Note: Descriptions are shown in the official language in which they were submitted.
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LONG-LIFE ENGINE OIL COMPOSITION WITH LOW
OR NO ZINC CONTENT
FIELD OF THE INVENTION
[001] The present invention relates to lubricating compositions for use in
natural gas fired internal combustion engines.
BACKGROUND OF THE INVENTION
[002] Internal combustion engines fueled with natural gas are typically used
to
drive compressors used in the oil and gas industry to compress natural gas at
well heads and along pipelines. These engines typically have up to 16
cylinders
and often generate between 500 to 3,000 HP. Because of how they are used, they
need to be able to run continuously near full load conditions, with shut downs
only for periodic maintenance such as oil changes. Under these operating
conditions, the engine lubricant is subjected to high temperatures promoting
oxidation and nitration processes that can limit lubricant life. Therefore,
oil
formulators and gas engine operators are continually seeking engine oils that
have improved resistance to oxidation and nitration.
10031 In addition to controlling oxidation and nitration susceptibility of gas
engine oils, the oil must also be formulated to have an ash content
appropriate
for correct operation of a given engine because the ash acts as a solid
lubricant,
protecting the valve-seat interface of the engine. For this reason, gas engine
oils
are classified according to their ash content. The classifications are:
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Ash Designation Ash level, mass% (ASTM D874)
Ashless Ash < 0.1 %
Low Ash 0.1% < Ash < 0.6%
Medium Ash 0.6% < Ash < 1.5%
High Ash Ash > 1.5%
[0041 A gas engine oil having a low sulfated ash content is the subject of US
5,726,135. The oil contains a mixture of detergents, one of which has a total
base
number (TBN) of 250 or less and a second having a TBN of about half or less
than the ftrst.
[005] US 6,191,081 discloses a gas engine oil having a medium or high sulfated
ash content. The oil contains three groups of metal detergents. The first
group is
selected from metal salicylates, sulfonates, phenates and other metal salts
having
a TBN of 150 or higher. The second group is selected from similar groups as
the
first but having a TBN of 50 to 150. The third group is selected from metal
sulfonates and salicylates having a TBN of about 10 to 50. Also, one of the
low
or medium TBN detergents is a metal salicylate.
[006] In US 6,140,281 there is disclosed a gas engine oil in which the
detergent
is a mixture of one or more metal sulfonates and/or one or more metal phenates
combined with one or more metal salicylates in which each metal salt has
substantially the same TBN.
[007] In patent publication US 2005/0153851 Al, a long life lubricating oil
for
gas fired engines is disclosed. The oil contains a mixture of neutral and
overbased metallic detergents and at least one trinuclear molybdenum
compound.
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1008] The foregoing references illustrate what is well known in the art,
namely,
that the proper combination of additives is necessary to assure that an oil
formulation will possess the requisite effectiveness. For example, some
friction
modifiers affect metal surfaces differently than do antiwear agents. When both
are present, the friction reducing and antiwear agents may compete for the
surface of the metal parts subject to lubrication. This competition can
produce a
lubricant that is less effective than is suggested by the individual
properties of
the additive components.
[009] Accordingly, the components of a gas engine lubricant need to be
selected
to meet the specified ash level and to provide, among other functions, a high
level of oxidation and nitration resistance. Whether selected components and
their amounts can be balanced to meet desired specifications is not a priori
predictable.
SUMMARY OF THE INVENTION
[010] The present invention relates to a lubricating oil of extended life as
evidenced by reductions in viscosity increase oxidation and nitration relative
to
current commercial and reference oils. The oil, especially useful as a natural
gas
engine lubricating oil, comprises a major amount of a base oil of lubricating
viscosity and a mixture of certain metallic detergents in an amount sufficient
to
provide a sulfated ash in the range of about 0.3 mass % to about 2.2 mass %
based on the total mass of the composition, the ash level being determined by
ASTM D874. The oil of the invention is further characterized as having less
than
about 0.1 mass %, based on the total mass of the composition, of a zinc
dialkyldithiophosphate.
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[0111 The lubricating composition of the invention may also include other
standard additives used in formulating commercial lubricating compositions
other than trinuclear molybdenum friction reducing additives.
DETAILED DESCRIPTION OF THE INVENTION
[0121 The lubricating compositions of the present invention include a major
amount of a base oil of lubricating'viscosity. No particular limitation is
placed
on the base oil. In general, the base may be any oil used in ordinary
lubricating
compositions. Suitable base oils include natural and synthetic oils and
mixtures
thereof in API categories I, II and Ill. Typically, the base oil will have a
kinematic viscosity in the range of about 9 to about 16 cSt at 100oC, and
preferably from about 10 to about 13 cSt at 100oC. As used herein, the
kinematic viscosity is determined by method ASTM D445.
10131 The metallic detergents included in the lubricating compositions of the
invention are: (i) a first neutral calcium alkylsalicylate detergent, and (ii)
a
second neutral or overbased metallic detergent or mixture of detergents other
than neutral calcium alkylsalicylate, selected from the group consisting of
calcium and barium sulfonates, phenates, and alkylsalicylates. Typically, the
alkylsalicylates will have from about 4 to about 30 carbon atoms in the alkyl
group, which may be linear or branched.
[0141 Also, the mass ratio of (i):(ii) will be from about 0.1:1.0 to about
3:1,
preferably from 0.2:1 to 2:1, and more preferably from 0.3:1 to 1:1.
10151 The neutral calcium alkylsalicylate (i) typically has a TBN in the range
of
about 150 or less. If metal detergent (ii) includes a neutral metallic
detergent,
such neutral metallic- detergent will also typically have a TBN in the range
of
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about 150 or less. If metal detergent (ii) includes an overbased metallic
detergent, such overbased metallic detergent will typically have a TBN of
about
160 to about 400. As used herein, TBN is determined by the method ASTM
2896-98. If both neutral and overbased metallic detergents are present, the
ratio
of neutral to overbased metallic detergent is in the range of about 10:1 to
about
0.1 to 1.
10161 The total amount of metallic detergents (i) and (ii) is in an amount
sufficient to provide the complete lubricant composition with a sulfated ash,
as
determined by ASTM method D874 in the range of about 0.3 mass % to about
2.2 mass %. The person skilled in the art will appreciate that the amounts of
metallic detergents suitable to achieve this property may vary depending on
the
type of metallic detergents (i) and (ii) used. Conveniently, the neutral
calcium
alkylsalicylate (i) is present in the range of about 0.1 mass% to about 2.1
mass%,
based on the mass of the total composition. In a separate embodiment, metallic
detergent (ii) is conveniently present in the range of from about 0.5 mass% to
about 10 mass %, preferably in the range of from about 0.6 mass % to about 8
mass%, more preferably in the range of from about 0.7 mass % to about 7
mass%.
[017] The composition of the invention may include a zinc
dialkyldithiophosphate in an amount of about 0.1 mass % and less, for exampte,
.
between about 0.1 mass % and 0.0 mass %, and preferably 0.0 mass %, based on
the mass of the total composition.
[018] Desirably, the compositions of the invention also include one or more
additives typically used in standard additive packages such as ashless
dispersants
(about 0.5 to 8 vol%), ashless antioxidants (about 0.05 to 15 vol%), metal
passivators (about 0.01 to 0.2 vol%), pour point depressants (about 0.05 to
0.6
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vol%), viscosity index improvers, dyes, and antifoamants (about 0.001 to 0.2
vol%) with the proviso that such additives will not include a trinuclear
molybdenum compound.
[019] Thus, the fully formulated oil may contain ashless dispersants such as
succinimide dispersants, ester dispersants, ester-amide dispersants and the
like.
Preferably, the dispersant is a succinimide dispersant, especially a
polybutenyl
succinimide. The molecular weight of the polybutenyl group may range from
about 800 to about 4,000 and preferably from about 1,300 to about 2,500. The
dispersant may be head capped or borated or both.
[020] Examples of suitable antioxidants include aminic antioxidants and
phenolic antioxidants. Typical aminic antioxidants include alkylated aromatic
amines, especially those in which the alkyl group contains no more than 14
carbon atoms. Typical phenolic antioxidants include derivatives of
dialkylhydroxy aryl compounds in which the alkyl groups are in the o- and/or p-
position. Such additives may be used in an amount of about 0.02 to 5 mass %
based on the total mass of the composition.
[021] Examples of metal deactivators include arylthiazole, triazoles or alkyl
substituted dimercaptothiadiazoles.
[022] Pour point depressants that may be included are exemplified by poly
(meth) acrylates, dialkylfumarates and alkylaromatic polymers.
[023] Silicon antifoaming agents and polysiloxane oils are illustrative of
suitable antifoamants.
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[0241 Viscosity index improvers (VII's) may be any polymer which imparts
multiviscosity properties to the finished oil such as olefin copolymers,
styrene-
diene block copolymers, star copolymers and the like used in amounts up to
about 15 vol%.
[025] Lubricating oil additives are described generally in "Lubricants and
Related Products" by Dieter Klamann, Verlag Chemie, Deerfield, Fla., 1984, and
also in "Lubricant Additives" by C. V. Smalheer and R Kennedy Smith, 1967,
pages 1 to 11, the disclosures of which are incorporated herein by reference.
[026] The present invention is further described in the following non-limiting
examples and comparative examples.
EXPERIMENTAL '
Lab Nitration Screener Test
10271 A lab nitration screener test was used to assess the oil life
performance of
various oil compositions. The test results identify a number of parameters,
including oil viscosity increase, oxidation, and nitration. Basically, the
oils are
evaluated by maintaining them at a fixed elevated temperature while subjecting
them to oxidizing conditions. The oil performance is evaluated by measuring
the viscosity increase, oxidation and nitration throughout the test. In each
test, a
Reference Oil is always tested, and all results are reported as a ratio of the
result
for the test oil divided by the result for the Reference Oil so that large
values
represent greater levels of lubricant degradation and lower values represent a
measure of longer oil life. For example, if the test oil has an oxidation
result less
than 1, then the test oil demonstrates performance superior to that of the
Reference Oil.
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EXAMPLES AND COMPARATIVE EXAMPLES
[028] The accompanying Table sets forth the composition and test results for a
series of gas engine oil lubricating compositions. All the oils use an API
Group
I base oil. Example 3 and Comparative Oi15 are low ash oils; all others are
nominally high ash. All are SAE 30 Grade except Comparative Oil 1, which is
SAE 40 grade. In the Table, Additive Package 1 and Additive Package 2 are
typical high ash natural gas engine oil additive combinations. -
[029] Reference Oil 1 is a premium, zinc-free, commercial gas engine oil, and
Comparative Oils I and 2 are commercial zinc-free oils.
[030] In Example Oils 1, 2 and 3 and Comparative Oils 3, 4 and 5, the balance
of the additive system was the same for each and was kept constant. This
additive system included an ashless dispersant, ashless antioxidant, pour
point
depressant, metal passivator and antifoamant. As shown in the Table,
Comparative Oils 3, 4 and 5 were identical to Example Oils 1, 2 and 3,
respectively, but with inclusion of 0.29 vol % (0.36 mass %) of zinc
dialkyldithiophosphate, ZDDP, an amount used in most modern commercial gas
engine oils.
10311 The results in the Table demonstrate the wide performance range of the
current commercial oils, viz., Reference Oil l and Comparative Oils 1 and 2.
As
can be seen, the formulations of Examples 1, 2 and 3 have superior oil life
(as
reflected in oxidation, nitration and/or oil thickening control) compared to
the
zinc-free formulations of Reference Oil 1 and Comparative Oils 1 and 2.
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