[0001] In the past, metal corrosion caused by conventional motor fuels such as gasoline
was not much of a problem because such hydrocarbon fuels are inherently non-corrosive.
However, with the advent of fuels containing alcohols such as gasohol or straight
alcohol fuels, corrosion has become a major problem because such fuels are corrosive.
It has been reported that this corrosion is due to the presence of acidic contaminants
in such fuels such as formic acid. It is almost impossible to avoid such contaminants
because they occur in fuel grade alcohols and are also formed in storage as normal
alcohol oxidation products.
[0002] It is known from U.S. 4,305,730 that polymerized linoleic acid, especially trimer,
is an effective corrosion inhibitor for alcohol-type motor fuels. It has now been
discovered that the corrosion inhibiting properties of such polymerized polyunsaturated
aliphatic monocarboxylic acids are improved by use of the co-additives described herein..
The substituted imidazoline co-additives of the invention, more fully described hereafter,
also are known compounds which heretofore have found use, for example, in motor fuel
compositions to prevent carburetor icing as disclosed in U.S. 3,036,902.
[0003] It is also known from U.S. 2,993,772 that alkenyl succinic acids as well as their
anhydrides inhibit and/or prevent the deposit-forming tendency of hydrocarbon fuels
during combustion and/or modify the deleterious effect of the formed deposits in both
leaded and unleaded fuels particularly in gasoline and jet fuels. It has now also
been discovered that a combination of certain substituted imidazolines with a monoalkenylsuccinic
acid wherein the alkenyl group contains 8 to 30 carbon atoms provides corrosion inhibiting
properties to fuels containing alcohols such as gasohol or straight alcohol fuels.
[0004] According to the present invention, metal corrosion caused by alcohol-type motor
fuels is inhibited by adding to the fuel a combination of (A) a member selected from
(i) polymerized polyunsaturated aliphatic mono- carboxylic acid or (ii) at least one
monoalkenylsuccinic acid wherein the alkenyl group contains 8 to 30 carbon atoms and
(B) substituted imidazoline.
[0005] The invention provides a liquid fuel adapted for use in an internal combustion engine,said
fuel comprising from 5 to 100 weight percent of one or more alcohols, from 0 to 95
weight percent gasoline and as a corrosion inhibitor the combination of (A) a member
selected from (i) a polymer of one or more
Cl6 to
C18 polyunsaturated aliphatic monocarboxylic acids, (ii) at least one monoalkenylsuccinic
acid wherein the alkenyl group contains 8 to 30 carbon atoms and (B) a substituted
imidazole.
[0006] The additive combination of this invention can be beneficial in any engine fuel containing
or consisting of an oxygenate. Such fuels include gasoline-alcohol mixtures referred
to as "gasohol" as well as straight alcohol fuels. Useful alcohols are methanol, ethanol,
n-propanol, isopropanol, 1-butanol, 2-butanol, t-butanol, 2-methyl-2-propanol, isobutanol
or mixtures thereof such as methanol and t-butanol. Gasohols usually contain 2 to
30 volume percent alcohol. At concentrations above 10 volume percent phase separation
problems y
beencountered especially in the presence of water.
[0007] Phase separation can be minimized by including cosolvents in the gasohol such as
ethers, ketones or esters, for example. An especially useful co-solvent is methyl
tert-butyl ether which also serves to increase octane value.
[0008] The additive combination is used in a corrosion inhibiting amount. A useful
range of additive concentration is 1 to 5000 pounds per thousand barrels (ptb). A
more preferred range is 5 to 2000 ptb and the most preferred concentration is 5 to
500 ptb.
[0009] Component A (i) is a polymer of one or more 16 to 18 carbon polyunsaturated aliphatic
monocarboxylic acids. Examples of these are tall oil fatty acid, oleic acid, linoleic
acid and linolenic acid including mixtures thereof. The polymers comprise mainly dimers
and trimers of the polyunsaturated acids. Suitable polymers of linoleic acid are available
commercially. Mixtures high in trimer content are most preferred.
[0010] The monoalkenylsuccinic acids( Component Aii) are well known in the art. These acids
may be readily prepared by the condensation of an olefin with maleic anhydride followed
by hydrolysis (see U.S. Pat. NO, 2,133,734 and U.S. Pat. No. 2,741,597). Suitable
monoalkenylsuccinic acids include octenylsuccinic acid, decenylsuccinic acid, undecenylsuccinic
acid, dodecenylsuccinic acid, pentadecenylsuccinic acid, octadecenylsuccinic acid
and isomers thereof having alkenyl groups of various hydrocarbon structures. The preferred
monoalkenylsuccinic acid is dodecenylsuccinic acid, more preferably, dodecenylsuccinic
acid prepared from propylene tetramer.
[0011] While an alkenyl group ranging fron. 8 to 30 carbon atoms is preferred as indicated
above, it is contemplated that substantially any alkenylsuccinic acid or its equivalent
anhydride may be employed in the fuels of The present invention provided it is sufficiently
soluble in the fuel to be effective in combination with the substituted imidazoline
compounds of the invention as a corrosion inhibitor. Further, since relatively pure
olefins are difficult to obtain and are often too expensive for commercial use, alkenylsuccinic
acids prepared as mixtures by reacting mixed olefins with maleic anhydride may be
employed in this invention as well as relatively pure alkenyl succinic acids. Mixed
alkenylsuccinic acids wherein the alkenyl group averages 6-8, 8-10 and 10-12 carbon
atoms are commercially available.
[0012] Component B of the combination is a substituted imidazoline.
[0013] The substituted imidazoline used in this invention can be represented by the following
general formula (
I):

in which R is a'hydrocarbon alkenyl group having from 7 to 24 carbon atoms.
[0014] The imidazolines having Formula I which are useful in this invention may be readily
obtained by reacting suitable organic acids with N-(2-hydroxyethyl)ethylene diamine.
This reaction involves the elimination of 2 molecules of water between the acid and
the amine. This reaction is represented by the following equation:

[0015] In addition to the imidazoline, small amounts of a corresponding linear amino amide
are also obtained. This amino amide is the result of eliminating only one molecule
of water between the acid and the amine. Methods of preparing the imidazolines are
well known. Useful procedures are described in Wilson, U.S. 2,267,965, and Wilkes,
U.S. 2,214,152. As can be seen from the reaction equation given above, the R group
in the imidazoline is the alkenyl residue of the particular acid which is used in
its preparation. In other words, the R group will have one carbon atom less than the
acid which is used to prepare the imidazoline.
[0016] Acids which are useful in preparing the imidazolines are hydrocarbon mono-carboxylic
acids having up to about 20 carbon atoms. The preferred acids are unsaturated organic
acids such as 9,10 decylenic acid, octenoic acid, oleic acid, linoleic acid and the
like. Preferred acids are commonly obtained as hydrolysis products of natural materials.
These acids thus obtained are mixtures. For example, acids obtained from olive oil,
typically, are a mixture of about 83 percent oleic acid, 6 percent palmitic acid,
4 percent stearic acid and 7 percent linoleic acid. This mixture is quite useful for
preparing imidazolines to be used in this invention. Organic acid mixtures obtained
on saponifying and acidulating babassu oil, castor oil, peanut oil-or palm oil are
examples of useful acids. Several imidazoline compounds which can be used in the present
invention are available commercially. A preferred imidazoline is 2-heptadecenyl-l-(2-hydroxyethyl)-imidazoline.
[0017] The weight ratio of component A to component B in the combination can vary over a
wide range, typically 1 to 10 parts A to 1 to 10 parts B. In a preferred embodiment,
the weight ratio is about 0.5-5 parts component A for each part component B. In a
more preferred embodiment there are 0.6-4.0 parts component A per each part component
B. The most preferred ratio is 1:1.
[0018] Components A and B can be separately added to the fuel. More preferably components
A and B are pre-mixed to form a package and this package is added to the fuel in an
amount sufficient to provide the required degree of corrosion protection.
[0019] Most preferably components A and B are also pre- mixed with a solvent to make handling
and blending easier. Suitable solvents include alcohols (e.g., methanol, ethanol,
isopropanol), ketones (acetone, methyl ethyl ketone), esters (tert-butyl acetate)
and ethers (e.g., methyl tert-butyl ether).
[0020] Aromatic hydrocarbons are very useful solvents. These include benzene, toluene, xylene
and the like. Excellent results can be obtained using xylene.
[0021] The concentration of the active components A and B in the package can vary widely.
For example, the active content can range from 5 weight percent up to the solubility
limit of A or B in the solvent. With xylene, a total active content of 5-60 weight
percent is generally used, especially about 50 weight percent.
[0022] Tests were conducted to measure the anticorrosion properties of the additive combination.
In the tests, the corrosion of steel cylinder rods (1/8 in. x 3 in.) (0.3175 cm x
7.62 cm) semisubmersed in test fluid was measured under different test conditions.
The rods were first cleaned with carborundum 180, polished with crocus cloth, washed
with acetone and then dried at room temperature.
[0023] Each rod was weighed and then semisubmersed in 10 milliliters of the test fluid in
a sealed bottle for the specified time at the specified temperature.
[0024] At the end of the test period, the rods were removed from the fuel, and after loose
deposits were removed with a light brush, the rods were washed, and dried as at the
start of the test and then reweighed. Any change in rod weight was recorded. Loss
of weight indicated corrosion.
[0025] A series of three tests were carried out lasting 7 days, 14 days and 30 days, respectively.
The series of tests were conducted in fuels comprising 5 volume percent methanol and
5 volume percent t-butanol in gasoline (indolene) containing 0.5 weight percent of
5.0 percent acetic acid in water. The tests were conducted at 25°C.
[0026] The test additives added to the test fuels were equal weight mixtures (100 ptb) of
either (i) predominantly oleic acid dimer or predominantly oleic acid trimer or (ii)
dodecenylsuccinic acid prepared from dodecene or propylene tetramer in combination
with 2-heptadecenyl-l-(2-hydroxyethyl)imidazoline and 50 ptb of each individual component.
1. A liquid fuel adapted for use in an internal combustion engine, said fuel comprising
5 to 100 weight percent of one or more alcohols, 0 to 95 weight percent gasoline and,
as a corrosion inhibitor, a combination of (A) a member selected from (
i) a polymer of one or more C
16 to C
18 polyunsaturated aliphatic monocarboxylic acids or (ii) at least one monoalkenylsuccinic
acid in which the alkenyl group contains 8 to 30 carbon atoms and (B) at least one
substituted imidazoline having the structural formula:

wherein R represents a hydrocarbon alkenyl group having from 7 to 24 carbon atoms.
2. A liquid fuel as claimed in Claim 1 wherein said polymer of one or more C16 to C18 polyunsaturated aliphatic monocarboxylic acids comprises linoleic acid dimer, trimer
or a m xture thereof.
3. A liquid fuel as claimed in either Claim 1 or Claim 2 wherein said monoalkenylsuccinic
ac:d is dodecenylsuccinic acid.
4. A liquid fuel as claimed in any one of Claims 1 to 3 wherein said substituted imidazolire
is 2-heptadecenyl-1-(2-hydroxy-ethyl)imidazoline.
5. A liquid fuel as claimed in any one of Claims 1 to 4 wherein the weight ratio of
component A to component B in the combination is from 1:10 to 10:1, preferably 1:1.
6. A liquid fuel as claimed in any one of Claims 1 to 5 wherein the corrosion inhibitor
is present at an amount ranging from 1 to 5000 pounds (0.45 to 2250 kg) per thousand
barrels, preferably 5 to 500 pounds (2.25 to 225 kg) per thousand barrels.
7. A liquid fuel as claimed in any one of claims 1 to 6 wherein said fuel comprises
a major amount of a hydrocarbon distillate in the gasoline distillation range and
from 2 to 30 volume percent of one or more alkanols containing from 1 to 4 carbon
atoms.
8. A corrosion inhibitor concentrate comprising a solvent containing 5 to 60 weight
percent of a combination of (A) a polymer of one or more C
16 to c
18 polyunsaturated aliphatic monocarboxylic acids and (B) at least one substituted imidazoline
having the structural formula:

in which R is a hydrocarbon alkenyl group having from 7 to 24 carbon atoms.
9. A method of preparing a liquid fuel comprising blending a fuel comprising 5 to
100 weight percent of one or more alcohols and 0 to 95 weight percent gasoline with,
as a corrosion inhibitor, a combination as defined in any one of Claims 1 to 5, the
components of said combination being either premixed or added separately.
10. A method as claimed in Claim 9 wherein the corrosion inhibitor is present at an
amount ranging from 1 to 5000 pounds (0.45 to 2250 kg) per thousand barrels, preferably
5 to 500 pounds (2.25 to 225 kg) per thousand barrels or the fuel is as defined in
Claim 7.