Note: Descriptions are shown in the official language in which they were submitted.
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LONG LIFE LUBRICATING OIL COMPOSITION
USING PARTICULAR ANTIOXIDANT COMPONENTS
Field of Invention
[0001] The present invention relates to gas engine oils. More particularly the
present invention relates to gas engine oils that provide enhanced resistance
to
oxidation, nitration and viscosity increase.
Background of Invention
[0002] Typical natural gas fired engines such as those used in the petroleum
industry to compress natural gas at well heads and along pipelines have up to
16
cylinders, often generating between 500 to 3000 HP. These engines normally
are run continuously near full load conditions with shut downs being primarily
for maintenance such as for oil changes. Such continuous operation near full
load, of course, places severe demands on the engine lubricant. Indeed,
because
the lubricant is subjected to a high temperature environment, oxidation
processes
can occur rapidly which limit lubricant life. Also, natural gas engines emit
nitrogen oxides (NOX), some of which come into contact with the lubricant
resulting in nitration processes also limiting lubricant life. Typically these
processes are accompanied by increases in oil viscosity.
[0003] Thus, it is desirable to extend the life of gas engine oils by
enhancing
the oil's resistance to oxidation and nitration and to reduce viscosity
increases in
the oil.
[0004] To extend lubricant life, base oils are formulated with various
additives such as dispersants, detergents, antioxidants, viscosity index
improvers
and the like to provide a lubricating oil composition. This art of lubricating
oil
formulation, however, has become increasingly more complex with ever more
stringent requirements by end-users. Indeed, experience has shown that
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incorporation of one type of additive in a lubricant composition can have a
negative impact on the function of another type of additive. Consequently,
extensive research continues in the quest for lubricants of improved life and
function.
[0005] An object of the present invention is to provide a gas engine
lubricating composition that has enhanced resistance to oxidation and
nitration.
[0006] ~ Another object of the invention is to provide a gas engine
lubricating
composition that has improved life as evidenced by reduction in viscosity
increase.
Summary of Invention
[0007] Accordingly, a natural gas engine lubricant composition having
enhanced resistance to oxidation, nitration and viscosity increase comprises:
(a) a major amount of an oil basestock of lubricating viscosity having
a kinematic viscosity at 100°C of about 5 to 16 cSt and preferably
about 10 to
about 13 cSt;
(b) a minor amount of a detergent mixture comprising low/neutral
TBN and over based metallic detergents, selected from the group consisting of
alkali and alkaline earth sulphonates, phenates, and salicylates;
(c) a minor amount of an antioxidant comprising an
alkylthiocarbamoyl compound or a mixture of an alkylthiocarbamoyl compound
and an ashless, non-sulfur containing hindered phenol; and,
(d) a zinc dihydrocarbyl dithiophosphate in an amount sufficient to
provide the lubricant composition with from 250 to 450 wppm of phosphorus.
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[0008] Other gas engine oil additives also may be present. These include:
ashless dispersants, metal passivators, pour point depressants, VI improvers
and
antifoamants.
Detailed Description of the Invention
[0009] The lubricating oil composition of the invention comprises a major
amount of a lubricating oil basestock which may be a mineral oil, synthetic
oil or
blends of oils to give a basestock of the desired viscosity for a natural gas
engine
oil. Typically, the basestock of the invention will have a kinematic viscosity
at
100°C in the range of about 5 to about 16 cSt and preferably from about
10 to
about 13 cSt. Especially preferred are API category Group II basestocks.
[0010] The composition of the invention includes a mixture of low/neutral
TBN and overbased (high TBN) metallic detergents selected from the groups
consisting of alkali and alkaline earth metal sulphonates, phenates, and
salicylates. Preferably the metallic detergents will be calcium sulphonates,
calcium phenates and calcium salicylates. Low/neutral TBN metallic detergents
typically have a TBN in the range of about 10 to about 80. High TBN metallic
detergents typically have a TBN in the range of about 150 to 300 or higher.
[0011] The metallic detergents are used in amounts sufficient to contribute a
sulfated ash (ASTM D-874) to the formulated lubricant oil composition of about
0.2 mass % to about 2.0 mass %. Expressed in terms based on active ingredient
in the detergent mixture, the metallic detergents comprise from about 0.5
volume
% to about 10 volume % and preferably 0.5 volume % to 5.0 volume % of the
lubricating composition. The volume ratio (based on active ingredient) of
overbased to low/neutral TBN metallic detergents is in the range of from about
0.05 to 3.5, and preferably about 0.25 to 1Ø
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[0012] The lubricating composition of the. invention contains a minor but
effective amount of an antioxidant comprising an alkylthiocarbamoyl compound
or a mixture of an alkylthiocarbamoyl compound and an ashless, non-sulfur
containing, hindered phenol. , ~ '
[0013] Suitable alkylthiocarbamoyl compounds are represented by the
formula:
S
~~ /R3
~IV C -f-X'~- C~ 4 ( I )
R R
where Rl, Ra, R3 and R4 are the same or different linear and branched alkyl
groups of from 1 to 18 carbon atoms, X is ~S, S-S, S-(CHZ)y-S, S-CH2-CH(RS)-S;
y is an integer o~ 1 to 4, and RS is an alkyl group of 1 to 2 carbons.
Preferably
Rl, R2, R3 and R4 are C4 alkyl groups, X is S(CHa)yS, Y is 1-3.
[0014] The alkylthiocarbamoyl compound when used in the absence of the
ashless, non-sulfur containing, hindered phenol generally comprises from about
0.25 volume % to about 2.0 volume % and preferably 0.5 volume % to 1.5
volume % of the total volume of the lubricating oil composition.
[0015] In an alternate embodiment, the composition of the invention contains
an antioxidant comprising a mixture of an alkylthiocarbamoyl compound and an
ashless, sulfur free, hindered phenol. In this embodiment, suitable
alkylthiocarbamoyl compounds are represented by the same formula above. The
hindered phenols suitable for use in conjunction with the alkylthiocarbamoyl
compounds may be represented by the following formulae:
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OH
R1 Rz
(R)
and
OH
R1 R2
(
R3
where R1, R~ and R3 are the same or different alkyl groups of 1 to 18 carbon
atoms.
[0016] In the embodiment where the antioxidant is a mixture of
alkylthiocarbamoyl and ashless, non-sulfur containing hindered phenols, the
alkyl dithiocarbamoyl comprises 0.25 volume % to 1.5 volume %, and
preferably 0.5 volume % to 1.0 volume % of the composition and the phenol
from 0.25 volume % to 1.5 volume % and preferably 0.5 volume% to 1.0
volume %.
[0017] The natural gas engine lubricating composition also includes a zinc
dihydrocarbyl dithiophosphate (ZDDP) or mixture of ZDDPs in which the
hydrocarbyl groups may be the same or different alkyl groups or alkylaryl
groups with the alkyl group, in each instance, having 3 to about 18 carbon
atoms. Preferably the hydrocarbyl group is an alkyl group. The ZDDP or ZDDP
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mixture is present in the amount sufficient to provide the lubricating oil
composition with 250 to 450 wppm of phosphorus.
[0018] The invention also contemplates the use of other gas engine oil
additives such as ~ashless dispersants, metal passivators, pour point
depressants,
VI improvers and antifoamants. Some of these additives are only required in
minor amounts (antifoamants, metal passivators), while others may be required
in significant amounts (dispersants). Thus, these additives will typically
range
from 0.(~1 volume % to about 10 volume % based on the total volume of the
engine oil composition.
Examples and Comparative Examples
[0019] The invention will be further illustrated by the following Examples
and Comparative Examples.
[0020] Table 1 below details a series of formulations: (a) two for
particularly preferred embodiments of the invention and (b) three other
formulations included for comparative purposes. The basestock in all
formulations was an API Group II category basestock. All oils were SAE 40
grades with nominally 0.45 mass % sulphated ash.
[0021] Comparative Oil 1 is a low ash commercial gas engine oil which
employed a commercial gas engine oil additive package.
[0022] Reference Oil 1 was blended to represent an oil of U.S. Patent
6,140,282, while Comparative Oil 2 was blended to represent an oil of U.S.
Patent 5,569,405.
[0023] The various formulations were subjected to a nitration screener test
and the results are presented in Table 1. The nitration screener test is a lab
test
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which assesses several facets of the degradation of natural gas engine oils.
All
results are expressed as normalised against the results for the Reference Oil.
Therefore, all results for the Reference Oil will have a result of 1.00 and
any
results lower than 1.00 signify enhanced performance.
Table 1
Formulation
ComparativeReferenceInventionComparativeInvention
Description. Oil Oil ExampleOii Example
~ 1 1 1 2 2
Based Based
on on
USP USP
6,140,282 5,569,405
Component Basestock DescriptionGroup Group Group Group Group
(vol%) ~J II II II II II
,4
basestocksbasestocksbasestocksbasestocksbasestocks
Grou II basestock 87.90 90.00 90.00 90.00 90.00
NGEO Commercial Additive9.60 ----------------------------
acka a
VII 1.00 1.00 1.00 1.00 1.00
PPD 0.50 ____________________________
Calcium alk lsalic -------2.00 2.00 2.00 2.00
late, 64 TBN
Calcium alk Isalic -------0.40 0.40 0.40 0.40
late, 280 TBN
Balance of Additive -------5.60 5.60 5.60 5.60
S stem
Phenolic antioxidant1.00 1.00 --------------0.50
Sul hur-containin ---------------------0.50 -------
Phenolic antioxidant
Ashless alk lthiocarbamo--------------1.00 0.50 0.50
1
w.,x ".. .....
. ~ ~ 7 ~ y ~1.
~ ~~
ICinematic measured kV @ 100C 13.25 13.21 13.15 13.12 13.19
viscosity,
cSt
Phos horus 334 295 295 295 295
content,
m
Nitration
Screener
Test
oxidation (relative 2.92 1.00 1.07 1.37 0.83
to reference Oil
1)
nitration (relative 1.59 1.00 0.79 0.73 0.59
to reference Oil
i)
viscosity increase 2.80 1.00 -0.43 0.21 0.17
(relative to Reference
Oil 1) '
PPD = pour point depressant
[0024] As can be seen, Comparative Oil 1 is inferior in all respects to the
Reference Oil while Comparative Oil 2 provides better nitration and thickening
control than the Reference Oil but inferior oxidation control. The Example 1
oil
in contrast provides roughly equivalent oxidation control to that of the
Reference
Oil and improved nitration and thickening control. The oil of Example 2 is
better than the Reference Oil in all three parameters.
