiling point of either ingredient thereof. Thus acetone boils at 134 F. and diisopropyl boils at 136 F. and both have about 'i p. s. i. Reid Vapor pressure but a mixture of 57% acetone and 43% diisopropyl has a boiling point of only 114 F.
and l1 p. s. i. Reid vapor pressure. Although cyclopentane and neohexane boil near 121 F. and have about 9 p. s. i. Reid vapor pressure, mixtures of about 35% cyclopentane or 4neohexane with about 65% acetone boil at only 105 F. and have about 13 p. s. i. Reid vapor pressure. In practicing our invention we utilize these phenomenal decreases in boiling point or increases in volatility which are thus provided by the azeotropes for obtaining results which could not be accomplished by the use of corresponding amounts of either ingredient by itself. In other words, the properties of theacetone and the hydrocarbons such as cyclopentane, diisopropyl and neohexane are not simply additive but a new and unexpected result is obtained by their conjoint use Within the defined limits.
An antiknock agent e.V g. lead alkyls, can be added in conventional quantities to the blends varying from small amounts up to the upper limit tolerated by other considerations having to do with engine design. This upper limit at present is'iixed at'about 4 cc. of lead tetraethyl per gallon of fuel. Our blends, however, have a high lead response and meet the octane number specifications without excessive amounts of lead.
We have found that certain blends comprising isooctanes with cyclopentane, neohexane or diisopropyl and certain azeotrope-forming ketones are excellent pursuit or combat aviation fuels, as such or with lead alkyls added. Selected lowboiling ketones can be used to form an azeotrope. with cyclopentane, neohexane, and/or diisopropyl in order that the vapor pressure and volatility of the isooctane blend is adjusted. Certain other ketones boiling at temperatures in the vicinity of isooctane form an azeotrope with iso- TABLE I Hydrocarbon-ketone aeeotropes of high, octane hydrocarbons V. Boiling point, F. Ketone Hydrocarbon percent Component Azeotrope Acctone 134 Cyclopentane 35 121 105 Neohexane 33 121 105 Diisopropyl 43 135 1 114V Methylethyl 175 ketone.
Benzene 50 175 172 Cyclohexane. 33 177 159 Triptane 24 177 159 Methylisobu- 240 tyl ketoneA 2,3,4-trimethyl- 47 236 225 v pcntane.
Those hydrocarbon-ketone azeotropes which boil in the range of between about 90 and 135 F.
" lare of great importance in aviation fuels because octane itself and thereby lower the end point of ythen be added of the paucity of hydrocarbons which boil in this range and which when blended with isooctane yield a superfuel having a Reid vapor pressure approaching thel specification maximum, 7.0 p. s. i., a high clear octane number, and a high lead response. Y
The addition of the low boiling ketones, for example,'acetone, to form an azeotropic mixture with diisopropyl, neohexane and/ or cyclopentane has several interesting effects. 'I'he boiling point of the hydrocarbon is lowered so that less blending agent need be added to commercial isooctaneto reduce the 10% point below 167 F. The total volume of blending agent available is increased by the volume of ketone added and this together with the reduction in the 10% point permits for more aviation superfuel production from com- .Y
mercial isooctane and a limited amount of 'diisopropyl, neohexane, and/or cyclopentane. The Reid vapor pressure of the azeotrope is greater than the hydrocarbon addition agent alone, hence less blending agent is necessary to raise the R. V. P. of the isooctane to the desired level.
WhenA a higher boiling ketone is added toisooctane' the ketone-isooctane azeotrope formed lowers the distillation range of the commercial isooctane to pass the 50% point specication'with less volatile hydrocarbon'present Ketones or mixtures thereof suitable for additionA to'commercial isooctane to lower the mid-point include ethylpropy1,methylbutyl andV dipropyl ketones. The ketones may suitably be prepared from Waste petroleum products such as propylene or'bute'nesv through reaction with sulfuric acid to'produce isopropyl or secondary butyl alcohols, followed by dehydrogenation to acetone or methylethyl ketone. Thehigher ketones may be prepared by oxidation, for example, with air, of polymers of such oleiins. One advantage of addition of such a ketone to commercial isooctane is that a smaller amount of a light hydrocarbon containing no more than six carbon atoms, as such or as an azeotropic mixture with a light ketone, need to lower the 10% point below 167F. Y
We have discovered that the azeotropes can be used according to our invention to bring -both the boiling point range and vapor pressure of isooctane within the specificationsV illustrated in Figure 1. The distillation characteristic of various blends are shown in the drawings and are summarized in-'Iable' II.
The drawings demonstrate graphically the nearly ideal'way inwhich azeotropes vcan be used to Tbring the commercial isooctane within the present aviation superfuel distillation specications. The rreference numerals of thecurves refer tothe like-'numbered blends set "out kin Table II,
and the drawings should be read in -conjunction with Athe table. These curves indicate the effects of the `'various ketones Vand 'in general illustrate our invention.
A suitable blending agent comprises 1an aseotropic mixture of between about 50 and about 70 volume percent ketone -and between about '30 and about 50 volume percent `of a high octane number 5 or 6"carbon 'atom hydrocarbon. AExamples of such `blends are illustrated in Table 1I.- For example, .a diisopropyl-acetone azeotrope having 57 volume percent kacetone boils at 114 `and has a Reid vapor pressure of Aabout 1013 p. s. 1ii. The boiling point of the diisopropyl is'lOw-ered some 22 F.. so that a greater percentageof "isooctane can be used in preparing a lblend 'whose 'point is below 167 F. 'shown inTableII, a blend of 50% lisooctane and 50% diisopropyl has 94.0 -o'ctane number l'where'asablend :of 70% isooctane and lof a blend 'of 1equal volumes of diisopropyl 'and acetone 'has a slightly `better octane number of 94.5 even though it contained farless diisopropyl. rSuch 'a 'blending agent is useful for modifying commercial isooctane to improve Ythe volatility, lead response frand the general suitability of the blend as an-aviation superfuel.
Another blended fuel according `to our invention comprises 70 volume percent lisoocta-ne and an azeotropic mixture of acetone and cyclopentane. Anazeotropic'mixtureof 4about 65 volume percent acetone and about volume percent cyclopentane has a lower boiling point of about 105 F. and a higher Reid vaporpressureof about 13 p. s. i., as well as a larger volume than cyclopentane itself. permits the relatively limited amountof cyclopentane available to go further when blended with the base fuel such as isooctane since a nished aviation fuel having a higher vapor pressure can be made with a smaller percentage of azeotrope than of the hydrocarbon blending agent and the aviation fuel contains a smaller Volume of cyclopentane. The neohexaneacetone azeotrope may be used equally well in this blend,
'Another aspect of Ethe invention consistsof the addition of ketones, Vespecially methylethyl :ketone, to `hydrocarbons of intermediate boiling range. Provided a suitable f-uel were available, engines lcould be designed `to` operate rffar more efficiently than at present. Such an ideal fuel would be of constant `volatility `'throughout and would consist, Vfor example, of a pure hydrocarbon. Methylcycl'opentane '(B. P. 163F.) passes all present day volatility Vspecifications since its 10% point is belowl'l'" F.-and its 10%-50% points total 1326 which exceeds -307. 'Butin certain respects cyclohexane and triptane are -Superioriuel hydrocarbons 'to methylcyclopentane. 'These hydrocarbcns are toohigh-boiling `(176-72) rtoibcas suitable. By the addition of ymethylethylketone to cyclohexane or triptane an-azeotrope shown in Table I results, which does 'pass all volatility specications-` Corresponding `azeotropes of methylisopropyl ketone with cyclohexa-ne and with *triptane Vycontain `mainlyhydrocarbon and likewise give -flat `lower-"boiling distillation curves.
We Acontemplate ia `vfurther modification lof )the invention. With *the use of pentene 4and hexene alkylation, iso-noname and isodecane vaviation'iuel bases 'are *obtained which approach the and end point specications of aviation fuels. By the addition of the "proper ketonewhi'ch may actually exceed 'the 'specification pointsth'ese temperatures may lbe 'brought finto line. We also contemplate blending higher "ket'ones, for 'example mixtures of Cs zketones, to-the reaction product described in your copending application S. 437,050, now United States Patent 2,308,562.
'In 'this specification and'in "the accompanying claimsthe term cyclopentane is hereby defined as including 'not 'only the pure chemical lc'ornpound'but also as includingtechnical or commercial grades of cyclopentan'e obtainable by 'close fractionation of Anaphtha. Preferably this cyclopentane should'h'ave an A. S. octanenumber of at leastabout 90, Ashould have La narrow boiling range and should consist chiefly o'f cyclic 05H16 (pentamethylene) The term neohexane as employed in this specification and in the accompanying claims is hereby defined as including not only the hydrocarbon 2,2-dimethylbutane but as also including commercial neohexane as produced by the thermal alkylation of isobutane with ethylene at a pressure of about 4500 pounds -per square inch and a temperature of about 950 F., by the catalytic isomerization of hexanes with an aluminum chloride or aluminum chloride-hydrocarbon complex catalyst in the presence of hydrogen chloride and added hydrogen at temperatures of about 200 to 300 F. and at a pressure of about 850 pounds l 4. A superf'uel comprising a blend of a major proportion of isooctane and between about 10 and about 40 volume per cent of an azeotrope of propanone and a high octane number hydrocarbon per square inch, or by any other commercial proctane with ethylene effected inthe presence of an' aluminum chloride-hydrocarbon complex catalysty at a temperature within the range of about 50 to' the reactants in liquid form, usually about 50 to? 150 pounds per square inch, preferably inthe 150 F., under a pressure sufficient to maintain presence of an excess of isobutane. The diisopropyl may, however, be obtained from any other commercial source. It should have an A. S. T. M. octane number of at least about 90, should have a narrowjboiling range and should contain predominantly the hydrocarbon 2,3-dimethylbutane.
Likewise, the terms fbenzenej cyclohexane and triptane are hereby defined to mean commercial products of relatively narrow boiling range and high octane number and these terms are not limited to the use of pure or even substantially pure hydrocarbons.
From the above it will be apparent that we have provided new aviation superfuels andrmethods of preparing the same. Although we have described in detail preferred embodiments of our invention, itshould be understood that various modifications thereof will be apparent from the above description to those skilled in the art. Therefore it is to be understood that our invention is not limited thereto but only by the appended claims.
1. A super aviation Vfue] comprising between about 85' and about 60 volume percent isooctane and .between about 15 and about 40 volume percent of an azeotropic mixture comprising between about 40 and 60 volume percent of disopropyl and between about 60 and 40 volume percent of acetone. l
2. A superfuel which comprises a blend including between about 60 and about 90 volume percent of trimethylpentane and an azeotropic mixture of propanone and a hydrocarbon selected from the group consisting of cyclopentane, neohexane, and diisopropyl. y Y 3. A superfuel comprising a blend of a major proportion of iso-octane and between about 10 and about 40 volume per cent of an azeotropic mixture of between about 50 and about 70 volume selected from the group consisting of cyclopentane, neohexane, and diisopropyl, said azeotrope boiling within the range of betweenv about 90 and about 165 F. f
5. A superfuel comprising'a blend of between about 60 and about 90 volume per cent of iso'- octane and an azeotrope of butanone and a high octane number hydrocarbon selected from the group consisting of benzene, cyclohexane, and trimethylbutane, said azeotropeboiling within theY range of between about 90 andabout 165 F.
6.. An aviation combat fuel which comprises a q blend' of between about 10 and about 40 volume percent of an azeotropic mixture of butanone and a high octane number hydrocarbonselectedfrom the group'consisting of Vbenzene,cyclohexane, and l trimethylbutane, between about 50and about 80 volume percent of trimethylpentane and between percent of acetone and .between about 30 and about 50 volume percent of a hydrocarbon selected from the group consisting of cyclopentane, neohexane, and diisopropyl, said azeotropic mixture boiling in the range of between about and about F,
, of trimethylbutane and butanone.
about 5 and about 20 volume percent of an azeotropic mixture of trimethylpentane and a hexanone. Y i. I 7. An -aviation superfuel comprising between about 60 and about 80 volume percent of trimethylpentane, between about 10 and about 40 volume percent of an azeotropic mixture which comprises between about 30 and about 50 volume percent o-aV high octane number hydrocarbon selected from the group consisting of neohexane, diisopropyl, and cyclopentane and between about 50 and about 70 volume percent of propanone and between about 5 and about 20 volume percent of hexanone. v
8. The method of adjusting the over-all distillation characteristics of commercial trimethylpentane comprising the steps of adding between about 15 and about 40 percent of a propanone azeotrope of a hydrocarbon selected from the group consisting of neohexane, diisopropyl, and cyclopentane to adjust the vaporpressure and the front end volatility and adding between about 5 and about 20 volume per cent of methyl iso butyl ketone to lower the mid-point of the blend. V j v 9. An .aviation superfuel which comprises essentially an isooctane and between about l0 and about 40 volume per cent an azeotropic mixture 10. An aviation superfuel which comprises essentially an isooctane and between about 10 and about 40 volume per cent an azeotropic mixture of cyclohexane and butanone.
11. An aviation fuel comprising between about 60 and about 90 per cent of an isooctane and between about 40 and about 10 per cent of at least one of two classes of azeotropes, the first class comprising propanone and a hydrocarbon selected from the class consisting of neohexane, cyclopentane, and diisopropyl and the second class comprising butanone and a hydrocarbon selected from the class consisting of cyclohexane, benzene, and trimethylbutane.