FIELD OF THE INVENTION
[0001] The present invention relates to diesel fuel compositions that are extremely stable
against thermal degradation, sedimentation, and discoloration. The diesel fuel compositions
of the present invention have been designed to be void or essentially void of certain
heteroatomic compounds often present in diesel fuel and which have been discovered
to cause the thermal degradation in the presence of nitrate-based cetane improver
additives.
BACKGROUND OF THE INVENTION
[0002] The benefits of operating a diesel engine on a diesel fuel treated with a nitrate-based
cetane improver are well known: improved cold starting, less combustion noise, smoother
engine operation and reduced toxic pollutant emissions. It is known that diesel fuels
containing nitrate-containing cetane improvers often exhibit instability in the form
of discoloration and sedimentation when heated to high temperatures (>120°C). It is
also known that organic nitrate cetane improvers (e.g. 2-ethylhexyl nitrate, commercially
available from Ethyl Corporation as HiTEC® 4103 cetane improver, also known as DII-3)
can worsen diesel fuel discoloration and sedimentation in the 150°C pad stability
test (ASTM D6468). The reasons for this phenomenon, however, have never been satisfactorily
explained and several studies carried out over the years have failed to establish
a correlation between any of a fuel's physical and chemical characteristics and its
thermal stability. It has been widely observed that severely hydrotreated fuels are,
in general, less susceptible to thermal degradation than conventionally refined fuels.
Severe hydrotreatment reduces the amounts of heteroatomic species (i.e., compounds
containing oxygen, nitrogen and/or sulfur atoms) in diesel fuel. Additionally, many
published studies have implicated heteroatomic compounds in diesel fuel sedimentation
at relatively low temperatures (below about 100°C). These results imply that heteroatomic
compounds may be responsible for high-temperature instability. None of these studies,
however, addresses the issue of high-temperature diesel fuel instability in the presence
of additives such as cetane improvers.
[0003] Several diesel fuels containing low amounts of total sulfur and/or nitrogen have
been described. U.S. Patent No. 6,150,575 shows low sulfur diesel fuels; U.S. Patent
No. 5,807,413 shows very low sulfur content and nitrogen content diesel fuels; U.S.
Patent No. 5,792,339 shows low sulfur content and higher nitrogen content diesel fuels;
U.S. Patent No. 5,389,111 and 5,389,112 show low sulfur content diesel fuels; EP 457589
shows a low sulfur content diesel fuel; and WO 00/12654 shows a very low sulfur content
and nitrogen content diesel fuel. In all of these cases,the amounts of sulfur and
nitrogen are considered only as bulk properties of the fuel; differences between chemical
types of heteroatomic compounds are not taken into account. We have discovered that
different types of heteroatomic molecules have different effects on a fuel's high-temperature
stability in the presence of nitrate-based cetane improvers.
[0004] In the patents and patent applications involving ultralow-sulfur content diesel fuels
(i.e., fuels with less than about 50 ppmw sulfur), the presence of nitrogen-containing
additives such as nitrate-based cetane improvers is severely limited by the allowable
or preferred total nitrogen content of the disclosed fuel compositions. Some of these
patents and patent applications also require fuel compositions of limited aromatic
content; however, low aromatic content is not required for this invention.
[0005] The patents, patent applications, and other documents recited herein are fully incorporated
by reference.
[0006] Discoloration and sedimentation induced by nitrate-based cetane improvers can be
undesirable to the consumer and can also interfere with common petroleum industry
tests (e.g., ASTM D189, "Conradson Carbon Residue of Petroleum Products" and ASTM
D524, "Ramsbottom Carbon Residue of Petroleum Products"). It is therefore desired
to have a diesel fuel composition which can demonstrate excellent thermal stability,
i.e., lack of sedimentation and minimal discoloration upon heating to >120°C. It has
been discovered that certain components in the diesel fuel are responsible for these
undesired effects, and that by eliminating these certain components, an improved diesel
fuel is produced.
SUMMARY OF THE INVENTION
[0007] A feature of the present invention is to provide a diesel fuel composition exhibiting
improved ignition quality, which can demonstrate excellent thermal stability, i.e.,
lack of sedimentation and minimal discoloration when heated.
[0008] It has been discovered that certain heteroatomic compounds when present in diesel
fuel containing nitrate-containing cetane improver cause severe discoloration and/or
sedimentation when the fuel is heated.
[0009] It has also been discovered that the absence or removal of these certain heteroatomic
compounds from diesel fuel containing, or to later contain, nitrate-containing cetane
improver, significantly improves the fuel's thermal stability and minimizes discoloration
and/or sedimentation.
[0010] Another feature of the present invention is to provide a diesel fuel composition
containing a major amount of a hydrocarbon boiling in the middle distillate boiling
range, and a minor amount of a nitrate-containing cetane improver, wherein the composition
is free of, or essentially free of, certain heteroatomic compounds.
[0011] A further feature of the present invention is to provide a method of reducing the
sedimentation and/or discoloration of a middle distillate fuel containing nitrate-based
cetane improver.
[0012] Accordingly, the present invention relates to a diesel fuel composition containing
a major amount of a hydrocarbon fuel boiling in the middle distillate boiling range,
and a minor amount of a nitrate-containing cetane improver, wherein the composition
is free of, or essentially free of, one or more heteroatomic compounds selected from
pyrroles, indoles, sulfides, disulfides, mercaptans, thioacids, sulfonic acids, and/or
indolines.
[0013] By "heteratomic compound" herein is meant one or more heteroatomic compounds selected
from pyrroles, indoles, sulfides, disulfides, mercaptans, thioacids, sulfonic acids,
and/or indolines.
[0014] By "deleterious" heteroatomic compound herein is meant a heteroatomic compound that
in a diesel fuel containing nitrated cetane improver causes discoloration and/or sedimentation
of the diesel fuel upon heating of the fuel.
[0015] By "free of" in the present invention is meant a deleterious heteroatomic compound
level generally undetectable in terms of adverse effect on color and sediment formation
of the diesel fuel. This level is generally a level of less than about 2 ppm of deleterious
heteroatomic compound in the finished diesel fuel. Similarly, by "removing all of"
herein is meant a remaining level, if any, of deleterious heteratomic compound of
less than about 2 ppm.
[0016] By "essentially free of" in the present invention is meant a level of less than about
5 ppm of heteroatomic compound in the finished diesel fuel. Similarly, by "removing
essentially all of" herein is meant a remaining level, if any, of heteratomic compound
of less than about 5 ppm.
[0017] By "nitrate-containing cetane improver" herein is meant chemical compounds that contain
a nitrate group covalently bonded, ionically bonded, or generated
in situ. Examples of nitrate-containing cetane improvers useful in the present invention include
methyl nitrate, ethyl nitrate, propyl nitrate, isopropyl nitrate, allyl nitrate, butyl
nitrate, isobutyl nitrate,
sec-butyl nitrate,
tert-butyl nitrate, amyl nitrate, isoamyl nitrate, 2-amyl nitrate, 3-amyl nitrate,
n-pentyl nitrate, hexyl nitrate, heptyl nitrate, 2-heptyl nitrate, octyl nitrate, isooctyl
nitrate, 2-ethylhexyl nitrate, nonyl nitrate, decyl nitrate, undecyl nitrate, dodecyl
nitrate, cyclopentyl nitrate, cyclohexyl nitrate, methylcyclohexyl nitrate, cyclododecyl
nitrate, 2-ethoxyethyl nitrate, 2-(2-ethoxyethoxy)ethyl nitrate, tetrahydrofuranyl
nitrate, tetraethyleneglycol dinitrate, isomers thereof, and mixtures thereof. A preferred
nitrate-containing cetane improver in an embodiment of the present invention is 2-ethyl
hexyl nitrate ("2-EH nitrate").
[0018] It is to be understood that both the foregoing general description and the following
detailed description are exemplary and explanatory only and are intended to provide
further explanation of the present invention, as claimed:
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0019] According to an embodiment of the present invention, an improved diesel fuel is prepared
by combining a major amount of a middle distillate fuel, and a minor amount of a nitrate-based
cetane improver, and removing before or after the addition of the nitrate-based cetane
improver all or essentially all of one or more the following heteroatomic compounds:
pyrroles, indoles, sulfides, disulfides, mercaptans, thioacids, sulfonic acids, and/or
indolines.
[0020] It has been discovered that middle distillate diesel fuel containing nitrate-based
cetane improver has significantly improved thermal stability, i.e., reduced discoloration
and reduced sedimentation, if the deleterious heteroatomic compounds of pyrroles,
indoles, sulfides, disulfides, mercaptans, thioacids, sulfonic acids, and/or indolines
are removed or essentially removed from the fuel, relative to the comparable diesel
fuel from which these heteroatomic compounds have not been removed. The aforementioned
deleterious heteroatomic species may be removed by any method known to those skilled
in the art, including hydrotreatment, selective adsorption, or oxidation.
[0021] The nitrate-based cetane improver can be present in the diesel fuel compositions
of the present invention at a level of from about 100 ppm to about 10,000 ppm.
[0022] It has also been discovered that certain heteroatomic compounds do not have an adverse
or deleterious effect on sedimentation and discoloration of middle distillate fuel
containing nitrate-based cetane improver. The heteroatomic compounds that do not have
an adverse or deleterious effect on these properties of diesel fuel include anilines,
pyridines, quinolines, amides, thiophenes, sulfoxides, phenols, carboxylic acids,
nitriles, nitro compounds, aldehydes, esters, alcohols, peroxides, and carbazoles
(see Table 1).
[0023] A benefit of this particular invention over the prior art is that certain species
that are hard to remove from the diesel fuel by desulfurization and/or denitrogenation
can be left in the fuel because they have been discovered herein to be innocuous in
terms of thermal stability of the resulting diesel fuel. For example, most nitrogen
compounds and thiophenes are more difficult to remove by hydrogenation than sulfides,
mercaptans, etc. However, since most nitrogen compounds and thiophenes do not cause
thermal instability of the diesel fuel, they can be left in the fuel at substantial
savings to the refiner.
Table 1.
Summary of tendencies of heteroatomic compounds to cause thermal instability of diesel
fuel containing 2-EH nitrate |
Compounds that cause thermal instability (degree of effect) |
Compounds that do not cause thermal instability |
Pyrroles (severe) |
Anilines |
Indoles (moderate to severe) |
Pyridines |
Indolines (moderate) |
Quinolines |
Sulfides (severe) |
Amides |
Disulfides (severe) |
Carbazoles |
Mercaptans (severe) |
Thiophenes |
Thioacids (severe) |
Sulfoxides |
Sulfonic acids (very severe) |
Phenols |
|
Carboxylic acids |
|
Nitriles |
|
Nitro compounds |
|
Aldehydes |
|
Alcohols |
|
Esters |
|
Peroxides |
[0024] Thus, in another embodiment of the present invention is provided a low sulfur D-2
(ASTM D975) diesel fuel having the following properties:
Cetane number, ASTM D613 35-60, and preferably 40-55
Cetane index, ASTM D4737 <60
Aromatics, total, wt. % ASTM D5186 <40
Polynuclear aromatics, wt. %, ASTM D2425 <11
Sulfur, ppmw, ASTM D2622-1 <50
Nitrogen, ppmw ASTM D4629 <1000 (from all sources)
Pyrroles, indoles, sulfides, disulfides, mercaptans, thioacids, sulfonic acids, and
indolines < 5 ppm total heteroatomic content. In a preferred embodiment, the amount
of each of pyrroles, indoles, sulfides, disulfides, mercaptans, thioacids, sulfonic
acids, and indolines is no more than 5 ppm, and in a more preferred embodiment, no
more than 2 ppm.
[0025] In addition, the present invention provides in another embodiment a diesel fuel meeting
the requirements of ASTM D 975 for a low sulfur No. 2-D diesel and providing emission
benefits at least equivalent to a diesel fuel as per Section 2282(g), Title 13, California
Code of Regulations, said fuel containing from about 10 vol. % to about 30 vol. %
aromatics and having (1) a Cetane number of at least 40 but less than 60, and preferably
from 45 to 55; (2) a nitrogen content of no greater than 1000 ppmw; (3) a sulfur content
of no greater than 50 ppmw; and (4) a total amount of nitrogen and sulfur from pyrroles,
indoles, sulfides, disulfides, mercaptans, thioacids, sulfonic acids and/or indolines
of no more than 5 ppm, preferably no more than 2 ppm. In a preferred embodiment, the
amount of each of pyrroles, indoles, sulfides, disulfides, mercaptans, thioacids,
sulfonic acids, and indolines is no more than 5 ppm, and in a more preferred embodiment,
no more than 2 ppm.
[0026] The following examples further illustrate aspects of the present invention but do
not limit the present invention.
EXAMPLES:
[0027] An ultralow-sulfur diesel fuel (Fuel 9041), with inspection data as listed in Table
2, was separately treated with enough of each of the additives listed in Table 1 to
deliver 350 ppm of oxygen, nitrogen, or sulfur. Fuel 9041 contained very low amounts
of sulfur and nitrogen, but was in all other properties typical for a No. 2 diesel
fuel. The base fuel with no added heteroatomic compound was very stable in the presence
of 2-EH nitrate, ensuring that any instability observed in subsequent experiments
arose from the introduced heteroatomic species. The heteroatomic compounds were selected
as representative of compounds that might typically be expected to be found in a diesel
fuel. Half of each fuel composition was treated with 2500 ppmv of 2-EH nitrate. The
nitrate-free and nitrate-containing fuel compositions were subjected to 180-minute
thermal stability testing at 150°C as described in pad stability test ASTM D6468.
Table 2.
Inspection data for Fuel 9041 |
Aromatics, vol. % |
33.6 |
Olefins, vol. % |
2.1 |
Saturates, vol. % |
64.3 |
Specific gravity |
0.850 |
T10, °C |
222 |
T50, °C |
271 |
T90, °C |
323 |
Sulfur, ppmw |
7 |
Nitrogen, ppmw |
27 |
Cetane number |
44.2 |
Kinematic viscosity, cSt, 40°C |
2.87 |
In the thermal pad stability test ASTM D6468, the reflectance of light on a filter
pad is measured and higher pad reflectances are desired as indicia that less sedimentation
has occurred in the fuel.
Results from Thermal Stability Pad Test (ASTM D6468)
Oxygen-containing compound |
w/o DII-3 |
w/ DII-3 |
None |
98.7 |
97.3 |
Phenylacetaldehyde |
99.6 |
99.7 |
Dimethylmalonate |
99.5 |
99.6 |
p-Cresol |
98.6 |
98.2 |
Lauric acid |
98.6 |
96.1 |
2-Ethylhexanol |
94.9 |
97.1 |
di-t-butyl peroxide |
94.9 |
95.8 |
Benzoic acid |
94.0 |
95.0 |
Sulfur-containing compound |
w/o DII-3 |
w/ DII-3 |
None |
98.7 |
97.3 |
Thianaphthene |
97.5 |
97.2 |
Dimethyl sulfoxide |
96.5 |
97.2 |
Di-t-butyl sulfide |
48.7 |
3.7 |
4-methylbenzenethiol |
24.8 |
12.0 |
1-octanethiol |
12.6 |
3.3 |
Di-t-butyl disulfide |
7.4 |
2.5 |
Thiobenzoic acid |
7.3 |
1.8 |
p-Toluenesulfonic acid |
3.8 |
1.0 |
Nitrogen-containing compound |
w/o DII-3 |
w/ DII-3 |
None |
98.7 |
97.3 |
N,N-dimethylaniline |
98.6 |
96.0 |
3,5-lutidine |
98.5 |
97.1 |
2,5-dimethylaniline |
98.1 |
98.3 |
3-nitrotoluene |
98.0 |
94.4 |
Quinaldine |
97.4 |
97.5 |
2,4,6-collidine |
97.1 |
96.9 |
Benzonitrile |
94.9 |
97.9 |
2-pyrrolidinone |
91.6 |
97.7 |
Indole |
84.8 |
91.5 |
2-methylindole |
79.6 |
48.6 |
Indoline |
62.3 |
65.7 |
2,5-dimethylpyrrole |
7.0 |
3.1 |
[0028] A number of conclusions can be drawn from these results. First, oxygen-containing
compounds, even moderately strong carboxylic acids, have no adverse effect on the
diesel fuel containing 2-EH nitrate cetane improver when the fuel was subjected to
thermal stressing. With the exception of pyrroles and indoles, the same is true for
the nitrogenous compounds investigated. In contrast, most of the sulfur-containing
species studied had a strongly detrimental effect on the thermal stability of diesel
fuel containing 2-EH nitrate.
[0029] Other embodiments of the present invention will be apparent to those skilled in the
art from consideration of the specification and practice of the invention disclosed
herein. It is intended that the specification and examples be considered as exemplary
only, with a true scope and spirit of the invention being indicated by the following
claims. This invention is susceptible to considerable variation in its practice. Accordingly,
this invention is not limited to the specific exemplifications set forth hereinabove.
Rather, this invention is within the spirit and scope of the appended claims, including
the equivalents thereof available as a matter of law.
[0030] The patentee does not intend to dedicate any disclosed embodiments to the public,
and to the extent any disclosed modifications or alterations may not literally fall
within the scope of the claims, they are considered to be part of the invention under
the doctrine of equivalents.
ANNEX : MIDDLE DISTILLATE FUELS
[0031] Middle distillate fuels are used particularly in running diesel engines (especially
for automobiles), aircraft engines and turbines. The great majority of such fuels
have a boiling range of 140-360°C and most conform to the following distillation profile:
initial b.p. |
140-220°C |
10% b.p. |
190-240°C |
50% b.p. |
220-290°C |
90% b.p. |
260-340°C |
endpoint |
280-360°C |
[0032] Such fuels are particularly preferred in connection with the present invention.
1. A diesel fuel composition comprising a hydrocarbon fuel boiling in the middle distillate
boiling range, and a minor amount of a nitrate-containing cetane improver, wherein
the composition is essentially free of one or more heteroatomic compounds selected
from pyrroles, indoles, sulfides, disulfides, mercaptans, thioacids, sulfonic acids,
and/or indolines.
2. A low sulfur D-2(ASTM D975) diesel fuel according to claim1 having the following properties:
Cetane number ASTM D613 35 to 60
Cetane index ASTM 4737 <60
Aromatics, total, wt. %ASTM D5186 <40
Polynuclear aromatics, wt %, ASTM D2425 <11
Sulfur, ppmw, ASTM D2622-1 <50
Nitrogen, ppmw ASTM D4629 <1000, and
A total amount of nitrogen and sulfur from pyrroles, indoles, sulfides, disulfides,
mercaptans, thioacids, sulfonic acids, and indolines of no more than 5 ppm.
3. A diesel fuel according to claim 1 meeting the requirements of ASTM D975 for a low
sulfur No. 2-D diesel and providing emission benefits at least equivalent to a diesel
fuel as per Section 2282(g), Title 13, California Code of Regulations, said fuel containing
from 10 vol. % to 30 vol. % aromatics and having a Cetane number of at least 40 but
less than 60; a nitrogen content of no greater than 1000 ppmw; a sulfur content of
no greater than 50 ppmw; and a total amount of nitrogen and sulfur from pyrroles,
indoles, sulfides, disulfides, mercaptans, thioacids, sulfonic acids and/or indolines
of no more than 5 ppm.
4. A diesel fuel according to claim 1 comprising:
a hydrocarbon boiling in the middle distillate boiling range;
2-ethyl hexyl nitrate cetane improver present in an amount of from 100 to 10,000 ppm;
and
wherein the total amount of nitrogen and sulfur present in the fuel from pyrroles,
indoles, sulfides, disulfides, mercaptans, thioacids, sulfonic acids and/or indolines
is no more than 5 ppm.
5. A diesel fuel composition according to any one of claims 1 to 4, wherein the total
amount of nitrogen and sulfur present in the fuel from pyrroles, indoles, sulfides,
disulfides, mercaptans, thioacids, sulfonic acids and/or indolines is no more than
2 ppm.
6. A fuel according to any of claims 1 to 4, wherein the amount of each of the heteroatomic
compounds pyrroles, indoles, sulfides, disulfides, mercaptans, thioacids, sulfonic
acids, and indolines is no more than 5 ppm.
7. A diesel fuel composition according to any of claims 1 to 4, wherein the amount of
each of pyrroles, indoles, sulfides, disulfides, mercaptans, thioacids, sulfonic acids
and/or indolines is no more than 2 ppm.
8. A fuel according to any of claims 1 to 4, wherein the total amount of pyrroles, indoles,
sulfides, disulfides, mercaptans, thioacids, sulfonic acids, and indolines is no more
than 5 ppm.
9. A fuel according to any of claims 1 to 4, wherein the total amount of pyrroles, indoles,
sulfides, disulfides, mercaptans, thioacids, sulfonic acids, and indolines is no more
than 2 ppm.
10. A diesel fuel composition according to any of the preceding claims, wherein the nitrate-containing
cetane improver is present in an amount of from 100 to 10,000 ppm, and the heteroatomic
compounds, if present, are present at a level of less than 2 ppm total heteroatomic
content.
11. A composition according to any of the preceding claims, wherein the nitrate-containing
cetane improver is selected from methyl nitrate, ethyl nitrate, propyl nitrate, isopropyl
nitrate, allyl nitrate, butyl nitrate, isobutyl nitrate, sec-butyl nitrate, tert-butyl nitrate, amyl nitrate, isoamyl nitrate, 2-amyl nitrate, 3-amyl nitrate, n-pentyl nitrate, hexyl nitrate, heptyl nitrate, 2-heptyl nitrate, octyl nitrate, isooctyl
nitrate, 2-ethylhexyl nitrate, nonyl nitrate, decyl nitrate, undecyl nitrate, dodecyl
nitrate, cyclopentyl nitrate, cyclohexyl nitrate, methylcyclohexyl nitrate, cyclododecyl
nitrate, 2-ethoxyethyl nitrate, 2-(2-ethoxyethoxy)ethyl nitrate, tetrahydrofuranyl
nitrate, tetraethyleneglycol dinitrate, isomers thereof, and mixtures thereof.
12. A composition according to any of the preceding claims, wherein the nitrate-containing
cetane improver is 2-ethyl hexyl nitrate.
13. A process of reducing the amount of discolouration or sedimentation which occurs in
diesel fuel containing a major amount of a hydrocarbon fuel boiling in the middle
distillate boiling range, and a minor amount of a nitrate-containing cetane improver,
said method comprising removing from said diesel fuel essentially all of the pyrroles,
indoles, sulfides, disulfides, mercaptans, thioacids, sulfonic acids, and/or indolines.
14. A process according to claim 13, wherein the diesel fuel produced is as claimed in
any one of claims 2 to 12.