Description
Title of Invention: FUEL EFFICIENT ENGINE OIL COMPOSITION
Technical Field
[0001]
The present invention relates to a fuel efficient engine oil having
excellent anti-corrosion and anti-wear properties.
Background Art
[0002]
In recent years, improvement of fuel efficiency of the automobiles and
reduction of the CO2 emissions are becoming increasingly desirable in order
to prevent imminent global warming. While providing more efficient engine
designs is important, reducing friction within the engines may also
contribute to improved fuel efficiency. Therefore, use of low-friction
materials in the sliding parts as well as use of fuel efficient-type engine oils
is becoming more prevalent.
[0003]
For obtaining a fuel efficient engine oil, lowering viscosity of the oil
as in viscosity grade of 5W - 30 or 0W - 30 as defined by the SAE (Society of
Automotive Engineers) J300 standard is known to be an effective approach,
as well as inclusion of an additive for reducing friction (friction modifier;
abbreviated to "FM') e.g. an organic-molybdenum-based FM such as
molybdenum dithiocarbamate (MoDTC).
[0004]
However, it has been known that sulfuric acid may be generated from
the sulfur components contained in the fuel or the engine oil and that some
of the sulfuric acid may contaminate the engine oil, causing corrosion and
wear of the engine parts. Therefore, there is a strong demand for engine
oils that, have excellent anti-corrosion properties regardless of inclusion of
MoDTC or the like.
[0005]
Examples of such lubricant oil compositions for internal combustion
engines characterized by improved anti-corrosion and anti-wear properties
include the composition of Patent Literature (PLT) 1 which comprises
sulfated oxymolybdenum dithiocarbamate, an acid amide compound, a
fatty-acid partial ester compound and/or a fatty-acid amine compound, and a
benzotriazole derivative in a lubricant base oil (PLT 1). However, the
anti-corrosion effect and the anti-wear effect of this composition are still not
satisfactory.
Patent Document 2 proposes a lubricant oil characterized by
improved corrosion resistance on lead and copper comprising a specific
epoxidized ester compound (PLT 2). PLT 2 enumerates various types of
epoxidized ester compounds comprising cycloalkyl groups, but the only
specific compound disclosed therein is the epoxidized 2-ethylhexyl tallate.
Moreover, although PLT 2 perfunctorily mentions organomolybdenum
compounds as an example of friction modifier, the document does not disclose
anything about its effect, and in particular, there is no disclosure about a
synergistic effect of the epoxy compound and the organomolybdenum
compound.
Citation List
Patent Literature
[0006]
PLT 1: JP 2008-106199 A
PLT 2: JP 2008-518080 A
Summary of Invention
Technical Problem
[0007]
An object of the present invention is to provide an engine oil having
excellent anti-corrosion, anti-wear, and fuel-saving properties.
Solution to Problem
[0008]
In order to achieve the above object, the present inventors have
conducted extensive research on a wide variety of lubricant base oil
materials and lubricant additives that may be used in engine oils, and found
that an engine oil comprising a combination of an alicyclic epoxy compound
and a specific amount of an organic molybdenum compound as lubricant
additives exhibits excellent fuel efficiency, anti-corrosion property, and
anti-wear property. This finding has led to the completion of the present
invention.
[0009]
Thus, the fuel efficient engine oil composition of the present
invention for achieving the above object comprises an organic molybdenum
compound at a concentration of 0.02 mass% or higher in terms of the mass of
the molybdenum (Mo), and an alicyclic epoxy compound, in addition to a
lubricant base oil.
In a preferable embodiment of the present invention, the said organic
molybdenum compound is molybdenum dithiocarbamate (MoDTC), the said
alicyclic epoxy compound has an ester bond and two epoxidized cycloalkane
moieties, and the said lubricant base oil has a kinematic viscosity of 4.5
mm2/s or lower at 100 °C.
Advantageous Effects of Invention
[0010]
The fuel efficient engine oil composition of the present invention
allows little corrosion and wear of the engine parts even after long-term use
and furthermore provides an excellent low-friction property. Thus the
engine oil composition excels in fuel efficiency especially at high temperature
ranges.
Description of Embodiments
[0011]
The lubricant base oil used in the fuel efficient engine oil composition
of the present invention may be a mineral oil, a synthetic oil, or mixture
thereof. The mineral oil is preferably a high viscosity index lubricant base
oil having a viscosity index of 120 or higher. The lubricant base oil having a
viscosity index of 120 or higher can be obtained by hydroisomerizing wax or
hydrocracking heavy oil and then solvent-dewaxing or hydrodewaxing the
resulting oil product.
[0012]
Hydroisomerization of wax can be carried out by contacting a wax
material having a boiling point in the range of 300 to 600 °C and a carbon
number of 20 to 70 (such as slack wax obtained in a solvent-dewaxing
process for mineral lubricant oil and wax obtained in the Fischer-Tropsch
synthesis in which hydrocarbon gas or the like is converted to carbon
monoxide and hydrogen to synthesize liquid fuel) with a hydroisomerization
catalyst (such as a catalyst comprising any one or more of group 8 metals (e.g.
nickel, cobalt, etc.) and group 6A metals (e.g. molybdenum, tungsten, etc.)
supported on an alumina or silica-alumina carrier, a zeolite catalyst, or a
catalyst comprising platinum or the like supported on a zeolite-containing
carrier), at a temperature of 300 to 450 °C and an LHSV (liquid hourly space
velocity) of 0.1 to 2 h"1 in the presence of hydrogen at a partial pressure of 5
to 14 MPa. Preferably, in the above process, the conversion rate of
straight-chain paraffin is 80% or higher and the rate of conversion into light
distillates is 40% or lower.
[0013]
The lubricant base oil with a high viscosity index may be obtained
also from hydrocracking of heavy oil as follows. An atmospheric distillate
oil, a vacuum distillate oil, or a bright stock having a boiling point in the
range of 300 to 600 °C, which may have been subjected to
hydrodesulfurization and hydrodenitrification as needed, is contacted with a
hydrocracking catalyst (such as a catalyst comprising one or more of group 8
metals (e.g. nickel, cobalt, etc.) and one or more of group 6A metals (e.g.
molybdenum, tungsten, etc.) supported on a silica-alumina carrier) at a
temperature of 350 to 450 °C and an LHSV (liquid hourly space velocity) of
0.1 to 2 h'1 in the presence of hydrogen at a partial pressure of 7 to 14 MPa.
In this process, the cracking rate (i.e. reduction rate of a fraction
corresponding to the distillation range of 360 °C or higher seen in the
resulting product, expressed as mass%) is preferably 40 to 90%.
[0014]
The hydroisomerized oil product or the hydrocracked oil product
obtained in the processes described above may be subjected to removal of the
light fractions.by distillation to produce a lubricant fraction. This fraction
as it is, however, usually has a high pour point and high viscosity, and
moreover, its viscosity index is usually not sufficiently high. Therefore; the
said fraction may be further subjected to a dewaxing process to remove the
wax components and to produce a lubricant base oil having a %Cp.of 80 or
higher as determined by the n-d-M ring analysis, a pour point of -10 °C or
lower, and a viscosity index of 120 or higher.
[0015]
If the dewaxing process above is to be done by a solvent'dewaxing
treatment, the prior removal of the light fractions by distillation is
preferably carried out by using a precision distillation apparatus so that the
fraction corresponding to boning points of at least 371 °C but below 491 °C is
pre-adjusted to 70 mass% or more as determined by the gas chromatography
distillation method. This way, the efficiency of the subsequent
solvent-dewaxing treatment can be improved. The solvent-dewaxing
treatment may be preferably carried out by using methylethyl
ketone/toluene (volume ratio 1/1) as a dewaxing solvent, for example, at a
solvent/oil ratio of 2/1 to 4/1 and at a temperature of "15 to -40 °C.
[0016]
On the other hand, if the dewaxing process is to be done by the
hydrodewaxing method, the prior removal of the light fractions by
distillation is preferably carried out only to the extent that it will not
adversely affect the subsequent hydrodewaxing process, and after
hydrodewaxing is finished, distillation is preferably carried out by using a
precision distillation apparatus so that the fraction corresponding to boiling
points of at least 371 °C but below 491 °C is adjusted to 70 mass% or higher
as determined by the gas chromatography distillation method. The
hydrodewaxing step may be preferably performed by contacting the raw
material with a zeolite catalyst at a temperature of 320 to 430 °C and an
LHSV (liquid hourly space velocity) of 0.2 to 4 h-1 in the presence of hydrogen
at a partial pressure of 3 to 15 MPa so that the pour point of the final
lubricant base oil is -10 °C or lower.
[0017]
A lubricant base oil having a viscosity index of 120 or higher may be
obtained through the processes described above, but if desired, further
solvent-refining or further hydrorefining may also be carried out.
[0018]
Examples of the synthetic oil include oligomers of a-olefin, diesters
synthesized from a dibasic acid (such as adipic acid) and a monohydric
alcohol, polyol esters synthesized from a polyhydric alcohol (such as
neopentyl glycol, trimethylolpropane and pentaerythritol) and a monobasic
acid, and mixture thereof.
[0019]
Moreover, a blended oil comprising a suitable mineral oil and a
suitable synthetic oil may also be used as a base oil in the engine oil of the
present invention.
Whether it is a mineral oil, a synthetic oil, or a blended oil, the base
oil used in the fuel efficient engine oil composition of the present invention
preferably has a kinematic viscosity of 4.5 mm2/s or lower at 100 °C and a
viscosity index of 120 or higher as determined by the JIS K2283 test method,
and furthermore, the base oil preferably has a kinematic viscosity of 1.0
mm2/s or higher at 100 °C, a %Cp of 80 or higher as determined by the n-d_M
ring analysis according to ASTM D2140, and a pour point of -10 °C or lower
as determined by the JIS K2269 test method.
[0020]
The fuel efficient engine oil composition of the present invention has
an organic molybdenum compound content of 0.02 mass% or higher in terms
of the mass of the molybdenum (Mo) relative to the total mass of the engine
oil composition. If the molybdenum content is below 0.02 mass%, the fuel
efficiency would not be sufficiently sustainable. The organic molybdenum
compound content is preferably 0.03 to 0.20 mass% in terms of the mass of
the molybdenum (Mo).
Specific examples of the organic molybdenum compounds include
molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate
(MoDTP), and Mo-amine complexes. Among these, MoDTC is the most
preferable, and MoDTP is not very preferable due to the poisoning of the
three-way catalyst for purification of the exhaust gas, the said poisoning
being caused by the phosphorus.
Preferable MoDTC used in the present invention may be expressed
by the following general formula (l).
[0021]
[Chemical Formula l]

[0022]
In the formula above, Ri to PU represent linear and/or branched alkyl
groups and/or alkenyl groups having carbon numbers of 4 to 18, and each X
represents an oxygen atom or a sulfur atom wherein the oxygen atoms and
the sulfur atoms are present in the ratio of 1/3 to 3/1. R1 to R4 are
preferably alkyl groups, and especially preferably branched alkyl groups
having carbon numbers of 8 to 14, specific examples of which include butyl
group, 2-ethylhexyl group, isotridecyl group, stearyl group, and the likes.
The four "R" groups present in a single molecule, namely R1 to R4, may be
identical to or different from each other. Moreover, two or more kinds of
MoDTC molecules having different R1 to R4 groups may be used in mixture.
[0023]
Examples of the alicyclic epoxy compounds that may be used in the
present invention include epoxidized cycloalkanes and derivatives thereof.
The epoxidized cycloalkane preferably has a carbon number of 3 to 12.
Specific examples of the epoxidized cycloalkanes include epoxidized
cyclopropane, epoxidized cyclobutane, epoxidized cyclopentane, epoxidized
dicyclopentane, epoxidized cyclohexane, epoxidized cycloheptane, epoxidized
cyclooctane, epoxidized cyclononane, epoxidized cyclodecane, epoxidized
cyclododecane, epoxidized norbornane, and the likes.
[0024]
Examples of the derivatives of epoxidized cycloalkanes include
alkylated or alkenylated epoxy cycloalkanes having one or more alkyl or
alkenyl groups on the alicyclic moiety, ether compounds having one or more
fatty alkyloxy or aryloxy groups on the alicyclic moiety, imide and bisimide
compounds having one or more imide groups on the alicyclic moiety, amide
compounds having one or more amide groups on the alicyclic moiety, and the
likes. An ester compound having one or more carboxylic groups on the
alicyclic moiety is a more preferable example. A compound having two
epoxidized cycloalkane moieties is still more preferable, especially
3,4-epoxycycloalkyl-3,4-epoxycycloalkyl carboxylate (wherein the carbon
number of each alkyl group is 3 to 12), specific examples of which include
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate which is most
preferable. These alicyclic epoxy compounds may be used individually or in
combination of two or more.
The alicyclic epoxy compound may be contained in the composition in
any effective amount, which may be suitably selected in the range of 0.05 to 2
mass% relative to the total mass of the engine oil composition.
[0025]
The fuel efficient engine oil composition of the present invention may
further contain various other additives not mentioned above in order to
achieve well-balanced lubricating performance. In particular, a
metal-based detergent, an ashless dispersant, and/or an anti-wear agent are
preferably added in order to achieve superior cleanliness, sludge dispersion,
and/or anti-wear performance.
[0026]
The metal-based detergent is preferably at least one alkaline earth
metal based detergent selected from alkaline earth metal sulfonate, alkaline
earth metal phenate, and alkaline earth metal salicylate.
The alkaline earth metal sulfonate is preferably an alkaline earth
metal salt (especially a magnesium salt and/or a calcium salt, the calcium
salt being preferred) of alkylaromatic sulfonic acid having a molecular
weight of 300 to 1500, especially a molecular weight of 400 to 700.
[0027]
The alkaline earth metal phenate is preferably an alkaline earth
metal salt (especially a magnesium salt and/or a calcium salt) of alkylphenol,
alkylphenol sulfide, or a Mannich reaction product of alkylphenol, wherein
the alkyl group is a linear or branched alkyl group having a carbon number
of 4 to 30, preferably a carbon number of 6 to 18.
The alkaline earth metal salicylate is preferably an alkaline earth
metal salt (especially a magnesium salt and/or a calcium salt) of
alkylsalicylic acid wherein the alkyl group is a linear or branched alkyl
group having a carbon number of 1 to 30, preferably a carbon number of 6 to
18.
The amount of the said metal-based detergent to be added may be
varied freely, but preferably, the metal-based detergent content is 0.05 to
0.22 mass%, more preferably 0.1 to 0.2 mass%, in terms of the mass of the
metal relative to the total mass of the fuel efficient engine oil composition.
[0028]
Examples of the ashless dispersant include alkenylsuccinimide and
alkylsuccinimide derived from polyolefin, and derivatives thereof. An
exemplary succinimide is obtainable from the reaction between succinic
anhydride bearing a high molecular weight alkenyl or alkyl substituent and
polyalkylenepolyamine having 4 to 10 nitrogen atoms, more preferably 5 to 7
nitrogen atoms, per molecule on average. In particular,
polybutenylsuccinimide having polyisobutene of a number average molecular
weight of 700 to 5000, especially 900 to 3000, as a high molecular weight
alkenyl or alkyl group is preferable.
[0029]
The polybutenylsuccinimide is obtainable from polybutene which is
obtainable by polymerization of high-purity isobutene or mixture of 1-butane
and isobutene with the use of a boron-fluoride-based catalyst or an
aluminium-chloride-based catalyst. Usually, 5 to 100 mol% of the
polybutenylsuccinimide has a vinyhdene group at the end of the polybutene.
For obtaining an excellent inhibitory effect against sludge formation, the
polyalkylenepolyamine chain preferably has 2 to 5, more preferably 3 to 4,
nitrogen atoms.
The derivative of polybutenylsuccinimide used in the invention may
be what is called a modified succinimide which is obtainable from the
polybutenylsuccinimide mentioned above by reacting it with a boron
compound (e.g. boric acid) or an oxygen-containing organic compound such as
alcohol, aldehyde, ketone, alkylphenol, cyclic carbonate, and organic acid to
neutralize or amidate part or all of the remaining amino groups and/or imino
groups. In particular, boron-containing alkenyl (or alkyl) succinimide
obtainable from a reaction with a boron compound such as boric acid exhibits
excellent heat- and oxidation-stability.
The amount of the said ashless dispersant to be added may be varied
freely, but preferably, the ashless dispersant content is 0.5 to 15 mass%
relative to the total mass of the fuel efficient engine oil composition.
[0030]
The fuel efficient engine oil composition of the present invention
preferably contains zinc dithiophosphate (ZnDTP) as an anti-wear agent at
0.01 to 0.10 mass%, more preferably 0.05 to 0.08 mass%, in terms of the
mass of the phosphorus (P) relative to the total mass of the fuel efficient
engine oil composition. If the phosphorus atom content originating from
ZnDTP is below 0.01 mass% relative to the total mass of the engine oil
composition, sufficient anti-wear performance may not be obtained, and if
the phosphorus content originating from ZnDTP exceeds 0.10 mass%,
poisoning of the catalyst for purification of the automotive exhaust gas may
become significant.
The ZnDTP compound preferably has a linear or branched alkyl
group of a carbon number of 1 to 24, a linear or branched alkenyl group or
alkyl cycloalkyl group of a carbon number of 3 to 24, or an aryl group or
linear or branched alkylaryl group of a carbon number of 6 to 18. The alkyl
group and the alkenyl group may be primary, secondary, or tertiary.
[0031]
Specific examples of zinc dithiophosphate include zinc
dipropyldithiophosphate, zinc dibutyldithiophosphate, zinc
dipentyldithiophosphate, zinc dihexyldithiophosphate, zinc
diisopentyldithiophosphate, zinc diethylhexyldithiophosphate, zinc
dioctyldithiophosphate, zinc dinonyldithiophosphate, zinc
didecyldithiophosphate, zinc didodecyldithiophosphate, zinc
dipropylphenyldithiophosphate, zinc dipentylphenyldithiophosphate, zinc
dipropylmethylphenyldithiophosphate, zinc dinonylphenyldithiophosphate,
zinc didodecylphenyldithiophosphate, zinc didodecylphenyldithiophosphate,
and the likes.
The ZnDTP content is preferably 0.01 to 0.10 mass%, more preferably
0.03 to 0.08 mass%, in terms of the mass of the phosphorus (P) atoms
relative to the total mass of the engine oil composition.
[0032]
The engine oil of the present invention may optionally contain
further additives such as ashless antioxidant, viscosity index improver, pour
point-depressant, metal-deactivating agent, anti-rust agent, and
anti-foaming agent.
Examples
[0033]
Below, the present invention will be described in further details by
Examples.
A mineral oil (kinematic viscosity: 17.7 mm2/s at 40 °C and 4.1 mm2/s
at 100 °C; viscosity index: 134; %CP: 85; pour point: -20 °C) obtained by
hydrocracking heavy oil and hydrodewaxing the resulting oil product was
used as a base oil.
[0034]
To the said base oil, MoDTC described below as an additive, a
benzotriazole derivative (BTA) which is widely used as a lubricant additive
for inhibiting corrosion, an epoxy compound, a viscosity index improver (VI),
and other additives were added in the ratios shown in Table 1 to prepare the
engine oils of Examples 1 and 2 and Comparative Examples 1 to 6. The
other additives consisted of a mixture of zinc alkyldithiophosphate (ZnDTP),
Ca sulfonate, alkenylsuccinimide, pour point depressant, and anti-foaming
agent, and were added equally to all Examples and Comparative Examples
in the same amounts. The viscosity index improver was added to all
Examples and Comparative Examples so that the kinematic viscosity at 100
°C was 9.3 to 9.5 mm2/s (corresponding to the SAE viscosity grade of 30) in
each composition.
[0035]
The MoDTC used here was a compound expressed by the general
formula (1) wherein R1 to R4 were mixture of 2-ethylhexyl and isotridecyl
groups and the oxygen atom/sulfur atom ratio was 1/1.
N,N-bis[(2-ethylhexyl)aminomethyl]-lH-benzotriazole (Irgamet 39
manufactured by Ciba Speciality Chemicals) was used as a benzotriazole
derivative.
As epoxy compounds,
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate which is an
alicyclic epoxy compound was used, as well as 2-ethylhexylglycidyl ether
(Epoxy Compound l) and glycidyl neodecanoate ester (Epoxy Compound 2)
which are non-alicyclic epoxy compounds for comparison.
A polymethacrylate compound was used as a viscosity index
improver.
[0036]
[Table l]

[0037]
A corrosion and oxidation stability test was conducted on each of the
engine oils of Examples and Comparative Examples shown in Table 1, and
after the test, the oils were subjected to elemental analysis by Inductively
Coupled Plasma-Atomic Emission Spectrometry (ICP_AES). The corrosion
and oxidation stability test was carried out according to JIS K2503 except
that the test temperature was 135 °C and the test pieces were copper (Cu),
lead (Pb) and tin (Sn).
The engine oils tested above were also evaluated for their fuel
efficiency by the SRV friction test (test conditions were as follows: load : 400
N' amplitude- 1.5 mm; oscillation frequency: 50 Hz; temperature- 100 oC) and
graded as either good (denoted by the symbol "O") or poor (denoted by the
symbol "X").
The results are shown in Table 2.
[0038]
[Table 2]

[0039]
As shown in Table 2, the engine oil compositions of Examples 1 and 2
exhibited excellent fuel efficiency while eluting little Cu, Pb and Sn in the
corrosion and oxidation stability test. Thus, the engine oil compositions of
Examples 1 and 2 were capable of providing excellent anti-corrosion and
anti-wear properties and high fuel efficiency.
Comparative Example 1 to which MoDTC and alicyclic epoxy had not
been added eluted little Cu and Pb in the corrosion oxidation stability test
but its fuel efficiency was poor. Comparative Example 2, to which MoDTC
had been added but not an alicyclic epoxy compound, exhibited excellent fuel
efficiency but it also exhibited significant corrosion of Cu in the corrosion and
oxidation stability test.
Comparative Examples 3 and 4 to which a benzotriazole derivative
and MoDTC had been added exhibited more Cu elution with a smaller
amount of the benzptriazole derivative, and more Pb elution with a larger
amount of the benzotriazole derivative, indicating excellent fuel efficiency
but poor corrosion and oxidation stability. Moreover, Comparative
Examples 5 and 6 to which MoDTC and a non-alicyclic epoxy compound had
been added exhibited a considerable level of Cu elution and the
anti-corrosion property was extremely poor especially with the ester of a
fatty acid and an epoxy.
Industrial Applicability
[0040]
The present invention provides excellent anti-corrosion and
anti-wear properties and fuel efficiency and therefore may be utilized as
engine oils for internal combustion engines, such as gasoline engines, diesel
engines, gas engines, and the likes.
Claims
1. A fuel efficient engine oil composition comprising a lubricant base oil, an
organic molybdenum compound at a concentration of 0.02 mass% or higher
in terms of the mass of the molybdenum (Mo) relative to the total mass of the
composition, and an alicyclic epoxy compound.
2. The fuel efficient engine oil composition according to claim 1 wherein the
alicyclic epoxy compound comprises an ester bond.
3. The fuel efficient engine oil composition according to claim 1 or 2 wherein
the alicyclic epoxy compound comprises two epoxidized cycloalkane moieties.
4. The fuel efficient engine oil composition according to any one of claims 1 to
3 wherein the organic molybdenum compound is molybdenum
dithiocarbamate (MoDTC).
5. The fuel efficient engine oil composition according to any one of claims 1 to
4 wherein the lubricant base oil has a kinematic viscosity of 4.5 mm2/s or
lower at 100 °C.