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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.
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