US2758916A - Fuel compositions - Google Patents

Description

United States Patent FUEL COMPOSITIONS John E. Mahan, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application July 9, 1951, Serial No. 235,901

19 Claims. (Cl. 44-69) This invention relates to improved aviation fuels. More specifically it relates to an aviation fuel conforming to rigid specifications of antiknock rating, vapor pressure and distillation characteristics, and having, in addition, combustion characteristics which provide superior power output over a broad range of fuel-air ratios and particularly over the range classified as rich mixtures. It relates further to a method of operating an aviation gasoline engine requiring a fuel having an octane number of at least about 90.

High octane number aviation fuels are manufactured and blended according to specifications so strict that the selection of suitable components is limited in many cases to high purity synthetic blending stocks and naturally occurring base stocks which are segregated with such precision as to approximate the purity of the synthetic hydrocarbons. Such fuels must have high octane number ratings and this in turn means that the components must have high octane number ratings and/or excellent response to the addition of antidetonants. Further, the unsaturation of the components must be exceedingly low in order that the fuels be substantially free of gum and of susceptibility to gum formation. These qualifications together with rigid requirements for vapor pressure, end points, and distillation characteristics, sharply limit the choice of fuel components to the relatively low boiling, predominantly parafiinic hydrocarbons, say of 5 to 9 carbon atoms, and preferably to the higher octane number branched chain or isoparafiins.

In the manufacture of aviation fuels of 90 to 100 octane number or of those fuels having antiknock ratings beyond the conventional octane scale, the procedure usually includes the manufacture of synthetic isoparatfins as one blending component. For example, processes, such as selective polymerization, thermal or catalytic alkylation, or the like, may be utilized to prepare concentrates of isooctanes together with usually much smaller amounts of higher and lower homologues. Alkylation may produce such stocks as neohexane or diisopropyl, which are highly desirable blending stocks. As a second component, base stocks comprising isohexanes, isoheptanes, isooctanes, etc., may in many instances be prepared by precise fractionation schemes from crude oil and/ or natural gasolines.

A third component, which is ordinarily considered separately, is isopentane, which can be prepared in sub stantially 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 as a source of volatility to adjust the vapor pressure of the blend, and to produce desirable distillation characteristics, especially in the initial portion of the distillation curve.

Since the synthetic isoparaffin blending stocks are ordinarily available in somewhat smaller volume than base stocks prepared from naturally occurring distillates, blending formulas which require minimum volumes of such synthetic stocks are preferred. Assuming that isopentane is plentiful 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 octane number and low vapor pressure. These characteristics are most conveniently obtained by segregation of isoparaffins, such as the isohexanes, etc., as being more valuable than a full boiling range naphtha, unless the naphtha is deficient in normal (low octane number) paraffins or has unusually high octane number as a result of its content of naphthene hydrocarbons.

The net result of the above described blending procedure is the production of fuels of suitable distillation characteristics, vapor pressure, gum stability, and octane number rating comprising largely isoparafiins of 5 to about 8 or 9 carbon atoms, substantially free of C4 hydrocarbons, and preferably containing only minor amounts of C5 to C9 normal paraffins. The content of naphthenes is often small, since these compounds are usually present in only small quantities or in many cases are removed more or less completely by the precise fractionation which separates the normal C5, C6, and C7 parafiins from the isoparaifins in naphtha base stocks.

The complex and strenous requirements of military aviation under war conditions have emphasized some deficiencies of aviation fuels under certain conditions. Such conditions, for example, are those which require increased or emergency power for improved and rapid takeoff, particularly with heavy loads, rapid acceleration and climb during combat. The production of maximum power output under these conditions is of primary importance and the development of fuels which will meet these severe requirements under all conditions is an essential military requirement. It is also obvious that fuels which meet rigid military requirements will be of great value in the development of commercial aviation. The present invention, therefore, provides a novel fuel composition as well as mode of operating aviation engines requiring high octane fuels, particularly of 100 octane or higher. In the practice of this invention, as described herein, a gasoline essentially comprising a mixture of isoparaffin hydrocarbons having 59 carbon atoms per molecule, containing TEL, usually at least about 3 ml. per gallon, together with a minor proportion of an additive material, preferably 1-10 per cent, and having a Reid vapor pressure not greater than about seven pounds, and a maximum per cent ASTM distillation procedure evaporated temperature of about 275 F., is supplied to an aviation engine during an operating period, and particularly when rich mixture performance is required.

The term rich mixture performance as now used by the art, and as referred to herein, describes the power output of aviation engines under rich mixture conditions, such, for example, as would be obtained by substantially increasing the fuel concentration in an air-fuel mixture at the intake of an aviation engine. This performance is usually defined in terms relating to a standard octane number reference fuel, the relative improvement being stated in ml. of tetraethyl lead.

Use of multiple engines in aircraft has often necessitated the overloading of a portion of the engines by reason of the fact that another portion of the engines may cease to operate during flight. At such times, it has been found to be very desirable to have a fuel which will give an increased power output over that normally utilized under cruising conditions. Additional power output has also been found to be necessary for take-01f and high rate of climb of aircraft when operating at fuel-air ratios much higher than the lean mixture ratios ordinarily employed for cruising operation. By reason of the necessity for such increased power output, a new consideration for blending formulas has been introduced 3 for the purpose of increasing of finished fuels.

lsoparafiinic fuel compositions generally are very satisfactory from the standpoint of most specifications when it is not necessary to utilize additional power over that normally required under lean mixture ratios usedunder cruising conditions. Use of these isoparaffinic fuels permits the production of larger volumes of finished fuel per volume of synthetic blending stocks than are possible with other blending formulas. It is thus ordinarily most advantageous to retain the isoparatfin blending formulas insofar as possible. This procedure requires that such special performance characteristics as lean and rich miX- ture ratings be obtained through the inclusion of minor proportions of substantially pure chemical additives. These additive compounds must be carefully selected so that the desired improvements are obtained with such small quantities that other fuel characteristics are not impaired and blend specifications are not infringed.

An object of this invention is. to provide an improved fuel composition for use in aircraft engines whereby the effective operation and power output of the engines are improved. Another object, of the invention is to provide an improvement in the blending formula for preparing predominantly isoparaffinic. aviation. fuels whereby the potential power output thereof is greatly increased. Another object of this invention is to provide an isoparaffinic aviation fuel of at least 90- leaded aviation octane number rating containing a relatively minor proporation of an added compound providing greatly improved power output characteristics without undesirably effecting the other characteristics of the fuel. Another object is to provide an isoparafiinic aviation fuel of about 100 aviation octane number rating or better containing a relatively minor proportion of an added compound providing greatly improved rich mixture characteristics without undesirably afiecting the other characteristics of the fuel. Another object is to provide a fuel composition comprising an aviation base stock containing a relatively minor proportion of a selected monoalkenylamine. Another object is to provide an improved method for operating aviation engines under conditions requiring increased power output by the addition to the isoparafiinic aviation fuel utilized therein a minor proportion of a selected monoalkenylamine. Other objects will be apparent, to one skilled in the art fromthe accompanyingndiscussion and disclosure.

1 have found that aviation fuels of, thetype. described and comprising essentially isoparaflinic. hydrocarbons have greatly improved power output ratings particularly over the rich mixture range of fuel-air ratios, when they contain minor proportions of monoalkenylamines. characterized by the structural formula NX wherein X is an alkenyl radical ofbranched or straight chain configuration containing from 3 to 8 carbon atoms, and R and R can each be hydrogen, CH3, or C2H5, and the sum of the carbon atoms in the R and Rdoes not exceed 2; the alkenyl radical is preferably monoolefinic, i. e., containing one olefinic carbon-to-carbon bond, although in some instances it may contain 2 or even- 3 olefinic bonds. The mono substituted amines such as butenylamine, pentenylamine, hexenylamine, and the like are preferred additive compounds of my-invention. However, di-. or tri-substituted amines such as N-methylbutenylamine, N,N-dimethylpentenylamin e and the like are adaptable as fuel additives, and are within the scope of my invention.

The unsaturated amines described above are employed as substantially pure compounds or mixtures of these pure compounds, since their efficiency is highly: specific the potential power output and superior to certain other nitrogen compounds which might be present in crude unsaturated amine fractions. A further purpose served by the use of substantially pure compounds or mixtures thereof is the elimination of associated impurities which have deteriorative effects on the fuel and/ or aircraft fuel systems in which it is used. In addition to the unsaturated monoalkenylamines ap plicable in the process of my invention, already named, are included N-ethyloctenyl'amine, N,N-dimethylheptenylamine, Nethylpentenylamine, N-methylpropenylamine, N,N-dimethylbutenylamine, allylamine, heptenylamine, iso octenylamine, N,N-dimethylisobutenylamine, and the like. These compounds are exemplary of those unsaturated amines which in accordance with my invention, when added to an aviation fuel of the type described, improve the rich mixture performance of the fuel, as determined by the supercharged engine test (ANVVF-748a).

While specific embodiments of the present invention may be invoked in a great variety of blending operations involving isoparaffinic blending and base stocks, one satisfactory procedure is outlined in the following operations. A fuel is prepared according to a blending formula from isooctane, isopentane and a naphtha comprising Cs and C7 isoparaffins in proportions which produce octane number with 4 ml. of tetraethyl lead per gallon.

This formula is altered according to the present invention to include at least, one of the unsaturated amines described above by use of a predetermined volume per cent of an unsaturated 'amine-pentane mixture having a vapor pressure substantially equal to that of the finished fuel (usually about seven pounds Reid vapor pressure). The volume of. a mixture used replaces a corresponding volume of isopariflin base stock and synthetic blending stock with the blending proportions of the latter ordinan'ly being readjusted to produce the same aviation octane number rating as before.

The unsaturated amine. additives may be added alone to fuel blends,.but it is often more convenient to employ the isopentanized. mixture. The advantages lie in the maximum utilization of the isoparafii'n ingredients. particularly isopentane, and less difiiculty in blending to meet vapor pressure specifications, and in improving the rich rating of the fuel.

The unsaturated amines described above may be prepared in any desired manner. One. such specific preparation is described in the copending application of I. E. Malian and K. Bursack, Serial No. 135,290, filed December 27, 1949, now abandoned. in accordance with the process disclosed in that copending application a conjugated hydrocarbon diene containing at least 4 carbon atoms in the molecule is reacted with ammonia or an organic amine'in liquid phase in-the presence of sodium hydrideor sodamide as. a catalyst to formthe monoalkenylarnine, together with diand trial kenyl products. Accordingly-in the preparation of monobutenylamine, 1,3-butadiene is reacted with ammonia in the presence of the. catalyst. Operating temperatures are from 5{lto 500 F., temperatures approximating F. being often desirable. It is understood, of course, that monobutenylamines as well as other unsaturated amines applied to theproeess of my invention can be prepared in any suitable manner' although for reasons described'above I prefer generally that the additive to be employed is applied in a high state of purity.

The proportions of the above described unsaturated amine additives to be added to the fuel will obviously be dependent on the other fuel components and on the particular lean mixture and rich mixture octane, ratings which are desired, in the final blend. In most cases the quantity of the unsaturated amine additive employed; will he in the range of from 1 to 10 volume per cent of-the finished fuel."

The amine additives in accordance with my invention N methylisopentenylamine, V

are applied to both clear and leaded fuels, although my preferred fuel compositions contain tetraethyl lead in proportions generally from 3.0 to 4.6 ml. per gallon; however, proportions of tetraethyl lead outside the prethe present time the aviation octane ratings obtained in the ordinary aircraft engine tests (AN-VVF746 and ASTM Aviation method D-614-48T) which are carried out under lean mixture conditions, are considered a more ferred range can be employed as desired, as for example 5 reliable measure of lean mixture performance and the proportions as low as about 1 mL/gallon and as high as lean mixture ratings obtained in the supercharged test 7 ml./ gallon. The unsaturated amine additives described have fallen into disuse. above exhibit water solubility and generally when applied It has been found that it is generally not possible to add in the practice of my invention the maximum concentrai e ly h rich mixture ratings of the components of an tion of additive that can be used will be equal t th 10 aviation fuel blend in their volumetric proportions and amount that will provide a finished fuel which passes arrive at a correct value for the rating of the blend, or the maximum Water tolerance concentration as deterconversely, from the rating of the blend to determine the mined for example by the test AN-F 48b. This amount value of the additive. This is particularly true Where the on a volume basis is at least 1 per cent, and preferably Components difier widely in their rating, and results in at least 1.5 per cent and generally does not exceed 10 P from the conventions used in expressing rich ratingsper cent, although in cases where a larger amount can While rich ratings superior to the performance of isoocbe used and the fuel passes the said water tolerance test, time are given in terms of the Value of tetfaethyl lead the use of a larger amount is within the scope of my that must be added to reference fuel S (essentially pure invention. isooctane) to reproduce the same engine performance, In another embodiment of my inve ti 1 am bl to rich ratings inferior to isooctane are expressed in terms take particular advantage of the water solubility of the 0f the volume P Cent of fuel 5 in a blend With reference above described unsaturated amine additives, inasmuch fuel M Octane Straight Tut! gasoline) t0 reproduce as appreciable quantities of water can thus be incorthe engine performance. To reconcile these two methods porated with the finished fuel to aid in knock suppression of xpr s i n and the non-lin rity of the Conc ntrat and to aid in alleviating formation of piston and cylinder hon-Performance relationship, the Procedure has beetl deposits. adopted of assigning a number known as the rich mixture In another embodiment of my invention the solubility blending ihdeX number to measurable Performance of the unsaturated amine additive in water can be utilized levels- These numbers are SO assigned and tabulated by injecting the additive into th c b tio system i that they may be used directly with the volumetric perthe form of a water solution whe eeded, i a manner centage of the constituents to give the performance rating generally analogous to the use of water injection at high of the blend- Thus, a fuel of Very P Performance, powers. These latter embodiments of my invention, as Which is equivalent to a blend of P Cent fuel 5 in applied to the water solubility characteristics described, l M has a blending index number f P r i are particularly applicable when applying monobutenyl- Octane has a blending iIIdeX number 0f While a amine as the desired unsaturated amin 5 superior fuel whose performance is equal to that of iso- Test method AN VV F 746 as r fe d t h i i octane with 6.0 cc. of lead added has a blending index the method identified as Army-Navy Aeronautical Sp'ecinumber of 1 fication Fuel: Aircraft Engine General Specification AS illustrations of the improved Performance a (Method for Knock-Test AN VV-F 746), d t d O t teristics obtained by the addition of monoalkenylamines h 5, 1940, Thi th d i ili d fo d i i 40 in isoparafi'inic aviation fuels, the following example is ordinary aviation octane number ratings of aviation fuels. cited. Test method AN-VV-F-748a, as referred to herein is Example I identified as Army-Navy Aeronautical Specification Fuel; Aircraft Engine General Specification (Method for Three portions of a 91/98 aviation base stock were suprcharged Knock'Test) ANTYVTFTMSFI June blended with monobutenylamine. A portion of the unzi fiii fgzg igi gzsgg jg i g 6 225 2; blended 9l/98 stock and each of the three resulting blends were subjected to octane number and rich rating tests. number aviation fuels. In this latter specification Smil 1 f 100/13 d (AN-VV-F-748a) a lean mixture is shown to be about 1 ary a per Ion 9 a 0 avlatlon base 006 pound of fuel Per pound of air and a rich mixture stocl; was blended with monobutenylamme and another at least about 009 Pound of fuel per pound of port1on of the same base stock was blended with mono- More recently, however, it has been shown that while allylamme and: a Pomon of the unblended 100/130 this latter method 7 3, can be used to base stock and each of the resulting blends thereof, were give an excellent measure of the performance of fuels subjected to Octane number and Iieh rating teStS- in rich mixtures, lean mixture ratings obtained i thi tails and results of these tests are summarized in the supercharged engine test are erratic and unreliable. At tabulation below:

Composition ASTM e Aviation ASTM Supe Aviation Blending ASTM Supercharge Rich a Octane Octane charge Rich ixture Formula Grade Grade Mono- Mono- Number Number Rating (4.0 Blending In- 91/98 /130 butenylallyl- (4.0 m1. (4.01111 m1. TEL dex Number Agzzgion Agtiagteign amine amine TEL) TEL) (4.0ml. TEL) B 14.4 percent iC base stock 41.3 percent i0;

b 50 percent HF percent 105.

alkylate 9.7 percent mixed cyc 31.3 percent iCa 13.0 percent 1'05.

lies 11.0 percent 101 12.7 percent 10 base stock 16.6

Determined in accordance with Test Method D-614-48T, described hereinabove.

etermined in accordance with Test Method A VV-F-748a, described hereinabove.

6 M1. of TEL that must be added to isooctane (2,2,3-trimethylpentane).

1 Volume percent isooctane (2,2,3-tr1methylpentane) in n-heptane.

A portion of a 91/98 aviation base stock was blended with diallylamine. The resulting blend, and a separate portion of the 91/98 base stock were subjected to rich rating tests. Details and results of these tests are summarized in the tabulation below:

Composition ASTM ASTM Supercharge Supereharge Grade Rich Rating Rich blend- Dially- 91/98 (4.0 ml. TEL) ing Index No. lamine aviation (4.0 ml. TEL) base 1 14.4 percent, 105 base stock 41.3 percent 101 31.3 percent 10:,

13.0 percent 105.

The above tabulated data illustrate that diallylamines cannot be considered as equivalents of monoalkenylamines in effecting improvement in rich-mixture characteristics of aviation fuels. This is particularly demonstrated by the low blending index number of 8.8 as determined for diallylamine as compared to the blending index number of 145 as determined for monoallylamine, set forth in Example I above.

As will be evident to those skilled in the art, various modifications can be made or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims.

I claim:

1. A gasoline containing from 1 to 10 volume per cent of at least one unsaturated amine characterized by the structural formula radical containing from 3 to 8 are each radicals selected from the group consisting of hydrogen, CH3 and CzHs, and wherein the number of carbon atoms in the total R and R radicals does not exceed 2.

2. A gasoline according to claim 1 is monopentenylamine.

3. A gasoline according to claim 1 wherein said amine is monohexenylamine.

4. A gasoline according to claim 1 is N-methylbutenylamine.

5. An improved gasoline containing from 1 to 10 vol-, ume per cent of monobutenylamine.

6. An improved gasoline containing ume per cent of monoallylamine.

7. An improved gasoline consisting essentially of an aviation base stock, including a substantial proportion of isoparaflinic hydrocarbons having from to 9 carbon atoms in the molecule, a small proportion of tetraethyl lead, and from 1 to 10 per cent of its volume of at least one unsaturated amine characterized by the structural formula wherein X is an alkenyl carbon atoms, R and R wherein said amine wherein said amine from 1 to 10 vol wherein X is an alkenyl radical containing from 3 to 8 carbon atoms, and R and R are each radicals selected from the group consisting of hydrogen, CH3 and CzHs, and wherein the number of carbon atoms in the total R and R radicals does not exceed 2.

8. An improved gasoline consisting essentially of a small proportion of tetraethyl lead, an aviation base stock, including a substantial proportion of isoparafl'inic hydrocarbons having from 5 to 9 carbon atoms in the molecule, and from 1 to 10 volume per cent of monobutenylamine, and having a maximum Reid vapor pressure of seven pounds and a maximum per cent ASTM evaporated temperature of 275 F.

9. An improved gasoline consisting essentially of a small proportion of tetraethyl lead, an aviation base stock, including a substantial proportion of isoparaffinic hydrocarbons having from 5 to 9 carbon atoms in the molecule, and from 1 to 10 volume per cent of monoallylamine, and having a maximum Reid vapor pressure of. seven pounds, and a maximum 90 per cent ASTM evaporated temperature of 275 F.

10. An improved gasoline consisting essentially of a grade aviation base stock containing a small proportion of tetraethyl lead and from 1 to 10 volume per cent monobutenylamine.

11. An improved gasoline consisting essentially of a grade 100/ 130 aviation base stock containing a small proportion of tetraethyl lead and from 1 to 10 volume per cent monoallylamine.

12. An improved gasoline consisting essentially of a grade 91/98 aviation base stock containing a small proportion of tetraethyl lead and from 1 to 10 volume per cent monobutenylamine.

13. An improved gasoline consisting essentially of a grade 91/98 aviation base stock containing a small proportion of tetraethyl lead and from 1 to 10 volume per cent monoallylamine. 14. A gasoline containing a minor proportion, in an amount suflicient to increase the rich mixture blending index number of said gasoline, of at least one unsaturated amine characterized by the structural formula /NX RI radical containing from 3 to 8 are each radicals selected from CH3 and C2H5, and in the total R and claim 14 wherein said amine References Cited in the file of this patent UNITED STATES PATENTS 1,724,640 Calcott et al Aug. 13, 1929 1,992,014 Rogers et a1 Feb. 19, 1935 2,021,088 Pevere Nov. 12,1935 2,324,118 Sweeney July '13, 1943 2,618,612 Howell NOV. 18, 1952 2,653,862 Trimble et al Sept. 29, 1953

Claims (1)

1. A GASOLINE CONTAINING FROM 1 TO 10 VOLUME PER CENT OF AT LEAST ONE UNSATURATED AMINE CHARACTERIZED BY THE STRUCTURAL FORMULA