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2,409,157
Patented Oct. 8, 1946
UNHTED STATES PATT OFFICE
2,409,157
FUEL COMPOSITION
Walter A. Schulze and Richard C. Alden, Bart
lesville, Okla, assignors to Phillips Petroleum
Company, a corporation of Delaware
No Drawing. Application March 28, 1942,
Serial No. 436,715
7 Claims. (Cl. 44—-80)
1
This invention relates to an improved motor
fuel composition for use in high output aircraft
engines. More speci?cally, this invention relates
to an aviation fuel conforming to rigid speci?ca
tions of antiknock rating, vapor pressure, and
distillation characteristics, and having, in addi
2
pressure of the blend and to produce desirable
distillation characteristics, especially in the ini
tial portion of the distillation curve.
_
.
Since the synthetic iso-para?in blending agents
are often available in somewhat smaller volume
than base stocks prepared from naturally occur
ring distillates, blending formulas which require
minimum
volumes of such synthetic stocks may
superior power output over a broad range of
be preferred. Assuming that isopentane is plen
fuel-air ratios, and particularly over the range
10 tiful and used to the maximum extent possible
classi?ed as rich mixtures.
'- '
within vapor pressure and front-end volatility
High octane number aviation fuels are manu
limits, it then remains to select and prepare other
factured and blended according to speci?cations
tion, combustion characteristics which provide
so strict that the selection of suitable components
is limited in many cases to high purity synthetic
components, commonly termed base stocks, of
both high octane number and low vapor pres
blending agents and naturally occurring base 15 sure. These characteristics are most convenient
stocks which are segregated with such precision
as to approximate the purity of the synthetic hy
drocarbons. Such fuels must have high octane
number ratings and this in turn means that the
ly obtained by segregation of iso-paraf?ns, such
as the iso-hexanes, etc, as being more valuable
than a full boiling range naphtha, unless the
naphtha is deficient in normal (low octane)
paraf?ns or has an unusually high octane num
components must have high octane number rat 20
ber.
ings and/or excellent response to the addition of
The net result of the above-described blending
antidetonants. Further, the unsaturation of the
procedure is the production of fuels of suitable
components must be exceedingly low in order that
distillation characteristics, vapor pressure, gum
the fuels be'substantially free of gum and of
stability and octane number rating, comprising
25
susceptibility to gum formation. These quali?
largely
isopara?lns of 5 to about 8 or 9 carbon
cations together with rigid requirements for va
atoms, substantially free of C4. hydrocarbons, and
por pressure, end point. and distillation charac
preferably containing only minor amounts of C5
teristics sharply limit the choice of fuel compo»
to
C9 normal paraf?ns. The content of naphthenes
nents to the relatively low-boiling predominantly
may vary and is often small, since these com
para?'inic hydrocarbons, say of 5 to 9 carbon 30 pounds
are usually present in only small quanti
atoms. and preferably to the higher octane num_
ties, or in many cases, are removed more or less
ber branched-chain or isopara?ins.
completely by the precise fractionation which sep
In the manufacture of aviation fuels of 90 to
arates the normal C5, C6, and Cd paraf?ns from
100 octane number or those fuels having anti
the iso-paraiiins in naphtha base stocks.
35
knock ratings beyond the conventional octane
The complex and strenuous requirements of
number scale. the procedure usually includes the
military aviation under present war conditions
manufacture of synthetic isoparaf?ns as one
have emphasized some de?ciencies of aviation
blending component. For example, processes,
fuels under certain conditions. Such conditions,
such as selective polymerization, thermal or cat
for example, are those which require increased
alytic alkylation, or the like, may be utilized to 40 or emergency power for improved and rapid take
prepare concentrates of iso-octanes together with
off, particularly with heavy loads, rapid accelera
usually much smaller amounts of higher and
tion and climb during combat. The production
lower homologues. Thermal alkylation may
of maximum power output under these conditions
produce such stocks as neohexane which are
is of primary importance and the development of
45
highly desirable blending agents. As a second
fuels which will meet these severe requirements
component, base stocks comprising isohexanes,
under all conditions is an essential military re
isoheptanes, iso-octanes, etc., may in many in
quirement. It is also obvious that fuels which
stances be prepared by precise fractionation
schemes from crude oil and/or natural gasolines.
A third component which is ordinarily consid
ered separately is iso-pentane which can be pre
pared in substantially pure forrm by fractiona
tion of hydrocarbon mixtures containing it. This
last-named material is ordinarily the lowest boil
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
der rich mixture conditions, such, for example,
as would be obtained by substantially increasing
ing stock included in aviation fuels, and it func 55 the fuel concentration in an air-fuel mixture at
tions as a source of volatility to adjust the vapor
2,409,157
3
the intake of an aviation engine. This perform
ance is usually de?ned in terms related to a stand
ard 100 octane reference fuel, the relative im
provement being stated in ml. of tetraethyl lead.
While laboratory test and octane number rat 5
ings by the conventional methods employed for
aviation fuels indicate satisfactory performance,
more recent test procedures involving fuel per
4
purities which may have a deteriorative effect on
the fuels and/or on the aircraft fuel systems in
which said fuels are used.
In our co-pending application, Serial No.
{136,714, ?led March 28, 1942, we have disclosed
the specific bene?ts obtained from the addition
of isopropylbenzene to aviation fuels, and have
further disclosed that isopropylbenzene is gen
formance in supercharged test engines (for ex
erally superior to benzene, toluene, and ethyl
ample Method AN-VV-F-748) have indicated a 10 benzene for the purposes described although the
de?ciency in the power output of said predomi
latter may be used in some instances. In accord
nantly isopara?inic fuels. This de?ciency has
ance with the present disclosure, we have further
been shown to occur most markedly in rich mix
discovered that the butylbenzenes in which the
ture ratings of the fuel corresponding to take
alkyl group exhibits a branched chain structure,
o? or emergency power requirements in aircraft 15 namely, the isomeric butyl benzene compounds
at fuel-air ratios very much higher than the lean
which include secondary and tertiary butylben
mixture ratios ordinarily employed for e?icient
cruising operation. This discrepancy in the in
cremental power output with greatly increased
fuel-air ratio and fuel consumption has intro
zenes as well as isobutyl benzene, are superior to
the normal (straight chain) derivative. Further
more, as shown hereinafter, the tertiary deriva
20 tive is superior to the secondary derivative. The
formulas of these preferred compounds are as
duced a new consideration into the previous
follows:
blending formulas to deal with the rich mixture
rating of the ?nished fuels.
CH3
OH:
H
Since the predominantly isopara?inic fuel com
positions are very satisfactory from the stand 25
point of most speci?cations not involving rich
Qt];ta Ores
ta. Gala.
t
mixture requirements, and permit the produc
6113
tion of larger volumes of ?nished fuel per volume
of synthetic blending stocks than are possible
Sec.-buty1benzene Tcrt.-butylbenzene
Isobutylbenzeno
with other blending formulas, it is ordinarily 30 Isobutylbenzene is not ordinarily encountered
most advantageous to retain the isoparanin blend
because the conditions and reagents necessary
ing formulas insofar as possible. This procedure
for
its formation produce the tertiary derivative
requires that such special performance charac
almost exclusively. The properties of the isoteristics as lean and rich mixture ratings be ob
' butylbenzene for the purposes of this invention
tained through the inclusion minor proportions 35 are intermediate those of the secondary and ter
of substantially pure hydrocarbon additives.
tiary derivatives. In view of the related proper
These additive compounds must be carefully se
ties of isopropyl benzene and the mono-butyl
lected so that the desired improvements are ob
benzenes described herein, for the improvement
tained with such small quantities that other fuel ‘ of rich mixture rating, mixtures of these additive
characteristics are not impaired and blend speci 40
vcomponents may be utilized in any desired rel
ative proportion, such mixtures being utilized as
minor proportions of the ?nal fuel composition
and being compounded to produce fuels having
desired vapor pressure and. distillation charac
?cations are not infringed.
It is an object of the present invention to pro
vide an improved fuel composition for use in air- 1 I
craft engines whereby the power output of the
engines is improved. It is a further object of this
invention to provide an improvement in the blend
ing formulas for preparing predominantly iso
'
teristics.
In the investigation and testing of isopara?inic
aviation fuel blends containing aromatic hydro
carbon additives, the wide variations in the prop
para?inic aviation fuels whereby rich mixture
de?ciencies which may characterize said isopar
erties and uses of said aromatic hydrocarbons
a?in blends are effectively eliminated. Another 50 have been emphasized. For example, whereas
object is to provide a method for improving the
aromatics, as a class, have been regarded here
power output of aviation fuels under rich mixture
tofore as improving the octane number of ordi
conditions. A further object is to provide an
nary fuels, it is necessary in the present instance
isopara?inic aviation fuel of 100 octane number
to limit the quantity of aromatic additive to avoid
rating or better containing a relatively minor pro—
degradation of the octane number and response
portion of an added compound provided greatly
to lead alkyl antidetonants. Further, while aro
improved rich mixture characteristics without
matic hydrocarbons have been regarded hereto
undesirably affecting the other characteristics of
fore as substantially equivalents within the limits
the fuel. A still further object is to provide a
of their physical properties, such equivalency is
hydrocarbon fuel composition which will meet all 60 lacking in the present application as will be illus
desired speci?cations for volatility, vapor pres
trated hereinafter.
sure, distillation characteristics, and octane num
While the present invention may be employed
ber together with a method for its preparation.
in a great variety of blending operations involving
We have now found that aviation fuels of the r all suitable blending agents and base stocks, one
type described and comprising isoparai?n hydro
satisfactory procedure may be outlined in the fol
carbons have greatly improved octane number
lowing operations. A fuel may be prepared ac
ratings at high fuel-air ratios when minor ‘pro
cording to a blending formula which requires
portions of mono-butylbenzenes are added. These
de?nite proportions of iso-octane, isopentane, and
mono-butylbenzenes are employed as the substan
a naphtha comprising Cs and C7 isoparaf?ns in
tially pure compounds since their efficacy is highly 70 order to produce a composition rating 100 octane
speci?c and definitely superior to other aromatic
number with a given concentration of tetraethyl
homologues which might be present in varying
lead. Said blending formula is altered according
quantities in crude or impure alkylated benzenes.
to the present invention to include the mono—
A further purpose served by the use of the pure
butyl-benzene by use of an isopentane-butyl
compounds is the elimination of associated im 75 benzene mixture having a vapor pressure substan~
2,409, 1 57
5
tially equal to that of the ?nished fuel, usually
or rubber-like materials with which the com
’7-pound Reid vapor pressure. The volume of the
pounds or fuels containing them are in contact.
mixture used replacesasubstantially correspondComparative data are given below for an iso
ing volume of base stock and blending agent with
para?inic aviation fuel (blend A) and for said
the blending proportions of the latter usually 5 fuel after addition of 5 and 15 volume percent
being readjusted to produce the same octane ratof benzene, secondary butylbenzene, and tertiary
ing as before. The butylbenzene may be added
outylbenzene, in- contact with a moderately oil
alone to fuel blends, but it is often more con-
resistant type of synthetic rubber as represented
venient to employ the isopentanized mixture.
by Hycar OR.
The
~ - - Y ‘
Aromatic additive
BlendA
'
'
'
S ee-b 11 t7-’
Benzene ‘
benzene
Aromatic concentration (volume per cent)
Per cent swelling (24 hours) __________ _Diffusion (grams/hour)
Increased solvency due
Trtb
e” ‘- ‘l1 tyl -'
benzene
5
15
5
1.99
0 022 0.027
5.4
hours).
advantages lie in the maximum utilization of
isopentane and less difficulty in blending to meet
vapor pressure and distillation speci?cations.
The butylbenzene employed in the fuel com-
These results indicate that the swelling, diffusion,
and solvency effects with these butylbenzenes are
appreciably less than with benzene itself. This
e?ect is apparently due to decreased aromaticity
Positions may be Obtained from any Suitable 25 resulting from the alkyl substituent, and particu
SOurce, provided a substantially Pure product is
larly due to the size and con?guration of the side
obtained. In many cases, it is di?cult to separate butylbenzenes, and particularly, one speci?c
chain. This means that better service character
istics result from the use of these butylbenzenes
butylbenzene from complex mixtures of aromatic
and/or that larger concentrations of the butyl
and other types of hydrocarbons such as may re- 30 benzenes may be employed without encountering
sult from the non-selective alkylation of gasoline
stocks or the like. For this reason, the' preferred
di'?iculties in service.
'
Test method AN-VV-F-746 as referred to here
source of the butylbenzenes is the selective alkyla-
in is the method identi?ed as Army-Navy Aero
tion of benzene with butylenes and/or isobutylene
nautical Speci?cation Fuel;
Aircraft-Engine,
or their equivalent alkylating agents in the pres- 35 General Speci?cations (Method for Knock-Test)
ence of suitable catalysts such as hydrogen
AN-VV-F-746, dated October 5, 1940. This
?uoride or boron fluoride which produce the cormethod is utilized for determining ordinary 0c-'
responding branched-chain derivatives, exclusive—
tane number ratings of 100 octane aviation fuels.
iv. The butylbenzene which is produced by such
Test method AN-VV-F-‘748, as referred to herein
methods is substantially free of undesirable im- 40 is identi?ed as Army-Navy Aeronautical Speci?
purities and is readily separated from unreacted
cation Fuel; Aircraft-Engine, General Speci?ca
- benzene and/or polyalkylated derivatives.
tion (Method for Supercharged Knock Test)
The amount of the butylbenzene added to spe-
AN-VV-FJ748 dated September 22, 1941. The
ci?c fuels will obviously be dependent to a large
test method described therein is used for deter
extent on the nature and quality of the other 45 mining lean and rich mixture ratings of 100 0c
componsnts and on the rich mixture rating which
tane number aviation fuels. In this latter speci
is desired in the ?nal blend. In most cases, the
?catjon (AN_vV_F_748) a, 182m mixture is shown
butylbenzene will vary between about 1 and about
to be about .06 pound of fuel per pound. of air
10 Volume Per cent of the blend. With a some“
and a rich mixture at least about .09 pound of
what narrower range of about 2 to about ‘7 vol- .50 fuel per pound of air,
lime P61‘ 081115 usually preferred. The compound
in substantially pure form is relatively expensive
alld hence is not Ordinarily used to replace the
conventional blending ingredients. Also, excessive
_
As illustrations of the improved performance
characteristics obtained by the addition of butyl
benzene to aviation fuels, the following typical
data, are cited;
amounts may tend to decrease the lead response 55
of the blend and/or impart sufficient aromaticity
Example
to the fuel to increase the solvent and swelling
A 100 octane number aviation fuel was pre
action on rubber-lined fuel tanks.
pared according to blending formula A given be
In this connection, it has been found that the
low, with 4 ml. TEL per gallon. This formula
butylbenzenes described herein, particularly 60 was then modi?ed to permit the inclusion of 5
those having the branched chain alkyl substituent exhibit quite different properties from those
volume per cent of each of the following aromatic
additives: (l) benzene, (2) sec-butylbenzene, and
of the commoner aromatics, such as benzene.
(3) tert-butylbenzene. These three modi?ed
One way in which the more desirable properties
blends noted below as B, C‘, and D conformed to
of these butylbenzenes are evidenced is in re- 65 fuel speci?cations and rated approximately 100
duced swelling of and di?usion through rubber
octane number with 4 ml. TEL per gallon.
Isoparaf?n components, vol. per cent
Aromatic
Isa-octane Isoheptane Isohexane Isopentane
additive
(5 vol‘ per cent)
Formula
33. 0
30. 9
30. 9
30. 9
18. 0
16. 9
l6. 5
16. 5
36.0
33. 8
33. 7
33. 7
13. 0
13. 5
l3. 9
13. 9
None.
Benzene.
Sec‘bu tylbenzene.
Text-butylbenzene.
$4509.15’?
7
8
These blends were rated according to test method
about 7% by volume of a mono-butylbenzene oth
er than normal butylbenzene and at least about 3
m1. of tetraethyl lead fluid per gallon, said hy
AN-VV-F-745 and also according to the super
charged-engine method AN-VV-F-74=8.
Octane
numbers above 100 are recorded as ml, of tetra
ethyl lead in 100 octane number iso-octane in
drocarbons being so proportioned that said mix
turehas gasoline characteristics of distillation
range and contains isopentane in an amount not
more than is su?icient to result in a Reid vapor
the following table:
Antilmock rating
pressure not greater than seven pounds, and
maintaining during said operating period for
10 said aviation engine rich-mixture operating con
AN-VV-F- 746
-
Lean mixture Rich mixture
Ml. TEL
Ml. TEL
0.
100
0. 02
O. 03
~
Ml. TE
0. 20
0. 65
0. 3O
0. 80
O. 10
0. 22
l. 00
1. 45
ditions such that the fuel-air ratio is at less
about .09.
3. An improved method of operating an avia
tion gasoline engine requiring a fuel having an
15 octane number of at least about 100, which com-
These results indicate the substantially improved
rich mixture rating provided by the butylben- ~
zenes as compared to fuel A alone and to formula
B containing benzene, while the effect on lean
mixture rating and on the conventional (Fl-746)
rating is slight.
‘ prises supplying to said engine as the fuel dur
ing an operating period a gasoline which con
sists of a mixture of isopara?in hydrocarbons
having not less than ?ve nor more than nine car
bon atoms per molecule and a mono-butylbenzene
other than normal butylbenzene in an amount
between about 1 and about 10% by volume of the
total and at least about 3 ml. of tetraethyl lead
?uid per gallon, said hydrocarbons being so pro
While the foregoing speci?c examples provide 25 portioned that said mixture has gasoline char
illustrations
of
the
improvement
obtained
through the practice of the present invention, it
will be apparent that the variations which can
be produced through changing the volume ratio,
acteristics of distillation range and contains iso
pentane in an amount not more than is sufficient
to result in a Reid vapor pressure not greater
than about seven pounds, and maintaining dur
qua 'ty and hydrocarbon type of the blending 30 ing said operating period for said aviation engine
Therefore, no limi
rich-mixture operating conditions such that the
tation of the scope of the invention is intended.
fuel-air ratio is at least about .09.
Also,'while the invention has been described and
4. An improved method of operating an avia
exemplified in applications to predominantly iso
tion gasoline engine requiring a fuel having an
para?inic fuel blends, it is broadly applicable to 35 octane number of at least about 100, which com
fuel compositions suitable for the purposes out
prises supplying to said engine as the fuel dur
lined and within the limits prescribed.
ing an operating period a gasoline comprising
We claim:
essentially a mixture of isoparaf?n hydrocarbons
compenents are numerous.
1. An improved method of operating an avia
having not less than ?ve nor more than nine
tion gasoline engine requiring a fuel having an 40 carbon atoms per molecule and a mono-butyl
octane number of at least about 100, which con
benzene other than normal butylbenzene in an
sists of supplying to said engine as the fuel during
amount between about 2 and about 7% by vol—
an operating period a gasoline comprising essen
ume of the total and at least about 3 ml. of
tially a mixture of iscparai?n hydrocarbons hav
tetraethyl lead ?uid per gallon, said hydrocar
45
ing five, six, seven, eight and nine carbon atoms
bons being so proportioned that said mixture
per molecule and between about 2 and about
has gasoline characteristics of distillation range
'7 % by volume of a mono-butylbenz-ene other than
and contains isopentane in an amount not more
normal butylbenzene and at least about 3 ml. of
than is su?icient to result in a Reid vapor pres
tetraethyl lead ?uid per gallon, said hydrocar
sure not greater than about seven pounds, and
bons being so proportioned that said mixture has 50 maintaining during said operating period for
gasoline characteristics of distillation range and
said aviation engine rich-mixing operating con
contains isopentane in an amount not more than
ditions such that the fuel-air ratio is at least
is sufficient to result in a Reid vapor pressure
not greater than seven pounds, and maintain
about .09.
5. The method of claim 1 in which the mono
ing during said operating period for said avia 55 butylbenzene in the fuel supplied is tertiary butyl
tion enigine rich-mixture operating conditions
benzene.
such that the fuel-air ratio is at least about .09.
6. The method of claim 3 in which the mono
2. An improved method of operating an avia
butylbenzene in the fuel supplied is tertiary butyl
tion gasoline engine requiring a fuel having an
benzene.
octane number of at least about 100, which con 60
7. The method of claim 4 in which the mono
sists of supplying to said engine as the fuel dur
butylb-enezene in the fuel supplied is tertiary
ing an operating period a gasoline comprising
butylbenzene.
essentially a mixture of isopara?in hydrocarbons
WALTER A. SCHULZE.
having not less than 5 and not more than 9 car
RICHARD C. ALDEN.
65
bon atomsper molecule and between about 2 and
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